Implementation of functional safety in a robotic manufacturing cell using IEC 61508 standard and Siemens technology

The past 50 years have seen a staggering amount of change in the technology and the business of process automation. The programmable logic controller (PLC) based control and monitoring system is a proven technology used to not only control processes but also to perform safety functions for processes in many industrial applications. There are many opportunities for improvements in any process or manufacturing system. One of the opportunities is achieving accurate safety function for measurement and process control to prevent human injury or death. The programmable electronic systems (PES) such as PLC systems are increasingly being used to perform safety functions as an integral part of the process or plant control system. A Robotic Manufacturing Cell is an example of a PES system and is used as an experimental setup for this work. The IEC 61508 standard defines various phases involved in the overall safety lifecycle for the PES system. This thesis study concentrates on such phases that include safety analysis methods, selection of an appropriate safety control system, implementation of safety as per the standard and safety validation. In this study four test cases are selected to perform safety analysis and implementation. It is verified how the conventional safety analysis method (FMEA) can be used to estimate the risk associated with each test case. As recommended by IEC 61508, a Risk-Graph method is used to calculate the Safety Integrity Level (SIL) requirement for each test case. A number of factors are required to be considered for selecting the appropriate safety control system architecture. After studying these factors and the safety analysis results, the Siemens safety PLC-based control system with SIL 3 configuration is selected for this application. IEC 61508 also recommends implementation of independent control systems for normal operation and safety. This study demonstrates how two independent PLC based control systems, one for normal operations and other for safety-related functions, are implemented to offer the most effective solution for this application. This is achieved by using PLCs from two different manufacturers, a non-safety PLC for normal operations and a Siemens safety PLC for safety-related functions. This study focuses on Machine Safety, and it can be used as a guideline for implementation of functional safety in real-life manufacturing environment.