Grade control devices utilizing global positioning system (GPS) technology have been available for dozers and motor graders for more than a decade. Yet, they have only recently become available for hydraulic excavators.
"The complex and variable movements of the excavator are the reason for its popularity, and the reason for the lag in a positioning solution," says Randy Noland, machine control product manager for Topcon Positioning Systems.
Several manufacturers now offer GPS-based systems that have converted excavators into fine-grading tools. According to Leica Geosystems, the technology has developed to a level where excavators can supply grading accuracies down to .10 ft. (1 1/4 in.).
Following is a look at some of the recent advancements in GPS-based excavator grade control from several key suppliers, as well as their thoughts on the benefits such systems can provide.
GPS grade control technology utilizes the Global Navigation Satellite System (GNSS) to pinpoint location and transmit data. Yet, according to Noland, this is only a part of the equation.
"GNSS can monitor the position of a machine on a jobsite and the movements of a blade quite easily," he states. "But when you consider the anatomy of an excavator — with the boom, stick and bucket and their respective motions — combined with the fast 360° movement of the machine itself, it becomes apparent that other 'sensor' technology is required."
Consequently, a heavy focus has been placed on the tilt angle sensor. "The tilt sensor must be durable and reliable in all weather conditions, and must be 'abuse friendly'," says Noland. "These sensors must also be 'social' and talk to one another."
With the Topcon 3DXi 3-D positioning system, tilt sensors are placed on the excavator body, boom, stick and bucket. "The sensors constantly monitor two axes of their respective positions, while instantly talking to each other," Noland explains. "At the same time, this information is communicated back to the control box or computer."
The control box, along with the software, report the convergence of sensor information (GNSS and CAN-based tilt axis) to the excavator operator via the in-cab display screen. The operator then dictates how the excavator responds.
"With 3-D positioning, the operator is able to dig to grade without over-excavating, while verifying the grade progress instantly, even in a blind cut," Noland points out. "This is possible while freeing up the grade checker to perform other tasks."
Other benefits include more accurate material placement, as well as the ability to reference the same data used by other heavy equipment, enabling all operators to be "working from the same page," Noland adds. This leads to increased productivity.
Accuracy of 3-D systems is specified at .20 ft. industry-wide, with costs varying anywhere from $15,000 to $60,000, depending on the levels of functionality required.
Noland comments, "The return on investment from the automated equipment — which can cut the work required for a specified task by half — is fast, so it can be easily justified."
The Trimble GCS900 GPS-based grade control system is an upgraded version of the GCS600 excavator system. The GCS900 with dual GPS can be installed on excavators with standard buckets or tilt buckets for mass excavation projects. The system uses two GPS receivers and solid-state angle sensors to measure the precise 3-D position of the bucket tip.
The GCS900 places the site plans directly at the operator's fingertips via the CB430 operator control box. The dual GPS antenna configuration is able to compute the exact position and orientation of the machine blade or bucket. Then, the CB430 determines the position and compares this to the design elevation. Coupled with the in-cab mounted lightbars, the operator can visually see what bucket movement is required to achieve grade, allowing for faster excavation of even complex designs without the need for staking.