JPH01274171A - Image forming device - Google Patents

Abstract

PURPOSE:To prevent a partial transfer failure and deterioration in picture quality due to the scattering and sticking of toner on a guide member which guides a transfer material to an image carrier and to prevent a CPU from malfunctioning by grounding the guide member through a high resistance element and a constant voltage element which are connected in parallel. CONSTITUTION:The guide member which guides the transfer material 6 to the image carrier 1, i.e., both upper and lower guides 4 and 5 are grounded through the high resistance element 8 and constant voltage element 7 which are connected in parallel. Consequently, even when a guide metal part which are conductive to the transfer guide members 4 and 5 is exposed to outside the device, the partial transfer failure, the sticking of toner on the transfer material guide members 4 and 5, etc., are prevented and the malfunction of the CPU caused by noises is eliminated to perform stable image formation.

Description

Detailed Description of the Invention (1) Purpose of the Invention (Field of Industrial Application) This invention relates to an image forming apparatus that uses an electrostatic transfer process, such as an electrostatic copying machine or a printer, in particular an image forming apparatus that obtains an image by reversal development. It is related to the device.

(Prior art and problems to be solved) The transfer material is guided to the transfer site by the transfer material guide member in synchronization with the transferable toner image formed on the surface of the moving image carrier, and at this position, the transfer material is In a well-known image forming apparatus configured to transfer the toner image to a transfer material using a transfer device that applies corona discharge, especially in high humidity, transfer current leakage causes partial transfer defects, so-called transfer defects. Phenomena may occur during transfer removal.

In order to prevent this, it has been proposed to ground the transfer material guide member through a constant voltage element such as a varistor or a high resistance element. When forming an image by using a constant voltage element, when a constant voltage element is used, the potential of the transfer material guide member reaches 550 to 700 V, the polarity opposite to that of the toner, due to the inflow of transfer current, and the toner adheres to it, causing transfer. Since the material is contaminated, it is common to use a high impedance resistor to prevent transfer failure and to prevent contamination of the transfer material.

By the way, in an image forming apparatus that performs one reversal development,
Traditionally, a cassette was used as a paper feeding mechanism, but in recent years, devices equipped with manual paper feeding mechanisms such as multi-feeders have come into practical use. In some cases, the metal part of the paper feed guide that is electrically connected to the transfer material guide member is exposed outside the main body of the image forming apparatus.
Due to static electricity from the outside, thousands to 100
High voltage of 00V may be applied to metal parts exposed outside the device.

In such a case, since a high resistance member is connected to the protruding metal part of the multi-feeder part and the transfer material guide member, this high voltage is not instantly relieved and is temporarily maintained, causing the CPU to This could generate noise and cause malfunctions.

The present invention was made in view of the drawbacks such as ridges, and in image forming apparatuses that perform reversal development, the feeding guide metal part that is in electrical conduction with the transfer material guide member is exposed outside the apparatus. To provide a transfer device which can perform stable image formation by eliminating malfunctions of a CPU due to noise while maintaining functions such as transfer omission and toner adhesion to a transfer material guide member even in such cases. The purpose is to

(2) Structure of the invention (technical means for solving the problem and their effects) In order to achieve the above object, the present invention provides an image in which a toner image formed on an image carrier by reversal development is electrostatically transferred to a transfer material. The forming apparatus is characterized in that a guide member for guiding the transfer material to the image carrier is grounded via a high resistance element and a constant voltage element connected in parallel.

With this configuration, it is possible to prevent transfer omission and toner adhesion to the guide member, and also to prevent C due to noise.
Malfunctions of the PU can be prevented.

(Description of Embodiments) FIG. 1 is a schematic side view of the main parts of an image forming apparatus to which the present invention is applied. A negative toner 2 of the same polarity is applied to the photosensitive layer of the photoreceptor 1, which is negatively charged.
It is assumed that a toner image is formed by.

Reference numeral 4 indicates a lower guide constituting the transfer material guide member, and reference numeral 5 indicates an upper guide, both of which are electrically connected to a metal portion (not shown) exposed outside the apparatus.

The transfer material 6, which advances from the right in the figure to the left in synchronization with the toner image on the surface of the photoreceptor, comes into contact with the photoreceptor at a transfer position where the transfer charger 3 faces the photoreceptor 1, and the transfer charger 3 After the toner image on the photoreceptor is received by a transfer bias having a polarity opposite to that of the photoreceptor, the toner image is separated from the photoreceptor 1 and advances to a fixing site (not shown).

In such a device, in the present invention, both the upper and lower guides 4, 5 are grounded via a varistor 7, which is a constant voltage element, and a high resistance element 8, which are connected in parallel. in this case,
In the experiment, a 680v rated varistor was used as a constant voltage element.
An IOMΩ resistor was used as the resistor.

In normal operating conditions, even in a normal humidity or low humidity environment, the negative part of the corona discharge flow (indicated by the dotted arrow in the figure) from the transfer charger 3 flows into the guides 4 and 5, as shown in Figure 2. In a high-humidity environment, leakage occurs through the transfer material, which has a lower resistance, so that the current flowing into the guide becomes even larger.

