JPS606966A - Electrophotographic device - Google Patents

Abstract

PURPOSE:To prevent a carrier from sticking to a no-image part and toner from sticking to an image ground part by switching a developing roll bias voltage for the no-image part between images on a photosensitive body so that the voltage is lower than that for image parts on the photosensitive body. CONSTITUTION:The developing roll bias circuit 13 consisting of a boosting and rectifying circuit 10, oscillation control circuit 11, and reference signal circuit 12 is provided so as to prevent a carrier from sticking to the no-image part. The bias voltage V of a developing roll 7 is switched between the image part and no- image part. Namely, the bias voltage V is so controlled that V=VB>VD+VL when the image part faces the developing roll and VB>V>VD when the no- image part faces the developing roll. In this case, VL is the potential of the image background part and VB is the potential for density. Thus, the developing roll bias voltage is controlled to prevent completely the toner from sticking to the image background part and the carrier from sticking to the no-image part between images.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an electrophotographic apparatus, and more specifically, to an electrophotographic apparatus in which developing roll bias voltage is controlled to prevent carrier from adhering to a photoreceptor. There is one thing.

Prior Art In a normal electrophotographic device, light is uniformly irradiated on the non-image area between the original images on the photoreceptor between the charging section and the front of the developing section according to the image size, and the surface potential of the non-image area is is made lower than the surface potential of the image background area to prevent toner from adhering to the non-image area. When performing such light irradiation, take into consideration the temperature and humidity characteristics of photoreceptor sensitivity and the deterioration of the photoreceptor, and the scene irradiated to the non-image area is several times that of the light irradiated to the image background area. There is a large amount of 1 as described above, and therefore the surface potential of the non-image area irradiated with light is approximately Odz. On the other hand, a bias higher than the surface potential of the image background area is applied to the developing roll to prevent the toner from adhering to the developing roll.

However, in conventional two-component developers that use toner and carrier, the amount of charge on the carrier increases depending on the toner concentration and environmental conditions, and on the other hand, since a deep bias is applied to the image roll, non-images on the photoreceptor may This causes problems such as the occurrence of scratches on the surface of the photoreceptor due to cleaning of the surface of the photoreceptor by the cleaner, the occurrence of scratches on the surface of the fixing roll, and the reduction of carrier in the developer. There is. This problem is particularly noticeable when microtoning is performed or when a small particle size carrier is used. However, when the application of the developing bias is cut off, the response time is delayed and toner adheres to the developing roll due to self-noise.

OBJECTS OF THE INVENTION An object of the present invention is to provide an electrophotographic apparatus that prevents carrier from adhering to non-image areas between original images on a photoreceptor and toner from adhering to image background areas as described above.

SUMMARY OF THE INVENTION The above objects are achieved by switching the developer roll bias voltage for non-image areas between images on the photoreceptor to be lower than for image areas on the photoreceptor. The apparatus of the present invention will be described in detail below with reference to the drawings.

Generally, in an electronic copying machine, in order to obtain good contrast in the low-density part of an N-document image, the potential (VL) of the background part of the image is set to be higher than the residual potential (0 in VR).
(see figure). The potential of the non-image area between the images on the photoreceptor (1) is erased by irradiation from the inter-image lamp (6) installed between the charging corotron (2) and the developing roll (7). vRt =, s is lowered.

In Figure 1, (3) is the light spit, (4) is the platen,
(5) is a slit. On the other hand, the background area is constrained by the upper limit concentration as shown in Figure 3, and the potential (
It is necessary to determine the development and 9-earth (VB) so as to obtain VD). That is, VB is set so that VD)■B-■L. However, the potential of the non-image area (VR
0) is F1! Since the potential (V) of the B image area is also lower, Vn
- If VD > VD, toner will not adhere to the surface of the photoreceptor; if VB-VB: VB > Vc (carrier potential), no carrier will adhere to the surface of the photoreceptor. The relationship between the amount of gear attached to the non-image area on the photoreceptor and the potential of the non-image area is shown in the diagram of FIG. Varies depending on concentration and environmental conditions.

In order to prevent such carrier adhesion to non-image areas on the photoreceptor, according to the present invention, a developing roll noise circuit a3 as shown in FIG. 5 is provided.

Then, the developing roll's voltage (V) is switched between the image area and the non-image area, and when the image area faces the developing roll, the developing roll's voltage (V) = V
s＞VD10VL Tofx le! W-K L, non-ii
! 1iyi! When facing the developing roll, Vn>
The developing roll pressure (V) is controlled so that the developing roll voltage (V) > VD.Here, II is a step-up rectifier circuit, (11) is an oscillation control circuit, and α is a reference signal circuit. By controlling the developing roll bias voltage in this manner, it is possible to completely prevent toner from adhering to the image background area on the photoreceptor and carrier from adhering to the non-image area between images.

