JPH0434568A - Image writing position setting device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an image writing position setting device for a laser scanning image forming apparatus capable of switching pixel density.

[Conventional technology]

Personal computer, EWS (Engineering Workstation) 2 document creation devices.

Image forming apparatuses are used as external or internal pressure devices for office automation equipment such as digital copying machines and high-speed facsimile machines.

As image forming apparatuses that meet the demands for improved processing speed of OA equipment, that is, host machines, and for high-quality images, such as laser scanning image forming apparatuses with excellent print speed and resolution, such as laser printers (laser beam printers:
The use of printers (hereinafter simply referred to as "printers") is increasing.

Such laser printers not only have a high pixel density, but also can relatively easily change the dot size, dot pitch, or line pitch, that is, change the pixel density, compared to other types of printers. There are high-performance models on the market that have the ability to select pixel density depending on the purpose.

Regarding the technology related to variable pixel density, 1, for example, as shown in Japanese Patent Application Laid-Open No. 117372/1980, dot size, image clock, etc. are controlled according to the dot pitch and the number of dots constituting an image unit (characters, etc.). A proposal to control the intensity and scanning speed of a laser beam (hereinafter also simply referred to as "beam J") according to the magnification of a created image, as disclosed in Japanese Patent Application Laid-Open No. 120658/1982,
93873, in which optical systems with different resolutions (pixel densities) are removably attached to the printer body, and the dot size and scanning speed are controlled according to the installed optical systems, or There have been many proposals, including a proposal to control the rotational speed of a polygon motor by dividing the reference clock according to the pixel density, as shown in Japanese Patent No. 62-162547.

Regarding the positioning of the paper and the image, for example, as shown in Japanese Unexamined Patent Publication No. 1-210347, when performing one-sided printing, the shrinkage of the paper due to heating during image fixation on the first side is taken into consideration, and the second side is Proposals have been made to correct the timing of alignment during writing.

However, these proposals do not consider or propose any positional shift in the main scanning direction (horizontal direction) of the formed image that inevitably occurs due to changes in the image clock or scanning speed due to switching of pixel density.

For this reason, some systems count image clocks in units of, for example, eight clocks, and perform correction based on a data table as shown in Table 4 during alignment.

In other words, in order to cancel the positional deviation due to paper feeding and conveyance errors specific to each printer, for example, a 4-unit dip switch (hereinafter referred to as dip SWJ or rDPsWJ) is set to a center value of 8h (h indicates a hexadecimal number) during adjustment. The count number is 1 for each (8 for the pixel clock)
The value 0h-Fh is set to increase or decrease, and the count number corresponding to the DPSW setting value is corrected according to the pixel density.

[Problem to be solved by the invention]

In this conventional method, since the count number is proportional to the pixel density at the center value of 8h, the correction amount (length) on the photoreceptor (and paper) remains constant even if the pixel density changes.

However, as the amount of correction increases, positional deviations due to the difference between the pixel density at the time of adjustment and the pixel density at the time of execution become noticeable.

For example, when adjusting the pixel density to 240 dpi, the DPSW setting value is 2h (difference from the center value of the count number to be corrected is 6h).
If you print at 400dPi with a printer that was
=0.08 inch, that is, a positional deviation of 2- from the adjusted position occurs.

Further, even if adjusted at 300 dpi and set to 2h, when printing is executed at 240 dpi and 400 dpi, a positional deviation of 0.04 inches, that is, 1 mm will occur, respectively.

This invention has been made in view of the above points, and it is an object of the present invention to provide an image without positional deviation with a simple configuration without bothering the operator even when the pixel density is changed.

[Means to solve the problem]

In order to achieve the above-mentioned object, the present invention has a laser scanning type image forming apparatus capable of switching pixel density, by counting the image clock from the synchronization signal to the start of image writing, thereby positioning the image relative to the paper in the main scanning direction. The image writing position setting device that performs alignment includes an adjustment data storage means for recording the image clock count adjustment value and adjusted pixel density set at the time of alignment adjustment, and an adjustment data storage means for recording the image clock count adjustment value and adjusted pixel density set at the time of image writing execution. A correction value setting means is provided for setting a count correction value for alignment according to the density, the count adjustment value recorded in the adjustment data holding means, and the adjusted pixel density.

Also, when the execution pixel density is higher than the adjusted pixel density, the count correction value is set larger than the count adjustment value.

