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Motors, Drives & Motion
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TABLE OF CONTENTSSmooth driving with linear motion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4
Expert panel offers some design potholes to steer clear of
How will VSDs alter motor efficiency? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
New ideas for tying motors and variable-speed drives together for better control
Hydraulic muscle, as needed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .39
Sometimes brute force is needed, and a little hydraulic knowledge
can get things moving in the right direction
Get motors rolling, and add feedback . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
Keep an ear out for electromagnetic interference and radio frequency interference
Smart control and drive integration fills the bill . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
Italy’s Goglio wins Smart Machines category in Best Future Machine Awards
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Smooth driving with linear motionNew ideas for tying motors and variable-speed drives together for better control
By Mike Bacidore, editor in chief
WHAT ARE SOME DESIGN PROBLEMS YOU HAVE SEEN THAT SHOULD BE AVOIDED WHEN IMPLEMENTING LINEAR MOTION?
Design issues can be the source of headaches, especially when you’re implementing linear
motion . The technology can bring accuracy and precision to many applications, but select-
ing components requires a bit of forethought . Our panel of industry experts discusses some
potholes to steer clear of .
BROC GRELLapplications engineer,
Nexen Group (www.nexengroup.com)
Designers forget to add the mass of the motor, gearbox and linear system to the mass that
needs to be moved by the linear system . Designers forget the cables will pull on the sys-
tem, as well . When going into an existing system as a retrofit, make sure there is room for
the new system and that it can be attached properly to the machine . Designers don’t un-
derstand how all the components—motor, gearbox—in the system add up to affect aspects
such as friction, inertia mismatch and total required force to move the system .
When using a software calculator system for motor sizing, it is the same old saying with a
hand calculator, where junk in equals junk out . Making sure the inertias are correct and being
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located correctly through the different ratios
in the system and making sure drag is under-
stood are very important . A designer should
always look at the motor that the system
recommends and make sure that it makes
sense with the load and ratios in the system
before just running with that motor . Some-
times mistakes are made in the calculator
that can cost a lot of money if the motor is
extremely oversized or undersized because
of a mistype in one of these calculators .
MATT PRELLWITZmotion product specialist,
Beckhoff Automation
(www.beckhoff.com)
Before you start the implementation, you
need to be sure of the exact linear-motion
requirements in your application—distance,
load, mass, inertia—in addition to the limita-
tions of your components and controller .
This is a major reason why we suggest a
PC-based control system with the motion
handled in software, because it provides the
ability to more easily scale your controller
as the needs of your application grow and
change . In addition, choosing robust com-
ponents, with the help of motion-configu-
ration software, will go a long way to avoid
future mechanical failures or underwhelm-
ing performance .
GARY ROSENGRENdirector of engineering,
Tolomatic (www.tolomatic.com)
As it pertains to linear actuators, not con-
sidering the effects of resulting moments, or
torques, the position and size of the load on
the cylinder determines the resulting bend-
ing moments applied to the cylinder itself .
Even if a load is located on and directly
over the center of the load-carrying device,
it will still be subjected to bending moments
on acceleration . It is important to determine
if the cylinder is capable of handling the
resulting moments . For off-center or side
loads, determine the distance from the cen-
ter of mass of the load being carried to the
center of the cylinder’s load-carrying device
and calculate the resulting bending moment
(Figure 1) .
Don’t overlook the effects of dynamic mo-
ment loading . Unlike rod-style actuators,
many rodless actuators must support the
load during acceleration and deceleration
at each end of stroke . When there are side
or overhung loads, the dynamic moments
must be calculated to determine which rod-
less actuator is best equipped to handle the
resulting forces .
Remember to account for forces which
occur during motion—dynamic forces—par-
ticularity those which occur at the point of
acceleration or deceleration . These forces
acting upon the bearing system may over-
come the capability of the bearing system
and shorten life .
When an actuator is mounted vertically in
an application, additional force and load
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eHANDBOOK: Motors & Drives 6
air considerations must be addressed . An
actuator mounted vertically needs to over-
come the force of gravity first before it
can accelerate a load upward . A vertically
mounted cylinder will need to produce
more force than a horizontally oriented cyl-
inder to achieve this .
Oversizing actuators is a bad habit left over
from fluid power applications where over-
sizing was considered inexpensive insur-
ance against not having enough power .
With fluid power cylinders, the additional
cost of a slightly larger actuator than nec-
essary was minor compared to the extra
engineering time that might be involved in
sizing it correctly . It was common for engi-
neers to build in a 2:1 safety factor on fluid-
power applications for a variety of reasons .
These included erring on the conservative
side to compensate for imprecise knowl-
edge of the loads, fluctuations in available
air pressure and oversizing in anticipation of
higher loads in the future due to production
growth or application changes . Electric ac-
tuators can cost significantly more up front,
so over-sizing is a more costly mistake .
The environment in which the actuator will
be operating can have a profound effect on
PRECIOUS MOMENTSFigure 1: Mx Moment (roll) is created by loads applied at a distance from the x axis. My Moment (pitch) is created by loads applied at a distance from the y axis. Mz Moment (yaw) is created by loads applied at a distance from the z axis.(Source: Tolomatic)
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eHANDBOOK: Motors & Drives 7
performance, durability and maintenance .
High temperatures can affect seals, lubrica-
tion, bearings and motor life . Extremely low
temperatures can also affect performance,
lubrication and wear . Contamination with
oil, water or abrasive grit can destroy seals
unless the actuator has an appropriate IP
rating . Since IP ratings only address static
conditions, dynamic conditions such as
vibration, heat, cold or movement also have
to be considered .
Rod-style actuators, characterized by the
piston rod or actuator rod extending and
retracting with each cycle, typically of-
fer numerous mounting options . Mounting
options such as drilled and tapped holes
in the device, mounting feet, spherical
rod joints, alignment couplers, clevises or
trunnions are commonly offered by most
suppliers of rod-style actuators . When
employed with a guided mechanism, care
must be exercised to assure each subsys-
tem, actuator and guide assembly is capa-
ble of unimpeded, smooth motion . Systems
that attempt to rigidly couple the drive
element to the driven element may exhibit
inconsistent performance as these two
elements try to move in separate planes
with one or both of the subsystems loaded
beyond its capability .
A rod-style actuator in such a system is
best employed with some compliance
member between the drive member—ac-
tuator—and the driven—guide system . For
example, a spherical rod end mounted
to the actuator rod allows the mounting
point to swivel about the spherical joint .
This type of connection at the guide is
best used in conjunction with a trunnion or
clevis at the opposite end of the actuator
where it attaches to the machinery frame
element . Such a mounting scheme allows
compliance in the connection without add-
ing undue stress to either the drive—actua-
tor—or the driven—guide system .
Rodless style actuators, characterized by
their strokes being contained within their
overall lengths, may also contain a guide
system built into the actuator . Rodless
actuators, when used in conjunction with
a separate guide system, as I mentioned,
will also need to include a compliant
member in the connection between the
drive and driven members . Most actuator
suppliers offer a variety of mounts in-
tended for this type of installation, such as
floating brackets .
Rodless actuators that include a guide
system can perform the task of guiding
and supporting the equipment while taking
the place of a separate guide system . This
feature can be particularly useful and many
times saves the machinery builder time and
money in the process . Rodless actuators
with integral guides can be built into the
machinery in combinations to meet a wide
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eHANDBOOK: Motors & Drives 8
variety of motion needs . Multi-axis con-
figurations such as x-y or x-y-z along with
gantry configurations are all possible with
proper sizing . In the installation of rodless
actuators with integral guides, alignment is
equally important .
When mounting an actuator or a series of
actuators to a structure you must consider
parallelism and perpendicularity . Parallel
misalignment can apply an unfavorable
Mx-axis bending moment on the bear-
ing system . Carriages of rodless actuators
must be mounted at the same height . They
also need to be mounted at a consistent
distance apart from each other from one
end to the other to prevent an unfavorable
Fy-axis side load on the bearing system
which can cause binding . In addition, they
need to be mounted level to each other to
prevent an unfavorable bending moment in
the My-axis on the bearing system .
Perpendicular misalignment in an x-y-z
system in the x plane applies an unfavorable
y-axis bending moment on the actuator’s
bearing system . In a gantry system where
two actuators are in the x-axis or y-axis,
they need to move simultaneously . Misalign-
ment or inadequate servo performance will
apply an undesirable bending moment in
the Mz-axis to the bearing system .
Actual tolerances related to alignment
recommendations and mounting vary
from actuator manufacturer to actuator
manufacturer, as well as from bearing
type to bearing type . However, a general
rule of thumb is to consider the bearing
system type . High-performance bearing
types such as profile rail systems tend
to be quite rigid, and alignment is more
critical . Medium-performance systems
using rollers or wheels often have clear-
ance which offers some forgiveness in
alignment . Plain bearing or sliding systems
often have greater clearance and may be
even more forgiving . When installing lin-
ear actuator mounting systems, there are
a number of measurement tools ranging
from gauges to laser systems . Whatever
tools are used, always create one axis as
a reference for the x-y and z planes and
mount the other devices with respect to
the reference axis . Doing so will help to
get the maximum performance and lon-
gest life from your actuator system .
BRIAN ZLOTORZYCKIEtel motors product specialist,
Heidenhain (www.heidenhain.com)
Make sure the motor being used is prop-
erly sized to avoid any overheating due
to the motor working close to its capac-
ity . To help alleviate any unwanted heat
generation, users can dissipate the heat
through an external cooling method, such
as a heat sink, or increase its size . Also,
the tolerances of the air gap need to be
maintained . The standard gap is typically
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eHANDBOOK: Motors & Drives 9
0 .9 mm, and, if it increases, then the per-
formance of the motor suffers .
CLINT HAYESproduct sales manager,
linear motion technology,
Bosch Rexroth (www.boschrexroth-us.com)
Not accounting for full loading condi-
tions—mass load, tooling or process
forces—results in undersized components
for the application . Not achieving the re-
quired degree of precision results typically
from a poor understanding of the differ-
ence between travel accuracy, repeatabil-
ity and positional accuracy . Oversizing of
bearings—build to perception—can result
in missing the required price points for
the market . And there’s not accounting
for environmental impact on the life of the
bearings—humidity, washdown require-
ments and contamination .
Rexroth uses the acronym LOSTPED as a
way to remember all critical factors in de-
signing linear motion systems: load, orienta-
tion, speed, travel, precision, environment,
and duty cycle .
DERRICK STACEYsolutions engineer,
B&R Industrial Automation
(www.br-automation.com)
Alignment of the load bearing elements
is crucial . Most linear motors, including all
electrical, as well as ball screw and belt type,
are designed to provide higher thrust force
than the load they are physically able to
carry, so they are often coupled with load-
bearing elements . This can be recirculated
ball guides or roller bearings among others .
Ensuring that you have enough overhead to
handle the load is important, but in the end
we need to be able to smoothly and control-
lably move from A to B .
