Medical instrument having single input for driving multiple cables
A medical instrument includes a shaft, a wrist, a mechanical structure, a first cable, and a second cable. The wrist is coupled to the distal end portion of the shaft. The mechanical structure is coupled to a proximal end portion of the shaft and includes a capstan assembly. The capstan assembly includes a first cable drum having a first radius and a second cable drum having a second, different radius. The first cable is routed along the shaft. A distal end portion of the first cable is coupled to the wrist and a proximal end portion of the first cable is wrapped about the first cable drum. The second cable is routed along the shaft. A distal end portion of the second cable is coupled to the wrist and a proximal end portion of the second cable is wrapped about the second cable drum.
1 . A medical instrument, comprising:
an instrument shaft comprising a distal end portion and a proximal end portion;
a wrist coupled to the distal end portion of the instrument shaft, the wrist including a first link rotatable relative to the instrument shaft about a first axis and a second link rotatable relative to the instrument shaft about a second axis;
a mechanical structure coupled to the proximal end portion of the instrument shaft, the mechanical structure including a capstan assembly that includes a first cable drum defining a first radius and a second cable drum defining a second radius different than the first radius, the first cable drum and the second cable drum being rotatable about a common capstan axis,
a first cable of a first cable pair, the first cable including a proximal end portion and a distal end portion, the first cable being routed along the instrument shaft, the distal end portion of the first cable being coupled to the first link, and the proximal end portion of the first cable being wrapped about the first cable drum in a first wrap direction; and
a second cable of the first cable pair, the second cable including a proximal end portion and a distal end portion, the second cable being routed along the instrument shaft, the distal end portion of the second cable being coupled to the second link, and the proximal end portion of the second cable being wrapped about the second cable drum in the same first wrap direction as the proximal end portion of the first cable, wherein:
a rotation of the capstan assembly about the common capstan axis moves the distal end portion of the first cable in a first direction and along a first distance that is defined in part by the first radius,
the same rotation of the capstan assembly about the common capstan axis moves the distal end portion of the second cable in the first direction and along a second distance that is defined in part by the second radius,
the movement of the distal end portion of the first cable causes the first link to rotate in a first link direction relative to the instrument shaft,
the movement of the distal end portion of the second cable causes the second link to rotate in the first link direction relative to the instrument shaft, and
a difference between a magnitude of the rotation of the first link and a magnitude of the rotation of the second link in the same direction is defined by a proportion between the first radius and the second radius.
2 . The medical instrument of claim 1 , wherein:
the capstan assembly comprises an input disc;
the input disc is configured to be driven by an actuator to rotate the capstan assembly about the common capstan axis; and
rotation of the capstan assembly about the common capstan axis moves the first cable at a first speed proportional to the first radius and the second cable at a second speed proportional to the second radius.
3 . The medical instrument of claim 2 , wherein:
the first cable drum comprises a first center line; and
the second cable drum comprises a second center line that is nonconcentric to the first center line.
4 . The medical instrument of claim 1 , wherein:
the movement of the distal end portion of the first cable and of the distal end portion of the second cable actuates the wrist.
5 . The medical instrument of claim 1 , further comprising:
a second cable pair including a third cable and a fourth cable, wherein:
the third cable includes a proximal end portion and a distal end portion and is routed along the instrument shaft, the distal end portion of the third cable is coupled to the wrist, and the proximal end portion of the third cable is wrapped about the first cable drum in a second wrap direction opposite the first wrap direction; and
the fourth cable includes a proximal end portion and a distal end portion and is routed along the instrument shaft, the distal end portion of the fourth cable is coupled to the wrist, and the proximal end portion of the fourth cable is wrapped about the second cable drum in the second wrap direction as the proximal end portion of the third cable.
6 . The medical instrument of claim 5 , wherein:
the capstan assembly comprises an input disc;
the input disc is configured to be driven by an actuator to rotate the capstan assembly about the common capstan axis;
rotation of the capstan assembly about the common capstan axis moves the first cable and the third cable at a first speed proportional to the first radius; and
rotation of the capstan assembly about the common capstan axis moves the second cable and the fourth cable at a second speed proportional to the second radius.
7 . The medical instrument of claim 5 , wherein:
the capstan assembly comprises an input disc;
the input disc is configured to be driven by an actuator to rotate the capstan assembly about the common capstan axis;
rotation of the capstan assembly about the common capstan axis moves the first cable pair in a first direction along the instrument shaft to actuate the wrist; and
rotation of the capstan assembly about the common capstan axis moves the second cable pair a second direction along the instrument shaft to actuate the wrist, the second direction opposite the first direction.
