What Is Image Processing Equipment?
Image processing equipment is a device that inspects the appearance and dimensions of an object based on images obtained from a camera or sensor.
Image processing equipment is used as an alternative to visual inspection by inspectors. Visual inspection is used to maintain and guarantee the quality of parts and products. Image processing equipment is important to prevent variations in inspection accuracy due to individual differences and fatigue.
Uses of Image Processing Equipment
Image processing equipment is used in manufacturing lines in a variety of fields. The main applications are as follows:
- Inspection for scratches, stains, and defects on parts, etc. in the factory
- Over/under inspection of the number of products and parts to be packed
- Inspection of products and parts for dimensional and size differences
- Color inspection of products and parts
The introduction of image processing equipment has prevented human error and increased the speed of stable 24-hour operation and inspection.
Principle of Image Processing Equipment
Image processing equipment consists of an image input system consisting of a camera or sensor and lighting, and an image processing device. The principle of image processing equipment is to determine whether a product is acceptable or not by extracting information, such as features from images captured by a camera, and comparing it with the registered information on good products.
The functions of the image input system and image processor are as follows:
1. Image Input System
The image input system consists of lighting, a camera, and a lens. For the image input system, it is necessary to select, install, and control the most appropriate equipment (area camera or line sensor camera, indirect or direct illumination, etc.) according to the object, object transport conditions, and inspection objectives (size of defects, degree of contamination, etc.).
2. Image Processing Equipment
Image processing equipment performs image transformation, image deformation, feature extraction, and other processing on images obtained from the image input system. Image processing equipment registers the criteria (numerical values, ranges of feature values, and graphic patterns) for judging a product as good beforehand, and compares them with the feature values obtained from the image input system to make a pass/fail judgment.
How to Choose Image Processing Equipment
For image processing equipment, the image input system and image processing equipment should be selected according to the object to be inspected, the specifications of the transfer line, and the purpose of the inspection. In selecting image processing equipment, it is necessary to quantify the benefits, such as improved productivity and reduced workload for personnel, in relation to the costs incurred, so that cost-effectiveness can be obtained.
The following points should be considered when selecting image processing equipment:
1. Image Input System
Lighting
Illumination that is even and stable in brightness makes image inspection stable. It is necessary to select the type of light source, the type of filter, the way the light is applied, and the number of units so that the item to be inspected can be emphasized.
For example, when photographing uneven metal surfaces, use positive reflection type lighting; when prone to halation, use diffuse reflection type lighting.
Camera
Depending on the item to be inspected, select from color cameras, monochrome cameras, high-speed cameras, line sensor cameras, contact image sensor cameras, etc. Color cameras are employed when inspecting the color of products or parts.
Color cameras are more expensive than monochrome cameras. If the color of the object to be inspected is simple, a monochrome camera and a color filter may provide a stable inspection. When selecting a camera, do not simply think of a color camera for color inspection.
A high-speed camera is used when the object to be inspected moves at high speed, causing blurring with a normal camera. When a high-speed camera is used, the lighting must be bright.
Line sensor cameras and contact image sensor cameras are employed when the object to be inspected is a sheet-shaped object or a circular or cylindrical rotating object. A contact image sensor camera is a camera that integrates a fixed-focus lens and illumination, and is effective when the distance between the object to be inspected and the camera is stable.
Lens
Lens selection is based on focal length and object depth. For image inspection, the field of view must be set so that the inspection object can be captured with the necessary accuracy.
The focal length is the distance from the lens to the image element. The focal length is the distance from the lens to the image sensor of the camera. The focal length is determined by the size of the object to be inspected (field of view), the distance between the lens and the object to be inspected, and the size of the image sensor.
Depth of field is the range in which the focused inspection object remains in focus even if the object moves away from or closer to the camera. The deeper the depth of field, the more in-focus the image will be, even if the distance between the object to be inspected, and the camera varies.
In a production line, there are restrictions, such as installing the camera in such a way that it does not interfere with other equipment. The lenses used in image processing equipment must be selected to provide the focal length and depth of field that meet the imaging conditions required for inspection. In addition, lenses with short focal lengths will cause distortion in the image, so it is necessary to confirm that this will not affect the inspection accuracy.
2. Image Processing Equipment
Image processing equipment is selected based on the accuracy required for the inspection (size of flaws, degree of irregularity, length error, recognition rate of characters and bar codes, etc.) and speed (whether the inspection can be completed within the time allowed by the production line or faster than the current inspection speed).