JP2021002006A - Image forming apparatus - Google Patents

Abstract

To provide an image forming apparatus that can accurately estimate the amount of carrier development and determine an image forming condition based on a result of the estimation to prevent carrier development.SOLUTION: An image forming apparatus comprises: an image forming unit; a high voltage generation circuit; a density detection device; a current detection unit; and a control unit. The image forming unit includes image carriers, charging devices, an exposure device, and developing devices that have developer carriers carrying a two-component developer containing a magnetic carrier and toner. The high voltage generation circuit applies, to the developer carriers, a developing voltage in which an AC voltage is superimposed on a DC voltage. The control unit estimates the amount of carrier development based on a carrier current that is a DC component of a developing current when the printing rate is 0% and the amount of charge of toner in the developing devices calculated based on the density of toner images detected by the density detection device, and changes an image forming condition based on the estimated amount of carrier development.SELECTED DRAWING: Figure 4

Description

The present invention relates to an image forming apparatus such as a copier, a printer, a facsimile, and a multifunction device thereof provided with an image carrier, and particularly to an image carrier in a developing method using a two-component developer containing toner and a carrier. It relates to a method of suppressing carrier movement.

In a developing method using a two-component developer containing a magnetic carrier and toner, the carriers are triboelectrically charged, and the charged carriers move to the surface of the photoconductor drum by a reverse electric field formed in a non-image area on the photoconductor drum. So-called carrier development becomes a problem. Since the carrier has a larger particle size than the toner and has a different charge polarity, when the carrier moves onto the photoconductor drum, the toner around the carrier is not transferred from the drum and becomes a white spot. In particular, in a half image in which dots are repeated, the color portion and the white background portion are repeated, so the influence is remarkable.

Further, when a large amount of carrier development occurs, the carriers in the developing apparatus decrease, the toner cannot be sufficiently charged, and problems such as image fog and toner scattering occur. Further, there is a problem that the carrier reaches the cleaning device and is embedded in the surface of the photoconductor drum or bites into the cleaning blade.

It was found that carrier development depends on the toner charge (or carrier charge) and carrier resistance, and that the carrier development increases as the toner charge (or carrier charge) increases or the carrier resistance decreases. doing. Therefore, usually, image formation conditions in which carrier development does not occur are set in advance to prevent the occurrence of these defects.

As a method for measuring the amount of toner charge, for example, Patent Documents 1 and 2 describe a first mode for forming a toner image based on image data for printing, a patch image for forming a patch image based on patch image data, and a density sensor and development. It is possible to execute the second mode of measuring the charge amount of the toner contained in the developing means based on the output of the current detecting means, and the transfer condition of the primary transfer means or the development condition of the developing means is referred to as the second mode. An image forming apparatus that is controlled so as to be different from that of the first mode is disclosed.

JP-A-2009-294504 JP-A-2009-294505

However, the toner (carrier) charge amount changes depending on the usage environment and printing rate of the image forming apparatus, and the carrier resistance also changes depending on the usage conditions such as scraping of the coat layer on the carrier surface and adhesion of the toner component to the coat layer. To do. Therefore, even if the image forming conditions for preventing carrier development are set at the initial stage of use of the image forming apparatus, the carrier state may change due to durable printing, and carrier development may occur.

In view of the above problems, an object of the present invention is to provide an image forming apparatus capable of suppressing carrier development by accurately estimating the amount of carrier development and determining image forming conditions based on the estimation result.

In order to achieve the above object, the first configuration of the present invention is an image forming apparatus including an image forming unit, a high voltage generating circuit, a concentration detecting device, a current detecting unit, and a control unit. The image forming unit is an exposure that forms an electrostatic latent image by exposing an image carrier having a photosensitive layer formed on its surface, a charging device for charging the image carrier, and an image carrier charged by the charging device. It has an apparatus and a developer carrier that is arranged opposite to the image carrier and carries a two-component developer containing a magnetic carrier and toner, and the toner is attached to an electrostatic latent image formed on the image carrier. Includes a developing device that forms a toner image. The high-voltage generation circuit applies a developing voltage obtained by superimposing an AC voltage on a DC voltage to the developer carrier. The density detection device detects the density of the toner image formed by the developing device. The current detection unit detects the DC component of the developing current that flows when the developing voltage is applied to the developer carrier. The control unit controls the image forming unit and the high voltage generation circuit. The control unit determines the carrier current, which is a DC component of the developing current when the printing rate is 0%, and the amount of toner charged in the developing device, which is calculated based on the density of the toner image detected by the density detection device. The carrier development amount is estimated based on this, and the image formation conditions are changed based on the estimated carrier development amount.

