JP2001272869A - Image forming device - Google Patents

Abstract

(57) [Problem] To provide an image forming apparatus which is highly reliable because current flowing through an image carrier such as a photoreceptor is directly measured, and which can prevent a design error of overlooking a member flowing out of the image carrier. provide. A latent image is formed on a photoconductor, and the latent image is developed with a charged toner to form a charged toner image on the photoconductor. An image forming apparatus 2 that applies a bias to the contact transfer body 20 while the recording medium P is held therebetween to transfer the toner image on the photoconductor to the recording medium P, between the photoconductor 2 and the housing of the image forming apparatus 2 The image forming apparatus 2 is provided with a current measuring circuit, measures a current flowing from the contact transfer member 20 to the photoconductor 2, and controls a bias value applied to the contact transfer member 20 based on the measured value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus provided with a transfer device for forming an image on an image carrier using a toner and transferring the toner to a recording medium, and more particularly, to a contact intermediate transfer. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus that can supply an appropriate transfer bias by absorbing variations in the electrical resistance of members, environmental and temporal variations.

[0002]

2. Description of the Related Art In an electrophotographic image forming apparatus for forming an image corresponding to image information on an image carrier such as a photoreceptor, an image is transferred from a toner image on the image carrier to recording paper as a recording medium. Transfer device is provided. The transfer device includes a corona transfer system, a bias roller system, a belt system, and the like. In the corona transfer method, a high voltage is applied to a gold-plated tungsten wire to carry out corona discharge, and a toner image is transferred to recording paper by electric charges generated at that time. However, there are problems such as low current efficiency and generation of a large amount of ozone. Therefore, a method using a bias roller has recently been developed. In this method, a recording paper is sandwiched between a member carrying a toner image, such as an image carrier or an intermediate transfer body, and a transfer bias is applied to the intermediate transfer body or the recording paper so that the image carrier comes into contact with the intermediate transfer body or the recording paper. In this method, a toner image is transferred onto recording paper at a transfer position. As described above, if the toner image on the image carrier is not faithfully transferred, the image on the recording paper is deteriorated.

However, the transfer bias for the transfer is
Appropriate conditions are required because the conditions of the image carrier, the intermediate transfer member, the recording paper, and the like, and the conditions change over time. for that reason,
JP-A-5-297740 proposes an image forming apparatus that determines a bias voltage based on an output current value of a high-voltage power supply that applies a bias to a contact transfer member. Also,
Japanese Patent Application Laid-Open No. 6-348145 discloses a transfer method in which a bias value is controlled so that a current value obtained by subtracting, as a feedback current, a current flowing out of a high-voltage power supply for applying a bias to a contact transfer member as a feedback current is constant. Belt devices have been proposed. Also, in JP-A-3-23127,
An image forming apparatus configured to detect a sum of currents flowing through a plurality of rollers supporting the transfer material transport belt and control a current amount of the charge supply device when the charge supply unit supplies the charge to the transfer material transport belt; Has been proposed.

[0004]

However, the above-described apparatus has the following problems. JP-A-5-297
In the image forming apparatus disclosed in Japanese Patent Publication No. 740, it is sufficient that all the current flowing from the high-voltage power supply to the contact transfer member contributes to the transfer. It cannot be measured accurately. For this reason, there is a problem that a current flowing to the transfer roller is reduced, and image defects such as a decrease in image density due to transfer failure and a white spot due to transfer failure of a solid black image portion occur. Further, in the transfer belt device disclosed in JP-A-6-348145, it is sufficient that all the current flowing out of the photoconductor be captured by the feedback current. However, when the device is complicated, there is a problem that the portion flowing out of the photoconductor is increased. is there. In the image forming apparatus disclosed in JP-A-3-23127, all of these members must be disconnected from the housing of the image forming apparatus and the current must be measured. Furthermore, the constant current control shown here is less susceptible to the fluctuation of the resistance of the transfer object than the constant voltage control, but is susceptible to the fluctuation of the latent image charge of the latent image carrier. There is a point. Further, each of the above proposals has a problem that the device becomes complicated and wiring must be performed for that purpose, resulting in an increase in cost.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to directly measure a current flowing through an image carrier such as a photoreceptor, so that the reliability is high and the image carrier is high. Provided is an image forming apparatus capable of preventing a design error in which a member flowing out of a body is overlooked. In addition, by using only the photoconductor as a member that must be disconnected from the housing of the image forming apparatus to perform current measurement wiring, the image forming apparatus can be manufactured at low cost.

