Trajectory Planners for Cooperative Control of Two Industrial Robots and Belt Drives

Abstract

This thesis focuses on trajectory planning strategies for high-speed, vibration restrained position control of belt drives and cooperative contour control of two robots in view of increasing the speed of cooperative task. The proposed solutions have been devised, implemented and verified for effective functionality. The trajectory planning in this context is carried out considering the relevant kinematic constraints met in actual practice; the maximum joint velocity constraints and the maximum joint acceleration constraints. The proposed planners are based on the principles of kinematics and the trajectory planning scenarios and, the issues are critically reviewed. For belt driven machine, a fourth order kinematic model integrating belt reaction torque is systematically derived, and thereby explained the spiky phenomenon in velocity profile of motor position, when an acceleration change is experienced. Further, a feed forward dynamic compensator is proposed to restraint vibration and to improve dynamic characteristics of the belt drives. The proposed feed forward compensator is a combination of inverse dynamics of the system and a desirable dynamic filter, which reforms the dynamic characteristics of the existing system. The planned trajectories at low speeds and high speeds are extensively tested for accurate performance with an actual belt driven machine and the results are illustrated. The proposed trajectory planners for two-robot cooperation are basically of two types. 1) Given objective cooperative trajectory exceeding the dynamic bounds of a single robot is decomposed into two concurrent complementary trajectories of two robots maneuvered simultaneously 2) For a specified objective locus, the minimum time complementary trajectories for cooperation are planned. The objective locus used to exemplify the concept of trajectory planners in both cases is an Sshaped locus and realization of the trajectories are carried out under maximum joint acceleration constraints. In the former cooperative trajectory planner, a fair task distribution is accomplished by minimizing the difference in maximum joint velocities of two robots. The complexities in planning trajectories are coped with a two-stage trajectory-planning paradigm backed with a short-listing criterion. A fourth order spline technique for position, minimizing the joint acceleration is also derived theoretically. The latter, minimum time cooperative trajectory planner, is of bang-bang type in acceleration profile and the fairness of each robot contribution is achieved through an additional contribution constraint for each robot to the cooperative task. The applicability of the trajectory-planning concept has been verified with cooperative trajectories having sharp corners. Since the proposed trajectory planners concerned under the thesis work are off-line and therefore they can be conveniently applied to existing servo systems irrespective of the computational power of in-use controller. Neither, a dramatic change in the existing hardware setup nor a considerable reconfiguration of the system is demanded in instrumentation point of view. This requirement of minimal changes in adaptation enhances the pragmatic significance of the proposed schemes.