Clock control apparatus and method and image forming apparatus using clock control apparatus

• US 6,512,534 B2
• Filed: 02/07/2001
• Issued: 01/28/2003
• Est. Priority Date: 02/08/2000
• Status: Active Grant

• Current Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Original Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Inventors: Koga, Katsuhide
• Primary Examiner(s): PHAM, HAI CHI
• Application Number:
  US09/777,659
• Publication Number:
  US 20020003568A1
• Time in Patent Office: 720 Days
• Field of Search: 347/232, 347/234, 347/235, 347/239, 347/248, 347/249, 347/250, 347/116, 358/296
• US Class Current: 347/249
• CPC Class Codes: G06K 15/1219 Detection, control or error compensation of scanning velocity or position, e.g. synchronisation G06K15/1223 takes precedence

Abstract

A clock control apparatus generates a clock for laser drive in latent image formation in an image forming apparatus. A main-scanning synchronizing clock generation unit generates a synchronizing clock synchronized with a main-scanning synchronizing signal based on the main-scanning synchronizing signal and an original clock. A delay unit delays the synchronizing clock so as to correct for a mechanical shift upon latent image drawing by a laser drive. A pseudo-main-scanning synchronizing signal generation unit generates a pseudo-main-scanning synchronizing signal based on the synchronizing clock delayed by the delay unit, and supplies the pseudo-main-scanning synchronizing signal to the main-scanning synchronizing clock generation unit. The main-scanning synchronizing clock generation unit, which generates a clock synchronized with the pseudo-main-scanning synchronizing signal. The clock is supplied via a clock selection unit to a PWM generation unit, and is used for the laser drive.

Claims

1. A control apparatus for controlling a clock for drawing drive in each of plural color image forming units of a color image forming apparatus which forms a color image by overlapping plural color images formed by the color image forming units, said control apparatus comprising:

a first synchronizing clock generation unit that generates a first synchronizing clock synchronized with a main-scanning synchronizing signal based on said main scanning synchronizing signal and an original clock;

a delay unit that generates a delayed clock by delaying said first synchronizing clock in accordance with a designated correction amount, the designated correction amount corresponding to a positional shift in the main-scanning direction of a color image formed by one of the color image forming units;

a pseudo-synchronizing signal generation unit that generates a pseudo-synchronizing signal based on said delayed clock generated by said delay unit; and

a second synchronizing clock generation unit that generates a second synchronizing clock synchronized with said pseudo-synchronizing signal based on said pseudo-synchronizing signal and said original clock.

2. The apparatus according to claim 1, wherein said pseudo-synchronizing signal generation unit counts said delayed clock and outputs a one-shot pulse.

3. The apparatus according to claim 1, wherein said first synchronizing clock generation unit and said second synchronizing clock generation unit are realized as one clock generation circuit,

and wherein said apparatus further comprises a selection unit that outputs said first synchronizing clock to said delay unit while said clock generation circuit outputs said first synchronizing clock, and outputs said second synchronizing clock for drawing drive while said clock generation circuit outputs said second synchronizing clock.

4. The apparatus according to claim 3, wherein said selection unit provides an output from said clock generation circuit as said first synchronizing clock to said delay unit from a point where said selection unit inputs said main-scanning synchronizing signal to a point where said selection unit inputs said pseudo-synchronizing signal, and provides the output from said clock generation circuit as said second synchronizing clock to the drawing drive from the point where said selection unit inputs said pseudo-synchronizing signal to a point where said selection unit inputs a next main-scanning synchronizing signal.

5. The apparatus according to claim 1, wherein drawing for which said drawing drive is provided includes latent image drawing by laser, and wherein said correction amount is designated so as to correct a mechanical shift upon said latent image drawing.

6. A control method for controlling a clock for drawing drive in each of plural color image forming units of a color image forming apparatus which forms a color image by overlapping plural color images formed lay the color image forming units, said control method comprising the steps of:

generating a first synchronizing clock synchronized with a main-scanning synchronizing signal based on the main-scanning synchronizing signal and an original clock;

generating a delayed clock by delaying the first synchronizing clock in accordance with a designated correction amount, the designated correction amount corresponding to a positional shift in the main-scanning direction of a color image formed by one of the color image forming units;

generating a pseudo-synchronizing signal based on the delayed clock; and

generating a second synchronizing clock synchronized with the pseudo-synchronizing signal based on the pseudo-synchronizing signal and the original clock.

