JP2023079281A - Image-forming device - Google Patents

Abstract

To provide an image-forming device capable of effectively suppressing image fogging and toner scattering in an environment in which the toner scattering occurs easily in a two-component development system.SOLUTION: An image-forming device includes: multiple image-forming parts including an image carrier, an electrification device, an exposing device, and a developing device; a middle transfer body; a primary transfer member; a secondary transfer body; a cleaning mechanism; a development voltage power source; a transfer voltage power source; an electrification power voltage power source; a transfer voltage power source; and a control part. The control part rotates the image carrier, a developer carrier, and the middle transfer body for predetermined time and adsorbs a scattering toner in the middle transfer body in a state in which a transfer voltage applied to the primary transfer member or a transfer current flowing to the primary transfer member by application of the transfer voltage is increased much more than that at the time of formation of images when no images are formed if a decrease in the amount of electrification of toner housed in the developing device is predicted, and executes a scattering toner collection mode for collecting the scattering toner by the cleaning mechanism.SELECTED DRAWING: Figure 4

Description

The present invention relates to image forming apparatuses such as copiers, printers, facsimiles, and multi-function machines equipped with an image carrier, and more particularly to an image forming apparatus using a two-component developer containing toner and carrier.

2. Description of the Related Art Conventionally, a two-component development type developing device includes a supply transfer chamber for supplying developer containing toner to a developing roller (developer carrier), a stirring transfer chamber for supplying new toner, a supply transfer chamber, and a feed transfer chamber. and an agitating/conveying member for agitating and conveying the developer in the agitating/conveying chamber. In such a developing device, when the toner is consumed for development, new toner is replenished to the developer in the agitating/conveying chamber to maintain a constant toner concentration in the developing device, thereby stabilizing image formation. can.

However, when continuously printing images with a high coverage rate (the ratio of the printable area to the printable area on the paper, the same shall apply hereinafter), a large amount of toner is consumed in a short period of time, so a large amount of toner must be supplied at once. be done. As a result, the charge amount of the newly supplied toner does not increase sufficiently, and image fogging in which the low-charge toner adheres to the white background portion of the image and toner scattering in the image forming apparatus tend to occur. Further, the same phenomenon occurs even in a high-temperature and high-humidity environment or after leaving for a long time after completion of image formation.

Various methods have been proposed to reduce toner scattering and image fogging. and a developing bias for developing an image other than a patch image are disclosed. By controlling the developing bias in this way, for example, when forming a patch image, the amount of toner is greatly changed with respect to the developer concentration, which is the mixing ratio of toner and carrier. It is possible to reduce the change in the amount of toner with respect to the density. As a result, it is possible to reliably control the developer concentration and improve the image quality during image formation.

Japanese Patent Application Laid-Open No. 2001-331003

However, even if the developer concentration is controlled using the method of Patent Document 1, when images with a high coverage rate are printed continuously, or when printing is performed in a high-temperature and high-humidity environment or after leaving for a long time after the completion of image formation, printing is performed. In this case, it has been difficult to effectively suppress image fogging and toner scattering caused by a decrease in toner charge amount.

SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus capable of effectively suppressing image fogging and toner scattering even in an environment where toner scattering easily occurs in a two-component developing method.

To achieve the above object, a first configuration of the present invention comprises a plurality of image forming units, an intermediate transfer member, a primary transfer member, a secondary transfer member, a cleaning mechanism, a developing voltage power source, and a transfer voltage. An image forming apparatus includes a power supply, a charging voltage power supply, a transfer voltage power supply, and a control section. The image forming unit includes an image carrier having a photosensitive layer formed on its surface, a charging device that charges the image carrier, and an exposure that forms an electrostatic latent image by exposing the image carrier charged by the charging device. a developing container containing a two-component developer containing a device, a magnetic carrier and a toner; a conveying member rotatably supported by the developing container and conveying the developer while agitating it; and a developing device for forming a toner image by attaching toner to an electrostatic latent image formed on the image carrier. A toner image formed in the image forming section is primarily transferred onto the intermediate transfer member. The primary transfer member primarily transfers the toner image formed on the image carrier onto the intermediate transfer member. The secondary transfer member secondarily transfers the toner image transferred to the intermediate transfer member onto the recording medium. A cleaning mechanism removes toner adhering to the intermediate transfer body. A development voltage power supply applies a development voltage to the developer carrier. A charging voltage power supply applies a charging voltage to the charging device. A transfer voltage power supply applies a transfer voltage to the primary transfer member and the secondary transfer member. The control section controls the image forming section, the developing voltage power supply, the transfer voltage power supply, and the charging voltage power supply. The control unit predicts a decrease in the charge amount of the toner accommodated in the developing container, and when it is predicted that the charge amount of the toner has decreased, the transfer voltage applied to the primary transfer member during non-image formation or The image carrier, the developer carrier, and the intermediate transfer member are rotated for a predetermined time in a state in which the transfer current flowing through the primary transfer member due to the application of the transfer voltage is higher than that during image formation, and the scattered toner is attracted to the intermediate transfer member. , a scattering toner recovery mode is executed in which the cleaning mechanism recovers the scattering toner attracted to the intermediate transfer member.

