JP7424067B2 - image forming device - Google Patents

Description

The present invention relates to an image forming apparatus.

Conventionally, image forming devices such as printers, copiers, facsimile machines, and multifunction devices, such as electrophotographic color printers, are equipped with a plurality of image forming units, LED heads, transfer units, fixing devices, etc. The image forming unit is provided with a photosensitive drum, a charging roller, a developing roller, a supply roller, etc., and the transfer unit is provided with a transfer belt, a transfer roller, etc. as a transfer medium.

In this type of printer, the surface of a photoreceptor drum that is uniformly charged by a charging roller is exposed to light by an LED head to form an electrostatic latent image, and toner is supplied to a developing roller by a supply roller. The electrostatic latent image is developed to form a toner image, a transfer unit transfers the toner image onto a sheet of paper conveyed through a paper conveyance path, and a fixing device fixes the toner image to the sheet of paper to form an image. , printing is performed.

By the way, the sensitivity of the photoreceptor of the photoreceptor drum, the chargeability of the toner, etc. may change over time, or the environment such as temperature and humidity in which the printer is placed may change, and in such cases, the image quality may change. The density of the image will change, and the image quality will deteriorate. Therefore, in the printer, a pattern image for density correction is formed on the transfer belt, the density of the pattern image is detected by a density sensor, and density correction is performed based on the detected density (for example, , see Patent Document 1).

Japanese Patent Application Publication No. 2018-185485

However, in the conventional printer, the pattern image on the transfer belt may be reversely transferred to the photoreceptor drum of the downstream image forming unit among the image forming units, and in that case, the pattern image is detected by the density sensor. concentration will be lower.

Therefore, it is possible to separate the image forming units of colors that are not used when forming the pattern image from the paper conveyance path to prevent the pattern image from being reversely transferred to the photoreceptor drum. If the number of times the photoreceptor drum and transfer belt come into contact during image formation differs from the number of times the photoreceptor drum and transfer belt come into contact when actually forming an image on paper, it is difficult to perform density correction accurately. image quality will deteriorate.

The present invention solves the problems of the conventional printers, enables accurate density correction based on the detected density of a pattern image for density correction, and improves image quality. The purpose is to provide equipment.

For this purpose, the image forming apparatus of the present invention includes a plurality of image forming units each including an image carrier, a transfer medium that is made to run along each of the image forming units, and a pattern image on each of the image carriers. A transfer unit equipped with a transfer member that transfers images onto a transfer medium, and an image forming unit disposed on the most upstream side in the traveling direction of the transfer medium are placed in an operating state in which an image is transferred onto the transfer medium, and an image forming unit provided on the downstream side A monochrome pattern image forming process in which a first pattern image for density correction is formed on the transfer medium while another image forming unit disposed in the transfer medium is placed in an inactive state in which no image is transferred to the transfer medium. a full-color pattern image forming processing section that forms a second pattern image for density correction on the transfer medium when all the image forming units are in an operating state; The image forming apparatus includes a density correction processing section that performs density correction based on the pattern image, and a density detection processing section that detects the density of the first and second pattern images.
Further, the density correction processing section is configured to calculate the overall density of the other image forming units disposed on the downstream side based on the density difference between the densities of the first and second pattern images detected by the density detection processing section. When the reverse transfer amount is calculated and the number of image forming units placed in an operating state among the other image forming units is at least a plurality and less than the total number, at least a plurality and the total number Density correction is performed when multicolor printing is performed using at least a plurality of image forming units and a number less than the total number of image forming units, based on the number less than the total number and the calculated total reverse transfer amount.

According to the present invention, the image forming apparatus of the present invention includes a plurality of image forming units each including an image carrier, a transfer medium that is caused to travel along each of the image forming units, and a transfer medium that is disposed on each of the image carriers. A transfer section including a transfer member that transfers the pattern image onto the transfer medium, and an image forming unit disposed at the most upstream side in the traveling direction of the transfer medium are placed in an operating state to transfer the image onto the transfer medium. , a monochromatic pattern for forming a first pattern image for density correction on the transfer medium while another image forming unit disposed downstream is placed in an inactive state in which no image is transferred to the transfer medium; an image forming processing section; an all-color pattern image forming processing section that forms a second pattern image for density correction on the transfer medium with all the image forming units in an operating state; The image forming apparatus includes a density correction processing section that performs density correction based on the second pattern image, and a density detection processing section that detects the density of the first and second pattern images.
Further, the density correction processing section is configured to calculate the overall density of the other image forming units disposed on the downstream side based on the density difference between the densities of the first and second pattern images detected by the density detection processing section. When the reverse transfer amount is calculated and the number of image forming units placed in an operating state among the other image forming units is at least a plurality and less than the total number, at least a plurality and the total number Density correction is performed when multicolor printing is performed using at least a plurality of image forming units and a number less than the total number of image forming units, based on the number less than the total number and the calculated total reverse transfer amount.

In this case, the image forming unit disposed on the most upstream side in the traveling direction of the transfer medium is in an activated state, and the other image forming units disposed on the downstream side are in an inoperative state. A first pattern image for density correction is formed on the transfer medium, and a second pattern image for density correction is formed on the transfer medium with all image forming units in an operating state, and a second pattern image for density correction is formed on the transfer medium. 1. Since the image density is corrected based on the second pattern image, the number of times the image carrier and the transfer medium come into contact when forming the first and second pattern images, and the actual number of times the image is transferred to the medium Density correction can be performed with high accuracy regardless of the number of times the image carrier and the transfer medium come into contact during formation.

Therefore, image quality can be improved.

