Reliability model generator

• US 5,014,220 A
• Filed: 09/06/1988
• Issued: 05/07/1991
• Est. Priority Date: 09/06/1988
• Status: Expired due to Fees

• Current Assignee: The Boeing Co.
• Original Assignee: The Boeing Co.
• Inventors: Cohen, Gerald C., McMann, Catherine M.
• Primary Examiner(s): Gruber, Felix D.
• Application Number:
  US07/241,540
• Time in Patent Office: 973 Days
• Field of Search: 364/186, 364/187, 364/188, 364/189, 364/513, 364/578, 364/200, 364/900
• US Class Current: 706/45
• CPC Class Codes: G06F 11/008 Reliability or availability analysis
• CPC Class Codes: G06F 11/2257 using expert systems
• CPC Class Codes: Y10S 706/911 Nonmedical diagnostics
• CPC Class Codes: Y10S 706/913 Vehicle or aerospace

Abstract

An improved method and system for automatically generating reliability models for use with a reliability evaluation tool is described. The reliability model generator of the present invention includes means for storing a plurality of low level reliability models which represent the reliability characteristics for low level system components. In addition, the present invention includes means for defining the interconnection of the low level reliability models via a system architecture description. In accordance with the principles of the present invention, a reliability model for the entire system is automatically generated by aggregating the low level reliability models based on the system architecture description.

Claims

1. A computer system for generating reliability models comprising, in combination:

a first memory having stored therein a first knowledge base for storing a plurality of low level reliability models which represent the reliability characteristics for low level system components;

a second memory having stored therein a second knowledge base for storing definitions of the interrelationship of said low level models based on a desired system configuration; and

means for aggregating the low level reliability models stored in said first knowledge base into a single reliability model based on the system configuration definitions stored in said second knowledge base.

2. The computer system of claim 1 further including means for manually inputting reliability parameters into said first knowledge base said, reliability parameters corresponding to individual components;

and

means for automatically generating low level reliability models based on said user defined reliability parameters for individual components and for storing said low level reliability models in said first knowledge base.

3. A reliability model generator comprising a programmed computer, memory means for storing

a first knowledge base, said first knowledge base for defining a plurality of basic components in terms of a plurality of component input and output characteristics, failure modes and failure rates of said basic components wherein said output characteristics are affected by said failure modes, and further wherein said component characteristics describe component operation independent of any system configuration, said memory means for further storing

a second knowledge base, said second knowledge base for storing desired system configurations which define the interconnections of said basic components;

means for modifying the definitions stored in said first and second knowledge bases; and

means for automatically calculating the effect of a failed basic component on the operation of said desired system by aggregating said component definitions stored in said first knowledge base based on the interconnection definitions stored in said second knowledge base.

4. The reliability model generator of claim 3 wherein said means for modifying definitions comprises an interactive graphics based user interface.

5. A programmed computer system for generating reliability models comprising in combination:

first memory means for storing a plurality of component model definitions;

second memory means for storing definitions of the interrelationships of said components; and

means for mapping said component models into a global reliability model, wherein a component may comprise a plurality of subcomponents.

6. A method of automatically generating a reliability model of a system with a reliability model generator, said reliability model generator comprising a computer system having a memory, said memory storing a first knowledge base for encoding a function and a reliability model for each of a plurality of system components and said memory for further storing a second knowledge base for encoding a high level configuration of said system and a failure mode for said high level configuration, said method comprising the steps of:

identifying the intermediate subcomponents of said system components and the failure modes for each of said subcomponents which contribute to the failure modes of said system components;

identifying the lower level subcomponents of said intermediate level components and the failure modes of each said lower level subcomponents which contribute to the failure modes of said intermediate level components;

inputting a set of inputs from said intermediate levels component identified with said lower level components for each of said identified lower level components;

tracing the effects of all inputs through said lower level components to determine resulting output characteristics and transitions for possible failure modes of said lower level components for each operational state of said identified lower level components; and

aggregating failure mode states and input characteristic conditions of said intermediate and lower level components to produce a global reliability model for said high level system configuration.

7. The method of claim 6 wherein said step of defining said component models includes the step of automatically performing failure mode effect analysis on said components.

