Detection of Imminent Control Instability

• US 20120283982A1
• Filed: 05/05/2011
• Published: 11/08/2012
• Est. Priority Date: 05/05/2011
• Status: Active Grant

• Current Assignee: The Boeing Co.
• Original Assignee: The Boeing Co.
• Inventors: Englund, Norman J.
• Granted Patent: US 9,658,627 B2
• Time in Patent Office: Days
• US Class Current: 702/124
• 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 a stimulus to an object, the system providing a signal that represents a parameter indicating oscillation of the object while the stimulus is being applied to the object, the method comprising:

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.

2. The method of claim 1, wherein only the maximum amplitude and corresponding frequency content are monitored and used to determine whether control instability is imminent.

3. The method of claim 1, wherein the dominant tone is a multiple of driving frequency of the system.

4. The method of claim 3, wherein oscillations at the driving frequency are ignored.

5. The method of claim 1, wherein energy of peaks of the dominant tone and harmonics of the dominant tone are summed, and the sum is compared to a threshold to determine whether control instability is imminent.

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

7. The method of claim 1, wherein taking the action includes adjusting gain of the control.

8. The method of claim 1, further comprising simultaneously analyzing different spectral bands, and selectively adjusting control parameters that would otherwise tend to trigger oscillation modes at specific frequencies.

9. The method of claim 8, 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 a high frequency component of the control signal, integral gain and percent contribution are adjusted automatically in response to a lingering peak of a low frequency component of the control signal, and proportional gain is adjusted in response to intermediate frequency components.

10. The method of claim 9, wherein the adjustment to the proportional gain is based on the absolute values of control signal oscillations in real time.

11. The method of claim 8, 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.

12. The method of claim 8, wherein the control uses a compensation filter to adjust phase shift in a specific spectral band.

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 actuator 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 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 actuator includes lowering control gains before other actuators are driven into oscillation.

16. A method comprising:

using an effector to apply a stimulus to an object;

generating a signal representing a parameter that indicates oscillation 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 effector for applying a stimulus to an object;

a sensor for measuring a parameter indicating oscillation 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 effector 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 effector for applying a stimulus to an object;

a sensor for measuring a parameter indicating oscillation of the object while the stimulus is being applied to the object;

a first control having adjustable 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.