According to the first configuration of the present invention, the carrier development amount is estimated accurately by estimating the carrier development amount using the DC component of the development current and the toner charge amount when the printing rate is 0%. Appropriate image formation conditions that do not cause carrier development can be set. Therefore, it is possible to effectively suppress image defects due to carrier development and image fog and toner scattering due to a decrease in carriers in the developing apparatus.

Side sectional view showing an internal structure of an image forming apparatus 100 according to an embodiment of the present invention. Side sectional view of the developing apparatus 3a mounted on the image forming apparatus 100 Partial enlarged view around the image forming unit Pa including the control path of the developing device 3a A flowchart showing a control example of the carrier development amount estimation mode in the image forming apparatus 100 of the present embodiment. A graph showing the relationship between the development amount and the development current when reference images with different print rates are formed. Graph showing the relationship between the amount of carrier current and the amount of toner charge and the amount of carrier development A flowchart showing an example of controlling the estimation of the carrier development amount in the normal printing mode in the image forming apparatus 100 of the present embodiment.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view showing an internal structure of an image forming apparatus 100 according to an embodiment of the present invention. In the main body of the image forming apparatus 100 (here, a color printer), four image forming portions Pa, Pb, Pc and Pd are arranged in order from the upstream side in the transport direction (right side in FIG. 1). These image forming units Pa to Pd are provided corresponding to images of four different colors (cyan, magenta, yellow, and black), and are cyan, magenta, and yellow, respectively, depending on each step of charging, exposure, development, and transfer. And black images are formed sequentially.

Photoreceptor drums (image carriers) 1a, 1b, 1c and 1d that support visible images (toner images) of each color are arranged on these image forming portions Pa to Pd, and further, driving means (FIG. FIG. An intermediate transfer belt (intermediate transfer body) 8 rotating in the clockwise direction in FIG. 1 is provided adjacent to each of the image forming portions Pa to Pd. The toner images formed on the photoconductor drums 1a to 1d are sequentially first-transferred and superimposed on the intermediate transfer belt 8 that moves while abutting on the photoconductor drums 1a to 1d. After that, the toner image primaryly transferred onto the intermediate transfer belt 8 is secondarily transferred by the secondary transfer roller 9 onto the transfer paper P as an example of the recording medium. Further, the transfer paper P on which the toner image is secondarily transferred is discharged from the image forming apparatus 100 main body after the toner image is fixed in the fixing portion 13. The image forming process for each of the photoconductor drums 1a to 1d is executed while rotating the photoconductor drums 1a to 1d in the counterclockwise direction in FIG.

The transfer paper P on which the toner image is secondarily transferred is housed in a paper cassette 16 arranged in the lower part of the main body of the image forming apparatus 100, and is housed in a paper cassette 16 and is interposed via a paper feed roller 12a and a resist roller pair 12b. It is conveyed to the nip portion between 9 and the drive roller 11 of the intermediate transfer belt 8. A sheet made of a dielectric resin is used for the intermediate transfer belt 8, and a seamless (seamless) belt is mainly used. Further, a blade-shaped belt cleaner 19 for removing toner and the like remaining on the surface of the intermediate transfer belt 8 is arranged on the downstream side of the secondary transfer roller 9.

Next, the image forming units Pa to Pd will be described. In the periphery and below the rotatably arranged photoconductor drums 1a to 1d, charging devices 2a, 2b, 2c and 2d for charging the photoconductor drums 1a to 1d, and image information on the photoconductor drums 1a to 1d. The exposure apparatus 5 for exposing the above, the developing apparatus 3a, 3b, 3c and 3d for forming a toner image on the photoconductor drums 1a to 1d, and the developing agent (toner) remaining on the photoconductor drums 1a to 1d are removed. Cleaning devices 7a, 7b, 7c and 7d are provided.

When image data is input from a higher-level device such as a personal computer, first, the surfaces of the photoconductor drums 1a to 1d are uniformly charged by the charging devices 2a to 2d. Next, the exposure apparatus 5 irradiates light according to the image data to form an electrostatic latent image according to the image data on each of the photoconductor drums 1a to 1d. The developing devices 3a to 3d are filled with a predetermined amount of a two-component developer containing toners of cyan, magenta, yellow, and black, respectively. When the ratio of toner in the two-component developer filled in the developing devices 3a to 3d falls below the specified value due to the formation of the toner image described later, the toner containers 4a to 4d to the developing devices 3a to 3d are used. Toner is replenished. The toner in this developer is supplied onto the photoconductor drums 1a to 1d by the developing devices 3a to 3d, and is electrostatically adhered to the toners according to the electrostatic latent image formed by the exposure from the exposure device 5. A toner image is formed.

