Earth-moving equipment gets guidance from above

Twenty-four satellites orbit 11,000 nautical miles above the earth in a widely dispersed constellation, constantly transmitting their positions, identities and times of signal broadcasts (clocks within the satellites are synchronized with each other and with a master atomic clock on the ground).

Back on terra firma, a survey vehicle zips down the high, way at normal speeds. It is equipped with an impressive arsenal of sensors, lasers, accelerometers and inertial navigation units, enabling it to receive signals beamed from space. Performing high-precision computations, the “Automated Road Analyzer” automatically detects cracks, potholes and other road defects — while simultaneously mapping and logging the condition of signs, highway markers and right of ways.

While the above scenario sounds more like a scene from “Star Trek” or “Space 1999” than the lead story in today’s newspaper, the Global Positioning System (GPS) satellite constellation was actually created by the Department of Defense in 1973 for a very down-to-earth reason — to maneuver troops, position ships and target missiles.

Recently declared fully operational by the United States Air Force, the system first gained fame during Desert Storm by providing unprecedented navigational accuracy for allied air and ground forces.

It currently is being integrated into a wide variety of civilian uses like that of the Road Analyzer, developed by Roadware Corp., Paris, Ontario, Canada, and equipment used by the Navigation and Positioning Division of Leica, Torrance, Calif.

Under the auspices of the Computer-aided Earth Moving (CAEM) Project (part of the president’s Technology Reinvestment Program [TRPI, which supports private-industry initiatives dually aimed at strengthening military effectiveness and converting the defense technology toward “horizontal construction” — i.e., highways, dams, landfills and airports), the technology is being applied to fields that include agriculture, surveying, fleet management, aviation, emergency medical response, dissaster management and transportation.

It is quickly becoming the newest trend in the construction equipment arena, encompassing such areas as open-trench mining operations and the not-so-distant operator-free robotic backhoe.

A BOON TO THE CIVILIAN SECTOR

“This is a major milestone,” says Air Force Vice Chief of Staff Gen. Thomas Moorman. “GPS has become integral to our warfighters and is rapidly becoming a true `utility’ in the civilian community.”

To help develop the technology for the civilian sector, three companies — Leica; Caterpillar, Peoria, Ill.; and Spectra-Physics Laserplane, Dayton, Ohio — have signed a cooperative agreement to develop GPS-based technology for high-precision CAEM.

These partners have been awarded a total of $4.3 million in federal matching funds from the NASA Ames Research Center for a two-year project.

The U.S. Army Corps of Engineers also will play an important role in testing and concept validation.

“The CAEM project seeks to transform a huge and powerful earth-moving machine into a carefully and automatically controlled tool capable of carving a roadbed or other surface exactly as desired, more quickly and with less rework than is customary today,” says Thomas Stansell of Leica’s Navigation and Positioning Division, one of the project’s team leaders.

This will be accomplished by using signals from the GPS satellites, aided by ground-based laser beams, to measure the precise position and orientation of the earth moving blade, in 3-D, in real-time and with an accuracy of better than one inch, Stansell explains.

Digital terrain maps, such as those produced by Space Imaging, Thornton, Colo., are being used to permit real-time control in the field.

“Integration with laser-plane technology will improve vertical accuracy to within a few millimeters and will permit a GPS solution with fewer satellites in view,” says Scott Beathard, a spokesman for Spectra-Physics.

“GPS-based control systems are a natural evolution to laser-based grade control systems pioneered more than 28 years ago,” he explains.

Experimentation has already begun. In a demonstration trial in August 1995 in Peoria, Ill., two GPS antenna’s were mounted on either end of a Caterpillar motor grader’s blade, and OPS signals were integrated with a topographical database in the motor grader cab.

This provided the operator with a picture of the terrain and the position and orientation of the blade relative to it. “[The experiment] was successful,” says Dave McNally, project manager for NASA at the Ames Research Center in Moffett Field, Calif. A second trial was scheduled for February.

CAEM technology offers wide ranging benefits by enhancing productivity and reducing costs in construction of roads, dams, airports, building sites and landfills, as well as mining, agricultural and military construction applications, among others.

WHAT IS GPS?

GPS is a spaced-based radio-navigation system managed for the federal government by the U.S. Air Force, the system operator. The satellites are positionedin orbit so that a minimum of five are in view at any point on the earth’s surface. The satellite signals, aided by ground-based laser beams, are continuously available anywhere in the world, at any altitude and in any weather. They can be decoded by specially designed receivers to determine positions precisely, comparing the time it was sent with the time it was received.

GPS has three major segments: space, control and user, according to “A Technical Report to the Secretary of Transportation on a National Approach to Augmented OPS Services,” provided by the Institute for Telecommunication Sciences, National Telecommunications and Information Administration, the U.S. Department of Commerce, the Federal Highway Administration (FHWA) and the U.S. Department of Transportation (DOT).

