JP2003233026A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inexpensive image forming apparatus by reducing the number of expensive photosensors. <P>SOLUTION: In the image forming apparatus performing exposure by respectively simultaneously reflecting a plurality of light beams 5 and 6 on the different surfaces of a rotary polygon mirror 9, the light beam 5 being reference out of the light beams is detected by a photosensor 4 and a horizontal synchronizing signal being reference is generated, and then the horizontal synchronizing signal of the light beam 6 simultaneously reflected on a different surface from the surface on which the light beam 5 being the reference is reflected is generated based on a time difference from a horizontal synchronizing signal being the reference stored in advance, for instance, when shipped from a factory. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus for scanning with a light beam, and more particularly to generation of a synchronizing signal thereof.

[0002]

2. Description of the Related Art Conventionally, an image forming apparatus such as a laser printer or a digital copying machine is provided with a rotary polygon mirror (hereinafter referred to as a polygon mirror) for beam polarization.

As a color image forming apparatus for forming a color image at high speed, there is an in-line system. As one of the in-line methods, there are yellow (Y), magenta (M), cyan (C), black (B) along the conveyor belt.
There is one in which a photosensitive drum is arranged for each color of k), two polygon mirrors and two polygon motors are provided, and two lasers are polarized to perform optical scanning to expose the photosensitive drum. The horizontal sync signal for image generation is generated by four photosensors, one for each laser. After that, the transfer paper is sequentially conveyed by the conveyor belt to sequentially transfer the images of the respective colors, or the toner images of the respective colors are sequentially transferred to the intermediate transfer belt so as to be superimposed on each other, and then the toner images are collectively transferred to the transfer paper. There is. Finally, the toner image on the transfer paper is fixed by heating.

[0004]

However, in the above-mentioned conventional method, the horizontal synchronizing signal is expensive because it is generated by four expensive photosensors, one for each laser. There's a problem.

The present invention has been made under such circumstances, and it is an object of the present invention to reduce the number of expensive photosensors and provide an inexpensive image forming apparatus.

[0006]

In order to achieve the above-mentioned object, in the present invention, an image forming apparatus is constructed as in the following (1) to (7).

(1) In an image forming apparatus in which a plurality of light beams are simultaneously reflected and exposed on different surfaces of a rotary polygon mirror, a reference light beam among the plurality of light beams is detected and a reference horizontal beam is detected. The position of the specific surface of the rotary polygon mirror and the scanning means for performing optical scanning with the plurality of light beams based on the reference horizontal synchronizing signal generated by the synchronizing signal generating means and the synchronizing signal generating means A specific surface position determining means for determining, and a surface position determining means for determining the position of the surface performing the optical scanning based on the specific surface determined by the specific surface position determining means, based on the number of the horizontal synchronization signals. Image forming apparatus equipped.

(2) In an image forming apparatus in which a plurality of light beams are simultaneously reflected and exposed on different surfaces of a plurality of superimposed rotary polygon mirrors, the light beams are detected and synchronization is generated to generate a horizontal synchronization signal serving as a reference. Specific surface position determination for determining the position of the specific surface of the rotating polygon mirror and the scanning means for performing optical scanning with the plurality of light beams based on the reference horizontal synchronizing signal generated by the signal generating means and the synchronizing signal generating means. An image forming apparatus comprising: means for determining the position of the surface on which the optical scanning is performed based on the specific surface determined by the specific surface position determining means based on the number of the horizontal synchronization signals.

(3) In the image forming apparatus described in (1) or (2), a memory for storing a time difference between the reference horizontal synchronizing signal and a horizontal synchronizing signal of a light beam other than the reference light beam. An image forming apparatus comprising: means for generating a horizontal synchronization signal of a light beam other than the reference light beam based on a time difference stored in the storage means.