Designers need to take into account that the
higher the precision and load capabilities of a
linear bearing usually mean a loss of flexibility
and misalignment tolerance . This lack of flex-
ibility often leads to control/tuning issues that
can yield delays or performance degradation
of the overall system . By keeping this in mind
from the start, these downstream issues can
be minimized or even avoided .
CHRIS BULLOCKapplications engineer I,
Bishop-Wisecarver Group
(www.bwc.com)
Not including proper lubrication systems
is, by far, the most common . The next is
trying to design a machine without having
adequately determined the system require-
ments . Never purchase until you figure out
exactly what needs to be done by the ma-
chine and how .
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JOSH TESLOWapplications engineer,
Curtiss-Wright
(www.curtisswright.com)
One age-old issue is machine-tool program-
mers guessing the user units during initial
programming and crashing servo mecha-
nisms the first time they push the start but-
ton . It is so important to double-check all
parameters/user units before test-running
expensive equipment .
There tends to be a strong focus on the
mechanical portion when sizing a system
and not enough focus on the controls . The
controls, especially the programming, are
just as important as the mechanics . The me-
chanical portion will only do what it’s told .
Different types of misalignment can occur
during installation or operation . The load
must be properly guided, whether that’s
with the actuator or some kind of external
guide . It must be properly guided when
long life or high force is required .
JAY JOHNSONnational product manager,
Sick (www.sickusa.com)
Linear motion is a wide scope, so I’ll focus
this response to a problem that may arise
with the addition of a linear feedback de-
vice to a rotary servo motor driven axis .
Ball screw or belt driven linear axes typi-
cally have compliance and/or backlash,
and it increases with use as the mechani-
cal components wear . In addition, there
will be some degree of non-linearity in the
manufacturing and assembly of the drive
components . Therefore, in applications
requiring high positioning accuracy and
repeatability, it may be necessary to add
a linear encoder to close the position loop
while the motor mounted encoder is used
for speed control and commutation . With
this addition, the system is now positioning
to the linear encoder, eliminating the vari-
ability of the ball screw grind accuracy or
linear bearing alignment .
In this scenario a new problem can be in-
troduced depending on the control scheme
and how much compliance is in the me-
chanical system . Consider that when an
axis is enabled and holding position, there
may be external forces such as a cutting
tool or gravity in a z-oriented axis . The axis
will move slightly from the pressure, and so
will the linear encoder . The encoder signals
this movement, and the controller sends a
corrective signal to the drive amplifier . Yes,
this is normal PID loop behavior, but the
problem comes if the lost motion is large
enough that the corrective move doesn’t
complete quickly . For instance, if there is
.003 inch of backlash in a ball screw and
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eHANDBOOK: Motors & Drives 11
the axis is loaded to one side, the position
feedback will be delayed while the slack is
being taken up . With typical gain settings,
the control will quickly react with a stronger
corrective signal because the feedback isn’t
changing . Now the axis is traveling faster
and it moves slightly past the target posi-
tion . The control immediately reverses the
signal to correct, but again the lost motion
must be taken up . A hunting effect can be-
gin resulting in an axis continuously revers-
ing in an attempt to close the position loop .
This problem is magnified in systems with
high stiction such as with large machine
tools or heavy moveable structures .
One solution is to lower the system gain
so that the controller doesn’t respond too
harshly, but this may not be practical for
the application as it softens the overall
performance . Another option is to increase
the feedback resolution, but this will only
help but not eliminate the problem . Some
motion controllers are able to effectively
deal with this issue, especially in the CNC in-
dustry . Methods include different gain and
acc/dec settings for commanded moves
versus holding position, or the use of me-
chanical clamps during idle/holding opera-
tions . Obviously, the best synopsis is to re-
duce the backlash to a minimum if possible .
A Control Design reader writes: As part of a spare-parts readiness and moderniza-
tion initiative at our material processing and packaging plant, I have inventoried
more than 140 motors in our facility from sub-horsepower to 100 hp, and there are
many more . After a preliminary analysis, my manager wants me to include opportunities to
advance our green initiative, as well .
I need to identify plant-modernization projects to improve motor efficiencies . This in-
cludes updating motor-control design by adding variable speed drives (VSDs) where ap-
plicable . To start, any suggestions on integrating a controller or PLC to a VSD and motor
are appreciated .
Additionally, I am having a hard time understanding which motor applications would benefit
from use of a VSD . I think fans and pumps would definitely benefit, but I’m not sure how to
make that decision . How do I know if adding a VSD to a fan, conveyor, agitator, mixer or
rock crusher has efficiency benefits? How is the decision made? Does size matter?
I also have several process lines with six or more motors each, all running conveyors, agita-
tors and mixers at full speed to process or convert materials . Sometimes we could just run
half speed or a set-point speed, depending on demand . Some things I can slow down, and
some things I cannot . How do I tie all the motors and drives together for better control?
How will VSDs alter motor efficiency?New ideas for tying motors and variable-speed drives together for better control
By Mike Bacidore, editor in chief
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eHANDBOOK: Motors & Drives 13
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ANSWERSTHE SOFT STARTIdeally, you would start by installing soft
starts on most large motors . A soft start
is a VFD hybrid with a bypass across-the-
line contactor that ramps up motors to the
across-the-line speed and then closes the
across-the-line contactor to take the ramp-
ing module off-line . Next, keep in mind that
for every VFD you install, you will have to
also stock an equivalent VFD unit and that
the shelf life of a VFD is relatively short—
six months—until it needs maintenance
to polarize the drive . Installing a replace-
ment VFD that has not been polarized in
more than a year will oftentimes cause it to
explode . From an overall kindness to your
stocking room and its shelf space, I would
only consider VFDs on those motors that
can directly benefit for other reasons than
a green initiative . A soft-start module will
keep your power factor in a much better
state and result in less peak demand on
your utility, especially around shift change,
and they are simple to retrofit, assuming
you have panelboard space . For smaller
motors, say less than 10 hp, the case for a
soft start is hard to make .
Back in the day, we used to tie a whole con-
veyor-line section together using a single
VFD in Volts-Hertz mode . We would have a
large VFD that would have several across-
the-line motor starters on the secondary
side of it, each one feeding a different
motor . You could change the drive speed,
and all of the motors would change speed
together in perfect synchronization, almost
like they were electronically geared togeth-
er . Using this old-school method does not
utilize the newer drive modes like sensor-
less vector mode, so the drive is a little less
efficient, but you can add a dynamic brak-
ing module to the main drive, and you can
gain braking capability on multiple motors
at the same time with one module .
Doug Taylor, principal engineer / Concept Systems /
www .conceptsystemsinc .com / member of Control Sys-
tem Integrators Association (CSIA, www .controlsys .org)
VARIABLE SPEEDThis is a very big subject, but it’s very rel-
evant to modern technology . What applica-
tions are good ones for applying a variable
speed drive? In the old days, the acronym
VSD meant variable speed device and also
included such devices as adjustable gear-
boxes, belt shifters, wound rotor motors,
eddy current clutches and anything else that
could affect speed . To avoid any confusion,
I’ll use the acronym VFD, if you don’t mind .
Generally, any application that requires the
speed to be changed over time is a good ap-
plication . An example of a VFD application is
the supply and exhaust fans for air handlers .
The old way was to operate a fan motor at
full speed and have a damper operator that
opens and closes to vary the air flow . This is
very inefficient since the motor load stays
high even when the damper is closed . The
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eHANDBOOK: Motors & Drives 15
VFD is a perfect fit for this application . The
damper is removed or blocked wide open,
and now the speed of the fan is directly
controlled by the VFD which controls the air
flow . This reduces the load on the motor at
lower speeds . There are many utilities across
the United States that will help to pay for
adding VFDs to these types of applications
because of the energy savings . The best ap-
plications for saving are the ones that have
the biggest speed change from minimum to
maximum . If you run above 80% speed at
all times, it might not be worth it strictly on
energy savings .
Typical applications include fans, pumps,
conveyors, agitators, mixers, coordinated
drives and elevators .
Motors that run at a fixed speed all the time
should have gearboxes to make sure the mo-
tor is running near rated load at rated speed .
Many people oversize fixed-speed applica-
tions because they think, if they need 15 hp,
then 20 hp is better . The mistake is that each
motor draws reactive as well as real power
to run, and, if you continually oversize the
motors in a facility, it can affect the power
factor and cause increased utility costs .
Regarding integration of VFDs with PLCs
or other controllers, manufacturers these
days are making their drives compatible
with many different control systems . Most
have Ethernet ports on them for communi-
cations to PLCs directly . All the major PLC
manufacturers that sell both PLCs and drives
already have a straightforward way to get all
the drives communicating over the Ethernet
network for start/stop, forward/reverse and
speed set point . In your case, if you have any
existing drives that do not have communica-
tion ports available, it is usually easy to just
hardwire from the PLC outputs to the drive
inputs for the same type of controls that you
can do over Ethernet in the newer drives .
Once you have control over the starting,
stopping and the speed set point for a drive,
the control becomes fairly straightforward .
For the motors without VFDs, you’ll need
to consider adding them . Be aware of a few
things that can trip you up .
The ac “across the line” motors are full-
voltage non-reversing (FVNR) motors and
can regenerate back into the ac line for
overhauling loads . The VFDs do not accept
regenerative energy very well unless you
add what is called a dynamic braking resis-
tor or have a line-regen ac drive .
The dynamic braking resistor generally
connects to specific terminals on the drive
called BRK+ and BRK- . The purpose of the
dynamic brake resistor is to absorb the
energy created by an overhauling load . That
is a load that causes the motor to actually
run faster than the called-for speed you are
running at . For example, if you want a large
fan to stop quickly by asking the VFD to
stay connected and to decelerate rapidly,
the inertia of the fan keeps it spinning . This
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eHANDBOOK: Motors & Drives 16
causes the VFD dc bus voltage to begin to
rise . If something isn’t done in this instance,
the voltage will eventually go high enough
to trip the drive on overvoltage . With dy-
namic braking, the energy from the dc bus
is dissipated as heat in the braking resistor,
and the fan slows more quickly while the
dc-bus voltage is maintained at a safe level .
The ac drives can run at frequencies much
higher than the normal nameplate of the
motor . It is not unusual to run a VFD up to
90 Hz in some applications . With increased
speed/frequency you have to remember
that, above 60 Hz, your horsepower stays
constant but your available torque drops
off . To compensate, the motor must draw
more Amps to stay at the correct speed .
The general rule of thumb for liquid pumps
is the horsepower requirement goes up as a
square of the speed, while, for an air fan, the
horsepower goes up as a cube of the speed .
So be careful about sizing your motor and
drive, if you intend to use the extended
speed range .