According to the first configuration of the present invention, when the charge amount of the toner accommodated in the developing container is reduced and it is predicted that the toner is likely to scatter, the scattered toner recovery mode is executed to recover the image carrier and the image carrier. Scattered toner floating around a portion of the developing device facing the developer carrier is attracted to the intermediate transfer body, and the scattered toner attracted to the intermediate transfer body is removed and collected by a cleaning mechanism. As a result, it is possible to effectively suppress image fogging due to toner having a low charge amount, contamination of the inside of the image forming apparatus due to toner scattering, and the like.

FIG. 1 is a side cross-sectional view showing the internal configuration of an image forming apparatus 100 according to one embodiment of the present invention; Side cross-sectional view of developing device 3a mounted in image forming apparatus 100 Partially enlarged view around image forming unit Pa including control path of image forming apparatus 100 3 is a flow chart showing a control example of the scattered toner collection mode in the image forming apparatus 100 of the present invention; Graph showing the relationship between the endurance number of sheets and image fogging when the scattered toner collection mode is executed after printing an image with a high coverage rate in the embodiment and when it is not executed.

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

Photoreceptor drums (image bearing members) 1a, 1b, 1c and 1d for carrying visible images (toner images) of respective colors are arranged in these image forming portions Pa to Pd, and belt drive motors ( (not shown), an intermediate transfer belt 8 rotating counterclockwise in FIG. 1 is provided adjacent to each of the image forming stations Pa to Pd. The toner images formed on these photoreceptor drums 1a to 1d are sequentially primary-transferred and superimposed on an intermediate transfer belt 8 that moves in contact with each of the photoreceptor drums 1a to 1d. After that, the toner image primarily transferred onto the intermediate transfer belt 8 is secondarily transferred onto a transfer paper P as an example of a recording medium by a secondary transfer roller 9 . Further, the transfer paper P on which the toner image has been secondarily transferred is ejected from the main body of the image forming apparatus 100 after the toner image is fixed in the fixing section 13 . An image forming process is performed on each of the photosensitive drums 1a to 1d while rotating the photosensitive drums 1a to 1d clockwise in FIG.

The transfer paper P onto which the toner image is to be secondarily transferred is accommodated in a paper cassette 16 arranged at the bottom of the main body of the image forming apparatus 100, and is transferred to the secondary transfer roller via a paper feed roller 12a and a pair of registration rollers 12b. 9 and the driving roller 11 of the intermediate transfer belt 8. A dielectric resin sheet is used for the intermediate transfer belt 8, and a seamless belt is mainly used. Further, a blade-shaped belt cleaner 19 for removing toner 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. Charging devices 2a, 2b, 2c and 2d for charging the photosensitive drums 1a to 1d and image information on the respective photosensitive drums 1a to 1d are provided around and below the rotatably arranged photosensitive drums 1a to 1d. , developing devices 3a, 3b, 3c and 3d for forming toner images on the photosensitive drums 1a to 1d, and removing developer (toner) remaining on the photosensitive drums 1a to 1d. Cleaning devices 7a, 7b, 7c and 7d are provided for cleaning.

