Programmable Logic Controller Programming Research Articles

An overview of model checking practices on verification of PLC software

Programmable logic controllers (PLCs) are heavily used in industrial control systems, because of their high capacity of simultaneous input/output processing capabilities. Characteristically, PLC systems are used in mission critical systems, and PLC software needs to conform real-time constraints in order to work properly. Since PLC programming requires mastering low-level instructions or assembly like languages, an important step in PLC software production is modelling using a formal approach like Petri nets or automata. Afterward, PLC software is produced semiautomatically from the model and refined iteratively. Model checking, on the other hand, is a well-known software verification approach, where typically a set of timed properties are verified by exploring the transition system produced from the software model at hand. Naturally, model checking is applied in a variety of ways to verify the correctness of PLC-based software. In this paper, we provide a broad view about the difficulties that are encountered during the model checking process applied at the verification phase of PLC software production. We classify the approaches from two different perspectives: first, the model checking approach/tool used in the verification process, and second, the software model/source code and its transformation to model checker's specification language. In a nutshell, we have mainly examined SPIN, SMV, and UPPAAL-based model checking activities and model construction using Instruction Lists (and alike), Function Block Diagrams, and Petri nets/automata-based model construction activities. As a result of our studies, we provide a comparison among the studies in the literature regarding various aspects like their application areas, performance considerations, and model checking processes. Our survey can be used to provide guidance for the scholars and practitioners planning to integrate model checking to PLC-based software verification activities.

Construction and verification of PLC LD programs by the LTL specification

An approach to the construction and verification of LD programs of programmable logic controllers (PLC) for discrete problems is proposed. The specification of the program behavior is performed using the linear temporal logic language (LTL). Programming is performed using the Ladder Diagram (LD) language by the LTL specification. The correctness analysis of the LTL specification is performed using the Cadence SMV symbolic model-checking tool. An approach to programming and verifying the PLC LD programs is shown using an example. The LD program, its LTL specification, and an SMV model are given for a discrete problem. This article is aimed at the description of an approach to PLC programming that will provide the correctness analysis of PLC LD programs using the model-checking method. Therefore, the variation in each programmable variable is described using a pair of LTL formulas. The first LTL formula describes situations in which the corresponding variable increases and the second LTL formula specifies conditions leading to a decrease in the variable. LTL formulas, which are considered to specify the behavior of variables, are constructive in the sense that the PLC program corresponding to the temporal properties expressed by these formulas is constructed by them. Thus, PLC programming is reduced to the construction of the LTL specification for the behavior of each programmed variable. In addition, the SMV model of the PLC LD program is constructed by the LTL specification. Then, the SMV model is analyzed for correctness (relative to additional conventional general-programming LTL properties) by the Cadence SMV symbolic model-checking tool.

Research on the Design and Manufacture of Steam Cleaning Machine Based on PLC

In this paper, the programmable logic controller (PLC) produced the steam cleaning machine controller based on PLC and foundation design, and steam cleaning device controlled the process of the realization .The programmable logic controller PLC programming and logic design, system realizes according to different artifact types, complete cleaning, blowing, drying the corresponding action. This system after careful design, manufacturing and detailed inspection, and after the running test, the experimental results shows that: as long as the proper maintenance and proper use of equipment, the project can improve the efficiency to a great extent.

Towards a taxonomy of errors in PLC programming

Based on previous studies on programming errors and their causes, the presented paper investigates errors that application engineers in the area of machine and plant automation make while creating either function block diagrams, plcML [an adaption of the unified modelling language (UML)] or modAT4rMS code (a newly developed modelling language that adapts and combines aspects of UML and SysML). A laboratory-based study with 52 mechatronics apprentices and electrical engineering technicians with knowhow in manufacturing system design but comparably undeveloped programming skills has been conducted, in which the subjects' errors and think-aloud statements during code creation were recorded. In a subsequent step, these data have been analysed by the cognitive causes of the coding errors applying the skill-rules-knowledge framework. As a result, a taxonomy of errors is presented. Results indicate that most of the errors in the subjects' code are due to insufficient understanding of the notation's syntax, problems with the rules of encapsulation, the creation of modules and finally with the creation of variants and aggregations, which are all located at the rule-based level. Errors at the skill-based level mainly occurred during behavioural modelling with modAT4rMS. It is argued that the provided insights can be used for improving education on programmable logic controller (PLC) languages and for the design of tools that support PLC programmers at detecting and fixing errors within their code.

