JP5083266B2 - Determination apparatus, image forming apparatus, and program - Google Patents

Description

  The present invention relates to a determination apparatus, an image forming apparatus, and a program.

  2. Description of the Related Art Conventionally, an image forming apparatus that forms an electrostatic latent image by charging after charging the surface of a photoconductor, and forming an image by attaching toner to the formed electrostatic latent image has been widely used. In such an image forming apparatus, as a means for exposing the surface of the photoreceptor, a type having a plurality of LEDs (hereinafter referred to as “LED head”) is known in addition to a type that scans a laser beam. Yes.

  For example, in Patent Document 1, a test pattern is printed on a sheet of paper in order to suppress light emission unevenness of an LED head (LPH) included in the image forming apparatus, the density of the test pattern is read from the sheet, and based on the read density distribution. A configuration for correcting the amount of light of the LED is shown. Specifically, when correcting the light amount, the positional relationship between the density data and the LED is determined by detecting and correcting the inclination of the test pattern based on the deviation of the two markers formed in the test pattern. The light amount is corrected with accuracy.

JP 2004-188665 A

  By the way, in an image forming apparatus provided with an LED head, the positional relationship between the LED head and the photosensitive member due to various factors such as a positional deviation at the time of assembling the LED head, a positional deviation that occurs after the assembling, variation in member accuracy, and member deterioration. It is conceivable that there will be a gap. When the optical path length from the LED to the surface of the photoconductor changes due to such a positional shift, the focus position of the LED shifts from the surface of the photoconductor, and the light from the LED does not converge on the surface of the photoconductor. As a result, there is a problem that the electrostatic latent image is not properly formed and the reproducibility of the image is lowered.

  In addition, in the above-mentioned patent document 1, in view of the problem that the test pattern is printed on the paper in a tilted state due to the LED head being inclined, both ends of the test pattern in the sub-scanning direction. Describes a configuration in which a marker is formed and the inclination of the test pattern is detected and corrected based on the deviation in the main scanning direction. However, the configuration described in Patent Document 1 is only for detecting the inclination of the test pattern. For example, when the LED head is inclined and the paper on which the test pattern is printed is skewed. The case where the LED head is placed cannot be distinguished, and it cannot be accurately determined whether or not the LED head is tilted. In the first place, since the LED head moves relatively in the sub-scanning direction due to the rotation of the photosensitive member, the position of each LED in the main scanning direction does not change even if the LED head is tilted, and is formed at both ends in the sub-scanning direction. Since the marked marker is not shifted in the main scanning direction, this method cannot even detect the inclination. Further, even if the markers are formed at both ends of the test pattern in the main scanning direction and the inclination is detected based on the deviation in the sub scanning direction, the LED head is not inclined in the sub scanning direction (for example, rotation of the photoconductor). It cannot be detected when it is inclined on a plane including the axis).

The present invention has been made in view of these problems, and an object of the present invention is to provide a determination apparatus, an image forming apparatus, and a program that can easily determine the positional deviation of the focal point of the exposure unit with respect to the surface of the photosensitive member. It is said.

  The determination apparatus according to claim 1 of the present invention, which has been made to achieve the above object, determines whether or not the focus position of the exposure means in the image forming apparatus is normal. Specifically, an image forming apparatus that forms an image by attaching a developer to an electrostatic latent image formed on the surface of the photoconductor by an exposure unit that exposes the surface of the photoconductor with a plurality of light emitting elements is an object. .

  In this determination apparatus, the density measurement result of the density patch representing the density of the plurality of levels formed by the image forming apparatus is such that the low density patch is thinner than the normal density and the high density patch is normal. A determination unit is provided that determines that the focus position of the exposure unit is not normal on the condition that the density characteristic is higher than the current density.

According to such a determination apparatus, it is possible to easily determine the positional deviation of the focus of the exposure unit with respect to the surface of the photoreceptor.
That is, although the density of the density patch may be shifted due to various factors, it is generally shifted in a certain direction as a whole (for example, a direction in which the density increases). On the other hand, the inventor of the present invention has found a density characteristic that the low density and the high density are shifted in different directions when the focus position of the exposure means is not normal (deviation).

  Specifically, a low-density image is represented by isolated dots, but the isolated dots are not properly formed when the position of the focus of the exposure unit is deviated. The concentration is lowered. On the contrary, a high density image is expressed by isolating the dotless portion, but the dotless portion is crushed due to factors such as the scattering of the developer, so that the density is higher than that in the normal state.

  That is, the low density patch has a density characteristic that is lighter than the normal density and the high density patch has a density higher than the normal density. Therefore, it is possible to easily determine the positional deviation of the focal point of the exposure means simply by detecting such density characteristics.

  Incidentally, as the density patch, a dedicated patch can be formed, but a density patch formed for other purposes can also be used. For example, if the image forming apparatus performs a calibration process for correcting image forming characteristics by forming density patches representing a plurality of levels of density and measuring the density, the method according to claim 2 The measurement result of the density patch formed for the calibration process may be used.

