1:Composition and working principle of photoelectric imaging system of high-speed video camera
High-speed video cameras is an approach of image recording; this approach closely combines space and time information of process of high-speed moving and changing. high-speed video cameras can continuously record transient changes and process of high-speed moving, it is an approach of quantitative calculation with image analysis equipment .It is first applied in ballistic analysis, and now application has expanded from the military area to civilian area, from industrial area to medical biological area, from research of the macroscopic mechanical motion area to microcosmic mechanism area.
High-speed video cameras can complete sampling of high-speed moving target in a very short period repeatedly, when shown at regular speed; process of the target recorded is clearly and slowly present in front of our eyes. High-speed photoelectric imaging technology has a real-time image capture of target, fast record, instant replays, clear and visual image and other outstanding advantages.
Working principles of high-speed video cameras system are: lighted by natural or artificial supplementary lighting, high speed moving object reflects light, or moving target lights from within itself, some of these light goes through the imaging objective of high speed imaging system. After imaging, these lights falls on the photoelectric image device like sensor, controlled by the driving circuit, photoelectric device will rapidly response to target on the sensor, that is, sampling points called pixels produce corresponding quantity of charge packet, according to light energy distribution of the target images on the surface of sensor, and photoelectric conversion is completed. The charge packet with image information was quickly transferred to read register. Readout signal will be transferred to the computer after being processed, and then the computer reads the signal out, displays it, interprets it, and output the results. Therefore, a complete set of high-speed imaging system consists of optical imaging and photoelectric imaging, signal transmission, control, image storage and processing, etc.
(1)Optical imaging system includes imaging lens. Imaging lens will be moving target imaging, and ensure on target as photoelectric imaging of imaging devices, to ensure there is enough caliber, even at the same time to meet in a short exposure time imaging surface still have enough light, can meet the needs of the response of photoelectric imaging devices. In addition, the resolution of the imaging lens, aberration, parameters such as focal length must also match the electro-optical imaging device.
(2)Photoelectric imaging system includes photoelectric imaging devices and signal processing system, and the photoelectric image device is undoubtedly the key role, for it largely determines the whole performance of the imaging system. Photoelectric imaging device mainly completes multi times and fast sampling of high-speed moving target images which falls on the surface of imaging device, and every sampling process includes accumulation of light electric charge, transfer and readout of charge packet containing image information, and process of output signal, etc. The most vital indices of Photoelectric imaging device are number of pixels and response time, because these two determines the resolution of the image and frequency of capture; Photoelectric imaging device generally uses high-speed imaging CCD (charge-coupled device) and CMOS (complementary metal oxide semiconductor) sensor and its combination with other photoelectric image device. This combination is to form photoelectric imaging system which is suitable for application of certain occasions, for example, adding enhancer in front of the CCD or CMOS, and this will make it better adaptable to lower light conditions.
(3)Signal transmission system is responsible for transmitting long distance, high quality of the image signals to the image recording and displaying system. According to the mode, transmission is divided into wireless transmission and cable transmission.
(4)Control system is to complete control of the lens aperture, focal length and focusing, if there are others like enhancers, controller to operate voltage, gain, shutter and so on is necessary. For high-speed imaging system, main operations is to set some parameters, such as presetting of frequency ratio, exposure time, trigger mode, storage format, etc. for those Occasion which needs supplementary lighting system, it is also necessary to control the brightness of the light. During processing, experimental personnel who participates in the control system according to actual situation is necessary as well.
(5)Fast image storage system is to complete image storage; now mostly digital storage is used, and the compute directly controls recording and playback. Quantity, quality and size of stored image is proportional to the capacity of memory chips, so it needs to be rational to use storage capacity, and record the experiment data within limited storage.
(6)Application software of Image processing system is to improve and interprets the quality of the images. You can use the software which is part of the high speed camera instrument, and also, you can use other image processing software.
(7)Other auxiliary system is determined by the actual using occasions, such as: auxiliary lighting system, seismic waterproof system, anti-jamming system, etc.
2:high-speed video cameras has a very wide range of applications, including: trajectory analysis, fuel study, explosion test, dynamic damage , flight tests and elastic analysis studies, crack propagation, anti-vibration performance analysis, agricultural machinery, biological and medical research, analysis of chemical process, vehicle crash test, weld inspection, automatic production line detection, injection and particle analysis, universities, security monitoring, sports, etc. Applications of high-speed video cameras in the field of military, Su Zengli and others put forward approach of aberrance parameters measurement , this approach was applied in speed of rockets off from the orbital, acceleration and deflection quantity of projectile. they discussed the war plan of equipment, measurement principle and data processing method. And specify parameter calculation formula. Zhang Xianzhong and others use high speed camera system, complete possibility, measuring method and accuracy analysis of some type missile being virtually on and off target, use relatively simple and fixed point high speed video camera system and complete the task of measurement of some missile being off from target .
