JP2007057617A - Developing device and image forming apparatus using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To form an excellent image by adjusting developing bias according to the change of toner concentration, especially, out of the change of developer. <P>SOLUTION: The developing device is equipped with: a developing housing 2 in which two-component developer (developer) containing toner and magnetic carrier is stored; a developer carrier 3 carrying and conveying the developer; a developing bias applying means 4 provided between an image carrier 1 and the developer carrier 3, and applying the developing bias obtained by superposing an AC component on a DC component for developing an electrostatic latent image on the image carrier 1; a toner concentration detection means 5 detecting the toner concentration of the developer in the developing housing 2; and a developing bias adjusting means 6 setting the AC component of the developing bias to a reference value when the toner concentration detected by the toner concentration detection means 5 is within a predetermined range, while correcting the AC component of the developing bias so that an image quality evaluation parameter may be within tolerance when the toner concentration exceeds the predetermined range. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device used in a copying machine, a printer, or the like, and in particular, a developing device capable of obtaining a higher quality image by devising a developing bias at the time of development, and an image using this developing device. The present invention relates to an improvement of a forming apparatus.

Conventionally, in an image forming apparatus such as an electrophotographic copying machine or printer, a two-component developer containing toner and a carrier is used, and the photosensitive member is directly developed by a developer magnetic brush. The method is known. In such a development method, when development is continued, the toner density in the developer changes, and the image quality of the output image changes.
On the other hand, even if a change in toner density is simply detected and toner is replenished accordingly, it is difficult to obtain an appropriate image quality due to changes in the flowability and chargeability of the developer itself over time. Become.

  In general, in order to obtain high image quality, it is known to superimpose an AC component on a DC component as a developing bias. Thus, by superimposing the AC component on the developing bias, there is an advantage that the image density of the solid portion (solid portion), the fogging of the background (non-image portion), the fine line reproducibility, the graininess, and the like are improved. For this reason, there has been proposed a method for maintaining the image quality by changing the amplitude and frequency of the AC component of the developing bias in accordance with the usage history information of the developing device (see, for example, Patent Documents 1 and 2).

Japanese Patent Application Laid-Open No. 2004-228561 presents a method in which the frequency of the AC component of the developing bias is changed based on the input image information, the output image information, or the usage environment information of the developing device. By obtaining the relationship with the density level of the output image in advance so as to change the frequency in accordance with the change in charging characteristics, it is possible to obtain an image in which the gradation of the output image is sufficiently ensured. The usage environment information of the developing device includes usage history information such as the number of developments and changes in toner charging characteristics.
In Patent Document 2, the usage history of the developer is estimated from the number of developments, the development time, the charging characteristics of the photoconductor, and the like, or the usage history of the developer is detected from the charging characteristics of the toner and the resistance change of the carrier. A proposal has been made that the toner transfer performance can be maintained as a result of correcting the change in developer fluidity over time by changing the amplitude of the AC component of the developing bias.

JP-A-7-325468 (Example, FIG. 3) JP 10-142908 A (Embodiment of the Invention, FIG. 2)

  Certainly, the above method may maintain the gradation and transfer performance in the long term as compared to the method in which the AC component of the developing bias is kept constant, but the toner density of the developer has changed. The relationship between the development amount (the difference in toner density and the actual development amount varies), banding (band-like density unevenness appearing in the halftone portion of the image), and the development bias is taken into consideration In addition, as shown in Patent Document 2, even if a change in the current of the developing bias is detected, the change in the developer is directly detected in order to detect the mutual effects between the developer and the photosensitive member. Therefore, there is a concern that a change in toner density is insufficient for maintaining an appropriate image quality.

  The present invention has been made to solve the above technical problem, and forms a good image by adjusting the developing bias according to the change in the toner density, among the changes in the developer. An image forming apparatus using the developing device and an image forming apparatus using the developing device.

  Usually, for example, when toner is supplied to the developer so that the image density (toner density) on the photoreceptor is constant, the toner density of the developer changes due to the influence of the granularity of the developer. It has been. Accordingly, the inventors of the present invention have focused on the influence on the image quality caused by the change in the toner density of the developer, and have found the present invention while examining the conditions for obtaining a comprehensively good image quality. .

