Patent ID: 6208367
Filing Date: 2001-03-27
Classification: B41J,H04N

Abstract:
A light beam scanning apparatus comprising:a plurality of beam generating means for generating light beams;scanning means for optically combining the light beams generated at said beam generating means, reflecting the combined beams to a scanning surface including the surface of an image retaining element, and causing said light beams to scan said scanning surface;first sensing means, provided near said image retaining element, for sensing the first one of said light beams caused by said scanning means to scan;clock generating means for generating a pixel clock to be used in said beam generating means for each of said light beams, in response to a sense signal indicating that said first beam has exposed said first sensing means;second sensing means, provided on the more downstream side in the main scanning direction than said first sensing means, for sensing said light beams;first control means for giving control data to said clock generating means so that said light beams may expose a target area between said first and second sensing means; andimage formation area setting means for determining a pixel clock area corresponding to a target image formation area on said image retaining element on the basis of the control data from said control means and setting the pixel clock area in said clock generating means,whereinsaid clock generating means includesclock means for generating a clock signal a specific time after said first beam exposed said first sensing means;delay means for delaying said clock signal generated at said clock means, selecting the delay of said clock in a range of one clock or less for each beam, and providing a delayed clock signal as a pixel clock to be used to generate a beam; andclock setting means for setting, for the respective beams, exposure pixel clock areas used by said beam generating means in the pixel clocks given by said delay means and providing exposure pixel clocks,whereinsaid delay means includes a delay line and delay clock selectors, said delay line having taps, and each of said delay clock selectors designed to select and output a delayed clock generated at one tap, which is to be used to generate one beam,whereinthe target area between said first and second sensing means is an area overlapping with said second sensing means,said light beam scanning apparatus further comprisinga counter for counting the number of times said beams expose said second sensing means;second control means for driving one of said beam generating means using the exposure pixel clock obtained from said clock setting means controlled on the basis of said control data and causing said scanning means to scan said scanning surface a specific number of times;comparison means for reading a value in said counter after said second control means has scanned the specific number of times and comparing the value with a predetermined number;means for selecting the next tap whose amount of delay is greater than that of said selected tap when the result of the comparison at said comparison means has shown that the value in said counter is smaller than said predetermined number; andamount-of-delay setting means, when the result of the comparison at said comparison means has shown that the value in said counter is equal to said predetermined number, for setting a delay selected at that time as the amount of delay for the one of said beam generating means.