Adaptive sliding manifold slope via grasped object stiffness detection with a prosthetic hand

• An adaptive sliding mode prosthetic hand controller is developed with a variable-slope manifold.
• The manifold slope is adaptively dependent upon the stiffness of the grasped object.
• The stiffness detection method can be used for objects with nonlinear stiffness.
• Statistically significant improvement in tracking performance with the adaptive controller.

Upper limb amputees have expressed the desire for their prosthetic hands to better adapt to the parameters of different grasped objects. In response to this need, an adaptive sliding mode controller (ASMC) is developed that has a variable-slope manifold which is dependent upon the stiffness of the grasped object. The ASMC is experimentally compared to a sliding mode controller (SMC) which has a constant manifold slope over a wide range of grasped object stiffness, ranging from an empty hand to a steel bar. Experimental results indicate that both controllers have satisfactory percent overshoot characteristics; however, the ASMC has significantly less absolute error for all experiments performed with eight different levels of grasped object stiffness.