When image data is input from a host device such as a personal computer, first, the surfaces of the photosensitive drums 1a to 1d are uniformly charged by the charging devices 2a to 2d. Then, the exposure device 5 irradiates the photosensitive drums 1a to 1d with light according to image data to form electrostatic latent images according to the image data on the photosensitive drums 1a-1d. Each of the developing devices 3a to 3d is filled with a predetermined amount of two-component developer containing yellow, cyan, magenta, and black toners. When the ratio of the toner in the two-component developer filled in each of the developing devices 3a to 3d falls below a specified value due to the formation of a toner image, which will be described later, each of the developing devices 3a to 3d is removed from the toner containers 4a to 4d. Toner is supplied to the The toner in the developer is supplied onto the photosensitive drums 1a to 1d by the developing devices 3a to 3d, and adheres electrostatically to an electrostatic latent image formed by 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 photosensitive drums 1a to 1d by the primary transfer rollers 6a to 6d with a predetermined transfer voltage, and yellow, magenta, cyan and yellow, magenta, cyan, and yellow on the photosensitive drums 1a to 1d are applied. A black toner image is primarily transferred onto the intermediate transfer belt 8 . These four-color images are formed with a predetermined positional relationship for predetermined full-color image formation. After that, in preparation for subsequent formation of new electrostatic latent images, cleaning devices 7a to 7d remove toner and the like remaining on the surfaces of the photosensitive drums 1a to 1d after the primary transfer.

The intermediate transfer belt 8 is stretched over a driven roller 10 on the upstream side and a driving roller 11 on the downstream side. When the intermediate transfer belt 8 starts rotating in the counterclockwise direction as the drive roller 11 is rotated by a belt drive motor (not shown), the transfer paper P is transferred from the registration roller pair 12b to the drive roller 11 at a predetermined timing. , and the toner image on the intermediate transfer belt 8 is secondarily transferred onto the transfer paper P. A belt cleaner 19 removes toner and the like remaining on the surface of the intermediate transfer belt 8 after the secondary transfer. The transfer paper P on which the toner image has been secondarily transferred is conveyed to the fixing section 13 .

The transfer paper P conveyed to the fixing section 13 is heated and pressed by the fixing roller pair 13a to fix the toner image on the surface of the transfer paper P, forming a predetermined full-color image. The transfer paper P on which the full-color image is formed is divided in the conveying direction by the branching unit 14 branched in a plurality of directions, and is sent to the double-sided conveying path 18 as it is (or after the images are formed on both sides thereof), and is sent to the discharge roller. The pair 15 ejects to the ejection tray 17 .

Further, an image density sensor 40 is arranged at a position facing the intermediate transfer belt 8 on the downstream side of the image forming section Pd. As the image density sensor 40, an optical sensor having a light emitting element such as an LED and a light receiving element such as a photodiode is generally used. When measuring the amount of toner adhered on the intermediate transfer belt 8, each reference image formed on the intermediate transfer belt 8 is irradiated with measurement light from the light emitting element. The light reflected by is incident on the light receiving element.

Reflected light from the toner and the belt surface includes regular reflected light and irregularly reflected light. The specularly reflected light and the irregularly reflected light are separated by the polarizing splitting prism and then enter separate light receiving elements. Each light-receiving element photoelectrically converts the received specularly reflected light and irregularly reflected light and outputs an output signal to the main control section 80 (see FIG. 3). Then, the amount of toner is detected from changes in the characteristics of the output signals of specularly reflected light and irregularly reflected light, and compared with a predetermined reference density. ) is performed.

FIG. 2 is a side sectional view of the developing device 3a mounted in the image forming apparatus 100. As shown in FIG. In the following description, the developing device 3a arranged in the image forming portion Pa in FIG. 1 is illustrated, but the configuration of the developing devices 3b to 3d arranged in the image forming portions Pb to Pd is basically the same. Therefore, the explanation is omitted.

As shown in FIG. 2, the developing device 3a includes a developing container 20 containing a two-component developer containing a magnetic carrier and toner (hereinafter simply referred to as developer). It is partitioned into an agitation transfer chamber 21 and a supply transfer chamber 22 by the . The agitating/conveying chamber 21 and the supply/conveying chamber 22 are provided with agitating/conveying chambers 21 and 22 for mixing and agitating new toner supplied from the toner container 4a (see FIG. 1) with the developer in the developing container 20 to charge the toner. A screw 25 and a feed/conveying screw 26 are rotatably arranged.

Then, the developer is conveyed in the axial direction (perpendicular to the paper surface of FIG. 2) while being stirred by the stirring conveying screw 25 and the supply conveying screw 26, and the developer passing paths (see FIG. 2) formed at both ends of the partition wall 20a. (not shown) to circulate between the stirring transfer chamber 21 and the supply transfer chamber 22 . That is, a developer circulation path is formed in the developer container 20 by the agitating/conveying chamber 21, the supply/conveying chamber 22, and the developer passage.

The developer container 20 extends obliquely upward to the right in FIG. A part of the outer peripheral surface of the developing roller 30 is exposed from the opening of the developing container 20 and forms a developing area D facing the photosensitive drum 1a. The developing roller 30 rotates counterclockwise in FIG.