PLC 기반 머신 비전 시스템 개발

This paper proposes a machine vision module for PLCs (Programmable Logic Controllers). PLC is the industrial controller most widely used in factory automation system. However most of the machine vision systems are based on PC (Personal Computer). The machine vision system embedded in PLC is required to reduce the cost and improve the convenience of implementation. In this paper, we newly propose a machine vision module based on PLC. The image processing libraries are implemented and integrated with the PLC programming tool. In order to interface the libraries with ladder programming, the ladder instruction set was also designed for each vision library. By use of the developed system, PLC users can implement vision systems easily by ladder programming. The developed system was applied to sample inspection system to verify the performance. The experimental results show that the proposed system can reduce the cost of installing as well as increase the ease-of-implementation.

SCADA Based Automated Bottle Quality & Quantity Detection and Filling System by Using PLC

In this paper, we propose an automated bottle quality, quantity detection and filling system in a manufacturing department using a PLC (Programmable Logic Controller) and SCADA. SCADA stands for Supervisory Control and Data Acquisition system. The main objective of the project has four processing stages. Firstly, detect the fault of the bottle by using optical sensor. In the second stage, remove the faulted bottle from the conveyer belt using electronic pusher. In the next stage, detect the quantity (size) of the bottle using proximity sensor. In the final stage, bottle filling process regarding size of the bottle. The quality and quantities of the physical system in the field is sensed by the sensors and fed as inputs to the PLC which in turn sent to PC through RS-232 for necessary processing. A PLC program is developed based on the signals received from the PLC input module, process the signals and send the output signals to the PLC output modules, which is programmed to actuate the necessary electronic actuator. The SCADA screens are developed regarding four processing stages on PC using Wonderware-Intouch SCADA software. The Allen Bradley micrologix 1000 PLC to be link up with the supporting SCADA Wonderware-Intouch 9.0 by giving necessary tag names. With the help of SCADA, simulation of the physical system is also developed to monitor the quantities to be measured and status of the equipment in the plant from field point.

Bringing Automated Model Checking to PLC Program Development — A CERN Case Study —

Verification of critical software is a high priority but a challenging task for industrial control systems. Model checking appears to be an appropriate approach for this purpose. However, this technique is not widely used in industry yet, due to some obstacles. The main obstacles encountered when trying to apply formal verification techniques at industrial installations are the difficulty of creating models out of PLC programs and defining formally the specification requirements. In addition, models produced out of real-life programs have a huge state space, thus preventing the verification due to performance issues. Our work at CERN (European Organization for Nuclear Research) focuses on developing efficient automatic verification methods for industrial critical installations based on PLC (Programmable Logic Controller) control systems.In this paper, we present a tool generating automatically formal models out of PLC code. The tool implements a general methodology which can support several input languages, like the PLC programming languages defined in the IEC 61131 standard, as well as the model formalisms of different model checker tools. The tool supports the three main stages of model checking: system modelization, requirement formalization and counterexample analysis. In addition, a verification case study of a PLC program, written in Structured Text (ST) language implemented at CERN is described. The paper shows that the verification process is automatized and supported by the proposed tool, thus its difficulty is completely hidden for the control engineer.

Usability Experiments to Evaluate UML/SysML-Based Model Driven Software Engineering Notations for Logic Control in Manufacturing Automation

Many industrial companies and researchers are looking for more efficient model driven engineering approaches (MDE) in software engineering of manufacturing automation systems (MS) especially for logic control programming, but are uncertain about the applicability and effort needed to implement those approaches in comparison to classical Programmable Logic Controller (PLC) programming with IEC 61131-3. The paper summarizes results of usability experiments evaluating UML and SysML as software engineering notations for a MDE applied in the domain of manufacturing systems. Modeling MS needs to cover the domain specific characteristics, i.e. hybrid process, real time requirements and communication requirements. In addition the paper presents factors, constraint and practical experience for the development of further usability experiments. The paper gives examples of notational expressiveness and weaknesses of UML and SysML. The appendix delivers detailed master models, representing the correct best suited model, and evaluation schemes of the experiment, which is helpful if setting up own empirical experiments.

