JP2001142013A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device capable of effectively preventing image noise caused accompanying skew adjustment with respect to an image forming device where a surface to be scanned is simultaneously scanned with three or more leaser beams. SOLUTION: Whether a row(L-th row) being an image data writing object is a row in which the image data served for the modulation of any one of four laser diodes is written is judged in an image memory (steps S4, S9 and S11). After storing null data in the top of each row by an amount equivalent to the deviation in a main scanning direction between respetive scanning lines caused accompanying the skew adjustment (steps S5, S10, S12, S13 and S6), one line of image data is written (step S7).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a digital copying machine,
The present invention relates to an image forming apparatus such as a laser printer, and more particularly, to an image forming apparatus having a multi-beam scanning optical system for simultaneously scanning a surface to be scanned with a plurality of laser beams.

[0002]

2. Description of the Related Art Recently, in an image forming apparatus such as a digital copying machine and a laser printer, two laser beams having a constant interval in a sub-scanning direction are simultaneously received by a laser beam in order to cope with a high speed of image formation. A device equipped with a two-beam scanning optical system for scanning the surface of the photosensitive drum serving as a scanning surface has been put to practical use. When scanning with two laser beams simultaneously, 1
Compared to scanning with a book, for example, in the case of a copying machine,
As a result, approximately twice the number of copies can be obtained per unit time.

In order to further increase the speed of image formation, it has been studied to increase the number of laser beams simultaneously writing on the photosensitive drum to three, four,....

[0004]

However, the more the number of laser beams is increased, the more the reproduced image quality deteriorates. This problem occurs when the scanning optical unit is attached to the image forming apparatus main body.
This is due to skew adjustment that is usually performed. What is skew?
A scanning line in the main scanning direction on the photosensitive drum (hereinafter, referred to as a scanning line)
This is called "main scanning line". ) Refers to a state in which the scanning drum is inclined with respect to the generatrix of the cylindrical photosensitive drum, and the skew adjustment is performed by adjusting the relative positional relationship between the scanning optical unit and the photosensitive drum. Means that the main scanning line is eliminated in parallel with the generatrix of the photosensitive drum.

[0005] Scanning is performed simultaneously with n laser beams.
The case of a beam scanning optical system will be described as an example. FIG. 10 (a)
Suppose that n parallel main scanning lines are inclined at an angle θ with respect to the generatrix of the photosensitive drum indicated by a dashed line. By the skew adjustment described above, the main scanning line can be made parallel to the generatrix of the photosensitive drum as shown in FIG. 3B, but this time, the main scanning line is adjusted according to the inclination correction amount (angle θ). In this case, a deviation occurs in the main scanning start position between the n beams.

FIG. 1C is a conceptual diagram showing a state near the start of scanning of a certain n scan lines and the next n scan lines when scanning is performed by the skew-adjusted scanning optical system. . In this case, the shift amount between the scan start position of the last scan line of the n scan lines and the scan start position of the first scan line of the next n scan lines becomes the largest ( In this section, this shift amount is referred to as a “maximum shift amount.) Within the range of the correction amount required in the skew adjustment that is normally performed, the maximum amount that occurs in the two-beam scanning optical system (that is, when n = 2) The shift amount is small, and is small enough to be visually unrecognizable. However, in the three-beam scanning optical system, the maximum shift amount is twice as large as that in the two-beam scanning optical system, and appears as visible image noise.

As the number of beams further increases, the above-described maximum shift amount increases accordingly, image noise increases, and image quality further deteriorates. The present invention has been made in view of the above problems,
It is an object of the present invention to provide an image forming apparatus having a scanning optical system for simultaneously scanning with three or more laser beams, and which can effectively prevent the above-described image noise even if skew adjustment is performed. And

[0008]

In order to achieve the above object, an image forming apparatus according to the present invention comprises an image forming apparatus for storing three or more continuous lines in a sub-scanning direction from an image memory for storing image data for each main scanning line. An image forming apparatus comprising: scanning means for simultaneously reading image data, generating a laser beam for each line, and scanning a surface to be scanned with the laser beam, wherein a relative position between the surface to be scanned and the scanning means is provided. A skew adjustment mechanism that adjusts the scanning direction of the laser beam so as to match the main scanning direction on the surface to be scanned by changing the positional relationship, and each scanning line on the surface to be scanned, which is caused by the skew adjustment. Storage means for storing the amount of shift in the main scanning direction between the image data and the image data by shifting the input image data in the main scanning direction by an amount corresponding to the amount of shift stored in the storage means. Characterized by comprising an image data writing means for writing into the memory.