Scott L . Kinney, P .E . / electrical engineer / Taurus Power
/ www .tauruspower .com / member of Control System
Integrators Association (www .controlsys .org)
BELOW 100%If a motor will always run at 100% speed,
there is no benefit to driving it from a vari-
able frequency drive (VFD) above putting it
on a soft starter . However, if a motor could
perform the required task running well be-
low 100% speed much of the time, a VFD is
probably worth getting . This is true even if
other throttling equipment, such as valves
or dampers, must also be retained .
Variable frequency drives are more accu-
rate and repeatable than valves or dampers
and do not suffer from hysteresis
Variable frequency drives are more efficient .
Power is proportional to flow multiplied by
pressure; slowing a pump or fan and opening
a valve or damper means the same flow may
be achieved with less change in pressure .
Savings can be significant, often less than
half the power used with full-speed motors .
Variable frequency drives reduce wear on
ducts, pipes, valves and dampers caused by
excessive pressure drop . Variable frequency
drives may be oversped—above 60 Hz—to
increase the capacity of undersized equip-
ment . Variable frequency drives reduce the
strain on rotating parts during starts, extend-
ing life and reducing maintenance cost . And
variable frequency drives draw lower amper-
ages during starts, reducing peak loads and
voltage sag on switchgear . More operational
data about the motor is available without ad-
ditional instrumentation . A soft start has the
last three advantages, but not the others .
If a motor could be run below 100% speed,
it becomes a payback period question .
How long will it take for the savings from
improved control, reduced power consump-
tion and reduced maintenance to surpass
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eHANDBOOK: Motors & Drives 17
the cost of purchasing and installing the
VFD . That calculation is beyond the scope
of a brief response, but it’s usually less than
two years, and often well under a year .
Size matters a little bit . Generally bigger
motors offer more energy savings relative to
the purchase and installation cost . Note that
most equipment has a minimum speed to
work properly . Integrated cooling fans and
bearings with slinger rings depend on motor
speed to work properly, so running too slow-
ly will result in damaged equipment . Pumps
benefit greatly from VFDs, but pumps dis-
charging into high-pressure headers often
must run 80-90% of full speed to move any
fluid at all . Running too slowly will cause the
pump to overheat . Pumps running in paral-
lel to the same header must be matched and
driven together . Base-loading one pump and
swinging another could easily result in one
pump handling all of the flow and the other
pump overheating . Read more about con-
trolling large variable-speed fans and pumps
at www .controldesign .com/vsfans .
As for integration, I greatly prefer a com-
munication link between PLC and VFDs to
hardwired controls . VFDs can be configured
to safely trip on loss of communication
with the PLC . Redundant device-level-ring
(DLR) communication is available on many
models . Safety circuits—from e-stops and
guard sensors—can be hardwired to dis-
crete inputs on VFDs to work in conjunction
with networked control . In addition, to run
command and feedback, as well as speed
reference, a communication link also gives
easy access to speed and Amp feedback
and many other parameters with no addi-
tional wiring, and it allows configuration of
the VFD from a networked laptop .
Again, motors that would always run full
speed might benefit from a soft starter, but
would not additionally benefit from a VFD .
Agitators and mixers certainly benefit from
running more slowly—less power usage and
maintenance, plus better control over mixing .
Some materials benefit from initially vigorous
mixing followed by slower mixing to maintain
homogeneity, while others benefit from ini-
tially slow mixing and gradually speeding up .
Conveyors can definitely benefit from VFDs .
When programming them, there are a few
things to keep in mind .
Ideally you control height of material on the
conveyor . If you are feeding slowly, run the
belt slowly . When feed speeds up, speed
up the belt . The pile height will therefore
remain consistent . This can be a huge help
if you have a control challenge maintaining
the level/weight of the equipment fed by
the conveyor . With constant speed convey-
ors, once material is fed onto the conveyor,
it’s committed . But with VFDs, you can see
a change in feed rate almost instantly at
the discharge end because the conveyors
speed up and slow down with the feeders .
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eHANDBOOK: Motors & Drives 18
Any conveyor can run at the same speed
or faster than the conveyor upstream, but
generally running a conveyor more slowly
than the one upstream will cause problems .
I’ve worked on some conveyor systems
where the first four or five are on VFDs, but
the last two are constant speed . That’s fine .
But there’s no point in putting a VFD on a
conveyor downstream of a constant speed
conveyor, unless the VFD conveyor spends
much of its time being fed from an alternate
variable speed source .
I normally control such a system by pro-
ducing a demand based on the destination
equipment, and run the feeders based on
the demand . Then each conveyor has an
auto/manual bias station with the up-
stream equipment as an input . It can either
follow the upstream equipment, or be set
to run a constant speed . If all the conveyor
speeds are in auto, they all accelerate and
decelerate with the feeder . To prevent ma-
terial problems, often I’ll allow only zero or
positive bias and force even manual speeds
up to the upstream speed unless a techni-
cian is logged in .
Consider the capacity of the conveyor and
motors . The limit on such motors is Amper-
age/torque . Many conveyors do not do well
below 40-50% of full speed, so their turn-
down is not very flexible .
Chris Hardy, senior controls engineer / Cross Integrated
Systems Group / www .crossisg .com / member of Control
System Integrators Association (www .controlsys .org)
CONSIDER SHELF LIFEThere are many considerations that drive
the decision to use a VFD to save energy .
Since there is more potential for saving en-
ergy on high-demand equipment, it would
be a good idea to index motors in terms of
the highest horsepower and length of oper-
ating time . For example, a 50-hp motor that
runs 24/7/365 will use more energy than a
100-hp motor that runs 8/5/288 . The best
strategy is to concentrate on these high-
energy consumers because that is where
one will get the biggest return for efficiency
improvements .
One of the first things to check is the cur-
rent motor loading . Many times a load is 10
hp and someone in the past put a 20-hp
motor on the application, just to be safe . So
now, even a high-efficiency motor running
at half load will be very inefficient . Attempt
to have the motor size the next standard
rating above the maximum anticipated load .
Then, the application will be running in the
high-efficiency range of the motor .
Then next thing to find out is if there are
any times the load can be run at reduced
speed . If it can’t, then move on to the next
project . Putting a VFD on an application
that always runs at 60 Hz speed will use
more energy . This is because of the losses
in the insulated-gate-bipolar-transistor
(IGBT) power semiconductors in the drive .
If the speed can be reduced, then there is
a good chance a VFD would be a good fit .
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eHANDBOOK: Motors & Drives 19
Essentially, an electric motor is a constant
torque device, so, as one reduces speed, the
energy usage also reduces .
Also, look at the load type . If the load is a
machine, chances are it is a constant-torque
load, and cutting the speed in half will cut
the energy usage in half . If the load is a
pump or fan, the loading is typically a cube
function and cutting the speed in half will
cut the energy usage by 7/8 . One needs to
pay attention to the duty cycle . If the time
spent at low speed is significant, the motor
cooling fan is ineffective at cooling the mo-
tor . An external fan may be needed . Invert-
er-rated motors will have a turndown ratio
specification indicating the lowest speed
the motor can run without adding an exter-
nal constant-speed blower .
Lastly, PLCs and other logic solvers, some-
times onboard the VFD, can be used to
monitor the system and decide when
speeds can be decreased or increased .
They can be used to set speeds based upon
recipes . They can be perhaps programmed
to turn off equipment when not being used .
They can be used to match line speeds . It is
common today for a drive to be controlled
over a fieldbus—EtherCAT, Modbus/TCP,
EtherNet/IP—connected right to a PLC . This
makes control easy .
If the application does not appear to be
suitable for a VFD, one can consider a
soft starter . A utility power bill always has
two components—an energy charge and a
demand charge . While a VFD affects both
because it can soft-start the load and re-
duce speed, the soft starter only affects the
demand charge . The soft starter will start a
motor direct on line (DOL) using semicon-
ductors to limit the starting current thereby
controlling the demand . When the motor is
up to speed, a bypass contactor will close,
shorting across the semiconductors . Be-
cause the motor current is shunted through
the contactor, there is no longer an energy
loss due to the current flowing through the
silicon-controlled rectifiers (SCRs) .
One other thing to consider is that any
electronic product adds complexity to a
control system . VFDs and soft starters, be-
ing power electronics, are not as rugged
as a DOL starter . There will be equipment
failures . Most manufacturers will cover
the cost of the drive if it failed during the
warranty period . However, troubleshoot-
ing, removal and re-install are generally not
covered under a manufacturer’s warranty .
If the process is critical, one may want to
keep spares . Soft starters generally have a
long shelf life . Not so with VFDs . The VFD
problem centers around the electrolytic bus
capacitors that filter the dc bus . When the
drive is not powered, the electrolytes in the
caps will migrate out of position . If power is
off for less than a year, most modern caps
are OK . Between one and two years, migra-
tion has started . After two years, the bus
caps should be reformed . A good drives
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eHANDBOOK: Motors & Drives 20
service center can perform this procedure .
This problem is applicable to all VFDs with a
dc bus; every manufacturer has this prob-
lem . Needless to say, just because a drive
goes two years without power doesn’t
mean it will blow up . But it happens enough
that, if it is the only unit left that will get the
equipment running again, one should not
take the chance and opt to reform the caps .
The most successful upgrades are done
when the end user retains the services of a
reputable control system integrator (CSI)
experienced in the drives market . The CSI
will spend the time with the various appli-
cations and recommend the best compo-
nents for the particular application . Work-
ing with a vendor salesperson may work,
but then equipment recommendations will
consist of items they sell . For example, the
application in question may need precise
position control, and a vendor may only
have a PLC-based motion control that is
based upon velocity . Both solutions are
technically motion control, but only one
solution is right for the application .
Kenn Anderson, President / Nova Systems / www .nova-
systemsinc .com / member of Control System Integra-
tors Association (www .controlsys .org)
PLANTWIDE GOALSThere are many ways and philosophies to
perform plant-modernization projects that
include green initiatives . This can be diffi-
cult without a clear understanding of what
equipment exists and what the true end
goal is . I have more than 25 years of experi-
ence working in ammonia-refrigeration con-
trols with energy management along with
plantwide process-automation projects .
Some of the key items you are asking are
logical and looking down the correct path .
I’ll try and break down my thought process
on a project like this as best as I can, under-
standing that there are a lot of variables .
If the mindset and funding is the “total”
plant upgrade, I would start with picking
a foundation control system for the end
game, instead of adding little pieces and
parts as we slowly and methodically go
through the entire plant and upgrade the
equipment . The initial cost will be higher,
but the overall savings will more than pay
for it in the long run . Not to mention, the
end system will be easier to maintain and
expand as you go along . A good end result
always results with a well-executed plan .
Some base questions to ask:
• What is the big picture?
• How many motors in all?
• Are you wanting to track power utilization
for specific products or functions?
• Where are they located throughout the
plant?
• Can they be logically grouped into com-
mon power distribution points or product-
specific applications?
• Are there safety concerns with all or some
of the motors?
• Are there some loads that are critical and
some that are not?
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eHANDBOOK: Motors & Drives 21
• What motors can be run as truly variable
speed or can have multiple speed set points
• What kind of environment will the equip-
ment be in—hot, cold, humid, dry, classified?
