JP2021113919A - Image forming apparatus - Google Patents

Abstract

To provide means that prevents the occurrence of printing failure.SOLUTION: An image forming apparatus has: image carriers on which developer images are formed; a belt member to which the developer images are transferred; transfer members to which a transfer voltage is applied, which is for transferring the developer images on the image carriers to the belt member; a detection unit that detects the concentration of developer in the developer images transferred to the belt member; and a control unit that controls the transfer voltage. The developer images are transferred to the belt member as a plurality of developer transferred images in which the transfer voltage is changed, and the control unit controls the transfer voltage based on the amount of change in the concentration of developer in the developer transferred images detected by the detection unit.SELECTED DRAWING: Figure 2

Description

The present invention relates to an image forming apparatus that transfers a developer to form an image.

In a conventional image forming apparatus, an exposure means corresponding to each process unit is arranged together with a process unit including a photoconductor, a charging means, a developing means, etc., and used as black K, yellow Y, magenta M, and cyan C image forming means, respectively. , The toner image is sequentially transferred onto the intermediate transfer belt, and then the toner image is secondarily transferred to the paper fed according to the position of the toner image primaryly transferred on the intermediate transfer belt to form the toner image. (See, for example, Patent Document 1).

Japanese Unexamined Patent Publication No. 2014-106413

However, in the conventional technique, in the image forming apparatus, poor image quality (streaks caused by toner charging unevenness due to discharge during transfer) called color horizontal streaks may occur. Image quality defects due to horizontal streaks occur when multiple conditions such as resistance values of transfer belts and transfer rollers, toner charging characteristics, printing patterns, and transfer voltage values are met. Therefore, image quality due to horizontal streaks occurs. There is a problem that it is difficult to predict the occurrence of defects and it cannot be easily avoided.
An object of the present invention is to solve such a problem, and an object of the present invention is to suppress the occurrence of printing defects.

Therefore, in the present invention, an image carrier on which the developer image is formed, a belt member on which the developer image is transferred, and a transfer voltage for transferring the developer image on the image carrier to the belt member are applied. It has a transfer member to be processed, a detection unit for detecting the developer concentration of the developer image transferred to the belt member, and a control unit for controlling the transfer voltage, and the developer image is the transfer voltage. Is transferred to the belt member as a plurality of developing agent transfer images in which the above is changed, and the control unit controls the transfer voltage based on the amount of change in the developer concentration of the developer transfer image detected by the detection unit. It is characterized by that.

The present invention in this manner has the effect of suppressing the occurrence of printing defects.

Schematic cross-sectional view showing the configuration of the printer in the embodiment Block diagram showing the control configuration of the printer in the embodiment Explanatory drawing of concentration sensor in Example Explanatory drawing of detection voltage-concentration value conversion table in Example Explanatory drawing of concentration detection pattern in Example Cross-sectional view of the concentration detection pattern in the examples Explanatory drawing of concentration change and concentration detection pattern in Example Explanatory drawing of density change when color horizontal streak does not occur in Example Explanatory drawing of density change at the time of occurrence of color horizontal streak in Example Explanatory drawing of concentration change in Example Explanatory drawing of concentration change in Example A flowchart showing the flow of the primary transfer voltage calculation process in the embodiment. Explanatory drawing of printer dimensions in Example Schematic cross-sectional view showing the configuration of the printer in the comparative example

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

FIG. 1 is a schematic side sectional view showing a structure of a linter in an embodiment.
In FIG. 1, the printer 1 is an electrophotographic image forming apparatus capable of forming (printing) a toner image on paper as a recording medium based on print data input from a host computer or the like.

The printer 1 is formed by a printing mechanism 2K, 2Y, 2M, 2C that forms and transfers a toner image, LED (Light Emitting Diet) heads 11K, 11Y, 11M, 11C mounted on each printing mechanism, and toner by each printing mechanism. An intermediate transfer belt 12 on which an image is transferred, a drive roller 13 that conveys the intermediate transfer belt 12, a driven roller 14 that follows the intermediate transfer belt 12, and a secondary transfer roller 23 that performs secondary transfer on paper. The transfer facing roller 24, the paper feed mechanism 16 for feeding the paper, the secondary transfer discharge sensor 28 for monitoring the wrapping of the paper around the secondary transfer roller 23, and the secondary transfer remaining on the intermediate transfer belt 12. A cleaning blade 25 for removing residual toner, a waste toner tank 26 for collecting secondary transfer residual toner scraped off by the cleaning blade 25, a fixing mechanism 29 for fixing a toner image transferred to paper, and a fixing mechanism 29. It has a fixing / discharging sensor 34 for monitoring paper jams and the like, guides 27 and 36 for guiding the paper in the transport direction, and a stacker 35 for collecting and storing the printed paper.

The printer 1 has four independent process units, printing mechanisms 2K, 2Y, 2M, and 2C, which correspond to four colors (black K, yellow Y, magenta M, and cyan C), in the transport direction of the intermediate transfer belt 12. Placed along. The printing mechanism 2K forms a toner image corresponding to each color of black, the printing mechanism 2Y forms a yellow color, the printing mechanism 2M forms a magenta image, and the printing mechanism 2C forms a toner image corresponding to each color of cyan.

In each of the printing mechanisms 2K, 2Y, 2M and 2C, the surface is uniformly charged by the charging rollers 3K, 3Y, 3M and 3C and the charging rollers 3K, 3Y, 3M and 3C. 4C, developing rollers 5K, 5Y, 5M, 5C forming a developing unit for forming a toner image, developing blades 6K, 6Y, 6M, 6C, supply rollers 7K, 7Y, 7M, 7C, and a photosensitive drum. It has static elimination light sources 8K, 8Y, 8M, 8C that remove static electricity from the surfaces of 4K, 4Y, 4M, and 4C, and toner cartridges 9K, 9Y, 9M, 9C for supplying toner, which is a developer, to the developing unit. is doing.

In the photosensitive drums 4K, 4Y, 4M, and 4C as the image carrier, a toner image as a developer image is formed by the developing rollers 5K, 5Y, 5M, and 5C.

The LED heads 11K, 11Y, 11M, and 11C cause the LED array to emit light in response to the image data signal. A black image data signal among the color image data signals is input to the LED head 11K, and similarly, a yellow image data signal, a magenta image data signal, and a cyan are input to the LED heads 11Y, 11M, and 11C, respectively. The image data signal of is input. The LED heads 11K, 11Y, 11M, and 11C irradiate the surfaces of the photosensitive drums 4K, 4Y, 4M, and 4C with light based on the input image data signal to form an electrostatic latent image.

Toner is conveyed to the electrostatic latent images formed on the photosensitive drums 4K, 4Y, 4M, and 4C, and a toner image is formed.
The intermediate transfer belt 12 as a belt member transfers the toner image formed on the photosensitive drums 4K, 4Y, 4M, and 4C.

