Fuzzy controller group control system

Abstract: A group control system in which a plurality of fuzzy controllers are interconnected by a communication line and the parameters of rules and membership functions of each fuzzy controller are capable of being adaptively changed depending upon the state of the controlled system so as to improve the control performance of the overall system.

Description: BACKGROUND OF THE INVENTION This invention relates to a system provided with a a plurality of fuzzy controllers each of which receives as input a signal representing one or a plurality of controlled variables from a controlled system, execute fuzzy inferential reasoning in accordance with predetermined rules using prescribed membership functions, and output a definite value as manipulated variable regarding the controlled system. A conventional fuzzy controller is of the stand-alone type, in which a single such controller controls a controlled system. Consequently, in a case where a control system which includes a controlled system is complicated and massive in size, control cannot be carried out by using several fuzzy controllers and operating them in cooperative fashion. Hence, a problem in the art is that only a comparatively simple, small-scale controlled system can be subjected to fuzzy control. SUMMARY OF THE INVENTION An object of the present invention is to provide a system in which a plurality of fuzzy controllers can be made to operate in cooperation with one another. In order to attain the foregoing object, the present invention provides a fuzzy controller group control system characterized by comprising a plurality of fuzzy controllers and control means, wherein operating states of the fuzzy controllers are monitored by the control means and control is performed by the control means in such a manner that, in conformity with a change in the operating state of one fuzzy controller, a parameter of at least one of the other fuzzy controllers is varied. In accordance with the present invention, a plurality of fuzzy controllers are interconnected by a communication line, the input/output state and internal processing state of each of the fuzzy controllers are monitored and judged by the control means, and the parameters of rules, membership functions, etc., of one or a plurality of the fuzzy controllers are varied adaptatively, thereby making it possible to control even a massive, complicated controlled system. With regard to altering parameters of rules, membership functions and the like, it can be arranged so that judgment and designation are performed collectively by a host computer or so that each fuzzy controller autonomously performs an exchange of data with the other fuzzy controllers. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a block diagram showing the overall construction of a fuzzy controller group control system; Fig. 2 is a block diagram showing an example of the construction of a fuzzy controller; Fig. 3 is a block diagram for describing an example of control; Fig. 4 is a graph showing an example of a membership function; and Figs. 5 and 6 are flowcharts illustrating a control procedure. DESCRIPTION OF THE PREFERRED EMBODIMENT Fig. 1 shows an example of the construction of a group control system composed of a plurality of fuzzy controllers. Specifically, a plurality of fuzzy controllers 10 are provided in order to control a controlled system 20. Each fuzzy controller 10 receives, as an input thereto, controlled variables obtained by the controlled system, executes fuzzy inferential reasoning in accordance with predetermined rules using a prescribed membership functions regarding the controlled variables, and provides the controlled system with a manipulated variable represented by the results of the inferential reasoning. It goes without saying that the controlled variables applied to the fuzzy controllers 10 may be redundant. In other words, it can be arranged so that a controlled variable of a certain type is applied to a plurality of the fuzzy controllers. The plurality of fuzzy controllers are connected to a host computer 21 by a communication line (communication channel). With regard to the communication channel, any configuration will suffice, such as a MAP or ETHERNET, as long as it is capable of interconnecting a plurality of fuzzy controllers. Fig. 2 illustrates a single fuzzy controller extracted from the plurality in order to illustrate an example of the construction of the fuzzy controllers 10. The fuzzy controller 10 has three digital units 11 - 13 and a number of analog units 14 - 16. The digital unit 11 is a CPU unit and has a CPU and memories such as a ROM and RAM. The CPU unit 11 is for setting various constants and coefficients in the analog units 14 - 16 and for monitoring the operation of the analog units 14 - 16. The digital unit 12 is a memory unit and has a RAM for storing various data, by way of example. The digital unit 13 is a communication I/F unit and makes it possible for the CPU in the unit 11 to communicate with the host computer 21. The analog unit 14 is an input/output circuit unit which acts to interface the controlled system 20 with the other analog units 15, 16. The analog unit 16 is a fuzzy inference operational unit which executes a predetermined fuzzy inferential operation based on an input of a controlled variable received from the controlled system 20 via the input/output circuit unit 14. A number of these fuzzy inference operational units 16 are provided. The analog unit 15 is a definite value operational unit for synthesizing the results of fuzzy inferential reasoning obtained from the fuzzy inference operational units 16 and determining a definite value corresponding thereto. In other words, the analog unit 15 operates as a defuzzifier. The output of the definite value from the analog unit 15 