JP2018146911A - Image formation apparatus and control method of image formation apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image formation apparatus which can highly accurately determine whether or not printing position adjustment should be executed again when an image to be printed is switched.SOLUTION: An image formation apparatus which develops with a developer a latent image formed on a photoreceptor based on image data specified by a job and performs thermal fixation processing after transferring the developed image to a sheet, displays an adjustment button receiving that printing position adjustment is performed by adjustment means adjusting the printing position of an image printed on the sheet on display means when the average value of the image densities calculated from the image data specified by the job exceeds a prescribed threshold before starting image formation with respect to the job.SELECTED DRAWING: Figure 10

Description

  The present invention relates to an image forming apparatus and a method for controlling the image forming apparatus.

2. Description of the Related Art Conventionally, an image forming apparatus has a function of adjusting an image print position (hereinafter referred to as “print position adjustment”) so that an image is printed at an intended position on a sheet. This makes it possible to correct the position of the image to an ideal position when printing an image on a sheet with pre-printed ruled lines such as preprinted paper, or when printing an image on the front and back sides. Can do.
This print position adjustment needs to be adjusted for each paper used. This is because the printing position differs depending on the paper size, basis weight (weight), material, and the like. Also, due to the difference in paper hygroscopicity, the shrinkage rate of the paper caused by the fixing heat during front surface (first surface) printing changes, so there is a difference in the image printing position and expansion / contraction rate on the back surface (second surface). This is because the printing position is different.

  In general, the print position adjustment uses a “predetermined mark” printed on a sheet to be adjusted (hereinafter referred to as “print position adjustment chart”). The positional deviation amount of the printing position is obtained from the relative position of the mark on the printing position adjustment chart. After performing the print position adjustment, when performing printing using the same type of paper as the paper used for the adjustment, the print position is adjusted so as to cancel out the displacement amount of the print position.

The operator can measure the position of the mark using a ruler, etc., and input it to the printing device. However, it is time consuming and may cause errors and mistakes due to human measurement. There was nothing.
Therefore, a method has been proposed in which a print position adjustment chart is read using an image reader such as a reader, the scanned image data is analyzed, the mark position is automatically detected with high accuracy, and the print position is adjusted. (Patent Document 1).
According to the method described in Patent Document 1, a reference image for alignment is printed in at least four corners of the front and back surfaces of a sheet, the paper on which the reference image is printed is read by a reader, and the amount of positional deviation is based on the read result. To get.

JP 2003-173109 A

  However, if the toner consumption of the image printed on the print position adjustment chart and the toner consumption of the output image are significantly different, the position of the image relative to the sheet may not be adjusted with high accuracy despite the execution of the print position adjustment. There was sex. This is because the shrinkage rate of the sheet caused by the fixing heat differs depending on the density of the image to be printed (output image).

  The present invention has been made to solve the above-described problems, and an object of the present invention is to determine with high accuracy whether or not the print position adjustment should be performed again when the image to be printed is switched. .

The image forming apparatus of the present invention that achieves the above object has the following configuration.
An image forming apparatus that thermally fixes an image transferred to a sheet based on image data specified by a job, and an adjustment unit that adjusts a printing position of the image to be printed on the sheet, and starts image formation for the job If the average value of the image density calculated from the image data specified by the job exceeds a predetermined threshold before the adjustment, an adjustment button for accepting print position adjustment by the adjustment unit is displayed on the display unit. And a control means.

  According to the present invention, it is possible to determine with high accuracy whether or not the print position adjustment should be executed again when the image to be printed is switched.

1 is a diagram illustrating a configuration of an image forming apparatus. 2 is a block diagram illustrating a control configuration of the image forming apparatus. FIG. It is a figure which shows an example of an operation display apparatus. It is a figure which shows an example which printed the image pattern from which density differs on the same paper. It is a printing position adjustment chart. It is a figure explaining the method to change average density. It is a schematic diagram showing the printing position adjustment chart. It is a figure which shows the image data read from the chart for printing position adjustment. It is a figure which shows the image data read from the chart for printing position adjustment. 3 is a flowchart illustrating a method for controlling the image forming apparatus. 3 is a flowchart illustrating a method for controlling the image forming apparatus. 3 is a flowchart illustrating a method for controlling the image forming apparatus.