The developing roller 30 is composed of a cylindrical developing sleeve rotating counterclockwise in FIG. 2 and a magnet (not shown) having a plurality of magnetic poles fixed in the developing sleeve. Here, a developing sleeve with a knurled surface is used, but a developing sleeve with a number of concave shapes (dimples) formed on the surface, a developing sleeve with a blasted surface, or a knurling process or a concave shape may be used. In addition to the formation of , it is also possible to use those subjected to blasting or plating.

A development voltage obtained by superimposing an AC voltage on a DC voltage is applied to the development roller 30 by a development voltage power source 43 (see FIG. 3).

A regulating blade 27 is attached to the developing container 20 along the longitudinal direction of the developing roller 30 (the direction perpendicular to the plane of FIG. 2). A slight gap is formed between the tip of the regulation blade 27 and the surface of the developing roller 30 .

A toner concentration sensor 29 is arranged on the side surface of the agitating/conveying chamber 21 so as to face the agitating/conveying screw 25 . The toner density sensor 29 detects the toner density in the developer in the developer container 20 (mixing ratio of toner to carrier in the developer; T/C). As the toner concentration sensor 29, for example, a magnetic permeability sensor that detects the magnetic permeability of the two-component developer composed of toner and magnetic carrier in the developer container 20 is used. The toner in the toner container 4a (see FIG. 1) is replenished into the agitation transfer chamber 21 of the developer container 20 according to the toner density detected by the toner density sensor 29. FIG.

FIG. 3 is a partially enlarged view of the image forming unit Pa and its surroundings including the control path of the image forming apparatus 100. As shown in FIG. In the following description, the configuration and control path of the image forming portion Pa will be described, but the configuration and control path of the image forming portions Pb to Pd are also the same, so description thereof will be omitted.

The developing roller 30 is connected to a developing voltage power supply 43 that generates an oscillating voltage in which a DC voltage and an AC voltage are superimposed. The development voltage power supply 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 pulse-modulated low-voltage DC voltage 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 pulse-modulated low-voltage DC voltage using a step-up transformer.

The development voltage power supply 43 outputs a development voltage obtained by superimposing an AC voltage on a DC voltage from an AC constant voltage power supply 43a and a DC constant voltage power supply 43b during image formation. The charging voltage power source 45 applies a charging voltage in which an AC voltage is superimposed on a DC voltage to the charging roller 34 of the charging device 2a. The configuration of the charging voltage power supply 45 is the same as that of the developing voltage power supply 43 .

A transfer voltage power supply 47 applies a primary transfer voltage and a secondary transfer voltage having a polarity opposite to that of the toner (negative polarity) to the primary transfer rollers 6a to 6d and the secondary transfer roller 9 (see FIG. 1), respectively. In this embodiment, a transfer voltage is applied to the primary transfer rollers 6a to 6d and the secondary transfer roller 9 so that a constant current (transfer current) having a polarity opposite to that of the toner (negative polarity) flows through the primary transfer rollers 6a to 6d and the secondary transfer roller 9. This is constant current control applied to the roller 9 .

The cleaning device 7a includes a cleaning blade 32 for removing residual toner on the surface of the photosensitive drum 1a, and a rubbing roller 33 for removing residual toner on the surface of the photosensitive drum 1a and rubbing and polishing the surface of the photosensitive drum 1a. , and a conveying spiral 35 for discharging residual toner removed from the photosensitive drum 1a by the cleaning blade 32 and the rubbing roller 33 to the outside of the cleaning device 7a.

Next, a control system of image forming apparatus 100 will be described with reference to FIG. The image forming apparatus 100 is provided with a main control section 80 including a CPU and the like. The main control unit 80 is connected to a storage unit 70 made up of ROM, RAM and the like. The main control unit 80 controls each unit of the image forming apparatus 100 (charging devices 2a to 2d, developing devices 3a to 3d, exposure device 5, primary transfer roller 6a to 6d, cleaning devices 7a to 7d, secondary transfer roller 9, fixing unit 13, developing voltage power supply 43, charging voltage power supply 45, transfer voltage power supply 47, voltage control unit 50, etc.).

Based on control signals transmitted from the main control unit 80, the voltage control unit 50 controls a development voltage power supply 43 that applies a development voltage to the development roller 30, a charging voltage power supply 45 that applies a charging voltage to the charging roller 34, a primary transfer A transfer voltage power supply 47 that applies a transfer voltage to the rollers 6a to 6d and the secondary transfer roller 9 is controlled. Note that the voltage control unit 50 may be configured with a control program stored in the storage unit 70 .

