motion feedback 101: select the right feedback for your application by knowing the basics
TRANSCRIPT
Encoders and Resolvers Series:Motion Feedback 101
Select the Right Feedback for Your Application by Knowing the Basics
This webinar will be available afterwards at designworldonline.com & email
Q&A at the end of the presentation
Hashtag for this webinar: #DWwebinar
Before We Start
Moderator
Miles BudimirDesign World
Presenter
Mark LangilleTechnology Planner, Dynapar Corp.
Mark Langille is the Technology Planner for Dynapar. He has worked in the encoder industry for 15years both on the manufacturing and commercial side of the business, with 7 years spent as a manufacturing engineer. He holds a BS in Industrial Technology with an emphasis in manufacturing from Iowa State University.
Closed-loop feedback can deliver: Speed data—spindle applications,
CNC tools, conveyor belts Velocity data—web applications Position data—packaging, pick-and-
place
You can close the loop on: Shaft velocity/position provided from
an encoder or resolver The motor torque via motor current The load—high-performance apps
o removes lost motion, hysteresis
Knowledge is Powerposition velocity
Resolution (optical versus magnetic) Accuracy (optical or magnetic subtype) Velocity ripple- Symmetry specification Uptime/reliability (incremental
versus absolute) Cost of material/time during reset
(incremental versus absolute) Mechanical constraints—shaft type,
speed Environmental constraints (IP ratings)
How to Choose…
Different Horses for Different
CoursesEncoders vs. Resolvers
Special type of rotary transformero Stationary stator, rotor
moves with the loado Voltage from input
winding couples to output winding
o Ratio of voltages gives angular position
Resolvers
Single Speed Resolver Output
-1
-0.5
0
0.5
1
0 45 90 135 180 225 270 315 360 405
Degrees
Am
pli
tud
e
Sine
Mod Sine
Cosine
155ºC Rated Winding (Optional 220ºC) for High Temp Environments
Flux Shield Eliminates Crosstalk (pat. pend.)
Precision Laminations Help Assure High Accuracy
No On-Board Electronics Means Resolvers Can Be Used Where Encoders Cannot. Multi-Pole Versions in
Both Housed and Frameless Models to Size 55 Available
Housed Version
High res--no onboard electronics, very ruggedo Temperature extremeso Elevated radiation levels—no SEUso Contaminationo Shock and vibration
Analog—infinite resolution Good for tough applications like
aerospace, servo, and CNC.
But… The electronics have to go somewhere Skill required for integration
Resolver Trade-Offs
Linear or rotary feedback Moving load/motor modulates signal Output driver converts signal to
speed/velocity/position
Encoders
Complete – All digital electronic output Robust
o Potted electronicso Many design utilize ASIC’s
Lots of optionso Optical vs. magnetico Incremental vs. absoluteo IP ratedo Multiple mounting styles
But… Know your design criteria both electrical/mechanical.
Selecting the right device for specific for the applications can make the difference.
Encoder Tradeoffs
Poll Question #1In rugged environments it is best to specify:
a) Resolversb) Magnetic encodersc) Optical encodersd) Depends on the application
Optical vs. Magnetic
Disk—mounted on load or motor shafto Glass substrate patterned with metal thin filmo Mylar substrate (speed limitations--flutter)
Sensor—mounted on housingo LED to generate beamo Photodiode to detect beamo Board level or chip level integration
Turning/moving disk modulates beam Device uses this info to derive
velocity/position feedback
Optical Encoders
Mask (multichannel encoders only)o Prevent spillover between channelso Or introduces phase shift between channels
Phased-array encoder—onboard ASICo Array of detectors averages signalo Compensates for misalignmento More robust—shock loads up to 400 go Easier to integrate—no need for potentiometerso Larger air gap [give amount– millimeters?]o Batch processing keeps price down
Best for: Medical, semiconductor, elevators, oil and gas,
aerospace, heavy vehicles
Optical Encoders
High resolution (up to 10,000 PPR incremental direct read or 1×106 PPR for absolute versions (more on that later).
Ease of installation EMI immune Shock resistant Lower-cost
But… IP (ingress protection) is important Most optical encoders utilize bearings and
LED which can have a finite life.
