JP7714955B2 - Image forming apparatus and patch forming method - Google Patents

Description

The present invention relates to an image forming apparatus and patch forming method that forms patches made of toner on a belt.

Conventionally, there is a known image forming device that, when using a sensor to detect the density of a patch formed on a belt, does not read the density at the leading and trailing edges of the patch, but instead reads the density of the intermediate area between the leading and trailing edges (see Patent Document 1). This technology allows the sensor to accurately read the density of the patch by not reading the density at the leading and trailing edges of the patch, where the density becomes unstable due to the edge effect of the electric field.

Japanese Patent Application Publication No. 09-006124

However, if a patch is formed at a predetermined location on the photosensitive drum and then another patch is formed at that location before the photosensitive drum makes one rotation, the effect of the previous patch remaining at that location can prevent the patch from being formed cleanly. To solve this problem, it is necessary to place a subsequent patch upstream of the predetermined patch formed on the belt in the direction of belt movement, at a distance equal to the circumferential length of the photosensitive drum, and outside the range corresponding to the outline of the predetermined patch. However, when placing a subsequent patch in this way, the problem arises of reduced flexibility in patch placement.

This problem also occurs in relation to the developing roller. Specifically, if toner from a specific portion of the developing roller is transferred to the photosensitive drum to form a patch on the photosensitive drum, and then the toner from that specific portion is transferred back to the photosensitive drum before the developing roller makes one rotation, there will not be enough toner in that specific portion, preventing the patch from being formed cleanly. To solve this problem, it is necessary to place a subsequent patch upstream of the specific patch formed on the belt in the direction of belt movement, within a range spaced a distance equal to the circumferential length of the developing roller, and outside the range corresponding to the contour of the specific patch. However, when placing a subsequent patch in this way, the problem arises of reduced flexibility in patch placement.

Therefore, the present invention aims to increase the degree of freedom in patch placement.

In order to solve the above problem, an image forming apparatus according to the present invention includes an image forming unit, a detection unit, and a control unit.
The image forming unit includes a photosensitive drum, a developing roller, and a belt, and forms a patch made of toner of a predetermined color on the belt by transferring the patch from the photosensitive drum to the belt.
The detection unit detects the patch formed on the belt.
The control unit can form a preceding patch of the predetermined color on the belt, and then form a subsequent patch of the predetermined color on the belt at a distance upstream from the preceding patch in the direction of movement of the belt.
When forming the subsequent patch, the control unit forms the subsequent patch in a first range that is a range between a first position that is a distance upstream from the leading edge of the preceding patch that is the drum circumference, which is the circumference of the photosensitive drum, and a second position that is a distance upstream from the trailing edge of the preceding patch that is the drum circumference, so that a portion of the subsequent patch, including the leading edge or trailing edge, overlaps with the subsequent patch, but the other portion does not overlap.
An overlapping length Lo, which is the length in the movement direction of the portion of the subsequent patch that overlaps with the first range, is 3 mm or less.

Furthermore, the patch forming method of the present invention is a patch forming method by the control unit, in which after forming a preceding patch of the predetermined color on the belt, a subsequent patch of the predetermined color is formed on the belt at a distance upstream from the preceding patch in the direction of movement of the belt, and when forming the subsequent patch, the subsequent patch is formed so that a portion of the subsequent patch, including the leading or trailing end, overlaps with a first range that is a range between a first position that is separated upstream from the leading end of the preceding patch by the drum circumference, which is the circumference of the photosensitive drum, and a second position that is separated upstream from the trailing end of the preceding patch by the drum circumference, and the subsequent patch does not overlap with the first range.
An overlapping length Lo, which is the length in the movement direction of the portion of the subsequent patch that overlaps with the first range, is 3 mm or less.

With this image forming device and patch forming method, a portion of the subsequent patch overlaps the first range where the influence of the formation of the preceding patch remains, thereby increasing the degree of freedom in patch placement. Furthermore, by setting the overlap length Lo to 3 mm or less, the edges of the patch, where density becomes unstable due to the edge effect and the difference in peripheral speed between the photosensitive drum and the developing roller, can be overlapped with the first range, while the length in the movement direction of the middle portion of the patch outside the first range, which is not affected by the edge effect and the difference in peripheral speed between the photosensitive drum and the developing roller, can be increased, thereby increasing the number of reading points in the middle portion.

Furthermore, when forming the subsequent patch on the belt, the control unit may form the subsequent patch so that a portion of the subsequent patch, including the rear end thereof, overlaps the first range.

This configuration allows the distance between the preceding and succeeding patches to be reduced, thereby shortening the time it takes to form multiple patches.

Alternatively, the drum circumferential length may be Lc1, and the length from the leading edge of the preceding patch to the trailing edge of the succeeding patch may be Le1, such that Lc1 < Le1.

Furthermore, the patch may have an intermediate portion that is separated from the leading and trailing ends of the patch by the overlap length Lo or more, and that is read by the detection unit and acquired by the control unit as information to be used for processing by the control unit; where Lr1 is the length from the leading end of the intermediate portion of the preceding patch to the trailing end of the intermediate portion of the following patch, Lr1 may satisfy Lr1 < Lc1.

Furthermore, when forming the subsequent patch on the belt, the control unit may form the subsequent patch so that a portion of the subsequent patch, including the leading end, overlaps the first range.

Alternatively, the drum circumference may be Lc1, the length from the leading edge of the preceding patch to the leading edge of the succeeding patch may be La1, and the length of the patch in the movement direction may be Lg1, so that Lc1 + Lg1 > La1.

Furthermore, the patch may have an intermediate portion that is separated from the leading and trailing ends of the patch by the overlap length Lo or more, and that is read by the detection unit and acquired by the control unit as information to be used for processing by the control unit; where Lb1 is the length from the leading end of the preceding patch to the leading end of the intermediate portion of the following patch, Lb1 > Lc1 + Lg1 may be satisfied.

An image forming apparatus according to the present invention includes an image forming unit, a detection unit, and a control unit.
The image forming unit includes a photosensitive drum, a developing roller, and a belt, and forms a patch made of toner of a predetermined color on the belt by transferring the patch from the photosensitive drum to the belt.
The detection unit detects the patch formed on the belt.
The control unit can form a preceding patch of the predetermined color on the belt, and then form a subsequent patch of the predetermined color on the belt at a distance upstream from the preceding patch in the direction of movement of the belt.
When forming the subsequent patch, the control unit forms the subsequent patch in a second range that is a range between a third position that is located upstream from the leading edge of the preceding patch by the roller circumference, which is the circumference of the developing roller, and a fourth position that is located upstream from the trailing edge of the preceding patch by the roller circumference, so that a portion of the subsequent patch, including the leading edge or trailing edge, overlaps with the subsequent patch, but the other portion does not overlap.
An overlapping length Lo, which is the length in the movement direction of the portion of the subsequent patch that overlaps with the second range, is 3 mm or less.

