Dynamic physical constraint for hard surface emulation

Abstract

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.

What is claims is: 
     
         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.