It is preferable to provide a correction value setting means that sets the value to be small when the value is low.

[For production]

In the image writing position setting device configured in this way, no matter what pixel density is adjusted, the adjustment data holding means records the count adjustment value and the adjusted pixel density, and the correction value setting means records the actual pixel density. Since the count correction value for alignment is set according to the adjusted pixel density and the count adjustment value, even if the execution pixel density is different from the adjusted pixel density, accurate correction is performed and no one position shift occurs.

〔Example〕

Hereinafter, one embodiment of the present invention will be specifically described with reference to the drawings.

FIG. 2 is a schematic diagram showing the internal mechanism of a laser printer that is an embodiment of the present invention.

Around the photosensitive drum 10 rotating clockwise as shown by the arrow, chargers 11 . Optical writing unit 12. Phenomenon unit 13, transfer charger 1
4. Cleaning units 15 are arranged respectively.

The surface of the photosensitive drum 10 is first uniformly charged by a charging charger 11, and then the photosensitive drum 10 is scanned in the main scanning direction by a spot on which a beam modulated by image data from the optical writing unit 12 and deflected in the main scanning direction forms an image. to form an electrostatic latent image.

The electrostatic latent image is developed by the developing unit 13 and converted into a visualized toner image, which is then transferred by the transfer charger 14 onto the sheet of paper that has been conveyed along the route shown by the dashed line. transcribed.

The toner and charge remaining on the photosensitive drum 10 are removed by the cleaning unit 15, and the removed toner is collected by the cleaning unit 15.

The paper is fed by a paper feed roller 19 from a paper stack 18 on a paper feed cassette 17, and is fed by a pair of registration rollers 2.
0, the toner image is conveyed to the position of the transfer charger 14 by a pair of registration rollers 20 at a timing that matches the image written on the photoreceptor drum 10 by the optical writing unit 12. is transcribed.

The paper onto which the toner image has been transferred is conveyed to the fixing unit 21, and the pressure roller 2 is applied to the heated fixing roller 21a.
1b and is fixed by the heat and pressure, the paper is conveyed to the paper ejection roller 22 and ejected from the paper ejection port 23 onto the paper ejection tray 24.

FIG. 3 is a perspective view of essential parts showing an example of the optical writing unit 12. FIG.

The optical writing unit 12 includes an LD (laser diode) unit 30, which is a modulated light source, and a first cylinder lens 31. First mirror 32. A pre-object type imaging lens 33, a rotary deflector 36 consisting of a polygon motor 34 and a polygon mirror 35 rotated actively in the direction of arrow A, and a second mirror 37. 2nd cylinder lens 3
8, and a third mirror 40.
゜Light receiving lens 41. It is constituted by a synchronous optical system consisting of a synchronous sensor 42.

The LD unit 30 has an LD, a collimator lens that converts a diverging beam emitted from the LD into a parallel light beam, and an aperture that regulates the thickness of the beam.

The parallel light beam emitted from the LD unit 30 passes through the first cylinder lens 31 and is reflected by the first mirror 32, and then passes through the imaging lens 33 and enters the reflective surface 35a of the polygon mirror 35.

The imaging lens 33 acts to form an image of the parallel main scanning direction component of the incident beam on the photoreceptor drum 10 (described later), and the first cylinder lens 31 uses the combined power of the imaging lens 33 to It acts to form an image of the sub-scanning direction component of the parallel beam once on the reflective surface 35a of the polygon mirror 35.

The beam reflected by the polygon mirror 35 and repeatedly deflected in the main scanning direction is reflected by the second mirror 37, passes through the second cylinder lens 38, and reaches the photosensitive drum 1o rotating in the direction of arrow B.

The second cylinder lens 38 re-images the sub-scanning direction component of the beam once imaged on the reflecting surface 35a onto the photoreceptor drum 10, so that the beam is focused in the main scanning direction where it is imaged by the imaging lens 33. The image is formed into a spot along with the components, and main scanning is performed on the main scanning line 10a of the photosensitive drum 10 in the direction of arrow C.

Further, just before the beam deflected by the one-rotation deflector 36 enters the effective image area on the main scanning line 10a, the beam is reflected by the third mirror 40 and focused on the light receiving surface by the light receiving lens 41. A synchronization sensor 42 that outputs a main scanning synchronization signal is also provided.

