Interpretation Petri net model to IEC 1131-3: LD for programmable logic controller

Petri nets have been extensively applied for specification, design, verification, performance evaluation, and simulation of discrete event control systems (DECS). The usual way to verify the dynamic behaviour of DECS design is to employ a process-based model, which proves to be impractical in application because the process-based model does not usually fully correspond to the control programming behaviour. This paper proposes a sensor-based stage Petri net (SBSPN) to represent a programmable logic controller (PLC) stage logic diagram (LD) for discrete-event control design. The new technique is able to simplify the modelling process of the complex PLC program without considering the interlocking problem within the ladder diagram. An illustrated example is used to explore the new methodology. The proposed method contains the power and flexibility of the Petri net analysis prior to the PLC implementation. It is believed that this technique is significant for industry practice.

This paper considers a whitelisting system for programmable logic controllers (PLCs). In control systems, controllers are final fortresses to continues the operation of field devices (actuators/sensors), but they are fragile with respect to malware and zero-day attacks. One of the countermeasures applicable for controllers is a whitelisting system which registers normal operations of controller behavior in a “whitelist” to detect abnormal operations via a whitelist. The previous research of the current author proposed a PLC whitelisting system with a control via a ladder diagram (LD). LD representations have a wide applicability because LDs can be implemented for all PLCs and security functions without hardware/firmware updates. However, the current status requires that all instances are manually entered in the whitelist. In this talk, we show how the setting up of the can be automatized whitelist from the PLC behavior. This paper introduces an auto-generation approach for the whitelist using sequential function chart (SFC) instead of the LD. SFC and LD are compatible representations for the PLC. Using Petri Net modeling, this paper proposes how to generate the whitelist from the SFC and how to detect abnormal operations via the whitelist. We call the SFC-based approach the model-based whitelist, the Petri Net based approach the model-based detection. Further, this paper carries out an experimental validation of the algorithms using an OpenPLC based testbed system.

For large-scale and long-distance distributed systems, this paper proposes a systematical multiparadigm approach to develop the simple network management protocol (SNMP) agents for remote monitoring and control. The standard unified modeling language (UML) is adopted for modeling the system, and then the Petri-net model is applied to achieve both qualitative and quantitative analyses for the system's dynamic behavior. In real applications, the present design can be further implemented with Java and ladder diagrams on programmable logic controllers (PLC). The developed system has been used successfully in a mobile switching center (MSC) of Taiwan Cellular Corporation for the remote monitoring and control, through the Internet, of its environmental conditions, including the temperature, humidity, power, and security, with a total of 316 sensors and 140 actuators.

Powerful advantages of programmable logic controller (PLC) dominate process industries. Scan time of PLC increases with the number of inputs, rungs added in ladder diagram (LD). Researchers have identified and proved that field programmable gate array (FPGA) is more suitable than PLC for high speed applications. PLC executes the instructions represented through LD. PLC programmers are not familiar with FPGA programming. But, FPGA does not support LD based programming. This work has developed application software to generate equivalent VerilogHDL code for LD using LabVIEW. Novelty in this work is that each rung is defined using an "assign" statement which helps simultaneous execution of all the rungs. A data acquisition system was created to monitor the digital signals handled by the FPGA. The software was verified with a case study of substances mixing and traffic light control system.

Traffic lights are commonly used in the intersection in urban areas nowadays. In fact a network of the traffic lights regulating the urban vehicle can be viewed as a complex discrete-event system (DES). It is proved that Petri nets are one of the methodologies for modeling, analyzing and controlling on DES. A new approach via programmable logic controller (PLC) and Petri net synthesis is proposed in this paper. Firstly, we described the typical urban traffic lights control using Petri nets. Having compared with three methods for Petri nets realization, the best implementation method of the traffic lights control system was one which made with the PLC. The sequential function chart (SFC) of the PLC system is also given in the thesis. The result shown that the method has many advantages at improving flexibility and troubleshoots of system and reducing the difficulty in its realization.

The paper introduces a Programmable Logic Controller (PLC) / Human Machine Interface (HMI) system incorporated along with machine learning (ML) classifiers. Although some other studies have incorporated ML techniques to predict and control petroleum product terminals in terms of concentration, the proposed framework incorporates Add On Instruction (AOI) programming, PLC, and ML methods to automatically monitor petroleum products terminals. The framework adds an AOI in programming to achieve maximum usage of processor capabilities. Moreover, it uses AOI for programming in cooperation with the ladder diagram (LD). This leads to simplifying the LD graphical programming language, reducing the time of scanning, and making facilitate troubleshooting. The AOI is merged with ML to automate tank level detection and maintain good operational conditions and consequently protect these expensive essential assets. The introduced framework consists of three stages. The first stage is the PLC programming phase where the PLC is created using Add-On instructions. Next, HMI graphic displays are drawn and linked to the PLC tags in the following stage. During the third stage, the actual process readings are applied to the system based on ML algorithms to test its functionality. The proposed system results indicates a reduction in the LD number, highest program size, and maximum time of scanning. The results indicate that the AOI can help to trace the program more easily in fault situations. Besides, additional program instructions could reduce processor memory, system construction costs, and upgrade projects.