  That is, as shown in FIG. 1, the present invention accommodates a two-component developer (developer) that is disposed opposite to an image carrier 1 on which an electrostatic latent image is carried and includes toner and a magnetic carrier. A developing housing 2 provided in the developing housing 2 so as to be spaced apart from the image carrier 1, and a developer carrier 3 for carrying and carrying a developer for developing the electrostatic latent image on the image carrier 1. The developing bias applying means 4 is provided between the image carrier 1 and the developer carrier 3 and applies a developing bias in which an AC component is superimposed on a DC component that develops the electrostatic latent image on the image carrier 1. And a toner density detecting means 5 for detecting the toner density of the developer in the developing housing 2, and when the toner density detected by the toner density detecting means 5 is within a predetermined range, the AC component of the developing bias is used as a reference value. While set to When it exceeds circumference is characterized in further comprising a developing bias adjustment means 6 for correcting the AC component of the developing bias so that the image quality evaluation parameter within an allowable range.

In such technical means, the developing system according to the present application is of a type using a two-component developer (developer), and therefore, toners having various color components can be used. Of course, the present invention can be applied to a developing method used in, for example, a monochrome image forming apparatus using an apparatus, and can also be applied to a developing method used in, for example, a full-color image forming apparatus using a plurality of developing devices. Is possible.
Further, if the developer carrier 3 is spaced from the image carrier 1, the movement direction thereof is the Against direction (moving in a direction opposite to each other), the With direction (same at each other) Move in the direction).
Further, the image carrier 1 may be any one that can carry an electrostatic latent image, and the shape thereof may be either a roll shape or a belt shape.
Furthermore, the developer carrier 3 may be any material as long as it can carry and transport the developer. As a typical embodiment, the developer carrier 3 includes a rotatable non-magnetic sleeve and a magnet body fixedly disposed therein.

The toner concentration detecting means 5 may be installed in the developing housing 2 as long as the toner concentration in the developer in the developing housing 2 can be detected, and the detection method is magnetic, optical, or electrical. However, from the viewpoint of effectively detecting the toner concentration in the two-component developer, it is preferable to detect by a magnetic method using magnetic permeability at a site upstream from the developer carrier 3.
Here, the “predetermined range” of toner density means a range that does not reach a region where image defects such as fogging or carrier fogging (BCO: Bead Carrier Over) occur due to toner density. Normally, if the toner concentration is too high, image deterioration is likely to occur due to fogging, graininess, banding, etc., whereas if the toner concentration is too low, image deterioration due to carrier fogging, graininess, etc. is likely to occur.

  The “image evaluation parameter” means the above-described fog, carrier fog, graininess, banding, image density, edge enhancement, etc., and these evaluation items may be at least one of them. However, from the viewpoint of further improving the image quality, it is preferable to evaluate a plurality of image evaluation parameters simultaneously. Further, it is preferable to correct the AC component of the developing bias with all image evaluation parameters.

The developing bias adjusting unit 6 only needs to be capable of correcting the AC component of the developing bias. Further, from the viewpoint of obtaining a better image, the development bias adjusting unit 6 preferably corrects the AC component of the development bias based on a correction condition obtained in advance, for example, based on a correction table. Examples include an aspect of adjusting the developing bias and an aspect of adjusting based on an arithmetic expression. The correction condition obtained in advance means the correction condition obtained in order to obtain a good image from the correlation between the AC component of the developing bias obtained by the same type apparatus and the image quality evaluation parameter.
Furthermore, it is preferable that the developing bias adjusting unit 6 corrects at least one of the amplitude and frequency of the developing bias AC component. If only one of them is corrected, the control of the developing bias is simplified, which is effective for simplifying the apparatus itself.

  Furthermore, the present invention provides an image density detecting means for detecting an image density of an image visualized with toner in the developer, and an AC component other than a developing bias based on information from the image density detecting means. And a control means for adjusting the developing conditions. At this time, the timing for adjusting the developing conditions by the control unit and the correction of the developing bias by the developing bias adjusting unit 6 is not particularly limited, and may be performed at any timing. From the standpoint of effectively correcting the AC component of the developing bias along the toner density detected by 5 and further maintaining the desired image density, after the adjustment by the developing bias adjusting means 6, the control means It is preferable that the development conditions are adjusted by the above.

