JP2019159254A - Developing device and image forming apparatus - Google Patents

Abstract

To detect a reduction over time in the amount of developer conveyed to a developing area, increase the amount of developer conveyed to the developing area, and prevent a problem, such as poor density of a solid image.SOLUTION: The above-mentioned problem is solved by a developing device comprising: a developer carrier 141; and a developer regulation member 146 that is arranged opposite to the surface of the developer carrier with a gap DG therebetween, the developing device having potential measuring means 150 that measures the potential of the developer regulation member.SELECTED DRAWING: Figure 7

Description

  The present invention relates to a developing device and an image forming apparatus.

  2. Description of the Related Art Conventionally, there has been known a developing device that includes a developer carrying member and a developer regulating member that is disposed to face the surface of the developer carrying member with a gap.

  For example, Patent Document 1 discloses a developing device in which a round bar member functioning as a developer regulating member is rotatably disposed with a predetermined gap (doctor gap) provided between the developer carrying member and the member. . In this developing device, by forming the round bar member with a magnetic member, the round bar member and the internal magnetic pole of the developer carrier disposed close to the round bar member cooperate to form a strong magnetic field. It is said that the magnetic binding force of the developer passing through the toner increases.

  However, in the conventional developing device, the amount of developer transported by the developer carried and transported on the developer carrier through the doctor gap to the development area decreases with time, and the density of the solid image is reduced. There was a problem of causing defects such as defects.

  In order to solve the above-described problems, the present invention provides a developer having a developer carrying member and a developer regulating member disposed to face the surface of the developer carrying member with a gap therebetween. It has a potential measuring means for measuring the potential of the regulating member.

  According to the present invention, it is possible to detect that the amount of developer transported by the developer carried and transported on the developer carrying body passes through the doctor gap and is transported to the development region has decreased over time. As a result, the developer conveyance amount can be improved, and problems such as a solid image density defect can be suppressed.

1 is a schematic configuration diagram of a printer according to an embodiment. FIG. 2 is a schematic configuration diagram illustrating an image forming apparatus for generating a Y toner image in the printer. FIG. 2 is a perspective view illustrating an appearance of a developing device in the printer. The perspective view of the state which removed the upper casing so that the inside of the developer accommodating part of the developing device can be visually recognized. FIG. 3 is a cross-sectional view when the developing device is cut in a direction orthogonal to a developing sleeve rotation axis. FIG. 2 is an explanatory diagram showing a distribution of normal direction magnetic flux density (absolute value) on the surface of the developing sleeve, along with a two-dot chain line, along with a schematic configuration of the developing device. Explanatory drawing which shows the mode of the developer of the doctor gap vicinity in the initial stage. Explanatory drawing which shows the mode of the developer of the doctor gap vicinity in time. The graph which shows a time-dependent change of the electric potential measurement result of a round bar doctor. The graph which shows the relationship between the electric potential measurement result of a round bar doctor, and the developer conveyance amount to a development area. The graph which shows the change of the developer conveyance amount to the image development area when using the developer at the time of initial stage, and the developer after use, and changing the voltage applied to a round bar doctor.

An embodiment in which the present invention is applied to an electrophotographic printer (hereinafter simply referred to as “printer”) as an image forming apparatus will be described below.
FIG. 1 is a schematic configuration diagram of a printer according to the present embodiment. Y, C, M, and K indicate members for yellow, cyan, magenta, and black, respectively.
In this printer, image forming apparatuses 10Y, 10C, 10M, and 10K for four colors as process cartridges are detachable from an image forming station (not shown) formed on the apparatus main body 1 side. These use Y, M, C, and K toners of different colors as the image forming material, but the other configurations are the same and are replaced when the lifetime is reached. The printer further includes an optical unit 20, an intermediate transfer unit 30, a paper feed unit 40, a fixing unit 50, and the like as exposure means capable of irradiating laser light.

  The image forming apparatuses 10Y, 10C, 10M, and 10K have the same structure, and the photosensitive drums 12Y, 12C, 12M, and 12K as latent image carriers are charged, and the photosensitive drums are charged as process means that act on the photosensitive drums. The charging devices 13Y, 13C, 13M, and 13K, and the cleaning devices 15Y, 15C, 15M, and 15K for removing the toner remaining on the photosensitive drum are integrally configured, and formed on each photosensitive drum. The developing devices 14Y, 14C, 14M, and 14K for developing the latent images are connected.

  The intermediate transfer unit 30 is formed on an intermediate transfer belt 31 as an intermediate transfer member, a plurality of (here, three) rollers 32, 33, and 34 that rotatably support the intermediate transfer belt 31, and each photosensitive drum 12. A primary transfer roller 35 for transferring the toner image to the intermediate transfer belt 31 and a secondary transfer roller 36 for transferring the toner image transferred onto the intermediate transfer belt 31 to a recording paper P as a recording material are provided. The paper supply unit 40 includes a paper supply roller 43 that conveys the recording paper P from the paper supply cassette 41 or the manual paper supply tray 42 to the secondary transfer region, a registration roller 44, and the like. The fixing unit 50 includes a fixing roller 51 and a pressure roller 52, and has a known configuration in which fixing is performed by applying heat and pressure to the toner image on the recording paper P.

