JPH04204149A - Resistance-value measuring device for recording paper in image forming apparatus - Google Patents

Abstract

PURPOSE:To make it possible to measure the resistance value of recording paper highly accurately by applying a voltage so that 8 counter electrode and a main electrode have approximately the same potential and a current flows across a guard electrode and the counter electrode through the thickness of the recording paper. CONSTITUTION:When the resistance of recording paper P is measured, a specified voltage is applied from a DC power supply 30 to electrodes 53 and 54. At this time, the counter electrode 53 and a main electrode 54a have approximately the same potential. A current flows across a guard electrode 54b and the counter electrode 53 through the thickness of the recording paper P. A current flows across the guard electrode 54b and a main electrode 54a through one surface of the recording paper P. The voltage is applied on the electrodes 53 and 54 in this way. At this time, the value of the current flowing through the surface of the recording paper between the guard electrode 54b and the main electrode 54a is detected by a current-value detecting means 31. Namely, the resistance value of the surface of the recording paper P is detected highly accurately.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a recording paper resistance measuring device in an image forming apparatus.

[Conventional technology]

Image forming apparatuses that use electrophotography or electrostatic recording technology, such as electronic copying machines, facsimiles, or laser printers, form images on recording paper, but when forming such images, the resistance of the recording paper The value affects the image quality.

For this reason, a method has already been proposed in which the resistance value of the recording paper to be used is determined and the various process devices of the image forming apparatus are controlled accordingly (for example, Japanese Patent Laid-Open No. 62-50782
(see publication). For example, when a recording paper is brought into close contact with a toner image formed on a photoconductor and a transfer charger applies corona discharge from the back side of the toner image to transfer the toner image onto the recording paper,
When the humidity is high, the resistance value of the recording paper decreases, so the current supplied to the transfer charger is increased to compensate for the decrease in transfer efficiency. In addition, the separation performance of the separation charger used to separate the recording paper from the photoreceptor changes depending on the wet state of the recording paper, that is, fluctuations in its resistance value.
A current matching the resistance value of the recording paper can be supplied to the separate charger.

One conventional example of measuring the resistance value of recording paper is a method in which a pair of electrodes are provided with the recording paper in between, and the resistance value of the recording paper is measured by detecting the current flowing between the electrodes. This method has the advantage of having a simple device configuration and being easy to implement. However, during this measurement operation, a portion of the current is transmitted along the surface of the recording paper, causing damage to various elements of the image forming device, such as the recording paper. The leakage current flows to the registration rollers for conveyance, and this leakage current may cause a measurement error.

Especially under high humidity, the resistance value of the recording paper decreases.
Leakage current increases and measurement reliability decreases. If leakage current can be predicted in advance, it can be improved by devising control.
Although it is possible to eliminate measurement errors, the leakage current value becomes extremely unstable due to environmental changes and subtle behavior of the recording paper, and it is practically impossible to predict this. In the end, it is necessary to eliminate measurement errors by suppressing leakage current as much as possible, but this approach has the disadvantage of complicating the configuration of the measuring device and increasing its cost.

[Problem to be solved by the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a recording paper resistance measuring device for an image forming apparatus that eliminates the above-mentioned conventional drawbacks with a simple configuration.

[Means to solve the problem]

In order to achieve the above object, the present invention includes: a main electrode that contacts one surface of recording paper; a guard electrode that contacts the same surface and surrounds the main electrode; and the guard electrode and the main electrode. A counter electrode facing the electrode and in contact with the other surface of the recording paper, the counter electrode and the main electrode having approximately the same potential, and a gap between the guard electrode and the counter electrode via the thickness of the recording paper. means for applying a voltage to each electrode such that a current flows through one surface of the recording paper between the guard electrode and the main electrode; An apparatus for measuring the resistance value of recording paper in an image forming apparatus is proposed, which includes a current value detection means for detecting the value of current.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a diagram schematically showing an electronic copying machine which is an example of an image forming apparatus equipped with a resistance value measuring device according to the present invention.
First, its overall configuration and operation will be briefly explained.

A photoreceptor 1 formed in the shape of a drum is rotated clockwise, and at this time, the photoconductive layer on the surface is uniformly charged to a predetermined polarity by a charging charger 2, imagewise exposed in an exposure section 3, and a photoreceptor is exposed on the photoreceptor. An electrostatic latent image is formed. When this latent image passes through the developing device 4, it is visualized as a toner image.