Furthermore, the patch forming method of the present invention is a patch forming method by the control unit, in which after forming a preceding patch of the predetermined color on the belt, a subsequent patch of the predetermined color is formed on the belt at a distance upstream from the preceding patch in the direction of movement of the belt, and when forming the subsequent patch, the subsequent patch is formed so that a portion of the subsequent patch, including the leading or trailing end, overlaps with a second range that is a range between a third position that is located upstream from the leading end of the preceding patch by the roller circumference, which is the circumference of the developing roller, and a fourth position that is located upstream from the trailing end of the preceding patch by the roller circumference, and the subsequent patch does not overlap with the second range.
An overlapping length Lo, which is the length in the movement direction of the portion of the subsequent patch that overlaps with the second range, is 3 mm or less.

With this image forming device and patch forming method, a portion of the subsequent patch overlaps the second range where the influence of the formation of the preceding patch remains, thereby increasing the degree of freedom in patch placement. Furthermore, by setting the overlap length Lo to 3 mm or less, the edge of the patch, where density becomes unstable due to the edge effect, can be overlapped with the second range, while the length in the movement direction of the middle portion of the patch outside the second range, which is not affected by the edge effect, can be increased, thereby increasing the number of reading points in the middle portion.

Furthermore, when forming the subsequent patch on the belt, the control unit may form the subsequent patch so that a portion of the subsequent patch, including the rear end thereof, overlaps the second range.

This configuration allows the distance between the preceding and succeeding patches to be reduced, thereby shortening the time it takes to form multiple patches.

Alternatively, the roller circumferential length may be Lc2, and the length from the leading edge of the preceding patch to the trailing edge of the succeeding patch may be Le2, satisfying Lc2 < Le2.

Furthermore, the patch may have an intermediate portion that is separated from the leading and trailing ends of the patch by the overlap length Lo or more, and that is read by the detection unit and acquired by the control unit as information to be used for processing by the control unit; the length from the leading end of the intermediate portion of the preceding patch to the trailing end of the intermediate portion of the following patch may be Lr2, satisfying Lr2 < Lc2.

Furthermore, when forming the subsequent patch on the belt, the control unit may form the subsequent patch so that a portion of the subsequent patch, including the leading end, overlaps the second range.

Alternatively, the roller circumferential length may be Lc2, the length from the leading edge of the preceding patch to the leading edge of the succeeding patch may be La2, and the length of the patch in the movement direction may be Lg2, so that Lc2 + Lg2 > La2 is satisfied.

Furthermore, the patch may have an intermediate portion that is separated from the leading and trailing ends of the patch by the overlap length Lo or more, and that is read by the detection unit and acquired by the control unit as information to be used for processing by the control unit; where Lb2 is the length from the leading end of the preceding patch to the leading end of the intermediate portion of the following patch, Lb2 > Lc2 + Lg2 may be satisfied.

The control unit may also form multiple patches, including the preceding patch and the succeeding patch, on the belt, and set the development bias to be applied to the development roller based on the results of reading the multiple patches with the detection unit.

The control unit may also form multiple patches, including the preceding patch and the succeeding patch, on the belt, and set the correspondence between the target density and the exposure density based on the results of reading the multiple patches with the detection unit.

This invention allows for greater flexibility in patch placement.

1 is a diagram showing a color printer according to an embodiment of the present invention; FIG. 4 is a diagram showing a printing pattern image. FIG. 10 is a diagram showing the correspondence relationship between target density and exposure density. FIG. 10 is a diagram showing the order of images formed on the conveyor belt. 1A to 1D are diagrams illustrating the problems that arise when developing is performed continuously at a predetermined location on a developing roller, and when exposing a predetermined location on a photosensitive drum continuously. FIG. 10 is a diagram illustrating the relationship between a preceding patch and a subsequent patch. FIG. 10 is a diagram showing the relationship between a preceding patch and a subsequent patch according to a first modified example. FIG. 10 is a diagram showing the relationship between a preceding patch and a subsequent patch according to a second modified example. FIG. 11 is a diagram illustrating a relationship between a preceding patch and a subsequent patch according to a third modified example. FIG. 13 is a diagram showing the relationship between a preceding patch and a subsequent patch according to a fourth modified example.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings.
1, a color printer 1, which is an example of an image forming apparatus, includes a main body housing 2, a supply unit 3, an image forming unit 4, a detection unit PS, a fixing device 8, a conveyance unit 9, and a control unit 100. The main body housing 2 has a discharge tray 21 on its top surface.

The supply unit 3 is located at the bottom of the main body housing 2 and includes a supply tray 31 that stores sheets S, and a supply mechanism 32 that supplies the sheets S in the supply tray 31 to the image forming unit 4. The supply mechanism 32 includes a pickup roller 33, a separation roller 34, a separation pad 35, and a registration roller 36.

In the supply unit 3, a pickup roller 33 supplies sheets S in the supply tray 31 toward a separation roller 34, which separates the sheets S into single sheets between the separation roller 34 and a separation pad 35. Registration rollers 36 align the leading edge of the sheets S, and then transport the sheets S toward the image forming unit 4.

The image forming unit 4 includes an exposure device SC, a process unit PU, and a transfer unit 7.

The exposure device SC is located at the top of the main body housing 2 and is equipped with a light source, a polygon mirror, and other components (not shown). The exposure device SC exposes the surface of the photosensitive drum 51 by irradiating it with light.

The process unit PU includes a drawer 5 and four developer cartridges 6. The drawer 5 can be pulled out from the main body casing 2. The drawer 5 includes four photosensitive drums 51, four chargers 52, four drum cleaners 53, and four static elimination lamps 54.

The charger 52 is a member that charges the surface of the photosensitive drum 51. When the charged surface of the photosensitive drum 51 is exposed by the exposure device SC, an electrostatic latent image based on image data is formed on the surface of the photosensitive drum 51. The drum cleaner 53 is a member that cleans the surface of the photosensitive drum 51. The static elimination lamp 54 is a member that irradiates the surface of the photosensitive drum 51 with light to eliminate static electricity.

The developer cartridge 6 contains toner. The developer cartridge 6 is equipped with a developer roller 61 that supplies toner to the electrostatic latent image on the photosensitive drum 51 to form a toner image on the photosensitive drum 51.

The developer cartridges 6, designated by the reference numerals 6K, 6C, 6M, and 6Y, each containing black, cyan, magenta, and yellow toner, are arranged in the order 6K, 6C, 6M, and 6Y from downstream to upstream in the transport direction of the sheet S. In other words, the developer cartridges 6K, 6C, 6M, and 6Y are arranged in the order 6K, 6C, 6M, and 6Y from downstream to upstream in the direction in which the transport belt 73 described below moves toward the detection unit PS. Furthermore, the photosensitive drums 51 corresponding to each developer cartridge 6 are also arranged in the order K, C, M, and Y from downstream to upstream in the direction in which the transport belt 73 moves toward the detection unit PS. In this specification and drawings, when identifying components such as the photosensitive drum 51 and developing roller 61 that correspond to the color of toner, the symbols K, C, M, and Y will be added to correspond to black, cyan, magenta, and yellow, respectively, and the names of the components will be prefixed with the letters "first," "second," "third," and "fourth."

