Safety relays are self-monitored interlocked contacts that can improve your chances of passing a risk assessment. They are an additional safety measure that can be added to your hydraulic press controls.
Safety relays can act as another layer of protection on your press. When the contacts are triggered, they can shut off an entire system if something is reported amiss from their source component. Since they are self-monitored, they can also trigger if an issue is detected on itself, such as the contacts welding together.
Let’s explore the impact of incorporating safety relays on e-stops, palm buttons, and light curtains!
Upgrade Your E-Stop
An e-stop, or emergency stop, is a kill switch for hydraulic presses. E-stops, once triggered, will shut down the power outputs, stopping the motion of the press while still allowing operators to have control of the machine.
Adding a safety relay to an e-stop allows you to take preventative action and decrease the chance of an e-stop malfunction or misfire which could harm your workers or product. Adding a safety relay to your e-stop can also help protect the press from damaging itself. It may seem redundant to add a second safety measure, but safety switches can save you a great deal of time and money in the future by providing you with extra protection against hazardous situations.
E-stops are wired in series to safety relays. The e-stop's safety relay controls and monitors the safety contactor(s) as well as provides power to outputs/motions of the press. For example, your e-stop contacts are wired normally closed, therefore if they were to open, the safety relay would be triggered and shut down the outputs/motion until the problem is resolved.
Upgrade Your Palm Button If Applicable
A palm button is a two-handed device used for hydraulic presses allowing operators to activate the press from a safe distance. To control the press with palm buttons, a single person will simultaneously apply pressure to both trigger buttons to activate the press. The safety relay will not allow the machine to turn on if both buttons are not triggered within milliseconds of each other.
Adding a safety relay to the palm button creates a safer process that cannot be tampered with. When paired, safety relays are wired to stop operators from tying down one or both palm buttons to run their operations faster; this is designed to prevent workers from running the press continuously while moving the product in and out by hand.
The palm button safety relay is connected to the PLC (Programmable Logic Controller). Before palm button safety relays, palm button logic was performed directly in a PLC, allowing programmers to manipulate, change, or make errors when implementing the code. Operators would sometimes figure out the holes in the programming and could create workarounds to circumvent the intention of the palm button code. When wiring a safety relay into this process, you help remove the liability and limit the risk of potential coding errors from the programmer. If the safety relay detects an error in the palm button wiring or contacts, it will not allow the machine to cycle. This upgrade can help develop an effective anti tie-down safety relay.
Upgrade Your Safety Light Curtains if Applicable
Light curtains emit infrared light by means of two light bars: one, an emitter of light and the other, a receiver of light. When paired, they are used to protect operators from getting too close to potentially hazardous situations created by the equipment. The light bars act as a barrier between worker and machine, and once a light beam is disrupted, it will shut down the press. The beams are disrupted when a person or thing crosses a beam emitted by the light bars.
When adding a safety relay to light curtains, the safety relay acts as a second line of defense by monitoring the light curtain’s status and health. A broken barrier will alert the safety relay that the light curtain has been broken, causing the relay to change state from safe to unsafe and shut down the press. The light curtain safety relay controls an additional safety contactor on the light curtain similar to the e-stop safety contactor. They can be used in tandem with your e-stop relay, depending on the needs of your application. Often, for efficiency, a second safety contactor is needed.