The image density detecting means may be any means that detects the density of an image visualized by development. Examples of detected images include an image on the image carrier 1 and an image carrier 1. To any of the images transferred onto the recording medium (including the intermediate transfer member).
Further, the development conditions here may be anything other than the AC component of the development bias, and include an aspect including a DC component of the development bias, various potential conditions of the image carrier 1, and further a developer supply means 7 (described later). (Ii), the developer replenishing means 7 may be controlled. Further, the development conditions may be more specifically adjusted based on information from the image density detection unit and, for example, a parameter table obtained in advance.
Further, the control means may be any means that can adjust the general development conditions, and the control means may include the development bias adjustment means 6.

The present invention further includes a developer replenishing means 7 for replenishing a new developer in the developing housing 2 in order to compensate for toner consumption by the output image, and based on the accumulated information of the output image. It is preferable to set a new operating time of the developer replenishing means 7. In this case, the developer replenishment from the developer replenishing means 7 is further optimized, and the output image can be stabilized. It becomes like this.
At this time, the developer replenishing means 7 may be configured so that a new developer can be replenished in the developing housing 2. As a typical aspect, the developer replenishing means 7 has a conveying member inside and operates the conveying member. A mode in which a predetermined amount of developer is replenished by the above is mentioned. The newly replenished developer includes a two-component developer mode and a toner-only mode.
Further, the accumulated information of the output image only needs to be calculated by a method in which the accumulation of used toner is known. For example, the accumulation of the image area ratio of the output image and the accumulation of the change in the toner density. And a method based on accumulation of output image density.

  Further, the present invention is not limited to the developing device, and is also intended for an image forming apparatus using the developing device. In this case, the image carrier 1 that carries an electrostatic latent image, and the image The developing device described above may be used as a developing device for developing the electrostatic latent image on the carrier 1.

According to the present invention, in a developing method using a two-component developer composed of toner and carrier and using a developing bias in which an AC component is superimposed on a DC component, the toner concentration detected by the toner concentration detecting means is within a predetermined range. In this case, the AC component of the developing bias is set to the reference value, while the AC component of the developing bias is corrected so that the image quality evaluation parameter falls within the allowable range when the predetermined range is exceeded. Therefore, it is possible to provide a developing device that can maintain good image quality.
Also, by using this developing device, it is possible to provide an image forming apparatus with stable image quality.

Hereinafter, the present invention will be described in detail based on embodiments shown in the accompanying drawings.
FIG. 2 shows an embodiment of an image forming apparatus to which the present invention is applied.
In the figure, the image forming apparatus in the present embodiment is a so-called tandem type color image forming apparatus, and each color component (for example, yellow (Y), magenta (M), The photosensitive drums 11 (11a to 11d) on which the cyan (C) and black (K) toner images are formed and supported are arranged on the intermediate transfer belt 20 in parallel.

  Around the photosensitive drum 11, a charging device 13 such as a charging roll for charging the photosensitive drum 11, an exposure device 14 including an LED array for forming an electrostatic latent image on the charged photosensitive drum 11, a photosensitive member, and the like. A developing device 12 (12a to 12d) that visualizes the latent image formed on the drum 11 with toner, and is provided at a position facing the photoconductor drum 11 and the intermediate transfer belt 20, with the photoconductor drum 11 therebetween. A primary transfer device 15 such as a transfer roll for transferring the upper toner image onto the intermediate transfer belt 20 is provided. Reference numeral 16 denotes a cleaning device such as a cleaning brush for cleaning residual toner on the photosensitive drum 11, and reference numeral 18 measures the image density of the toner image formed on the photosensitive drum 11. A density sensor 19 comprising an optical sensor is a potential sensor that measures the photosensitive member potential (charging potential, exposed portion potential) on the photosensitive drum 11.

  Further, the intermediate transfer belt 20 is stretched around three tension rolls 21 to 23, and circulates and moves in the direction of the arrow in the figure using the tension roll 22 as a drive roll, for example. In addition, a belt cleaner 24 for cleaning residual toner on the intermediate transfer belt 20 is located on the intermediate transfer belt 20 at a position facing the stretching roll 21 positioned on the upstream side of the photosensitive drum 11 a of the intermediate transfer belt 20. It is provided so that it can be touched and separated.