FIG. 4 is a block diagram showing an example of a control section of this laser printer.

The controller 50 is a main microcomputer (
(hereinafter referred to as "rMPU") 51, programs and constant data required by the sono MPU 51.

A ROM 52 that stores character fonts, etc., a RAM 53 that stores temporal data, dot patterns, etc., an I 1054 that controls command and data input/output, and
7) Consists of an operation panel 55 connected to the LMPU 51 via the l1054, and an internal interface (I/F) 56, which are connected to each other via a data bus, an address bus, etc.

In addition, the host machine 58 that outputs print commands, character data, and image data is also connected to the MPU 5 via the I 1054.
Connected to 1.

The engine driver 60 includes a sub microcomputer (hereinafter referred to as rcPUJ) 61 and a ROM 62 that stores programs and constant data required by the CPU 61.
, a RAM 63 for storing temporal data, and an I1064 for controlling data input/output, and are connected to each other by a data bus, an address bus, etc.

The l1064 is connected to the internal interface 56 of the controller 50, and inputs video signals from the controller 50 and the states of various switches on the operation panel 55, and outputs status signals such as image clock and paper end to the controller 50.

The l1064 is also connected to the optical writing unit 12 and other sequence equipment groups 66 that constitute the printer engine 65, each of which is a printing means, and to various sensors 67 including the synchronization sensor 42.

The controller 50 receives print commands, character codes, and image data from the host machine 58, edits these codes, and data, and in the case of character codes, creates a dot pattern necessary for image writing using the character font stored in the ROM 52. After converting the dot patterns of those characters and images (hereinafter collectively referred to as "images") to
It is stored in memory in the VRAM (video RAM) area in the AM53.

When the image clock is input together with the ready signal from the engine driver 60, the controller 50 outputs the dot pattern stored in the VRAM area to the engine driver 60 serially or in parallel as a video signal synchronized with the image clock.

The engine driver 60 controls the optical writing unit 12 of the printer engine 65 based on data from the controller 50.
A video signal necessary for controlling the sequence equipment group 66 and image writing is input from the controller 50 and output to the optical writing unit 12, and signals indicating the status of each part of the engine are sent from the synchronization sensor 43 and other sensors 67. It inputs and processes it, and outputs necessary information and error signals to the controller 50.

FIG. 1 is a circuit diagram showing an example of a control system of a printer engine 65 and an engine driver 6o mainly related to optical writing in the control section shown in FIG.
Components that are the same as those in the drawings are given the same reference numerals and their explanations will be omitted.

The printer engine 65 includes an MM (main motor) 70, an MM driver 71 that controls it, a PM (polygon motor) 34, a PM driver 72 that controls it, and a paper feed clutch (CL) 73° and a registration clutch (CL).
Sequence equipment group 66 consisting of 75 and CL (clutch) drivers 74, 76 and others that operate them respectively.
and the LD (laser diode) 7 of the optical writing unit 12
7 and an LD driver 78 that activates it. and PD (
A synchronous sensor 42 consisting of a photodiode) and a synchronous signal pressure detection circuit 43. It is composed of a registration sensor 79 and other sensors 67.

Each part constituting the printer engine 65 is connected to the engine driver 60 directly or via a driver, or to the controller 50 via a control circuit.

The MM driver 71 inputs the on/off signal MMC,
Controls constant speed rotation of MM70, which is a common power source for each part of the printer.

The PM driver 72 receives an on/off signal PMST.

(Execution) Input the signal PMDI that indicates the pixel density,
The PM 34 is synchronously controlled to be kept rotating at a constant speed according to the pixel density, and when the synchronization is maintained, a signal PMLK indicating that it is locked is output to the engine driver 60.

When the paper feed command signal FC is turned on, the CL driver 74 turns on the paper feed clutch 73, which is a one-way clutch that connects the paper feed roller 19 and MM70, and the paper is fed from the paper feed cassette 17 by the paper feed roller 19. When the paper sheet contacts the registration roller pair 20 and the registration sensor 79 detects it, the engine driver 60 turns off the signal FC, and the CL driver 74 turns off the paper feed clutch 73 to stop the paper feed rollers 19.

Based on the signal from the registration sensor 79, the engine driver 6
0 starts printing, the LD driver 78 outputs the signal V
The LD 77 is turned on and off while monitoring the light amount output according to IDEO to output a modulated laser beam.

