Conventional, rigid safety concepts represent a significant hurdle on the way to the much-discussed Industry 4.0 production. This concerns two aspects of safety technology that must always be treated as a whole, but which deserve to be considered in isolation in this context. Firstly, of course, there is still a need for sophisticated safety devices. However, in view of increasing modularity and functional integration, the transition from safety fences to equipping individual machines and system components with door contacts, light grids and similar measures is becoming increasingly evident in this context. The second aspect concerns the logic that brings the system into a safe state for people by means of safety-oriented evaluation of the sensors and the control of safe actuators. It therefore forms a substantial part of the overall control intelligence. In order to solve the new challenges in smart factories, machine manufacturers and automation specialists need to merge these two areas of expertise into a single unit.

Franz Aschl, Sigmatek: "Hard-wired safety solutions are fading into the background and bus-integrated, programmable safety systems are clearly setting the trend."

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According to Franz Aschl, responsible for innovation management at Sigmatek, the tried and tested safety relay is still justified in individual cases, but: "The more complex machines and systems become, the more practical safety control concepts with data transport via Ethernet are." This simplifies the cabling considerably, as the safety-related signals share the existing system bus over longer distances. In addition, double wiring of the safety sensors is no longer necessary, as the function-oriented control unit receives current status information simultaneously via the shared bus.

This opens up new possibilities for adapting the control behaviour and for visualization. This also applies to status transmission to higher-level ERP and MES data systems. Even the keyword cloud is already occasionally used in connection with safety control systems.

While programmable and configurable control systems were long associated with comparatively high investment costs and complex programming, this image has changed significantly to date. Cost-effective and equally powerful safety controllers dominate the market. With their extremely small footprint, they have replaced classic relay circuits even for simple applications. And with TÜV-certified function blocks, software applications can be implemented in minutes and at the same time documented in accordance with standards. Automation systems created in this way meet current safety standards such as SIL CL 3 in accordance with IEC 62061 or Performance Level PLe, Cat. 3 and 4 in accordance with EN ISO 13849-1/-2.

One example of such a safety solution is the S-Dias safety system. The core of the modular system for the DIN rail is the safety controller, which monitors and controls the application and provides the bus interface to modules with safe inputs and outputs. This includes additional modules for the evaluation of absolute and incremental encoders. Drive systems with safety-related functions complete the system. Communication takes place via the local system bus and via Varan or Ethernet if the system is decentralized. Different topologies and design variants are possible. All safety modules in the S-Dias family are just 12.5 mm wide, and there is also a safe relay output module that is twice as wide.

Modularity also in safety engineering

The flexible configuration of complex machines requires an increasing degree of modularity. Equipping decentralized units with independent safety controllers solves this situation: several safety controllers are now operated in a network and exchange relevant information securely with each other. "The simple programmability of the overall system plays a key role here, as increasing complexity in various areas is to be expected," emphasizes Aschl in this context and adds: "In addition to the increased application effort due to the often high number of sensors and actuators, functions to support maintenance and cleaning activities are added. Safe semi-automatic and fully automatic operating modes are needed for this."

With graphical programming tools, error-free applications can be implemented in modern mechanical engineering in a matter of minutes - including standard-compliant documentation.

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Development tools that protect the user from sources of error and minimize the effort required for training and programming help here. If such tools also provide tested logical safety functions, this considerably simplifies the documentation and commissioning of extensive safety applications. The graphical editor of the 'Lasal Safety Designer' from Sigmatek, for example, includes a library based on PLCopen with more than 20 certified safety function blocks. Similar to reference marks for inputs and outputs, blocks for 'Emergency Stop', 'Two Hand Control' or 'Guard Locking' are dragged and dropped from the project tree and organized in logical units. Despite the functional separation required by the separate acceptance of safety-relevant control components, the 'Safety Designer' is seamlessly integrated into the in-house all-in-one development environment.

