JP7690786B2 - Image forming device - Google Patents

Description

The present invention relates to an image forming device equipped with a control unit that performs processes such as adjusting print density based on the results of an image formed on a transfer medium such as a belt read by a detection unit.

Conventionally, there is known an image forming apparatus that includes an image forming section that forms a multi-color image on a belt, a detection section that detects the image formed on the belt, and a control section that executes a correction image forming process, a bias setting process, and a pattern image forming process (see Patent Document 1). The correction image forming process is a process in which a first bias correction image is formed on the belt while a first development bias is applied to the development roller, and then a second bias correction image is formed on the belt while a second development bias of a different value from the first development bias is applied to the development roller.

The bias setting process is a process for setting a development bias based on the results of reading the first bias-corrected image and the second bias-corrected image by the detection unit. The pattern image formation process is a process for forming multiple pattern images on the belt while the development bias set in the bias setting process is applied to the development roller.

The image forming device also has four photosensitive drums. The photosensitive drums are arranged in the order of K, C, M, and Y from the side closest to the detection unit.

JP 2020-003637 A

Conventionally, in the correction image forming process and the pattern image forming process, the multiple images formed on the belt are regularly arranged in the order of Y, M, C, and K, starting from the side closest to the detection unit. However, in this case, the black (K) image formed on the photosensitive drum closest to the detection unit is read by the detection unit later than the images of the other colors, which creates a problem in that it takes a long time from the start of the correction image forming process to the end of the pattern image forming process.

The present invention aims to shorten the time from the start of the correction image formation process to the end of the pattern image formation process.

In order to solve the above problem, the image forming apparatus of the present invention includes an image forming unit that forms a multi-color image on a transfer medium, a detection unit that detects the image formed on the transfer medium, and a control unit.
The image forming unit has a developing roller and a photosensitive drum corresponding to a first color, a developing roller and a photosensitive drum corresponding to a second color, a developing roller and a photosensitive drum corresponding to a third color, and a developing roller and a photosensitive drum corresponding to a fourth color.
The photosensitive drums are arranged in the order of the first color, the second color, the third color, and the fourth color from downstream to upstream in the movement direction in which the transfer medium moves toward the detection unit.
The control unit is capable of executing a correction image forming process, a bias setting process, and a pattern image forming process for each of the first color, the second color, the third color, and the fourth color.
The corrected image forming process is a process in which a first bias-corrected image is formed on the transfer medium by the image forming unit while a first developing bias is applied to the developing roller, and then a second bias-corrected image is formed on the transfer medium by the image forming unit while a second developing bias having a value different from the first developing bias is applied to the developing roller.
The bias setting process is a process for setting a development bias based on the result of reading the first bias-corrected image and the second bias-corrected image by the detection unit.
The pattern image forming process is a process in which the image forming unit forms a plurality of pattern images on the transfer medium in a state in which the developing bias set in the bias setting process is applied to the developing roller.
The control unit performs the corrected image formation process so that, in the movement direction, the first bias-corrected image of the first color is positioned in front of the first bias-corrected images of the second color, the third color, and the fourth color, and the second bias-corrected image of the first color is positioned between the first bias-corrected images of two of the second color, the third color, and the fourth color.

With this configuration, the bias setting process for the first color can be completed quickly, so the pattern image formation process for the first color can be started earlier, and as a result, the time from the start of the correction image formation process to the end of the pattern image formation process can be shortened.