Further, in the apparatus main body 10, toner replenishing bottles 17 (17a to 17d) for replenishing the respective color toners to the developing devices 12 (12a to 12d) are provided, and the respective developing devices are connected via communication paths not shown. 12 can supply toner. For example, in the case where the developing device 12 is provided with a mechanism for collecting and discharging excess developer from the device itself, a developer that appropriately includes a carrier instead of the toner in the toner supply bottle 17 is used. May be.
Furthermore, in the present embodiment, a control device 50 is provided in the apparatus main body 10 for controlling the developing bias, which is a feature of the present case.

In the present embodiment, a paper feed cassette 25 that can supply paper S as a recording material is provided below the apparatus main body 10 so as to be able to be drawn out from the apparatus main body 10. Further, in the vicinity of the paper feed cassette 25, there are provided a pickup roll 26 for picking up the paper S from the paper feed cassette 25, a feed roll 27 and a retard roll 28 which are arranged opposite to the downstream side of the pickup roll 26, Only the uppermost sheet S is picked up by the picked up paper S and is conveyed to a predetermined paper conveyance path.
In addition, on the downstream side thereof, a registration roll 29 is provided that regulates the positioning of the sheet S that has been rolled and conveyed, and on the further downstream side, the toner image that has been primarily transferred onto the intermediate transfer belt 20 is disposed. A secondary transfer device 30 such as a secondary transfer roll that performs batch transfer onto the paper S is provided with the stretching roll 23 as a backup roll.

  Further, on the downstream side of the secondary transfer device 30, a fixing device 32 for fixing the toner image transferred onto the paper S is provided, and is constituted by a heating roll 32a and a pressure roll 32b, for example. ing. A discharge roll 31 is provided at one end of the apparatus main body 10 on the downstream side of the fixing device 32 to discharge the fixed sheet S to a discharge tray 10a provided on the casing surface of the apparatus main body 10. .

As shown in FIG. 3, the developing device 12 in the present embodiment stores a two-component developer containing toner and a magnetic carrier in a developing housing 41, and the photosensitive drum 11 is opened in an opening of the developing housing 41. A developing roll 42 is provided so as to face the developer.
The developing roll 42 of the present embodiment includes a rotatable non-magnetic developing sleeve 42a and a magnet body 42b that is fixedly disposed inside the developing sleeve 42a and has a plurality of magnetic poles. The photosensitive drum 11 rotates in the Against direction. Further, the magnet body 42b has a plurality of magnetic poles (S2, N3, S1, N1, N2) on the outer peripheral portion thereof, and provides the magnetic pole S1 at a position facing the photosensitive drum 11, while facing the magnetic pole S2. A trimmer 43 for regulating the amount of developer on the developing sleeve 42a is provided at the position.
Thus, in this embodiment, the magnetic pole N2 of the magnet body 42b is the pickup magnetic pole, the magnetic pole S2 is the trimming magnetic pole, the magnetic pole N3 is the transport magnetic pole, the magnetic pole S1 is the developing magnetic pole, and the magnetic pole N1 and the magnetic pole N2 are repulsive magnetic poles (pick-off magnetic poles). ). In the present embodiment, the arrangement and number of magnetic poles are not limited to this embodiment, and may be appropriately selected.

Further, in the present embodiment, a pair of augers 45 (45a, 45b) that stirs, conveys and charges the developer behind the developing roll 42 and supplies the developer to the developing roll 42, for example, supplies the auger 45a. The auger and auger 45b are provided as an admix auger.
Further, a toner concentration sensor (TC sensor) 46 for detecting the toner concentration of the developer in the developing housing 41 is attached to the developing housing 41 portion obliquely below the admix auger 45b. A magnetic sensor is used.

Here, the cross section of the pair of augers 45 as seen from above in FIG. 3 is as shown in FIG.
The supply auger 45a and the admixed auger 45b are provided with blades as shown in FIG. 4, and the supply auger 45a is provided with spiral blades 451 in the developer transport direction A over substantially the entire length. The blades 452 having different directions are provided in the portion, and a predetermined amount of toner is supplied to one end portion thereof from a toner supply device 70 described later via the communication port 48.
The admix auger 45b is provided with a spiral blade 453 extending substantially in the entire length in the developer conveyance direction B, and a blade 454 having a narrow interval in one direction is provided at one end.
Therefore, the toner replenished from the communication port 48 is mixed with the developer on the supply auger 45a side, immediately blocked by the blades 451 of the supply auger 45a, and guided to the admixing auger 45b side. Then, the mixing of the developer is promoted by the rotation of the admix auger 45b, and the developer is conveyed in the B direction.
The sufficiently mixed developer is blocked by the blades 454 of the admix auger 45b and conveyed to the supply auger 45a side.

