Operating self-antagonistic drives of 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 passive preload system may maintain minimum tensions in the tendons.
1. A method for operating an instrument including an actuated structure mounted at a distal end of a shaft, the method comprising:
rotating a capstan that is coupled to the actuated structure through a first tendon and a second tendon, the 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, the 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
during the rotating of the capstan, passively controlling a first tension in the third portion of the first tendon and a second tension in the third portion of the second tendon.
2. The method of claim 1 , wherein the passively controlling the first tension and the second tension comprises:
applying a force to the third portion of the first tendon; and
applying the force to the third portion of the second tendon.
3. The method of claim 2 , wherein the third portions of the first and second tendons are connected together and engaged with a pulley system.
4. The method of claim 3 , wherein the applying of the force to the third portion of the first tendon comprises employing a biased spring system to attached to a pulley.
5. The method of claim 3 , wherein a spring system connects the third portions of the first and second tendons together, the spring system being biased to apply the force to the third portions of the first and second tendons together.
6. The method of claim 1 , wherein:
the passively controlling of the first tension comprises keeping the first tension constant throughout a range of motion of the actuated structure; and
the passively controlling of the second tension comprises keeping the second tension constant throughout the range of motion of the actuated structure.
7. The method of claim 1 , wherein the passively controlling of the first tension comprises:
applying a force to a proximal end of the first tendon; and
keeping the force constant throughout a range of motion of the proximal end of the first tendon.
8. The method of claim 7 , wherein applying the force comprises connecting a constant force spring to the proximal end of the first tendon, action of the constant force spring keeping the force constant over the range of motion of the proximal end of the first tendon.
9. The method of claim 1 , wherein the rotating of the capstan comprises:
rotating the capstan manually at a first time; and
rotating the capstan using a drive motor at a second time.
10. The method of claim 9 , wherein:
the instrument is a medical instrument;
rotating the capstan manually is performed during insertion of the instrument for a medical procedure; and
rotating the capstan using the drive motor follows manual rotation of the capstan.
11. The method of claim 10 , wherein rotating the capstan using the drive motor is during robotic operation of the instrument.
12. The method of claim 1 , wherein the passively controlling of the first tension and the second tension comprises connecting a biased spring system to a slide mounting of the capstan, the slide mounting permitting the rotating of the capstan and permitting the biased spring system to linearly move the capstan.
13. The method of claim 1 , wherein the passively controlling of the first tension and the second tension comprises, without need to respond to a control or feedback system, applying the first tension to the third portion of the first tendon and applying the second tension to the third portion of the second tendon.