JP2023009573A - Image forming apparatus - Google Patents

Abstract

To prevent transfer current from flowing to an image carrier through a non-image area on a medium, thereby preventing the image carrier and the medium from becoming dirty.SOLUTION: An image forming apparatus has: a plurality of image forming units that each include an image carrier, an electrifying member, and a developing section; exposure devices that each form a latent image on the image carrier; a transfer device that transfers developer images to a medium; a developer area ratio calculation processing section that, in each line in a predetermined image forming unit, calculates a developer area ratio representing the ratio at which a developer image in a color of one of the predetermined image forming unit and an upstream side image forming unit is formed; and an electrification voltage control processing section Pr5 that corrects electrification voltage applied to the electrifying members. In the image forming apparatus, printing with high printing duty is performed, and when the developer images are transferred to the medium in the predetermined image forming unit and the upstream side image forming unit, a large amount of transfer current can be prevented from flowing into non-print areas of the image carriers. The image carriers and the medium are prevented from becoming dirty.SELECTED DRAWING: Figure 1

Description

The present invention relates to an image forming apparatus.

Conventionally, in an image forming apparatus such as a printer, a copier, a facsimile machine, and a multifunction machine, for example, an electrophotographic color printer, in each color image forming unit, the surface of a photosensitive drum as an image carrier is charged. An electrostatic latent image is formed on the photosensitive drum by being charged by a charging roller as a member and exposed by an LED head as an exposure device, and then the electrostatic latent image is transferred to a developing roller as a developer carrier. A toner image is formed as a developer image by developing with the toner as the developer. Then, a toner image of each color is transferred by a transfer device onto a sheet of paper as a medium that is conveyed along with the running of a transfer belt as a belt member, and fixed by a fixing device as a fixing device to form an image on the paper. formed and ready for printing.

By the way, in the printer, when the toner on the developing roller deteriorates, the electrostatic latent image cannot be developed smoothly, and the image quality deteriorates.

Therefore, a printer has been provided that prevents deterioration in image quality by correcting the voltage applied to the charging roller according to the print duty of the image (see, for example, Japanese Patent Application Laid-Open No. 2002-200310).

Japanese Patent Application Laid-Open No. 2007-34087

However, in the conventional printer, when printing with a high print duty is performed and a toner image formed in a predetermined image forming unit and another image forming unit is transferred to paper, the toner is an insulator. Therefore, in the predetermined image forming unit, the transfer current of the transfer device is less likely to flow through the image area onto which the toner image has been transferred on the paper, and through the non-image area on the paper to which the toner image has not been transferred. In some cases, the toner flows to the non-printing area of the photoreceptor drum as an image carrier, and both end portions of the photoreceptor drum are charged to a positive polarity.

In this case, the toner adheres to both ends of the photoreceptor drum and the photoreceptor drum becomes dirty, or the toner adhering to both ends of the photoreceptor drum adheres to the paper and the paper becomes dirty.

The present invention solves the problems of conventional printers by preventing the transfer current from flowing to the image carrier through the non-image areas on the media, so that the image carrier and media are not smeared. An object of the present invention is to provide an image forming apparatus.

For this reason, in the image forming apparatus of the present invention, the image carrier, the charging member that charges the image carrier, and the image carrier are provided from the upstream side to the downstream side in the medium conveying direction, respectively. a plurality of image forming units each having a developing section for developing a latent image and forming a developer image of each color on an image carrier; an exposure device having a plurality of light emitting elements arranged in a row, and forming the latent image on an image carrier by causing the light emitting elements to emit light based on dot data; and a developer image formed on each image carrier. Either a transfer device for transferring onto a medium, or an image forming unit or an upstream image forming unit arranged upstream from the image forming unit in each line of the image forming unit, which is a predetermined image forming unit. a developer area ratio calculation processing unit for calculating a developer area ratio representing a ratio of forming a developer image of a color; and a charging voltage applied to the charging member is corrected based on the developer area ratio. and a charging voltage control processing unit.

According to the present invention, in the image forming apparatus, the image carrier, the charging member that charges the image carrier, and the charging member that is formed on the image carrier are arranged from the upstream side to the downstream side in the conveying direction of the medium, respectively. a plurality of image forming units each having a developing section for developing a latent image and forming a developer image of each color on an image carrier; an exposure device having a plurality of light emitting elements arranged in a row, and forming the latent image on an image carrier by causing the light emitting elements to emit light based on dot data; and a developer image formed on each image carrier. Either a transfer device for transferring onto a medium, or an image forming unit or an upstream image forming unit arranged upstream from the image forming unit in each line of the image forming unit, which is a predetermined image forming unit. a developer area ratio calculation processing unit for calculating a developer area ratio representing a ratio of forming a developer image of a color; and a charging voltage applied to the charging member is corrected based on the developer area ratio. and a charging voltage control processing unit.

In this case, in each line of the image forming unit, which is a predetermined image forming unit, the developer area ratio representing the rate at which the developer image of the color of either the image forming unit or the upstream image forming unit is formed is Since the charging voltage applied to the charging member is corrected based on the calculated developer area ratio, printing with a high print duty is performed, and the medium is developed in the image forming unit and the upstream image forming unit. When the agent image is transferred, it is possible to prevent a large amount of transfer current from flowing to the non-printing area of the image carrier. Therefore, the image carrier is not soiled by the developer adhering to both ends of the image carrier, and the medium is not soiled by the developer adhering to both ends of the image carrier adhering to the medium.

