Force Control Law Design for a Five Degree-of-freedom Haptic Mechanism

In this paper the effect of a force control law in the transparency of a five degree-of-freedom (dof) haptic mechanism is investigated. The mechanism, which is a part of a training medical simulator for urological operations, consists of a two-dof, five bar linkage and a three-dof spherical joint. The force control algorithm is described and discussed. The open and closed loop schemes are compared. It is shown that the use of the control law aims at the maximization of the haptic device transparency increasing the realism of the simulation. A stability analysis of a one-dof haptic device is performed determining the force control law margin, i.e. a quantitative indication of the haptic mechanism ability to simulate a wide range of virtual environments, maintaining at the same time its stability. Simulation results of the force control law application on the five-dof mechanism are presented and discussed. The closed loop system shows substantially improved response with respect the open loop system.