JPH1062700A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To uniform the dot interval in the main scanning direction of an image transferred from an image carrier onto a recording paper by regulating the starting position of image recording, the image recording width, the number of image recording dots and the position of each recording dot. SOLUTION: A dummy operation for performing no image recording is executed before starting a scanning for image recording, and the frequency of a video clock is changed by frequency variable means 241, 249-256 in the dummy scanning period. The frequency variable means 241, 249-256 change the frequency of the video clock during the dummy scanning period before a scanning period for performing an image recording so that a first detected value A and a second detected value B, B/A are conformed to a first set value A0 and a second set value B0, respectively. The set values are properly set, whereby the video clock can be conformed to a target value. Thus, when toner images having a plurality of colors are recorded one over another on a transfer paper, an image having no color drift can be recorded.

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 printer, and more particularly, to an image forming apparatus having a laser writing device used when writing an electrostatic latent image on an image carrier using a laser beam. The present invention writes an electrostatic latent image corresponding to an image of a different color by using a laser writing device provided for each of a plurality of image carriers, and develops the electrostatic latent image into a toner image. It is particularly preferably applied to an image forming apparatus provided with a transfer material transporting device for sequentially transporting a transfer material onto which an image is transferred to a toner image transfer position from each image carrier to the transfer material. Also, the present invention can be applied to an image forming apparatus using a laser writing device.

[0002]

2. Description of the Related Art FIG. 14 is a perspective view of a main part of a digital color copying machine F as an image forming apparatus to which the present invention is applied. In FIG. 14, a digital color copying machine F has R (red),
It has an image processing unit U1 to which G (green) and B (blue) image data are input. The image processing unit U1 includes a microcomputer,
The R, G, and B which are constituted by a memory or the like and input
Image data of Y (yellow), M (magenta), C
(Cyan) and K (black) digital image signals, and temporarily store them in a memory of an image processing unit U1 (to be described in detail later).
It has the function of outputting to y, Um, Uc and Uk. The image recording devices Uy, Um, Uc, Uk are respectively Y (yellow), M (magenta), C (cyan), and K (black).
This is an apparatus for forming a toner image of each color. The Y image recording device Uy includes an image carrier Dy, a laser writing device 01y disposed around the image carrier Dy, a developing device 02y, a cleaner 03y,
It has a charger 04y and the like. Other image recording device U
m, Uc and Uk are each configured similarly to the Y image recording device Uy.

The image recording devices Uy, Um, Uc, Uk are:
The Y, M, C, K input from the image processing unit U1
Laser writing device 01 according to the digital image signal of each color
y, 01m, 01c, and 01k are driven, and the chargers 04y, 04
m, 04c and 04k, the image carrier Dy charged uniformly
An electrostatic latent image is written to Dm, Dc, and Dk. Image carrier Dy, D
m, Dc, and Dk are used as developing devices 02y, 02m,
The toner image is developed by 02c and 02k.

FIG. 15 is a detailed explanatory view of the image recording devices Uy, Um, Uc, Uk of the digital color copying machine F. The image recording devices Uy, Um, U shown in FIG.
c, Uk, each image carrier Dy, Dm, Dc, Dk, each laser writing device 01y, 01m, 01c, 01k, each developing device 02y,
02m, 02c, 02k, each cleaner 03y, 03m, 03
c, 03k, and each charger 04y, 04m, 04c, 04k
And the like are configured in the same manner, so that the image recording apparatus U, the image carrier D, the laser scanning system 0
13, the developing device 02, the cleaner 03, and the charger 04 will be described. As shown in FIG. 15, the image recording apparatus U has a transfer unit 05 facing the lower surface of the image carrier D.

In FIG. 14, the image carriers Dy,
A transfer material transport device H is disposed below Dm, Dc, and Dk. The transfer material transport device H includes a drive roll 06, a peeling roll 07, an idler roll 08, and a tension roll 09, and a transfer material transport belt 011 supported by these rolls. Each of the image carriers D
The transfer unit 05 shown in FIG. 15 is disposed at a transfer position where y, Dm, Dc, and Dk come into contact with the belt 011. Further, the transfer material (paper) P is supplied at a predetermined timing from a right side of the transfer material transport device H in FIG. 14 to a predetermined transfer material suction position on the upper surface of the belt 011.

The transfer material P sucked on the belt 011 at the transfer material suction position is conveyed by the belt 011. The transfer material P conveyed by the belt 011 is sequentially transferred to the image carriers Dy, Dm, Dc, and Dk and the respective transfer units 05 (FIG. 15).
), And the toner images of each color are transferred, and the image writing timing of the image carriers Dy, Dm, Dc, and Dk is determined by the timing of writing the Y, M, C, and K toner images. The positions are determined so as to match on the transfer material P. The transfer material P on which the toner images of the respective colors have been transferred is peeled off by a peeling corotron or a stripper (not shown) at the position of the peeling roller 07, and is conveyed to a fixing device (not shown) arranged on the left side in FIG. It is configured as follows.

FIG. 16 is a sectional view taken along the line XVI-XVI in FIG. FIG. 17 is a perspective view of a laser scanning system 013 constituting the laser writing device 01 and an explanatory diagram of a driving circuit thereof. 15 to 17, a laser writing device 01 that irradiates a latent image writing laser beam L for writing an electrostatic latent image onto an image carrier D includes a laser driving circuit 012 (see FIG. 17).
And a laser scanning system 013. The laser scanning system 013 includes a semiconductor laser light source 014 driven by the laser driving circuit 012. In the optical path of the semiconductor laser light source 014, a collimator lens 016, a cylindrical lens 017, a rotating polygon mirror 018, an fθ lens 019, and a cylindrical lens 21 are arranged. The laser beam L scans the surface of the rotating image carrier D in the main scanning direction (the axial direction of the image carrier D). A beam position detection sensor 022 constituted by an optical sensor is provided at an end of the image carrier D, and an image signal to be described later is generated by a beam position detection signal S1 (see FIG. 17) output from the beam position detection sensor 022. Output timing is set.

The beam position detection signal S1 output from the beam position detection sensor 022 is input to a clock selection circuit 023 of the image processing unit U1. Clock selection circuit 02
3 generates a plurality of video clocks having a phase shift from the video clock input from the video clock generation circuit 024, and selects a video clock having the smallest phase shift from the beam position detection signal S1 (ie, a synchronous clock). And outputs it to the writing position control circuit 025. The writing position control circuit 025 outputs a read clock to the image counter 026 according to the synchronization clock input from the clock selection circuit 023. Image counter 02
Reference numeral 6 denotes an image memory 027 according to the input read clock.
, And outputs the image data to the laser drive circuit 012.

The laser drive circuit 012 turns on and off the semiconductor laser light source 014 according to the input image data. When the semiconductor laser light source 014 is on, the laser light L (see FIG. 17) is emitted. In this way,
The semiconductor laser light source 014 writes one line of image data on the surface of the image carrier D in synchronization with the rotation of the rotary polygon mirror 018. When the scanning of one line is completed, the writing scanning of the next one line is performed at a position shifted by one line in the sub-scanning direction (circumferential direction) on the surface of the image carrier D.

In a multi-transfer type image forming apparatus for sequentially transferring a plurality of toner images to a transfer material as shown in FIG. 14, the main scanning direction and the sub-scanning direction of the toner images of each color on each transfer material P. If the writing start position is shifted, a color shift occurs and the image quality deteriorates. Therefore, Y,
In order to align the writing start positions of the toner images of each color of M, C, and K in the main scanning direction and the sub-scanning direction, the timing at which the transfer material P is conveyed to the transfer position and the transfer when the transfer material P is conveyed to the transfer position In accordance with the position of the material P in the main scanning direction, laser writing devices 01y, 0y to the image carriers Dy, Dm, Dc, Dk.
It is necessary to adjust the latent image writing timing of 1m, 01c, and 01k.

Conventionally, each of the image recording devices Uy, Um, U
A technique of detecting a pattern image for image position detection formed by c and Uk using a sensor for image position detection, calculating a shift amount of each color, and correcting the shift amount by an image recording device of each color. Are known. In the prior art, as shown in FIG. 14, a downstream side of the belt 011 of the image recording device Uk for detecting a position of a pattern image for image position detection, which is necessary for adjusting a latent image writing timing. Are located on both sides of the belt 011 in the width direction (X direction).
31 and 031 and image position sensors 032 and 032. These image position sensors 032 and 032
When a jam occurs or when a temperature change exceeding a specified value inside the apparatus occurs, the belt is removed from the image recording apparatuses Uy, Um, Uc, and Uk.
11 is a sensor for reading the position detection pattern transferred to 11, and its detection signal is input to the signal processing unit U2. The signal processing unit U2 is a part that calculates the shift of each color image from the input signal.

FIG. 18 is a view showing an example of the position detecting pattern. FIG.
FIG. 3 is an example of a position detection pattern (sub-scanning direction writing position detection pattern) that is recorded at a constant interval in Y and is composed of lines of each color extending in the main scanning direction (the width direction of the transfer material P) X. Reference numeral 18B denotes an example of a position detection pattern (a main scanning direction writing position detection pattern) composed of lines of each color extending in the sub-scanning direction. In the position detection pattern of FIG. 18A, lines of each color of Y, M, C, and K are recorded so as to have an interval of, for example, 1 mm, and the variation of the actual interval is described by the image position sensors 032 and 032 (see FIG. 14). , The amount of color misregistration of the formed image can be detected. Thereby, the image recording devices Uy, Um, U
The timing of recording start in the sub-scanning direction Y at c and Uk can be adjusted. In the position detection pattern of FIG. 18B, lines of each color of Y, M, C, and K are recorded so as to be a straight line extending in the sub-scanning direction Y, for example, and the actual scanning of each color line in the main scanning direction ( Variations in the position of the transfer material P (in the width direction) X are detected by the image position sensors 032 and 032.
(See FIG. 14), the image recording device U
It is possible to adjust the timing of starting recording in the main scanning direction X in y, Um, Uc, Uk.