Space. NAVSTAR, the military satellite system, supports naval and aerial navigation and has contributed substantially to civilian geodetic surveying. GPS is the civilian application name and uses 24 satellites of known position (and earth-based satellite sensors or tracking devices).

The satellites operate in six orbital planes at an inclination angle of 55 degrees.

Control. There are five monitor stations and three ground antennas with uplink capabilities. “The monitor stations use a OPS receiver to passively track all satellites in view and accumulate ranging data from the satellite signals,” the report says. “The information from the monitor stations to processed at the Master Control Station to deter, line satellite clock and orbit states and to update the navigation message of each satellite.

“This updated information is transmitted to the satellites via the ground antennas, which are also used for transmitting and receiving satellite health and control information.” User. This segment consists of user equipment that can be applied in a variety of configurations and integration architectures.

It includes an antenna and receiver-processor to receive and compute navigation solutions to provide positioning, velocity and precise timing to the user.

“At any given point on earth, you can see four to eight satellites above the horizon,” McNally says. “The GPS receiver, which is an electronic box, allows you to measure the distance to each visible satellite from your antenna.

“You can determine where the satellite is in respect to the center of the earth, and from there, you can figure out where you are through triangulation.”

In the case of construction equipment, two GPS receivers would be used to capture and collect satellite data. One is situated on a known point while the other is attached to the earthmover. Differential GPS, as it is known, allows for more correction of errors than a single OPS receiver would allow. A computer housed in the earthmover makes the positioning calculations, and a radio link between GPS receivers completes the set-up.

Civilian usage of GPS has been deliberately degraded to 100 meters — an occurrence referred to as Selective Availability (SA). The system’s full accuracy is degraded to unauthorized users by corrupting satellite clock and ephemeris data to ensure that an adversary does not use GPS as a military force enhancer against the United States and its allies. While GPS provides civilian users with 100-meter positional accuracy, meter-level accuracies are required and can be achieved through differential GPS.

Differential corrections are generated by a GPS receiver that is fixed at a known position. The receiver uses its own position and GPS satellite positions to calculate errors and corrections. The corrections thus cancel the errors caused by SA, as well as satellite clock errors, orbit errors and atmospheric errors.

The corrections “are computed at a reference station and broadcast from Coast Guard beacon transmitters,” says Frank van Diggelen, marketing manager at Ashtec, Sunnyvale, Calif. “The GIS/GPS receiver will add the differential corrections to its measured ranges to cancel any errors to about one meter.”

Differential corrections are used two ways, van Diggelen says: (1) A radio receiver monitors corrections transmitted by a DGPS service. The corrections can be used for real-time differential operation. (2) Corrections are collected and stored at the reference receiver for post-processing with the data stored in the field.

PUTTING IT INTO PRACTICE

The technology is being used in land transportation to improve safety and provide more efficient use of the existing infrastructure. For instance, traffic management includes systems that collect and process real-time traffic information to control adaptive signals, ramps and signs.

Vehicle control includes systems designed to monitor vehicle position/velocity and road conditions to avoid collisions and, automate certain aspects of vehicle operation.

Rural transportation includes systems that provide navigation aids, deliver information on dangerous weather or road conditions and transmit a distress alert in cage of an accident or breakdown. GPS will aslo assist transit operators in the maintenance, operation and emergency response of transit systems.

Commercial vehicle operations include systems that provide automated vehicle identification/automated vehicle location (AVI/AVL) to improve dispatching, fleet management and monitoring of hazardous materials transport.

Intelligent Vehicle High, way Systems (IVHS) will combine GPS with communications, controls, navigation and information systems to improve highway safety, ease traffic congestion and reduce harmful environmental effects.

Use of GPS in geographic information system applications will permit state and local governments to more efficiently coordinate roadway maintenance and construction in rural areas, provide effiicient means of maintaining roadway data bases and maintain accident location inventories.

CIVILIAN APPLICATIONS

GPS can cut time, increase accuracy and make manual work easier. For example, farmers are using GPS to link crop yield data to specific land parcels and soil types, supporting land management and crop selection decision making. Precision farming, or controlled application methodology, combines prior-year yield data collected on the go using GIS/GPS with soil test data, such as pH, phosphorous and potassium content, to calculate appropriate amounts of fertilizer for a particular crop on a particular parcel.

Fertilizer applicator equipment is loaded with spatial application rate data and outfitted with a OPS receiver linked to a control processor, which regulates the amount of fertilizer being applied.

Additionally, a OPS data logger helps improve “crop scouting” by locating affected areas. Locations of potential problems can be logged in, creating a map of infested areas. Later, the effectiveness of the decisions supported by precision farming techniques can be measured through real-time sensors and GPS receivers mounted on harvesting equipment.

Other applications include helping fleet managers to deliver products to the right location on time.

The technology even helps monitor in-transit temperatures for perishable cargo and enables safety applications that allow dispatchers to alert drivers ahead of time to road hazards — as it did in january 1994 when California experienced massive earthquakes.