• What platform do you want to be on—
Rockwell Automation, Siemens, Schneider
Electric?
• Do you want to collect any performance
data or have a centralized control of all the
equipment, such as an an operator room?
• Do you want any data reporting, remote
monitoring or remote service/access?
Let’s start with some assumptions . I would
design a core control system capable of
running all of my future needs or design
it to be easily expanded as I go through
the plant to meet my end goal . I person-
ally prefer Allen-Bradley, but Siemens and
Schneider both have more than enough ca-
pability to do the same thing . I would make
a determination if I need any redundancy in
my design to help to prevent unexpected
or unanticipated downtime . This primar-
ily includes processors and networks . I
would use an Ethernet-based network as
my communications backbone in any of
the platforms . I would also look at safety
concerns to determine if any of the motors
need to be controlled in a safe manner . For
example, if a mixer is readily accessible by
an operator, we would need to consider
designing the control of that mixer to a Cat .
3 level and utilize a delayed safety relay to
allow the mixer to make a controlled stop
versus a coast to stop .
I would start with a design/build of a cen-
tralized control system consisting of an
Allen-Bradley ControlLogix platform . I
would consider a large enough rack to
house multiple processors and network
cards to meet my end design goals . To keep
costs down, I would only put in the base
components I needed to start the project
and plan for additional components as more
of the plant came on line . I would include
redundant power supplies along with an
uninterruptible power supply (UPS) system
and surge protection for the main control
cabinet power . I would do some preliminary
network design and choose a Layer 3 man-
aged switch to be the central hub for my
networked groups . From there, I would look
at the entire plant and divide up the equip-
ment/motors in a logical grouping, either by
location or functionality or both .
For example, building ventilation, dust col-
lection and overall system utilities such as
chillers and fluid coolers may be one group;
process and production lines may be anoth-
er group, packaging and receiving may be
other groups . Or you could look at general
areas: shipping and receiving, production,
east side of building, northwest corner—
whatever makes logical sense to you and
your end-control and data-collection needs .
Once the plant is divided up, I would look
for centralized motor distribution points to
meet those needs, along with the estimated
full-load amperage (FLA) . Within each
group, I would determine my safety needs/
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eHANDBOOK: Motors & Drives 22
concerns and then identify each area as
phases of the overall project . Phase I would
be the design and build of the centralized
control and monitoring system along with
the first grouping of upgrades . I would then
designate and provide preliminary bud-
gets to the additional phases of the project
based upon budgeting needs and timing .
On motors that cannot be slowed down,
I would consider their overall horsepower
requirements; I would be less concerned
with small motors, unless they start and
stop frequently . On larger motors, I would
consider a soft start or variable frequency
drive (VFD) for any motor 20 hp or larger .
You may be able to work with your local
power company and get credits based upon
changing the across-the-line (ATL) start-
ers out with soft starts or VFDs . Typically,
the costs of VFDs are now below the cost
of soft starts once you get above 5-10 hp
when networked .
From there, I would design a panel to serve
as the motor control center (MCC) for these
motors, unless a true MCC is required to
meet serviceability requirements . Custom
MCCs can be designed and built but may
or may not be a little more costly than,
say, a Rockwell Automation IntelliCenter . It
all depends on the overall equipment and
negotiated pricing . Always force two ven-
dors to face off on pricing of MCCs; never let
one assume they are the only answer to the
project, even if they truly are . It’s the only
way you will get a fair price . A custom MCC
is nice, because you can design it and build
it to meet your exact needs . Otherwise, you
will be purchasing an off-the-shelf system
that has to be field-modified to meet your
specific needs, such as hardwired safety
interlock circuits and networking . If you go
with an off-the-shelf MCC design, I would
consider purchasing extra sections and emp-
ty buckets for future use . It will cost less to
purchase them with the main project than to
add them later . I would then design in a local
ControlLogix rack or Flex I/O rack to pick up
any local analog or discrete control needed
within the MCC or local area . For all other
motors in which true variable speed can be
implemented, I would use the Allen-Bradley
PowerFlex family of VFDs and design them
to be networked back to the centralized
control system along with the larger motor
sizes . I would then implement any interlock
safety wiring into the base design .
I would include all local control power
distribution and networking needs within
this local MCC . I would also consider a local
control display depending on the need for
local control of the equipment and whether
local hand/off/auto (HOA) or start/stop
control and indication exists or is not in
the base MCC design . I would include a
local power meter networked back to the
centralized control system so the overall
equipment power diagnostics can be moni-
tored and trended in the central control
system . If individual equipment information
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eHANDBOOK: Motors & Drives 23
is needed, it can be pulled from its asso-
ciated VFD or soft start . If an ATL status
is needed, local power monitors can be
added to pick up key components or areas
of components—a set of conveyor mo-
tors, for example—based upon the overall
design . If there is a need for grouping of
motors on a conveyor or fan grouping that
you would like to have variable, this can
be done, as long as the VFD is sized to the
overall FLA and not the overall hp; there is
a difference . There are also limits as to the
amount of motors that can be connected
to a single VFD in the manufacturer’s
specifications . This is typically limited to
a maximum of five motors . There is also
a typical maximum hp per motor, and all
motors must be identical in ratings . In the
past, we have found that running a 60-Hz
fan or mixing motors at or around 50 Hz
improves the overall amperage demand
on the units without decreasing the overall
performance . Of course, you would need
to look at the torque curves and perfor-
mance curves to see if this is accurate for
your application . I do want to point out
that with the consideration of adding so
many VFDs to a plant, one must really
consider installing line reactors on all the
VFDs to prevent harmonics issues and to
ensure proper installation . This includes
using properly rated VFD cable and poten-
tially load reactors based upon installation
distances . These little steps will help to
prevent premature failure of motors, VFDs
and upstream equipment .
Once everything is determined, you can
look at overall energy savings methods .
Control-wise, you can monitor the peak de-
mand of the entire plant along with the total
kW usage . Knowing your peak demand
charges and your kW usage, you can deter-
mine actual power bills . If you have equip-
ment that is not critical and can potentially
be shut down or scaled back, software can
be developed to allow for load shedding of
equipment based upon a maximum peak
demand set point . As the system sees peak
demand increasing to a preset threshold,
key equipment can be stopped or loads
reduced to curb the peak . A schedule can
be developed as priority lists and allow-
able limits on load shedding . As a simple
example, if a conditioned space is ideally 70
°F and there is a set load required to main-
tain that temperature but it is not critical,
the conditioning of that space can be shut
down or scaled back and the temperature
can be allowed to rise or fall depending on
the space . However, there may be a thresh-
old that it cannot get above 75 °F . As that
load shed is active, if the space reaches 75
°F, the equipment is restarted to prevent
further temperature rise . You can then set
up priority levels for load shedding . That
space may be a Priority 1 load shed, and you
may have another space or piece of equip-
ment as Priority 2 . If Priority 1 load shed
goes into effect and peak demand is still not
curbed after a preset amount of time or a
secondary limit, Priority 2 kicks in . You can
set up continuing levels to act in the same
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eHANDBOOK: Motors & Drives 24
manner, although we usually limit it to five
levels of load shed .
Another option to add to the list that
hasn’t been mentioned is power-factor cor-
rection . This can be done plantwide with a
central unit or individually at each motor .
Either way, significant power-bill reduc-
tions can be realized depending on the
plant and power company .
All in all, it really comes down to under-
standing the process, end goals and over-
all controllability one wants to have on
the overall facility . Once you know that, it
comes down to understanding whether or
not there is a true payback on the cost of
implementation—the return on investment
(ROI) . A lot of facilities that are produc-
tion-based really don’t have enough flexi-
bility in the system to allow for true energy
management, or at least not one that will
have a sufficient ROI . They may be able to
improve a few percentage points in overall
efficiency, but that may not relate into the
overall bottom line . In ammonia refrigera-
tion, we have found the most significant
implementation to be in cold-storage facili-
ties rather than production facilities . Pro-
duction facilities have a base demand that
cannot be modified without catastrophi-
cally affecting production, whereas cold-
storage facilities have functional limits that
can be manipulated to control a peak de-
mand . Other industries concentrate more
on understanding their costs by monitor-
ing specific aspects of their plants, such
as specific product lines or core utilities .
That way they have a better understand-
ing of where their costs are for accounting
purposes . Every customer is unique, and
every project is unique, both in the thought
process and in the needs . It’s always our
responsibility as an integrator to determine
what that is and meet their goals .
Bradly A . Johnson,vice president, maintenance services
division; vice president, industrial process group divi-
sion / Dilling Group / www .dillinggroup .com / mem-
ber of Control System Integrators Association (www .
controlsys .org)
STANDARD VS. CUSTOMRelative to the motor, we plot efficiency
curves for our motors (Figure 1) . Motor
efficiency peaks at approximately 4,300
rpm for this standard motor . If you had a
lower-speed application, we could cus-
tomize the winding so that peak efficiency
happens at a lower rpm . Figure 2 is the
same motor with custom winding, and
now peak efficiency is happening at ap-
proximately 2,700 rpm .
Here’s another way to describe it . Let’s
say your application required 2,700 rpm .
If you buy a motor that has a rated speed
of 4,300 rpm, you are not using all of the
speed that the motor can provide . How are
you paying for this? Essentially you now
have a voltage constant (V/Krpm) that is
too low, giving you more speed than you
need . With a lower voltage constant, you
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eHANDBOOK: Motors & Drives 25
also have a lower torque
constant (Nm/Amp), so you
need to provide more cur-
rent relative to the torque
that the application needs .
By designing the winding
more around the 2,300 rpm
requirement, your voltage
constant is more in line
with providing you only
with the speed you need .
So, in this example, you
could have a higher voltage
constant—less speed rela-
tive to voltage provided—
which would also give you
a higher torque constant—
less current for the torque
you require .
The motor is operating more
efficiently because there is
no speed or torque capabil-
ity that is sitting stagnant .
These types of modifications
can easily be made to a mo-
tor by changing the AWG
(American wire gauge) of
the copper and its number
of turns in the stator .
There are other things that
can be done to improve
overall efficiency relative
to heat dissipation via rotor
and stator design . But those
types of considerations are
usually looked at during ini-
tial product design and are
not something that would
be offered via a customiza-
tion to an existing motor .
Jeff Nazzaro, gearhead and motor
product manager / Parker Hannifin
/ www .parker .com
AFFINITY LAWSYou can certainly save
energy and improve effi-
ciency by integrating drives
with your motors . Pumps
and fans are great targets
STANDARD MOTORFigure 1: Motor efficiency peaks at approximately 4,300 rpm for this standard motor.
CUSTOM WINDINGFigure 2: The same motor with custom winding now has peak ef-ficiency happening at approximately 2,700 rpm.(Source: Parker Hannifin)
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eHANDBOOK: Motors & Drives 26
for energy savings if you can slow them
down and still perform the needed applica-
tion . You have indicated that is the case, so
here’s how it works .
