JP5092514B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus.

  2. Description of the Related Art In recent years, image forming apparatuses that perform image formation using an electrophotographic method have been widely used as printers, copiers, facsimile machines, and the like.

  In an electrophotographic image forming apparatus, characteristics of the apparatus, particularly gamma characteristics, change due to environmental changes such as temperature and humidity, changes with time, and the like, and as a result, gradation may be significantly reduced. Thus, in general, an electrophotographic image forming apparatus has a function of correcting image forming conditions including gradation correction. That is, in order to maintain a high-quality image output, a toner patch image is formed on an image carrier such as an intermediate transfer belt or a recording medium at a predetermined timing, and the toner patch image is detected by a sensor or the like. The image forming conditions such as gradation correction, density adjustment, and color reproducibility correction are corrected based on the detection result.

  By the way, when correcting image forming conditions such as tone correction, it is desirable to form and detect toner patch images of a plurality of tone levels (density) in order to perform the correction with high accuracy. . This is because if the number of detected samples increases, the gamma characteristics and the like of the apparatus can be accurately grasped. However, an increase in the number of toner patch images formed leads to a longer processing time and an increase in toner consumption. For this reason, conventionally, it has been proposed to use a gradation patch image in which the gradation level changes stepwise at a pitch smaller than the detection area width of the detection means as a toner patch image of a plurality of gradation levels ( For example, see Patent Document 1).

Japanese Patent Application Laid-Open No. 2004-77873

  However, in the conventional gradation patch image, since a plurality of gradation levels are mixed within the detection area width of the detection means, for example, the average value of the plurality of gradation levels is obtained. The result obtained from the tone level needs to be the detection result, so that the relative relationship between each tone level can be correctly grasped, but the density value (absolute value) of a certain tone level can always be correctly detected. Not necessarily. For example, since the sensor detection region including the edge of the gradation patch image includes a non-patch image portion (density value “0”) without toner, an error occurs in a calculation result including the portion. In addition, for example, the detection timing of the detection unit may be shifted due to some factor (such as an increase in processing load in the control unit at the timing), or the conveyance speed variation of the image carrier or the recording medium on which the gradation patch image is formed or the gradation When the formation size variation of the patch image occurs, an error is included in the relationship (gradient of the detection result) between the arrangement pitch of each gradation level and each gradation level value.

  Therefore, in the present invention, in order to improve the accuracy of image formation condition correction, while avoiding a long processing time and an increase in toner consumption, the gradation level detection result is accurately obtained even in such a case. An object of the present invention is to provide an image forming apparatus that can be obtained.

The present invention is an image forming apparatus devised to achieve the above object.
According to a first aspect of the present invention, there is provided an image holding member that holds an image on a surface and the surface moves in a predetermined direction, an image forming unit that forms an image on the surface of the image holding member, and the image forming unit includes the image An image formed on the surface of the holding body is detected, patch detection means having a predetermined detection width in the predetermined direction, and image forming conditions of the image forming means are controlled based on a detection result by the patch detection means. And a control unit for controlling the gradation level of the image forming unit in a stepwise manner so that a plurality of gradation levels exist within the predetermined detection width region width as a patch image detected by the patch detection unit. Forming a patch image having a gradation portion that changes and a single gradation level portion in which the gradation level does not change depending on the detection area width, and the control unit is configured to control the single gradation level portion that constitutes the patch image. Based on detection results An image forming apparatus which is characterized in that the correction to the detection result of the gradation portion constituting the patch image.
According to a second aspect of the present invention, in the image forming unit according to the first aspect, the image forming unit forms the gradation portion and the single gradation level portion separately from each other by a distance equal to or larger than the detection region width. Device.
The invention according to claim 3 is characterized in that the gradation portion and the single gradation level portion are configured with an interval longer than the detection width of the patch detection means. This is an image forming apparatus.
According to a fourth aspect of the present invention, in the image forming apparatus according to the first aspect, the gradation portion and the single gradation level portion are continuously formed.