An image forming apparatus according to the present invention is an image forming apparatus provided with a scanning means for scanning a surface to be scanned with three or more laser beams, wherein a relative distance between the surface to be scanned and the scanning means is provided. A skew adjustment mechanism that adjusts the scanning direction of the laser beam so as to match the main scanning direction on the surface to be scanned by changing the positional relationship, and performs each scan on the surface to be scanned, which occurs with the skew adjustment. Storage means for storing the amount of shift in the main scanning direction between lines; and timing adjusting means for adjusting the generation timing of each laser beam according to the amount of shift stored in the storage means. And

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an image forming apparatus according to the present invention is provided with a four-beam scanning optical unit for simultaneously exposing and scanning the surface of a photosensitive drum, which is a surface to be scanned, with four laser beams. An example in which the present invention is applied to a digital copying machine will be described. FIG. 1 is a diagram showing a schematic configuration of the entire digital copier (hereinafter, simply referred to as “copier”).

The image of the original set on the original glass plate 1 at the top of the copying machine is read by the CCD sensor 3 of the image reader 2 and input to the control unit 100 as image data. The control unit 100 converts the input image data into a drive signal of a laser diode, and drives the laser diodes LD1 to LD4 inside a four-beam scanning optical unit (hereinafter simply referred to as “scanning unit”) 200 as an optical scanning device.
(FIG. 3). Laser diodes LD1 to LD4
The laser beams LB1 to LB4 emitted from the scanning unit 200 pass through predetermined optical elements in the scanning unit 200 as described later, and then return to the folding mirror 46 in the scanning unit 200.
And exposes the surface of the photosensitive drum 4 in the main scanning direction.

Around the photosensitive drum 4, a drum cleaner 5, an eraser lamp 6, a charging charger 7, a developing unit 8
And a transfer charger 9. Before exposure to the laser beams LB1 to LB4, the photosensitive drum 4 removes residual toner by a drum cleaner 5, and is irradiated with an eraser lamp 6 to remove electricity, and then uniformly charged by a charging charger 7. When the uniformly charged photosensitive surface is exposed, an electrostatic latent image is formed, and the electrostatic latent image is visualized as a toner image by the developing device 8.

On the other hand, a recording sheet S is fed from a sheet feeding cassette 10 by a pickup roller 11 and a timing roller 12, and the fed recording sheet S is transferred by a transfer belt 13 directly below the photosensitive drum 4. Transported to a location. At this transfer position, the toner image on the photosensitive drum 4 is transferred to the recording sheet S by the operation of the transfer charger 9. The recording sheet S to which the toner image has been transferred is further conveyed by a transfer belt 13 and a conveyance belt 14, and after the toner is fixed by a fixing device 15,
The sheet is discharged to the discharge tray 16.

An operation panel 17 is provided on the upper surface of the copying machine. The operation panel 17 includes a numeric keypad for inputting numerical values such as the number of copies, a start key for instructing start of copying, a setting key for setting various copy modes, a maintenance key for inputting maintenance information, and It is composed of a display unit that displays a mode and the like set by keys and the like by a message.

FIG. 2 is a diagram showing a schematic configuration of the scanning unit 200. The scanning unit 200 includes the unit base plate 2
1 and a top plate 22 (FIG. 2B).
FIG. 2A is a diagram of the scanning unit 200 viewed from above with the top plate 22 removed, and FIG.
FIG. 2A is a diagram cut along the line AA in FIG. 2A and mainly shows optical components located on the cutting line.

As shown in FIG. 2A, the scanning unit 2
No. 00 has two light source units for emitting a laser beam (30a, 30b). Two light source units 30
Since a and 30b have the same configuration, the light source unit 30a will be described as a representative. FIG. 3 is a cross-sectional view illustrating a schematic configuration of the light source unit 30a. As shown in the figure, a laser diode LD1 is provided on a base 31 via a holder 32, and a laser diode LD2 is provided via a holder 33.
Are attached. The two laser diodes LD1 and LD2 are mounted so that the laser beams emitted from each of them form an angle of 90 degrees with each other.

