Passive preload and capstan drive for surgical instruments

• US 20100082041A1
• Filed: 09/30/2008
• Published: 04/01/2010
• Est. Priority Date: 09/30/2008
• Status: Active Grant

• Current Assignee: Intuitive Surgical Operations, Inc. (Intuitive Surgical Holdings, LLC)
• Original Assignee: Intuitive Surgical Incorporated (Intuitive Surgical Holdings, LLC)
• Inventors: Prisco, Giuseppe M.
• Granted Patent: US 9,259,274 B2
• Time in Patent Office: Days
• US Class Current: 606/130
• CPC Class Codes: A61B 2017/00477 Coupling A61B2017/0046 takes precedence
• CPC Class Codes: A61B 2034/2061 using shape-sensors, e.g. fiber shape sensors with Bragg gratings
• CPC Class Codes: A61B 2034/302 specifically adapted for manipulations within body cavities, e.g. within abdominal or thoracic cavities
• CPC Class Codes: A61B 2034/305 Details of wrist mechanisms at distal ends of robotic arms
• CPC Class Codes: A61B 2034/715 Cable tensioning mechanisms for removing slack
• CPC Class Codes: A61B 34/30 Surgical robots
• CPC Class Codes: A61B 34/37 Master-slave robots A61B34/35 takes precedence
• CPC Class Codes: A61B 34/71 Manipulators operated by drive cable mechanisms
• CPC Class Codes: B25J 9/1045 comprising tensioning means

Abstract

A robotic surgical system uses a passive preload system attached to a tendon that is wrapped around a capstan to control relaxed tension in the tendon. The passive preload system can employ a spring or other structure to apply tension to the tendon. The capstan can be driven by a motor when the tendon is needed to pull on a structural member of the instrument. For example, for the application of clamping pressure or movement of the structural member against resistance, capstan friction can produce the tendon tension that is many times the tension applied by the passive preload system. However, when the tendon is not needed to apply force to the member, the capstan can be freed, so that the spring system provides enough tension to prevent derailment or other malfunctions of the tendon. The low tension in relaxed tendons can reduce tendon friction, particularly in instruments with flexible shafts.

Claims

1. A surgical instrument comprising:

a shaft;

a member mounted at a distal end of the shaft, the member being mounted to permit movement of the member relative to the shaft;

a mechanism attached to a proximal end of the shaft, the mechanism including a first capstan and a first passive preload system, wherein the first capstan is free to roll and has a coupling through which a motor can attach to and rotate the first capstan; and

a first tendon running down the shaft and wrapping around the first capstan, the first tendon having a first end attached to the member and a second end attached to the first passive preload system.

2. The instrument of claim 1, wherein the first passive preload system comprises a spring element that works through compression or extension to apply force to the tendon.

3. The instrument of claim 2, wherein the spring element is selected from a group consisting of a linear spring, a coil spring, and a leaf spring.

4. The instrument of claim 1, wherein the first passive preload system comprises a constant-force spring.

5. The instrument of claim 1, wherein the first passive preload system comprises a variable radius pulley and a spring element.

6. The instrument of claim 1, wherein the first passive preload system comprises a compliant member that works through compression or extension to apply force to the tendon.

7. The instrument of claim 6, wherein the compliant member is selected from a group consisting of a cantilever beam and elastic bands.

8. The instrument of claim 1, further comprising:

a first jointed member that is mechanically constrained to one degree of freedom of motion with respect to a previous member;

a second passive preload system in the mechanism;

a second capstan in the mechanism, wherein the second capstan is free to roll and has a coupling through which a second motor can attach to and rotate the second capstan; and

a second tendon running down the shaft and wrapping around the second capstan, the second tendon having a first end attached to the member and a second end attached to the second passive preload system;

wherein the first and second tendons act on the member to produce motion in opposing directions.

