Flow control system for medical ventilator

• US 5,331,995 A
• Filed: 07/17/1992
• Issued: 07/26/1994
• Est. Priority Date: 07/17/1992
• Status: Expired due to Fees

• Current Assignee: Bear Medical Systems Inc.
• Original Assignee: Bear Medical Systems Inc.
• Inventors: Caterina, Anthony J., Westfall, Thomas P., Visser, Clyde R., Ruiz-Vela, Alberto
• Primary Examiner(s): Michalsky, Gerald A.
• Application Number:
  US07/916,344
• Time in Patent Office: 739 Days
• Field of Search: 128/204.21, 137/8, 137/487, 137/487.5, 137/468
• US Class Current: 137/8
• CPC Class Codes: A61M 16/0051 with alarm devices
• CPC Class Codes: A61M 16/024 including calculation means, e.g. using a processor
• CPC Class Codes: A61M 16/0858 Pressure sampling ports
• CPC Class Codes: A61M 16/204 used for inhalation control
• CPC Class Codes: A61M 16/205 used for exhalation control
• CPC Class Codes: A61M 16/209 Relief valves
• CPC Class Codes: A61M 2016/0042 in the expiratory circuit
• CPC Class Codes: G05D 7/0635 by action on throttling means G05D7/0688, G05D7/0694 take precedence
• CPC Class Codes: Y10T 137/0357 For producing uniform flow
• CPC Class Codes: Y10T 137/7737 Thermal responsive
• CPC Class Codes: Y10T 137/776 Control by pressures across flow line valve
• CPC Class Codes: Y10T 137/7761 Electrically actuated valve

Abstract

A system including the method employed, for controlling the flow of a pressurized gas through a variable orifice flow control valve in a pressurized gas conduit system, such as a ventilator, in response to either a desired flow rate/volume input signal, a desired pressure signal or both. With respect to the flow rate input signal, the system generates a flow signal indicative of the actual flow rate of gas through the flow control valve by measuring the pressure drop across the valve and using the actual orifice area based on a control valve position signal given to the valve. This flow signal is compared to the flow rate input signal to give a correction signal which is used to form a volume flow reference signal. With respect to the desired pressure signal, a signal indicative of the effective pressure at a set location in the system is compared to the desired pressure signal and processed to give a pressure flow reference signal. Depending on the mode desired, either the volume flow reference signal or the pressure flow reference signal or the greater of the two becomes a flow reference signal that is used to generate a control valve position signal based on a predetermined relationship. This signal is then used to vary the valve orifice area and correct the flow rate.

Claims

1. A method for controlling the flow of a pressurized gas through a flow control valve in a pressurized gas conduit system in response to a volume input signal indicative of the desired flow rate comprised of the steps of:

generating a flow signal in a feedback loop indicative of the actual flow rate of gas flow through said flow control valve,

subtracting said flow signal from said volume input signal to generate a correction signal which is indicative of the magnitude and direction of the difference between said flow signal and said volume input signal,

forming a flow reference signal by adding said correction signal to the immediately previous flow reference signal,

generating a control valve position signal from said flow reference signal based on a first predetermined relationship,

inputting said control valve position signal to valve control means for varying the effective orifice flow area in said flow control valve in response to a control valve position signal to change the flow rate through said flow control valve,

after a predetermined short time interval repeating the steps by first generating a new flow signal and subtracting it from the then current input signal so as to continually correct the flow rate through said flow control valve based on the difference between the actual flow rate through the flow control valve and the desired flow rate.

2. A method for controlling the flow of a pressurized gas as in claim 1 wherein

said step of generating an electrical flow signal in a feedback loop indicative of the actual flow rate of gas flow through said flow control valve is comprised of the substeps of:

providing upstream and downstream electrical pressure signals from measurements of the pressures upstream and downstream of the flow control valve,

providing a gas temperature electrical signal from a measurement of the temperature of the gas flowing through said flow control valve,

using said control valve position signal to generate in accordance with a second predetermined relationship a valve orifice signal indicative of the effective orifice area within said flow control valve, and

processing said upstream and downstream pressure signals and said gas temperature signal with said valve orifice signal.

3. A method as in claim 2 wherein said upstream and downstream pressure signals are generated from pressure transducers mounted on a common printed circuit board connected by conduits to their respective positions in the pressurized gas system.