^{The intermediate transfer belt 12 is made of a high-resistance semi-conductive plastic film having a volume resistivity of about 10 10} Ω · cm to 10 ¹² Ω · cm, which is formed in a seamless endless shape, and includes a drive roller 13 and a driven roller. 14, It is stretched with a predetermined tension by the secondary transfer opposing roller 24.

The drive roller 13 is rotated by a belt motor 46 (see FIG. 2), and conveys the intermediate transfer belt 12 in the rotation direction (conveyance direction) indicated by the arrow e in the drawing.
The driven roller 14 and the secondary transfer opposing roller 24 rotate driven by the intermediate transfer belt 12.

The intermediate transfer belt 12 is pressed against the photosensitive drums 4K, 4Y, 4M, and 4C by the primary transfer rollers 10K, 10Y, 10M, and 10C, and the primary transfer rollers 10K, 10Y, 10M, and 10C are the intermediate transfer belts 12. Is in contact with photosensitive drums 4K, 4Y, 4M, and 4C to form a primary transfer nip.

A transfer voltage (primary transfer voltage) for transferring the toner image on the photosensitive drums 4K, 4Y, 4M, and 4C to the intermediate transfer belt 12 is applied to the primary transfer rollers 10K, 10Y, 10M, and 10C as the transfer members. By applying a transfer voltage (primary transfer voltage), the toner images on the photosensitive drums 4K, 4Y, 4M, and 4C are transferred to the intermediate transfer belt 12.

The primary transfer rollers 10K, 10Y, 10M, and 10C are driven to rotate on the intermediate transfer belt 12. The primary transfer rollers 10K, 10Y, 10M, and 10C are composed of a metal shaft and ^{urethane foam having a volume resistivity of about 10 7} Ω · cm to 10 ^{9 Ω · cm.}
A predetermined DC voltage is applied to the primary transfer rollers 10K, 10Y, 10M, and 10C by the primary transfer voltage generator 54 (see FIG. 2), and the toner images on the photosensitive drums 4K, 4Y, 4M, and 4C are intermediate. Transfer onto the transfer belt 12.

A paper feeding mechanism 16 for supplying paper to the transport path 15 (dotted line portion shown in FIG. 1) is provided in the lower part of the printer 1.

The paper feeding mechanism 16 is driven by a paper accommodating cassette 17, a hopping motor 44 (see FIG. 2), a hopping roller 18 that feeds out paper which is a recording medium contained in the paper accommodating cassette 17, and a skew (paper). Is called "skew"), the pinch roller 19 that corrects the skew of the paper, the registration roller 20 that feeds the paper to the secondary transfer roller 23, and the paper to the secondary transfer roller 23. It has a guide 21 for guiding the paper, and a paper feed sensor 22 for detecting that the paper has reached between the pinch roller 19 and the registration roller 20.

The intermediate transfer belt 12 is pressed against the secondary transfer opposing roller 24 by the secondary transfer roller 23, and the secondary transfer roller 23 contacts the intermediate transfer belt 12 with the secondary transfer opposing roller 24 in between and is secondary. It forms a transfer nip.

The secondary transfer roller 23 is driven to rotate by the intermediate transfer belt 12.
The secondary transfer roller 23, a metal shaft, the volume resistivity is constituted by a ^{10 7 Ω · cm~10 9 Ω ·} cm approximately urethane foam conductivity is imparted, the secondary transfer opposed roller 24 is a metal It is composed of a shaft and a metal roller.

A predetermined DC voltage is applied to the secondary transfer roller 23 by the secondary transfer voltage generating unit 55 (see FIG. 2), and the toner image on the intermediate transfer belt 12 is transferred onto the paper. The paper that has passed through the secondary transfer roller 23 is separated from the intermediate transfer belt 12 and conveyed to the guide 27 that guides the paper to the fixing mechanism 29. A secondary transfer discharge sensor 28 is provided on the downstream side of the secondary transfer roller 23 in the paper transport direction to monitor paper wrapping around the secondary transfer roller 23 and failure to separate the paper from the intermediate transfer belt 12. ing.

Further, below the intermediate transfer belt 12, a density sensor 58 is arranged at a position facing the intermediate transfer belt 12.

The density sensor 58 as a detection unit is a reflection type optical sensor having one light emitting system and two light receiving systems, and measures the intensity of the reflected light of the density detection pattern as the developer image transferred on the intermediate transfer belt 12. , The amount of toner (= toner density) of the density detection pattern is detected.

The fixing mechanism 29 includes a heat roller 30, a pressure roller 31 that pressurizes the heat roller 30, and the like. The fixing mechanism 29 is for heating and melting the toner on the paper to fix the toner image on the paper.

The heat roller 30 is driven by a heat motor 49 (see FIG. 2), and the pressure roller 31 is driven to rotate by the heat roller 30. The heat roller 30 has a built-in heater 32 including a halogen lamp that functions as a heat source.
The thermistor 33 is arranged near the surface of the heat roller 30 and monitors the temperature of the heat roller 30.

A fixing / discharging sensor 34 is provided on the downstream side of the fixing mechanism 29 to monitor a paper jam in the fixing mechanism 29 and wrapping of paper around the heat roller 30.
A guide 36 for transporting the paper to the stacker 35 at the upper part of the housing of the printer 1 is provided on the downstream side of the fixing / discharging sensor 34 in the paper transport direction, and the printed paper is ejected to the stacker 35.

Further, in the guide 36, a transport roller 37, a transport roller 38, and a transport roller 39 for transporting the paper to the stacker 35 are provided. The transfer roller 37, the transfer roller 38, and the transfer roller 39 are driven by a transfer motor 48 (see FIG. 2).
On the downstream side of the intermediate transfer belt 12 in the transport direction from the secondary transfer roller 23, a cleaning blade 25 that removes the residual secondary transfer toner that is not transferred to the paper in the secondary transfer and remains on the intermediate transfer belt 12 is driven. It is arranged so as to face the roller 14.

The cleaning blade 25 is made of a flexible rubber material or a plastic material, and scrapes off the secondary transfer residual toner remaining on the intermediate transfer belt 12 into the waste toner tank 26.

Next, the control configuration of the printer of this embodiment will be described.

FIG. 2 is a block diagram showing a control configuration of the printer in the embodiment.
In FIG. 2, the host interface unit 40 is a part that bears a physical hierarchical interface with the host computer.

The command / image processing unit 41 interprets the command received from the host computer side and expands the image data into bitmap data.
The LED head interface unit 42 processes the bitmap data developed by the command / image processing unit 41 according to the interfaces of the LED heads 11K, 11Y, 11M, and 11C of each color.