Pumps are fans are considered variable-
torque (VT) loads . The valuable point here
is that VT loads follow the affinity laws,
which really make three points .
Flow (water, air) through a VT system var-
ies directly with the motor speed . So, if you
run the motor at 50% speed, you get 50%
of the flow through the pump or fan .
Pressure varies with the square of the mo-
tor speed .
Power, or energy consumed, varies with the
cube of the motor speed . So, if you could
run the motor at 50% speed, you would
only consume one-eighth of the energy .
Figure 3 depicts the affinity laws in a graph-
ical manner .
In fact, due to the cubic relationship of the
motor speed and the power consumed,
even slowing down the motor a small
amount can make a dramatic impact on
energy consumption .
SLOW THE MOTORFigure 4: Energy consumption is reduced by reducing motor speed on a VT (centrifugal pump or fan) load.(Source: Baldor Electric)
AFFINITY LAWSFigure 3: Due to the cubic relationship of the motor speed and the power consumed, even slowing down the motor a small amount can make a dramatic impact on energy consumption.(Source: Baldor Electric)
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eHANDBOOK: Motors & Drives 27
Figure 4 shows how much energy con-
sumption is reduced by reducing motor
speed on a VT (centrifugal pump or fan)
load . If you slow the motor down only 20%,
you will consume half of the energy .
The other applications you mention can
save energy, as well, if variable speed
drives (VSDs) are applied, but it will not be
the dramatic impact you will see with VT
loads, so I would recommend that you start
with your VT loads .
Integrating the motors and drives with the
PLC can be simple or complex . It largely
depends on the design of your system .
Integrating drives/motors with PLCs can be
done in a couple of ways:
• via digital and analog I/O modules on the
PLC backplane
• via industrial communication networks, such
as Ethernet/IP, Modbus/TCP, Profibus-DP .
If you do choose to integrate the motors
with a PLC, a program will also have to be
written to control the motors and drives .
The program could be quite simple or
quite complex, depending on what you are
trying to control . For the more complex
systems, you may want to consult with a
system integrator to provide you the func-
tionality you require .
Rick Kirkpatrick, product manager, ac variable speed
motors / Baldor Electric / www .baldor .com
MOTOR INTELLIGENCEThere are VFDs that have integrated com-
munications . Modbus RTU and Ethernet IP
are the most common communication for
process controls such as machines or con-
veyors and would communicate back to a
PLC . Modbus RTU, BACnet MSTP and BAC-
net IP are most commonly used for building
management systems that would tie in the
HVAC, pumping, lighting and fire systems
together for improved management . Most
VFDs have the ability to communicate these
protocols and have PC tools that allow for
easy commissioning and configuration to
the different networks . Application or com-
munication manuals would have all of the
bit numbers and descriptions for easy setup
and connectivity .
There are two different application where
VFDs can be used and provide the most
benefit:
1 . Any application where there is the oppor-
tunity for variable speed . These could be
constant-torque application (conveyors,
mixers) or variable torque applications
(fans, pumps) . Using a VFD to vary the
speed, rather than mechanical devices
such as a damper on a fan or a relay, you
improve the reliability of the system and
performance of the motor reducing any
losses . You also achieve reduced energy
usage, which in turn is reduced energy
cost . Many regulations are requiring VFDs
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eHANDBOOK: Motors & Drives 28
be used in variable-torque applications on
motors that are rated down to 5 hp . Title
24 in California, ASHRAE Standard 90 .1
and the 2017 DOE refrigeration legislation
are all examples of these regulations .
2 . Any application where you would like
to communicate status on a motor and
increase the protections of the motor . An
example would be a critical application or
pump . The VFD has built-in applications
and algorithms that can provide increased
protections on motors without the use of
additional sensors or external devices . The
list of protections can improve the life of
the system and provide feedback that will
help to predict when systems will fail and
reduce unplanned downtime .
There is an application built into some VFDs
that allows the VFD to be a master of other
VFDs or motor starters . This means that the
VFD can accept feedback from a demand
source—temperature sensor, pressure sensor,
speed reference from a PLC—and take that
feedback to control other drives or com-
municate back to other systems based on a
configured process . The communication ca-
pability increases the ability to get feedback
from all systems at once with alarms, alerts
and faults information with time stamps . This
increases the visibility of the system and
reduces unplanned downtime . It is all about
bringing the intelligence to the motor .
Nicole Angiola, product manager, HVAC variable fre-
quency drives / Eaton / www .eaton .com
ENERGY SAVINGSThis really depends upon the level of control
you require . If you are looking for a low-level
control with just speed set point, starting/
stopping and fault indication, this can be ac-
complished by simple I/O wiring with a few
discretes or optionally a few discretes and an
analog signal . If you want to be more precise
and/or if you will have a controller running
several drives, networking is a better way
to go . Ensure your PLC and the slave VSDs
support the same communication protocol .
Networking gets a lot of novice users intimi-
dated, but truly it shouldn’t . It’s very simple
with modern PLCs and drives .
Many, many applications greatly benefit
from the use of VFDs for energy efficiency .
Let’s start by looking at centrifugal pumps
and fans . Pumps and fans are sized for their
maximum duty point but usually are then
throttled down to a lower demand . Mechan-
ical controls such as guide vanes, bypasses
and throttle valves do present some energy
savings; however, the maximum efficiency is
gained by slowing down the motor directly .
These applications are referred to as variable
torque applications and are governed by the
affinity laws . In these applications the torque
required is a function of a square of the mo-
tor speed . The power required however is a
function of a cube of the speed . For example,
reducing the speed to 50% can reduce the
power required to 12 .5% of the rated power .
www.controldesign.com
eHANDBOOK: Motors & Drives 29
Modern VFDs can take ad-
vantage of this and reduce
the motor voltage appropri-
ately to gain those energy
savings at lower speeds to
follow the curves of the af-
finity laws (Figure 5) .
The simplest and least
precise is to have one drive
control multiple motors .
You need to check with
your drive manufacturer
if this is acceptable for its
drive to do this . In this ap-
proach you size the drive
for the sum total of all mo-
tors and provide an exter-
nal motor overload relay
to protect each individual
motor . Often drives cannot
be switched to/from load
without damage, so in this
approach you must often
select motor overloads that
have an auxiliary contact
that is break first/make
last, and you run those all
in series to a drive input
configured for external
fault—the idea being if one
of the motor overloads trip,
it first faults the drive and
doesn’t allow the drive to
be restarted unless all mo-
tor overloads are clear .
Another simple and still
imprecise way is to com-
mand speed to one drive
and then have that drive’s
analog output annunciate
its actual speed . Run that
analog in turn to the next
drive as its speed set point .
You can also use the drive’s
run/status output as a run/
stop command to the next
drive . It is imprecise, and it
is very basic . Error handling
of individual drives can be
an issue with this method .
Another approach that can
often be done—check with
your drive manufacturer—is
using a fieldbus such as
CANopen where the nodes
are peers and you would
have a master drive which
you command speed and
run stop to via its keypad or
control wiring, but then map
that master drive’s status
words on the network as the
command words to the slave
drives to have them follow
the master’s state . Precision
in this approach is a func-
tion of the motor control
method used by the drives .
Closed-loop vector is the
most precise . Open loop V/
Hz is the least . Error handling
of individual drives can be an
issue with this method .
A better way to do this is
networking the drives to a
REDUCED VOLTAGEFigure 5: Modern VFDs can reduce the motor voltage appropri-ately to gain those energy savings at lower speeds to follow the curves of the affinity laws.(Source: Lenze Americas)
www.controldesign.com
eHANDBOOK: Motors & Drives 30
PLC . The PLC can set speed
and control each drive and
also read each drive’s status
so faults can be annunciat-
ed and controlled reactions
easily set up to respond to
various conditions .
Joel Kahn, product manager, in-
verters / Lenze Americas /
www .lenze .com
ROI ANALYSISMany industrial plants
that are in the process
of implementing green
initiatives or moderniz-
ing to reduce costs must
evaluate the energy costs
associated with motors in
their plants . Motors tend
to play a large part in plant
efficiency and cost-reduc-
tion efforts because they
are usually responsible for
a substantial amount of
the monthly electric utility
costs . Some statistics indi-
cate that motors consume
70% of all domestic manu-
facturing energy and 55%
of total energy generated
in America . Interestingly,
most motors will consume
10 to 20 times their capi-
tal cost in energy every
year so any effort aimed at
reducing these costs can
yield significant savings .
In many applications where
motors are used to drive
pumps, fans or compres-
sors (centrifugal loads) and
are using throttling, either
valves or dampers to con-
trol the process flow or
pressure, variable frequency
drives (VFDs) may be ap-
plied to great economic
benefit . By changing con-
stant motor loads to vari-
able speed, payback ben-
efits may be realized in as
little as one to two years .
If you are reviewing your
plant for a modernization
initiative, reviewing the mo-
tors in the facility is a good
place to start since, in most
cases, they will represent
the bulk of your monthly
utility payment . If these mo-
tors drive centrifugal loads
like fans, pumps or com-
pressors and the process
operates below 100% flow
or pressure, there may be a
real opportunity for energy
cost reductions . The motors
are typically started with
motor starters .
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eHANDBOOK: Motors & Drives 31
There are three charac-
teristics with centrifugal
loads known as affinity laws
that define the relationship
between shaft speed or the
speed your motor is running
and process parameters
such as flow, pressure and
power consumption .
• Flow (of material) is di-
rectly proportional to the
shaft speed .
• Differential pressure is di-
rectly proportional to the
square of shaft speed .
• Process power is directly
proportional to the cube
of shaft speed .
Therefore any plant pro-
cess that requires reduced
flow (air, water, oil, gas) can
utilize the affinity laws . For
example, if your process
is rated for a material flow
of 10,000 gallons/minute
(gpm) but can be operated
at a reduction to 7,000 gpm
or a 30% reduction in flow,
changing the motor speed
may yield impressive energy
savings . From the affin-
ity laws we know flow and
speed are directly propor-
tional, so if the motor speed
is reduced by 30%, the pro-
cess flow will also drop by
30% (10,000 gpm to 7,000
gpm), but the energy con-
sumption is a cubic function,
so the amount of energy
used drops even more; and,
in this case, a 30% reduction
in motor speed yields a 66%
reduction in energy usage .
This approach can also work
on many systems where
speed is adjusted such as
agitators, mixers, conveyors
and mills, and these typically
will also benefit from more
precise speed control .
As long as the plant pro-
cess is using a centrifugal
load that is being throttled
or controlled with dampers
or valves, it is likely that the
process can benefit from the
addition of a VFD . This argu-
ment applies for low-voltage
and medium-voltage mo-
tors . Other applications may
also benefit but may require
additional analysis and may
not yield the same energy
cost savings .
