Adaptive admittance control for grasping of the omnidirectional dexterous hand

Purpose The need for compliant control of dexterous hands as end-effectors in environmental interactions is increasingly emphasized. Traditional compliant control methods are often characterized by significant grasping force errors and poor adaptability. To address the constant force control requirements for object grasping and posture adjustment for the omnidirectional dexterous hand (ODH), this paper aims to propose a nonlinear disturbance observer-based adaptive admittance control (NDOAAC) method. Design/methodology/approach Based on the established kinematic model, an admittance control framework is constructed. A gradient descent-based adaptation law is designed to continuously estimate environmental stiffness and dynamically modify the reference trajectory. A nonlinear disturbance observer is incorporated to aggregate unmodeled dynamics and external disturbances as composite disturbances. The parameters of the admittance model are then regulated according to the observed values. The stability of the proposed control system is theoretically demonstrated. Findings The superiority of the NDOAAC method is validated through comparative simulations with Classical Admittance Control (CAC) and Adaptive Admittance Control (AAC), while its effectiveness is confirmed via physical experiments. Results demonstrate that the NDOAAC strategy achieves precise tracking of desired grasping forces, improves system response speed and maintains excellent adaptability to objects with varying stiffness levels. Originality/value The NDOAAC strategy is proposed in this paper, which effectively fulfills the requirements of grasping tasks and provides a viable solution for compliant manipulation with the ODH.