According to experiments, for a total transfer current of +100 µA, the inflow into the transfer guide is approximately 10 μA to +10 μA under all conditions.

Under such conditions, the varistor 7 becomes a high impedance to minute currents, and its resistance value becomes extremely large compared to the resistor 8 connected in parallel. The current flowing into .5 is approximately resistor 8.
flows to ground through.

At this time, the voltage of the guide was approximately 100V or less.

Figure 3 shows the momentary 1
This example shows a case where a current of OkV flows into the transfer material guide member. In such a state, a high voltage is applied to the guide member, so the varistor has a low resistance, and the resistance value is lower than that of the resistor 8. Since the inflow current momentarily escapes to the ground via the varistor 7, no malfunction of the CPU occurs at all.

When the distance between the photoconductor 1 and the guides 4 and 5 of the guide member is 1.5 J, an experiment was conducted to determine the guide voltage and the presence or absence of toner scattering from the photoconductor to the guide, and the results are shown in the table below. Obtained.

From this, it was found that in order to prevent the toner from scattering and adhering to the guide member, it is sufficient to suppress the voltage of the guide to +200V or less, and with the above-mentioned configuration, it is possible to prevent toner from missing or toner from scattering. It was confirmed that it is also possible to prevent malfunctions of the CPU.

FIG. 4 shows another embodiment of the present invention. In this figure, parts corresponding to those of the above-mentioned embodiment are denoted by the same reference numerals, and no explanation is necessary. It will be omitted unless otherwise specified (this also applies to the following examples).

In the case shown in FIG. 4, a Zener diode is used instead of a varistor, and at least a pair of forward-reverse diodes 91 and 92 connected in series is arranged in parallel with the high-resistance element 8. and each guide 4, 5 of the guide member
is grounded through these.

It will be easily understood that by configuring this way, the same effect as that of the previous embodiment can be obtained.

Furthermore, as shown in FIG. 1, a plurality of forward-reversely connected Zener diode pairs 9 are connected in series to increase the Zener voltage, thereby further improving the noise prevention function.

Note that it is sufficient to use at least one Zener diode in either the forward or reverse direction, but in that case, the desired effect can only be obtained with respect to one polarity, so the above It is preferable to use them in pairs.

FIG. 5 shows still another embodiment of the present invention.

In this device, resistance elements 8 were connected in parallel in opposite directions. It is connected in parallel with at least one diode pair, and both guides 4.5 of the guide member are connected via these.

It will be readily understood that this device performs the same functions as those of each of the embodiments described above.

FIG. 6 shows yet another embodiment of the present invention, in which only the lower guide 4 constituting the guide member of the image forming apparatus is electrically connected to a metal part (paper feed guide) exposed outside the apparatus. In this example, the upper guide 5 is insulated from the lower guide and the paper feed guide.

In this case, as shown in Figure 1, the insulated upper guide 5 is grounded only through a high-resistance element 82 that prevents transfer failure, toner adhesion, etc., and is connected in parallel to the lower guide 4. The structure is such that it is grounded via the high resistance element 81 and the helistaph.

FIG. 7 shows a further embodiment of the invention, in which the upper guide 5 of the guide member extends outside the device, and the lower guide is separated into guides 41, 42, which are Although it is necessary to extend the guide 41 outside the device, it is assumed that it is insulated from the guide 41. The guide 41 on the inside is usually made of metal and grounded on the bottom substrate 4 of the main body of the image forming apparatus, so it is not susceptible to external influences, so it can be grounded only through the resistor 82. It is sufficient that only the upper guide 5 is grounded via the resistive element 81 and the varistor 7.

Examples of embodiments of the present invention are as follows.

(2) The image forming apparatus according to the claims, wherein the constant voltage element is a varistor.

(2) An image forming apparatus according to the claims, wherein the constant voltage element is a diode.

(2) The image forming apparatus according to the claims, wherein the constant voltage element is a Zener diode.

(3) As described in detail, the present invention can prevent image quality deterioration due to transfer omissions and toner scattering and adhesion to the guide member, especially in image forming apparatuses that form images by reversal development. In addition, such a simple configuration reliably prevents malfunctions of the CPU, which has a significant effect on maintaining normal operation of the image forming apparatus.

[Brief explanation of the drawing]

FIG. 1 is a schematic side view of the main parts of an image forming apparatus showing an embodiment of the present invention, FIGS. 2 and 3 are explanatory diagrams explaining the operation of the same apparatus, and FIGS. FIG. 7 is a side view showing another embodiment of the invention. DESCRIPTION OF SYMBOLS 1... Image carrier, 3... Transfer charger, 411... Lower guide of the guide member, 5... φ same guide, 7 φ constant voltage element (varistor), 8... e high resistance element , 9110・
Zener diode, lO... diode. Figure 4 Figure 5 Figure 6 Figure 7

Claims (1)

[Claims] In an image forming apparatus that electrostatically transfers a toner image formed on an image carrier by reversal development to a transfer material, there is provided a high-resistance system in which guide members for guiding the transfer material to the image carrier are connected in parallel. An image forming apparatus that is grounded via an element and a constant voltage element.