[0006]

According to a first aspect of the present invention, a latent image is formed on a photoreceptor, and the latent image is developed with a charged toner. Forms a charged toner image on the photoreceptor, and applies a bias to the contact transfer body with the recording medium sandwiched between the photoreceptor and the contact transfer body to transfer the toner image on the photoreceptor to the recording medium In an image forming apparatus, a current measurement circuit is provided between the photoreceptor and the housing, the current flowing from the contact transfer body to the photoreceptor is measured, and the bias value applied to the contact transfer body is controlled based on the measured value. Image forming apparatus. According to a second aspect of the present invention, a latent image is formed on a photoconductor, and the latent image is developed with a charged toner to form a charged toner image on the photoconductor, and a bias is applied to the intermediate transfer member. An image forming apparatus that electrostatically transfers the toner image on the photosensitive member to the intermediate transfer member by transferring the toner image to the recording medium from the intermediate transfer member to form a toner image on the recording medium; A current measurement circuit is provided between the
This is an image forming apparatus that measures a current flowing from an intermediate transfer member to a photoconductor and controls a bias value applied to the intermediate transfer member based on the measured value. The invention according to claim 3 is
3. The image forming apparatus according to claim 1, wherein the current is measured in a current measuring mode different from the image forming mode and before the image forming mode. According to a fourth aspect of the present invention, in the image forming apparatus according to the first or second aspect, the current is measured during the image forming mode in a current measuring mode different from the image forming mode. It is a forming device. According to a fifth aspect of the present invention, there is provided the image forming apparatus according to any one of the first to fourth aspects, wherein the applied bias value is controlled at a constant voltage.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) An embodiment of the present invention will be described below with reference to the drawings. The image forming apparatus according to the first and third aspects will be described. FIG.
1 is a schematic sectional view illustrating a configuration of an image forming apparatus according to a first embodiment of the present invention. The image forming apparatus 1 includes a photoconductor 2 rotatably supported by an image forming apparatus housing (not shown).
And a pair of transport rollers 6 that transport a recording medium (hereinafter, referred to as “recording paper”) P, a transfer device 7, and a supply unit. 8, a cleaning device 9, a static eliminator 10, and the like. Further, in addition to the image forming unit, an image reading unit 11 such as a scanner, an image processing unit 12 for processing an image signal to be read, and the like are provided. The exposure device 4 includes an exposure unit 13 that emits a laser beam by a light emitting element, an fθ lens 14 that converges the laser beam, and the like. Developing device 5
Are a developing roller 15 having a fixed magnet built therein, and transport rollers 16 and 1 for transporting the developer stored in the developing roller 15.
7 is comprised. The transfer device 7 includes a contact transfer member (hereinafter, referred to as a “transfer belt”) 20 and a driving roller 2.
1, a bias roller 22, an earth roller 23, a high voltage power supply 24, and the like. The transfer belt 20 allows the recording paper P conveyed from the conveyance roller 6 to pass through between the photoconductor 2 and the bias roller 22 and conveys the recording paper P to a fixing device (not shown). The cleaning device 9
The blade includes a blade supported so as to be in contact with the photoconductor 2, and a storage unit for storing the developer collected by the blade.

Here, the operation of the image forming apparatus 1 will be described. The photosensitive member 2 having the photosensitive layer rotates, and the surface thereof is uniformly charged by applying a voltage to the charging roller 3. Then, the image reading unit 11 forms the image of the original, reads the original image, and transmits the image to the image processing unit 12 in place of a signal.
The photosensitive member 2 is irradiated with a laser beam L based on the signal from the image processing section 12 to form a latent image on the photosensitive member 2. On the other hand, while the developing roller 15 of the developing device 5 is rotated, the developer is supplied to the surface of the developing roller 15 by the conveying rollers 16 and 17. The developer supplied to the surface of the developing roller 15 is frictionally charged by a developer regulating member (not shown) and forms a developer layer on the surface of the developing roller 15. The photosensitive member 2 on which the latent image is formed is rotated to a position facing the developing roller 15, and the developer layer is transferred to the surface of the photosensitive member 2 in accordance with the latent image, and the latent image is made visible, A toner image is formed on the body 2. The recording paper P is conveyed to a transfer site with the photoconductor 2 by the transfer belt 20, and a voltage having a polarity opposite to that of the toner image is applied to the bias roller 22 to transfer the toner image onto the recording paper P. afterwards,
The toner remaining on the photoconductor 2 is scraped off by the blade of the cleaning device 9 for the photoconductor 2 and stored in the storage unit. Then, after the photoconductor 2 is neutralized by the neutralizer 10, a series of operations is repeated again.