Then, an electric field is applied between the primary transfer rollers 6a to 6d and the photoconductor drums 1a to 1d at a predetermined transfer voltage by the primary transfer rollers 6a to 6d, and cyan, magenta, yellow and cyanide, magenta, yellow and cyanide, magenta, yellow and The black toner image is primarily transferred onto the intermediate transfer belt 8. These four-color images are formed with a predetermined positional relationship predetermined for forming a predetermined full-color image. After that, in preparation for the subsequent formation of a new electrostatic latent image, the toner and the like remaining on the surfaces of the photoconductor drums 1a to 1d after the primary transfer are removed by the cleaning devices 7a to 7d.

The intermediate transfer belt 8 is hung between the driven roller 10 on the upstream side and the drive roller 11 on the downstream side, and the intermediate transfer belt 8 rotates clockwise as the drive roller 11 is rotated by the drive motor (not shown). When the rotation is started in the direction, the transfer paper P is transferred from the resist roller pair 12b to the nip portion (secondary transfer nip portion) between the drive roller 11 and the secondary transfer roller 9 provided adjacent thereto at a predetermined timing. Then, the full-color image on the intermediate transfer belt 8 is secondarily transferred onto the transfer paper P. The transfer paper P on which the toner image is secondarily transferred is conveyed to the fixing portion 13.

The transfer paper P conveyed to the fixing portion 13 is heated and pressurized by the fixing roller pair 13a to fix the toner image on the surface of the transfer paper P, and a predetermined full-color image is formed. The transfer paper P on which the full-color image is formed is distributed in the transport direction by the branching portions 14 branched in a plurality of directions, and is sent to the double-sided transport path 18 as it is (or after being sent to the double-sided transport path 18 to form an image on both sides), as it is It is discharged to the discharge tray 17 by pair 15.

Further, the image density sensor 40 is arranged at a position facing the drive roller 11 with the intermediate transfer belt 8 interposed therebetween. As the image density sensor 40, an optical sensor including a light emitting element made of an LED or the like and a light receiving element made of a photodiode or the like is generally used. When measuring the amount of toner adhering to the intermediate transfer belt 8, when the measurement light is irradiated from the light emitting element to each reference image formed on the intermediate transfer belt 8, the measurement light is reflected by the toner and the belt surface. It is incident on the light receiving element as light reflected by.

The reflected light from the toner and the belt surface includes specularly reflected light and diffusely reflected light. The specularly reflected light and the diffusely reflected light are separated by a polarization separation prism and then incident on separate light receiving elements. Each light receiving element photoelectrically converts the specularly reflected light and the diffusely reflected light received and outputs an output signal to the main control unit 80 (see FIG. 3). Then, the toner amount is detected from the characteristic change of the output signals of the specularly reflected light and the diffusely reflected light, and the density correction (calibration) is performed for each color by adjusting the characteristic value of the developing voltage in comparison with a predetermined reference density. ) Is performed.

FIG. 2 is a side sectional view of the developing device 3a mounted on the image forming device 100. Note that FIG. 2 shows a state seen from the back side of the paper surface of FIG. 1, and the arrangement of each member in the developing apparatus 3a is reversed from that of FIG. Further, in the following description, the developing device 3a arranged in the image forming unit Pa of FIG. 1 is illustrated, but the configuration of the developing devices 3b to 3d arranged in the image forming units Pb to Pd is basically the same. Therefore, the description is omitted.

As shown in FIG. 2, the developing apparatus 3a includes a developing container 20 in which a two-component developer containing a magnetic carrier and toner (hereinafter, simply referred to as a developer) is stored, and the developing container 20 includes a partition wall 20a. It is divided into a stirring transport chamber 21 and a supply transport chamber 22. In the stirring transfer chamber 21 and the supply transport chamber 22, a stirring transfer screw 25a and a supply transfer screw 25b for mixing the toner supplied from the toner container 4a (see FIG. 1) with a magnetic carrier to stir and charge the toner, respectively. It is rotatably arranged.

Then, the developer is conveyed in the axial direction (direction perpendicular to the paper surface of FIG. 2) while being agitated by the stirring transfer screw 25a and the supply transfer screw 25b, and passes through the developer (not shown) formed at both ends of the partition wall 20a. It circulates between the stirring transport chamber 21 and the supply transport chamber 22 via the path. That is, a circulation path for the developer is formed in the developing container 20 by the stirring transfer chamber 21, the supply transfer chamber 22, and the developer passage path.

The developing container 20 extends diagonally upward to the right in FIG. 2, and a developing roller 31 is arranged diagonally upward to the right of the supply transport screw 25b in the developing container 20. Then, a part of the outer peripheral surface of the developing roller 31 is exposed from the opening 20b of the developing container 20 and faces the photoconductor drum 1a. The developing roller 31 rotates counterclockwise in FIG.

The developing roller 31 is composed of a cylindrical developing sleeve that rotates counterclockwise in FIG. 2 and a magnet (not shown) having a plurality of magnetic poles fixed in the developing sleeve. Although a developing sleeve having a knurled surface is used here, a developing sleeve having a large number of concave shapes (dimples) formed on the surface or a developing sleeve having a blasted surface can also be used.

