JPH0463385A - Image forming device - Google Patents

Abstract

PURPOSE:To improve the image quality by giving electric charge so that an applied voltage is varied in accordance with the ambient humidity for image formation. CONSTITUTION:When the electric resistance value of sheet paper is reduced, roll testers 26a and 26b measure this reduction, and a controller 28 controls a variable DC power source 27a of a guide 27 before transfer to give optimum electric charge to sheet paper, and a good copy image is obtained regardless of degradation of sheet paper.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention is directed to transferring an image consisting of an electrostatic latent image or a toner image formed on a photoreceptor onto sheet paper using a transfer device,
The present invention relates to improvements in image forming apparatuses that obtain images.

(Prior Art) In an image forming apparatus such as an electrophotographic apparatus, an electrostatic latent image or a toner image formed on a photoconductor is transferred to a sheet paper or the like by using a conventional charge applying means such as a transfer charger. 2. Description of the Related Art Devices are often used that electrostatically transfer an image formed on a photoreceptor to a sheet of paper by applying a charge from the back side of the sheet of paper.

However, such a device has a problem in that its transfer efficiency is greatly affected by the surrounding humidity and decreases as the humidity increases, resulting in deterioration of image quality.

This is because the electrical resistance of the sheet paper changes depending on the humidity, and when the surrounding humidity increases, the sheet paper absorbs moisture and the electrical resistance value decreases, or the electrical resistance value of the sheet paper has decreased. , the charge applied by the charge applying device tends to escape, and during transfer, the charge applied by the transfer charger escapes from the contact area between the sheet paper and the conveying means, making it impossible to obtain sufficient charge necessary during transfer. This is because it disappears.

Further, such a reduction in transfer efficiency occurs regardless of the ambient humidity at the time of transfer, and also when the sheet paper absorbs moisture due to long-term storage or poor storage management.

(Problem to be solved by the invention) Conventionally, when the surrounding humidity becomes high or the sheet paper absorbs moisture due to poor storage, and its electrical resistance value decreases, it forms on the photoreceptor. The problem is that the transfer efficiency of the image onto the sheet paper is significantly reduced, and the image quality is significantly deteriorated, such as low density, fogging, and image omission.

Therefore, the present invention eliminates the above-mentioned problem, and prevents fluctuations in transfer efficiency during transfer and stabilizes it regardless of changes in the electrical resistance value of the sheet paper due to changes in ambient humidity or changes in the amount of moisture absorbed by the sheet paper. It is an object of the present invention to provide an image forming apparatus that can obtain high transfer efficiency and obtain good images.

[Structure of the Invention] (Means for Solving the Problems) In order to solve the above problems, the present invention provides an environment that contributes to transfer efficiency when electrostatically transferring an image on an image carrier to a transfer target. A measuring means for measuring the conditions, a charge applying means provided on the transfer path of the transferred object and applying an electric charge to the transferred object near the transfer means, and a voltage applied to the charge applying means is controlled based on the measurement result of the measuring means. A control means is provided.

Moreover, in order to solve the above-mentioned problems, the present invention provides a humidity measuring means for measuring the humidity around the transfer object as the above-mentioned measuring means.

Furthermore, in order to solve the above-mentioned problems, the present invention provides a resistance value measuring means for measuring the electrical resistance value of the transferred object as the above-mentioned measuring means.

(Function) By the above-mentioned means, the present invention makes it possible to obtain stable and good transfer regardless of changes in the electric resistance value of the sheet paper due to changes in ambient humidity or the amount of moisture absorbed by the sheet paper, and there is no fogging or image omission. It becomes possible to obtain clear and high quality images.

(Embodiment) A first embodiment of the present invention will be described below with reference to FIGS. 1 to 5. FIG. 1 shows an image forming apparatus 1, in which a charging device 11, an exposure section 12a of an exposure device 12, a developing device 13, and a transfer device are arranged around a photoreceptor 10, which is an image carrier and is charged to a positive polarity. +Ili by DC power supply 15a
The transfer charger 14a to which a voltage of [kV] is applied and the AC power supply 15b generate 4.5Ei [kvl, 500[H]
A transfer peeling charger 14 integrally formed with a peeling charger 14b to which a voltage of 4F is applied, a cleaning device 16, and a discharge lamp 17 are provided. Furthermore, on the right side of the image forming apparatus 1, there are a first cassette 18a and a second cassette 18b that accommodate sheet paper P, which is a transfer target.
A manual paper feed table 18C is also installed. Also, in the image forming apparatus 1, pickup rollers 20a and 2 are connected from each cassette 18a and 18b or the manual paper feed tray 18c.
The sheet paper P taken out by 0b and 20c is transferred to the photoreceptor 1
A paper transport path 22 is formed which leads to a paper discharge tray 21 provided on the left side of the image forming apparatus 1 through the paper transport path 22 . First and second separation rollers 23a and 23b and a registration roller 24 are arranged upstream of the photoreceptor 10 in the paper conveyance path 22. And each separation roller 23a, 23b
and the registration roller 24, there are first and second roller testers 26a and 26b made of conductive rollers.
It is provided so as to be in contact with the sheet paper, and constitutes a resistance measuring means for measuring the electrical resistance value of the sheet paper P, which is a transfer condition.