Also, an image forming apparatus according to the present invention includes an image forming section that forms an image of a plurality of colors on a transfer medium, a detection section that detects the image formed on the transfer medium, and a control section.
The image forming unit has a developing roller and a photosensitive drum corresponding to a first color, a developing roller and a photosensitive drum corresponding to a second color, a developing roller and a photosensitive drum corresponding to a third color, and a developing roller and a photosensitive drum corresponding to a fourth color.
The photosensitive drums are arranged in the order of the first color, the second color, the third color, and the fourth color from downstream to upstream in the movement direction in which the transfer medium moves toward the detection unit.
The control unit is capable of executing a correction image forming process, a bias setting process, and a pattern image forming process for each of the first color, the second color, the third color, and the fourth color.
The corrected image forming process is a process in which a first bias-corrected image is formed on the transfer medium by the image forming unit while a first developing bias is applied to the developing roller, and then a second bias-corrected image is formed on the transfer medium by the image forming unit while a second developing bias having a value different from the first developing bias is applied to the developing roller.
The bias setting process is a process for setting a development bias based on the result of reading the first bias-corrected image and the second bias-corrected image by the detection unit.
The pattern image forming process is a process in which the image forming unit forms a plurality of pattern images on the transfer medium in a state in which the developing bias set in the bias setting process is applied to the developing roller.
The control unit executes the correction image formation process and the pattern image formation process so that the color of the first bias-corrected image located at the front of a first image group consisting of the first bias-corrected images of multiple colors and the second bias-corrected images of multiple colors, and the color of the pattern image located at the front of a second image group consisting of the pattern images of multiple colors, are the first color, and so that the color of the second bias-corrected image located at the rearmost of the first image group is different from the color of the pattern image located at the rearmost of the second image group.

With this configuration, the bias setting process for the first color can be completed quickly, so the pattern image formation process for the first color can be started earlier, and as a result, the time from the start of the correction image formation process to the end of the pattern image formation process can be shortened.

The control unit may also execute the correction image formation process so that, in the movement direction, the second bias-corrected image of the first color is positioned in front of the first bias-corrected image of one of the second color, the third color, and the fourth color.

With this configuration, the bias setting process for the first color can be completed more quickly, further shortening the time from the start of the correction image formation process to the end of the pattern image formation process.

The control unit may also execute the correction image formation process so that the second bias-corrected image of the fourth color is positioned in front of the second bias-corrected image of at least one of the second color and the third color in the movement direction.

With this configuration, the bias setting process for the fourth color can be completed quickly, so the pattern image formation process for the fourth color can be started earlier, and as a result, the time from the start of the correction image formation process to the end of the pattern image formation process can be shortened.

The control unit may also execute the correction image formation process so that the first bias-corrected image of the fourth color is positioned in front of the first bias-corrected image of at least one of the second color and the third color in the movement direction.

The control unit may also execute the corrected image formation process so that the images are arranged in the following order from the front in the movement direction: the first bias-corrected image of the first color, the first bias-corrected image of the fourth color, the first bias-corrected image of the third color, the second bias-corrected image of the first color, and the first bias-corrected image of the second color.

The control unit may also execute the correction image formation process such that, in the movement direction, after the first bias-corrected image of the second color, the second bias-corrected image is arranged in the order of the fourth color, the third color, and the second color.

With this configuration, the bias setting process for the fourth color can be completed more quickly than, for example, a configuration in which the second bias correction image is arranged in the order of the third color, the fourth color, and the second color.

The transfer medium may be an endless belt, and the distance from the front end of the forward-most first bias-corrected image to the rear end of the rear-most pattern image in the direction of movement may be smaller than the circumference of the belt.

With this configuration, there is no need to perform belt cleaning processing, which rotates the belt one or more revolutions, between the bias setting process and the pattern image forming process, so the time from the start of the correction image forming process to the end of the pattern image forming process can be shortened.

The pattern image may also be a gradation setting image for setting the correspondence between the target density and the exposure density.

The pattern image may also be a misalignment correction image for correcting misalignment of an image.

According to the present invention, it is possible to reduce the time from the start of the correction image formation process to the end of the pattern image formation process.

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. 13 is a diagram showing the correspondence relationship between target density and exposure density. FIG. 4 is a diagram showing the order of images formed on a conveyor belt. 1A to 1D are diagrams illustrating problems that arise when developing is continuously performed at a predetermined location on a developing roller, and problems that arise when exposing a predetermined location on a photosensitive drum continuously. 5A to 5C are diagrams illustrating the first half of the order in which a first bias-corrected image and a second bias-corrected image are transferred onto a conveyor belt. 11A to 11C are diagrams illustrating the latter half of the order in which a first bias-corrected image and a second bias-corrected image are transferred onto a conveyor belt. FIG. 13 is a diagram showing a modified example of a pattern image.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings as appropriate.
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 the top surface.

The supply unit 3 is provided 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.