3 is a control block diagram of the printer according to the embodiment of the invention; FIG. 1 is a schematic diagram of a printer according to an embodiment of the invention; FIG. 4 is a flow chart showing the operation of the control device of the printer; FIG. 5 is a diagram showing an example of dot data of one line and determination results by a dot determination processing unit according to the embodiment of the present invention; FIG. 10 is a diagram showing an example of transition of the surface potential of the photoreceptor drum when forming a solid blank image on paper with a print duty of 0[%]; FIG. 10 is a diagram showing the state of paper when a solid cyan image is formed with a print duty of 100[%]; FIG. 10 is a diagram showing an example of transition of the surface potential of the photoreceptor drum when forming a solid cyan image on paper with a print duty of 100[%]; A cyan image with a print duty of 30[%] and a magenta image with a print duty of 70[%] are printed on paper in the embodiment of the present invention without overlapping the cyan toner image and the magenta toner image. FIG. 5 is a diagram showing an example of transition of the surface potential of a photoreceptor drum during formation;

BEST MODE FOR CARRYING OUT THE INVENTION 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 schematic diagram of a printer according to an embodiment of the invention.

In the figure, 10 is a printer, Cs is a housing that is the exterior of the printer 10, Bd is the main body of the printer 10, i.e., the device main body, Wt is the top wall of the housing Cs, and sk1 is part of the top wall Wt. 1 is a stacker as a first stacking unit formed in the .

A paper cassette 11 as a paper feeding unit and as a medium storage unit is arranged in the lower part of the apparatus main body Bd. It is housed in a state where it is loaded on the A hopping roller 12 as a delivery member is arranged adjacent to the front end of the paper cassette 11, and a separating member (not shown) is arranged opposite to the hopping roller 12. Then, the sheet is separated one by one by the separating member, fed to the paper transport path Rt1 as the medium transport path, and transported on the paper transport path Rt1 by the paper feed rollers 13 of the paper feed roller pair m1 as the first transport member. After the skew is corrected by a pair of registration rollers m2 as a second conveying member arranged downstream of the pair of paper feed rollers m1, the sheet is sent to the image forming section Q1.

The image forming section Q1 includes image forming units 16Bk, 16Y, 16M, and 16C for four colors of black, yellow, magenta, and cyan arranged side by side from the upstream side to the downstream side in the conveying direction of the paper P, It consists of an LED head Hd, a transfer unit u1 as a transfer device, and the like.

Each of the image forming units 16Bk, 16Y, 16M, and 16C is detachably attached to the main body of the image forming units 16Bk, 16Y, 16M, and 16C. A toner cartridge Ct as a developer containing portion containing toner, a photosensitive drum 21 as an image carrier disposed rotatably in the direction of arrow A, and a drum 21 in contact with the photosensitive drum 21 in the direction of arrow B. A charging roller 22 as a rotatably disposed charging member, a developing roller 23 as a developer bearing member disposed rotatably in the direction of arrow C in contact with the photosensitive drum 21, and the developing roller 23 a supply roller 24 as a supply member disposed rotatably in the direction of arrow D in contact with the developing roller 24; a developing blade 25 as a regulation member disposed in contact with the developing roller 23 at a predetermined location; A toner collecting portion Bx1 as a first developer collecting device arranged to face the body drum 21, and disposed in the toner collecting portion Bx1, and arranged so as to abut against the photosensitive drum 21 at its tip end. It includes a cleaning blade 26 as a first cleaning member, a static eliminator 27 disposed facing the photosensitive drum 21, and the like.

A developing section is formed by the developing roller 23 , the supply roller 24 and the developing blade 25 . A toner receiving portion Rm as a developer receiving portion for receiving toner supplied from the toner cartridge Ct is formed above the developing portion in the main body portion of each of the image forming units 16Bk, 16Y, 16M, and 16C.

A polyester resin is used as a binder resin in the toner of each color, and internal additives, such as charge control agents, release agents, and colorants, are added to the toner particles outside the toner particles. External additives such as silica, titanium oxide, etc. are added to maintain fluidity and chargeability. A copper phthalocyanine pigment (CI Pigment, Blue 15, etc.) is used as the coloring agent. The toner has a specific surface area of 2.7 [m ² /g], a sphericity of 0.95, and a volume average particle diameter of 6.1 [μm].

The photoreceptor drum 21 is made of an organic photoreceptor, and includes a conductive support and a photoconductive layer formed on the surface of the conductive support. The conductive support is formed by a metal pipe made of aluminum, and the photoconductive layer is formed by laminating a charge generation layer and a charge transport layer.

The charging roller 22 has a metal shaft and a semi-conductive rubber layer made of epichlorohydrin rubber or the like formed on the outer circumference of the metal shaft, and uniformly charges the surface of the photosensitive drum 21 .

The developing roller 23 includes a metal shaft, and an elastic body of semiconductive silicone rubber having a thickness of 6 mm and a rubber hardness of 58° (Asker C) formed on the outer periphery of the metal shaft. , the electrostatic latent image formed on the surface of the photosensitive drum 21 is electrostatically adhered with toner to develop the electrostatic latent image.

The supply roller 24 includes a metal shaft and a semiconductive silicone sponge foam having a thickness of 5 mm and a rubber hardness of 55° (Asker F) formed on the outer periphery of the metal shaft. It rotates in the same direction as the developing roller 23, supplies the toner supplied from the toner cartridge Ct to the toner receiving portion Rm to the developing roller 23, and electrifies the toner by friction. A large number of cells consisting of depressions are formed on the surface of the foam.

The developing blade 25 is made of a springy plate-like member such as stainless steel having a thickness of 0.08 mm. The thickness of the toner layer on 23 is regulated to form a toner layer as a developer layer.