  According to such a determination apparatus, since the density patch for calibration processing is used for the determination of the positional deviation of the focus of the exposure unit, the density patch dedicated for determining the positional deviation of the focus is separate from the density patch for the calibration process. The processing time can be shortened as compared with the case of forming. Further, the amount of developer necessary for forming the density patch can be saved.

  Further, for example, in the determination apparatus according to claim 3, the determination means includes the above-described density characteristics (the low density patch is thinner than the normal density and the high density patch is higher than the normal density). If the image has a high density characteristic), an image for making the user visually recognize the density characteristic is formed, and whether or not the focus position of the exposure means is normal according to an instruction input from the user based on the image. Determine whether.

According to such a determination apparatus, the density characteristic in a state where the focus position of the exposure unit is shifted is
It is possible to prevent misjudgment even when it occurs by chance due to other factors.
For example, in the determination apparatus according to claim 4, whether the determination unit has a density characteristic based on an integral value of a difference between a measurement density line based on a measurement result and a normal density line based on a normal density. Determine whether.

According to such a determination apparatus, the density characteristic can be detected based on the overall tendency even when the measurement results have some variation.
Note that the determination apparatus of the present invention can be a component of an image forming apparatus, for example, as described in claim 5. That is, the image forming apparatus according to claim 5 forms an image by attaching a developer to the electrostatic latent image formed on the surface of the photosensitive member by an exposure unit that exposes the surface of the photosensitive member with a plurality of light emitting elements. An image forming apparatus that includes the determination device according to any one of claims 1 to 4.

  Moreover, according to the program of Claim 6, a computer can be functioned as a determination apparatus of Claim 1, Thereby, the effect mentioned above can be acquired.

1 is a side sectional view showing a schematic configuration of an image forming apparatus according to an embodiment. FIG. 3 is a side cross-sectional view illustrating an open state of a top cover of the image forming apparatus according to the embodiment. It is explanatory drawing about the structure of an internal sensor. 1 is a block diagram illustrating an electrical configuration of an image forming apparatus according to an embodiment. It is explanatory drawing about the shift | offset | difference of the positional relationship of a LED head and a photosensitive drum. It is explanatory drawing about the influence which the shift | offset | difference of the positional relationship of a LED head and a photosensitive drum has on an image. It is a graph which shows the relationship between input density and output density. It is explanatory drawing of a density patch. It is a flowchart of the position shift determination process of 1st Embodiment. It is explanatory drawing of the image for visual confirmation. It is an enlarged view of a low density part confirmation image. It is an enlarged view of a high density part confirmation image. It is a flowchart of the position shift determination process of 2nd Embodiment. It is explanatory drawing of the process of 3rd Embodiment, (A) is a flowchart of a patch determination process, (B) is a flowchart of a user determination process.

Embodiments to which the present invention is applied will be described below with reference to the drawings.
[1. First Embodiment]
First, the first embodiment will be described.

[1-1. overall structure]
FIG. 1 is a side sectional view showing a schematic configuration of an image forming apparatus 1 according to the first embodiment. In the following description, the left side in FIG. 1 is the front, and the near side in FIG. 1 is the right.

The image forming apparatus 1 is a direct transfer tandem type color printer, and includes a substantially box-shaped housing 2 as shown in FIG. A front cover 3 is provided on the front surface of the housing 2. A paper discharge tray 5A on which paper 4 as a recording medium after image formation is stacked is formed on the upper surface of the housing 2, and the paper discharge tray 5A is provided integrally so that the image forming apparatus 1 is located upward. The top cover 5 is provided so as to be openable and closable around the upper rear end of the image forming apparatus 1 (see FIG. 2). By opening the top cover 5, an image forming unit 30 and a belt unit 20 to be described later can be drawn upward from the inside of the housing 2.

  A paper feed tray 7 that accommodates paper 4 for forming an image is attached to the lower portion of the housing 2 so as to be able to be drawn forward. A pressure plate (not shown) that can be tilted so as to stack and support the paper 4 and lift the front end side of the paper 4 is provided in the paper feed tray 7. Further, a paper feed roller 11 that conveys the paper 4 is provided at a position above the front end of the paper feed tray 7, and a paper that is conveyed by the paper feed roller 11 on the downstream side in the paper conveyance direction by the paper feed roller 11. A separation roller 12 and a separation pad 13 are provided for separating the four pieces one by one.

  The uppermost sheet 4 in the sheet feeding tray 7 is separated one by one by the separation roller 12 and further conveyed while being sandwiched between a paper dust removing roller 14 and a counter roller 15, and a pair of registration rollers 16, Sent between 17. The registration rollers 16 and 17 send the paper 4 onto the rear belt unit 20 at a predetermined timing.

  The belt unit 20 is attachable to and detachable from the housing 2, and a conveyor belt 23 (a so-called transfer conveyor belt) is installed horizontally between a belt driving roller 21 and a tension roller 22 that are spaced apart from each other. ). The transport belt 23 is an endless belt made of a resin material such as polycarbonate, and the paper placed on the upper surface thereof is circulated in the clockwise direction in FIG. 1 when the rear belt drive roller 21 is rotationally driven. 4 is conveyed backward.

