Challenges in Testing

1. The conflict between inspection efficiency and production cycle time. An automated production line can produce hundreds of bolts per minute, requiring 100% inspection of parameters such as diameter, shank diameter, head thickness, and diagonal dimensions. Traditional contact gauges, such as calipers and micrometers, take several seconds to measure a single dimension, making them suitable only for sampling inspections. They cannot keep pace with the production line’s rhythm, resulting in a significant risk of missed defects.

2. The difficulty of achieving micron-level precision. Tolerance bands for high-precision bolts are often controlled within ±0.02 mm. Manual readings are subject to subjective errors, and uneven contact pressure from measuring tools can introduce deformation errors, making it difficult to consistently achieve micron-level precision.

3. The complexity of simultaneous multi-feature measurement. Bolt inspection involves multiple parameters; it requires simultaneous measurement of several features, including head outer diameter, shank diameter, thread major diameter, head thickness, and hexagon diagonal length. Traditional vision systems often rely on static imaging, which requires the workpiece to be paused. It is difficult to complete all feature measurements at a single station, and moving the workpiece between multiple stations leads to cumulative positioning errors.

Testing Requirements

1. The tolerance range for the head outer diameter and shaft diameter must be within ±0.02 mm;

2. The tolerance range for the head thickness and hexagonal opposite side dimensions must be within ±0.03 mm;

3. Measurements of multiple dimensions—including diameter, height, and opposite sides—must be performed simultaneously at the same workstation;

4. The measurement and inspection time per piece must be less than 0.5 seconds to achieve 100% online full inspection;

5. The system must be capable of outputting automatic sorting signals to reject non-conforming products in real time.

Inspection Solution: Telecentric Measurement System

The POMEAS Telecentric Measurement System provides a comprehensive, real-time online measurement solution for bolt dimension inspection. This solution combines a high-resolution industrial camera with a telecentric lens featuring a large depth of field, and is equipped with a high-speed image processing platform. It is directly integrated into automated production lines following bolt cold heading and thread rolling.

The workflow of the solution is as follows: Bolts pass through the measurement station at high speed via a vibrating feeder or conveyor belt without stopping; a Telecentric Measurement System continuously captures images at a rate of tens to hundreds of frames per second, capturing the side profile of the bolts in real time; Built-in algorithms process the images in less than 50 ms, extracting key dimensions such as head outer diameter, shank diameter, head thickness, and hexagon opposite side length, and comparing them in real time against preset tolerance limits; measurement data, inspection results, and statistical trend charts are displayed in real time on an industrial touchscreen, while OK/NG signals are simultaneously output to drive the sorting mechanism, automatically diverting non-conforming products to the reject channel.

The system is specifically optimized for online continuous inspection: a telecentric lens with a large depth of field ensures that image size remains unaffected even when the workpiece experiences slight vibrations within the depth of field; a high-speed global shutter sensor eliminates motion blur, ensuring clear and sharp images during high-speed capture; and the edge detection algorithm achieves sub-pixel accuracy with a repeatability of ±0.005 mm, meeting stringent micron-level tolerance requirements.

Advantages of the Solution

First, it offers extremely high efficiency, truly enabling 100% online inspection. Measurements can be completed while bolts pass through the line at high speed without any pauses, matching the production line’s maximum cycle time. The inspection time per part is easily kept under 0.5 seconds, achieving 100% real-time inspection and eliminating the need for sampling.

Second, it offers exceptional accuracy with consistent and stable data. Sub-pixel edge detection algorithms and a telecentric optical system ensure micron-level measurement accuracy, eliminating human error and contact deformation. Repeated measurements yield highly consistent results, providing precise data support for process optimization.

Third, it enables simultaneous measurement of multiple dimensions with flexible deployment. A single system can measure various features—such as diameter, height, and opposite sides—at the same time, eliminating the need for multi-station processing. The compact design facilitates integration into existing production lines, supports rapid switching between product specifications, and allows one-click access to parameter presets.

Fourth, closed-loop quality management drives process improvement. Real-time trend charts visually display dimensional drift, enabling early intervention through out-of-tolerance alerts; measurement data is traceable and exportable, and integrates with MES systems to establish a closed-loop quality management system from inspection to feedback, helping to continuously improve yield rates.