Positioning earth moving machines exactly on site

Modern guidance technology is now bringing major benefits to the earth moving industry. Although global positioning systems (GPS) were first developed for the military by the US government, they now allow contractors to work onsite independently without surveyors. Construction Week spoke to local operators to see how the systems have been used in the UAE and visited a site in Des Moines, Iowa to find out just how far the technology has now progressed.

  • E-Mail
By  Colin Foreman Published  November 27, 2004

Positioning earth moving machines exactly on site |~|50 Tech Body.jpg|~||~|GPS technology is having a great impact on the earthmoving business. “It’s the biggest change in this industry that I have seen in my lifetime,” says Dwayne McAninch, CEO, McAninch Corp. By combining two separate positional systems, earth movers and the blades that they are using can be positioned very precisely for both depth of grade and within an area. This saves manpower, and contributes to accuracy and the speed with which a job can be done. The system works by mounting a GPS system onto the earth-mover and then combining data from the GPS systems with a separate laser system that has both on board and off board components. A series of laser receivers are mounted directly on the blade of the machine. Off board, a laser transmitter produces a rotating 360 deg beam that creates a grade reference over the work area. The onboard laser receivers are then able to produce precise eleveation information for the blade. Using this reference, the blade’s lift and tilt are automatically adjusted as the machine moves over the area. An in-cab display provides a simple view of all system information. It has an easy-to-read LED grade indicator and a backlit graphical LCD numeric elevation display that shows the blade’s position relative to grade and indicates cut or fill requirements at that point. The display also allows the operator to select either manual or automatic operating modes to match the specific working requirements. For example, manual mode can be used for rough grading while automatic mode is used for finishing and fine grading. The system can achieve extremely tight tolerances as is accurate to within +/- 6 mm of grade. The technology not only offers more accurate grading. It allows contractors to start work on site without having to wait for surveyors to set grade stakes. In the Mid-West USA this problem was particularly acute because seasonal weather changes mean that on site construction work can only really be carried out between March and November. “We simply could not maintain our current activity without circumventing the problem of waiting for surveyors,” says McAninch. In 1999 McAninch Corp. began investigating the potential benefits that GPS systems offer. Putting a value on the lost time was difficult although it was estimated that it was costing the company about $1 million every year. The contractor became the first earthmoving operation in the world to install SiteVision GPS receivers on scrapers and dozers, and later the system was fitted to a supervisor’s truck. Interestingly the contractor uses track type tractors to tow their scrapers instead of the usual wheeled trucks. The decision to equip supervisors with the system was made because they were unable to fully monitor the work onsite because the operators held all the information. “Once we started using the system we realised that we had under estimated the cost of lost time, the figure was nearer to $3 million,” says McAninch. Soon after SiteVision’s introduction, Caterpillar and Trimble fromed a joint venture to refine and market GPS technology and Dwayne McAninch was invited to join the development board to provide a contractor’s point of view to the system’s developers at Caterpillar. The difference can be clearly seen on site. Stakes are replaced with GPS machine guidance as the scrapers and dozers take their cue from five inch computer monitors in their cabins that’s show precisely where the machines are at a given moment in relation to the planned elevation. “Every hundred feet there would be a stake, and on a job site like this with 150 acres there would be easily a thousand stakes, and each one of them would have to be moved according to whether it is cut or fill. Maybe in the bigger cuts they might be moved as many as five times, maybe six. So we’ve eliminated all that,” says a foreman working for the McAninch Corporation on an earthmoving project in Des Moines. “Now that I don’t have to set the stakes, and I can pay more attention to which way they’re cutting, and the shortest way from point A to point B. It gives me more time to concentrate on that,” he adds. The overall result is a more accurate grading job, and more productivity from every machine used on site. “GPS gave us significant increases in speed and accuracy,” says McAninch. Safety is also visibly better as people are no longer working on the site setting out stakes with machines rolling past. Although the benefits are seen on site, a lot of work offsite is also required. The site drawings need to be converted into a computer program that is installed into the machines that guide them around the site. “For those of us in the office, however, there are some complications. We wrote a software utility to simplify the process of converting design files into SiteVision machine files,” says Tim Tometich, GPS project manager, McAninch Corp. GPS systems are not as widely used in this region. “There are some systems being used in this market, but not to a great extent at this stage,” says Peter Walters, industry manager - heavy construction, Caterpillar. One project where a GPS system was used was the Dubai Autodrome, where the system was retrofitted to Caterpillar 14H motor graders in order to achieve the very tight tolerances required for world class racing circuit. “The machines were used for the entire track and all the run off areas which was quite considerable, about 300 m2 of graded formation,” says Malachy Breslin, project manager, Al Futtaim Carillion. Together with the relevant information, the system means that the grader’s blade was automatically adjusted to within 5 mm of the required grade without any manual adjustment or stakes. “When using that system there was no setting out required, it was just the GPS,” says Breslin. “The tolerances were also better for the sub grades which enabled us to save money on aggregates,” he adds. Many contractors in the region have reservations about the system because it is perceived to be too complex for most operators. “We actually used a reasonably good operator on the machine, but in theory you should be able to put a lower grade operator on the machine because all he does is drive the machine. As long as the data is inputted into the machine in the morning and the operator stays within 200 m of the station then it shouldn’t really need anyone with great experience,” says Breslin. The complicated part of the system is setting up the program that guides the machine, but surveyors would normally do this work anyway. “Maybe the setting up of the program into the machine is not that easy, but actually operating the machine is fairly simple,” says Walters. “There are light bars in the cab which either go red or green depending on whether you hit the right grade and that should be relatively simple for the operator to understand,” he adds. For the future, contractors in the USA and the UAE would seem to agree that GPS grading systems help get the job done quicker, offers costs savings and free up the contractor from waiting for surveyors, which helps maintain the workflow on site. “The system doesn’t even affect [contractor’s] cash flow because that money would be spent on surveyors anyway,” says McAninch.||**||

Add a Comment

Your display name This field is mandatory

Your e-mail address This field is mandatory (Your e-mail address won't be published)

Security code