DEGRADED ACTUATOR DETECTION

• US 20100286959A1
• Filed: 12/28/2007
• Published: 11/11/2010
• Est. Priority Date: 12/28/2007
• Status: Active Grant

• Current Assignee: Rtx Corporation
• Original Assignee: United Technologies Corporation (Rtx Corporation)
• Inventors: Johnson, Christopher A., Novis, Ari
• Granted Patent: US 7,970,583 B2
• Time in Patent Office: Days
• US Class Current: 702/183
• CPC Class Codes: F15B 15/2815 Position sensing, i.e. means for continuous measurement of position, e.g. LVDT
• CPC Class Codes: F15B 19/005 Fault detection or monitoring
• CPC Class Codes: G05B 23/0235 based on a comparison with predetermined threshold or range, e.g. "classical methods", carried out during normal operation; threshold adaptation or choice; when or how to compare with the threshold

Abstract

An actuator control system is disclosed that includes an actuator continuously movable between multiple positions. The controller is configured to command the actuator to a desired actuator position and to apply the command to an actuator model. The controller is configured to compare the modeled and actual actuator positions to determine if the position difference exceeds a fault detection accommodation limit and if the position difference is within a band that is different than the fault detection accommodation limit. The controller is configured to calculate a threshold, which is based upon an estimated load on the actuator. The controller is configured to calculate a band comprised of the threshold applied to the modeled position and to determine if the actual actuator position is within the calculated band. The threshold is calculated at regular intervals, and a fault is declared if the actual actuator position is outside the band for a number of consecutive intervals.

Claims

1. A method of detecting a degraded actuator comprising the steps of:

a) commanding an actuator to a desired actuator position;

b) detecting an actual actuator position of the actuator;

c) comparing the desired and actual actuator positions to determine if the actual actuator position exceeds a fault detection accommodation limit;

d) comparing the desired and actual actuator positions to determine if the actual actuator position is within a band that is different than the fault detection accommodation limit;

e) calculating a threshold at a regular interval based upon an estimated load on the actuator;

f) applying the threshold to adjust the band; and

g) determining if the actual actuator position is within the adjusted band.

2. The method according to claim 1 comprising the step of applying an actuator model to the desired actuator position prior to the comparing steps to produce an expected actuator position, the comparing steps including comparing the expected and actual actuator positions.

3. The method according to claim 1, wherein the band includes upper and lower bands.

4. The method according to claim 1 comprising the step of triggering a first fault if the fault detection accommodation limit is exceeded, and commanding a system accommodation in response to the first fault.

5. The method according to claim 1 comprising the step of repeating steps e)-g) for a predetermined number of events.

6. The method according to claim 5 comprising the step of triggering a second fault if the actual actuator position is outside the adjusted band for the predetermined number of events.

7. The method according to claim 6, wherein the predetermined number of events is a consecutive number of events.

8. The method according to claim 1 comprising the step of determining actuator load by referencing the actual actuator position relative to an actuator load model and at least one of engine and aircraft parameters.

9. The method according to claim 8, wherein step e) includes multiplying the time interval and the actuator load to produce a maximum distance.

10. The method according to claim 9, wherein step e) includes multiplying an allowable actuator degradation threshold and the maximum distance.

11. The method according to claim 1, wherein the actuator includes an actuator null shift, and step e) includes dividing the actuator null shift by the actuator driver gain to produce a position offset.

12. The method according to claim 2, wherein the actuator model is based upon a first order system producing an error in the expected actuator position, and step e) includes providing a dynamic compensation constant to reduce the error.

13. The method according to claim 1, wherein step e) includes summing transient, steady-state and dynamic elements to produce the threshold.

14. The method according to claim 13, wherein the transient element includes the actuator load multiplied by the time interval.

15. The method according to claim 14, wherein the actuator includes an actuator null shift, and the steady-state element includes dividing the actuator null shift by the actuator gain.

16. The method according to claim 15 comprising the step of applying an actuator model to the desired actuator position prior to the comparing steps to produce an expected actuator position, the comparing steps including comparing the expected and actual actuator positions, wherein the actuator model is based upon a first order system producing an error in the expected actuator position, and wherein the dynamic element includes providing a dynamic compensation to reduce the error.

17. An actuator control system comprising:

an actuator movable between multiple positions;

a position sensor configured to detect the multiple positions, which includes an actual actuator position;

a controller in communication with the actuator and the position sensor, the controller configured to command the actuator to a desired actuator position, wherein the controller is configured to compare the desired and actual actuator positions to determine if the actual actuator position exceeds a fault detection accommodation limit and if the actual actuator position is within a band that is different than the fault detection accommodation limit, wherein the controller is configured to calculate a threshold if the actual actuator position is within the band, the calculation based upon an actuator load on the actuator, and wherein the controller is configured to apply the threshold to adjust the band and determine if the actual actuator position is within the adjusted band.