JP5482084B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus.

  Generally, an electrophotographic method is used as an image forming method used in an image forming apparatus such as a copying machine or a printer. This is because an electrostatic latent image is formed by irradiating a photoconductor charged with a charger such as a corona discharger or a charging roll with a laser or LED array to form an electrostatic latent image. The electrostatic latent image is developed with a charged toner so as to be visualized.

On the other hand, an image forming apparatus that forms an electrostatic latent image without using a photosensitive member has already been proposed (see, for example, Patent Documents 1 to 5).
Patent Document 1 proposes an image forming apparatus of a type in which thin film transistors (TFTs) are formed in a matrix and storage capacitors are provided in the respective TFTs, and stable development is performed by a charge storage effect in the storage capacitors. It is.
Patent Document 2 proposes an image forming apparatus of a type in which switching elements are arranged in a matrix and laser irradiation is performed to change the surface potential generated for each pixel.
In Patent Document 3, each switching element arranged in a matrix has a storage capacitor divided into two layers to adjust the potential of the image / non-image part.
In Patent Document 4, if a charge is selectively applied to each of a plurality of pixel electrodes through a plurality of TFTs, or if the charges are selectively erased, the surface of the electrostatic latent image forming medium has a potential around it. An image forming apparatus in which electrostatic latent images having different potentials are formed is proposed.
Patent Document 5 proposes an image forming apparatus that forms a latent image for each pixel using switching elements arranged in a matrix.

Japanese Patent No. 3233463 (Example, FIG. 4) Japanese Patent No. 3826013 (Embodiment 1, FIG. 1) Japanese Patent Laying-Open No. 2003-32440 (Embodiment of the Invention, FIG. 1) Japanese Patent Laying-Open No. 2005-331955 (Best Mode for Carrying Out the Invention, FIG. 2) JP 2004-219635 A (Embodiment of the Invention, FIG. 1)

  The technical problem of the present invention is that, in an embodiment provided with an image carrier in which pixel electrodes are arranged, an electrostatic latent image having a high pixel density can be substantially scanned without changing the rotation speed of the image carrier. An object of the present invention is to provide an image forming apparatus capable of stably writing an electrostatic latent image while securing time.

The invention according to claim 1 has a support body that has a peripheral surface that is equal to or larger than the maximum image forming area and is capable of revolving around the support body, and a moving direction of the support body and a crossing direction that intersects the moving direction on the support body. Along the crossing direction of the image holding body by applying a scanning signal, an image holding body in which pixel electrodes are arranged in a matrix for each pixel unit, driving means for driving the image holding body to circulate, and a scanning signal A scanning operation of applying a latent image voltage based on an image signal to the pixel electrodes of each row is configured so that when the image holding body is moved around by the driving unit, the pixel electrodes of the image holding body are moved. Latent image writing means for writing a latent image based on the latent image voltage on an image holding member by performing a plurality of round scanning operations, and the latent image writing means performs a plurality of round scanning operations on the pixel electrode. For each lap An image forming apparatus and applying superimposed latent voltage based on the same image signal in one pixel electrode position.

The invention according to claim 2 has a support body that has a peripheral surface that is equal to or larger than the maximum image forming region and is capable of revolving around the support body, and a moving direction of the support body and a crossing direction intersecting the moving direction on the support body. Along the crossing direction of the image holding body by applying a scanning signal, an image holding body in which pixel electrodes are arranged in a matrix for each pixel unit, driving means for driving the image holding body to circulate, and a scanning signal A scanning operation of applying a latent image voltage based on an image signal to the pixel electrodes of each row is configured so that when the image holding body is moved around by the driving unit, the pixel electrodes of the image holding body are moved. Latent image writing means for writing a latent image based on the latent image voltage on an image holding member by performing a plurality of round scanning operations, and the latent image writing means performs a plurality of round scanning operations on the pixel electrode. For each lap An image forming apparatus, characterized in that varying the pixel electrode row to be査.
According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect , the latent image writing unit is configured to hold the image by the driving unit when performing a plurality of scanning operations on the pixel electrode. The image forming apparatus is characterized in that the image forming apparatus performs a scanning operation on the pixel electrodes in the corresponding row in a direction opposite to the rotation direction of the image holding member and at a speed equal to the rotating speed of the image holding member.
According to a fourth aspect of the present invention, in the image forming apparatus according to any one of the first to third aspects, the latent image writing unit includes a first writing system that performs a plurality of round scanning operations on the pixel electrode ; The second writing method for performing a single round scanning operation on the pixel electrode has a selection means that can be selected, and the first writing method or the second writing is selected according to the selection result by the selection means. An image forming apparatus that performs any one of the methods.
According to a fifth aspect of the present invention, in the image forming apparatus according to the first or second aspect , the latent image writing unit scans at least the first first round when performing a plurality of rounds of scanning operation on the pixel electrode. In the image forming apparatus, the scanning operation is performed in a state where driving of the image holding member by the driving unit is stopped during the operation.

According to a sixth aspect of the present invention, in the image forming apparatus according to any one of the first to fifth aspects, the latent image writing unit includes a pixel density selection unit capable of selecting a plurality of pixel densities for the pixel electrode , An image forming apparatus that performs a scanning operation on a pixel electrode based on a pixel density selected by the pixel density selection unit.
According to a seventh aspect of the present invention, in the image forming apparatus according to the sixth aspect , the latent image writing unit performs a scanning operation on the pixel electrode when a low pixel density is selected by the pixel density selection unit. In doing so, the image forming apparatus is characterized in that the pixel electrode rows to be scanned are thinned out.
The invention according to claim 8, in an image forming apparatus according to claim 4, wherein the latent image writing means, when writing a plurality of the same latent image on the image carrier, the pixel electrode during writing a latent image for the first time An image is characterized in that a first writing method for performing a scanning operation for a plurality of rounds is adopted, and a second writing method for carrying out a scanning operation for a single round with respect to the pixel electrode is adopted for the second and subsequent times. Forming device.
According to a ninth aspect of the present invention, in the image forming apparatus according to the eighth aspect , when the latent image writing unit writes a plurality of latent images whose partial changes are made on the image holding member, an initial latent image is formed. Adopting a first writing method for performing a scanning operation for a plurality of rounds on the pixel electrode at the time of writing, adopting a second writing method for performing a scanning operation for a single round on the pixel electrode , and In the image forming apparatus, the scanning time for the pixel electrode row for the changed latent image portion is lengthened.

The invention according to claim 10 develops an image forming apparatus according to any one of claims 1 to 9, an electrostatic latent image on the image holding member that has been written by the image writing means in the image forming material development An image forming apparatus comprising: a transfer unit configured to transfer a visible image made of an image forming material formed on the image carrier by the developing unit to a transfer medium.
According to an eleventh aspect of the present invention, in the image forming apparatus according to the tenth aspect , the transfer means applies a transfer voltage based on an image signal to each of the pixel electrodes and is developed by the developing means. An image forming apparatus is characterized in that a transfer electric field transferred to a transfer medium is applied to an image.
The invention according to claim 12, in the image forming apparatus according to claim 10, further comprising a cleaning means for cleaning the image forming material remaining on the image carrier, the cleaning means, the pixel electrodes each in the image The image forming apparatus is characterized in that a cleaning electric field for cleaning the image holding member is applied to the image holding member that has been transferred by applying a cleaning voltage based on a signal.

