How to customize a photoelectric switch control box for a conveyor belt with start-stop functions

The following is a detailed solution for customizing a photoelectric switch control box for a conveyor belt with start-stop functions,

 including principles, component selection, wiring, and debugging steps, which is applicable to industrial automation scenarios:

I. Analysis of Control Requirements

 Functional Requirements:

1. **Start and stop triggered by the photoelectric switch**:

   - The conveyor belt automatically starts when an object is detected, and stops with a time delay after the object leaves (to avoid

 idling).

   - Or it can be manually started and stopped by buttons, and the photoelectric switch is only used for detection (the requirements

 need to be clarified. In this article, the example is automatic start-stop + manual emergency stop).

2. **Safety protection**:

   - Overload protection, short-circuit protection, and emergency stop function.

 II. Design of the Control Scheme

1. Control Logic Diagram

Photoelectric switch signal → Control circuit → Contactor → Motor start and stop

(With a time-delay relay to achieve shutdown delay)

2. Selection of Electrical Components

 III. Electrical Schematic Diagram

1. Main Circuit

Three-phase power supply → Circuit breaker (QF) → Main contacts of the contactor (KM) → Thermal relay (FR) → Motor (M)

2. Control Circuit

L/N → Circuit breaker (QF2) → Emergency stop button (STP) → Control logic → Contactor coil (KM)

**Details of the control logic**:

- **Automatic mode**:

  Photoelectric switch signal (NO) → Time-delay relay coil (KT) → Normally open contact of the time-delay relay (KT-NO) → 

Contactor (KM)

- **Manual mode**:

  Start button (SB1) → Self-locking of the contactor (KM) → Stop button (SB2)  

 IV. Wiring Steps

1. Wiring of the Main Circuit

1. Connect the three-phase power supply to L1/L2/L3 of the circuit breaker QF, and connect N to the neutral terminal.

2. Connect the output terminal of QF to the main contacts (T1/T2/T3) of the contactor KM.

3. Connect the output terminal of KM to the input terminal of the thermal relay FR, and connect the output terminal of FR to the 

U/V/W terminals of the motor M.

2. Wiring of the Control Circuit

1. **Wiring of the photoelectric switch**:

   - Brown wire: DC24V+ (Connect to the positive pole of the switching power supply)

   - Blue wire: DC24V- (Connect to the negative pole of the switching power supply)

   - Black wire: Signal output (NO contact, connect to the positive pole of the time-delay relay coil)

2. **Wiring of the time-delay relay**:

   - Coil: AC220V (Connect to L/N)

   - Time-delay closed contact: Connect in series to the coil circuit of the contactor KM

3. **Wiring of the button and indicator light**:

   - Emergency stop button (STP): Normally closed contact, connected in series to the main circuit power supply.

   - Operation indicator light: Connected in parallel to the auxiliary contact (KM-NO) of the contactor KM.

 V. Layout Design of the Control Box

1. Panel Layout

2. Internal Layout

- Top: Circuit breaker, contactor, thermal relay (Installed vertically for easy heat dissipation).

- Bottom: Switching power supply, time-delay relay, terminal block (Convenient for wiring).

- Right side: Ground terminal, cable inlet hole (With a waterproof joint).

 VI. Debugging Steps

1. **Power Test**:

   Connect the power supply and check whether the circuit breaker and indicator lights are normal.

2. **Calibration of the Photoelectric Switch**:

   - Block the photoelectric switch and test whether the signal indicator light lights up.

   - Adjust the sensitivity of the photoelectric switch (through the potentiometer) to ensure reliable detection of objects.

3. **Test of the Time-delay Function**:

   - Trigger the photoelectric switch, and the motor starts; move the object away, the time-delay relay starts timing, and the

 motor stops after reaching the set time.

   - Adjust the time-delay time (such as 5 seconds) to meet the production rhythm.

4. **Test of the Manual Mode**:

   Press the start button, and the motor runs; press the stop button, and the motor stops; the emergency stop button needs to 

cut off all power supplies.

VII. Precautions

1. **Safety Protection**:

   - The control box must be reliably grounded (PE terminal).

   - Ground the motor casing to prevent electric leakage.

2. **Environmental Adaptability**:

   - The photoelectric switch needs to avoid strong light and dusty environments. For the opposed type, ensure that the transmitting

 end and the receiving end are aligned.

   - The protection level of the control box is IP54, which can prevent water spray and dust.

3. **Troubleshooting**:

   - If the motor does not start: Check whether the circuit breaker and thermal relay are tripped due to overload.

   - If the photoelectric switch is triggered by mistake: Check whether the signal line is grounded or has poor shielding.

 VIII. Cost Budget (Reference)

Through the above solution, the control of the conveyor belt with automatic detection start-stop + manual control + safety protection

 can be realized, which is applicable to scenarios such as production line sorting and packaging. If functions need to be expanded (such

 as multi-motor linkage, PLC remote control), small PLCs such as Siemens S7-1200 can be further integrated.