According to the first aspect of the present invention, when density detection is performed using the gradation portion, there is an error between the detected density level and the density value of each gradation level of the patch image formed on the image carrier. Although it may occur, since the single gradation level portion is formed together, the detection result for the gradation portion is corrected based on the result of the density level detected for the single gradation level portion. This makes it possible to obtain each gradation level constituting the gradation portion with high accuracy.
In the invention according to claim 2, it is easy to separate the detection result for the gradation portion and the detection result for the single gradation level portion, and the gradation portion is based on the detection result for the single gradation level portion. The detection result can be corrected with high processing efficiency and accuracy.
In the invention according to claim 3, when detecting the single gradation level portion, it becomes possible to detect the gradation portion and the single gradation level portion in the entire area without being affected by the gradation portion. It can be done more easily.
In the invention which concerns on Claim 4, the increase in the area of the area | region for forming the patch image which has a gradation part and a single gradation level part can be suppressed. Further, through the suppression of the increase in the area of the region, the detection result for the patch image is less likely to receive the result of the speed fluctuation of the image carrier or the recording medium on which the patch image is formed.

  Hereinafter, an image forming apparatus according to the present invention will be described with reference to the drawings.

[Schematic configuration of image forming apparatus]
First, a schematic configuration of the image forming apparatus will be described.
FIG. 1 is an explanatory diagram schematically showing a schematic configuration example of an image forming apparatus according to the present invention.

  The image forming apparatus 1 shown in the figure is roughly configured to have functions as an image forming unit 10, a patch detecting unit 30, a detection result correcting unit 40, and an image forming condition correcting unit 50.

The image forming unit 10 is a function for forming an image through each process of charging → exposure → development → transfer → fixing. For this purpose, the image forming unit 10 includes a photosensitive drum 11 that is rotationally driven, a charger 12 that uniformly charges the surface of the photosensitive drum 11, and an electrostatic latent image on the surface of the photosensitive drum 11. An exposure device 13 for forming, a developing device 14 for developing a latent electrostatic image on the photosensitive drum 11 to form a toner image, and an intermediate transfer belt 15 that is formed in an endless belt and is circulated and driven at the same speed. A primary transfer device 16 for transferring the toner image on the photosensitive drum 11 onto the intermediate transfer belt 15, a cleaning device 17 for removing foreign matters such as residual toner and paper dust on the photosensitive drum 11, and an intermediate transfer A secondary transfer device 18 that transfers the toner image on the body belt 15 onto a medium P such as recording paper; a cleaning device 19 that removes foreign matter such as residual toner and paper dust on the intermediate transfer belt 15; and a toner image. Is transcription Is configured to include a fixing device 20 for fixing the transferred image on the medium P by performing the fixing processing by heat and pressure to the medium P after being, a.
In the illustrated example, the developing device 14 is of a rotary type that sequentially performs development of toner images of yellow (Y), magenta (M), cyan (C), and black (K) while rotating. However, a tandem type in which a photosensitive drum and a developing device corresponding to each color are arranged in parallel may be used.

In the image forming means 10 having such a configuration, the toner image formed on the intermediate transfer belt 15 includes a toner patch for correcting the image forming conditions in addition to the toner image corresponding to the output image on the medium P. There is a statue. As will be described in detail later, the toner patch image for image formation condition correction is configured to have a gradation portion and a single gradation level portion, and images such as density adjustment, color reproducibility correction, gradation correction, etc. Served to correct the forming conditions.
Here, the case where the toner patch image for image formation condition correction is a toner image formed on the intermediate transfer body belt 15 will be described as an example. However, as the toner patch image, the photosensitive drum 11 is used. Those formed above or formed on the intermediate transfer belt 15 and then transferred and fixed on the medium P may be used. In order to correct the image forming conditions, it is conceivable to use an electrostatic latent image formed on the photosensitive drum 11 instead of the toner image as a patch image for correcting the image forming conditions.
That is, the image forming unit 10 corrects the image forming condition on either the image carrier such as the photosensitive drum 11 or the intermediate transfer belt 15 or on the medium P such as copy paper, transfer paper, paper, or an OHP transparent sheet. Any patch image can be used.

