Enhancement of the operating speed and accuracy of parallel and cooperating robots with smart materials

Robot manipulators with parallel kinematics chains and two or more robots manipulating an object form closed kinematics chains. When revolute joints are used in the construction of such robotic manipulation systems, the presence of closed chains and their associated kinematics nonlinearity demands high harmonic motions in at least a number of the actuated joints. This is the case even if all the links are relatively rigid and attempt is made to synthesise the joint motions with minimal harmonic content. The presence of high harmonic components in the actuated joint motions is undesirable since as the operating speed is increased, their frequencies would rapidly increase and move beyond the dynamic response limitations of the actuating drives, thereby causing vibration and control problems. The performance of the system in terms of cycle time, tracking precision and the like would therefore suffer. This is particularly the case since the dynamics of such systems is also highly nonlinear and require higher harmonic components in the actuating torques (forces). In this paper, a systematic method is presented for optimal integration of smart (active) materials based actuators into the structure of cooperating robots and robot manipulators with parallel kinematics chain for the purpose of eliminating the high harmonic components of their actuated joint motions. As the result, the potential excitation of the natural modes of vibration of such systems and their related control problems can be greatly reduced. The resulting robotic systems should therefore be capable of operating at higher speeds with increased precision.