  In contact-rich tasks, setting the stiffness of the control system is a
critical factor in its performance. Although the setting range can be extended
by making the stiffness matrix asymmetric, its stability has not been proven.
This study focuses on the stability of compliance control in a robot arm that
deals with an asymmetric stiffness matrix. It discusses the convergence
stability of the admittance control. The paper explains how to derive an
asymmetric stiffness matrix and how to incorporate it into the admittance
model. The authors also present simulation and experimental results that
demonstrate the effectiveness of their proposed method.