And, at certain approved airports, the Federal Aviation Administration (FAA) and a number of airlines are experimenting with GPS in an attempt to try and eliminate delays and save fuel by identifying more direct routes for passenger jets.

The Automated Road Analyzer (ARAN) vehicle provides a geographic reference location, which can be used by municipalities to create map-based Geographic Information Systems (GIS) showing the condition of roads, bridges, signs, signals, drainage structures and other roadside features. “In the past, locations had to be identified by route or highway number and the distance from an identifiable reference point such as a mile marker or highway intersection,” says Bill Swindall, senior vice president for Roadware.

“Now, civil engineers can build and update map-based databases of these features without extensive time-consuming site surveys, explains.

The Leica DGPS receiver determines the exact geographic location of the vehicle by using signals from the GPS satellites orbiting above the earth. It also uses signals from ground-based reference stations to remove errors in the satellite measurements, enhancing accuracy to one meter or better.

The receiver itself combines a handheld computer, differential GPS receiver, antenna and powerful processing in a single compact package that weighs three pounds.

It uses both carrier-phase and code differential techniques to achieve accuracies of 10 cm to 30 cm in real-time or post-processing modes, and it can operate under foliage or other attenuating conditions.

BENEFITS, LIMITATIONS FOR CONSTRUCTION SITES

Riverside County, Calif., is located about 60 miles east of Los Angeles. The Flood Control District surveys the area for flood control and building bridges and dams, as well as performs, all of the mapping services for other departments within the county.

All are based on GPS, says Bill Young, chief of surveying and mapping for Riverside County.

Five GPS units are available, some of which are owned by the Southern California Earthquake Center, and information and data are shared.

“The accuracies are phenomenal,” he says. “That use to be the main concern. We used So bring the information back to the office and adjust it. In comparison, GPS doesn’t need adjusting. What we used to do in eight weeks — to break down the township, which is 36 square miles, and put both horizontal and vertical information in –now takes about nine days with GPS.

“We used to be happy if we could keep errors within one foot. Now, we’re down to one-tenth of a foot,” Young says.

Using differential GPS signals that are gathered by a mounted receiver, a vehicle is driven over the site to be leveled. The information is then used to create a map and construction plan for the site.

GPS also monitors the progress of bulldozers and other equipment once grading has begun.

“We can’t be off at all,” Young says. “The dozer operator needs constant attention of the surveyor to keep him on grade. With differential GPS, we’re getting accuracies to the millimeter in some instances.”

Additional benefits include the ability to rapidly check the grade and layout of construction sites, monitor project progress at sites and provide more accurate cut-and-fill estimates during the bidding process.

Still, the most obvious benefits — reduction of error, decreased cost and quicker work times — don’t quite outweigh the worry that this technology, as high technology has done in the past, will eventually mean fewer jobs for fewer people. “People will be putting GPS on bulldozers,” Young says. “We won’t need a driver. Automation and robots will do all the work.”

Aside from that concern, the biggest stumbling block for the technology currently is its expense. Prices for the GPS system range from $90,000 to more than $100,000. But as the technology continues to develop, researchers predict that the GPS system will become more affordable. “Still,” Young says, “GPS has changed our lives out here.”

When S & S Underground Construction, Tulsa, Okla., got the nod to outfit the city with a network of buried fiber-optic and coaxial TV cables, it turned to work-saving equipment to save time and backs.

But that wasn’t the only reason the company went with the work-saver system from Bobcat, Broken Arrow, Okla.

“Most of our work is in residential areas, and it is constantly scrutinized by the cable TV company, homeowners and city officials,” says Mike Smith, company president.” “Imagine 15 men working in a backyard, digging utility lines, and then having to restore the site back to its original condition. It can get pretty hair at times.”

At one time, a trenching machine was used for much of the digging work, and shovels, wheel-barrows and strong backs were used to haul away rock and dirt.

But several years ago, the company bought a 743 loader from White Star Machinery and Supply, Tulsa, and began leasing a 325 compact excavator to do the trenching. When S & S landed the multi-year Tulsa project, the company bought its own 325 excavator.

In addition to the bucket, which is used for scooping up, hauling and dumping dirt and rock, the loader can be equipped with pallet forks, allowing it to lift heavy reels of cable up and onto a specially built 20-foot trailer.

The excavator can be used for digging trenches with its 12-inch-wide bucket or digging pits four-feet to five-feet deep on either side of a road under which the cable line must go. This makes it easier to maintain the proper boring depth when boring underneath the road. Sometimes, though, the borer may end up half a foot or more below the bottom of the receiving pit.

“The machine is sensitive enough that the operator can locate the buried boring rod by feeling with the bucket,” Smith says. “The equipment has eliminated a lot of time-consuming and costly hand labor for us. Also, we’re very safety conscious.

“The loader and excavator help reduce the chance of a backache or worse. They are real handy tools to have.”