Transparency maximization methodology for haptic devices

In this paper, a design methodology is presented aimed at maximizing haptic device transparency, as seen from the user side. The methodology developed focuses on endpoint side fidelity, and optimizes not only mechanism dimensions, but also all relevant design parameters including relative position of endpoint desired path to device location, motor transmission ratios, and rotor inertias or motor sizes. The methodology is applied to a 5-degree-of-freedom (5-DOF) haptic device, part of a training medical urological simulator, and is applicable to any haptic mechanism. The transparency maximization is achieved using a multivariable optimization approach and an objective function including mechanism-induced parasitic torques/forces and motor and transmission parameters, as seen from the user side, under several constraints. The objective function and the kinematical and operational constraints are described and discussed. A new 5-DOF haptic mechanism is constructed according to the developed procedure, resulting in a substantially improved device with respect to an existing one, developed with a standard optimization method.