Connected safety for improved productivity
What is a Safe Network and what benefits does it offer for system designers and users? Dr Martin Kidman, Safety Specialist at Sick UK, provides a useful, step-by-step ‘walk through’ of the principles of Safe Networks, how safe information can be transmitted over them, and the advantages that can be gained.
Ever since they became an option in the 1960s, automation systems have traditionally been ‘hard wired’ using programmable logic controllers (PLCs). The introduction of digital logic circuits is seen as central to the industrial digital age and is sometimes called the ‘Third Industrial Revolution’.
The PLC offered increasing automation versatility and, when hardwired to field devices, it could use the inputs from them to drive outputs through combinational and sequential logic. As PLC technology developed, communication between different devices and other PLCs was enabled, such that more information could be transferred, for example between remote I/Os, motor drives and servo controllers.
Communication between electrical components requires a bus system and a protocol - either open standard protocols or proprietary protocols. When two or more devices communicate, each device in the network is referred to as a ‘node’. These nodes, which would normally have a unique address, can communicate via the bus system, providing HIGH/LOW signals according to the protocol. This offers many advantages over traditional hardwired systems: the time and cost needed for wiring the system are dramatically reduced, as is the installation time. There are new opportunities to monitor and diagnose maintenance issues. Systems can be easily expanded, or devices replaced, and it’s possible to add more intelligent field devices to the network.
There are now many different types of networks used in industrial environments, which allow the exchange of data between systems and the connections between devices can be established using either cable or wireless media.
Adding safety over networks
The possibility to transfer safe (as opposed to ‘non-safe’) data over networks has only really been possible since the turn of the 21st century, when the standard IEC 61784-3 was published. This covers functional safety fieldbuses and gives the general rules and profile definitions of adding a safe data layer on top of existing fieldbus protocols. Today, there are many safety protocols such as PROFIsafe, Functional Safety over EtherCAT (FSoE) and Common Industrial Protocol Safety (CIP safety).
Implementing a Safe Network offers similar benefits to using a standard network over hard wiring. However, there are significant additional advantages:
Let’s consider automated guided vehicles (AGVs). As applications and devices have become more complex and bespoke, the need for greater communication between the safety controller and safety laser scanners has increased. This is because all information is Boolean (on/off) and each signal has previously required a separate cable. What’s more, the safe I/O has been limited to the number of Output Signal Switching Devices (OSSDs). So, if an AGV application is realised using a scanner front and back with 64 field sets, each of which is selected based on the speed derived from encoder signals via a safety PLC, then the required number of individual cables on the AGV, just for safety, could easily be upwards of 50.
Same bus system
Safety device manufacturers, including Sick, have, therefore, introduced their own proprietary safety protocols. Sick’s EFI (Enhanced Function Interface), for example, enables fail-safe communication using the ‘Black Channel’ approach allowing the transmission of both failsafe and standard data on the same bus system. Using EFI, safe communication has a very low probability of dangerous failure and does not normally reduce a system’s integrity, enabling performance levels of up to PLe (EN ISO 13849) and safety integrity levels of up to SIL3 (IEC 62061) to be maintained.
EFI has supported safe communication between Sick safety laser scanners and Sick Flexi Soft controllers for more than a decade. A key benefit was the ability to simultaneously monitor more than one protective field at the same time without having to use multiple OSSD’s each requiring an additional two wires. By having the status of several protective fields available at the same time, the designer could create complex applications involving sequence monitoring, autonomous field switching, self-muting and safe sequential logic programmes. Another benefit was to transmit inputs to the scanner to switch between field sets without the addition of many wires.
More recently, the release of the Sick Flexi Soft EFI-pro Gateway has enabled open and safe integration via EtherNet/IP based on the CIP Safety protocol. This has allowed connection to devices like the Sick microScan3 safety laser scanner as well as to third party robot controllers from leading manufacturers, remote I/O modules and safety PLCs.
Safe data over one cable
Connecting a safety laser scanner to a safety controller over EFI Pro allows the designer to access all safe and standard data over one cable to create adaptive, scalable modular safety. Field switching, adding multiple scanners or connecting to robots, encoders and other devices with CIP Safety or standard Ethernet on board no longer requires multiple cables and programming tools.
Connected to the Flexi Soft modular controller, EFI Pro provides value-added services on top of Ethernet/IP CIP Safety, such as time synchronisation of multiple devices for advanced diagnostics and data processing. Non-safe communication to any other network facilitates the simultaneous output of data, for example for AGV navigation over the same cable.
As an example, when MasterMover developed its new heavy weight AGV300 Tow, safety was the unequivocal starting point. Each standard MasterMover AGV model uses two Sick microScan3 scanners that communicate via the EFI Pro Gateway (EtherNet/IP CIP Safety) to the Sick Flexi Soft Safety Controller. Using Sick’s Flexi Soft Safety Controller and Sick Safety Designer software provided an ecosystem for MasterMover to confidently integrate their own safety system and achieve an integrated and standards-compliant safety design. Together with Sick’s DFS60 safety encoders, and the Sick Drive Monitor FX3-MOC1, all of these devices are integrated into an application achieving PLd (EN ISO 13849)/SIL2 (EN 62061).
Fanuc robots have worked together with Sick to bridge a gap in connectivity between robot tending an injection moulding machine. The resulting development achieved a simple I/O ‘handshake’ between the robot and the machine by using Sick’s Flexi-Soft safety controller with the addition of the Sick Safe EFI-PRO gateway solution for standard industrial EtherNet-based safety network integration over CIP Safety. The solution was groundbreaking in bridging a gap in connectivity, as well as providing a proven, extremely simple system that provides future-proof security as both standards and connected devices align with CIP Safety over EtherNet/IP in future.
Networks can be used to reduce wiring and increase automation. By additionally implementing Safety over Networks, complex applications can be realised whilst increasing productivity and availability with high levels of diagnostics. The openness of the system makes it a versatile component to help production teams navigate a path to Industry 4.0 and the IIoT.
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