Asymmetric gear drive for robotic surgical tools

1. A robotic surgical tool, comprising:

an elongate shaft extended through a handle and having an end effector arranged at a distal end thereof;

a rack extending along a portion of the shaft and operatively coupled to a knife located at the end effector;

a first actuation system housed within the handle and operable to drive the rack and thereby advance or retract the knife at the end effector, the first actuation system including a sector gear engageable with the rack and including a tooth-free zone; and

a second actuation system housed within the handle and operable to cause z-axis translation of the shaft through the handle,

wherein rotating the sector gear such that the tooth-free zone faces the rack decouples the shaft from the first actuation system to allow the shaft to freely move in z-axis translation.

2. The robotic surgical tool of claim 1 , wherein the shaft comprises an outer shaft portion and the rack is at least partially received within a longitudinal channel defined in the outer shaft portion.

3. The robotic surgical tool of claim 1 , wherein the sector gear provides gear teeth outside of the tooth-free zone and the gear teeth are engageable with the rack to drive the rack and thereby advance or retract the knife at the end effector.

4. The robotic surgical tool of claim 1 , wherein the first actuation system includes:

a drive shaft extending from a drive input included in the handle; and

a drive mechanism extending between the drive shaft and the rack and configured to drive the rack, wherein the sector gear forms part of the drive mechanism.

5. The robotic surgical tool of claim 4 , wherein the drive mechanism includes:

a beveled drive gear coupled to the drive shaft; and

a beveled driven gear arranged to be driven by the beveled drive gear, wherein the sector gear is coupled to the beveled driven gear such that rotating the beveled driven gear rotates the sector gear.

6. The robotic surgical tool of claim 1 , wherein the second actuation system includes:

a spool operatively coupled to a drive input included in the handle such that actuation of the drive input rotates the spool;

a first drive cable having a first end anchored to the shaft distal to the handle and a second end secured to the spool; and

a second drive cable having a first end anchored to the shaft proximal to the handle and a second end secured to the spool,

wherein rotating the spool in a first angular direction pays out the first drive cable from the spool to the shaft, while simultaneously paying in the second drive cable from the shaft to the spool and thereby causing the shaft to move distally relative to the handle, and

wherein rotating the spool in a second angular direction opposite the first angular direction pays out the second drive cable from the spool to the shaft, while simultaneously paying in the first drive cable from the shaft to the spool and thereby causing the shaft to move proximally relative to the handle.

7. The robotic surgical tool of claim 6 , further comprising:

a first idler pulley arranged to redirect the first drive cable between the shaft and the spool; and

a second idler pulley arranged to redirect the second drive cable between the shaft and the spool.

8. A method of operating a robotic surgical tool, comprising:

arranging a robotic surgical tool adjacent a patient, the robotic surgical tool including:

an elongate shaft extending through a handle and having an end effector arranged at a distal end thereof;

a rack extending along a portion of the shaft and operatively coupled to a knife located at the end effector;

a first actuation system housed within the handle and including a sector gear engageable with the rack and including a tooth-free zone; and

a second actuation system housed within the handle;

rotating the sector gear with the first actuation system until the tooth-free zone faces the rack and the sector gear thereby disengages the rack; and

operating the second actuation system to cause z-axis translation of the shaft through the handle.

9. The method of claim 8 , the method further comprising:

ceasing operation of the second actuation system to stop z-axis translation of the shaft;

rotating the sector gear with the first actuation system and thereby engaging gear teeth of the sector gear on the rack to drive the rack; and

moving the knife at the end effector by driving the rack with the sector gear.

10. The method of claim 9 , further comprising moving the rack within a longitudinal channel defined in an outer shaft portion of the shaft.

11. The method of claim 8 , wherein the first actuation system includes a drive shaft extending from a drive input included in the handle, and a drive mechanism extending between the drive shaft and the rack, the method further comprising:

actuating the drive input and thereby operating the first actuation system to rotate the drive shaft; and

driving the drive mechanism by rotating the drive shaft, wherein the sector gear forms part of the drive mechanism.

12. The method of claim 11 , wherein the drive mechanism includes:

a beveled drive gear coupled to the drive shaft; and

a beveled driven gear arranged to be driven by the beveled drive gear, wherein the sector gear is coupled to the beveled driven gear such that rotating the beveled driven gear rotates the sector gear.

13. The method of claim 8 , wherein operating the second actuation system includes:

actuating a drive input included in the handle and thereby rotating a spool operatively coupled to the drive input in a first angular direction;

paying out a first drive cable from the spool to the shaft, the first drive cable having a first end anchored to the shaft distal to the handle and a second end secured to the spool;

paying in a second drive cable from the shaft to the spool, the second drive cable having a first end anchored to the shaft proximal to the handle and a second end secured to the spool; and

moving the shaft distally relative to the handle.

14. The method of claim 13 , wherein operating the second actuation system further includes:

actuating the drive input and thereby rotating the spool in a second angular direction opposite the first angular direction;

paying out the second drive cable from the spool to the shaft;

paying in the first drive cable from the shaft to the spool; and

moving the shaft proximally relative to the handle.

15. The method of claim 13 , further comprising:

redirecting the first drive cable between the shaft and the spool with a first idler pulley coupled to the handle; and

redirecting the second drive cable between the shaft and the spool with a second idler pulley coupled to the handle.

16. A robotic surgical tool, comprising:

an elongate shaft extendable through a handle and having an end effector arranged at a distal end thereof;

a rack extending along a portion of the shaft and operatively coupled to a knife located at the end effector;

a first actuation system housed within the handle and including a drive mechanism engageable with the rack to drive the rack and thereby advance or retract the knife at the end effector; and

a second actuation system housed within the handle and operable to cause z-axis translation of the shaft through the handle, the second actuation system including:

a spool operatively coupled to a drive input coupled to the handle such that actuation of the drive input rotates the spool;

a first drive cable having a first end anchored to the shaft distal to the handle and a second end secured to the spool; and

a second drive cable having a first end anchored to the shaft proximal to the handle and a second end secured to the spool,

wherein the first actuation system is operable to decouple the drive mechanism from the rack and thereby allow the shaft and the rack to freely move in z-axis translation.

17. The robotic surgical tool of claim 16 , wherein the drive mechanism includes a sector gear engageable with the rack and including a tooth-free zone, and wherein rotating the sector gear such that the tooth-free zone faces the rack decouples the drive mechanism from the shaft and allows the shaft and the rack to move in z-axis translation.

18. The robotic surgical tool of claim 17 , wherein the sector gear provides gear teeth outside of the tooth-free zone and the gear teeth are engageable with the rack to drive the rack relative to the shaft and thereby advance or retract the knife at the end effector.

19. The robotic surgical tool of claim 17 , wherein the first actuation system includes a drive shaft extending from a drive input coupled to the handle, and wherein the drive mechanism includes:

a beveled drive gear coupled to the drive shaft; and

a beveled driven gear arranged to be driven by the beveled drive gear, wherein the sector gear is coupled to the beveled driven gear such that rotating the beveled driven gear rotates the sector gear.

20. The robotic surgical tool of claim 16 , wherein rotating the spool in a first angular direction pays out the first drive cable from the spool to the shaft, while simultaneously paying in the second drive cable from the shaft to the spool and thereby causing the shaft to move distally relative to the handle, and

wherein rotating the spool in a second angular direction opposite the first angular direction pays out the second drive cable from the spool to the shaft, while simultaneously paying in the first drive cable from the shaft to the spool and thereby causing the shaft to move proximally relative to the handle.