On almost every machine, an emergency-stop pushbutton is essential, but is it required to have other operator input equipment and functionalities? The human-machine interface (HMI) includes a lot of buttons, indicators, data entry, and display options. However, it can’t replace all of the functions that indicator lights, alarm horns, pushbuttons, stack lights can provide. It was recommended to not be cheap when it comes to operator-interface devices. An emergency button, a power-on illuminated push button, a power-off push-button, and a reset button that fits in a 22-mm or 30mm hole should be included. They usually fit nicely beneath or beside almost any HMI. Other than that, LED status lights and alarm signs such as an LED stack light and alarm horn should also be included to ensure the prompt reaction to a machine malfunction.
Whenever the operators or other related workers require help, they would push the emergency stop button, however, only for intended purposes. When it comes to extreme urgent situations such as the operator in danger or a product getting stuck in the machine, it is fine to slam the button more. Yet, the e-stop clearly cannot be a button on the HMI. All applicable safety regulations generally need the e-stop to be a wiring push button in the safety circuitry. A red mushroom-head button with a push-pull or twist-to-release configuration for the e-stop button is encouraged to be made to keep it in place. A yellow background is usual while it could be LED lighted to make it easier to see whether the e-stop button has been activated though it is not necessary.
To conduct these machine power-on, power-off, and reset actions, many designers prefer to employ an HMI and a relay. The HMI can perform everything except the e-stop, but it’s not the fastest or most reliable way to operate during production. The same would be true for indicating faults and machine status. Push buttons, indicator lights, and stack lights can sometimes be superior solutions. Some believe that alarm indication, machine status, and operation may all be displayed on a screen due to the advancements in HMIs and computer graphics. Conversely, a stack light, status light, fault indicator, or alarm horn, may cut down the response time to a machine-failure scenario. It can also convey machine status information at a glance from a distance, and you don’t have to look with an alert bell.
It’s a good idea to standardise the number of lights, colour, and use of each colour for every machine, independent of the provider, when it comes to LED stack lights. Red, amber, green, and blue are the most common colours. During production, a line of green lights is the goal, but each colour light can be set to solid, flashed slowly, or flashed quickly to represent three different machine states. For instance, when the equipment is stopped, the red light can be set to stay on solid, set to flash slowly if there is a minor defect or flash quickly if there is a serious fault.
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