Articulatable members having constrained motion and related devices and methods
An articulatable member includes a distal end, a proximal end, an actuation member, and a constraint member. The actuation member extends from the proximal end to the distal end. The actuation member transmits force to bend the articulatable member from a neutral position. The constraint member extends from the proximal end to the distal end. The constraint member may have opposite ends that are fixed to the distal end and the proximal end. In one embodiment, the constraint member follows a helical path along at least a portion of the articulatable member from the proximal end to the distal end. In another embodiment, the actuation member follows a helical path along at least a portion of the articulatable member.
1 . An articulatable member, comprising:
a plurality of links extending in a series from a proximal end link to a distal end link, adjacent links of the plurality of links being pivotably coupled to form joints between the adjacent links;
a first cable extending between the proximal end link and the distal end link; and
a second cable extending between and fixed to the proximal end link and the distal end link;
wherein each link of the plurality of links comprises an annular shape defining a central aperture and an outer perimeter;
wherein the first cable extends through a first aperture in each link of the plurality of links, the first aperture located between the central aperture and the outer perimeter and radially inward a first distance from the outer perimeter of each link of the plurality of links;
wherein the second cable extends through a second aperture in each link of the plurality of links, the second aperture located between the central aperture and the outer perimeter and radially inward a second distance greater than the first distance from the outer perimeter of each link of the plurality of links; and
wherein the second cable follows a helical path along at least a portion of the articulatable member from the proximal end link to the distal end link as the second cable extends through the second aperture in each of the links.
2 . The articulatable member of claim 1 , wherein the first cable comprises an actuation cable configured to articulate the articulatable member in response to a tensile force applied to the actuation cable.
3 . The articulatable member of claim 2 , wherein the actuation cable follows a straight path along the articulatable member.
4 . The articulatable member claim 1 , wherein the second cable comprises a constraint member configured to passively constrain articulation of the articulatable member.
5 . The articulatable member of claim 1 , wherein:
the articulatable member comprises a third cable extending between and fixed to the distal end link and the proximal end link;
the third cable extends through a third aperture in each link of the plurality of links; and
the third aperture is positioned radially inward the second distance from the outer perimeter of each link of the plurality of links and spaced 180 degrees from the second aperture around a circumference of each link of the plurality of links.
6 . The articulatable member of claim 1 , wherein the first aperture and the second aperture are spaced 90 degrees from one another around a circumference of each link of the plurality of links.
7 . The articulatable member of claim 1 , wherein the helical path extends at least 180 degrees around a circumference of the articulatable member from the proximal end link and the distal end link.
8 . The articulatable member of claim 1 , wherein the helical path extends at least 360 degrees around a circumference of the articulatable member from the proximal end link and the distal end link.
9 . An articulatable member, comprising:
a plurality of links extending in a series from a proximal end link to a distal end link, adjacent links of the plurality of links being pivotably coupled to form joints between the adjacent links, and each link of the plurality of links having a central longitudinal axis and an outer lateral surface;
a first constraint member extending between and fixed to the proximal end link and the distal end link, the first constraint member following a first, right-handed helical path spiraling along at least a portion of the articulatable member; and
a second constraint member extending between and fixed to the proximal end link and the distal end link, the second constraint member following a second, left-handed helical path spiraling along at least the portion of the articulatable member,
wherein the first and second constraint members pass through respective enclosed apertures in each of the plurality of links at locations between the central longitudinal axis and the outer lateral surface.
10 . The articulatable member claim 9 , wherein the plurality of links comprises:
a first link, a second link adjacent the first link, a third link adjacent the second link, a fourth link adjacent the third link, and a fifth link adjacent the fourth link;
a first joint between the first link and the second link, the first joint permitting relative rotation of the first and second links about a first axis;
a second joint between the second link and the third link, the second joint permitting relative rotation of the second and third links about a second axis orthogonal to the first axis;
a third joint between the third link and the fourth link, the third joint permitting relative rotation of the third and fourth links about the first axis; and
a fourth joint between the fourth link and the fifth link, the fourth joint permitting relative rotation of the fourth and fifth links about the second axis.
11 . The articulatable member claim 9 , wherein the plurality of links comprises:
a first link, a second link adjacent the first link, a third link adjacent the second link, a fourth link adjacent the third link, and a fifth link adjacent the fourth link;
a first joint between the first link and the second link, the first joint permitting relative rotation of the first and second links about a first axis;
a second joint between the second link and the third link, the second joint permitting relative rotation of the second and third links about a second axis orthogonal to the first axis;
a third joint between the third link and the fourth link, the third joint permitting relative rotation of the third and fourth links about the second axis; and
a fourth joint between the fourth link and the fifth link, the fourth joint permitting relative rotation of the fourth and fifth links about the first axis.
12 . The articulatable member of claim 9 , wherein:
the first constraint member is laterally spaced from the central longitudinal axis of the articulatable member a first distance;
the second constraint member is laterally spaced from the central longitudinal axis a second distance; and
the second distance is greater than the first distance.
13 . The articulatable member of claim 9 , wherein the first constraint member extends through a first enclosed aperture of the respective enclosed apertures, in a link of the plurality of links, the first enclosed aperture being radially offset from the central longitudinal axis of the link and positioned radially inward from the outer lateral surface of the link by a first distance.
14 . The articulatable member of claim 13 , wherein the second constraint member extends through a second enclosed aperture of the respective enclosed apertures, in the link of the plurality of links, the second enclosed aperture being radially offset from the central longitudinal axis of the link and positioned radially inward from the outer lateral surface of the link by a second distance, wherein the second distance is greater than the first distance.
15 . The articulatable member of claim 9 , wherein the first helical path and the second helical path extend an equal amount around the articulatable member.
16 . The articulatable member of claim 9 , wherein the first helical path and the second helical path each extend at least 180 degrees around the articulatable member from the proximal end link to the distal end link.
17 . The articulatable member of claim 9 , wherein the first helical path and the second helical path each extend at least 360 degrees around the articulatable member from the proximal end link to the distal end link.
18 . The articulatable member of claim 5 , wherein the third cable follows a helical path along at least a portion of the articulatable member from the proximal end link to the distal end link as it extends through the third aperture in each of the links.
19 . The articulatable member of claim 18 , wherein the helical paths of the second cable and the third cable spiral in opposite directions from each other.
20 . The articulatable member of claim 1 , wherein in each link of the plurality of links comprises:
a first plurality of apertures, including the first aperture, spaced apart around the link and located radially inward the first distance from the outer perimeter; and
a second plurality of apertures, including the second aperture, spaced apart around the link and located radially inward the second distance from the outer perimeter.