The mechanism control unit 43 as a control unit controls each unit of the printer 1, and follows instructions from the command / image processing unit 41 from the paper feed sensor 22, the secondary transfer discharge sensor 28, and the fixing discharge sensor 34. The drive control of the hopping motor 44, the resist motor 45, the belt motor 46, the drum motor 47, the conveyor motor 48, and the heater motor 49 is performed based on the signal of the above, and the temperature control of the heater 32 is performed based on the signal from the thermistor 33. The voltage output control to the high pressure control unit 50 and the primary transfer voltage control based on the signal from the concentration sensor 58 are performed.

Further, the mechanism control unit 43 controls the primary transfer voltage, and controls the primary transfer voltage calculation unit 56 that calculates the optimum primary transfer voltage based on the signal from the concentration sensor 58.
The primary transfer voltage calculation unit 56 calculates and determines the primary transfer voltage value output by the primary transfer voltage generation unit 54 based on the signal from the concentration sensor 58.

The memory 59 is a storage unit that stores the sensor detection voltage-concentration value conversion table 60 shown in FIG. 4 and the concentration detection patterns 61 and 62 shown in FIG. 5, which are used in the primary transfer voltage calculation process described later.
The high-voltage control unit 50 controls the charging voltage generation unit 51, the supply voltage generation unit 52, the development voltage generation unit 53, the primary transfer voltage generation unit 54, and the secondary transfer voltage generation unit 55 in accordance with the instructions of the mechanism control unit 43. Is what you do.

The charging voltage generation unit 51 generates and stops the charging voltage on the charging rollers 3K, 3Y, 3M, and 3C in accordance with the instruction of the high voltage control unit 50.
The supply voltage generation unit 52 generates and stops the supply voltage to the supply rollers 7K, 7Y, 7M, and 7C in accordance with the instruction of the high voltage control unit 50.

The developing voltage generating unit 53 generates and stops the developing voltage on the developing rollers 5K, 5Y, 5M, and 5C in accordance with the instruction of the high voltage control unit 50.
The primary transfer voltage generation unit 54 generates and stops the primary transfer voltage to the primary transfer rollers 10K, 10Y, 10M, and 10C in accordance with the instruction of the high voltage control unit 50.

The secondary transfer voltage generation unit 55 generates and stops the secondary transfer voltage to the secondary transfer roller 23 in accordance with the instruction of the high voltage control unit 50.
The memory 57 is a storage unit that stores various set values of the charging voltage generation unit 51, the supply voltage generation unit 52, the development voltage generation unit 53, the primary transfer voltage generation unit 54, and the secondary transfer voltage generation unit 55. ..

The printer 1 configured in this way includes a control means such as a CPU (Central Processing Unit), and the control means controls the operation of the entire device based on a control program (software) stored in a storage unit such as a memory. Will be done.

The operation of the above-described configuration will be described.

First, the printing operation of the printer 1 in this embodiment will be described with reference to FIGS. 1 and 2.

When the printer 1 receives the image data sent from the host computer, the command / image processing unit 41 instructs the mechanism control unit 43 to start warming up the fixing mechanism 29, and expands the image data. Bitmap data for each page is generated corresponding to each color, and the bitmap data is transmitted to the LED head interface unit 42.
Upon receiving the instruction to start warm-up from the command / image processing unit 41, the mechanism control unit 43 controls the heater motor 49, drives the heat roller 30, and monitors the signal of the thermistor 33 while turning the heater 32 ON / OFF. And adjust the fixing temperature.

The mechanism control unit 43 starts the printing operation when the fixing temperature reaches a temperature at which the toner image on the recording medium set in advance can be fixed.
The mechanism control unit 43 controls the belt motor 46 and the drum motor 47, and drives the drive rollers 13, the printing mechanisms 2K, 2Y, 2M, and 2C photosensitive drums 4K, 4Y, 4M, and 4C. Further, the mechanism control unit 43 instructs the high voltage control unit 50 to output a high voltage.

When the high-voltage control unit 50 receives an instruction for high-voltage output from the mechanism control unit 43, the high-voltage control unit 50 reads out the set values of the charging voltage, the supply voltage, and the development voltage stored in the memory 57, and the charging voltage generation unit 51 and the supply voltage generation unit. 52, the development voltage generation unit 53 supplies the charging voltage, the supply voltage, and the development voltage to the rollers of the printing mechanisms 2K, 2Y, 2M, and 2C.

Here, the operation of forming a toner image in the printing mechanisms 2K, 2Y, 2M, and 2C will be described. Here, the black printing mechanism 2K will be described as a representative. Since yellow, magenta, and cyan are the same as black, duplicate explanations will be omitted. When the charging voltage, supply voltage, and developing voltage are supplied to each roller by the high-voltage control unit 50, a charging voltage of -1100V is supplied to the charging roller 3K, and the surface of the photosensitive drum 4K is charged to about -600V.

Further, a developing voltage of −200 V is supplied to the developing roller 5K, and a supply voltage of −250 V is supplied to the supply roller 7K. The electric field is formed.

Black toner is contained in the toner cartridge 9K of the printing mechanism 2K, and the toner supplied from the toner cartridge 9K is strongly rubbed and triboelectricly charged in the contact region between the developing roller 5K and the supply roller 7K. In this embodiment, the toner is triboelectrically charged due to the characteristics of the developing roller 5K, the supply roller 7K, and the toner.

The triboelectrically charged toner adheres to the developing roller 5K by the Coulomb force received from the electric field directed from the developing roller 5K to the supply roller 7K near the contact region between the developing roller 5K and the supply roller 7K.

The adhered toner is carried to the contact portion between the developing roller 5K and the developing blade 6K as the developing roller 5K rotates, and is smoothed to a uniform thickness by the developing blade 6K to form a toner layer.

The developing roller 5K continues to rotate and carries the toner layer to the nip portion with the photosensitive drum 4K.
On the other hand, the LED head interface unit 42 blinks the LED of the LED head 11K corresponding to the transmitted bitmap data, exposes the photosensitive drum 4K charged at −600V, eliminates static electricity at −50V, and electrostatically lurks. Write the image. As the photosensitive drum 4K rotates, the electrostatic latent image written on the surface of the photosensitive drum 4K reaches the contact region with the developing roller 5K.

Between the developing roller 5K and the photosensitive drum 4K, the electric field in the direction from the photosensitive drum 4K to the developing roller 5K is in the opposite direction in the unexposed area where the charge is reduced to -50V, and in the non-exposed area where the charge is kept at -600V. Since the electric field of the above is formed, the toner is selectively adhered only to the exposed portion from the negatively polarized toner layer on the developing roller 5K, and the electrostatic latent image is developed as a toner image.

The mechanism control unit 43 instructs the high-voltage control unit 50 to generate the primary transfer voltage at the timing when the toner images developed on the photosensitive drums 4K, 4Y, 4M, and 4C reach the respective primary transfer nip units in sequence. Is issued.
The high-voltage control unit 50 reads the primary transfer voltage value determined by the primary transfer voltage calculation unit 56 from the memory 57, and the primary transfer voltage generation unit 54 transfers the primary transfer to the primary transfer rollers 10K, 10Y, 10M, and 10C. Supply voltage.

