Direct-drive manipulator for pen-based force display

Abstract

A pen-based direct-drive manipulator enables precision manipulation and force display of a control point within three degrees of freedom. The control point exhibits substantially no backlash, very low friction and very low inertia making it useful as a force display. The manipulator also has a very high force generation bandwidth allowing high frequency force components to be displayed. A parallel actuator structure controls motion over two degrees of freedom in a horizontal plane. The parallel structure is a redundant structure including three chains in parallel coupled at the control point. The redundant structure provides a uniform force capability throughout the manipulator workspace. A pair of rotational actuators rotate the parallel structure about an axis to approximate a linear motion along a third axis. The rotational actuators provide a third degree of freedom for the control point. Motion about the third axis is substantially decouple from motion about the horizontal plane.

What is claimed is:  
     
       1. A direct drive actuator system responsive to operator manipulation of a control point, comprising: 
       an end effector defining a control point accessible to manipulation by an operator within an end effector workspace;  
       first, second and third kinematic chains coupled in parallel to the end effector in common alignment to the control point to define a redundant actuator structure for allowing motion of the control point within a first plane of the workspace to not more than two degrees of freedom;  
       the first kinematic chain comprising: a first actuator, a first inner link and a first outer link, the first actuator fixed relative to the first plane and coupled to the first inner link, the first inner link coupled to the first outer link to define a first joint, the first outer link coupled to the end effector in alignment with the control point;  
       the second kinematic chain comprising: a second actuator, a second inner link and a second outer link, the second actuator fixed relative to the first plane and coupled to the second inner link, the second inner link coupled to the second outer link to define a second joint, the second outer link coupled to the end effector in alignment with the control point; and  
       the third kinematic chain comprising: a third actuator, a third inner link and a third outer link, the third actuator fixed relative to the first plane and coupled to the third inner link, the third inner link coupled to the third outer link to define a third joint, the third outer link coupled to the end effector in alignment with the control point.  
     
     
       2. The actuator system of  claim 1  in which positions of the first, second and third actuators in response to operator manipulation at the control point are determined by choosing a torque vector for the respective first, second and third kinematic chains that substantially maximizes the force that can be applied at the control point. 
     
     
       3. The actuator system of  claim 1  in which the first kinematic chain further comprises a first optical encoder for sensing position of the first actuator, the second kinematic chain further comprises a second optical encoder for sensing position of the second actuator, and the third kinematic chain further comprises a third optical encoder for sensing position of the third actuator. 
     
     
       4. The actuator system of  claim 1  in which the end effector defines a free control point interface allowing an operator to apply a pen-like tool to the control point without the system holding the tool to the control point. 
     
     
       5. The actuator system of  claim 1  in which the first, second and third kinematic chains define a common structure, and further comprising a fourth actuator for moving the common structure substantially orthogonal to the first plane within the end effector workspace, wherein the orthogonal movement movement is substantially decoupled from movement within the first plane within the end effector workspace. 
     
     
       6. The actuator system of  claim 1  in which the first, second and third kinematic chains each have a respective anchor point and are coupled in parallel at a common joint; and wherein the control point is aligned with the common joint along a line perpendicular to the first plane; and wherein joint angle for the first joint, second joint and third joint are controlled respectively to define the redundant actuator structure which enables motion of the control point within the first plane of motion to not more than two degrees of freedom. 
     
     
       7. The actuator system of  claim 1  in which the first, second and third kinematic chains each have a respective anchor point and are coupled in parallel at a common joint; and wherein the control point is aligned with the common joint along a line perpendicular to the first plane; and wherein output torque for each one of the first actuator, second actuator and third actuator are controlled to define the redundant actuator structure which enables motion of the control point within the first plane of motion to not more than two degrees of freedom. 
     
     
       8. A kinematic system responsive to operator manipulation of a control point, comprising: 
       first, second and third kinematic chains each having a respective anchor point and being coupled in parallel at a common joint;  
       an end effector in alignment with the common joint along a line perpendicular to a first plane of motion, the end effector defining a control point accessible to manipulation by an operator to move the control point within an end effector workspace;  
       wherein position of the common joint with respect to each one of the respective anchor points is controlled respectively to define a redundant control structure which allows motion of the control point within the first plane of motion to not more than two degrees of freedom.  
     
     
       9. The system of  claim 8 , further comprising a tool for being held to the control point only by a force applied by an operator via the tool, the tool being free to make contact and discontinue contact with the control point under operator control. 
     
     
       10. The system of  claim 8  in which the position of the common joint with respect to each anchor point is controlled for each of the first, second and third kinematic chain by applying a respective torque vector to the respective first, second and third kinematic chains that substantially maximizes the force that can be applied at the control point. 
     
     
       11. The system of  claim 8  in which the position of the common joint with respect to each anchor point is controlled respectively for each of the first, second and third kinematic chain by defining a joint angle for the respective first, second and third kinematic chains that substantially maximizes the force that can be applied at the control point. 
     