The supply unit 3 supplies the sheet S in the supply tray 31 to the separation roller 34 by the pickup roller 33, and separates the sheet S into a single sheet between the separation roller 34 and the separation pad 35. The registration roller 36 aligns the leading edge of the sheet S, and then conveys the sheet 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 disposed at the top of the main body housing 2 and is equipped with a light source and a polygon mirror (not shown). The exposure device SC exposes the surface of the photosensitive drum 51 by irradiating the surface 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 housing 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 electricity removal lamp 54 is a member that removes static electricity by irradiating the surface of the photosensitive drum 51 with light.

The developing cartridge 6 contains toner. The developing cartridge 6 is equipped with a developing 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 developing cartridges 6, indicated by the reference characters 6K, 6C, 6M, and 6Y containing toner of each color, black, cyan, magenta, and yellow, are arranged in the order of 6K, 6C, 6M, and 6Y from downstream to upstream in the conveying direction of the sheet S. In other words, the developing cartridges 6K, 6C, 6M, and 6Y are arranged in the order of 6K, 6C, 6M, and 6Y from downstream to upstream in the moving direction in which the conveying belt 73 described later moves toward the detection unit PS. In addition, each photosensitive drum 51 corresponding to each developing cartridge 6 is also arranged in the order of K, C, M, and Y from downstream to upstream in the moving direction in which the conveying belt 73 moves toward the detection unit PS. In this specification and drawings, when identifying components such as the photosensitive drum 51 and the developing roller 61 that correspond to the color of the toner, the symbols K, C, M, and Y are added to correspond to black, cyan, magenta, and yellow, respectively, and the letters "first," "second," "third," and "fourth" are added to the beginning of the name of the component.

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. In this embodiment, black corresponds to the first color, cyan corresponds to the second color, magenta corresponds to the third color, and yellow corresponds to the fourth color.

The transfer unit 7 includes a drive roller 71, a driven roller 72, a conveyor belt 73 as an example of a transfer medium, four transfer rollers 74, and a belt cleaner BC. The conveyor belt 73 is an endless belt. The drive roller 71 and the driven roller 72 are members for rotating the conveyor belt 73. The drive roller 71 is disposed 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 disposed inside the conveyor belt 73 and holds the conveyor belt 73 between the transfer roller 74 and the corresponding photosensitive drum 51.

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

The detection unit PS is a sensor that detects the print density of the test image formed on the conveyor belt 73. The detection unit PS is disposed opposite the end of the conveyor belt 73 on the drive roller 71 side. The 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 section 9 is mainly configured to convey the sheet S discharged from the fixing device 8 toward the outside of the main body housing 2. The conveying section 9 mainly includes 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 is discharged by the discharge roller 92 onto the discharge tray 21.

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

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

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

As described above, the control unit 100 selects one print pattern image that corresponds to the target density from among the multiple print pattern images, 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 print pattern images correspond to the exposure densities and are stored in advance in the storage unit. The multiple print 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 executing image quality adjustment for adjusting the image quality of the printed toner image. The control unit 100 executes the image quality adjustment when a predetermined condition is satisfied. Specifically, for example, the control unit 100 may be configured to execute the image quality adjustment when any one of the following conditions is satisfied:
First condition: The developing cartridge 6 or the 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 printed pages since the previous image quality adjustment has been increased to a predetermined number or more. 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 executing 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 correction image forming process is a process in which, with a first developing bias applied to the developing roller 61, the image forming unit 4 forms a first bias-corrected image on the conveyor belt 73, and then, with a second developing bias of a different value from the first developing bias applied to the developing roller 61, the image forming unit 4 forms a second bias-corrected image on the conveyor belt 73. Here, the developing bias is a bias applied to the developing roller 61 by a bias application unit (not shown). The image forming unit 4 has a bias application unit.

The first and second developing biases are set to optimal values for each color. The first developing bias may be a different value for each color, or may be the same value for some or all of the multiple colors. For example, the first developing bias corresponding to black may be a different value from the first developing bias corresponding to yellow, or may be the same value. Similarly, the second developing bias may be a different value for each color, or may be 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 developing bias to form a print pattern image with an exposure density of 40% as shown in FIG. 2, for example. In this case, the second bias-corrected image is formed by using the second developing bias to form a print pattern image with an exposure density of 40%.