The patch detection unit 30 is a function for detecting a patch image formed by the image forming unit 10. Specifically, for example, when the image forming unit 10 forms a toner patch image for image forming condition correction on the intermediate transfer member belt 15, the patch detection unit 30 includes the outer periphery of the intermediate transfer member belt 15. A reflection type photoelectric sensor arranged along the surface is used to detect the density of the toner patch image based on the amount of light received from the toner patch image on the intermediate transfer belt 15.
As the detection element for detecting the patch image, if the patch image is a toner image on the intermediate transfer belt 15, a photoelectric sensor for detecting the density or equivalent is used, but the patch image is a medium. In the case of a fixed toner image on P, it is conceivable to use a sensor for detecting density or color. Further, when the patch image is an electrostatic latent image on the photosensitive drum 11, a surface potentiometer for detecting the potential or an equivalent may be used. Since these detection elements may be realized using a known technique, the description thereof is omitted here.

  The detection result correction unit 40 is a function for correcting the detection result by the patch detection unit 30. Specifically, as will be described in detail later, based on the detection result for the single gradation level portion constituting the toner patch image to be detected, the detection result for the gradation portion constituting the toner patch image is detected. Correction is made.

The image forming condition correcting unit 50 is a function for correcting the image forming condition in the image forming unit 10. However, the image forming condition correcting unit 50 corrects the image forming condition by using the detection result obtained by the patch detecting unit 30 and corrected by the detection result correcting unit 40.
The image forming conditions to be corrected include density adjustment, color reproducibility correction, gradation correction, and the like, but the correction items are not particularly limited. Further, the details of the correction method may be performed using a known technique as in the past, such as performing data conversion with reference to a gradation correction table registered in advance in a nonvolatile memory. The description is omitted here. This is the same for the correction timing. For example, when the gradation correction mode is designated, or at an appropriate timing immediately after the power is turned on, it may be performed using a known technique. The description is omitted.

  Among these units 10, 30, 40, and 50, the detection result correction unit 40 and the image forming condition correction unit 50 include a CPU (Central Processing Unit), a RAM (Random Access Memory), and a ROM included in the image forming apparatus 1. It can be realized by causing a computer function including a combination of (Read Only Memory) to execute a predetermined program. In this case, the predetermined program may be provided by being stored in a computer-readable storage medium prior to installation in the image forming apparatus 1 or distributed via wired or wireless communication means. It may be done.

  Next, regarding the patch image for correcting the image forming condition formed by the image forming apparatus 1 and the correction for the detection result, the patch image is a toner patch image formed on the intermediate transfer belt 15. Will be described as an example.

[First implementation example]
FIG. 2 is an explanatory diagram illustrating a specific example of a toner patch image.
As shown in FIG. 2A, the toner patch image 60 formed by the image forming apparatus 1 according to the present invention includes a gradation portion 61 and a single gradation level portion 62.

  The gradation portion 61 is formed in a strip shape extending along the moving direction of the intermediate transfer belt 15 that is the sensor scanning direction of the patch detection means 30, and the gradation level gradually increases along the moving direction. Alternatively, it is formed so as to gradually decrease. Taking the case of 256 gradations as an example, the gradation level (Cin) may cover all gradations from “0” to “255”. For example, “26” to “ Only a part of it may be extracted, such as up to 128 ". Further, the change in gradation level is not necessarily continuous, and may be stepped (for example, one having 32 gradation levels that change every 8 gradation levels).

