Tension control in actuation of jointed instruments

1. A medical instrument system including:

a plurality of actuators;

a medical instrument comprising

an end portion, and

a plurality of transmission systems, each transmission system coupling the end portion to an actuator of the plurality of actuators such that the plurality of actuators is operable to drive the plurality of transmission systems to move the end portion; and

a control system operably connected to the plurality of actuators, the control system configured to execute operations comprising:

determining a difference between a current configuration of the end portion and a desired configuration of the end portion, and

operating the plurality of actuators to apply a plurality of tensions to the plurality of transmission systems based on the difference and based on constant offset tensions, the constant offset tensions being independent of current tensions experienced by the plurality of transmission systems.

2. The instrument system of claim 1 , wherein:

the plurality of tensions, when applied to the plurality of transmission systems, generate a desired net torque at the end portion, and

the constant offset tensions, when applied to the plurality of transmission systems, generate a zero net torque at the end portion.

3. The instrument system of claim 1 , wherein at least two offset tensions of the constant offset tensions are equal.

4. The instrument system of claim 1 , wherein at least two offset tensions of the constant offset tensions differ.

5. The instrument system of claim 1 , wherein operating the plurality of actuators to apply the plurality of tensions comprises:

operating the plurality of actuators such that an average of the plurality of tensions is maintained.

6. The instrument system of claim 1 , wherein the operations further comprise determining the constant offset tensions based on a number of uses of the medical instrument, a torque range for the medical instrument during a medical operation, or a range of motion for the end portion during the medical operation.

7. The instrument system of claim 1 , wherein:

operating the plurality of actuators to apply the plurality of tensions comprises: when one or more of the current tensions is greater than or equal to a predefined tension, operating the plurality of actuators to apply the plurality of tensions, and

the operations further comprise:

when the one or more of the current tensions is less than the predefined tension, operating the plurality of actuators to apply a plurality of second tensions to the plurality of transmission systems based on the difference and based on a minimum tension, a second tension of the plurality of second tensions being no less than the minimum tension.

8. The instrument system of claim 7 , wherein the second tension of the plurality of second tensions is equal to the minimum tension.

9. The instrument system of claim 7 , wherein operating the plurality of actuators to apply the plurality of second tensions comprises operating the plurality of actuators to inhibit slack in all transmission systems of the transmission systems.

10. The instrument system of claim 7 , wherein operating the plurality of actuators to apply the plurality of tensions comprises:

determining baseline torques based on the desired configuration,

adjusting the baseline torques such that the plurality of tensions of the transmission systems are each above the minimum tension, and

applying the adjusted baseline torques to the plurality of actuators.

11. The instrument system of claim 10 , wherein adjusting the baseline torques comprises:

determining a biasing torque to adjust a baseline torque in one of the transmission systems such that tension in the one of the transmission systems is above the minimum tension, the biasing torque being a maximum of a plurality of biasing torques to adjust the baseline torques of the transmission systems such that the tensions in the transmission systems are each above the minimum tension, and

adjusting each of the baseline torques based on the biasing torque.

12. The instrument system of claim 1 , wherein operating the plurality of actuators to apply the plurality of tensions comprises:

operating the plurality of actuators such that a tension of the plurality of tensions is maintained at a maximum tension and a remainder of the plurality of tensions is no more than the maximum tension.

13. The instrument system of claim 1 , wherein the operations further comprise:

determining a current velocity of an actuator of the plurality of actuators, and

determining a damping function based on the current velocity and a desired velocity of the actuator of the plurality of actuators,

wherein operating the plurality of actuators to apply the plurality of tensions comprises operating the plurality of actuators to apply the plurality of tensions based on the damping function.

14. The instrument system of claim 1 , wherein the plurality of transmission systems is configured to be slack when the plurality of transmission systems is decoupled from the plurality of actuators.

15. The instrument system of claim 1 , wherein each actuator of the plurality of actuators is coupled to a single transmission system of the plurality of transmission systems.

16. The instrument system of claim 1 , wherein each actuator of the plurality of actuators is operable to move the end portion in multiple degrees of freedom of motion.

17. A method of operating an instrument, the method comprising:

determining, by one or more computer processors, a difference between a current configuration and a desired configuration of an end portion of the instrument; and

operating, by the one or more computer processors, a plurality of actuators to apply a plurality of tensions to a plurality of transmission systems, the transmission systems coupled to move the end portion, the tensions based on the difference and constant offset tensions, the constant offset tensions being independent of current tensions experienced by the plurality of transmission systems.

18. The method of claim 17 , wherein

the plurality of tensions, when applied to the plurality of transmission systems, generate a desired net torque at the end portion, and

the constant offset tensions, when applied to the plurality of transmission systems, generate a zero net torque at the end portion.

19. The method of claim 17 , wherein operating, by the one or more computer processors, the plurality of actuators to apply the plurality of tensions comprises:

operating, by the one or more computer processors, the plurality of actuators such that an average of the plurality of tensions is maintained.

20. The method of claim 17 , wherein:

operating, by the one or more computer processors, the plurality of actuators to apply the plurality of tensions comprises: when one or more of the current tensions is greater than or equal to a predefined tension, operating, by the one or more computer processors, the plurality of actuators to apply the plurality of tensions, and

the method further comprises:

when the one or more of the current tensions is less than the predefined tension, operating the plurality of actuators to apply a plurality of second tensions to the plurality of transmission systems based on the difference and based on a minimum tension, a second tension of the plurality of second tensions being no less than the minimum tension.

21. The method of claim 17 , wherein operating, by the one or more computer processors, the plurality of actuators to apply the plurality of tensions comprises:

operating, by the one or more computer processors, the plurality of actuators such that a tension of the plurality of tensions is maintained at a maximum tension and a remainder of the plurality of tensions is no more than the maximum tension.

22. The method of claim 17 , further comprising:

determining, by the one or more computer processors, a current velocity of an actuator of the plurality of actuators, and

determining, by the one or more computer processors, a damping function based on the current velocity and a desired velocity of the actuator of the plurality of actuators,

wherein operating, by the one or more computer processors, the plurality of actuators to apply the plurality of tensions comprises operating, by the one or more computer processors, the plurality of actuators to apply the plurality of tensions based on the damping function.

23. A non-transitory computer readable medium storing instructions that are executable by a processing device, and upon such execution cause the processing device to perform a method of operating an instrument, the method comprising:

determining a difference between a current configuration and a desired configuration of an end portion of the instrument; and

operating a plurality of actuators to apply a plurality of tensions to a plurality of transmission systems, the transmission systems coupled to move the end portion, the tensions based on the difference and constant offset tensions, the constant offset tensions being independent of current tensions experienced by the plurality of transmission systems.

24. The computer readable medium of claim 23 , wherein operating the plurality of actuators to apply the plurality of tensions comprises:

operating the plurality of actuators such that an average of the plurality of tensions is maintained.

25. The computer readable medium of claim 23 , wherein:

operating the plurality of actuators to apply the plurality of tensions comprises: when one or more of the current tensions is greater than or equal to a predefined tension, operating the plurality of actuators to apply the plurality of tensions, and

the method further comprises:

when the one or more of the current tensions is less than the predefined tension, operating the plurality of actuators to apply a plurality of second tensions to the plurality of transmission systems based on the difference and based on a minimum tension, a second tension of the plurality of second tensions being no less than the minimum tension.

26. The computer readable medium of claim 23 , wherein operating the plurality of actuators to apply the plurality of tensions comprises:

operating the plurality of actuators such that a tension of the plurality of tensions is maintained at a maximum tension and a remainder of the plurality of tensions is no more than the maximum tension.