What Is a Surface Inspection System?
A surface inspection system is a device used to inspect products on factory production lines.
It is mainly used to identify defective products and detect defective parts.
Uses of Surface Inspection Systems
Surface inspection systems are used in various fields for product inspection. For example, they are used in the inspection of continuously produced products such as film, glass, and metal plates.
A surface inspection system helps prevent the shipment of defective products by detecting defects based on image data obtained from capturing images of each product’s surface. However, the inspection criteria vary depending on the product.
For products where smoothness is crucial, such as film and glass, the system detects unevenness, while for metal plates, it targets fine scratches for detection.
Principle of Surface Inspection Systems
A surface inspection system detects defects using image data captured by a camera. It consists of an inspection section with a light receiver and a light projector, and a control section for image processing, including a computer. A CCD camera is generally used as the light receiver in the inspection section.
The projector, acting as the light source, may use various types of lamps such as fluorescent, LED, and halogen lamps, depending on the application. The light from the source, the floodlight, is reflected or transmitted on the object’s surface, captured by the CCD camera, and converted into an electrical signal.
The signal from the CCD camera is processed in the control unit to detect defects in the image data. This involves comparing the data with that of a defect-free product and identifying a defect when a variation exceeding a threshold is confirmed. For instance, surface inspection systems used in printing traditionally employed analog waveforms instead of image data.
This method sometimes failed to detect thin defects or misjudged the ground tone as a defect. Using image data resolves these issues by enabling detailed analysis based on pixel size.
Other Information on Surface Inspection Systems
1. Light Reflection and Transmission in Surface Inspection Systems
In surface inspection systems, light from a projector is reflected or transmitted on the surface to be inspected. The five types of reflection and transmission are direct reflection, diffuse reflection, direct transmission, diffuse transmission, and scattering transmission.
Each method has distinct characteristics, making it essential to choose the appropriate method for detecting either “flaws” or “irregularities” during surface inspection.
2. Camera and Projector in Surface Inspection Systems
The accuracy of the camera in the inspection section of a surface inspection system is a critical factor. A camera with insufficient accuracy may miss detecting abnormal areas.
The performance of the projector, which illuminates the object under inspection, significantly influences the camera’s imaging performance. To ensure uniform illumination on the object’s surface, a bar light with a diffuser is often used. Additionally, using a grating light (slit light) allows the inspection of curved surfaces and the detection of minute defects.
3. Image Processing in Surface Inspection Systems
In a surface inspection system, the light captured by the CCD camera’s lens is projected as image data onto the image sensor and transmitted to the image processing computer in the control section. Image processing typically involves pre-processing, measurement, determination of abnormality, and output.
The image data captured by the sensor often contains noise, which is reduced through pre-processing techniques like smoothing, edge extraction, and shrinkage. The computer then compares the processed image data against a set of criteria to determine abnormalities and outputs the results.
Cameras used in surface inspection systems are usually highly accurate with a large pixel count. However, a high pixel count necessitates extensive pre-processing, requiring a computer with a high-performance CPU.