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A flux regulation method with passivity-based control (PBC) for a variable reluctance (VR) finger gripper is presented. The performance and stability of the proposed control scheme is verified through mathematical derivations and computer simulation. These verifications indicate that the direct-drive VR finger gripper control has robustness despite certain parameters variations and modelling uncertainties. A novel two-finger gripper based on VR driving principle is also introduced. This kind of gripper has certain advantages over the conventional permanent magnet voice coil gripper, the most notable advantages are the ease of construction, high robustness and very low cost. The work described is the first of its kind in carrying out passivity based control for a direct-drive VR actuator. In the study, the flux and torque behaviour of a mutually-coupled VR gripper was investigated, and its state dynamic equations were derived. Then its flux and torque models were constructed. A similar two-finger VR gripper was fabricated and its characteristics were measured. The PBC controller is designed to regulate the flux linking through the magnetic circuit of the VR finger gripper. Computer simulation and hardware implementation were carried out. The two sets of results compare favourably with each other. Both sets of result show that the system is highly robust and has excellent trajectory tracking performance.
Date of Publication: 6 May 2005