The primary transfer voltage calculation process performed by the primary transfer voltage calculation unit 56 to determine the primary transfer voltage value will be described later.
In this embodiment, the primary transfer voltage is + 200V to + 2000V. At this time, in the primary transfer nip portion, an electric field is formed in the direction from the transfer rollers 10K, 10Y, 10M, and 10C toward the photosensitive drums 4K, 4Y, 4M, and 4C, and the electric field is developed on the photosensitive drums 4K, 4Y, 4M, and 4C. The negatively polar toner image is first-order transferred onto the intermediate transfer belt 12.

The mechanism control unit 43 drives the hopping motor 44 to rotate the hopping roller 18 before the toner image primaryly transferred on the intermediate transfer belt 12 reaches the secondary transfer nip, and causes the paper storage cassette 17 to rotate. Only one sheet of paper is sent between the pinch roller 19 and the registration roller 20.

The mechanism control unit 43 monitors the output of the paper feed sensor 22 and stops the hopping motor 44 when it detects that the tip of the paper has reached between the pinch roller 19 and the resist roller 20. Further, the mechanism control unit 43 drives the resist motor 45 at the timing when the toner image primaryly transferred on the intermediate transfer belt 12 reaches the secondary transfer nip portion, and between the pinch roller 19 and the resist roller 20. Paper is conveyed to the guide 21. The paper is guided by the guide 21 and reaches the secondary transfer nip portion.

The mechanism control unit 43 issues an instruction to generate the secondary transfer voltage to the high voltage control unit 50 at the timing when the toner image primaryly transferred on the intermediate transfer belt 12 reaches the secondary transfer nip portion.

The high-voltage control unit 50 reads out the set value of the secondary transfer voltage stored in the memory 57, and supplies the secondary transfer voltage from the secondary transfer voltage generation unit 55 to the secondary transfer roller 23. In this embodiment, the secondary transfer voltage is + 2500V.
At this time, in the secondary transfer nip portion, an electric field is formed in the direction from the secondary transfer roller 23 toward the secondary transfer opposing roller 24, and the negatively polar toner image primary transferred on the intermediate transfer belt 12 is a recording medium. It is secondarily transferred onto the paper as.

The mechanism control unit 43 monitors the winding of the paper around the secondary transfer roller 23 and the failure to separate the paper from the intermediate transfer belt 12 by the secondary transfer discharge sensor 28, and guides the paper for which the secondary transfer process has been completed. Guided by 27, it is sent to the fixing mechanism 29. When the paper reaches the fixing mechanism 29, it is narrowly conveyed to the heat roller 30 that has already reached the fixable temperature and the pressure roller 31 that is in pressure contact with the heat roller 30, and the toner on the paper is heated and melted to heat and melt the toner. Is fixed on the paper.

The mechanism control unit 43 drives the transfer motor 48 to rotate the transfer roller 37, the transfer roller 38, and the transfer roller 39 before the paper for which the fixing process has been completed reaches the guide 36.
The mechanism control unit 43 monitors the paper jam in the fixing mechanism 29 and the wrapping of the paper around the heat roller 30 by the fixing discharge sensor 34, and guides the paper for which the fixing process is completed to the guide 36, and the transfer roller 37 and the transfer It is conveyed to the roller 38 and the transfer roller 39 and discharged to the stacker 35.

At the same time as the fixing step is performed, the secondary transfer residual toner remaining on the intermediate transfer belt 12 is scraped off to the waste toner tank 26 by the cleaning blade 25.
When all the steps are completed, the mechanism control unit 43 stops the belt motor 46, the drum motor 47, and the conveyor motor 48, and at the same time issues an instruction to the high voltage control unit 50, and the charging voltage generating unit 51 and the supply voltage generating unit 51. 52, the development voltage generation unit 53 stops the supply of the charging voltage, supply voltage, and development voltage to each roller of each printing mechanism 2K, 2Y, 2M, and 2C, and also stops the heater motor 49 and the heater 32 to print. Complete the operation.

Next, the primary transfer voltage control performed by the mechanism control unit 43 will be described.

In this embodiment, the density sensor 58 shown in FIG. 1 is used to detect the presence or absence of horizontal streaks of the density detection pattern formed on the intermediate transfer belt 12, and when horizontal streaks occur, the primary transfer is performed. The voltage calculation unit 56 calculates the primary transfer voltage value at which no horizontal streaks occur. The presence or absence of horizontal streaks generated by the density sensor 58 is detected by the mechanism control unit 43 changing the primary transfer voltage and generating horizontal streaks based on the density change of the density detection pattern formed on the intermediate transfer belt 12. Judge the presence or absence.

Here, the concentration detection method by the concentration sensor 58 will be described with reference to the explanatory diagram of the concentration sensor in the embodiment of FIG. Note that FIG. 3A is a schematic diagram of the density sensor 58, FIG. 3B is an explanatory diagram when detecting the density of yellow, magenta, and cyan, and FIG. 3C is a diagram when detecting the density of black. It is explanatory drawing.

As shown in FIG. 3A, the density sensor 58 is composed of an infrared LED 5801, a phototransistor for receiving specular reflected light 5802, and a phototransistor for receiving diffuse reflected light 5803. Both yellow, magenta, and cyan toner concentrations can be detected.

As shown in FIG. 3B, when detecting the density of yellow, magenta, and cyan toners, yellow is emitted from the infrared LED 5801 to form a density detection pattern 5804 printed on the intermediate transfer belt 12. Light diffused and reflected by any of toner, magenta toner, and cyan toner is received by the diffuse reflected light receiving phototransistor 5803, and the diffuse reflected light receiving phototransistor 5803 generates a voltage corresponding to the amount of light. Therefore, if the amount of yellow toner, magenta toner, or cyan toner forming the density detection pattern 5804 is large (= the density is high), the diffuse reflected light received by the diffuse reflected light receiving phototransistor 5803 increases.

As shown in FIG. 3C, when detecting the density of black toner, the black toner emitted from the infrared LED 5801 and forming the density detection pattern 5805 printed on the intermediate transfer belt 12 is used. The light reflected on the mirror surface by the intermediate transfer belt 12 is received by the phototransistor 5802 for receiving the specularly reflected light, and the phototransistor 5802 for receiving the specularly reflected light generates a voltage corresponding to the amount of the light. Since the black toner forming the density detection pattern 5805 absorbs the emitted light from the infrared LED 5801, if the amount of black toner is large (= the density is high), the intermediate transfer belt 12 receives the light with the specular reflected light receiving phototransistor 5802. The amount of specularly reflected light is reduced. On the other hand, if the amount of black toner is small (= the density is low), the amount of specularly reflected light by the intermediate transfer belt 12 received by the phototransistor 5802 for receiving specularly reflected light increases.

