Parallel guidance system for tractor-trailer system with active joint

Parallel tracking or auto guidance systems are becoming common in tractors. Auto guidance systems with accurate positioning allow driving very accurately in straight driving lines. If the driving lines include curves, however, it is mathematically much harder to keep the shortest distance to the adjacent driving line constant. And it becomes even harder if the vehicle is a tractor-trailer and a certain point in the trailer has to follow the curve. If the field has slopes, the trailer necessarily does not follow the kinematical route and more measurements are required to compensate for the error. In this paper a developed path tracking system is presented. An ISO 11783 compatible tractor was used together with a towed combine seed drill. The drawbar of the seed drill was customized by adding a hydraulically controlled joint. The measurements used in navigation were: a RTK-GPS receiver in the tractor, a laser scanner in the seed drill to detect previous swath, and attitude estimation from the inertial and magnetometer measurements. Two different algorithms were developed: a simple one which is based solely on tractor navigation with direct laser scanner based drawbar control; and an advanced one which is based on nonlinear Model Predictive Control (MPC). In MPC approach, a full kinematic model of the tractor-trailer system with active joint is utilized and the laser scanner measurement is in an auxiliary state. For testing purposes a simulator was also developed. The active joint in the trailer drawbar was found to be valuable as the response from control to error is much quicker than from front wheel control. The laser scanner was found to be reliable to detect an edge of the previous swath when the produced small furrow at the edge is clear. The model predictive control also worked nicely and gave a smoother control curve than traditional control algorithms without affecting the response and settling time.