Robot trajectory control in Cartesian space with sliding modes

Trajectory generation and tracking in Cartesian space are essential in many industrial robotics applications. A control method using the relation between the force applied to the tool tip and joint torques is applied in this paper to track desired trajectories specified in Cartesian space. The controlled variables are the coordinates of the tip of the robot. The coupled and nonlinear dynamics involved cause difficulties in the robot control. The dynamics equations when expressed in tip coordinates get even more complicated. Variable structure systems based control methodologies are proposed in the literature to overcome the difficulties encountered, without using elaborated models of the plants to be controlled. High frequency oscillations in the joint velocities - chattering -, is a problem faced when using such methods. A chattering free sliding mode control algorithm is considered here in order to deal with the complicated dynamics without causing oscillations in the velocity. Variable structure systems and Lyapunov designs are combined in the method implemented. The controller possesses the robustness properties of-sliding mode systems. Experiment results obtained with a direct drive SCARA type manipulator are presented.