| 摘要 |
A method and apparatus is presented for registering a plurality of color images formed on a photoconductive member in a process direction. The registration is enabled by a feedback loop wherein the phase and frequency of start-of-scan signals and a stable reference output signal are compared to produce an error signal representing frequency differences between the rotating polygons associated with each Raster Output Scanner. In one embodiment, the stable reference frequency is generated as a digital value by a microcontroller. In another embodiment, the digital value to be compared with the start-of-scan signal is generated by an encoder which provides a signal representing the motion of the moving photoconductive member. With either reference frequency, an error signal is generated which is applied as a pulse width modulated signal to the polygon drive motors to change the speed and frequency of the associated rotating polygon and, the speed, in turn, changing the SOS signals to complete the feedback loop. The process is iterative with pulse width modulated correction signals being applied until the comparison of the digital values representing the reference frequency and the SOS signals is reduced to zero. In a third embodiment, a phase correction circuit is described to enable subpixel registration.
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