Further, a regulation blade 35 is attached to the developing container 20 along the longitudinal direction of the developing roller 31 (perpendicular to the paper surface of FIG. 2). A slight gap is formed between the tip of the regulation blade 35 and the surface of the developing roller 31.

A developing voltage composed of a DC voltage Vslv (DC) (hereinafter, also referred to as Vdc) and an AC voltage Vslv (AC) is applied to the developing roller 31 by a high voltage generating circuit 43 (see FIG. 3).

FIG. 3 is a partially enlarged view of the periphery of the image forming unit Pa including the control path of the developing device 3a. In the following description, the configuration of the image forming unit Pa and the control path of the developing device 3a will be described, but the description will be omitted because the same applies to the configuration of the image forming units Pb to Pd and the control path of the developing devices 3b to 3d.

The developing roller 31 is connected to a high voltage generating circuit 43 that generates a vibration voltage in which a DC voltage and an AC voltage are superimposed. The high voltage generation circuit 43 includes an AC constant voltage power supply 43a and a DC constant voltage power supply 43b. The AC constant voltage power supply 43a outputs a sinusoidal AC voltage generated from a low-voltage DC voltage pulse-modulated using a step-up transformer (not shown). The DC constant voltage power supply 43b outputs a DC voltage obtained by rectifying a sinusoidal AC voltage generated from a low-voltage DC voltage modulated in a pulse shape using a step-up transformer.

The high-voltage generation circuit 43 outputs a development voltage obtained by superimposing an AC voltage on a DC voltage from the AC constant voltage power supply 43a and the DC constant voltage power supply 43b at the time of image formation. The current detection unit 44 detects the DC current value flowing between the developing roller 31 and the photoconductor drum 1a.

The cleaning device 7a includes a cleaning blade 32 for removing residual toner on the surface of the photoconductor drum 1a, and a rubbing roller 33 for removing residual toner on the surface of the photoconductor drum 1a and rubbing and polishing the surface of the photoconductor drum 1a. , A transport spiral 37 that discharges residual toner removed from the photoconductor drum 1a by the cleaning blade 32 and the rubbing roller 33 to the outside of the cleaning device 7a.

Next, the control system of the image forming apparatus 100 will be described with reference to FIG. The image forming apparatus 100 is provided with a main control unit 80 composed of a CPU or the like. The main control unit 80 is connected to a storage unit 70 including a ROM, a RAM, or the like. The main control unit 80 is based on the control program and control data stored in the storage unit 70, and each part of the image forming apparatus 100 (charging apparatus 2a to 2d, developing apparatus 3a to 3d, exposure apparatus 5, primary transfer roller 6a to 6d, cleaning devices 7a to 7d, fixing unit 13, high voltage generation circuit 43, current detection unit 44, voltage control unit 45, etc.) are controlled.

The voltage control unit 45 controls a high-voltage generation circuit 43 that applies a developing voltage to the developing roller 31. The voltage control unit 45 may be composed of a control program stored in the storage unit 70. The in-flight temperature / humidity sensor 50 constantly detects the temperature and humidity inside the image forming apparatus 100, specifically, in the vicinity of the photoconductor drum 1a, and the detected temperature / humidity is transmitted to the main control unit 80.

A liquid crystal display unit 90 and a transmission / reception unit 91 are connected to the main control unit 80. The liquid crystal display unit 90 functions as a touch panel for the user to make various settings of the image forming apparatus 100, and displays the state of the image forming apparatus 100, the image forming status, the number of prints, and the like. The transmission / reception unit 91 communicates with the outside using a telephone line or an Internet line.

The image forming apparatus 100 of the present invention forms a reference image by changing the printing rate to a plurality of stages (for example, 40%, 30%, 20%, 10%) under normal image forming conditions, and at the time of forming the reference image. By measuring the flowing development current, the correlation between the development current and the print rate is acquired to measure the toner charge amount, and the development current value when the print rate is 0% is predicted as the carrier current, and the toner charge amount is predicted. It is possible to execute a carrier development amount estimation mode in which the carrier development amount is estimated based on the carrier current.

Further, a voltage in the direction of attracting toner from the photoconductor drums 1a to 1d to the developing roller 31 side between the photoconductor drums 1a to 1d and the developing roller 31 (development reverse voltage, for example, a positively charged toner, the photoconductor drum 1a). When the surface potential V0 = 280V of ~ 1d, the carrier current can be obtained from the developing current when Vdc = 200V) is applied. Therefore, in the present invention, attention is paid to the developing current of the non-image area as a method of estimating the carrier developing amount. The development current of the non-image portion in the present specification refers to the current flowing through the developing roller 31 when the non-image portion (margin portion) of the photoconductor drums 1a to 1d faces the developing roller 31 at the time of image formation. Say. Using the development current of the non-image area, the carrier development amount can be estimated even during normal image formation (normal printing mode).

