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Inertial measurement units


Taking 3D grade control systems up a notch, -or three


Inertial measurement unit (IMU) in 3D grade control system
Available on:



Trimble GCS900
Topcon 3D-MC²

Caterpillar AccuGrade
Leica PowerGrade 3D

Carlson Carlson Grade












One of the biggest advances in 3D grade control technology in recent years has been the introduction of the inertial measurement unit, often referred to as an IMU.

Topcon Positioning Systems lead this effort with the introduction of their 3D-MC² system for dozers in 2008, followed by Leica Geosystems and their SP technology in 2010.

This IMU is mounted on the dozer blade in the same manner as a traditional slope sensor is. Unlike a slope sensor, however, the IMU can measure slope, pitch and yaw of the blade, including the acceleration of each of these movements.

The addition of this sensor technology really turns the traditional operating principle of a 3D grade control system on its head.

The IMU uses its array of on-board sensors (it comprises a solid-state gyro and a compass in addition to accelerometers) to calculate and keep track of the dozer blade's position.

In fact, GNSS is really only used to update the system periodically with absolute positions, -to correct the IMU sensor drift.



Inertial measurement units from Topcon (left) and Leica

The result is a more responsive system capable of a hydraulic correctional rate of 100 times per second versus 20 times per seconds on most traditional 3D grade control systems.

With its particular machine geometry (the blade is way forward of the machine's gravitational center) the dozer is the main beneficiary of this technology. The two manufacturers claim it can now perform well in 3rd gear at full throttle.

Because the IMU is in reality a self-contained positioning system, the 3D machine control system can now sustain momentary GNSS outages that before would cause it to stop working. This can be of benefit when working in areas with marginal GNSS coverage.

Topcon has stated their 3D-MC² product is compatible with existing Z63 and System 5 machines already in the field, although some new hardware may be necessary, depending on the age and configuration of the system.

Leica states the SP sensor is available as an upgrade to existing PowerGrade 3D systems already in use.

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