DYNAMIC PHYSICAL CONSTRAINT FOR HARD SURFACE EMULATION
A method and apparatus for haptic hard surface emulation using a dynamic physical constraint are provided. The movement and position of the dynamic physical constraint is actively controlled in order to emulate a hard surface. The dynamic physical constraint may be controlled by a computer. In another aspect of the invention, the dynamic physical constraint limits the motion of a manipulator joint in space. The position at any time of the dynamic physical constraint is dependent on the position in space of the manipulator's end effector.
1 . An apparatus for guiding a user comprising:
a robot having an end-effector which is adapted to be manipulated by an application of external forces, wherein the robot has at least one actuated joint and zero or more passive joints; wherein the at least one actuated joint is configured to position a physical constraint that limits the motion of at least one other joint in at least one direction.
2 . The apparatus of claim 1 , further comprising a tool is attached to an end of the end-effector.
3 . The apparatus of claim 1 , further comprising a milling tool is attached to an end of the end-effector.
4 . The apparatus of claim 3 , wherein a base of the apparatus is configured to be mounted to a bone.
5 . The apparatus of claim 1 , wherein the at least one actuated joint includes an active linkage that is controlled by relating a constrained position of the physical constraint to a function of the current position of the end-effector.
6 . The apparatus of claim 5 , wherein the current position of the end-effector is determined using an external position measurement system.
7 . A method for controlling movements of an end-effector comprising the steps of:
applying a force on the end-effector of a manipulator causing motion at joints of the manipulator;
determining a current position of the end-effector;
comparing the current position of the end-effector to a predetermined position;
determining a required position of a physical constraint based on the comparison of the current position of the end-effector to the predetermined position in order to prevent incursion of the end-effector beyond the predetermined position; and
positioning the physical constraint at the required position.
8 . The method of claim 7 , wherein the manipulator comprises a robot.
9 . The method of claim 7 , wherein the current position of the end-effector is determined using measurements of positions of the joints of the manipulator.
10 . The method of claim 7 , wherein the current position of the end-effector is determined using an external position measurement system.
11 . An apparatus for guiding a user's control of an end-effector comprising:
a robot having:
at least one actuated joint,
at least one other joint connected to the at least one actuated joint, and
a physical constraint assembly movable by actuation of the at least one actuated joint, wherein the physical constraint assembly consists of a single physical constraint that limits the motion of the at least one other joint in only one direction; and
an end-effector configured to be manipulated by an application of external forces and connected to the at least one other joint.
12 . The apparatus of claim 11 , further comprising at least one passive joint connected to the at least one actuated joint.