Functional redundancy control system

What is claimed is:

1. A function redundancy control system for an apparatus including a plurality of elements controllable by a control means, each of said plurality of controllable elements having ability to perform a predetermined function inherently required in the apparatus, said system comprising:

retrieving means for determining whether controllable elements of said plurality are controllable to perform a potential function which is substantially the same as a predetermined inherent function of another one of said plurality of controllable elements and which potential function is not ordinarily performed, and for identifying controllable elements having said potential function; and

redundancy system control means for causing one of said controllable elements to perform the potential function thereof after said one controllable element has been identified by said retrieving means.

2. The function redundancy system control system according to claim 1, wherein said retrieving means comprises:

storing means for storing data describing at least a part of an apparatus, which is a control object, in a predetermined relational representation using functions, behaviors and states, said representation defining a FBS diagram;

FBS retrieving means for retrieving data indicative of present potential functions on the basis of the FBS diagram stored in the storing means; and

means for determining a potential function to be performed on the basis of retrieved data from said FBS retrieving means.

3. The function redundancy system control system according to claim 2, wherein

said FBS diagram clearly represents a many-to-many correspondence between a plurality of functions and a plurality of behaviors.

4. The function redundancy system control system according to claim 1, which further comprises diagnosing means for diagnosing a fault in the apparatus which is a control object,

said retrieving means being operated when it is judged by said diagnosing means that a fault occurs in the apparatus which is a control object.

5. The function redundancy system control system according to claim 3, which further comprises diagnosing means for diagnosing a fault in the apparatus which is a control object,

said retrieving means being operated when it is judged by said diagnosing means that a fault occurs in the apparatus which is a control object.

6. A function redundancy system control system comprising:

storing means for storing data describing at least a part of an apparatus in predetermined relational representation using function, behaviors and states, said representation defining a FBS diagram, said data representing controllable elements of the apparatus, which elements perform inherent functions required during normal operation of the apparatus, at least some of the controllable elements being controllable, during redundancy operation of the apparatus, to perform a substitutable function that is substantially the same as the inherent function of other controllable elements of the apparatus;

retrieving means for retrieving a substitutable function which can be substituted for a particular inherent function of a certain controllable element in the apparatus on the basis of the FBS diagram stored in the storing means; and

redundancy system control means for operating the apparatus by causing one of said at least some controllable elements to perform the substitutable function retrieved by said retrieving means.

7. The function redundancy system control system according to claim 6, wherein

said FBS diagram clearly represents a many-to-many correspondence between a plurality of functions and a plurality of behaviors.

8. The function redundancy system control system according to claim 7, which further comprises diagnosing means for diagnosing a fault in the apparatus which is a control object,

said retrieving means being operated when it is judged by said diagnosing means that a fault occurs in the apparatus which is a control object.

9. The function redundancy system control system according to claim 8, wherein said diagnosing means comprises:

storing means for storing qualitative data representing the apparatus which is a control object as a combination of a plurality of elements including said controllable elements and qualitatively representing behaviors and attributes of the respective elements and the combinational relationship among the elements using parameters;

operating means for diagnosing an operating state when the apparatus which is a control object is operated by said redundancy system control means, for simulating operation of the apparatus on the basis of the qualitative data stored in said storing means when it is judged that the operating state is not normal, and for obtaining an adjusting work plan which can be carried out by adjusting a parameter on the basis of the results of the simulation; and

parameter type state adjusting means for executing the adjusting work plan obtained by the operating means.

10. The functional redundancy system control system according to claim 8, wherein said diagnosing means comprises:

storing means storing qualitative data representing functional means in said apparatus as a combination of a plurality of elements including said controllable elements and qualitatively representing behaviors and attributes of the respective elements and the combination relationship among the elements using parameters;

operating means for obtaining a fault repair work plan which can be performed by changing a parameter on the basis of qualitative data stored in the storing means when it is judged that a fault occurs in the apparatus which is a control object;

parameter type fault repair means for executing the fault repair work plan obtained by the operating means; and

means for outputting, when the fault in the apparatus which is a control object cannot be repaired by executing the fault repair work plan by the parameter type fault repair means, the occurrence of the fault.

11. The function redundancy system control system according to claim 10, wherein said diagnosing means further comprises:

operating means for diagnosing an operation state when the apparatus which is a control object is operated by said redundancy system control system, for simulating operation of said functional means in said apparatus on the basis of qualitative data stored in said storing means when it is judged that the operating state is not normal, and for obtaining an adjusting work plan which can be carried out by adjusting a parameter on the basis of the results of the simulation; and

parameter type state adjusting means for executing the adjusting work plan obtained by the operating means.