Here, the portion to be transferred will be described in detail.
As shown in FIG. 1, here, a driving source (not shown) transmits a rotational force in a direction indicated by an arrow to the drive roller 21, and the rotational force of the drive roller 21 is transmitted to the transfer belt 20 to rotate. The driven roller 23a rotates in conjunction with the movement of the transfer belt 11. A bias roller 22 is in contact with the transfer belt 20 on the opposite side of the transfer surface of the recording sheet P downstream of the transfer portion. The bias roller 22 is provided at a position slightly shifted downstream of the transfer direction of the photosensitive member 2 with respect to the recording paper P in the vertical direction with respect to the recording paper P transport direction. This is because, when the bias roller 22 is arranged and transferred in the vertical direction of the photoconductor 2, the photoconductor 2 and the recording paper P or the transfer belt 20 are transferred.
This is because the toner burst occurs in the toner image on the recording paper P due to the toner burst when the. Separate ground rollers 23b are provided upstream of the transfer site and downstream of the bias roller 22, and are grounded. The driven roller 23 a, which is also an earth roller 23 a, stretches the transfer belt 20 and rotates following the rotation of the driving roller 21.

Although not shown, the bearing of the photosensitive member 2 or the holder of the bearing is made of a material such as insulating resin, and the photosensitive member 2 is electrically isolated from the housing of the image forming apparatus 1. For this purpose, the photoconductor bearing is connected to a current measuring circuit in a control board 26 through an ammeter 25 instead of the housing of the image forming apparatus 1. Current measurement circuit is control board 2
6 may be provided separately, but this is more inexpensive than providing a separate board, and the reliability against noise and the like can be improved. Here, the photoreceptor 2 has a structure in which a charge generation layer and a charge transport layer are applied on a conductive substrate such as aluminum. When a charge is applied to the photoconductor 2 by the charging device 3 and charged, a charge opposite to the charge by the charging device 3 is induced on the conductive substrate from the ground. When the toner is developed, the charge on the photoreceptor 2 increases, and accordingly, the charge on the substrate of the photoreceptor 2 is induced by the amount of charge of the toner,
Next, when the transferred toner on the photoconductor 2 runs out, the charge of the photoconductor 2 is released accordingly. Therefore, by electrically separating the photosensitive member 2 from the housing of the image forming apparatus 1 at the time of transfer, it is possible to measure a charge amount required for transfer as a current value. Further, the control board 26
By storing the exposure time of the laser light in the image processing unit 12, the data of the exposure time of the laser light in the next image processing is transmitted from the control board, and further, in accordance with the amount of toner to be transferred. The amount of current can be controlled accurately.

(Second Embodiment) Claims 2 and 3
Will be described. FIG. 2 shows the first embodiment of the present invention.
1 is a schematic sectional view illustrating a configuration of an image forming apparatus according to an embodiment. Here, the transfer device 7 includes an intermediate transfer member (hereinafter, referred to as an “intermediate transfer belt”) 27, a driving roller 21, a driving roller 21, a bias roller 22, an earth roller 23,
It comprises a high voltage power supply 24, a paper transfer roller 28 and the like. A bias roller 22 supplied with a bias from a high-voltage power supply 24 downstream of a contact point between the photoconductor 2 and the intermediate transfer belt 27 transfers the toner image of the photoconductor 2 onto the intermediate transfer belt 27. On the opposite side of the recording sheet P transport surface downstream of the transfer portion, the bias roller 22 is connected to the intermediate transfer belt 2.
7 is in contact. Separate ground rollers 23 are provided on the upstream side of the transfer site and on the downstream side of the bias roller 22,
Grounded. After that, the intermediate transfer body 27 and the recording paper P also come into contact with each other, and at this transfer site, the toner image on the intermediate transfer belt 27 is transported between the paper transfer roller 28 and the opposing roller 29,
The image is transferred to the recording paper P by the bias.

Although not shown, the bearing of the photosensitive member 2 or the holder of the bearing is made of a material such as an insulating resin, and the photosensitive member is electrically isolated from the housing of the image forming apparatus 1.
Instead of the housing of the image forming apparatus 1, the photosensitive member shaft or bearing is connected to the input of the current measuring circuit. The current measurement circuit may be provided on the control board 26, which is cheaper and more reliable with respect to noise and the like than providing a separate board. In addition, the recording paper P contains paper fibers such as cellulose and additives such as calcium carbonate, kaolin, and talc, and the electrical resistance changes depending on humidity, so that the transfer efficiency of the toner fluctuates. However, the intermediate transfer belt 27 and the transfer belt 20
By using a polyimide resin or the like, it is possible to suppress the transfer efficiency due to fluctuation due to the environment. Therefore, it is possible to suppress a change in transfer efficiency due to a current value, and to obtain a stable transfer efficiency.

