Compressor control system for a portable ventilator

• US 20050031322A1
• Filed: 05/18/2004
• Published: 02/10/2005
• Est. Priority Date: 08/04/2003
• Status: Active Grant

• Current Assignee: Vyaire Medical 203 Incorporated (Cardinal Health, Inc.)
• Original Assignee: Carefusion 303 Incorporated (Becton, Dickinson & Co)
• Inventors: Williams, Malcolm, Holmes, Michael, Boyle, David
• Granted Patent: US 7,607,437 B2
• Time in Patent Office: Days
• US Class Current: 388/800
• CPC Class Codes: A61M 11/00 Sprayers or atomisers specially adapted for therapeutic purposes in general B05B; aerosol containers B65D83/14
• CPC Class Codes: A61M 16/0051 with alarm devices
• CPC Class Codes: A61M 16/0057 Pumps therefor
• CPC Class Codes: A61M 16/0063 Compressors
• CPC Class Codes: A61M 16/0066 Blowers or centrifugal pumps
• CPC Class Codes: A61M 16/0069 the speed thereof being controlled by respiratory parameters, e.g. by inhalation
• CPC Class Codes: A61M 16/026 specially adapted for predicting, e.g. for determining an information representative of a flow limitation during a ventilation cycle by using a root square technique or a regression analysis
• CPC Class Codes: A61M 16/107 in the inspiratory path
• CPC Class Codes: A61M 16/12 by mixing different gases
• CPC Class Codes: A61M 16/202 electrically actuated
• CPC Class Codes: A61M 16/205 used for exhalation control
• CPC Class Codes: A61M 16/206 Capsule valves, e.g. mushroom, membrane valves
• CPC Class Codes: A61M 16/209 Relief valves
• CPC Class Codes: A61M 2016/0021 with a proportional output signal, e.g. from a thermistor
• CPC Class Codes: A61M 2016/0036 in the breathing tube and used in both inspiratory and expiratory phase
• CPC Class Codes: A61M 2016/1025 the O2 concentration
• CPC Class Codes: A61M 2202/0208 Oxygen
• CPC Class Codes: A61M 2205/16 with back-up system in case of failure
• CPC Class Codes: A61M 2205/3317 Electromagnetic, inductive or dielectric measuring means
• CPC Class Codes: A61M 2205/3365 Rotational speed
• CPC Class Codes: A61M 2205/3368 : Temperature
• CPC Class Codes: A61M 2205/3553 : remote, e.g. between patient's home and doctor's office
• CPC Class Codes: A61M 2205/3569 : sublocal, e.g. between console and disposable
• CPC Class Codes: A61M 2205/3584 : using modem, internet or bluetooth
• CPC Class Codes: A61M 2205/42 : Reducing noise
• CPC Class Codes: A61M 2205/505 : Touch-screens; Virtual keyboard or keypads; Virtual buttons; Soft keys; Mouse touches
• CPC Class Codes: A61M 2205/52 : with memories providing a history of measured variating parameters of apparatus or patient
• CPC Class Codes: A61M 2205/581 : by audible feedback
• CPC Class Codes: A61M 2205/583 : by visual feedback
• CPC Class Codes: A61M 2205/70 : with testing or calibration facilities
• CPC Class Codes: A61M 2205/8206 : battery-operated
• CPC Class Codes: A61M 2205/8237 : Charging means
• CPC Class Codes: A61M 2205/8262 : connectable to external power source, e.g. connecting to automobile battery through the cigarette lighter
• CPC Class Codes: A61M 2209/086 : Docking stations
• CPC Class Codes: A61M 2230/205 : partial oxygen pressure (P-O2)
• CPC Class Codes: A61M 2230/432 : partial CO2 pressure (P-CO2)
• CPC Class Codes: A61M 2230/435 : partial O2 pressure (P-O2)
• CPC Class Codes: H02P 6/17 : and for generating speed information

Abstract

A method and apparatus for controlling a brushless DC (BLDC) motor over a wide range of angular speeds is presented. Analog magnetic sensors provide continuous signal measurements related to the rotor angular position at a sample rate independent of rotor angular speed. In one embodiment, analog signal measurements are subsequently processed using an arctangent function to obtain the rotor angular position. The arctangent may be computed using arithmetic computation, a small angle approximation, a polynomial evaluation approach, a table lookup approach, or a combination of various methods. In one embodiment, the BLDC rotor is used to drive a Roots blower used as a compressor in a portable mechanical ventilator system.

Claims

1. A method for controlling a portable ventilator comprising:

obtaining one or more analog sensor signals having an amplitude related to an angular position of a rotor of a brushless DC (BLDC) motor;

computing an angular position of said rotor from said analog sensor signals;

computing an angular speed from said angular position;

applying said angular speed in a speed control servo for said BLDC motor; and

driving a compressor of a portable ventilator with said BLDC motor.

2. The method of claim 1, wherein said analog sensor signals are obtained using analog Hall effect sensors.

3. The method of claim 1, wherein said analog sensor signals are obtained from anisotropic magneto-resistive (AMR) sensors.

4. The method of claim 1, wherein said angular position is obtained by computing an arctangent of said analog sensor signals.