A synchronization sensor (PD) 42 receives laser light for each scanning line, and the engine driver 60 detects the signal and uses it as a reference timing for starting writing of the scanning line.

Further, the engine driver 60 turns on the transport command signal RC at a timing from the start of writing to the photoreceptor drum 10.

The CL driver 76 operates a resist clutch 75 that connects the resist roller pair 20 and the MM 70 in response to a signal RC.
is turned on, and the registration roller pair 20 is rotated to convey the paper until the signal RC is turned off according to the length of the paper.

The optical writing will be explained in detail below.

The engine driver 60, which is also a correction value setting means, includes an optical writing control circuit 45, and a dip 5W (DPSW) that sets an execution pixel density and also serves as an adjustment data holding means.
46 is connected thereto, and an LD driver 78 is also connected thereto.

The optical write control circuit 45 further includes a controller 50, a synchronization detection circuit 43. It is also connected to the LD driver 78.

The dip 5W46 is, for example, as shown in FIG.
Consists of 8 switches corresponding to each bit of 7,
Upper 2 bits (6, 7) and lower 4 bits (0 to 3)
are the adjusted pixel density and the count adjustment value of 0h-Fh with 8h as the center value, which are set when adjusting the left margin, which is alignment in the main scanning direction, and the intermediate 2
Bits (4, 5) are used to set the execution pixel density when the printer actually executes the job.

Both the adjusted pixel density and the execution pixel density are represented by 2 bits, 0 and 1.2 are each 240 dpi.

It corresponds to 300 dpi and 400 dpi, and 3 is undefined.

That is, in the example shown in FIG. 5, the pixel density is 300 dp.
i The count adjustment value when adjusted with C code 1) is 6h
Currently, the pixel density is 240dpi (code O)
It shows that it is set to .

In principle, the printer operates according to the practical pixel density set by the middle two bits (4, 5), but especially when the pixel density is specified from the operation panel 55 or host machine 58, the latter high priority.

Please note that when setting or changing the execution pixel density using the dip 5W46, you may accidentally change the data that was set and held when adjusting the left margin, and if the data at the time of adjustment is unknown, it may become impossible to restore. be.

In order to prevent such an accident, as shown by the broken line in Fig. 1, for example, an EEPROM 47 is provided as a dedicated adjustment data storage means, and it is separated from the DIP 5W46 used by the user or service personnel for setting or changing. Even better.

When a print start command is input from the host machine 58 via the controller 50, the engine driver 60 controls each sequence equipment group 6 at the appropriate timing.
In addition to outputting the standby or start command to 6, it also outputs the paper size (width and length) and dip 5W46.
Data LDATA, such as the count number of the left margin according to the data set to 9, is sent to the optical writing circuit 45, and a signal LDP, which instructs the optimum power of the laser beam according to the ambient temperature, etc., is sent to the LD driver 78. Output.

Next, when the registration sensor 79 detects paper.

A signal FSYNC for starting optical writing is output to the optical writing control circuit 45.

When the optical write control circuit 45 detects the signal FSYNC,
The signal FGATE, which is held at "Hjj" until printing for one page is completed according to the length of the paper, is output to the controller 50, and the synchronization signal DETP in the main scanning direction is output to the controller 50.
The signal VI output to the LD driver 78 in order to detect
Set DEO to 'lH' to cause LD77 to emit light.

The synchronization signal detection circuit 43 detects the laser beam received by the synchronization sensor 42 and outputs the synchronization signal DETP, and when the optical write control circuit 45 receives the signal DETP, it outputs the signal VI
In addition to returning DEO to "L", the signal LSYNC indicating the start of line printing and the signal LGATE, which is held at "Ht+" until 1542 minutes of printing is completed, are set at the left margin timing according to the paper width. Output to the controller 50.

When the controller 50 detects the signal LSYNC, it outputs one line of image data signal WD synchronized with the image clock.
ATA, and the optical write control circuit 45 receives the input signal WDA.
It converts TA into a signal VIDEO and outputs it to the LD driver 78.

The LD driver 78 outputs a drive current signal that turns on and off according to the signal VIDEO to the LD 77, and controls the drive current signal to the power instructed by the signal LDP from the engine driver 60 while monitoring the power.

As explained above, the signal FGATE is
Image writing is repeated line by line until it returns to 1.
An electrostatic latent image for one page is formed on the surface of the photoreceptor of the photoreceptor drum 10.

