GB2234353A

GB2234353A - Incipient failure detector

Info

Publication number: GB2234353A
Application number: GB8917367A
Authority: GB
Inventors: James Ormond Beaumont
Original assignee: Individual
Current assignee: Individual
Priority date: 1989-07-28
Filing date: 1989-07-28
Publication date: 1991-01-30
Anticipated expiration: 2009-07-28
Also published as: GB8917367D0; GB2234353B

Abstract

An apparatus provides warning of incipient failure of a physical system so as to allow corrective action to be taken to avoid serious failure. Indices of failure imminence are calculated, base upon measurements of system forcing functions and system responses. The calculated indices may be modified to allow for the effects of system operational parameters which are also measured. Said indices may be communicated to a human operator, or may be used directly to initiate corrective action. A specific example is given of the application of the apparatus to detecting imminent failure of the skin of an aircraft, using sensors measuring the difference between internal and external pressure (the forcing function) and strain gauges, vibration sensors etc. to detect the response. <IMAGE>

Description

INCIPIENT FAILURE DETECTOR This invention relates to an apparatus for the detection of incipient failure of physical systems to enable precursory warning before serious failure occurs.

Current preventive maintenance techniques include frequent inspections, tests, and measurements, particularly between periods of normal operation, in an attempt to detect flaws or abnormalities. Such procedures are unsatisfactory for three reasons: (1) they are expensive, (2) the flaws, if they exist, may be in inaccessible locations, making detection improbable, and (3) deterioration may progress at such a rate that failure occurs even though no flaw was detectable at the last previous inspection.

According to the present invention, which avoids failure of a physical system by early warning of incipient failure, there are provided: three groups of sensors for insitu sensing, during normal operation, of the system forcing function(s), the system response(s), and system operational parameters respectively, a signal processing means, a human interface means, and a recording means for recording both sensor data and processed data.

A specific embodiment of the invention, namely its application to detecting incipient failure of the skin of an aircraft, will now be described by way of example, with reference to the accompanying block diagram, Figure 1.

Referring to the diagram, the forcing function sensor consists of a differential pressure transducer measuring the difference between inside and outside air pressure. The skin response sensors consist of a multiplicity of strain gauges and contact microphones placed on the skin of the aircraft to measure strain and acoustic vibration. The operational parameter sensors consist of an airspeed indicator, a multiplicity of skin temperature sensors, a 3-axis accelerometer measuring surge, heave, and sway components of acceleration, engine power-setting sensors, an attitude sensor, and landing-gear strut compression sensors.In a preferred embodiment, the signal processor consists of a digital computer with analog-to-digital conversion means and analog signal pre-processing means appropriate to the various sensors; the human interface unit consists of a visual cathode ray tube display, an acoustic alarm device, and a keyboard; the recorder unit consists of a digital magnetic tape recorder.

In order to detect incipient failure of the skin before serious rupture occurs, the signal processor implements two distinct algorithms to detect (1) non-linear strain and/or non-elastic yield of the skin and (2) skin crack formation and/or fastener failure.

Non-linear strain is determined, for each gauge location, by continually calculating a modulus of elasticity by dividing the differential pressure by the strain. Elastic fatigue and plastic yield are determined by continually comparing the strain with previous values of strain measured at the same differential pressure. Skin crack formation and/or fastener (rivet, weld, or other bonding means) failure are detected by continually examining the acoustic power spectra from the several microphone devices for the frequency components characteristic of such events. The magnitude of each of these determinations (non-linearity, yield, crack formation, and fastener failure) is compared with pre-set limits, which may be modified by the user through the keyboard, to characterise it as normal, abnormal but not alarming, or alarming.These findings are displayed on the visual display screen and if one or more reach the alarming level, an audible alarm is sounded.

The simple algorithms presented in the previous paragraph describe the concept, and are adequate in some simple cases, but must be modified in a more general case to allow for the effects of temperature, airspeed, attitude, acceleration, power setting, and airborn status, as follows: 1. Each value of local skin strain is compensated for local skin temperature and also for the structural effects due to airspeed, attitude, and acceleration. A further compensation is made based upon whether the aircraft is airborn or on ground, as determined from the landing-gear strut compression.

2. The expected acoustic power spectrum for each of the microphone devices is modified to allow for effects of airspeed, attitude, engine power, and airborn or on-ground status.

In the foregoing description it has been assumed that the output of the incipient failure warning apparatus would be through the human interface means to a human being who would be responsible for taking ameliorative action, such as aborting the flight or decreasing cabin pressurization. While human intervention is considered prudent at the present state of the art, it is clear that it is not necessary, and ameliorative action could be taken automatically, under direct control of the signal processor, with or without human supervision.

The recorder is not essential to the incipient failure warning during the current flight, but it is used to build a signal library for each aircraft type, to be used for subsequent modification of the compensation algorithms and normal limits in order to enhance the discrimination between normal and abnormal signals.

While the present invention has been described with respect to detecting incipient failure of the skin of an aircraft, it should be clear that it is applicable to detecting incipient failure of any instrumentable physical system.

Claims

1. An apparatus for the detection of incipient failure of a physical system, comprising sensing means, signal processing means, and human interface means.

2. An apparatus as claimed in Claim 1, wherein sensing means are adapted for sensing system forcing functions, system responses, and system operational parameters.

3. An apparatus as claimed in Claim 1 or Claim 2, wherein the signal processing means implements algorithms to calculate indices of incipient failure probability from system forcing functions and system responses, compares these indices with adjustable pre-set norms, and alerts the operator accordingly through the human interface means.

4. An apparatus as claimed in Claim 3, wherein the calculated indices are modified to allow for the effect of the system operational parameters.

5. An apparatus as claimed in any of the above claims, wherein recording means are provided to record data from both the sensing means and the signal processing means.

6. An apparatus as claimed in Claim 3 or Claim 4, adapted to detecting incipient failure of the skin of an aircraft, wherein the means for sensing system forcing functions comprise a differential air-pressure sensor, the means for sensing system response comprise a multiplicity of strain gauges and microphone devices, and the means for sensing operational parameters comprise a multiplicity of skin temperature sensors, an airspeed sensor, a three-axis acceleration sensor, an engine powersetting sensor or sensors, an attitude sensor, and landing-gear strut compression sensors.

7. An apparatus as claimed in Claim 6, wherein indices of imminent failure probability are calculated from: non-elastic strain, determined by continually calculating moduli of elasticity from strain gauge and differential pressure sensor data; elastic fatigue and/or plastic yield, determined by comparing strain data with previous values measured at the same differential pressure; skin crack formation and/or fastener failure, determined from the acoustic power spectra from the several microphone devices.

8. An apparatus as claimed in Claim 7, wherein the algorithms for calculating the indices of imminent failure probability are modified to compensate for the effects of temperature, airspeed, attitude, acceleration, engine power, and airborn or onground status

9. An apparatus as claimed in any of the above claims, wherein the human interface is either replaced or augmented by automatic control means enabling the signal processor to take direct ameliorative action.