However, a portion where the pitch at which the gradation level changes is set to be smaller than the width of the detection region 31 of the patch detection means 30 (hereinafter referred to as “detection region width”) is the gradation portion in this embodiment. To do. Here, the “detection area width” means the size of an area (detection field of view) per detection of the patch detection means 30 in the direction along the direction in which the gradation portion 61 extends. If the beam spot diameter when the reflected light reaches the light receiving element is smaller than the size of the light receiving area of the light receiving element, the detection on the toner patch image of the reflective photoelectric sensor is performed. If the beam spot diameter corresponds to this and the beam spot diameter when the reflected light reaches the light receiving element is larger than the size of the light receiving area of the light receiving element, it corresponds to the portion of the beam incident on the light receiving area. The length of the beam on the toner patch image of the reflective photoelectric sensor along the moving direction of the intermediate transfer belt 15 corresponds to this. Note that the shape of the detection region 31 is determined by the structure of the detection element in the patch detection means 30. Here, the detection element means all elements necessary for detection. For example, a reflection type photoelectric sensor includes both a light emitting element and a light receiving element. Therefore, in the case of a reflective photoelectric sensor, a circular shape as shown in the figure is generally used, but is not necessarily limited to this, and may be, for example, an oval or a rectangle. However, in order to increase the detection accuracy, it is preferable that the detection region 31 has a symmetrical shape in the width direction.
Thus, the gradation unit 61 changes the gradation level stepwise so that a plurality of gradation levels exist within the detection area width of the patch detection unit 30.

On the other hand, the single gradation level portion 62 is formed so that the gradation level does not change with the detection area width of the patch detection unit 30 and the single gradation level continues in a range wider than the detection area width. It is a thing. It is conceivable that the single gradation level is any density value between the upper limit value and the lower limit value of each gradation level constituting the gradation portion 61. However, the concentration value is not particularly limited. Further, as long as the density value is set in advance, it may be out of the range of each gradation level constituting the gradation portion 61.
It is sufficient that at least one single gradation level portion 62 exists for each toner patch image 60. In the illustrated example, when the gradation portion 61 has 256 gradations of Cin = 0 to 255, Cin = 204 (80% of Cin = 255) and Cin = 51 (20% of Cin = 255). This shows the case where the two exist.

  Further, the toner patch image 60 is configured by separately arranging a gradation portion 61 and a single gradation level portion 62. Here, “separately” means that they are arranged at physically separated positions. That is, a portion that does not constitute the toner patch image 60 is interposed between the gradation portion 61 and the single gradation level portion 62 and between the plurality of single gradation level portions 62.

Next, the processing operation when the patch detection unit 30 detects the toner patch image 60 having the above configuration will be described.
In the gradation portion 61 in the toner patch image 60 having the above-described configuration, the gradation level changes along the moving direction of the intermediate transfer belt 15, so that the image density varies depending on the position in the moving direction. The pitch at which the gradation level changes is set to be smaller than the detection area width of the patch detection unit 30.

  Therefore, as shown in FIG. 2C, when the detection area width of the patch detection unit 30 is located within the gradation portion 61 in the toner patch image 60, the upstream density and the downstream in the detection area width are determined. For example, by calculating the average value of the density values of each gradation level existing within the detection area width, the upstream density and the downstream density are averaged. The difference will be offset. That is, by averaging the sensor detection values for the respective gradation levels of the gradation portion 61 that continuously and uniformly change within the detection area width, the averaged detection value is the center within the detection area width. This value corresponds to the density value of the gradation level in the area.

  However, the detection region including the edge of the gradation portion 61 in the toner patch image 60 includes a non-patch image portion (Cin = 0 portion) without toner, as shown in FIG. 2B or 2D. . Therefore, when the sensor detection values are averaged, continuous and non-uniform portions are also reflected in the averaging result.

When the detection results obtained by the patch detection means 30 thus obtained, that is, the sensor detection values obtained at each point of the gradation portion 61 are plotted in correspondence with the respective detection positions, the gradation portion 61 is shown in FIG. A signal profile as shown in 2 (E) is obtained.
This signal profile is obtained through the above-described averaging. Further, since the area including the edge of the gradation portion 61 is averaged including the non-patch image portion, the density value of each gradation level is obtained. There may be an error in the absolute value of (the value on the vertical axis of the signal profile).
In addition, for example, when detecting the gradation unit 61 by the patch detection unit 30, a deviation may occur in the detection timing by the patch detection unit 30 due to some factor (such as an increase in processing load in the control unit at the timing). . Furthermore, the conveyance speed of the intermediate transfer belt 15 on which the toner patch image 60 is formed may vary, or the size of the toner patch image 60 may vary when it is formed. In these cases, an error occurs in the relationship (gradient of the signal profile) between the arrangement pitch of each gradation level and the density value of each gradation level in the signal profile.
Such an error can occur as in the case of using a conventional gradation patch image (see, for example, Patent Document 1).