12. An apparatus having a functional redundancy system and being operable in an ordinary operation sequence and a redundancy operation sequence, said apparatus comprising:

control means; and

a plurality of elements controlled by the control means,

each of the plurality of controlled elements being controlled, during the ordinary operation sequence of said apparatus, by the control means to perform only a predetermined inherent function that is performed thereby and

at least one element of the plurality of controlled elements being controllable by the control means to perform a potential function which is substantially the same as the predetermined inherent function of another one of the controlled elements, and which is not ordinarily performed by the said at least one controlled element,

the control means including:

ordinary control means for operating the plurality of controlled elements in accordance with the ordinary operation sequence such that said plurality of controlled elements perform their inherent functions; and

redundancy system control means for operating the said at least one controlled element in accordance with the redundancy operation sequence which is different from said ordinary operation sequence such that the inherent function of the said another one of the controlled elements is replaced by the potential function performed by the said at least one controlled element.

13. The apparatus having a functional redundancy system according to claim 12, wherein

the said another one of the controlled elements can designate a predetermined plurality of said controlled elements, and

said redundancy system control means performs operation in accordance with a predetermined sequence out of a predetermined plurality of redundancy operation sequences depending on which of the controlled elements has been designated by the said another one of the controlled elements.

14. The apparatus having a functional redundancy system according to claim 13, which comprises

a ROM storing said predetermined plurality of sequences.

15. An apparatus having a functional redundancy system and being operable in an ordinary operation sequence and a redundancy operation sequence, said apparatus comprising:

functional means, said functional means including

a plurality of controlled elements, each controlled element of said plurality having a predetermined inherent function that is performed thereby during the ordinary operation sequence of said apparatus, and

at least one controlled element of said plurality having a potential function which is substantially the same as the predetermined inherent function of another one of the controlled elements and which is not ordinarily performed;

diagnosing means for making a diagnosis to judge whether or not a fault is present in said functional means;

ordinary control means for controlling said plurality of controlled elements in accordance with the ordinary operation sequence such that such plurality of controlled elements perform the inherent functions thereof when it is judged by said diagnosing means that no fault is present; and

redundancy system control means for controlling, when it is judged by said diagnosing means that a fault is present, a controlled element other than a controlled element which has failed in accordance with the redundancy operation sequence which is different from the ordinary operation sequence such that the inherent function of the controlled element which has failed is replaced by the potential function performed by another controlled element.

16. The apparatus having a functional redundancy system according to claim 15, wherein

said redundancy system control means performs a control operation in accordance with a predetermined sequence out of a predetermined plurality of redundancy control sequences to correspond to the type of a controlled element which has failed.

17. The apparatus having a functional redundancy system according to claim 16, which comprises

a ROM storing said predetermined plurality of sequences.

18. The apparatus having a functional redundancy system according to claim 15, wherein

said diagnosing means diagnoses, when a controlled element is controlled by said redundancy system control means, an operating state of the controlled element controlled by the redundancy control means.

19. The apparatus having a functional redundancy system according to claim 18, wherein said diagnosing means comprises:

storing means for storing qualitative data representing said functional means as a combination of a plurality of elements including said controlled elements and qualitatively representing behavior and attributes of the respective elements and the combinational relationship among the elements using parameters;

operating means for simulating, when a controlled element is controlled by said redundancy system control means, operation of the controlled element controlled by the redundancy system control means on the basis of qualitative data stored in said storing means when it is judged that an operating state of the controlled element is not normal, and for obtaining an adjusting work plan which can be carried out by adjusting a parameter on the basis of the results of the simulation; and

parameter type state adjusting means for executing the adjusting work plan obtained by the operating means.

20. The apparatus having a functional redundancy system according to claim 15, wherein said diagnosing means comprises:

storing means for storing qualitative data representing said functional means as a combination of a plurality of elements including said controlled elements and qualitatively representing behaviors and attributes of the respective elements and the combinational relationship among the elements using parameters;

operating means for obtaining, when it is judged that a fault occurs in said functional means, a fault repair work plan which can be performed by changing a parameter on the basis of the qualitative data stored in the storing means;

parameter type fault repairing means for executing the fault repair work plan obtained by the operating means; and

means for outputting, when the fault in the functional means cannot be repaired by executing the fault repair work plan by the parameter type fault repairing means, the occurrence of the fault.

