Stiffness-gradient-based Grasping Force Control for an Underactuated Prosthetic Hand

Background: In order to avoid undesired slide or damage, desired grasping force should be discrepant by the prosthetic hand when grasping soft or hard objects. Methods: A method was proposed in which a force sensor and an optical encoder are used to estimate the stiffness of the object being grasped. Based on contact-impact force model, a fuzzy logic system for stiffness estimation determined by contact force and the rotating angle of motor is constructed. Results: In order to avoid undesired deformation, the main controller modifies the PID gains based on the estimated stiffness of the grasped objects. Conclusion: The experiment results are presented to demonstrate the effectiveness of the proposed method.