On-line trajectory resolution for two-armed systems with conflicting performance criteria

Recent automation research has proposed robotic machining as an alternative to traditional CNC machining. However, unlike traditional machine tools, robots are subject to relatively larger dynamic disturbances and operate closer to their torque limits. As a result of these conditions, combined with inaccurate models of the manipulators and the machining process, joint actuators can often saturate during machining operation, resulting in damage to the tool, or the part, or both. As off-line planned trajectories are executed by the controller, unmodeled disturbances arising due to inaccurate manipulator and blank models may necessitate on-line trajectory re-planning to provide alternate joint trajectories. Such joint trajectories must be constrained to maintain a desired tool path relative to a blank, to respect the manipulators' torque and joint limits, and to avoid collisions. This paper presents a new method for selecting the null-space motion based on torque limits and conflicting performance criteria. The effectiveness of the null-space motion algorithm has been demonstrated via extensive simulations.