For example, the photosensitive drum 51 and developing roller 61 corresponding to black are also referred to as the first photosensitive drum 51K and first developing roller 61K. The photosensitive drum 51 and developing roller 61 corresponding to cyan are also referred to as the second photosensitive drum 51C and second developing roller 61C. The photosensitive drum 51 and developing roller 61 corresponding to magenta are also referred to as the third photosensitive drum 51M and third developing roller 61M. The photosensitive drum 51 and developing roller 61 corresponding to yellow are also referred to as the fourth photosensitive drum 51Y and fourth developing roller 61Y.

The transfer unit 7 includes a drive roller 71, a driven roller 72, a conveyor belt 73 (an example of a belt), four transfer rollers 74, and a belt cleaner BC. The conveyor belt 73 is an endless belt. The drive roller 71 and driven roller 72 are members for rotating the conveyor belt 73. The drive roller 71 is positioned downstream of the driven roller 72 in the conveying direction of the sheet S.

The transfer roller 74 is a member that transfers the image on the photosensitive drum 51 to the sheet S or the conveyor belt 73. The transfer roller 74 is positioned inside the conveyor belt 73 and sandwiches the conveyor belt 73 between itself and the corresponding photosensitive drum 51.

The belt cleaner BC has the function of cleaning toner off the conveyor belt 73. The belt cleaner BC is located on the opposite side of the conveyor belt 73 from the photosensitive drum 51.

Detection unit PS is a sensor that detects the print density of the test image formed on the conveyor belt 73. Detection unit PS is positioned opposite the end of the conveyor belt 73 on the drive roller 71 side. Detection unit PS is a light-reflection sensor equipped with a light-emitting element such as an LED and a light-receiving element such as a phototransistor, and it irradiates light onto the image on the conveyor belt 73 and detects the reflected light.

The fixing device 8 is a device that thermally fixes the toner image to the sheet S. The fixing device 8 includes a heating roller 81 that heats the sheet S, and a pressure roller 82 that sandwiches the sheet S between the heating roller 81 and the pressure roller 82.

The conveying unit 9 is configured to primarily convey the sheet S discharged from the fixing device 8 toward the outside of the main body housing 2. The conveying unit 9 primarily comprises a conveying roller 91 and a discharge roller 92. The sheet S discharged from the fixing device 8 is conveyed by the conveying roller 91 to the discharge roller 92, and then discharged onto the discharge tray 21 by the discharge roller 92.

The control unit 100 has a CPU, ROM, RAM, etc., and is configured to execute various processes in response to receiving print commands, etc., according to pre-prepared programs, etc.

The control unit 100 has the function of executing a printing process that forms an image on a sheet S based on a print job output from a computer (not shown). During the printing process, the control unit 100 executes an exposure process that exposes the photosensitive drum 51 based on a printing pattern image, which is a binary image. More specifically, when executing the printing process, when printing an image on a sheet S, the control unit 100 executes the exposure process by selecting one printing pattern image from multiple printing pattern images with different exposure densities (gradations) so that the print density of this image reaches a predetermined target density. The printing pattern image is composed of a binary image as shown in Figure 2. The exposure density refers to the area ratio of exposed pixels in the printing pattern image.

Here, print density refers to the density of the toner image developed by the developing roller 61, and is detected by the detection unit PS. Furthermore, target density refers to the target density specified in the print command. For example, if the target density specified in the print command is 20%, the control unit 100 selects a print pattern image with an exposure density of 20% and performs the exposure process using this print pattern image. However, the relationship between target density and exposure density is changed by the gradation setting process described below. For example, if a state in which a print pattern image with an exposure density of 20% is associated with a target density of 20% is changed to a state in which a print pattern image with an exposure density of 10% is associated with a target density of 20%, the exposure process will be performed using the print pattern image with an exposure density of 10% when forming an image at the target density of 20%.

As described above, the control unit 100 selects one print pattern image from the multiple print pattern images that corresponds to the target density, and then performs exposure and development using that print pattern image to form a toner image of the target density on the photosensitive drum 51.

The multiple printing pattern images correspond to the exposure densities and are stored in advance in the storage unit. The multiple printing pattern images also correspond to the colors yellow, magenta, cyan, and black and are stored in advance in the storage unit.

The control unit 100 is capable of performing image quality adjustment to adjust the image quality of the printed toner image. The control unit 100 performs image quality adjustment when predetermined conditions are met. Specifically, for example, the control unit 100 can be configured to perform image quality adjustment when any one of the following conditions is met:
First condition: The developing cartridge 6 or photosensitive drum 51 is new. Second condition: An instruction to perform image quality adjustment has been received from the user. Third condition: The environment, such as temperature and humidity, has changed by a predetermined value or more since the previous image quality adjustment. Fourth condition: The number of pages printed since the previous image quality adjustment was performed has exceeded a predetermined number. Fifth condition: A developing cartridge 6 with a different serial number has been installed.

In adjusting image quality, the control unit 100 has the function of performing correction image formation processing, bias setting processing, pattern image formation processing, and gradation setting processing for each of the colors yellow, magenta, cyan, and black.

The corrected image formation process involves applying a first development bias to the development roller 61, and then forming a first bias-corrected image on the conveyor belt 73 by the image forming unit 4. Then, applying a second development bias, which has a value different from the first development bias, to the development roller 61, the image forming unit 4 forms a second bias-corrected image on the conveyor belt 73. Here, the development bias is a bias applied to the development roller 61 by a bias application unit (not shown). The image forming unit 4 has a bias application unit.

The first development bias and second development bias are set to optimal values for each color. The first development bias may be a different value for each color, or the same value for some or all of the multiple colors. For example, the first development bias corresponding to black may be a different value from the first development bias corresponding to yellow, or the same value. Similarly, the second development bias may be a different value for each color, or the same value for some or all of the multiple colors.

The first bias-corrected image and the second bias-corrected image are both print pattern images corresponding to a predetermined exposure density. Specifically, the first bias-corrected image is formed by using the first development bias to form a print pattern image with an exposure density of 40%, for example, as shown in Figure 2. In this case, the second bias-corrected image is formed by using the second development bias to form a print pattern image with an exposure density of 40%.

The bias setting process sets the development bias based on the results of reading the first bias-corrected image and the second bias-corrected image with the detection unit PS. In the bias setting process, the control unit 100 converts the intensity of the reflected light from each bias-corrected image detected by the detection unit PS into print density, and calculates the development bias that will result in the target print density based on the two types of print density and two types of development bias. The development bias set in the bias setting process is set to the optimal value for each color.

The pattern image formation process is a process in which the image forming unit 4 forms multiple pattern images on the conveyor belt 73 while the development bias set in the bias setting process is applied to the development roller 61. Here, the multiple pattern images are gradation setting images used in the gradation setting process. Specifically, the multiple pattern images are multiple print pattern images corresponding to multiple exposure densities; for example, five types of print pattern images corresponding to exposure densities of 5%, 20%, 40%, 60%, and 80% are used.