In each of the image forming units 16Bk, 16Y, 16M, and 16C, the toner supplied from the toner cartridge Ct to the toner receiving portion Rm is charged while being supplied to the developing roller 23 by the supply roller 24, and is charged by the developing blade 25. After the layer thickness is regulated, it is adhered to the photosensitive drum 21 to form a toner image. The toner not used for forming the toner image on the developing roller 23 is collected in the toner receiving portion Rm as the developing roller 23 rotates, rubbed off by the supply roller 24, and replaced with new toner supplied from the toner cartridge Ct. mixed with

The cleaning blade 26 is made of a rubber-like elastic material such as polyurethane rubber, and is brought into contact with a counter so that the tip thereof abuts against the rotation direction of the photosensitive drum 21. After the toner image is transferred to the paper P, the cleaning blade 26 is exposed. The toner remaining on the body drum 21 and the external additives and the like peeled off from the toner and adhering to the photosensitive drum 21 are scraped off and removed.

The static elimination device 27 includes a static elimination plate (not shown) disposed in the axial direction of the photoreceptor drum 21 so as to face the photoreceptor drum 21, and light emitting elements for static elimination disposed at equal intervals along the static elimination plate. is provided with a plurality of LEDs (not shown), each of the LEDs is made to emit light when a static elimination voltage is applied, the photoreceptor drum 21 is irradiated with static elimination light, and the toner image is transferred to the paper P. The surface of 21 is neutralized to eliminate variations in surface potential.

The LED head Hd is composed of an LED array composed of a plurality of LEDi (i=1, 2, . , each LEDi irradiates the surface of the photosensitive drum 21 charged by the charging roller 22 with light in units of dots based on dot data described later, and lowers the potential of the irradiated portion by light attenuation. , forming an electrostatic latent image.

The transfer unit u1 includes a drive roller r1 as a first roller rotatably arranged in the direction of arrow E, a driven roller r2 as a second roller rotatably arranged in the direction of arrow F, A transfer belt Bt as a belt member stretched between the drive roller r1 and the driven roller r2 so as to be free to run in the direction of arrow G, and the transfer belt Bt opposed to each of the photosensitive drums 21 via the transfer belt Bt. a transfer roller 28 as a transfer member disposed rotatably in the direction, a toner collecting portion Bx2 as a second developer collecting device disposed facing the lower running portion of the transfer belt Bt, the toner; In the collecting section Bx2, a cleaning blade 29 or the like is provided as a second cleaning member, the tip of which is in contact with the transfer belt Bt.

The transfer belt Bt is pressed against the photosensitive drums 21 by the respective transfer rollers 28 to form nip portions with the respective photosensitive drums 21 . Each nip portion constitutes a transfer portion.

A fixing device 31 as a fixing device is arranged on the downstream side of the image forming section Q1 in the paper transport path Rt1. The fixing device 31 includes a heat roller 32 as a first fixing member that is rotatably arranged in the direction of arrow I, and a facing member that is arranged to face the heat roller 32 and is rotatable in the direction of arrow J. and a backup roller 33 as a second fixing member.

A discharge roller pair m3 as a third transport member is arranged downstream of the fixing device 31 in the paper transport path Rt1.

Next, operation of the printer 10 will be described.

When the print processing unit Pr2 (FIG. 1), which will be described later, drives the drive motor M1 by the drive control unit 45, which will be described later, the photosensitive drums 21, the charging rollers 22, The developing roller 23 and the supply roller 24 are rotated, and each transfer roller 28 in the transfer unit u1 is rotated, and the charging roller 22, the developing roller 23, the supply roller 24, and the developing blade 25 are controlled by the voltage control section 43, which will be described later. , the charge removing device 27 and the transfer roller 28 are applied with a charging voltage Vch, a developing voltage, a supply voltage, a regulation voltage, a charge removing voltage and a transfer voltage.

Next, the print processing unit Pr2 sends dot data to each LED head Hd by means of an exposure control unit 44, which will be described later, and drives the LED head Hd to expose the surface of each photosensitive drum 21, thereby forming an electrostatic latent image. Form. The potential difference between each developing roller 23 and the electrostatic latent image causes the toner on the developing roller 23 to adhere to the electrostatic latent image, and the electrostatic latent image is developed. An image is formed.

At this time, the toner is charged to a negative polarity due to the potential difference and friction between the developing roller 23 and the supply roller 24 , and the toner is supplied from the supply roller 24 to the developing roller 23 . Further, due to the potential difference and friction between the developing blade 25 and the developing roller 23, the toner is further charged to a negative polarity, and the excess toner on the developing roller 23 is scraped off to form a uniform toner layer on the developing roller 23. is formed.

Toner not supplied from the supply roller 24 to the developing roller 23 and toner scraped off by the developing blade 25 are returned to the toner container Rm.

When the print processing unit Pr2 drives the transport motor M2 by the drive control unit 45 to rotate the hopping roller 12, the paper P in the paper cassette 11 is sent out to the paper transport path Rt1 by the hopping roller 12, and the transport roller pair The sheet is conveyed by m1, corrected for skew by a pair of registration rollers m2, and supplied to the image forming section Q1.

Then, in the image forming section Q1, when the paper P is conveyed along with the running of the transfer belt Bt, black, yellow, magenta, and black, yellow, and magenta colors are formed according to the potential difference between each transfer roller 28 and the toner image on the photosensitive drum 21. The cyan toner images are sequentially superimposed and transferred onto the paper P to form a color toner image on the paper P. As shown in FIG. At this time, a transfer current flows from each transfer roller 28 to the photosensitive drum 21 .

Toner remaining on each photosensitive drum 21 after transfer is scraped off by a cleaning blade 26 and removed. In addition, by applying a static elimination voltage to the static eliminator 27, the photoreceptor drum 21 is irradiated with static elimination light.