1 is a control block diagram of a printer in an embodiment of the present invention. FIG. 1 is a conceptual diagram of a printer in an embodiment of the present invention. FIG. 3 is a conceptual diagram of a transfer unit in an embodiment of the present invention. FIG. 3 is a diagram showing a state in which the image forming unit according to the embodiment of the present invention is placed in an operating position. FIG. 3 is a diagram showing a state in which the image forming unit according to the embodiment of the present invention is placed in a retracted position. FIG. 2 is a comparison diagram of the density of a yellow image when five-color printing and single-color yellow printing are performed in an embodiment of the present invention. FIG. 3 is a comparison diagram of the density of a magenta image when five-color printing and magenta monochrome printing are performed in the embodiment of the present invention. FIG. 3 is a comparison diagram of the density of a cyan image when five-color printing and cyan monochrome printing are performed in an embodiment of the present invention. FIG. 3 is a comparison diagram of the density of a black image when five-color printing and black monochrome printing are performed in an embodiment of the present invention. FIG. 3 is a diagram showing the density of a white image when monochrome white printing is performed in an embodiment of the present invention. It is a flow chart showing operation of a control part in an embodiment of the present invention. FIG. 3 is a diagram showing an example of a first pattern image in an embodiment of the present invention. It is a figure which shows the example of the 2nd pattern image in embodiment of this invention. FIG. 3 is a diagram showing an example of a target concentration table in an embodiment of the present invention. FIG. 7 is a diagram showing an example of a density difference-reverse transfer development voltage correction value table in an embodiment of the present invention. It is a figure showing an example of a reverse transcription variable table in an embodiment of the present invention. FIG. 7 is a diagram showing evaluation results of image density when N-color printing is performed in an example. 7 is a diagram showing evaluation results of image density when N-color printing is performed in Comparative Example 1. FIG. 7 is a diagram showing evaluation results of image density when N-color printing is performed in Comparative Example 2. FIG.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In this case, a printer as an image forming apparatus will be described.

FIG. 2 is a conceptual diagram of a printer according to an embodiment of the present invention, and FIG. 3 is a conceptual diagram of a transfer unit according to an embodiment of the present invention.

In the figure, 10 is a printer, Cs is a housing of the printer 10, Bd is a main body of the printer 10, that is, the main body of the apparatus, and Rt1 is a paper transport path as a medium transport path through which paper P as a medium is transported. The housing Cs includes a front wall Wf, a back wall Wr, and a top wall Wt, and a stacker St1 as a medium loading section is formed on the top wall Wt.

An image forming section Q1 is disposed in the upper part of the apparatus main body Bd, a paper feeding part K1 as a medium supplying part is arranged in the lower part of the apparatus main body Bd, and a transfer part U1 is arranged between the image forming part Q1 and the paper feeding part K1. be done.

The image forming unit Q1 includes a plurality of image forming units 20Y, 20M, 20C, 20Bk, and 20W of yellow, magenta, cyan, black, and white as a special color in this embodiment, as well as each image forming unit. The units 20Y, 20M, 20C, 20Bk, and 20W each include an LED head Hd (FIG. 1) as an exposure device, which will be described later, and is disposed facing the photosensitive drum 21 as an image carrier.

In the image forming section Q1, the uniformly charged surface of each photoreceptor drum 21 is exposed to light by the LED head Hd, and an electrostatic latent image is formed as a latent image on the photoreceptor drum 21. is developed, and a toner image as a developer image of each color and as a pattern image is formed on the photoreceptor drum 21.

The image forming units 20Y, 20M, 20C, 20Bk, and 20W are detachably attached to the apparatus main body Bd and movable in the vertical direction (moveable toward and away from the paper conveyance path Rt1) from the back wall Wr. They are arranged side by side across the front wall Wf. Further, the LED head Hd is formed by arranging a plurality of LEDs (not shown) as light emitting elements in the main scanning direction.

In this embodiment, the color white is used as the special color, but colors such as clear, gold, silver, neon, etc. can also be used as the special color. Further, a laser or the like may be used instead of the LED head Hd.

The transfer unit U1 includes an intermediate transfer unit u1 and a secondary transfer roller 32 as a transfer member for secondary transfer. The intermediate transfer unit u1 is detachably disposed with respect to the apparatus main body Bd, and includes an endless intermediate transfer belt 44 as a transfer medium and as a belt member. The toner images on the drum 21 are sequentially transferred in an overlapping manner to form a color toner image, and the color toner image is transferred onto the paper P by the secondary transfer roller 32.

For this purpose, the intermediate transfer unit u1 includes a drive roller 41 as a first roller that is rotatably disposed near the image forming unit 20W, a drive roller 41 that is rotatably disposed near the image forming unit 20Y, and a drive roller 41 that is rotatably disposed near the image forming unit 20Y. A driven roller 42 serving as a second roller rotates as the roller 41 rotates, is rotatably disposed below the driving roller 41 and the driven roller 42, and rotates as the driving roller 41 and the driven roller 42 rotate. A backup roller 43 for secondary transfer, which serves as a third roller to be transferred, is stretched between the drive roller 41, the driven roller 42, and the backup roller 43 so that the drive roller 41, the driven roller 42, and the backup roller 43 can move freely. The intermediate transfer belt 44 is caused to run in the direction of arrow A along the image forming units 20Y, 20M, 20C, 20Bk, and 20W as it rotates, and each of the image forming units 20Y, 20M, 20C, A primary transfer roller 45 and an intermediate transfer belt 44 are arranged to face the 20Bk and 20W photoreceptor drums 21, respectively, and serve as primary transfer transfer members that transfer the toner images on the photoreceptor drums 21 to the intermediate transfer belt 44. A reverse bending roller 47 that bends the image in the opposite direction, first and second pattern images Imy, Jmi (i=y, m, c, b, w) for density correction, which will be described later, are formed on the intermediate transfer belt 44. The cleaning device 48 and the like are provided for removing. The cleaning device 48 includes a cleaning blade (not shown) as a first cleaning member that scrapes off the toner as the developer of the first and second pattern images Imy and Jmi, and a waste developer storage section that stores the scraped toner. It also has a waste toner storage section (not shown).