When evaluating a motor
system as a candidate for a
VFD, one should look at the
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eHANDBOOK: Motors & Drives 32
turn-down speeds . As stated
above a 30% reduction of
speed yields large energy
cost savings . In processes
where the speed turn-down
rates are less than 90%, then
the viability and payback
of adding a VFD becomes
less clear . If the process runs
close to 100%, then the cost
savings of the VFD may be
minimal and possibly elimi-
nated by the efficiency of
the VFD itself . By adding
a VFD, the VFD itself has a
rated efficiency, typically
95% to 97%, and adds losses
to the overall system . The
savings associated with the
operating speed reduction
must be greater than the
efficiency losses of the VFD .
One note here is that there
is no such thing as a 98% or
99% efficient drive . These
numbers are bandied about
and usually represent only
the inverter section of the
VFD . Although they are true,
they represent only one sec-
tion of the entire system and
not the actual VFD compo-
nents required to run . Most
VFDs today operate with 3%
to 5% losses for the entire
VFD end to end . Sometimes,
input filters, sine wave filters
and output filters are not
included in this efficiency
rating as they are separate
from the VFD but are still
required . The VFD user must
be aware of all components
required to safely operate
the VFD to protect the plant
from unwanted harmonics
and to protect the motor
from insulation failure, har-
monics and bearing currents
leading to premature motor
bearing failures . The VFD
manufacturer should work
with you to develop a wire-
to-shaft overall efficiency
rating to clearly define the
actual losses and to identify
the installation requirements
for filters, additional cabling
connections and mounting
pads for various separate
components outside the
VFD cabinet .
In addition, most VFD manu-
facturers will work with the
process plant to identify the
potential costs savings and
generate ROI payback peri-
ods . These can include not
only the energy saving asso-
ciated with the VFD operat-
ing at reduced speeds but
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eHANDBOOK: Motors & Drives 33
could include additional HVAC costs—addi-
tional control room air conditioning—but also
plant requirements like site arrangements .
There are several other advantages to in-
stalling VFDs on motors which are harder to
quantify but, nevertheless, very real advan-
tages . The use of a VFD eliminates the start-
ing inrush event that the motor experiences .
This has two advantages .
First, the elimination of the inrush current
when starting the motor, which can be six to
10 times the motor FLA rating, has the effect
of reducing the peak demand charges on
the monthly utility statement . Obviously, the
cost savings is dependent on the number of
motor starts but eliminating this phenom-
enon should have a positive cost impact on
reducing the peak demand charge on the
utility statement . Secondly, the elimination
of the inrush event dramatically reduces the
mechanical and electrical stress on the mo-
tor leading to longer motor life and lower
maintenance costs . However, this may be
negated by the selection of a VFD with an
inferior output waveform leading to har-
monic heating or insulation damage in the
motor, so care must be taken in the VFD
topology selection . The addition of output
filters to protect the motor leads to reduced
efficiency, which adds cost and possibly
plant power grid and safety issues (motor
self-excitation), which must be analyzed and
accounted for . These issues can easily be
overcome but may yield a longer payback
period, as well as additional operating ex-
penses if the plant power grid is changed .
Lastly, most modern VFDs will present a
constant power factor to plant power grid
of 0 .95 or greater, which will tend to reduce
the power factor penalty on the monthly
utility statement . This is a small charge and
is at most a secondary effect of the VFD .
However, care should be taken with older-
style current source drives where the power
factor is proportional to speed and can
become very poor when operating below
80% speed, potentially requiring the addi-
tion of power-factor correction components
in the plant . This adds installation costs and
possibly reduces efficiency, which again can
increase the anticipated payback period
and energy savings .
The discussion presented here applies to
low-voltage or medium-voltage motors and
their applications . Any VFD manufacturer
should be able to assist the end user, en-
gineering firm or electrical contractor with
the ROI analysis . Understanding the operat-
ing scenario and examining the plant single
line should be within the scope of the VFD
manufacturer’s expertise and part of the
proposal process . Additionally, the VFD
manufacturer should be able to evaluate the
plant motor, especially if it is an older, exist-
ing motor to verify proper operation and
motor life with the selected VFD .
Mark Harshman, director of system engineering / Sie-
mens / www .siemens .com
www.controldesign.com
eHANDBOOK: Motors & Drives 34
3 STEPS TO EFFICIENCY AND PAYBACKBlindly adding a VSD will not automatically
increase the efficiency of an axis (drivetrain
+ motor + VSD) . VSDs have power losses
and could worsen the overall system effi-
ciency . Determining efficiency increases and
fastest payback rates can be summarized
by the following generalized process .
1 . Does the application run at the motor’s “full
speed” and seldom start and stop? If the an-
swer is yes, then adding a VSD will hurt sys-
tem efficiency and simply add losses (VSD
losses and motor PWM heating) . Replacing
the motor with a higher efficiency version
is the best option . Determine if the motor
should be replaced now or later based on
current age of the motor, new motor cost
and energy savings payback rate . Fans and
pumps typically fall under this category .
2 . Does the application run at the motor’s
“full speed” but also starts and stops of-
ten? If the answer is yes, then a VSD can
reduce motor starting currents . The bigger
the motor, the more reduction in current
spikes (line start currents are typically six
times motor rated current) . The payback
rate is determined by how often the motor
starts and stops and how large the motor
is . You can also replace the motor with a
higher efficiency version, but check with
the VSD manufacturer . High-efficiency
motors may require an upsized drive due
to the low winding impedance .
3 . Would the application be better suited
running slower or faster than motor line
speed? If the answer is yes, then you
will need a VSD, or perhaps a gearbox
change, but be aware changing the
speed of the axis can affect required
torque and power . For example, saws
that run slower have dramatically higher
torque . Increasing fan speed increases
motor load quadratically and can be
mechanically dangerous .
If you are converting a whole line to vari-
able speed and it can mechanically handle
it, there are typically two control schemes:
velocity-follower and electronic gearing .
Velocity-follower systems can be thought of
as open loop controls running at 50% or 70%
speed . If an axis that is commanded to run
70% speed can run at 68% or 71% without
issue, then this type of control can be used .
In the olden days, the master axis would
have an analog output that was wired to the
analog input of the next axis . More modern
systems can use a fieldbus control and send
digital commands to each drive .
Electronic gearing is required for applica-
tions that have some type of registration—
closed loop, shaft lock . These are closed-
loop systems that can maintain shaft angle
relationships as if there was a mechanical
line shaft running the whole machine . It is
easiest to control these systems with a real-
time fieldbus like EtherCAT where each axis
www.controldesign.com
eHANDBOOK: Motors & Drives 35
can receive the master axis position over
the bus instead of running encoder cables
between each drive .
Scott Cunningham, product and application manager,
controls and automation / KEB America / www .ke-
bamerica .com
REDUCE COST, INCREASE CONTROLTo answer the first part of your question,
you should start by looking at applications
where there’s a need to control the speed
of the motor that is currently being con-
trolled by mechanics, a contactor for start-
ing and stopping or older variable-speed
drives . There are benefits that come with
using the variable-speed drive for starting
and controlling the application and ways to
improve not only the efficiencies of the ap-
plication and the way it’s running the motor,
but also the overall process . Product waste
is an area where improved control of the
motor and application can reduce product
or material waste, making the process and
the plant more efficient and saving costs .
Using a variable-speed drive, with or with-
out a PLC, in an application is accompanied
by significant benefits . Those include im-
proving the efficiency of the system, reduc-
ing waste, reducing maintenance cost and
having better control of the application . A
lot of times, people think that you’re just
adjusting the speed, but in reality you’re
reaping a lot more benefits than just having
variable speeds to run the motor at .
In terms of which motor applications would
benefit from a variable-speed drive, you need
to ask yourself, “Does the application run at
60 Hz?” That’s typically the base speed of a
motor in North America . If the motor is cur-
rently running at 60 Hz, day in and day out,
then the application may not benefit from
the variable-speed control but would benefit
when starting the motor and from the feed-
back the drive can provide on the application .
If it’s not running at 60 Hz because it’s being
adjusted by mechanics or other equipment
in the system, or if there’s a lot of starting
and stopping, those are the applications
where we would look at easily applying a
variable-speed drive . Any time you’re not
running at a base speed all of the time, if
there are any adjustments being made,
that’s where variable-speed drives help out .
Variable-speed drives provide precise speed
control . If you use a VSD, you can reduce the
inrush current when starting and the amount
of power to get things moving just by the
nature of using the variable-speed drive .
When it comes to tying all the motors and
drives together, you’re getting at the heart
of where variable-speed drives integrate
best in the process . Installing a VSD here
gives you the benefit of unlimited speed
points, so you can adjust speed to whatever
value you need for your application and co-
ordinate the movement of product . You can
also better control those applications and
eliminate any kind of waste .
www.controldesign.com
eHANDBOOK: Motors & Drives 36
There are two ways of going about control-
ling the process line, depending on how
much control is needed . There are settings
and application-specific setups within the
drive, as well as some additional program-
ming that can be dealt with . Drives handle
a number of different applications, so the
control can be as simple as being the de-
fault programming of the drive, configuring
the parameters to increase control of the
application while using the drive’s inputs
and outputs or going to a controller or PLC
to work with a number of different drives .
Using a controller or PLC to communicate
to drives and the different pieces of equip-
ment to control them and to receive the
data back can increase the number of drives
being controlled at one point all from a cen-
tral location . One of the major benefits of a
VSD is the data it collects . Not only are you
controlling the application, but you receive
information about the process and the ap-
plication . You can analyze how much power
you’ve been using and use the data you
receive to understand what’s going on in
the application and help you to identify any
issues to improve overall system efficiency .
Adding variable-speed drives to your ap-
plications can provide significant benefits in
terms of reducing waste and maintenance
costs, increasing control and improving ef-
ficiency across the board .
Jim Kluck, senior product marketing manager / Danfoss
Drives / drives .danfoss .us
ENERGY SAVINGSEfficiency is usually a derivative of cost up
front . This is where the interest of equip-
ment supplier and user can vary . Every
industrial application can be made more
efficient, so it generally comes down to
how much work it’s going to take, how
much money it will cost and when I can
expect the efficiency savings to pay back
the investment .
The first scenario for motors running across
the line is going to a more efficient motor .
Government regulations are mandating new
motors installed meet minimum efficiencies
that continue to increase . Today’s premium-
efficiency induction motors have a very
high efficiency, but motor manufacturers
are approaching the design limits to how
much more metal or copper they can put
into the motor to make them more efficient
before the frame size will increase .