However, the toner patch image 60 having the above-described configuration has a single gradation level portion 62 in addition to the gradation portion 61 as shown in FIG.
The single gradation level portion 62 is formed such that a single gradation level continues in a range wider than the detection area width of the patch detection means 30. Therefore, even if the sensor detection values are averaged, the detection result of the single gradation level unit 62 is the place where the detection values obtained from a single gradation level are averaged, that is, the detection result. Since there is always a place where the density value of one gradation level itself is a detection result, the detection result of the density value of that gradation level can be obtained without causing an error. That is, the density value of the gradation level is detected without including an error.
Specifically, as shown in FIG. 2E, from the single gradation level portion 62 of Cin = 204 and the single gradation level portion 62 of Cin = 51, Cin = 204 and Cin = 51, respectively. A signal profile having a flat portion with the density value itself as a detection result is obtained.

  When a signal profile based on the detection results from the gradation unit 61 and the single gradation level unit 62 is obtained, the detection result correcting unit 40 thereafter performs a single-order processing as shown in FIG. Based on the detection result for the tone level portion 62, the detection result for the gradation portion 61 is corrected. Specifically, using the detection result of the density value of each single gradation level portion 62 with Cin = 204 and Cin = 51, the absolute value or inclination of the signal profile for the gradation portion 61 is corrected.

For example, if the absolute value of the signal profile is to be corrected, the location that should be Cin = 204 or Cin = 51 in the gradation unit 61 is specified from the arrangement pitch of each gradation level of the gradation unit 61 and the location. The signal profile for the gradation portion 61 is generally shifted up and down or left and right so that the detection result of the density value matches the detection result of the density value of the single gradation level portion 62 with Cin = 204 or Cin = 51. Let That is, each gradation level value in the detection result for the gradation portion 61 is corrected based on the detection result for at least one single gradation level portion 62.
By performing such correction, even if an error occurs in the absolute value (value on the vertical axis of the signal profile) of the density value of each gradation level in the gradation portion 61, the error is eliminated.

Further, for example, in the case of correcting the inclination of the signal profile, it corresponds on the signal profile for the gradation portion 61 from the detection result of the density value of the single gradation level portion 62 with Cin = 204 and Cin = 51. The location of the density value is specified, and the slope of the signal profile for the gradation portion 61 is adjusted so that the distance between the locations matches the original distance specified from the arrangement pitch of each gradation level in the gradation portion 61. Correct it. That is, based on the detection results for the plurality of single gradation level portions 62, the arrangement pitch of each gradation level (input image density corresponding to the density of each gradation) and the density of each gradation level in the detection result for the gradation portion 61. The relationship with the value is corrected.
If such correction is performed, even if an error occurs in the relationship (gradient of the signal profile) between each input image density and each gradation density value in the signal profile of the gradation unit 61, the error is eliminated.

  The correction for the signal profile of the gradation unit 61 may be performed only for the absolute value of the signal profile as long as the detection result of the density value of each single gradation level unit 62 is used. It may be performed only for the tilt or both.

  Further, when correcting the slope of the signal profile, correction may be performed using the single gradation level portion 62 for the portion within the density value range of each single gradation level portion 62. It is conceivable that a portion outside the range of the density value of each single gradation level portion 62 is obtained by complementing a value outside the range based on the density value, and correction is performed using the complemented value. .

  By performing the correction as described above, even when the detection start timing of the toner patch image 60 by the patch detection unit 30 is shifted or the size of the toner patch image 60 is changed, the toner patch is changed. The relationship between the positional relationship between each Cin of the gradation portion 61 in the image 60 and the density detection value corresponding to each Cin can be accurately obtained without including an error.