  In addition, toner bottles 60Y, 60C, 60M, and 60K that store toner to be supplied to a toner supply port 145, which will be described later, are provided on the upper portion of the apparatus main body 1 separately from the image forming apparatuses 10Y, 10C, 10M, and 10K. The main body 1 is detachably mounted.

  In such a configuration, first, in the first color yellow image forming device 10Y, the photosensitive drum 12Y is uniformly charged by the charging device 13Y and then irradiated from the optical unit 20 as a latent image forming unit. The latent image is developed by the developing device 14Y with the laser beam to form a toner image. The Y toner image formed on the photosensitive drum 12Y is transferred onto the intermediate transfer belt 31 by the action of the primary transfer roller 35Y. The photosensitive drum 12Y after the primary transfer is cleaned by the cleaning device 15Y to prepare for the next image formation. The residual toner collected by the cleaning device 15Y is stored in a waste toner collection bottle 16 installed in the take-out direction of the image forming device 10Y (the rotation axis direction of the photosensitive drum). The waste toner collection bottle 16 is detachable from the image forming apparatus main body 1 so that it can be replaced when the storage amount is full.

  A similar image forming process is performed in each of the image forming apparatuses 10C, 10M, and 10K for C, M, and K to form toner images of the respective colors, and are sequentially transferred to the previously formed toner images. On the other hand, the toner image formed on the intermediate transfer belt 31 is transferred to the recording paper P conveyed from the paper feed cassette 41 or the manual paper feed tray 42 to the secondary transfer region by the action of the secondary transfer roller 36. . The recording paper P to which the toner image has been transferred is conveyed to the fixing unit 50, where the toner image is fixed at the nip portion between the fixing roller 51 and the pressure roller 52 of the fixing unit 50, and the discharge roller 55 discharges the upper part of the apparatus. The paper is discharged to the paper tray 56.

Next, a specific configuration of the image forming apparatus will be described.
Since the configurations of the image forming apparatuses 10Y, 10C, 10M, and 10K are the same except that the color of the toner to be used is different, the yellow image forming apparatus 10Y will be described below as an example.
FIG. 2 is a schematic configuration diagram showing an image forming apparatus 10Y for generating a Y toner image.
The charging device 13Y provided in the image forming device 10Y includes a charging roller 131 and a cleaning roller 132 that cleans the surface of the charging roller 131. The cleaning device 15Y includes a cleaning brush 151 and a cleaning blade 152 that are in contact with the surface of the photosensitive drum, and a toner recovery coil 153 that transports the toner scraped off by the cleaning brush 151 and the cleaning blade 152 toward the waste toner recovery bottle 16. I have.

  The developing device 14Y carries a two-component developer (hereinafter simply referred to as “developer”) made of a magnetic carrier and toner, and rotates and moves counterclockwise in FIG. 2 to a developing area facing the photosensitive drum 12Y. A non-magnetic developing sleeve 141 constituting a hollow member of the developer carrying member to be conveyed is provided. Inside the developing sleeve 141, a magnet roller 147 is fixedly disposed as magnetic field generating means having a plurality of magnetic poles in the circumferential direction. A developer carrier is constituted by the developing sleeve 141 and the magnet roller 147.

  Further, a developer regulating member that is disposed to face the developing sleeve 141 and forms a doctor gap DG between the developing sleeve 141 and the developer gap 141 for regulating the layer thickness of the developer carried on the surface of the developing sleeve 141. A round bar doctor 146 is also provided. Two conveying screws as stirring and conveying members for reciprocally conveying the magnetic carrier housed in the developing device 14Y and the replenishing toner supplied from the toner replenishing port 145 in the axial direction of the photosensitive drum 12Y 142 and 143 are also provided. These members are housed and supported in the developing case 144.

  The round bar doctor 146 is perpendicular to the direction in which the developer passes through the doctor gap DG (development sleeve surface movement direction) and in the direction along the surface of the developer carrier (development sleeve rotation axis direction). A long rod-shaped member having a circular cross section. The round bar doctor 146 may be a cylindrical one having a hollow inside or a columnar one having no hollow part. In this embodiment, a rod-shaped member having a circular cross section is used. However, the cross section may be a shape separated from a perfect circle, such as an elliptical shape, or a regular polygonal cross section.

  The rod-shaped member developer regulating member such as the round rod doctor 146 is easily bent as compared with a general flat plate-shaped developer regulating member (doctor blade). For example, the round bar doctor 146 may bend to widen the doctor gap DG in response to the developer pressure on the developing sleeve 141 that passes through the doctor gap DG during operation of the developing device. Moreover, the round bar doctor 146 may bend by the dead weight of the round bar doctor 146. In addition, since the round bar doctor 146 in the above-described embodiment is formed of a magnetic member, a magnetic force attracting the N2 pole (regulatory pole) of the magnet roller 147 acts on the round bar doctor 146, thereby causing the round bar doctor 146 to operate. 146 may bend. For this reason, the round bar doctor 146 needs to have a rigidity that can suppress bending against such a force.

