Machine Safety Components and Wiring

This page contains all of the different electrical safety devices used on the Stuga machines and how they are wired.

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Below is a list of safety devices used on Stuga machines and 'typically' how they are wired and a breif description of how they work.

1. Emergency stop buttons - Wired with 2 N/C and 1 N/O contact. The estop loops use the N/C contacts and the feedback (input to PLC) uses the N/O contact.
2. Interlock guardswitch - Wired with 2 N/C contacts (out of 3), 1N/O contact and 1 solenoid (Door Unlock). The 2 N/C contacts are split into 2 categories, you have the N/C contact that monitors the state of the solenoid, the N/C contact that monitors the state of the key actuation and a N/C contact that monitors both in series. The N/O contact monitors the state of the key actuation. The solenoid wiring is for unlocking and locking the guardswitch. When no voltage is present on the solenoid wires, the guardswitch will be locked and when voltage is applied, the guardswitch will be unlocked. This is know as a 'power to unlock' guardswitch and this is the type we use on the Stuga machines.
3. Guardswitch - Wired with 2 N/C and 1 N/O contact. The estop loops use the N/C contacts and the feedback (input to PLC) uses the N/O contact.
4. Safety hinge switch - Wired with 2 N/C and 1 N/O contact. The estop loops use the N/C contacts and the feedback (input to PLC) uses the N/O contact.
5. Safety magnetic switch - Wired with 2 N/C and 1 N/O contact. The estop loops use the N/C contacts and the feedback (input to PLC) uses the N/O contact.

Below is a list of other devices fitted on the Stuga machines which are considered safety related but are not necessarily related or impact the main safety circuit.

1. Light curtain - The light curtains are wired with 2 OSSD outputs (Output Signal Switching Device). These are outputs from the light curtain that interact with a designated relay which then controls 2 switches which are wired into the safety circuit. The light curtain is considered part of the safety circuit but it is actually the relay that the light curtain controls which does the safety circuit switching!
2. Zero Speed Detector - This is a device that is used to monitor the status of a 3 phase motor. The zero speed detector is not wired into the safety circuit. However, the zero speed detector does stop the interlock guardswitches from unlocking if it does not detect zero speed. It can sometimes be diagnosed that a guardswitch has failed when actually the issue is with the zero speed detector!
3. Safety Timer - On some models of the ZX5 you will find a yellow safety timer fitted in the machining centre cabinet. This timer is not wired into the safety circuit but it is controlled by it! This timer allows us a safe amount of time before actuating something. In the case of the machining centre, the timer is used to monitor the safety circuit and when it detects the safety circuit is inactive (emergency stopped pressed for example), it triggers a set time to not allow the door unlock signal to activate. This does 2 things, firstly it only allows the doors to open when the machine is safe and also it allows us to set a time to make sure the machine has come to a complete stop before allowing the doors to open.

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