5. The method of claim 1, wherein said angular speed is obtained by differentiating said angular position.

6. The method of claim 1, wherein said compressor comprises a Roots blower.

7. The method of claim 1, wherein said analog sensor signals are obtained at a constant sample rate.

8. The method of claim 1, wherein computing said angular position comprises:

obtaining a first analog sensor signal from a first analog sensor;

obtaining a second analog sensor signal from a second analog sensor displaced from said first analog sensor by 180 degrees; and

subtracting said second analog sensor signal from said first analog sensor signal.

9. The method of claim 1, wherein computing said angular position comprises applying a DC offset correction to said one or more analog sensor signals.

10. The method of claim 1, wherein computing said angular position comprises applying a commutation correction angle to a computed position value.

11. The method of claim 1, wherein computing said angular position comprises:

identifying a current quadrant of rotation;

obtaining stored coefficients for said current quadrant;

solving a polynomial equation with said current coefficients and a plurality of digitized sensor readings.

12. A portable ventilator apparatus comprising:

a brushless DC (BLDC) motor;

a compressor within a portable ventilator, said compressor driven by said BLDC motor;

a plurality of sensors providing a plurality of analog signals representative of an angular position of said BLDC motor;

a computation circuit configured to compute said angular position and a speed of said BLDC motor from said plurality of analog signals; and

a speed control servo for driving said angular speed to a command speed.

13. The apparatus of claim 12, wherein each of said plurality of sensors comprises an analog Hall effect sensor.

14. The apparatus of claim 12, wherein each of said plurality of sensors comprises an anisotropic magneto-resistive (AMR) sensor.

15. The apparatus of claim 12, wherein said plurality of analog sensors comprises four analog sensors arranged ninety degrees apart from each other in a circular pattern.

16. The apparatus of claim 12, wherein said command speed is calculated by a flow-rate control loop to provide a required flow-rate through said compressor.

17. The apparatus of claim 16, wherein said required flow rate is calculated by a pressure control function.

18. The apparatus of claim 12, wherein said computation circuit comprises a processor.

19. The apparatus of claim 12, wherein said computation circuit computes said angular position from said plurality of analog signals using an arctangent function.

20. The apparatus of claim 12, wherein said computation circuit computes said angular position from said plurality of analog signals using a table lookup function.

21. The apparatus of claim 12, wherein said computation circuit computes said angular position from said plurality of analog signals using polynomial evaluation.

22. The apparatus of claim 12, further comprising an analog-to-digital converter which samples said plurality of analog signals at a constant sample rate, and which provides corresponding digital values to said computation circuit.

23. The apparatus of claim 12, wherein said computation circuit comprises a plurality of stored coefficient values for computing said angular position from a polynomial equation.

24. The apparatus of claim 23, wherein said plurality of coefficient values comprises a set of coefficients associated with each quadrant of a rotation.

25. A method for controlling an electric motor comprising a plurality of analog sensors sensing a magnetic flux associated with rotation of a rotor, said method comprising

sampling the outputs of said plurality of analog sensors to obtain a plurality of digitized sensor signals, said sampling occuring at a constant sample rate;

subtracting a first digitized signal associated with a first sensor from a second digitized signal associated with a second sensor to obtain a first sinusoidal value related to an angular position of said rotor, said first sensor and said second sensor offset from each other by 180 degrees;

deriving said angular position from said first sinusoidal value;

deriving said angular speed from said angular position; and

applying said derived angular speed to a speed control servo to drive said rotor to a desired angular speed.

26. The method of claim 25, further comprising:

subtracting a third digitized signal associated with a third sensor from a fourth digitized signal associated with a fourth sensor to obtain a second sinusoidal value related to said angular position of said rotor;

wherein said second sinusoidal value is used with said first sinusoidal value to derive said angular position.

27. The method of claim 25, wherein said electric motor is used to drive a compressor of a mechanical ventilator, said method further comprising applying said derived angular speed to an airflow control loop to obtain said desired angular speed from a desired airflow.

28. The method of claim 27, further comprising comparing a desired pressure with a measured pressure to obtain said desired airflow.

29. The method of claim 25, wherein deriving said angular position comprises applying a DC offset to said first sinusoidal value.

30. The method of claim 25, wherein deriving said angular position comprises adding a commutation correction angle to a computed position value.

31. The method of claim 25, wherein deriving said angular position comprises obtaining one or more stored coefficients to solve a polynomial equation.

32. The method of claim 31, wherein obtaining one or more stored coefficients comprises:

determining a current quadrant; and

obtaining one or more coefficients associated with said current quadrant.

33. A method of calibrating a speed servo comprising an electric motor having a magnet attached to a rotor shaft and a plurality of pairs of opposing analog sensors positioned in a circle adjacent to said magnet, said method comprising:

rotating said rotor shaft at a constant speed;

for each pair of opposing analog sensors, subtracting a digitized sensor signal of a first analog sensor from a digitized sensor signal of a second analog sensor to obtain a sinusoidal signal; and

for each quadrant, determining a plurality of coefficents of a polynomial equation fitted to a plurality of said sinusoidal signals.

34. The method of claim 33, further comprising determining, for each sinusoidal signal, a DC offset based on one or more signal peaks.

35. The method of claim 33, further comprising determining a commutation correction angle based on one or more zero crossings of said sinusoidal signal.