  Inside the conveyance belt 23, four transfer rollers 24 arranged to face each photosensitive drum 31 included in the image forming unit 30 to be described later are arranged at regular intervals in the front-rear direction, and a transfer corresponding to each photosensitive drum 31. The conveyance belt 23 is sandwiched between the rollers 24. When transferring a toner image, which will be described later, a transfer bias is applied between the transfer roller 24 and the photosensitive drum 31, and a predetermined amount of transfer current is applied.

  The image forming unit 30 is paired with four LED heads 40 that expose the surface of the photosensitive drum 31, and corresponds to each color of black (K), yellow (Y), magenta (M), and cyan (C) from the front. The image forming unit 30 and the LED head 40 are arranged in series along the conveyance direction of the paper 4. The LED head 40 includes a plurality of LEDs arranged in a line along the main scanning direction (left-right direction), and a lens (optical system) that collects irradiation light from the LEDs on the surface of the photosensitive drum 31.

  Each image forming unit 30 includes a photosensitive drum 31, a toner storage chamber 33, a developing roller 35, and the like. The photosensitive drum 31 includes a grounded metal drum main body, and is configured by covering the surface layer with a positively chargeable photosensitive layer. The surface of the photosensitive drum 31 is uniformly positively charged by a charging wire (not shown) at the time of rotation, and then exposed to a plurality of LEDs arranged in a row at the lower end of the LED head 40, so that the sheet 4 is exposed. An electrostatic latent image corresponding to the image to be formed is formed.

Here, print data representing an image to be formed on the paper 4 (image for printing) is transmitted from, for example, an external personal computer. Then, the image forming apparatus 1 according to the present embodiment converts print data (256-gradation image data expressed in the RGB color system in this embodiment) transmitted from the outside into a CMYK table corresponding to the toner color. A color conversion process for converting to color image data is performed. Further, binarization processing is performed to binarize the image data after color conversion processing (256-level CMYK data) and generate binary image data of each color of CMYK. In this binarization processing, for each pixel of the image represented by the image data, an input level (0 to 255) that is the pixel value and a threshold value of a dither matrix (1 to 255) prepared in advance are set. If the input level is greater than or equal to the threshold value, the dot at that location is turned on, and if the input level is less than the threshold value, the dot at that location is turned off. Based on the binary image data of each color generated in this way, an image represented by the binary image data is formed as an electrostatic latent image on the surface of the photosensitive drum 31 by the LED head 40 corresponding to each color.

  In the toner storage chamber 33, positively chargeable nonmagnetic one-component toners of CMYK colors are stored as developers. The toner stored in the toner storage chamber 33 is positively frictionally charged by the rotation of the developing roller 35 or the like, and is carried on the developing roller 35 as a thin layer having a constant thickness. Next, the electrostatic latent toner formed on the surface of the photosensitive drum 31 when the positively charged toner carried on the developing roller 35 comes into contact with the photosensitive drum 31 by the rotation of the developing roller 35. Supplied to the image. As a result, the electrostatic latent image on the photosensitive drum 31 is visualized, and a toner image (a visible image formed by the toner) in which toner is attached only to the exposed portion is carried on the surface of the photosensitive drum 31. The

  Thereafter, the toner image carried on the surface of each photosensitive drum 31 is sequentially applied to the paper 4 by the transfer current when the paper 4 conveyed by the conveyance belt 23 passes between the photosensitive drum 31 and the transfer roller 24. Transcribed. The paper 4 on which the color image is formed by transferring the toner images of the respective colors in this manner is then conveyed to the fixing device 50.

  The fixing device 50 is disposed behind the conveyance belt 23 in the housing 2. The fixing device 50 includes a heating roller 51 that is rotationally driven with a heat source such as a halogen lamp, and a pressure roller 52 that is disposed below the heating roller 51 so as to face the heating roller 51 and is driven to rotate. It has. In the fixing device 50, the toner image (color image) is fixed to the paper 4 by heating the paper 4 on which the toner image of each color is transferred while being nipped and conveyed by the heating roller 51 and the pressure roller 52. . The sheet 4 on which the toner image is fixed is further conveyed by a conveying roller 53 disposed obliquely above and behind the fixing device 50, and is discharged by the discharge roller 54 provided on the upper portion of the housing 2. It is discharged onto the tray 5A.

  In addition, an internal sensor 60 is provided at a position facing the surface of the conveyor belt 23 obliquely below the belt driving roller 21. The internal sensor 60 detects the density patch P or the like when the density patch P (see FIG. 3) or the like is formed on the transport belt 23 by the image forming unit 30. That is, the image forming apparatus 1 forms density patches P representing the density of multiple levels of CMYK colors on the conveyance belt 23, and corrects the image forming characteristics based on the measurement results obtained by measuring the density of the density patches P with the internal sensor 60. A well-known calibration process is executed. Further, a well-known belt cleaner 99 for erasing density patches P and the like formed on the surface of the conveyor belt 23 abuts on the lower surface of the conveyor belt 23 installed between the belt driving roller 21 and the tension roller 22. ing.