  On the other hand, as shown in FIG. 6, the round bar doctor 146 is disposed in a narrow space between the photosensitive drum 12 and the developing sleeve 141. Therefore, if the round bar doctor 146 has a large diameter, the photosensitive drum 12 has a large diameter. And the like, or the laser beam from the optical unit 20 is blocked. Therefore, the diameter of the round bar doctor 146 is preferably in the range of 4 mm or more and 7 mm or less, for example, in consideration of suppressing this problem while ensuring rigidity capable of suppressing bending.

  Further, as the toner of the present exemplary embodiment, it is preferable to use a toner having a volume average particle diameter of 3 μm or more and 8 μm or less in order to reproduce minute dots of 600 dpi or more. The ratio (Dv / Dn) between the volume average particle diameter (Dv) and the number average particle diameter (Dn) is preferably in the range of 1.00 to 1.40. The closer this ratio (Dv / Dn) is to 1.00, the sharper the particle size distribution. If the toner has such a small particle size and a narrow particle size distribution, the toner charge amount distribution can be easily made uniform, and a high-quality image with little background fogging can be obtained. Can be high.

  Moreover, as a magnetic carrier of this embodiment, a thing with a weight average particle diameter of 20 micrometers or more and 65 micrometers or less can be used. When the weight average particle size is less than 20 μm, the uniformity of the particles is lowered and carrier adhesion is likely to occur. On the other hand, when the weight average particle diameter exceeds 65 μm, the reproducibility of the image details is lowered and it is difficult to obtain a fine image. In addition, the weight average particle diameter of a carrier can be measured by the range setting of 0.7 micrometer or more and 125 micrometers or less using the SRA type of a micro track particle size analyzer (made by Nikkiso Co., Ltd.). At this time, methanol is used as the solvent of the dispersion, and the refractive index is set to 1.33 and the refractive indexes of the carrier and the core material are set to 2.42.

Further, the magnetic carrier of the present embodiment has a magnetization intensity of 40 [A · m ² / kg] or more and 90 [A · m] in a magnetic field of 1 × 10 ⁶ / 4π [A / m] (1 k [Oe]). ² / kg] or less. As a result, the holding force between the carrier particles is properly maintained, so that the toner is easily dispersed in the magnetic carrier or the developer. When the strength of magnetization in a 1 × 10 ⁶ / 4π [A / m] magnetic field is less than 40 [A · m ² / kg], carrier adhesion tends to occur. On the other hand, when the intensity of magnetization in a magnetic field of 1 × 10 ⁶ / 4π [A / m] exceeds 90 [A · m ² / kg], the rising of the developer formed during development (magnetic brush) It becomes hard, the reproducibility of image details is reduced, and it is difficult to obtain a fine image.

The strength of magnetization can be measured as follows.
Using a BH tracer BHU-60 (manufactured by Riken Denshi Co., Ltd.), a cylindrical cell (inner diameter 7 mm, height 10 mm) is packed with 1.0 g of carrier and set in the apparatus. After gradually increasing the magnetic field to 3 × 10 ⁶ / 4π [A / m] (3 k [Oe]), and then gradually decreasing it to 0 [A / m], the opposite magnetic field was applied. Gradually increase to 3 × 10 ⁶ / 4π [A / m] (3 k [Oe]). Further, after gradually reducing the magnetic field to 0 [A / m], the magnetic field is applied in the same direction as the first. In this way, the BH curve is shown, and the intensity of magnetization in a magnetic field of 1 × 10 ⁶ / 4π [A / m] (1 k [Oe]) is calculated from the figure.

  Further, the magnetic carrier of the present embodiment has a resin coat film on the core of the magnetic member, and the resin coat film is a resin component obtained by crosslinking a thermoplastic resin such as acrylic and a melamine resin. In which a charge adjusting agent is contained. By using a magnetic carrier, it is possible to obtain a good balance between the effect of absorbing impact and suppressing scraping and holding large particles with a strong adhesive force, and the effect of preventing impact on the coating film and cleaning spent materials. . Therefore, it is possible to prevent the long life of the magnetic carrier, that is, film scraping and spent.

Next, the configuration and operation of the developing device will be further described.
FIG. 3 is a perspective view showing an appearance of the developing device.
FIG. 4 is a perspective view of a state in which the upper casing is removed so that the inside of the developer container of the developing device can be visually recognized.
FIG. 5 is a cross-sectional view of the yellow developing device 14Y in the present embodiment when cut in a direction perpendicular to the developing sleeve rotation axis.
FIG. 6 is an explanatory diagram showing the distribution of the normal direction magnetic flux density (absolute value) on the surface of the developing sleeve 141 with a two-dot chain line, along with the schematic configuration of the yellow developing device 14Y in the present embodiment.

