reliabilitySurvivalModel

Probabilistic failure-time model for estimating remaining useful life

Description

Use reliabilitySurvivalModel to estimate the remaining useful life (RUL) of a component using a probability distribution of component failure times. Reliability survival models are useful when the only data you have are the failure times for an ensemble of similar components, such as multiple machines manufactured to the same specifications.

To configure a reliabilitySurvivalModel object for a specific type of component, use fit, which estimates the probability distribution coefficients from a collection of failure-time data. Once you configure the parameters of your reliability survival model, you can then predict the remaining useful life of similar components using predictRUL. For a basic example illustrating RUL prediction, see Update RUL Prediction as Data Arrives.

For general information on predicting remaining useful life, see Models for Predicting Remaining Useful Life.

Creation

Syntax

mdl = reliabilitySurvivalModel

mdl = reliabilitySurvivalModel(distribution)

mdl = reliabilitySurvivalModel(initModel)

mdl = reliabilitySurvivalModel(___,Name,Value)

Description

mdl = reliabilitySurvivalModel creates a reliability survival model for estimating RUL model that uses a Weibull distribution and initializes the model with default settings.

mdl = reliabilitySurvivalModel(distribution) creates a reliability survival model that uses the specified probability distribution function and sets the Distribution property of the model.

mdl = reliabilitySurvivalModel(initModel) creates a reliability survival model and initializes the model parameters using an existing reliabilitySurvivalModel object initModel.

mdl = reliabilitySurvivalModel(___,Name,Value) specifies user-settable model properties using name-value pairs. For example, reliabilitySurvivalModel('LifeTimeUnit',"days") creates a reliability survival model that uses days as a lifetime unit. You can specify multiple name-value pairs. Enclose each property name in quotes.

Input Arguments

initModel — Reliability survival model

reliabilitySurvivalModel object

Reliability survival model, specified as a reliabilitySurvivalModel object.

Properties

Distribution — Probability distribution function

"Weibull" (default) | "Normal" | "Poisson" | "Kernel" | "Rayleigh" | "Gamma" | ...

Probability distribution function used to model the lifetime distribution, specified as one of the following:

Distribution String	Distribution Object
"BirnbaumSaunders"	BirnbaumSaundersDistribution
"Exponential"	ExponentialDistribution
"Gamma"	GammaDistribution
"GeneralizedPareto"	GeneralizedParetoDistribution
"HalfNormal"	HalfNormalDistribution
"InverseGaussian"	InverseGaussianDistribution
"Kernel"	KernelDistribution
"Logistic"	LogisticDistribution
"Loglogistic"	LoglogisticDistribution
"Lognormal"	LognormalDistribution
"Nakagami"	NakagamiDistribution
"Normal"	NormalDistribution
"Poisson"	PoissonDistribution
"Rayleigh"	RayleighDistribution
"Stable"	StableDistribution
"Weibull"	WeibullDistribution

To configure the parameters of the probability distribution function, use the fit function.

ParameterValues — Distribution coefficients

Read-only: vector

This property is read-only.

Distribution coefficients estimated by the fit function, specified as a vector. For more information on the coefficients of each distribution function, see the corresponding distribution object listed in Distribution. For more information on model fitting, see fitdist.

ParameterCovariance — Covariance of the distribution coefficients

Read-only: array

This property is read-only.

Covariance of the distribution coefficients estimated by the fit function, specified as a positive array with size equal to the number of coefficients. For more information on the coefficients of each distribution function, see the corresponding distribution object listed in Distribution.

ParameterNames — Distribution coefficient names

Read-only: string array

This property is read-only.

Distribution coefficient names assigned when the model is trained using the fit function, specified as string array. For more information on the coefficients of each distribution function, see the corresponding distribution object listed in Distribution.

CensorVariable — Censor variable

"" (default) | string

Censor variable, specified as a string that contains a valid MATLAB^® variable name. The censor variable is a binary variable that indicates which life-time measurements in data are not end-of-life values.

