Method and apparatus for controlling a temperature-controlled probe

• US 20030060818A1
• Filed: 06/28/2002
• Published: 03/27/2003
• Est. Priority Date: 04/21/1999
• Status: Active Grant

• Current Assignee: Oratec Interventions Incorporated
• Original Assignee: Oratec Interventions Incorporated
• Inventors: Marion, Duane W., Kannenberg, Donald P.
• Granted Patent: US 6,939,346 B2
• Time in Patent Office: Days
• US Class Current: 606/34
• CPC Class Codes: A61B 18/04 by heating by applying electromagnetic radiation A61B18/18; hyperthermia using electric or magnetic fields, radiation or ultrasound A61N
• CPC Class Codes: A61B 18/08 by means of electrically-heated probes
• CPC Class Codes: A61B 18/1206 Generators therefor
• CPC Class Codes: A61B 18/14 Probes or electrodes therefor
• CPC Class Codes: A61B 2017/00084 Temperature
• CPC Class Codes: A61B 2017/00482 with a code
• CPC Class Codes: A61B 2018/00642 with feedback, i.e. closed loop control
• CPC Class Codes: A61B 2018/00684 using lookup tables
• CPC Class Codes: A61B 2018/00702 Power or energy
• CPC Class Codes: A61B 2018/00791 Temperature
• CPC Class Codes: A61B 2018/00988 Means for storing information, e.g. calibration constants, or for preventing excessive use, e.g. usage, service life counter
• CPC Class Codes: A61B 2018/0237 with a thermoelectric element in the probe for cooling purposes
• CPC Class Codes: A61B 2018/0262 using a circulating cryogenic fluid

Abstract

A thermal energy controller system useful in medical procedures includes a controller coupled to a probe, and a thermal element to vary probe temperature. The controller includes memory storing a non-continuous algorithm that permits user-selectable settings for various probe types such that controller operation is self-modifying in response to the selected probe setting. Probe output power Pout is constant in one mode to rapidly enable probe temperature to come within a threshold of a target temperature. The controller can then vary Pout dynamically using a proportional-integral-derivative (PID) algorithm Pout=Kp·P+Ki·I+Kd·D, where feedback loop coefficients Kp, Ki, Kd can vary dynamically depending upon magnitude of an error function e(t) representing the difference between a user-set desired target temperature and sensed probe temperature. Advantageously, target temperature can be rapidly attained without overshoot, allowing the probe system to be especially effective in arthroscopic tissue treatment.

Claims

1. A method of dynamically controlling power output of a probe that has a probe thermal element and -a probe temperature sensor and is coupled to a system that includes a controller to maintain a target probe temperature without substantial thermal overshoot, the method including the following steps:

(a) providing in a memory at least one set of settings for said probe including at least one gain parameter and corresponding predetermined operating characteristics for said probe;

(b) receiving as a threshold input said target probe temperature;

(c) receiving a first probe setting corresponding to a desired set of operating characteristics for said probe;

(d) dynamically selecting from said at least one set of probe settings a set of settings in response to said first probe setting;

(e) generating an error signal e(t) from a comparison of temperature sensed by said sensor and said target probe temperature;

(f) providing said controller with a closed-loop discontinuous control function definable in part by;

Pout=k4,

where Pout is an output power control signal, and k4 is a constant, when probe temperature is less than a desired target probe temperature; and

definable in part by;

Po=Kp·

P+Ki·

I+Kd·

D

 

when probe temperature is within a threshold range of said desired target probe temperature;

where Pout is an output power control signal, Kp is a proportional gain factor associated with said control function, Ki is an integral gain factor associated with said control function, Kd is a derivative gain factor associated with said control function, and P, I, and D are proportion, integration, and derivation functions associated with said control function; and

(g) using magnitude of said error signal e(t) to dynamically control at least one said factor of said control function to determine said Pout; and

(h) controlling power output to said thermal element responsive to said Pout to maintain said target probe temperature.