  The magnet roller 147 of the developing device in the present embodiment is a cylindrical member formed by mixing magnetic powder in a resin and magnetizing the peripheral surface to form a plurality of magnetic poles. The diameter of the magnet roller 147 of this embodiment is 18 mm. In the present embodiment, the magnetic poles formed on the magnet roller 147 are developed in order from the developing pole S1 facing the photosensitive drum 12Y in the counterclockwise direction in the drawing (the developer conveying direction by the developing sleeve 141) in order. "S1 pole"), transport pole N1 (hereinafter referred to as "N1 pole"), out-of-agent upstream pole S2 (hereinafter referred to as "S2 pole"), out-of-agent / pumping pole S3 (hereinafter referred to as "S3 pole"). ), And a regulation pole N2 (hereinafter referred to as “N2 pole”).

  The magnet roller 147 of the present embodiment is integrally formed as a whole, but a magnet member separately formed for each magnetic pole may be disposed around the shaft. As the integrally molded magnet roller 147 as in this embodiment, it is desirable that magnetic powder is dispersed in a resin such as ethylene ethyl acrylate or nylon (registered trademark). The magnetic powder is preferably a rare earth magnet such as strontium ferrite, NdFeB, or SmFeN.

  On the other hand, the developing sleeve 141 is a nonmagnetic hollow member, and its material is preferably aluminum or stainless steel in view of processability, cost, and durability. More preferably, a large number of elliptical dents may be randomly provided on the outer peripheral surface of the developing sleeve 141 by, for example, forming a lot of random elliptical dents on the outer peripheral surface of the developing sleeve 141. According to this configuration, the surface of the developing sleeve 141 has a rough pit, so that the situation in which the developer slips without being able to follow the rotation of the developing sleeve 141 can be suppressed. In addition to forming thick spikes with roots, it is difficult for the dents to wear, so a stable and good image without image unevenness can be obtained over a long period of time. Such a dent is preferably formed by causing a medium made of a relatively large cut wire (a metal wire cut into a short length) to collide with the surface of the developing sleeve, as in a conventional blasting method. . In order to facilitate the conveyance of the developer, it is generally performed to form grooves or irregular irregularities (sand blast, bead blast, etc.) on the surface of the developing sleeve. In particular, in a color image forming apparatus, a developing sleeve having a concavo-convex surface formed by blasting the surface has become the mainstream because of its superior image quality. Such roughing processing such as grooving and blasting is performed in order to prevent a decrease in image density caused by the developer slipping and stagnation on the surface of the developing sleeve rotating at high speed.

  By the developing case 144, a developer container is formed inside the developing device 14Y. The developer accommodating portion is divided into a supply chamber 149A that is positioned below the developing sleeve 141 and extends in the developing sleeve axial direction, and a stirring chamber 149B that is adjacent to the supplying chamber 149A and extends in the developing sleeve axial direction. Yes. Conveying screws 142 and 143 are provided in the supply chamber 149A and the stirring chamber 149B, respectively. The developer transported to the downstream end (back side in the figure) of the supply chamber 149A by the transport screw 143 is transferred to the stirring chamber 149B, and the downstream end (front side in the figure) of the stirring chamber 149B by the transport screw 142 in the stirring chamber. It is conveyed toward. The developer conveyed to the downstream end of the stirring chamber 149B is transferred to the supply chamber 149A and is conveyed toward the downstream end of the supply chamber 149A by the conveyance screw 143 in the supply chamber. As described above, the developer is circulated and conveyed in the developer accommodating portion.

  Replenishment toner for replenishing the amount of toner consumed by development is supplied from the toner replenishment port 145 to the developer in the stirring chamber 149B. The developer in the supply chamber 149A is pumped onto the developing sleeve 141 by the magnetic force of the magnet roller 147 (magnetic force by the N3 pole) during the conveyance. After that, the developer pumped up on the developing sleeve 141 is regulated by the round bar doctor 146, passes through the developing area facing the photosensitive drum 12Y, and returns to the developer containing portion again.

  In the present embodiment, the developer pumped up from the supply chamber 149A by the magnetic force (magnetic force) by the S3 pole and adsorbed on the developing sleeve 141 is conveyed counterclockwise in the drawing as the developing sleeve 141 rotates. . The developer controlled to a predetermined amount by the round bar doctor 146 is spiked by the magnetic force generated by the S1 pole in the development area, and the developing electric field is transferred from the spiked developer to the electrostatic latent image on the surface of the photosensitive drum 12Y. Then, the toner is supplied and development processing is performed. The developed developer is transported as the developing sleeve 141 rotates while being held on the developing sleeve 141 by the magnetic force of the N1 pole and the S2 pole. After that, it receives the action of the repulsive magnetic force (peeling force) and centrifugal force generated between the S2 pole and the S3 pole, and is separated (departed from the developer) from the developing sleeve 141 and dropped into the supply chamber 149A in the developer accommodating portion. To do.