Further, 27 guides the sheet paper P from the registration roller 24 to the transfer peeling charger 14, and also introduces a resistance [27] of 2 [MΩ].
A variable DC power supply 27a whose applied voltage has the same polarity as the DC power supply 15a of the transfer charger 14a and is varied from 0 to +2.8 [kvl] by a control device 28, which will be described later, is applied via H1F.
This is a pre-transfer guide which is a charge applying means to which a voltage is applied and which applies a charge to the sheet paper P.

Next, the first and second roller testers 2, which are resistance measuring means,
6a and 26b will be explained in detail.

A constant voltage [Er] is applied to the first roller tester 26a by a DC power supply 32 via a Zener diode 31 and a resistor R. On the other hand, the second roller tester 26b is grounded via a reference resistor [Rs]. The potential [EIIl] generated in the second roller tester 26b by the reference resistor [Rs] is a function of the electrical resistance value of the sheet P between both roller testers.

That is, if the electrical resistance value of the sheet paper P between both roller testers 26a and 26b is [Rp], then the following equation is obtained.

On the other hand, the optimal value [Eo] of the applied voltage applied to the pre-transfer guide 27 is a function of the electrical resistance value [Rpl] of the sheet paper P, and is expressed as E o −f (Rp) (2)
becomes.

That is, according to equations (1) and (2), the optimum value [Eo] of the voltage applied to the pre-transfer guide 27 is determined by the second roller tester 2.
It becomes a function of the potential [Em] of 6b.

Reference numeral 28 denotes a control device that is a control means, which controls the potential [[
Em] is input while this second roller tester 26
The variable DC power supply 27a is controlled so that the voltage applied to the pre-transfer guide 27 becomes the optimum value [Eo] according to the electric potential [E+n].

Note that a conveyor belt 34 , a fixing device 36 , and a paper discharge roller 37 are provided downstream of the photoreceptor 10 .

Further, 38 is a document table, and 13a is a toner image formed on the photoreceptor 10 by the developing device 13.

Next, we will discuss the effect. However, here, we use a sheet paper P of our domestic specifications whose surface specific electrical resistance changes as shown in FIG. 4 due to changes in ambient humidity. Further, the control device 28 measures the electric potential [Em] generated between the second port and the lattester 26b, and calculates the electric potential [Em] shown in FIG. The variable DC power supply 27a is controlled so as to apply a voltage as shown to the pre-transfer guide 27. The applied voltage shown in FIG. 5 is to compensate for the decrease in the electric resistance value of the sheet paper P, so even if the voltage applied to the pre-transfer guide 27 is increased, if the voltage exceeds a certain level, the transfer charger will This is the optimum applied voltage obtained experimentally, taking into consideration the fact that the transfer efficiency by 14a is reduced.

After inputting various image forming conditions such as paper size, number of copies, exposure amount, etc. from an operation panel (not shown), copying is started. As a result, the photoreceptor 10 is uniformly charged by the charging device 11 as it rotates in the direction of the arrow, while an electrostatic latent image corresponding to the original is formed in the exposure section 12a, and then the electrostatic latent image is developed. The image is developed and visualized in the device 13.

On the other hand, in synchronization with the toner image formed on the photoreceptor 10, a sheet of paper P of a size specified on an operation panel (not shown) is fed from one of the cassettes 18a, 18b. Then, as the sheet paper P passes through the first and second roller testers 26a and 26b as it is being transported, the potential [E+nl] generated in the second roller tester 26b is input to the control device 28 via the A/D converter 33. Accordingly, the control device 28 calculates the surface specific electrical resistance value of the sheet paper P, and if it is reduced to 2.5×1010 [Ωcm] or less and the electric charge is likely to escape, the control device 28 sequentially turns on the variable DC power supply 27a according to FIG. It will be controlled from 0 to 2.8 [kV]. That is, for example, the surface specific electrical resistance value is about 8.5×10
9 [Ωcm], the variable DC power supply 27a is controlled to apply a voltage of about 1400 [V] to the pre-transfer guide 27.

