Robotic catheter systems and methods

1. A method of controlling a robotic instrument system, the system comprising an elongate sheath instrument and an elongate catheter instrument positioned within a working lumen of the sheath instrument, the method comprising:

operating an instrument driver coupled to the catheter instrument to place a control element extending through the catheter instrument in tension, and thereby articulate at least a distal end portion the catheter instrument; and

automatically compensating for a torsional force exerted on the sheath instrument in a first direction due to articulation of the distal end portion of the catheter, by urging the sheath instrument to twist in a second direction opposite of the first direction.

2. The method of claim 1 , wherein the sheath instrument is urged to twist by operating the instrument driver to place a control element of the sheath instrument in tension.

3. The method of claim 1 , wherein compensating for the torsional force is performed when the catheter instrument is bent in a first plane and the sheath instrument is bent in a second plane different than the first plane.

4. The method of claim 3 , wherein the sheath instrument defines a first axis and is bent to define a second axis, and the catheter instrument is bent to define a third axis, wherein compensating for the torsional force is based on:

β= K sin(θ)sin(α)

wherein

β=compensation of the rotational position of the catheter instrument within the sheath instrument,

α=an angle defined between the first axis and the second axis,

θ=an angle defined between the second axis and the third axis,

K=a tuning gain factor.

5. A robotically controlled medical instrument system, comprising:

a controller;

an instrument driver operatively coupled to the controller;

a sheath instrument operatively coupled to the instrument driver; and

a catheter instrument operatively coupled to the instrument driver, wherein the catheter instrument is positioned in a working lumen of the sheath instrument, the catheter instrument having a control element extending there through for controllably articulating a distal end portion of the catheter instrument,

wherein placing the control element in tension places a torsional force on the sheath instrument that urges the sheath instrument to twist in a first direction, and

wherein the controller is configured to automatically compensate for the torsional force exerted on the sheath instrument by urging the sheath instrument to twist in a second direction opposite of the first direction through selected operation of the instrument driver.

6. The system of claim 5 , wherein the sheath instrument defines a first axis and is bent to define a second axis, and the catheter instrument is bent to define a third axis, wherein the controller is configured to compensate for the torsional force based on the relationship:

β= K sin(θ)sin(α)

wherein

β=compensation of the rotational position of the catheter instrument within the sheath instrument,

α=an angle defined between the first axis and the second axis,

θ=an angle defined between the second axis and the third axis,

K=a tuning gain factor.

7. A method of controlling a robotic instrument system, the system comprising an elongate flexible sheath instrument and an elongate flexible catheter instrument positioned within a working lumen of the sheath instrument, the method comprising:

determining a length of a distal end portion of the catheter instrument that extends beyond a distal end opening of the sheath instrument; and

selectively actuating one or more motors in an instrument driver to thereby cause articulation of a distal end portion of the catheter instrument extending through a distal end opening of the sheath instrument, wherein actuation of the motors is based at least in part on the determined length so that the resulting articulation of the distal end portion of the catheter instrument is scaled.

8. The method of claim 7 , wherein articulation of the distal end portion of the catheter instrument is scaled based on a filtered curvature relationship,

K F =a*K C

wherein

K F =a filtered or adjusted position or curvature of the catheter instrument,

K C =the commanded position or curvature of the catheter instrument, and

“a”=a scaling factor.

9. The method of claim 8 , wherein the scaling factor “a” is a non-linear function.

10. The method of claim 9 , wherein the non-linear function is a function of the length “l’ of the catheter instrument that extends beyond the distal end of the sheath instrument, based on the expression:

a

⁡

(

l

)

=

1

-

1

-

b

1

+

l

c

d

wherein “b”, “c”, and “d” are tuning factors for shaping the non-linear function.

11. The method of claim 8 , wherein the scaling factor is a minimum for maximum compensation of articulation of the catheter instrument when the catheter instrument is fully retracted within the sheath instrument.