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A non-intrusive method to make safe existing PLC Program

机译：确保现有PLC程序安全的非侵入性方法

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This paper presents an original non-intrusive method to make safe existing Programmable Logic Controller (PLC) program for manufacturing systems. In this work, manufacturing systems are considered as Discrete Event Systems (DES) with logical Inputs (sensors) and logical Outputs (actuators). Usually, to guarantee the safety of a PLC program it is necessary to use either tests or formal methods like model-checking to verify that safety and functional properties are respected. This works has to be managed by an expert who is not often the engineer in charge of PLC programming because it requires specific competencies. The idea in this paper is not to check a specific PLC program but to add at the end of the PLC program, a specific algorithm based on Boolean safety constraints (designed and formally checked by the expert) which is going to authorize or forbid the PLC outputs in order to guarantee the safety. The set of Boolean safety constraints is defined independently from the controller specification and depends only on the system. The algorithm is presented in details in the paper and illustrated with a 4 cylinders system. The approach has also been successfully applied on real PLC programs from SNCF (French acronym for National Society of French Railways) to control the Power Supply Equipment of the Electric Lines (PSEEL). This approach can also be used to design safe PLC program by separating the functional part from the safety part. That allows to result in a safe control, really different from a conventional approach based on a complete specification for instance in GRAFCET (IEC 60848) that does not distinguish the functional aspect from the safety aspect.
机译：本文提出了一种原始的非侵入式方法，可以使制造系统安全地使用现有的可编程逻辑控制器（PLC）程序。在这项工作中，制造系统被视为具有逻辑输入（传感器）和逻辑输出（执行器）的离散事件系统（DES）。通常，为了保证PLC程序的安全性，必须使用测试或形式化方法（例如模型检查）来验证是否遵守安全性和功能特性。这项工作必须由专家来管理，因为专家需要特定的能力，所以该专家通常不是负责PLC编程的工程师。本文的想法不是检查特定的PLC程序，而是在PLC程序的末尾添加基于布尔安全约束（由专家设计并正式检查）的特定算法，该算法将授权或禁止PLC输出以保证安全。布尔安全约束的集合独立于控制器规范而定义，并且仅取决于系统。该算法在本文中进行了详细介绍，并以4缸系统进行了说明。该方法也已成功地应用于SNCF（法国铁路协会的法语缩写）的实际PLC程序中，以控制电线的供电设备（PSEEL）。通过将功能部分与安全部分分开，该方法还可用于设计安全的PLC程序。这使得可以实现安全控制，这与基于完整规范的传统方法（例如GRAFCET（IEC 60848）中的常规方法）完全不同，该传统规范没有将功能方面与安全方面区分开。

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