Three, CCD:

CCD is a kind of digital semiconductor components (also called photoelectric coupling device), it is divided into linear CCD and CCD two kinds. It is developed in the early 1970 s new semiconductor integrated optoelectronic devices, it is on a silicon surface integration with thousands of separate photosensitive element, when the light to the photosensitive surface, yuan will gather photoelectron of the light, through the way of displacement, the light output, produce light position information of light intensity, so the CCD has high measurement precision (within 0.05 degrees), temperature coefficient, long life and other characteristics.

Using CCD has a good environmental adaptability. All other technology have restrictions on the use of all kinds, such as cannot be used in the light the place with complex, cannot have strong electromagnetic field, the temperature can't have too big change, and so on, and these are all the typical environment of garage. Those who can't open the door, can't open the window, the cool morning measurement data and noon heat measurement is different, cannot have big motor at the request of the nearby, for four-wheel positioning, it is a bit too much. So the European and American countries in the production of four-wheel adopts CCD technology.