Automatic control of passive, towed implements
An automatic control system for passive, towed implements is described. The system provides a strategy for optimal control of a towed implement using a nudge input to an autopilot-controlled tractor. Implement path-tracking error, as measured by a GNSS receiver, is consistently corrected to zero.
1. A method for guiding a passive implement along a desired path comprising:
providing a tractor guided by an autopilot having a nudge input;
introducing a test input to the tractor autopilot;
providing a GNSS receiver fixed to the passive implement;
towing the passive implement behind the tractor via a hitch;
using a model of the tractor-hitch-implement system to provide feedback to a control system that provides nudge inputs to the autopilot-controlled tractor and to the model; wherein,
the model estimates the immediate passive implement offset from the path;
tractor, hitch and implement elements within the model are arranged such that nudge inputs from the control system are applied to the implement element directly;
the tractor element of the model includes information obtained from measurements of the motion of the tractor in response to the test input; and,
the control system nudge inputs cause the difference between the actual implement path and the desired path to be minimized.
2. The method of claim 1 wherein the test input is a step offset and the information obtained from measurements of the motion of the tractor is the time, t 1/2 , required for the tractor to achieve half the step offset.
3. The method of claim 1 wherein the test input is a step, a pulse, or a sinusoid and the information obtained from measurements of the motion of the tractor is a set of parameters that best fit the motion to a transfer function.
4. The method of claim 1 wherein the test input is a pseudorandom sequence and measurements of the motion of the tractor are cross-correlated with the pseudorandom sequence to determine a tractor response function.
5. The method of claim 1 wherein measurements of the motion of the tractor are obtained using a GNSS receiver fixed to the tractor.
6. The method of claim 1 wherein the hitch element of the model includes the distance from the hitch to the midpoint of the tractor's rear axle.
7. The method of claim 1 wherein the implement element of the model includes the distance from the implement's control point to the hitch.
8. The method of claim 1 wherein the GNSS receiver is a GPS receiver employing SBAS corrections.
9. The method of claim 8 wherein the SBAS corrections are obtained from the FAA WAAS.
10. The method of claim 1 wherein the GNSS receiver is a GPS receiver employing RTK positioning.