Further, the estimation of the carrier development amount in the normal print mode is affected by the usage environment and durability of the image forming apparatus 100, but the carrier development amount estimated in the carrier development amount estimation mode and the carrier estimated in the normal print mode. By taking the correlation with the developed amount, it is possible to estimate with the same accuracy regardless of which mode the carrier developed amount is estimated. Hereinafter, a method for estimating the carrier development amount in the carrier development amount estimation mode and the normal printing mode will be described.

(Carrier development amount estimation mode)
FIG. 4 is a flowchart showing a control example of the carrier development amount estimation mode in the image forming apparatus 100 of the present embodiment. The procedure for executing the carrier development amount estimation mode will be described in detail along the steps of FIG. 4 with reference to FIGS. 1 to 3 and FIG. 5 described later, if necessary.

In the control of FIG. 4, first, the main control unit 80 determines whether or not a print command has been received (step S1). When a print command is received (Yes in step S1), printing is executed by a normal image forming operation (step S2). If the print command is not transmitted (No in step S1), it is determined whether or not it is the execution timing of the carrier development amount estimation mode (step S3).

The carrier development amount estimation mode is highly accurate because it estimates the carrier development amount based on the measured values of the toner charge amount and the carrier current, but if it is executed frequently, the image formation efficiency of the image forming apparatus 100 is lowered. On the other hand, if the execution interval is too wide, the toner charge amount and the carrier resistance may change during that period, which may impair the image quality. Therefore, it is necessary to execute the carrier development amount estimation mode at appropriate intervals. Examples of the execution timing of the carrier development amount estimation mode include a case where the cumulative number of prints from the previous carrier development amount estimation mode is equal to or more than a predetermined number at the end of the printing operation.

If it is not the execution timing of the carrier development amount estimation mode (No in step S3), the process returns to step S1 and shifts to the standby state of the print command. When it is the execution timing of the carrier development amount estimation mode (Yes in step S3), the carrier development amount estimation mode is started (step S4).

Specifically, after the surfaces of the photoconductor drums 1a to 1d are charged by the charging devices 2a to 2d, an electrostatic latent image of the reference image is formed on the photoconductor drums 1a to 1d by the exposure device 5. Then, a developing voltage is applied to the developing roller 31 by the high-voltage generating circuit 43 to develop the electrostatic latent image into a toner image, thereby forming a plurality of reference images having different printing rates on the photoconductor drums 1a to 1d (). Step S5). At the same time, the DC component of the developing current flowing through the developing roller 31 when the reference image is formed is detected by the current detecting unit 44 (step S6).

FIG. 5 is a graph showing the relationship between the printing rate and the developing current when reference images having different printing rates are formed. The value of the y-intercept of the approximate straight line (y = 0.0997x-0.2087) shown by the dotted line in FIG. 5 is −0.21 [μA]. This is the calculated carrier current when the printing rate is 0%. The main control unit 80 acquires the developing current when the printing rate is 0% as the calculated carrier current (step S7). In the actual calculation, it is necessary to calculate the amount of current [μA / cm ² ] per unit area by dividing the developing current by the measured area. Further, if the developing current is measured a plurality of times and the average value of each measured value is used, the error becomes small.

Next, a predetermined primary transfer voltage is applied to the primary transfer rollers 6a to 6d to transfer the reference image onto the intermediate transfer belt 8. Then, the density of each reference image is detected by the image density sensor 40 (step S8). By replacing the horizontal axis of the graph shown in FIG. 5 with the toner development amount from the print rate based on the detected density of the reference image, an approximate straight line showing the relationship between the toner development amount and the development current can be obtained. The toner charge amount is calculated from the slope of this approximate curve (step S9).
).

Next, the main control unit 80 predicts the carrier development amount based on the toner charge amount and the calculated carrier current (step S10). FIG. 6 is a graph showing the relationship between the carrier current amount and the toner charge amount and the carrier development amount. The carrier development generation curve (indicated by a broken line or a dotted line) shown in FIG. 6 indicates a line in which a predetermined amount of carriers are developed with a predetermined number of prints (here, a line in which the carrier development amount is 10 g when 100 k sheets are printed). ing. Carrier development occurs in a region where the carrier current amount and the toner charge amount are higher than the carrier development generation curve (upper right in FIG. 6). Further, the amount of carrier development increases as the distance from the carrier development generation curve increases in the upper right direction of FIG.