(4) In the image forming apparatus described in (1) or (2), the specific surface position detecting means is a mark provided on the rotary polygon mirror or the specific surface depending on the shape of the rotary polygon mirror. Image forming apparatus for detecting

(5) In an image forming apparatus in which a plurality of light beams are simultaneously reflected and exposed on different surfaces of a rotary polygon mirror, a reference light beam among the light beams is detected and a reference horizontal synchronization is performed. A reference synchronization signal generation unit for generating a signal; and a synchronization signal generation unit for generating a horizontal synchronization signal of the light beams simultaneously reflected on a surface different from the surface on which the reference light beam is reflected, An image forming apparatus in which the synchronization signal generating means generates a horizontal synchronization signal based on a time difference from the reference horizontal synchronization signal stored in advance at the time of factory shipment.

(6) In an image forming apparatus in which a plurality of light beams are simultaneously reflected and exposed on different surfaces of a plurality of superimposed rotary polygon mirrors, a reference light beam of the light beams is detected. Reference synchronization signal generation means for generating a reference horizontal synchronization signal, and synchronization signal generation means for generating a horizontal synchronization signal of a light beam simultaneously reflected on a surface different from the surface on which the reference light beam is reflected. The image forming apparatus, wherein the synchronization signal generating unit generates the horizontal synchronization signal based on a time difference from the reference horizontal synchronization signal stored in advance at the time of factory shipment.

(7) In the image forming apparatus described in (5) or (6), the time difference is stored for each surface of the rotary polygon mirror.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The embodiments of the present invention will be described in detail below with reference to examples of color laser printers.

[0015]

(Embodiment 1) A "color laser printer" which is Embodiment 1 will be described with reference to FIGS. 1, 2 and 3.

FIG. 1 is a conceptual diagram of a scanner unit (also called a laser scanning system) in this embodiment. In FIG. 1, the first laser 5 is scanned by a polygon mirror 9 rotating in the direction of arrow C. After that, the light is specularly reflected by the folding mirror 10 and passes through the lens group 3 to expose the photoconductor 21.
Expose the top. The scanning direction at this time is the direction of arrow A. The second laser 6 is scanned by the polygon mirror 9 which also rotates in the direction of arrow C, and the folding mirror 8
Then, the light is specularly reflected by the lens group 7 and is exposed through the lens group 7. The scanning direction at this time is the direction of arrow B.

On the polygon mirror 9, there is a black marking 16 which can be detected once per revolution. The marking 16 is detected by the reflective photo interrupter 15 to identify the surface on which laser scanning is performed. Specifically, due to the poor response of the photo interrupter 15, the photo interrupter 15 detects the specific surface position of the rotary polygon mirror when the rotary polygon mirror rotates at a low speed immediately after the rotation starts. Count the number of horizontal sync signals detected,
The surface position is determined based on the counted number. For example, the count number is divided by 4, and when the remainder is 0, the first surface (specific surface), when the remainder is 1, the second surface is specified, and the surface position where the laser scanning is performed is specified.

The scanning reference of the first laser 5 is detected by the photo sensor 4. This is a so-called "direct horizontal sync signal" (corresponding to the "reference horizontal sync signal" in the claims). First on each side of polygon mirror 9
Based on the direct horizontal synchronization signal of the laser 5, the so-called "pseudo horizontal synchronization signal" of the second laser 6 on the corresponding surface
Is created with a time difference stored in advance at the time of factory shipment and used as a reference for scanning the second laser 6.

FIG. 2 is a sectional view showing a schematic structure of the present color laser printer. In FIG. 2, 11 is a yellow and magenta first scanner unit, 12 is a cyan and black second scanner unit, 21, 22, 23 and 24 are photosensitive drums of respective colors 31, 32, 33 and 34, respectively.
Are the charging rollers of each color, 41, 42, 43, 4 respectively.
4 is a sleeve roller of each color, 51, 52, 5
3, 54 are transfer rollers of respective colors, 61 is an intermediate transfer belt, 62 and 63 are intermediate transfer belt holding rollers, 6
Reference numeral 4 is a cassette paper feed pickup roller, 65 is a registration roller, 71 is a fixing device, 81 is a plain paper cassette, and 90 is a toner image detection sensor. Toner image detection sensor 90
Detects a color shift amount measurement pattern as a light intensity distribution waveform by a photo sensor or the like and outputs it as a voltage. Each output voltage is input to a control circuit board (not shown), the position of the toner image is detected from the voltage waveform input by the image position detection circuit, and is input to the control circuit.