The fθ lens 019 of each laser scanning system 013 shown in FIG. 17 of the laser writing devices 01y, 01m, 01c, and 01k for each color shown in FIG. , Dc, and Dk, the main scanning width of the laser beam L scanning each image carrier D varies due to variations in the main scanning width caused by errors in the positions of Dc and Dk. FIG.
Are the image carriers Dy, Dm, Dc,
FIG. 9 is an explanatory diagram of variations in the main scanning width caused by an error in the position of Dk. Next, according to FIG. 19, a virtual image carrier D0 assumed to be arranged perpendicular to the optical axis of the writing laser beam
(Hereinafter referred to as an “ideally arranged virtual image carrier D0”) and an actual image carrier D (D is Dy, Dm, Dc,
Dk means each. ) Will be described in that the main scanning width on the image carrier for forming an image of the same width on recording paper is different.

The meanings of the reference numerals in FIGS. 19A and 19B are as follows. D0: A virtual image carrier ideally arranged R0: Image writing start position on the image carrier D0 Q0: Image writing end position on the image carrier D0 P0: Image writing on the image carrier D0 Intermediate position 2L0: Image width of one line on image carrier D0 L0: Image width of 1/2 line on image carrier D0 2θ0: Image writing scanning angle θ0 of one line on image carrier D0 : Image writing scanning angle for 1/2 line on image carrier D0

D: Actual image carrier (image carrier arranged at a position deviated from the ideal position) R1 ': Same writing as writing start timing to the ideally arranged virtual image carrier D0 Image writing start position on the image carrier D when writing is performed on the image carrier D at the start timing Q1 ': Same writing as writing to the ideally arranged virtual image carrier D0 Image writing end position (scan angle 2θ0) on image carrier D when writing is performed on image carrier D at the timing
R1: Start writing an image on the image carrier D for recording the same image on the transfer material P or the belt 011 as when using the ideally arranged virtual image carrier D0. Position (in the case of a scanning angle θ1 + θ2 described later) Q1: An image for recording the same image as when the ideally arranged virtual image carrier D0 is used on the transfer material P or the belt 011 Image writing end position on carrier D (in the case of scanning angle θ1 + θ2 described later) P1: When virtual image carrier D0 ideally arranged on transfer material P or belt 011 is used Image writing intermediate position on the image carrier D for recording the same image as

L (= L1 + L2): R1Q1 on the image carrier D
L1: Image width in the main scanning direction between R1 and P1 on the image carrier D (for the first half line of scanning) L2: P1Q1 on the image carrier D Image width in the main scanning direction (for the second half of scanning) θ1 + θ2: Image writing scanning angle for one line on image carrier D θ1: 1/2 line for the first half scanning on image carrier D Θ2: Image writing scanning angle for 1/2 line in the latter half of scanning on image carrier D

In FIGS. 19A and 19B, the actual image carrier D and the ideally arranged virtual image carrier D0 are shown.
Is scanned at the same scanning angle 2θ0, the scanning width in the main scanning direction on each of the image carriers D and D0 is R1′Q1 ′.
And R0Q0, and the widths of the two are different.
In this case, based on the difference in the scanning width, the width of the recorded image transferred onto the transfer material P or the belt 011 is not the same, and a color shift occurs in the recorded image or the character to obtain a high-quality image. Becomes difficult. The transfer material P or belt 011
In order to record the same image as when the ideally arranged virtual image carrier D0 is used on the top, in FIG. 19, ideally arranged perpendicular to the optical axis of the writing laser light Main scanning width 2L0 on the virtual image carrier D0 (2L0 is R0Q0
And the actual main scanning width L on the image carrier D = L1
+ L2 (L is the distance in the main scanning direction X between R1 and Q1, L1 is R1
The distance between P1 in the main scanning direction X and the distance L2 between P1 and Q1 must be the same.

In response to the circumstances described above, the following techniques are conventionally known. (J01) Technology described in JP-A-62-243467 In the technology described in this publication, a laser scanning system 01 for each color is used.
Laser light L with an image signal synchronized with each video clock
In the laser writing device 01 that modulates the transfer material P or the belt 0, the scanning width of the laser scanning system 013 for each color is corrected by changing the frequency of each video clock.
11 have the same width of the recorded image transferred. That is, when writing is performed on the actual image carrier D shown in FIG. 19A by the laser beam, the main scanning width R1 shown in FIG.
Writing is performed during Q1 (= R0Q0). The main scanning width R1Q
The scanning angle (θ1 + θ2) of the laser beam on the image carrier D when writing 1 (= R0Q0) is the scanning angle (θ0 + θ0) of the laser beam on the ideally arranged virtual image carrier D0.
Less than. In the scanning at the scanning angle (θ1 + θ2), it is necessary to write the same number of dots as the scanning angle (θ0 + θ0) at a scanning angle smaller than the scanning angle (θ0 + θ0), so that the frequency of the video clock is increased. . By adjusting the video clock frequency in this way, it is possible to adjust the main scanning width R1Q1 on the image carrier D to a value of α (α is a proportional constant) times the distance between R0Q0. The main scanning width on the carrier can be adjusted in the same manner.

[0019]

[Problems to be solved by the invention]

(Problem of (J01)) FIG. 19B shows a main scanning of the ideally arranged virtual image carrier D0 and the actual image carrier D in a tilted state on the image carrier. Indicates a line. In the inclined actual image carrier D shown in FIG. 19B, the optical path length of the laser light incident on the write end position is longer than that of the laser light incident on the write start position. There is a difference in the optical path length. Such a state is caused by an angle between the laser scanning system 013 and the image carrier D, a lens position error of the laser scanning system 013, and the like. When a difference occurs in the laser light path length as shown in FIG. 19B, R1P1 ≠ P1Q1. In this case, the scan angle (θ1) corresponding to the scan width of R1Q1 is obtained by using the technique (J01).
+ Θ2), the length of one line is the same as that of the scan angle (θ0 + θ0) when the frequency of the video clock is adjusted so that the image recording of the same number of dots as in the case of the scan angle (θ0 + θ0) is performed. However, color shift cannot be prevented.

The reason is as follows. That is,
For example, when printing 3000 dots by scanning at a scan angle θ0 + θ0 = 2θ0 on an ideally arranged virtual image carrier D0, 1500 dots between R0P0 and 150 dots between P0Q0.
Printing of 0 dots is performed. Incidentally, in order to arrange the print dots on the actual image carrier D and the print dots on the ideally arranged virtual image carrier D0 at the same position in the X direction, the actual image carrier D In this case, it is necessary to print 3000 dots by scanning at the scan angle θ1 + θ2. FIG. 19B
In the example, the scan angle θ1 + θ2 on the actual image carrier D is the scan angle θ0 + on the ideally arranged virtual image carrier D0.
Since it is smaller than θ0, the frequency of the video clock at the time of writing an image on the actual image carrier D is higher than the frequency of the video clock at the time of image writing of the ideally arranged virtual image carrier D0. There is a need to. Moreover, in FIG. 19B, printing of 1500 dots is performed by scanning at the scan angle θ1,
It is necessary to print 1500 dots by scanning at the scan angle θ2. However, if the video clock frequency is simply adjusted to α times as described above, the scanning at the scan angle θ
The printing of 00 dots cannot be performed, and the printing of 1500 dots is performed by scanning at the scan angle (θ1 + θ2) / 2. For this reason, the print position in the X direction is shifted from the print dot on the actual image carrier D and the print dot in the X direction on the ideally arranged virtual image carrier D0.

That is, for example, in the ideally arranged virtual image carrier D0 shown in FIG.
When writing 0 dots and writing 1500 dots between P0 and Q0, in order to prevent color misregistration, the actual image carrier D writes 1500 dots between R1 and P1,
It is necessary to write 1500 dots between 1Q1. However, the scanning angle θ1 of the laser beam scanning between R1 and P1 is different from the scanning angle θ2 of the laser beam scanning between P1 and Q1. That is, in the example of FIG. 19B, θ1> θ2. In order to write 1500 dots while performing the scan at the scan angle θ1, and to write 1500 dots while performing the scan at the scan angle θ2, a video at the time of writing the scan angle θ1 is used. The scan angle θ compared to the frequency of the clock.
It is necessary to increase the frequency of the video clock during the scanning period of the scanning angle θ2 smaller than 1.

That is, in the case of the image carrier D shown in FIG. 19B,
When scanning one main scan line, unless the video clock frequency is gradually increased, the dot intervals will not be uniform.
In other words, by maintaining the video clock frequency when scanning one main scanning line at a constant adjusted value (for example, a value obtained by adjusting the video clock frequency by α times as described above), each of the image carriers Dy and Dm is adjusted. , Dc, Dk,
It is possible to make the main scan width the same (in the case of FIG. 19A), but if the video clock frequency is not gradually increased or decreased while scanning one scan line, the Y ( Yellow), M (magenta), C
It is impossible to prevent color shift of an image of (cyan) and K (black) colors.

The present invention has been made in view of the above circumstances, and has the following content as an object. (O01) To make uniform the dot interval in the main scanning direction of the image transferred from the image carrier onto the recording paper when there is a difference in the optical path length of the laser light incident on both ends of the image carrier.

[0024]

Next, the present invention for solving the above-mentioned problems will be described. The elements of the present invention will be described in detail in order to facilitate correspondence with the elements of the embodiments described later. The parentheses around the sign of the element are added. The reason why the present invention is described in correspondence with the reference numerals of the embodiments described below is to facilitate understanding of the present invention, and not to limit the scope of the present invention to the embodiments.