The next scenario is changing a fixed-
speed application to a variable speed with
a variable-frequency drive (VFD) . For vari-
able-torque applications, such as a fan or
pump, this is typically a no-brainer as the
payback from energy savings is very short
if you can run at reduced speeds . A pre-
caution I would give is to verify the motor
is designed to be run from a VFD . There is
also an emerging trend for variable-speed
applications to use a synchronous motor
as they offer even higher efficiency with
smaller footprint .
www.controldesign.com
eHANDBOOK: Motors & Drives 37
There are also numerous VFDs and servo
drives that offer energy-saving functions and
configurations . A few typical functions are
ECO mode to reduce motor losses; bypass
mode to reduce inverter losses; and hiber-
nation mode to go into sleep mode during
long pauses . Since motors can generate
energy when stopping or with overhauling
loads such as cranes using drives that can
regenerate energy back to the power sup-
ply are preferred for certain applications . On
production machines with multiple drives a
common dc bus arrangement is very popular
to take advantage of energy sharing when
one or more motors are generating power
and other motors can utilize this power .
This is also a good time to mention that hy-
draulic and mechanical solutions are being
switched to electrical solutions due to the
high potential for energy savings . A hydrau-
lic pump with a fixed-speed application can
be replaced by a servo pump that supplies
energy only when required and can save
up to 70% the energy consumption . Even
replacing a gear box or pulley with a direct
drive can result in large increases in system
efficiency, so using a holistic approach to
energy savings is always best .
For payback calculations, I would use one
of the many free software tools available
from motor and drive manufacturers to help
to compare savings with different solutions
and help to validate the payback is expect-
ed on your investment .
Craig Nelson, senior product manager / Siemens Digital
Factory / www .siemens .com
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C6SMART
There is no doubt hydraulics has unmatched muscle, compared to pneumatics or
electrical power transmission in linear and rotary motion applications . While pneu-
matics may win the game when it comes to simple, low-cost and fast linear motion,
hydraulics has never been better .
Although many oil-leaking, hot, noisy hydraulic power units are still in service today, hy-
draulic technology has developed well over the years . Don’t let oil leaks from the past sway
your decision to use hydraulics . Leaks have been addressed and power units are quieter
making it a great option for some applications . New sealing technology has all but eliminat-
ed the puddles of oil under and around hydraulic devices . Fewer leaks also open the door
to higher operating pressures, and adding sound insulation in key locations has dramatically
lowered system noise, as well .
Check out a few basics on hydraulic systems and don’t reinvent the wheel when designing
and using this capable power transmission method . It does have its advantages .
In a closed system, Pascal’s law, which is the foundation of hydraulic drive systems, states
that the pressure anywhere is the same . Therefore, the force that the fluid transfers to the
surroundings is equal to pressure x area . The bigger the piston, the larger the force .
Hydraulic muscle, as neededSometimes brute force is needed, and a little hydraulic knowledge can get things moving in the right direction
By Dave Perkon, technical editor
www.controldesign.com
eHANDBOOK: Motors & Drives 39
www.controldesign.com
eHANDBOOK: Motors & Drives 40
Both pneumatic and hydraulic fluid-power
systems are used in a variety of industrial
machinery and off-highway equipment .
While pneumatics can transfer high force
and torque in power-transmission appli-
cations, it is often used in linear-motion
applications such as transferring, lifting,
clamping, gripping and stamping . These
applications are usually repetitive and fast
moving, as well .
It’s the heavy force and torque applica-
tions that benefit from the use of hydrau-
lic systems . These applications typically
involve tons of force such as pressing
metal, lifting large loads, digging or crush-
ing rock . While these hydraulic systems
eliminate many of the drives, gears,
chains, pulleys, drive shafts and ball
screws of an electrically driven system,
there are many fluid-power system com-
ponents that need to work together .
Considering the amount of power pro-
duced, hydraulic components are relatively
compact . It’s one of the reasons they’re
used in mobile construction and agricul-
tural equipment . A 5-hp hydraulic motor
could fit in the palm of your hand . It’s just a
fraction of the size of an equivalent combi-
nation gearbox and electric motor .
These hydraulic systems use an electrical
hydraulic power unit that includes an elec-
tric motor and hydraulic pump to supply
fluid power to the system . The power unit
also includes supporting equipment, such as
hydraulic reservoirs, heat exchangers, filters
and manifolds . It’s the hydraulic version of
an air compressor .
The pumping device, the prime mover that
converts mechanical power into hydraulic
energy, is often called an electric hydrau-
lic power unit . Unless you are an hydraulic
distributor or a fluid power expert, it’s best
to purchase this power unit assembled as a
system . Piecing an hydraulic prime mover
together takes some expertise and proper
methods to supply the flow and power
necessary to exceed pressure created by
dynamic loads .
Complicating the hydraulic-system design
are the many types of hydraulic pumps
available to create the needed flow . This
includes piston, vane and gear pumps .
Which one to use depends on the applica-
tion . Each pumping method has character-
istics that may make it a better choice for
some applications than others . Efficiency
and related heat generated play a big fac-
tor . For example, if an application always
needs full flow and pressure, a piston pump
may work just fine, but it will continue to
consume the same energy when the sys-
tem is at idle . I recommend creating your
hydraulic system work requirements and
then collaborating with your favorite hy-
draulic vendor to select the proper power
unit, as there are many options .
www.controldesign.com
eHANDBOOK: Motors & Drives 41
There are also many specialized and some-
times custom hydraulic fittings and mani-
folds, along with tubing and hoses that may
require special tools to assemble and build .
Whether flexible hose or high-pressure
tube, the hydraulic fluid conductors deliv-
ering flow and pressure to motion-causing
devices takes some planning and design . It’s
significantly different
than typical pneumat-
ic components .
The valves for start-
ing, stopping and
direction control are
much different, as
well . Given the non-
compressible nature of oil, servo-controlled
hydraulic valves provide more rigid and
stable position of cylinders than other com-
pressible methods .
With the correct hydraulic power unit
selected, consider the maintenance in-
volved . Hydraulic flow and pressure are
just some of the operational parameters
that are monitored today . Other diag-
nostic instrumentation can be added to
aid troubleshooting and future predictive
maintenance . This includes filter differen-
tial pressure, fluid level and temperature
sensors . Taking the time to add some
sensors and electronic controls can make
a more efficient,
precise and reliable
hydraulic system .
When hydraulics is
the best choice for
an application, take
the time to work
with the hydraulic
vendors and distributors . These hydraulic
power units are some of the low-hanging
fruit for cloud-based analytics, so add
sensors for data collection and monitor-
ing and get it connected to the plant net-
work . Proper hardware, design and moni-
toring will ensure a leak-free, efficient,
long-term solution .
Don’t let oil leaks from the past
sway your decision to use hydraulics .
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Get motors rolling and add feedbackKeep an ear out for electromagnetic interference and radio frequency interference
By Tom Stevic, contributing editor
Modern motors such as ac, dc and brushless dc servos are all different in con-
struction but have some performance characteristics . However, each design has
particular strengths and weaknesses . A dc motor typically has a bit more starting
torque than an ac motor, but brush-style dc motors may require maintenance to replace the
brushes . The brush action can also cause electrical electromagnetic (EM) and radio frequen-
cy (RF) noise . Having a good model of the mechanical requirements will make choosing the
correct motor torque, speed and power easier . There are many free motor-sizing tools avail-
able on the Internet to make the selection easier .
Both the National Electrical Manufacturers Association (NEMA) and the International Elec-
trotechnical Commission (IEC) have standard motor size specifications . Using a standard-
sized motor allows different manufacturers’ equipment to be used interchangeably . If a
motor must be changed from one brand to another, consider also changing the drive or
amplifier to the same brand, especially with servo motors . If technical issues arise when dif-
ferent motors and drives are employed, many manufacturers offer little assistance and tend
to blame each other instead of trying to solve the problem .
Manufacturers often offer many options when ordering a motor . Brakes, shaft seals, connec-
tor style, smooth shafts or keyways and connector styles are a few . Having many options
makes picking the perfect product for your application easier . A downside to the many
www.controldesign.com
eHANDBOOK: Motors & Drives 43
www.controldesign.com
eHANDBOOK: Motors & Drives 44
options is the availability of a replacement
part . Distributors and warehouses may not
keep one part of each possible combination
in stock . Choosing a motor that is normally
stocked, even if it has options that will not
be used, may better serve your customer .
One machine builder I have worked with
would list all of the possible motor combi-
nations that could be used directly on the
electrical prints .
Some motor manufacturers offer special or
custom designs . These should be utilized
only as a last resort in manufacturing equip-
ment . Be aware of the lead time required if
motor replacement becomes necessary at
some point . Plant managers are usually not
very understanding when machines are idle
waiting on some special part to be built .
In a closed-loop servo motion control sys-
tem, the motor’s actual position is com-
pared with its commanded position . Typical
feedback devices include resolvers, incre-
mental encoders, absolute encoders and
Hall effect sensors . Although not typically
used in an industrial system, analog ta-
chometers and rotary potentiometers may
also serve as feedback devices .
Resolvers are simple rotary transformers .
An analog excitation wave is supplied to
a single primary winding . Two secondary
windings are typically mechanically spaced
90° apart . As the resolver’s primary winding
is rotated, the secondary winding generates
sine and cosine waveforms that represent
the rotational angle of the primary . Resolv-
ers provide an absolute position whenever
they are under power . However, electro-
magnetic interference (EMI) and radio
frequency interference (RFI) may influence
the analog output signals . Proper shielding
is essential . Resolvers are rugged and can
operate in the harshest environments .
Incremental encoders produce one to three
pulsing signals . A single-phase encoder sup-
plies x number of square wave pulses per
rotation . A quadrature encoder outputs two
signals that are 90° apart . With this infor-
mation, the controller can determine rota-
tional direction . A third square wave pulse,
called the z phase, is output once every
revolution . If power is interrupted for the
encoder or the controller, a system using
an incremental encoder would need to be
“homed” before use .
An absolute encoder outputs a binary
count, depending on the angular position of
the encoder . Typical count values are 255
(8 bit), 1,023 (10 bit) and 4,095 (12 bit) . An
advantage of an absolute encoder is the
encoder supplies its rotational angle upon
power application . Mechanical and electri-
cal multi-turn options can provide direct
positional information to remove the need
to home a system . A considerable price dif-
ference once existed between incremental
and absolute encoders . This difference is
becoming less and less .
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eHANDBOOK: Motors & Drives 45
Feedback signals from an encoder may be
transmitted to the controller in several ways .
The oldest, and perhaps the simplest based
upon electronic component count, is a direct
wire connection between the motor-mount-
ed encoder and the system controller . A dis-
advantage of this approach is the low volt-
age susceptibility to EMI; and, if the encoder
is an absolute style, increasing the resolution
increases the signal wire count .
Manufacturers have developed proprietary
serial communication protocols as an im-
provement over the parallel method . Some
manufacturers have allowed their systems
to be open standard, free to be used by
anyone else . They include these three .
1 . Synchronous serial interface (SSI) was
developed in 1984 by Max Stegmann, now
Sick Stegmann (www .sick .com) . The SSI
interface is based upon RS-422 standards
and removed the need for multi-conduc-
tor cables and replaced them with two or
three twisted-pair communication cabling .