Further, in the image forming mode, since the charging device 3, the exposing device 4, the developing device 5, the charge removing device 10 and the like act on the photosensitive member 2 in a complicated manner, it is difficult to take out only the electric current from the transfer device 7. It is. Therefore, the image forming apparatus according to claim 3 develops a fixed amount of toner on the photoreceptor 2 for current value measurement immediately before entering the image forming mode.
By measuring the current value by transferring this, it is possible to measure only the current value necessary for transferring the toner. Further, as in the image forming apparatus according to claim 4,
Continuously in the image forming mode, by providing a current measurement mode separately from the image forming mode and measuring the current value,
The toner value is transferred by accurately measuring a current value required for the transfer. Thus, a high quality image can be obtained by transferring the toner image from the photosensitive member onto the recording paper P.
Further, the data in the image processing unit 12 is transferred to the control board 2
By transmitting 6, the amount of current can be further accurately controlled in accordance with the amount of toner to be transferred.

(Third Embodiment) The invention according to claim 5 will be described. In the image forming apparatus of FIG. 1 or FIG.
The constant voltage control is performed by the control board 26. The constant voltage control is more susceptible to fluctuations in resistance due to environmental fluctuations of the transfer belt 20 than the constant current control, but is less susceptible to fluctuations in the electrostatic latent image on the photoconductor 2. For example, in the case of reversal development, the charge of the photoconductor 2 and the charge of the toner are the same polarity,
The charge for transfer has the opposite polarity, but a transfer charge that is more than neutralized with respect to the latent image charge is required. For this reason, the transfer charge amount required by the latent image charge amount, in other words, For example, the transfer current amount changes. Therefore, constant current control that can provide a necessary electric field during the transfer operation is preferable.

[0015]

As described above, in the image forming apparatus according to the first aspect, the transfer efficiency can be increased by accurately measuring only the current value required for transfer. Further, by suppressing the excess current, it is possible to faithfully transfer the image from the photosensitive member onto the recording paper, and the image quality can be improved. Further, by increasing the transfer efficiency, the amount of toner consumption can be reduced, and the image cost can be reduced. In the image forming apparatus according to the second aspect, by using the intermediate transfer belt, it is possible to prevent a change in transfer efficiency due to environmental changes such as humidity, and it is possible to more accurately read a current value required for transfer. Transfer efficiency can be improved. In the image forming apparatus according to the third aspect, by providing the current measuring mode required for transfer before the image forming mode, it is possible to more accurately measure only the current value required for transferring the toner. In the image forming apparatus according to the fourth aspect, a high-quality image can be obtained by accurately measuring a current value required for transfer and transferring the toner. In the image forming apparatus according to claim 5, the current value according to the charge of the latent image on the photoconductor is controlled even during the transfer operation,
By transferring the toner, a high-quality image can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view illustrating a configuration of an image forming apparatus according to first and third embodiments of the present invention.

FIG. 2 is a schematic cross-sectional view illustrating a configuration of an image forming apparatus according to second and third embodiments of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 image forming device 2 photoreceptor 3 charging device 4 exposure device 5 developing device 6 transport roller 7 transfer device 8 supply means 9 cleaning device 10 static eliminator 11 image reading unit 12 image processing unit 13 exposure unit 15 developing rollers 16, 17 transport rollers Reference Signs List 20 transfer belt 21 drive roller 22 bias roller 23 ground roller 23a driven roller 24 high voltage power supply 25 ammeter 26 control board 27 intermediate transfer belt 28 paper transfer roller 29 driven roller L laser beam P recording paper

Claims (5)

[Claims] A latent image is formed on a photoreceptor, and the latent image is developed with a charged toner to form a charged toner image on the photoreceptor. In an image forming apparatus that applies a bias to a contact transfer member while holding a toner image therebetween to transfer a toner image on a photosensitive member to a recording medium, a current measuring circuit is provided between the photosensitive member and a housing, and the photosensitive member is exposed to light from the contact transfer member. An image forming apparatus, comprising: measuring a current flowing through a body; and controlling a bias value applied to the contact transfer body based on the measured value. 2. A charged toner image is formed on a photoconductor by forming a latent image on a photoconductor and developing the latent image with charged toner, and the photosensitive image is formed by applying a bias to an intermediate transfer member. In an image forming apparatus that electrostatically transfers a toner image on a body to an intermediate transfer member, and further transfers the toner image from the intermediate transfer member to a recording medium to form a toner image on the recording medium, a photosensitive member and a housing An image forming apparatus, comprising: a current measuring circuit provided therebetween; measuring a current flowing from the intermediate transfer member to the photoreceptor; and controlling a bias value applied to the intermediate transfer member based on the measured value. 3. The image forming apparatus according to claim 1, wherein the current is measured before the image forming mode in a current measuring mode different from the image forming mode. Image forming device. 4. The image forming apparatus according to claim 1, wherein the current is measured during the image forming mode in a current measuring mode different from the image forming mode. Image forming device. 5. The image forming apparatus according to claim 1, wherein the applied bias value is controlled at a constant voltage.