Next, the best mode for carrying out the present invention will be described with reference to the drawings.
<Description of system configuration>
[First embodiment]

First, a basic printing operation of the image forming apparatus 10 will be described.
FIG. 1 is a diagram illustrating a configuration of the image forming apparatus 10. Note that the image forming apparatus is configured to perform heat fixing processing on one side or both sides of a sheet to be fed. Further, the printing position adjustment function described in the cited document 1 is provided.
In FIG. 1, an image signal is generated when a reader 100 reads an image of a document conveyed from the document conveying device 30. Alternatively, an image signal generated by instructing a job to be executed from the operation unit 20 or a PC (not shown) is input to the exposure control unit 103. The exposure control unit 103 includes exposure control units 103k, 130c, 130m, and 130y corresponding to the developer colors yellow (Y), magenta (M), cyan (C), and black (K). The exposure controllers 103k, 130c, 130m, and 130y irradiate the photosensitive drum 102 with laser light based on the image signal on the rotating photosensitive drums 102k, 120c, 120m, and 120y.
As a result, a latent image is formed on the photosensitive drum 102. The latent image on the photosensitive drum 102 is developed by a developing device. On the photosensitive drum 102, each color of yellow (Y), magenta (M), cyan (C), and black (K) is arranged at a predetermined interval, and a toner image of each color component is developed. The toner images formed on the photosensitive drums 102k, 120c, 120m, and 120y are primarily transferred onto the intermediate transfer member 104 at a predetermined timing by the charging rollers 105k, 105c, 105m, and 105y. Each color image is overlapped on the intermediate transfer member 104 to form a desired color image.

On the other hand, the sheets fed from the sheet storage units 110 a and 110 b are conveyed to the registration rollers 111. When the leading edge of the sheet reaches the registration roller 111, the registration roller 111 is driven at an arbitrary timing, and the sheet is conveyed between the intermediate transfer member 104 and the secondary transfer unit.
In the secondary transfer unit 106, the toner image primarily transferred onto the intermediate transfer member 104 is secondarily transferred onto the sheet. In the secondary transfer unit 106, when the toner image on the intermediate transfer member 104 is secondarily transferred onto the sheet, the toner may remain on the intermediate transfer member 104. This residual toner is removed by the intermediate transfer member cleaning unit 108.

  Subsequently, the fixing unit 107 fixes the toner image transferred onto the sheet on the sheet by heating and pressing. The sheet after fixing is discharged from a paper discharge roller 112 to a paper discharge tray 113 of the image forming apparatus 10. The flapper 112 guides the sheet to a double-sided path when forming images on both sides of the conveyed sheet. The sheet is conveyed again between the intermediate transfer member 104 and the secondary transfer unit 206 via the duplex path. On the other hand, when the sheet is discharged, the flapper 112 guides the sheet to the discharge path. The sheet is discharged from the image forming apparatus 10 through a discharge path.

FIG. 2 is a block diagram illustrating a control configuration of the image forming apparatus illustrated in FIG.
In FIG. 2, the system controller 200 has a CPU 201, a ROM 202, and a RAM 203. The CPU 201 is connected to the ROM 202, the RAM 203, the image processing unit 210, and the reader 100 via a bus. The CPU 201 is connected to the operation unit 20.
The image processing unit 210 performs image processing on the input image data, and stores the data in the image memory 213. The image memory 213 can store image data in units of pages. Further, a video count unit 214 that counts the density value of the image data as a digital signal is connected between the image processing unit 210 and the image memory 213. The video count unit 214 acquires the image density (toner applied amount) based on the image processed data. Note that the video count unit 214 calculates the value of the image density according to the procedure of the flowchart described later. At this time, the video count unit 214 counts the density of the image data specified by the job for each page, and sets the average density value of all pages included in the job as the value of the image density.

All the devices are controlled by the system controller 200 in a centralized manner. The system controller 200 mainly plays a role of data exchange with the operation unit 20, that is, the user interface, in addition to driving of each load in the apparatus, information collection analysis of sensors, and the image processing unit 210.
The system controller 200 sends specification setting value data of each unit necessary for the image processing unit 210. Furthermore, the system controller 200 receives signals from each unit, for example, a document image or density signal from the reader 100, and performs calculations and settings for controlling the image processing unit 210 to perform optimum image formation.