The laser beams LB1 and LB2 emitted from the laser diodes LD1 and LD2 enter a beam splitter 34 formed by bonding two polished prisms. Laser beam L incident on beam splitter 34
While B1 is deflected by 90 degrees, the laser beam LB2 passes through the beam splitter 34 without being deflected. As a result, the traveling directions of the two laser beams LB1 and LB2 are aligned, and the
1 and LB2 enter the collimator lens 35 attached to the base 31. The laser beams LB1 and LB2 that have entered the collimator lens 35 pass through the collimator lens 35, and are converted from divergent light to parallel light.

Here, in the other light source unit 30b, the laser diode LD1 of the light source unit 30a is used.
The laser diode LD3 corresponds to the laser diode LD3, and the laser diode LD4 corresponds to the laser diode LD2 of the light source unit 30a. The laser beam emitted from the laser diode LD3 is LB3,
The laser beam emitted from the laser diode LD4 is LB4.

It should be noted that the four laser beams LB1, LB2, LB3, LB4 after passing through the collimator lens are arranged in this order at predetermined regular intervals in the sub-scanning direction (vertical direction in the drawing). The laser diode LD is set so that the interval between the spots of the laser beam that forms an image on the photosensitive drum 4 is an interval corresponding to the resolution in the sub-scanning direction.
A mounting position of each of the light source units LD1, LD2, LD3, and LD4 and a relative position between the two light source units are determined.

Returning to FIG. 2, the laser beams LB1 and LB2 emitted from the light source unit 30a and the light source unit 30
The laser beams LB3 and LB4 emitted from b enter the beam splitter 41 at an angle of substantially 90 degrees with each other, and the laser beams LB3 and LB4 are deflected by 90 degrees, while the laser beams LB1 and LB2 are deflected. The light passes through the beam splitter 41 without being changed. As a result, the laser beams LB1 and LB2 and the laser beam LB
3, the traveling directions of LB4 are aligned, and the
Laser beams LB1, LB2, LB3, LB4 (hereinafter, "LB" when collectively referring to four beam groups)
It is described. ) Is condensed in the sub-scanning direction by the cylindrical lens 42, then enters the polygon mirror 43, which is rotated at high speed in the direction of the arrow by a polygon motor (not shown), and is reflected on the mirror surface of the polygon mirror 43.

The laser beam LB reflected on the mirror surface of the polygon mirror 43 passes through the fθ lens 44, the cylindrical lens 45, the turning mirror 46, and the window glass 47, and is a photosensitive member which is a surface to be scanned which rotates in the sub-scanning direction. An image is formed on the surface of the drum 4, and the surface is exposed and scanned in the main scanning direction. Further, the scanning unit 200 has an SOS (Start Of Scan) sensor 48 as a photo sensor and an SOS mirror 49 for guiding the laser beam LB to the SOS sensor 48. The SOS sensor 48
Provided for aligning the writing start positions of the scanning line groups to be written on the photosensitive drum 4 four by four on one surface of a polygon mirror 43 having a regular polygon (a regular octagon in the illustrated example). Have been. That is, the laser beam LB deflected by the polygon mirror 43 is
An SOS sensor 48 is provided at a position on the upstream side (a position where the light beam arrives earlier) than when scanning is performed. The SOS sensor 48 receives the laser beam LB, and starts modulating the laser beam in synchronization with the SOS signal generated thereby. I am trying to do it.

Various optical components from the light source units 30a and 30b to the window glass 47 and the SOS mirror 4
9 and the SOS sensor 48 are all mounted on the unit base plate 21. The unit base plate 21 is attached to the main body base plate 61, and the main body base plate 61 is provided with two side plates (not shown) which stand in parallel in the copying machine so as to face each other.
It is mounted horizontally with the space between them. The photosensitive drum 4 is also mounted on the same side plate.

The unit base plate 21 is provided with three screw insertion holes 51, 52, 53 in a main body base plate 61 attached to the side plate.
, And is fixed by a screw (not shown). Prior to this fixing, skew adjustment is performed. Next, a mechanism for skew adjustment will be described. A first positioning pin P1 is provided at a position extending in the longitudinal direction of the folding mirror 46. As shown in FIG.
Are press-fitted into holes formed in the unit base plate 21 and are integrally fixed to the unit base plate 21. On the other hand, a first positioning hole H1 is formed in the main body base plate 61. The diameter of both the pin P1 and the hole H1 is
1 is formed so that it can be smoothly inserted into the hole H1 and has a size without rattling. Therefore,
When the pin P1 is inserted into the hole H1 and the unit base plate 21 is placed on the main body base plate 61, the unit base plate 21
Is held so as to be rotatable around the.