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

The pattern image forming process is a process in which the image forming unit 4 forms multiple pattern images on the conveyor belt 73 while the developing bias set in the bias setting process is applied to the developing roller 61. Here, the multiple pattern images are gradation setting images for performing the gradation setting process. Specifically, the multiple pattern images are multiple print pattern images corresponding to multiple exposure densities, and 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 by the detection unit PS. Specifically, in the gradation setting process, the control unit 100 sets the correspondence between the target density and the pattern image to be printed, thereby setting the correspondence between the target density and the density of the toner image that is actually printed, i.e., the exposure density.

To explain in more detail, 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 to change the correspondence between the target density and the print pattern image.

Specifically, if the gradation setting process has never been performed in the past, the correspondence between the target density and the print pattern image (exposure density) is, for example, a default gamma table as 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 for selecting a print pattern with a specified exposure density that corresponds to a specified target density when printing at a specified target density. The gamma table shown by the two-dot dashed line, i.e., the default gamma table, has the same value for the target density and the exposure density.

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

In addition, in the gradation setting process at this time, if the print density is 40% when the print pattern image with an exposure density of 40% is detected by the detection unit PS, that is, if the target density, exposure density, and print density are the same, the relationship between the target density and the exposure density is linearly interpolated as shown by the dashed line in the figure. As a result, for example, in the next print control, when an image is formed with a target density of 20%, a print pattern image corresponding to the exposure density X corresponding to the intersection of the target density 20% 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 of the default gamma table (two-dot chain line) with an exposure density of less than 40% are replaced with the dashed line in the figure. In other words, the area between the black circle shown in the figure and the white circle corresponding to the exposure density of 40% is supplemented as shown by the dashed straight line.

As shown in FIG. 4, 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 in the correction image formation process. The control unit 100 forms a second image group G2 consisting of multiple color pattern images Kγ1 to Kγ5, Cγ1 to Cγ5, Mγ1 to Mγ5, and Yγ1 to Yγ5 in the pattern image formation process. The order of the first bias-corrected images K1 to Y1, the second bias-corrected images K2 to Y2, and the pattern images Kγ1 to Yγ5 on the conveyor belt 73 is set in the order 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 order of exposure is determined so that the order of the images for inspection on the conveyor belt 73 is the order shown in the figure. The order of exposure is stored in a storage unit (not shown). Note that each image is shown in a simplified form in FIG. 4.

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

Here, the length of each image in the direction of movement is set according to the number of reading points (number of positions to be read) 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 direction of movement 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 direction of movement is set to a second length corresponding to the second predetermined number, which is smaller than the first length. The interval between each image is set taking into consideration the variation in color shift and the reduction of toner consumption.

The bias-corrected images are set to be 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 above-mentioned order.

The pattern images are arranged in the following order from the top in the movement direction: 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 about two pattern images. More specifically, pattern image Kγ3 is arranged with a pitch of 3×Lp2 relative to pattern image Kγ2. Note that the expression of 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 about two pattern images. Pattern image Cγ1 is arranged after pattern image Kγ5 with a gap of about one pattern image. Pattern image Mγ1 is arranged after pattern image Cγ2 with a gap of about one pattern image. Pattern image Kγ1, which is the frontmost in the movement direction, is arranged after second bias-corrected image C2 with a gap of about three pattern images. The distance from the front end of the frontmost first bias-corrected image K1 to the rear end of the rearmost pattern image Yγ5 in the movement direction is smaller than the circumference of the conveyor belt 73.

The order of the images for inspection is determined so as to satisfy the following conditions: In the following description, the images for inspection are also referred to as patches Gp.
<Regarding the First Image Group G1>
1. Patches Gp of the same color are arranged at intervals of 2×Lp1 or more.
2. The interval between patches Gp of the same color is not set to 5×Lp1.

