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3D grade control systems explained

Heavy equipment and satellites, -a match made in heaven

To explain the basics of this technology, we are using a single-antenna, GPS-based system on a dozer as an example. This is a common system configuration that you can encounter on many job sites.

GPS stands for Global Positioning System and is a constellation of 24 navigation satellites owned and operated by the US Department of Defense.

A GPS antenna and receiver are capable of receiving signals sent out from these satellites and use these to calculate the position of the antenna. This can be done many times per second, making it a real-time positioning device.

3D grade control on dozer

The GPS antenna is mounted on top of a mast that is bolted directly onto the machine blade. (The antenna is mounted on a mast because it needs to be higher than the cab of the machine in order for it to get a clear line of sight to the satellites). The signals received by this antenna travel to the GPS receiver which decodes them and in turn sends them to the control box.

In order for the 3D grade control system to calculate an accurate position for the cutting edge of the blade, it needs to get both the signal from the on-machine GPS receiver and a correctional signal via a radio from a GPS base station located on or near the job site. This base station consists of a GPS antenna and receiver along with a transmitting radio that broadcasts the correctional signals to the machine.

3D grade control antenna, receiver,
                              slope sensor and control box
The brains of the system is the control box and it is always placed inside the cab. It should be mounted close to the operator and be easily accessible, but should also allow a clear view of the blade so the operator can see to manage the material.

The control box uses all the inputs from the on-machine GPS receiver, the GPS base station and a blade-mounted slope sensor to calculate the exact 3D position of the cutting edge of the blade several times per second.

The system then looks in the data model to see what the design elevation should be at this exact spot on the job site.
Antenna, receiver, slope sensor and control box from Topcon

The difference between the current elevation of the cutting edge and the design elevation is your cut/fill information. This cut/fill information is then displayed to the operator in real time on the screen of the control box.

If the operator has set the system to automatic mode, the cut/fill information will be sent to the valves so the blade can be automatically driven to the design elevation.

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