FIG. 6 shows a signal LSYNC for determining the left margin and a signal LG for determining the image convergence in the optical writing control circuit 45.
FIG. 2 is a block diagram showing an example of a line signal generating section that generates an ATE.

As shown in FIG. 6, the line signal generating section 80 includes data registers 81. It consists of a down counter 82° decoder 83 and a frequency divider 84.

The data register 81 registers the data LDATA input from the engine driver 60, and sends the count number N for taking the left margin to the down counter 82, and sends the signal LG to the down counter 82.
Data defining the length of the ATE is output to the decoder 83, respectively.

The splitter 84 divides the input image clock WCLK into 1/8
The frequency-divided clock WCLKN obtained by frequency division is output to the down counter 82.

The down counter 82 is initialized by the synchronization signal DETP, that is, loaded with the count number N that is input (in parallel) from the data register 81, and then inputted by the divided clock WC.
Count down according to LKN.

The decoder 83 checks the contents of the down counter 82, and when the contents become O, outputs the signal LSYNC with a width of 1 count, and then outputs the signal LG with a delay of 1 count.
Set ATE to “H”.

Furthermore, the contents of the down counter 82 are stored in the data register 8.
When the signal matches the data specifying the length input from 1, the signal LGATE is returned to t(L'1).

FIG. 7 is a waveform diagram showing an example of each signal of the line signal generating section 8o, in order from the top: the image clock WCLK, the divided clock WCLKN, and the signals DETP, LSYNC.
, LGATE are shown, respectively.

The image clock WCLK is frequency-divided to ⅛ by the frequency divider 84 and converted into a frequency-divided clock WCLKN, and the frequency-divided clock WCLKN becomes the clock of the line signal generation section 80.

When the synchronization signal DETP is input, the timing of the count number N required for the left margin is taken and the signal L is input.
SYNC is “H” for 1 frequency division clock (8 image clocks)
Then, with a delay of one frequency division clock, the signal LGATE becomes "Htj".

The signal LGATE returns to "L" when writing of the image width corresponding to the paper width is completed, and waits for input of the next synchronizing signal DETP.

Here, the count number N required for the left margin varies greatly depending on the setting of the paper stack 18 in the paper feed cassette 17 (although it changes approximately proportionally depending on the actual pixel density).

When the left edges of the sheets are aligned, the left margin amount (length) is constant regardless of the paper size, and when the sheets are set so that the centers are aligned, the left margin amount (length) changes depending on the width of the paper.

In other words, the wider the paper's convergence, the larger the effective image area (
Signal LGATE becomes long) and left margin (length)
becomes smaller; conversely, if the width is narrower, the effective image area also becomes smaller (signal LGATE becomes shorter) and the left margin becomes larger.

In either case, count correction is performed for a predetermined left margin (length) in order to cancel paper feeding and conveyance errors.

Tables 1 to 3 each have an adjusted pixel density of 240 dp.
An example of a data table is shown in which the count number for correction corresponding to each execution pixel density is determined from the setting value of dip 5W46 when left margin adjustment is performed at i, 300 dpi, and 400 dpi.

This data table is stored in advance in the ROM 62 (including EEPROM) of the engine driver 60, which is correction value setting means.

For example, when performing left margin adjustment at a (adjustment) pixel density of 240 dpi (see Table 1), dip 5W4
If the correct left margin was obtained by setting Ah instead of the center value 8h for 6, the count number at that time would be 14 (
The image clock was 8 times that value, 112).

Therefore, if the pixel density is 240 dpi, the corrected count number remains unchanged, if the pixel density is 300 dpi, it is 18 counts (144 clocks), and if the pixel density is 400 dpi, it is 23 counts (184 clocks) to obtain the correct left margin.

Although not shown in the table, the left margin amount (length) number varies depending on the fixed amount when setting the left side of the paper or the width of the paper when setting the center; the image determined by the corresponding count amount and the width of the paper. Although the count amount according to the width of the pixel width is unrelated to the adjusted pixel density, it is clear that it changes in proportion to the execution pixel density, so we prepared separate data tables for the count amounts corresponding to them. I'll keep it.

The correction count number is added (or subtracted) to the former to become the count number N that actually determines the left margin, and the latter becomes data that defines the length of the signal LGATE.
Together, they constitute data LDATA.

