Systems, methods and devices for tracking and calibration of flexible instruments
Systems, methods and devices are provided for calibrating a flexible implement that employs fiber Bragg gratings (FBGs) for shape sensing. In some embodiments, methods and devices are provided for determining the longitudinal location of a FBG within an optical fiber that is employed for shape sensing. In other embodiments, methods and devices are employed for the determination of calibration parameters that relate the measured wavelength shift of a set of FBGs to the curvature at the location within the flexible implement where the set of FBGs resides. Various calibration devices are disclosed that employ guiding features for bending the flexible portion of the flexible implement along known curved profiles. In some embodiments, keyed features are incorporated into the flexible implement and the calibration device, such that the flexible implement is inserted into the device in a known orientation. In some embodiments, the flexible implement may incorporate a strain isolation mechanism.
1. A method of determining a longitudinal location of a fiber Bragg grating within an optical fiber, wherein the optical fiber is attached to or housed within an elongate flexible implement, the method comprising:
recording an initial reflected optical wavelength of the fiber Bragg grating in the absence of bending of the elongate flexible implement;
providing a calibration device comprising:
one or more first guiding features suitable for receiving the elongate flexible implement and bending the elongate flexible implement along a first known curved profile; and
one or more second guiding features suitable for receiving the elongate flexible implement and bending the elongate flexible implement along a second known curved profile;
wherein said first and second guiding features are configured such that a ratio of the curvature of the first known curved profile to the curvature of the second known curved profile, as determined at a common longitudinal distance along each known curved profile, varies with longitudinal distance;
wherein said first and second guiding features are configured to bend the elongate flexible implement along a common direction; and
wherein the first known curved profile and the second known curved profile are selected such that a dependence, on longitudinal distance, of the ratio of the curvature of the first known curved profile to the curvature of the second known curved profile, is single-valued;
inserting the elongate flexible implement into the first guiding feature such that the elongate flexible implement is bent according to the first known curved profile and recording a first reflected optical wavelength shift of the fiber Bragg grating;
inserting the elongate flexible implement into the second guiding feature such that the elongate flexible implement is bent according to the second known curved profile and recording a second reflected optical wavelength shift of the fiber Bragg grating; and
determining, as the longitudinal location of the fiber Bragg grating, a longitudinal distance for which a ratio of the curvature of the first known curved profile to the curvature of the second known curved profile equals a ratio of the first reflected optical wavelength shift to the second reflected optical wavelength shift.
2. The method according to claim 1 wherein the calibration device is keyed to corresponding features of the elongate flexible implement, such that the elongate flexible implement is bent according to the first known curved profile and the second known curved profile in a common angular orientation relative to a rotational axis of the elongate flexible implement.
3. The method according to claim 1 wherein the guiding features comprise a first curved channel configured to bend the elongate flexible implement according to the first known curved profile, and a second curved channel configured to bend the elongate flexible implement according to the second known curved profile.
4. The method according to claim 3 wherein each channel of the calibration device is keyed to a corresponding feature of the elongate flexible implement, such that the elongate flexible implement is inserted into each channel in a common angular orientation relative to a rotational axis of the elongate flexible implement.
5. The method according to claim 1 wherein the guiding features comprise a first set of discrete of guide posts configured to bend the elongate flexible implement according to the first known curved profile, and a second set of discrete of guide posts configured to bend the elongate flexible implement according to the second known curved profile.
6. The method according to claim 1 wherein the first known curved profile and the second known curved profile are polynomials having different degrees, wherein the degree of each known curved profile is at least two.
7. A calibration apparatus for use in determining a longitudinal location of a fiber Bragg grating within an optical fiber, wherein the optical fiber is attached to or housed within an elongate flexible implement, the calibration apparatus comprising:
one or more first guiding features suitable for receiving the elongate flexible implement and bending the elongate flexible implement along a first known curved profile; and
one or more second guiding features suitable for receiving the elongate flexible implement and bending the elongate flexible implement along a second known curved profile;
wherein said first and second guiding features are configured such that a ratio of the curvature of the first known curved profile to the curvature of the second known curved profile, as determined at a common longitudinal distance along each known curved profile, varies with longitudinal distance;
wherein said first and second guiding features are configured to bend the elongate flexible implement along a common direction; and
wherein the first known curved profile and the second known curved profile are selected such that a dependence, on longitudinal distance, of the ratio of the curvature of the first known curved profile to the curvature of the second known curved profile, is single-valued.
8. The calibration apparatus according to claim 7 wherein said first and second guiding features comprise:
a first curved channel configured to bend the elongate flexible implement according to the first known curved profile; and
a second curved channel configured to bend the elongate flexible implement according to the second known curved profile.
9. The calibration apparatus according to claim 8 wherein each channel is keyed to a corresponding feature on the elongate flexible implement, such that the elongate flexible implement is inserted into each channel in a common angular orientation relative to a rotational axis of the elongate flexible implement.
10. The calibration apparatus according to claim 7 wherein said first and second guiding features comprise:
a first set of discrete of guide posts configured to bend the elongate flexible implement according to the first known curved profile; and
a second set of discrete of guide posts configured to bend the elongate flexible implement according to the second known curved profile.
11. The calibration apparatus according to claim 7 wherein the first known curved profile and the second known curved profile are polynomials having different degrees, wherein the degree of each known curved profile is at least two.
12. The calibration apparatus according to claim 7 further comprising one or more additional guiding features that are configured to receive the elongate flexible implement without bending the elongate flexible implement.