A three element sliding mode control system for robot manipulators

The path planning problem consists in finding an obstacle-free path for a robot manipulator to follow starting from an initial position and ending at a target position so that a task can be carried out safely in a cluttered environment. This paper proposes an innovative path planning and motion control approach. The path planning approach, in the manipulator´s configuration space, consists in forming a global attractive artificial potential field around a target configuration and in generating repulsive potential fields around obstacle regions. Obstacle free motion of the robot manipulator is achieved via a three-element sliding mode control system. The three control elements are: (i) global sliding mode control, (ii) repulsive sliding mode control and (iii) tangential sliding mode control. The first element ensures that the robot reaches the target configuration by following the attractive potential field lines. The second element ensures the robot does not enter the obstacle regions. The third element allows the robot to move along an obstacle boundary tangentially as it is moving towards the target position, which results in shorter travel path. The effectiveness of the proposed approach has been evaluated analytically and demonstrated through computer simulations for the cases of single and multiple obstacles.