The gradation setting process is a process that sets the correspondence between the target density and the exposure density based on the results of reading multiple pattern images with the detection unit PS. Specifically, in the gradation setting process, the control unit 100 sets the correspondence between the target density and the print pattern image, thereby setting the correspondence between the target density and the density of the toner image that is actually printed, i.e., the exposure density.

More specifically, the control unit 100 detects multiple pattern images using the detection unit PS and converts the intensity of reflected light from each pattern image into a print density. The control unit 100 then compares each calculated print density with the corresponding exposure density, and if the compared print density and exposure density differ, corrects the correspondence between the print density and exposure density, thereby changing the correspondence between the target density and the print pattern image.

Specifically, if the gradation setting process has never been performed, the correspondence between the target density and the print pattern image (exposure density) is, for example, a default gamma table such as that shown by the two-dot chain line in Figure 3. In the following explanation, the correspondence between the target density and the print pattern image is also referred to as the "gamma table."

A gamma table is a table used to select a print pattern with a specified exposure density that corresponds to a specified target density when printing at that target density. The gamma table shown by the dashed double-dashed line, i.e., the default gamma table, has the same values for the target density and exposure density.

During the gradation setting process, for example, if the detection unit PS detects a print pattern image corresponding to an exposure density of 20%, as shown by the black circle in the figure, and the print density of that image ends up being 10%, the control unit 100 will re-store the print pattern image as a pattern image corresponding to a target density of 10%. In other words, if an image is formed at a target density of 10% during the next print control, forming the image using the first print pattern image corresponding to an exposure density of 20% will result in a print density of 10%, so the control unit 100 associates a print pattern image with an exposure density of 20% with a target density of 10%.

Furthermore, during this gradation setting process, if the print density is 40% when a print pattern image with an exposure density of 40% is detected by the detection unit PS, i.e., if the target density, exposure density, and print density match, the relationship between the target density and exposure density is linearly interpolated, as shown by the dashed line in the figure. As a result, for example, if an image is formed with a target density of 20% during the next print control, a print pattern image corresponding to exposure density X, which corresponds to the intersection of the 20% target density line and the dashed line in the figure, is selected. Note that the gamma table at this time is a table in which the lines in the default gamma table (two-dot chain line) with exposure densities below 40% have been replaced with the dashed line in the figure. In other words, the gap between the black circle in the figure and the white circle corresponding to an exposure density of 40% is interpolated as shown by the dashed straight line.

As shown in FIG. 4, during the correction image formation process, the control unit 100 forms a first image group G1 consisting of multiple color first bias-corrected images K1, C1, M1, and Y1 and multiple color second bias-corrected images K2, C2, M2, and Y2. During the pattern image formation process, the control unit 100 forms a second image group G2 consisting of multiple color pattern images Kγ1-Kγ5, Cγ1-Cγ5, Mγ1-Mγ5, and Yγ1-Yγ5. The order of the first bias-corrected images K1-Y1, the second bias-corrected images K2-Y2, and the pattern images Kγ1-Yγ5 on the conveyor belt 73 is set as shown in the figure so that the time from the start of the correction image formation process to the end of the pattern image formation process is as short as possible. More specifically, the exposure order is determined so that the order of the inspection images on the conveyor belt 73 is the order shown in the figure. The exposure order is stored in a memory unit (not shown). Note that the images are shown in a simplified form in FIG. 4.

The inspection images are arranged in the movement direction at intervals. Specifically, the first bias-corrected images K1-Y1 and the second bias-corrected images K2-Y2 are arranged at a first pitch Lp1. Of the multiple pattern images Kγ1-Yγ5, two adjacent pattern images (e.g., Kγ1 and Kγ2) are arranged at a second pitch Lp2.

Here, the length of each image in the movement direction is set according to the number of reading points (number of reading positions) of the detection unit PS. For example, if the number of reading points in the bias setting process is a first predetermined number, the length of each image constituting the first image group G1 in the movement direction is set to a first length corresponding to the first predetermined number. If the number of reading points in the gradation setting process is a second predetermined number that is smaller than the first predetermined number, the length of each image constituting the second image group G2 in the movement direction is set to a second length corresponding to the second predetermined number, which is shorter than the first length. The spacing between each image is set taking into consideration variations in color registration and reduced toner consumption.

The bias-corrected images are arranged in the following order from the front in the direction of movement: K1, Y1, M1, K2, C1, Y2, M2, C2. The control unit 100 executes the correction image formation process so that the bias-corrected images are arranged in the aforementioned order.

The pattern images are arranged in the following order from the front in the direction of movement: Kγ1, Kγ2, Kγ3, Kγ4, Kγ5, Cγ1, Cγ2, Mγ1, Mγ2, Cγ3, Yγ1, Yγ2, Mγ3, Cγ4, Yγ3, Mγ4, Mγ5, Cγ5, Yγ4, Yγ5. Pattern image Kγ3 is arranged after pattern image Kγ2, with a gap of approximately two pattern images. More specifically, pattern image Kγ3 is arranged at a pitch of 3 x Lp2 relative to pattern image Kγ2. Note that the expression for the gap between two images as a pitch is similar for other images, so it will not be explained below.

Pattern image Kγ5 is arranged after pattern image Kγ4, with a gap of approximately two pattern images between them. Pattern image Cγ1 is arranged after pattern image Kγ5, with a gap of approximately one pattern image between them. Pattern image Mγ1 is arranged after pattern image Cγ2, with a gap of approximately one pattern image between them. Pattern image Kγ1, which is the foremost in the direction of movement, is arranged after second bias-corrected image C2, with a gap of approximately three pattern images between them. The distance in the direction of movement from the front end of the foremost first bias-corrected image K1 to the rear end of the rearmost pattern image Yγ5 is shorter than the circumference of the conveyor belt 73.

The control unit 100 forms the test image so that it satisfies the following conditions. In the following description, the test image will also be referred to as the patch Gp.

As shown in FIG. 6, the control unit 100 is capable of forming a first black preceding patch Gpf1 on the conveyor belt 73, and then forming a first black succeeding patch Gpr1 on the conveyor belt 73 at a distance upstream in the movement direction from the first preceding patch Gpf1. Here, the first succeeding patch Gpr1 refers to a patch that partially overlaps with the first range A11 described below. In the example of FIG. 6, the first preceding patch Gpf1 is pattern image Kγ1, and the first succeeding patch Gpr1 is pattern image Kγ4.

When forming the first subsequent patch Gpr1, the control unit 100 forms the first subsequent patch Gpr1 in a first range A11, which is the range between a first position P1 located upstream from the leading edge of the first preceding patch Gpf1 by the drum circumferential length Lc1, which is the circumferential length of the photosensitive drum 51, and a second position P2 located upstream from the trailing edge of the first preceding patch Gpf1 by the drum circumferential length Lc1. The first subsequent patch Gpr1 is formed so that a portion of the first subsequent patch Gpr1, including its trailing edge, overlaps the first range A11, but the remaining portion does not overlap. The overlap length Lo, which is the length in the movement direction of the portion of the first subsequent patch Gpr1 that overlaps the first range A11, is 3 mm or less.