In this embodiment, the detection voltage of the toner concentration of black, yellow, magenta, and cyan detected by the density sensor 58 is converted into a density value based on the sensor detection voltage-density value conversion table 60 shown in FIG. The density value conversion method for converting the toner concentration detection voltage into a density value based on the sensor detection voltage-density value conversion table 60 will be described later.

Next, a density detection pattern for detecting the toner concentration with the density sensor 58 will be described with reference to an explanatory diagram of the density detection pattern in the example of FIG. 5 and a cross-sectional view of the density detection pattern in the embodiment of FIG.

The density detection pattern 61 as the first developer pattern image and the density detection pattern 62 as the second developer pattern image shown in FIG. 5 are density detection patterns for detecting the presence or absence of color horizontal streaks by the density sensor 58. be.

In this embodiment, two types of concentration detection patterns 61 and different pattern widths (lengths in a direction orthogonal to the transport direction of the intermediate transfer belt 12 indicated by the arrow in FIG. 1 (rotation direction indicated by the arrow e in FIG. 1)) and The concentration detection pattern 62 is used. Further, the density sensor 58 detects the amount of change in the toner density of the density detection pattern 61 and the density detection pattern 62.
The pattern width of the density detection pattern 61 is Wp1 [mm], which is the same size as the diameter of the detection spot SR of the density sensor 58, and the pattern width of the density detection pattern 62 is Wp2 [mm], which is the maximum printable width of the printer 1. do.

Further, the pattern lengths of the density detection pattern 61 and the density detection pattern 62 (the length in the transport direction of the intermediate transfer belt 12 indicated by the arrow in the figure (the rotation direction indicated by the arrow e in FIG. 1)) are detected by the density sensor 58. The Lp [mm] is the same as the diameter of the spot SR.

In this embodiment, in order to detect the density change of the density detection pattern while changing the primary transfer voltage 10 times, the density detection pattern 61 is configured as a set of patches 61a to 61j as 10 developer transfer images. Further, the density detection pattern 62 is configured as a set of patches 62a to 62j as 10 developer transfer images.

The number of patches of the density detection patterns 61 and 62 is not limited to 10, and may be appropriately decreased or increased according to the number of times the primary transfer voltage is changed. The reason for using the two types of density detection patterns 61 and 62 having different pattern widths will be described later.

Further, since the presence or absence of horizontal streaks is detected for each of the black, yellow, magenta, and cyan colors and the primary transfer voltage value is calculated for each, the patch of the density detection pattern 61 and the patch of the density detection pattern 62 are For each set, black, yellow, magenta, and cyan are used, and the toner image print rate (the area ratio (area ratio) occupied by the toner developed on the intermediate transfer belt 12 within the predetermined area where the patch is formed). This is hereinafter referred to as "Duty", and a solid color image is 100% Duty).

As shown in FIG. 6 (a), the black of the first set is one type of 100% duty of black only, and as shown in FIG. 6 (b), the yellow of the second set is one type of 100% duty of yellow only. As shown in FIG. 6 (c), there are two types of magenta in the third set: a magenta-only duty 100%, and a fourth set yellow duty 100% and magenta duty 100% combined duty 200%, and FIG. As shown in (d), there are two types of cyan in the fifth set: 100% due to cyan only, and 100% due to yellow in the sixth set, 100% due to magenta, and 100% due to cyan. The reason why the Duty is different for each color will be described later.

In this embodiment, 10 patches of density detection patterns 61 and 62 are configured by the patch of 100% duty of black only, and similarly, the patch of 100% duty of yellow only, the patch of 100% duty of magenta only, and the patch of yellow. Density detection pattern 61 with a Duty 200% patch that combines 100% Duty and 100% Magenta Duty, a 100% Cyan Duty patch, and a 300% Duty patch that combines 100% Yellow Duty, 100% Magenta Duty, and 100% Cyan Duty. Each of 62 constitutes 10 patches.

Here, the density sensor 58 uses the density detection pattern 61 of 100% cyan Duty formed on the intermediate transfer belt 12 while changing the primary transfer voltage when the color horizontal streaks are generated / not generated, and the density detection pattern 61. The change in the concentration detected in FIG. 7 will be described with reference to FIG.

7 (a) to 7 (d) are schematic views of the concentration detection pattern 61, and FIG. 7 (e) shows the density detection of 100% of the cyan Duty formed on the intermediate transfer belt 12 while changing the primary transfer voltage. It is a graph which shows the density change of the pattern 61.
The horizontal axis of FIG. 7E represents the primary transfer voltage [V], and the vertical axis represents the concentration (concentration value) detected by the concentration sensor 58.

Looking at the density change of the concentration detection pattern 61 formed on the intermediate transfer belt 12 by increasing the primary transfer voltage from +200 V to + 2000 V in increments of 200 V, the primary transfer voltage is increased in the blurred region due to insufficient transfer voltage. As it goes, the concentration also rises.
When the primary transfer voltage is further increased, as shown in FIG. 7A, fading due to insufficient transfer voltage does not occur, but the transfer efficiency is low as a whole and the density remains low (flat).

After that, when the primary transfer voltage is further increased, the color horizontal streak generation range becomes which the color horizontal streak starts to occur. As the primary transfer voltage is increased, the number of horizontal streaks generated increases as shown in FIG. 7 (b), and the horizontal streaks spread over the entire pattern. The transfer efficiency is high and the density is high in the places where the horizontal streaks are generated. In the color horizontal streak generation range, the density also increases as the primary transfer voltage is increased.

After that, when the primary transfer voltage is further increased, when the color horizontal streaks spread uniformly over the entire surface of the pattern, the transfer efficiency also peaks, the transfer becomes in a good range, and the density remains high (flat).
After that, when the primary transfer voltage is further increased, the transfer voltage becomes excessive and begins to fade, and the density also decreases.

In this way, if horizontal streaks occur, is there a faint transfer (increased density) → low density (flat density) → horizontal streaks (increased density) → good transfer (flat density) → excessive transfer? A two-step increase in concentration such as slippage (decrease in concentration) is detected.

On the other hand, as shown in FIG. 8, when the color horizontal streaks are not generated, the density change as shown in FIG. 7 (e), such as the state where the density is low or the color horizontal streak generation range, is not observed.
Note that FIG. 8 shows a density change (cyan Duty 100%) when no horizontal streaks occur.
Further, the range of color horizontal streaks varies depending on the width of the print pattern.

FIG. 9 shows the density change (cyan) of two types of density detection patterns 61 and 62 having different pattern widths when horizontal streaks occur.

