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Much more than directions and roadmaps, an integrated GPS system is now available for land development. To facilitate grading of large areas, GPS-controlled earthmoving equipment including bulldozers, backhoes, road graders, excavators and compactors can greatly increase productivity during the land development process. This approach significantly reduces the labor needed for laying out grade stakes and reduces the amount of earth that is being moved more than one time.
The sytem consists of two major components, a digital three-dimensional model for the grade information (3-D site plan) and earthmoving equipment that has been fitted with automatic computer-operated controls on the cutting surface (machine blade).
The components of the machine control system can be understood by dividing them into three generalized groups:
- Machine interface
- Operator interface
- Sensors and input devices
Machine interface:
The cutting edge of any earthmoving machine is positioned by mechanical links to the hydraulic drive cylinders. The cylinders, actuated by electrically controlled servo type valves, rather than the standard mechanical linkages from control levers in the machine cab, move the blades up and down and through vertical and horizontal angles. With automated GPS control, the hydraulic cylinders are connected electrically to the software-driven control box, which is part of the operator interface.
Operator interface:
The operator interface is the control box, which is the primary control for the cutting surface. The control box contains onboard computers and operating software that uses satellite positioning information and digital design files created from the projects grading plan. The 3D digital design files may be supplied on compact flash memory cards or they may be broadcast on a local Controlled Area Network “CAN”). The CAN allows frequent updates of the site design data. The processing of the two information sources--satellite positioning data and the design grades--enables the positioning of the cutting edge to match the design grade. Electrical cables connect the control box to the servo valves on the hydraulic cylinders, thereby controlling the position of the cutting surface. Typically, there is the ability to quickly switch between manual override on the cutting edge controls and automated positioning of the cutting edge. Advanced control boxes often have voice prompts and/or a touch screen display that provides the cutting surface information to the operator. Typically, the operator can choose between plan view, section view and profile view options of the site plan.
Sensors and Input devices:
The GPS sensor on the earth-moving machine, called “the rover,” is a rugged GPS antenna mounted on a shock-absorbing pole that transmits the signal to a receiver. There is also a GPS antenna and receiver combination at the base station, located at a known “benchmark” stationary position on the site. The stationary base and the mobile “rover” work together to provide accurate and precise position information on the cutting surface to the control box in the operator cab.
Sonic sensors and laser sensors are also available to either enhance or substitute for the GPS sensor:. In a sonic sensor, sound wave generators and receivers are used for distance measurement, typically from a curb or existing road surface. Lasers on a base station can be rotated in a horizontal plane and are used for elevation information to fine grade areas for building pads and athletic fields with minimal slopes.
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Land development contractors using this technology should be able to present lower land development bids, a cost savings that in some scenarios would trickle down to the home owner. This cost savings would be maximized if several contractors using the GPS earth moving capability are bidding on the earthwork contract.
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The potential lower equipment operating time required for earthmoving will result in lower fuel requirements for earth moving equipment.
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Grading should take less time, meaning less diesel exhaust from earth working machines. In addition, less time to complete grading could result in less time for bare earth to be exposed to erosion-causing rainfall events.
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Lower requirements for grade stake layout work around large earth moving machinery could potentially result in a safer work environment.
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While the software and components may require a short learning period to familiarize equipment manufacturers, once the system is fully installed, and the in-cab display system displays the design in a number of views, all the settings and views can easily be customized to the operator’s preference. In automated mode, the hydraulic system will control the blade; the operator uses the guidance from the display to steer the tractor to complete the grading. The system also offers manual modes. The largest learning curve for the earthwork contractor will likely be in the conversion from standard two-dimensional CAD files to three-dimensional digital data models. This is typically done by a construction data conversion specialist.
For developers, the GPS system must be integrated into current or new machines, and includes additional components and software that must be set up and calibrated. Training is also required, as is conversion of CAD files from two to three dimensions.
While investment in the technology will present a significant upfront cost to the earthwork contractor, the GPS machine control system significantly reduces the time spent surveying, staking, and grading, resulting in a lower overall job cost.
There are no typical code requirements for the method of achieving desired final site grades.
Not Applicable
For developers, the system is an option for select Caterpillar machines. Other manufacturers sell GPS components and systems that can be integrated with a variety of land grading machinery.
Not specified.
Because the cutting edge is controlled automatically, the operator can focus on steering and make the most efficient use of the machine forward motion. Also because the GPS signal is received virtually continuously by the control box on the earthmoving equipment, the operator doesn’t have to keep making visually based corrections and interpolations when he or she is located between grade stakes. The accuracy of the graded land surface is improved, eliminating much of the time and expense of reworking areas not at the design grade.
Operator fatigue is reduced and job site safety is improved. Fewer people are required to work close to the earth moving machines because the need for layout crews and grade checkers is reduced. According to Professional Surveyor magazine: “3DMachine Control can provide a 50 percent increase in productivity for a construction site. The statement is true; but keep in mind: 3D Machine Control is a process, not a product. There is a lot that goes into making an automated job site function properly and achieve that 50 percent increase in productivity.”
The cost associated with the system is the upgrade to new machines with GPS components installed, the purchase of the fixed benchmark GPS receiver required for the job site, and any operator training. The cost for a simple system for one bulldozer is in the range of $100,00-125,000.
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