Force/Torque Sensorless Compliant Control Strategy for Assembly Tasks Using a 6-DOF Collaborative Robot

The flexibility of the robot assembly process is critical, and a robot assembly system that is not flexible may damage the workpieces. Most researchers make the assembly process flexible by installing a six-dimensional force/torque sensor at the end of robots, but doing so will result in an increase in the costs of the robotic assembly system. To this end, this paper proposes an external force/torque calculation algorithm based on dynamic model identiflcation to replace the six-dimensional force/torque sensor; the algorithm can reduce the costs while achieving a flexible assembly. In this paper, the impedance model of the environment and the dynamic model of the robot with friction are unified. Based on the unified model, the virtual contact surface is proposed to optimize the assembly. To ensure the accuracy of the assembly, the compliant control method of this paper uses the PD-based position control as the control inner loop and the impedance control as the control outer loop. To verify the accuracy of the compliant control method, a 6-DOF series collaborative robot which is developed in our laboratory is used to complete the peg-in-hole assembly experiment. The experimental results show that the algorithm has good flexibility and positional accuracy.