  As shown in FIG. 2, the top cover 5 rotates around a shaft 5 </ b> B disposed at the rear end thereof in the left-right direction (that is, the direction orthogonal to the moving direction of the conveyor belt 23). The four LED heads 40 are slidably connected to the lower surface via connection links (not shown). Therefore, by opening the top cover 5, each LED head 40 can be separated from the photosensitive drum 31 as shown in FIG. 2, and by closing the top cover 5, each LED head as shown in FIG. 40 can be disposed at a position facing the photosensitive drum 31.

  As shown in FIG. 3A, the internal sensor 60 is provided in the vicinity of one end portion of the conveyor belt 23 in the left-right direction so as to face the lower surface of the conveyor belt 23 folded back by the belt driving roller 21. Yes. Note that the internal sensor 60 may be disposed opposite to the conveyor belt 23 that is curved along the surface of the belt driving roller 21 as shown in FIG.

[1-2. Electrical configuration]
Next, the electrical configuration of the image forming apparatus 1 will be described with reference to the block diagram of FIG. In addition, illustration and description are abbreviate | omitted about a structure with little relation with the characteristic part of this invention.

As shown in FIG. 1, the image forming apparatus 1 includes a control unit 70, an operation unit 71, a display unit 72, a communication unit 73, and a storage unit 74 in addition to the LED head 40 and the internal sensor 60 described above.
The control unit 70 is a computer that comprehensively controls each unit of the image forming apparatus 1 and includes a CPU, a ROM, a RAM, and the like. The CPU executes a later-described positional deviation determination process (FIG. 9) according to a program stored in the ROM.

The operation unit 71 is an input device for inputting a command by an external operation from a user, and includes various operation buttons.
The display unit 72 is an output device for displaying various information as an image that can be visually recognized by the user, and a small liquid crystal display is used.

The communication unit 73 is an interface for performing data communication with an external device (in this embodiment, the personal computer 80).
The storage unit 74 is a nonvolatile storage device that can rewrite stored data, and a flash memory is used in this embodiment.

[1-3. Overview of processing]
Next, an outline of processing executed by the image forming apparatus 1 of the first embodiment will be described.
In the image forming apparatus 1, the LED head 40 and the photosensitive drum 31 are caused by various factors such as a position shift when the LED head 40 is assembled, a position shift caused by opening and closing the top cover 5, a variation in member accuracy, a member deterioration, and the like. It is conceivable that there is a deviation in the positional relationship between

  5A and 5B show a normal state in which the positional relationship between the LED head 40 and the photosensitive drum 31 is not displaced (hereinafter referred to as “the state without positional displacement”) viewed from the front and above. It is a schematic diagram. On the other hand, FIGS. 5C and 5D show a state in which the positional relationship between the LED head 40 and the photosensitive drum 31 is shifted (hereinafter referred to as “the state with positional shift”) as viewed from the front and above. It is a schematic diagram.

  When there is a positional deviation, the optical path lengths L1 and L2 (FIG. 5C) from the LED disposed at the lower end of the LED head 40 to the surface of the photosensitive drum 31 are normal optical paths when there is no positional deviation. It may be different from the length L0 (FIG. 5A). When the optical path length changes in this way, the focus of the LED is deviated from the surface of the photosensitive drum 31, and the light from the LED does not converge on the surface of the photosensitive drum 31, so that the electrostatic latent image is not properly formed. . Specifically, the voltage change on the surface of the photosensitive drum 31 becomes dull, and the toner does not adhere correctly or adheres to a location outside the target.

6A to 6D are enlarged views of images printed with only black toner. Among these, FIG. 6A is an enlarged image of a light portion (low-density image) of the image without a positional shift, and FIG. 6B is a light portion of the image with a positional shift. It is an enlarged image. On the other hand, FIG. 6C is an enlarged image of a dark portion (high-density image) of the image in a state without misalignment, and FIG.
Is an enlarged image of a dark part in a state where there is a displacement.

  As shown in these figures, in the light portion of the image, isolated dots that are clearly formed in a state without misalignment (FIG. 6A) are correctly formed in a state with misalignment (FIG. 6B). It becomes a state of being blurred without being. On the other hand, in the dark part of the image, the dot-free (blank) portion that is clearly formed in the state without misalignment (FIG. 6C), and the toner in the state with misalignment (FIG. 6D). Crushing occurs due to factors such as scattering.

  Therefore, as shown in FIG. 7, the output density (measured density of the actually formed toner image) with respect to the input density (density based on the binary image data) is not misaligned when there is misalignment (dotted line). Compared to the above state (solid line), the density characteristic of the light part decreases and the density of the dark part increases conversely (hereinafter referred to as “position shift characteristic”).

