A constraint-based programming approach for robotic assembly skills implementation

Abstract

• A constraint-based programming formalism for the task-level implementation of robotic assembly skills that allows the skill developer to integrate force control requirements within the skill specification, independently of the specific robotic platform and assembly application. • Reactive force controlled motions are generated in real-time based on force-related objectives and constraints. • The proposed framework opens up the possibility for a non-expert factory worker to intuitively program complex assembly task by simple concatenation of assembly skills. • Demonstrations of a complete assembly process performed with the ABB YuMi dualarm robot in a sensorless configuration. The features of modern collaborative robots, mainly their kinematic redundancy combined with the light-weight structure, can be fully exploited in parts assembly. Traditional robot-level paradigm to robot programming, that requires to explicitly specify the motion of the robot and allows to use contact forces for motion supervision only, cannot be easily applied to complex interaction tasks, such as robotic assembly. Instead, by shifting paradigm to skill-based programming, it is possible to specify force control actions at task level and inherently provide compliant capabilities, without the need to specify the motions of the robot. To this end, this paper presents a constraint-based programming framework for the implementation of assembly skills for light-weight redundant robots, enabling a reactive generation of motion trajectories based on force control requirements. The effectiveness of the proposed approach is experimentally validated on a bimanual assembly use case performed with the ABB YuMi dual-arm robot, requiring a peg-in-hole insertion and a cap-rotation task. Estimation of the interaction force/torque additionally enables the execution of the assembly operation without the need for exteroceptive sensors.