Frequency modulation apparatus and frequency modulation method

• US 20090009582A1
• Filed: 09/04/2008
• Published: 01/08/2009
• Est. Priority Date: 03/11/2003
• Status: Active Grant

• Current Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Original Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Inventors: Shiraishi, Mitsuo
• Granted Patent: US 7,692,679 B2
• Time in Patent Office: Days
• US Class Current: 347/249
• CPC Class Codes: H04N 1/053 in main scanning direction, e.g. synchronisation of line start or picture elements in a line
• CPC Class Codes: H04N 1/1135 for the main-scan only
• CPC Class Codes: H04N 1/12 using the sheet-feed movement or the medium-advance or the drum-rotation movement as the slow scanning component, e.g. arrangements for the main-scanningsheet-feed movement by translatory movement of a flat picture-bearing surface H04N1/1008; main-scanning using oscillating or rotating mirrors H04N1/113; using multi-element arrays H04N1/19
• CPC Class Codes: H04N 2201/02439 Positioning method
• CPC Class Codes: H04N 2201/0471 using dedicated detectors
• CPC Class Codes: H04N 2201/04732 Detecting at infrequent intervals, e.g. once or twice per line for main-scan control
• CPC Class Codes: H04N 2201/04744 by detecting the scanned beam or a reference beam
• CPC Class Codes: H04N 2201/04774 using a reference clock or oscillator H04N2201/04772 takes precedence
• CPC Class Codes: H04N 2201/04793 using stored control or compensation data, e.g. previously measured data
• CPC Class Codes: H04N 2201/04794 Varying the control or compensation during the scan, e.g. using continuous feedback or from line to line

Abstract

A frequency modulation apparatus capable of reducing a peak level of a radiation noise of a characteristic frequency band due to an image clock.

This frequency modulation apparatus is used in an image formation apparatus having an image bearing body to be scanned by a laser beam, and comprises an auxiliary clock calculating portion for calculating an auxiliary clock period based on a reference clock period and a modulation coefficient, and an image clock generating portion for generating the image clock in which a frequency is different at least in one portion and other portions of an image area on a main scan line to be scanned by the laser beam on said image bearing body based on the initial period value set in advance and said auxiliary clock period, and said image clock generating means perform a frequency modulation so that the frequency of said image clock changes within a predetermined fluctuation.

Claims

1-12. -12. (canceled)

13. A frequency modulation apparatus used in an image forming apparatus having an image bearing body to be scanned by a laser beam, comprising:

a reference clock generating portion for generating a reference clock having a constant frequency;

a first frequency control portion for outputting a clock having a predetermined frequency fluctuation, based on the reference clock;

a second frequency control portion for generating a clock having a constant frequency approximately close to the reference clock, based on the clock having a predetermined frequency fluctuation outputted by said first frequency control portion; and

a segment dividing portion for dividing a main scan line by the laser beam into a plurality of segments each constituted by a plurality of pixels,

wherein said second frequency control portion further generates image clocks respectively corresponding to the plurality of segments, based on the clock having a constant clock as generated and modulation coefficients corresponding to respective ones of said plurality of segments.

14. A frequency modulation apparatus according to claim 13, wherein said second frequency control portion includes a holding portion for holding a correction coefficient set so as to reduce the predetermined frequency fluctuation of the clock outputted by said first frequency control portion, and controls the clock having a constant frequency based on the correction coefficient.