The main control unit 80 predicts the carrier development amount based on the relationship between the measured carrier current amount and the toner charge amount, the carrier current amount and the toner charge amount shown in FIG. 6, and the carrier development amount, and the carrier development amount. The image formation condition is changed based on the prediction result of (step S11), and the carrier development amount estimation mode is terminated. Examples of the image forming condition to be changed include a peak-to-peak value (Vpp) of the AC component of the developing voltage, a potential difference V0-Vdc of the surface potential V0 of the photoconductor drums 1a to 1d and the DC component Vdc of the developing voltage. Specifically, as the carrier development amount increases, the Vpp of the AC component of the development voltage is reduced, and V0-Vdc is reduced.

For example, when V0-Vdc = 100V before the change, by changing to V0-Vdc = 70V, the carrier development generation curve (indicated by the broken line) when V0-Vdc = 100V shown in FIG. 6 is V0. Move to the carrier development generation curve (indicated by the dotted line) when −Vdc = 70V. As a result, the image formation conditions are changed in a direction in which carrier development is unlikely to occur, so that the occurrence of carrier development can be suppressed.

As described above, by executing the carrier development amount estimation mode in which the carrier development amount is predicted using the measured value of the toner charge amount and the calculated carrier current, the carrier development amount is accurately estimated and carrier development does not occur. Appropriate image formation conditions can be set. Therefore, it is possible to effectively suppress image defects due to carrier development and image fog and toner scattering due to carrier reduction in the developing devices 3a to 3d.

However, as described above, if the carrier development amount estimation mode is frequently executed, the image formation efficiency of the image forming apparatus 100 is lowered. Therefore, in the image forming apparatus 100 of the present embodiment, the developing current of the non-image portion (between papers) in the normal printing mode is acquired as the carrier current, and the carrier developing amount is estimated from the carrier current.

(Normal print mode)
FIG. 7 is a flowchart showing an example of estimation control of the carrier development amount in the normal printing mode in the image forming apparatus 100 of the present embodiment. The procedure for estimating the carrier development amount in the normal printing mode will be described in detail along the steps of FIG. 7 with reference to FIGS. 1 to 3 and 5 as necessary.

In the normal print mode, the toner charge amount cannot be measured directly. Therefore, as the toner charge amount, a predicted value with reference to the time-dependent change of the toner charge amount up to that point is used. Specifically, the change in the toner charge amount from the toner charge amount calculated in the carrier development amount estimation mode shown in FIG. 4 and the execution time of the carrier development amount estimation mode (elapsed time from the start of using the toner) is changed. An approximate expression to be estimated is created (step S1). Next, the toner charge amount is estimated using the approximate expression created in step S1 and the elapsed time from the start of use of the toner to the present (step S2).

On the other hand, the development current of the non-image portion (between papers) during printing is detected by the current detection unit 44 and acquired as the non-image portion carrier current (step S3). In the non-image portion during printing, a voltage (development reverse voltage) Vdc in the direction of attracting toner (V0> Vdc) from the photoconductor drums 1a to 1d to the developing roller 31 side is applied to the developing roller 31. This voltage is for suppressing the adhesion of toner to the non-exposed portion (white background portion) of the photoconductor drums 1a to 1d, and the toner does not actively move from the photoconductor drums 1a to 1d to the developing roller 31. .. Therefore, the current that flows due to the movement of the toner is small, and most of the flowing current becomes the carrier current.

The main control unit 80 predicts the carrier development amount from the toner charge amount estimated in step S2 and the non-image part carrier current acquired in step S3 (step S4). The carrier development amount is predicted based on the relationship shown in FIG. 6 in the same manner as in the carrier development amount estimation mode.

The main control unit 80 changes the image formation conditions based on the prediction result of the carrier development amount (step S5), and ends the estimation of the carrier development amount in the normal print mode. Examples of the image forming condition to be changed include a peak-to-peak value (Vpp) of the AC component of the developing voltage, a potential difference V0-Vdc of the surface potential V0 of the photoconductor drums 1a to 1d and the DC component Vdc of the developing voltage. Specifically, as the carrier development amount increases, the Vpp of the AC component of the development voltage is reduced, and V0-Vdc is reduced.

In the estimation of the carrier development amount in the normal printing mode, since the predicted value from the change with time is used as the toner charge amount, the estimation accuracy is lower than that in the carrier development amount estimation mode. Further, when the toner charge amount becomes very low in a high temperature and high humidity environment, the toner easily moves from the photoconductor drums 1a to 1d to the developing roller 31, and the measurement error of the non-image portion carrier current becomes large. That is, the non-image carrier current acquired in the normal print mode and the carrier current acquired in the carrier development amount estimation mode are both measured in an approximate state, but in the measurement in the normal print mode, the toner is transferred to the developing roller. An error will occur by the amount of movement.