After that, the paper P is sent to the fixing device 31, and in the fixing device 31, the color toner image on the paper P is melted by the heat roller 32 and pressed by the backup roller 33 to be fixed on the paper P. , a color image is formed on the paper P. The paper P on which the color image is formed is discharged outside the apparatus main body Bd by the discharge roller pair m3 and stacked on the stacker sk2.

Toner remaining on the transfer belt Bt is scraped off by the cleaning blade 29 and collected in the toner collecting section Bx2.

By the way, a predetermined image forming unit among the image forming units 16Bk, 16Y, 16M, and 16C, for example, the image forming unit 16C is defined as the image forming unit, and the image in the conveying direction of the paper P (the running direction of the transfer belt Bt) is When the image forming units 16Bk, 16Y, and 16M on the upstream side of the forming units are assumed to be upstream image forming units, in the nip portion between the photosensitive drum 21 and the transfer belt Bt in the image forming units, the paper P has: In addition to the cyan toner image, black, yellow and magenta toner images formed in the upstream image forming unit are transferred. Since the toner of each toner image is an insulator, when printing with a high print duty is performed, in the image forming unit, the transfer current of the transfer roller 28 is applied to the image area where the toner image of each color is transferred on the paper P. , and flows to the photosensitive drum 21 via the non-image area where the toner image on the paper P is not transferred. As a result, both ends of the photoreceptor drum 21 are charged to a positive polarity, and toner adheres to both ends of the photoreceptor drum 21 to stain the photoreceptor drum 21 or adhere to both ends of the photoreceptor drum 21. The toner adheres to the paper P and the paper P becomes dirty.

Therefore, in the present embodiment, it is determined whether or not the toner image makes it difficult for the transfer current to flow in the nip portion between the transfer belt Bt and the photosensitive drum 21. When it is determined that the transfer current does not easily flow, In addition, both ends of the photosensitive drum 21 are prevented from being positively charged.

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

FIG. 1 is a control block diagram of a printer according to an embodiment of the invention.

In the figure, reference numeral 10 denotes a printer, and PC denotes a host computer as a host computer connected to the printer 10 via a wired or wireless LAN or the like.

Reference numeral 50 denotes a control unit, and IF connects the printer 10 to the host computer PC, receives a print command, print data, etc. from the host computer PC, and transmits status information of the printer 10 to the host computer PC. 53 is a ROM as a first memory, and 54 is a RAM as a second memory. In this embodiment, a rewritable flash ROM or the like is used as the ROM 53 .

Reference numeral 55 denotes a printed sheet counting unit for counting the number of sheets P printed by the printer 10, 56 an operation panel as an operation/display unit, and s1 as a first environmental variable detection unit. A temperature sensor and s2 are a humidity sensor as a second environmental variable detector. The temperature sensor s1 is arranged at a location that is not affected by the temperature of the fixing device 31 .

Reference numeral 43 designates a charging voltage Vch, a developing voltage, a supply voltage, a regulation voltage, a static elimination voltage, and a transfer voltage for each of the charging roller 22, the developing roller 23, the supply roller 24, the developing blade 25, the static elimination device 27, and the transfer roller . , 44 is an exposure control unit for controlling light emission of each LEDi of the LED head Hd, and M1 is a drive motor ( ID motor), M2 is a transport motor as a drive unit for transport that rotates the hopping roller 12, the pair of paper feed rollers m1, the pair of registration rollers m2, the pair of discharge rollers m3, etc., and M3 rotates the drive roller r1. to rotate the driven roller r2 and to run the transfer belt Bt. It is a drive control unit that drives the conveying motor M2 and the transfer motor M3. When the drive control unit 45 drives the driving motor M1 to rotate the photosensitive drum 21, the charging roller 22 is rotated following the rotation of the photosensitive drum 21, and the developing roller 23, the supply roller 24, and the transfer roller 24 are rotated. The roller 28 and the like are rotated via a gear train (not shown) connected to the photosensitive drum 21 .

The control unit 50 includes a CPU as an arithmetic device (not shown), an input/output port, a timer, and the like, controls the printer 10 as a whole, and performs various processes based on programs recorded in the ROM 53 .

In addition to the programs, the ROM 53 stores various setting values, threshold values, and the like.

In the RAM 54, the print data, dot data (image data) generated based on the print data and used to emit light from each LEDi of the LED head Hd, various control data, etc. are temporarily recorded. . The RAM 54 functions as a work area when the CPU performs calculations.

The operation panel 56 includes an operation unit 58 comprising switches, keys, etc. (not shown) for the operator to input instructions to the printer 10, and a display unit comprising an LED screen, etc. (not shown) for displaying the status of the printer 10. 59. Note that when the operation panel 56 is formed by a touch panel, the display section 59 also functions as an operation section.

The temperature sensor s1 detects the temperature around the printer 10 as a first environmental variable, and the humidity sensor s2 detects the humidity around the printer 10 as a second environmental variable. The temperature detected by the temperature sensor s1 and the humidity detected by the humidity sensor s2 are sent to the control unit 50, and the voltage control unit 43 receives instructions from the control unit 50 and The charging voltage Vch applied to the charging roller 22, the developing roller 23, the supply roller 24, the developing blade 25, the static elimination device 27, and the transfer roller 28, the development voltage, the supply voltage, the regulation voltage, the static elimination voltage, and the transfer voltage are changed depending on the humidity. to control.

The control unit 50 includes an image conversion processing unit Pr1, a print processing unit Pr2, a dot determination processing unit Pr3, a toner area ratio calculation processing unit Pr4 as a developer area ratio calculation processing unit, a charging voltage control processing unit Pr5, and the like.

The image conversion processing unit Pr1 performs image conversion processing, converts print data received by the printer 10 from the host computer PC into black, yellow, magenta, and cyan dot data, and records the dot data in the RAM 54 .