According to the first aspect of the present invention, in the aspect including the image carrier in which the pixel electrodes are arranged, an electrostatic latent image having a high pixel density can be substantially obtained without changing the rotation speed of the image carrier. Besides it is possible to write an electrostatic latent image stably by securing the do scanning time, as compared with the case where the present constitution is not provided, it is possible to increase the substantial scan time by multiple orbiting minute.
According to the second aspect of the present invention, in an aspect including the image carrier in which the pixel electrodes are arranged, an electrostatic latent image having a high pixel density can be substantially obtained without changing the rotation speed of the image carrier. In addition to ensuring stable scanning time and stable writing of electrostatic latent images, as the number of pixel electrodes scanned in one round is reduced as compared with the case without this configuration, the number of pixel electrodes per round is reduced. The substantial scanning time can be increased.
According to the third aspect of the present invention, compared to the case without this configuration, the pixel electrodes in each row can be scanned at a predetermined position, and the written latent image is visualized. The degree of attenuation of the latent image potential during the movement to the developing site can be made uniform, and the latent image potential at the developing site can be stabilized.
According to the fourth aspect of the invention, it is possible to select a plurality of round scanning operations for the pixel electrode of the image carrier as required.
According to the invention which concerns on Claim 5 , the frequency | count of a circumference | surroundings of an image holding body can be reduced, and deterioration, such as abrasion of the various functional components and mechanism parts accompanying the circumference | surroundings of an image holding body, can be suppressed.
According to the sixth aspect of the invention, it is possible to write a latent image on the image holding body according to a plurality of image densities.
According to the seventh aspect of the invention, in the latent image writing process, a latent image with a high pixel density is used at the same speed as the latent image writing process with a low pixel density without using a latent image writing speed switching mechanism. Write processing can be realized.
According to the eighth aspect of the present invention, it is possible to shorten the latent image writing processing time when a plurality of the same latent images are written on the image holding member as compared with the case where this configuration is not provided.
According to the ninth aspect of the present invention, it is possible to reduce the latent image writing processing time when writing a plurality of partially changed images on the image holding member as compared with the case where this configuration is not provided. .
According to the tenth aspect of the present invention, prior to development and transfer, in an aspect provided with an image carrier in which pixel electrodes are arranged, an electrostatic image with a high pixel density can be obtained without changing the rotation speed of the image carrier. As for the latent image, it is possible to stably write the electrostatic latent image while securing a substantial scanning time.
According to the eleventh aspect of the present invention, it is possible to efficiently realize the transfer operation for each pixel unit by using the pixel electrode of the image carrier as compared with the case where this configuration is not provided.
According to the twelfth aspect of the present invention, it is possible to efficiently realize the cleaning operation for each pixel unit by using the pixel electrode of the image carrier as compared with the case where this configuration is not provided.

(A) is explanatory drawing which shows the outline | summary of embodiment of the image forming apparatus to which this invention was applied, (b) is explanatory drawing which shows the structural example of the image holding body used with the image forming apparatus shown to (a). is there. 1 is an explanatory diagram illustrating an overall configuration of an image forming apparatus according to a first embodiment. (A) is a perspective explanatory view showing an image carrier used in Embodiment 1, and (b) is an explanatory view showing a configuration example of a TFT as a drive element for driving a pixel electrode used in (a). (A) is explanatory drawing which shows the example of the electric power feeding structure of the image holding body used by Embodiment 1, (b) is explanatory drawing which shows the structural example of a slip ring. (A) is explanatory drawing which shows the example of an arrangement | sequence of the pixel electrode of the image carrier used in Embodiment 1, (b) is explanatory drawing which shows the one pixel electrode, (c) is the example of wiring to a pixel electrode It is explanatory drawing shown. 3 is an explanatory diagram illustrating a configuration of a pixel electrode panel used in Embodiment 1. FIG. 3 is an explanatory diagram illustrating an example of a developing device used in Embodiment 1. FIG. (A) and (b) are explanatory views showing an example of a conductive toner used in the developing device shown in FIG. 3 is an explanatory diagram illustrating an example of an image writing control device used in Embodiment 1. FIG. FIG. 3 is an explanatory diagram showing a gradation method used in Embodiment 1. (A) shows a gradation conversion signal when the image signal is gradation-converted in the first embodiment, (b) shows a generation signal for setting a latent image voltage, and (c) shows a set latent signal. It is explanatory drawing which shows a mode that the image voltage was allocated to the pixel electrode. 6 is a flowchart showing the contents of a latent image writing mode determination process performed by the image writing control apparatus used in the first embodiment. (A) is explanatory drawing which shows the scanning example at the time of high pixel density, (b) is explanatory drawing which shows the scanning example at the time of low pixel density. (A) is explanatory drawing which shows the example of scanning operation | movement with respect to a pixel electrode, (b) is the example of scanning operation of (a) of the latent image electric potential accumulate | stored in a pixel electrode in the 1st round, the 2nd round, and the 3rd round. It is explanatory drawing which shows a change state. It is explanatory drawing which shows typically the scanning operation | movement when producing n sheets of the different images or the same image. FIG. 10 shows a first modification of the latent image writing method used in the first embodiment, where (a) is an explanatory diagram schematically showing a job for producing n partially changed images, and (b) is a part of FIG. It is explanatory drawing which shows typically the scanning operation | movement when producing n sheets of the changed images. FIG. 10 is an explanatory diagram showing a second modification of the latent image writing method used in the first embodiment. FIG. 9 shows a third modification of the latent image writing method used in the first embodiment, where (a) shows an example of the first round scanning operation, and (b) shows an example of the second and third round scanning operations. FIG. FIG. 6 is an explanatory diagram illustrating an overview of an image forming apparatus according to a second embodiment. 6 is an explanatory diagram illustrating an example of an image writing control device used in Embodiment 2. FIG. It is explanatory drawing which shows the time responsiveness of CR circuit represented as an equivalent circuit around the pixel electrode used in an Example. In an Example, it is explanatory drawing which shows the relationship between the charge time constant of a-SiTFT, and a process speed. In an Example, it is explanatory drawing which shows the time responsiveness at the time of forming a latent image electric potential in 3 times. In an Example, it is explanatory drawing which shows the time responsiveness of the latent image electric potential when producing the same image several sheets.

Outline of Embodiment FIG. 1A shows an outline of an embodiment of an image forming apparatus to which the present invention is applied, and FIG. 1B is an explanatory view showing a configuration example of an image carrier.
In the figure, the image forming apparatus has a support 1a having a peripheral surface that is larger than the maximum image forming area and is capable of moving around, and on the support 1a, the moving direction of the support 1a and the moving direction intersect. An image holding body 1 in which pixel electrodes 1b are arranged in a matrix for each pixel unit along the intersecting direction, driving means 2 that drives the image holding body 1 to move around, and a scanning signal to give the image. A scanning operation of applying a latent image voltage based on an image signal to the pixel electrodes 1b in each row along the intersecting direction of the holding body 1 is configured to be capable of being scanned, and the image holding body 1 is moved around by the driving unit 2. And a latent image writing means 3 for writing a latent image by the latent image voltage to the image holding body 1 by performing a plurality of rounds of scanning operation on the pixel electrode 1b of the image holding body 1. It is. In the present embodiment, the surface of the image carrier 1 is provided with a protective layer 1c for maintaining insulation between the pixel electrodes 1b.
Further, as this type of image forming apparatus, normally, developing means 6 for developing the electrostatic latent image of the image carrier 1 written by the latent image writing means 3 with an image forming material, and this developing means 6 Transfer means 7 for transferring a visible image made of the image forming material formed on the image holding body 1 to the transfer medium 9, and further, a cleaning means for cleaning the image forming material remaining on the image holding body 1. 8 is often provided. The transfer medium 9 here is not limited to the final recording material such as paper, but also includes an intermediate transfer member.

In such technical means, the image carrier 1 may be in the form of a drum or a belt as long as it moves around.
Further, since the support 1a needs a scanning operation of a plurality of rounds in order to be able to form a maximum size image, it needs to have a peripheral surface that is equal to or larger than the maximum image forming region.
Furthermore, the pixel electrode 1b only needs to be arranged in a matrix in the moving direction of the support 1a and the intersecting direction intersecting the moving direction, and the arrangement density corresponds to a pixel density that can be formed.
The driving means 2 may be appropriately selected as long as it moves the image carrier 1 in a circular manner. Usually, the rotational speed v of the image carrier 1 is adjusted to a predetermined image forming process speed. Any device that drives the image carrier 1 may be used. However, in a mode in which a plurality of image forming process speeds can be selected, the rotation speed v of the image carrier 1 may be changed according to each.
Furthermore, the latent image writing unit 3 needs to be capable of performing a plurality of rounds of scanning operation on the pixel electrode 1b of the image carrier 1. At this time, the latent image writing timing includes a development process for visualizing the normally written electrostatic latent image and a transfer process for transferring the developed visible image to the transfer medium 9. Since the image process is continuously performed after the latent image writing process, it is necessary that the timing includes at least the timing of rotating the image holding member 1 by the driving unit 2. However, it is not always necessary to move the image carrier 1 around the entire scanning operation of a plurality of turns (for example, k turns).
The significance of the scanning operation is “applying a latent image voltage based on an image signal to pixel signals in each row along the crossing direction by applying a scanning signal”.