(Invention) In order to solve the above problems, an image forming apparatus of the invention has the following requirements: (A01) an image carrier (D) moving in the sub-scanning direction
A laser for writing image information on the surface of the image carrier (D) by irradiating a write line along the main scanning direction on the surface with laser light (L) modulated by image data read out in synchronization with a video clock. Scanning system (13), (A02) the laser scanning in which writing of image information is started after a lapse of a predetermined delay time (t) from the time when the beam position is detected by the beam position detecting means (22) in the main scanning direction. System (13), (A
03) A first clock count period (Ta) set during a period for writing one line in the main scanning direction and a second clock count period (Tb) set for the first half or the second half of the one line write period. ) For detecting the first detection value (A) and the second detection value (B, B / A) determined by the number of video clocks counted respectively.
Detecting means (242 + 244) and second detecting means (24
3 + 245 + 246,243 + 245) (A04) The first detection value (A) and the second detection value (B,
B / A), a first set value storage means (247) and a second set value storage means (248) for storing a first set value (A0) and a second set value (B0), and (A05) 1
The detected value (A) and the second detected value (B, B / A) are the first set value (A0) and the second set value (B0), respectively.
Frequency variable means (241 + 249-256) for changing the frequency of the video clock so as to match
06) The first clock count period (Ta) when the first detected value (A) matches the first set value (A0).
The first set values (A0) and (A07) set so that the number of video clocks counted therein becomes the first target value.
The second detection value (B, B / A) is equal to the second set value (B
0), the second set value (B0) set so that the number of video clocks counted during the second clock count period (Tb) becomes the second target value.

[0026]

[Action]

(Operation of the Present Invention) In the image forming apparatus (F) of the present invention having the above-described features, the laser beam (L) modulated by the image data read out in synchronization with the video clock is used for the image carrier (D). A) A laser scanning system (13) for irradiating the surface writes image information on a writing line along the main scanning direction on the surface of the image carrier (D) moving in the sub-scanning direction. The laser scanning system (13) starts writing the image information after a lapse of a predetermined delay time (t) from the time when the beam position is detected by the beam position detecting means (22) in the main scanning direction. Therefore, by adjusting the delay time (t), the image writing start position in the main scanning direction can be adjusted.

The first detecting means (242 + 244) generates a first detection value (1) determined by the number of video clocks counted in a first clock counting period (Ta) set during a period for writing one line in the main scanning direction. A) is detected. The first set value storage means (247) stores a first set value (A0) corresponding to the first detected value (A). Frequency changing means (241 + 249 to 256) changes the frequency of the video clock so that the first detection value (A) matches the first set value (A0). The first set value (A0) is the number of video clocks counted during the first clock count period (Ta) when the first detection value (A) matches the first set value (A0). It is set to be the first target value. Therefore, by appropriately setting the first clock count period (Ta) or the first set value (A0), the video clock counted during the first clock count period (Ta) matches the first target value. Can be done.

That is, for example, the image writing width L / 2 of the first half line is scanned at the scanning angle θ1 to perform printing of 1500 dots, and the image writing width L / L of the second half line is performed.
2 is scanned at the scan angle θ2 to print 1500 dots, and to print 3000 dots within a predetermined image writing width L of one line, the first clock count period (Ta) is set to 1 Time T required to scan a scanning angle (θ1 + θ2) for scanning a predetermined image writing width L of a line
And the first set value (A0) is set to 3000 dots, it is possible to record an image of 3000 dots within the predetermined image writing width. Note that 3 within the image writing width L
In order to record an image of 000 dots, the first clock count period (Ta) is set to the time T required for scanning at the scanning angle (θ1 + θ2) corresponding to the image recording width L, and the first Set value (A0) is 300 for the number of recorded images
Instead of setting to 0, for example, the first clock count period (Ta) is set to T × 0.9 = 0.9T, and the first set value (A0) is set to 3000 × 0.9 = 2700. Is also possible. Further, the first detection value (A) and the first detection value (A)
The set value (A0) does not necessarily need to be the number of video clocks itself, and a numerical value processed by an appropriate four arithmetic operation expression can be adopted.

The second detecting means (243 + 245 + 246,
243 + 245) is a second detection value (B, B / B / B) determined by the number of video clocks counted in the second clock count period (Tb) set in the first or second half of the period for writing one line in the main scanning direction. A) is detected. The second set value storage means (248) stores a second set value (B0) corresponding to the second detected value (B, B / A). The frequency variable means (241 + 249 to 256) is configured to change the second detection value (B, B / A) to the second set value (B0).
Is changed to match the frequency of the video clock. The second set value (B0) is counted during the second clock count period (Tb) when the second detected value (B, B / A) matches the second set value (B0). The number of video clocks is set to be the second target value. Therefore, by appropriately setting the second clock count period (Tb) or the second set value (B0), the video clock counted during the second clock count period (Tb) matches the second target value. Can be done.

That is, for example, when printing 3000 dots in a predetermined image writing width L of one line on a transfer material (P) such as an image recording paper or a transfer material conveying belt (11), In order to make the dot interval constant, it is necessary to record an image of 1500 dots in a width of L / 2 in the first half of the image writing width L. In this case, the second clock count period (Tb) is set to a time required for scanning the scanning angle θ1 for scanning the image writing width of L / 2, and the second set value (B0) is set. If it is set to 1500 dots, an image recording of 1500 dots can be performed within the predetermined image writing width L / 2. Note that the image writing width L /
In order to record an image of 1500 dots in the second
Instead of setting the image recording number 1500 in the second clock count period (Tb) required for scanning of the image recording width L / 2 as described above to the set value (B0), for example, (1500 /
(3000) = １ ／ can also be set. In this case, the second detection value (B, B / A) is a value obtained by dividing the video clock count value in the second clock count period (Tb) by the video clock count value in the first clock count period (Ta). It is also possible to employ. That is, the second set value (B0) does not necessarily need to be the video clock number itself, but can be a numerical value processed by the above-described four arithmetic operations.

As can be seen from the foregoing description, the present invention provides:
The start position, the image recording width, the number of image recording dots, and the position of each recording dot of one line on the transfer material such as image recording paper or the transfer material conveying belt (11) can be adjusted. Therefore, in a case where a plurality of color toner images are superimposed and recorded on the transfer material in the color image forming apparatus, an image without color shift can be recorded.

[0032]

BEST MODE FOR CARRYING OUT THE INVENTION

(Embodiment 1) Embodiment 1 of the image forming apparatus according to the present invention is characterized in that the image forming apparatus according to the present invention has the following requirements. (A08) Scan for performing image recording (A09) The frequency varying means (241 + 249-256) for changing the frequency of the video clock during the dummy scanning period.

(Operation of the First Embodiment) In the first embodiment of the image forming apparatus of the present invention having the above-described configuration, the frequency variable means (241 + 249 to 256) performs the dummy scanning period before the scanning period in which the image is recorded. The frequency of the video clock is adjusted so that the first detection value (A) and the second detection value (B, B / A) match the first setting value (A0) and the second setting value (B0), respectively. Change. In this case, since the video clock frequency has a predetermined value during the dummy scanning period, in the image recording scan performed after the dummy scanning period, the image writing scan can be performed at the predetermined video clock frequency.

Second Embodiment An image forming apparatus according to a second embodiment of the present invention is characterized in that the image forming apparatus according to the present invention or the first embodiment of the present invention has the following requirements. (A09) The frequency of the video clock is held at a constant value from the time when the beam position is detected by the beam position detecting means (22) in the main scanning direction to the time when the writing of the image information is started. The frequency variable means (241 + 249-256).

(Operation of the Second Embodiment) In the second embodiment of the image forming apparatus of the present invention having the above-described configuration, the frequency variable means (241 + 249-256) is used as the beam position detecting means (22) in the main scanning direction. The frequency of the video clock is held at a constant value from the time when the beam position is detected to the time when the writing of the image information is started. Therefore, the delay time t from the beam position detection time to the start of the image writing when performing the image writing scan of one line can be measured by the count value of the number of video clocks.

Example 1 Next, an example (example) of an embodiment of the present invention will be described with reference to the drawings, but the present invention is not limited to the following example. FIG. 1 is a schematic explanatory view of a digital color copying machine F as an image forming apparatus according to a first embodiment of the present invention, and corresponds to FIG. 14 used in the description of the conventional technique. FIG. 2 is an overall explanatory diagram of the image forming apparatus F according to the first embodiment of the present invention, and corresponds to FIG. 17 used in the description of the conventional technique. FIG. 3 is an explanatory diagram of a scanning angle of the laser beam L when the image carrier D shown in FIG. 2 is arranged at a position shown by a two-dot chain line deviated from a set position shown by a solid line. FIG. 7 is a diagram showing a positional relationship and a scanning angle relationship between a virtual image carrier D0 ideally arranged at a solid line position) and an actual image carrier D arranged farther from a laser light source than a set position. FIG. 3B shows a virtual image carrier D0 ideally arranged at the set position and an actual image carrier D whose rear end (right end in FIG. 3B) is far from the laser light source with respect to the set position. FIG. 4 is a diagram showing a positional relationship and a scanning angle relationship with the above.

FIG. 4 is an explanatory view of a scanning angle of the laser beam L when the image carrier D shown in FIG. 2 is arranged at a position shown by a two-dot chain line deviated from a set position shown by a solid line. The positional relationship and the scan angle relationship between the virtual image carrier D0 ideally arranged at the set position (solid line position) and the actual image carrier D arranged closer to the laser light source than the set position are described. FIG. 4B is a diagram showing a virtual image carrier D0 ideally arranged at a set position (solid line position) and a front end (left end in FIG. 4B) distant from the laser light source with respect to the set position. FIG. 6 is a diagram showing a state in which a rear end (right end in FIG. 4B) is arranged at a position close to a laser light source. FIG. 5 is a detailed explanatory diagram of the video clock generation circuit 24 in the first embodiment. FIG. 8 is a time chart of output signals of the components of the video clock generation circuit 24 shown in FIG. FIG. 9 is a time chart of output signals of components of the image processing unit U1 of the first embodiment. FIGS. 1 and 2, which are explanatory views of the first embodiment, are almost the same as FIGS. 14 and 17 used in the description of the conventional technique. In the description, components corresponding to the components used in the description of the related art are denoted by the same reference numerals as those used in the description of the related art except for the most significant digit “0”. The detailed description that overlaps the description will be omitted.

