EQUIPMENT PRODUCTIVITY

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EQUIPMENT PRODUCTIVITY
CHAPTER - 12
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LASER BASED MACHINE CONTROL

• The Need
• Construction equipment using laser control
  technology can achieve higher levels of
  productivity

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Grader with Topcon 30-MC
Computer and Total-Station
Receiver
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THE TECHNOLOGY

• New systems use three modules to control the
  piece of equipment
• survey that upload in a total station using a
  computer notebook.
• A receiver mounted on the blade of the equipment,
  intercepts the laser beam.
• The interface between the positioning information
  and the actual steering of the equipment is
  performed through the use of a control system
  device which converts the digital data into
  machine hydraulic pulses.
• The main benefit of these systems is the gain of
  productivity. The laser devices can triple the
  productivity of equipment on highway projects

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PRODUCTIVITY CONCEPTS

• The cycle of equipment pieces is the sequence of
  tasks which is repeated to produce a unit of
  output (e.g., a cubic yard, a trip load, etc.)
• There are two characteristics of the machine and
  the cycle that dictate the rate of output the
  cycle capacity of the machine and the cycle rate
  or speed of the machine
• A hauler such as a scraper pan, usually has a
  rated capacity. Struck vs. Heaped capacity.
  The bowl of the scraper can be filled level
  (struck) yielding one capacity or can be filled
  above the top to a heaped capacity
• The material has a different weight-to-volume
  ratio when it is placed in its construction
  location (e.g., a road fill) and is compacted to
  its final density
• This leads to three types of measurement 1) bank
  cubic yards ( in situ vol ), 2) loose cu. yd. and
  3) compacted cu. yd.

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PRODUCTIVITY CONCEPTS (continued)

• Payment based on the placed earth construction so
  that the pay unit is final compacted cu. yd.
  (see fig. 12-1)
• See pg. 186 equations to calculate percent swell
  and 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-up
• Therefore, with a high load factor, the loose
  volume and 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 machine or machine combination is the time
  required to complete a cycle
• 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
• The power required is related to the rolling
  resistance (RR) inherent in the machine due to
  internal friction and the friction developed
  between the wheels or tracks and the related
  surface
• The power required is also a function of the
  grade resistance
• Rolling resistance in tracked vehicles is zero
  since tracks 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 penetration of the surface under wheeled
  traffic
• If the deflection is 2 in. and wt. on wheels of a
  hauler is 70 tons, then RR is
• RR 40 2 (30)lb/ton x 70 tons 7000 lbs
• The second factor involved in calculating power
  required is the grade resistance (GR) see fig
  12-3. In most cases slopes (both uphill and
  downhill) will be encountered and lead to higher
  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 Rolling
Resistance

• Figure 12-3 Grade Resistance
• Negative (resting) Force
• 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 the equipment and the drive train, which
  allows transfer of power to the driving wheels or
  power take-off point
• The amount of power transferred is a function of
  the gear being used
• Most automobile drivers realize that lower gears
  transfer more power to overcome hills and rough
  surfaces
• Lower gears sacrifice speed in order to provide
  more power
• Higher gears deliver less power, but allow higher
  speed
• See table 12-4 for the power available in each
  gear
• See fig 12-5, nomograph, to determine power
  available 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 of rimpull. This is the force
  that can be developed by the wheels at its point
  of contact with the road surface
• Manufacturers also provide rated power and
  maximum power
• Rated power is the level of power that is
  developed in a given gear under normal load and
  over extended work periods
• The maximum power is the peak power that can be
  developed for a short period of time, e.g. a
  bulldozer is used to pull a truck out of a ditch,
  a quick surge of power is used to dislodge the
  truck
• Most calculations are done using rated power
• 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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Fig. 12-5 Gear Requirements Chart-35 Ton 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 the road surface traction characteristics
  (for wheeled vehicles) and the attitudes are
  which the operations are conducted
• Tires of a car spin on a wet or slippery
  pavement. Although, engine and gears are
  delivering a certain horsepower, no traction to
  develop power into the ground
• Combustion engines operating at high altitudes
  experience a reduction in oxygen, which leads to
  reduce power
• First, is a problem with traction. The factors
  that influence the usable power are the
  coefficient of traction and the vehicle weight
• The coefficient of traction is a measure of the
  ability of a 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)

• Power that can be developed coefficient of
  traction X weight on drivers
• In the consideration of RR and GR, the entire
  weight was used in calculating usable power only
  the weight on the driving wheels is used
• See fig 12-7 for determination of driver weights
• Illustration of usable power, see the example on
  pg. 194 195
• The altitude is also a problem with respect to
  usable power. Bogota, Columbia (elevation 8600ft)
  cant develop the same power as one operating in
  Atlanta, Georgia (elevation 1080ft)
• A rule of thumb to correct this effect is to
  decrease pounds 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

• In situations where two types of equipment work
  together to 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 waiting for other unit to catch
  up
• Consider the problem of balancing productivity
  within the context of a push dozer loading a
  tractor scraper. A simple model of this process
  is shown in fig 12-9
• The circles represent delay in waiting states,
  while square designated active work activities
  with associated times can be estimated
• The haul unit is a 30 cu. yd. scraper and is
  loaded in the cut area with the aid of a 385-hp
  pusher dozer. The system consists 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

• In systems where the randomness of cycle times is
  considered, system productivity is reduced
  further
• The influence of random durations on the movement
  of resources causes various units to become
  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
  idle states pending release to productive work
  tasks
• Fig. 12-13 indicates the influence of random
  durations on the scraper fleet production

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RANDOM WORK TASK DURATIONS (continued)

• The curved line of fig. 12-13 slightly below the
  linear plot of production based on deterministic
  work task times shows the reduction caused by the
  addition of random variations of cycle
• 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
  variations of cycle times, bunching occurs on
  the haul cycle as seen in fig. 12-14b.
• The bunching effect is most determined to the
  production