Next, typical aspects of the latent image writing unit 3 will be described.
Applying latent Representative aspects of the writing section 3, carrying out the scanning operation of the plurality orbit relative to the pixel electrode 1b, overlapping the latent image voltage based on the same image signal to the same pixel electrode 1b located in each cycle To do. As described above, when the latent image voltage based on the same image signal is applied to the same pixel electrode 1b in each round as a scanning operation, the application time of the latent image voltage is substantially increased correspondingly, and the pixel electrode 1b A stable potential stored in the capacitor is obtained.
Further, as another typical mode of the latent image writing means 3, there is a method in which the pixel electrode rows to be scanned are different for each rotation when the pixel electrode 1b is scanned a plurality of times. In this mode, the number of pixel electrodes 1b scanned in one round is reduced, and a substantial scanning time is secured as compared with a system in which scanning operation is performed on all the pixel electrodes 1b in one round. Is intended.
Further, although the latent image potential written on the pixel electrode 1b of the image carrier 1 is gradually attenuated, the degree of attenuation of the latent image potential up to the development site by the developing means 6 is made substantially equal. In this case, the latent image writing unit 3 causes the driving unit 2 to rotate the image holding body 1 a plurality of times when the pixel electrode 1b is scanned a plurality of times. It is preferable that the scanning operation is performed on the pixel electrodes 1b in the corresponding row at a speed opposite to the rotational speed of the image carrier 1 in the opposite direction.

Further, as the latent image writing unit 3, a method of stopping the driving of the image carrier 1 during the writing operation by the latent image writing unit 3 may be employed. Considering that the transition to the developing process, which is the next image forming process, is made smoother with respect to the electrostatic latent image, at least the first round of scanning operation is performed for the pixel electrode 1b. The scanning operation may be performed in a state in which the driving of the image holding body 1 by the driving means 2 is stopped during the scanning operation, and the image holding body 1 is driven by the driving means 2 at the end of writing of the electrostatic latent image. Is preferably driven so as to move around at a speed of the image forming process.
Moreover, typical embodiments of the latent image writing unit 3, the implement and the first write strategy for implementing the scanning operation of the plurality orbit relative to the pixel electrode 1b, the scanning operation of the single lap with respect to the pixel electrode 1b There is a selection unit 4 that can select one of the two writing methods, and performs either the first writing method or the second writing method according to the selection result by the selecting unit 4. .
The latent image writing unit 3 may always perform a plurality of rounds of scanning operation. However, for example, when forming a latent image based on an image signal having a low pixel density, a plurality of rounds of scanning operation is performed. In consideration of the fact that it is not always necessary, selection means 4 for selecting as necessary is added.

Further, as a preferable aspect of the latent image writing unit 3, the pixel image selection unit 5 includes a pixel density selection unit 5 that can select a plurality of pixel densities for the pixel electrode 1b, and is based on the pixel density selected by the pixel density selection unit 5. For example, the pixel electrode 1b may be scanned.
This is effective for forming images with different pixel densities because it has a configuration for selecting a plurality of pixel densities.
In the embodiment in which the pixel density selection unit 5 is added, the latent image writing unit 3 performs a scanning operation on the pixel electrode 1b when a low pixel density is selected by the pixel density selection unit 5. In doing so, the row of pixel electrodes 1b to be scanned may be thinned out. In this case, by thinning out the row of pixel electrodes 1b to be scanned, image information is removed by the thinned scanning lines.

Moreover, as a preferable mode when writing a plurality of the same latent images, the latent image writing means 3 is configured to write a plurality of latent images to the pixel electrode 1b when writing the same latent images on the image holding body 1 at the first writing of the latent images. A first writing method that performs a circular scanning operation is adopted, and a second writing method that performs a single circular scanning operation on the pixel electrode 1b is used after the second time.
This is a preferable mode based on a mode in which the first writing method and the second writing method are selected. When the latent image is written by the first writing method at the time of the first latent image writing, 2 Since the latent image potential formed at the first time remains after the first time, it is sufficient to compensate for the potential decay, and the first writing method is sufficient.
In addition, as a preferable mode when writing a plurality of partially changed images, the latent image writing unit 3 performs the initial latent image writing on the image holding body 1 when a plurality of partially changed latent images are written. A first writing method for performing a scanning operation for a plurality of rounds on the pixel electrode 1b at the time of image writing is employed, and a second writing method for performing a scanning operation for a single round on the pixel electrode 1b is employed thereafter. In addition, the scanning time for the pixel electrode 1b row for the changed latent image portion is increased.
This is because if the latent image is written by the first writing method at the time of writing the first latent image, the latent image potential formed at the first time remains after the second time. In this case, the scanning time is secured only for the changed latent image portion, and the scanning operation is performed once.

The developing unit 6, the transfer unit 7, and the cleaning unit 8 may be appropriately selected. For example, the pixel electrode 1b on the image carrier 1 may be used for the transfer unit 7 and the cleaning unit 8. .
In this case, the transfer unit 7 applies a transfer voltage based on the image signal to each of the pixel electrodes 1b, thereby applying a transfer electric field for transferring the visible image developed by the developing unit 6 to the transfer medium 9. What should I do? The cleaning means 8 applies a cleaning voltage based on the image signal to each of the pixel electrodes 1b so that a cleaning electric field for cleaning the image holding body 1 is applied to the image holding body 1 that has been transferred. do it.

Hereinafter, the present invention will be described in more detail based on embodiments shown in the accompanying drawings.
Embodiment 1
FIG. 2 shows Embodiment 1 of an image forming apparatus to which the present invention is applied.
<Overall configuration of image forming apparatus>
In the figure, the image forming apparatus of the present embodiment is a so-called tandem type color image forming apparatus, and each color component (for example, yellow (Y), magenta (M)) is formed in the apparatus housing 15 by, for example, electrophotography. , Cyan (C) and black (BK) toner image bodies 20 (20a to 20d) on which toner images are formed are arranged in parallel in a substantially vertical direction, and circulate and rotate in opposition to these image carriers 20. An intermediate transfer belt 50 serving as a transfer medium is stretched in a substantially vertical direction, and the color toner images on the image carrier 20 are multiplexed on the intermediate transfer belt 50.

In the present embodiment, a developing device 40 that develops an electrostatic latent image formed on the image holding body 20 with a toner into a visible image around the image holding body 20, and the image holding body 20 And a cleaning device 62 for cleaning the remaining toner, and the toner image on the developed image carrier 20 is transferred to the intermediate transfer belt at a position opposite to the image carrier 20 and the intermediate transfer belt 50. A transfer unit 63 for transferring to 50 is provided. Reference numeral 41 denotes a developing roll for supplying toner directly to the image carrier 20 in the developing device 40.
On the other hand, the intermediate transfer belt 50 is stretched around a plurality of stretching rolls 51 to 53 (three in this example), and circulates and rotates using, for example, the stretching roll 51 as a driving roll. On the surface side of the belt 50, a secondary transfer device 60 is provided at a position facing the stretch roll 53 and the intermediate transfer belt 50, and a multiple toner image multiplexed on the intermediate transfer belt 50 is recorded later. A batch transfer is performed on the recording material supplied from the material supply device 70. At this time, the secondary transfer device 60 is configured such that a predetermined secondary transfer bias is applied between the tension roll 53 as a backup roll.

A recording material supply device 70 that supplies a recording material is provided below the apparatus housing 15. For example, one recording material accommodated in a supply container 71 is supplied by a supply roll 72 and a separating mechanism 73. It is supplied to the recording material conveyance path 74 extending in the vertical direction every time.
The recording material supplied from the recording material supply device 70 to the recording material conveyance path 74 is once aligned by an alignment roll (registration roll) 75 disposed on the downstream side of the recording material conveyance path 74. The sheet is conveyed to the downstream secondary transfer device 60 side at a predetermined timing. Thereafter, the multiple toner images on the intermediate transfer belt 50 are collectively transferred onto the recording material at the secondary transfer portion by the secondary transfer device 60, and the toner image is fixed by the fixing device 76, and then discharged from the discharge roll 77 to the device housing. The recording material is discharged to a recording material discharge receiver 16 constituted by a part of the body 15. Needless to say, the recording material conveyance path 74 is appropriately provided with a conveyance member (for example, a conveyance roll) 78 for conveying the recording material.