  The TC sensor 46 provided on the admix auger 45b side is disposed in the vicinity of the upstream side of the position where the developer is transported from the admix auger 45b to the supply auger 45a side. The toner density can be detected.

In the present embodiment, a toner replenishing device 70 that supplies toner to the communication port 48 (see FIG. 4) is configured as shown in FIG.
In the figure, a reserve tank 71 is provided with two spiral coil augers 72 and 73, respectively, and the toner is circulated and conveyed in the direction of arrow E in the figure by these coil augers 72 and 73. ing. Further, on the upstream side of the coil auger 72, a toner insertion port 74 through which toner is introduced from the toner supply bottle 17 (see FIG. 2) into the reserve tank 71 is provided, and another coil auger 73 side on the downstream end side is provided. Is provided with a discharge portion 75 for supplying toner from the reserve tank 71 to the developing housing 41 (see FIG. 3). The discharge unit 75 is provided with an auger 76 having spiral blades, and the toner supplied to the discharge unit 75 is conveyed to the developing housing 41. Note that the developer conveyed by the auger 76 reaches the developing housing 41 (specifically, corresponding to the communication port 48 shown in FIG. 4) from one end 77 of the discharge portion 75 via the toner conveying path 80. Become.

  Further, in the toner replenishing device 70, a driving device 81 configured by, for example, a motor and a transmission gear for driving the two coil augers 72 and 73 and the auger 76 is provided outside the reserve tank 71. By turning ON / OFF the device 81, desired toner is supplied from the reserve tank 71 to the developing housing 41 side.

As shown in FIG. 3, in the developing device 12 in the present embodiment, a bias power source 47 is connected as a developing bias applying means to the developing sleeve 42a, and one end of the photosensitive drum 11 and the developing sleeve 42a are connected to the ground. A developing bias is applied between the two.
Further, as the developing bias in the present embodiment, an alternating current component is superimposed on a direct current component, and a sine wave shape is used as the alternating current component. However, the alternating current waveform is not particularly limited to this, and a triangular wave is used. Various shapes such as rectangular waves can be used. In this embodiment, the bias power supply 47 is controlled by the control device 50 (see FIG. 2) described above.

FIG. 6 shows circuit blocks around the developing device 12 and the control device 50 in the present embodiment. For simplicity, only one color developing device 12 is shown here. In the figure, the control device 50 includes information on the toner density in the developing device 12 from the TC sensor 46, information on the density of the patch pattern formed on the photosensitive drum 11 from the density sensor 18, and information from the potential sensor 19. Potential information on the photosensitive drum 11 (charging potential VH, exposure portion potential VL) is input.
On the other hand, the control device 50 drives the correction control for correcting the AC component of the bias power supply 47 that supplies the developing bias, and the driving device 81 (see FIG. 5) of the toner replenishing device 70 that replenishes toner into the developing device 12. A motor driving circuit 61 for controlling, a high voltage generating circuit 62 for applying a high voltage potential to the charging device 13 for supplying the charging potential VH of the photosensitive drum 11, and an exposure device 14 for supplying a latent image on the photosensitive drum 11. Supply control of an image signal (signal for image formation) and a patch pattern signal for checking the image density is performed on the exposure device drive circuit 63.

On the other hand, the circuit block described above is shown in more detail in the control block centered on the control device 50 as shown in FIG.
In the figure, the control device 50 according to the present embodiment includes a correction table in which a table value obtained from the relationship between the toner density and the AC component of the developing bias for maintaining an appropriate image quality is stored in advance. 51, a parameter table 52 storing development conditions (excluding AC components of development bias) for maintaining proper image quality on the photosensitive drum 11, the operating time of the toner supply device 70, the input image density, and the like are counted. A storage unit such as a counter 53 is provided, and arithmetic processing is performed by a CPU, for example, based on input information and information in the storage unit.
As input information of the control device 50, the toner density 54 from the TC sensor 46, the image density 55 from the density sensor 18 on the photosensitive drum 11 side, the photoreceptor potential 56 from the potential sensor 19, and the operation time of the toner replenishing device 70 are included. (Dispensing time) 57, image input information 58 such as input image density, and the like.
Based on these pieces of information, arithmetic processing is performed in the control device 50 to set a developing bias, a photosensitive member potential, a dispensing time, and the like.
Here, the developing bias includes a direct current component VDC and an alternating current component (including amplitude and frequency), both of which are controlled by the control device 50. The photosensitive member potential includes a charging potential VH and an exposed portion potential VL, and a DC component VDC of an appropriate developing bias is calculated from these values.

