Extended state observer-sliding mode admittance control for grasping by the omnidirectional dexterous hand

Abstract

Compliant control of dexterous hands is increasingly demanded for environmental interaction. Conventional strategies often suffer from significant force tracking errors and poor adaptability when interacting with unknown environments. To meet the constant-force contact requirements in omnidirectional dexterous hand (ODH) grasping and object pose adjustment, this paper proposes an admittance control strategy integrating an extended state observer (ESO) with sliding mode control (SMC), termed extended state observer and sliding-mode admittance control. This method maintains the required contact forces for grasping and manipulation while demonstrating good adaptability to unknown object properties. A modified D-H method is employed to establish the kinematic model of the ODH, based on which its workspace and graspable object range are analyzed. Within the virtual mass-damping admittance framework, SMC is introduced to enhance the system’s robustness against unknown environmental parameters. The ESO is utilized to estimate and compensate for the disturbance in the derivative of the force error, thereby reconstructing a smooth sliding surface to suppress chattering. Furthermore, a continuous SMC law is designed based on Lyapunov stability theory, guaranteeing stable convergence and smooth force tracking. Experimental results confirm that the proposed strategy can well track the desired grasping force and satisfy the requirements of grasping tasks. This work demonstrates the effectiveness of the proposed strategy in achieving robust and precise force control, offering a viable solution for the compliant manipulation of dexterous hands in complex environments.