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We have developed high-speed color copier using electrophotographic process (called CLC1000, announced in September of 1995 in Japan.) In this color copier color image can be created by independently forming four color-images (Y, M, C and Bk) on separate four drums and then by accurately overlaying these images on the same receiver. The key challenge lies on how to correct a shift in each color position caused by environmental changes such as location and temperature and how to keep the registration accuracy. Our technologies for design and production have concentrated for resolving this problem. It has been found that the shift in each color position is caused by the change in relative position between laser-beam and drum due to the fluctuation in driving system and image-writing system. So, a mechanism controlling a laser beam relative position to the drum has been developed. This is called registration servo system. Brief explanation of the registration servo system follows. Separate four color-image patterns specially created by each shifted laser beam are transferred on the belt. The CCD in the registration search unit reads the patterns, calculates a magnitude of the shift and decomposes the magnitude into the components: (1) Magnification (M-Shift), (2) Slope (S-Shift), (3) Horizontal (H-Shift) and (4) Vertical (V-Shift). Each component is fed back to the machine in the manner: for M-shift and S-shift, a relative position of the laser beam to the drum is changed by moving reflecting mirrors, and for V-shift and H-shift, by changing a scanning timing. One laser beam (ex. M) is used as a reference for the other beams. The registration servo system is activated at a short interval when environmental conditions change largely and at a long interval when conditions change gently. In this way, a highly accurate registration is achieved.
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