Condition 1 is a condition for ensuring the time required to switch the developing bias from the first developing bias to the second developing bias, and for preventing continuous development at the same location on the developing roller 61. In this embodiment, the time required to switch the developing bias from the first developing bias to the second developing bias is approximately equal to the time it takes for the conveyor belt 73 to move the first pitch Lp1. Therefore, considering the conditions for switching the developing bias, the interval between patches Gp of the same color needs to be equal to or greater than the first pitch Lp1.

When development is performed continuously at the same location on the developing roller 61, the formed patch Gp may become unclear. This phenomenon will be explained below with reference to FIG. 5. Note that the length of one patch Gp in the movement direction will be explained as approximately 1/2 the circumference of the developing roller 61 and approximately 1/6 the circumference of the photosensitive drum 51.

As shown in Figs. 5(a) and (b), when the first range R1 of the photosensitive surface of the photosensitive drum 51 is exposed, the toner located in the second range R2 of the developing roller 61 is transferred to the first range R1, and a patch Gp is formed in the first range R1 of the photosensitive drum 51. As shown in Fig. 5(c), when the developing roller 61 rotates half a turn from the position of Fig. 5(b) and the second range R2 reaches the development nip position Pn, which is the contact point between the photosensitive drum 51 and the developing roller 61, again, the amount of toner on the second range R2 may be reduced. In this case, if the toner on the second range R2 is transferred to the photosensitive drum 51 to form the patch Gp, the patch Gp may become unclear. Therefore, the patches Gp of the same color must be arranged at an interval of 2 x Lp1 or more so that two patches Gp of the same color are not arranged at an interval of the first pitch Lp1.

The condition 2 is a condition for preventing poor formation of an electrostatic latent image due to the influence of the previous exposure remaining at a specific location when the photosensitive drum 51 is exposed to light and then the specific location is exposed again when the photosensitive drum 51 has made exactly one rotation. This phenomenon will be described below with reference to FIG. 5. As shown in FIG. 5(d), the first range R1, which is the exposed range of the photosensitive drum 51, is discharged when it passes the discharge lamp 54, but the influence of the previous exposure may remain. If the first range R1 is exposed again while the influence of such exposure remains, there is a risk of poor formation of an electrostatic latent image. Therefore, it is necessary that the interval between patches Gp of the same color is not 5×Lp1.

<Regarding the Second Image Group G2>
The order of the pattern images in the second image group G2 is set so as to satisfy the following condition in addition to the above-mentioned conditions 1 and 2.
3. The distance from the rear end of a second bias-corrected image of a certain color (for example, K2) to the forefront pattern image of that color (for example, Kγ1) is set to a predetermined distance La or more.
La = Lb + Lc
Lb: distance Lc that the patch Gp moves from the development nip position Pn to the reading position Pr (see FIG. 6) at the detection unit PS = distance that the patch Gp moves during the time from reading the second bias correction image to switching the development bias to the development bias set by the bias setting process

The distance Lb differs for each color. Specifically, the distance LbK corresponding to black (see FIG. 6(a)) is the smallest, the distance LbC corresponding to cyan is the second smallest, the distance LbM corresponding to magenta is the third smallest, and the distance LbY corresponding to yellow is the largest.

The distance Lc is the same for each color. However, the distance Lc may vary slightly for each color.

As a result, the specified distance LaK corresponding to black is the smallest, the specified distance LaC corresponding to cyan is the second smallest, the specified distance LaM corresponding to magenta is the third smallest, and the specified distance LaY corresponding to yellow is the largest.

As shown in FIG. 4, the first bias-corrected image K1 is positioned at the beginning of the movement direction so that the formation of the black pattern images Kγ1 to Kγ5 corresponding to the smallest predetermined distance LaK can be started earlier than the images of other colors, and the second bias-corrected image K2 is positioned so that the distance between the first bias-corrected image K1 and the second bias-corrected image K2 is the shortest, 2×Lp1. Note that in the following description, the names of each image may be omitted and only the reference symbols may be used.

To speed up the timing for completing the formation of the yellow pattern images Yγ1 to Yγ5, which correspond to the longest predetermined distance LaY, Y1 is placed immediately after K1, and Y2 is placed before M2 and C2. It is also possible to reverse the order of C1 and Y2 and set the distance between Y1 and Y2 to the shortest 2×Lp1, but in this case, the distance between C1 and C2 must be 2×Lp1, which creates a blank (area where no image is formed) between M2 and C2 and increases the length of the first image group G1. For this reason, the arrangement shown in the figure is preferable.