The laser color printer of this embodiment is the first
As a means for correcting the deviation amount between the image scanned by the scanner unit 11 and the image scanned by the second scanner unit 12, color misregistration amount measurement patterns are formed at predetermined intervals on the intermediate transfer belt 61, and this measurement pattern is used as toner. The color shift amount is detected by the image detection sensor 90, the color shift amount is calculated based on the detection result, and the image forming position is corrected based on the calculation result.

At this time, the pattern for measuring the amount of color misregistration is, for example, as shown in FIG.
Lines for two units are formed at equal intervals L, and an average value of the respective measured values is stored as a color shift amount. Figure 3
I is a measurement pattern scan-formed by the first scanner unit 11, and II, III, and IV are measurement patterns scan-formed by the second scanner unit 12.

As described above, according to this embodiment,
As described above, from the direct horizontal synchronizing signal of the first laser on each surface of the polygon mirror, the pseudo horizontal synchronizing signal of the second laser on the surface corresponding to each surface is generated with a time difference stored at the time of factory shipment. As a result, it is possible to reduce the number of expensive photosensors from two to four in the related art.

(Embodiment 2) A "color laser printer" which is Embodiment 2 will be described. Since the basic structure is the same as that of the first embodiment, the description will be made with reference to FIGS. At that time, the description of the same parts as those in the first embodiment will be omitted, and only the parts different from the first embodiment will be described.

First, a procedure for forming a pattern for measuring the amount of color misregistration and correcting each surface of the polygon mirror will be described.

First, as in the first embodiment, the pseudo horizontal synchronizing signal of the second laser 6 is generated based on the direct horizontal synchronizing signal of the first laser 5 with a time difference stored in advance at the time of factory shipment or with a previously corrected value. . A pattern for measuring the color misregistration amount is formed on the basis of the pseudo horizontal synchronizing signal of the second laser. At this time, the pattern for measuring the color misregistration is, for example, as shown in FIG.
As shown in, lines on each surface are formed at equal intervals L in the direction perpendicular to the horizontal scanning direction (sub-scanning direction), and the average value of the respective measured values is stored as the color misregistration amount. Pseudo horizontal synchronizing signals are generated on the basis of the horizontal synchronizing signals directly for all the surfaces to form measurement patterns and store the correction values. FIG. 3 is a diagram showing a measurement pattern in the scanner unit 11, in which I is a measurement pattern obtained by scanning the first surface, II is the second surface, III is the third surface, and IV is the fourth surface. is there.

Then, the correction preparation operation is performed on all the surfaces of the scanner unit 12 in the same manner as described above.

Finally, a color misregistration amount measurement pattern drawn with the direct horizontal synchronizing signal of the scanner unit 11 as a reference,
The pattern for measuring the color shift amount drawn by the direct horizontal synchronizing signal (not shown) of the scanner unit 12 is used as the scanner unit 11
Similarly, the correction value is stored.

When all the above processing is completed, the correction preparation operation is completed. Based on these values, the control circuit changes the writing timing of the image and performs exposure while performing correction for each surface.

In this embodiment, the correction of the scanner unit 11 is first performed, then the correction of the scanner unit 12 is performed, and finally the correction between the scanner unit 11 and the scanner unit 12 is performed. However,
The order may be replaced in any order, or the correction preparation operation may be performed at a time by simultaneously drawing the patterns for measuring the color misregistration amount.

As described above, according to this embodiment,
Similar to the first embodiment, the first on each surface of the polygon mirror
By generating the pseudo horizontal sync signal of the second laser on the surface corresponding to each surface with the time difference stored at the time of factory shipment from the direct horizontal sync signal of the laser, expensive photosensors can be changed from the conventional four. It can be reduced to two.

Further, by performing the correction operation, the amount of color misregistration caused by environmental changes and changes over time can be suppressed within the allowable value, and an image with optimum image quality can always be obtained.

