Grasping Force Control of Robotic Gripper With High Stiffness

In this article, a robotic gripper is developed to study the grasping force control of rigid gripper with high stiffness. As observed in experiments, the dynamics of rigid gripper involves heavy uncertainties and nonlinearities, including backlash and force-dependent friction. The backlash is considered as a major discontinuous disturbance that can be compensated by a Preisach-operator-based inversion control. When increasing the tactile force, the backlash is strongly coupled with the force-dependent friction, which is considered as a continuous disturbance. To reject such continuous disturbance, an active disturbance rejection control (ADRC) is used to estimate the disturbance using an extended state observer and, then, actively reject it by adding a feed-forward control. The ADRC and backlash compensation work in parallel to reject both continuous and discontinuous disturbances, as observed in the rigid gripper. The robustness and stability analysis of the hybrid control proves that the hybrid control is stable, effective, and robust to the unknown disturbances involved in the rigid gripper. Both simulation and experimental results have shown that the ADRC can eliminate the steady-state error, and the Preisach-operator-based compensation can reduce the settling time and overshoot.