  Therefore, the image forming apparatus 1 according to the present embodiment determines whether the focus position of the LED head 40 is normal (whether the position is not misaligned or is not misaligned). The determination is made for each of the LED head 40 and the photosensitive drum 31 (for each color of CMYK).

  Here, the determination of whether there is no misalignment or a misalignment is made based on whether the measurement result of the density patch P in the calibration process has misalignment characteristics. That is, the calibration process is performed at the timing when the power of the image forming apparatus 1 is turned on. In this calibration process, as shown in FIG. In addition, a toner image representing the density of a plurality of levels (5 levels in this example) of each color of CMYK is formed as a density patch P. Then, the density of the formed density patch P is measured by the internal sensor 60, and the image forming characteristics are corrected based on the measurement result. In this embodiment, it is determined whether or not the measurement result has a misregistration characteristic (in other words, using the density patch P formed for the calibration process), and there is misregistration. The state of is determined. Therefore, the determination of the presence / absence of the positional deviation is performed in accordance with the calibration processing execution timing (timing when the power is turned on).

  Note that the execution timing of the calibration process is merely an example, and other timings may be used. In particular, in the image forming apparatus 1 of the present embodiment, the LED head 40 is swingably connected to the lower surface of the top cover 5 as described above, and the position of the LED head 40 is shifted by opening and closing the top cover 5. Since there is a possibility, it is also effective to set the timing at which the top cover 5 is closed instead of (or at the same time as) the timing when the power is turned on. Moreover, it is good also as the timing instruct | indicated by the user.

  As shown in FIG. 8A, the density patch P represents a solid image of each color of CMYK in five levels of density of 20%, 40%, 60%, 80%, and 100%. This is binarized with a dither matrix for density patches shown in (B). The binarized dot arrangement pattern for each density is as shown in FIGS. 8C to 8G. For example, if the density patch P has a density of 20%, “1” in FIG. A pattern in which toner adheres to a portion is arranged in a pattern corresponding to the size of the density patch P.

Then, when the measurement result of the density patch P has the position shift characteristic, it is determined that there is a position shift. Specifically, for each CMYK color, each measurement result of five levels of density is linearly interpolated to obtain a measurement density line (dotted line shown in FIG. 7) based on the measurement result. Then, this measured density line and a normal density line based on the density without misalignment (normal) (
The solid line shown in FIG. 7 is stored in advance as a determination reference value. ) To determine whether or not it has misalignment characteristics.

  For example, the integrated value of the value obtained by subtracting the “value on the measured density line” from the “value on the normal density line” in the range of the input density less than 50% with the input density of 50% as a boundary (in other words, the normal density line From the “value on the measured density line” to the “normal density line” in the range where the input density is 50% or more. When the condition that the integral value (in other words, the area of the region formed between the measurement density line and the normal density line) is less than or equal to the second determination reference value is satisfied, It determines with having a position shift characteristic. By determining with the integral value in this way, it is possible to detect the misregistration characteristic based on the overall tendency even when the measurement results have some variation.

  Note that the value of the output density relative to the input density may deviate due to secular changes (such as changes over time or changes due to the operation amount), but it is normal for the output density to change in the overall increase direction. . Therefore, a change in output density due to a secular change and a change in output density due to a positional deviation of the LED head 40 can be distinguished based on characteristics of how the output density is shifted.

[1-4. Specific processing procedure]
Next, a specific processing procedure executed by the control unit 70 to realize the above-described processing will be described.

First, the misregistration determination process executed by the control unit 70 when the power of the image forming apparatus 1 is turned on will be described with reference to the flowchart of FIG.
When the positional deviation determination process is started, the control unit 70 first performs a process for forming the density patch P (FIG. 8A) on the transport belt 23 in S101.

  Subsequently, in S102, a process for measuring the density of the density patch P formed on the transport belt 23 in S101 by the internal sensor 60 is performed. Note that the processing of S101 and S102 is processing executed as calibration processing.

  Subsequently, in S103, one unprocessed color (a color that has not been determined in S105 or S106, which will be described later, and is specified in S108, which will be described later) from the four CMYK colors, is selected. Analyze the measurement results for color. Specifically, as described above, a calculation process is performed in which the measurement result is linearly interpolated to obtain an integral value.

Subsequently, in S104, it is determined whether or not the measurement result of the density patch P has a positional deviation characteristic.
If it is determined in S104 that the position deviation characteristic is not provided, the process proceeds to S105, and it is determined that there is no position deviation. Thereafter, the process proceeds to S107.

On the other hand, if it is determined in S104 that the position shift characteristic is present, the process proceeds to S106, and it is determined that there is a position shift. Thereafter, the process proceeds to S107.
In S107, it is determined whether or not the determination has been completed for all four colors of CMYK.

If it is determined in S107 that the determination has not been completed for all four colors (the undetermined color exists), the process proceeds to S108, and the determination target color is changed to the next color (the undetermined color). Change to one of them). Thereafter, the process returns to S103.