The internal temperature/humidity sensor 60 constantly detects the temperature and relative humidity inside the image forming apparatus 100, specifically near the developing devices 3a to 3d. The detected temperature and humidity are sent to the main controller 80 .

A liquid crystal display section 90 and a transmission/reception section 91 are connected to the main control section 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 printed sheets, and the like. The transmission/reception unit 91 communicates with the outside using a telephone line or an Internet line. The transmitting/receiving unit 91 functions as an input unit that receives print commands and image data from a host device such as a personal computer.

As described above, when images with a high coverage rate are printed continuously, a large amount of toner is replenished from the toner containers 4a to 4d into the developing devices 3a to 3d at once. Therefore, the charging of the toner due to the stirring with the carrier in the developer container 20 does not keep up, and the charging amount of the toner in the developer decreases. In addition, the charge amount of the toner in the developer also decreases in a high-temperature and high-humidity environment or when a predetermined time or more has passed since the previous image forming operation. As a result, problems such as image fogging and toner scattering occur.

In the image forming apparatus 100 of the present embodiment, a decrease in the charge amount of toner in the developing devices 3a to 3d is predicted from the usage state of the image forming apparatus 100. FIG. Then, when a decrease in the toner charge amount is predicted, the scattered toner collection mode is executed during non-image formation. A method of predicting a decrease in the charge amount of toner, which is a characteristic part of the present invention, and an execution procedure of the scattered toner collection mode based on the prediction method will be described below.

(Method for Predicting Decrease in Charge Amount)
The charge amount of the toner in the developing devices 3a to 3d decreases when images with a high coverage rate are printed continuously. Therefore, it is possible to calculate the average print rate for the most recent predetermined number of sheets, and predict that the charge amount of the toner in the developing devices 3a to 3d has decreased when the average print rate exceeds a predetermined value.

For the calculation of the average print rate, first, the print rate P for each image is calculated based on the image data received by the transmitting/receiving section 91 . The calculated print rate P is stored in the storage unit 70 . Then, the average coverage rate is calculated by dividing the cumulative coverage rate ΣP obtained by adding the coverage rate for each image by the number of printed sheets.

Also, the charge amount of the toner in the developing devices 3a to 3d decreases as the absolute humidity increases. Therefore, when the absolute humidity exceeds a predetermined value, it can be predicted that the charge amount of the toner in the developing devices 3a to 3d has decreased.

The absolute humidity can be calculated from the internal temperature T [° C.] detected by the internal temperature and humidity sensor 60 and the relative humidity RH [%] using the following equations (1) to (3). First, the saturated water vapor pressure E is obtained from the in-machine temperature T by the formula (1).
E=6.11*10 ^{(7.5*T/(237.3+T))} (1)

Next, from the obtained saturated water vapor pressure E, the water vapor partial pressure Ep is calculated by Equation (2).
Ep=E*RH/100 (2)

Then, the absolute humidity H [g/m ³ ] can be obtained from the obtained water vapor partial pressure Ep by Equation (3).
H=217*Ep/T (3)

Also, the charge amount of the toner in the developing devices 3a to 3d decreases as the elapsed time from the end of the previous printing increases. Therefore, it can be predicted that the charge amount of the toner in the developing devices 3a to 3d has decreased when the elapsed time from the end of the previous printing exceeds a predetermined time.

(Scattered toner collection mode)
In the scattered toner collection mode, the primary transfer current flowing through the primary transfer rollers 6a to 6d is higher than that during image formation, and the photosensitive drums 1a to 1d, the developing rollers 30 in the developing devices 3a to 3d, and the intermediate transfer belt 8 is rotated for a certain period of time.

By increasing the primary transfer current flowing through the primary transfer rollers 6a to 6d, the force of attracting the toner to the intermediate transfer belt 8 is increased. Therefore, the scattered toner whose charge amount has decreased can be efficiently attracted to the intermediate transfer belt 8 .

Further, since the developing roller 30 and the photosensitive drums 1a to 1d rotate upward in the developing area D (see FIG. 2), upward air currents are generated between the developing roller 30 and the photosensitive drums 1a to 1d. The toner scattered randomly from the developing roller 30 concentrates and flies toward the intermediate transfer belt 8 by this rising air current.

