3-D Grade Control Systems

Technology in the construction industry has the potential to help companies increase productivity, overcome skilled labor shortages, improve quality and reduce overall costs. One advancing technology can address all of these concerns: 3-D Grade Control Systems with machine controls. While this technology is not new, it has developed significantly the past several years.

3-D Grade Control Systems use three pieces of electronic advancements, enabling the systems to operate accurately and consistently:
 

• Electronics locate the exact 3-D position of machinery and its work tool on the jobsite

• Onboard computers consult with the electronic 3-D model of the jobsite to:
  • Determine how material below the machine tool should be shaped
  • Determine how the tool should be adjusted to meet the 3-D jobsite specification.
• The system relates all of the information to the operator in the cab via a monitor. Machines are eliminating the need for operator interaction and are instead using machine controls to direct the hydraulics of the machine to conform to direction from the electronics.

Currently, two primary types of 3-D grade controls are used:

1. Global Positioning Systems –Use satellites to locate equipment
2. Local Positioning Systems – Use precision surveying equipment to locate and direct equipment

The positioning systems have similar outcomes while using different forms of technology:

• GPS Systems use an antenna/receiver on the machine to receive the signal from satellites in the U.S. and Russian satellite systems. The systems locate the equipment and provide xyz coordinates (latitude, longitude and elevation). These signals are interpreted by the grade control systems into local jobsite coordinates using compass headings.

  A second antenna in a permanent location is placed on the jobsite, its exact location (coordinates) is known. This “reference station” determines and calculates corrections to any satellite “timing” issues and transmits corrections that allow for exact position of equipment and tools.
   

• Local Positioning Systems use a robotic total station (RTS). This station is a surveying instrument that can track a machine and determine its xyz coordinates. The RTS uses a prism or light beam on the machine (active target) to track the machine. If the line of sight is lost, the RTS can quickly search and relocate the active target. In most instances, the 3-D model of the jobsite is located in the on-board computer equipment. The RTS sends positioning information via radio and the hydraulics are controlled by the onboard computer.

Both systems are capable, have advantages/disadvantages and effectively reduce the need for extensive surveying, survey crews and staking on the jobsite.

• GPS – The system can control multiple machines at one time, has a range of up to five to six miles, does not need line of sight for operation, has a vertical accuracy of + 3 centimeters and limited indoor use.
• LPS – It requires a RCS for each piece of equipment, has a limited range of 1,000 to 1,500 feet, requires line of sight between the RTS and equipment, has a vertical accuracy of + 2 millimeters, can be used in tunnels and covered areas, and the RTS has other surveying uses.

Typical equipment using GPS and LPS include equipment used to grade and shape the earth for roads, buildings, airport runways, subdivisions, resurfacing etc. GPS and LPS are often found on dozers, motor graders, excavators and scrapers.