IEC 61131-7 Fuzzy Control Programming released

With the voting process closed on June 30, 2001, we have a new approved part to the IEC 61131 standard. It is part 7,

and deals with Fuzzy Control Programming.

The goal of this Standard is to offer the manufactures and the users a well defined common understanding of the basic 

means to integrate fuzzy control applications in the Programmable Controller languages according to Part 3, as well as the

possibility to exchange portable fuzzy control programs among different programming systems.

The theory of fuzzy logic in the application of control is named fuzzy control. Fuzzy control is emerging as a technology 

that can enhance the capabilities of industrial automation, and is suitable for control level tasks generally performed in 

Programmable Controllers (PC).

Fuzzy Control is based upon practical application knowledge represented by so-called linguistic rule bases, rather than by 

analytical (either empirical or theoretical) models. Fuzzy control can be used when there is an expertise that can be 

expressed in its formalism. That allows to take available knowledge to improve processes and perform a variety of tasks,

for instance:

	control (closed or open loop, single or multi-variable, for linear or non linear systems)
	on-line or off-line setting of control systems' parameters
	classification and pattern recognition
	real-time decision making (send this product to machine A or B ?)
	helping operators to make decisions or tune parameters
	detection and diagnosis of faults in systems

Its wide range of applications and natural approach based on human experience makes Fuzzy Control a basic tool that

should be made available to Programmable Controller users as a standard.

Fuzzy control can also in a straightforward way be combined with classical control methods.

The application of fuzzy control can be of advantage in such cases where there is no explicit process model available, or in

which the analytical model is too difficult to evaluate or when the model is too complicated to evaluate in real time.

Another advantageous feature is, that human experience can be incorporated in a straightforward way. Also it is not

necessary to model the whole controller with fuzzy control: sometimes fuzzy control just interpolates between a series of

locally linear models, or dynamically adapts the parameters of a "linear controller", thereby rendering it non linear, or

alternatively just "zoom in" onto a certain feature of an existing controller that needs to be improved.

Fuzzy control is a multi-valued control, no longer restricting the values of a control proposition to "true" or "false". This

makes it particularly useful to model empirical expertise, stating, which control actions have to be taken under a given set

of inputs.

The existing theory and systems already realized in the area of fuzzy control differ widely in terms of terminology

(definitions), features (functionalities) and implementation (tools).

Fuzzy control is used from small and simple applications up to highly sophisticated and complex projects. To cover all kinds

of usage by this part of IEC 61131, the features of a compliant fuzzy control system are mapped into defined

conformance classes.