In such correction, if the toner patch image 60 is configured by separately arranging the gradation portion 61 and the single gradation level portion 62, the portion that does not constitute the toner patch image 60 is interposed. Therefore, it is easy to separate the detection result for the gradation portion 61 from the detection result for the single gradation level portion 62. Therefore, the correction of the signal profile of the gradation unit 61 using the detection result of the density value of the single gradation level unit 62 can be performed with high processing efficiency and high accuracy without requiring complicated separation processing.
Further, if the gradation portion 61 and the single gradation level portion 62 are configured to be spaced apart from the detection visual field of the patch detection means 30, the entire gradation level portion 62 is detected when the single gradation level portion 62 is detected. This is preferable in that it can be detected without being affected by the gradation portion 61 in the region, and the gradation portion 61 and the single gradation level portion 62 can be more easily separated.

[Second embodiment]
FIG. 3 is an explanatory diagram showing another specific example of the toner patch image.
The toner patch image 60 in the illustrated example is configured such that the gradation portion 61 includes a single gradation level portion 62, and the gradation portion 61 and the single gradation level portion 62 are separately arranged. This is different from the first embodiment (see FIG. 2).
More specifically, as shown in FIG. 3A, the gradation portion 61 has 256 gradations of Cin = 0 to 255, and the portion of Cin = 255 and the portion of Cin = 128 constituting the gradation portion 61. And Cin = 0 are formed so that each becomes a single gradation level portion 62, that is, a single gradation level continues in a range wider than the detection area width of the patch detection means 30. Shows the case.

When the toner patch image 60 having such a configuration is detected by the patch detection unit 30, a signal profile as shown in FIG. 3B is obtained.
Even if this signal profile has been averaged within the detection area width of the patch detection means 30, the single gradation level portion 62 is included in the signal profile. The density value of the gradation level of the unit 62 is detected without including an error.
Therefore, as in the case of the first embodiment described above, after the signal profile based on the detection results from the gradation unit 61 and the single gradation level unit 62 is obtained, as shown in FIG. If the detection result correction unit 40 corrects the detection result for the gradation unit 61 based on the detection result for the single gradation level unit 62, the detection start timing of the toner patch image 60 by the patch detection unit 30 is reached. Even when the toner patch image 60 is shifted or the size of the toner patch image 60 is changed, the positional relationship between the Cin of the gradation portion 61 in the toner patch image 60 and the density detection value corresponding to each Cin. The relationship is obtained accurately without error.

  Further, if the toner patch image 60 is configured such that the gradation portion 61 includes the single gradation level portion 62, there is no need to interpose a portion that does not constitute the toner patch image 60 between them. Therefore, an increase in the area of the area for forming the toner patch image 60 can be suppressed. In addition, it is expected that the detection result of the toner patch image 60 is less likely to receive the result of the speed fluctuation of the intermediate transfer belt 15 on which the toner patch image 60 is formed through the suppression of the increase in the area of the region.

[Examples of using patch image detection results]
As described in the first or second embodiment, the patch detection unit 30 detects the toner patch image 60 having the gradation portion 61 and the single gradation level portion 62, and the detection result of the gradation portion 61 is detected. The detection result correction means 40 performs correction based on the detection result of the single gradation level portion 62 for the toner patch image 60 to obtain an accurate gradation characteristic (between each Cin of the gradation portion 61 in the toner patch image 60). After obtaining the relationship between the positional relationship and the density detection value corresponding to each Cin), the image forming condition correcting unit 50 subsequently corrects the image forming condition in the image forming unit 10 based on the gradation characteristics. Do. Examples of the correction of the image forming condition include gradation correction (correction of highlight reproducibility, tone jump, etc.) using a lookup table.

  As described above, the image forming condition correcting unit 50 uses the corrected detection result based on the detection result of the single gradation level portion 62 among the detection results of the gradation portion 61 having a plurality of gradation levels. If the condition correction is performed, the gradation characteristics that are the basis of the image forming condition correction are accurate without any error, so that the accuracy of the image forming condition correction can be improved.

Here, a specific example of image forming condition correction will be described by taking tone jump suppression of an output image as an example.
For example, when an accurate gradation characteristic when the image forming unit 10 forms a toner image is obtained by the processing operation described in the first or second embodiment, the gradation characteristic is referred to while referring to the gradation characteristic. The presence or absence of a so-called tone jump, which corresponds to the nonuniformity of the tone change, is detected. This detection itself may be performed using a method similar to the conventional one. When a tone jump has occurred, the gradation area where the tone jump has occurred is extracted, and more detailed gradation correction is performed by paying attention to only the gradation area.
Through such processing operation, the tone correction specialized for the tone jump generation region can be accurately performed without any error.

