Kinematics-based objectives for task scheduling in concurrent robot-CNC hybrid manufacturing

Cooperation between a robot and a CNC machining center can be beneficial for some hybrid manufacturing processes. Here, a robot task scheduling and assignment problem is introduced for such a system where the robot and CNC operate concurrently. Current robot-CNC systems do not use concurrent processing, but allowing for concurrent operation can bring significant makespan reductions for hybrid manufacturing. This mode of operation also introduces challenges across several domains, including robot scheduling. Unlike in traditional robot scheduling problems, where the motion plan for each task is independent, here motion of the CNC table relative to the robot allows for choice of schedule to affect the robot motion plan for task execution. This work explores the addition of two new objectives that harness the effects of relative motion between the robot and CNC to minimize work done by the robotic arm during task execution and traverse movements between tasks. Experiments are run on scheduling additive-additive and additive-subtractive multi-robot manufacturing tasks using the two new objectives in conjunction with the traditional minimum distance objective from the traveling salesman problem. Results show that concurrent manufacturing using the proposed objectives results in shorter makespans with reduced robot joint movement.