Therefore, the non-image area carrier current is also measured when the carrier development amount estimation mode is executed, and the non-image area carrier current is converted into the calculated carrier current when the printing rate is 0% in the carrier development amount estimation mode. Is memorized and the conversion formula is acquired. Then, when estimating the carrier development amount in the normal print mode, the non-image portion carrier current is converted into the calculated carrier current, and the carrier resistance is calculated from the converted value.

By taking the correlation between the calculated carrier current and the non-image carrier current in this way, the same estimation accuracy can be obtained regardless of whether the carrier development amount is estimated in the carrier development amount estimation mode or the normal print mode. Is possible. Therefore, it is possible to set the optimum image formation conditions in which carrier development does not occur without frequently executing the carrier development amount estimation mode.

It is also possible to set the interval of the carrier development amount estimation mode using the non-image portion carrier current detected in the normal print mode. For example, if the carrier development amount estimation mode is started when the carrier current of the non-image area measured in the normal print mode changes by a predetermined value or more, the carrier development amount is predicted to change at the timing when the carrier development amount is predicted to change. Estimate mode can be performed.

Alternatively, by using the above-mentioned approximation formula of the toner charge amount, it is possible to predict the change of the toner charge amount with time to some extent. Therefore, if it is set in advance how much the toner charge amount changes to execute the carrier development amount estimation mode, the carrier development amount estimation mode can be executed at an appropriate timing. Furthermore, since it is known that the toner charge amount changes suddenly when the print pattern or environmental conditions change suddenly, the start condition of the carrier development amount estimation mode under such special conditions is set. You may leave it.

Others The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention. For example, in the above embodiment, a plurality of measurement patterns having different image densities (printing rates) are formed, and based on the relationship between the difference in the amount of development (difference in density) of each measurement pattern and the difference in the developing current flowing when the measurement patterns are formed. The toner charge amount was measured, but the method for measuring the toner charge amount is not limited to the above-mentioned method. For example, an electrostatic latent image having the same measurement pattern is developed into a toner image by switching the frequency of the AC component of the developing voltage. A method of forming different types of measurement patterns and measuring the toner charge amount based on the relationship between the difference in the developing current that flows when each measurement pattern is formed and the difference in the amount of development (density difference) of the measurement pattern, or the difference between the frequency and the amount of development. A method of measuring the toner charge amount based on the relationship with (concentration difference) can also be used.

Further, in the above embodiment, the image forming apparatus 100 has been described by taking a color printer as shown in FIG. 1 as an example, but the present invention is not limited to the color printer, and other monochrome and color copiers, digital multifunction devices, facsimiles and the like. It may be an image forming apparatus. Hereinafter, the effects of the present invention will be described in more detail with reference to Examples.

A verification test was conducted on the relationship between the carrier current measured in the carrier development amount estimation mode and the normal printing mode. As the conditions of the testing machine, in the image forming apparatus 100 as shown in FIG. 1, the photoconductor drums 1a to 1d having an amorphous silicon (a-Si) photosensitive layer are used, the non-exposed part potential V0 = 270V, and the exposed part. The potential VL = 20V. The drum wire speed (process speed) was set to 55 sheets / min.

The developing devices 3a to 3d used a developing roller 31 having a diameter of 20 mm in which 80 rows of recesses were formed in the circumferential direction by knurling, and a magnetic blade made of stainless steel (SUS430) was used as the regulating blade 35. The amount of developer conveyed by the developing roller 31 was set to 250 g / m ² . The peripheral speed ratio between the developing roller 31 and the photoconductor drums 1a to 1d was set to 1.8 (trail rotation at the opposite position), and the distance between the developing roller 31 and the photoconductor drums 1a to 1d was set to 0.30 mm. A voltage obtained by superimposing a DC voltage Vslv (DC) of 170 V as a development voltage and a rectangular wave AC voltage having a frequency of 4.2 kHz and a duty = 50% was applied to the developing roller 31.

Further, a two-component developer composed of a positively charged toner having an average particle diameter of 6.8 μm and a ferrite / resin coat carrier having an average particle diameter of 35 μm was used, and the toner concentration was set to 8%.

As a test method, the carrier development amount estimation mode is executed, the toner charge amount is calculated based on the densities of a plurality of reference images having different print rates, and the development current when the print rate is 0% is acquired as the calculated carrier current. did. Further, in the normal printing mode, the development current of the non-image portion (between papers) was detected by the current detection unit 44 and acquired as the carrier current of the non-image portion. Table 1 shows the calculated carrier current and the non-image area carrier current together with the toner charge amount.

As is clear from Table 1, the calculated carrier current acquired in the carrier development amount estimation mode was 0.21 μA for both the toner charge amount of 32 μC / g and 18 μC / g. On the other hand, the non-image portion carrier current acquired in the normal printing mode was 0.21 μA when the toner charge amount was 32 μC / g and 0.18 μA when the toner charge amount was 18 μC / g.