On the other hand, if it is determined in S107 that the determination has been completed for all four colors, the positional deviation determination process ends.
[1-5. effect]
As described above, in the image forming apparatus 1 of the first embodiment, the density of the density patch P is measured, and when the measurement result has the misregistration characteristic (S104: YES), the focus position of the LED head 40 Is not normal (there is a position misalignment) (S106). For this reason, it is possible to easily determine the position shift of the focus of the LED head 40 with respect to the surface of the photosensitive drum 31 (the state with position shift).

  Further, since the density patch P for calibration processing is diverted for determination of the focal position deviation of the LED head 40, a density patch dedicated for focal position deviation determination is formed separately from the density patch P for calibration processing. Compared to the case, the processing time can be shortened. In addition, the amount of toner required to form the density patch can be saved.

  In addition, since the reproducibility of the image is deteriorated in a state where there is misalignment, it is preferable to take measures to prevent a decrease in reproducibility when it is determined that there is a misalignment. The method is not particularly limited. For example, the position of the LED head 40 may be finely adjusted, or the binary image data may be adjusted.

[1-6. Correspondence with Claims]
In the first embodiment, the photosensitive drum 31 corresponds to a photosensitive member, and the LED head 40 corresponds to an exposure unit (LED is a light emitting element). Moreover, the control part 70 which performs the process of S103-S108 is equivalent to a determination means.

[2. Second Embodiment]
Next, a second embodiment will be described.
[2-1. overall structure]
The image forming apparatus 1 of the second embodiment is different from the image forming apparatus 1 of the first embodiment in the content of the misregistration determination process executed by the control unit 70. In addition, since the basic configuration is the same as that of the first embodiment, the same reference numerals are used for the common parts and the description thereof is omitted, and differences will be mainly described.

[2-2. Overview of processing]
An outline of processing executed in the image forming apparatus 1 of the second embodiment will be described.
The image forming apparatus 1 according to the second embodiment is different from the image forming apparatus 1 according to the first embodiment in a determination method for determining which of the state without misalignment and the state with misalignment. In other words, in the image forming apparatus 1 according to the first embodiment, the determination as to which of the no-shift state and the mis-position state is made depends on whether the measurement result of the density patch P has a mis-position characteristic. Like to do.

  On the other hand, in the image forming apparatus 1 of the second embodiment, when the measurement result of the density patch P has the misregistration characteristic, the visual confirmation image 100 (FIG. 10) for making the user visually recognize the misregistration characteristic. After printing on the paper 4 and making the user visually recognize the visual confirmation image 100, the determination result is input. That is, the user is asked to confirm.

  As shown in FIG. 10, the visual confirmation image 100 includes CMYK low-density portion confirmation images 110C, 110M, 110Y, and 110K for visually confirming the printing state of the low-density image, and the high-density image printing state. For high density portion confirmation images 120C, 120M, 120Y, and 120K for each color of CMYK. Note that the four low-density portion confirmation images 110C, 110M, 110Y, and 110K are all the same image, and are different only in color. The same applies to the high-density portion confirmation images 120C, 120M, 120Y, and 120K.

FIG. 11 is an enlarged view of the low density portion confirmation image 110K. In addition, although the low density part confirmation image 110K of black is illustrated here, the same applies to other colors.
In the low-concentration portion confirmation image 110K, four confirmation marks 111 each having four visual dots 112 arranged in a square frame 113 are arranged vertically and horizontally (16 in total). The size of the visual dot 112 in the mark 111 differs depending on the arrangement position of the confirmation mark 111.

  Specifically, the horizontal width of the visual dot 112 in the confirmation mark 111 arranged in the leftmost column (“× 1” column) is one dot, and the horizontal width is shifted every time the column is shifted to the right. It increases by one dot, and in the rightmost column (“× 4” column), the horizontal width becomes four dots. Similarly, the vertical width of the visual dot 112 in the confirmation mark 111 arranged in the uppermost row (“× 1” row) is one dot, and the vertical width every time the row is shifted downward. Increases by one dot, and the vertical width of the bottom row (“× 4” row) is four dots. That is, 16 patterns of confirmation marks 111 are arranged in which the size of the visual dot 112 is one dot each vertically and horizontally and four dots vertically and horizontally.

  The square frame 113 in each confirmation mark 111 has slits 114 formed at the center positions of the four sides, and the width (vertical width or horizontal width) of the slit 114 is the vertical width of the visual dot 112 or It corresponds to the width.

  On the other hand, FIG. 12 is an enlarged view of the high density portion confirmation image 120K. Since the high density portion confirmation image 120K is simply a reverse of the low density portion confirmation image 110K, a detailed description thereof will be omitted.

  Based on such 16 patterns of confirmation marks 111, it is possible to determine the formation state of isolated dots in a low-density image and the formation state of no-dot (blank) portion in a high-density image relatively visually. For example, let the user determine how large the isolated dot and no-dot portion can be seen, and if both the isolated dot and no-dot portion cannot be confirmed with a size of 2 dots × 2 dots, determine that the position is shifted. It becomes possible.