On the other hand, the recording sheets P stored in the paper feed cassette 5 of the paper feed section are fed out from the uppermost sheet by the rotation of the paper feed roller 17. At the bottom of the paper feed roller 17, a paper feed pad 18 whose surface is made of cork material is provided as shown in the figure.
Only one sheet of the recording paper P is fed to the registration roller 6 without being fed multiple times due to friction with the cork material.

The recording paper P sent out in this manner stops once its leading edge reaches the registration roller 6, and then is fed to the surface of the photoreceptor 1 at a predetermined timing by the rotation of the registration roller 6. The toner image is aligned with the above-mentioned toner image, and at this time, the toner image on the photoreceptor is transferred onto the recording paper P by corona discharge from the transfer charger 7. Subsequently, due to the action of corona discharge from the separation charger 10, the recording paper P is separated from the photoreceptor-1 and transferred to the conveyor belt 11.
The toner image on the recording paper is transported to the fixing device 12 and passed between two fixing rollers of the device 12, at which time the toner image on the recording paper is fused to the recording paper by heat and pressure. In this way, the final image is formed on the recording paper, and this recording paper P is discharged onto the paper discharge tray 13.

The toner remaining on the photoreceptor 1 after the toner image transfer is removed by the cleaning device 14 and initialized.

A high voltage is applied to each charge wire of the transfer charger 7 and the separation charger 10 by a high voltage power supply 15, 16, and this L causes a corona discharge as described above. The same applies to the charger.

As shown in FIG. 2, the paper feed roller 7 and the registration roller 6
A recording paper resistance measuring device 20 is provided along the recording paper conveyance path between the recording paper and the recording paper, and its specific configuration is as follows.

Assume that the leading edge of the recording paper P has reached the registration roller 6 and is stopped as shown in FIG. A main electrode 54a made of a conductor is in contact with the main electrode 54a. In addition, for example, a main electrode 54a is provided so as to surround this main electrode 54a.
A guard electrode 54b is provided which is formed in a concentric ring shape with the center at . The guard electrode 54b is also made of a conductor such as metal, and contacts one surface of the recording paper P while being electrically insulated from the main electrode 54a.

Further, a counter electrode 53 is arranged to be in contact with the other surface of the recording paper P, facing the guard electrode 54b and the main electrode 54a, and this electrode 53 is also made of a conductor such as a metal plate.

In the illustrated example, the main electrode 54a and the guard electrode 54b located on one side of the recording paper P are integrated, and the electrode 54a and the guard electrode 54b are integrated.
This electrode 54 and the counter electrode 53 located on the other side of the recording paper P are indicated by arrows A and 53 in FIG. 2, respectively.
As shown by B, it is supported so as to be movable in the direction away from the recording paper P, and the recording paper P is moved between these electrodes 53 and 54.
When passing, both electrodes 53.5'4 separate from the recording paper P so as not to interfere with the conveyance of the recording paper P. Only when measuring the resistance value of the recording paper P, for example, by the pressurizing action of a spring (not shown), both electrodes 53 and 54 strongly sandwich the recording paper P as shown in FIG. Contact.

The resistance value of the recording paper P is measured while the leading edge of the recording paper P reaches the registration roller 6 and stops. Further, this measurement may be performed for each recording sheet, or may be performed at intervals of a number of sheets.

Alternatively, a humidity sensor (not shown) may be installed at a suitable location on the copying machine.
In this way, measurement may be performed only when a change in humidity is detected.

When each electrode 53, 54 is separated from the recording paper P, it is sufficient to prevent the aforementioned spring force from being applied to each electrode 53, 54 using, for example, an electromagnetic clutch (not shown).

When measuring the resistance value of the recording paper P, a predetermined voltage is externally applied to each of the electrodes 53 and 54 by the DC power supply 30 as shown in FIG. At this time, as can be seen from the circuit configuration of FIG. 2, the opposing type 'WA 53 and the main electrode 54a are at substantially the same potential. In this way, the main electrode 5 with almost the same potential
Almost no current flows between 4a and the counter electrode 53. Also, with respect to the thickness of the recording paper P, the main electrode 54a
Since the distance between the guard electrode 54b and the guard electrode 54b is sufficiently large, most of the current flowing from the guard electrode 54b into the recording paper P flows to the counter electrode 53, and the current flowing from the guard electrode 54b to the main electrode 54a flows into the recording paper from the guard electrode 54b. Only the current flows through the surface of P to the main electrode 54a. In this way, the counter electrode 53 and the main electrode 54a have almost the same potential,
In addition, a current flows between the guard electrode 24b and the counter electrode 53 through the thickness of the recording paper P, and a current flows through one side of the recording paper P between the guard electrode 54b and the main electrode 54a. , a voltage is applied to each electrode 53,54. At this time, the guard electrode 54b and the main electrode 5
The value of the current flowing on the recording paper surface between the current value and the recording paper surface is detected by the current value aspect ratio means 31. That is, the surface resistance of the recording paper P is detected.