<Image carrier>
Next, the image carrier 20 used in the present embodiment will be described in detail.
As shown in FIG. 3A, the image carrier 20 in the present embodiment has a large number of pixel electrodes 34 (see FIG. 3B) on a rigid drum 21 that is a rotatable support. The pixel electrode film 30 formed in a matrix arrangement (so-called matrix) is wound and fixedly supported.
In this example, the pixel electrode film 30 is produced by using a thin film technology used in a so-called IC manufacturing process or the like for a heat-resistant PET (polyester resin) film substrate 301, for example, and the pixel electrodes 34 are arranged in a matrix. It has become. For example, the pixel electrodes 34 arranged in a matrix form a data line in the direction along the rotation axis direction of the rigid drum 21 and a scan line in the direction along the rotation direction of the rigid drum 21. Therefore, an appropriate number of data drivers 31 and scanning drivers 32 connected to each pixel electrode 34 are provided on the data lines and scanning lines of the pixel electrode film 30, and input lines to these drivers 31 and 32 are provided. Are further integrated and wired through the pixel electrode film 30 to the inner surface side of the rigid drum 21 when the number is reduced.
In FIG. 3B, reference numeral 302 denotes a surface protective layer that protects each pixel electrode 34 and peripheral components so as to ensure mutual insulation between the pixel electrodes 34 on the film substrate 301. For example, silicon oxide is used as the surface protective layer 302.

-Power supply structure-
As shown in FIG. 3A, the rigid drum 21 is provided with a groove 21 a along the rotation axis direction on a part of its outer peripheral surface, and at the center of the axis of the rigid drum 21, the pixel electrode film 30 and A slip ring 24 is provided as a power supply member for electrical connection with the outside, and the rigid drum 21 rotates around the fixed slip ring 24.
Further, as shown in FIGS. 3A and 4A and 4B, an appropriate number of terminals 22 are provided on the inner peripheral surface side of the rigid drum 21 along the rotation axis direction of the rigid drum 21. These terminals 22 are connected to the data driver 31 and the scanning driver 32 of the pixel electrode film 30, respectively. Further, these terminals 22 are provided with sliders 23 extending in the direction of the center of the rotation axis and in the directions in which the respective end portions are separated from each other, and are connected to the terminals 22. A current collecting ring 24a is attached. The current collecting ring 24a portion of the slip ring 24 is smaller in diameter than the insulating rings 24b on both sides, and the slider 23 is always in contact with the facing current collecting ring 24a even when the rigid drum 21 rotates. It is like that. The groove 21a of the rigid drum 21 is closed with, for example, a seal tape, so that the resistance of the air current when the image carrier 20 rotates is reduced and the influence of toner during development is prevented. ing.
Therefore, signal transmission between the pixel electrode film 30 and the outside is performed from the lead wire 25 wired in the slip ring 24 corresponding to the current collection ring 24 a of the slip ring 24 via the current collection ring 24 a and the slider 23. This is performed between the pixel electrode film 30 and the signal transmission with the pixel electrode film 30 can be appropriately performed even if the rigid drum 21 rotates.

-Drive system-
The driving method of the image carrier 20 may be appropriately selected as long as the driving force from a driving source (not shown) (for example, a driving motor) is transmitted to the rigid drum 21 via the driving transmission mechanism.
In this case, the image carrier 20 is configured to move around at a speed that matches a predetermined image forming process speed. For example, in an aspect in which the image forming process speed can be variably adjusted, It moves around at the image forming process speed.
Here, the driving method of the rigid drum 21 is not particularly limited, and for example, the outer peripheral surface end portion side of the rigid drum 21 may be rotationally driven by being brought into pressure contact with the rotating roll, or the insertion side of the slip ring 24 may be May have a rotating shaft for rotating the rigid drum 21 itself on different sides.

-Peripheral structure of pixel electrode-
Next, the peripheral structure of the pixel electrode of the pixel electrode film 30 will be described.
In the present embodiment, as shown in FIGS. 3B and 5A, the pixel electrode film 30 has pixel electrodes 34 arranged in a matrix, and each pixel electrode 34 is shown in FIG. As shown in the figure, it is configured by a so-called active matrix system, and for example, a TFT (Thin Film Transistor) 33 is used as a switching element, and a storage capacitor 35 and wiring (source line Ls, gate line Lg, etc.) are added thereto.
Here, as shown in FIG. 3B, the basic structure of the TFT 33 is that an a-Si (amorphous silicon) channel layer 332 is stacked on the gate GT via a gate insulating film 331, and this channel layer 332 is formed. A source ST and a drain DT are arranged on the top with a predetermined interval d. The resistance adjustment of the TFT 33 increases the resistance by increasing the distance d between the source ST and the drain DT, and decreases the resistance by increasing the depth dimension between the source ST and the drain DT. It is performed appropriately based on the above.
The connection between each pixel electrode 34 and the pixel electrode 34 is summarized as a source line Ls to which the source ST of the TFT 33 is connected for each data line, and a gate line Lg to which the gate GT of the TFT 33 is connected for each scanning line. Yes. A pixel electrode 34 and a storage capacitor 35 are connected in parallel to the drain DT of the TFT 33, and one of the storage capacitors 35 is grouped for each scanning line (not shown), and an equivalent circuit as shown in FIG. It is configured to present.

Since the pixel electrode film 30 has a configuration in which a large number of the pixel electrodes 34 are arranged in this way, the driving method is performed as follows.
That is, in the pixel electrode film 30, as shown in FIG. 6, a predetermined number of pixel electrodes 34 are collected for each data line and scanning line, and the source ST side of the TFT 33 is connected to the data driver 31 for each data line. On the other hand, the gate GT side of the TFT 33 is connected to the scanning driver 32 for each scanning line, and the data driver 31 and the scanning driver 32 are connected to the image writing control device 100 (for details, provided in the image forming apparatus). (Described later). Therefore, by driving the data driver 31 and the scanning driver 32, a predetermined latent image voltage is applied to a predetermined pixel electrode.
Here, the data driver 31 includes, for example, a shift register with a sample hold, a latch, a buffer, and the like, and the scanning driver 32 includes, for example, a counter, a latch, a buffer, and the like. Although the pixel electrode 34 is omitted in FIG. 6, it goes without saying that the pixel electrode 34 is connected between the TFT 33 and the storage capacitor 35 as shown in FIG.

<Developer>
-Example configuration of the developer-
In the present embodiment, the developing device 40 employs a configuration using conductive toner as the toner.
For example, as shown in FIG. 7, the developing device 40 in the present embodiment has a developing container 40 a that stores conductive toner (hereinafter abbreviated as toner as appropriate), and the developing container 40 a includes an image carrier 20. A developing opening 40b is formed to face the developing opening 40b, and a developing roll 41 that faces the developing opening 40b and is spaced apart from the image carrier 20 and rotates in the same direction (With) at the opposite portion is disposed. The developing roll 41 is caused by an electric field effect caused by the latent image potential of the bias power supply 90 and the pixel electrode 34 applied between the image holding body 20 and the developing roll 41 at the development position Pd where the holding body 20 and the developing roll 41 face each other. The upper toner moves toward the image carrier 20. The developing roll 41 of the present embodiment is set to rotate at 1 to 2 times the peripheral speed of the image carrier 20.

  Further, on the side of the developing roll 41 different from the image holding body 20, an intermediate roll 42 is provided as an intermediate toner holding body that holds and conveys charged conductive toner, facing the developing roll 41. . In the present embodiment, the intermediate roll 42 rotates in different directions (Against) at a portion facing the developing roll 41, and its peripheral speed is 1.2 to 2 times the peripheral speed of the developing roll 41. It is set to be. Further, by applying a predetermined moving bias between the intermediate roll 42 and the developing roll 41 by a bias power source 91, a moving electric field acts on a moving region where the intermediate roll 42 and the developing roll 41 face each other, and the intermediate roll 42 The toner on 42 is easily moved to the developing roll 41.