That is, the folding mirror 46 can be rotated in a horizontal plane about one point (the axis of the pin P1) extended in the longitudinal direction. By rotating the folding mirror 46 about the axis of the pin P1, the angle between the reflection surface 46a (FIG. 2) of the folding mirror 46 and the axis (generic line) of the cylindrical photosensitive drum 4 is changed. be able to. Therefore, the reflection surface 4 of the folding mirror 46
The skew can be adjusted by changing the inclination of the main scanning line of the laser beam LB that is reflected by 6a and forms an image on the surface of the photosensitive drum 4 with respect to the generatrix of the photosensitive drum 4.

At the time of skew adjustment, a CCD image sensor replaces the photosensitive drum 4 with a laser beam LB.
Are provided at the image forming positions. This CCD image sensor is an area image sensor in which photosensitive pixels are two-dimensionally arranged. When the CCD image sensor is provided at an image forming position of the laser beam LB, its longitudinal direction (main scanning direction) is substantially equal to that of the photosensitive drum 4. The length is the same, and is slightly longer in the sub-scanning direction than the length of the simultaneous exposure by four laser beams. In addition, the pixel pitch in both the main scanning direction and the sub-scanning direction is an interval corresponding to the resolution of the image to be formed (dot pitch of the laser beam).

At the time of skew adjustment, the unit base plate 21 is rotated while the scanning unit 200 is actually operated and the detection result of the CCD image sensor is monitored by a device connected to the CCD image sensor. When one laser beam scans one line in the main scanning direction of the CCD image sensor (that is, when the main scanning line of the laser beam is parallel to the generatrix of the photosensitive drum), the position at that time is set to the unit table. This is the fixed position of the plate 21.

To maintain this fixed position, a mechanism as shown in FIG. 5 is provided. This mechanism is provided at the position indicated by arrow B in FIG. FIG. 5A is a view of the mechanism as viewed from the same direction as in FIG.
FIG. 5B is a diagram cut along the line CC in FIG. 5A. A second hole is formed in the center of the skew adjustment plate 54.
Are press-fitted, and the pin P2 is integrally fixed to the skew adjustment plate 54.

The unit base plate 21 is provided with a hole 55 having a diameter larger than the shaft diameter of the pin P2. This hole 55
As described later, the unit base plate 21 at the time of skew adjustment is adjusted.
It is a hole to allow the movement of. The pin P2 is inserted into the second positioning hole H2 provided in the main body base plate 61 via the hole 55, and the skew adjustment plate 54 is placed on the unit base plate 21. The relation between the diameter of the pin P2 and the diameter of the hole H2 is the same as the relation between the diameter of the pin P1 and the diameter of the hole H1.

The skew adjusting plate 54 has elongated holes 56 and 57 on both sides of the pin P2, while screw holes S1 and S2 are formed on both sides of the hole 55 of the unit base plate 21, respectively.
Are formed. A screw 58 is screwed into the screw hole S1 via the long hole 56, and a screw 59 is screwed into the screw hole S2 via the long hole 57. The width of the long holes 56, 57 is substantially equal to the outer diameter of the screws 58, 59,
The length of 7 is substantially equal to the diameter of the hole 55.

In a state where both screws 58 and 59 are lightly screwed (in a state where the seat surface of the screw is not in contact with the upper surface of the skew adjusting plate 54), the unit base plate 21 is moved to the first positioning pin P1.
The skew adjustment is performed by rotating about (FIG. 2). At this time, the position of the pin P2 is fixed with respect to the main body base plate 61, and the unit base plate 21 and the screw 5 are positioned with respect to the pin P2.
8, 59 move (the skew adjustment plate 54 and the pin P2 slightly rotate around the axis of the pin P2).

