Method and apparatus for controlling a temperature-controlled probe

• US 6,939,346 B2
• Filed: 06/28/2002
• Issued: 09/06/2005
• Est. Priority Date: 04/21/1999
• Status: Expired due to Fees

• Current Assignee: Oratec Interventions Incorporated (Smith & Nephew PLC)
• Original Assignee: Oratec Interventions Incorporated (Smith & Nephew PLC)
• Inventors: Marion, Duane W., Kannenberg, Donald P.
• Primary Examiner(s): GIBSON, ROY DEAN
• Application Number:
  US10/187,462
• Publication Number:
  US 20030060818A1
• Time in Patent Office: 1,166 Days
• Field of Search: 606/34, 606/38, 606 40- 42, 606 49- 50, 607101-105
• 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 controlling a power output to a probe, the method comprising:

(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 a 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 a sensed temperature sensed by a probe temperature sensor and said target probe temperature;

(f) providing a controller with a control function for generating an output power control signal Pout definable in part by;

Pout=k4,

when said error signal is greater than or equal to a threshold value, and definable in part by;

Pout=Kp·

P+Ki·

I+Kd·

D

when said error signal is less than the threshold value;

where k4 is a constant, 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 said error signal e(t) to dynamically control at least one of said Kp, Ki, and Kd to determine said Pout; and

(h) controlling the power output to a probe thermal element responsive to said Pout.

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 said Kp, Ki, and Kd as a function of a quantized one of said ranges.

4. The method of claim 1, wherein said k4 comprises a maximum power.

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 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 further includes a set-specific proportional gain factor and a set-specific integral gain factor.

8. The method of claim 7, wherein providing the controller with the control function further comprises:

(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 error signal e(t) and multiplying by said selected set-specific integral gain factor.

9. The method of claim 7, wherein:

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

providing the controller with the control function further comprises generating said Kd·

D 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.

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 controlling a power output to a probe, the method comprising:

(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 a 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 a sensed temperature sensed by a probe temperature sensor and said target probe temperature;

(f) providing a controller with a control function that examines a rate at which said sensed temperature approaches said target temperature, and determines whether said sensed temperature will attain but not exceed said target temperature;

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

(h) controlling the power output to a probe thermal element responsive to said output power control signal.

14. The method of claim 13, wherein using said error signal e(t) comprises 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 replacing said determined output power control signal with a maximum power based on said error signal.

16. The method of claim 13, wherein providing the controller with the control function comprises limiting said output power control signal to a predetermined output value when said output control signal exceeds a predetermined threshold value.

17. A system to control a power output to 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 routine executable by said processor to cause said processor to carry out the following;

(a) to receive 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 a sensed temperature sensed by said sensor and said target probe temperature;

(e) to provide said controller with a control function that examines a rate at which temperature approaches said target probe temperature, and determines whether said sensed temperature will attain but not exceed said target temperature;

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

(g) to control the power output to said thermal element responsive to said output power control signal.

18. The system of claim 17, wherein said control function is defined in part by:

Pout=Kp·

P+Ki·

I+Kd·

D

where Pout is said 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 replacing said output power control signal with a maximum power, based on said error signal.

22. A computer readable medium comprising:

software for execution by a computer processor to control a power output to a probe having a probe thermal element and a probe temperature sensor, and

a 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,

said software carrying out the following

(a) receiving 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 a sensed temperature sensed by said sensor and said target temperature;

(e) providing a control function for generating an output power control signal, said control function comprising a first mode wherein said output power control signal comprises a constant power, and a second mode wherein said output power control signal is generated based on an examination of a rate at which said sensed temperature approaches said target temperature and a determination of whether said sensed temperature will attain but not exceed said target temperature;

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

(g) controlling power output to said thermal element responsive to said power output control signal.

23. The computer readable medium of claim 22, wherein said second mode is defined in part by:

Pout=Kp·

P+Ki·

I+Kd·

D

where Pout is said 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 using said error signal e(t) comprises 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, wherein said first mode comprises overriding said output power control signal with said maximum power.