The CPU 201 installed in the system controller 200 executes various sequences based on a predetermined image forming sequence by a program stored in the ROM 202 installed in the system controller 200.
The RAM 203 secures work memory necessary for arithmetic processing executed by the CPU 201. The RAM 203 stores rewritable data that needs to be temporarily or permanently stored. In the RAM 203, for example, image formation command information from the operation unit 20 is also stored. The CPU 201 sends information such as a copy magnification and a density setting value set by the operator to the operation unit 20. Further, the CPU 201 sends data for indicating to the operator the status of the image forming apparatus 10, for example, the number of images formed, information on whether or not an image is being formed, occurrence of a jam, and the location thereof. Further, the CPU 201 controls driving of a drive motor and the like included in the image forming apparatus 10 via the load driving unit 212. The image forming apparatus 10 performs a pattern printing process for printing the adjustment pattern image according to the procedure of the flowchart described later.

FIG. 3 is a diagram illustrating an example of the operation unit 20.
3A and 3B, the touch panel 620 displays the status of the image forming apparatus 10 and performs input processing when the user touches a soft button displayed on the panel. A start key 602 is pressed when executing a job. A stop key 603 is pressed to stop the job. Number keys 604 to 614 are pressed when inputting numbers.
An ID key 614 is pressed when inputting an ID. A clear key 615 is pressed to clear the setting. A reset key 616 is pressed to reset the contents being set. A mode key 617 is pressed when entering the user mode.

As shown in FIG. 3A, the touch panel 620 displays a guidance screen for prompting the print position adjustment. On the guidance screen, the user can select either the image output start key 621 or the print position adjustment key 622 which is an adjustment button.
In addition, on the guidance screen, a message 625 for prompting the user to adjust the print position is displayed below the touch panel unit 620. When the user presses the image output start key 621, the image processing unit 210 starts the image forming process of the output image based on the image data stored in the image memory 213 described above. When the user presses the print position adjustment key 622, the guidance screen shown in FIG. 3A is switched to the guidance screen shown in FIG.

As shown in FIG. 3B, the touch panel 620 displays a guidance screen for adjusting the print position. On the print position adjustment screen, a print position adjustment PG output key 623 that is an output button and a reader reading start key 624 that is a reading button can be selected on the touch panel unit 620.
When the CPU 201 detects that the print position adjustment PG output key 623 has been pressed by the user, the CPU 201 starts an image forming process for a print position adjustment chart, which will be described later. The printing position adjustment chart printed by the image forming unit 10 is placed on the reader 100 by the user. Here, when the user presses the reader reading start key 624, the CPU 201 starts a print position adjustment process described later. Note that the UI screen for adjusting the print position can also be entered from the key 617 for entering the user mode.

FIG. 4 is a diagram illustrating an example in which image patterns having different densities are printed on the same sheet.
4A is a sheet on which an image having a low density is printed, and FIG. 4B is a sheet on which an image having a high density is printed. The amount of expansion / contraction of the paper varies according to the amount of toner attached to the paper (toner adhesion amount). That is, the amount of expansion / contraction of the paper varies depending on the image density.
The dimensions of the respective sheets shown in FIGS. 4A and 4B are 40x> 41x and 40y> 41y, and the sheet length of the sheet having a lower density is longer. The reason is that when the image density is high, the toner aggregates in the fixing unit 107 and the paper shrinks.

FIG. 5 is an example of a print position adjustment chart output by pressing the print position adjustment PG output key 623 shown in FIG.
In FIG. 5, the density of images 840 to 843 can be switched in the range of 0 to FF (decimal number 256). The density of the images 840 to 843 is controlled by changing the print pattern by thinning out necessary bits from the 8 × 8 bit pattern as shown in FIGS.

(Print position adjustment chart)
FIG. 7 is a schematic diagram showing a print position adjustment chart used for print position adjustment.
In FIG. 7, a chart surface 800 represents the surface of a printed printing position adjustment chart. A chart back surface 801 represents the back surface of the print position adjustment chart. In this example, the image writing side in the direction in which the sheet is conveyed (sub-scanning direction) is the leading end side, and the image writing end side is the trailing end side, and the leading edge of the front surface, the trailing edge of the front surface, the leading edge of the back surface, and the leading edge of the back surface are 1 The printing position adjustment chart is read 4 times and the printing position is specified.
Marks 810 to 813 are guides (indexes) for positions where the operator places the print position adjustment chart on the reader 100. In this example, the colors of the marks 810 to 813 are set to red, blue, cyan, and magenta, thereby instructing the operator the order of reading the print position adjustment chart.
A mark 820 represents a mark printed at a specific position on the print position adjustment chart. Note that the mark 820 is formed of a color toner having a large difference in reflectance with respect to the paper.
In the present embodiment, it is assumed that the mark 820 is printed on white paper, and the mark 820 is formed of black toner. Marks 820 are printed in a total of eight places at the four corners of the front and back surfaces of the print position adjustment chart.
The mark 820 is arranged so as to be printed at a position away from the sheet edge by a certain distance if the printing position is ideal. By measuring the relative position of the mark 820 on the print position adjustment chart from the image data to be read, the amount of deviation of the print position can be obtained.
In this example, the portions represented by (A) to (R) shown in FIG. 7 are measured values for adjusting the printing position. (A) and (B) are the length in the sub-scanning direction and the length in the main scanning direction of the print position adjustment chart, respectively.
(C) to (R) are distances from the mark 820 to the nearest sheet edge. Ideally, it is assumed that printing is performed at a position 1 cm away from the corresponding paper edge. When a plurality of print position adjustment charts are output, average values are used for (C) to (R).

