Stability Analysis of Admittance Control Using Asymmetric Stiffness Matrix

Setting the stiffness parameters of a control system in contact-rich tasks is a critical factor when designing physical interaction/contacts with its environment. Therefore, studies on active compliance are being actively conducted across a wide range of domains, including industrial applications. The asymmetric design of stiffness parameters in active compliance can potentially enable interactions that are not possible with conventional methods of either active or passive compliance. However, asymmetric stiffness does not satisfy passivity, stability of the system is the issue. This study focuses on the stability of compliance control in a robot arm with an asymmetric stiffness matrix. The convergence stability of the admittance control is discussed. The paper presents the derivation of an asymmetric stiffness matrix and its incorporation into the admittance model. The experimental results validate the effectiveness of the proposed method and realize stable control using asymmetric stiffness.