JPH02129678A - Image forming device - Google Patents

Abstract

PURPOSE:To prevent uneveness in transferring density by impressing intermittent voltage to a transferring roller while the transferring material is absent when the transferring material is detected to be absent. CONSTITUTION:While connecting a DC power source 8 to a transferring roller 2 through a switch 3, a switch controlling means 5, which controls the switch 3, and a non-image area discriminating means 6, which discriminates a pre- rotating part of a photosensitive body 1 etc. are provided. Then when the non- image area of the photosensitive body 1 is detected by the non-image area discriminating means 6, the switch controlling means 5 is controlled to be ON/ OFF, and the output form the power source 8 is made to be a rectangular shaped wave form. As a result, the voltage to the transferring roller in the non-image part is made smaller. Thus, eneveness in transferring density becomes unnoticeable, and the image is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Object of the Invention (Field of Industrial Application) The present invention relates to an image forming apparatus using an electrostatic transfer process, such as an electrostatic copying machine and a printer thereof.

(Prior art and issues to be solved) After uniformly charging the surface of an image carrier and adding optical image information to form an electrostatic latent image, a charged developer is supplied to form a developed image. In a well-known image forming apparatus that electrostatically transfers a developed image to a transfer material such as paper, a one-reversal development method has been proposed in which a developer is supplied to an electrostatic latent image to create a developed image. It is well known that there are.

In the reversal development method, after the image carrier is primarily charged and exposed, it is developed with a developer charged to the same polarity.
During transfer, a voltage with a polarity opposite to that of the negative charge is applied to the transfer material.

By the way, the photoreceptor normally used for -order charging is only charged either positively or negatively depending on the material, so it is not sensitive to charging of the opposite polarity, or there is no charge in the photosensitive layer. was injected, which could become trapped and create a charged memory.

For this reason, there is no particular problem when the transfer material is present at the transfer site where the image carrier faces the transfer member such as a transfer charger or transfer roller placed close to or in contact with the image carrier, but if the During post-rotation or during continuous sheet feeding, the potential of the areas where the transfer material directly faces the image carrier and receives the transfer voltage, such as the area between adjacent transfer materials, is temporarily lowered during the next image formation. Density unevenness called paper marks may occur on the image.

In order to avoid such drawbacks, it is known to turn off the transfer bias when the transfer member directly faces the image carrier, as described above. As time passes, the bright area potential of the photoreceptor gradually increases, and when continuous paper feeding is carried out, there is an inconvenience that the density decreases, and this situation is particularly noticeable in OPC photoreceptors.

The present invention has been made to deal with this situation, and by appropriately controlling the amount of charge caused by transfer in areas where there is no transfer material, it is possible to prevent the density unevenness described above from occurring. It is an object of the present invention to provide an image forming apparatus that can always and stably obtain high-quality images.

(2) Structure of the invention (technical means for solving the problem and its operation) In order to achieve the above object, the present invention provides an image forming apparatus equipped with an image bearing member and a transfer roller that comes into contact with the image bearing member. a detection means for detecting that there is no transfer material between the two;
The apparatus is characterized by comprising means for applying an intermittent voltage to the transfer roller during the absence of the transfer material when the detection means detects the absence of the transfer material.

With this configuration, it is possible to prevent the occurrence of image unevenness due to an increase in the cumulative number of sheets passed and an increase in the bright area potential of the photosensitive layer, thereby obtaining a high-quality image.

(Description of Embodiments) FIG. '1 is a side view showing an embodiment in which the present invention is applied to an image forming apparatus equipped with a photoreceptor on a rotating cylinder.

It is assumed that a transfer roller 2 has an axis perpendicular to the plane of the paper, is disposed in contact with a photoreceptor l rotating in the direction of arrow A, and travels in synchronization with the photoreceptor l in the direction of arrow B.

When the toner image formed on the surface of the photoreceptor 1 is brought to the transfer site where the transfer roller 2 comes into contact as it rotates, a transfer material (not shown) is transferred from the conveyance path 4 in time with the toner image. is supplied to the transfer site and enters the abutting nip between the photoreceptor 1 and the transfer roller 2, and the toner image on the photoreceptor 1 is transferred to the transfer material by the action of the transfer bias applied by the power source 8.

It is assumed that the transfer material carrying the toner image and passing through the nip portion is conveyed to a fixing site (not shown) by the conveyance path 7 while carrying the toner image.

In addition, around the photoreceptor 1, there is a primary charger for uniformly charging the surface, an image-modulated laser beam, reflected light from the document, etc. to form an electrostatic latent image on this charged surface. image information writing means for adding image information, a developing device for supplying toner to the latent image to form a toner image, a cleaning means for removing residual toner, a pre-exposure means for removing residual charge, and others. It goes without saying that members necessary for forming the mountain image are provided, but since they are not directly related to the present invention, they are all omitted.

In the image forming apparatus shown in FIG. 1, a DC power supply 8 is connected to the transfer roller via a switch 3, and a switch control means 5 for controlling the switch 3 is connected to A non-image area discriminating means 6 is provided for discriminating non-image areas such as rotating parts.

When the non-image area of the photoreceptor l as described above is detected by the non-image area discrimination means 6, the switch control means 5 is controlled to turn on/off so that the output from the power source 8 is changed as shown in FIG. It has a rectangular wave shape.

As a result, the voltage applied to the transfer roller in the non-image area is
It is substantially weakened as shown by the broken line in the figure.