In addition, the reference mark 830 for combining the image data on the front end side and the image data on the rear end side after the front end side and the rear end side of the printing position adjustment chart are read separately is provided at two positions on the front and back sides, respectively. A total of four places are printed. A method of synthesizing separately read image data will be described with reference to FIG.
FIG. 8A is a diagram illustrating image data read by the reading unit 211 from the front end side of the surface of the print position adjustment chart. FIG. 8B is a diagram showing image data in which the rear end side is read by replacing the front end and the rear end of the surface of the print position adjustment chart by the reading unit 211.
The mark 830 is read both when the leading end side is read and when the trailing end side is read. The coordinates of the image center position of the mark 830 are (x01, y01) and (x02, y02), respectively, so that (x01, y01) and (x02, y02) in FIGS. 8 (a) and 8 (b) match. Then, the image data is synthesized to obtain the image data of FIG.

(Print position adjustment calculation)
Next, a method for calculating the printing position deviation amount will be described with reference to FIG.
FIG. 9 is a diagram illustrating an example of a result of reading the surface of the print position adjustment chart illustrated in FIG. Hereinafter, the right angle correction processing by the image processing unit 210 will be described.
9 (C) to (J), with the distance between the paper edges as a reference position, (x11, y11), (12, y12), (x13, y13) in the coordinate system shown in (a) of FIG. ), (X14, y14).
The image processing unit 210 connects each coordinate with a straight line. First, right angle correction is performed so that the straight line connecting (x11, y11) and (x12, y12) on the front end side of the image is perpendicular to the straight line connecting (x11, y11) and (x13, y13).
As shown in FIG. 9B, the image processing unit 210 calculates position coordinates (x101, y101) that are half the length of the straight line connecting the position coordinates (x11, y11) and the position coordinates (12, y12). As a reference, right angle correction is performed for the following positions. Specifically, the image processing unit 210 is configured so that the position coordinates (x11, y11) are the position coordinates (x21, y21) and the position coordinates (x12, y12) are the position coordinates (x22, y22) in the main scanning direction. The sub-scanning writing position of the image at each position is obtained and corrected. Similarly, the image processing unit 210 sets the position coordinates (x13, y13) at each position in the main scanning direction so that the position coordinates (x23, y23) and the position coordinates (x14, y14) become position coordinates (x24, y24). The sub-scan writing position of the image is obtained and corrected. Accordingly, the image processing unit 210 performs right angle correction on the read image.
Next, the image processing unit 210 connects the position coordinates (x21, y21) and (position coordinates x23, y23) with a straight line connecting the position coordinates (x23, y23) and the position coordinates (x24, y24) on the rear end side of the image. Perform trapezoidal correction to make it perpendicular to the straight line. As shown in FIG. 9C, the image processing unit 210 uses the position coordinates (x102, y102) that are half the length of the straight line connecting the position coordinates (x23, y23) and the position coordinates (x24, y24) as a reference. The keystone correction is performed for the following positions.
The image processing unit 210 uses the position coordinates (x23, y23) as the position coordinates (x33, y33) and the position coordinates (x24, y24) as the position coordinates (x34, y34). Keystone correction is performed by obtaining and correcting the magnification in the scanning direction.
Next, as shown in FIG. 9 (d), the image processing unit 210 has an ideal length of the image in the main scanning direction and the sub scanning direction (paper length of −2 cm in each of the main scanning direction and the sub scanning direction). In order to achieve this, a magnification correction is performed. Here, the image processing unit 210 obtains magnifications in the main scanning direction and the sub-scanning direction, and performs magnification correction at the following positions with reference to the center of the image. The image processing unit 210 performs magnification correction by correcting the position coordinates (x21, y21) to be position coordinates (x41, y41) and the position coordinates (x22, y22) to be position coordinates (42, y42). Similarly, the image processor 210 performs magnification correction by correcting the position coordinates (x33, y33) to be position coordinates (43, y43) and the position coordinates (x34, y34) to be position coordinates (x44, y44). Do.
Next, as shown in FIG. 9 (e), the image processing unit 210 includes a straight line connecting the paper position coordinates (x103, y103) and the position coordinates (x104, y104), and the image position coordinates (x41, y41). Skew correction is performed so that the straight line connecting the position coordinates (x43, y43) is parallel. Specifically, the image processing unit 210 rotates the image by θ2 with respect to the position coordinates (x41, y41), and corrects skew. Further, the image processing unit 210 is configured such that the position coordinates (x42, y42) are position coordinates (x52, y52), the position coordinates (x43, y43) are position coordinates (x53, y53), and the position coordinates (x44, y44) are position coordinates. The skew is corrected so as to be (x54, y54).
Next, as shown in FIG. 9F, position correction is performed by obtaining the writing positions in the main scanning direction and the sub-scanning direction so that the center of the image comes to the center of the sheet. By calculating and correcting in this way, the image is corrected as shown in FIG. Correct the back side in the same way.