A predetermined position on the intermediate transfer belt 44, in this embodiment, is located downstream of the drive roller 41 and upstream of the backup roller 43 in the running direction of the intermediate transfer belt 44, and is opposed to the intermediate transfer belt 44. A concentration sensor s1 as a concentration detection section is provided. The density sensor s1 is a reflective optical sensor that includes a light emitting section and a light receiving section, and uses the light emitted by the light emitting section to transfer the light emitted from the light emitting section to the first and second pattern images Imy, Jmi formed on the intermediate transfer belt 44. The density of the first and second pattern images Imy and Jmi is detected for each color based on the intensity of the reflected light received by the light receiving section.

The photosensitive drums 21, intermediate transfer belt 44, and primary transfer rollers 45 constitute a primary transfer section, and the backup roller 43, intermediate transfer belt 44, and secondary transfer roller 32 constitute a secondary transfer section.

The paper feed section K1 includes a paper cassette 11 as a medium storage section in which paper P is stored, and a hopping roller 12 as a feeding member rotatably disposed at the front end of the paper cassette 11 in contact with the paper P. As the hopping roller 12 rotates, it separates the paper P one by one and feeds it out onto the paper transport path Rt1.

A first conveyance roller pair m1 consisting of a registration roller 13 and a pinch roller pc1 is rotatably disposed downstream of the hopping roller 12 in the paper conveyance path Rt1, and downstream of the first conveyance roller pair m1. , a second conveyance roller pair m2 consisting of a guide roller 13 and a pinch roller pc2 is rotatably disposed, and the secondary transfer roller 32 and a backup roller 43 are disposed downstream of the second conveyance roller pair m2. The paper P is transported along the paper transport path Rt1 in the direction of arrow B.

Furthermore, a fixing device 51 as a fixing device is disposed downstream of the transfer unit U1 in the paper transport path Rt1. The fixing device 51 includes a heating roller 52 as a first fixing member and a pressure roller 53 as a second fixing member.

A third transport roller pair m3 including a discharge roller 55 and a pinch roller pc3 is disposed downstream of the fixing device 51 in the paper transport path Rt1.

Next, the image forming units 20Y, 20M, 20C, 20Bk, and 20W will be explained. Note that each of the image forming units 20Y, 20M, 20C, 20Bk, and 20W has the same structure except for the toner used, so in this case, only the yellow image forming unit 20Y will be described.

FIG. 4 is a diagram showing the image forming unit according to the embodiment of the present invention in the operating position, and FIG. 5 is a diagram showing the image forming unit in the embodiment of the present invention in the retracted position. be.

In the figure, 20Y is an image forming unit, 45 is a primary transfer roller, and 57 is swingably disposed at the lower end of the image forming unit 20Y. This is an operating lever that serves as a lifting mechanism for moving in the direction. When the operating lever 57 is tilted, the image forming unit 20Y is placed in the operating position shown in FIG. The image is placed in an operating state where it is transferred onto the transfer belt 44. Further, when the operating lever 57 is raised, the image forming unit 20Y is placed in the retracted position shown in FIG. It is placed in an inactive state in which it is not transferred to the transfer belt 44.

The image forming unit 20Y includes a photoreceptor drum 21, a charging roller 22 that is rotatably disposed in contact with the photoreceptor drum 21, and serves as a charging device that uniformly charges the surface of the photoreceptor drum 21; A developing roller 23 serving as a developer carrier that is rotatably disposed in contact with the photosensitive drum 21 and adheres toner to the photosensitive drum 21 to form a toner image; a developing roller 23 that supplies toner to the developing roller 23; a developing blade 25 as a developer layer regulating member that uniformly thins the toner supplied onto the developing roller 23, and a photoreceptor after the toner image is transferred to the intermediate transfer belt 44. A cleaning blade 26 as a second cleaning member that scrapes and removes the toner remaining on the drum 21, a waste toner transport member (not shown) that transports the removed toner as waste toner, a toner cartridge 27 as a developer storage unit, etc. Equipped with. The toner cartridge 27 includes a first storage chamber Rm1 that stores unused toner, and a second storage chamber Rm2 that stores the waste toner.

The developing roller 23, the supply roller 24, and the developing blade 25 constitute a developing device.

Further, the charging roller 22, the developing roller 23, and the cleaning blade 26 are pressed against the photosensitive drum 21 with a predetermined nip amount, and the supply roller 24 and the developing blade 25 are pressed against the developing roller 23 with a predetermined nip amount.

The developing roller 23 is formed by coating a semiconductive elastic layer around a metal shaft having a cylindrical shape. The elastic layer is made of urethane rubber, and its surface is treated with isocyanate to increase charging properties.

The supply roller 24 is formed by coating a semiconductive foamed elastic layer around a metal shaft having a cylindrical shape. Silicone rubber with high wear resistance is used for the foamed elastic layer.

The developing blade 25 is formed by bending a stainless steel plate into an "L" shape, and the bent part 25a contacts the developing roller 23 in the counter direction (the part between the bent part 25a and the holding part 25b). (extending downstream in the direction of rotation of the developing roller 23).

Next, a control device for the printer 10 will be explained.

FIG. 1 is a control block diagram of a printer in an embodiment of the present invention.

In the figure, 61 is a control unit that controls the entire printer 10 (FIG. 2), 63 is a ROM as a first storage unit consisting of non-volatile memory, and 64 is a second storage unit consisting of volatile memory. RAM, 65 is an interface unit that receives print data and control commands from a host computer (not shown) as a host device, s1 is a density sensor, s2 is a temperature sensor that detects the temperature of the environment in which the printer 10 is placed, s3 is a printer This is a humidity sensor that detects the humidity of the environment in which No. 10 is placed.