Automatic test of safety specifications for PLC programs in the Oil and Gas Industry

This research is focused on laboratory based analysis on hardware module of traffic light with Programmable Logic Controller (PLC) software. There are four ways in hardware model for detection of vehicle; each way has one sensor button, three Light Emitted Diodes (LEDs) with individual colors say red, yellow and green represents the traffic light in each lane. Sensor and LEDs are connected to Mitsubishi Programmable Logic Controller (PLC) and each part on hardware being controlled by PLC. Ladder diagrams are programmed by software to monitor the system and helps to improve public transportation services, thereby improving traffic guidance and traffic light control. The system was developed by setting the appropriate time for the traffic lights to respond accordingly. The controller checks the priority and provides an exit signal to the traffic light post to turn the red, yellow or green lights on or off. Finally, the signal lights were successfully controlled by the PLC. Hence the system used in traffic control systems contain low power consumption, low engineering cost and increased safety.

There are several critical processes in the industry that are automated with the goal of optimizing available resources and increasing production of products such as gas and oil. Ladder diagrams is a language used in systems developed to manufacturing industry that uses Programmable Logic Controllers. Such systems have reliability and security issues. To simulate and verify the properties of systems, mathematical tools like Petri Nets (PN) are used. Some researchers propose methods to convert Ladder in some PN class. This work presents some conversion methods, compares them briefly, and presents an implementation of one of them. Such an implementation converts Ladder code to Colored Petri Nets model.

This paper deals with a "digital twin" (DT) approach for processing, reprocessing, and scrapping (P/R/S) technology running on a modular production system (MPS) assisted by a mobile cyber-physical robotic system (MCPRS). The main hardware architecture consists of four line-shaped workstations (WSs), a wheeled mobile robot (WMR) equipped with a robotic manipulator (RM) and a mobile visual servoing system (MVSS) mounted on the end effector. The system architecture integrates a hierarchical control system where each of the four WSs, in the MPS, is controlled by a Programable Logic Controller (PLC), all connected via Profibus DP to a central PLC. In addition to the connection via Profibus of the four PLCs, related to the WSs, to the main PLC, there are also the connections of other devices to the local networks, LAN Profinet and LAN Ethernet. There are the connections to the Internet, Cloud and Virtual Private Network (VPN) via WAN Ethernet by open platform communication unified architecture (OPC-UA). The overall system follows a DT approach that enables task planning through augmented reality (AR) and uses virtual reality (VR) for visualization through Synchronized Hybrid Petri Net (SHPN) simulation. Timed Petri Nets (TPNs) are used to control the processes within the MPS's workstations. Continuous Petri Nets (CPNs) handle the movement of the MCPRS. Task planning in AR enables users to interact with the system in real time using AR technology to visualize and plan tasks. SHPN in VR is a combination of TPNs and CPNs used in the virtual representation of the system to synchronize tasks between the MPS and MCPRS. The workpiece (WP) visits stations successively as it is moved along the line for processing. If the processed WP does not pass the quality test, it is taken from the last WS and is transported, by MCPRS, to the first WS where it will be considered for reprocessing or scrapping.

The relationship between system independent logic controller programs (IEC standard 1131-3, Programmable Controllers, part 3: programming languages) and rule-based formal specifications is discussed. The Petri net and knowledge base theories can be joined together in the one context (Gentzen Logic). It combines the advantages taken from mathematical logic with the analysis power of Petri nets. The declarative specification, which is extracted from the description given in the initial standard IEC language (for example from structured text), can increase the efficiency of the logic controller program development. The well-structured specification, which is represented in the human-readable logic language, has direct impact on validation, formal verification and implementation of logic controller programs. The formality is introduced into the design technique, but it also can be used for post-design validations and maintenance. The symbolic deduction technique for PLC declarative program development appears very attractive. The CAD environment for application specific logic controllers is part of a research project at the University of Minho. The specification in the form of symbolic logic expressions may be verified, and then transformed into a format accepted by standard CAD tools (FPLD and FPGA compilers, VHDL tools).