POSITION CHARACTERIZATION OF ELECTRO-PNEUMATIC CLOSED LOOP CONTROL VALVE

This paper presents position characterization of an Electro-pneumatic closed loop control valve BOSCH 0 820 040 001. The experimental measurements carried out gives pressur e gain and the precise position repetition accuracy . A Programmable Logic Controller (PLC) program is developed in ladder log ic using IndraLogic L20 software of Rexroth Bosch t o determine position repetition accuracy.

On construction and verification of PLC programs

A review of methods and approaches for programming of “discrete” problems for programmable logic controllers (PLC) based on the example of constructing a program for controlling a code lock. The usability of the analysis of a program correctness by the model checking method with respect to a Cadence SMV automatic verification tool is evaluated for these approaches. Possible PLC program vulnerabilities arising at some approaches for programming of PLC are revealed.

PLC Control System of Cutting Fixed-Length Plates and Simulation Debugging

PLC (programmable logic controller) is one type of general industrial control platforms. Based on the PLC of SIMENS S7-200 series, this paper introduces a control scheme of cutting metal plates control system in the flame cutting machine. The hardware design and PLC program are given in details, which achieve accurate position and fixed-length cutting by the stepper motor through the control of PLC. In addition, the configuration simulation of the system is performed by the application of King view software. The control system has multiple operating modes, high reliability, stability and is able to meet the variety of different work requirements. The automatic control of cutting metal plates is achieved. The control system is applied to actual projects and can greatly enhance productivity.

Control level simulation of an automatic storage and retrieval system in the automotive industry

Conventional simulators have focused on the abstract aspects of an automatic storage and retrieval system, which mainly deals with design verification, alternative comparison, and system diagnosis. Although such simulators can provide overall system visibility by monitoring how well the process works, the simulation models are not sufficiently realistic for detailed design and implementation purposes. To address this problem, we propose a method of control level simulation of an automatic storage and retrieval system in an automobile plant. The proposed method involves four major steps: (1) designing the process and layout for effective storage and retrieval; (2) abstract simulation of the automatic storage and retrieval system; (3) preparing the mechanical design to obtain three-dimensional kinematic models and the electrical design to produce a control program and a plant model; and (4) control level simulation of the automatic storage and retrieval system, including both manual mode and automode simulations via a human–machine interface. The major benefit of the proposed method is the reduction of the construction time and effort required to validate the programmable logic controller program of a real automatic storage and retrieval system, since potential errors can be detected and fixed before actual implementation.

Boolean and Modular Abstractions for Programmable Logic Controllers

This paper introduces a Boolean and a modular abstraction of programs for programmable logic controllers in order to make them amenable for formal verification. In the Boolean abstraction, complex control-flow conditions are replaced by fresh Boolean input variables to defer the evaluation of such conditions. The modular abstraction replaces function block calls by so-called function block summaries, which over-approximate their possible return values. Both abstractions can subsequently be refined in an automatic process to allow for checking of complex programs using expressive formulae. The approach has been implemented in the Arcade.PLC model checker, which is used to show the effectiveness in a case-study.

Virtual and Remote Laboratories for Industrial Automation E-learning

Nowadays one of the fundamental aspects of industrial automation concerns modeling discrete manufacturing processes and their control through Programmable Logic Controllers (PLC). These subjects, apparently distinct, are indeed related because PLC programming in most cases are based on these models. Another essential topic is the use of SCADA systems and web panels as part of the monitoring process. Teaching these subjects require intensive use of laboratories with dedicated equipment and software. The problem arises when the course has more than one hundred students and the university policy is not to spend too many resources in teaching labs. This paper presents our last solution to the problem based on virtual experimental setups and the use of a remote laboratory with web panels and LabVIEW interfaces. The solution has been tested successfully and very important, using legal software at free cost for the student.