[2-3. Specific processing procedure]
Next, the displacement determination process executed by the control unit 70 instead of the displacement determination process (FIG. 9) of the first embodiment will be described with reference to the flowchart of FIG. This misregistration determination process is executed when the image forming apparatus 1 is turned on, as in the first embodiment.

When the position deviation determination process is started, the control unit 70 first performs a process for forming the density patch P (FIG. 8A) on the transport belt 23 in S201.
Subsequently, in S202, processing for measuring the density of the density patch P formed on the conveyance belt 23 in S201 by the internal sensor 60 is performed. Note that the processing of S201 and S202 is processing executed as calibration processing.

Subsequently, in S203, the measurement result for each color of CMYK is analyzed. Specifically, as described above, a calculation process is performed in which the measurement result is linearly interpolated to obtain an integral value.
Subsequently, in S204, it is determined whether or not there is a color having a misregistration characteristic in the measurement result of the density patch P of each color of CMYK.

If it is determined in S204 that there is no color having the position shift characteristic, the position shift determination process is terminated.
On the other hand, if it is determined in S204 that even one color having the misregistration characteristic exists, the process proceeds to S205, and a process of printing the visual confirmation image 100 on the paper 4 is performed.

  Subsequently, in S <b> 206, a determination result input screen that prompts the user to input a determination result of the visual confirmation image 100 (input operation on the operation unit 71) is displayed on the display unit 72. Specifically, a visual determination result (“with deviation” or “without deviation”) is sequentially input for each color of CMYK, and an undetermined color (determination in S208 or S209 described later is performed). The second and subsequent times are specified in S211 to be described later), and the input of the determination result for the color is prompted.

Subsequently, in S207, it is determined whether or not the determination result input by the user on the determination result input screen displayed on the display unit 72 in S206 is “with deviation”.
If it is determined in S207 that the determination result is not “displacement”, the process proceeds to S208, and it is determined that there is no displacement. Thereafter, the process proceeds to S210.

On the other hand, if it is determined in S207 that the determination result is “with deviation”, the process proceeds to S209, where it is determined that there is a position deviation. Thereafter, the process proceeds to S210.
In S210, it is determined whether determination results have been input for all four colors of CMYK.

  If it is determined in S210 that determination results have not been input for all four colors (there is an uninput color), the process proceeds to S211 and the input color is changed to the next color (the uninput color). Change to one of them). Thereafter, the process returns to S206.

On the other hand, if it is determined in S210 that the determination results have been input for all four colors, the positional deviation determination process ends.
[2-4. effect]
As described above, in the image forming apparatus 1 according to the second embodiment, the density of the density patch P is measured, and the focus of the LED head 40 is obtained on the condition that the measurement result has a misregistration characteristic (S204: YES). Is not normal (there is a position misalignment) (S209). Specifically, when the measurement result has a misregistration characteristic (S204: YES), the visual confirmation image 100 is printed on the paper 4, and an instruction (determination) input from the user based on the visual confirmation image 100 is determined. According to the result), the presence / absence of positional deviation is determined (S205 to S209).

According to the image forming apparatus 1 of the second embodiment, the same effect as that of the image forming apparatus 1 of the first embodiment can be obtained. In particular, in the image forming apparatus 1 according to the second embodiment, since the user is surely determined whether or not there is misalignment, even when misalignment characteristics are accidentally caused by other factors. It becomes possible to prevent erroneous determination.

[2-5. Correspondence with Claims]
In the second embodiment, the control unit 70 that executes the processes of S203 to S211 corresponds to a determination unit.

[3. Third Embodiment]
Next, a third embodiment will be described.
[3-1. overall structure]
The image forming apparatus 1 according to the third embodiment performs a patch determination process (FIG. 14A) and a user determination process (FIG. 14B) instead of the misregistration determination process (FIG. 13) according to the second embodiment. This is different from the image forming apparatus 1 of the second embodiment. In addition, since the basic configuration is the same as that of the second embodiment, the same reference numerals are used for the common parts and the description thereof is omitted, and differences will be mainly described.

[3-2. Overview of processing]
The patch determination processing (S301 to S305) executed in the third embodiment is obtained by removing the processing of S206 to S211 from the positional deviation determination processing (S201 to S211) of the second embodiment. On the other hand, the user determination process (S401 to S406) executed in the third embodiment is the same as the process of S206 to S211 in the positional deviation determination process (S201 to S211) of the second embodiment. That is, the image forming apparatus 1 according to the third embodiment performs the positional deviation determination process (FIG. 13) according to the second embodiment as a patch determination process (FIG. 14A) and a user determination process (FIG. 14B). Run in two parts.

  Specifically, the user determination process is executed at an arbitrary timing specified by the user (for example, triggered by an operation for selecting an input of a determination result from a menu displayed on the display unit 72). Therefore, even when the visual confirmation image 100 is printed in the patch determination process, the input of the determination result is not forced, which is different from the second embodiment. A description of the specific processing procedure is omitted.