With this configuration, unevenness in density due to paper marks does not occur, and charging in non-image areas such as during pre-rotation is suppressed to suppress the rise in bright area potential that is particularly noticeable when using an OPC photoreceptor. The amount can be set to an appropriate value.

Charging unevenness can be effectively prevented by setting the pulse length (sec) in Figure 2 to 172 or less, which is the value obtained by dividing the contact nip width (5ea) between the photoreceptor and the transfer roller by the circumferential speed of the photoreceptor. We were able to.

FIG. 3 shows another embodiment of the output waveform applied to the transfer roller in the non-image area in an image forming apparatus whose basic configuration is similar to the above-mentioned apparatus. 6. The switch control means 5 converts the pulsed output from the DC power source 8 into rectangular waveform outputs with different duty ratios, as shown in the figure.

As a result, the average voltage applied to the transfer roller in the non-image area becomes a gentle curve with a low center at the center, as shown by the broken line in the figure, and the changes in the applied voltage become smoother overall. Paper marks become less noticeable and image quality improves.

FIG. 4 shows another embodiment of the present invention, in which the basic configuration for image forming operation is not particularly different from the apparatus of the above-described embodiment, and corresponding parts are given the same reference numerals. They are shown as follows, and their explanation will be omitted unless particularly necessary.

In the apparatus of H, the non-image area discriminating means 6 and the DC power supply 8 are
While controlling the voltage applied to the transfer roller 2 by
AC power supply9. A DC power supply 10 is connected to the transfer roller via a switch 3b, and this switch 3b is also connected to the non-image area discriminating means 6. It is configured to be controlled by switch control means 5.

When the non-image area discrimination means 6 detects that the transfer roller 2 is facing a non-image area such as the pre-rotation, the switch control means 5 opens the switch 3a and closes the switch 3b to perform the second transfer. While the roller 2 faces the non-image area of the photoreceptor 1, a sinusoidal output as shown in FIG. 5 is applied to the transfer roller 2. When the non-image area is completed, the switches 3a and 3b are opened and closed in the opposite manner, and a flat DC transfer bias is applied to the transfer roller 2.

As a result of the application of the output, the voltage applied to the transfer roller 2 is substantially weakened to about half the voltage during transfer, as shown by the broken line in the figure, and in the case of parentheses, the change in the voltage waveform is 1. No rectangular image unevenness as shown in the figure,
Also, it is possible to prevent the bright area potential from increasing in the case of an OPC photoreceptor.

It becomes possible to optimally set the amount of charge in the non-image area.

FIG. 6 shows still another embodiment of the present invention, and this device basically has the same configuration as the device shown in FIG. 4, and further controls the frequency etc. of the AC power source 9. The AC power supply control means 11 for this purpose is arranged so as to be controlled by the non-image area discriminating means 6.

When the non-image area discrimination means 6 detects a non-image area where the photoreceptor 1 and the transfer roller 2 are directly facing each other, the switch control means 5 opens the switch 3a, closes the switch 3b, and turns on the AC power source. 9. A voltage having a waveform as shown in FIG. 7 is applied to the transfer roller 2 by the DC power supply 10. As a result, while the transfer roller 2 is facing the non-image area of the photoreceptor l, the bias voltage at the transfer roller 2 gradually decreases to the normal bias voltage, as shown schematically by the broken line. A voltage is applied that drops to about half of the voltage and then rises gently.

By smoothing the change in the applied voltage in this way, the paper marks become even less noticeable and the image quality improves.

(3) As described in detail, in the present invention, in an image forming apparatus including an image bearing member and a transfer roller in contact with the image bearing member, there is no transfer material between the two, and the transfer roller By intermittently applying voltage to the transfer roller when the transfer roller directly contacts the image carrier, it is possible to prevent density unevenness caused by paper marks without the need for a separate power supply, and to prevent unevenness in density from occurring due to paper marks. , it is possible to prevent the bright area potential of the photosensitive layer from increasing, which greatly contributes to obtaining high-quality images.

[Brief explanation of drawings]

FIG. 1 is a schematic side view of an image forming apparatus showing an embodiment of the present invention, FIG. 2 is a voltage waveform applied to the transfer roller by the same device in a region where no transfer material is present, and FIG. 3 is a voltage waveform applied to the transfer roller. Other voltage waveforms, FIG. 4 is a side view of an image forming apparatus showing another embodiment of the present invention, and FIG. 5 is a voltage waveform applied to a transfer roller in a region where no transfer material is present by the same device. FIG. 6 shows a voltage waveform applied to the transfer roller in an image showing still another embodiment of the present invention. l...Photoreceptor, 2. Transfer roller, 3, 3a, 3b
...Switch, 5...φ switch control means, 6 Emperor e...
Non-image area discrimination means, 8.10.e. DC power supply, 9.
·AC source. Figure 2 Figure 3 Figure Figure Figure Figure Figure Zero Roller's Murayama

Claims (3)

[Claims] (1) In an image forming apparatus including an image bearing member and a transfer roller in contact with the image bearing member, a detection means detects the absence of a transfer material between the two, and the detection means detects the absence of the transfer material. An image forming apparatus comprising means for applying an intermittent voltage to a transfer roller during the absence of the transfer material when the transfer material is detected. (2) The image forming apparatus according to claim 1, wherein the voltage applied to the transfer roller when no transfer material is present is a rectangular wave voltage. (3) The image forming apparatus according to claim 1, wherein the voltage applied to the transfer roller when no transfer material is present is a sinusoidal voltage.