Surgical training is an important and recent application where haptic interfaces are used to enhance the realism of virtual training simulators. Tissue cutting with surgical scissors is a common interaction mode in the simulations. The haptic interface needs to render a wide range of tissue properties and resistance forces accurately. In this research, we developed a hybrid haptic device made of a DC servomotor and a magnetorheological (MR) brake. The motor can provide fast dynamic response and compensate for inertia and friction effects of the device. But alone, it cannot supply high force levels and the sensation of stiff interaction with hard tissues such as tendons. On the other hand, the MR-brake can provide very stiff interaction forces yet cannot reflect fast dynamics that are encountered as the virtual scissors go through the tissue. The hybrid actuator developed in this work combines the two based on a control scheme that decomposes the actuator command signal into two branches considering each actuator's capabilities. It is implemented on a compact single degree-of-freedom (DOF) interface to simulate virtual tissue cutting with three different scissor types (Mayo, Metzenbaum, Iris) and four types of rat tissue (liver, muscle, skin, tendon). Results have shown close tracking of the desired force profile in all cases. Compared to just using a DC motor, the hybrid actuator provided a wider range of forces (up to 18 N) with fast response to render quick force variations without any instability for all simulated tissue and scissor types.
A Novel Method for Tuning PID Controller