The magnetic force is calculated by the following formula.
Fr = G × (Hr × (∂Hr / ∂r) + Hr × (∂Hθ / ∂r))
Fθ = G × (1 / r × Hr × (∂Hr / ∂θ) + 1 / r × (Hr × ∂Hθ / ∂θ))
Here, “Fr” represents a component in the normal direction of the developing sleeve surface of the magnetic force, “Fθ” represents a component in the tangential direction of the developing sleeve surface of the magnetic force (hereinafter referred to as “normal magnetic force”), and “Hr”. "Indicates the normal component of the magnetic flux density in the developing sleeve surface (hereinafter referred to as" tangential magnetic force "), and" Hθ "indicates the magnetic flux density of the developing sleeve surface in the tangential direction. “R” is a calculation radius, and “G” is a constant (7.8 × 10 ⁻¹⁵ ). In the following description, when the normal direction magnetic force Fr shows a positive value, the magnetic force acts in the direction in which the magnetic carrier moves away from the developing sleeve 141, and when the normal direction magnetic force Fr shows a negative value. The magnetic force acts in the direction in which the magnetic carrier is attracted to the developing sleeve 141. In the following description, the terms “upstream” and “downstream” simply refer to “upstream” and “downstream” in the developer transport direction by the developing sleeve 141.

  The round bar doctor 146 in this embodiment is formed of a magnetic member. Therefore, the magnetic flux density between the N2 pole (regulatory pole) of the magnet roller 147 inside the developing sleeve 141 and the round bar doctor 146 is increased, and the normal direction magnetic flux density of the doctor gap DG is high as shown in FIG. It will be a thing. As a result, the amount of developer passing through the doctor gap DG (that is, the amount of developer transported to the development area) decreases. This is because when the magnetic flux density in the normal direction of the doctor gap DG increases, the developer on the developing sleeve 141 becomes sprouting when passing through the doctor gap DG, and the developer density becomes sparse. It is thought that. Further, as a result of increasing the magnetic binding force of the developer passing through the doctor gap DG, it is considered that the developer conveyance resistance when passing through the doctor gap DG is increased and the amount of developer passing through the doctor gap DG is reduced. It is done.

  If the density of the developer passing through the doctor gap DG can be reduced, the doctor gap DG can be set wider than the target passing amount (developer transport amount to the developing region). The wider the doctor gap DG, the smaller the variation of the passage amount (developer transport amount to the development area) with respect to the error of the doctor gap DG. Therefore, by using the round bar doctor 146 formed of a magnetic member, it is possible to suppress a variation in the developer conveyance amount to the development region with respect to the error of the doctor gap DG. In addition, as the doctor gap DG becomes wider, the doctor gap DG is less likely to be clogged with foreign matter, so that it is possible to suppress image quality degradation such as a white streak image caused by the clogged foreign matter in the doctor gap DG.

Next, estimation of the developer conveyance amount to the development area, which is a characteristic part of the present invention, will be described.
FIG. 7 is an explanatory diagram showing the state of the developer near the doctor gap DG at the initial time.
FIG. 8 is an explanatory diagram showing the state of the developer near the doctor gap DG over time.
7 and 8, the developer indicated by a black circle is a staying developer G ′ that remains in place even when the developing sleeve 141 rotates and conveys the developer on the developing sleeve 141. The developer indicated by the circle is the developer G that is conveyed as the developing sleeve 141 rotates.

  At the initial stage, as shown in FIG. 7, the amount of staying developer G ′ present in the vicinity of the doctor gap DG is relatively small. Therefore, the developer G transported with the rotation of the developing sleeve 141 can pass through the doctor gap DG without being affected by the staying developer G ′. Therefore, the amount of developer transported to the development area at the initial stage is relatively large.

  On the other hand, as time passes, as shown in FIG. 8, the amount of staying developer G ′ present in the vicinity of the doctor gap DG increases compared to the initial time. Therefore, the developer G transported with the rotation of the developing sleeve 141 is affected by the staying developer G ′, and the passage of the doctor gap DG is hindered by the staying developer G ′. As a result, the amount of developer transported to the development area over time is smaller than in the initial stage. Note that the increase in the amount of the staying developer G 'over time is considered to be mainly due to a decrease in the flow rate of the developer due to use over time. If the amount of developer transported to the development area is reduced in this way, the amount of toner supplied to the development area becomes insufficient, causing problems such as a solid image density defect.

  Here, it is difficult for the developing device in operation to directly measure the developer conveyance amount to the development region. Further, if the amount of staying developer G ′ in the vicinity of the doctor gap DG that has a high correlation with the developer conveyance amount can be measured, the developer conveyance amount to the development region can be estimated from the measurement result. However, it is difficult to directly measure the amount of the staying developer G ′.

  As a result of research, the present inventors have found that there is a high correlation between the amount of staying developer G 'and the amount of charge stored in the staying developer G'. Therefore, if the amount of charge stored in the staying developer G ′ can be measured, the amount of developer transported to the development area can be estimated.