When the fixed position of the unit base plate 21 is determined,
The screws 58 and 59 are tightened, and the skew adjustment plate 54 is fixed to the unit base plate 21 to complete a series of skew adjustment. When the skew adjustment is completed, the unit base plate 21
It is fixed to the main body base plate 61 with screws (not shown) through the three screw insertion holes 51, 52, and 53. The fact that the skew adjustment plate 54 is fixed to the unit base plate 21 means that the position of the second positioning pin P2 with respect to the unit base plate 21 is fixed. As a result, the unit base plate 21 is positioned relative to the main body base plate 61 by the first positioning pin P1, the second positioning pin P2, the first positioning hole H1, and the second positioning hole H2.

Therefore, due to the necessity of maintenance and the like,
If the screw attached via the screw insertion holes 51, 52, 53 is removed, and the scanning unit 200 (unit base plate 21) is once removed from the main body base plate 61, but is mounted again, The positional relationship of the scanning unit 200 with respect to the main body base plate 61 is the same as before the removal, and the positional relationship of the scanning unit 200 with respect to the photosensitive drum 4 is similarly maintained.

If there is no problem in the scanning unit 200, an image (electrostatic latent image) can be accurately formed on the photosensitive drum 4 by the skew adjustment described above. In the case where the optical axis of the fθ lens 44 or the like in the scanning unit 200 is deviated from a predetermined position, a new inconvenience occurs due to the skew adjustment.

If the optical axis of the fθ lens 44 deviates from the prescribed position, the main scanning line before the skew adjustment is
(A) or FIG. 6 (c). On the other hand, when the skew adjustment is performed, it becomes as shown in FIG. 6B or FIG. 6D, respectively. That is, the problem described in the section “Problems to be solved by the invention” occurs. Therefore, of the four laser beams, the first laser beam L
Another laser beam LB2 for the writing start position of B1
To LB4, the deviation E in the main scanning direction between the write start positions.
1 to E3 are measured, and the image noise is prevented by the method described later using the measurement results. Note that each of the shift amounts E1 to E3 is measured by the above-described CCD image sensor used for skew adjustment.
In addition, when the writing is started with a delay as shown in FIG. 6A, each of the deviation amounts E1 to E3 is represented by a negative value.
When writing is started early as in (c), it is represented by a positive value.

FIG. 7 is a block diagram mainly showing a schematic configuration of the control unit 100. As shown in FIG.
Is composed of an A / D converter 101, an image data receiver 102, an image data writer 103, an image memory 104, a laser diode driver 105, a CPU 106, a ROM 107 and a RAM 108. A / D converter 10
Reference numeral 1 denotes an image data receiving unit 102 which converts analog image data sent from the CCD sensor 3 into digital image data.
Send to

The image data receiving unit 102 performs various correction processes such as edge enhancement on the image data received from the A / D conversion unit 101, and then converts the image data in the main scanning direction into one.
The image data is transmitted (input) to the image data writing unit 103 line by line. At this time, when the transmission of one page of image data is completed, the image data receiving unit 102 transmits an end signal to the image data writing unit 103.

The image data writing section 103 writes the image data input from the image data receiving section 102 line by line into the image memory 104. The image memory 104 is a memory that stores image data for each page. FIG.
FIG. 5 shows a leading portion (a portion corresponding to the upper left of the document image) in the storage area of the image data for one page. The image memory 104 stores image data in pixel units, and includes a row direction (main scanning direction) and a column direction (sub scanning direction).
Is stored in one area specified by the address assigned to the address (in this figure, approximately 15 rows and 3 rows).
A storage area for 0 columns is displayed. ). Here, the address number assigned in the main scanning direction is called a column number (FIG. 8).
In the figure, up to column number 30 is shown. ), The address number allocated in the sub-scanning direction is called a line number (FIG. 8).
In the figure, up to line number 15 is shown. ). In addition, the pixel information includes white pixel information (hereinafter, referred to as “O”) in the figure.
It is simply called "white pixel". ) And black pixel information (hereinafter, simply referred to as “black pixel”) represented by “●”. As described later, the laser diode is modulated based on this pixel information, and the laser diode is turned on for a black pixel and turned off for a white pixel. When the laser diode is turned on, a (toner) image is formed on the photosensitive drum 4 at the position irradiated with the laser beam. As will be described later, the image data stored in the image memory 104 is simultaneously read four lines at a time in order from the image data of the row number 1, and the modulation driving of the laser diodes LD1 to LD4 is performed in ascending order of the row number. Provided. At this time, the pixel information is sequentially read out in ascending order of the column numbers, and the modulation driving of all the laser diodes LD1 to LD4 is simultaneously performed based on the pixel information of the same column number.