In FIG. 1, digital color copier F
Is used to detect the position of the pattern image for image position detection necessary for adjusting the latent image writing timing (that is, the timing at which the transfer material P is transferred to the transfer position and the transfer material P is transferred to the transfer position). (In order to detect the position of the transfer material P in the main scanning direction at that time), the light sources 31, 31 and the image position sensors 32, 32 are arranged. This point is the same as the conventional example in FIG.
In the first embodiment, a light source 31 and an image position sensor 32 are further arranged at the center of the belt 11 in the width direction. Each of the three image position sensors 32, 32, 32 includes a plurality of light receiving elements arranged side by side in the main scanning direction.
32 denotes positions R1, P on the image carrier D shown in FIGS.
1. It has a light receiving element for detecting the position of Q1. The detection signals of the image position sensors 32, 32, 32 are input to a signal processing unit U2 which calculates the shift of the image of each color from the input signal.

FIG. 2 is a block diagram of FIG. 1 used in the description of the prior art.
7, the detailed description which is the same as that of FIG. 17 is omitted. The configuration of the video clock generation circuit 24 of FIG. 2 is different from that of the video clock generation circuit 024 of the prior art shown in FIG. The details of the video clock generating circuit 24 of the present embodiment shown in FIG. 2 are shown in FIG. 5 and will be described later. 2 and 8, the beam position detection signal S1 (see FIGS. 2, 8, and 9) of the beam position detection sensor 22 is output from the clock selection circuit 2 of the image processing unit U1.
3 has been entered. The clock selection circuit 23 receives the video clock S2 input from the video clock generation circuit 24.
A plurality of video clocks having phases shifted from each other (see FIG. 8) are generated.
3 (see FIGS. 2 and 8) to select the writing position control circuit 2
5 is output. The write-out position control circuit 25 receives the synchronous clock S3 input from the clock selection circuit 23.
Accordingly, after the elapse of the delay time t (see FIG. 8), the synchronous clock S3 is output to the image counter 26 as the read clock S4 (see FIGS. 2 and 8). The image counter 26 reads out image data from the image memory 27 in accordance with the input read clock S4 and outputs it to the laser drive circuit 12. The beam position detecting sensor 22 constitutes a beam position detecting means 22.

The laser drive circuit 12 turns on and off the semiconductor laser light source 14 according to the input image data,
When the semiconductor laser light source 14 is on, the laser light L
Is emitted. Thus, the semiconductor laser light source 14
Writes one line of image data on the surface of the image carrier D in synchronization with the rotation of the rotary polygon mirror 18. When the scanning of one line is completed, the writing scanning of the next one line is performed at a position shifted by one line in the sub-scanning direction (circumferential direction) on the surface of the image carrier D.

In FIG. 3A showing an example of the arrangement of the actual image carrier D with respect to the ideally arranged virtual image carrier D0, the virtual image carrier D0 ideally arranged at the set position shown by the solid line. The first half is θ0 and the second half is θ0. The scanning width on the image carrier D0 scanned by the former scanning angle θ0 is R0P0, and the scanning width on the image carrier D0 scanned by the latter scanning angle θ0 is P0Q0. Then, R0P0 = P0Q0. On the other hand, in the actual image carrier D shown in FIG. 3A when it is arranged at a position farther from the laser light source 14 (see FIG. 2) than the set position, the first half and the second half are scanned at the same scanning angle θ0 as that of D0. Then, the actual scanning width on the image carrier D is R1'P1 in the first half and P1Q1 'in the second half, and the width of the image transferred onto the recording paper is D1.
The case of 0 is different from the case of D. As can be seen from FIG. 3A, in order to make the width of the transferred image transferred on the recording paper the same when using D0 and D, the actual scanning width of the image carrier D needs to be R1Q1. That is, it is necessary to set the actual scanning angle of the first half of the image carrier D to θ1 and the scanning angle of the latter half to θ2. In the case of FIG. 3A, since the actual image carrier D is displaced in parallel from the set position, θ1 = θ2 and θ0> θ1.

FIG. 3B shows another example of the arrangement of the actual image carrier D with respect to the ideally arranged virtual image carrier D0. The scanning angle is θ0 in the first half and θ0 in the second half. Further, the actual image carrier D is arranged such that the laser light writing end position (the right end position in FIG. 3B) is farther from the laser light source 14 (see FIG. 2) than the set position. This actual image carrier D
In the above, the actual scanning angle of the image carrier D for forming the same image as D0 on the recording paper is indicated by θ1 in the first half and θ2 in the second half. In the case of FIG. 3B, the actual image carrier D shows a state inclined from the set position, and θ1>
θ2 and θ0 = θ1.

In FIG. 4A showing another example of the arrangement of the actual image carrier D with respect to the ideally arranged virtual image carrier D0, a virtual image carrier D0 ideally arranged at a set position is shown. The scanning angle is θ0 in the first half and θ0 in the second half. The actual image carrier D is disposed at a position closer to the laser light source 14 (see FIG. 2) than the set position. In the actual image carrier D in this case, the scanning angle of D for forming an image similar to D0 on a recording sheet is indicated by θ1 in the first half and θ2 in the second half. In the case of FIG. 4A, since the actual image carrier D is displaced in parallel from the set position, θ1 = θ2 and θ0 <θ1.

FIG. 4B shows another example of the arrangement of the actual image carrier D with respect to the ideally arranged virtual image carrier D0. The scanning angle is θ0 in the first half and θ0 in the second half. Also, in the actual image carrier D, the laser light writing start position (the left end in FIG. 4B) is higher than the set position by the laser light source 14 (see FIG. 2).
The laser light writing end position (right end in FIG. 4B) is located at a position far from the laser light source 14 (see FIG. 2). In the actual image carrier D in this case, the first half of the scanning angle for forming the same image as D0 on the recording paper is indicated by θ1, and the second half is indicated by θ2. In the case of FIG. 4B, the actual image carrier D is disposed in a state inclined from the set position, and θ1 <θ0 <θ2.

Θ0 shown in FIGS. 3 and 4 is the first half and the second half of the scan angle when scanning the virtual image carrier D0 ideally arranged at the set position. In the example of the arrangement of the virtual image carrier D0 and the actual image carrier D which are ideally arranged with respect to the laser scanning system 13 shown in FIGS. 3 and 4, the image recording width of one line on the transfer material P is matched. For example, if the number of dots to be written in one scan line R0Q0 or R1Q1 is, for example, 3000, the scan angles θ0, θ1,
It is necessary to write 1500 dots each during the scan period of θ2. In FIG. 3A, when printing 1500 dots on the actual image carrier D during the scan period of the scan angle θ1 and 1500 dots during the scan period of the scan angle θ2,
Since the scanning angles θ1 and θ2 are smaller than the scanning angle θ0, the frequency of the video clock (image writing clock) when scanning at the scanning angles θ1 and θ2 is the frequency of the video clock when scanning at the scanning angle θ0. Need to be higher. As a result, the dot interval written on one scan line becomes smaller.

In FIG. 4A, θ0 <θ1, θ2.
In this case, during the scanning period of the scanning angles θ1 and θ2 in FIG. 4A, the frequency of the video clock needs to be lower than in the case of performing the scanning at the scanning angle θ0. As a result, the interval between dots written on one scan line increases. FIG.
In B, θ2 <θ0 = θ1. In this case, the frequency of the video clock needs to be higher during the scan period of the scan angle θ2 in FIG. 3B than during the scan periods of the scan angles θ0 and θ1. In FIG. 4B, θ1 <θ0 <θ2. In this case, in order to print 3000 dots on one scan line, the frequency of the video clock needs to be higher during the scan period of the scan angle θ1 in FIG. 4B than in the case of performing the scan at the scan angle θ0.
During the scanning period of the scanning angle θ2, the frequency of the video clock needs to be lower than in the case of performing the scanning at the scanning angle θ0.

In FIGS. 3 and 4, the scanning angle when scanning the actual image carrier D is indicated by θ1 in the first half and θ2 in the second half. The image writing positions of the image carriers D0 and D can be matched by the conventional technique described with reference to FIG. Matching the image writing widths in the main scanning direction can be performed by using (J01) described with reference to FIG. 19A.
Of the transfer material P by changing the frequency of the video clock
Alternatively, it is possible to use the technique of matching the width of the image formed on the belt 11 in the main scanning direction).

The actual image carrier D (that is, the image carrier D
The writing time for one line in the main scanning direction (y, Dm, Dc, Dk) is the time required for scanning R1Q1 shown in FIGS. 3A to 4B (the time for writing the 3000 dots).
Also, it is the time required to scan the scan angle θ1 + θ2. The writing time can be detected for each image carrier D (Dy, Dm, Dc, or Dk). The time required for writing for one line (the time required for scanning the scanning angle θ1 + θ2) that can be detected for each image carrier D is Ta (S6 in FIG. 9).
See). The method of determining Ta and S6 will be described later.

In the first embodiment, as shown in FIG. 1, the light source 31 and the image position sensor 32 are also arranged at the center in the width direction of the belt 11, so that, for example, as shown in FIG. Using the image carriers Dy, Dm, Dc, and Dk,
First dot, 1500th dot, 3000th in main scanning direction
The pattern image formed by the recording dots of the dot
On the X-axis direction.

The pattern image recorded by the first recording dot (hereinafter referred to as the "first dot pattern image") is a latent image written in R1 on the actual image carrier D in FIGS. It is a pattern image to be recorded. Fifteen
A pattern image recorded by the 00th dot (hereinafter referred to as a “1500th dot pattern image”)
Is a pattern image recorded by the latent image written in P1 on the actual image carrier D in FIGS. 3000
The pattern image recorded by the recording dot of the dot (hereinafter referred to as the “3000th dot pattern image”) is the pattern recorded by the latent image written on Q1 on the actual image carrier D in FIGS. It is an image.