  Further, a charge injection roll 43 as a charge injection member capable of injecting charges into uncharged toner is provided at a position facing substantially above the intermediate roll 42. The charge injection roll 43 according to the present embodiment is configured by a roll member made of metal such as aluminum or stainless steel, for example, and a predetermined charge injection bias is applied to the intermediate roll 42 by a bias power source 92, thereby A charge injection electric field is applied to the charge injection region where the injection roll 43 and the intermediate roll 42 face each other. Further, the charge injection roll 43 rotates in the same direction (With) at a portion facing the intermediate roll 42, and the peripheral speed is 1.5 to 2.5 times the peripheral speed of the intermediate roll 42. It has become.

  Further, in the developing device 40 of the present embodiment, in order to supply toner to the intermediate roll 42, a toner supply roll 44 having a conductive foam roll configuration made of, for example, polyurethane resin or the like is provided with the intermediate roll 42 from the charge injection roll 43. Are arranged opposite to the intermediate roll 42 at positions upstream in the rotation direction, and are provided so as to rotate in different directions (Against) at portions facing the intermediate roll 42. Further, the toner supply roll 44 is set to rotate at a peripheral speed that is 0.3 to 1.0 times the peripheral speed of the intermediate roll 42. In this embodiment, the toner supply roll 44 and the intermediate roll 42 are electrically short-circuited. Therefore, even if the surface of the intermediate roll 42 is charged between the charge injection roll 43 and the intermediate roll 42, the action of making the potentials of the toner supply roll 44 and the intermediate roll 42 uniform becomes effective, and the surface of the intermediate roll 42 is charged. An effect of suppressing, that is, a charge eliminating effect is activated, and toner attached on the intermediate roll 42 can be cleaned, and the toner supply roll 44 performs a refresh function of the intermediate roll 42.

  Then, a layer restriction that restricts the toner supplied from the toner supply roll 44 to the intermediate roll 42 and forms a layer between the toner supply roll 44 and the charge injection roll 43 facing each other with respect to the intermediate roll 42. A layer regulating blade 45 as a member is provided. This layer regulating blade 45 is made of a plate spring member such as stainless steel or phosphor bronze having a thickness of 0.05 to 0.2 mm, for example, and is fixed to the free end side of the support member 45a whose one end is fixed to the developing container 40a. It has come to be supported. In particular, the layer regulating blade 45 is provided so that the surface on the free end side is pressed against the intermediate roll 42 with a predetermined pressing force, and the layer regulation blade 45 is layered without excessively scraping off the toner on the intermediate roll 42. The effect of arranging can be further demonstrated. The layer regulating blade 45 is not particularly limited as long as the toner can be layered, and an elastic body may be provided on the surface of the plate spring member.

  On the other hand, a refresh roll 46 made of, for example, an aluminum metal roll is provided so as to come into contact with the development roll 41 between the development position Pd of the development roll 41 and the intermediate roll 42 downstream. Then, by grounding the refresh roll 46, the residual toner on the developing roll 41 is electrostatically removed and the charge removing function on the surface of the developing roll 41 is achieved. Further, the refresh roll 46 is provided with a metal blade (not shown) so as to collect the toner adhering to the refresh roll 46. Here, the refresh roll 46 is not limited to a metal roll, and for example, a brush using conductive fibers may be used. Reference numeral 48 in the drawing denotes an agitator as a toner supply member that supplies toner to the toner supply roll 44 while stirring the toner in the developing container 40a.

-Constitution example of conductive toner-
The conductive toner used in the present embodiment has a conductive toner base (conductive core) 81 made of a conductive material, as shown in FIG. 8A, for example. The periphery of 81 is covered with an insulating coating layer (for example, an insulating resin layer) 82, and the insulating coating layer 82 is provided with an appropriate number of recesses 83 so that a part of the conductive core 81 is exposed. It is done. The conductive toner can be produced by a polymerization method or various known encapsulation techniques. At this time, the conductive core 81 is a particle made of polyester resin, styrene acrylic resin, or the like in which a conductive agent such as conductive carbon or transparent conductive powder such as ITO is dispersed, or polyester resin, styrene acrylic resin, or the like. It is produced by coating the surface with the conductive agent.
When a high electric field is applied to the conductive toner of such an aspect, the resistance tends to decrease. The magnitude of the electric field that lowers the resistance depends mainly on the occupation ratio of the concave portion 83 of the toner or the thickness of the insulating coating layer 82. With respect to this mechanism, since the conductive core 81 is covered with the insulating coating layer 82, the conductive core 81 itself does not come into contact with each other or directly with the electrode member, etc. As a result, it is presumed that when a high electric field is applied, for example, when a high electric field is applied, conduction is caused by a tunnel effect or the like.

  As another embodiment of the conductive toner, for example, as shown in FIG. 8B, the conductive core 81 is covered with an insulating or semiconductive coating layer 84, and the thickness h of the coating layer 84 is set. The toner resistance can be adjusted by appropriately adjusting the toner resistance. At this time, the semiconductive coating layer 84 may itself be made of a semiconductive material. For example, a metal oxide such as titanium oxide or tin oxide or conductive carbon is added to the insulating resin. You may make it use the semiconductive resin made to contain a trace amount. As the conductive core 81, for example, a mode in which conductive fine particles are attached to the vicinity of the outer surface of an insulating toner base (insulating core) made of a normal insulating toner, or conductive fine particles are provided inside the insulating core. You can select the one to be mixed as appropriate.

-Developer operation-
An outline of the operation of the developing device 40 when using such a conductive toner will be described.
After the toner agitated by the agitator 48 is supplied to the toner supply roll 44 side, the toner supply roll 44 is rotated and is conveyed to a position facing the intermediate roll 42 and supplied to the intermediate roll 42 side of Against rotation. The layer thickness of the toner supplied onto the intermediate roll 42 is regulated by the layer regulating blade 45 to form a substantially uniform toner layer. The uniformly formed toner layer on the intermediate roll 42 is sandwiched and rubbed between the intermediate roll 42 and the charge injection roll 43 by the charge injection electric field provided by the bias power source 92 while being sandwiched between the two. Charge is injected.
In such a state, since the toner sandwiched between the two is aligned to a single layer or less, the contact probability between the toner and the charge injection roll 43 is increased, and the contact resistance of the toner can be reduced. Accordingly, the apparent resistance of the toner is reduced, and the toner is injected with a low resistance. For this reason, even when the electric charge injection field is relatively low, the electric charge is efficiently injected into the toner. In particular, the present embodiment has a feature that the charge injection function can be stably performed because the charge injection roll 43 can perform the charge injection function to the toner exclusively.

  In this way, by performing charge injection on the toner having a single layer or less, charge injection into the toner is effectively performed and generation of WST (Wrong Sign Toner) can be suppressed. Then, on the intermediate roll 42 that has passed through the portion facing the charge injection roll 43, a toner layer of a single layer or less in which uniform charge injection is performed is held and conveyed by the intermediate roll 42. At this time, since the toner is sandwiched between the charge injection roll 43 and the intermediate roll 42 and in particular, the charge is injected while being rubbed, the probability of contact of the toner with the charge injection roll 43 is further increased, and Since the contact resistance can be further reduced, the toner can be efficiently injected in a single layer state with a low charge injection electric field. Further, since shear force is applied between the toner layers, it is possible to prevent the toners from overlapping in a polarized state, and it is possible to prevent the occurrence of WST even if the charge injection electric field is a high electric field.

  Next, the toner charged by the charge injection is conveyed to a portion where the intermediate roll 42 and the developing roll 41 are opposed to each other. Here, since the intermediate roll 42 and the developing roll 41 are rotated against each other and a moving electric field is applied by the bias power supply 91, the toner does not pass through the nip between the intermediate roll 42 and the developing roll 41. The toner moves electrostatically toward the developing roll 41, and the toner charge amount is not changed. Furthermore, since the peripheral speed of the intermediate roll 42 is increased by 1.2 to 2 times the peripheral speed of the developing roll 41, the amount of toner moving from the intermediate roll 42 to the developing roll 41 can be increased. Therefore, the toner amount density on the developing roll 41 can be approximately 1.2 to 2 times the toner amount density on the intermediate roll 42. At this time, the intermediate roll 42 and the developing roll 41 do not necessarily have to rotate Against, but may rotate with With. This is because the moving electric field is set to be smaller than the electric charge injection electric field, so that there is less possibility of changing the charged state of the toner during the movement.