Y2, M2, and C2 are arranged from the front in descending order of the specified distance La. This makes it possible to minimize the number of blanks.

The distance from the rear end of K2 to the front end of Kγ1 is equal to or greater than a predetermined distance LaK.
The distance from the rear end of Y2 to the front end of Yγ1 is equal to or greater than a predetermined distance LaY.
The distance from the rear end of M2 to the front end of Mγ1 is equal to or greater than a predetermined distance LaM.
The distance from the rear end of C2 to the front end of Cγ1 is equal to or greater than a predetermined distance LaC.
In this embodiment, the difference between the distance from the rear end of the second bias-corrected image (e.g., K2) to the front end of the foremost pattern image of that color (e.g., Kγ1) and the predetermined distance for that color (e.g., LaK) is smaller for K and Y than for M and C. This makes it possible to shorten the overall length from the front end of the first image group G1 formed on the conveyor belt 73 to the rear end of the second image group G2.

With the image order determined as above, the control unit 100 starts the correction image formation process in the order K, Y, M, C, and ends it in the order K, Y, M, C. The control unit 100 also starts the bias setting process in the order K, Y, M, C, and ends it in the order K, Y, M, C. The control unit 100 also starts the pattern image formation process in the order K, C, M, Y, and ends it in the order K, M, C, Y.

Next, the method for forming the first image group G1 by the control unit 100 will be described. Note that the method for forming the second image group G2 is similar to the method for forming the first image group G1, so a description thereof will be omitted.

When the control unit 100 executes the correction image formation process, it exposes each photosensitive drum 51 according to the exposure sequence stored in the memory unit. As a result, as shown in FIG. 6(a), Y1 is first formed on the conveyor belt 73.

After that, as shown in FIG. 6(b), Y2 is formed at a position 3×Lp1 behind Y1. Then, as shown in FIG. 6(c), M1 is formed behind Y1 with the first pitch Lp1.

After that, as shown in FIG. 7(a), M2 is formed at the first pitch Lp1 after Y2. Then, as shown in FIG. 7(b), K1 is formed at the first pitch Lp1 before Y1, and C1 is formed at the first pitch Lp1 before Y2. Then, as shown in FIG. 7(c), K2 is formed at the first pitch Lp1 after M1, and C2 is formed at the first pitch Lp1 after M2.

As described above, the following effects can be obtained in this embodiment.
Since the bias setting process for black can be completed early, the start of the pattern image forming process for black can be brought forward, and as a result, the time from the start of the first correction image forming process to the end of the last pattern image forming process for all colors can be shortened.

By positioning the second black bias-corrected image K2 ahead of the first cyan bias-corrected image C1 in the direction of movement, the bias setting process for black can be completed sooner, thereby further shortening the time from the start of the first correction image formation process to the end of the final pattern image formation process for all colors.

By positioning the second bias-corrected image Y2 for yellow ahead of the second bias-corrected images M2 and C2 for magenta and cyan in the direction of movement, the bias setting process for yellow can be completed earlier, and the start of the pattern image formation process for yellow can be brought forward, thereby shortening the time from the start of the first correction image formation process to the end of the last pattern image formation process for all colors.

By making the distance in the movement direction from the front end of the first bias correction image K1, which is the foremost, to the rear end of the rearmost pattern image Yγ5 smaller than the circumference of the conveyor belt 73, it is not necessary to perform a belt cleaning process in which the conveyor belt 73 rotates one or more revolutions between the bias setting process and the pattern image forming process, so it is possible to shorten the time from the start of the first correction image forming process to the end of the last pattern image forming process for all colors. Note that in the conventional belt cleaning process, the conveyor belt 73 rotates two revolutions, making it possible to significantly shorten the time compared to this conventional technology.

The present invention is not limited to the above embodiment, but can be used in various forms as exemplified below. In the following description, the same reference numerals are used for components that have substantially the same structure as the above embodiment, and the description thereof will be omitted.

