Tracing Control for a Tracked Vehicle Based on a Virtual Wheeled Mobile Robot

Abstract

Although a tracked vehicle enables stable movements on rough terrain, in a rotating motion no fixed kinematic model such as the model of wheeled mobile robot exists. Hence, it is difficult to realize a autonomous driving control of the tracked vehicle. In this paper, a new tracking control method for a tracked vehicle is described. The proposed method is constructed by using a virtual wheeled mobile robot. A instantaneous motion of the vehicle with slip can be regarded as a motion of a mobile robot with independent driving wheels. From the kinematic constraints, the virtual mobile robot model is derived. The virtual desired trajectory for the vir- tual robot is obtained from the given desired trajectory for the original tracked vehicle under the assumption that the virtual model is fixed. A control rule is derived by applying a differential feedback control method for wheeled mobile robots, and guarantees that the virtual mobile robot follows the virtual desired trajectory. We also describe a on-line prediction method for the virtual robot so as to discard the assumption that the virtual model is fixed. This paper presents a new control method for a tracked vehicle to track a given trajectory. the proposed method is based on the control rule for a virtual wheeled mobile robot. The paper is organized as follows: In the next section the kinematic model of the vehicle with slip is discussed. The instantaneous motion of the vehicle with slippage can be regarded as a motion of a mobile robot with independent driving wheels. The virtual wheeled mobile robot is derived from the vehicle motion as the kinematic model. In the third section, the control method for the tracked vehicle with slip is proposed. Kinematic restrictions clarify that the vehicle with slippage can not no longer track the given trajectory strictly. The desired posture of the vehicle is slightly al- tered so that the position of the vehicle's origin can follow the trajectory. Then, the virtual desired trajectory for the virtual robot is derived from the altered trajectory under the assumption that the virtual model is fixed. Finally, a control rule for the tracked vehicle is derivedby applyinga differen- tial feedback control method for wheeled mobile robots. the control method guarantees that the virtual mobile robot fol- lows the virtual desired trajectory. In the fourth section, the prediction method of the virtual robot is described so as to discard the assumption mentioned in previous section. The parameters concerning the virtual mobile robot are the po- sition of its origin with respect to the original vehicle, and the tread length between two virtual wheels. These param- eters will change if the property of ground or the contact condition between crawler and ground changes. However, when the motion of the vehicle shifts to clockwise rotation from counterclockwise rotation, or the reverse motion oc- curs, the parameters cause the discontinuity on representa- tion. To avoid this, the parameters are projected on a unit sphere and converted to the polar-coordinate representation. The converted parameters have the continuity and linearity. The parameters are predicted by using a linear time series model. The control rule mentioned in the section 3 is ap- plied on the predicted parameters. Final section makes con- clusions and presents the future work.