Detection of imminent control instability

• US 9,658,627 B2
• Filed: 05/05/2011
• Issued: 05/23/2017
• Est. Priority Date: 05/05/2011
• Status: Active Grant

• Current Assignee: The Boeing Co.
• Original Assignee: The Boeing Co.
• Inventors: Englund, Norman J.
• Primary Examiner(s): Everett, Christopher E
• Application Number:
  US13/102,043
• Publication Number:
  US 20120283982A1
• Time in Patent Office: 2,210 Days
• Field of Search: 700 33, 700 35, 700 37, 700 42, 700 54, 700 71, 700280
• CPC Class Codes: G05D 19/02 characterised by the use of electric means

Abstract

Imminent control instability is detected in a system that applies a stimulus to an object. The system provides a parameter signal that represents a system parameter indicating oscillation of the object while the stimulus is being applied to the object. The method comprises monitoring maximum amplitude of a dominant tone in a selected frequency band of the parameter signal; and taking an action to avoid imminent control instability if the maximum amplitude persists over a specified period of time.

Claims

1. A method of detecting imminent control instability in a system that applies stimulus to an object using an actuator, the method comprising:

receiving a signal from the system corresponding to linear oscillations and non-linear oscillations of the object while the stimulus is being applied to the object, the signal including a first frequency component corresponding to a driving frequency and a second frequency component having an amplitude that is lower than amplitude of the first frequency component;

monitoring maximum amplitude of the second frequency component; and

taking an action to avoid imminent control instability if the maximum amplitude of the second frequency component persists over a specified period of time.

2. The method of claim 1, wherein a frequency domain representation of the signal is analyzed to identify the second frequency component and at least one additional frequency component having an amplitude that is lower than the amplitude of the first frequency component, the method further comprising monitoring maximum amplitude of each additional component to determine whether control instability is imminent.

3. The method of claim 2, further comprising applying the monitoring of the second frequency component and the at least one additional frequency component to a control to avoid the imminent control instability.

4. The method of claim 3, wherein the second component and the at least one additional component includes a high frequency component, an intermediate frequency component, and a low frequency component, wherein the control is a proportional integral derivative (PID) control;

and wherein derivative gain of the control is adjusted automatically in response to a lingering peak of the high frequency component, integral gain and percent contribution are adjusted automatically in response to a lingering peak of the low frequency component, and proportional gain is adjusted in response to the intermediate frequency component.

5. The method of claim 4, wherein the adjustment to the proportional gain is based on the absolute values of real time oscillations in the signal.

6. The method of claim 3, wherein the control is a model reference adaptive control having parameters including convergence rate;

and wherein the convergence rate is lowered if the imminent instability is detected.

7. The method of claim 3, wherein the control uses a compensation filter to adjust phase shift in a specific spectral band.

8. The method of claim 1, wherein frequency of the second component is a multiple of frequency of the first component.

9. The method of claim 8, wherein the first frequency component is ignored.

10. The method of claim 1, wherein energy of peaks of the second frequency component and harmonics of the second frequency component are summed, and the sum is compared to a threshold to determine whether control instability is imminent.

11. The method of claim 1, wherein taking the action includes shutting down the system.

12. The method of claim 1, wherein taking the action includes adjusting gain of a control to avoid imminent control instability.

13. The method of claim 1, wherein taking the action includes controlling power to cutter and feed motors to avoid instabilities during machining of a part.

14. The method of claim 1, wherein force is applied to different regions of the object by a plurality of force actuators;

wherein parameter signals are generated for the different regions; and

wherein each force actuator is independently controlled by monitoring maximum amplitude of the second frequency component in a selected frequency band of the corresponding parameter signal; and

taking an action to avoid imminent control instability if the maximum amplitude persists over a specified period of time.

15. The method of claim 14, wherein the object is an aircraft wing having a control surface, wherein the force actuators apply force to the wing during testing, and wherein taking action on an offending force actuator includes lowering control gains before other force actuators are driven into oscillation.

16. A method comprising:

using an actuator to apply a stimulus to an object;

generating a parameter signal representing linear oscillations and non-linear oscillations of the object while the stimulus is being applied to the object;

monitoring maximum amplitude of a dominant tone in each of a plurality of different frequency bands of the parameter signal; and

selectively adjusting control parameters that would otherwise tend to trigger oscillation modes at specific frequencies.

17. A system comprising:

an actuator for applying a stimulus to an object;

a sensor for measuring linear oscillations and non-linear oscillations of the object while the stimulus is being applied to the object; and

a control for monitoring maximum amplitude of a dominant tone in a selected frequency band of the parameter signal, and taking an action to avoid imminent control instability if the maximum amplitude persists over a specified period of time.

18. The system of claim 17, wherein the actuator and the control comprise a plurality of channels, each channel including a force actuator and an actuator control;

wherein force is applied to different regions of the object by the channels;

wherein parameter signals are generated for the different regions, and wherein each channel is independently controlled by monitoring maximum amplitude of a dominant tone in a selected frequency band of the corresponding parameter signal; and

taking an action to avoid imminent control instability if the maximum amplitude exceeds a threshold over a specified period of time.

19. The system of claim 18, wherein the object is an aircraft wing or a control surface, wherein the force actuators operate on different regions of the wing or the control surface during testing, and wherein gain is lowered in an actuator control of an offending channel before the other channels are driven into oscillation.

20. A system comprising:

an actuator for applying a stimulus to an object;

a sensor for measuring a parameter corresponding to linear oscillations and non-linear oscillations of the object while the stimulus is being applied to the object;

a first control having adjustable control parameters that tend to trigger oscillation modes at specific frequencies; and

a second control, responsive to the sensor, for determining maximum amplitude of a dominant tone in each of a plurality of frequency bands of the measured parameter; and

automatically adjusting those parameters so as not to trigger those oscillation modes at the specific frequencies.