Pulley arrangement and pulley guard for articulating a surgical instrument

1. A surgical robotic instrument comprising:

a shaft;

an end effector element;

an articulation connecting the end effector element to the shaft, the articulation comprising:

a first joint driveable by a first pair of driving elements, the first joint permitting the end effector element to rotate about a first axis transverse to a longitudinal axis of the shaft;

a second joint driveable by a second pair of driving elements;

a pulley arrangement around which the second pair of driving elements is constrained to move, the pulley arrangement comprising:

a first set of pulleys rotatable about the first axis; and

a second set of pulleys proximal to the first set of pulleys and comprising a first pulley rotatable about a second axis, and a second pulley rotatable about a third axis parallel to and offset from the second axis; and

a clevis unit comprising two arms supporting the first set of pulleys and the second set of pulleys of the pulley arrangement, and a pulley guard extending from one of the arms configured to guard one of the first and second pulleys.

2. A surgical robotic instrument as claimed in claim 1 , wherein the second joint is distal to the first joint.

3. A surgical robotic instrument as claimed in claim 1 , wherein the second and third axes are offset from the first axis.

4. A surgical robotic instrument as claimed in claim 3 , wherein the second and third axes are offset from the first axis in a direction transverse to the longitudinal axis of the shaft.

5. A surgical robotic instrument as claimed in claim 3 , wherein the second and third axes lie in a plane perpendicular to the longitudinal axis of the shaft.

6. A surgical robotic instrument as claimed in claim 1 , wherein the first axis intersects the longitudinal axis of the shaft.

7. A surgical robotic instrument as claimed in claim 1 , wherein the second and third axes are parallel to the first axis.

8. A surgical robotic instrument as claimed in claim 1 , wherein a first of the two arms supports the first pulley, and a second of the two arms supports the second pulley.

9. A surgical robotic instrument as claimed in claim 1 , wherein the first and second arms are on opposing sides of a plane that contains the longitudinal axis of the shaft and is transverse to the first axis.

10. A surgical robotic instrument as claimed in claim 1 , wherein the clevis unit comprises a first pulley guard extending from the first arm configured to guard the first pulley, and a second pulley guard extending from the second arm configured to guard the second pulley.

11. A surgical robotic instrument as claimed in claim 10 , wherein the first and second pulley guards are located on opposing sides of a first plane that contains the longitudinal axis of the shaft, and is transverse to the first axis, and on opposing sides of a second plane that contains both the longitudinal axis of the shaft and the first axis.

12. A surgical robotic instrument as claimed in claim 10 , wherein the clevis unit further comprises first and second drive element guides, one driving element of the first pair of driving elements passing through the first drive element guide, and the other driving element of the first pair of driving elements passing through the second element guide, each of the first and second drive element being located between the first and second arms of the clevis unit.

13. A surgical robotic instrument as claimed in claim 10 , wherein the first pulley guard comprises an interior sidewall that part-encompasses the first pulley, and the second pulley guard comprises an interior sidewall that part-encompasses the second pulley.

14. A surgical robotic instrument as claimed in claim 1 , wherein the pulley guard is located within an interior space of the clevis unit bound by the profile of the shaft.

15. A surgical robotic instrument as claimed in claim 1 , wherein the clevis unit further comprises first and second drive element guides, one driving element of the first pair of driving elements passing through the first drive element guide, and the other driving element of the first pair of driving elements passing through the second drive element guide, each of the first and second drive element guides being located between the first and second arms of the clevis unit.

16. A surgical robotic instrument as claimed in claim 15 , wherein the pulley guard extends between said one of the arms and one of the drive element guides.

17. A surgical robotic instrument as claimed in claim 15 , wherein the clevis unit comprises a first pulley guard extending from the first arm configured to guard the first pulley, and a second pulley guard extending from the second arm configured to guard the second pulley, wherein the first pulley guard extends between the first arm and first drive element guide, and the second pulley guard extends between the second arm and second drive element guide.

18. A surgical robotic instrument as claimed in claim 15 , wherein the first and second driving element guides are located on opposing sides of a plane containing the longitudinal axis of the shaft and the first axis.