Classification of light sources
Commonly used light sources include LED light sources , halogen lamps (fiber optic light sources), and high-frequency fluorescent lamps. Currently, LED light sources are the most commonly used, and they have the following characteristics:
Can be made into various shapes, sizes and various irradiation angles;
Can be made into various colors as needed, and the brightness can be adjusted at any time;
Through the heat dissipation device, the heat dissipation effect is better and the brightness is more stable;
· long lasting;
Fast response , reaching maximum brightness in 10 microseconds or less;
The power supply has an external trigger, can be controlled by a computer, has a fast starting speed, and can be used as a strobe light;
LEDs with low operating costs and long life will show greater advantages in terms of comprehensive cost and performance;
· Special designs can be made according to customer needs.
LED light sources can generally be divided into the following categories according to their shape:
1. Ring light source
The ring light source provides different illumination angles and different color combinations, which can highlight the three-dimensional information of the object; high-density LED array, high brightness; a variety of compact designs, saving installation space; solving the problem of diagonal illumination shadow; optional diffuser light guide, light evenly diffused. Application areas: PCB substrate inspection, IC component inspection, microscope lighting, LCD calibration, plastic container inspection, integrated circuit printing inspection
2. Backlight
High-density LED array surface provides high-intensity backlighting, which can highlight the outline features of the object, and is especially suitable as a microscope stage. Red and white dual-purpose backlight, red and blue multi-purpose backlight, can be mixed with different colors to meet the multi-color requirements of different objects. Application areas: measurement of mechanical parts dimensions, appearance inspection of electronic components and ICs, film stain inspection, transparent object scratch inspection, etc.
3. Strip light source
Strip light source is the preferred light source for larger square structure objects; the color can be freely combined according to the needs; the irradiation angle and installation can be adjusted at will. Application areas: metal surface inspection, image scanning, surface crack detection, LCD panel detection, etc.
4. Coaxial light source
Coaxial light source can eliminate shadows caused by uneven surface of objects, thus reducing interference; some adopt beam splitter design to reduce light loss, improve imaging clarity, and evenly illuminate the surface of objects. Application areas: Series light sources are most suitable for objects with extremely high reflectivity, such as scratch detection on the surface of metal, glass, film, wafer, etc., damage detection of chips and silicon wafers, mark point positioning, and packaging barcode recognition.
5. AOI dedicated light source
Three-color light illumination at different angles can highlight the three-dimensional information of solder; additional diffuser plate can guide light and reduce reflection; different angle combinations; application areas: used for circuit board solder detection.
6. Spherical integral light source
The hemispherical inner wall with an integral effect evenly reflects the light emitted from the bottom 360 degrees, making the illumination of the entire image very uniform. Application areas: Suitable for curved surfaces, concave and convex surfaces, arc surface detection, or surface detection of objects with strong reflective surfaces such as metal and glass.
7. Linear light source
Ultra-high brightness, using cylindrical lens to focus light, suitable for various assembly line continuous detection occasions. Application areas: dedicated to array camera lighting, dedicated to AOI.
8. Point light source
High-power LED, small size, high luminous intensity; a substitute for fiber optic halogen lamp, especially suitable as a coaxial light source for lenses, etc.; high-efficiency heat dissipation device, greatly improving the service life of the light source. Application areas: suitable for telecentric lenses, used for chip detection, Mark point positioning, wafer and LCD glass base correction.
9. Combined strip light source
Strip lights are configured on four sides, and the lighting on each side is independently controllable; the required lighting angle can be adjusted according to the requirements of the object to be tested, and it has a wide range of applicability. Application cases: CB substrate inspection, IC component inspection, solder inspection, Mark point positioning, microscope lighting, packaging barcode lighting, spherical object lighting, etc.
10. Alignment of light sources
Fast alignment speed; large field of view; high precision; small size, easy to detect and integrate; high brightness, optional auxiliary ring light source. Application field: VA series light source is a special light source for the alignment of fully automatic circuit board printing machines.
4. Light source selection
1. Prerequisite Information
1. Test content
Appearance inspection, OCR, dimension measurement, positioning
2. Object
①What do you want to see? (Foreign matter, scars, defects, marks, shapes, etc.)
②Surface condition (mirror surface, rough surface, curved surface, flat surface)
③Three-dimensional? Two-dimensional?