4. A method for controlling the flow of a pressurized gas as in claim 1 wherein the substep of using said control valve position signal to generate a valve orifice signal includes using said control valve position signal in a look-up table defining the second predetermined relationship which has been derived by empirical testing.

5. A method as in claim 4 wherein said look up table has been specifically determined for the specific flow control valve being utilized.

6. A method as in claim 1 wherein said step of generating a control valve position signal from said flow reference signal based on a first predetermined relationship includes the substeps of:

generating a valve reference signal based on said first predetermined relationship,

subtracting from said valve reference signal the current control valve position signal to form a valve position error signal,

limiting the maximum magnitude of the valve position error signal to a predetermined maximum value, which value is based on the maximum correction to the change in orifice area that can be obtained within the predetermined short time interval, and

adding said limited valve position error signal to the control valve position signal to form a new control valve position signal.

7. A method for controlling the flow of a pressurized gas through a flow control valve in a pressurized gas conduit system in response to an electrical input signal indicative of the desired flow rate comprised of the steps of:

providing upstream and downstream electrical pressure signals from pressure measurements upstream and downstream of the flow control valve,

providing a gas temperature electrical signal from a measurement of the temperature of the gas flowing through said flow control valve,

generating a valve orifice signal indicative of the effective orifice area within said flow control valve,

processing said upstream and downstream pressure signals and said gas temperature signal together with said valve orifice signal to generate a flow signal in a feedback loop indicative of the actual flow rate of gas flow through said flow control valve,

subtracting said flow signal from said volume input signal to generate a correction signal which is indicative of the magnitude and direction of the difference between said flow signal and said volume input signal,

forming a flow reference signal by adding said correction signal to an immediately previous flow reference signal,

generating a control valve position signal from said flow reference signal,

inputting said control valve position signal to valve control means for varying the effective orifice flow area in said flow control valve in response to a control valve position signal to change the flow rate through said flow control valve,

after a predetermined short time interval repeating the steps by first generating a new flow signal and subtracting it from the then current input signal so as to continually correct the flow rate through said flow control valve based on the difference between the actual flow rate through the flow control valve and the desired flow rate;

wherein the valve orifice signal is generated based on a second predetermined relationship using the then current control valve position signal.

8. A method as in claim 7 wherein said step of forming a flow reference signal includes the substeps of:

adding said correction signal to the immediately previous flow reference signal to form an intermediate flow reference signal, and

limiting the intermediate flow reference signal to a flow reference signal which reflects a change in flow rate through the flow control valve which does not exceed the maximum change in flow rate through the flow control valve that can be obtained within the predetermined short time interval.

9. A method for controlling the flow of a pressurized gas through a flow control valve in a pressurized gas conduit system in response to an electrical pressure input signal indicative of the desired pressure at a specific location in said gas conduit system comprised of the steps of:

generating a delta pressure signal in a feedback loop indicative of the negative of the actual effective pressure at said specific location in the pressurized gas conduit system,

adding said delta pressure signal from said pressure input signal to generate a pressure error signal which is indicative of the magnitude and direction of the difference between said pressure input signal and said actual effective pressure,

forming a pressure flow correction signal by processing said pressure error signal,

forming a flow reference signal by adding said pressure flow correction signal to the immediately previous flow reference signal,

generating a control valve position signal from said flow reference signal based on a first predetermined relationship,

inputting said control valve position signal to valve control means for varying the effective orifice flow area in said flow control valve in response to a control valve position signal to change the flow rate through said flow control valve,

after a predetermined short time interval repeating the steps by first generating a new delta pressure signal and subtracting it from the then current pressure input signal so as to continually correct the flow rate through said flow control valve based on the difference between the measured effective pressure at said specific location and the desired pressure.

10. A method as in claim 9 wherein said step of forming a pressure flow correction signal includes the substeps of:

processing said pressure error signal to form an intermediate pressure flow correction signal, and

limiting the intermediate pressure flow correction signal to a pressure flow correction signal whose maximum magnitude reflects a change in flow rate through the flow control valve which does not exceed the maximum change in flow rate through the flow control valve that can be obtained within the predetermined short time interval.

11. A method as in claim 9 wherein said step of forming a pressure flow correction signal includes the substeps of separately processing said pressure error signal and said delta pressure signal and combining the resulting signals to form a pressure flow correction signal.

