Fixture for shape-sensing optical fiber in a kinematic chain
View Patent ↗Localized strain is effectively eliminated in a shape sensing optical fiber where the fiber exits a link in a kinematic chain. In one aspect, the fiber is positioned in a channel within a fiber fixture portion of the link, and a surface of a lip of the channel is curved. The curved surface of the lip begins tangent to a wall of the channel and has a maximum radius of curvature that is less than the minimum bend radius that the fiber will experience during shape sensing. In another aspect the fiber is positioned within a shape memory alloy tube that extends from the link.
1. An apparatus comprising:
a first link, a second link, and a joint that couples the first and second links;
an optical fiber extending between the first link and the second link, wherein a limit range of motion of the joint defines a minimum bend radius of the optical fiber; and
a fixture by which the optical fiber is constrained with reference to the first link, wherein the fixture comprises a channel defined therein in which the fiber is positioned to place a length of fiber containing fiber Bragg gratings adjacent a lip of the channel where the channel opens out of the fixture, wherein a curve of a surface of the lip begins effectively tangent to a wall of the channel, and wherein the radius of curvature of the surface of the lip that substantially intersects a bending plane of the fiber as the joint moves is effectively less than the defined minimum bend radius of the optical fiber.
2. The apparatus of claim 1 further comprising:
a strain interrogator;
wherein the strain interrogator receives strain information from the fiber Bragg gratings.
3. The apparatus of claim 1 :
wherein the optical fiber extends out of the first link at the longitudinal centerline of the first link.
4. The apparatus of claim 1 :
wherein the optical fiber extends out of the first link offset from the longitudinal centerline of the first link.
5. The apparatus of claim 1 :
wherein the fixture comprises a first piece and a second piece positioned within the first piece; and
wherein the channel defined in the fixture is defined in the second piece.
6. The apparatus of claim 1 further comprising:
a flexible tube surrounding the optical fiber.
7. The apparatus of claim 1 :
wherein the channel comprises a slit having a width that is approximately equal to the diameter of the fiber.
8. The apparatus of claim 1 :
wherein the channel comprises a cylinder that permits the fiber to slide longitudinally with reference to the first link.
9. The apparatus of claim 1 :
wherein the channel comprises a cylinder that permits the fiber to roll or twist with reference to the first link.
10. The apparatus of claim 1 :
wherein the fixture comprises a collet having the channel and the lip defined therein.
11. The apparatus of claim 1 :
wherein the first and second links are links in a surgical instrument.
12. A method comprising:
assembling a first link, a second link, and a joint that couples the first and second links;
extending an optical fiber between the first link and the second link, wherein a limit range of motion of the joint defines a minimum bend radius of the optical fiber; and
constraining the optical fiber with reference to the first link, wherein the optical fiber is positioned in a constraining channel to place a length of fiber containing fiber Bragg gratings adjacent a lip of the channel, wherein a curve of a surface of the lip begins effectively tangent to a wall of the channel, and wherein the radius of the curve of surface of the lip that substantially intersects a bending plane of the fiber as the joint moves is effectively less than the defined minimum bend radius of the optical fiber.
13. The method of claim 12 further comprising:
interrogating the fiber Bragg gratings for strain information.
14. The method of claim 12 :
wherein the optical fiber extends out of the first link at the longitudinal centerline of the first link.
15. The method of claim 12 :
wherein the optical fiber extends out of the first link offset from the longitudinal centerline of the first link.
16. The method of claim 12 :
wherein constraining the optical fiber comprises positioning a second piece within a first piece and positioning the fiber within the second piece; and
wherein the channel is defined in the second piece.
17. The method of claim 12 further comprising:
wherein the channel comprises a slit having a width that is approximately equal to the diameter of the fiber.
18. The method of claim 12 :
wherein constraining the optical fiber comprises permitting the fiber to slide longitudinally with reference to the first link.
19. The method of claim 12 :
wherein constraining the optical fiber comprises permitting the fiber to roll or twist with reference to the first link.
20. The method of claim 12 further comprising:
configuring a collet with the constraining channel and the lip.
21. The method of claim 12 further comprising:
positioning a flexible tube around a length of the optical fiber.
22. The method of claim 12 :
wherein the first and second links are links in a surgical instrument.
23. The method of claim 12 :
wherein constraining the optical fiber comprises allowing the optical fiber to slide longitudinally with reference to the first link.
24. The apparatus of claim 6 :
wherein the flexible tube surrounding the optical fiber comprises a shape memory alloy.
25. The apparatus of claim 24 :
wherein the shape memory alloy comprises a Nickel/Titanium alloy.
26. The method of claim 21 :
wherein positioning a flexible tube around a length of the optical fiber comprises positioning a shape memory alloy tube around a length of the optical fiber.
27. The method of claim 26 :
wherein the shape memory alloy comprises a Nickel/Titanium alloy.