A grasping force control strategy is proposed in order to complete various fine manipulations by using anthropomorphic prosthetic hand. The position-based impedance control and force-tracking impedance control are used in free and constrained spaces, respectively. The fuzzy observer is adopted in transition in order to switch control mode, and a same position-based impedance controller is used in those two control modes. In order to achieve grasping force control, a reference force is added to the impedance controller in the constrained space. Trajectory tracking in free space and torque tracking in constrained space are realized, and reliability of mode switch and stability of system are achieved in transition. An adaptive sliding mode friction compensation method is proposed. The terminal sliding mode idea is used to design sliding mode function, which makes the tracking error converge to zero in finite time and avoids the problem of conventional sliding surface that the state tracking error can not converge to zero in finite time. Based on the characteristic of the exponential form friction, the sliding mode control law including the estimation of friction parameter is obtained through terminal sliding mode idea, and the on-line parameter update laws are obtained based on Lyapunov stability theorem. The experiments on the HIT prosthetic hand IV are carried out to evaluate the grasping force control strategy, and the experiment results verifies the effectiveness of this control strategy.
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