GPS Machine Control Systems

Sept. 28, 2010

Although global positioning system (GPS) technology has been around since the mid-90s, it's really taken off in the construction industry during the last few years.

One reason for that, says Fred Rogers, director of sales – machine control at Leica Geo Systems, is that it provides the operator with a three-dimensional view of the jobsite, solving the challenge of slope and cross slope.

“Both laser and sound sensor technologies display the site in two dimensions,” says Rogers. “If the operator is going down a road that has, for example, a 2 percent cross slope to the crown, and the operator is running on a string as a reference point, he has to run parallel to it. He can't veer toward the right or left because it would change the desired cross slope. A three-dimensional reference pulls the cross slope in the direction of travel, so it's always setting a new target to the cross slope side.”

According to Murray Lodge, director of sales for construction at Topcon Positioning Systems, GPS technology's three-dimensional capability allows contractors to do a better job of building a subdivision or road.

“The majority of that work is simply moving dirt on a massive scale and balancing the jobsite,” says Lodge, “With GPS, the operator knows not only where the grade is, but where he is on the job at all times. He has a 3-D model of what the finished design should look like. And he has a 3-D control system that can be used all the way through the job – at the beginning with clearing and scrubbing; while rough-grading; during utility installation; and when adding the base, stone and finish.”

Another benefit of a GPS system that controls both elevation and slope is that it can make an average operator into a good operator, and a good operator even better.

“A good operator who already knows how the machine works and all the nuances of how to move material can really shine,” says Lodge. “You're taking out the guess work where the grade is concerned, and the operator can work more efficiently.”

A GPS system can increase productivity, which increases equipment utilization.

“You use the equipment a shorter amount of time, which means you get the work done quicker, not to mention that you save on surveying costs,” says Lodge.

“If you think about it in terms of material,” he says, “you've got dirt and rock, and you're putting asphalt or concrete on top of that. If you know the grade will be more consistent all the way through, you can put down less concrete or asphalt and save a considerable amount of money.”

On the Job

One fleet manager who uses both GPS and laser technology is Theresa F. Anderson, CEM, corporate equipment manager for Parsons Construction. The company currently has approximately 12 units equipped with the technology.

According to Anderson, adopting the technology has gotten easier.

“Previously, a hydraulics control package, sensors and a monitor to control the hydraulics had to be installed on the machine, but that's changed,” she says. “Although different manufacturers use different approaches, starting this year, all of them seem to be moving toward a fully operational package from the factory. When we order a new dozer now, it's already set up and ready to go”

The company switched from another brand of technology to Trimble/Spectra Precision Laser systems about five years ago, primarily because of Trimble's nationwide product support.

“Trimble was out there first, and they're tied in with a number of big players,” says Anderson. “With some systems, if you move a piece of equipment, you might not get the support you need if the company doesn't have a dealer in the area.”

The system used on the Parsons fleet, according to a spokesperson with Trimble Construction Division, is based on triangulation from satellites.

“Knowing where the satellites are requires high orbits and careful monitoring,” he says. “That's the secret.” The Trimble system corrects any delays in the signal.

How GPS Works

The advantages of GPS technology compared to conventional methods of machine control are possible because the technology makes use of a digital train model (DTM) created by an engineer.

“A model shows how the project is supposed to be,” says Rogers. “That model is loaded onto a computer on the equipment and the GPS antenna is mounted on the blade. There are off-set measurements from the antenna down to the cutting edge of the blade. It calculates to the cutting edge and compares that to the design surface.”

That coordinate should be at a certain elevation. If it's not, Roger says, the system shows the operator a deviation that can be a cut or a fill.

“He would then manually move the blade up or down,” he says. “If the system is automatic, he turns a switch to automatically move the blade up or down.”

“By tracking the satellite signals, you essentially triangulate to calculate your position on earth,” says Rogers. “It's similar to pulling string – 20 feet from that rock, 35 feet from that tree and 15 feet from that hydrant. If I pull all three together, the point where they cross is where I am. That's what GPS does: It triangulates off those satellites to determine where you are.”

On the machine, the GPS system requires an antenna to track the satellite, a receiver to calculate position, and a radio to pick up corrections from a base station.

Although it doesn't matter where the antenna, receiver and radio are mounted on the equipment, generally the antenna and radio are located inside the machine to protect them. Once the GPS components are on the equipment, that's all there is to do.

“The operator turns the computer on and sees where he left off on the project,” says Rogers. “It's easier for an operator to run 3-D than it is to set up a grader with dual lasers.”

Installation on electronic machines, such as Caterpillar and John Deere, is simply a matter of locking into the wiring harness, according to Rogers.

“But there are a lot of machines in the field that are not plug and play,” he says. “They are hydraulically controlled. With those machines, you have to install a valve and hose kit.”

With some systems, after the initial installation, fleet managers don't pay for software updates.

“Some manufacturers do charge,” says Lodge, “but we don't. Once you make your initial investment, you're covered with that product.”

There can, however, be fees for data preparation.

“If a construction company has the internal capabilities to create the digital train model needed for the machine, that company is a step ahead,” says Rogers. “If the company doesn't have that in-house capability or people who can be trained to do it, there are companies that will provide DTMs.”

DTM providers usually charge by the acre, by the mile, by the entire subdivision or by the number of lots in the subdivision.


While GPS technology on a dozer, grader or excavator, costs more than traditional laser or sound sensor systems, the return on investment is quicker, because a GPS system can increase production 35 percent to 50 percent.

”It can be more on certain applications,” says Lodge. “It all depends on what you are comparing it to. If you're comparing ROI to a guy running a machine manually or an operator running a laser, the ROI is going to be significant.”

In addition to increasing productivity, saving on materials, saving on surveying and better utilization of the machine, says Rogers, you're getting jobs done on or ahead of schedule and many times there are bonuses for meeting deadlines.

“Too often fleet professionals think in terms of eliminating a person on the job,” says Rogers. “But the way I look at it, you're making your operators much more valuable to your company. Operators tend to shy away from machine control technology for that reason. If they would embrace it, it would make them more valuable employees.”

Anderson says when Parsons calculated all the hidden savings, the ROI was excellent.

“One major job of a year or more and the package pays for itself,” she says.

As for the future, fleet professionals who haven't already done so are going to have to make the investment in GPS to run equipment more efficiently and more profitably.

By the same token, operators will have to adjust to GPS developments, because, as Rogers put it, “The whole industry is going to this technology.”