Closed-Loop Force Control for Haptic Simulation of Virtual Environments

摘要

Force feedback control is investigated for improving the quality of the haptic feedback in virtual reality applications. Advanced control design can increase the transparency of the haptic device at the haptic interface thereby increasing the realism of the simulation. Force feedback also enables the implementation of admittance control approaches heretofore considered the domain of large robotic platforms. The quality of the haptic interface is "rst quanti"ed, and the standard open-loop impedance approach to haptic control is reviewed. Dual-inputcontrolschemeswithsensoryforcefeedbackarethen introduced, and the resulting quality of the haptic interface is derived. Afour-bar linkage example is used to illustrate the improvement in "delity realized with the various approaches. The tradeoffs encountered in moving to force feedback controllers forhaptic applicationsare alsodiscussed. Nomenclature q joint angle vector,rad qc commanded joint angle vector,rad x position vector,m xd desired positionvector,m xc commanded positionvector,m t actuator torque input vector,N-m t fwd feedforward torque vector,N-m td desired torque input vector,N-m tc commanded torque vector,N-m F force output vector,N Fd desired force output vector,N jZh joint impedance matrix,N-m j ˆZh modeled joint impedance matrix,N-m impedance matrix,N/m