Specifically, the lower limit of the overlap length Lo is preferably 0.5 mm, more preferably 1.0 mm. The upper limit of the overlap length Lo is preferably 3.0 mm, more preferably 2.5 mm. The combination of the lower limit and the upper limit is arbitrary.
For example, in this embodiment,
・Patch Gp total length: 12 mm
・Middle part CP length: 7.0 mm
Length of the part where density tends to become unstable at the front and rear ends: 2.5 mm
Therefore, the overlap length Lo is preferably 0.5 mm or more and 3.0 mm or less, and more preferably 1.0 mm or more and 2.5 mm or less.
Specifically, in this embodiment, the length Lo of the overlap with the first range A11 (photosensitive drum period) is set to 1.3 mm.

Patch Gp has a middle portion CP, indicated by diagonal hatching in the figure. The middle portion CP is a portion that is separated from the leading and trailing ends of patch Gp by an overlap length Lo or more. The middle portion CP is read by detection unit PS and acquired by control unit 100 as information to be used in processing by control unit 100. In this embodiment, control unit 100 is configured to read the range from the leading to trailing end of patch Gp with detection unit PS, perform various processes based on the results of reading the middle portion CP, and not use the results of reading portions other than middle portion CP in the processing. Note that control unit 100 may also be configured to read only the middle portion CP of patch Gp with detection unit PS, and not read portions other than middle portion CP with detection unit PS.

The drum circumference Lc1, the length Le1 from the leading edge of the first preceding patch Gpf1 to the trailing edge of the first succeeding patch Gpr1, and the length Lr1 from the leading edge of the middle portion CP of the first preceding patch Gpf1 to the trailing edge of the middle portion CP of the first succeeding patch Gpr1 satisfy the following conditions:
Lr1<Lc1<Le1

After forming a second black preceding patch Gpf2 on the conveyor belt 73, the control unit 100 is capable of forming a second black succeeding patch Gpr2 on the conveyor belt 73 at a distance upstream in the movement direction from the second preceding patch Gpf2. Here, the second succeeding patch Gpr2 refers to a patch that partially overlaps the second range A22 described below. In the example of Figure 6, the second preceding patch Gpf2 is pattern image Kγ2, and the second succeeding patch Gpr2 is pattern image Kγ3.

When forming the second subsequent patch Gpr2, the control unit 100 forms the second subsequent patch Gpr2 in a second range A22, which is the range between a third position P3, which is located upstream from the leading edge of the second preceding patch Gpf2 by the roller circumference Lc2, which is the circumference of the developing roller 61, and a fourth position P4, which is located upstream from the rear end of the second preceding patch Gpf2 by the roller circumference Lc2, so that a portion of the second subsequent patch Gpr2, including its leading edge, overlaps with the second range A22, but the remaining portion does not overlap. The overlap length Lo, which is the length in the movement direction of the portion of the second subsequent patch Gpr2 that overlaps with the second range A22, is 3 mm or less.

Specifically, the lower limit of the overlap length Lo is preferably 0.5 mm, more preferably 1.0 mm. The upper limit of the overlap length Lo is preferably 3.0 mm, more preferably 2.5 mm. The combination of the lower limit and the upper limit is arbitrary.
For example, in this embodiment,
・Patch Gp total length: 12 mm
・Middle part CP length: 7.0 mm
Length of the part where density tends to become unstable at the front and rear ends: 2.5 mm
Therefore, the overlap length Lo is preferably 0.5 mm or more and 3.0 mm or less, and more preferably 1.0 mm or more and 2.5 mm or less.
Specifically, in this embodiment, the length Lo of the overlap with the second range A22 (developing roller cycle) is set to 2.4 mm.

The roller circumference Lc2, the length from the tip of the second preceding patch Gpf2 to the tip of the second succeeding patch Gpr2 La2, the length in the movement direction of the patch Gp Lg2, and the length from the tip of the second preceding patch Gpf2 to the tip of the middle portion CP of the second succeeding patch Gpr2 Lb2 satisfy the following conditions:
Lb2>Lc2+Lg2>La2

The first range A11 mentioned above is the area on the photosensitive drum 51 where the first preceding patch Gpf1 was formed. The second range A22 is the portion on the developing roller 61 where the toner for forming the second preceding patch Gpf2 was placed. Because the first range A11 or the second range A22 retains the effects of forming the previous patch Gp (hereinafter also referred to as the "memory effect"), if a patch Gp is formed within the first range A11 or the second range A22, the density of the formed patch Gp may become unstable. This phenomenon is explained below with reference to Figure 5.

As shown in Figures 5A and 5B, when the first predetermined area R1 on the photosensitive surface of the photosensitive drum 51 is exposed, the toner located in the second predetermined area R2 of the developing roller 61 moves to the first predetermined area R1, and a patch Gp is formed in the first predetermined area R1 of the photosensitive drum 51. As shown in Figure 5C, when the developing roller 61 rotates half a turn from the position shown in Figure 5B and the second predetermined area R2 again reaches the development nip position Pn, which is the contact point between the photosensitive drum 51 and the developing roller 61, the amount of toner in the second predetermined area R2 may be less than when the patch Gp was formed in the first predetermined area R1 of the photosensitive drum 51. In this case, if the toner in the second predetermined area R2 is moved to the photosensitive drum 51 to form the patch Gp, the density of the patch Gp may become unstable. If the toner on the second predetermined range R2 is transferred to the photosensitive drum 51 to form the patch Gp, the patch Gp transferred to the conveyor belt 73 will be formed over the entire second range A22 shown in FIG.
In this embodiment, the leading edge of the second subsequent patch Gpr2 overlaps the second range A22. The leading edge of the second subsequent patch Gpr2 is not used for control because it is an area that includes parts where the density becomes unstable due to the influence of the edge effect and the difference in peripheral speed between the photosensitive drum 51 and the developing roller 61 and is not suitable for obtaining density. Therefore, even if the density of this area becomes unstable because the leading edge of the second subsequent patch Gpr2 overlaps the second range A22, there is no problem with control.

As shown in Figure 5(d), the first predetermined range R1, which is the exposed range of the photosensitive drum 51, is discharged when it passes through the discharge lamp 54, but the effects of the previous exposure may remain. If the first predetermined range R1 is exposed again while the effects of such exposure remain, poor formation of the electrostatic latent image may occur, and the density of the patch Gp formed in the first predetermined range R1 may become unstable. If the patch Gp formed in the first predetermined range R1, while still affected by the previous exposure, is transferred to the conveyor belt 73, the patch Gp is formed over the entire first range A11 shown in Figure 6.
In this embodiment, the trailing edge of the first subsequent patch Gpr1 overlaps the first range A11. The trailing edge of the first subsequent patch Gpr1 is not used for control because it is an area that includes parts where the density becomes unstable due to the influence of the edge effect and the difference in peripheral speed between the photosensitive drum 51 and the developing roller 61 and is not suitable for obtaining density. Therefore, even if the density of this area becomes unstable because the trailing edge of the first subsequent patch Gpr1 overlaps the first range A11, it does not hinder control.

