NO-OVERSHOOT CONTROL OF ROBOTIC MANIPULATORS IN THE PRESENCE OF OBSTACLES

The long standing problem of guiding robotic manipulators in cluttered workspaces is treated here by a unified approach, taking into account both motion planning and control aspects. Planning the collision-free operation is based on the notion of roadmaps. To reduce the complexit y of the roadmaps, the real problem is approximated by a simplified bu t still realistic graph structure. Motion planning relies on the robot closely following the defined collison-free path, so the errors in ro bot control must be contained within bounded regions. Satisfying this assumption ideally requires no-overshoot control. Overshooting demands special attention in tasks that require high speed operations of robo ts in the presence of obstacles. To stabilize at the specified collisi on-free trajectory, before going actually beyond it, joint control sch emes demand slow movements through a number of intermediate subgoals. This significantly delays the completion of the task. By using ideas f rom variable structure control (VSC), a control policy is suggested he re that switches between PD+ and CEA+ (constant error acceleration) sc hemes, where the CEA+ scheme applies a ''constant error acceleration'' of the largest possible magnitude in the appropriate direction. the p erformance of 'the path planning and the control algorithms is present ed through simulations of a four-link SCARA robot in various cluttered workspaces. (C) 1994 John Wiley & Sons, Inc.