The print processing unit Pr2 performs print processing, reads dot data of each color from the RAM 54, drives each LED head Hd based on each dot data, forms an image on the paper P, and performs printing. The dot data consists of binary data (0, 1), and the print processing unit Pr2 selectively causes the LEDi on one line in the scanning direction of the LED head Hd to emit light based on the dot data. That is, when the dot data is 0, the LEDi is not caused to emit light, and when the dot data is 1, it is caused to emit light.

The dot determination processing unit Pr3 performs dot determination processing, reads out dot data of each color from the RAM 54, and based on the dot data, determines the LED i of each line in either the image forming unit or the upstream image forming unit. It is determined whether or not the LEDi of the head Hd is allowed to emit light. The dot determination processing section Pr3 sets the determination result to 1 when the LEDi is caused to emit light in either the image forming unit or the upstream image forming unit, and the LEDi is caused to emit light in any of the image forming units. If not, the determination result is set to 0 and the determination result of each LEDi is recorded in the ROM 53 .

The toner area ratio calculation processing unit Pr4 performs a toner area ratio calculation process as a developer area ratio calculation process, reads the determination result of the dot determination processing unit Pr3 for each line from the ROM 53, and based on the determination result, For each line, the toner area ratio εj (j=bk, y, m, c) as the developer area ratio of each color is calculated, and for each predetermined range in the sub-scanning direction, in this embodiment, the image The maximum value εmax of the toner area ratio εj for each line is calculated for each width of the nip portion formed between the photosensitive drum 21 of the forming unit and the transfer belt Bt, that is, for each nip width range.

Note that the toner area ratio εj is the number nj of LEDi, where nj (j=bk, y, m, c) is the number of LEDs of each color for which the determination result of the dot determination processing unit Pr3 is 1 in each line. The ratio of the number N of is expressed as a percentage,
εj = (nj/N) x 100
become.

Further, the toner area ratio εj is the ratio of the toner image formed in either the image forming unit or the image forming unit on the upstream side and transferred to the paper P. represents the degree to which it becomes difficult to flow.

The charging voltage control processing unit Pr5 performs charging voltage control processing, determines whether the maximum value εmax of the toner area ratio εj for each nip width range is equal to or greater than a threshold value εth, and determines whether the maximum value εmax of the toner area ratio εj is greater than or equal to the threshold value εth, the charging voltage Vch is corrected and increased, and if it is less than the threshold value εth, the charging voltage Vch is not corrected.

Next, the operation of the controller of printer 10 will be described.

FIG. 3 is a flow chart showing the operation of the printer control device according to the embodiment of the present invention, and FIG. 4 is a diagram showing an example of dot data of one line and determination results by the dot determination processing section according to the embodiment of the present invention. .

When the printer 10 receives a print command, print data, etc. from the host computer PC (step S1), the image conversion processing unit Pr1 converts the print data into dot data of each color (step S2) and records it in the RAM 54. The dot data of each color takes a value of 0 or 1 for each line and for each LEDi of each color, as shown in FIG. For example, in the LED head Hd of the image forming unit 16Bk for black, the dot data of LEDs 1 to 10 take values of 1, 0, 0, 0, 0, 0, 0, 1, 0, 0, and yellow image formation is performed. In the LED head Hd of the unit 16Y, the dot data of the LEDs 1 to 10 take values of 0, 1, 0, 1, 0, 1, 0, 0, 0, 1.

Subsequently, the dot determination processing unit Pr3 reads the dot data of each color from the RAM 54, and determines whether the LEDi of the LED head Hd is caused to emit light in either the image forming unit or the upstream image forming unit for each line. If the LEDi is caused to emit light in any image forming unit, the determination result is set to 1, and if the LEDi is not caused to emit light in any image forming unit, the determination result is set to 0, and the determination result is recorded in the ROM 53. (Step S3).

For example, when the image forming unit is the image forming unit 16Bk, the dot determination processing section Pr3 determines whether or not each LEDi of the LED head Hd in the image forming unit 16Bk is caused to emit light for each line. is set to 1, 0, 0, 0, 0, 0, 0, 1, 0, 0.

When the image forming unit is the image forming unit 16C, the dot determination processing section Pr3 causes each LEDi to emit light in one of the image forming units 16Bk, 16Y, and 16M for each line. 1, 1, 1, 1, 0, 1, 1, 1, 1, 1.

Subsequently, the toner area ratio calculation processing unit Pr4 reads the determination result of the dot determination processing unit Pr3 for each line from the ROM 53, and calculates the toner area ratio εj of each color for each line based on the determination result (step S4 ).

For example, if the image forming unit is the image forming unit 16Bk, the number nbk of LEDs with the determination result of 1 among the 10 black LEDs is 2, so the toner area ratio εbk is 20%. Become.

If the image forming unit is the image forming unit 16Y, the number ny of the ten yellow LEDs whose determination result is 1 is 6, so the toner area ratio εy is 60[%]. Become.

When the image forming unit is the image forming unit 16M, the toner area ratio εm is 80%, and when the image forming unit is the image forming unit 16C, the toner area ratio εc is 90%. . Note that the toner area ratio εj is 100% when a toner image with a print duty of 100% is formed regardless of whether the image forming unit is one of the image forming units 16Bk, 16Y, 16M, and 16C. 〕become.

Subsequently, the toner area ratio calculation processing unit Pr4 calculates the maximum value εmax of the toner area ratio εj of each line for each nip width range in the sub-scanning direction (step S5).

Next, the charging voltage control processor Pr5 determines whether or not the maximum value εmax of the toner area ratio εj is equal to or greater than the threshold value εth, 90% in this embodiment (step S6).