26. The computer readable medium of claim 22, wherein using said error signal e(t) comprises limiting said output control signal to a predetermined output value when said output control signal exceeds a predetermined threshold.

27. A method comprising:

receiving a gain factor corresponding to an electrosurgical instrument;

receiving a target temperature;

receiving a sensed temperature; and

generating a power signal from a control function operating on the target temperature, the sensed temperature, and the gain factor.

28. The method of claim 27, further comprising generating an error signal based on a comparison of the sensed temperature with the target temperature.

29. The method of claim 28, wherein the gain factor comprises a proportional gain factor and generating the power signal comprises generating a proportional signal based on a product of the error signal and the proportional gain factor.

30. The method of claim 28, wherein generating the power signal comprises generating an integral signal based on an integral of the error signal.

31. The method of claim 30, wherein the gain factor comprises a proportional gain factor and generating the power signal comprises generating a proportional signal based on a product of the error signal and the proportional gain factor and combining the proportional signal and the integral signal.

32. The method of claim 28, wherein generating the power signal comprises generating a derivative signal based on a derivative of at least one of the error signal and the sensed temperature.

33. The method of claim 32, wherein the gain factor comprises a proportional gain factor and generating the power signal comprises generating a proportional signal based on a product of the error signal and the proportional gain factor, generating an integral signal based on an integral of the error signal, and combining the proportional signal, the integral signal, and the derivative signal.

34. The method of claim 32, wherein the gain factor comprises a proportional gain factor and generating the power signal comprises generating a proportional signal based on a product of the error signal and the proportional gain factor and combining the proportional signal and the derivative signal.

35. The method of claim 28, wherein the gain factor comprises a derivative gain factor and generating the power signal further comprises generating a derivative signal based on a product of the derivative gain factor and a derivative of at least one of the error signal and the sensed temperature.

36. The method of claim 35, wherein generating the power signal comprises generating an integral signal based on an integral of the error signal and combining the derivative signal and the integral signal.

37. The method of claim 28, wherein the gain factor comprises an integral gain factor and generating the power signal comprises generating an integral signal based on a product of the integral gain factor and an integral of the error signal.

38. The method of claim 27, wherein generating the power signal comprises generating an intermediate output signal, the power signal being limited to a predetermined maximum output value when the intermediate output signal exceeds a predetermined threshold value.

39. The method of claim 38, wherein generating the power signal comprises generating an antiwindup adjustment signal based on a comparison of the intermediate output signal and the power signal.

40. The method of claim 39, wherein generating the power signal comprises generating an error signal based on a comparison of the sensed temperature and the target temperature, generating a modified error signal based on a comparison of the antiwindup adjustment signal and the error signal, and generating an integral signal based on an integral of the modified error signal.

41. The method of claim 27, wherein receiving a gain factor comprises choosing the gain factor from one or more electrosurgical instrument gain factors.

42. The method of claim 27, further comprising providing the power signal to the electrosurgical instrument.

43. A method comprising:

choosing proportional, derivative, and integral gain factors corresponding to an electrosurgical instrument;

receiving a target temperature;

receiving a sensed temperature;

generating an error signal based on a comparison of the sensed temperature with the target temperature;

generating a power signal from a control function operating on a proportional signal based on a product of the error signal and the proportional gain factor, a derivative signal based on a product of the derivative gain factor and a derivative of at least one of the error signal and the sensed temperature, and an integral signal based on a product of the integral gain factor and an integral of the error signal; and

providing the power signal to the electrosurgical instrument.

44. The method of claim 43, wherein generating the power signal comprises generating an intermediate output signal, the power signal being limited to a predetermined maximum output value when the intermediate output signal exceeds a predetermined threshold value.