It has been experimentally found that when the width of the density detection pattern is widened, horizontal streaks are likely to occur at a low transfer voltage, and when the width is narrowed, horizontal streaks are likely to occur at a high transfer voltage.
Therefore, in this embodiment, two types of density detection patterns 61 and 62 having different pattern widths are used.

Since the pattern width of the density detection pattern 61 is desired to be as narrow as possible, the diameter of the detection spot SR of the density sensor 58 is set to the same size as shown in FIG.

On the other hand, the pattern width of the density detection pattern 62 is set to the maximum printable width of the printer 1 in order to make the pattern width as wide as possible.

In this way, if the presence or absence of color horizontal streaks in the two types of density detection patterns 61 and 62 having different pattern widths is detected, the color horizontal in various pattern widths printed by the printer 1 when the color horizontal streaks occur. The streak generation range can be estimated.

Further, the range of occurrence of the color horizontal streaks changes depending on the duty of the print pattern.

FIG. 10 shows the density change of the different duty density detection patterns 61 when the color horizontal streaks occur, and FIG. 11 shows the density change of the different duty density detection patterns 62 when the color horizontal streaks occur.
As shown in FIGS. 10 and 11, it is experimentally known that the concentration change shifts to the high voltage side at Duty 300% with respect to Duty 100%.

It is also experimentally known that horizontal streaks are more likely to occur in a solid image (solid image) having a high duty than in a halftone image having a low duty. Therefore, in this embodiment, a plurality of Duties of the density detection patterns 61 and 62 are used for each color.

In this embodiment, the black printing mechanism 2K located at the uppermost stream (first color) in the transport direction of the intermediate transfer belt 12 shown in FIG. 1 has a maximum printable duty of 100%, so it is used as one type of 100% duty. The yellow printing mechanism 2Y located in the second color in the transport direction of the intermediate transfer belt 12 has a maximum printable duty of 100% (usually, the colors yellow, magenta, and cyan are not overlapped on black), so 1 of 100% duty. The magenta printing mechanism 2M located in the third color has a maximum printable duty of 200%, so there are two types, a duty 100% and a duty 200%, and the cyan printing mechanism 2C located in the fourth color can print. Since the maximum Duty is 300%, there are two types, 100% Duty and 300% Duty.

If the presence or absence of color horizontal streaks in the density detection patterns 61 and 62 of 100% of the solid image and the maximum printable duty that makes it easy for such color horizontal streaks to occur is detected, the printer 1 in the case where the color horizontal streaks occur. It is possible to estimate the color horizontal streak generation range in the duty of various patterns printed by.

Next, the primary transfer voltage calculation process performed by the printer 1 shown in FIGS. 1 and 2 is performed in FIG. 1 and FIG. This will be described with reference to 2.

Here, the primary transfer voltage Vtr calculated by the printer 1 by performing the primary transfer voltage calculation process is a primary transfer voltage at which no horizontal streaks occur, and the primary transfer voltage generation unit 54 during the printing operation of the printer 1. This is the primary transfer voltage supplied to the primary transfer rollers 10K, 10Y, 10M, and 10C.

S1: When the printer 1 receives the image data sent from the host computer, the high-voltage control unit 50 of the printer 1 starts calculating the primary transfer voltage Vtr. The calculation of the primary transfer voltage Vtr may be started when the power of the printer 1 is turned on or when the density adjustment process is instructed by the operation panel or the like.

In this embodiment, the primary transfer voltage Vtr is calculated after the charging voltage, the supply voltage, and the developing voltage are supplied to the rollers of the printing mechanisms 2K, 2Y, 2M, and 2C, and before the start of the toner image forming operation. I will do it.

S2: The mechanism control unit 43 changes the primary transfer voltage by the high-voltage control unit 50 and the primary transfer voltage generation unit 54, and displays the concentration detection pattern 61 shown in FIG. 5 stored in the memory 59 on the intermediate transfer belt 12 Print on top.

Six sets of density detection patterns 61 are arranged in the order of black duty 100%, yellow duty 100%, magenta duty 100%, duty 200%, cyan duty 100%, and duty 300% from the downstream side in the transport direction, and the last tenth patch of each set. Prints without intervals from the end to the beginning of the first patch in the next set.

In this embodiment, 10 patches of each set are used, the primary transfer voltage of the first patch is + 200V, the second is + 400V, the third is + 600V, and the primary transfer voltage is increased in increments of + 200V thereafter. The 10th one is set to + 2000V.

S3: The mechanism control unit 43 detects the density of the density detection pattern 61 printed on the intermediate transfer belt 12 with the density sensor 58.

Here, FIG. 13 shows a dimensional drawing of the printer 1.

In FIG. 13, the distances between the contact points of the photosensitive drums 4K, 4Y, 4M, 4C of the printing mechanisms 2K, 2Y, 2M, and 2C and the transfer rollers 10K, 10Y, 10M, and 10C are set to L [mm], respectively, and intermediate transfer is performed. The distance from the contact point between the photosensitive drum 4C of the printing mechanism 2C and the transfer roller 10C, which is the most downstream in the transport direction of the belt 12, to the density sensor 58 is 5 L [mm].

The density detection pattern 61 drives and moves the intermediate transfer belt 12 by 8 L [mm] from the printing start position (contact point between the photosensitive drum 4K and the transfer roller 10K) of the first patch of the black duty 100% pattern, and moves the density sensor 58. Reach the detection position of.

Further, the intermediate transfer belt 12 is driven and moved by Lp / 2 [mm] to align the detection position of the density sensor 58 with the central portion of the first patch.

The mechanism control unit 43 causes the infrared LED 5801 of the density sensor 58 to emit light according to the color of the pattern to be read, and irradiates the density detection pattern 61 with infrared light. The specularly reflected light receiving phototransistor 5802 and the diffusely reflected light receiving phototransistor 5803 are driven by a drive circuit, and a current proportional to the light receiving energy flows. This current is converted into a voltage by the circuit and read by the mechanism control unit 43.

The mechanism control unit 43 reads the output voltage of the diffuse reflected light receiving phototransistor 5803 when the read pattern is yellow, magenta, or cyan, and reads the output voltage of the specular reflected light receiving phototransistor 5802 when the read pattern is black.

Since the density detection pattern 61 of the first set is black, the first patch reads the output voltage of the phototransistor 5802 for receiving specularly reflected light.
Next, the mechanism control unit 43 aligns the detection position of the density sensor 58 with the central portion of the second patch by driving and moving the intermediate transfer belt 12 by Lp [mm], and the phototransistor for receiving specular reflected light. Read the output voltage of 5802.

Further, the mechanism control unit 43 drives and moves the intermediate transfer belt 12 with the density detection pattern length Lp [mm] to align the detection position of the third central portion with the density sensor 58, and the photo for receiving the specular reflected light. Read the output voltage of transistor 5802.

Hereinafter, in the same manner, the mechanism control unit 43 sequentially reads the output voltage for all the patches of the black density detection pattern 61 of the first set.