9. The instrument of claim 1, wherein the member is mechanically constrained to two degree of freedom of motion with respect to a previous member;

and wherein the instrument further comprises;

a second capstan;

a second passive preload system;

a second tendon running down the shaft and wrapping around the second capstan, the second tendon having a first end attached to the member and a second end attached to the second passive preload system;

a third capstan;

a third passive preload system; and

a third tendon running down the shaft and wrapping around the third capstan, the third tendon having a first end attached to the member and a second end attached to the third passive preload system, wherein

the first and second tendons act on the member to produce bidirectional motion in a first degree of freedom of the member and the first and third tendons act on the member to produce bidirectional motion in a second degree of freedom of the member.

10. The instrument of claim 1, wherein the shaft is flexible.

11. The instrument of claim 1, further comprising a sheath attached to the mechanism and extending through the shaft, wherein the first tendon traverses the shaft inside the sheath.

12. The instrument of claim 1, wherein a rotation axis of the first capstan is perpendicular to the shaft.

13. The instrument of claim 1, wherein a rotation axis of the first capstan is parallel to the shaft.

14. The instrument of claim 1, wherein the coupling of the first capstan comprises a detachable connection mechanism including a spring loaded projection that is shaped to fit into a slot in a motor pinion.

15. The instrument of claim 1, wherein the coupling of the first capstan comprises a bore sized to provide a frictional connection to a motor pinion inserted in the bore, wherein the first capstan is sufficiently flexible that tightening of the first tendon around the capstan increases the friction between the capstan and the pinion.

16. A robotic surgical system comprising:

a docking port containing a first drive motor; and

a first instrument including;

a shaft;

a member mounted at a distal end of the shaft, the member being mounted to permit movement of the member relative to the shaft;

a mechanism attached to a proximal end of the shaft, the mechanism including a first capstan and a first passive preload system, wherein the first capstan has a coupling through which the first drive motor attaches to and is able to rotate the first capstan; and

a first tendon running down the shaft and wrapping around the first capstan, the first tendon having a first end attached to the member and a second end attached to the first passive preload system.

17. The system of claim 16, wherein:

the docking port further comprises a second drive motor; and

the first instrument further comprises

a joint that permits a first degree of freedom of motion of the member;

a second passive preload system in the mechanism;

a second capstan in the mechanism, wherein the second capstan has a coupling through which the second drive motor attaches to and is able to rotate the second capstan; and

a second tendon running down the shaft and wrapping around the second capstan, the second tendon having a first end attached to the member and a second end attached to the second passive preload system;

wherein the first and second tendons act to move the member in opposite directions in the first degree of freedom of motion of the member.

18. The system of claim 17, further comprising a computer system that executes a program implementing a process for operating the first instrument, wherein the process includes operating the first drive motor to apply torque to the first capstan to pull in the first tendon while at the same time permitting the second capstan to rotate freely.

19. The system of claim 18, wherein the first instrument further comprises a sensor that measures a position of the member, the computer system using information from the sensor as feedback for control of the first and second drive motors when moving the member.

20. The system of claim 19, wherein the computer systems uses the information from the sensor to choose the torque that the first drive motor applies to the first capstan.

21. A method for operating a medical instrument containing a jointed member, a first tendon attached to move the jointed member in one direction along a degree of freedom of motion of the jointed member, and a second tendon attached to move the jointed member in an opposite direction along the degree of freedom of motion of the jointed member, the method comprising:

applying a first torque to a first capstan about which the first tendon is wrapped; and

at the same time, freeing a second capstan about which the second tendon is wrapped so that a passive preload system attached to an end of the second tendon extending from the second capstan control tension in the second tendon.

22. The process of claim 21, further comprising:

applying a second torque to the second capstan; and

at the same time as applying the second torque, freeing the first capstan so that a passive preload system attached to an end of the first tendon extending from the first capstan controls tension of the first tendon.

23. The process of claim 21, wherein applying the first torque to the first capstan comprises operating a motor that is mechanically coupled to rotate the first capstan.

24. The process of claim 21, further comprising:

sensing a position of the jointed member; and

choosing the first torque according a difference between a sensed position of the jointed member and a desired position of the jointed member.