The image data writing unit 103 stores the row number 1,
In the area specified by 5, 9,..., That is, the area in which the image data used for the modulation drive of the laser diode LD1 is stored, the image data for one line input from the image data receiving unit 102 (hereinafter, referred to as In the case where “line data” is stored, white pixels are stored in the storage locations of column numbers 1 to 10 and the line data is stored in column numbers 11 and thereafter. That is, the image data writing unit 103 stores the line data using the address of the column number 11 as the reference address in the above row number. Here, the white pixels stored regardless of the content of the image data, such as the white pixels stored in the storage locations of column numbers 1 to 10 above, are hereinafter referred to as “empty data”.

On the other hand, the image data writing section 103 stores other row number storage areas (laser diodes LD2 to LD
Area for storing image data to be used for modulation drive 3)
When storing the line data, the reference address is changed by increasing or decreasing the empty data as necessary. If the reference addresses are aligned for all the rows, the main scanning lines on the photosensitive drum 4 have the above-mentioned shift amounts E1 to E3.
The main scanning direction. Therefore, by changing the reference address by an amount corresponding to the shift amount, as a result, the scanning start positions of the main scanning lines on the photosensitive drum 4 are aligned.

More specifically, for example, line number 2,
When line data is stored in an area specified by 6, 10,..., That is, an area in which image data used for modulation driving of the laser diode LD2 is stored, an amount corresponding to the shift amount E1 is used. The number of empty data is increased or decreased from ten. When E1 is a negative value (FIG. 6A)
Means that the scan start position of the main scan line generated by the laser diode LD2 is delayed from the scan start position of the main scan line generated by the laser diode LD1, so the empty data is reduced by e1 according to E1. As a result, the reading time of the line data is advanced.
Conversely, when E1 is a positive value (FIG. 6D), the scan start position of the main scan line generated by the laser diode LD2 is more than the scan start position of the main scan line generated by the laser diode LD1. Since the position is advanced, the empty data is increased by e1 in accordance with E1, and as a result, the reading time of the line data is delayed. If there is no empty data number that just cancels the deviation amount E1, the number of empty data is determined so that the deviation amount E1 is minimized.

Similarly, the areas specified by the row numbers 3, 7, 11,... (The areas where the image data used for the modulation drive of the laser diode LD3 are stored) and the row numbers 4,
8, 12,... (The laser diode LD
Area for storing image data to be used for modulation drive 4)
When the line data is stored in the
In accordance with 2, E3, empty data is increased or decreased by e2 or e3.

FIG. 8 shows that the deviation of each main scanning line is shown in FIG.
An example of a storage state of pixel information when there is a tendency as shown in (b) is shown. Normally, the line data has a mixture of black pixels and white pixels, but in the figure, all the line data are represented by black pixels for simplicity. Note that, as a result of the skew adjustment, the above-described deviation does not occur (that is, E1 = E2 = E3 = 0).
It is needless to say that 10 sets empty data for all rows and aligns the reference addresses between the rows.

The laser diode driving unit 105 has a CPU
In accordance with the instruction of 106, the line data is read out four lines at a time sequentially from the line data of the line number 1,
Based on the data, each of the laser diodes LD1 to LD1
D4 is modulated and driven. That is, when the SOS signal is input from the SOS sensor 48, the CPU 106 instructs the laser diode driving unit 105 to simultaneously read four consecutive line data in the sub-scanning direction. The laser diode driving unit 105 sequentially reads out pixel information in ascending order of column number, and modulates the laser diode LD1 based on the pixel information of the smallest row number among the read-out pixel information, thereby obtaining the second row number. The laser diode LD2 is modulated on the basis of the youngest pixel information, the laser diode LD3 is modulated on the basis of the third youngest pixel information of the row number, and the fourth youngest pixel information of the row number (the last line data of the four lines). ) To modulate the laser diode LD4.

The ROM 107 stores a control program and the like relating to a process of writing image data into the image memory 104 by the image data writing unit 103 described above.
The RAM 108 is a nonvolatile RAM, and stores the above-described shift amounts E1 to E3. The deviation amounts E1 to E3 are stored via the operation panel 17 at the time of skew adjustment.

