ST-P Series Laser Displacement Sensor in Mobile Phone Middle Frame Step Detection

Industry Background In 3C electronics manufacturing, the middle frame of a mobile phone serves as a structural support, and its machining accuracy directly affects the assembly quality of the entire device. If the step (height difference) between the middle frame and the screen or back cover exceeds tolerance, it can lead to uneven assembly gaps, waterproof failure, or appearance defects. Traditional contact measurement methods are inefficient and prone to scratching surfaces, making them unsuitable for online full inspection. Therefore, non-contact laser displacement sensors have become the mainstream solution for step detection. Detection Requirements Detection Object: Step (height difference) between each side of the mobile phone middle frame and the screen or back cover.

Detection Purpose: Ensure the step is within the allowable tolerance to guarantee assembly quality and appearance consistency. Measurement Parameters: Step value (μm level), typically requiring repeatability ≤1 μm and linearity error <±5 μm. Measurement Challenges Highly Reflective Surfaces: The middle frame is often made of metal (aluminum alloy, stainless steel) or coated surfaces, which are sensitive to laser reflection and prone to stray light interference. Small Steps: Steps are often tens to hundreds of micrometers, requiring high resolution and stability from the sensor. High-Speed Production Line: Fast cycle times (≤2 seconds per part) require high-speed sampling (≥10 kHz) and real-time data output. Multi-Material Compatibility: The middle frame may include metal, plastic, glass, etc., requiring the sensor to adapt to various surface characteristics.

Recommended Sensor Solution The ST-P series laser displacement sensor uses laser triangulation for non-contact measurement, suitable for precision inspection in 3C electronics. Based on installation distance and accuracy requirements, the following models are recommended: Model | Reference Distance | Measurement Range | Repeatability | Linearity Error | Application Scenario ST-P25 | 25 mm | ±1 mm | 0.05 μm | <±0.6 μm | Ultra-small step, high-precision measurement ST-P30 | 30 mm | ±5 mm | 0.15 μm | <±3 μm | General step detection ST-P50 | 50 mm | ±10 mm | 0.25 μm | <±4 μm | Medium distance step detection ST-P80 | 80 mm | ±15 mm | 0.5 μm | <±6 μm | Larger installation space ST-P150 | 150 mm | ±40 mm | 1.2 μm | <±16 μm | Long distance or large range measurement

The sensor features a maximum sampling frequency of 160 kHz and supports Ethernet, RS485, analog, and IO signal outputs, enabling integration with PLCs, host computers, or vision inspection equipment. Implementation Method Installation Layout: Install sensors on both sides or at four corners of the middle frame to measure the height difference between the middle frame surface and a reference datum (e.g., screen surface). Typically, opposing or same-side installation is used, with the sensor optical axis perpendicular to the measured surface. Measurement Process: When the part arrives on the production line, sensors are triggered synchronously to sample, acquiring height data at multiple points. The step value is calculated via algorithm. Data is transmitted via Ethernet or RS485 to an industrial PC, where it is compared with standard values to determine pass/fail.

Signal Output: Analog output (0-10V or 4-20mA) can be sent to a PLC for real-time control, or OK/NG signals can be output via IO. Selection Considerations Accuracy and Range: Select a model with appropriate repeatability and linearity error based on step tolerance. For example, if repeatability ≤0.5 μm is required, ST-P25 or ST-P30 can be chosen. Installation Distance: Choose the reference distance based on available space. If space is limited, short-distance models (e.g., ST-P25, ST-P30) are preferred. Surface Characteristics: For highly reflective metal or black plastic surfaces, sample testing is necessary. Adjust the sensor angle or use polarizing filters to reduce interference if needed.

Sampling Frequency: For fast production lines, select high-speed sampling models (e.g., ST-P series up to 160 kHz) to ensure sufficient data per measurement point. Output Interface: Choose Ethernet, RS485, or analog output based on the control system. Ethernet is recommended for large data transmission, while RS485 is suitable for multi-sensor networking. Application Value Improved Inspection Efficiency: Non-contact online measurement with inspection time <1 second per part, meeting high-speed production line requirements. Ensured Assembly Quality: Real-time feedback of step data allows timely adjustment of process parameters, reducing defect rates. Reduced Labor Costs: Replaces manual sampling inspection with 100% full inspection, minimizing the risk of missed defects. Data Traceability: Measurement data can be stored and uploaded to MES systems for quality traceability.

Precautions Sample Testing: Due to variations in middle frame material, color, and surface roughness, conduct tests with actual samples before formal application to verify measurement stability and accuracy on different surfaces. Ambient Light Interference: Avoid direct strong light on the sensor receiver window; install a light shield if necessary. Installation Calibration: Perform zero-point calibration and linearity calibration after installation to ensure consistent measurement reference. Regular Cleaning: Keep the sensor lens clean to prevent dust or oil from affecting measurements. Temperature Compensation: If ambient temperature fluctuates significantly, consider temperature compensation measures or select models with good temperature stability.