When the maximum value εmax of the toner area ratio εj is 90[%] or more, the charging voltage control processing section Pr5 corrects the charging voltage Vch applied to the charging roller 22 by the correction value δVch (in the negative direction). ) is raised (step S7).

The correction value δVch is a ratio γ that indicates how much the maximum value εmax of the toner area ratio εj exceeds 90%.
γ = (εmax-90)/(100-90)
Assuming that the value of the positive surface potential formed on both ends of the photosensitive drum 21 when the toner area ratio εj is 100% is the reference value Vst, the ratio γ multiplied by,
δVch=Vst×γ
=Vst×((εmax−90)/(100−90))
be made.

Then, the print processing unit Pr2 performs print processing (step S9).

Further, when the maximum value εmax of the toner area ratio εj is less than 90%, the charging voltage control processor Pr5 does not correct the charging voltage Vch (step S8).

Subsequently, the print processing unit Pr2 performs print processing (step S9).

Next, the flowchart will be described.
Step S1 The printer 10 receives a print command, print data, etc. from the host computer PC.
Step S2 The image conversion processing section Pr1 converts the print data into dot data of each color.
Step S3: The determination result of the dot determination processing unit Pr3 is recorded in the ROM53.
Step S4 The toner area ratio calculation processing unit Pr4 calculates the toner area ratio εj of each color for each line.
Step S5 The toner area ratio calculation processing unit Pr4 calculates the maximum value εmax of the toner area ratio εj of each line.
Step S6 The charging voltage control processor Pr5 determines whether the maximum value εmax of the toner area ratio εj is equal to or greater than the threshold value εth. If the maximum value εmax of the toner area ratio εj is equal to or greater than the threshold value εth, the process proceeds to step S7, and if the maximum value εmax of the toner area ratio εj is less than the threshold value εth, the process proceeds to step S8.
Step S7 The charging voltage control processor Pr5 corrects the charging voltage Vch to be applied to the charging roller 22, increases it by the correction value δVch, and proceeds to step S9.
Step S8 The charging voltage control processor Pr5 does not correct the charging voltage Vch.
Step S9 The print processing unit Pr2 performs print processing, and terminates the processing.

Thus, in the present embodiment, for each line in the image forming unit, the toner area ratio εj representing the rate at which a toner image of either the color of the image forming unit or the upstream image forming unit is formed is Since the charging voltage Vch applied to the charging roller 22 is corrected based on the calculated toner area ratio εj, printing with a high print duty is performed, and the paper P Therefore, it is possible to prevent a large amount of transfer current from flowing to the non-printing area of the photosensitive drum 21 when the toner image is transferred to the surface of the photosensitive drum 21 . Therefore, the toner adheres to both ends of the photoreceptor drum 21 and the photoreceptor drum 21 is not soiled, and the paper P is not soiled by the toner adhering to both ends of the photoreceptor drum 21. .

Next, transition of the surface potential of the photosensitive drum 21 when forming an image on the paper P in the printer of the reference example will be described.

FIG. 5 shows an example of transition of the surface potential of the photosensitive drum when a solid blank image is formed on paper with a print duty of 0[%]. FIG. FIG. 7 shows the state of the paper when a solid cyan image is formed. FIG. 7 shows the transition of the surface potential of the photosensitive drum when a solid cyan image is formed on the paper with a print duty of 100%. FIG. 4 is a diagram showing an example; 5 and 7, the horizontal axis represents time, and the vertical axis represents the surface potential of the photosensitive drum 21. In FIG. Also, on the horizontal axis, charging, exposure, transfer, and static elimination represent the charging process, exposure process, transfer process, and static elimination process, respectively.

In FIG. 5, L1 is a line representing changes in the surface potential of the photoreceptor drum 21 during the first and second rounds when a solid blank image is formed on the paper P with a print duty of 0[%]. be.

When printing is started, the photosensitive drum 21 is charged by the charging roller 22 in the charging process of the first rotation of the photosensitive drum 21, and the surface potential of the photosensitive drum 21 becomes -500 [V]. Next, in the exposure process, since the print duty is 0[%], each LEDi of the LED head Hd is not caused to emit light, and the photosensitive drum 21 is not irradiated with light. Therefore, the surface potential of the photosensitive drum 21 remains at -500 [V]. Subsequently, in the transfer process, a transfer voltage of +3000 [V] is applied to the transfer roller 28, and the toner image on the photoreceptor drum 21 is transferred to the paper P due to the potential difference between the transfer roller 28 and the photoreceptor drum 21. FIG. At this time, a transfer current flows from the transfer roller 28 to the photosensitive drum 21, and the surface potential of the photosensitive drum 21 decreases to -200 [V]. Next, in the static elimination process, the static elimination device 27 causes the LED to emit light, irradiates the photosensitive drum 21 with static elimination light, and the surface potential of the photosensitive drum 21 becomes -50 [V]. Then, in the charging process of the second rotation of the photosensitive drum 21, the photosensitive drum 21 is charged again by the charging roller 22, and the surface potential of the photosensitive drum 21 becomes -500 [V].

6, P is the paper, TC is a solid cyan toner image formed on the paper P with a print duty of 100[%], and Ar1 is the paper corresponding to the printing area of the photosensitive drum 21. An image area Ar2 on which a toner image is formed on P is a non-image area on the sheet P, on which no toner image is formed, corresponding to the non-printing area of the photosensitive drum 21 .

In FIG. 7, L2 is the surface potential of the first and second printing regions of the photosensitive drum 21 when a solid cyan image is formed on the paper P with a printing duty of 100[%]. The line L3 representing the transition is the surface potential of the non-printing regions of the photosensitive drum 21 during the first and second rounds when a solid cyan image is formed on the paper P with a print duty of 100[%]. It is a line representing transition.