  Therefore, the developing device 14 in the present embodiment includes a surface potential sensor 150 as a potential measuring unit that measures the potential of the round bar doctor 146. Since the staying developer G ′ is present in a region in contact with the round bar doctor 146, the potential of the round bar doctor 146 increases as the amount of charge stored in the staying developer G ′ increases. In particular, since the round bar doctor 146 of the present embodiment is made of metal and made of a conductive member, the amount of charge stored in the staying developer G ′ easily flows into the round bar doctor 146, and the staying developer. The potential of the round bar doctor 146 is likely to change according to the amount of charge stored in G ′. It should be noted that the round bar doctor 146 of the present embodiment does not necessarily need to be formed of a conductive member as long as the potential can be changed according to the amount of charge stored in the staying developer G ′. .

  In this embodiment, the potential of the round bar doctor 146 correlated with the amount of charge stored in the staying developer G ′ is measured by the surface potential sensor 150, and the developer conveyance amount to the development area is estimated from the measurement result. To do.

  It should be noted that since the developer transport amount to the development area can be estimated, it is also possible to estimate the target parameter correlated with the decrease in the developer transport amount to the development area. For example, it is possible to estimate the degree of developer fluidity deterioration (developer deterioration) that causes a decrease in the developer transport amount to the development area.

FIG. 9 is a graph showing the change with time of the potential measurement result of the round bar doctor 146.
This graph is an experiment in which a blank printing operation is continued for 1 hour at a process linear velocity of 256 mm / s, and the measurement result of the potential of the round bar doctor 146 is plotted by the surface potential sensor 150. The measurement results (potential of the round bar doctor 146) are taken on the vertical axis. The round bar doctor 146 is configured to be in an electrically floating state when measuring the potential of the round bar doctor 146. Specifically, the round bar doctor 146 is configured to be in an electrically floating state by using all of the holding members that hold the round bar doctor 146 made of a conductive member as insulating members. However, it is considered that a part of the electric charge of the round bar doctor 146 flows out to the developing sleeve 141 through the developer.

  As shown in the graph of FIG. 9, it can be seen that the potential of the round bar doctor 146 increases with time.

FIG. 10 is a graph showing the relationship between the potential measurement result of the round bar doctor 146 and the developer conveyance amount to the development area.
In this experiment, the amount of developer transported to the development region at a predetermined timing was measured in the above-described experiment, and the measurement result was plotted in relation to the potential of the round bar doctor 146 measured at the corresponding timing. The horizontal axis indicates the measurement result of the potential of the round doctor 146, and the vertical axis indicates the measurement result of the developer conveyance amount to the development area.

  As shown in the graph of FIG. 10, it was found that the potential measurement result of the round bar doctor 146 and the measurement result of the developer conveyance amount to the development area have a linear relationship. By grasping this relationship in advance, the developer transport amount to the development region can be calculated (estimated) from the potential measurement result of the round bar doctor 146 by the surface potential sensor 150 in the developing device 14 in operation. .

  In the present embodiment, it is possible to grasp the decrease in the developer conveyance amount to the development region from the potential measurement result of the round bar doctor 146 by the surface potential sensor 150 in this way. Therefore, in the present embodiment, the developer transport amount to the development region is adjusted based on the measurement result of the surface potential sensor 150, and the decrease in the developer transport amount to the development region over time is suppressed. Until a stable amount of developer is conveyed to the development area.

  In the present embodiment, the developer conveyance amount adjusting means for adjusting the developer conveyance amount to the development area changes the voltage applied to the round bar doctor 146 when performing the development process, for example, to the development area. For adjusting the developer transport amount.

  In the present embodiment, a doctor power source 161 as a voltage applying unit is connected to the round bar doctor 146 as shown in FIGS. The doctor power supply 161 has a function as voltage switching means for switching whether to apply a voltage to the round bar doctor 146 or not. Further, the doctor power supply 161 of the present embodiment can change the voltage applied to the round bar doctor 146 by the control unit 160 by variable control.

FIG. 11 shows the change in the developer conveyance amount to the development area when the voltage applied to the round bar doctor 146 is changed using the initial developer and the developer after use (developer deteriorated by use). It is a graph which shows.
Specifically, the solid line in FIG. 11 uses the initial developer (plotted on the leftmost in FIG. 10) in the graph shown in FIG. This corresponds to the case where the potential measurement result of the doctor 146 is 14V. Further, the broken line in FIG. 11 uses the developer after use in the graph shown in FIG. 10 (plotted in the center of FIG. 10), and the potential measurement of the round bar doctor 146 by the surface potential sensor 150 is performed. Corresponds when the result is 17V.

  As shown in the graph of FIG. 11, in both the initial developer and the developer after use, the developer conveyance amount to the development region varies by changing the voltage applied to the round bar doctor 146. I understand. Therefore, by changing the voltage applied to the round bar doctor 146, the developer transport amount to the development area can be adjusted.