Further, by rotating the photosensitive drums 1a to 1d along with the rotation of the intermediate transfer belt 8, it is possible to suppress film scraping of the photosensitive drums 1a to 1d due to rubbing against the intermediate transfer belt 8. FIG. At this time, by attaching toner to the surfaces of the photoreceptor drums 1a to 1d, the friction between the photoreceptor drums 1a to 1d and the intermediate transfer belt 8 can be reduced, and film scraping can be suppressed more effectively.

Therefore, it is preferable to electrify the surfaces of the photosensitive drums 1a to 1d by the charging devices 2a to 2d and apply a developing voltage to the developing roller 30 so that the toner adheres to the photosensitive drums 1a to 1d. At this time, while the photosensitive drums 1a to 1d are charged to a surface potential lower than that during image formation, a development voltage lower than that during image formation is applied to the development roller 30. FIG. As a result, it is possible to effectively suppress film scraping of the photosensitive drums 1a to 1d due to rubbing against the intermediate transfer belt 8, and reduce power consumption in the scattered toner recovery mode.

When the charge amount of the toner is expected to decrease, by executing the above-described scattered toner collection mode, the areas (development areas D) facing the developing rollers of the developing devices 3a to 3d and the photosensitive drums 1a to 1d The floating scattered toner is attracted to the intermediate transfer belt 8. - 特許庁Scattered toner attracted to the intermediate transfer belt 8 is removed by a belt cleaner 19 and collected. As a result, it is possible to effectively suppress image fogging due to toner having a low charge amount, contamination of the inside of the image forming apparatus 100 due to toner scattering, and the like. Table 1 shows an example of execution conditions for the scattered toner collection mode.

In the example shown in Table 1, when the absolute humidity exceeds 10.3 [g/m ³ ], when an image with a coverage rate exceeding 20% is continuously printed on more than 20 sheets, the elapsed time from the previous printing is The scattered toner collection mode is executed when 12 hours are exceeded.

In actual control, it is preferable to execute the scattered toner collection mode when all three conditions shown in Table 1 are satisfied. As a result, the execution frequency of the scattered toner recovery mode can be minimized, and image fogging and contamination due to scattered toner can be effectively suppressed without reducing image forming efficiency (productivity) as much as possible. . The scattered toner collection mode may be executed when any one of the three conditions in Table 1 is satisfied.

The execution time (duration) of the scattered toner collection mode is not particularly limited, but if the execution time is too short, the scattered toner cannot be sufficiently collected. On the other hand, if the execution time is too long, the image forming efficiency will decrease. The execution time of the scattered toner collection mode is preferably about 10 to 30 seconds.

FIG. 4 is a flow chart showing a control example of the scattered toner recovery mode in the image forming apparatus 100 of the present invention. The execution procedure of the scattered toner collection mode will be described along the steps of FIG. 4 while referring to FIGS. 1 to 3 as necessary.

First, the main control unit 80 determines whether or not a print command has been received (step S1). If the print command is not transmitted (No in step S1), the print standby state is continued. When the print command is received (Yes in step S1), the average print rate Pn of the latest n sheets (for example, 20 sheets) is calculated (step S2). After that, printing is executed by a normal image forming operation (step S3).

Next, the main control section 80 determines whether or not printing has ended (step S4). If printing has been continued (Yes in step S4), it is determined whether or not the average print rate Pn calculated in step S2 exceeds a predetermined value A (for example, 20%) (step S5). If Pn>A (Yes in step S5), the scattered toner collection mode is executed (step S6) because it is predicted that the charge amount of the toner has decreased.

Specifically, the surfaces of the photoreceptor drums 1a to 1d are charged to a surface potential lower than that in image formation, a development voltage lower than that in image formation is applied to the development roller 30, and the voltage flows to the primary transfer rollers 6a to 6d. The developing roller 30, the photoreceptor drums 1a to 1d, and the intermediate transfer belt 8 are rotated for a predetermined time while the primary transfer current is set higher than that during image formation, and then the processing ends.

On the other hand, if Pn≦A (No in step S5), it is predicted that the charge amount of the toner has not decreased, so the process ends without executing the scattered toner recovery mode.

According to the control example shown in FIG. 4, when the average print rate Pn of the last n sheets (here, 20 sheets) exceeds the predetermined value A (here, 20%), the toner charge amount is insufficient. Then, the scattered toner collection mode is executed to collect the scattered toner around the development area D. FIG. As a result, it is possible to effectively suppress problems such as image fogging and toner scattering caused by a decrease in the toner charge amount.