Further, 66 supplies a charging voltage to the charging roller 22 via the power supply section Ps1, a developing voltage to the developing roller 23 via the power supply section Ps2, and a supply voltage to the supply roller 24 and the developing blade 25 via the power supply section Ps3. A power supply control section 67 applies a regulation voltage to the primary transfer roller 45 via the power supply section Ps4, and a secondary transfer voltage to the secondary transfer roller 32 via the power supply section Ps5. A drum motor M1 serves as a drive source for image formation to rotate the photosensitive drums 21 of 20Y, 20M, 20C, 20Bk, and 20W, and a belt motor serves as a drive source for belt running to run the intermediate transfer belt 44. M2, a drive source control unit that drives the transport motor M3 as a drive source for transport for rotating the hopping roller 12, the first to third transport roller pairs m1 to m3, etc.; 68, each image forming unit 20Y; , 20M, 20C, 20Bk, and 20W. A lifting mechanism control unit 69 drives the lifting motor M4 as a driving source for lifting the LEDs 20M, 20C, 20Bk, and 20W. 21 is an exposure device control section that exposes 21.

The control unit 61 includes a CPU (not shown) as an arithmetic unit, an input/output port, a timer, etc., and performs various processes based on programs recorded in the ROM 63.

To this end, the control section 61 includes a density correction condition establishment determination section Pr1, a single color pattern image formation processing section Pr2, a full color pattern image formation processing section Pr3, a density detection processing section Pr4, a density correction processing section Pr5, and the like.

The density correction condition satisfaction determination unit Pr1 determines whether or not the density correction conditions recorded in the ROM 63 are satisfied when performing density correction.

The monochrome pattern image forming processing unit Pr2 is disposed on the most upstream side (hereinafter referred to as the "most upstream side") in the running direction of the intermediate transfer belt 44 among the image forming units 20Y, 20M, 20C, 20Bk, and 20W. With the image forming unit 20Y placed in the operative state and the other image forming units 20M, 20C, 20Bk, and 20W disposed on the downstream side in the inoperative state, density correction is applied to the intermediate transfer belt 44. A first pattern image Imy is formed.

The all-color pattern image forming processing section Pr3 forms a second pattern image Jmi for density correction on the intermediate transfer belt 44 with all the image forming units 20Y, 20M, 20C, 20Bk, and 20W in operation. form.

The density detection processing unit Pr4 detects the density Diy of the first pattern image Imy formed on the intermediate transfer belt 44 and the density Dji (i=y, m, c, b, w) of the second pattern image Jmi. do.

The density correction processing unit Pr5 corrects the density of the image formed on the paper P, that is, performs density correction based on the densities Diy and Dji.

In addition to the program, the ROM 63 records various setting values, pattern data for forming the first and second pattern images Imy and Jmi for density correction, conditions for executing density correction processing, and the like. In this embodiment, the first pattern image Imy has yellow pattern data, which is one of the colors yellow, magenta, cyan, black, and white, and the second pattern image Jmi has yellow pattern data. , magenta, cyan, black, and white are recorded.

Further, the ROM 63 includes a target density table Tb1 (FIG. 14), a density difference-reverse transfer developing voltage correction value table Tb2 (FIG. 15), a reverse transfer variable table Tb3 (FIG. 16), a developing voltage correction value table (not shown), etc. is recorded.

The RAM 64 records print data received from the host computer, image data generated by editing the print data, and the like. The RAM 64 also functions as a work area when the CPU performs calculations.

Next, the operation of the printer 10 will be explained.

When the transport motor M3 is driven, the paper P in the paper cassette 11 is fed out to the paper transport path Rt1 by the hopping roller 12, and is transported by the first and second transport roller pair m1, m2 to the secondary paper. Sent to the transcription department.

On the other hand, when the drum motor M1 is driven, the photosensitive drum 21 is rotated counterclockwise in the image forming units 20Y, 20M, 20C, 20Bk, and 20W, and the developing roller 23 (FIG. 4) and the supply roller 24 are rotated counterclockwise. is rotated in a clockwise direction.

Then, a charging voltage is applied to the charging roller 22, and the surface of the photoreceptor drum 21 is uniformly charged. As a result, the surface potential of the photoreceptor drum 21 is set to about -600 [V].

Subsequently, the LED head Hd causes the LED to emit light according to the image data, and irradiates the photoreceptor drum 21 with light, thereby exposing the photoreceptor drum 21. The surface potential of the portion irradiated with light becomes 0 [V] to -600 [V], thereby forming an electrostatic latent image on the photosensitive drum 21.

The toner contained in the first storage chamber Rm1 of the toner cartridge 27 is sent to the supply roller 24 by falling under its own weight, and is supplied to the developing roller 23 by the supply roller 24. In the present embodiment, the toner contained in the first storage chamber Rm1 is supplied to the supply roller 24 by falling under its own weight, but the toner is transferred to the supply roller 24 by a conveying member (not shown). It can also be supplied.

Then, the toner is rubbed by the supply roller 24, the developing roller 23, and the developing blade 25, thereby being charged to a negative polarity (frictional charging).

Further, a supply voltage and regulation voltage of -250 [V] to -400 [V] are applied to the supply roller 24 and the developing blade 25, and a developing voltage of -100 [V] to -200 [V] is applied to the developing roller 23. Since a potential difference is generated between the supply roller 24 and the developing roller 23 and between the developing roller 23 and the developing blade 25, the negatively charged toner is transferred to the supply roller 24 by Coulomb force. On the developing roller 23, excess toner is scraped off by the bent portion 25a of the developing blade 25, and the negatively charged toner is selected and uniformly distributed on the developing roller 23. A toner layer with a certain thickness is formed. At this time, since a potential difference is generated between the developing roller 23 and the photosensitive drum 21, the toner in the toner layer is attached to the electrostatic latent image on the surface of the photosensitive drum 21 by Crohn's force, and the electrostatic latent image is It is developed to form a toner image.