Optical Encoder Trade-Offs
Drum/strip with alternating magnetic—mounted to shaft/load
Readout electronics—mounted on housing Output based on responses system to
perturbed magnetic field
Best for: Mill applications, cranes, extruders, wash-
down environments
Magnetic Encoders
Variable reluctanceo Magnetic pickup—permanent
magnet wound with coilo Changing magnetic field
generates voltage pulseo Pro: simple; con: limited to 240 PPR
Magnetoresistiveo Resistor array changes resistance
when drum turnso Pro: better resolution, lithographically
patternedo Cons: larger, not actually integrated,
needs support circuitry
Magnetic Encoders
Hall-effect sensor arrays: Solid-state detector – applied
magnetic field separates charge carriers Separation triggers voltage spike Process to get speed/displacement
Pros: Sensor and processor on same chip Integrated – robust, compact, economical Data averaged over multiple detectors – lower
noise, higher sensitivity
Magnetic Encoders
Tough—unaffected byo contaminationo Temperature extremeso Shock/vibrationo Stable performance – no degradation
But… Lower resolution than optical encoders Can be affected by high magnetic fields
Magnetic Encoder
Which type of rotary feedback typically can provide the highest accuracy resolver, optical encoder, or magnetic encoder?a) Resolverb) Optical encoderc) Magnetic encoderd) Depends more on the
more on the application/environment
Poll Question #2
Incremental vs. Absolute
Can measure speed, velocity, and direction, depending
Track counts traveled from some home position
Generate pulse stream only—need PLCs, drives, etc. to convert to info
Incremental Encoders
2+ channels, 90° out of phase (in quadrature) One channel goes high first—directionally
dependent More channels equals more resolution Triggering (leading edge, trailing edge) ups
resolution Index channel monitors turns
Best for: Web apps, e.g. printing, paper Packaging equipment Motor/Drive application with tight PID
speed loops
Quadrature Encoders
Up to 32768 PPR with interpolation Simple to integrate Easy to maintain Variety of form factors and prices
But… Need to be re-homed on start up Can require 10 conductor cables
Incremental Encoder Trade-Offs
Output as a digital word corresponding to absolute position Code disc -- each ring corresponds to one bit of resolution Each ring read by separate LED/detector pair Standard resolution--12 bits (4096 PPR)
o As high as 22 bits (4.19 x 106 positions) Multi-turn designs to track multiple turns of shaft (to 4096) Support many bus/Ethernet based communication protocols
Best for: Hi-accuracy applications: Medical, aerospace, semiconductor Multi Axis machines with coordinated motion Serial versions are best for ultra low speed PID loop
Absolute Encoders
No need to re-home on start-up Faster start up time Greater accuracy Bus compatible Deliver real-time diagnostics
But… Tend to be more expensive More complex to install
Absolute Trade-Offs
Poll Question #3
Which device allows you sense the absolute shaft position with in one rotation a) Optical – Incremental with indexb) Optical - Absolutec) Magnetic d) Resolvere) All of the above
Mounting Types
Coupled to: o non-loadbearing end of motor shafto gear box/measuring wheel.
Robust Greatest variety of options
Tip: Connect to rotating shafts via belts, wheels, or flexible coupler. Be mindful that the dynamic loads don’t exceed the encoders’ bearings rating.
Shafted Encoders
Fits over motor shaft with a pressure connection
Automatic alignment No need for couplers Rapid installation
But… Tether mounting shouldn’t be
shouldn’t be taken for granted
Best for: AC Induction Motor Feedback
Hollow-Shaft Encoders
Sensor unit on the motor shaft Housing connected to the motor
housing No bearing—less maintenance, fewer
failures, smaller, lighter Non-contact sensing
Application tip: Play close attention to shaft run out and end play under mechanically loaded conditions.
Bearingless Encoders
IP Ratings
IEC 60529 --protection against solid and liquid Two digit system
o first digit, solids----fingers to dust o second digit, liquids----droplets to high-
pressure Jets IP ratings specify time durations, depth, etc. , so
pay attention No one seal can do both----identify your
priorities
Know the Code
Know the CodeIP 67 – 6 7
Pay attention to Time limits, Pressure limits, Depth limits, Angle dependence.
Solids
Putting It All Together
Performance requirementso Accuracyo Resolutiono Symmetry/Phaseo Electrical interface
Environmental conditionso Temperatureo IP Ratingo Shock/vibrationo Overall reliability
Budgeto TCA versus TCO
Know your application…
Choose a resolver for the very harshest applications. Choose optical encoder when you need the best
resolution possible. Choose a magnetic encoder when you need the best of
both worlds. A high IP rating can’t compensate for the wrong choice of
encoder type. No one feedback device can do it all – decide what’s most
important and design to it.
In Summary
Questions?
Design WorldMiles Budimir [email protected]
Phone: 216.860.5271Twitter: @DW_RapidMfg
DynaparMark [email protected]: 847.782.5211Twitter: @encoders
Thank You This webinar will be available at designworldonline.com
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