The pattern image is not limited to a gradation setting image as in the above embodiment. For example, as shown in FIG. 8, the pattern image may be misalignment correction images Kp1, Yp1, Mp1, Cp1, Kp2, Yp2, Mp2, and Cp2 for correcting misalignment of the image. Specifically, the first misalignment correction images Kp1, Yp1, Mp1, and Cp1 extend in a predetermined direction. Here, the predetermined direction may be a direction inclined with respect to the width direction of the conveyor belt 73, or a direction parallel to the width direction.

The second misalignment correction images Kp2, Yp2, Mp2, and Cp2 are inclined with respect to a predetermined direction. Furthermore, multiple image groups G11 consisting of misalignment correction images Kp1, Yp1, Mp1, Cp1, Kp2, Yp2, Mp2, and Cp2 are arranged in the movement direction. Even in this form, the time from the start of the first correction image formation process to the end of the final pattern image formation process for all colors can be shortened.

The order of the images is not limited to that of the above embodiment. The second bias-corrected image of the first color may be located between the first bias-corrected images of two of the second, third, and fourth colors. For example, in the above embodiment, K2 may be located between Y1 and M1.

Furthermore, the color of the first bias-corrected image located at the front of the first image group and the color of the pattern image located at the front of the second image group may be the first color, and the color of the second bias-corrected image located at the rearmost of the first image group and the color of the pattern image located at the rearmost of the second image group may be different. For example, in the above embodiment, the color of the second bias-corrected image located at the rearmost of the first image group G1 may be magenta, and the color of the pattern image located at the rearmost of the second image group G2 may be yellow.

In addition, in the direction of movement, the second bias-corrected image of the first color may be located in front of the first bias-corrected image of one of the second, third, and fourth colors. For example, in the above embodiment, K2 may be located in front of M2.

Furthermore, the second bias-corrected image of the fourth color may be located in front of the second bias-corrected image of at least one of the second and third colors in the movement direction. For example, in the above embodiment, Y2 may be located between M2 and C2.

Furthermore, the first bias-corrected image of the fourth color may be located in front of the first bias-corrected image of at least one of the second and third colors in the movement direction. For example, in the above embodiment, Y1 may be located between M1 and K2.

The first developing bias for a predetermined color and the first developing bias for a color different from the predetermined color may be the same value or different values. The second developing bias for a predetermined color and the second developing bias for a color different from the predetermined color may be the same value or different values.

In addition to the first bias-corrected image and the second bias-corrected image, a third bias-corrected image may also be formed between the first bias-corrected image and the second bias-corrected image, and the development bias may be corrected using these three bias-corrected images.

The transfer medium may be a sheet such as paper. 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 the present invention may be applied to other image forming apparatuses, such as a copying machine or a multifunction machine.
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 photosensitive drum, the second photosensitive drum, the third photosensitive drum, and the fourth photosensitive drum 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 combined in any manner.

REFERENCE SIGNS LIST 1 color printer 4 image forming section 51 photosensitive drum 51K first photosensitive drum 51C second photosensitive drum 51M third photosensitive drum 51Y fourth photosensitive drum 61 developing roller 73 conveyor belt 100 control section K1 first bias corrected image C1 first bias corrected image M1 first bias corrected image Y1 first bias corrected image K2 second bias corrected image Kγ1 to Yγ5 pattern image PS detection section

Claims (9)

