| 摘要 |
A system for changing the rate of a bit clock based on errors of individual facets of a rotating polygon utilized in laser scanning system, the errors that exist between facets causing the velocity of the scan associated with the facet to be different from other scans. Facet erros are detected initially by having a start of scan pulse initiate a bit clock counter which counts the clock pulses generated by a voltage controlled oscillator. The counter provides an output to an interval detector when a desired total bit count for a scan line is reached. At some time with respect to the counter output an end of scan pulse is generated. The interval between the counter output and the end of scan pulse is the error for a particular facet. Logic allows memory locations to be addressed and loaded with the errors produced by the remaining facets in sequence, the sequence being continually repeated as the polygon rotates. During the time between the end of scan and start of scan pulses for a scan line, the error for the next facet is read out of memory to a digital to analog converter, which changes the frequency of the voltage controlled oscillator. If the error indicates the scan velocity is slow for the next facet, the oscillator frequency is reduced. If the error indicates the scanned velocity is fast for the next facet, the oscillator frequency is increased.
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