(I) System working principle
The four photoelectric sensors in the system are installed on the upper and lower sides of the two timing belts respectively, so that when the timing belt is broken from above or below, it can be ensured that it can be detected in the early stage of fracture. When the timing belt fails, the timing belt detection device will disconnect the upper and lower limits of the host, thereby preventing the host from continuing to run and issuing an alarm.
If the 4 photoelectric sensors in the system are used as the "eyes" for detecting the timing belt, the intermediate relay is the "hand" for performing the action, and the buzzer is the "mouth" for performing the alarm. During normal operation, one photoelectric sensor drives one intermediate relay (the four photoelectric sensors correspond to K1, K2, K3, and K4, respectively). When starting up, if there are no faults on the synchronous belt, photoelectric switch, and K1 ～ K5, K1 ～ K5 will be activated and will be powered on; if any one of them is faulty, it will not be powered on. If a synchronous belt failure is detected during operation after power-on, the photoelectric switch that detects the failure will stop driving the corresponding intermediate relay (K1 ～ K4). At this time, K6 and K7 are engaged, and K6 is responsible for self-locking and alarming. K7 is responsible for cutting off the upper and lower limits.
note:
1.Because the synchronous belt has a large inertia when rotating, even if the system detects a fault and cuts off the upper and lower limits, the fault point of the synchronous belt is likely to have passed the detection range of the photoelectric switch. This system does not have a CPU and cannot store fault states. When a fault is detected, the relay board relies on self-locking to maintain the alarm state. If the point of failure has moved beyond the detection range, it may still operate after shutdown and restart. Therefore, once an alarm occurs, you must first carefully check whether the timing belt is faulty!
2. If the failure point of the synchronous belt is just within the detection range when the machine is just turned on, the alarm will not occur, but the system will cut off the 12VDC power supply. Of course, if any of the 4 photoelectric switches or 5 intermediate relays (K1, K2, K3, K4, and K5) is damaged, the power cannot be turned on when the device is turned on.

(Two) system composition
The whole system is mainly composed of the following parts:
1.Relay board
2.Photoelectric switch
3.Buzzer
All three are installed in the host device.