An image forming unit that forms a multi-color image on a transfer medium,
a developing roller and a photosensitive drum corresponding to a first color;
a developing roller and a photosensitive drum corresponding to a second color;
a developing roller and a photosensitive drum corresponding to a third color;
an image forming unit having a developing roller and a photosensitive drum corresponding to a fourth color;
A detection unit that detects an image formed on the transfer medium;
A control unit,
an image forming apparatus in which photosensitive drums for the first color, the second color, the third color, and the fourth color are arranged in this order from a downstream side to an upstream side in a moving direction in which the transfer medium moves toward the detection unit,
The control unit is
For each of the first color, the second color, the third color, and the fourth color,
a correction image forming process in which a first bias-corrected image is formed on the transfer medium by the image forming unit while a first developing bias is applied to the developing roller, and then a second bias-corrected image is formed on the transfer medium by the image forming unit while a second developing bias having a value different from the first developing bias is applied to the developing roller;
a bias setting process for setting a development bias based on a result of reading the first bias-corrected image and the second bias-corrected image by the detection unit;
a pattern image forming process for forming a plurality of pattern images on the transfer medium by the image forming unit in a state in which the developing bias set in the bias setting process is applied to the developing roller;
an image forming apparatus that performs the corrected image formation process such that, in the movement direction, the first bias-corrected image of the first color is positioned in front of the first bias-corrected images of the second color, the third color, and the fourth color, and the second bias-corrected image of the first color is positioned between the first bias-corrected images of two colors among the second color, the third color, and the fourth color. An image forming unit that forms a multi-color image on a transfer medium,
a developing roller and a photosensitive drum corresponding to a first color;
a developing roller and a photosensitive drum corresponding to a second color;
a developing roller and a photosensitive drum corresponding to a third color;
an image forming unit having a developing roller and a photosensitive drum corresponding to a fourth color;
A detection unit that detects an image formed on the transfer medium;
A control unit,
an image forming apparatus in which photosensitive drums for the first color, the second color, the third color, and the fourth color are arranged in this order from a downstream side to an upstream side in a moving direction in which the transfer medium moves toward the detection unit,
The control unit is
For each of the first color, the second color, the third color, and the fourth color,
a correction image forming process in which a first bias-corrected image is formed on the transfer medium by the image forming unit while a first developing bias is applied to the developing roller, and then a second bias-corrected image is formed on the transfer medium by the image forming unit while a second developing bias having a value different from the first developing bias is applied to the developing roller;
a bias setting process for setting a development bias based on a result of reading the first bias-corrected image and the second bias-corrected image by the detection unit;
a pattern image forming process for forming a plurality of pattern images on the transfer medium by the image forming unit in a state in which the developing bias set in the bias setting process is applied to the developing roller;
a color of the first bias-corrected image located at the forefront of a first image group consisting of the first bias-corrected image of a plurality of colors and the second bias-corrected image of a plurality of colors, and a color of the pattern image located at the forefront of a second image group consisting of the pattern images of a plurality of colors are the first color; and
the color of the second bias-corrected image located at the rearmost position of the first image group is different from the color of the pattern image located at the rearmost position of the second image group; and
such that, in the movement direction, the second bias-corrected image of the first color is located in front of the first bias-corrected image of one of the second color, the third color, and the fourth color.
an image forming apparatus which executes the correction image forming process and the pattern image forming process; The control unit is
3. The image forming apparatus according to claim 1, further comprising: a step of: performing the correction image forming process so that the second bias-corrected image of the fourth color is positioned in front of the second bias-corrected image of at least one of the second color and the third color in the movement direction . The control unit is
4. The image forming apparatus according to claim 1, further comprising: a first bias-corrected image forming unit for forming a first bias-corrected image of the fourth color, the first bias-corrected image of the fourth color being positioned in front of the first bias-corrected image of at least one of the second color and the third color in the moving direction. The control unit is
In order from the front in the moving direction,
the first bias-corrected image of the first color;
the first bias-corrected image of the fourth color;
the first bias-corrected image of the third color;
the second bias-corrected image of the first color;
5. The image forming apparatus according to claim 1 , wherein the corrected image forming process is executed so that the images are arranged in the order of the first bias corrected image of the second color. The control unit is
6. The image forming apparatus according to claim 5, wherein the correction image forming process is performed such that, in the movement direction, the second bias-corrected image is arranged in the order of the fourth color, the third color, and the second color, after the first bias-corrected image of the second color. the transfer medium is an endless belt,
7. The image forming apparatus according to claim 1, wherein the distance from the front end of the first bias correction image, which is the forwardmost, to the rear end of the rearmost pattern image in the movement direction is smaller than the circumference of the belt . 8. The image forming apparatus according to claim 1 , wherein the pattern image is a gradation setting image for setting a correspondence relationship between a target density and an exposure density. 8. The image forming apparatus according to claim 1 , wherein the pattern image is a positional deviation correction image for correcting a positional deviation of an image.

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