2. The method of claim 1, wherein step (g) includes quantizing said e(t) into one of at least two ranges, and selecting at least two of said Kp, Ki, and Kd as a function of a quantized one of said ranges.

3. The method of claim 1, wherein step (g) includes quantizing said e(t) into one of at least two ranges, and selecting a value for said Kp, Ki, and Kd as a function of a quantized one of said ranges.

4. The method of claim 1, further including overriding an amount of power determined at step (g) and instead providing a user-selected maximum amount of power as a function of said e(t).

5. The method of claim 1, wherein step (f) includes limiting said output control signal to a predetermined output value when said output control signal exceeds a predetermined threshold.

6. The method of claim 1, wherein said computation of integration function I is disabled when said output control signal exceeds a predetermined threshold value.

7. The method of claim 1 wherein said at least one gain parameter includes a set-specific proportional gain factor and a set-specific integral gain factor.

8. The method of claim 7, wherein:

step (f) includes;

(i) generating said Kp·

P by multiplying said error signal e(t) by said selected set-specific proportional gain factor; and

(ii) generating said Ki·

I by integrating said e(t) and multiplying an integration thereby by said selected set-specific integral gain factor.

9. The method of claim 7, wherein:

said at least one gain parameter includes a set-specific derivative gain factor; and

step (f) includes generating a derivative signal by applying a derivative function to a sensed said temperature to generate an intermediate signal, and multiplying said intermediate signal by said selected set-specific derivative gain factor, and summing said derivative signal to generate said output control signal.

10. The method of claim 1 wherein said at least one gain parameter includes a set-specific proportional gain factor, a set-specific integral gain factor, and a set-specific derivative gain factor.

11. The method of claim 1, further including:

generating an antiwindup adjustment signal;

subtracting said antiwindup adjustment signal from said error signal e(t) to yield a modified error signal;

wherein integration function I integrates said modified error signal.

12. The method of claim 1, further including:

receiving a ramp parameter corresponding to a particular profile at which to ramp up output power; and

changing said target temperature responsive to said ramp parameter.

13. A method of dynamically controlling power output of a probe that has a probe thermal element and a probe temperature sensor and is coupled to a system that includes a controller to maintain a target probe temperature at the probe without substantial thermal overshoot, the method including the following steps:

(a) providing in a memory at least one set of settings for said probe including at least one gain parameter and corresponding predetermined operating characteristics for said probe;

(b) receiving as input said target probe temperature;

(c) receiving a first probe setting corresponding to a desired set of operating characteristics for said probe;

(d) selecting from said at least one set of probe settings a set of settings in response to said first probe setting;

(e) generating an error signal e(t) from a comparison of temperature sensed by said sensor and said target temperature;

(f) providing said controller with a closed-loop control discontinuous function that examines a rate at which probe temperature approaches said target temperature, and determines whether present characteristics of said closed-loop system will attain but not exceed said target temperature;

(g) using magnitude of said error signal e(t) to dynamically control at least one factor of said control function to determine an output power control signal Pout; and

(h) controlling power output to said thermal element responsive to said Pout to maintain said target temperature.

14. The method of claim 13, wherein step (g) includes quantizing said e(t) into one of at least two ranges, and selecting a characteristic coefficient associated with said closed-loop as a function of a quantized one of said ranges.

15. The method of claim 13, further including overriding an amount of power determined at step (g) and instead providing a user-selected maximum amount of power as a function of said e(t).

16. The method of claim 13, wherein step (f) includes limiting said output control signal to a predetermined output value when said output control signal exceeds a predetermined threshold.