Effects of the Invention According to the present invention, when the non-image area between images on the photoreceptor faces the developing roll, the developing roll noise voltage is cut so that it is lower than when the image area faces the developing roll. This not only greatly prevents carrier adhesion to non-image areas, but also reduces the response speed of the rise and fall of the noise sensor compared to the conventional method of switching the bias power supply from 0N10FF. One advantage is that it can be applied particularly to the operation of high-speed photographic equipment.

[Brief explanation of the drawing]

Figure 1 shows the main parts of the electrophotographic device, Figure 2 shows the light attenuation characteristics of the photoreceptor, and Figure 6 shows the surface potential (V) of the photoreceptor.
FIG. 4 is a diagram showing the relationship between the potential difference between the photoconductor and the developing bias voltage and the amount of carrier attached to the photoconductor; FIG. 5 is a diagram showing a developing roll bias circuit according to the present invention. Symbols in the figure: 1... Photoreceptor, 2... Charged corotron, 6... Light source, 4... Platen, 5... Slit, 6... Inter-image lamp, Procedural Amendment 1981 August/Japan Patent No. 11454<S No. 1988 2, Name of the invention Electrophotographic device 3, Relationship with the person making the amendment case, Name of the patent applicant 1. tN-Shize Tsuku Co., Ltd. 2) Please refer to the letter a in ``Detailed Description of the Invention''. (1) "Developing roll" in lines 12-13 of page 2 of the specification is corrected to "image background". (2) Page 6, lines 5 to 7, “Development
...There was a drawback. ' shall be corrected as follows. "Also, when the application of the developing bias voltage is cut off, there is a delay in response time, and there is a drawback that toner adhesion to the photoreceptor due to self-biasing occurs." ts+ tt Change "slit" in line 4717 to " Correct with "Selfoc Lens". (4) "On the other hand, the background section controls..." from line 7 on page 4 to line 10 on page 5 is corrected as follows. ``On the other hand, as shown in Figure 3(a), the background area is constrained by the upper limit density.
is the developing roll bias voltage (VB) and I[! The difference from the II image background potential (VL) corresponds to the upper limit density DK'
so that it is larger than the potential (VD), that is, the following formula 1
It must be adjusted so that the relationship expressed by the formula % is maintained (see Figure 3(b)). However, since the potential of the non-image area between the images on the photoreceptor (approximately vR = 8-0 due to the irradiation of the VB moon and inter-image lamp (6)), the surface potential of the photoreceptor between the developing roll and the non-image area is The potential difference (VB in VB-vR) is much thicker than the potential difference (VB-VL) between the developing roll and the image background potential (see Figure 3(b)). As shown in Figure 4, it is known that the amount of carrier adhering to the area increases rapidly from a constant potential difference (CVC), but the potential difference (Vc) at which carrier adhesion starts varies depending on the toner concentration and environmental conditions. Therefore, when the difference between the developing roll bias acid pressure vB and the potential VR of the non-image area between images on the photoreceptor becomes larger than the carrier adhesion start voltage (Vc), that is, (VB When the relationship vB > v (in VR) occurs (see Fig. 6(b)), carrier adhesion occurs on the non-image area of the photoreceptor, and the image quality of the copy decreases due to the decrease of carrier in the developing device. This results in problems such as deterioration and the occurrence of scratches on the surface of the photoconductor and the roll.In order to prevent carrier adhesion to non-image areas between images on the photoconductor, which causes such disadvantages, the present invention has been developed. According to the development roll A477 circuit (16) as shown in FIG.
will be established. Then, the developing roll bias voltage (VB) is switched for the image area and the non-image area on the photoconductor, respectively, and when the image area faces the developing roll, the developing roll bias voltage (VB) is changed so that VB > VL + l When the non-image area between images faces the developing roll, the developing roll bias voltage (vn) is controlled so that IVDI<VB<VC. ” 6) The column “Brief explanation of drawings” should be amended as follows. (1) “Figure 6 is...” on page 6 lines 8-10 of the specification
Figure 3(a) is a diagram showing the relationship between the potential difference between the photoreceptor surface potential (Vp) and the developing roll bias voltage ffB) and the image normality, and Figure 3(b) is Figures for Detailed Explanation of the Present Invention. (2) Correct the "slit" in the 5th line from the bottom of page 6 to "Selfoc lens". 4) Figure 6 and Figure 4 are revised to Figure 3(a) 1, 3 (and Figure 4) as attached. Figure 3(a) Figure 3(b)

Claims (1)

[Scope of Claims] 1) An electrophotographic apparatus having means for erasing charges in non-image areas between images on a photoreceptor to lower the potential thereof,
An electrophotographic apparatus characterized in that a developing roll bias voltage is switched each time for an image area and a non-image area on a photoreceptor. 2) The electrophotographic apparatus according to claim 1, wherein the developing roll bias voltage is switched each time for a non-image area on the photoreceptor so that it is lower than for an image area.