  In the present embodiment, an appropriate toner replenishment amount is obtained from the image input information 58, and toner replenishment control (ICDC: Image Coverage Dispense Control) for calculating and controlling a required dispense time is performed. The counter 53 is used to count input data from the dispense time 57 and the image input information 58 so that the next dispense time is set.

Next, a general operation of the developing device 12 in the present embodiment will be described.
The developer charged by the admix auger 45b and the supply auger 45a is supplied from the supply auger 45a onto the developing roll 42 by the pickup magnetic pole N2 of the magnet body 42b of the developing roll 42. The developer supplied onto the developing roll 42 is adsorbed and conveyed by the developing sleeve 42 a of the developing roll 42, and the developer that has passed through the trimmer 43 is adjusted to a predetermined amount, and a developing area that faces the photosensitive drum 11. To reach. In the development area, the development magnetic pole S1 makes the head rise sufficiently effectively, and the toner in the developer adheres to the latent image (image portion) on the photosensitive drum 11 by the development bias by the bias power source 47, and the toner image. As a visible image (development).
The developer that has passed through the developing zone is carried and conveyed along the rotation of the developing sleeve 42a as it is, and is collected from the developing sleeve 42a by the repulsive magnetic field of the pick-off magnetic poles N1 and N2, and returns to the supply auger 45a side.

In the operation of the developing device 12, the control flow in the present embodiment will be described in detail based on FIG.
Now, a case where only the amplitude of the AC component of the developing bias is varied will be described as follows. Here, Vpp is the amplitude of the AC component, Vpp ′ is the actual output value of the AC component, TC is the toner density, Dt is the dispense time per output sheet, and the Xero parameter is the development bias of various image forming conditions. It is a parameter excluding the AC component.
When the apparatus is turned on, setup of Vpp ′, Xero parameters, and Dt is started (for example, step S1). When TC (toner density) is detected, it is determined whether or not the obtained TC is within the range between the lower limit value TCmin and the upper limit value TCmax. At this time, the upper limit value and the lower limit value of the TC are calculated from the relationship between the output image quality and the TC. If the development bias is left as it is, if the upper limit value is exceeded, In particular, fogging, graininess, and banding are deteriorated. On the other hand, if the lower limit is not reached, carrier fogging, graininess is poor, and the developer is deteriorated (for example, steps S2 to S4).

  If the result of the determination is that TC is within the range, Vpp ′ is set to the standard Vpp (continues as it is if it is standard in advance), and if it exceeds the predetermined range, TC is set. The correction coefficient r is calculated based on the Vpp correction table corresponding to (for example, steps S5 to S8).

  Next, after outputting a density measurement patch for density measurement on the photosensitive drum and measuring the patch density by the density sensor, an appropriate photosensitivity is obtained from the Xero parameter calculation table (parameter table) based on the measurement result. The body potential (VH, VL) and the DC component VDC of the developing bias are calculated (for example, steps S9 to S12).

Thereafter, the toner dispensing time Dt is calculated based on the input area ratio counter integrated value C performed by the counter (for example, steps S13 and S14). At this time, the C value is the integrated value of the image area ratio of the input image (proportional to the product of the image size, the average area ratio, and the number of prints) in the print after the end of the previous setup.
Then, the input area ratio counter integrated value C is initialized, and the setup is completed (for example, steps S15 and S16).

In this embodiment, the above-described flow is performed when the power is turned on or when the cumulative print from the end of the previous setup reaches a specified value, so that the developing bias can be applied even if the toner density exceeds a predetermined value. Thus, the AC component is corrected, and the image quality can be maintained. Further, by performing such a flow for each color, color image quality can be improved.
Further, in the present embodiment, the amplitude of the AC component of the developing bias is changed, but the same effect can be obtained even if the frequency of the AC component is changed, and the amplitude and frequency are also changed. May be changed simultaneously.
Furthermore, in the present embodiment, an example is shown in which the toner dispensing time Dt is calculated by the input area ratio counter integrated value C (see steps S13 and S14 in FIG. 8) at the end of the setup cycle. Either can be used.

