Development of a 7-DoF Haptic Operator Interface Based on Redundantly Actuated Parallel Mechanism

This paper proposes a novel 7-DoF operator interface based on a redundantly actuated parallel architecture of 2(RRRS)-RRRSP. This design effectively avoids the workspace-internal singularities, thereby addressing the limitations associated with the orientational workspace of traditional parallel operator interfaces. Furthermore, the redundantly actuated mechanism enables 3-DoF full actuation of each branch chain, and the motors are specially positioned near the base, significantly reducing the operating inertia without the need for gravity compensation. This arrangement contributes to a reduction in operator fatigue during prolonged operation. A hybrid tendon-linkage transmission is utilized in the operator interface to enhance its positioning accuracy. A prototype of the operator interface has been developed, and its kinematics, along with the Jacobian, have been derived. Optimization of structural parameters has been executed to enhance operational dexterity and relative workspace. Static force analysis has been conducted, and a strategy for static force output has been implemented to effectively decouple the interference between the clamping feedback force and the sixdimensional spatial feedback force. Experimental investigations on the translational and orientational workspace are carried out. The results demonstrate an expansive translational workspace measuring 315 mm (X), 248.5 mm, and 133.8 mm (Z), along with a wide range of orientation angles -108, 98(α), -134, 134(b) and -115, 115(γ). Trajectory tracking experiments have been performed and yielded an average error value of 1.021mm. The accuracy of the feedback force output has been studied, with average errors in output force recorded as 0.084 N (X), 0.124 N (Y), and 0.237 N (Z). Investigations into decoupling capability have been carried out, with average output errors of the clamping force at 5 N and 7 N operating forces in X and Y directions recorded as 0.095 N and 0.081 N, respectively. The experimental results demonstrate its potential for integration into RAMIS systems to align with diverse configurations of slave manipulators.