FIG. 8 shows that the engine driver 60 (cPU 61) is L.
FIG. 3 is a flow diagram showing an example of a subroutine that outputs DATE.

When started, the code for the FM regular pixel density set in the upper two bits (6, 7) of the dip 5W46 is read, and if it is 3, it is undefined, so an error is processed and the process returns.

If the code is 0.1.2, it is 240 dpi as shown in Tables 1, 2, and 3, respectively.

Select the data table for 300dpi and 400dpi adjustment.

Next, the set value set in the lower 4 bits (0 to 3) and the code for the execution pixel density set in the middle 2 bits (4, 5) are read.

The correction count number is determined from the data table selected based on the set value and the execution pixel density, and after outputting the data LDATA obtained by the calculation to the data register 81, the process returns.

In the embodiment shown in FIG. 6, the image clock WCLK
Instead of counting directly, a divider 84 is provided to reduce the
The frequency-divided clock WCLKN is counted.

Therefore, the difference between the clocks divided by 1 is 0.0 on the paper.
Although a difference of 51 mm to 0.85 mm appears, it does not pose much of a problem when determining the left margin and the width of the image.

Rather, the image clock WC is
If LK is directly counted, the number of bits in each process increases by 4 bits, and the number of bits in each process increases by 4 bits. Data register 81. The down counter 82 and the decoder 83 have larger configurations, leading to higher costs, and the data becomes more complex, making setting errors more likely to occur.The disadvantages of increasing accuracy more than necessary are greater than the advantages.

In the conventional example using the data table shown in Table 4, an error in the amount of correction (length) due to changes in pixel density occurred by 1 mm to 2 mm in some cases, but similarly,
When counting clocks divided by /8, in this example, even if you adjust to an arbitrary pixel density and print at a different pixel density, the error in the correction amount is 0.3 m at most.
Since it falls within m, 8 can be considered as O in practical terms.

Although an example in which the present invention is applied to a laser printer has been described above, the present invention is not limited to laser printers, and is applicable to OA devices such as digital copying machines and high-speed facsimile machines.
Needless to say, the present invention can be applied to a laser scanning image forming device built into a device.

〔Effect of the invention〕

As described above, the image writing position setting device according to the present invention does not bother the operator even when the pixel density is changed, and can obtain an image without positional deviation with a simple configuration.

Table 1 Data table (for 240dpi adjustment) Table 2 Data table (for 300dpi adjustment) Table 4 Data table (conventional example) Table 3 Data table (for 400dpi adjustment)

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a control system related to optical writing of a printer according to the present invention. FIG. 2 is a schematic configuration diagram of the internal mechanism of a laser printer showing an embodiment of the present invention, FIG. 3 is a perspective view of the main parts of the writing unit, and FIG. 4 is a block diagram showing an example of the control unit. FIG. 5 is an explanatory diagram showing an example of the dip switch, and FIG. 6 is a block diagram showing an example of the LSYNC generating section. FIG. 7 is a waveform diagram showing an example of each signal, and FIG.
The figure is a flow diagram showing an example of the data processing routine. 12... Optical writing unit 30... LD unit 42... Synchronous sensor 45... Optical writing control circuit 46... Dip switch (adjustment data holding means)
47...EEPROM (adjustment data holding means) 60
...Engine driver (correction value setting means) 61...
CPU (microcomputer) 77... LD (laser diode) 80... LSYNC generation section 84... Branch unit 1 LGATE Figure 3 Figure 5 Figure 6 Figure 7 Figure 8

Claims (1)

[Claims] 1. A laser scanning image forming device capable of switching pixel density,
In an image writing position setting device that performs positioning of an image on paper in the main scanning direction by counting image clocks from a synchronization signal to the start of image writing, the image clock count adjustment set at the time of adjusting the positioning. adjustment data storage means for recording the value and the pixel density at the time of adjustment, that is, the adjusted pixel density; and the execution pixel density set at the time of image writing execution and the count adjustment recorded in the adjustment data storage means. An image writing position setting device comprising: correction value setting means for setting a count correction value for alignment according to the value and the adjusted pixel density. 2. The image writing position setting device according to claim 1, wherein the count correction value is set to be larger than the count adjustment value when the execution pixel density is higher than the adjusted pixel density, and set to be smaller when it is lower. An image writing position setting device comprising a value setting means.