21. The apparatus having a functional redundancy system according to claim 20, wherein said diagnosing means further comprises:

operating means for diagnosing, when a controlled element is controlled by said redundancy system control means, an operating state of the controlled element controlled by the redundancy system control means, for simulating operation of the controlled element on the basis of qualitative data stored in said storing means when it is judged that the operating states is not normal, and for obtaining an adjusting work plan which can be carried out by adjusting a parameter on the basis of the results of the simulation; and

parameter type state adjusting means for executing the adjusting work plan obtained by the operating means.

Description Submit all comments and votes

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a redundancy control system, and more particularly, to a machine or an apparatus comprising a functional redundancy control system.

"Functional redundancy" means "using a part which originally exists in an apparatus and making use of the part utilizing a potential function of the part as a substitute for another part".

2. Background of the Invention

At the present time machine civilization advances, failures in an apparatus system exert very great effects on society. Accordingly, various types of maintenance have been performed on the apparatus system.

The following three means have been generally considered for the maintenance on the apparatus system. Specifically:

1. High-reliability design: making such design so that no fault occurs in the apparatus system.

2. Preventive maintenance: preventing a fault from occurring in the apparatus system during the use.

3. Corrective maintenance: preventing, even if a fault occurs in the apparatus system, the fault from affecting the whole apparatus system to recover its function in a short period of time.

However, there are limitations of such concepts. First, as for the high-reliability design, there is a physical limitation of increase in quality of parts, and the cost of the apparatus is liable to suddenly rise. In addition, in considering redundant design for ensuring the reliability, the sudden rise in cost due to the size of the system cannot be ignored. Furthermore, in considering a fault tolerant design or as to preventive maintenance, fault expectation ability must be present. However, it is difficult to expect the fault as the apparatus system is complicated.

On the other hand, if the effect of the failures in the apparatus system is considered, it is actually very dangerous to consider only fail-safe and corrective maintenance.

Therefore, it is necessary to positively recognize the possibility that a fault occurs and consider measures taken to prevent, even if a fault occurs, the fault from exerting a functional effect.

DESCRIPTION OF THE PRIOR ART

As one of the measures taken to prevent, when a fault occurs, the fault from exerting a functional effect, it has been known that a redundancy system is provided to an apparatus.

The most common redundancy system is to prepare excess means having the same function, and this redundancy system is for the purpose of increasing the reliability of the whole apparatus. The redundancy system is actually realized by arranging a plurality of parts of the same type in parallel, which shall be referred to as "part redundancy". One example of the part redundancy is disclosed in, for example, Japanese Patent Laid-Open Gazette No. 11520/1988. The part redundancy is effective in which the larger the number of parts arranged in parallel is, the higher the reliability becomes. As a result, the weight and the cost of an apparatus system are increased. In addition, the apparatus system may, in some cases, be inversely complicated, thereby causing the reliability to be decreased.

Japanese Patent Laid-Open Gazette No. 110601/1990 discloses as another redundancy system a control system referred to as "coordination dispersion". A coordination dispersion control system disclosed in this gazette is a system in which when a fault occurs in a certain control device, a subsystem of a plant controlled by the control device is assigned so as to be placed under control of another suitable control device. Specifically, in a case where a system has a plurality of control devices, if a fault occurs in a certain control device, a task related to the control device which fails is assigned to the other control device in accordance with a predetermined sharing rule so that control carried out by the control device which fails is shared with the other control device. This coordination dispersion control system is effective as a redundancy system for a control device in a system comprising a plurality of control devices, but cannot be a redundancy system for apparatus parts controlled by the control device, that is, an apparatus system itself.

As described in the foregoing, the "part redundancy" out of the conventional redundancy systems is a redundancy system for an apparatus system itself (controlled parts). However, the "part redundancy" requires parts to be arranged in parallel so as to realize the redundancy system in addition to parts inherently required, so that it has several disadvantages. For example, the cost is increased, the weight is increased, and the construction becomes complicated. In addition, the "coordination dispersion" is a redundancy system for a control device and cannot be applied to a controlled device.

SUMMARY OF THE INVENTION

The present invention has been made from a point of view which is entirely different from the conventional redundancy system, and provides an image forming apparatus having a redundancy system based on a new concept of a functional redundancy system. That is, the present invention is completed on the basis of a new concept of designing such an apparatus as to make, even if a fault occurs, self-repair of the fault so that its function can be automatically recovered by reconstructing the structure in any method, that is, using functional redundancy.

