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