8. A method for generating a reliability model with a reliability model generator, said reliability model for use with a reliability analysis tool, said reliability model generator comprising a computer system having a memory said memory for storing a first knowledge base of encoding definitions of the function and reliability of a plurality of one or more high level components, said method comprising the steps of:

grouping said high level components into a set of subcomponents arranged in a hierarchical arrangement;

analyzing each set separately and identifying critical failure modes for each set;

combining failure modes of said subcomponents according to severity and common effects on said high level component to produce a composite model for each high level component; and

repeating steps a-c until a composite model for the highest level component in the system is produced.

9. A computer system for automatically generating a reliability model for use with a reliability analysis tool, comprising in combination, a first memory means for storing a first knowledge base encoding predefined knowledge of

a plurality of system components wherein each of said components has at least one input;

a second memory means for storing a second knowledge base encoding predefined knowledge of a predefined set of output characteristics and failure modes for each of said system components based on said inputs;

a third memory means for storing a third knowledge base encoding predefined knowledge of the interrelationship of said system components;

a fourth memory means for storing a fourth knowledge base encoding predefined knowledge of an output condition of a system being modeled; and

a knowledge base interpreter for interpreting said first, second, third, and fourth knowledge bases means for tracing through said components to determine which of said failure modes of said system components contributed to said system output condition.

10. A method of generating a reliability model for use with a reliability analysis tool, said reliability model generator comprising a computer system having a memory said memory for storing a first knowledge base for storing definitions of A method of automatically generating a reliability model for use with a reliability analysis tool,

local reliability models for each basic component in a system wherein each of said basic components provides a predetermined function expressed in terms of a sequence of operations mapping component inputs to outputs wherein said local reliability model defines the behavior of a component independent of any system configuration, said method comprising the steps of

defining a desired system configuration comprising the interrelationship of said basic components to define the structural characteristics of a system;

defining the failure modes and failure rates for each of said basic components; and

automatically calculating the effects of basic component failures on other components in the system to produce a global reliability model.

11. A method of generating a reliability mode, with a reliability model generator, said reliability model for use with a reliability analysis tool, said reliability model generator comprising a computer system having a memory, said memory for storing a first knowledge base for storing definitions of

a plurality of basic system components in terms of function, and output characteristic definitions said method comprising the steps of:

defining a plurality of intermediate level components wherein said intermediate level components comprise a plurality of intermediate or basic system components coupled in series or parallel in a predefined configuration;

defining a system based on component interconnectivity;

calculating the output characteristic definition for each of said intermediate level components by aggregating the output characteristic definitions of said basic system components which comprise said intermediate level components based on said component interconnectivity;

defining a global system model with said intermediate level components coupled in a predetermined configuration by aggregating the output characteristic definitions of said intermediate level components and eliminating overlaps between said output characteristic definitions of said intermediate level components to produce a global system output characteristic definition; and

calculating the effects of failures of lower level components on said global system model.

12. The method of claim 11 wherein input and output characteristics are used to represent the effects of component failure modes emanating to other components in the system.

13. The method of claim 11 wherein said step of determining the effects of failures of lower level components includes the step of determining the effects of corrupted inputs on component'"'"'s outputs regardless of inputted values.

14. The method of claim 11 wherein said step of defining a plurality of basic system components includes the step of defining the relationship between what is input to the component and the information that is produced by the component based on said input and known functions performed by said component.

15. The method of claim 11 wherein each of said components is mathematically defined by a series of statements separated by a semicolon to indicate sequential flow among statements wherein a plurality of clauses may be defined within a statement and further wherein each clause represents a condition under which component state changes.

16. The method of claim 15 wherein each clause is delineated by "|" and takes the form:

space="preserve" listing-type="equation">y=x|x>

z

where x, y and z comprise input or output variables.

17. The method of claim 16 wherein the basic system components are defined to allow the effects of input characteristics to be traced through the function to define output characteristics wherein said output characteristics become input characteristics for other components.

18. The method of claim 17 wherein rules define output characteristics of good, bad or nil for all possible input characteristics good, bad or nil based on predefined component functions and failure modes.

19. The method of claim 17 wherein logical rules define output characteristics of one, zero or data values based on predefined logical functions and failure modes.

20. The method of claim 11 wherein generic functions are defined to characterize nil-sensitive and non-nil-sensitive operations.

21. The method of claim 11 wherein failure modes are defined as a change in component'"'"'s outputs produced by a change in a component function representing degraded operation.

22. The method of claim 11, further including the step of automatically accounting for failure modes which do no affect system operation.

23. The method of claim 11, further including the step of accounting for failure modes wherein said system automatically compensates for said failure modes.