Background of the Proposal

Injection-molded gears are widely used in precision transmission applications due to their lightweight, low-noise, and self-lubricating properties. However, the injection molding process is susceptible to fluctuations in temperature and pressure, leading to defects such as shrinkage, burrs, material shortages, and excessive gate height. Traditional manual visual inspection is inefficient and prone to missed defects, while 2D machine vision struggles to capture height information, failing to meet the demands of precision assembly. To address this, this solution incorporates 3D line laser profilometry technology to achieve full-dimensional, high-precision automated in-line inspection.

Testing Requirements

 In accordance with product manufacturing standards, inspection must cover the following key metrics:

1. Detect burrs and material shortfalls on gear edges;

2. Identify in-plane shrinkage defects;

3. Ensure that gate locations do not protrude above the reference plane;

4. Gear diameter measurement errors must be controlled within ±0.1 mm; 5. The overall inspection cycle time must be 7.5 seconds per unit.

Challenges in Detection

The surfaces of injection-molded gears typically have a certain degree of gloss, which can cause glare; minute burrs and shrinkage marks are only tens of micrometers deep, resulting in low contrast; the height of gate residues must be calculated by fitting a reference surface, which demands high algorithmic precision; simultaneously, the stringent 7.5-second cycle time requires data acquisition and processing to be highly parallelized.

Testing Protocol

 The system utilizes a high-precision 3D line laser profile sensor developed in-house by POMEAS to scan the three-dimensional profile of gears and generate point cloud data.

1. Positioning and Reference Establishment: Use a template matching tool to select clear and stable feature regions in the gear image (such as the bore or tooth root) as positioning references, ensuring that the coordinate system remains consistent for each measurement.

2. Sprue Height Detection: Extract point cloud data from four points around the sprue location to fit and construct a reference plane. Use the height tool to calculate the vertical distance from the highest point of the sprue to the reference plane. If the distance is negative or zero, the sprue is determined not to be higher than the plane.

3. Diameter and Defect Detection: Based on the positioning results, the “Circle Fit” tool is used to fit the outer circumference of the gear, obtain radius data, and calculate the diameter, with an accuracy meeting the 0.1 mm tolerance requirement. At the same time, by analyzing the grayscale gradient of the 3D contour, the system identifies edge burrs, material shortages, and depth anomalies caused by in-plane shrinkage.

Advantages of the Solution 

The POMEAS 3D line laser profile sensor features non-contact, high-precision measurement capabilities and can accurately capture even minute deformations. Compared to 2D vision systems, this solution provides accurate Z-axis height data, effectively addressing the challenges of inspecting gate height and flatness. At the algorithmic level, the combination of template matching and geometric fitting tools ensures measurement stability during high-speed motion, enabling a full inspection of dimensions and defects in a single scan.

Program Results

Field testing on the production line has demonstrated that the solution achieves a repeatability of 0.05 mm in diameter measurement, fully meeting the 0.1 mm tolerance requirement; the total inspection time per part is consistently 6.8 seconds, outperforming the 7.5-second cycle time target. The system successfully detects burrs as small as 0.03 mm and minor shrinkage, with 100% accuracy in determining gate height, thereby enabling fully automated, high-precision quality control for injection-molded gears.