Therefore, when the maximum number of dots for one line in the main scanning direction is 3000, the end position of the 1500-dot image recorded in the actual image carrier D in the first half of the main scanning (that is, the 1500-th dot pattern) Image) can be detected. Then, each image carrier Dy, Dm,
It is necessary to perform recording so that the pattern image of the first dot, the 1500th dot, and the 3000th dot formed on the belt 11 using Dc and Dk is detected by a predetermined light receiving element. By doing so, the image width recorded in the first half of the main scan on the belt 11 formed by the actual image carrier D (the image width formed by scanning at the scan angle θ1)
Can be matched with the image width formed by the ideally arranged virtual image carrier D0.

The actual writing time of the first half of one line in the main scanning direction of the image carrier D is the time required for writing the first half of one line in each case shown in FIGS. 3A to 4B, that is, The time required to scan the scanning angle θ1 can be detected for each actual image carrier D (Dy, Dm, Dc, or Dk). The time required for writing the first half of one line that can be detected is Tb (see S7 in FIG. 9). Note that Tb
The method of determining and S7 will be described later.

In FIG. 5, the video clock generating circuit 24 has a voltage controlled oscillator 241. The voltage controlled oscillator 241 has a function of changing the frequency of the output pulse according to the input voltage value. The output signal S2 of the voltage controlled oscillator 241 is the output signal of the video clock generation circuit 24, that is, the video clock S2. Further, the video clock generation circuit 24 has a first,
It has the second pulse generators 242 and 243. Each of the first and second pulse generators 242 and 243 is configured to form an output pulse from a clock pulse generated by a crystal oscillator used in the laser scanning system 13. FIG.
, The output signal S6 of the first pulse generator 242
Outputs a pulse having the same pulse width Ta as the writing time during the one-line image writing period, as shown in FIG.
Therefore, as shown in FIG.
And the pulse width Ta of the output signal S6 of the first pulse generator 242 matches. The output signal S7 of the second pulse generator 243 outputs a pulse having a pulse width Tb during the first half of the writing time Tb of the one line image writing period.

The first and second counters 244 and 245
While the first and second pulse generators 242 and 243 are active (durations during which pulses of pulse widths Ta and Tb are being output), the video clock S2 output from the voltage controlled oscillator 241 is counted, and inactive. Has a function to stop counting. The first and second counters 2
The count values A and B of 44 and 245 are input to the divider 246. Divider 246 outputs the value of B / A. The first set value storage means 247 stores a set value A0 (A0) to be recorded in the scan period (one line scan period) of the scan angle θ1 + θ2.
== 3000 dots). The second set value storage means 248 stores a second set value B0 (that is, the target value of B / A). In this embodiment, the target number of dots to be recorded in the scanning period (one line scanning period) of the scanning angle θ1 + θ2 is 3000, and the target number of dots to be recorded in the scanning period of the scanning angle θ1 is 1500. Means 248 contains B0 = (1500/3000)
= (１ ／) is stored.

The output signal A0 (= 3000) of the first set value storage means 247 and the counter 2
The output signal of 44, that is, the first detection signal A is input. At the end of the output pulse of the first pulse generator 242, the comparator 249 calculates (A-A0) = (A-3000)
U / D counter (up / down counter) 250
Output to The U / D counter 25 of the present embodiment outputs a signal of the most significant 1 bit indicating positive / negative and a lower-order bit (eg, 12 bits) indicating the count value. The U / D counter 250 increments the count value (that is, the output value) when the input signal from the comparator 249 is negative, and decrements it when it is positive. Then, the U / D counter 250 outputs a video clock frequency offset control signal S8 (see FIGS. 5 and 9) corresponding to the count value.

The comparator 251 receives the set value B 0 = (１ ／) of the second set value storage means 248 and the value of the second detection signal B / A which is the output signal of the divider 246. The comparator 251 outputs a digital value corresponding to the value of (B / A)-(1/2) to the U / D counter (up / down counter) 252 at the end of the output pulse of the first pulse generator 242. I do. The U / D counter 252 increments the count value (that is, the output value) when the input signal from the comparator 251 is negative, and decrements the count value when the input signal is positive. The U / D counters 250 and 25
The increment or decrement of 2 is performed a predetermined number of times (for example, several thousand times) before laser scanning for actually performing image recording.
Is performed during the dummy scanning period. When performing image recording scanning, the U / D counter 25
The count value of 0,252 is A = A0 (A0 = 3000),
It is adjusted so that B / A = B0 (B0 = 1500). The laser writing device 1, the beam position detection sensor 22, and the image processing unit U1 constitute a dummy scanning execution unit (1 + 22 + U1).

The U / D counter 252 includes, as in the case of the U / D counter 250, the most significant bit indicating whether the count value is positive or negative, and the least significant bit (eg, 12 bits) indicating the count value. Signal tilt control circuit 253
Output to The inclination control circuit 253 is a circuit that controls the inclination of the frequency of the video clock S2 (the rate of increase or decrease in frequency) according to the value of the U / D counter 252. That is, if the count value of the U / D counter 252 is positive, the inclination control circuit 253 changes the frequency of the video clock S2 to an inclination angle according to the magnitude of the count value as the laser scanning proceeds in the main scanning direction. A circuit that outputs a digital gradient control signal S9 (FIG. 9 shows a case where the frequency gradient increases) for controlling to increase gradually and to decrease gradually when the count value is negative. It is. FIG. 6 shows a tilt control circuit 253 according to the first embodiment.
FIG. FIG. 7 is an operation explanatory diagram of the inclination control circuit 253 according to the first embodiment. 6, an inclination control circuit 253 includes an adder 253a and a 12-bit parallel input / parallel output DFF (D flip-flop) 2.
53b. D flip-flop 25
The clock input to 3b is input only during the writing scan period of the image data, and its frequency can be arbitrarily determined. For example, 5 MHz to 20 MHz (20 MHz is a frequency close to the frequency of the video clock) can be used. . Further, the CLR pulse is output immediately after the end of the writing scan of one line. The adder 253a adds the output values of the U / D counter 252 and the D flip-flop 253b and outputs the result.

In FIG. 7, for example, U / D counter 25
When the output (count value) of 2 is "10", "10" is always input to the adder 253a in a steady state. The output of the D flip-flop 253b is “0” from the time when the CLR pulse is output until the next clock is input. When a clock is input to the D flip-flop 253b, the output of the D flip-flop 253b becomes “10” by the first clock, and this “10” is input to the adder 253a.
The output of the adder 253a is "20". This "20"
Is input to the D flip-flop 253b. When the second clock is input to the D flip-flop 253b, the output of the D flip-flop 253b becomes "20",
The output of the adder 253a to which this “20” is input is “3”
0 ". Therefore, when the count value (output) of the U / D counter 252 is 10, the output S9 of the slope control circuit 253, which is the output of the D flip-flop 253b,
Each time the clock pulse is input, it increases by “10”. When the count value of the U / D counter 252 is, for example, "5", the output S9 of the inclination control circuit 253 is output.
Will increase by "5".

Therefore, the inclination control signal S9 is expressed as U
This is a digital value whose rate of increase / decrease changes in accordance with the output value of the / D counter 252. As described above, since the value of S9 increases each time the clock pulse is input to the D flip-flop 253b, the value of S9 increases as the frequency of the clock increases. If the clock frequency is, for example, about 5 MHz, the output S9 of the inclination control circuit 253 needs about 20 bits. When this 20-bit signal is used, the upper 12 bits are used and the number of lower bits is discarded. That is,
When the slope control signal S9 is added to the video clock frequency offset control signal S8 in the adder 254, if S8 is 12 bits, the lower bits of the slope control signal S9 are discarded and the addition is performed with the upper 12 bits. The tilt control circuit 253 is configured to be reset when the output signal S6 (see FIG. 9) of the first pulse generator 242 is inactive (that is, when writing for one scan is completed). Therefore, at least the beam position detection signal S1
Is output and the image export starts,
The video clock S2 is not frequency-modulated and has a constant frequency.

Therefore, as shown in FIG. 9, the digital inclination control signal S9 output from the inclination control circuit 253 is
Simultaneously with the start of image writing (that is, the first pulse generator 2
42 at the same time as the output signal S6 becomes active)
An inclination control signal S9 of an inclination corresponding to the count value of the D counter 252 is output, and is reset and stopped at the same time as the completion of image writing. As described above, by outputting the tilt control signal S9 only during the image writing period, even when the frequency modulation of the video clock S2 is performed, the influence of the frequency modulation is determined when the image writing position is determined based on the count number of the video clock. You can decide without receiving it.

The video clock frequency offset control signal S 8 and the inclination control signal S 9 are added by an adder 254 and input to a D / A converter 255. D / A converter 255 outputs a voltage according to the input signal. D
/ A converter 255 output voltage is low-pass filter 2
The signal is smoothed by 56 and input to the voltage controlled oscillator 241. A frequency variable means (241 + 249-256) is constituted by the elements indicated by the reference numerals 241, 249-256. In addition, the first pulse generator 242 and the first counter 244 output first detecting means (242 + 2
44), and the second pulse generator 243, the second counter 245, and the divider 246 constitute second detecting means (243 + 245 + 246). The voltage controlled oscillator 241 outputs a video clock S2 having a frequency according to the input voltage. As shown in FIG. 9, the frequency of the video clock S2 is determined according to a voltage which is a D / A conversion value of a value obtained by adding the digital offset control signal S8 and the digital inclination control signal S9 of the video clock frequency. Frequency. Note that FIG.
In the time chart of the frequency of the video clock S2 shown at the bottom of the figure, f0 is the normal video clock frequency, and the virtual image carrier D0 ideally arranged at the set position in FIGS. ) Is the video clock frequency for scanning.