Further, a primary transfer voltage of +800 [V] to +1600 [V] is applied to the primary transfer roller 45. As a result, the toner image is transferred to the intermediate transfer belt 44 due to the potential difference between the photosensitive drum 21 and the primary transfer roller 45 . As the intermediate transfer belt 44 runs, toner images of each color are sequentially transferred onto the intermediate transfer belt 44 in an overlapping manner, forming a color toner image. Toner remaining on the photosensitive drum 21 without being transferred to the intermediate transfer belt 44 is scraped off and removed by the cleaning blade 26. The removed toner is transported as waste toner by a waste toner transporting member, and is supplied to the second storage chamber Rm2 of the toner cartridge 27.

The color toner image formed on the intermediate transfer belt 44 is sent to the secondary transfer section as the intermediate transfer belt 44 runs, and is transferred onto the paper P by the secondary transfer roller 32.

Subsequently, the paper P is sent to the fixing device 51, and in the fixing device 51, the color toner image is heated and pressurized to be fixed on the paper P, thereby forming a color image. Then, the paper P discharged from the fixing device 51 is discharged to the outside of the apparatus main body Bd by the third pair of transport rollers m3, and is stacked on the stacker St1.

Incidentally, the toner image transferred to the intermediate transfer belt 44 may adhere to the photoreceptor drum 21 and be reversely transferred in an image forming unit on the downstream side in the running direction of the intermediate transfer belt 44.

Next, when all the image forming units 20Y, 20M, 20C, 20Bk, and 20W are placed in the operating position and five-color printing is performed to form five-color images on paper P, the density of each color image and one The density of each color image will be described when monochrome printing is performed to form an image of one color, that is, a single color, on paper P with only the image forming unit in the operating position.

FIG. 6 is a comparison diagram of the density of a yellow image when performing five-color printing and single-color yellow printing in the embodiment of the present invention, and FIG. 7 is a comparison diagram of the density of a yellow image when performing five-color printing and single-color magenta printing in the embodiment of the present invention. FIG. 8 is a comparison diagram of the density of a magenta image when performing five-color printing and single-color cyan printing according to the embodiment of the present invention. FIG. A comparison diagram of the density of a black image when five-color printing and monochrome black printing are performed in the embodiment of the invention, and FIG. 10 is a white image when monochrome printing is performed in the embodiment of the invention. FIG. In each figure, the horizontal axis represents the developing voltage, and the vertical axis represents the density.

In this case, an A4 size paper P is conveyed in the vertical direction, and an image consisting of patches with an area of 5 [cm] x 5 [cm] is formed on the paper P with a print duty (density) of 100 [%] for each color. The density of the image was detected using a spectrodensitometer "X-Rite528" (manufactured by X-Rite). Note that the printing duty is also called a printing rate, and is expressed as a percentage of the area of the toner occupying a predetermined area.

When an image of each color is formed on the intermediate transfer belt 44, the toner image on the intermediate transfer belt 44 is reversely transferred onto the photoreceptor drum 21 in an image forming unit on the downstream side in the running direction of the intermediate transfer belt 44. When the amount of movement of the toner in the toner image is defined as the amount of reverse transfer, the amount of reverse transfer for each color is equal to the number of image forming units disposed downstream of a predetermined image forming unit in the running direction of the intermediate transfer belt 44. is proportional to.

Therefore, the amount of reverse transfer of the yellow image formed in the image forming unit 20Y is the largest, and that of the magenta image formed in the image forming unit 20M, the cyan image formed in the image forming unit 20C, and the image forming unit 20Bk. The amount of reverse transfer decreases in the order of the black images formed in the image forming unit 20W, and the white image formed in the image forming unit 20W is not reverse transferred.

The density difference between the density of each color image when monochrome printing is performed and the density of each color image when 5-color printing is performed is the largest for yellow images, magenta images, cyan images, and black images. The density difference decreases in the order of , and the density difference becomes 0 in a white image.

Next, first and second pattern images Imy and Jmi for density correction are formed on the intermediate transfer belt 44, and images are formed on the paper P based on the densities of the first and second pattern images Imy and Jmi. The operation of the control unit 61 in this case will be explained.

FIG. 11 is a flowchart showing the operation of the control unit in the embodiment of the invention, FIG. 12 is a diagram showing an example of the first pattern image in the embodiment of the invention, and FIG. 14 is a diagram showing an example of the target density table in the embodiment of the present invention, and FIG. 15 is a diagram showing an example of the density difference-reverse transfer developing voltage correction value table in the embodiment of the present invention. FIG. 16 is a diagram showing an example of a reverse transcription variable table according to an embodiment of the present invention.

First, the density correction condition satisfaction determination unit Pr1 determines whether the density correction conditions recorded in the ROM 63 (FIG. 1) are satisfied.

In this embodiment, the density correction conditions include, for example, when the image forming units 20Y, 20M, 20C, 20Bk, and 20W are replaced, when the intermediate transfer unit u1 is replaced, or the environmental conditions in which the printer 10 is placed. holds true when the temperature and humidity change significantly.

When the density correction condition is satisfied, the monochrome pattern image forming processing unit Pr2 drives the lifting motor M4 by the lifting mechanism control unit 68, and the most upstream side of each image forming unit 20Y, 20M, 20C, 20Bk, 20W. The image forming unit 20Y is placed in the operating position, and the image forming units 20M, 20C, 20Bk, and 20W are placed in the retracted position. Note that if the density correction condition is not satisfied, the control unit 61 ends the process.

