Real-world problems motivate engineering leadership: Our clients must overcome real-world challenges and constraints in life test and operational maintenance. Therefore Ops A La Carte has invented a practical new technology, using a "Leading Indicator", and a patent is pending. To strengthen your engineering and your product, Ops can provide you with engineering leadership skills and services.
Leading Indicators can improve common challenges and constraints:
- There are too few specimens and too little time available for life testing.
- For a life test to be meaningful, the acceleration must be mild.
- Life testing results are too late to improve product development.
- Maintenance is too expensive and too disruptive.
- Maintenance ought to be based on the real-time status of each specific unit.
- By contrast, engineering methods typically describe the average status of a population of similar units in similar operation.
Leading Indicators to provide advance warning: For some degradation mechanisms, there are "Leading Indicators" (L.I.'s). These can provide nearly real-time measurement of wear and fatigue, and thus provide advance warning for future failure.
In an electro-mechanical rotary system, Vibration Spectrum Analysis (VSA) uses an accelerometer to directly measure mechanical vibrations. Motor Current Spectrum Analysis (MCSA) measures fluctuations in the motor current. These correspond to vibrations in the drive train and mechanical load. VSA and MCSA each start with a wide-band time-domain signal. This is transformed into a frequency spectrum. This can measure simultaneously but separately the vibrations for each bearing, shaft, wheel, fan, pump, belt, gear, lead-screw, motor, frame, structure and more. VSA and MSA are shown in Fig 1 below.
Often each vibration mode has a distinct spectral peak, and its height is related to the degradation. In many cases, these measurements provide advance indication of future failures. Thus these are Leading Indicators.
This example is directly applicable to electro-mechanical rotary systems in many products. More generally, there are analogous techniques for wear, fatigue and future failure involving electrical and electronic hardware.
For a rotary mechanical system, Vibration Spectrum Analysis (VSA) uses an accelerometer and signal analyzer to measure and to analyze mechanical vibrations. For an electro-mechanical rotary system, Motor Current Spectrum Analysis (MCSA) measures fluctuations in the power current into the motor. These correspond closely to vibrations in the motor, drive train and load.
VSA and MCSA each transform the signal from time-domain to frequency-domain. This frequency filtering helps to separate, to identify, and to measure many different vibration modes. Thus the vibration of each and every physical item labeled above can be measured separately but simultaneously. VSA and MCSA are well known and very useful in maintenance engineering and mechanical engineering.
Leading Indicators to improve Accelerated Life Testing: An accelerated life test should use a L.I. together with exaggerated stress. This can provide earlier feedback, more informative feedback. These enable better product engineering, hence better product quality and reliability. Also earlier feedback enables stronger reduction ("acceleration") in time required for accelerated testing. (A patent is pending.)
During early system development, there is an accelerated life test of a sub-system vulnerable to degradation. Simultaneously, the L.I. is measured. This observes the relation between the measured L.I. and failure for this mechanism. This validates and calibrates this L.I as a Leading Indicator for this failure mechanism.
Later, when a more complete system becomes available, it is life-tested using exaggerated stress and L.I. measurement. Often this provides engineering feedback that is more informative and considerably faster, compared to classical life testing.
Furthermore, this L.I. measurement plus L.I. calibration predicts the time until future failure due to this degradation mechanism. Often this prediction can be done considerably before manifest failure actually occurs. This "prognostication" is a new way to reduce ("accelerate") the time required for life test. Also, this new factor multiplies the time-reduction factor due to exaggerated stress during accelerated life test. This is shown in Fig 3. This enables accelerated life tests to have stronger time reduction but also to correspond to normal operation and normal failures.
These better accelerated life tests can be combined with Early Reliability Test (ERT) tactics, as described recently in OALC newsletter issue Summer 2007. These provide better engineering feedback earlier in product development, and this facilitates better product engineering and better products, and also prevents problems during late development.
"Duration" is defined as operating time, adjusted for relative duty factor and relative speed. Fig 2A shows the observed L.I. value, failure rate and survival fraction as functions of duration since start. This is transformed into the calibration graph Fig 2B. This shows L.I. value, survival fraction and failure rate as functions of duration until failure peak.
A real-time L.I. measurement and its change rate enable prediction of future L.I. measurements. Combined with calibration Fig 2B, this can enable prediction of the time until future failure. This is called "prognostication".
Exaggerated stress reduces (accelerates) test-time until manifest failure. A Leading Indicator reduces (accelerates) test-time until prognostication of future failure. Accelerated life testing should simultaneously use both L.I. measurement and exaggerated stress. A patent is pending. In some cases, the degradation mechanism is one-dimensional. Therefore time-reduction (acceleration) factors combine by multiplication. This can be quite useful as shown in Figure 3 below.
TotalTimeReduction = LeadingIndicatorFactor * ExaggeratedStressFactor = (1/2.5) * (1/2) = (1/5).
In other cases, the leverage may be even more useful: (1/2.5) *(1/8) = (1/20)
Leading Indicators to improve Operational Maintenance: For system operation with maintenance, a L.I. can be very useful. L.I. measurement provides real-time observation of wear and fatigue. Combined with the L.I. calibration described above, this also provides real-time prediction of lead time until future failure. This is sometimes called "prognostication".
This enables "predictive maintenance". This skips devices that are far from failure. This selects and services only devices predicted to fail. However this provides considerable lead time, and thus enables maintenance service when it is most convenient and least disruptive. This reduces maintenance costs for hardware, labor and disruption. Even so, this enables improved overall reliability.
Invitation: This describes just a few examples out of many. For example, we already have good solutions for fans and diverse rotary electro-mechanical sub-systems. Also we have other solutions: for degradation of a Printed Wire Board (PWB); for degradation in electronic packages; and lots more.
Please tell us about your real-world problem. We probably can provide a suitable L.I., plus related technology and technical services. Even if your product is unique and test acceleration is difficult, we are interested in collaborating.
Leading Indicator methods offer practical but leading edge technology. Using this, we can help your team to transcend prior challenges and constraints in reliability engineering, and thus provide more competitive products.
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