After this, the sheet paper P is conveyed toward the photoreceptor 10 by the registration rollers 24 so as to be synchronized with the leading edge of the toner image on the photoreceptor 10. Then, while passing through the pre-transfer guide 27, a positive charge is applied to the sheet paper.

Next, the sheet paper P reaches the transfer charger 14a and the toner image 13a on the photoreceptor 10 is transferred, but at this time, although the sheet paper P has a low surface specific electrical resistance value, Since a charge is applied from the pre-transfer guide 27, there is no charge escaping from the pre-transfer guide 27.
As shown in FIG. 3, the charge applied by the transfer churner 14a is held. After the transfer, the sheet paper P is peeled off from the photoreceptor 10 by the peeling chatter 14b, conveyed to the conveyor belt 34, fixed by the fixing device 36, and then discharged onto the paper discharge tray 21 by the paper discharge roller 37. be done. On the other hand, after the sheet paper P is peeled off, the remaining toner is removed from the photoreceptor 10 by the cleaning device 16, and the charge is removed by the charge removal lamp 17, so that the photoreceptor 10 is ready for the next copy.

Note that while copying is performed sequentially as described above, if the ambient humidity changes or if a new sheet of paper P is added, etc.
When the potential [E+nl] generated in the second roller tester 26b changes and a change in the electrical resistance value of the sheet paper P is detected, the control device 28 controls the variable DC power supply 27a according to FIG. This will change the voltage applied to.

With this configuration, when the electrical resistance value of the sheet paper P decreases, the first and second roller testers 26a, 26b
The control device 28 or the variable DC power supply 27a of the pre-transfer guide 27 is controlled according to the measurement result, so that the sheet paper P is given the necessary and not too much optimum electric charge by the pre-transfer guide 27. Therefore, during transfer, the charge applied to the sheet paper P by the transfer charger 14a does not escape from the pre-transfer guide as in the conventional case. Therefore, a good transferred image can be obtained without reducing the transfer efficiency, and a good copy image without fogging or image omission can be obtained regardless of the deterioration of the sheet paper P. Furthermore, by controlling the voltage applied to the pre-transfer guide 27, unnecessary power consumption can be prevented.

Next, a second embodiment of the present invention will be described with reference to FIGS. 6 and 7. Note that the same parts as in the first embodiment are given the same reference numerals, and the explanation thereof will be omitted.

In this embodiment, since the electrical resistance value of the sheet paper P is changed according to changes in the surrounding humidity, the first and second roll testers 26a 26 in the first embodiment
In place of the resistance measuring means consisting of b, a humidity sensor is used as the measuring means for measuring the transfer conditions.

That is, a humidity sensor 41 is provided on the inner wall 1a of the casing above the paper feed tray 18c of the image forming apparatus 1, and the output from the humidity sensor 41 is input to the control device 43. The control device 43 controls the variable DC power supply 27a so that the voltage applied to the pre-transfer guide 27 is optimized according to the output from the humidity sensor 41.

Therefore, when copying uses the same sheet of paper P as in the first embodiment, the control device 43 applies the voltage shown in FIG. 8 to the pre-transfer guide 27 in accordance with the humidity from the humidity sensor 41. , which controls the variable DC power supply 27a.

When copying is started, the humidity inside the image forming apparatus 1 is measured by the humidity sensor 41.
The potential from is input to the control device 43. Accordingly, the control device 43 controls the variable DC power supply 27a so that the voltage applied to the pre-transfer guide 27 is optimized according to FIG.

In this state, a toner image 13a is formed on the photoreceptor 10 in the same way as in the first embodiment, while each cassette 18a is
, 18b or the paper feed tray 18c, the sheet paper P is conveyed toward the photoreceptor 10 by the registration rollers 24, and while passing through the pre-transfer guide 27, the sheet paper P is charged at the same rate as the charge applied to the transfer charger 14a. A polar charge will be applied. Then, the sheet paper P is transferred to the transfer charger 14
When the toner image 13a is reached, the pre-transfer guide 27 applies an appropriate amount of charge to sufficiently hold the charge from the transfer charger 14a, and transfer the toner image 13a.

Thereafter, the sheet paper P is peeled off from the photoreceptor 10, passes through the fixing device 36, completes the copy image, and is discharged to the paper discharge tray 21. On the other hand, the photoreceptor 10 is cleaned by a cleaning device 16.
, the next copy is made possible through the static elimination lamp 17.