In the printing area of the photoreceptor drum 21, when printing is started, the photoreceptor drum 21 is charged by the charging roller 22 in the charging process, and the surface potential of the photoreceptor drum 21 becomes -500 [V]. Next, in the exposure process, since the print duty is 100[%], each LEDi of the LED head Hd is caused to emit light, and the photosensitive drum 21 is irradiated with light. Therefore, the surface potential of the photosensitive drum 21 becomes -100 [V]. Subsequently, in the transfer process, a transfer voltage of +3000 [V] is applied to the transfer roller 28, but since the toner image has been transferred to the image area Ar1 on the paper P, the transfer roller 28 transfers to the photosensitive drum 21. The transfer current becomes difficult to flow, and the surface potential of the photosensitive drum 21 does not decrease and remains at -100 [V]. Next, in the static elimination process, the static elimination device 27 causes the LED to emit light, irradiates the photosensitive drum 21 with static elimination light, and the surface potential of the photosensitive drum 21 becomes -50 [V]. Then, in the charging process of the second rotation of the photosensitive drum 21, the photosensitive drum 21 is charged again by the charging roller 22, and the surface potential of the photosensitive drum 21 becomes -500 [V].

Further, in the non-printing area of the photoreceptor drum 21, when printing is started, the photoreceptor drum 21 is charged by the charging roller 22 in the charging process, and the surface potential of the photoreceptor drum 21 is -500 [V]. become. Next, in the exposure process, each LEDi of the LED head Hd cannot emit light, so the surface potential of the photosensitive drum 21 remains -500 [V]. Subsequently, in the transfer process, a transfer voltage of +3000 [V] is applied to the transfer roller 28, but since the toner image is not transferred to the non-image area Ar2 on the paper P, the transfer roller 28 is applied to the photosensitive drum 21. A transfer current that does not flow through the image area Ar1 flows in the second direction, and the surface potential of the photosensitive drum 21 decreases to +50 [V]. The reference value Vst is set to -50 [V] so that +50 [V], which is the surface potential of the positive electrode at this time, becomes 0 [V]. Next, in the static elimination process, the static elimination device 27 cannot eliminate the positively charged portion, so the surface potential of the photosensitive drum 21 remains +50 [V].

In the charging process of the second rotation of the photosensitive drum 21, the charging roller 22 charges the photosensitive drum 21 again. The surface potential of the photoreceptor drum 21 becomes lower than the first round and becomes -400 [V]. After that, the photosensitive drum 21 continues to rotate, and the surface potential of the non-printing area of the photosensitive drum 21 continues to decrease. cyan toner adheres to the non-printing area, and both ends of the photosensitive drum 21 are stained.

As shown in FIG. 6, in addition to forming a solid cyan image on paper P with a print duty of 100%, cyan images with a print duty of 30% are also used. image and a magenta image with a print duty of 70% without overlapping the cyan toner image and the magenta toner image, the non-printing area of the photosensitive drum 21 of the image forming unit 16C continues to decrease, and when the surface potential becomes equal to or lower than the developing voltage applied to the developing roller 23, the cyan toner on the developing roller 23 adheres to the non-printing area of the photosensitive drum 21 in the image forming unit 16C, Both ends of the photosensitive drum 21 become dirty. That is, in the image forming unit and the upstream image forming unit, even when forming images of different colors without superimposing toner images so that the combined print duty is 100[%], in the image forming unit, Toner adheres to the non-printing area of the photoreceptor drum 21, and both end portions of the photoreceptor drum 21 become dirty.

On the other hand, a cyan image with a print duty of 30[%] and a magenta image with a print duty of 70[%] are formed on the paper P by overlapping the cyan toner image and the magenta toner image. In this case, the non-printing area Ar2 where the toner image on the paper P is not transferred is widened, and the transfer current easily flows from the transfer roller 28 to the photosensitive drum 21. Therefore, the non-printing area of the photosensitive drum 21 becomes positive. You will no longer be charged with polarity. Therefore, in the image forming unit, the toner does not adhere to the non-printing area of the photoreceptor drum 21, and both ends of the photoreceptor drum 21 are not stained.

Even if the nip width is only 5 mm, the maximum value εmax of the toner area ratio εj within the range of the nip width is 90% or more in either the image forming unit or the upstream image forming unit. Experiments have shown that the surface potential of the photosensitive drum 21 takes a positive value in the transfer process.

Next, transition of the surface potential of the photosensitive drum 21 when forming an image on the paper P in the present embodiment will be described.

FIG. 8 shows a cyan image with a print duty of 30[%] and a magenta image with a print duty of 70[%], a cyan toner image and a magenta toner image, on paper according to the embodiment of the present invention. FIG. 10 is a diagram showing an example of transition of the surface potential of the photoreceptor drum when forming without overlapping. In the figure, the horizontal axis represents time, and the vertical axis represents the surface potential of the photosensitive drum. Also, on the horizontal axis, charging, exposure, transfer, and static elimination represent the charging process, exposure process, transfer process, and static elimination process, respectively.

In the figure, L4 is a cyan toner image with a print duty of 30[%] and a magenta image with a print duty of 70[%] on a sheet of paper P (FIG. 2). The line L5 represents the transition of the surface potential of the printing area of the photoreceptor drum 21 in the first and second rounds when forming without overlapping. and a magenta image with a print duty of 70[%] without superimposing each toner image, the transition of the surface potential of the non-printing area of the photosensitive drum 21 in the first and second rounds is It is a line that represents In this embodiment, the environmental conditions of the printer 10 are temperature of 22[° C.] and humidity of 55[%].

In the printing area of the photoreceptor drum 21, when printing is started, the photoreceptor drum 21 is charged by the charging roller 22 in the charging process. A magenta image with a print duty of 70[%] is formed without overlapping the toner images.