FIG. 10 is a flowchart illustrating a method for controlling the image forming apparatus. Each step is realized by the CPU 201 executing the stored control program.
First, when the job starts, in S10, the CPU 201 executes processing for sampling the image density to be printed. Details of the process for sampling all the image densities to be printed will be described later.
After the process of sampling the image density scheduled for printing, the CPU 201 advances the process to S11.
In S11, the CPU 201 abbreviates the total average value density data (abbreviated as “X”) determined in S10 and an adjustment value density level (abbreviated as “Z”) stored in an image position adjustment process described later. ) To determine whether there is a difference of 30 or more which is a threshold value. Here, the number 30 is a value defined since the amount of paper shrinkage corresponding to the density described with reference to FIG.

If the CPU 201 determines that the density difference between X and Z is 30 or more in S11, the process proceeds to S12. In S12, the CPU 201 performs guidance display (display 625) using (A) of FIG. 3, and advances the process to S13. As described above, in this example, the CPU 201 can display a message recommending the print position adjustment process at an appropriate timing to start a job and notify the user of the message.
In step S13, the CPU 201 determines whether the image output start key 621 has been pressed according to the user operation. If the CPU 201 determines that the image output start key 621 has been pressed, the process proceeds to S16. In step S16, the CPU 201 starts an image data image forming operation corresponding to the job stored in the image memory 213, and ends this processing.

On the other hand, if the CPU 201 determines in step S13 that the image output start key 621 has not been pressed, the process proceeds to step S14. In S14, the CPU 201 displays the UI screen shown in FIG. 3B after the print position adjustment key 622 is pressed on the UI screen shown in FIG. Here, the CPU 201 determines whether or not the user has pressed the print position adjustment PG output key 623. If the CPU 201 determines that the print position adjustment PG output key 623 has been pressed, the process proceeds to S15. In S15, the CPU 201 executes an image position adjustment process described later, and advances the process to S16.
On the other hand, if the CPU 201 determines in step S14 that the print position adjustment PG output key 623 has not been pressed, the process returns to step S13.

[Process to sample the image density to be printed]
FIG. 11 is a flowchart illustrating a method for controlling the image forming apparatus. This example is a detailed procedure of the processing of sampling the image density scheduled to be printed in S10 shown in FIG. Each step is realized by the CPU 201 executing the stored control program.
In S30, the CPU 201 clears the total average value density data (X) that stores the average value of the image density to be printed in accordance with the job in the RAM 203 to 0, and advances the process to S31.
In step S31, the CPU 201 checks the image data stored in the image memory 213 in units of one page, and determines whether there is an image in the image memory 213 that has not been subjected to image processing by the image processing unit 210. If the CPU 201 determines that there is an image in the image memory 213 that has not been subjected to image processing by the image processing unit 210, the process proceeds to S32.
In S32, the image processing unit 210 performs image processing in units of pages, the video count unit 214 starts counting image density values, and the process proceeds to S33. In S33, the video count unit 214 calculates the average density for the image area (calculated value Y), and the process proceeds to S34. In S34, the calculated value Y is added to the total average value density data X to obtain an average value (X = (X + Y) / 2), and the process returns to S31.
If it is determined in S31 that there is no image in the image memory 213 for which the image processing unit 210 has not performed image processing, the process returns.

