Outer-Loop Admittance And Motion Control Dual Improvement via A Multi-function Observer

Safe environment contact and high performance motion control are typically conflicting design goals. Admittance control can improve safety and stability in contact with a stiff environment, but remains challenging on industrial robots.

Typically high-performance motion control is achieved by low-admittance systems, which can give high transient forces or instability in contact with high-stiffness environments.

This paper proposes a linear admittance control framework from which a Multi-function OBserver (MOB)-based control scheme that succeeds in directly improving the motion control accuracy by suppressing disturbances, while achieving better loop shaping in the outer-loop admittance control is developed.

By using the task space force and position measurement of the robot, combined with linearized robot and payload models to design the MOB, the outer-loop controller can render improved interactive dynamics.

In addition, a methodology to design the proposed MOB based on the reduced-order model is developed.

Theoretical evaluations and experiments verify the effectiveness of the proposed MOB-based control method, in contact with an environment stiffness and with a 7~kg payload.