Next, the mechanism control unit 43 drives and moves the intermediate transfer belt 12 by the density detection pattern length Lp [mm] to move the density detection pattern 61 to the center of the first patch of the first set of yellow density detection patterns 61. The detection position of the sensor 58 is aligned, and the output voltage of the diffuse reflected light receiving phototransistor 5803 is read. Hereinafter, in the same manner, the mechanism control unit 43 sequentially reads the output voltage for all six sets of the concentration detection patterns 61.

S4: The mechanism control unit 43 uses the density value conversion method described below to convert the output voltage of each patch of the read concentration detection pattern 61 based on the sensor detection voltage-concentration value conversion table 60 shown in FIG. Convert to concentration value.

Here, the density value conversion method will be described.

The table values in the sensor detection voltage-concentration value conversion table 60 are values obtained by experimentally obtaining coefficients A and B, which are coefficients of a linear approximation formula showing the relationship between the sensor detection voltage and the concentration value.

Assuming that the detection voltages of black, yellow, magenta, and cyan are KV, YV, MV, and CV, the concentration values KOD, YOD, MOD, and COD can be obtained by the following equations (1) to (4).

KOD = K (A) x KV + K (B) ... Equation (1)
YOD = Y (A) x YV + Y (B) ... Equation (2)
MOD = M (A) x MV + M (B) ... Equation (3)
COD = C (A) x CV + C (B) ... Equation (4)
The above is the concentration value conversion method of this embodiment.

S5: The mechanism control unit 43 determines whether or not a color horizontal streak has occurred. In this embodiment, the amount of change in density of each patch of the read density detection pattern 61 is used to determine the presence or absence of horizontal color streaks.

As an example, a change in the density of the cyan Duty 100% density detection pattern 61 when the color horizontal streaks shown in FIG. 7 (e) are generated will be described. The density value of the first patch is COD1, the density value of the second patch is COD2, ..., The density value of the tenth patch is COD10, and the density values of the first patch and the second patch are The concentration change amount is ΔCOD1, the concentration change amount of the second patch and the third patch is ΔCOD2, ..., The concentration change amount of the ninth patch and the tenth patch is ΔCOD9. Obtained in 5).

ΔCODn = COD (n + 1) -CODn ... Equation (5)
However, n = 1-9.

The amount of change in concentration between each patch is ΔCOD1 = 0.33, ΔCOD2 = −0.01, ΔCOD3 = 0.08, ΔCOD4 = 0.19, ΔCOD5 = 0.02, ΔCOD6 = 0.00, ΔCOD7 = 0. 00, ΔCOD8 = −0.05, ΔCOD9 = −0.05.

In this embodiment, the mechanism control unit 43 determines that there is a concentration change when the amount of concentration change between each patch is 0.05 or more, which is a threshold value.

At this time, when the primary transfer voltage is increased, the density change changes in the order of rising → flat → rising → flat → falling, so that the mechanism control unit 43 states that color horizontal streaks have occurred. to decide.
That is, the mechanism control unit 43 changes the density value of the patch of the concentration detection pattern 61 with the increase of the transfer voltage for each predetermined voltage, and the concentration value does not exceed the threshold value during the plurality of increases of the concentration value exceeding the threshold value. When the change in is detected, it is determined that there is a horizontal streak as an image formation defect.

On the other hand, the amount of change in density between each patch of the density detection pattern 61 of 100% cyan Duty when the horizontal stripes shown in FIG. 8 does not occur is ΔCOD1 = 0.65, ΔCOD2 = 0.10, ΔCOD3 = 0.02. , ΔCOD4 = 0.00, ΔCOD5 = 0.00, ΔCOD6 = 0.00, ΔCOD7 = −0.01, ΔCOD8 = −0.05, ΔCOD9 = −0.05.

At this time, since the density change changes in the order of increase → leveling off → decrease when the primary transfer voltage is increased, the mechanism control unit 43 determines that no color horizontal streaks have occurred.
Since the determination of the presence or absence of color horizontal streaks is performed for each of the six sets of density detection patterns 61, the subsequent processing of S6 and S7 is performed individually for each set.

The mechanism control unit 43 shifts the process to S6 when it determines that the color horizontal streaks have occurred, and shifts the process to S7 when it determines that the color horizontal streaks have not occurred.

In this way, the mechanism control unit 43 detects the occurrence and non-occurrence of color horizontal streaks as image formation defects based on the amount of change in the toner density of the density detection pattern 61 detected by the density sensor 58.

S6: The mechanism control unit 43 determines the primary transfer voltage Vtr1 in which the color horizontal streaks do not occur in the density detection pattern 61 by the primary transfer voltage calculation unit 56, and shifts the process to S8.

In this embodiment, when the color horizontal streaks occur, the primary transfer voltage value is used when the density change shown in FIG. 7 (e) becomes flat for the second time (good transfer). Therefore, the primary transfer voltage Vtr1 of cyan Duty 100% shown in FIG. 10 is 1000 V, and the primary transfer voltage Vtr1 of cyan Duty 300% is 1200 V.

S7: The mechanism control unit 43 determines the primary transfer voltage Vtr1 when the color horizontal streaks do not occur in the density detection pattern 61 by the primary transfer voltage calculation unit 56, and shifts the process to S8.

In this embodiment, when the color horizontal streaks do not occur, the primary transfer voltage value is used when the density change is flat (good transfer). The primary transfer voltage value Vtr1 in this case is, for example, a set value of 800V.

S8: The mechanism control unit 43 changes the primary transfer voltage by the high voltage control unit 50 and the primary transfer voltage generation unit 54, and changes the concentration detection pattern 62 shown in FIG. 5 stored in the memory 59 in the same manner as in S2. Is printed on the intermediate transfer belt 12.

S9: The mechanism control unit 43 detects the density of the density detection pattern 62 printed on the intermediate transfer belt 12 with the density sensor 58 in the same manner as in S3.

S10: The mechanism control unit 43 converts the output voltage of each patch of the read density detection pattern 62 into a density value by the sensor detection voltage-density value conversion table 60 shown in FIG. 4 in the same manner as in S4.

S11: The mechanism control unit 43 determines whether or not a color horizontal streak has occurred, as in S5.

The amount of change in density between each patch of the density detection pattern 62 of 100% cyan Duty when horizontal streaks shown in FIG. 9 is ΔCOD1 = 0.28, ΔCOD2 = 0.03, ΔCOD3 = 0.01, ΔCOD4 = 0.17, ΔCOD5 = 0.12, ΔCOD6 = 0.00, ΔCOD7 = 0.00, ΔCOD8 = -0.04, ΔCOD9 = -0.05, and at this time, the primary transfer voltage was increased. Since the density change sometimes changes in the order of rising → flat → rising → flat → falling, the mechanism control unit 43 determines that a color horizontal streak has occurred.