In the first embodiment having the above-described configuration, the write start positions of the image carriers Dy, Dm, Dc, and Dk by the laser beam are ideally set to the recording start positions when the image is recorded on the belt 11. The recording start position (set recording start position) when the virtual image carrier D0 thus set is used is set. This setting is performed as follows. That is,
As shown in FIG. 10, one of Y, M, C, and K in the main scanning direction
The pattern images (line images) of the dot, the 1500th, and the 3000th dot are printed on the belt 11.
Then, for each of the image carriers Dy, Dm, Dc, and Dk, the pattern image of the first dot is a predetermined light receiving element among a plurality of light receiving elements arranged in a line of the image position sensor 32 (FIG. 3, FIG. This is performed by setting the delay time t shown in FIG. 8 so as to be detected by a light receiving element that detects an image corresponding to the latent image written in R0 and R1 in FIG. This setting method is a conventionally known technique. The toner images of each color recorded on the belt 11 are removed by a belt cleaner (not shown) arranged at an appropriate position along the surface of the belt 11.

Next, a method for determining the pulse width Ta of the first pulse generator 242 and the pulse width Tb of the second pulse generator 243 will be described. First, the values of Ta and Tb are temporarily set. The provisional set value of the pulse width Tb is set to 1/2 of the provisional set value of Ta. Then, as shown in FIG. 10, the first dot in the main scanning direction of Y, M, C, and K, 150
A pattern image (line image) of the 0th dot and the 3000th dot is printed on the belt 11. In this case, since the setting of the delay time t has been performed, the recording positions in the main scanning direction of the pattern image of the first dot coincide with each other.

The first set value storage means 247 stores 3000
Is set, １ ／ is set in the second set value storage means 248, and Ta and Tb are temporarily set, and a predetermined number of times (for example, if the number of input bits of the D / A converter 255 is 10 bits) (2 @ 10 = 1024 times, if the number of input bits is 11 bits, 2 @ 11 = about 2048 times) dummy scanning, a pulse width Ta of 30
The printing of 00 dots is performed. Pulse width Ta
Is changed, and the virtual image carrier D0 where the recording end position of the 3000th dot pattern image is ideally arranged
Is used, the pulse width Ta coincides with the recording end position (set recording end position, that is, a position detected by a predetermined light receiving element among a plurality of light receiving elements arranged in a line of the image position sensor 32). And determine the pulse width Ta.
The video clock frequency f at this time (see S8 in FIG. 9)
Is a slope determined by the tentatively set Tb, and the 1500th dot printing is not always arranged at the center of the 3000 dot printing. Ta determined in this way is the value of R1 on the actual image carrier D shown in FIGS.
The time required to scan between Q1, ie, the scan angle θ1
The time required to scan + θ2. In this case, in the state shown in FIG. 3B, the frequency f1 determined by the video clock frequency offset control signal in S8 of FIG. 9 is slightly lower than the reference frequency f0, and the frequency determined by the gradient signal S9 gradually increases. The areas A8 and A9 of the hatched portions of the graphs S8 and S9 in FIG. 9 are values obtained by integrating the frequency f determined by S8 and S9 with time (the number of pulses = 3000).
Dot).

Next, 30 is stored in the first set value storage means 247.
00, １ ／ is set in the second set value storage means 248, and Ta determined as described above is set.
The pulse width Tb of the second pulse generator 243 is changed so that the 1500th dot pattern image shown in FIG. 10 is detected by the predetermined light receiving element of the image position sensor 32. That is, the pulse width Tb is determined so that the 1500th dot pattern image coincides with the position of the middle point between the 1st dot and the 3000th dot in the main scanning direction. Tb thus determined is, for example, θ1 = θ2 in FIGS. 3A and 4A, so that Tb = Ta / 2. In the case of FIG. 3B, since θ1> θ2, the Tb is Tb> T
a / 2. In addition, in the case of FIG. 4B, since θ1 <θ2, Tb satisfies Tb <Ta / 2. In the state shown in FIG. 3B, the value A2 obtained by integrating the video clock frequency S2 in FIG. 9 with respect to time indicates (the number of pulses is 3000). When Ta, Tb, A0 and B0 are set and held constant, S2 = S8 + S9.

(Operation of the First Embodiment) The image forming apparatus of the first embodiment, which has the above-described configuration and in which the target values of the pulse widths Ta, Tb and A, the target values of B / A, and the like are set. In the digital color copying machine F provided, R, G, and B image data read by an image scanner unit (not shown) is input to an image processing unit U1. At this time, a dummy scan is performed prior to the laser writing scan using the image data. This dummy scan outputs a beam for position detection for obtaining a beam position detection signal S1, but does not output laser light for image writing, but only outputs the video clock S2. At this time, the first pulse generator 242 and the second pulse generator 243 provided corresponding to each of the laser writing devices 1y, 1m, 1c and 1k generate pulses of the set pulse widths Ta and Tb, respectively. Output.

When the dummy scanning is performed about several thousand times, the value of the output signal A of the counter 244 is stored in the first set value storage means 24.
7 and the count values of the U / D counters 250 and 252 so that the value of the output signal B / A of the divider 246 matches 1500 stored in the second set value storage means 248. Is determined. After this state, the image carriers Dy, Dm, Dc,
Start writing on Dk. In this case, the frequency of the video clock S2 output from the voltage controlled oscillator 241 of the video clock generation circuit 24 changes, for example, as shown in the graph of S2 in FIG. Although S8, S9 and S2 in FIG. 9 correspond to FIG. 3B, the average value of the video clock S2 is higher than the frequency f0 of the reference video clock. This means that the scanning angle θ1 + θ2 shown in FIG. 3B has the following relationship as compared with 2θ0. (Θ1 + θ2) <2θ0 In the case of FIG. 3B, the image writing period Ta by the laser beam is used.
Since the (scanning period of the scanning angle θ1 + θ2) is shorter than the scanning period of the scanning angle 2θ0 (reference scanning period), the average value of the frequency f1 of the video clock S2 is required to print 3000 dots in a short time. It is higher than the reference frequency f0. In FIG. 3B, θ0 = θ1, and
The average value of the frequency f1 of S2 during the scan at the scan angle θ1 is the same as the reference frequency f0, but the frequency f1 of S2 increases with time, so during the first half of the scan at the scan angle θ1. It is lower than the reference frequency and higher in the latter half.

As shown in FIG. 3A, the image carrier D
Is the reference position as a whole (the position where the scanning angle is 2θ0)
In the case where the video clock S2 shown in FIG. 9 is located far from the light source and the image writing end position is located farther from the light source than the image writing start position, the frequency of the video clock S2 shown in FIG. During Ta (a period during which the scanning angle θ1 + θ2 is scanned), the frequency becomes higher than the reference frequency (f0) from the beginning to the end.

As can be seen from the graph of the inclination control signal S9 in FIG. 9, the end of the image writing period (the first pulse generator 24
At the same time, the inclination control signal S9 is reset. The count value of the U / D counter 252 is held for writing the next image. Then, the U / D counter 252 starts outputting a tilt control signal based on the count value of the U / D counter 252 simultaneously with the start of the next image writing. By the operation described above, the laser writing devices 1y, 1m, 1c, 1k constituting the image forming apparatus F are formed.
Corresponds to the ideally arranged virtual image carrier D shown in FIGS.
The printing of 3000 dots is performed in the scanning period of the scanning angle θ1 + θ2 corresponding to the scanning angle 2θ0 of the virtual laser writing device having 0, and the 1500 dots in the scanning period of the first half scanning angle θ1 and the second half θ2 corresponding to θ0. Can be printed. Therefore, each of the laser writing devices 1y, 1m, 1c,
1k can prevent the image formed on the belt 11 from being displaced.

(Embodiment 2) FIG. 11 is an explanatory view of a main part of Embodiment 2 of an image forming apparatus F according to the present invention.
Counter 22 used corresponding to y, 1m, 1c, 1k
It is explanatory drawing of 4,225. Counter 2 of the first embodiment
24, 225 are first and second pulse generators 242, 24
3, the video clock S2 output from the voltage controlled oscillator 241 is simply counted. In the second embodiment, however, the counter 22 of the first embodiment is used.
4 and 225 are different from the first embodiment in that they have the configuration shown in FIG. In FIG. 11, the counters 224 and 225 according to the second embodiment include an output signal S6 (or S7) of the first (or second) pulse generator 242 (or 243) and a video clock S2 output from the voltage controlled oscillator 241. , An n-number of delay circuits D1 to Dn, n + 1 counters C0 to Cn, and an adder A2.

In the counter 244 (or 245) shown in FIG. 11, for example, n = 4 and the delay circuit D
When the delay time of 1 to D4 is set to 1/5 of the cycle of the video clock S2 of the reference frequency (f0), five counters C0
The total count value obtained by adding the count value counted by .about.Cn by the adder A2 is about five times as large. Therefore, the use of the counter 224 (225) shown in FIG. 11 makes it possible to count the accuracy of the count value of the video clock S2 with substantially five times the accuracy. By using this count value, Counter 2
24, 225 can be improved in comparison with the first embodiment.

(Embodiment 3) Next, the image forming apparatus F of the present invention
Example 3 will be described. In the description of the third embodiment, the description of the same configuration as that of the first embodiment will be omitted. In the third embodiment, the output pulse widths Ta and Tb of the first and second pulse generators 242 and 243 are different from those of the first embodiment.
Is different. Also, the first and second set value storage means 24
7 and 248 are different from each other, but are otherwise the same as the first embodiment. Therefore, the third embodiment
Then, the pulse widths Ta and Tb of the time chart shown in FIG. 9 of the first embodiment are set as shown in FIG. Therefore, the description of the third embodiment will be made with reference to FIGS. 1 to 8, 10, and 12 used in the description of the first embodiment. S8, S9 and S2 in the time chart of FIG.
This is the case in the state of A. 3 and 4, a rotating polygon mirror 18 and a virtual image carrier D0 ideally arranged.
Is set, and the rotation speed of the rotary polygon mirror 18 is also set. Also, the write length R0Q0 for one line
Is also set. The scanning angles θ0 and 2θ0 at the time of writing image data on the ideally arranged virtual image carrier D0 are also set. Accordingly, the time required to scan the scan angle 2θ0 (the time required to write a 3000 dot latent image in R0Q0) is also determined, and the time between R0Q0 on the ideally arranged virtual image carrier D0 is determined. The frequency f0 of the video clock S2 for writing 3000 dots is also determined.