17. A system to dynamically control power output of a probe having a probe thermal element and a probe temperature sensor such that a target probe temperature is maintained at the probe without substantial overshoot, the system comprising:

a controller including a processor and memory, said memory including at least one set of settings for said probe, including at least one gain parameter and corresponding predetermined operating characteristics for said probe, and further including a non-continuous routine executable by said processor to cause said processor to carry out the following steps;

(a) to receive as input said target probe temperature;

(b) to receive a first probe setting corresponding to a desired set of operating characteristics for said probe;

(c) to select from said at least one set of probe settings a set of settings in response to said first probe setting;

(d) to generate an error signal e(t) from a comparison of temperature sensed by said sensor and said target probe temperature;

(e) to provide said controller with a closed-loop discontinuous control function that examines a rate at which probe temperature is actually approaching said target probe temperature, and determines whether present characteristics of said closed-loop system will attain but not exceed said target temperature;

(f) to use magnitude of said error signal e(t) to dynamically control at least one factor of said control function to determine an output power control signal Pout; and

(g) to control power output to said thermal element responsive to said Pout to maintain said target temperature.

18. The system of claim 17, wherein at (e) said controller exhibits a dynamic closed-loop control function definable in part by:

Pout=Kp·

P+Ki·

I+Kd·

D

where Pout is an output power control signal, Kp is a proportional gain factor associated with said control function, Ki is an integral gain factor associated with said control function, Kd is a derivative gain factor associated with said control function, and P, I, and D are proportion, integration, and derivation functions associated with said control function.

19. The system of claim 18, wherein said processor quantizes said e(t) into one of at least two ranges, and selects at least two of said Kp, Ki, and Kd as a function of a quantized one of said ranges.

20. The system of claim 18, wherein said processor quantizes said e(t) into one of at least two ranges, and selects a value for said Kp, Ki, and Kd as a function of a quantized one of said ranges.

21. The system of claim 18, further including means for overriding an amount of power determined at (g) and instead providing a user-selected maximum amount of power as a function of said e(t).

22. A computer readable medium containing software for execution by a computer processor used in conjunction with a system to dynamically control power output of a probe having a probe thermal element and a probe temperature sensor, said memory including at least one set of settings for said probe including at least one gain parameter and corresponding predetermined operating characteristics for said probe, and said system functioning such that a target probe temperature is maintained at the probe, said software upon execution by said processor carrying out the following steps:

(a) receiving as input said target probe temperature;

(b) receiving a first probe setting corresponding to a desired set of operating characteristics for said probe;

(c) selecting from said at least one set of probe settings a set of settings in response to said first probe setting;

(d) generating an error signal e(t) from a comparison of temperature sensed by said sensor and said target temperature;

(e) providing said controller with a closed-loop discontinuous control function that in one mode operates said probe at a constant power Pout, and in a second mode dynamically controls said Pout by examining a rate at which probe temperature actually approaches said target temperature, and determines whether present characteristics of said closed-loop system will attain but not exceed said target temperature;

(f) using magnitude of said error signal e(t) to dynamically control at least one factor of said control function to determine an output power control signal Pout; and

(g) controlling power output to said thermal element responsive to said Pout to maintain said target temperature.

23. The computer readable medium of claim 22, wherein at step (t) said controller exhibits a dynamic closed-loop control function definable in part by:

Pout=Kp·

P+Ki·

I+Kd·

D

where Pout is an output power control signal, Kp is a proportional gain factor associated with said control function, Ki is an integral gain factor associated with said control function, Kd is a derivative gain factor associated with said control function, and P, I, and D are proportion, integration, and derivation functions associated with said control function.

24. The computer readable medium of claim 22, wherein step (f) includes quantizing said e(t) into one of at least two ranges, and selecting at least two of said Kp, Ki, and Kd as a function of a quantized one of said ranges.

25. The computer readable medium of claim 22, further including overriding an amount of power determined at step (e and instead providing a user-selected maximum amount of power as a function of said e(t).

26. The computer readable medium of claim 22, wherein step (f) includes limiting said output control signal to a predetermined output value when said output control signal exceeds a predetermined threshold.