An object of the present invention is to realize a so-called "softly broken apparatus" by constructing a self-repair apparatus based on functional redundancy.

The present invention provides an apparatus system comprising a functional redundancy system, which is characterized by comprising a plurality of function developing means, each of the function developing means being able to develop a predetermined function inherently required, retrieving means for retrieving, with respect to the plurality of function developing means, the presence or absence and the contents of a function which is different from the function inherently required and which each of the function developing means does not ordinarily develop but potentially has, and control means for developing a potential function retrieved by the retrieving means as required.

In the present invention, more redundancy can be given to an apparatus by increasing the minimum number of parts required using a potential function of a part which inherently performs another function by changing the configuration of a system at the time of occurrence of a fault. Specifically, when a fault occurs in an apparatus system, a lost function is recovered by utilizing a part which originally exists in the apparatus system and utilizing the existing part as a substitute for the part which fails. Such a concept is one type of stand-by redundancy in a functional sense. However, such a concept is new in that it has not any substitutes for the part which fails and utilizes a part inherently used for another purpose is utilized, and is a redundancy system which has not been conventionally known.

According to the present invention, the functional redundancy system is added to the apparatus system, thereby to make it possible to automatically recover the function by reconstructing the structure in any method even if a fault occurs. Therefore, it is possible to realize a so-called "softly broken apparatus", and to provide an apparatus system which is not functionally affected even if a fault occurs.

The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration for explaining the definition of "functional redundancy" taking as an example a driving system of an automobile;

FIG. 2 is a diagram showing, as one example of state description in an FBS diagram, the state description of a paperweight;

FIG. 3 is a diagram showing the relationship among functions, behaviors and states in an FBS diagram;

FIG. 4 is a diagram showing a method of writing development knowledge for a function "store electricity";

FIG. 5 is a diagram showing method of writing a function knowledge "store electricity" in a substantiated manner;

FIG. 6 is a diagram showing one example of an FBS diagram representing a function "charge" in an electrophotographic copying machine;

FIG. 7 is a diagram showing one example of an FBS diagram representing a function "transfer" in an electrophotographic copying machine;

FIG. 8 is a diagram for explaining a method of deriving candidates for a functional redundancy system;

FIG. 9 is a FBS diagram showing an example of a functional redundant design solution related to a function "charge a drum" derived in accordance with the method shown in FIG. 8;

FIG. 10 is a block diagram showing the basic construction of a self-repair apparatus having a functional redundancy system added thereto;

FIG. 11 is an illustration showing an energy transfer mechanism including an engine, an electricity generator, a battery and a starting motor of an automobile;

FIG. 12 is a flow chart showing fault repair control carried out by a computer 23 shown in FIG. 11;

FIG. 13 is a diagram showing a parameter model at the normal time in the construction shown in FIG. 11;

FIG. 14 is a diagram showing an example of display of an FBS diagram with respect to a function "generate electricity" stored in a memory of the computer in the construction shown in FIG. 11;

FIG. 15 is a diagram showing an example of display of an FBS diagram representing an engine starting system stored in the memory of the computer in the construction shown in FIG. 11;

FIG. 16 is a diagram obtained by modeling the FBS diagram with respect to the function "generate electricity" by simplifying an electricity generating system;

FIG. 17 is a diagram showing a function knowledge and development knowledges related to the function "generate electricity";

FIG. 18 is a diagram showing an FBS diagram representing a redundancy system of the function "generate electricity" derived in the construction shown in FIG. 11;

FIG. 19 is a diagram showing a parameter model in a case where the function "generate electricity" is replaced with a functional redundancy system using a starting motor in the construction shown in FIG. 11;

FIG. 20 is a diagram showing the control structure of an image forming mechanism in an electrophotographic copying machine;

FIG. 21 is a flow chart showing the outline of fault diagnosis and repair control in a computer shown in FIG. 20;

FIG. 22 is a diagram showing an FBS diagram of a charging functional portion simplified for convenience of illustration;

FIG. 23 is a diagram showing the contents of knowledge related to a function "charge" of a photosensitive drum and development knowledges;

FIG. 24 is a diagram for explaining structures and phenomena at the normal time of an objective model;

FIG. 25 is a diagram showing structures and phenomena of an objective model in a state where a principal charging phenomenon is developed by a transferring corona discharger when a fault occurs in a main charger;

FIG. 26 is a diagram showing an objective model in a case where a transferring corona discharger is used as a functional redundancy system using an FBS diagram;