In this case, as described above, the reference value Vst is set to -50 [V], and a cyan image with a print duty of 30 [%] and a magenta image with a print duty of 70 [%] are printed on the paper P. , the toner images are formed without overlapping each other, so the maximum value εmax of the toner area ratio εj is 100%. Therefore, the correction value δVch of the charging voltage Vch is
δVch=Vst×((εmax-90)/(100-90))
=-50 x ((100-90)/(100-90))
=-50 [V]
and the charged voltage Vch after correction is
Vch=-500-50
=-550 [V]
, and the surface potential of the photosensitive drum 21 becomes -550 [V]. Next, in an exposure process, each LEDi of the LED head Hd is caused to emit light, and the photosensitive drum 21 is irradiated with light. Therefore, the surface potential of the photosensitive drum 21 becomes -100 [V]. Subsequently, in the transfer step, a transfer voltage of +3000 [V] is applied to the transfer roller 28, but since the cyan and magenta toner images have been transferred to the image area Ar1 (FIG. 6) on the paper P, the transfer The transfer current is less likely to flow from the roller 28 to the photosensitive drum 21, and the surface potential of the photosensitive drum 21 does not decrease and remains at -100 [V]. Next, in the static elimination process, the static elimination device 27 causes the LED to emit light, irradiates the photosensitive drum 21 with static elimination light, and the surface potential of the photosensitive drum 21 becomes -50 [V]. Then, in the charging process of the second round of the photosensitive drum 21, the photosensitive drum 21 is charged again by the charging roller 22, and the surface potential of the photosensitive drum 21 becomes -550 [V].

On the other hand, in the non-printing area of the photoreceptor drum 21, when printing is started, the photoreceptor drum 21 is charged by the charging roller 22 in the charging process, and the surface potential of the photoreceptor drum 21 is -550 [V]. become. Next, in the exposure process, each LEDi of the LED head Hd cannot emit light, so the surface potential of the photosensitive drum 21 remains -550 [V]. Subsequently, in the transfer process, a transfer voltage of +3000 [V] is applied to the transfer roller 28, but since the toner image is not transferred to the non-image area Ar2 on the paper P, the transfer roller 28 is applied to the photosensitive drum 21. A transfer current that does not flow through the image area Ar1 flows in the second region, and the surface potential of the photosensitive drum 21 becomes low. As a result, since the surface potential is -550 [V] before it is lowered, it does not become positive and becomes 0 [V]. Next, in the static elimination step, the static elimination device 27 cannot eliminate the 0 [V] portion, so the surface potential of the photosensitive drum 21 remains +0 [V].

Then, in the charging process of the second rotation of the photosensitive drum 21, the charging roller 22 charges the photosensitive drum 21 again with the charging voltage Vch, so that the surface potential of the photosensitive drum 21 becomes -550 [V].

Although the printer 10 is described in the present embodiment, the present invention can be applied to image forming apparatuses such as copiers, facsimile machines, and multi-function machines.

It should be noted that the present invention is not limited to the above-described embodiments, and various modifications can be made based on the gist of the present invention, and they are not excluded from the scope of the present invention.

10 Printers 16Bk, 16Y, 16M, 16C Image forming unit 21 Photoreceptor drum 22 Charging roller 23 Developing roller 24 Supply roller 25 Developing blade Hd LED head P Paper Pr4 Toner area ratio calculation processing unit Pr5 Charging voltage control processing unit u1 Transfer unit Vhc Charging voltage εj Toner area ratio

Claims (5)

(a) an image carrier, a charging member that charges the image carrier, and an image carrier that develops a latent image formed on the image carrier and carries the image, respectively, from the upstream side to the downstream side in the medium conveying direction; a plurality of image forming units each having a developing section for forming a developer image of each color on the body;
(b) A plurality of light-emitting elements arranged in the scanning direction are provided so as to face the image carrier of each image forming unit, and the light-emitting elements are caused to emit light based on the dot data, thereby causing the image carrier to emit light. an exposure device that forms a latent image;
(c) a transfer device that transfers the developer image formed on each of the image carriers onto a medium;
(d) In each line of the image forming unit, which is a predetermined image forming unit, the developer of any color of the image forming unit and the upstream image forming unit arranged upstream from the image forming unit. a developer area ratio calculation processing unit that calculates a developer area ratio representing a ratio of image formation;
(e) an image forming apparatus, further comprising: a charging voltage control processing section that corrects the charging voltage applied to the charging member based on the developer area ratio; 2. The image forming apparatus according to claim 1, wherein the developer area ratio calculation processing unit calculates the developer area ratio based on dot data. When the number of light-emitting elements arranged in the scanning direction in the exposure device is N, and the number of light-emitting elements that emit light in either the image forming unit or the upstream image forming unit is nj, the area of the developer is The rate εj is
εj = (nj/N) x 100
3. The image forming apparatus according to claim 1 or 2. (a) the developer area ratio calculation processing unit calculates the maximum value of the developer area ratio for each predetermined range in the sub-scanning direction in the image forming unit;
(b) The image forming apparatus according to claim 3, wherein the charging voltage control processing section corrects and increases the charging voltage when the maximum value of the developer area ratio is equal to or greater than a threshold value. In the image forming unit, Vst is the reference value of the surface potential when the image carrier becomes positive due to the transfer current flowing from the transfer member of the transfer device to the image carrier in the transfer process, and the developer area is defined as Vst. When the maximum value of the ratio is εmax and the threshold value of the developer area ratio is εth, the correction value δVch for correcting the charging voltage is given by
δVch=Vst×((εmax−εth)/(100−εth))
5. The image forming apparatus according to claim 4.

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