In general, image forming apparatuses in recent years are required to have high image quality, and in particular, in photographic mode output, high image quality close to that of silver lead photography is required. As one of methods for realizing high image quality, it is known to prevent tone jump. In order to detect such a tone jump, it is indispensable to obtain an accurate and detailed gradation change curve (curve representing the degree of change in gradation level). Through the processing operation described in the specific example, an accurate gradation changing music can be obtained, and as a result, high image quality can be contributed.
The definition for detecting the tone jump is that the gradation property is broken. However, if the gradation property is detected on the intermediate transfer belt 15, for example, the intermediate transfer belt is detected. This occurs when there is unevenness (scratches or partial deterioration) in 15. Further, if the gradation characteristic is detected on the medium P, it occurs even if the medium P is uneven. Therefore, in order to avoid confusion with these, it is necessary to check the presence or absence of these occurrences and determine whether or not they are tone jumps. In order to confirm the presence or absence of these, a toner patch image 60 (hereinafter referred to as a “limited gradation area gradation patch image”) including the gradation portion 61 focused only on the gradation area where the tone jump is considered to have occurred. It is sufficient to obtain the gradation change curve in detail and accurately. Further, even when a tone jump actually occurs, more accurate gradation correction can be performed by obtaining a detailed gradation change curve from the limited gradation area gradation patch image. Even after tone jump correction has been completed, a concern gradation gradation may be created for a certain period of time. In addition to the above-described use, the limited gradation area gradation patch can be used when high precision gradation gradation is required in advance, such as a photo mode.

  In the above-described embodiment, the preferred specific examples of the present invention have been described. However, the present invention is not limited to the contents, and can be appropriately changed without departing from the gist thereof. For example, the aspects described in the above description, particularly numerical values, are merely specific examples, and the present invention is of course not limited thereto.

1 is an explanatory diagram schematically illustrating a schematic configuration example of an image forming apparatus according to the present invention. FIG. 6 is an explanatory diagram illustrating a specific example of a toner patch image. FIG. 10 is an explanatory diagram illustrating another specific example of a toner patch image.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 10 ... Image forming means, 11 ... Photoconductor drum, 12 ... Charger, 13 ... Exposure device, 14 ... Developing device, 15 ... Intermediate transfer belt, 16 ... Primary transfer device, 17 ... Cleaning device , 18 ... secondary transfer device, 19 ... cleaning device, 20 ... fixing device, 30 ... patch detection means, 31 ... detection area, 40 ... detection result correction means, 50 ... image formation condition correction means, 60 ... toner patch image, 61 ... gradation portion, 62 ... single gradation level portion, P ... medium

Claims (4)

An image holding body for holding an image on the surface and moving the surface in a predetermined direction;
Image forming means for forming an image on the surface of the image carrier;
Patch detection means for detecting an image formed on the surface of the image carrier by the image forming means, and having a predetermined detection width in the predetermined direction;
Control means for controlling the image forming conditions of the image forming means based on the detection result by the patch detecting means,
The image forming means detects the gradation portion in which the gradation level changes stepwise so that a plurality of gradation levels exist within the predetermined detection width area width as the patch image detected by the patch detection means. Forming a patch image having a single gradation level portion in which the gradation level does not change with the area width ;
The image forming apparatus according to claim 1, wherein the control unit corrects the detection result of the gradation portion constituting the patch image based on the detection result of the single gradation level portion constituting the patch image . The image forming apparatus according to claim 1, wherein the image forming unit forms the gradation part and the single gradation level part separately from each other by a distance equal to or larger than the detection area width. The image forming apparatus according to claim 2, wherein the gradation portion and the single gradation level portion are configured with an interval longer than a detection width of the patch detection unit. The image forming apparatus according to claim 1, wherein the gradation portion and the single gradation level portion are continuously formed in the image forming unit.