Image forming apparatus

• US 20030174200A1
• Filed: 03/04/2003
• Published: 09/18/2003
• Est. Priority Date: 03/12/2002
• Status: Active Grant

• Current Assignee: Konica Corporation (Konica Minolta Inc.)
• Original Assignee: Konica Corporation (Konica Minolta Inc.)
• Inventors: Ueda, Tadayuki, Kishi, Shinobu, Maruyama, Hiroyuki, Izumiya, Kenji, Ogata, Satoshi, Higashi, Yumiko, Nishikawa, Eiji, Okutomi, Ryuji, Motoi, Toshihiro
• Granted Patent: US 6,839,078 B2
• Time in Patent Office: Days
• US Class Current: 347/249
• CPC Class Codes: G02B 26/122 Control of the scanning speed of the polygonal mirror

Abstract

There is described a duplex image-forming apparatus having a function of forming images onto both sides of a transfer material. The apparatus includes an image-forming section to respectively form an obverse-side image and a reverse-side image on a photoreceptor element by scanning a light beam, modulated with image signals based on pixel-clock signals and reflected from a polygon mirror rotating at an operating velocity based on polygon-clock signals; a transferring section to transfer said obverse-side image and said reverse-side image onto both surfaces of said recording sheet; a fixing section to fix the images onto both surfaces of said recording sheet; and a clock-frequency changing section to change a pixel-clock frequency, and a polygon-clock frequency, corresponding to a degree of shrinkage of said recording sheet caused by a fixing operation performed in said fixing section, at a transition time of an image-forming operation from one side to another side.

Claims

1. An apparatus for forming a duplex image on a recording sheet, said duplex image includes an obverse-side image formed on an obverse surface of said recording sheet and a reverse-side image formed on a reverse surface of said recording sheet, said apparatus comprising:

an image-forming section to respectively form said obverse-side image and said reverse-side image on a photoreceptor element by scanning a light beam, modulated with image signals based on pixel-clock signals and reflected from a polygon mirror rotating at an operating velocity based on polygon-clock signals, onto said photoreceptor element;

a transferring section to transfer said obverse-side image and said reverse-side image formed on said photoreceptor element onto said obverse surface and said reverse surface of said recording sheet, respectively;

a fixing section to fix said obverse-side image and said reverse-side image onto said obverse surface and said reverse surface of said recording sheet, respectively; and

a clock-frequency changing section to change a pixel-clock frequency, being a frequency of said pixel-clock signals, and a polygon-clock frequency, being a frequency of said polygon-clock signals, corresponding to a degree of shrinkage of said recording sheet caused by a fixing operation performed in said fixing section, at a transition time of an image-forming operation in said image-forming section from said obverse-side image to said reverse-side image, and vice versa.

2. The apparatus of claim 1,

wherein said clock-frequency changing section determines a pixel-clock frequency changing-rate and a polygon-clock frequency changing-rate, based on a first shrinkage rate of said recording sheet in a paper conveying direction.

3. The apparatus of claim 2,

wherein said clock-frequency changing section further determines said pixel-clock frequency changing-rate, based on both said first shrinkage rate of said recording sheet in a paper conveying direction and a second shrinkage rate of said recording sheet in a main-scanning direction.

4. An apparatus for forming a duplex color image on a recording sheet, said duplex color image includes an obverse-side color image formed on an obverse surface of said recording sheet and a reverse-side color image formed on a reverse surface of said recording sheet, said apparatus comprising:

a plurality of image-creating units, each of which corresponds to each of a plurality of unicolor images and forms each of said plurality of unicolor images by scanning a light beam, modulated with image signals based on pixel-clock signals and reflected from a polygon mirror rotating at an operating velocity based on polygon-clock signals, to respectively form said obverse-side color image and said reverse-side color image on a photoreceptor element;

a transferring section to transfer said obverse-side color image and said reverse-side color image formed on said photoreceptor element onto said obverse surface and said reverse surface of said recording sheet, respectively;

a fixing section to fix said obverse-side color image and said reverse-side color image onto said obverse surface and said reverse surface of said recording sheet, respectively; and

a clock-frequency changing section to change a pixel-clock frequency, being a frequency of said pixel-clock signals for each of said plurality of image-creating units, and a polygon-clock frequency, being a frequency of said polygon-clock signals for each of said plurality of image-creating units, corresponding to a degree of shrinkage of said recording sheet caused by a fixing operation performed in said fixing section, at a transition time of an image-forming operation from said obverse-side color image to said reverse-side color image, and vice versa.

5. The apparatus of claim 4,

wherein said clock-frequency changing section determines a pixel-clock frequency changing-rate and a polygon-clock frequency changing-rate, based on a first shrinkage rate of said recording sheet in a paper conveying direction.

6. The apparatus of claim 5,

wherein said clock-frequency changing section further determines said pixel-clock frequency changing-rate, based on both said first shrinkage rate of said recording sheet in a paper conveying direction and a second shrinkage rate of said recording sheet in a main-scanning direction.

7. The apparatus of claim 5, further comprising:

a setting section to set timings for forming said plurality of unicolor images separately between a first phase for forming said obverse-side color image and a second phase for forming said reverse-side color image, based on said pixel-clock frequency changing-rate and said polygon-clock frequency changing-rate determined by said clock-frequency changing section.

8. The apparatus of claim 4,

wherein said clock-frequency changing section changes said pixel-clock frequency and said polygon-clock frequency separately for every one of said plurality of image-creating units.

9. The apparatus of claim 4,

wherein each of polygon-clock signals, corresponding to each of said plurality of image-creating units, is generated from each of a plurality of clock generating sources being independent from each other.

10. The apparatus of claim 4, further comprising:

a multi-clock generating section to generate a plurality of clock signals, each of which is independently employed for each of said plurality of image-creating units, from a clock signal outputted by a single clock generating source;

wherein each of polygon-clock signals, corresponding to each of said plurality of image-creating units, is generated from each of said plurality of clock signals generated by said multi-clock generating section.

11. The apparatus of claim 4, further comprising:

a reference signal detecting section to detect main-scanning reference signals in main-scanning paths of said light beam; and

a phase controlling section to control a phase of said polygon-clock signals, based on a phase difference between a first main-scanning reference signal of a reference color and a second main-scanning reference signal of another color, so as to determine said phase of said polygon-clock signals corresponding to said second main-scanning reference signal of the other color, each of said first and second main-scanning reference signals being one of said main-scanning reference signals detected by said reference signal detecting section.

12. The apparatus of claim 11,

wherein said phase controlling section independently performs a first operation for controlling said phase of said polygon-clock signals employed for forming said obverse-side color image on said obverse surface of said recording sheet, and a second operation for controlling said phase of said polygon-clock signals employed for forming said reverse-side color image on said reverse surface of said recording sheet;

and

wherein said phase controlling section changes said first operation to said second operation every time when said first operation for each of said plurality of unicolor images is completed, or vise versa.

13. The apparatus of claim 11,

wherein said phase controlling section independently performs a first operation for controlling said phase of said polygon-clock signals employed for forming said obverse-side color image on said obverse surface of said recording sheet, and a second operation for controlling said phase of said polygon-clock signals employed for forming said reverse-side color image on said reverse surface of said recording sheet;

and

wherein said phase controlling section changes said first operation to said second operation when said first operation for all of said plurality of unicolor images is completed, and vice versa.