Adaptive Hybrid Variable Impedance Control of Industrial Manipulators

Despite robot manipulators having been widely used by industry in recent years, contact between the robot manipulator and the environment is inevitable during operations such as assembly, peg-in-hole, deburring, grinding, milling, cutting, polishing, and human-robot interaction. When a robot manipulator interacts with its environment, if the contact force is not appropriately handled, the robot manipulator may become unstable. This paper studies the dynamic response between the robot manipulator and the environment by comparing several variants of hybrid impedance control schemes. In particular, the task space of the robot manipulator is divided into two subspaces-position control and force control-to develop a hybrid compliance control scheme which can simultaneously track the desired trajectory and desired force. To avoid large force tracking error due to fast moving tasks in the position control subspace or drastic environment changes, this paper proposes an adaptive hybrid variable impedance control scheme. Based on the force tracking error, the impedance coefficients can be adjusted to improve the transient force response so as to reduce force tracking error. Experimental results indicate that the proposed approach performs better than the other approaches also tested in the experiment.