Subsequently, the monochrome pattern image forming processing section Pr2 forms a first pattern image Imy for density correction on the intermediate transfer belt 44.

To this end, the monochromatic pattern image formation processing section Pr2 reads the pattern data of the first pattern image Imy for density correction from the ROM 63, sends it to the LED head Hd, and also causes the drive source control section 67 to drive the drum motor M1. The power supply control section 66 applies a charging voltage to the charging roller 22, a developing voltage to the developing roller 23, a supply voltage to the supply roller 24, and a regulation voltage to the developing blade 25, and the exposure device control section 69 drives the LED head Hd. As a result, a toner image of the first pattern image Imy is formed on the photoreceptor drum 21, the drive source control section 67 drives the belt motor M2, and the power source control section 66 applies a primary transfer voltage to the primary transfer roller 45. Then, the toner image on the photosensitive drum 21 is transferred to the intermediate transfer belt 44.

As a result, as shown in FIG. 12, the first pattern image Imy for density correction is formed on the intermediate transfer belt 44 that is run in the direction of the arrow.

The first pattern image Imy is formed with yellow toner at a print duty of 100%. Note that the first pattern image Imy has a rectangular shape with an arbitrarily set aspect ratio, and has a size that can be read by the density sensor s1.

Next, the density detection processing unit Pr4 detects the density Diy of the first pattern image Imy during monochrome printing using the density sensor s1.

Note that the developing voltage applied to the developing roller 23 in the image forming unit 20Y when the toner image of the first pattern image Imy is formed is DBbasey.

Subsequently, the full-color pattern image formation processing unit Pr3 drives the lifting motor M4 by the lifting mechanism control unit 68, and places all the image forming units 20Y, 20M, 20C, 20Bk, and 20W in the operating position.

Then, the full-color pattern image forming processing unit Pr3 forms a second pattern image Jmi for density correction on the intermediate transfer belt 44.

To this end, the full-color pattern image formation processing section Pr3 reads the pattern data of the second pattern image Jmi for density correction from the ROM 63, sends it to the LED head Hd, and causes the drive source control section 67 to drive the drum motor M1. , the power supply control section 66 applies a charging voltage to the charging roller 22, a developing voltage to the developing roller 23, a supply voltage to the supply roller 24, and a regulation voltage to the developing blade 25, and the exposure device control section 69 applies a charging voltage to the developing roller 23, a supply voltage to the supply roller 24, and a regulation voltage to the developing blade 25. By driving, a toner image of the second pattern image Jmi is formed on the photoreceptor drum 21, the drive source control section 67 drives the belt motor M2, and the power supply control section 66 applies a primary transfer voltage to the primary transfer roller 45. The toner image on the photoreceptor drum 21 is transferred to the intermediate transfer belt 44 by applying the voltage.

As a result, as shown in FIG. 13, a second pattern image Jmi for density correction is formed on the intermediate transfer belt 44 that is run in the direction of the arrow.

Each of the second pattern images Jmi is formed using yellow, magenta, cyan, black, and white toners at a printing duty of 100%. Note that the second pattern image Jmi has a rectangular shape with an arbitrarily set aspect ratio, and has a size that can be read by the density sensor s1. Further, the order of each pattern image can be changed in the running direction of the intermediate transfer belt 44.

Then, the density detection processing unit Pr4 detects the density Dji of the second pattern image Jmi during all-color printing using the density sensor s1.

Note that the developing voltage applied to the developing rollers 23 of the image forming units 20Y, 20M, 20C, 20Bk, and 20W when the second pattern image Jmi is formed is DBbasei (i=y, m, c, b, w ).

Next, the density correction processing unit Pr5 refers to the target density table Tb1 and the development voltage correction value table shown in FIG. , 20W to perform all-color printing, the target density Dti (i=y, m, c, b, w) of each color is read out, and the density Dji of the second pattern image Jmi becomes the target density Dti. Next, the development voltage correction value δDBi (i=y, m, c, b, w) for all-color printing is calculated.

For this purpose, each color and the target density Dti are recorded in correspondence with each other in the target density table Tb1, and the difference between the target density Dti and the density Dji of the second pattern image Jmi is recorded in the development voltage correction value table. , development voltage correction value δDBi are recorded in correspondence with each other.

Subsequently, the density correction processing unit Pr5 calculates the density difference ΔDy between the density Diy of the first pattern image Imy during monochrome printing and the density Djy of the second pattern image Jmy during full-color printing. The density difference ΔDy is the total amount of reverse transfer of the second pattern image Jmy in the image forming units 20M, 20C, 20Bk, and 20W disposed downstream of the image forming unit 20Y.

Then, the density correction processing unit Pr5 refers to the density difference-reverse transfer developing voltage correction value table Tb2 shown in FIG. read out.

Therefore, the density difference ΔDy and the reverse transfer developing voltage correction value εDBy are recorded in correspondence with each other in the density difference-reverse transfer developing voltage correction value table Tb2.

The reverse transfer development voltage correction value εDBy is determined so that the second pattern image Jmy formed in the image forming unit 20Y when full-color printing is performed is located downstream of the image forming unit 20Y in the running direction of the intermediate transfer belt 44. This value corresponds to the amount of reverse transfer performed in each image forming unit 20M, 20C, 20Bk, and 20W.

Note that the amount of reverse transfer in other image forming units disposed downstream of the predetermined image forming unit 20Y, that is, each of the image forming units 20M, 20C, 20Bk, and 20W, is equal, so the predetermined The total amount of reverse transfer on the downstream side of the image forming unit is proportional to the number of image forming units.