is applied as a manipulated variable to the controlled system 20 via the input/output circuit unit 14. These analog units 14 - 16 are interconnected by an analog bus 18. Accordingly, the number of fuzzy inference operational units 16 can be increased or decreased at will. The analog units 14 - 16 are interconnected with the digital units 11 - 13 via the digital bus 19. As a result, various constants and the like in the analog units 14 - 16 are capable of being set at will by the CPU of the CPU unit 11, and the operation of the analog units 14 - 16 is capable of being monitored by the CPU unit 11. The CPU unit 11 of each fuzzy controller 10 is capable of communicating with the host computer 21 and the other fuzzy controllers via the communication I/F 13. The CPU unit 11 monitors the input/output state from the input/output circuit unit 14 as well as the fuzzy operational states of the fuzzy inference operational units 16 and the definite value operational unit 15, creates data based on these monitored states, and transmits the data to the host computer 21 and to the other fuzzy controllers 10. The CPU unit 11 of each fuzzy controller 10 acts to adaptatively alter the presently prevailing rule and membership function based on the information from the other fuzzy controllers in order to improve control performance. Further, based on the data from each of the fuzzy controllers 10, the host computer 21 commands the CPU units 11 to alter the parameters of the rules and membership functions, etc., of these fuzzy controllers 10. It is possible to adopt an arrangement in which, by cooperatively controlling the plurality of fuzzy controllers, a failure in one of the fuzzy controllers can be compensated for by the other fuzzy controllers. Though there are many examples of group control of a plurality of fuzzy controllers, the arrangement shown in Fig. 3 will be considered here as a simple example for the sake of facilitating the description. Two fuzzy controllers 10 are provided. A sensor 21 in the controlled system 20 applies inputs A, B to a first fuzzy controller 10 (referred to as fuzzy controller 1) as controlled variables. An output X representing the inferential results from the fuzzy controller 1 is applied to an actuator 22 of the controlled system 20 as a manipulated variable. Another sensor 23 in the controlled system 20 applies inputs C, D to a second fuzzy controller 10 (referred to as fuzzy controller 2) as controlled variables. An output Y representing the inferential results from the fuzzy controller 2 is applied to an actuator 24 of the controlled system 20 as a manipulated variable. An example of a membership function used by these fuzzy controllers 10 is illustrated in Fig. 4, in which P, N, S, M and L represent positive, negative, small, medium and large, respectively. For example, PL represents a positive, large value and NS a negative small value. ZR expresses approximate zero. Let the rules set in the fuzzy controller 1 be as follows, by way of example: Rule 1: If A = NL, B = ZR then X = ZR Rule 2: ... ... Let the rules set in the fuzzy controller 2 be as follows, by way of example: Rule 1: If C = PL, D = PM then Y = NS Rule 2: ... ... It will be assumed here that when the input A of fuzzy controller 1 is very large, the conclusion of Rule 1 in fuzzy controller 2 must be made Y = ZR and not Y = NS. Accordingly, the CPU unit 11 of fuzzy controller 1 monitors input A and, if A becomes a very large value, requests the fuzzy controller 2, via the communication line, to change the conclusion of Rule 1 from NS to ZR. This processing is illustrated at steps 31 and 32 in Fig. 5. In response, the fuzzy controller 2 alters Rule 1 in accordance with the request from the fuzzy controller 1 (steps 41, 42 in Fig. 6). Conversely, in a case where the conclusion of Rule 1 in fuzzy controller 2 must be restored from Y = ZR to Y = NS when input A is very small, the CPU 11 of the fuzzy controller 1 monitors the input A and, if the input A becomes very small, requests the fuzzy controller 2, via the communication line, to restore the conclusion of the rule from ZR to NS, as indicated at steps 33, 34 in Fig. 5. In response, the fuzzy controller 2 alters the conclusion of Rule 1 in accordance with the request from the fuzzy controller 1 (steps 41, 42 in Fig. 6). The foregoing processing is executed under the control of the host computer 21. Specifically, the host computer 21 monitors the change in the input A via the CPU unit 11 of the fuzzy controller 1. When the input A becomes very large, the host computer 21 requests the CPU unit 11 of the fuzzy controller 2 to change the conclusion of Rule 1 from NS to ZR. By thus adaptatively altering the parameters of rules and membership functions via a communication line, it becomes possible to finely control a large-scale system. As many apparently widely different embodiments of the present invention can be made it is to be understood that the invention is not limited to the specific embodiments thereof except as defined in the appended claims.

Claims: A fuzzy controller group control system having a plurality of controllers which are interconnected by a communication line, characterized in that said controllers are fuzzy controllers, and each of said fuzzy controllers comprises means (13) for transmitting data representing the state of its fuzzy control to at least one of the other fuzzy controllers and control means (11) for changing a parameter for the fuzzy control carried out in itself upon receiving data representing the state of the fuzzy control transmitted from at least one of the other fuzzy controllers.

Inventors: TASAKA YOSHIRO, TASAKA, YOSHIRO, TASAKA, YOSHIRO, C/O OMRON CORPORATION
Applicants: OMRON TATEISI ELECTRONICS CO, OMRON CORPORATION
Application year: 1990
Main classification: G06J1
IPC codes: G05B13, G06N7