As shown in FIG. 6, patches Gp other than preceding patches Gpf1 and Gpf2 and succeeding patches Gpr1 and Gpr2 are formed in positions that do not overlap with the first ranges A11 and A12 and the second ranges A21 and A22. Here, the first range A12 is the area on the photosensitive drum 51 where the patch Gp of Kγ2 is formed. The second range A21 is the portion on the developing roller 61 where the toner for forming the patch Gp of Kγ1 was placed.

As shown in Figure 4, each patch Gp that makes up the first image group G1 has a different patch length (the length in the movement direction of the patch Gp) from each patch Gp that makes up the second image group G2, so there is no patch that satisfies the relationship between the preceding patch and the succeeding patch described above.
Among the patches Gp constituting the second image group G2, in addition to the black patch Gp described above and shown in FIG. 6, there are some patches Gp that satisfy the relationship between the preceding patch and the succeeding patch.
For example, for the black patch Gp, in addition to the patches shown in FIG. 6, Kγ4 corresponds to the second preceding patch Gpf2 and Kγ5 corresponds to the second succeeding patch Gpr2.
For the cyan patch Gp, Cγ1 corresponds to the first preceding patch Gpf1, and Cγ3 corresponds to the first succeeding patch Gpr1.
Furthermore, for the magenta patch Gp, Mγ1 corresponds to Gpf1 and Mγ3 corresponds to Gpr1, while Mγ3 corresponds to Gpf2 and Mγ4 corresponds to Gpr2.
For the yellow patch Gp, Yγ3 corresponds to Gpf1 and Yγ5 corresponds to Gpr1, while Yγ2 corresponds to Gpf2 and Yγ3 corresponds to Gpr2.

As described above, the following effects can be obtained in this embodiment.
Since a portion of the first succeeding patch Gpr1 overlaps the first range A11 where the influence of the formation of the first preceding patch Gpf1 remains, the degree of freedom in arranging the patch Gp can be increased. Furthermore, by setting the overlap length Lo to 3 mm or less, the edge of the patch Gp, where density becomes unstable due to the edge effect, can be overlapped with the first range A11, while the length in the movement direction of the middle portion CP of the patch Gp, which is not influenced by the edge effect, can be increased outside the first range A11, thereby increasing the number of reading points in the middle portion CP.

By overlapping a portion of the first subsequent patch Gpr1, including its rear end, with the first range A11, the distance between the first preceding patch Gpf1 and the first subsequent patch Gpr1 can be reduced, thereby shortening the time required to form multiple patches Gp.

By overlapping a portion of the second succeeding patch Gpr2 with the second range A22, where the effects of the formation of the second preceding patch Gpf2 remain, the degree of freedom in the placement of the patch Gp can be increased. Furthermore, by setting the overlap length Lo to 3 mm or less, the edge of the patch Gp, where density becomes unstable due to the edge effect, can be overlapped with the second range A22, while the length in the movement direction of the middle portion CP of the patch Gp, which is not affected by the edge effect, outside the second range A22 can be increased, thereby increasing the number of reading points in the middle portion CP.

The control unit 100 performs the gradation setting process based on the results of reading multiple patches Gp, including preceding patches Gpf1, Gpf2 and succeeding patches Gpr1, Gpr2, using the detection unit PS. This allows the gradation setting process to be performed accurately by using the density of parts of the patch Gp that are not affected by edge effects or memory effects.

The present invention is not limited to the above-described embodiment, but can be used in various forms, as exemplified below. In the following description, components, patches, etc. that have substantially the same structure as those in the above-described embodiment will be assigned the same reference numerals, and their description will be omitted.

The method of overlapping the preceding and succeeding patches is not limited to the above embodiment. For example, as shown in FIG. 7, a portion of the second succeeding patch Gpr2, including its rear end, may overlap the second range A21. In this embodiment, the roller circumference Lc2 is smaller than in the above embodiment. In this embodiment, the second preceding patch Gpf2 is the pattern image Kγ1. The range between a third position P3, which is located upstream from the leading edge of the pattern image Kγ1 by the roller circumference Lc2, and a fourth position P4, which is located upstream from the rear end of the pattern image Kγ1 by the roller circumference Lc2, forms the second range A21. The second succeeding patch Gpr2 is the pattern image Kγ2 whose rear end overlaps the second range A21.

The roller circumference Lc2, the length Le2 from the leading edge of the second preceding patch Gpf2 to the trailing edge of the second succeeding patch Gpr2, and the length Lr2 from the leading edge of the middle portion CP of the second preceding patch Gpf2 to the trailing edge of the middle portion CP of the second succeeding patch Gpr2 satisfy the following conditions:
Lr2<Lc2<Le2

In this form, by overlapping a portion of the second subsequent patch Gpr2, including its rear end, with the second range A21, the distance between the second preceding patch Gpf2 and the second subsequent patch Gpr2 can be reduced, thereby shortening the time required to form multiple patches Gp.

As shown in FIG. 8, a portion of the first subsequent patch Gpr1, including its leading edge, may overlap the first range A12. In this embodiment, the drum circumference Lc1 is larger than in the previous embodiment. Also, in this embodiment, the pitch of the patches Gp is not constant. In this embodiment, the first preceding patch Gpf1 is pattern image Kγ2. The range between a first position P1, which is the drum circumference Lc1 away upstream from the leading edge of pattern image Kγ2, and a second position P2, which is the drum circumference Lc1 away upstream from the rear end of pattern image Kγ2, is the first range A12. The first subsequent patch Gpr1 is pattern image Kγ5, whose leading edge overlaps the first range A12.

The drum circumference Lc1, the length La1 from the tip of the first preceding patch Gpf1 to the tip of the first succeeding patch Gpr1, the length Lg1 in the movement direction of the patch Gp, and the length Lb1 from the tip of the first preceding patch Gpf1 to the tip of the intermediate portion CP of the first succeeding patch Gpr1 satisfy the following conditions:
Lb1>Lc1+Lg1>La1

In the above embodiment, the first image group G1 does not include preceding patches Gpf1, Gpf2 and succeeding patches Gpr1, Gpr2, but the present invention is not limited to this. The first image group G1 may include preceding patches Gpf1, Gpf2 and succeeding patches Gpr1, Gpr2. In the following description, the length of the bias-corrected image in the movement direction is the same as the length of the pattern image in the movement direction, and the first pitch Lp1 is the same value as the second pitch Lp2.

Specifically, as shown in FIG. 9, by successively forming a first bias-corrected image K1 and a second bias-corrected image K2, K1 may be used as the second leading patch Gpf2 and K2 as the second trailing patch Gpr2. In this case, the range between a third position P3, which is located upstream from the leading edge of the first bias-corrected image K1 by the roller circumference Lc2, and a fourth position P4, which is located upstream from the trailing edge of the first bias-corrected image K1 by the roller circumference Lc2, becomes the second range A25. The trailing edge of the second bias-corrected image K2 overlaps with the second range A25.

