Use the force... guided relays

SAFETY SYSTEMS and requirements in human-machine interaction have one goal: protecting humans in the event of a failure of the operating application. When humans are involved, safety functions must change to a safe state when a specific fault occurs and fail in a predictable way.

New automation era

Industry 4.0 is creating exciting new possibilities for today’s factories and warehouses, but advancements in automation technologies must also be met with advancements in the safety systems that support them. More flexible and modular production lines are causing manufacturers to rethink risk management systems that have traditionally been developed and approved only for a fixed use case. The shift toward greater and more flexible automation will only continue, and ensuring operator safety amid these changes will continue to be a key challenge.

The aim of Industry 4.0 is to enable flexible and smart production, and this requires a growing amount of sensor data that is often processed by smaller, decentralised controllers. In order to equip smaller controller designs with safety functions, the components for a safe shutdown, such as relays with force guided contacts, must also be further miniaturised.

Efficiency improvement and cost reduction goals also have an impact on risk management principles. Designing safety systems to be more in line with evolving requirements is often a more economical solution than completely eliminating conditions that present potential risks. Take collaborative robots (cobots), which are used with and in close proximity to humans, for example. The surface of a cobot is usually soft and the overall weight is low to reduce the risk of injury resulting from any human-cobot collision. Designing cobots for safer human-machine interaction allows manufacturers and warehouse operators to improve efficiency while still prioritising safety.

Principles allowing non-redundant operation to continue for a limited time in the event of a partial failure of a safety controller within a cobot or other machine are also being discussed. Thus, a repair can be prepared while the production can continue in a degraded operation.

As machine builders design for the next generation of industrial automation, they must be able to prove their equipment and devices to be fail-safe in operation. How components work together in the machine’s safety-related control system is key, and one of the easiest ways to safely switch off circuits is with relay technology.

Supporting machine safety

A relay is an electronically operated switch that is remotely activated by an electromagnet, which pulls a set of contacts to either make or break a circuit. Relays are used in an array of safety-critical applications: You can find them in production lines, robotics, elevators, control panels, CNC machines, motion control systems, lighting, building systems, solar applications and HVAC systems. Among the many different types of relays that support this broad range of applications, force guided relays in particular are an important type to consider for safety-related control systems.

Force guided relays provide failsafe monitoring within safety circuits by preventing the possibility of all contacts being closed at the same time. They are used in safety applications in combination with light curtains, interlock switches and emergency stop switches, allowing for greater outputs for safety relay modules and safety controllers. With their compact design, force guided relays offer a cost- and space-saving alternative to contactors.

Force guided relays are designed to safely monitor the contacts within circuits, as compared to a simple transistor that requires extra measures to identify each conceivable failure. So force guided relays are the preferred choice for safety experts — especially when simple circuitry is used to develop safe outputs, even at high voltages. Monitoring all the electronic components that may be defective in a safe electronic switching output calls for considerable effort. Diagnostics for a safe relay output, however, involve nothing more than monitoring the opening of contacts.

The force guided relay design is different from a conventional control relay. In a force guided relay, the opening and closing contacts are firmly connected by the so-called actuator. This fixed connection prevents a normally closed contact and a normally open contact from being closed at the same time. That is, when a normally open contact is welded, the normally closed contact is necessarily always open. The same is true in reverse. Therefore, for example, you can be sure that the normally open contact has opened by including the normally closed in a monitoring circuit and evaluating its closing.

The IEC 61810-3 (EN 50205) standard describes how to design and test force guided relays in such a way that the antivalence of the normally open and normally closed contacts is not lost, even in the event of a fault. Here, the contacts are connected mechanically via an actuator which is sufficiently dimensioned so it will not break. In situations where such oversizing is not possible, such as at the bending points of springs, potential fragments are secured so that they do not short-circuit the antivalent contact.

The combination of these features supports safety-related control systems and helps protect people’s lives when potential danger needs to be addressed in industrial applications.

Relay innovation

While reliability is the most important consideration for safety applications, it is not the only factor to consider. As manufacturers manage the dramatic increase of signal, power and data in the modern production environment, there is growing demand for safety-related control systems that are not only reliable, but also more compact to free up space on controllers that are becoming smaller and more decentralised.

Innovation in this area has been a key focus for us at TE Connectivity (TE) and across the industry. In fact, TE recently entered a partnership agreement with Phoenix Contact to acquire the force guided slim safety relay elementary relay technology, adding a single-pole, force guided offering to our broad relay portfolio. The slim safety relay is one of the most compact relays of its kind in the market, and achieving this level of miniaturisation is the result of significant advancements in both product engineering and production processes.

This development and other new solutions are addressing the combined need for miniaturised solutions and advanced safety technology. We will continue to work closely with our customers to design, develop and manufacture force guided relays with a compact design that enables a high stacking density and an optimised module width.

Frank Liebusch is global product manager – industrial relays at TE Connectivity

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