Design and evaluation of an encountered-type haptic interface using MR fluid for surgical simulators

A novel encountered-type haptic interface for surgical simulators is proposed. This interface has a container of MR (MagnetoRheological) fluid, and an operator puts a surgical instrument into the fluid and can feel resistance force. The advantage of this interface is that an operator can move an instrument freely when it does not contact with MR fluid and change instruments easily. If an instrument is mounted mechanically on a haptic interface driven by servomotors, it is difficult to change surgical tools. On the other hand, the developed device does not require a procedure for changing tools and can increase a sense of reality. However, MR fluid cannot display large deformation of a tissue since its elastic region is small. Therefore, a container of the fluid is moved by servomotors. In this paper, concept and design of the interface and performance evaluations are described. In order to specify required display force, cutting force of a liver is analysed, and the maximum force is about 1.6 [N]. The device is designed based on this required force. Relationship between coil current and display force is measured, and the interface can exert 2.7 [N] when the current is 1 [A]. In addition, the validness of the proposed scheme using servomotors is evaluated.