Also, as shown in FIG. 10, by arranging the bias-corrected images in the order Y1, M1, K2, C1, M2, and Y2 from downstream in the movement direction, Y1 can be designated as the first preceding patch Gpf1 and Y2 as the first succeeding patch Gpr1. In this case, the range between a first position P1, which is located upstream from the leading edge of the first bias-corrected image Y1 by the drum circumference Lc1, and a second position P2, which is located upstream from the trailing edge of the first bias-corrected image Y1 by the drum circumference Lc1, becomes the first range A13. The trailing edge of the second bias-corrected image Y2 overlaps with the first range A13.

According to the configuration shown in Figures 9 and 10, the control unit 100 performs bias setting processing based on the results of reading multiple patches Gp, including preceding patches Gpf1, Gpf2 and succeeding patches Gpr1, Gpr2, using the detection unit PS. This allows the bias setting processing to be performed accurately by using the density of parts of the patch Gp that are not affected by edge effects or memory effects.

In the above embodiment, a conveyor belt 73 was used as an example of a belt, but the present invention is not limited to this. For example, the belt may be an intermediate transfer belt.

In the above embodiment, the present invention is applied to a color printer 1, but the present invention is not limited to this, and may be applied to other image forming apparatuses, such as copying machines and multifunction machines.
In the above embodiment, the color printer 1 exposes the photosensitive drum with a laser scanner, but other exposure devices such as an LED exposure head may also be used as the exposure device.
Furthermore, the first, second, third, and fourth photosensitive drums of the color printer 1 may be supported in one cartridge, or may be supported in separate cartridges.

The elements described in the above embodiments and variations may be implemented in any combination.

REFERENCE SIGNS LIST 1 color printer 4 image forming unit 51 photosensitive drum 61 developing roller 73 conveyor belt 100 control unit A11 first range Gp patch Gpf1 first preceding patch Gpr1 first succeeding patch Lc1 drum circumference Lo overlap length P1 first position P2 second position PS detection unit

Claims (16)