  For example, in the example of the graph shown in FIG. 11, when the potential measurement result of the round bar doctor 146 by the surface potential sensor 150 is 14 V (initial time), the doctor power supply 161 is as shown in the plot indicated by the symbol a in FIG. By setting the voltage to be applied to the round doctor 146 to 20 V, the developer transport amount to the development area can be set as the target value. On the other hand, when the potential measurement result of the round bar doctor 146 by the surface potential sensor 150 becomes 17V (after use), as shown in the plot indicated by symbol b in FIG. 11, the doctor power supply 161 applies the round bar doctor 146 to the round bar doctor 146. By setting the voltage to about 3 V, the developer transport amount to the development area can be set as the target value.

  In this way, the control unit 160 variably controls the voltage applied to the round bar doctor 146 by the doctor power source 161 in accordance with the potential measurement result of the round bar doctor 146 by the surface potential sensor 150, so that The developer transport amount can be adjusted to stabilize the developer transport amount transported to the development area.

  In the present embodiment, the developer regulating member is a direction (developing sleeve rotating shaft) that is perpendicular to the direction in which the developer passes through the doctor gap DG (developing sleeve surface moving direction) and that is along the surface of the developing sleeve. This is an example of a round bar doctor 146 that is a bar member that is long in the direction and has a circular cross section, but is not limited thereto. For example, a doctor blade that is a general flat plate-like developer regulating member may be used.

What was demonstrated above is an example, and there exists an effect peculiar for every following aspect.
[First aspect]
The first aspect is a development having a developer carrying member (for example, a developing sleeve 141) and a developer regulating member (for example, a round bar doctor 146) disposed to face the surface of the developer carrying member with a gap. The apparatus 14 includes a potential measuring unit (for example, a surface potential sensor 150) that measures the potential of the developer regulating member.
In general, a staying developer is generated in the vicinity of the gap (doctor gap) between the developer regulating member and the developer carrying member due to deterioration of the fluidity of the developer due to use over time. Such staying developer gradually increases with time. When the staying developer increases, the developer carried on the developer carrying member becomes difficult to pass through the doctor gap due to the obstruction of the staying developer, and the developer transport amount transported to the development area decreases. If the developer transport amount is reduced, the amount of toner supplied to the development area becomes insufficient, causing problems such as a solid image density defect.
In a developing device in operation, it is difficult to directly measure the developer conveyance amount conveyed to the development area. Further, the amount of staying developer in the vicinity of the doctor gap is highly correlated with the developer transport amount, but it is difficult to directly measure the amount of staying developer. As a result of research, the present inventors have found that there is a high correlation between the amount of staying developer and the amount of charge stored in the staying developer, and if the amount of charge stored in the staying developer can be measured. It has been found that the developer transport amount transported to the development area can be estimated.
In this aspect, the potential of the developer regulating member can be measured by the potential measuring means. Since the staying developer usually stays in a region in contact with the developer regulating member, the potential of the developer regulating member increases as the amount of charge stored in the staying developer increases. Therefore, the amount of charge stored in the staying developer can be estimated from the potential amount of the developer regulating member measured by the potential measuring means. Therefore, according to this aspect, it becomes possible to estimate the developer transport amount transported to the development area from the potential amount of the developer regulating member measured by the potential measuring means, and the developer transport amount is improved. It is possible to suppress problems such as a solid image density defect.

[Second embodiment]
A second aspect is characterized in that, in the first aspect, the developer regulating member is composed of a conductive member (for example, metal).
Since the staying developer generally exists in a region in contact with the developer regulating member, if the developer regulating member is composed of a conductive member, the developer regulating is performed according to the amount of charge stored in the staying developer. The potential of the member is likely to change. Therefore, the accuracy of estimating the developer transport amount transported to the development area from the potential measurement result of the developer regulating member by the potential measuring means is improved.

[Third Aspect]
A third aspect is characterized in that, in the first or second aspect, a two-component developer comprising a toner and a carrier is used as the developer.
According to this, it becomes possible to estimate the developer conveyance amount to the development area in the developing device using the two-component developer, improve the developer conveyance amount, and suppress defects such as a solid image density defect. Is possible.

[Fourth aspect]
According to a fourth aspect, in any one of the first to third aspects, the developer regulating member is formed of a magnetic member.
According to this aspect, the magnetic flux density in the doctor gap can be increased, the density of the developer passing through the doctor gap DG can be reduced, and the doctor gap can be reduced with respect to the developer transport amount to the target development area. A wider setting is possible. The wider the doctor gap, the smaller the variation in the developer transport amount to the development area with respect to the doctor gap error. Therefore, by using the developer regulating member formed of a magnetic member, it is possible to suppress a variation in the developer conveyance amount to the development region with respect to the doctor gap error. Further, as the doctor gap becomes wider, the doctor gap is less likely to be clogged with foreign matter, so that it is possible to suppress deterioration in image quality such as a white streak image due to clogging of the doctor gap with foreign matter.

