Self-antagonistic drive for medical instruments
A medical instrument including a shaft and an actuated structure mounted at a distal end of the shaft can employ a pair of tendons connected to the actuated structure, extending down the shaft, and respectively wound around a capstan in opposite directions. A preload system may be coupled to maintain minimum tensions in the tendons.
1. A medical instrument comprising:
a shaft;
an actuated structure mounted at a distal end of the shaft in a manner that permits movement of the actuated structure relative to the shaft;
a capstan that is rotatably mounted;
a first tendon having a first portion connected to the actuated structure and extending down the shaft to the capstan, a second portion wound around the capstan in a first direction, and a third portion extending from the capstan;
a second tendon having a first portion connected to the actuated structure and extending down the shaft to the capstan, a second portion wound around the capstan in a second direction that is opposite the first direction, and a third portion extending from the capstan;
and
a passive preload system directly connected to the third portion of the first tendon and the third portion of the second tendon, the passive preload system comprising at least one spring that is coupled to maintain tension in the first tendon and the second tendon.
2. The instrument of claim 1 , wherein the passive preload system comprises:
a first spring coupled to apply force to a proximal end of the first tendon; and
a second spring coupled to apply force to a proximal end of the second tendon.
3. The instrument of claim 2 , wherein:
the first spring comprises a constant force spring that applies a constant force to the proximal end of the first tendon over a range of motion of the proximal end of the first tendon; and
the second spring comprises a constant force spring that applies the constant force to the proximal end of the second tendon.
4. The instrument of claim 1 , wherein the passive preload system comprises a pulley system engaged with the third portion of the first tendon and the third portion of the second tendon.
5. The instrument of claim 4 , wherein the at least one spring applies tension to the first and second tendons by pulling on the pulley system.
6. The instrument of claim 4 , wherein the at least one spring is coupled between the third portion of the first tendon and the pulley system.
7. The instrument of claim 4 , wherein the proximal ends of the first and second tendons are connected together and wrap around a pulley in the pulley system.
8. The instrument of claim 1 , further comprising a motor coupled to rotate the capstan, wherein the motor has an interface that enables computer control of the motor.
9. The instrument of claim 8 , further comprising a mechanism that couples the motor to the capstan, wherein the mechanism allows the motor to be decoupled from the capstan for manual operation of the instrument.
10. The instrument of claim 8 , further comprising a knob coupled for manual rotation of the capstan.
11. The instrument of claim 1 , further comprising a second preload system that engages the first tendon at a location between the capstan and the actuated structure.
12. The instrument of claim 1 , wherein the passive preload system applies the tension without need to respond to a control or feedback system.
13. The instrument of claim 1 , wherein the at least one spring comprises a first spring directly connected to the third portion of the first tendon.