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In modern automated production process, machine vision system is widely used in condition monitoring, inspection and quality control, etc.
Machine vision system is mainly composed of lighting system, camera, video camera, image acquisition card and the image processing system, by the light source, lens and CCD imaging device matching image acquisition and processing system for product inspection, identification, etc. , this technique can greatly reduce the burden of artificial visual inspection product quality, to effectively improve the efficiency of detection, and is conducive to the production management.
Lighting system is an important part of machine vision system, is the key of collecting image quality and application effect, and the light controller is the core of the lighting system, its main function is to provide the different lighting levels for specific applications and lighting system, thus improve the quality of the lighting source, to obtain high quality images.
Is the current domestic manufacturers of light controller is manual regulation or adjusted by RS232 communication with a Pc, use less convenient, low efficiency, and high cost.
This paper designed a new type of light controller, this controller to ST companies based on ARM Codex -
M3 kernel STM32F107VCT6 STM32 micro controller as the core, through the plug and play, high transmission speed of the USB interface to communicate with a Pc, Pc application software for light controller parameters can be set in real time.
Using STM32 timer on chip to realize PWM digital dimming, and pulse frequency and duty ratio of a wide range of adjustment, and through the timer to work together to ensure precise timing between.
In addition, the controller implements three illumination mode, normal mode, stroboscopic mode and external trigger mode.
This design flexibility to adapt to the machine vision detection system application needs on different occasions.
1 overall scheme design, in a nutshell, the main functions of the light controller is received from the PC host pre-defined commands and set parameters, through main controller processing, then through the drive circuit control LED light source according to the set for digital PWM dimming.
light controller according to the architecture can be divided into the software part and hardware part, software part and can be divided into Pc application user interface, USB driver, the controller hardware and firmware.
The hardware part can be divided into main control module and LED driver module.
Master control module is mainly responsible for communication with a Pc, the command response, and management, it is the core part of the controller.
The LED driver module mainly provide suitable LED light source drive way.
LED light source drive mode have common inductive charge pump drive, drive and the inductive drive circuit for driving a number of series of LED.
LED brightness control method can be divided into analog dimming and digital PWM dimming two kinds.
Analog dimming by changing the LED current to adjust the brightness.
Its drawback is that the LED will produce with the forward current change color phenomenon, cannot satisfy the requirement of accuracy.
PWM dimming by opening and closing the LED to change forward current conduction time in order to achieve the brightness adjustment effect.
Because the leds are in constant current conduction, so there will be no analog dimming technology color deviation problem.
This design adopts inductive drive, PWM constant current dimmer.
