Vertical Wheel Force Control for a Planetary Rover

Abstract

The Lightweight Rover Unit (LRU) is a four-wheeled planetary rover for rough terrain exploration. The front and the rear wheels are each mounted on a bogie axis, respectively. These bogies are attached to the body via actuated swivel joints. The aim of this thesis is to employ these actuators to control the vertical wheel force distribution. The control of the vertical wheel forces can be utilized to increase the tip-over stability of the rover and to reduce wheel slippage. In the beginning, a mathematical model of the rover was derived. This model allows an estimation of the wheel forces depending on the system state of the rover. Based on this model, a control law was developed that uses the bogie actuators to distribute the vertical wheel forces in a predefined way. The chosen approach employs a quadratic optimization problem to distribute the wheel forces according to variable optimality measures. The mathematical model contained unknown system parameters which had to be identified for a precise estimation of the wheel forces. These parameters were used in the successful verification of the rover model. The errors between the estimated and the real vertical wheel forces stayed below the tolerable limit. Finally, the proposed controller was successfully validated in experimental tests on the LRU.