Robot-Assisted Disassembly Sequence Planning With Real-Time Human Motion Prediction
Meng-Lun Lee, Wansong Liu, Sara Behdad, Xiao Liang, Minghui Zheng
Abstract
This article presents a disassembly task planning algorithm considering human–robot collaboration (HRC) and human behavior prediction (HBP). Unlike assembly procedures, the disassembly of end-of-life (EOL) products has been a labor-intensive process with uncertainties difficult to cope with. Meanwhile, it is usually challenging to obtain an optimal sequence efficiently without excessive computational cost. Also, the conventional human-centered task planning, in which the robot has to halt frequently due to unsafe interruptions by human motions, may decrease the efficiency of the disassembly process. In this article, a sequence planner is proposed to assign tasks in real time between a human operator and a robot to overcome the aforementioned challenges. The cost function includes the effort of the human and the robot in terms of both movement distance and time spent on the tasks. The constraints include the disassembly rules and the safety of the human operation. The optimal sequence is generated by solving an optimization problem in a receding-horizon way. In particular, at each step, the proposed disassembly sequence planner locates the workers (a human operator and a robot) and the to-be-disassembled components, predicts human movement for the next several steps, and obtains the optimal disassembly sequence for the next several steps following disassembly rules and safety constraints. Experiments have been extensively conducted on the disassembly of a wooden toybox and a used hard disk drive (HDD) to validate the proposed disassembly sequence planner. The planner has successfully generated the disassembly sequence in an HRC setting explicitly considering real-time human motion prediction and assigned the human operator and the robot to collaboratively complete disassembly tasks without violating disassembly rules and safety constraints.