EQUIPMENT PRODUCTIVITY [Compatibility Mode].pdf

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CHAPTERCHAPTER -- 1212

PRODUCTIVITY



LASER BASED MACHINE

CONTROL

The Need: Construction e ui ment usin laser

control technology can achieve higher

levels of productivity



ra er w t opcon - Computer and Total-Station

Receiver



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



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.



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



Figure 12-1 Volume Relationships



Table 12-2 Typical Rolling

Resistance Factors



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



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



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



Table 12-3 Calculations for

Haul Road Sections



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



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



Table 12-4 Speed and Draw Pull

(270 hp) (Track type tractor

)



Fi . 12-5 Gear Re uirements Chart-35Ton off Highway Truck



Fig. 12-6 Travel time (a) empty and (b) loaded



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



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



Table 12-5 Coefficients of

Traction



Figure 12-7 Determination of

Driver Eeights



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



Fig. 12-9 Scraper-pusher dual cycle

model

Fig. 12-8 Impact of usable power

constraints



Figure 12-10 Travel Time

Nomographs



Fig. 12-11 Scraper-pusher cycle timing

Fig. 12-12 Productivity Plot



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



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

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EQUIPMENT PRODUCTIVITY [Compatibility Mode].pdf