     
       12. A direct drive actuator system responsive to operator manipulation of a control point, comprising: 
       a tool being held by an operator;  
       an end effector defining a control point accessible to the tool for manipulation via the tool within an end effector workspace, wherein the tool is free to make contact and discontinue contact with the contact point;  
       first, second and third kinematic chains coupled in parallel to the end effector in common alignment with the control point to define a redundant actuator structure for allowing motion of the control point within a first plane of the workspace to not more than two degrees of freedom;  
       the first kinematic chain comprising: a first actuator, a first inner link and a first outer link, the first actuator fixed relative to the first plane and coupled to the first inner link, the first inner link coupled to the first outer link to define a first joint, the first outer link coupled to the end effector in alignment with the control point;  
       the second kinematic chain comprising: a second actuator, a second inner link and a second outer link, the second actuator fixed relative to the first plane and coupled to the second inner link, the second inner link coupled to the second outer link to define a second joint, the second outer link coupled to the end effector in alignment with the control point; and  
       the third kinematic chain comprising: a third actuator, a third inner link and a third outer link, the third actuator fixed relative to the first plane and coupled to the third inner link, the third inner link coupled to the third outer link to define a third joint, the third outer link coupled to the end effector in alignment with the control point.  
     
     
       13. The system of  claim 12  in which output torque for each one of the first, second and third actuators is chosen in response to operator manipulation at the control point to define a torque vector for the respective first, second and third kinematic chains that substantially maximizes the force that can be applied at the control point. 
     
     
       14. The system of  claim 12  in which joint angle for each one of the first joint, second joint and third joint are controlled respectively to define the redundant actuator structure which enables motion of the control point within the first plane of motion to not more than two degrees of freedom. 
     
     
       15. A force feedback interface device for providing low inertia, low backlash, low friction force feedback, comprising: 
       
         a reference surface;  
       
       
         an end effector defining a control point for engagement by a user, wherein said control point is translatable in two degrees of freedom with respect to said reference surface;  
       
         a first chain coupled between said reference surface and said end effector, said first chain including a first direct drive flat - coil actuator, a first inner link coupled to said first direct drive flat - coil actuator, and a first outer link coupled between said first inner link and said end effector; and    
       
         a second chain coupled between said reference surface and said end effector, said second chain including a second direct drive actuator, a second inner link coupled to said second direct drive actuator, and a second outer link coupled between said second inner link and said end effector,  
       
       
         wherein said first chain and said second chain provide parallel couplings between said reference surface and said control point, said first chain and said second chain providing not more than said two degrees of freedom to said control point. 
       
     
     
       16. The force feedback interface device as recited in  claim 15  wherein said second direct drive actuator is a flat- coil actuator, and wherein said first direct drive flat - coil actuator includes a first movable flat coil coupled to a first fixed magnet and said second drive flat - coil actuator includes a second movable flat coil coupled to a second fixed magnet.   
     
     
       17. The force feedback interface device as recited in  claim 15  wherein said reference surface is a base plate. 
     
     
       18. The force feedback interface device as recited in  claim 15  wherein said reference surface is a ground surface. 
     
     
       19. The force feedback interface device as recited in  claim 16  wherein said first chain includes a first rotary joint coupling the first inner link and the first outer link and said second chain includes a second rotary joint coupling the second inner link and the second outer link. 
     
     
       20. The force feedback interface device as recited in  claim 19  wherein said two degrees of freedom are in a horizontal plane of motion. 
     
     
       21. The force feedback interface device as recited in  claim 20  wherein said end- effector includes a pen - like elongated member engaged and manipulated by the user.   
     
     
       22. The force feedback interface device as recited in  claim 19  wherein said end- effector includes an open tool interface point that can be engaged by a pen - like elongated member wherein the user can freely apply and remove the pen - like elongated member from the end - effector.   
     
     
       23. The force feedback interface device as recited in  claim 19  wherein said end- effector includes an open tool interface point that can be engaged by the user's finger.   
     
     
       24. The force feedback interface device as recited in  claim 20  further comprising: 
       
         a first sensor for detecting the position of the control point within said horizontal plane of motion; and  
       
       
         a second sensor for detecting the position of the control point within said horizontal plane of motion. 
       
     
     
       25. The force feedback interface device as recited in  claim 24  wherein said first and second sensors are optical encoders. 
     
     
       26. The force feedback interface device as recited in  claim 19  further including a third chain coupled between said reference surface and said end effector, said third chain including a third direct drive actuator, a third inner link, and a third outer link, one end of said third inner link being coupled to said third actuator through a rotary joint, another end of said third inner link being coupled to one end of said third outer link, another end of said third outer link being coupled to the end effector, wherein said first, second, and third chains provide parallel couplings between said reference surface and said control point. 
     
     
       27. The force feedback interface device as recited in  claim 20  further including a rotational actuation assembly coupled to said reference surface for providing an additional degree of motion to the control point by allowing the horizontal plane of motion to be rotated about an axis of rotation. 
     
     
       28. The force feedback interface device as recited in  claim 20  further including a vertical actuation assembly coupled to said reference surface for providing an additional degree of freedom to the control point by allowing the horizontal plane of motion to be translated along a z- axis of motion.   
     
     
       29. The force feedback interface device as recited in  claim 28  further including a fourth actuator for applying a force along said z- axis of motion.