Tension control in actuation of multi-joint medical instrument

1. A medical instrument system comprising a medical instrument, the system including:

a plurality of joints;

a plurality of actuators;

a plurality of transmission systems having proximal ends respectively coupled to the actuators, each transmission system of the plurality of transmission systems having a distal end attached to an associated one of the plurality of joints to allow transmission of a force for articulation of the medical instrument system;

a sensor coupled to measure a configuration of the medical instrument; and

a control system coupled to

receive configuration data, including a current configuration of a tip of the medical instrument from the sensor, and including a desired configuration of the tip of the medical instrument,

determine a difference between the desired configuration and the current configuration of the tip of the medical instrument,

determine, from the difference, a tip force and a tip torque that when applied to the tip of the medical instrument move the tip of the medical instrument from the current configuration toward the desired configuration,

determine joint torques for one or more of the plurality of joints that produce the determined tip force and the determined tip torque;

determine a set of tensions based on the determined joint torques, but not based on positions of the plurality of actuators; and

generate control signals for at least one of the plurality of actuators that cause the at least one of the plurality of actuators to apply the determined set of tensions to at least one of the plurality of transmission systems.

2. The system of claim 1 wherein the control system is further coupled to hold the set of tensions for a pre-determined time interval.

3. The system of claim 1 ,

wherein determining the difference includes determining a first difference between a current value of a first position coordinate of the tip and a desired value of the first position coordinate of the tip; and

wherein determining the tip force includes determining a first product of the first difference and a first gain factor and using the first product in determining a first component of the tip force.

4. The system of claim 3 ,

wherein determining the difference further includes determining a second difference between a current value of a second position coordinate of the tip and a desired value of the second position coordinate of the tip; and

wherein determining the tip force further includes determining a second product of the second difference and a second gain factor, wherein the second gain factor is different from the first gain factor, and using the second product in determining a second component of the tip force.

5. The system of claim 1 ,

wherein determining the difference includes determining a first difference between a current value of a first angular coordinate of the tip and a desired value of the first angular coordinates of the tip; and

wherein determining the tip force includes determining a first product of the first difference and a first gain factor, and using the first product in determining a first component of the tip torque.

6. The system of claim 5 ,

wherein determining the difference further includes determining a second difference between a current value of a second angular coordinate of the tip and a desired value of the second angular coordinate of the tip; and

wherein determining the tip force further includes determining a second product of the second difference and a second gain factor, wherein the second gain factor is set to be different from the first gain factor, and using the second product in determining a second component of the tip force.

7. The system of claim 1 , wherein determining the tip force comprises:

determining a difference between a component of a current velocity of the tip and a component of a desired velocity of the tip;

determining a product of the difference and a gain factor; and

using the product in determining a component of the tip force.

8. The system of claim 1 , wherein determining the tip force comprises:

determining a difference between an angular velocity of the tip and a desired angular velocity of the tip;

determining a product of the difference and a gain factor; and

using the product in determining a component of the tip force.

9. The system of claim 1 , wherein the plurality of joints provide more than six degrees of freedom of motion, including degrees of freedom of motion that are redundant for movement of the tip; and wherein the joint torques are computed to keep the joints away from limits of ranges of motion of the joints or away from joint torque limits.

10. The system of claim 1 wherein the sensor is an optical fiber shape sensor.

11. The system of claim 1 , wherein the control system regulates the set of tensions applied to the transmission systems to be independent of a compliance of the transmission systems or the joints.

12. The system of claim 1 , wherein the control system regulates the set of tensions applied to the transmission systems to be independent of a length of the transmission systems from their proximal ends to their distal ends.

13. The system of claim 1 , wherein the control system regulates the set of tensions applied to the transmission systems to be independent of shape of the transmission systems from their proximal ends to their distal ends.

14. A method for controlling a medical instrument, the method comprising:

measuring a configuration for a plurality of joints of the medical instrument;

receiving a command indicating a desired configuration of the medical instrument;

determining tensions respectively in a plurality of transmission systems that respectively connect a plurality of actuators to the plurality of joints, wherein determining tensions is independent of positions of the actuators and includes

determining a difference between a desired configuration and a current configuration of a tip of the medical instrument,

determining from the difference, a tip force and a tip torque that when applied to the tip of the medical instrument moves the tip of the medical instrument from the current configuration toward the desired configuration,

determining joint torques for one or more of the plurality of joints that produce the determined tip force and the determined tip torque, and

determining a set of tensions based on the determined joint torques, but not on positions of the plurality of actuators; and

generating control signals for at least one of the plurality of actuators that cause the at least one of the plurality of actuators to apply the determined set of tensions to at least one of the plurality of transmission systems.

15. The method of claim 14 ,

wherein determining the difference includes determining a first difference between a current value of a first position coordinate of the tip and a desired value of the first position coordinate of the tip; and

wherein determining the tip force includes determining a first product of the first difference and a first gain factor and using the first product in determining a first component of the tip force.

16. The method of claim 15 ,

wherein determining the difference further includes determining a second difference between a current value of a second position coordinate of the tip and a desired value of the second position coordinate of the tip; and

wherein determining the tip force further includes determining a second product of the second difference and a second gain factor, wherein the second gain factor is different from the first gain factor, and using the second product in determining a second component of the tip force.

17. The method of claim 14 ,

wherein determining the difference includes determining a first difference between a current value of a first angular coordinate of the tip and a desired value of the first angular coordinates of the tip; and

wherein determining the tip force includes determining a first product of the first difference and a first gain factor and using the first product in determining a first component of the tip torque.

18. The method of claim 17 ,

wherein determining the difference further includes determining a second difference between a current value of a second angular coordinate of the tip and a desired value of the second angular coordinate of the tip; and

wherein determining the tip force further includes determining a second product of the second difference and a second gain factor, wherein the second gain factor is set to be different from the first gain factor, and using the second product in determining a second component of the tip force.

19. The method of claim 14 , wherein determining the tip force comprises:

determining a difference between a component of a current velocity of the tip and a component of a desired velocity of the tip;

determining a product of the difference and a gain factor; and

using the product in determining a component of the tip force.

20. The method of claim 14 , wherein determining the tip force comprises:

determining a difference between an angular velocity of the tip and a desired angular velocity of the tip;

determining a product of the difference and a gain factor; and

using the product in determining a component of the tip force.