Based on this detection result, the characteristic value of at least one process device of the copying machine, for example, the current supplied to the charge wire of the transfer charger 7 or the separation charger 10 (transfer current, separation current) is controlled, and the resistance value of the recording paper is controlled. Provides the most suitable corona discharge for the environment, making it less susceptible to environmental changes, etc.
A stable image can be obtained. More specifically, based on the output value of the current value detection means 31, the control circuit inside the copying machine changes the set values of the transfer current and separation current, which are predetermined control items, and starts the copying operation. It is. FIG. 3 is a block diagram illustrating the control operation. A detection signal from the current value detection means 31 that detects the value of the current flowing through the main electrode 54a is transmitted to the CPU 41 via the A/D converter 40. 'U41 is memory 42
Necessary instructions are given to the transfer and separation control circuits 43 and 44 according to information written in advance in the transfer and separation control circuits 43 and 44. In response to this instruction, the settings of the high voltage power source 15 for the transfer charger and the high voltage power source 16 for the separate charger are changed, and the copying operation is executed.

According to the recording paper resistance measuring device 20 shown in FIG.
A current flows between the guard electrode 54b and the counter electrode 53,
Moreover, since no current substantially flows between the main electrode 54a and the counter electrode 53, the guard electrode 54b and the main electrode 54
Only the current flowing through the surface of the recording paper stably flows between the recording paper and the recording paper, and this current can be detected correctly by the current value detection means 31.

Moreover, since the guard electrode 54b surrounds the main electrode 54a, the current flowing between the two depends only on the surface resistance value of the recording paper P. Therefore, the resistance value of the recording paper P can be determined stably and accurately without being affected by the condition of the recording paper, the device configuration, or other external factors, and without being affected by leakage current as in the past. Can be measured.

Assuming that no current flows between the guard electrode 54b and the counter electrode 53, the guard electrode 54b and the main electrode 54a
A current also flows between the inside of the recording paper P and the surface of the recording paper on the side opposite to the guard electrode 54b, and such current is not stable, resulting in a decrease in measurement accuracy. Further, assuming that a current flows between the main electrode 54a and the counter electrode 53, the guard electrode 54b and the main electrode 54
It is difficult to accurately detect only the current flowing on the surface of the recording paper between the recording paper and the recording paper, that is, the surface resistance of the recording paper.

In the embodiment shown in FIG. 4, the counter electrode 53 is made of a conductive elastic material such as conductive rubber with low hardness, rather than a rigid metal.

Therefore, this counter electrode 53 is connected to the recording paper P as shown in FIG.
When the electrode 53 contacts the recording paper P, the electrode 53 comes into close contact with the recording paper P, and contacts the electrode 54 over a sufficiently large area via the recording paper P. Therefore, the function of the counter electrode 53 can be achieved more reliably. Other configurations are the same as in the previous embodiment.

〔Effect of the invention〕

According to the present invention, with a simple configuration, the resistance value of the recording paper can be controlled with almost no external influence.

By being able to measure with high precision and controlling the image forming apparatus based on the results, it is possible to obtain stable, high-quality images.

[Brief explanation of the drawing]

Figure 1 is a schematic configuration diagram of an electronic copying machine, Figure 2 is an enlarged partial cross-sectional view of a recording paper resistance value measuring device, and Figure 3 is a block diagram for controlling the electrification charger and separate charger based on the measurement results. FIG. 4 is a diagram similar to FIG. 2, showing another embodiment. 2o...Resistance value measuring device 31...Current value detection means 53...Counter electrode 54a...Main electrode 54b...Gart electrode P...Recording paper agent Patent attorney Norio Hoshino

Claims (1)

[Scope of Claims] A main electrode that contacts one surface of recording paper; a guard electrode that contacts the same surface and surrounds the main electrode; and a guard electrode that opposes the guard electrode and the main electrode; and a counter electrode that is in contact with the other surface of the recording paper, and the counter electrode and the main electrode have approximately the same potential, and a current flows between the guard electrode and the counter electrode through the thickness of the recording paper, and the Means for applying voltage to each electrode so that a current flows through one side of the recording paper between the guard electrode and the main electrode, and detecting the value of the current flowing on the recording paper surface between the guard electrode and the main electrode. 1. An apparatus for measuring a resistance value of recording paper in an image forming apparatus, comprising: a current value detecting means for detecting a current value.