an image forming unit having a photosensitive drum, a developing roller, and a belt, the image forming unit transferring a patch made of toner of a predetermined color from the photosensitive drum to the belt, thereby forming the patch on the belt;
a detection unit that detects the patch formed on the belt;
a control unit,
The control unit
After forming a preceding patch of the predetermined color on the belt, a succeeding patch of the predetermined color can be formed on the belt at a distance from the preceding patch on the upstream side in the moving direction of the belt,
When forming the subsequent patch,
the subsequent patch is formed in a first range between a first position that is spaced upstream from the leading edge of the previous patch by a drum circumferential length that is the circumferential length of the photosensitive drum, and a second position that is spaced upstream from the trailing edge of the previous patch by the drum circumferential length, such that a portion of the subsequent patch including the trailing edge overlaps with the subsequent patch, but the remaining portion does not overlap with the subsequent patch;
an overlapping length Lo, which is a length in the movement direction of the portion of the subsequent patch that overlaps with the first range, being 3 mm or less; The drum circumferential length is Lc1, and the length from the leading edge of the preceding patch to the trailing edge of the succeeding patch is Le1,
2. The image forming apparatus according to claim 1 , wherein Lc1<Le1. The patch comprises:
an intermediate portion of the patch that is separated from the leading end and the trailing end by the overlapping length Lo or more, the intermediate portion being read by the detection unit and acquired by the control unit as information to be used for processing by the control unit;
The length from the leading end of the intermediate portion of the preceding patch to the trailing end of the intermediate portion of the succeeding patch is defined as Lr1,
3. The image forming apparatus according to claim 2 , wherein Lr1<Lc1. an image forming unit having a photosensitive drum, a developing roller, and a belt, the image forming unit transferring a patch made of toner of a predetermined color from the photosensitive drum to the belt, thereby forming the patch on the belt;
a detection unit that detects the patch formed on the belt;
a control unit,
The control unit
After forming a preceding patch of the predetermined color on the belt, a succeeding patch of the predetermined color can be formed on the belt at a distance from the preceding patch on the upstream side in the moving direction of the belt,
When forming the subsequent patch,
the subsequent patch is formed in a first range between a first position that is spaced upstream from the leading edge of the previous patch by a drum circumferential length that is the circumferential length of the photosensitive drum, and a second position that is spaced upstream from the trailing edge of the previous patch by the drum circumferential length, such that a portion of the subsequent patch including the leading edge overlaps with the subsequent patch, but the remaining portion does not overlap with the subsequent patch;
an overlapping length Lo, which is a length in the movement direction of the portion of the subsequent patch that overlaps with the first range, is 3 mm or less;
The drum circumferential length is Lc1, the length from the leading edge of the preceding patch to the leading edge of the succeeding patch is La1, and the length of the patch in the movement direction is Lg1,
Lc1+Lg1>La1 is satisfied,
The patch comprises:
an intermediate portion of the patch that is separated from the leading end and the trailing end by the overlapping length Lo or more, the intermediate portion being read by the detection unit and acquired by the control unit as information to be used for processing by the control unit;
The length from the tip of the preceding patch to the tip of the intermediate portion of the succeeding patch is defined as Lb1,
An image forming apparatus characterized in that Lb1>Lc1+Lg1 is satisfied. an image forming unit having a photosensitive drum, a developing roller, and a belt, the image forming unit transferring a patch made of toner of a predetermined color from the photosensitive drum to the belt, thereby forming the patch on the belt;
a detection unit that detects the patch formed on the belt;
a control unit,
The control unit
After forming a preceding patch of the predetermined color on the belt, a succeeding patch of the predetermined color can be formed on the belt at a distance from the preceding patch on the upstream side in the moving direction of the belt,
When forming the subsequent patch,
the subsequent patch is formed in a second range between a third position that is spaced upstream from the leading edge of the previous patch by a roller circumferential length that is the circumferential length of the developing roller, and a fourth position that is spaced upstream from the trailing edge of the previous patch by the roller circumferential length, such that a portion of the subsequent patch, including the leading edge or the trailing edge, overlaps the subsequent patch, but the other portion does not overlap the subsequent patch;
an overlapping length Lo, which is a length in the movement direction of the portion of the subsequent patch that overlaps with the second range, being 3 mm or less; The control unit
When forming the subsequent patch on the belt,
6. The image forming apparatus according to claim 5 , wherein the subsequent patch is formed so that a part of the subsequent patch including the trailing edge thereof overlaps the second range. The roller circumferential length is Lc2, and the length from the leading edge of the preceding patch to the trailing edge of the succeeding patch is Le2.
7. The image forming apparatus according to claim 6 , wherein Lc2<Le2 is satisfied. The patch comprises:
an intermediate portion of the patch that is separated from the leading end and the trailing end by the overlapping length Lo or more, the intermediate portion being read by the detection unit and acquired by the control unit as information to be used for processing by the control unit;
The length from the leading end of the intermediate portion of the preceding patch to the trailing end of the intermediate portion of the succeeding patch is defined as Lr2,
8. The image forming apparatus according to claim 7 , wherein Lr2<Lc2 is satisfied. The control unit
When forming the subsequent patch on the belt,
6. The image forming apparatus according to claim 5 , wherein the subsequent patch is formed so that a part of the subsequent patch including the leading edge thereof overlaps the second range. The roller circumferential length is Lc2, the length from the leading edge of the preceding patch to the leading edge of the succeeding patch is La2, and the length of the patch in the movement direction is Lg2,
10. The image forming apparatus according to claim 9 , wherein Lc2+Lg2>La2 is satisfied. The patch comprises:
an intermediate portion of the patch that is separated from the leading end and the trailing end by the overlapping length Lo or more, the intermediate portion being read by the detection unit and acquired by the control unit as information to be used for processing by the control unit;
The length from the tip of the preceding patch to the tip of the intermediate portion of the succeeding patch is Lb2,
11. The image forming apparatus according to claim 10 , wherein Lb2>Lc2+Lg2 is satisfied. an image forming unit having a photosensitive drum, a developing roller, and a belt, the image forming unit transferring a patch made of toner of a predetermined color from the photosensitive drum to the belt, thereby forming the patch on the belt;
a detection unit that detects the patch formed on the belt;
a control unit,
The control unit
After forming a preceding patch of the predetermined color on the belt, a succeeding patch of the predetermined color can be formed on the belt at a distance from the preceding patch on the upstream side in the moving direction of the belt,
When forming the subsequent patch,
the subsequent patch is formed in a first range between a first position that is spaced upstream from the leading edge of the previous patch by a drum circumferential length that is the circumferential length of the photosensitive drum, and a second position that is spaced upstream from the trailing edge of the previous patch by the drum circumferential length, such that a portion of the subsequent patch, including the leading edge or the trailing edge, overlaps with the subsequent patch, but the remaining portion does not overlap with the subsequent patch;
an overlapping length Lo, which is a length in the movement direction of the portion of the subsequent patch that overlaps with the first range, is 3 mm or less;
The control unit
forming a plurality of patches on the belt, the patches including the preceding patch and the succeeding patch;
an image forming apparatus, wherein a developing bias to be applied to the developing roller is set based on the result of reading the plurality of patches by the detecting unit; an image forming unit having a photosensitive drum, a developing roller, and a belt, the image forming unit transferring a patch made of toner of a predetermined color from the photosensitive drum to the belt, thereby forming the patch on the belt;
a detection unit that detects the patch formed on the belt;
a control unit,
The control unit
After forming a preceding patch of the predetermined color on the belt, a succeeding patch of the predetermined color can be formed on the belt at a distance from the preceding patch on the upstream side in the moving direction of the belt,
When forming the subsequent patch,
the subsequent patch is formed in a first range between a first position that is spaced upstream from the leading edge of the previous patch by a drum circumferential length that is the circumferential length of the photosensitive drum, and a second position that is spaced upstream from the trailing edge of the previous patch by the drum circumferential length, such that a portion of the subsequent patch, including the leading edge or the trailing edge, overlaps with the subsequent patch, but the remaining portion does not overlap with the subsequent patch;
an overlapping length Lo, which is a length in the movement direction of the portion of the subsequent patch that overlaps with the first range, is 3 mm or less;
The control unit
forming a plurality of patches on the belt, the patches including the preceding patch and the succeeding patch;
an image forming apparatus that sets a correspondence relationship between a target density and an exposure density based on the results of reading the plurality of patches by the detection unit; an image forming unit that forms patches of toner of a predetermined color on a belt, the image forming unit having a photosensitive drum and a developing roller corresponding to the predetermined color;
a detection unit that detects the patch formed on the belt;
A patch forming method by a control unit of an image forming apparatus including:
forming a preceding patch of the predetermined color on the belt, and then forming a succeeding patch of the predetermined color on the belt at a distance from the preceding patch on the upstream side in the moving direction of the belt;
When forming the subsequent patch,
the subsequent patch is formed in a first range between a first position that is spaced upstream from the leading edge of the previous patch by a drum circumferential length that is the circumferential length of the photosensitive drum, and a second position that is spaced upstream from the trailing edge of the previous patch by the drum circumferential length, such that a portion of the subsequent patch, including the leading edge or the trailing edge, overlaps with the subsequent patch, but the remaining portion does not overlap with the subsequent patch;
an overlapping length Lo, which is a length in the movement direction of the portion of the subsequent patch that overlaps with the first range, is 3 mm or less;
forming a plurality of patches on the belt, the patches including the preceding patch and the succeeding patch;
a developing bias to be applied to the developing roller based on the result of reading the plurality of patches by the detecting unit; an image forming unit that forms patches of toner of a predetermined color on a belt, the image forming unit having a photosensitive drum and a developing roller corresponding to the predetermined color;
a detection unit that detects the patch formed on the belt;
A patch forming method by a control unit of an image forming apparatus including:
forming a preceding patch of the predetermined color on the belt, and then forming a succeeding patch of the predetermined color on the belt at a distance from the preceding patch on the upstream side in the moving direction of the belt;
When forming the subsequent patch,
the subsequent patch is formed in a first range between a first position that is spaced upstream from the leading edge of the previous patch by a drum circumferential length that is the circumferential length of the photosensitive drum, and a second position that is spaced upstream from the trailing edge of the previous patch by the drum circumferential length, such that a portion of the subsequent patch, including the leading edge or the trailing edge, overlaps with the subsequent patch, but the remaining portion does not overlap with the subsequent patch;
an overlapping length Lo, which is a length in the movement direction of the portion of the subsequent patch that overlaps with the first range, is 3 mm or less;
forming a plurality of patches on the belt, the patches including the preceding patch and the succeeding patch;
a patch forming method, characterized in that a correspondence relationship between a target density and an exposure density is set based on the results of reading the plurality of patches by the detection unit; an image forming unit that forms patches of toner of a predetermined color on a belt, the image forming unit having a photosensitive drum and a developing roller corresponding to the predetermined color;
a detection unit that detects the patch formed on the belt;
A patch forming method by a control unit of an image forming apparatus including:
forming a preceding patch of the predetermined color on the belt, and then forming a succeeding patch of the predetermined color on the belt at a distance from the preceding patch on the upstream side in the moving direction of the belt;
When forming the subsequent patch,
the subsequent patch is formed in a second range between a third position that is spaced upstream from the leading edge of the previous patch by a roller circumferential length that is the circumferential length of the developing roller, and a fourth position that is spaced upstream from the trailing edge of the previous patch by the roller circumferential length, such that a portion of the subsequent patch, including the leading edge or the trailing edge, overlaps the subsequent patch, but the other portion does not overlap the subsequent patch;
A patch forming method, characterized in that an overlap length Lo, which is a length in the movement direction of the part of the subsequent patch that overlaps with the second range, is 3 mm or less.