Therefore, in the third embodiment, the pulse width Ta of the output signal S6 of the first pulse generator 242 in FIG.
Is set to the time for scanning the scanning angle 2θ0 in FIGS. The pulse width Tb of the output signal S7 of the second pulse generator 243 is set to the time Tb for scanning the scanning angle θ0 in FIGS. Therefore, in the third embodiment, the pulse width Ta is a time for scanning the scanning angle 2θ0, and the pulse width Tb is a time for scanning the scanning angle θ0, so that Tb = Ta / 2. Note that the pulse (pulse width Ta) of the output signal S6 of the first pulse generator 242 and the pulse (pulse width Tb) of the output signal S7 of the second pulse generator 243 in FIG. The laser drive pulse S5 is output simultaneously with the start of the image writing period. Also, as can be seen from FIG. 3A, since the actual scanning angle θ1 + θ2 of the image carrier D is smaller than the above 2θ0, the video clock frequency offset control signal S8 (see FIG. 12) when printing 3000 dots at the scanning angle θ1 + θ2. ) Must be higher than f0.

Next, when the actual image carrier D is used,
A method for determining the set values of the first and second set value storage means 247 and 248 will be described. First, in a state where the output of the slope control circuit 253 is not input to the adder 254 and while changing the set value of the first set value storage means 247 around 3000, the first dot and the 300th dot in FIG.
The 0th dot pattern image is recorded on the belt 11.
8 so that the position of the pattern image on the belt 11 is detected by a predetermined light receiving element of the predetermined image position sensor 32.
And the set value A0 of the first set value storage means 247 is determined.

Next, the value of A0 determined as described above is
A description will be given of what values are obtained in the cases of FIGS. The Ta is the time required to scan the scanning angle 2θ0 in FIGS. When the actual image carrier D is, for example, in the state shown in FIG. 3A, the scanning angle θ1 + θ2 is smaller than 2θ0. In this case, as shown in FIG. 12, the image writing period T2 for scanning the scanning angle θ1 + θ2 (see S6 in FIG. 12) is shorter than Ta, and 3000 dots are printed during this short period T2. Therefore, in the case of FIG. 3A, the counter 244 shown in FIG.
Since the video clock S2 is counted, the count value A of the counter 244 becomes A> 3000. The value of A at this time is the set value A of the first set value storage unit 247.
0, that is, the target value A0 of A. Therefore, A0 in the case of FIG. 3A is A0> 3000. That is,
As shown in FIG. 12, the frequency f1 of the video clock frequency offset control signal S8 (see FIG. 12) is f0.
Higher than.

When the actual image carrier D is, for example, in the state shown in FIG. 3B, the scanning angle θ1 + θ2 is smaller than 2θ0. in this case,
The scanning time of the scanning angle θ1 + θ2 is shorter than Ta, and 3000 dots are printed during this short time. Therefore, in the case of FIG. 3B, the counter 2 shown in FIG.
44 counts the video clock S2 for a time Ta longer than the time for performing the recording of 3000 dots.
The count value A of the counter 244 should be A> 3000. The value of A at this time becomes the set value A0 of the first set value storage means 247, that is, the target value A0 of A. Therefore, A0 in the case of FIG. 3B is A0> 300.
It becomes 0.

When the actual image carrier D is, for example, in the state shown in FIG. 4A, the scanning angle θ1 + θ2 is larger than 2θ0. in this case,
The scanning time of the scanning angle θ1 + θ2 is longer than Ta, and 3000 dots are printed during this long time. Therefore, in the case of FIG. 4A, the counter 2 shown in FIG.
44 counts the video clock S2 for a time Ta shorter than the time for recording the 3000 dots,
The count value A of the counter 244 should be A <3000. The value of A at this time is the set value of the first set value storage means 247, that is, the target value A0 of A. Therefore, A0 in the case of FIG. 4A is A0 <300.
It becomes 0. When the actual image carrier D is, for example, in the state shown in FIG. 4B and the scanning angle θ1 + θ2 is larger than 2θ0, A0 becomes A0 <3000 as in the case of FIG. 4A.
Also, in FIG. 4B, when the scanning angle θ1 + θ2 is smaller than 2θ0, as in FIGS. 3A and 3B, A
0 is A0> 3000.

As described above, the target values A of Ta, Tb and A
After determining 0, the output signal of the inclination control circuit 253 of FIG.
7 and the Ta and Tb are set in the first and second pulse generators 242, the 1500th dot pattern image shown in FIG.
The set value (target value of B / A) of the second set value storage means 248 is changed centering on １ ／ so that it is detected by the two predetermined light receiving elements. That is, the set value (B / A of the B / A) of the second set value storage unit 248 is set so that the 1500th dot pattern image matches the position of the middle point between the 1st dot and the 3000th dot in the main scanning direction. (Target value). The target value B0 of B / A determined in this way is, for example, in the case of FIG. 3A, the target value of (B / A)> (1/2). The reason will be described with reference to FIG.

That is, in FIG. 12, the start of the image writing period of S5, the rise of the pulse with the pulse width Ta of S6, and the rise of the pulse with the pulse width Tb of S7 are at the same time t0.
It is. Then, Tb = Ta / 2. FIG. 3A shows θ1 =
Since it is θ2, an image recording of 1500 dots is performed at time t1, which is just half of the image writing period T2 of S5.
However, the pulse having the pulse width Tb is turned off after time t1. Therefore, the target value of B / A (B0)> (1
/ 2). 3B, FIG. 4A, and FIG. 4B, the B / B is obtained in the same manner as described with reference to FIG. 3A.
A target value B0 of A can be set. The set value B0 (B / B) of the second set value storage
The target value of A is the video counted by the counter 245 during the pulse output period of the pulse width Tb of the output signal S7 of the second pulse generator 243 (the scanning period of the scanning angle θ0 in the first half of FIGS. 3 and 4). This is a target value of a value (output value of the divider 246) B / A obtained by dividing the count value B of the clock S2 by the count value A of the counter 244.

(Operation of Embodiment 3) As described above, the first,
Even if the pulse widths Ta and Tb of the second pulse generators 242 and 243 are set to the times required for scanning at the scan angles 2θ0 and θ0, respectively, the set values of the first and second set value storage means 247 and 248 are set. As in the first embodiment, the length of a line image for 3000 dots in the main scanning direction on the belt 11 can be made constant, and half of the line image can be printed with 1500 dots. That is, the laser writing devices 1y, 1m, 1c, and 1k constituting the image forming apparatus F of the third embodiment are the same as those in FIG.
The scanning of the belt 1 by the scanning at the scan angle 2θ0 of the virtual laser writing device having the ideally arranged virtual image carrier D0 of FIG.
3,000 dots are printed in the scanning period of the scanning angle θ1 + θ2 for recording an image having the same width as the image recording width to be recorded on 1, and 1500 dots are respectively printed in the scanning period of the first half scanning angle θ1 and the second half scanning angle θ2. Can be printed. Therefore, each laser writing device 1y, 1m, 1c, 1k
Accordingly, it is possible to prevent an image formed on the belt 11 from being displaced.

(Embodiment 4) FIG. 13 is an explanatory view of a main part of an image forming apparatus F according to a fourth embodiment of the present invention, and corresponds to FIG. 5 of the first embodiment. In the description of the fourth embodiment, the same reference numerals are given to the components corresponding to the components of the first embodiment, and the detailed description thereof will be omitted. The fourth embodiment differs from the first embodiment in the following points.
In other respects, the configuration is the same as that of the first embodiment. FIG.
3, the fourth embodiment differs from the first embodiment in that the divider 2
46 is omitted. Then, the count value of the counter 245 (the video clock S during the scanning period Tb shown in FIG. 9, ie, during the pulse output period of the second pulse generator 243).
The count value B of 2 is input to the comparator 251. The second set value storage means 248 stores a B target value B0 (B0 = 1500) instead of the B / A target value B0 (B0 = 1/2) of the first embodiment. In the fourth embodiment, the first set value A0 is set to 3000, and the pulse widths Ta and Tb are set in the same manner as in the first embodiment.
The second pulse generator 243 and the second counter 245
This constitutes the second detection means (243 + 245).

(Operation of Embodiment 4) The comparator 251 has the second
The set value 1500 of the set value storage means 248 and the value of the output signal B of the counter 245 are input. Comparator 25
1 is a U / D conversion of the digital value corresponding to the value of B-1500.
Output to the counter (up / down counter) 252.
The U / D counter 252 increments the count value (that is, the output value) when the input signal from the comparator 251 is negative, and decrements the count value when the input signal is positive. Other operations are the same as those in the first embodiment.

(Embodiment 5) Next, the image forming apparatus F of the present invention
Example 5 will be described. In the description of the fifth embodiment, the description of the same configuration as that of the fourth embodiment will be omitted. In the fifth embodiment, the output pulse widths Ta and Tb of the first and second pulse generators 242 and 243 of the fourth embodiment are used.
Are different. That is, the pulse width Ta of the output signal S6 of the first pulse generator 242 in FIG. The pulse width Tb of S7 is set to the time for scanning the scanning angle θ0 in FIGS. Therefore, Ta and Tb are the same as in the third embodiment. Further, the set values of the first and second set value storage means 247 and 248 are different, but in other respects the configuration is the same as that of the fourth embodiment. Therefore, the description of the fifth embodiment will be made with reference to FIG. 13 used for the description of the fourth embodiment.

Next, the first and second set value storage means 24
A method of determining the setting values of 7, 248 will be described. While the output of the inclination control circuit 253 is not input to the adder 254 and the set value of the first set value storage means 247 is changed around 3000, the first dot and the 3000 dot of FIG. Belt 1 with pattern image
Record on 1. 8 so that the position of the pattern image on the belt 11 is detected by a predetermined light receiving element of a predetermined image position sensor 32.
4 and the set value A0 of the first set value storage means 247 are determined. The set value A0 of the first set value storage means 247 thus determined is stored in the first pulse generator 2
42 is a target value of the count value A of the video clock S2 counted by the counter 244 during the pulse output period of the pulse width Ta of the output signal S6 at 42.