2 . Biss, developed by iC-Haus (www .ichaus .
de), included concepts from SSI and
Interbus . Multi-slave bidirectional commu-
nications using RS-485 uses one twisted
pair and, optionally, one set of power wire .
Additional registers in the encoder allow
motor information and additional sensor
readings, such as motor temperature, to
be retrieved from the encoder at will .
3 . A rather recent development by Sick is
Hiperface DSL . This open technology in-
corporates the motor supply wiring with
the position feedback signals in a single
cable . Additionally, it can provide motor
information such as temperature, me-
chanical revolutions, diode current, motor
specifications and serial numbers . Hiper-
face uses eight wires for communications .
Two for RS-485 communications, two
for power and four for 1-V peak-to-peak
sine/cosine .
According to an informal, nonscientific
poll of some maintenance personnel I’ve
worked with over the years, the single
most common source of failure in a servo
system is the motor connection cable . This
part should be the easiest to build . Some
of these failures may be a misapplication
of nonrobotic cables in a system where
the motor movement causes the cable to
flex . However, most maintenance people
have told me, “If the servo stops, change
the cable first .” I would suggest that, if you
have an option to buy higher quality cable
when the system is built, spend the extra
money . The people who keep your machine
running may never know, but they will not
curse you for it .
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NETWORK SOLUTIONSFOR ANY ENVIRONMENT.
Smart control and drive integration fills the billItaly’s Goglio wins Smart Machines category in Best Future Machine Awards
By Giancarlo Truglio, Goglio
At the inaugural Rockwell Automation Best Future Machine awards, announced at
interpack 2017 in Düsseldorf, Germany, Goglio (www .goglio .it) of Milan, Italy, won
top honors in the Smart Machines category with its GCap6 filling machine for alu-
minum capsules . The judges were impressed with the machine’s remote-access capabilities
and its use of Rockwell Automation’s Connected Enterprise technologies . Goglio’s smart
machine showcased technology-related safety, integration, information, real-time diagnos-
tic, operating efficiency and data tracking .
The awards were created to recognize and
reward the high levels of innovation in the
packaging industry . Additional categories
included Modular Machines, Sustainability,
Traceability & Product Safety and Ease of
Use . The Goglio filling machine rated well in
all categories (Figure 1) .
Italy’s Cama Group won the Ease of Use
category, as well as the overall Best Fu-
ture Machine Award for its IF318 Robotised
Monoblock Loading Unit, which incorporates
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eHANDBOOK: Motors & Drives 47
SMART AND GOOD-LOOKINGFigure 1: The Goglio GCap6 filling machine is ergo-nomic, noiseless, safe and modular, making it easy to install, update operate, maintain and clean.(Source: Goglio)
www.controldesign.com
eHANDBOOK: Motors & Drives 48
cabinet-free technology and ergonomics
and uses the iTrak intelligent track system
from Rockwell Automation .
YEARS OF BEING SMARTGoglio is synonymous with quality, com-
petence and commitment in packaging .
The Italian company has gone through the
entire history of packaging . In 1850, the first
company of the group, specializing in paper
bags, was founded; in 1909, the first mecha-
nized factory was born; in the 1960s, the
Fres-Co System was designed to integrate
flexible packages with packaging machines
and technical service; in the ’70s, new facili-
ties were built in Daverio, Italy, to manufac-
ture flexible packaging material, in Milan,
Italy, to manufacture plastic for valves and in
Zeccone, Italy, to build machines . The Go-
glio Group invented the one-way degassing
valve, still an important component in coffee
applications, as well as in other packaging
processes . After a period of expansion in the
1980s, Fres-Co System International in the
Netherlands, Fres-Co System Espana and
Fres-Co System USA were opened . In the
’90s, the Goglio Group consolidated its pres-
ence in Europe with Goglio North Europe
located in the Netherlands . New branches
in the United States, Poland, Italy, Japan,
France, China and Brazil were opened at the
beginning of the 21st century and in 2016 the
company entered the capsules market .
Today, Goglio designs, builds and delivers
complete solutions for the coffee industry .
This includes packaging film material, de-
gassing valves, packaging machines, cap-
sules and capsule-filling machines, as well
as 24/7 technical assistance and service .
SMART COFFEEA good example of Goglio’s deep knowl-
edge in coffee is the GCap6, a filling ma-
chine for aluminum capsules . In addition to
coffee, this automatic line for capsule filling
and packing is also suitable for use with tea,
infusion and instant drinks (Figure 2) .
The GCap6 filling machine includes several
modules: a loading system for stacked cap-
sules, a twin-auger filling system, a check-
weigher, a tamping and cleaning device, a
top lid cut and seal group, an optical cam-
era control and an exit pick-and-place . The
capsules are fed to the conveyor through a
singulating device and a carousel . A pick-
and-place system takes six capsules at a
COFFEE, PLEASEFigure 2: The Goglio’s machine fills aluminum coffee capsules and is suitable for filling tea, infusion and instant-drink capsules as well.(Source: Goglio)
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eHANDBOOK: Motors & Drives 49
time from the carousel and releases them
on the indexing conveyor that transports
them to the different stations .
In a typical application, the machine fills
capsules with ground coffee, which is fed
directly from the grinder and pan-feeder .
The spinning blender above the twin augers
keeps the density of the coffee constant .
The weight of each capsule is then checked,
and feedback is sent to the augers . The in-
dexing conveyor moves the capsules under
the tamping device that presses the coffee
with a vertical motion and cleans the up-
per flange to remove any coffee that could
get stuck between it and the top lid with a
rotating motion .
The capsules are then brought to the cut and
seal group where another vertical movement
cuts a circle of aluminum and places it on the
upper flange of the capsules in the conveyor
(Figure 3) . A second part of the group then
seals them . A 180° rotating pick-and-place
device grabs the capsules that are lifted
from the conveyor by a pneumatic cylinder
and placed on a tilt device . The capsules are
then released on the exit conveyor with the
larger flange facing the belt .
SMART CONTROLGoglio designed the automation system of
the GCap6 selecting several Rockwell Au-
tomation solutions . Rockwell is one of our
main suppliers and works with us on a daily
basis in the development of new products .
It is one of the most important brands and
provides a wide-assistance network world-
wide, together with great technical support
to the machine builders .
The control system on the GCap6 consists
of an Allen-Bradley ControlLogix controller,
an EtherNet/IP network and several Kinetix
5700 EtherNet/IP servo drives (Figure 4) .
All of the devices are connected through
EtherNet/IP while a Stratix 2000 unman-
aged switch allows easy connections within
the control network .
WEB AND MATERIAL HANDLINGFigure 3: Over a dozen axes of servo motion controls the various modules on the machine, such as this cut-and-seal group.(Source: Goglio)
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eHANDBOOK: Motors & Drives 50
The Kinetix drives control
over a dozen axes including
the rotating table for inser-
tion of stacked capsules,
the pick-and-place system
inserting the capsules in the
conveyor and the indexing
movement of it, the augers,
the checkweigher lifting
movement, the tamping
device, the cut-and-seal de-
vice, the exit pick-and-place
and the reel unwinding .
Additional Kinetix ac servo
motors are used for the pan
feeder blender, the twin
auger blender, the cleaning
brush, the tamping heads
and the exit conveyor .
Coordination of each mo-
tor is essential on the filling
machine . The use of servo
motors allows each function
to be fully synchronized and
coordinated in an electronic
cam and enables noiseless
operation . All motorized
functions are linked to an
electronic cam with a virtual
axis within the machine,
which runs from 0° to
360° during each machine
cycle . Using this solution,
the optimal synchroniza-
tion is maintained, with
automation compensation
as machine speed varies,
improving overall machine
performance .
Servo motion provides an
automatic speed adaptation
among the different func-
tions and guarantees con-
stant timing of each feature,
whether a simple or com-
plex motion function . One
of the most critical motion-
control functions is the top-
lid piercing and sealing sta-
tion because it is a one-step
process in a single station .
Therefore, the requirements
of time and synchronization
are very demanding . Any
errors can lead to poor cycle
time and wasted material .
A motorized unwinder
enables use of up to 500
mm reels on the machine
instead of the standard 300
mm, which reduces the time
and manpower needed to
change reels . In addition,
the machine’s simplicity and
ergonomic design provide
easy operator access for
maintenance .
MORE AXES, LESS SPACEFigure 4: Servo drives include dual-axis modules with a single-cable connection between each axis and servo, saving space and integration time. (Source: Goglio)
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eHANDBOOK: Motors & Drives 51
SMART INTEGRATIONThanks to the Rockwell Automation single-
cable motion system, Goglio can minimize
wiring to the Kinetix 5700 servo drives .
These drives also use dual-axis modules to
help reduce the space needed in the electri-
cal cabinets . Even in the complex filling ap-
plication, this is a simple motion system to
integrate as its use reduces the amount of
cable installed for each motor by 50% . The
dual-axis modules are almost the same size
as a typical single-axis drive, reducing the
panel space needed by about 50%, as well .
Furthermore, the user-friendly software
programming environment made machine
development easier . The machine is de-
signed to be configurable to specific ap-
plication needs, using the PanelView Plus
7 operator interface, while still working in
complete synchronicity . Our programmers
developed and optimized this software to
include different process combinations, and
each function is separately accessible for
instant customization and machine opera-
tion (Figure 5) .
The machine is remotely accessible via
Ethernet and can communicate with both
a customer’s MES and/or with the Goglio
developed cloud platform . Production data,
including recipes, batch number and quan-
tity to be produced, can be remotely sent
to the machine . The design allows a cus-
tomer to collect all analog and digital data
from the machine and then use that data to
implement analytic and predictive mainte-
nance applications .
HOW DO YOU LIKE YOUR COFFEE?Figure 5: An operator interface enables quick configuration and control of machine operation.(Source: Goglio)
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eHANDBOOK: Motors & Drives 52
A separate PC allows operators to manage
data and information to produce alarm and
production reports and display any needed
manuals, catalogues and diagrams . The PC
also includes the tools needed to manage
maintenance and camera visualization .
This Goglio smart filler machine achieved
other advantages including reduced training
times, improved machine flexibility, better
troubleshooting of operational problems and
easier testing and validation; it also helped
to minimize installation and startup times .
Not only does this smart machine pro-
vide high performance and 94-95% overall
equipment efficiency (OEE), it looks good,
as well . The machine offers very good seal-
ing, cutting and dosing accuracy in addition
to precise defect checks . A combination of
the machine’s applied design, feedback to
load cells, photo eyes and cameras help to
detect the presence and quality of capsule
components . In addition, the servo tech-
nology allows the machine to efficiently
achieve high availability, speed and quality .
Giancarlo Truglio is the research and
development manager and machine
division technical department vice
director at Goglio in Zeccone, Italy . Contact him at
giancarlo .truglio@goglio .it .
©2
01
8 S
iem
ens
Ind
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Inc.
usa.siemens.com/anewwayofmotion-cd
A new way of MotionEasy to program, system simulation, integrated safety and built-in diagnostics.
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