(Image position adjustment processing)
FIG. 12 is a flowchart illustrating a method for controlling the image forming apparatus. This example corresponds to the detailed procedure of the image position adjustment process of S15 shown in FIG. Each step is realized by the CPU 201 executing the stored control program.
In S50, the CPU 201 sets the density of the print position adjustment chart images 840 to 843 to the value of the total average value density data (X) described above, and generates a print position adjustment chart image in the image memory 213. The process proceeds to S51. In S51, the CPU 201 starts the image forming operation of the image forming apparatus 10, and advances the process to S52.
In S52, the CPU 201 sets the adjustment value density level (Z) to the value of the total average value density data X, and advances the process to S53. In S53, the CPU 201 waits for the reader reading start key 624 to be pressed, detects that the reader reading start key 624 has been pressed, and reads the print position adjustment chart image with the reader 100. Then, the process proceeds to S54. Proceed.
In step S54, the CPU 201 performs print position adjustment on the image data subjected to the image correction shown in FIG. 9, and returns the process.
According to the present embodiment, at the timing when the user starts the job, the print position adjustment is performed when the difference between the image density of the page printed by the job and the threshold density set in advance is equal to or greater than a predetermined value. Can be recommended. That is, the print position adjustment process can be started in accordance with the sheet length that shrinks according to the image density printed on the paper.
Furthermore, the image position deviation due to the image density factor determines the image density before the image formation, so that guidance can be issued at the timing when the print position adjustment is necessary. it can.
In addition, the density of the chart image for adjustment of print position adjustment is adjusted at a level corresponding to the image density where image formation is scheduled to be performed. Printing position adjustment can be performed.

The present invention supplies a program that realizes one or more functions of the above-described embodiments to a system or apparatus via a network or a storage medium, and one or more processors in a computer of the system or apparatus read and execute the program This process can be realized. It can also be realized by a circuit (for example, ASIC) that realizes one or more functions.
Also, in the present embodiment, the job includes a print job received from a PC or the like and a job for reading and printing a document set on the image forming apparatus.
Furthermore, in secure printing, when a user selects and executes a job stored in the image forming apparatus, the image forming apparatus communicating with the driver on the PC side acquires information on the average image density of each page calculated on the PC side. Keep it. Accordingly, when the user moves to the image forming apparatus and selects and starts the accumulated job, the start of the print position adjustment process may be received as necessary.

10 Image forming unit
20 Operation unit
30 Document feeder
100 reader
201 CPU

Claims (8)

An image forming apparatus that thermally fixes an image transferred to a sheet based on image data specified by a job,
Adjusting means for adjusting a printing position of an image to be printed on the sheet;
Adjustment that accepts printing position adjustment by the adjusting means when the average value of image density calculated from image data specified by the job exceeds a predetermined threshold before starting image formation for the job Control means for displaying a button on the display means;
An image forming apparatus comprising:   2. The image according to claim 1, wherein when the adjustment button is pressed, the control unit displays an output button for receiving an output start of an adjustment chart for adjusting a printing position on the display unit. Forming equipment.   The image forming apparatus according to claim 1, wherein the control unit displays a reading button for reading an adjustment chart printed on a sheet on the display unit when the output button is pressed.   The image forming apparatus according to claim 1, wherein the predetermined threshold value is determined by a difference between a density value of a reference image printed on the sheet by the adjusting unit and the calculated image density.   2. The image forming apparatus according to claim 1, wherein the image density value calculated by the control unit is an average density value calculated from a value obtained by counting the density of image data specified by a job in units of pages. . Pattern printing means for printing an adjustment chart for adjusting a printing position on a sheet;
2. The image forming apparatus according to claim 1, further comprising a reading unit that reads the adjustment pattern image printed on the sheet by the pattern printing unit.   The image forming apparatus according to claim 6, wherein the pattern printing unit prints on the sheet a density adjustment chart according to an average image density calculated by the control unit. An image forming apparatus control method for thermally fixing an image transferred to a sheet based on image data specified by a job,
An adjustment step of adjusting a printing position for printing on the sheet;
An adjustment button for accepting print position adjustment by the adjustment step when an image density value calculated from image data specified by the job exceeds a predetermined threshold before starting image formation for the job A control step of displaying on the display means;
An image forming apparatus control method comprising:

Images