FIG. 27 is a diagram showing an example of display representing the dependent relationship among all phenomena which may occur on a view network with respect to an image forming mechanism of a copying machine;

FIG. 28 is a diagram showing a qualitative timing chart at the normal time in an image forming mechanism;

FIG. 29 is a diagram for explaining a method of forming a qualitative sequence at the time of occurrence of a fault;

FIG. 30 is a diagram for explaining a method of forming a qualitative sequence at the time of a fault;

FIG. 31 is a diagram for explaining a method of forming a qualitative sequence at the time of occurrence of a fault; and

FIG. 32 is a diagram showing a qualitative timing chart at the time of occurrence of a fault in an image forming mechanism.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

1. Concept of "functional redundancy" and outline of self-repair apparatus using functional redundancy.

In this term, description is now made of the concept of "functional redundancy" in the present invention as well as an FBS diagram required to represent functional redundancy of an apparatus and utilize the same. In addition, description is made of a design method for giving functional redundancy to an apparatus and the outline of a self-repair apparatus having functional redundancy.

1-1. Definition of "functional redundancy"

"Functional redundancy" means making it possible to make use of a part which originally exists in an apparatus system utilizing a potential function of the part as a substitute for another part.

For example, an automobile with a manual transmission usually runs by engine power. When the engine is not operated, however, the automobile can move by a starting motor. This is an example in which redundancy is given without increasing the number of parts by altering the structure of a driving system to cause the starting motor to develop a potential function "move the body of an automobile" and cause the engine to develop a potential function "transmit a driving force".

Specifically, redundancy is given without increasing the number of parts by changing the construction shown in FIG. 1(a) to the construction shown in FIG. 1(b) in which a starting motor is a driving source for "moving the body of an automobile" and a crank-shaft for "transmitting a driving force" is utilized as the engine.

In this specification, thus giving redundancy utilizing a potential function is defined as "functional redundancy".

If the functional redundancy is compared with the conventional part redundancy, they respectively have characteristics and problems, as shown in Table 1.

TABLE 1 ______________________________________ Part Redundancy and Functional Redundancy ______________________________________ Part redundancy Characteristics Such "attribute maintenance" that a faulty attribute is replaced with the attribute of a redundant part. The reliability of a particular area is surely increased. Design and reliability prediction are easy. Problems Weight and cost are increased. It corresponds to only a fault predicted at the time of design. The reliability may be decreased by an increased complexity in an apparatus. Functional redundancy Characteristics Such "functional maintenance" that a lost function is replaced with a part performing another function. More redundancy can be added by increasing the minimum number of parts required. It corresponds flexibly to a fault by considering redundancy at a functional level. It corresponds to various faults including an unexpected fault. The apparatus does not hard fail. Problems A design method and a method of reliability prediction are not arranged yet. Necessity of function judgment and value judgment. ______________________________________

"Necessity of function judgment and value judgment" listed as a problem of the functional redundancy in Table 1 is as follows: In general, it is not necessarily easy to completely recover a lost function A by a functional redundancy system. However, it is possible to enhance the lost function A to some extent.

For example, in the above described example of the automobile, the automobile only develops a speed of at most 5 km/h when it runs by the starting motor. Accordingly, a function of running at high speed is not performed. In addition, there is a significant restriction on the running time by the starting motor.

In recovering the lost function A, however, judgment whether or not a user can be satisfied with the degree to which the function is developed depending on the functional redundancy system depends on the use conditions and is determined by the value judgment of a human being. In the above described example of the automobile, there is a concept that a user can be satisfied with such function development by considering that the running speed is not so much a problem provided that the automobile can run to a gas stand or an auto repair shop. Alternatively, there is also a concept that a user cannot be satisfied with such function development.

The above described value judgment is distinguished from the essence of the present invention, which shall be determined by a dialogue with a user.

The functional redundancy according to the present invention is particularly useful for an apparatus whose operation is controlled by a computer such as a mechatoronics machine. The reason for this is that in an apparatus whose operation is controlled by a computer, the construction of the apparatus can be altered by altering a control pattern on software, thereby to make it sufficiently possible to add a functional redundancy system to the apparatus.

The present invention is so adapted, as one example, that a designer previously establishes a functional redundancy system and a method of changing the structure thereof in an apparatus system at the time of designing the apparatus system and utilizes this functional redundancy system depending on the circumstances of a fault in the apparatus system.

1-2. Object representing method for representing function: FBS diagram

In order to construct an apparatus system having a functional redundancy system incorporated therein, that is, a functional redundancy apparatus system, an apparatus must be represented in the form including functions.

