An on-line reference-trajectory generator for smooth motion of impulse-controlled industrial manipulators

Industrial manipulators driven by impulse-controlled servo motors commonly follow prescribed reference-trajectories which enable smooth movements (no discontinuity in acceleration profile). On-line generation of such smooth trajectories as a consequence of new target-settings during the motion, however, still suffers from the high computational effort for calculating an optimum solution, as far as the maximum limiting values of velocity, acceleration and jerk are taken into account. An additional problem increased by on-line target changes are position and speed deviations from the desired values at the final end-point, caused by the limited accuracy of clock-controlled pulse generation using a DSP or microcontroller and results in an undesired "creep" motion. In this paper we present a method for generating smooth motion reference-trajectory starting from the current velocity and acceleration and taking into account all given constraints. The calculation is based on purely kinematic models and is easy to implement as a real-time algorithm. Furthermore, a control loop for the correction of pulse generation using predicted position errors is proposed to eliminate the "creep" motion. Simulation and experimental results obtained by application of the proposed method to a pick and place machine using a microcontroller SAB C167 are presented.