④Material and surface color
⑤ Field of view?
⑥Dynamic or static (camera shutter speed)
3. Restrictions
① Working distance (distance from the bottom of the lens to the surface of the object being measured)
② Setting conditions (size of lighting, distance from the bottom of the lighting to the surface of the object to be measured, reflection type or transmission type)
③Surrounding environment (temperature, external light)
④ Camera type, area array or line array
2. Simple preliminary knowledge:
1. The light transmission characteristics (transparency) vary depending on the material and thickness.
2. The ability of light to penetrate matter (penetration rate) varies according to the length of its wavelength.
3. The longer the wavelength of light, the stronger its ability to penetrate matter; the shorter the wavelength of light, the greater its diffusion rate on the surface of matter.
4. Transmitted lighting is a lighting technique that allows light to penetrate an object and observe the transmitted light.
3. Light source:
1. Stable and uniform light source is extremely important
2. Purpose: To distinguish the object to be measured from the background as clearly as possible
3. When capturing an image, the most important thing is how to clearly obtain: the grayscale difference between the object being measured and the background
4. Currently, the most widely used technique in the field of image processing is: Binarization (white-black) processing
In order to highlight the feature points and feature images, commonly used lighting techniques include bright field and dark field.
Bright field: Use direct light to observe the entire object (scattered light appears black)
Dark field: Use scattered light to observe the entire object (direct light appears white)
The specific method of selecting the light source depends on the practical experience of the experiment.
5. Light source controller
The main purpose of the light source controller is to power the light source, control the brightness of the light source and control the lighting status (on/off) of the light source. It can also achieve the stroboscopic effect of the light source by giving the controller a trigger signal, thereby greatly extending the life of the light source. Commonly used controllers on the market are analog controllers and digital controllers. Analog controllers are manually adjusted, and digital controllers can be remotely controlled by computers or other devices.
Common controller categories:
Analog Controller
1. Stepless brightness control;
2. Short circuit protection;
3. External trigger input: Inputting an external signal, such as a camera trigger signal, into the controller can cause the light source to perform stroboscopic lighting, thereby greatly extending the life of the light source.
Digital Controller
1.256 levels of brightness control;
2. High integration;
3. Short circuit protection;
4. External trigger input: Inputting external signals, such as the trigger signal of a camera, into the controller can cause the light source to perform stroboscopic lighting, thereby greatly extending the life of the light source;
5. PC controllable: Connect the controller to the computer through the serial port, and you can control the brightness of the light source through the computer, making it convenient to integrate the light source into your product;
6. Manual control (optional): brightness can be adjusted manually;
7. Power-off saving: The power-off saving function saves you from having to set parameters every time you start the machine.
Strobe Brightness Enhancement Module
1. In the trigger brightness enhancement mode, the module increases the brightness of the light source by increasing the output voltage;
2. Features: 28V output, 4 standard channels, each channel can be controlled separately, trigger function;
3. Using the strobe brightening module can increase the brightness of ordinary light sources by more than 2 times.
High Power Analog Controller
1. Two standard outputs, output voltage is 14.0~24.0V;
2. Each channel is independently adjustable and has trigger function. The rated output power is 65W.
Analog Brightness Enhancement Integrated Controller
The analog brightening module combines the functions of the analog controller and the brightening module. A separate brightening module requires an external 24V voltage input, while the analog brightening module has a 24V voltage output internally and does not need to be powered from the outside. It has an infinitely adjustable function. Customers can adjust the input voltage and control the brightness of the light source through the knob on the outside of the analog brightening module. The analog brightening module has the following features: 28V output, short rise time (2us), 3 standard channels, each channel is individually controllable, and trigger function.
Digital Brightness Enhancement Integrated Controller
The digital brightening module is a controller that integrates the functions of a digital controller and a brightening module. It has the following functions: 256-level brightness adjustment function (standard channels have a maximum of 4 channels, and the brightness of each channel can be controlled separately), computer communication function (RS232 interface), and brightening function. The light source of this product will not light up without a trigger, and the light source will only turn on and off when triggered.
Light source controller selection:
When selecting a light source controller, different types of controllers should be selected according to different actual conditions.
For example, you can select 5V, 12V, 24V, 28V (brighter) according to the output voltage requirements;
Manual or software and manual can be selected according to the controller mode requirements;