[3-3. effect]
According to the image forming apparatus 1 of the third embodiment described above, the same effects as those of the image forming apparatus 1 of the second embodiment can be obtained. In particular, in the image forming apparatus 1 according to the third embodiment, even when the visual confirmation image 100 is printed, it is not necessary to input a determination result, so that the user is not forced to perform complicated operations. Can do.

[3-4. Correspondence with Claims]
In the third embodiment, the control unit 70 that executes the processes of S303 to S305 and S401 to S406 corresponds to a determination unit.

[4. Other forms]
As mentioned above, although embodiment of this invention was described, it cannot be overemphasized that this invention can take a various form, without being limited to the said embodiment.

  For example, in each of the embodiments described above, the density patch P for calibration processing is used for determining whether or not there is a positional deviation. However, the present invention is not limited to this, and the density patch P for calibration processing is not limited thereto. Alternatively, a dedicated density patch may be formed.

Further, in each of the above embodiments, the image forming apparatus 1 configured to form the density patch P on the transport belt 23 is illustrated, but the present invention is not limited to this, and may be configured to be formed on the intermediate transfer belt. Further, it may be formed on a recording medium such as paper 4.

  Furthermore, in each of the above-described embodiments, the image forming apparatus 1 that forms a color image using a plurality of LED heads 40 has been exemplified. However, the present invention is not limited to this. For example, an image is formed using only one LED head. It may be an image forming apparatus to be formed.

On the other hand, in each said embodiment, although LED was illustrated as a light emitting element of this invention, it is not limited to this, If it has the same function, it is applicable.
In addition, in each of the embodiments described above, the case where the determination device of the present invention is used as a constituent element of the image forming apparatus 1 is illustrated, but the present invention is not limited to this and may be separate from the image forming apparatus. Good. For example, a personal computer in which a printer driver corresponding to the image forming apparatus is installed can be caused to function as the determination apparatus of the present invention. Specifically, if the measurement result of the density patch P is transmitted from the image forming apparatus 1 to the personal computer and the determination based on the measurement result is performed on the personal computer side, the same process as the above-described misregistration determination process. Can be executed on a personal computer.

  DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 2 ... Housing, 4 ... Paper, 5 ... Top cover, 23 ... Conveyor belt, 24 ... Transfer roller, 30 ... Image forming unit, 31 ... Photosensitive drum, 33 ... Toner storage chamber, 35 ... Development Roller, 40 ... LED head, 50 ... fixer, 60 ... internal sensor, 70 ... control unit, 71 ... operation unit, 72 ... display unit, 73 ... communication unit, 74 ... storage unit, 80 ... personal computer, 99 ... belt Cleaner, 100 ... Visual confirmation image, 110C, 110M, 110Y, 110K ... Low density portion confirmation image, 111 ... Confirmation mark, 112 ... Visual dot, 113 ... Frame, 114 ... Slit, 120C, 120M, 120Y, 120K ... High density part confirmation image, P ... density patch

Claims (6)

The position of the focus of the exposure means in an image forming apparatus that forms an image by attaching a developer to the electrostatic latent image formed on the surface of the photoreceptor by an exposure means that exposes the surface of the photoreceptor with a plurality of light emitting elements. Is a determination device for determining whether or not is normal,
The density measurement results of density patches representing multiple levels of density formed by the image forming apparatus show that the low density patch is thinner than the normal density and the high density patch is darker than the normal density. A determination apparatus comprising: determination means for determining that the position of the focal point of the exposure means is not normal on condition that the image has density characteristics. The image forming apparatus performs a calibration process for correcting image forming characteristics by forming density patches representing a plurality of levels of density and measuring the density.
The determination apparatus according to claim 1, wherein the measurement result is a measurement result of a density patch formed for the calibration process. When the measurement result has the density characteristic, the determination unit forms an image for allowing the user to visually recognize the density characteristic, and in accordance with an instruction input from the user based on the image, the focus of the exposure unit It is determined whether the position of is normal. The determination apparatus according to claim 1 or 2, wherein: The determination means determines whether or not the density characteristic is present based on an integrated value of a difference between a measurement density line based on the measurement result and a normal density line based on a normal density. The determination apparatus according to any one of claims 1 to 3. An image forming apparatus for forming an image by attaching a developer to an electrostatic latent image formed on a surface of the photoreceptor by an exposure unit that exposes the surface of the photoreceptor with a plurality of light emitting elements,
An image forming apparatus comprising the determination device according to any one of claims 1 to 4. The position of the focus of the exposure means in an image forming apparatus that forms an image by attaching a developer to the electrostatic latent image formed on the surface of the photoreceptor by an exposure means that exposes the surface of the photoreceptor with a plurality of light emitting elements. Is a program for causing a computer to function as a determination device for determining whether or not is normal,
The density measurement results of density patches representing multiple levels of density formed by the image forming apparatus show that the low density patch is thinner than the normal density and the high density patch is darker than the normal density. A program that causes a computer to function as a determination unit that determines that the position of the focal point of the exposure unit is not normal on the condition that it has density characteristics.