Note that when a change in humidity within the image forming apparatus 1 is detected by the humidity sensor 41 while repeating the copy operation, the controller 4
3, the variable DC power supply 27a is controlled according to FIG. 8, and the voltage applied to the pre-transfer guide 27 is varied.

With this configuration, the pre-transfer guide 27 can apply an electric charge to the sheet paper P, and moreover, the applied voltage of the variable DC power supply 27a can be varied in accordance with changes in the output from the humidity sensor 41. Therefore, at the time of transfer, the sheet paper P receives an appropriate amount of charge that is necessary to retain the charge applied by the transfer charger 14a and is not too large, and is applied to the pre-transfer guide 2.
7, the transfer efficiency is stabilized and a good transferred image can be obtained regardless of the decrease in electrical resistance.

Further, excessive power consumption is also prevented.

It should be noted that the present invention is not limited to the above-mentioned embodiments, and can be modified in various ways. For example, the charging polarity of the image forming object, and even the charging polarity of the toner, etc., can be changed as desired. Of course, the polarity of the charge applied by the transfer means or the charge applied by the charge applying means changes. The image formed on the image forming body may be either a toner image or an electrostatic latent image. Furthermore, the position of the charge applying means is arbitrary as long as it is possible to prevent the charge applied to the image bearing member from escaping in the transfer means.
As in another modification shown in FIG. 9, a post-transfer guide 46 is provided downstream of the photoreceptor 10 and adjacent to the peeling charger 14b, and a variable DC power supply 47 applies voltage to the post-transfer guide 46. may be controlled by the control device 4B according to the output from the humidity sensor 41.

[Effects of the Invention] As explained above, according to the present invention, even if the electrical resistance value of the image bearing member decreases due to ambient humidity during image formation or moisture absorption of the image bearing member, during transfer, Separately from the transfer means, charge is applied to the image carrier by a charge imparting means whose applied voltage is varied in accordance with changes in transfer conditions such as humidity or electrical resistance of the image carrier. This prevents the applied charge from escaping.

Therefore, during transfer, the image carrier can hold sufficient charge necessary for transfer, and a clear and good transferred image can be obtained without reducing transfer efficiency or causing fog or image omission. In addition, it is possible to improve the image quality.

Further, since the voltage applied to the charge applying device is controlled to a level that is necessary and not too high, unnecessary power consumption is also prevented.

[Brief explanation of drawings]

1 to 5 show a first embodiment of the present invention, FIG. 1 is a schematic explanatory diagram of an image forming apparatus, FIG. 2 is a schematic explanatory diagram showing the area around the transfer charger and its control, and FIG. is an explanatory diagram showing the state of charge retention of sheet paper P during transfer,
Figure 4 is a graph showing changes in the surface specific electrical resistance of sheet paper P with respect to changes in ambient humidity, and Figure 5 is a graph showing changes in surface specific electrical resistance of sheet paper P.
6 to 8 show a second embodiment of the present invention, and FIG. 6 is a schematic explanatory diagram of an image forming apparatus. 7
FIG. 8 is a graph showing the variable DC power supply with respect to changes in humidity around the sheet paper P. FIG. 9 is a diagram showing the surroundings of the transfer charger and its control in another modification of the present invention. It is a schematic explanatory diagram showing the control. DESCRIPTION OF SYMBOLS 1... Image forming apparatus, 14... Transfer peeling charger, 26a, 1st roller tester, 26b, 2nd roller tester, 27... Pre-transfer guide, 27a... Variable DC power supply,
28... Control device, agent Patent attorney Norihiro Ogo Diagram [Ωcml Ix+O'1 [V] Long IY11nIi Hiromaru ↑ Mr. Milk [Qcm] Diagram Diagram 4th pair @ degree [0n RH ) Figure Figure

Claims (3)

[Claims] (1) In an image forming apparatus having a transfer means for electrostatically transferring an image formed on the image carrier to a transfer target opposite to the image carrier, the a measuring means for measuring environmental conditions that contribute to image transfer efficiency; a charge applying means provided in a conveyance path of the transferred object and applying an electric charge to the transferred object in the vicinity of the transfer means; and measurement of the measuring means. An image forming apparatus comprising: a control means for controlling the voltage applied to the charge applying means according to the result. (2) The image forming apparatus according to claim 1, wherein the measuring means is a humidity measuring means for measuring the humidity around the transfer target. (3) Claim 1, characterized in that the measuring means is a resistance value measuring means for measuring the electrical resistance value of the image carrier.
The image forming apparatus described in .