Sonlu durum makineleri ya da otomatlar, Ayrık Olay Sistemlerinin (AOS) analiz, tasarım ve kontrolüne yönelik formal yöntemlerin yer aldığı uygulamalarda yaygın olarak kullanılmaktadır. Ayrık olay sistemlerinin geribeslemeli kontrolü için kuramsal bir yapı tanımlayan Üstdenetim Kuramı ve bu kurama ilişkin uygulamalar buna örnek olarak verilebilir. Otomatın standart tanımının, tasarıma ilişkin ayrık olay sistem davranışını ifade edebilmesine rağmen, zamanlama ve sayma gibi bazı davranışları bu modelleme biçimi ile ifade etmek kolay değildir. Bu çalışmanın temel amacı, AOS davranışlarının, özel olarak kontrole yönelik davranış kurallarının tasarımını ve ifadesini mümkün kılan durum tabanlı bir modelleme biçiminin geliştirilmesi ve bu modele dayanarak tasarlanmış davranışın uygulanabilmesi için bir yöntemin elde edilmesidir. ZS-otomat olarak anılan yeni modelleme biçimi, uygulamada sıklıkla karşılaşılan zamanlama ve sayma davranışlarının durum gösterimi ile ifade edilmesini mümkün kılan Zamanlama ve Sayma Yapısına sahiptir. Modelin önemli bir özelliği, gerçekleme aşamasında kullanılan teknolojik araçlarda doğrudan uygulanabilecek yapısal bileşenler içermesidir. Bu çalışmada, modelleme biçiminin yanı sıra, bir gerçekleme yöntemi de tanıtılmaktadır. Gerçekleme yöntemi, ele alınan bir AOS için tasarlanmış kontrolörün ya da üstdenetleyicinin Programlanabilir Lojik Kontrolörlerle (PLC) gerçeklenmesine yönelik adımları sistematik olarak tanımlamaktadır. Yöntemin, tasarım davranışını yanlış olarak gerçeklemeye neden olan “çığ etkisi” adlı bir problem için çözüm oluşturduğu da gösterilmiştir. Geliştirilen yöntemle, tasarımda öngörülen zamanlama ve sayma davranışları, PLC’lerde kullanılan Zamanlayıcı ve Sayıcı bloklarını doğrudan kullanılmasını mümkün kılmaktadır. Sistematik olarak tanımlanan bu yöntem, programlanarak otomatik kod üretimini mümkün kılan bir yapıdadır.

When formal methods are applied in control design of Discrete Event Systems (DES), it becomes necessary to model the system behavior and specifications by a formalism such as automata or Petri nets. For example, the supervisory control theory (SCT) introduced by Ramadge and Wonham in 1987, uses formal languages to model system behavior and, specifications and formal languages are often expressed by automata. The synthesized controllers or supervisors are also represented by automata which are then needed to be realized by a programmable device. Standard definition of the automaton is capable of describing the DES behavior of a design; however some behaviors like timing and counting can not directly or easily be represented in the standard formalism. Implementing a timing mechanism is necessary for discrete event control systems when a certain amount of delay is required to make a decision after an event occurs. A green traffic light, turning on after a certain time period following the red light could be an example. Likewise, a counting mechanism is applied if it is necessary to count the occurrence of a particular event for a number of times before issuing a control signal. For the case of manufacturing systems, packaging the products when a certain number of products are reached could be an example for the requirement of counting mechanism. While it is possible to implement the timing and counting requirements easily with the technological elements, formal definition of the standard automaton does not include such kind of mechanisms. However, it is possible to realize a time delay when utilizing formal methods. It is straightforward to define a time delay by assigning an event to indicate that a predetermined time has elapsed. However, in this case, a timing mechanism is required in the realization stage which is not a part of the formal structure. For counting an event for n times, n successive states in the automaton representation of the supervisor could be used, but in the general case, this may necessitate using large number of states. Therefore, a structure that is capable of representing the timing and counting behavior without using external mechanisms and excessive number of states is required. Another requirement regarding the implementation of formal supervisors is an output mechanism that would issue control signals (enabling or disabling signals for the example of Supervisory Control Theory) or events to drive the DES system being controlled. This requirement is generally met by employing automata with outputs for the representation of the supervisor. When implementing a DES control strategy for discrete event systems, timing and counting behaviors are frequently applied by using predefined objects of the technological device which is used for the realization of control strategy. Programmable Logic Controllers (PLCs) have been used in industrial applications for more than 35 years, and in today’s industrial control systems Programmable Logic Controllers (PLCs) are extensively used for realizing control strategies. PLCs make it possible to realize timing and counting behaviors easily by utilizing ready-made objects called timers and counters. In this study, a formalism that enables designing and expressing DES behavior is developed, and a methodology that implements the designed behavior based on the introduced formalism is obtained. The new formalism, named TC-automaton, has a so called Timing and Counting Structure that enables the designer to assign timing and counting behaviors to the state based representation. An output function structure which enables outputting events depending on the states and/or on Timing-Counting Structure of the TC-automaton is also defined. TC-automaton is defined in such a way that, in the realization stage, it is possible to make use of the tools provided by the physical realization platform, i.e. PLCs. The implementation methodology introduced for the new formalism systematically defines the steps for realizing the designed controller or supervisor via PLCs. This systematic setting makes it possible to program the methodology, which is a step toward automatic code generation. It is also shown that, the methodology resolves “avalanche effect” problem, which might be encountered due to a particular structure of the automaton representation of the control behavior. PLC programs obtained by utilizing the methodology are also modular in structure which enhances program readability.