  Then, the toner that has moved onto the developing roll 41 is conveyed on the developing roll 41 as it is, and proceeds to a developing position Pd that is located at a position where the developing roll 41 and the image carrier 20 are opposed to each other. Here, the toner on the developing roller 41 develops the latent image to become a visible image by the electric field effect by the latent image potential of the pixel electrode 34 on the bias power source 90 and the image holding member 20. At this time, since the toner amount density on the developing roll 41 is high, it is possible to realize an image density that matches the latent image. This also eliminates the need to increase the peripheral speed of the developing roll 41, so that the toner on the image carrier 20 is not scraped off by the rotation of the developing roll 41, and fine line reproducibility, graininess, etc. A sufficient image density can be obtained without image quality deterioration.

<Image writing control device>
In the present embodiment, as shown in FIG. 9, the image writing control apparatus 100 includes an image signal to be written, a scanning start reference signal indicating the start timing of latent image writing on the image carrier 20, and a job for the image forming apparatus. A job command signal corresponding to this command information, a pixel density selection signal corresponding to selection information related to the pixel density of the image to be created, and the like are input signals, and the latent image voltage applied to the pixel electrode 34 is controlled based on the image signal. The scanning timing is set according to the writing mode determined by the latent image voltage control unit 101, the writing mode determination unit 106 for determining the writing mode for writing the electrostatic latent image, and the writing mode determination unit 106. And a scanning timing setting unit 107 for transmitting a predetermined control signal to the data driver 31 and the scanning driver 32.
Here, an image signal as an input signal corresponds to image information captured from, for example, a client terminal or read by an image reading apparatus such as a scanner, and the scan start reference signal is a scan start of the image carrier 20. The job command signal corresponds to a signal related to a job command based on information instructed by the user on the operation panel, such as how many images are to be formed. In addition, the pixel density selection signal corresponds to a signal based on information on the pixel density designated by the user on the operation panel, for example.

In this embodiment, as shown in FIG. 9, the latent image voltage control unit 101 includes a memory unit 102 that stores image data from an image signal, and a tone conversion that performs tone conversion of the image data from the memory unit 102. Unit 103, latent image voltage setting unit 104 for setting a latent image voltage for each pixel electrode 34 based on gradation-converted data, and latent image voltage for supplying various specific latent image voltages to latent image voltage setting unit 104 Power supply unit 105.
Further, the writing mode determination unit 106 executes, for example, a latent image writing mode determination process shown in FIG. 12 to determine what the determined writing mode is. Details will be described later.
Further, the scanning timing setting unit 107 sets scanning timing according to the writing mode determined by the writing mode determination unit 106.
The latent image voltage set by the latent image voltage setting unit 104 is applied to the corresponding pixel electrode 34 via the data driver 31, and the scanning timing signal set by the scanning timing setting unit 107 is scanned. A scanning signal is applied to the pixel electrode 34 in the corresponding row via the driver 32.

<Operation of image forming apparatus>
Next, the operation of the image forming apparatus according to the present embodiment will be described.
First, as shown in FIG. 2 and FIGS. 3A and 3B, the image writing control device 100 is used to statically based on the image signal of each color component for each pixel electrode 34 of the image carrier 20 of each color component. An electric voltage is applied, and an electrostatic latent image of each color component is written corresponding to each pixel electrode 34.
Next, an electrostatic latent image of each color component formed on the image carrier 20 by each developing unit 40 is visualized with each color toner with respect to each image carrier 20, and an intermediate transfer belt is obtained by each transfer unit 63. Each color toner image is primarily transferred onto the toner 50.
Thereafter, the secondary transfer device 60 secondary-transfers each color toner image on the intermediate transfer belt 50 to the recording material, and the fixing device 76 fixes the respective color toner images on the recording material. Is discharged.
Note that a part of the transferred toner remains on each image carrier 20, but this residual toner is cleaned by the cleaner 62.

In such an image forming process, the electrostatic latent image forming step is performed as follows.
―Gradation of latent image formation―
In the present embodiment, since the image signal is subjected to multiple gradations by the gradation conversion unit 103 and a latent image voltage is formed based on this, the latent image voltage is not simply a binary value but more than that. Multi-value can be set, and a latent image voltage matching the image density can be applied to the pixel electrode 34. This will be described with reference to FIG.
For example, for each color density of the image signal (image data), for example, three levels of threshold values (indicated by A, B, and C in the figure) are provided. If there is V / 3, B is greater than or equal to A and less than 2V / 3, and V is greater than A, then a four-tone latent image is formed.
Next, a method for applying the image data classified into the four stages to the pixel electrode 34 will be described with reference to FIG.
The tone-converted signal is a signal as shown in FIG. 11A, and “... a, b, c, d...” Along the data line and “... B, a,. Assuming that an image of “d, c...” is obtained, the latent image voltage setting unit 104 (see FIG. 9), for example, as shown in FIG. First, the quantified data is generated. That is, a data signal such as “... 00011011 …… 01001110...” Is generated. Then, by selecting voltages corresponding to “00” to “11” from the generated image signal from the latent image voltage power supply unit 105, four stages of latent image voltage waveforms are set. The latent image voltage waveform thus set is transmitted to the data driver 31, and the control signal from the scanning timing setting unit 107 (see FIG. 9) is transmitted to the scanning driver 32, so that FIG. As shown in the figure, images of each color having different densities are formed for each pixel electrode 34.

-Scanning timing of latent image formation-
FIG. 12 is a flowchart showing an outline of the latent image writing mode determination process processed by the writing mode determination unit 106.
In the figure, the writing mode determination unit 106 first checks whether or not there is a scanning start reference signal, and if there is a scanning start reference signal, determines a pixel density selection signal. Here, it is assumed that there are two types of pixel density selection signals, a high pixel density selection signal and a low pixel density selection signal.
When it is determined that the pixel density is low, the second writing mode (low pixel density) is determined. On the other hand, when it is determined that the pixel density is high, the job command signal is determined, When there are n different images, the first writing mode is determined, and when it is determined that the same image is n, the first one is the first writing mode, and the second and subsequent images are the first. 2 writing mode is determined.
Here, the “first writing mode” means that a plurality of scanning operations are performed on each pixel electrode 34 of the image carrier 20, and the “second writing mode” means the image carrier. This means that a single round of scanning operation is performed on each of the 20 pixel electrodes 34.

-Scanning example of latent image formation-
In the present embodiment, the image writing control device 100 changes the scanning operation for each pixel electrode 34 in accordance with the pixel density.
FIG. 13A shows an example of scanning when the pixel density is high. All the groups of pixel electrodes 34 arranged in a matrix are to be scanned, and S (1) to S (7)... The scanning operation is performed in the order shown.
On the other hand, FIG. 13B shows an example of scanning at a low pixel density, where half of the group of pixel electrodes 34 arranged in a matrix is a scanning target, and S (1) -S (4) The scanning operation is performed in the order shown in.
In FIGS. 13A and 13B, the data driver 31 and the scanning driver 32 are shown in a time-divided state. The same applies to FIG.