The CPU 106 reads out a necessary program from the ROM 107 and causes each unit such as the image data receiving unit 102 to perform various kinds of processing, and realizes a smooth image forming operation by uniformly controlling the operation of each unit. I do. FIG.
9 is a flowchart illustrating a procedure of a process of writing image data to the image memory 104 by the image data writing unit 103. The variable “L” used in this flowchart is for specifying the number of the line to which image data (line data) is to be written in the image memory 104. “MOD (L, 4)” is a function for obtaining a remainder when the variable L is divided by 4. Therefore, the line data written in the row (L-th row) is calculated according to the operation result (remainder) by MOD (L, 4).
It is possible to determine which of the laser diodes LD1 to LD4 is the line data used for modulation. For example, if MOD (L, 4) = 1,
Since L = 1, 5, 9,..., It can be determined that the line data written in the row is to be used for modulation of the laser diode of the LD1. A series of processes shown in this flowchart is started by an instruction from the CPU 106.

First, 1 is stored in the variable L as an initial value in order to set the line to be written to the first line (step S).
1) Wait for an input from the image data receiving unit 102 (step S2). If the input is an end signal (Yes in step S3), the process is terminated. If the input is a line data (No in step S3), the process proceeds to step S4.

Thereafter, MOD (L, 4) = 1 (step S4
MOD (L, 4) = 2 (Yes in step S9)
s), MOD (L, 4) = 3 (Ye in step S11)
s) and MOD (L, 4) = 0 (No in step S9), the number of empty data is determined (steps S5, S10, S12, S13), and the determined number of empty data is calculated. Writing is performed from the head of the L-th row of the image memory 104 (step S6).

Next, the line data received from the image data receiving unit 102 is written following the empty data (step S7), and the variable L is incremented by 1 (step S7).
8), the writing target row is shifted by one, and the process returns to step S2. As described above, in the present embodiment, 4
In a copying machine in which a photosensitive drum is main-scanned by a laser beam, image data to be written into an image memory in the main scanning direction is written in accordance with a shift amount in the main scanning direction between four main scanning lines caused by skew adjustment. I decided to shift it to
Actually, the writing start positions of the four main scanning lines are aligned on the photosensitive drum. That is, it is possible to effectively prevent image noise generated due to the skew adjustment.

Although the present invention has been described based on the embodiments, it is needless to say that the present invention is not limited to the above-described embodiments. (1) In the above embodiment, the number of laser beams for simultaneously scanning the photosensitive drum is four, but the number of laser beams is not limited to this, and may be three, or the number of light source units is increased. For example, the number may be five or more. (2) In the above embodiment, the writing start positions of the four main scanning lines are aligned by shifting the image data in the main scanning direction in the image memory. However, the present invention is not limited to this. You may do so.

The image data is output as usual without shifting,
Write to image memory. When the SOS signal is input from the SOS sensor, the CPU starts an internal timer,
The timing of reading line data from the image memory is shifted by an amount corresponding to the shift amounts E1 to E3 while referring to the time measurement result of the internal timer, and each laser diode L
The modulation start timing of D1 to LD4 is shifted.

More specifically, when the shift of each main scanning line is in a state as shown in FIG. 6D, the modulation of the laser diode LD2 is started by the laser diode L2.
The delay from the start of the modulation of D1 is delayed by a time corresponding to the shift amount E1. Similarly, with respect to the start of modulation of the laser diode LD1, the modulation start timing of the laser diode LD3 is shifted by the time corresponding to the shift amount E2, and the modulation start timing of the laser diode LD4 is shifted by the time corresponding to the shift amount LE3.

In the state shown in FIG. 6B, when the laser diode LD4 starts to modulate, the laser diode LD3 moves the laser diode LD2 for a time corresponding to the shift amount (E3-E2). Offset (E3
−E1), and the laser diode LD1 shifts the modulation start timing by the time corresponding to the shift amount E3.

[0053]

As described above, according to the image forming apparatus of the present invention, three or more lines of image data are simultaneously read out from the image memory for storing image data for each main scanning line, and generated for each line. In an image forming apparatus that scans a surface to be scanned with a laser beam, the laser beam is shifted in the main scanning direction by an amount corresponding to a shift amount in the main scanning direction between scanning lines on the surface to be scanned caused by skew adjustment. Since the image data is written into the image memory, the writing start positions of the respective scanning lines are actually aligned on the surface to be scanned.
That is, it is possible to effectively prevent image noise generated due to the skew adjustment.