45. A method comprising:

receiving a target temperature;

receiving a sensed temperature;

generating an error signal based on a comparison of the sensed temperature and the target temperature;

receiving a parameter for a control function for generating a power signal for an electrosurgical instrument; and

replacing the parameter for the control function with a second parameter for the control function based on a comparison of the error signal and a threshold value.

46. The method of claim 45, further comprising generating the power signal for the electrosurgical instrument by executing the control function.

47. The method of claim 46, wherein the parameter comprises a gain factor and generating the power signal comprises generating a proportional signal based on a product of the error signal and the gain factor.

48. The method of claim 46, wherein the parameter comprises a gain factor and generating the power signal comprises generating an integral signal based on a product of the gain factor and an integral of the error signal.

49. The method of claim 46, wherein the parameter comprises a gain factor and generating the power signal comprises generating a derivative signal based on a product of the gain factor and a derivative of at least one of the error signal and the sensed temperature.

50. The method of claim 45, further comprising switching the power signal to a maximum power based on a comparison of the error signal and a maximum power threshold value.

51. The method of claim 50, wherein the power signal is switched to the maximum power when the error signal is greater than the maximum power threshold value.

52. The method of claim 50, wherein the power signal is switched to the maximum power when the error signal is equal to the maximum power threshold value.

53. The method of claim 45, wherein the threshold value comprises a measured value.

54. The method of claim 53, wherein the measured value is selected from the group consisting of a temperature value, an impedance value, and a voltage value.

55. The method of claim 45, wherein receiving the parameter comprises choosing the parameter for the control function from among multiple parameters.

56. The method of claim 55, wherein replacing the parameter for the control function with the second parameter for the control function comprises choosing the second parameter from among multiple parameters.

57. The method of claim 45, wherein receiving the parameter comprises choosing the parameter based on a comparison of the error signal and a second threshold value.

58. The method of claim 45, wherein the parameter comprises a gain factor, and receiving the parameter comprises receiving the gain factor.

59. A method comprising:

receiving a target temperature;

receiving a sensed temperature;

generating an error signal based on a comparison of the sensed temperature and the target temperature;

choosing proportional, integral, and derivative gain factors, based on a comparison of the error signal and a first threshold value;

replacing original gain factors in a control function for generating a power signal for an electrosurgical instrument with the proportional gain factor, the integral gain factor, and the derivative gain factor;

generating the power signal with the control function including generating a proportional signal based on a product of the error signal and the proportional gain factor, generating an integral signal based on a product of the integral gain factor and an integral of the error signal, generating a derivative signal based on a product of the derivative gain factor and a derivative of at least one of the error signal and the sensed temperature, and combining the proportional signal, the integral signal and the derivative signal; and

switching the power signal to a maximum power based on a comparison of the error signal and a second threshold value.

60. A device comprising:

means for receiving a target temperature;

means for receiving a sensed temperature;

means for generating an error signal based on a comparison of the sensed temperature and the target temperature;

means for receiving a parameter for a control function for generating a power signal for an electrosurgical instrument and

means for replacing the parameter for the control function with a second parameter for the control function based on a comparison of the error signal and a threshold value.

61. The device of claim 60, further comprising means for generating the power signal for the electrosurgical instrument by executing the control function.

62. The device of claim 61, wherein the parameter comprises a gain factor and the means for generating the power signal comprises means for generating a proportional signal based on a product of the error signal and the gain factor.

63. The device of claim 61, wherein the parameter comprises a gain factor and the means for generating the power signal comprises means for generating an integral signal based on a product of the gain factor and an integral of the error signal.

64. The device of claim 61, wherein the parameter comprises a gain factor and the means for generating the power signal comprises means for generating a derivative signal based on a product of the gain factor and a derivative of at least one of the error signal and the sensed temperature.

65. The device of claim 60, further comprising means for switching the power signal to a maximum power based on a comparison of the error signal and a maximum power threshold value.

66. The device of claim 65, wherein the power signal is switched to the maximum power when the error signal is greater than the maximum power threshold value.

