Virtual needle insertion with haptic feedback using a hybrid actuator with DC servomotor and MR-brake with Hall-effect sensor

In many haptics applications, fast and stable force response with high strength is highly desired. While the existing active and passive actuators cannot fully satisfy these requirements alone, their cooperation could provide better results. This study aimed at the development of a hybrid actuator by combining a DC servomotor and a magnetorheological (MR) brake. Serpentine flux path architecture was used to design a compact MR-brake. By embedding a Hall-effect sensor in the brake, the hysteresis challenges and residual off-state torque were eliminated. In this approach, the sensor measures the flux across the MR-fluid while a PI controller directly manipulates the magnetic induction level. To the best of our knowledge, this is the first such design incorporated into an MR-brake. The control scheme determines the motor and brake inputs separately based on their capabilities. During operation, the brake is activated to provide an average force profile while the motor superimposes the finer details on this profile. The hybrid actuator can provide a stiff wall collision effect when the needle touches a bone. It can also enable fast tracking during sudden force variations as they happen during virtual needle insertion and removal into virtual tissue layers.