In the most downstream image forming unit 20W among the image forming units 20M, 20C, 20Bk, and 20W, the second pattern image Jmy is not reversely transferred, so the reverse transfer developing voltage correction value εDBy is 0. Become [V].

Next, the density correction processing unit Pr5 determines the developing voltage when printing N colors using a predetermined number N of image forming units 20Y, 20M, 20C, 20Bk, and 20W, that is, Developing voltage DBi (i=y, m, c, b, w) in each image forming unit corresponding to N-color printing is calculated.

To this end, the density correction processing unit Pr5 reads the reverse transcription variables Nj (j=y, m, c, b) with reference to the reverse transcription variable table Tb3 shown in FIG. The development voltage DBi is calculated based on the development voltage DBbasei, the development voltage correction value δDBi, the reverse transfer development voltage correction value εDBy, and the reverse transfer variable Nj.

That is, each developing voltage DBi is calculated using the following formulas.

DBy=DBbasey+δDBy+εDBy×(4-Ny) [V]
DBm=DBbasem+δDBm+εDBy×(3-Nm) [V]
DBc=DBbase+δDBc+εDBy×(2-Nc) [V]
DBb=DBbaseb+δDBb+εDBy×(1-Nb) [V]
DBw=DBbasew+δDBw
Therefore, the density correction processing unit Pr5 corrects the density of the image formed on the paper P by applying the calculated development voltage DBi to the development roller 23 of each image forming unit 20Y, 20M, 20C, 20Bk, and 20W. can do.

The reverse transfer variable table Tb3 includes the number N of image forming units to be used (5 colors, 4 colors, 3 colors, 2 colors, and single color) for each of print modes 1 to 6 when performing N color printing. and the colors used (yellow, magenta, cyan, black and white are represented by Y, M, C, B, W) and the image formation used (activated) in N color printing. A reverse transfer variable Nj representing the number of image forming units disposed downstream of the most upstream image forming unit among the units is recorded in correspondence.

The lower the number of image forming units on the downstream side, the lower the decrease in density due to reverse transfer, so the developing voltage DBi is lowered.

Next, the flowchart will be explained.
Step S1: The density correction condition satisfaction determining unit Pr1 determines whether the density correction condition is satisfied. If the density correction condition is satisfied, the process proceeds to step 2, and if the density correction condition is not satisfied, the control unit 61 ends the process.
Step S2: The monochrome pattern image forming processing section Pr2 places the most upstream image forming unit 20Y in the operating position.
Step S3: The monochrome pattern image forming processing unit Pr2 forms the first pattern image Imy on the intermediate transfer belt 44.
Step S4: The density detection processing unit Pr4 detects the density Diy of the first pattern image Imy.
Step S5: The full-color pattern image forming processing unit Pr3 places all image forming units 20Y, 20M, 20C, 20Bk, and 20W in the operating position.
Step S6: The full-color pattern image formation processing section Pr3 forms the second pattern image Jmi on the intermediate transfer belt 44.
Step S7: The density detection processing unit Pr4 detects the density Dji of the second pattern image Jmi.
Step S8: The density correction processing unit Pr5 calculates a development voltage correction value δDBi for all-color printing.
Step S9: The density correction processing unit Pr5 calculates the density difference ΔDy between the density Diy of the first pattern image Imy and the density Djy of the second pattern image Jmy.
Step S10: The density correction processing unit Pr5 reads the reverse transfer and development voltage correction value εDBy.
Step S11: The density correction processing unit Pr5 calculates the developing voltage DBi in each image forming unit according to N-color printing, and ends the process.

Next, the density of images when N-color printing is performed in Examples and Comparative Examples 1 and 2 will be described.

FIG. 17 is a diagram showing the evaluation results of image density when N-color printing is performed in Example, and FIG. 18 is a diagram showing the evaluation results of image density when N-color printing is performed in Comparative Example 1. 19 is a diagram showing the evaluation results of image density when printing in N colors in Comparative Example 2.

In this case, printing was performed on the paper P using different colors in each of print modes 1 to 6, and the density of the image formed on the paper P was detected and evaluated.

To do this, one [sheet] of A4 paper P is conveyed in the vertical direction, and an image consisting of patches with an area of 5 [cm] x 5 [cm] is printed on the paper P with a print duty of 100 [%] for each color. The density of the image was detected using a spectrodensitometer "X-Rite 528" (manufactured by X-Rite).

When the colors yellow, magenta, cyan, and black are used, "Excellent White 80 [g/m ² ]" (manufactured by Oki Data Co., Ltd.) is used as the paper P. When the color white is used, the paper As P, "Colored High Quality Paper Thick Blue" (manufactured by Hokuetsu Corporation) was used.

In print mode 1, printing is performed in five colors: yellow, magenta, cyan, black, and white, and in print mode 2, printing is performed in four colors, yellow, magenta, cyan, and black. In print mode 3, printing is performed in four colors: yellow, magenta, cyan, and white; in print mode 4, printing is performed in three colors, yellow, magenta, and cyan; and in print mode 5, printing is performed in four colors, yellow, magenta, cyan, and white. Two-color printing was performed, and in print mode 6, monochrome printing of black color was performed.
〔Example〕
According to the flowchart shown in FIG. 11, the first pattern image Imy is formed on the intermediate transfer belt 44 by monochrome printing, the density Diy of the first pattern image Imy is detected, and then the intermediate transfer belt 44 is formed by full-color printing. 44, the density Djy of the pattern image Jmy of the second pattern image Jmi is detected, and the density difference between the density Diy during monochrome printing and the density Djy when printing all colors is detected. Based on ΔDy, the density was corrected and the developing voltage DBi was adjusted to form yellow, magenta, cyan, black, and white images on the paper P.

