Ground Contact Detection
Ground contact detection is the electronic determination of the moment a descending leg touches the ground. While the leg descends unloaded the motor current is low; as the foot settles on the ground and load starts to build, the current rises markedly. The driver sees this change and records that position as the zero reference of the leg.
The current drawn by a DC motor is directly proportional to the torque demanded of its shaft. On a screw leg descending freely the torque is almost only friction; as the foot touches the ground and starts taking the weight of the vehicle, the torque and therefore the current jump. The control unit determines the moment of contact by comparing this jump against a threshold.
- If the detection threshold is set too low, friction fluctuation produces false contact; if it is set too high, the leg presses into the ground more than necessary.
- On soft ground the current rise is slow and indistinct; that is why using a base plate improves not only sinking but also detection.
On the KTS200 this step is the first stage of the automatic cycle: starting from the fully retracted position the four legs descend one by one and the contact point of each is recorded separately. The system therefore counts how far each leg has been extended from a known zero during the later angle corrections. If there is a loose stone, a piece of wood or broken ground under the legs, the contact point shifts and the correction cycle takes longer.
Context in which this term is used: How to choose levelling leg capacity