(Third Embodiment) A "color laser printer" which is a third embodiment will be described with reference to FIG. Since the basic configuration is the same as that of the first embodiment, only parts different from the first embodiment will be described.

In this embodiment, the polygon mirror has a trapezoidal shape as shown in FIG. The center of the axis is the position of the center of gravity.

When the polygon mirror 9-1 having this shape is rotated at a constant speed, the characteristics of long and short appear in the cycle of the horizontal synchronizing signal directly. 4 are A, A-α, A, and A + α. For example,
4a may be used as the first direct horizontal synchronizing signal. As described above, the feature of the present embodiment is that the position of the surface is specified from the characteristic of the interval of the horizontal synchronizing signal. The correction preparation operation and the correction operation are the same as those in the first or second embodiment.

As described above, according to this embodiment,
Similar to the first embodiment, the first on each surface of the polygon mirror
By generating the pseudo horizontal sync signal of the second laser on the surface corresponding to each surface with the time difference stored at the time of factory shipment from the direct horizontal sync signal of the laser, expensive photosensors can be changed from the conventional four. It can be reduced to two. Further, since the position of the specific surface can be detected at intervals of the horizontal synchronizing signal, it is not necessary to mark the polygon mirror, detect this marking with a sensor, and count the number of horizontal synchronizing signals.

Further, by performing the correction operation as described above, it is possible to realize a color laser printer with a small amount of color misregistration by optimal color misregistration correction without an extra cost increase.

(Fourth Embodiment) A "color laser printer" which is a fourth embodiment will be described with reference to FIG. In addition,
Since the basic configuration is the same as that of the first embodiment, the same parts as those of the first embodiment will be denoted by the same reference numerals and description thereof will be omitted, and only the parts different from the first embodiment will be described.

The feature of this embodiment is that the polygon mirrors 9 and 2 are
6 is overlaid and driven by one polygon motor (not shown).

The third laser 30 is scanned by the polygon mirror 26. After that, the light is specularly reflected by the folding mirror 35, passes through the lens group 25, and is exposed on the photoconductor 23. The fourth laser 27 is scanned by the polygon mirror 26, is regularly reflected by the folding mirror 29, and passes through the lens group 28 to expose the surface of the photoconductor 24.

With such a configuration, as in the first embodiment, each surface is dealt with by the time difference stored at the time of factory shipment from the direct horizontal synchronizing signal of the first laser 5 applied to each surface of the polygon mirror 9. By generating the pseudo horizontal synchronizing signals of the lasers 6, 27, 30 applied to the respective surfaces of the polygon mirrors 9, 26, the number of expensive photosensors is reduced from the conventional four to one.
Can be reduced to individual pieces.

Also in this embodiment, similarly to the first embodiment, the surface on which the laser scanning is performed is specified, and the time difference applied to the surface is used to generate a horizontal synchronizing signal other than the reference horizontal synchronizing signal. . Further, the color misregistration correction method is similar to that of the first embodiment in that the first to the first are based on the direct horizontal synchronization signal.
The four lasers 5, 6, 30, and 27 form a pattern for measuring the color misregistration amount, which is detected by the sensor for measuring the color misregistration amount, and the correction content is stored.

As described above, according to this embodiment, the
By changing the number of required photosensors to one,
Further, it is possible to realize a color laser printer with reduced cost.

In this embodiment, the marking 16 and the reflection type photo interrupter 15 are used to specify the position of the polygon surface. However, the polygon mirror may be configured similarly to the third embodiment, and the polygon surface position may be specified by the periodic pattern of the horizontal synchronizing signal.

[0044]

As described above, according to the present invention,
In an image forming apparatus that exposes a plurality of light beams by reflecting them on different surfaces of a rotary polygon mirror, the number of expensive photosensors can be reduced, and a color image forming apparatus that is inexpensive and has good image quality can be provided.

[Brief description of drawings]

FIG. 1 is a perspective view of a scanner unit used in the first embodiment.

FIG. 2 is a sectional view showing the overall configuration of the first embodiment.

FIG. 3 is a diagram showing an example of a pattern for measuring a color shift amount.