The densities of the yellow, magenta, cyan, black, and white images shown in FIG. 17 are within ±0.10 of the target densities Dti of the yellow, magenta, cyan, black, and white images shown in FIG. falls within the range.
[Comparative example 1]
According to each print mode 1 to 6, an image of each color is formed on the paper P, the density of the image formed on the paper P is detected, and the density of the image of each color reaches the target density Dti of the image of each color shown in FIG. The developing voltage was adjusted so that the image density was detected and the developing voltage was adjusted six times.

The densities of the yellow, magenta, cyan, black, and white images shown in FIG. 18 are within ±0.10 of the target densities Dti of the yellow, magenta, cyan, black, and white images shown in FIG. Although it falls within the range, it is necessary to repeatedly detect the image density and adjust the developing voltage, which is cumbersome.
[Comparative example 2]
Images of each color were formed on the paper P according to each print mode 1 to 6, and the density of the image formed on the paper P was detected.

The densities of the yellow, magenta, cyan, black, and white images shown in FIG. 19 are within ±0.10 of the target densities Dti of the yellow, magenta, cyan, black, and white images shown in FIG. Not within range.

As described above, in the present embodiment, the image forming unit 20Y disposed on the most upstream side in the running direction of the intermediate transfer belt 44 is put into operation, and the other image forming units 20M, 20C, 20Bk, 20W The first pattern image Imy for density correction is formed on the intermediate transfer belt 44 while the image forming units 20Y, 20M, 20C, 20Bk, and 20W are placed in an activated state. In this state, a second pattern image Jmi for density correction is formed on the intermediate transfer belt 44, and the image density is corrected based on the first and second pattern images Imy and Jmi. The number of times the photoreceptor drum 21 and the intermediate transfer belt 44 come into contact when forming the second pattern images Imy and Jmi, and the number of times the photoreceptor drum 21 and the intermediate transfer belt 44 contact each other when actually forming an image on the paper P. Density correction can be performed with high accuracy regardless of the number of times the contact is made.

Therefore, image quality can be improved.

Also, when performing N color printing using a predetermined number of image forming units among the image forming units 20Y, 20M, 20C, 20Bk, and 20W, each time the combination of the predetermined number of image forming units changes. Since there is no need to perform density correction, the number of times density correction is performed can be reduced. Furthermore, when performing density correction, the consumption amount of toner used to form a pattern image for density correction on the intermediate transfer belt 44 can be reduced.

In this embodiment, each of the image forming units 20Y, 20M, 20C, 20Bk, and 20W is brought into contact with the intermediate transfer belt 44 in the operating state, and is separated from the intermediate transfer belt 44 in the non-operating state. However, it is also possible to make the primary transfer roller 45 contact the intermediate transfer belt 44 in the operating state and to separate the primary transfer roller 45 from the intermediate transfer belt 44 in the non-operating state.

Further, in this embodiment, the intermediate transfer belt 44 is used as the transfer medium, but a conveyance belt that is run to convey the paper P may also be used as the transfer medium. Furthermore, paper can also be used as the transfer medium.

Although the printer 10 has been described in the embodiment, the present invention can be applied to image forming apparatuses such as copying machines, facsimile machines, and multifunction devices.

Note that the present invention is not limited to the embodiments described above, and various modifications can be made based on the spirit of the present invention, and these are not excluded from the scope of the present invention.

10 Printers 20Y, 20M, 20C, 20Bk, 20W Image forming unit 21 Photosensitive drum 44 Intermediate transfer belt 45 Primary transfer rollers Imy, Jmi First and second pattern images Pr2 Single color pattern image formation processing section Pr3 Full color pattern image formation Processing section Pr5 Density correction processing section U1 Transfer section

Claims (4)

(a) a plurality of image forming units each including an image carrier;
(b) a transfer section including a transfer medium that is caused to travel along each of the image forming units, and a transfer member that transfers the pattern image on each of the image carriers to the transfer medium;
(c) The image forming unit disposed on the most upstream side in the traveling direction of the transfer medium is placed in an operating state in which an image is transferred to the transfer medium, and the other image forming units disposed on the downstream side , a monochromatic pattern image forming unit that forms a first pattern image for density correction on the transfer medium in a non-operating state in which no image is transferred to the transfer medium;
(d) a full-color pattern image forming processing unit that forms a second pattern image for density correction on the transfer medium with all image forming units in an operating state;
(e) a density correction processing unit that performs density correction based on the first and second pattern images ;
(f) a density detection processing unit that detects the density of the first and second pattern images ;
(g) The density correction processing section:
Calculating the total amount of reverse transfer in other image forming units disposed on the downstream side based on the density difference between the first and second pattern images detected by the density detection processing section;
When the number of image forming units placed in an operating state among the other image forming units is at least plural and less than the total number, the number is at least plural and less than the total number, and the calculated number is at least plural and less than the total number. An image forming apparatus that performs density correction when performing multicolor printing by at least a plurality of image forming units and a number less than the total number of image forming units based on the total reverse transfer amount . The image forming apparatus according to claim 1 , wherein each of the image forming units is brought into contact with a transfer medium in an activated state and separated from the transfer medium in an inactive state. 3. The image forming apparatus according to claim 1 , wherein the density correction is performed by adjusting a developing voltage applied to a developer carrier disposed in each image forming unit. The development voltage includes a development voltage at which the second pattern image is formed on the transfer medium, a development voltage correction value calculated based on the density and target density of the second pattern image formed on the transfer medium, and the development voltage correction value calculated based on the density and target density of the second pattern image formed on the transfer medium. A reverse transfer development voltage correction value that corresponds to the density difference between the first and second pattern images, and is provided downstream from the most upstream image forming unit among the image forming units used in multicolor printing. The image forming apparatus according to claim 3 , wherein the number of image forming units is calculated based on the number of image forming units.

Images