Reconfiguration during operation

However, the implementation of the complex requirements of Industry 4.0 demands even more from safety technology systems: the needs-based reconfiguration of modular machines within a cell is one of the key challenges that needs to be solved. While conventional systems for machine safety interpret a non-responsive component as a safety violation and react with a 'fail-safe', flexible reconfiguration of machines and systems during operation is essential in terms of Industry 4.0. In the current library of the aforementioned Safety Designer, for example, users will find specially developed function blocks that are also TÜV-certified. They allow optional units to be logged on and off without interrupting operation.

Mobile HMI solutions are becoming increasingly important. From a safety perspective, this also requires the emergency stop function to be integrated into the devices via WLAN.

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The principle of dynamic device registration is also used in plant systems with battery-powered units. This includes the rapidly growing group of automated guided vehicles (AGVs). The nature of such systems lies in their mobility; wireless communication is a must. However, a limited energy budget and massively restricted space requirements make it difficult to find the ideal safety technology solution.

Franz Aschl is familiar with the safety-related sticking points of mobile applications: "Let's think, for example, of shuttles that work in a system network in intralogistics. We can already see that such systems are replacing the fixed conveyor systems installed in many production plants. They offer adaptive production lines the opportunity to dynamically change the associated material flows. If a single device becomes stranded outside the radio range, this must not lead to the entire system coming to a standstill - that would make such a concept absurd."

In the context of optional, flexible and mobile subsystems, portable HMI solutions for use in WLAN are becoming increasingly important. However, if a machine or system is controlled via mobile panels, the demand for integrated safety functions inevitably arises.

After all, a machine operator with the HMI in his hand can move quite far away from the nearest safety device permanently installed on the machine. Franz Aschl explains: "For this reason, we are currently working on the further development of our wireless WLAN handheld operating device. Using the technology from the safety controllers, it will soon be equipped with an emergency stop button, enabling button and key switch for safety-related use."

Safety and OPC UA?

Up to this point, the following applies: with the switch to bus-based, programmable safety controllers, modern machines rarely work in isolation, but together with other equipment such as robots and handling devices, with which they form a unit in terms of safety. However, the variety of bus systems represents a hurdle for the implementation of integrated safety control systems. Bus-integrated solutions generally use the 'black channel' principle for data transmission and are therefore independent of the protocol of the bus system used. However, their data formats are different. For this reason, it was common practice for a long time to connect the signals of different machines and devices via conventional safety contacts. However, this considerably restricts the exchange of information as an essential prerequisite for Industry 4.0.

The 'black channel' principle makes data transmission independent of the protocol of the bus system used. Although the data formats currently still vary, OPC UA should soon provide a remedy in safety technology too.

© Sigmatek

In the area of function-oriented control systems, OPC UA (Unified Architecture) is in the process of permanently changing the landscape of information exchange via digital networks. For the first time in the history of industrial automation, there is an independent protocol standard that is supported by a broad manufacturer base in a wide range of market segments. Currently used primarily at the control level, OPC UA is undisputedly seen as a driver for the rapidly advancing use of industrial cloud communication in the automation world. It is already clear that modern safety technology will also follow this path. For example, the European Committee of Plastics and Rubber Machinery Manufacturers has defined the electrical interface between injection molding machines and external safety devices as well as a manufacturer-independent interface between injection molding machines and robots with the new Euromap recommendations 78 and 79. OPC UA plays an important role here and could also provide a strong basis for an independent, modern communication standard for safe units working together.

Sigmatek has already implemented the OPC UA server and client functions for function-oriented controllers. This now opens up additional areas of application for the safety controllers, as they can be fully integrated into automation solutions in addition to stand-alone use. Information is exchanged with the function-oriented CPUs according to the same principle as between safety controllers. Safe data transport takes place either via the Varan real-time Ethernet system or by applying the 'Black Channel' principle via any other Ethernet configuration.

In conclusion, it can be said that In terms of increasing benefits for manufacturers, operators and users, a holistic approach to processes for the smart factory necessarily includes functional safety. Their implementation on the basis of modern technologies will remain the responsibility of machine manufacturers in the future. At the same time, they are jumping on a bandwagon that can take them forward at immense speed, both technologically and commercially. This safety train, fueled by the growing demands of smart factories, is picking up speed and is unlikely to stop in the foreseeable future.

Author: Ingrid Traintinger is Head of Marketing Communications at Sigmatek.