In the present invention, an apparatus is represented by an FBS (Function-Behavior-State) diagram. Specifically, the apparatus is represented by a diagram comprising functions, behaviors and states. The behaviors and the states are represented on the basis of the qualitative process theory by K. D. Forbus. This point will be described in detail later.

The FBS diagram will be first outlined and then, the representation of the functional redundancy apparatus on the FBS diagram will be described.

1-2-1. Definition of FBS diagram

Consideration is given to only the physical world, to define states, behaviors and functions constituting the FBS diagram as follows:

First, states S of a certain apparatus are expressed as the following equation (1) using internal states S.sub.i of the apparatus and external states S.sub.o such as an environment:

S=<S.sub.i, S.sub.o > (1)

The equation (1) means that a set of states S is described by sets of states S.sub.i and S.sub.o.

Furthermore, the internal states S.sub.i are defined as the following equation (2) using a set of substances E representing parts and the like in the apparatus, a set of attributes of substances A representing the size of a gear, a resistance value of a resistor and the like, a set of relationships R representing the connection among parts, the relationship among attributes and the like:

S.sub.i =<E, A, R> (2)

The external states S.sub.o are described in the same manner as the internal states. In addition, a so-called "structure" of the apparatus is considered as one type of state of the apparatus where the duration is long and is described as a part of the internal states S.sub.i. This is for making it possible to flexibly describe the change in the structure itself which may occur due to a fault in the apparatus.

One example of state description defined by the equations (1) and (2) is shown in FIG. 2. FIG. 2 shows the state description of a paperweight. In FIG. 2, the paperweight is placed on paper, parameters representing states such as the weight W, the volume V and the density D exist in the paperweight, and there is a relationship D=W/V among the parameters.

Behaviors B are then defined as "change of one or more states (including no change)" using the above described states S. This definition is expressed by the following equations (3), (4) and (5):

b=s.sub.1 .fwdarw.s.sub.2 .fwdarw. . . . (3)

b B (4)

s.sub.1, s.sub.2, . . . S (5)

Specifically, each of behaviors b included in a set of behaviors B is changed in state, for example, s.sub.1 .fwdarw.s.sub.2 .fwdarw. . . . , and respective states s.sub.1, s.sub.2, . . . obtained by the change are included in the states S.

It should be noted that it can be considered that the "change of state" is not brought about at random but brought about by a "physical law". A concept that the states S and the behaviors B are thus combined with each other by a physical law is one basic concept of the present invention. Conversely, a knowledge base of a physical law is constructed, thereby to make it possible to manage noncontradiction between the state representation and the behavior representation of an apparatus system by a computer.

On the basis of the foregoing, a function F is then defined as "description of behaviors recognized and abstracted for a certain purpose by a human being". That is, the function is basically described in the form of "make+an object+an objective complement". The definition of this function F is expressed by the following equation (6):

.GAMMA..sub.ab : B.fwdarw.F (6)

In the equation (6), .GAMMA..sub.ab indicates the process of recognition and abstraction by a human being, and the behaviors B are converted into the function F through the process.

The relationship between functions and behaviors depends on a human subjective point of view. Another basic concept of the present invention is that many functions can correspond to the same behavior, or vice versa depending on the point of view.

For example, if an electrophotographic copying machine is taken as an example, a plurality of behaviors such as a behavior "light from a neutralization lamp is irradiated on a photosensitive drum so that electrostatic charges are grounded" and a behavior "electrostatic charges on a photosensitive drum are canceled by a discharge phenomenon of a charger" may correspond to a function "remove charges on a photosensitive drum". Such a many-to-many correspondence between functions and behaviors is a basis for making the concept of functional redundancy possible, and an FBS diagram clearly representing the many-to-many correspondence is a prerequisite indispensable to the functional redundancy.

The above described relationship among functions, behaviors and states in the FBS diagram is shown in FIG. 3. In FIG. 3, a set of states and a set of behaviors are combined with each other by a physical law, and the set of behaviors and a set of functions correspond to each other by extraction of recognition.

1-2-2. Realization of FBS diagram

Description is now made of a method of realizing the FBS diagram, that is, a method of describing functions, behaviors and states described in the item 1-2-1.

1-2-2-1. Function representation

"Function" defined in the item 1-2-1. is described by a frame "function knowledge" shown in Table 2.

This function knowledge is collected on the basis of judgments of a designer and an engineer, to constitute a functio