  In this example, the monochrome image is evaluated by the image forming apparatus of the above-described embodiment, and the relationship between the amplitude (amplitude of the AC component of the developing bias) and the toner density when a proper image is obtained when printing is repeated. Is confirmed. After that, the obtained relationship was made into a table, and the effect was confirmed with an apparatus for adjusting the amplitude with respect to the toner density. The specific conditions were as follows.

[1] Developer used A mixed powder of a polymerized toner having an average particle diameter (d50) of 6 μm and a carrier of ferrite particles coated with a fluororesin was used. The initial toner concentration was adjusted to 7% by weight.
[2] Adjustment Method Using the developer described above, a 20 kPV (20 k print) running using a pattern in which the image area ratio of the input image was changed was performed to obtain a Vpp correction table.
At the start, the amplitude Vpp of the AC component of the developing bias was 600 V and the frequency was 9 kHz. Further, the contrast between the non-image portion potential (background portion photoreceptor potential) and the DC component VDC of the developing bias is 120 V, and the contrast between the solid image portion potential (solid portion photoreceptor portion potential) and the developing bias DC component is 300 V. Set to.

At this time, for the output image, the amplitude of the AC component of the developing bias was changed, and the condition for maintaining the appropriate image quality was obtained by subjective evaluation. The image evaluation parameters for selecting an appropriate image quality are as follows.
(A) Graininess: The degree of influence due to graininess in the halftone portion was evaluated. When the graininess is deteriorated, a coarse image quality particularly in a halftone becomes conspicuous.
(B) Image density: The image density of the solid portion was evaluated.
(C) Fog: The degree of toner fog on the background portion was evaluated.
(D) BCO: The degree of influence by transfer of the carrier to the background portion and the high density portion was evaluated. When the transfer of the carrier becomes remarkable, the image quality is greatly deteriorated.
(E) Edge enhancement: The image density when a solid image (1 × 1 cm) with an area ratio of 100% was formed at the center of a halftone image (3 × 3 cm) with an area ratio of 50% was evaluated. If the edge emphasis becomes too high, the density of the halftone around the solid portion becomes noticeable and the image quality deteriorates.
(F) Banding: The influence of periodic density fluctuation of the developing roll appearing in a halftone was evaluated.

Under the above conditions, output of 20 kPV was performed and a Vpp correction table was obtained. When TCmax was exceeded by ΔTC or below ΔTC, the following correction coefficient r was used, It has been found that Vpp ′ = r × Vpp should be used as Vpp ′.
When TCmax is exceeded, the value r = 1 + k1 × ΔTC may be used as r. On the other hand, when the value falls below TCmin, the value r = 1−k2 × ΔTC is used as r. do it. Here, k1 and k2 are proportional constants.
Further, it has been found that the upper and lower limits of the toner concentration may be 8 wt% for TCmax and 6 wt% for TCmin.

Next, in order to confirm the effectiveness of the obtained correction count, among the above-described proportional constants, k1 is 0.25, k2 is 0.2, and a correction table that describes the relationship between TC and Vpp of the developer. Was stored in a control device of three devices (e.g., corresponding to the control device 50 of FIG. 2), and evaluation similar to the above-described conditions was performed. At this time, the AC component of the developing bias is automatically adjusted from the control device side of the apparatus. At this time, the setup cycle and the dispensing time per sheet were as follows.
(A) Setup cycle: This was performed at the start of a job after the power was turned on and the cumulative number of prints since the end of the previous setup exceeded 30 sheets. The density setup was performed during the inter-image, and the potential setup was performed when the fixing device was OFF.
(B) Dispensing time per sheet Dt: a value obtained by taking into consideration the area ratio and image size of the actual image from the toner consumption on the chart of the reference area ratio (specifically, the above-mentioned toner consumption Dispensing required to replenish the toner corresponding to the actual toner consumption by adding the correction corresponding to the output value of the toner density sensor to the value obtained by multiplying the ratio of the area ratio and the image size) time.