With the rapid advancement of science and technology, the role of technology in industry is also increasing, particularly through automation that simplifies and enhances work process efficiency. To support this development, education plays a crucial role in enhancing students' competencies. One relevant subject in industrial technology is Programmable Logic Controller (PLC). In PLC education, trainer tools are used to help students understand industrial control concepts. At Politeknik Manufaktur Bandung, particularly in the Mechatronics and Automation Engineering Technology programs, the use of PLC trainers is still limited to basic input-output features. Survey results show that most students only understand Ethernet communication protocol and have never connected more than one PLC in a single system, resulting in a limited understanding of inter-PLC communication. This research aims to develop a trainer that teaches various PLC communication protocols, including Controller Link, DeviceNet, Serial RS-232C, and Ethernet, with inter-PLC and HMI communication implementation. The system uses three PLCs, where an Omron CP1H PLC as the master uses Controller Link to communicate with another Omron CP1H PLC as a slave, DeviceNet for remote slave devices, Serial RS-232C to communicate with an Omron CJ2M PLC as a slave, and Ethernet connected to Human Machine Interfaces (HMI) Omron NB7W and Kinco GL070E for PLC data monitoring. Based on the assessment results, the overall trainer tool evaluated received an effectiveness score of 95.1% from 6 aspects of the assessment. This trainer is expected to enhance students’ understanding of PLC communication protocols and their applications in integrated systems.

The major obstacles to teaching Programmable Logic Controller (PLC) is a variety of PLCs and the rapid pace of technological development with new models and innovations. Moreover, costs incurred in the setting up of comprehensive and modern PLC laboratory facilities, and in the required periodic updating of teaching material and equipment are, as a result, very high. After investigated the conception and features of PLC and embedded system, the development of the embedded PLC for teaching machatronics students is proposed in this paper with the seamless combination of the LabVIEW software and the ARM Microcontroller with the LabVIEW embedded module. The flexibility of the proposed PLC makes it relatively easy and less costly to teach the basic principle of different kinds of PLCs due to their variety and rapid change. The implementation of the embedded PLC is discussed and evaluated. The results of evaluation shows that embedded PLC can be taught in an uncomplicated manner.

최근 자동 생산 시스템은 PLC (Programmable Logic Controller) 제어 프로그램을 일반적으로 사용하고 있다. 생산제품의 수명 주기가 길지 않기 때문에 공법과 라인 및 설비 변경이 자주 일어난다. 대부분, 기존 공정을 바탕으로 이루어지고 설비의 위치 및 제어정보를 수정한다. PLC 제어 프로그램 또한 기존 공정을 바탕으로 수정이 이루어진다. 새로운 제어 프로그램을 검증하기 위해서는 실제 생산 시스템을 구축하기 전에 가상의 공간에서 실제 공정과 같이 구성하여 순차적으로 공정이 진행되는 지 확인할 수 있는 방법이 필요하다. 본 연구는 순차제어(sequential control)와 병목현상 처리에 유용한 Timed-FSA를 기반으로 하는 논리적인 모델링 방법을 사용한다. 기존에 연구되었던 I-O 모델링과 I-O 모델링에서 요구되었던 하나의 설비에 다양한 상태의 정의를 통해 사용자의 시간과 공수를 절감하기 위한 기존 모델링에 페트리네트의 토큰(Petri Nets Coloured Token) 개념을 추가한 확장된 I-O 모델링 방법을 제안한다. 예제 설비를 통하여 사용자의 모델링 시간을 절감하는 실험과 사용자 평가를 통해 제안하는 확장된 I-O 모델링의 편의성을 검증한다. Recently manufacturing companies have used PLC control programs popularly for their automated production systems. Since the life cycle of production process is not so long, the change of the production lines occur frequently. Most of changes happen with modification of the position information and control process of the equipment. PLC control program is also modified based on the fundamental process. Therefore, to verify new PLC program by configuring virtual space according to real environment is needed. In this paper we show a logical modeling method, based on Timed-FSA useful for sequence control and dead-lock prevention. There is a problem wasting user's labor and time when defining a variety of states in a device. To overcome this problem, we propose an extended I-O model based on existing methods by adding a token concept of Petri Nets. Also we will show the usability of the extended I-O modeling through user study.

A model based on a Petri net (PN) is proposed for controlling flexible manufacturing systems (FMSs). The model can describe not only normal sequential processes but also interruptive exceptional handling processes by means of simple structures. A layered structure and two types of token are introduced into a PN to describe exception handling and error recovery. An application in which this model was used to program a programmable logic controller (PLC) is described. The description of cell control can be simplified by the model. >