In the control example shown in FIG. 4, the scattered toner collection mode is executed when the average print rate Pn of the last n sheets exceeds the predetermined value A. However, instead of the average print rate Pn, absolute humidity H exceeds a predetermined value, or when the elapsed time from the last printing end exceeds a predetermined time, the scattered toner collection mode may be executed. Furthermore, the scattered toner collection mode may be executed when two or more of the average print rate Pn, the absolute humidity H, and the elapsed time from the end of the previous printing exceed predetermined values.

In addition, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the scope of the present invention. For example, the present invention is not limited to the developing device having the developing roller 30 as shown in FIG. 2, but can be applied to various developing devices using a two-component developer containing toner and carrier. For example, a magnetic roller (toner supply roller) that carries a developer on the outer peripheral surface is provided, and only the toner in the developer carried by the magnetic roller is supplied to the developing roller 30, thereby forming a toner layer on the outer peripheral surface of the developing roller 30. , and develops the electrostatic latent images on the photosensitive drums 1a to 1d.

Further, in the present embodiment, constant current control is performed by applying a transfer voltage to the primary transfer rollers 6a to 6d such that a constant current having a polarity opposite to that of the toner (negative polarity) flows through the primary transfer rollers 6a to 6d. A constant voltage control may be employed in which a constant voltage having a polarity opposite to that of the toner (negative polarity) is applied to 6a to 6d. In the case of constant voltage control, when the scattered toner recovery mode is executed, a transfer voltage lower than that during image formation should be applied to the primary transfer rollers 6a to 6d.

Further, in the above embodiment, the image forming apparatus 100 is described by taking the color printer as shown in FIG. An image forming apparatus of another type may be used. EXAMPLES Hereinafter, the effects of the present invention will be described more specifically with reference to examples.

[Effect of Suppressing Image Fogging When Scattered Toner Collection Mode is Executed]
The occurrence of image fogging was evaluated in cases where the scattered toner collection mode was executed and where it was not executed. In the test method, developing devices 3a to 3d as shown in FIG. 2 were filled with a two-component developer and mounted on a testing machine (manufactured by Kyocera Document Solutions Co., Ltd.) as shown in FIG.

Using this tester, a test image with a printing rate of 50% was printed at a printing speed (process speed) of 45 sheets/minute in a normal temperature and normal humidity environment (25° C., 50% RH). Then, the occurrence of image fogging was compared between the case where the scattered toner collection mode was executed every time 20 sheets were printed (this invention) and the case where the scattered toner collection mode was not executed (comparative example).

The development conditions were as follows: a developing roller 30 with an outer diameter of 20 mm having 80 rows of recesses formed (knurled) on the outer peripheral surface; board. The amount of developer conveyed by the developing roller 30 is 300 g/m ² , and the peripheral speed ratio of the developing roller 30 to the photosensitive drums 1a to 1d is 1.8 (trail rotation at the opposing position). A gap (development gap) with the roller 30 was set to 0.3 mm. To the developing roller 30, a development voltage was applied in which an AC voltage having a peak-to-peak value (Vpp) of 1200 V, a frequency of 6 kHz, and a duty of 50% was superimposed on a DC voltage.

The DC voltage applied to the developing roller 30 is varied within a certain range (for example, 150 to 250 V) according to the calibration result during image formation, and the DC voltage is lower than that during image formation during the scattered toner collection mode. It was set to 100V.

The transfer voltage to be applied to the primary transfer rollers 6a to 6d is constant current control in which the transfer voltage is applied to the primary transfer rollers 6a to 6d such that a constant current having a polarity opposite to that of the toner (negative polarity) flows through the primary transfer rollers 6a to 6d. During image formation, the transfer current flowing through the primary transfer rollers 6a to 6d is changed within a certain range according to the calibration result. 1 μA, which is a higher current than

As photoreceptor drums 1a to 1d, an organic photoreceptor (OPC) having an organic photoreceptor layer formed on its surface was used. As the toner, a positively charged toner having an average particle diameter of 6.8 μm was used, and the initial toner concentration (weight ratio of toner to carrier) in the developer was set to 6%.

As an evaluation method, the image density (ID; image density) of the white background portion was measured with an image densitometer (ID measuring instrument) every 30 printed sheets. The results are shown in FIG. In FIG. 5, the data series indicated by ◯ indicates the case where the scattered toner collection mode was executed (the present invention), and the data series indicated by  indicates the case when the scattered toner collection mode was not executed (comparative example).