8 . The medical instrument of claim 1 , wherein:
the capstan assembly comprises a capstan shaft, a first clamp, a second clamp, and an input disc;
the input disc is coupled to the capstan shaft such that rotation of the input disc causes rotation of the capstan shaft;
the first cable drum includes a first wrap member and a second wrap member;
the first wrap member is coupled to the capstan shaft by the first clamp;
the second wrap member is coupled to the capstan shaft by the second clamp;
the proximal end portion of the first cable is wrapped about the first wrap member in the first wrap direction; and
the proximal end portion of a third cable is wrapped about the second wrap member in a second wrap direction opposite the first direction.
9 . The medical instrument of claim 1 , wherein:
the first link is positioned between the instrument shaft and the second link.
10 . The medical instrument of claim 9 , wherein:
the wrist comprises one or more intermediate links;
the first link is coupled to the second link by the one or more intermediate links; and
the first axis is parallel to the second axis.
11 . A medical instrument, comprising:
a distal first movable component, a distal second movable component, a proximal rotatable capstan, a first drive member coupled to the capstan, and a second drive member coupled to the capstan, and a tension member pair including a first tension member and a second tension member, wherein:
the first drive member includes a first wrap region, and the second drive member includes a second wrap region,
the first tension member extends from the first movable component to wrap at least partially around the first drive member in a first wrap direction at the first wrap region,
the second tension member extends from the second movable component to wrap at least partially around the second drive member in the first wrap direction at the second wrap region,
the first drive member and the second drive member are rotatable about a common capstan axis,
the first drive member has a first radius of rotation at a location where the first tension member wraps on and off the first wrap region,
the second drive member has a second radius of rotation at a location where the second tension member wraps on and off the second wrap region,
the second radius of rotation is different from the first radius of rotation,
a rotation of the proximal rotatable capstan about the common capstan axis moves a distal end portion of the first tension member in a first direction and along a first distance that is defined in part by the first radius,
the same rotation of the proximal rotatable capstan about the common capstan axis moves a distal end portion of the second tension member in the first direction and along a second distance that is defined in part by the second radius,
the movement of the distal end portion of the first tension member causes the first distal movable component to rotate in a first distal component direction,
the movement of the distal end portion of the second tension member causes the second distal movable component to rotate in the first distal component direction, and
a difference between a magnitude of the rotation of the first distal movable component and a magnitude of the rotation of the second distal movable component in the same direction is defined by a proportion between the first radius and the second radius.
12 . The medical instrument of claim 11 , wherein:
the first radius of rotation is constant as the first drive member rotates with the capstan; and
the second radius of rotation is non-constant as the second drive member rotates with the capstan.
13 . The medical instrument of claim 11 , wherein:
the second radius of rotation is between 1.5 and 2.5 times as large as the first radius of rotation.
14 . The medical instrument of claim 11 , further comprising:
a rotatable drive disc coupled to the capstan; and
wherein the drive disc is configured to receive a motor drive input to rotate the capstan.
15 . The medical instrument of claim 11 , wherein:
a longitudinal orientation is defined for the medical instrument, and a longitudinal orientation is defined for the second movable component;
the second movable component is distal of the first movable component; and
rotation of the capstan moves the second movable component from a first state in which the longitudinal orientation of the second movable component is aligned with the longitudinal orientation of the medical instrument to a second state in which the longitudinal orientation of the second movable component is retroflexed with reference to the longitudinal orientation of the medical instrument.
16 . The medical instrument of claim 11 , further comprising:
a distal wrist and a distal end effector coupled to the wrist;
the wrist comprises the distal first movable component and the distal second movable component;
a longitudinal orientation is defined for the medical instrument, and a longitudinal orientation is defined for the end effector; and
rotation of the capstan moves the end effector from a first state in which the longitudinal orientation of the end effector is aligned with the longitudinal orientation of the medical instrument to a second state in which the longitudinal orientation of the end effector is retroflexed with reference to the longitudinal orientation of the medical instrument.
17 . The medical instrument of claim 1 , wherein:
the first cable of the first cable pair has a first cable path;
the second cable of the first cable pair has a second cable path;
a length of the second cable path is greater than a length of the first cable path; and
on a condition in which the wrist is moved from a first configuration to a second configuration having a larger bend than the first configuration, the second link bends to a greater degree than the first link in the same direction.
18 . The medical instrument of claim 1 , wherein:
the first radius of the capstan assembly is less than the second radius of the capstan assembly; and
the magnitude of the rotation of the first link is less than the magnitude of the rotation of the second link.