Abstract: A robot head, for example for use in surgery, provides a back-drivable system allowing a surgeon to closely control the position of a cutter or other tool. The cutter is mounted at the end of a telescopic arm (20) which can be rotated about two independent perpendicular axes. Rotation about each axis is controlled by a separate motor (30?) which turns a lead screw (32). A bearing (34) travels along the lead screw and changes the angle of an offset crank (36) to cause the required rotation about the axis. The current rotational position about each axis is determined by a sensor at the output. A second sensor independently determines the position of the corresponding motor (30) and the two measured positions are compared. If they differ, the power to the cutter is immediately switched off.

Abstract: A mechanism which constrains the spatial location of a working or a focal point of a tool (103), has a manipulator (101) and a remote centre mechanism (102) mounted thereon. The manipulator (101) provides at least one degree of freedom for positioning the remote centre mechanism (102) which itself provides at least a further degree of freedom for positioning a tool holder suitable for holding the tool (103) which is to be constrained in operation with respect to a remote centre point. The orientation of the tool holder is adjustable whilst still maintaining the position of the remote centre point fixed with respect to the manipulator (101).

Abstract: An active-constraint robot (4), particularly for surgical use, is controlled by means of a series of motorized joints to provide a surgeon with real-time tactile feedback of an operation in progress. The robot system holds, in memory, a series of constraint surfaces beyond which it would be dangerous for the surgeon to go, and a resistive force is applied to the cutting tool (14) as the surgeon approaches any such surface. To improve the overall quality of feedback experienced by the surgeon, the resistive force applied to the cutting tool (14) depends upon the point of intersection (I) between the force factor applied by the surgeon and the surface. Further improvements are achieved by adjusting the tangential resistive force, when the tool is adjacent to the surface, in dependence upon the surrounding shape of the surface.