As shown in FIG. 5, when the scattered toner recovery mode was not executed (comparative example), as the endurance printing progressed, the image density of the white background area after printing with a high coverage rate increased, and image fogging worsened. It was confirmed that On the other hand, it was confirmed that when the scattered toner recovery mode was executed (this invention), the image density of the white background portion did not increase, and the image fogging was greatly reduced.

From the above results, it was confirmed that image fogging in the white background portion can be effectively suppressed by executing the scattered toner recovery mode.

INDUSTRIAL APPLICABILITY The present invention is applicable to image forming apparatuses using two-component developer containing toner and carrier. By utilizing the present invention, an image forming apparatus capable of effectively suppressing image fogging and toner scattering even in an environment where toner scattering easily occurs in a two-component developing system using a two-component developer containing toner and carrier is provided. can do.

1a to 1d photoreceptor drum (image carrier)
2a to 2d charging device 3a to 3d developing device 5 exposure device 6a to 6d primary transfer roller (primary transfer member)
8 intermediate transfer belt (intermediate transfer body)
9 secondary transfer roller (secondary transfer member)
19 belt cleaner (cleaning mechanism)
20 Development container 25 Stirring and conveying screw (conveying member)
26 supply conveying screw (conveying member)
30 development roller (developer carrier)
43 Developing voltage power supply 45 Charging voltage power supply 47 Transfer voltage power supply 50 Voltage control unit 60 Internal temperature and humidity sensor (temperature and humidity detection sensor)
70 storage unit 80 main control unit (control unit)
91 Transmitting/receiving unit (input unit)
100 image forming apparatus

Claims (5)

an image carrier having a photosensitive layer formed on its surface;
a charging device that charges the image carrier;
an exposure device that forms an electrostatic latent image by exposing the image carrier charged by the charging device;
a developing container containing a two-component developer containing a magnetic carrier and a toner; a conveying member rotatably supported by the developing container and conveying the developer while agitating it; a developing device for forming a toner image by adhering the toner to the electrostatic latent image formed on the image carrier;
a plurality of image forming units including
an intermediate transfer member onto which the toner image formed by the image forming unit is primarily transferred;
a primary transfer member that primarily transfers the toner image formed on the image carrier onto the intermediate transfer member;
a secondary transfer member that secondarily transfers the toner image transferred onto the intermediate transfer member onto a recording medium;
a cleaning mechanism for removing the toner adhering to the intermediate transfer member;
a development voltage power supply that applies a development voltage to the developer carrier;
a charging voltage power supply that applies a charging voltage to the charging device;
a transfer voltage power supply that applies a transfer voltage to the primary transfer member and the secondary transfer member;
a control unit that controls the image forming unit, the developing voltage power supply, the transfer voltage power supply, and the charging voltage power supply;
In an image forming apparatus comprising
The control unit
predicting a decrease in the charge amount of the toner contained in the developing container, and applying the transfer voltage to the primary transfer member during non-image formation when the decrease in the charge amount of the toner is predicted; Alternatively, the image carrier, the developer carrier, and the intermediate transfer member are rotated for a predetermined time while the transfer current flowing through the primary transfer member due to the application of the transfer voltage is set to be higher than that during image formation, thereby removing scattered toner. An image forming apparatus characterized by executing a scattered toner collection mode in which the scattered toner attracted to the intermediate transfer body is collected by the cleaning mechanism. The controller applies the developing voltage lower than that in image formation to the developer carrier in a state where the image carrier is charged to a potential lower than that in image formation, thereby executing the scattered toner recovery mode. 2. The image forming apparatus according to claim 1, wherein: an input unit into which image data of the toner image formed in the image forming unit is input;
The control unit calculates an average print rate of the most recent predetermined number of sheets based on the image data, and predicts that the charge amount of the toner has decreased when the calculated average print rate exceeds a predetermined value. 3. The image forming apparatus according to claim 1, wherein the scattered toner collection mode is executed by pressing a button. A temperature and humidity detection sensor that detects the temperature and relative humidity inside the image forming apparatus,
The controller calculates absolute humidity based on the temperature and the relative humidity detected by the temperature/humidity detection sensor, and when the calculated absolute humidity exceeds a predetermined value, the charge amount of the toner decreases. 4. The image forming apparatus according to any one of claims 1 to 3, wherein the scattered toner collection mode is executed by predicting that the toner is scattered. The controller predicts that the charge amount of the toner is reduced and executes the scattered toner collection mode when the elapsed time from the end of the immediately preceding image forming operation exceeds a predetermined time. 5. The image forming apparatus according to any one of claims 1 to 4.

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