67. The device of claim 65, wherein the power signal is switched to the maximum power when the error signal is equal to the maximum power threshold value.

68. The device of claim 60, wherein the threshold value comprises a measured value.

69. The device of claim 68, wherein the measured value is selected from the group consisting of a temperature value, an impedance value, and a voltage value.

70. The device of claim 60, wherein the means for receiving the parameter comprises means for choosing the parameter for the control function from among multiple parameters.

71. The device of claim 70, wherein the means for replacing the parameter for the control function with the second parameter for the control function comprises means for choosing the second parameter from among multiple parameters.

72. The device of claim 60, wherein the means for receiving the parameter comprises means for choosing the parameter based on a comparison of the error signal and a second threshold value.

73. The method of claim 60, wherein the parameter comprises a gain factor, and the means for receiving the parameter comprises means for receiving the gain factor.

74. A device comprising:

means for receiving a target temperature;

means for receiving a sensed temperature;

means for generating an error signal based on a comparison of the sensed temperature and the target temperature;

means for choosing proportional, integral, and derivative gain factors, based on a comparison of the error signal and a first threshold value;

means for replacing original gain factors in a control function for generating a power signal for an electrosurgical instrument with the proportional gain factor, the integral gain factor, and the derivative gain factor;

means for generating the power signal with the control function comprising means for generating a proportional signal based on a product of the error signal and the proportional gain factor, means for generating an integral signal based on a product of the integral gain factor and an integral of the error signal, means for generating a derivative signal based on a product of the derivative gain factor and a derivative of at least one of the error signal and the sensed temperature, and means for combining the proportional signal, the integral signal and the derivative signal; and

means for switching the power signal to a maximum power based on a comparison of the error signal and a second threshold value.

75. A device comprising:

a first input component configured to receive a sensed temperature;

a second input component configured to receive a target temperature;

a third input component configured to receive a gain factor corresponding to an electrosurgical instrument;

a power control circuit coupled to the first input component, the second input component, and the third input component, the power control circuit operable on the sensed temperature, the target temperature, and the gain factor and configured to generate a power signal for the electrosurgical instrument.

76. The device of claim 75, wherein the power control circuit comprises a summing component configured to generate an error signal based on a difference between the sensed temperature and the target temperature.

77. The device of claim 76, wherein the gain factor comprises a proportional gain factor and the power control circuit further comprises an amplifier component configured to multiply the proportional gain factor and the error signal to generate a proportional signal.

78. The device of claim 76, wherein the gain factor comprises a derivative gain factor and the power control circuit further comprises a derivative component configured to take a derivative of the error signal to generate an intermediate signal and an amplifier component configured to multiply the intermediate signal and the derivative gain factor to generate a derivative signal.

79. The device of claim 76, wherein the gain factor comprises an integral gain factor and the power control circuit further comprises an integrator component configured to integrate the error function to generated an intermediate signal and an amplifier configured to multiply the intermediate signal and the integral gain factor to generate an integral signal.

80. The device of claim 75, wherein the gain factor comprises a derivative gain factor and the power control circuit further comprises a derivative component configured to take a derivative of the sensed temperature to generate an intermediate signal and an amplifier component configured to multiply the intermediate signal and the derivative gain factor to generate a derivative signal.

81. The device of claim 75, further comprising a memory containing multiple electrosurgical instrument gain factors and a selector configured to select the gain factor from among the multiple electrosurgical instrument gain factors.

82. A device comprising:

a first input component configured to receive a sensed temperature;

a second input component configured to receive a target temperature;

a power control circuit coupled to the first input component and the second input component, the power control circuit operable on the sensed temperature, the target temperature, and a parameter and configured to generate a power signal for an electrosurgical instrument, the power control circuit comprising (i) a summing component configured to generate an error signal based on a difference between the sensed temperature and the target temperature, and (ii) a selector component configured to choose the parameter for the control function and configured to replace the parameter for the control function with a second parameter for the control function based on a comparison of the error signal and a threshold value.