-Latent image writing position and latent image potential for latent image formation-
FIG. 14 (a), with respect to the image carrier 20 of the orbiting speed v _1, a predetermined latent image voltage based on the image signal is applied to the pixel electrode 34 at a predetermined latent image writing position Ps to a predetermined FIG. 2 is a schematic diagram when development is performed at a development position Pd that is a predetermined distance m away from the latent image writing position Ps.
Here, taking the case where the first writing mode is executed as an example, in the present embodiment, the image writing control apparatus 100 is illustrated when performing a plurality of round scanning operations on each pixel electrode 34. The image holding bodies 20 are rotated a plurality of times by a driving force from an external driving system, and the pixel electrodes 34 in each row are rotated at a speed v ₂ that is opposite to the rotating direction of the image holding body 20 and equal to the rotating speed v ₁ of the image holding body 20. The scanning operation is performed on the above.
Now, when the first scanning operation is performed on the pixel electrode 34, as shown on the left side of FIG. 14B, for example, a time twice as long as the charging time constant τ for the storage capacitor 35 for one pixel electrode 34. the if corresponding scan time, the latent image potential is charged in the storage capacitors 35 of the pixel electrode 34 is gradually increased as shown in V _1.
Thereafter, when the relative pixel electrode 34 to implement the 2 laps th scanning operation, as shown in the middle of FIG. 14 (b), the latent image potential is accumulated in the storage capacitors 35 of the pixel electrode 34 is shown in V ₂ as, gradually increases from a slightly attenuated than the maximum value of V _1.
Furthermore, when carrying out the 3 laps th scanning operation on the pixel electrode 34, as shown on the right side of FIG. 14 (b), the latent image potential is accumulated in the storage capacitors 35 of the pixel electrode 34, as shown in V ₃ a, gradually increases from a slightly attenuated than the maximum value of V _2.
As described above, when a predetermined latent image voltage is applied to each pixel electrode 34 of the image carrier 20, the latent image potential is slightly attenuated when the latent image voltage is not applied, as shown in FIG. 14B. The latent image potential corresponding to the pixel electrode 34 is stably formed to the level of V ₃ (max) by the scanning operation of a plurality of rounds.

Further, a driving method for the pixel electrode 34 during the application operation of the latent image voltage will be described with reference to FIGS. 3B and 5C.
In this figure, when an ON voltage is applied to the gate GT connected to the scanning line side of the TFT 33, the source ST-drain DT of the TFT 33 becomes conductive, and accumulation is performed until it becomes equivalent to the source voltage applied to the data line side. The capacity 35 is charged. This charged charge provides a latent image potential that forms an electrostatic latent image. In this state, even if an OFF voltage is applied to the gate GT and the source ST-drain DT is cut off, the charge charged by the capacitance component of the storage capacitor 35 is held as it is, and the source ST voltage subsequently changes. Even if the ON voltage is not applied to the gate GT, the latent image potential is maintained as it is.
Therefore, by applying a signal voltage (electrostatic voltage) corresponding to the image density to the source ST side of the TFT 33 of each pixel electrode 34 and applying an ON voltage to the gate GT side, the electrostatic potential of one data line is obtained. A latent image is formed. That is, in this embodiment, the gate GT position to which the ON voltage is applied is the latent image writing position. In the present embodiment, since the scanning speed v ₂ of the pixel electrode 34 is opposite to the rotation direction of the image carrier 20 and is the same speed, the relative position on the image carrier 20 is changed. Accordingly, the pixel electrodes 34 are sequentially scanned, and a new signal voltage is applied to the data line in accordance with this scanning, whereby a two-dimensional latent image in a matrix arrangement is formed on the image carrier 20. Become so.

-Formation of multiple latent images-
Next, as shown in FIGS. 12 and 15, the image writing control apparatus 100 performs different scanning operations when forming a plurality of images.
As an example of the case where the pixel density is high, when forming n images with different job commands, the latent image forming step is the first document at the latent image writing position Ps. A multi-turn mode (a plurality of rounds (for example, three rounds of scanning operation)) is performed, and the first write mode is similarly executed for the second and subsequent sheets.
On the other hand, when n images of the same job command are formed, the latent image forming step is performed in the first writing mode (multiple rounds (for example, three rounds), for example, at the latent image writing position Ps. Scanning operation)), and the second writing mode (single round (one round) scanning operation) is performed in consideration of the same latent image potential remaining on the second and subsequent sheets. do it.
In this way, when n sheets of the same image are formed, the scanning operation time associated with the latent image forming process is shortened compared to when n sheets of different images are formed.

◎ Deformation 1
In this embodiment, when n different images are formed, the first writing mode is selected. However, the present invention is not limited to this. For example, as shown in FIG. as described above, the image of high pixel density, have a common image portion G _0, if such a part is composed of different image portions G ₁ ~G _n, as shown in FIG. 16 (b) The first sheet is in the first writing mode (multiple rounds (for example, three rounds of scanning operation)), and the second and subsequent sheets are in the second writing mode (single round (one round) of scanning operations). What is necessary is just to carry out.
However, carrying out the second and subsequent scanning operation, the common image portion G ₀ is the latent image potential remaining exists, the latent image potential remains for image portions G ₁ ~G _n to change Therefore, it is preferable to stably form the latent image potential by extending the scanning time.

◎ Deformation form 2
In the present embodiment, the image writing control apparatus 100 performs the scanning operation for all the pixel electrodes 34 as the scanning operation for a plurality of rounds with respect to the pixel electrode 34. However, the present invention is not limited to this. For example, as shown in FIG. 17, regarding the scanning operation of the pixel electrode 34 in a plurality of rounds (in this example, two rounds are illustrated), the scanning operation in the first round is performed on the pixel electrodes 34 every other row. (1-1) to S (1-4) are performed in this order, and the second round scanning operation is performed on a pixel electrode 34 different from the first round pixel electrode 34 as a scanning target. On the other hand, the scanning operation may be performed in the order of S (2-1) to S (2-3).
In this embodiment, since the scanning operation time for the first round is performed for the pixel electrodes 34 in every other row, the scanning operation time is performed for the pixel electrodes 34 in all rows. It is possible to ensure twice the scanning operation time.

◎ Deformation 3
In the present embodiment, the scanning operation for a plurality of rounds with respect to the pixel electrode 34 is carried out while the image carrier 20 is always moved round, but the present invention is not limited to this. For example, as shown in FIG. Further, taking a scanning operation of a plurality of rounds (for example, three rounds) as an example, the scanning operation of the first round is performed on the pixel electrode 34 with the driving of the image carrier 20 stopped, and FIG. As shown in (b), in the second and third scanning operations, the pixel electrode 34 is scanned at a predetermined latent image writing position Ps while driving the image carrier 20 so as to rotate. You may make it implement operation | movement.
In this example, in the second round of scanning operation, the driving of the image carrier 20 is stopped in the same manner as in the first round, and the image carrier 20 is driven so as to move around in the third round of scanning operation. The scanning operation may be performed on the pixel electrode 34 at a predetermined latent image writing position Ps.

Embodiment 2
FIG. 19 is an explanatory diagram showing an outline of the image forming apparatus according to the second embodiment.
In the figure, the basic configuration of the image forming apparatus is substantially the same as that of the first embodiment, but unlike the first embodiment, the configurations of the transfer device 63 and the cleaning device 62 are different from those of the first embodiment. Components similar to those in the first embodiment are denoted by the same reference numerals as those in the first embodiment, and detailed description thereof is omitted here.
In the present embodiment, the transfer unit 63 uses the pixel electrode 34 of the image carrier 20, provides the transfer voltage control unit 110 in the image writing control device 100, and transfers the transfer voltage control unit to the pixel electrode 34. A transfer voltage controlled at 110 is applied, and a transfer electric field is formed between the counter electrode 115 provided facing the image carrier 20.
On the other hand, the cleaning device 62 uses the pixel electrode 34 of the image carrier 20 and provides the cleaning voltage control unit 120 in the image writing control device 100 and controls the pixel electrode 34 by the cleaning voltage control unit 120. A cleaning electric field is applied, and a cleaning electric field is formed between the counter electrode 125 provided to face the image carrier 20.

Further, as shown in FIG. 20, the transfer voltage control unit 110 sets a transfer voltage for each pixel electrode 34 based on image data stored in the memory unit 102 of the latent image voltage control unit 101. And a transfer voltage power supply unit 112 for supplying various specific transfer voltages to the transfer voltage setting unit 111.
Further, as shown in FIG. 20, the cleaning voltage control unit 120 sets a cleaning voltage for each pixel electrode 34 based on image data stored in the memory unit 102 of the latent image voltage control unit 101. And a cleaning voltage power supply unit 122 that supplies various cleaning voltages to the cleaning voltage setting unit 121.
Further, the image writing control apparatus 100 switches each control voltage (latent image voltage, transfer voltage, cleaning voltage) controlled by the latent image voltage control unit 101, the transfer voltage control unit 110, and the cleaning voltage control unit 120. The data is sent to the data driver 31 via 130.
As described above, in the present embodiment, the transfer device 63 and the cleaning device 62 form the transfer electric field and the cleaning electric field in a state where the control voltage such as the transfer voltage and the cleaning voltage is controlled in units of the pixel electrode 34. If the amount of toner image and the amount of residual toner are predicted in advance from image data, the transfer electric field and the cleaning electric field can be finely adjusted for each pixel electrode 34, and the transfer performance and the cleaning performance are further improved. This is preferable.
In this embodiment, both the transfer device 63 and the cleaning device 62 are configured using the pixel electrode 34, but the present invention is not limited to this, and either one may be employed. Good.