[Fifth aspect]
According to a fifth aspect, in any one of the first to fourth aspects, the developer regulating member is electrically in a float state when at least the potential of the developer regulating member is measured by the potential measuring unit. Features.
According to this, since the charge of the developer regulating member is less likely to flow out of the developer regulating member, the potential of the developer regulating member that changes according to the amount of charge stored in the retained developer can be maintained, and the retained developer Higher correlation between the amount of charge stored in the toner and the potential of the developer regulating member is obtained. Therefore, the accuracy of estimating the developer transport amount transported to the development area from the potential measurement result of the developer regulating member by the potential measuring means is improved.

[Sixth aspect]
According to a sixth aspect, in the fifth aspect, a voltage applying unit (for example, a doctor power supply 161) that applies a voltage to the developer regulating member, and a voltage is applied by the voltage applying unit when performing development processing, and the potential measuring unit And a voltage switching means (for example, a doctor power supply 161) for preventing the voltage application means from applying a voltage when measuring the potential of the developer regulating member.
According to this, even if a voltage applying means for applying a voltage to the developer regulating member is provided, the voltage is not applied by the voltage applying means when the potential measuring means measures the potential of the developer regulating member. The agent regulating member can be electrically floated.

[Seventh aspect]
In the seventh aspect, an image obtained by developing a latent image formed on a latent image carrier (for example, the photosensitive drum 12) with a developing device is transferred onto a recording material (for example, recording paper P) to form an image. In an image forming apparatus (for example, a printer), the developing device 14 according to any one of the first to fourth aspects is used as the developing device.
According to this aspect, since the developer transport amount transported to the development area can be estimated from the potential amount of the developer regulating member measured by the potential measuring means, the developer transport amount is improved and the solid image is improved. It is possible to suppress problems such as density defects.

[Eighth aspect]
According to an eighth aspect, in the seventh aspect, based on the measurement result of the potential measuring means, the developer carried and transported on the developer carrier passes through the gap and faces the latent image carrier. And a developer transport amount adjusting means (for example, control unit 160) for adjusting the developer transport amount transported to the developing region.
According to this, the developer transport amount to the development area is improved in accordance with the developer transport amount to the development area estimated from the potential amount of the developer regulating member measured by the potential measuring means, and the solid image Problems such as density defects can be suppressed.

[Ninth aspect]
A ninth aspect uses the developing apparatus according to the fifth aspect as the developing apparatus according to the eighth aspect, and the developer transport amount adjusting means changes an applied voltage by the voltage applying means when performing the developing process. Thus, the adjustment is performed.
According to this, it is possible to adjust the developer transport amount to the development area with a simple configuration.

10: Image forming device 12: Photoconductor drum 13: Charging device 14: Developing device 15: Cleaning device 20: Optical unit 30: Intermediate transfer unit 31: Intermediate transfer belt 35: Primary transfer roller 36: Secondary transfer roller 40: Feed Paper unit 50: Fixing unit 60: Toner bottle 141: Developing sleeve 146: Round bar doctor 147: Magnet roller 150: Surface potential sensor 160: Control unit 161: Doctor power supply DG: Doctor gap G: Developer G ': Retained developer

Japanese Patent Laid-Open No. 8-21745

Claims (9)

A developer carrier;
In a developing device having a developer regulating member disposed opposite to the surface of the developer carrying member with a gap therebetween,
A developing device comprising a potential measuring means for measuring a potential of the developer regulating member. The developing device according to claim 1,
The developing device according to claim 1, wherein the developer regulating member is made of a conductive member. The developing device according to claim 1 or 2,
A developing device comprising a two-component developer comprising a toner and a carrier as the developer. The developing device according to any one of claims 1 to 3,
The developing device, wherein the developer regulating member is formed of a magnetic member. The developing device according to any one of claims 1 to 4,
The developing device according to claim 1, wherein the developer regulating member is electrically floated at least when the potential of the developer regulating member is measured by the potential measuring means. The developing device according to claim 5,
Voltage application means for applying a voltage to the developer regulating member;
A voltage switching unit configured to apply a voltage by the voltage applying unit when performing the developing process and to prevent a voltage from being applied by the voltage applying unit when measuring the potential of the developer regulating member by the potential measuring unit; A developing device. In an image forming apparatus for forming an image by transferring an image obtained by developing a latent image formed on a latent image carrier with a developing device onto a recording material,
An image forming apparatus using the developing device according to claim 1 as the developing device. The image forming apparatus according to claim 7.
Based on the measurement result of the potential measuring means, the developer carried on the developer carrying member is carried to the developing region passing through the gap and facing the latent image carrying member. An image forming apparatus comprising developer transport amount adjusting means for adjusting the amount. The image forming apparatus according to claim 8.
The developing device according to claim 5 is used as the developing device.
The image forming apparatus according to claim 1, wherein the developer transport amount adjusting unit performs the adjustment by changing a voltage applied by the voltage applying unit when performing the developing process.

Images