According to the image forming apparatus of the present invention, in an image forming apparatus that scans a surface to be scanned with three or more laser beams, the distance between each scanning line on the surface to be scanned caused by skew adjustment is adjusted. Since the generation timing of each laser beam is adjusted by an amount corresponding to the shift amount in the main scanning direction, the writing start positions of the respective scanning lines are actually aligned on the surface to be scanned. That is, it is possible to effectively prevent image noise generated due to the skew adjustment.

[Brief description of the drawings]

FIG. 1 is a diagram showing a schematic configuration of an entire digital copying machine according to an embodiment.

FIG. 2A is a schematic configuration diagram of the inside of a four-beam scanning optical unit viewed from above. FIG. 2B is a view mainly showing optical components located on the cutting line by cutting FIG. 1A along the line A-A.

FIG. 3 is a cross-sectional view illustrating a schematic configuration of a light source unit.

FIG. 4A is a diagram illustrating a state before a first positioning pin is inserted into a main body base plate. FIG. 2B is a diagram showing a state where the first positioning pin is inserted into the main body base plate.

FIG. 5A is a diagram of the vicinity of a skew adjustment plate viewed from above. FIG. 2B is a view of FIG. 1A cut along the line CC.

FIG. 6A is a diagram illustrating an example of a skew.
FIG. 2B is a diagram showing a state in which the skew shown in FIG. FIG. 3C is a diagram illustrating an example of a skew. FIG. 4D is a diagram showing a state in which the skew shown in FIG.

FIG. 7 is a block diagram mainly showing a schematic configuration of a control unit 100;

FIG. 8 is a diagram showing a part of an image memory.

FIG. 9 is a flowchart illustrating a procedure of a process of writing image data to an image memory by an image data writing unit.

FIG. 10A is a diagram illustrating an example of a skew. FIG. 2B is a diagram showing a state in which the skew shown in FIG. FIG. 7C is a diagram showing a state near the start of scanning of a certain n scanning lines and the next n scanning lines in a state where the skew has been eliminated.

[Explanation of symbols]

 Reference Signs List 4 photosensitive drum 21 unit base plate 54 skew adjustment plate 61 main body base plate 100 control unit 103 image data writing unit 104 image memory 105 laser diode driving unit 106 CPU 107 ROM 108 RAM 200 4 beam scanning optical unit LD1 to LD4 laser diode P1 First positioning pin P2 Second positioning pin H1 First positioning hole H2 Second positioning hole

 ────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Yoshihiro Inagaki 2-13-13 Azuchicho, Chuo-ku, Osaka-shi, Osaka F-term in Osaka International Building Minolta Co., Ltd. (reference) 2H045 AA01 BA02 BA22 BA33 CA98 DA04

Claims (2)

[Claims] 1. An image memory for storing image data for each main scanning line, image data of three or more lines continuous in the sub-scanning direction are simultaneously read out, a laser beam is generated for each line, and the laser beam is received by the laser beam. An image forming apparatus including a scanning unit that scans a scanning surface, wherein a scanning direction of a laser beam is changed in a main scanning direction on the scanning surface by changing a relative positional relationship between the scanning surface and the scanning unit. A skew adjustment mechanism for adjusting so as to match with the following; storage means for storing the amount of shift in the main scanning direction between scanning lines on the surface to be scanned, which is caused by the skew adjustment; and input image data. Image data writing means for writing the image data in the image memory while shifting the image data in the main scanning direction by an amount corresponding to the shift amount stored in the storage means. Forming apparatus. 2. An image forming apparatus comprising scanning means for scanning a surface to be scanned with three or more laser beams, wherein a relative positional relationship between the surface to be scanned and the scanning means is changed. A skew adjustment mechanism that adjusts the scanning direction of the laser beam so as to match the main scanning direction on the surface to be scanned; and a shift in the main scanning direction between the respective scanning lines on the surface to be scanned, which is caused by the skew adjustment. An image forming apparatus comprising: a storage unit that stores an amount; and a timing adjustment unit that adjusts the generation timing of each laser beam according to a shift amount stored in the storage unit.