FIG. 4 is an outline and timing chart of the polygon mirror used in the third embodiment.

FIG. 5 is a perspective view of a scanner unit used in the fourth embodiment.

[Explanation of symbols]

4 Photo sensor 5,6 laser 9 polygon mirror 15 Reflective photo interrupter 16 Black marking

Continued front page    F-term (reference) 2C362 BA51 BA53 BA68 BA69 BA70                       BB30 BB32 BB37 BB38 CA39                       DA09                 2H045 AA53 BA22 BA34 CA88 CA98                       DA41                 5C051 AA02 CA07 DA02 DB02 DB22                       DB24 DB30 DC02 DC04 DC07                       DE02 EA01 FA01                 5C072 AA03 BA02 HA02 HA06 HA09                       HA13 HB08 HB13 QA14 XA01                       XA05

Claims (7)

[Claims] 1. An image forming apparatus for exposing a plurality of light beams by simultaneously reflecting a plurality of light beams on different surfaces of a rotary polygonal mirror, and detecting a reference light beam among the plurality of light beams to perform horizontal synchronization as a reference. The position of a specific surface of the rotating polygon mirror and the scanning means for performing optical scanning with the plurality of light beams is determined based on a synchronizing signal generating means for generating a signal and a horizontal synchronizing signal serving as a reference generated by the synchronizing signal generating means. Specific surface position determining means, and a surface position determining means for determining the position of the surface performing the optical scanning based on the specific surface determined by the specific surface position determining means based on the number of the horizontal synchronization signals. An image forming apparatus characterized by the above. 2. An image forming apparatus that simultaneously exposes a plurality of light beams on different surfaces of a plurality of superimposed rotary polygon mirrors, respectively, and exposes the light beams to generate a sync signal for generating a reference horizontal sync signal. Scanning means for performing optical scanning with the plurality of light beams and specific surface position determination means for determining the position of the specific surface of the rotary polygon mirror based on the reference horizontal synchronization signal generated by the generation means and the synchronization signal generation means. And a surface position determination means for determining the position of the surface performing the optical scanning based on the number of the horizontal synchronization signals based on the specific surface determined by the specific surface position determination means. Image forming apparatus. 3. The image forming apparatus according to claim 1, further comprising a storage unit that stores a time difference between the reference horizontal synchronizing signal and a horizontal synchronizing signal of a light beam other than the reference light beam, An image forming apparatus comprising: a second synchronization signal generation unit that generates a horizontal synchronization signal of a light beam other than the reference light beam based on the time difference stored in the storage unit. 4. The image forming apparatus according to claim 1, wherein the specific surface position detecting means detects the specific surface by a mark provided on the rotary polygon mirror or a shape of the rotary polygon mirror. A characteristic image forming apparatus. 5. An image forming apparatus for exposing a plurality of light beams by simultaneously reflecting a plurality of light beams on different surfaces of a rotary polygonal mirror, and detecting a reference light beam among the light beams to obtain a reference horizontal synchronizing signal. And a synchronization signal generation means for generating a horizontal synchronization signal of the light beams simultaneously reflected on a surface different from the surface on which the reference light beam is reflected, The image forming apparatus is characterized in that the signal generating means generates the horizontal synchronizing signal based on a time difference from the reference horizontal synchronizing signal stored in advance at the time of factory shipment. 6. An image forming apparatus for exposing a plurality of light beams by simultaneously reflecting a plurality of light beams on different surfaces of a plurality of superimposed rotary polygon mirrors, wherein a reference light beam among the light beams is detected and used as a reference. A reference synchronization signal generation unit that generates a horizontal synchronization signal that becomes, and a synchronization signal generation unit that generates a horizontal synchronization signal of the light beams that are simultaneously reflected on a surface different from the surface on which the reference light beam is reflected, The image forming apparatus is characterized in that the synchronization signal generating means generates a horizontal synchronization signal based on a time difference from the reference horizontal synchronization signal stored in advance at the time of factory shipment. 7. The image forming apparatus according to claim 5, wherein the time difference is stored for each surface of the rotary polygon mirror.