12. A method for controlling the flow of a pressurized gas through a flow control valve in a pressurized gas conduit system in response to electrical volume and pressure input signals indicative of the desired flow rate and the desired pressure comprised of the steps of:

generating a flow signal in a feedback loop indicative of the actual flow rate of gas flow through said flow control valve,

subtracting said flow signal from said volume input signal to generate a correction signal which is indicative of the magnitude and direction of the difference between said flow signal and said volume input signal,

forming a volume flow reference signal by adding said correction signal to the immediately previous volume flow reference signal,

generating a delta pressure signal in a feedback loop indicative of the negative of the actual effective pressure at a specific location in the pressurized gas conduit system,

adding said delta pressure signal from said pressure input signal to generate a pressure error signal which is indicative of the magnitude and direction of the difference between said pressure input signal and said delta pressure signal,

forming a pressure flow correction signal by processing said pressure error signal,

forming a pressure flow reference signal by adding said pressure flow correction signal to the immediately previous pressure flow reference signal,

comparing said pressure flow reference signal to said volume flow reference signal and allowing the larger of the two signals to become the flow reference signal,

generating a control valve position signal from said flow reference signal based on a first predetermined relationship,

inputting said control valve position signal to valve control means for varying the effective orifice flow area in said flow control valve in response to a control valve position signal to change the flow rate through said flow control valve,

after a predetermined short time interval repeating the steps by first generating a new flow signal and subtracting it from the then current input signal so as to continually correct the flow rate through said flow control valve based on the difference between the actual flow rate through the flow control valve and the desired flow rate and the difference between the effective pressure at a predetermined position in the circuit and the desired pressure at that position, whichever demands the higher flow rate.

13. A flow control valve system for use in a pressurized gas system including:

input means for providing a volume input signal indicative of the flow rate desired through a portion of said pressurized gas system,

a flow control valve located within said portion of said pressurized gas system, including means for defining a flow control orifice and a movable valve element adapted to be moved so as to change the effective flow control orifice area,

valve element drive means for moving said valve element in response to a control valve position signal to said drive means,

gas source means for providing a source of pressurized gas to the input of said flow control valve,

flow rate means for determining the actual flow rate through said flow control valve and generating a flow signal indicative of said actual flow rate,

correction means for taking the difference between said flow signal and said volume input signal to generate a correction signal which is indicative of the magnitude and direction of the difference between said flow signal and said volume input signal,

loop means for forming a flow reference signal by adding said correction signal to the immediately previous flow reference signal which has been stored,

valve position means for generating a control valve position signal from said flow reference signal based on a first predetermined relationship and inputting said control valve position signal to said valve element drive means.

14. A flow control valve system as in claim 13 wherein said flow rate means includes

pressure means for measuring the pressures of the gas upstream and downstream of said flow control valve and generating pressure signals indicative thereof,

temperature means for measuring the temperature of the gas flowing through said flow control valve and generating a temperature signal indicative thereof,

orifice area means for converting said control valve position signal to a valve orifice signal indicative of the effective orifice area within said flow control valve, and

flow processing means for processing said pressure signals, temperature signal and valve orifice signal to form a signal indicative of the actual flow through said flow control valve.

15. A flow control valve system as in claim 14 wherein said orifice area means includes an orifice area look up table derived by empirical testing.

16. A flow control valve system as in claim 15 wherein said orifice area look up table has been derived by empirical testing of the specific flow control valve which is part of the specific system.

17. A flow control valve system as in claim 14 wherein said pressure means includes pressure transducers mounted on a common printed circuit board and conduits connecting said pressure transducers to their respective upstream and downstream positions in the pressurized gas system.

18. A flow control valve system as in claim 13 wherein said valve position means includes:

position conversion means for converting the flow reference signal to a valve reference signal in accordance with a first predetermined relationship,

position error means for comparing said valve reference signal to the current control valve position signal to form a valve position error signal

position limiting means for limiting the maximum magnitude of the valve position error signal to a predetermined maximum value, which value is based on the maximum correction to the change in orifice area that can be obtained within the time interval used in the sampling/correction, and

adding means for adding said limited valve position error signal to the control valve position signal to form a new control valve position signal.