CensorVariable must not match any of the strings in DataVariables or LifeTimeVariable.

You can specify CensorVariable:

• Using a name-value pair when you create the model

• As an argument when you call the fit function

• Using dot notation after model creation

LifeTimeVariable — Lifetime variable

"" (default) | string

Lifetime variable, specified as a string that contains a valid MATLAB variable name. For survival models, the lifetime variable contains the historical life span measurements of components.

You can specify LifeTimeVariable:

• Using a name-value pair when you create the model

• As an argument when you call the fit function

• Manually using dot notation

LifeTimeUnit — Lifetime variable units

"" (default) | string

Lifetime variable units, specified as a string.

The units of the lifetime variable do not need to be time-based. The life of the test component can be measured in terms of a usage variable, such as distance traveled (miles) or fuel consumed (gallons).

DataVariables — Data variables

"" (default)

Data variables, specified as an empty string. This property is ignored for reliability survival models.

UserData — Additional model information

[] (default) | any data type or format

Additional model information for bookkeeping purposes, specified as any data type or format. The model does not use this information.

You can specify UserData:

• Using a name-value pair when you create the model

• Using dot notation after model creation

Object Functions

predictRUL	Estimate remaining useful life for a test component
fit	Estimate parameters of remaining useful life model using historical data

Examples

Train Reliability Survival Model

Load training data.

load('reliabilityData.mat')

This data is a column vector of duration objects representing battery discharge times.

Create a reliability survival model with default settings.

mdl = reliabilitySurvivalModel;

Train the survival model using the training data.

fit(mdl,reliabilityData,"hours")

Predict RUL Using Reliability Survival Model and View PDF

Load training data.

load('reliabilityData.mat')

This data is a column vector of duration objects representing battery discharge times.

Create a reliability survival model, specifying the life time variable and life time units.

mdl = reliabilitySurvivalModel('LifeTimeVariable',"DischargeTime",'LifeTimeUnit',"hours");

Train the survival model using the training data.

fit(mdl,reliabilityData)

Predict the life span of a new component, and obtain the probability distribution function for the estimate.

[estRUL,ciRUL,pdfRUL] = predictRUL(mdl);

Plot the probability distribution.

bar(pdfRUL.RUL,pdfRUL.ProbabilityDensity)
xlabel('Remaining useful life (hours)')
xlim(hours([40 90]))

Improve the distribution view by providing the number of bins and bin size for the prediction.

[estRUL,ciRUL,pdfRUL] = predictRUL(mdl,'BinSize',0.5,'NumBins',500);
bar(pdfRUL.RUL,pdfRUL.ProbabilityDensity)
xlabel('Remaining useful life (hours)')
xlim(hours([40 90]))

Predict the RUL for a component that has been operating for 50 hours.

[estRUL,ciRUL,pdfRUL] = predictRUL(mdl,hours(50),'BinSize',0.5,'NumBins',500);
bar(pdfRUL.RUL,pdfRUL.ProbabilityDensity)
xlabel('Remaining useful life (hours)')
xlim(hours([0 40]))

Extended Capabilities

C/C++ Code Generation

Generate C and C++ code using MATLAB® Coder™.

Usage notes and limitations:

• The predictRUL command supports code generation with MATLAB Coder™ for this RUL model type. Before generating code that uses this model, you must save the model using saveRULModelForCoder. For an example, see Generate Code for Predicting Remaining Useful Life.

• For a covariateSurvivalModel, you cannot generate code for predictRUL using covariate data specified as string or character-vector values in table or timetable form. Instead, convert the string or character-vector data to a different data type, or delete the data from the table.

• In addition to the read-only properties, you cannot change the following properties of survival models at run time:

  • LifeTimeVariable

  • LifeTimeUnit

  • DataVariables

  • CensorVariable

  • EncodedVariables (covariateSurvivalModel only)

  • EncodingMethod (covariateSurvivalModel only)

• See predictRUL for additional limitations on code generation.

Version History

Introduced in R2018a