Next, the output signal of the inclination control circuit 253 shown in FIG. 5 is input to an adder 254, the value A0 is set in the first set value storage means 247, and the first and second pulse generators 242 are set in the first and second pulse generators 242. In the state where the pulse widths Ta and Tb are set, the set value B0 of the second set value storage means 248 is changed so that the 1500-th dot pattern image shown in FIG. Change. That is, the second set value storage unit 2 is configured such that the 1500th dot pattern image matches the position of the middle point between the 1st dot and the 3000th dot in the main scanning direction.
Forty-eight set values (target values of B) B0 are determined. The set value (target value of B) B0 of the second set value storage means 248 is the pulse width Tb of the output signal S7 of the second pulse generator 243.
This is the target value of the count value B of the video clock S2 counted by the counter 245 during the pulse output period (the scan period of the scan angle θ0 in the first half of FIGS. 3 and 4).

(Operation of Embodiment 5) As described above, the first,
After setting the pulse widths Ta and Tb of the second pulse generators 242 and 243 to the time required for scanning at the scan angles 2θ0 and θ0, respectively, the set values A0 and B0 of the first and second set value storage means 247 and 248 are determined. However, in the same manner as in the fourth embodiment, the belt 1
The length of a line image corresponding to 3000 dots in the main scanning direction on 1 can be made constant, and half of the line image can be printed with 1500 dots. That is, the laser writing devices 1y, 1m, 1c, and 1k constituting the image forming apparatus F of the fifth embodiment are
In FIG. 3 and FIG. 4, 3000 dots are printed during the scanning period of the scanning angle θ1 + θ2 corresponding to the scanning angle 2θ0 of the virtual laser writing device having the ideally arranged virtual image carrier D0. Corresponding first half scan angle θ1 and second half θ
In the second scanning period, printing of 1500 dots can be performed. Therefore, each laser writing device 1y, 1m, 1c, 1k
Accordingly, it is possible to prevent an image formed on the belt 11 from being displaced.

(Modification) Although the embodiments of the present invention have been described in detail, the present invention is not limited to the above-described embodiments, but falls within the scope of the present invention described in the appended claims. Thus, various small design changes can be made. next,
The modification of this invention is illustrated. (H01) The present invention can be applied to various image forming apparatuses such as a laser printer and a laser facsimile other than the digital copying machine. (H02) The present invention can be applied to an image forming apparatus having one or more laser scanning systems 13 in addition to an image forming apparatus having four laser scanning systems 13. (H03) The values of the pulse widths Ta and Tb of the first and second pulse generators 242 and 243, and the first and second set value storage means 2
The set values A0 and B0 of 47 and 248 can be stored in the respective controllers of the laser writing devices 1y, 1m, 1c and 1k instead of being stored in the video clock generation circuit 24. It is. (H04) The second clock count period (Tb) can be set in the latter half instead of the first half in the period for writing one line in the main scanning direction.

[0088]

The fixing device according to the present invention has the following effects. (E01) When there is a difference in the optical path length of the laser light incident on both ends of the image carrier, the dot interval in the main scanning direction of the image transferred from the image carrier onto the recording paper can be made uniform.

[Brief description of the drawings]

FIG. 1 is a schematic explanatory view of a digital color copying machine F as an image forming apparatus according to a first embodiment of the present invention, and corresponds to FIG. 14 used in the description of the related art.

FIG. 2 is an overall explanatory diagram of an image forming apparatus F according to a first embodiment of the present invention, and corresponds to FIG. 17 used in the description of the related art.

FIG. 3 is an explanatory diagram of a scanning angle of a laser beam L when the image carrier D shown in FIG. 2 is arranged at a position shown by a two-dot chain line deviated from a set position shown by a solid line. Indicates a state where the ideally arranged virtual image carrier D0 is arranged at the set position (solid line position), whereas the actual image carrier D is located farther from the laser light source than the set position. FIG. 3B is a diagram showing a state in which the image carrier is arranged. FIG. 3B shows a state in which the ideally arranged virtual image carrier D0 is arranged at a set position (solid line position).
FIG. 4 is a diagram showing a state in which a rear end portion (right end portion in the figure) with respect to a set position is located at a position far from the laser light source.

FIG. 4 is an explanatory diagram of a scanning angle of a laser beam L when the image carrier D shown in FIG. 2 is arranged at a position shown by a two-dot chain line deviated from a set position shown by a solid line. Indicates a state where the ideally arranged virtual image carrier D0 is arranged at the set position (solid line position).
FIG. 4B is a diagram showing a state in which the virtual image carrier D0 that is ideally arranged is located at the set position (solid line position). In the actual image carrier D, the front end (left end in the figure) is located farther from the laser light source and the rear end (right end in the figure) is closer to the laser light source with respect to the set position. It is a figure showing the state at the time of being arranged in a position.

FIG. 5 is a detailed explanatory diagram of a video clock generation circuit 24 according to the first embodiment.

FIG. 6 shows a tilt control circuit 25 according to the first embodiment.
FIG. 3 is a detailed explanatory diagram of No. 3;

FIG. 7 is a tilt control circuit 25 according to the first embodiment;
3 is an operation explanatory diagram of FIG.

FIG. 8 is a time chart of output signals of components of the video clock generation circuit 24 shown in FIG. 5;

FIG. 9 is a time chart of output signals of components of another image processing unit U1 of the first embodiment.

FIG. 10 is a diagram illustrating an example of a position detection pattern formed on the belt 11 using each of the image carriers Dy, Dm, Dc, and Dk.

FIG. 11 is an explanatory view of a main part of an image forming apparatus F according to a second embodiment of the present invention.
It is explanatory drawing of the counters 224 and 225 used corresponding to 1k.

FIG. 12 shows a video clock generating circuit 24 shown in FIG. 5 in Embodiment 3 of the image forming apparatus F of the present invention.
5 is a time chart of output signals of the constituent elements of FIG.

FIG. 13 is an explanatory view of a main part of an image forming apparatus F according to a fourth embodiment of the present invention, and corresponds to FIG. 5 of the first embodiment.

FIG. 14 is a perspective view of a main part of a digital color copying machine F as an image forming apparatus to which the present invention is applied.

FIG. 15 shows a laser writing device 01y, 01m, 01c, 01k (hereinafter, 01) of the digital color copying machine F;
FIG. 15 is a detailed explanatory diagram of the laser scanning system (13) viewed from the same direction as in FIG.

FIG. 16 is a sectional view taken along the line XVI-XVI in FIG.

FIG. 17 is a perspective view of a laser scanning system (13) constituting the laser writing device 01 and an explanatory diagram of a drive circuit thereof.

FIG. 18 is a diagram showing an example of the position detection pattern, and FIG. 18A is a moving direction (sub-scanning direction) of the transfer material P;
18B is a position detection pattern which is recorded at a constant interval in Y and is composed of lines of each color extending in the main scanning direction (the width direction of the transfer material P) X. FIG. This is a position detection pattern to be performed.

FIG. 19 is an explanatory diagram of variations in the main scanning width caused by errors in the positions of the image carriers Dy, Dm, Dc, and Dk arranged at each set position, and illustrates the optical axis of the writing laser light. Virtual image carrier D0 assumed to be arranged vertically to
(That is, “the ideally arranged virtual image carrier D
0 ") and the actual image carrier D (D is Dy, Dm, Dc, D
k means each. FIGS. 7A and 7B are diagrams for explaining that the main scanning width on the image carrier for forming an image of the same width on recording paper is different.

[Description of Signs] A: first detection value, A0: first set value, (B, B / A) ...
Second detection value, B0: second set value, D: image carrier, F: image writing device, L: laser beam, Ta: first clock count period, Tb: second clock count period, t: main scan A predetermined delay time from the time when the beam position is detected by the beam position detecting means 22 in the direction 13 ... laser scanning system, 22 ... beam position detecting means, (2
4-26)... Dummy scanning execution means, (242 + 244)
... First detecting means, (243 + 245 + 246,243 +
245) ... second detection means, 247 ... first set value storage means, 248 ... second set value storage means, (241 + 249 ~)
256) Frequency variable means

Claims (3)

[Claims] An image forming apparatus having the following requirements: (A01) A writing line in a main scanning direction on a surface of an image carrier moving in a sub-scanning direction is synchronized with a video clock. A laser scanning system for irradiating a laser beam modulated by the read image data to write image information on the surface of the image carrier; (A03) a first clock count period set during a scanning period for writing one line in the main scanning direction and the one-line writing The first detection value and the second detection value determined by the number of video clocks counted in the second clock counting period set in the first half or the second half of the scanning period, respectively, are detected. First detection means and second detection means, (A04) first set value storage means for storing first set values and second set values corresponding to the first detected values and second detected values, and second set value storage (A05) Frequency varying means for changing the frequency of the video clock so that the first detection value and the second detection value match the first setting value and the second setting value, respectively. (A06) The first
A first set value set such that a video clock number counted during the first clock count period when a detected value matches the first set value becomes a first target value;
(A07) The second set value set so that the number of video clocks counted during the second clock count period becomes the second target value when the second detected value matches the second set value , 2. The image forming apparatus according to claim 1, wherein the following requirements are satisfied: (A08) A dummy scanning execution unit that does not perform image recording before the start of scanning for performing image recording;
(A09) The frequency variable unit that changes the frequency of the video clock during the dummy scanning period. 3. The image forming apparatus according to claim 1, wherein the image forming apparatus has the following requirements: (A010) The image forming apparatus starts from a time when a beam position is detected by the beam position detecting means in the main scanning direction. The frequency varying means for maintaining the frequency of the video clock at a constant value until writing of information is started.