The reason for this is that in the normal printing mode, when the toner charge amount becomes low, the toner moves from the photoconductor drums 1a to 1d side to the developing roller 31 side, and the moved toner becomes a resistance layer, which makes it difficult for the developing current to flow. is there. However, since the carrier resistance has not changed, there is no difference in the calculated carrier current even if the toner charge amount changes in the carrier development amount estimation mode. Therefore, by acquiring an equation for converting the non-image portion carrier current into the calculated carrier current in the carrier development amount estimation mode, the carrier development amount can be estimated accurately even in the normal print mode.

The present invention can be used in an image forming apparatus using a two-component developer containing a toner and a carrier. By utilizing the present invention, it is possible to provide an image forming apparatus capable of suppressing carrier development by accurately estimating the amount of carrier development and determining image forming conditions based on the estimation result.

1a-1d Photoreceptor drum (image carrier)
2a to 2d charging device 3a to 3d developing device 5 exposure device 31 developing roller (developer carrier)
33 Rubbing roller 40 Image density sensor (density detection device)
43 High-voltage generation circuit 43a AC constant voltage power supply 43b DC constant voltage power supply 44 Current detection unit 45 Voltage control unit 50 In-flight temperature / humidity sensor 70 Storage unit 80 Main control unit (control unit)
100 image forming device

Claims (8)

An image carrier having a photosensitive layer formed on its surface,
A charging device for charging the image carrier and
An exposure device that forms an electrostatic latent image by exposing the image carrier charged by the charging device,
It has a developer carrier that is arranged facing the image carrier and supports a two-component developer containing a magnetic carrier and toner, and the toner is attached to the electrostatic latent image formed on the image carrier. And a developing device that forms a toner image
Image forming part including
A high-voltage generating circuit that applies a developing voltage obtained by superimposing an AC voltage on a DC voltage on the developer carrier.
A density detection device that detects the density of the toner image formed by the developing device, and
A current detector that detects the DC component of the developing current that flows when the developing voltage is applied to the developer carrier, and
The image forming unit, the control unit that controls the high voltage generation circuit, and
In an image forming apparatus equipped with
The control unit is a toner in the developing device calculated based on a carrier current which is a DC component of the developing current when the printing rate is 0% and the density of the toner image detected by the density detecting device. An image forming apparatus characterized in that a carrier development amount is estimated based on a charge amount and an image formation condition is changed based on the estimated carrier development amount. The control unit
At the time of non-image formation, the developing apparatus forms a plurality of reference images having different printing rates on the image carrier, and the printing rate is based on the direct current component of the developing current detected by the current detection unit at the time of forming the reference image. The DC component of the developing current when is 0% is calculated as the calculated carrier current.
The relationship between the print rate of the reference image and the DC component of the development current based on the density of the reference image detected by the density detection device is the relationship between the toner development amount of the reference image and the DC component of the development current. The amount of charge of the toner is calculated by converting to
The image forming apparatus according to claim 1, wherein a carrier development amount estimation mode for estimating the carrier development amount based on the calculated toner charge amount and the calculated carrier current can be executed. The control unit detects the DC component of the developing current flowing through the developer carrier when the non-image portions of the image carrier face each other during image formation as the non-image carrier current, and detects the detection. The image forming apparatus according to claim 2, wherein the carrier developing amount is estimated based on the non-image portion carrier current and the toner charging amount in the developing apparatus. The control unit detects the non-image unit carrier current when the carrier development amount estimation mode is executed, acquires a conversion formula for converting the non-image unit carrier current into the calculated carrier current, and detects it at the time of image formation. The image forming apparatus according to claim 3, wherein the non-image unit carrier current is converted into the calculated carrier current by the conversion formula to estimate the carrier development amount. The image forming according to claim 3 or 4, wherein the control unit executes the carrier development amount estimation mode when the carrier current of the non-image unit detected at the time of image formation changes by a predetermined value or more. apparatus. The control unit creates an approximate expression for estimating the change over time of the toner charge amount based on the toner charge amount calculated in the carrier development amount estimation mode and the elapsed time from the start of use of the toner. The image forming apparatus according to any one of claims 3 to 5, wherein the carrier development amount is estimated using the toner charge amount calculated from the approximate expression. The sixth aspect of claim 6 is characterized in that the control unit executes the carrier development amount estimation mode when the toner charge amount calculated from the approximation formula changes by a predetermined value or more from the previous carrier development amount estimation mode. The image forming apparatus described. The image forming conditions that are changed based on the carrier development amount are Vpp, which is an AC component of the development voltage, or V0-Vdc, which is a potential difference between the surface potential V0 of the image carrier and the DC component Vdc of the development voltage.
The image forming apparatus according to any one of claims 1 to 7, wherein the control unit reduces at least one of Vpp and V0-Vdc as the amount of carrier development increases.

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