7. The method according to claim 6, wherein the pseudo-synchronizing signal is a one-shot pulse outputted by counting the delayed clock.

8. The method according to claim 6, wherein the first synchronizing clock and the second synchronizing clock are generated by one clock generation circuit,

and wherein said method further comprises a selection step, of determining an output destination so as to delay the first synchronizing clock to generate the pseudo-synchronizing signal while the clock generation circuit outputs the first synchronizing clock, and changing the output destination so as to use the second synchronizing clock in the drawing drive while the clock generation circuit outputs the second synchronizing clock.

9. The method according to claim 8, wherein, in said selection step, an output from the clock generation circuit is used as the first synchronizing clock from a point where the main-scanning synchronizing signal is inputted to a point where the pseudo-synchronizing signal is inputted, and the output from the clock generation circuit is used in the drawing drive as the second synchronizing clock from the point where the pseudo-synchronizing signal is inputted to a point where a next main-scanning synchronizing signal is inputted.

10. The method according to claim 6, wherein drawing for which the drawing drive is provided includes latent image drawing by laser, and wherein the correction amount is designated so as to correct a mechanical shift upon the latent image drawing.

11. An image forming apparatus having a plurality of color image forming units and forming a color image by overlapping plural color images formed by said plurality of color image forming units, said image forming apparatus comprising:

a first synchronizing clock generation unit that generates a first synchronizing clock synchronized with a main scanning synchronizing signal based on said main scanning synchronizing signal and an original clock;

a delay unit that generates a delayed clock by delaying said first synchronizing clock in accordance with a designated correction amount, the designated correction amount corresponding to a positional shift in the main-scanning direction of a color image formed by one of said color image forming units;

a pseudo-synchronizing signal generation unit that generates a pseudo-synchronizing signal based on said delayed clock generated by said delay unit;

a second synchronizing clock generation unit that generates a second synchronizing clock synchronized with said pseudo-synchronizing signal based on said pseudo-synchronizing signal and said original clock; and

drawing means for performing a drawing operation based on said second synchronizing clock and image data to be used in image formation.

12. The apparatus according to claim 11, wherein said pseudo-synchronizing signal generation unit counts said delayed clock and outputs a one-shot pulse.

13. The apparatus according to claim 11, wherein said first synchronizing clock generation unit and said second synchronizing clock generation unit are realized as one clock generation circuit,

and wherein said apparatus further comprises a selection unit that outputs said first synchronizing clock to said delay unit while said clock generation circuit outputs said first synchronizing clock, and outputs said second synchronizing clock for drawing drive while said clock generation circuit outputs said second synchronizing clock.

14. The apparatus according to claim 13, wherein said selection unit provides an output from said clock generation circuit as said first synchronizing clock to said delay unit from a point where said unit inputs said main-scanning synchronizing signal to a point where said unit inputs said pseudo-synchronizing signal, and provides the output from said clock generation circuit as said second synchronizing clock to the drawing drive from the point where said unit inputs said pseudo-synchronizing signal to a point where said unit inputs a next main-scanning synchronizing signal.

15. The apparatus according to claim 11, wherein said drawing means performs laser drive for latent image formation, and forms a visible image on a print sheet.

16. The apparatus according to claim 15, wherein drawing for which said drawing drive is provided includes latent image drawing by laser,

and wherein said apparatus further comprises designation means for designating said correction,amount so as to correct a mechanical shift upon said latent image drawing.

17. The apparatus according to claim 15, wherein said drawing means includes means for introducing optically-modulated laser light from a laser light source on an image holder, writing image information and forming a visible image, and said drawing means transfers the visible image onto a transfer medium thereby forming an image.

18. The apparatus according to claim 15, wherein said drawing means performs PWM modulation by using said second synchronizing clock.

19. An image forming method for image forming apparatus which comprises a plurality of color image forming units and forms a color image by overlapping plural color images formed by the plurality of color image forming units, said image forming method comprising the steps of:

generating a first synchronizing clock synchronized with a main-scanning synchronizing signal based on the main scanning synchronizing signal and an original clock;

generating a delayed clock by delaying the first synchronizing clock in accordance with a designated correction amount, the designated correction amount corresponding to a positional shift in the main-scanning direction of a color image formed by one of the color image forming units;

generating a pseudo-synchronizing signal based on the delayed clock;

generating a second synchronizing clock synchronized with the pseudo-synchronizing signal based on the pseudo-synchronizing signal and the original clock; and

performing a drawing operation based on the second synchronizing clock and image data to be used in image formation.