FIG. 21 shows the time response of the CR circuit.
Now, the equivalent circuit around the pixel electrode is represented as a CR circuit, and the charging time constant τ is represented by the product of the ON resistance of the TFT and a load capacity such as a storage capacity. In order to charge to a stable potential (99%) equivalent to the latent image voltage corresponding to the maximum image data, it is necessary to keep the TFT in the ON state for a time five times the charging time constant τ.
Here, the ON time of the TFT is substantially equivalent to the scanning time per line.
As shown in the first embodiment, the scanning speed is set to the circumferential direction of the image carrier 20 in order to always scan at a constant latent image writing position upstream of the development position with respect to the circumferential direction of the image carrier 20. When scanning is performed in the reverse direction and at the same speed, the scanning time is the reciprocal of the product of the image forming process speed and the pixel density. Therefore, in this case, the scanning time per line is expressed by 1 / (image forming process speed × pixel density).
Therefore, the higher the speed and the higher pixel density, the smaller the charging time constant is required.
In general, since the charging time constant of the a-Si TFT is about 10 μs, FIG. 22 showing the relationship between the charging time constant and the imaging process speed shows that at 2400 dpi, about 200 mm / s is the limit. For example, it is difficult to adapt to the printing market that requires a high image forming process speed of about 400 to 600 mm / s.
However, it is understood that if a scanning operation of a plurality of rounds is realized as in the embodiment, the scanning time can be substantially increased, so that it can be applied to the high-speed printing market.

FIG. 23 shows the time response when the latent image potential is formed in three rounds.
In the figure, the conditions of the image carrier 20 are as follows.
Charging time constant: 10 μs
Pixel density: 2400 dpi
Imaging process speed: 530 mm / s
Decay time constant: 11.7 s
Image carrier: φ168mm
The scanning time for one round under the same conditions is 20 μs, which corresponds to 2τ (twice the time constant).
Therefore, in the figure, it is understood that a stable latent image potential is secured by the scanning operation of three rounds.
FIG. 24 shows the time responsiveness of the latent image potential when a plurality of the same images are printed.
After the first latent image was formed in three rounds, the second and subsequent sheets were the same image, so the latent image was formed in a single round.
The conditions are the same as in FIG.
According to FIG. 24, when a plurality of identical images are formed, a stable latent image potential can be obtained even if a plurality of (three in this example) latent images are formed by a single scanning operation. It was confirmed.

  DESCRIPTION OF SYMBOLS 1 ... Image holding body, 1a ... Support body, 1b ... Pixel electrode, 1c ... Protective layer, 2 ... Drive means, 3 ... Latent image writing means, 4 ... Selection means, 5 ... Pixel density selection means, 6 ... Development means 7, transfer means, 8 ... cleaning means, 9 ... transfer medium

Claims (12)

It has a support that has a peripheral surface that is larger than the maximum image forming area and can be moved around, and on this support, pixel electrodes are arranged on a pixel unit along the direction of movement of the support and the crossing direction that intersects the direction of movement. An image carrier arranged in a matrix
Driving means for driving the image carrier to move around, and
By applying a scanning signal, it is possible to perform a scanning operation in which a latent image voltage based on the image signal is applied to the pixel electrodes in each row along the intersecting direction of the image holding body, and the image holding unit holds the image. A latent image writing means for writing a latent image by the latent image voltage to the image holding body by performing a plurality of round scanning operations on the pixel electrodes of the image holding body when the body is moved around;
Equipped with a,
The latent image writing means applies a plurality of latent image voltages based on the same image signal to the same pixel electrode position every rotation when performing a plurality of round scanning operations on the pixel electrode. Forming equipment. It has a support that has a peripheral surface that is larger than the maximum image forming area and can be moved around, and on this support, pixel electrodes are arranged on a pixel unit along the direction of movement of the support and the crossing direction that intersects the direction of movement. An image carrier arranged in a matrix
Driving means for driving the image carrier to move around, and
By applying a scanning signal, it is possible to perform a scanning operation in which a latent image voltage based on the image signal is applied to the pixel electrodes in each row along the intersecting direction of the image holding body, and the image holding unit holds the image. A latent image writing means for writing a latent image by the latent image voltage to the image holding body by performing a plurality of round scanning operations on the pixel electrodes of the image holding body when the body is moved around;
Equipped with a,
2. The image forming apparatus according to claim 1, wherein the latent image writing unit is configured to change a pixel electrode row to be scanned for each round when performing a plurality of rounds of scanning operation for the pixel electrode . The image forming apparatus according to claim 1 or 2,
The latent image writing means rotates the image holding body a plurality of times by the driving means when performing the scanning operation for the pixel electrode a plurality of turns, and the image holding body is in a direction opposite to the rotation direction of the image holding body. An image forming apparatus, wherein the scanning operation is performed on the pixel electrodes in the corresponding row at a speed equal to the circumferential speed of the image forming apparatus. The image forming apparatus according to any one of claims 1 to 3,
The latent image writing means comprises a first write strategy for implementing the scanning operation of the plurality orbit relative pixel electrode, and the second write strategy for implementing the scanning operation of the single lap with respect to the pixel electrode can be selected An image forming apparatus comprising: a first selecting unit, and performing either the first writing method or the second writing method according to a selection result by the selecting unit. The image forming apparatus according to claim 1 or 2,
The latent image writing unit performs the scanning operation in a state where driving of the image carrier by the driving unit is stopped at least during the first scanning operation when performing the scanning operation for the pixel electrode a plurality of times. An image forming apparatus for carrying out the invention. The image forming apparatus according to any one of claims 1 to 5,
The latent image writing means comprises a plurality of pixel density-selectable pixel density selection means to the pixel electrodes, carrying out the scanning operation on the pixel electrode based on the pixel density selected by the pixel density selection means An image forming apparatus. The image forming apparatus according to claim 6 .
The latent image writing unit thins out pixel electrode rows to be scanned when performing a scanning operation on the pixel electrode when a low pixel density is selected by the pixel density selection unit. . The image forming apparatus according to claim 4 .
The latent image writing means employs a first writing method in which when a plurality of the same latent images are written on the image carrier, a plurality of rounds of scanning operations are performed on the pixel electrodes during the initial latent image writing. An image forming apparatus characterized by adopting a second writing method for performing a single round scanning operation on the pixel electrode after the second time. The image forming apparatus according to claim 8 .
The latent image writing means performs a plurality of rounds of scanning operation on the pixel electrode at the time of writing the first latent image when writing a plurality of latent images partially changed on the image carrier. adopted write mode, since adopts a second write strategy for implementing the scanning operation of the single lap with respect to the pixel electrode, and a longer scan time for the pixel electrode rows in the modified latent image portion that An image forming apparatus. The image forming apparatus according to any one of claims 1 to 9,
A developing unit for developing an electrostatic latent image on the image holding member that has been written by the image writing means in the image forming material,
A transfer means for transferring a visible image by an image forming material formed on the image carrier by the developing means to a transfer medium;
An image forming apparatus comprising: The image forming apparatus according to claim 10 .
The transfer unit applies a transfer voltage based on an image signal to each of the pixel electrodes, thereby causing a transfer electric field to be transferred to a transfer medium to the visible image developed by the developing unit. Image forming apparatus. The image forming apparatus according to claim 10 .
Further comprising a cleaning means for cleaning the image forming material remaining on the image carrier,
The image forming apparatus characterized in that the cleaning unit applies a cleaning voltage based on an image signal to each of the pixel electrodes to apply a cleaning electric field for cleaning the image holding body to the image holding body that has been transferred. apparatus.

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