Since the determination of the presence or absence of color horizontal streaks is performed for each of the six sets of density detection patterns 62 as in the density detection pattern 61, the subsequent S12 and S13 will be individual for each set.

The mechanism control unit 43 shifts the process to S12 when it determines that the color horizontal streaks have occurred, and shifts the process to S13 when it determines that the color horizontal streaks have not occurred.
In this way, the mechanism control unit 43 detects the occurrence and non-occurrence of color horizontal streaks as image formation defects based on the amount of change in the toner density of the density detection pattern 62 detected by the density sensor 58.

That is, the mechanism control unit 43 changes the density value of the patch of the concentration detection pattern 62 with the increase of the transfer voltage for each predetermined voltage, and the concentration value does not exceed the threshold value during the plurality of increases of the concentration value exceeding the threshold value. When the change in is detected, it is determined that there is a horizontal streak as an image formation defect.

S12: The mechanism control unit 43 determines the primary transfer voltage Vtr2 in which the color horizontal streaks do not occur in the density detection pattern 61 by the primary transfer voltage calculation unit 56, and shifts the process to S14.

In this embodiment, when the color horizontal streaks occur, the primary transfer voltage value is used when the density change is leveled off for the second time (good transfer). Therefore, the primary transfer voltage Vtr2 of cyan Duty 100% in the concentration detection pattern 62 shown in FIG. 11 is 1200 V, and the primary transfer voltage Vtr2 of cyan Duty 300% is 1400 V.

S13: The mechanism control unit 43 determines the primary transfer voltage Vtr2 when the color horizontal streaks do not occur in the density detection pattern 61 by the primary transfer voltage calculation unit 56, and shifts the process to S14.

In this embodiment, when the color horizontal streaks do not occur, the primary transfer voltage value is used when the density change is flat (good transfer). The primary transfer voltage value Vtr2 in this case is, for example, a set value of 800V.

S14: The mechanism control unit 43 determines the primary transfer voltage Vtr, and ends this process. The mechanism control unit 43 has the lowest primary transfer voltage Vtr1 and primary transfer voltage Vtr2 that results in good transfer without color lateral streaks in all combinations of the density detection pattern 61 and the density detection pattern 62 for each color. Among them, the highest primary transfer voltage is selected and set in the memory 57 as the primary transfer voltage (primary transfer voltage value) at the time of normal image formation.

In the case of the above example, the mechanism control unit 43 sets the primary transfer voltage Vtr to 1400 V because the primary transfer voltage Vtr2 of the cyan Duty of 300% of the concentration detection pattern 62 is the highest 1400 V.

In this way, the mechanism control unit 43 controls the primary transfer voltage Vtr based on the amount of change in the density value of the patch of the density detection pattern 61 and the density detection pattern 62 detected by the density sensor 58.

In this embodiment, the density sensor 58 is used to detect the presence or absence of color horizontal streaks, and when color horizontal streaks occur, the color horizontal streaks are adjusted to a primary transfer voltage value at which no color horizontal streaks occur. Can be avoided.

In this embodiment, the example in which the density detection pattern 61 and the density detection pattern 62 are formed on the intermediate transfer belt 12 has been described, but the present invention is not limited to this, and as shown in FIG. The density detection pattern 61 and the density detection pattern 62 are formed on the transfer belt 12a that conveys the paper for transferring the toner image used and formed on the photosensitive drums 4K, 4Y, 4M, and 4C of the printing mechanisms 2K, 2Y, 2M, and 2C. It may be formed. In this case, the transfer voltage calculated based on the density detection pattern 61 and the density detection pattern 62 is converted into the transfer voltage when transferring to paper.

As described above, in this embodiment, the effect of suppressing the occurrence of printing defects can be obtained.

In this embodiment, the image forming apparatus has been described as a printer, but the present invention is not limited to this, and may be a copying machine, a facsimile machine, or a multifunction device (MFP) having functions such as printing, copying, and facsimile. good.
Further, in the present embodiment, the image forming apparatus having four image forming portions has been described, but the number is not limited to the number of image forming portions, and for example, an image forming apparatus having only black image forming portions may be used. good.

1 Printer 2K, 2Y, 2M, 2C Printing mechanism 4K, 4Y, 4M, 4C Photosensitive drum 10K, 10Y, 10M, 10C Primary transfer roller 11K, 11Y, 11M, 11C LED head 12 Intermediate transfer belt 23 Secondary transfer roller 43 Mechanism control unit 50 High-voltage control unit 51 Charging voltage generation unit 52 Supply voltage generation unit 53 Development voltage generation unit 54 Primary transfer voltage generation unit 55 Secondary transfer voltage generation unit 56 Primary transfer voltage calculation unit 57, 59 Memory 58 Concentration sensor

Claims (6)

An image carrier on which a developer image is formed and
The belt member to which the developer image is transferred and
A transfer member to which a transfer voltage is applied to transfer the developer image on the image carrier to the belt member, and
A detector that detects the developer concentration of the developer image transferred to the belt member, and
A control unit that controls the transfer voltage and
Have,
The developer image is transferred to the belt member as a plurality of developer transfer images in which the transfer voltage is changed.
The control unit
An image forming apparatus characterized in that the transfer voltage is controlled based on the amount of change in the developer concentration of the developer transfer image detected by the detection unit. In the image forming apparatus according to claim 1,
The detection unit has a first developer pattern image having the plurality of developer transfer images and a second developer having the plurality of developer transfer images, which is different from the first developer pattern image. An image forming apparatus characterized by detecting the amount of change in the developer concentration with respect to a pattern image. In the image forming apparatus according to claim 2,
An image forming apparatus characterized in that the first developer pattern image and the second developer pattern image have different lengths in a direction orthogonal to a transport direction of the belt member. In the image forming apparatus according to claim 2 or 3.
The first developer pattern image and the second developer pattern image are
An image forming apparatus comprising the plurality of developer transfer images in which the area ratio of the developer in a predetermined area is different. In the image forming apparatus according to any one of claims 2 to 4.
The control unit
The occurrence of image formation defects is detected based on the amount of change in the developer concentration of the first developer pattern image and the second developer pattern image detected by the detection unit.
Of the first transfer voltage at which no image formation failure occurs in the first developer pattern image and the second transfer voltage at which no image formation failure occurs in the second developer pattern image, a higher transfer voltage is usually used. An image forming apparatus characterized in that the transfer voltage at the time of image forming is used. In the image forming apparatus according to claim 5,
The control unit
In the change of the developer concentration of the first developer pattern image and the second developer pattern image with the increase of the transfer voltage for each predetermined voltage, during the plurality of increases of the developer concentration value exceeding the threshold value, An image forming apparatus characterized in that when a change in a developer concentration value that does not exceed a threshold value is detected, it is determined that an image forming defect has occurred.

Images