19. A flow control valve system for use in a pressurized gas system including:

input means for providing a volume input signal indicative of the flow rate desired through a portion of said pressurized gas system,

a flow control valve located within said portion of said pressurized gas system, including means for defining a flow control orifice and a movable valve element adapted to be moved so as to change the effective flow control orifice area,

valve element drive means for moving said valve element in response to a control valve position signal to said drive means,

gas source means for providing a source of pressurized gas to the input of said flow control valve,

flow rate means for determining the actual flow rate through said flow control valve and generating a flow signal indicative of said actual flow rate, said flow rate means including

pressure means for measuring the pressures of the gas upstream and downstream of said flow control valve and generating pressure signals indicative thereof,

temperature means for measuring the temperature of the gas flowing through said flow control valve and generating a temperature signal indicative thereof,

orifice area means for converting said control valve position signal to a valve orifice signal indicative of the effective orifice area within said flow control valve, and

flow processing means for processing said pressure signals, temperature signal and valve orifice signal to form a signal indicative of the actual flow through said flow control valve,

correction means for taking the difference between said flow signal and said volume input signal to generate a correction signal which is indicative of the magnitude and direction of the difference between said flow signal and said volume input signal,

loop means for forming a flow reference signal by adding said correction signal to the immediately previous flow reference signal which has been stored,

valve position means for generating a control valve position signal from said flow reference signal and inputting said control valve position signal to said valve element drive means.

20. A flow control valve system as in claim 19 wherein said loop means includes:

means for forming an intermediate flow reference signal by adding said correction signal to the immediately previous flow reference signal, and

flow limiting means for limiting said intermediate flow reference signal to a flow reference signal which reflects a change in flow rate through said flow control valve which does not exceed the maximum change in flow rate through said flow control valve that can be obtained within a predetermined short time interval.

21. A flow control valve system for use in a pressurized gas system including:

input means for providing a pressure input signal indicative of a desired effective pressure at a specific location in said gas system,

a flow control valve located within said portion of said pressurized gas system, including means for defining a flow control orifice and a movable valve element adapted to be moved so as to change the effective flow control orifice area,

valve element drive means for moving said valve element in response to a control valve position signal to said drive means,

gas source means for providing a source of pressurized gas to the input of said flow control valve,

delta pressure means for generating a delta pressure signal in a feedback loop indicative of negative of the actual effective pressure at said specific location in the gas system,

pressure correction means for comparing said delta pressure signal with said pressure input signal to generate a pressure error signal,

pressure processing means for forming a pressure flow correction signal by processing said pressure error signal,

pressure reference means for forming a flow reference signal by adding said pressure flow correction signal to the immediately previous flow reference signal which has been stored, and

valve position means for generating a control valve position signal from said flow reference signal based on a first predetermined relationship and inputting said control valve position signal to said valve element drive means.

22. A flow control valve system for use in a pressurized gas system including:

first input means for providing a pressure input signal indicative of a desired effective pressure at a specific location in said gas system,

a flow control valve located within said portion of said pressurized gas system, including means for defining a flow control orifice and a movable valve element adapted to be moved so as to change the effective flow control orifice area,

valve element drive means for moving said valve element in response to a control valve position signal to said drive means,

gas source means for providing a source of pressurized gas to the input of said flow control valve,

delta pressure means for generating a delta pressure signal in a feedback loop indicative of the negative of the actual effective pressure at said specific location in the gas system,

pressure correction means for comparing said delta pressure signal with said pressure input signal to generate a pressure error signal,

pressure processing means for forming a pressure flow correction signal by processing said pressure error signal,

pressure reference means for forming a pressure flow reference signal by adding said pressure flow correction signal to the immediately previous pressure flow reference signal which has been stored,

second input means for providing a volume input signal indicative of the flow rate desired through a portion of said pressurized gas system,

flow rate means for determining the actual flow rate through said flow control valve and generating a flow signal indicative of said actual flow rate,

correction means for comparing said flow signal with said volume input signal to generate a correction signal which is indicative of the magnitude and direction of the difference between said flow signal and said volume input signal,

loop means for forming a volume flow reference signal by adding said correction signal to the immediately previous volume flow reference signal which has been stored,

pressure augmentation means for comparing said volume flow reference signal to said pressure flow reference signal and allowing the larger of the two signals to become the flow reference signal,

valve position means for generating a control valve position signal from said flow reference signal based on a first predetermined relationship and inputting said control valve position signal to said valve element drive means, and

valve position means for generating a control valve position signal from said flow reference signal based on a first predetermined relationship and inputting said control valve position signal to said valve element drive means.