Every machine needs an emergency stop button, but what other operator interface devices and functions are required? The human-machine interface (HMI) can provide numerous functions, but it cannot replace push buttons, indicator lights, alarm horns, or stack lights. Don’t skimp on operator-interface devices. Include an emergency stop button, a power off button, a power on lighted button, and a reset button in a 22-mm or 30-mm hole. These buttons and indicators fit under or beside most HMIs. Assemble a machine with an LED status light and alarm indicators such as LED stack lights and alarm horns.
Operators, line supervisors, and engineers will use the emergency-stop push button (e-stop) for numerous purposes. If an operator is in danger or a product is stuck in the machine, add extra red to the mushroom head e-stop.
In an emergency, pounding on the e-stop is likely. Screaming “Stop” will jolt the e-stop. E-stops cannot be HMI buttons, and most safety regulations require them to be hardwired push buttons in the safety circuit. Make the e-stop a red mushroom-head button with a push-pull or twist-to-release configuration. A yellow background is also common, and although not required, it can be LED lighted to show if the e-stop is active.
Using an emergency stop button to turn off the computer is bad form. A machine should have a red extended-head, momentary power-off push button. This button is used to turn off the machine during lunch or overnight. On/off using a green LED lighted push button. If a PLC output controls the light, it can flash to remind the operator to click the power button as needed.
Using a fault-reset push button is also recommended. You could put a reset button on the HMI, however operators like to poke it hard and again. Resetting an HMI can destroy the touchscreen. It is possible to use an additional push button. Fault LED lights or a separate fault LED light can be used to signal a fault.
Many designers choose to utilize an HMI and a relay to start, stop, and reset machines. The HMI can accomplish anything except the e-stop, however it is not the quickest or most reliable method of operation. The same goes for fault and machine status. Pushbuttons, indication lights, and stack lights are sometimes better solutions.
Some believe that with modern HMIs and computer graphics, alarms, machine status, and operation can be displayed on screen. With the top famous patlite stack light Malaysia, a machine-fault response time can be substantially reduced. Also, with an alarm horn, you don’t have to be looking to get machine condition information.
The sooner an operator detects a problem, the better for machine productivity and efficiency. Saving 30 seconds each day for a year results in over two hours of extra production per machine. Adding extra machines to a production line can boost output days per year, paying for the purchase, installation, wiring, and programming of LED stack lights and alarm horns.