Towards Industrial Formal Specification of Programmable Safety Systems

Formal methods for specification and verification are promising in developing programmable logic controller (PLC) programs in manufacturing industry. Particularly this holds for safety PLCs, used to protect humans and equipment from injuries and damages. An important challenge though, is the development of formal specifications, typically a tough task for control engineers. This brief proposes a systematic work procedure that can be used as a first step of developing formal specifications of safety PLC programs in industry. The work procedure intends to facilitate the development of relevant formal properties for safety PLC program components. The formal specifications can be used for automatic formal verification of the components, using model checking techniques. This brief shows how the work procedure has been applied to industrial safety components, resulting in relevant and nontrivial specifications.

Sensor Graphs for Discrete Event Modeling Applied to Formal Verification of PLCs

This paper introduces Sensor Graphs, a discrete event modeling language directed at physical systems with binary and identity sensors (e.g., RFID). The aim of Sensor Graphs is to simplify the modeling of the plant/process that is to be controlled by a discrete controller, for example a programmable logic controller (PLC); thereby making formal verification and other model-based formal methods more applicable for PLC programmers. The formal syntax and semantics of Sensor Graphs are defined and a compact graphical representation is presented. The language is exemplified by modeling a conveyor module and a lab process. For comparison, the latter is also modeled using Statecharts and Net Condition/Event systems. A controller, modeled as a discrete state equation, can be composed with a Sensor Graph of the process in order to form a model of the closed-loop system. It is demonstrated how requirements on such a closed-loop system, based on a PLC program and a Sensor Graph process model, can be formally verified using the model checker Cadence SMV.

Developing control logic using aspect-oriented programming and sequence planning

A fundamental functionality of a Programmable Logic Controller (PLC) is to control and execute a set of operations. But a large part of the program code is more involved in supporting the user with concerns like alarm, HMI, communication, safety and manual control. Code related to these supporting concerns is often tangled with operation execution code, the core concerns, which makes it hard to reuse.This paper describes a method to reuse code and functionality when developing PLC programs and code libraries. The method proposes that core concerns are planned with a software tool called Sequence Planner, and the supporting concerns are integrated into the core concerns with a tool based on aspect-oriented programming.

PC-Based Automated Control System for Jordan Northern Grain Silo

This paper presents a PC-based automated control system operation of the Northern Grain Silo of Jordan. The system connects to a PLC (programmable logic controller) device, and combines operator interface, PLC programming and monitoring functions into one platform. The PLC portion handles direct operations control, while the PC portion handles interfacing and data intensive functions. A simulation package is developed. The package generates a graphical user interface for real-time graphic animations of the Grain Silo operation. We discuss anticipated benefits of such a system and phases of implementation.

The Control System Design of Rotary Li/MnO2 Button Battery Product Line Based on Human-computer interface

In this paper, human-computer interaction was applied as the main features. Human-computer interface programs and programmable logic controller (plc) programs were combined application and address matching and the same address communication mode were adopted. Through the buttons of human-computer interface to trigger the read address set. And further corresponding virtual relays of the plc addresses area were activated. In this paper, Li/MnO2 button battery product line control system was introduced as an example. In the system, according to the process route of product line some areas were set including parameter setting area, single working place debugging area, equipment running area and the alarm browsing area. In order to protect the normal operation of the product line, interlock programs were used to ban parameters modification and single station debugging, avoiding the occurrence of malfunction. At the same time, the fault diagnosis technology was used to have designed a more optimal alarm pattern. The control system has been tested in practice to get good results.

Semantic characterization of programmable logic controller programs

PLC is widely used in the field of automatic control. To use formal methods to verify the correctness of PLC programs, semantic characterization of PLC programs are needed. Based on the extended λ-calculus definition, this paper presents a novel semantic modeling of PLC programs. The results lay the solid underpinnings for theorem proving and modeling checking for PLC systems.