When the output images of the three devices were appropriately checked, it was confirmed that the image density and color did not change, the graininess was not deteriorated, and good image quality without fogging or carrier fogging could be maintained.
For comparison, when Vpp was kept constant and the same confirmation was performed, the image density and color did not change greatly, but granularity was observed at the initial 1000 sheets (1 kPV) and beyond 10 kPV. Deterioration was observed. Further, it was confirmed that fogging occurred from the initial stage up to 500 sheets. In addition, although these had no problem about several tens of sheets from the start, they started to occur after that.

This is because, for example, when several sheets are output from the start, the toner replenishment amount is reviewed in the setup cycle, and the toner density rapidly increases. At this time, in the embodiment, it is possible to maintain a good image quality by adjusting the amplitude of the AC component of the developing bias in accordance with the toner concentration, but in the comparative example, the toner concentration rapidly increases. On the other hand, if the setup is made, it cannot be followed and it is presumed that the image quality is affected as it is.
Further, after overlapping the number of output sheets, the toner density of the developer gradually changes and exceeds a predetermined range, so that it is difficult to maintain good image quality in the case of the comparative example. .

  Furthermore, when the same evaluation as described above was performed in a high temperature and high humidity environment, no problem was found under the conditions of the example. However, in the comparative example, the occurrence of carrier fog was confirmed when the pressure exceeded 15 kPV. It was.

Further, when the adjustment of the developing bias depending on the frequency of the AC component was also examined, it was confirmed that the same effect as that of the amplitude can be obtained if Vpp / r is used as Vpp ′.
From the above, the effectiveness of this case is understood. The amplitude and frequency of the AC component of the developing bias may be adjusted at the same time.
In this embodiment, the monochrome image is evaluated and confirmed in order to perform the image quality evaluation in detail. However, it can be said that a good image quality can be maintained for the color image by controlling each developing bias as described above. Not too long.

It is explanatory drawing which shows the outline | summary of the image development apparatus concerning this invention. 1 is an explanatory diagram showing an embodiment of an image forming apparatus to which the present invention is applied. It is explanatory drawing which shows the developing device of embodiment. It is explanatory drawing which shows the auger in the image development housing in embodiment. FIG. 4 is an explanatory diagram illustrating a toner supply device according to an embodiment. It is explanatory drawing which shows the circuit block of embodiment. It is explanatory drawing which shows the control block of embodiment. It is explanatory drawing which shows the control flow of embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Image carrier, 2 ... Development housing, 3 ... Developer carrier, 4 ... Development bias application means, 5 ... Toner density detection means, 6 ... Development bias adjustment means, 7 ... Developer supply means

Claims (6)

A developing housing disposed opposite to an image carrier on which an electrostatic latent image is carried and containing a two-component developer containing toner and a magnetic carrier;
A developer carrier that is provided in the development housing so as to be separated from the image carrier and carries a developer for developing an electrostatic latent image on the image carrier;
A developing bias applying means that is provided between the image carrier and the developer carrier and applies a developing bias in which an AC component is superimposed on a DC component that develops the electrostatic latent image on the image carrier;
Toner concentration detecting means for detecting the toner concentration of the developer in the developing housing;
When the toner density detected by the toner density detecting means is within a predetermined range, the AC component of the developing bias is set to a reference value, and when the toner density exceeds the predetermined range, the image quality evaluation parameter is set within an allowable range. A developing device comprising: a developing bias adjusting unit that corrects an alternating current component of the developing bias. The developing device according to claim 1,
The developing bias adjusting means corrects an alternating current component of the developing bias based on a correction condition obtained in advance. The developing device according to claim 1,
Furthermore, image density detection means for detecting the image density of an image visualized with toner in the developer,
And a control unit that adjusts development conditions other than the AC component of the development bias based on information from the image density detection unit. The developing device according to claim 1,
A developer replenishing means for replenishing a new developer in the developing housing;
A developing device characterized in that a new operating time of the developer replenishing means is set based on the accumulated information of the output image. The developing device according to claim 1,
The developing bias adjusting unit corrects at least one of the amplitude and frequency of the developing bias alternating current component. An image carrier for carrying an electrostatic latent image;
An image forming apparatus comprising: the developing device according to claim 1, wherein the electrostatic latent image on the image carrier is visualized.

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