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CHAPTERCHAPTER -- 1212
PRODUCTIVITY
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LASER BASED MACHINE
CONTROL
The Need: Construction e ui ment usin laser
control technology can achieve higher
levels of productivity
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ra er w t opcon - Computer and Total-Station
Receiver
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THE TECHNOLOGY
of equipment: survey that upload in a total station using a computer
.
A receiver mounted on the blade of the equipment,
intercepts the laser beam. e n er ace e ween e pos on ng n orma on an e
actual steering of the equipment is performed through theuse of a control system device which converts the digitaldata into machine h draulic ulses.
The main benefit of these systems is the gain ofproductivity. The laser devices can triple the
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PRODUCTIVITY CONCEPTS
which is repeated to produce a unit of output (e.g., a cubicyard, a trip load, etc.)
There are two characteristics of the machine and the c clethat dictate the rate of output; the cycle capacity of themachine and the cycle rate or speed of the machine
A hauler such as a scraper pan, usually has a ratedcapacity. Struck” vs. Heaped” capacity. The bowl of thescraper can be filled level (struck) yielding one capacity orcan be filled above the top to a heaped capacity
- -is placed in its construction location (e.g., a road fill) and iscompacted to its final density
yards ( in situ vol ), 2) loose cu. yd. and 3) compacted cu.
yd.
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PRODUCTIVITY CONCEPTS
(continued)
that the “pay” unit is final compacted cu. yd. (see fig.12-1)
.the load factor
Percent swell for fig. 12-1 is 30% Table 12-1 gives the load factor for various materials
Higher the load factor, the smaller tendency to “bulk-”
Therefore, with a high load factor, the loose volumeand the in situ vol tend to be closer to one another
See pg. 187
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Figure 12-1 Volume Relationships
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Table 12-2 Typical Rolling
Resistance Factors
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CYCLE TIME and POWER
REQUIREMENTS
The second factor affecting the rate of output of a machineor machine combination is the time required to complete acycle
This is a function of the 3 items; 1) the power required 2)the power available and 3) the usable portion of the power
available e power requ re s re a e o e ro ng res s ance
inherent in the machine due to internal friction and thefriction developed between the wheels or tracks and the
The power required is also a function of the graderesistance
act as its own roadbed
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CYCLE TIME and POWER
REQUIREMENTS (continued)
See table 12-2 for rolling resistance in lbs./ton of weight Rule of thumb, RR is 40lbs/ton plus 30lbs/ton for each
If the deflection is 2 in. and wt. on wheels of a hauler is 70
tons, then RR is : = on x ons = s
The second factor involved in calculating power required is
the grade resistance (GR) see fig 12-3. In most cases slopes
ot up an own w e encountere an ea tohigher or lower power requirements
Fig 12-4; for the haul road profile with RR and % grade see
table 12-3, which gives the power required for each section
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Figure 12-2 Factors Influencing RollingResistance
Figure 12-3 Grade Resistance
a) Negative (resting) Force
b) Positive (aiding) Force
Figure 12-4 Typical Haul Road Profile
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Table 12-3 Calculations for
Haul Road Sections
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POWER AVAILABLE The power available is controlled by the engine size of
e equ pmen an e r ve ra n, w c a ows rans er
of power to the driving wheels or power take-off point The amount of power transferred is a function of the
gear e ng use
Most automobile drivers realize that lower gears
transfer more power to overcome hills and roughsur aces
Lower gears sacrifice speed in order to provide morepower
Higher gears deliver less power, but allow higher speed
See table 12-4 for the power available in each gear
ee g - , nomograp , o e erm ne power ava a e
in graphical form
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POWER AVAILABLE
(continued) For tracked vehicles, the power available is quoted in drawbar
pull. This is the force that can be delivered at the pulling point
(i.e. pulling hitch) in a given gear for a given tractor type The power available for a wheeled vehicle is stated in pounds
.wheels at its point of contact with the road surface
Manufacturers also provide rated power and maximum power a e power s e eve o power a s eve ope n a g ven
gear under normal load and over extended work periods
The maximum power is the peak power that can be
, . .to pull a truck out of a ditch, a quick surge of power is used todislodge the truck
See example on pg 191, fig 12-5 and fig 12-6
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Table 12-4 Speed and Draw Pull
(270 hp) (Track type tractor
)
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Fi . 12-5 Gear Re uirements Chart-35Ton off Highway Truck
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Fig. 12-6 Travel time (a) empty and (b) loaded
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USABLE POWER To this point, it has been assumed that all of the available
power is usable and can be developed
Two main constraints in using the available power are theroad surface traction characteristics (for wheeled vehicles)
Tires of a car spin on a wet or slippery pavement. Although,
engine and gears are delivering a certain horsepower, no
Combustion engines operating at high altitudes experience areduction in oxygen, which leads to reduce power
, .usable power are the coefficient of traction and the vehicleweight
surface to receive and develop the power being delivered to
the driving wheels and has been determined by experiment.See table 12-5
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USABLE POWER (continued)
= weight on drivers
In the consideration of RR and GR, the entire weightwas used in calculatin usable ower onl the wei ht onthe driving wheels is used
See fig 12-7 for determination of driver weights
, .& 195
The altitude is also a problem with respect to usableower. Bo ota Columbia elevation 8600ft can’t
develop the same power as one operating in Atlanta,Georgia (elevation 1080ft)
A rule of thumb to correct this effect is to decreasepounds pulled 3% for each 1000ft above 3000ft
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Table 12-5 Coefficients of
Traction
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Figure 12-7 Determination of
Driver Eeights
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EQUIPMENT BALANCE
accomplish a task, it is important that a balance in the
productivity of the units be achieved
This is desirable so that one unit is not continually idle waitingor o er un o ca c up
Consider the problem of balancing productivity within the
context of a push dozer loading a tractor scraper. A simple-
The circles represent delay in waiting states, while squaredesignated active work activities with associated times can beestimated
The haul unit is a 30 cu. yd. scraper and is loaded in the cutarea with the aid of a 385-hp pusher dozer. The systemconsists of two interacting cycles. See example pg. 197-200
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Fig. 12-9 Scraper-pusher dual cycle
model
Fig. 12-8 Impact of usable power
constraints
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Figure 12-10 Travel Time
Nomographs
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Fig. 12-11 Scraper-pusher cycle timing
Fig. 12-12 Productivity Plot
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RANDOM WORK TASK
DURATIONS
considered, system productivity is reduced further The influence of random durations on the
movemen o resources causes var ous un s obecome bunched together and thus to arrive at and
overload work tasks Results delay impact the productivity of cycles by
increasing the time that resource units spend idlestates endin release to roductive work tasks
Fig. 12-13 indicates the influence of randomdurations on the scraper fleet production
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RANDOM WORK TASK
DURATIONS (continued)
The curved line of fig. 12-13 slightly below the linearplot of production based on deterministic work tasktimes shows the reduction caused by the addition ofran om var a ons o cyc e
This randomness leads to bunching of haulers on
their cycle Fig. 12-14a, haul units are exactly 1.35 min apart
In systems that include the effect of random
“ ” ,haul cycle as seen in fig. 12-14b.
The bunching effect is most determined to thepro uc on