JPH0451167A - Electrostatic charging controller for electrophotographic copying device - Google Patents

Abstract

PURPOSE:To obtain stable and high printing quality with simple constitution by providing a surface potential sensor between an exposing means and a developing means so that it may be approximately opposed to a photosensitive body, detecting the surface potential of the photosensitive body and controlling the surface potential of the photosensitive body to a desired value. CONSTITUTION:The surface potential sensor 8 is provided so as to be approximately opposed to the photosensitive body 1 at a position nearer to the developing means 4 between a light emitting diode head 3 and the developing means 4. Then, the surface potential of the photosensitive body 1 is measured by the sensor 8, and the value of the surface potential is controlled by an electrostatic charging control means 10 so that it may be a desired potential by utilizing the data on the surface potential of a non-printing part out of printed pages. Namely, the means 10 sets only the data on the non-printing part out of the printed pages sent from a printer control means out of the data on the surface potential from the sensor 8 as effective data so that an electrostatic charging current which flows to an electrostatic charging electrode 2 may be controlled based on this data by the means 10. Thus, the more stable printing quality is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to control of the surface potential of a photoreceptor in an electrophotographic apparatus such as a copying machine or a printer.

[Prior Art] FIG. 8 is a schematic layout diagram showing a conventional electrophotographic control device disclosed in, for example, Japanese Unexamined Patent Publication No. 58-159552.
In the figure, (1) is, for example, a cylindrical photoreceptor;
(2) is a charging electrode that is a means for charging this photoreceptor, (
3) is an exposure means, for example, a light emitting diode head, which exposes the photoreceptor (1) to the desired print shape, and (4) represents the intended print on the photoreceptor (1) produced by exposure. A developing means (5) is a recording sheet (9) on which the colored particle image on the photoreceptor (1) developed by this developing means will be described later. (6) is a cleaning brush that cleans the photoreceptor (1);
(7) is a static elimination lamp that eliminates static electricity from the photoreceptor (1);
) is a surface potential sensor (9) attached to face the photoreceptor (1) and measures the surface potential thereof, is a recording paper for recording the colored particle image, and (10) is the photoreceptor (1).
This is a charging control means for controlling the charging potential at a constant level based on the surface potential measurement value from the surface potential sensor (8).

Next, C, F, Carlson (C, F
, Carlson) has been widely adopted in copying machines, printers, and the like. Here, a brief explanation will be given using an electrophotographic printer as an example. The photoreceptor (1) receives a negative charge on its surface due to the corona discharge of the charged electrode (2) to which a DC high voltage is applied, and is charged, and only the printed portion is exposed by the light emitting diode head (3). Due to the photoconductivity of the photoreceptor (1), only the portion exposed to light changes from insulative to conductive, and charges only in the exposed portion escape to ground and disappear. The electrostatic charge pattern thus formed on the photoreceptor (1) is reversely developed by the developing means (4). In other words, colored particles charged to the same polarity as the predetermined electrostatic charge pattern are supplied to match the electrostatic charge pattern formed on the surface of the photoreceptor (1), and are applied to the locations where the charges in the electrostatic charge pattern have disappeared. An image is formed by depositing the colored particles.

This image is transferred from the photoreceptor (1) onto the recording paper (9) by the transfer pole (5), and the colored particle image on the recording paper (9) is transferred to the recording paper (9) by a fixing device (not shown). 9) It is fused and fixed onto the top, and the printed matter is completed. - After the photoconductor (1) has been transferred by the above process, the surface is cleaned with a cleaning brush (6), the entire surface is exposed to light with a discharge lamp (7), static charges are eliminated, and the process of charging is started again. In this way, printed matter is continuously formed.

Here, the charging potential of the photoreceptor (1) varies greatly depending on variations in charging characteristics of each photoreceptor (1), environmental conditions, repeated fatigue characteristics, and the like. Changes in the charged potential of the photoreceptor (1) affect the amount of colored particles deposited on the photoreceptor (1) by the developing means (4) for the same amount of exposure to the photoreceptor (1), e.g. If too many particles adhere to the photoreceptor (1), printing may become too dark, etc.
Change the print quality of printed matter. Therefore, a surface potential sensor (8) is placed on the surface of the photoreceptor (1) in a space directly below the charging electrode (2), and the charging electrode (2) is placed so that the charging potential becomes a preset constant value. The charging current is controlled by charging control means (
Feedback control is performed by lO). As a result, the overall charging potential was kept constant immediately after the photoreceptor (1) was charged, but the charging potential varied during development of the photoreceptor (1).

[Problems to be Solved by the Invention] Since the charge control device of the conventional electrophotographic apparatus is configured as described above, even though the charging potential of the photoreceptor immediately after charging is constant, the dark decay characteristics of the photoreceptor vary individually. As the surface potential changes depending on the characteristics, environmental conditions, edge fatigue characteristics, etc., when a change appears in the surface potential during development of the printing process, the white background level in particular changes in the print quality, and the dark printing becomes worse. When this happens, there is a problem in that the entire surface of the paper becomes pale and stands out as a background stain.

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a charge control device for an electrophotographic device that can provide more stable printing quality than the conventional method.

[Means for Solving the Problems] A charge control device for an electrophotographic apparatus according to the present invention includes a surface potential sensor provided between an exposure means and a developing means, close to and facing the photoreceptor, and detects the surface potential of the photoreceptor. However, a charging control means is provided to control this value to a desired value.

Further, an exposure amount control means is provided for intermittently detecting the surface potential of the photoreceptor at desired printing timing and controlling the exposure amount to a desired value.

[Function] The charging control device for the electrophotographic apparatus according to the present invention includes a surface potential sensor installed immediately before the developing means, and the charging portion of the photoreceptor,
In other words, the electric potential of the non-exposed area is detected, and the electric charge control means controls this value to a desired value, thereby serving as a electric charge control device for an electrophotographic apparatus.

Further, the surface potential at the printing portion of this photoreceptor is intermittently detected at desired printing timing, and the exposure amount control means controls the potential at the exposed portion to a desired value, thereby serving as a charging control device for an electrophotographic device.

[Embodiments of the Invention] Hereinafter, embodiments of the invention will be described with reference to the drawings. In FIG. 1, steps (1) to (9) are the same as those explained in the conventional example shown in FIG. However, surface potential sensor (8)
The photoreceptor (1) in the printing process shows its mounting position.
Immediately after the upper charged electrode (2), the light emitting diode head (3
) and the developing means (4) to a position closer to the developing means (4) (a position immediately in front of the developing means (4)).

In the block diagram of FIG. 2, (10) is a charging control means;
(11) is printer control means controlled by this charging control means.

In an electrophotographic apparatus, it is desirable to keep the potential of the unexposed and exposed parts of the photoreceptor (1) constant in the developing means (4), but if the photoreceptor (1) is repeatedly charged and uncharged, the surface The potential may drop. Therefore, the surface potential of the photoreceptor (1) is measured with a surface potential sensor (8) installed just before the developing means (4), and the value is calculated using the surface potential data of the non-printed area between printed pages. Control is performed by the charging control means (10) so that the desired potential is achieved. That is,
The charging control means (lO) selects the printer control means (lO) from among the surface potential data received from the surface potential sensor (8).
Only the data in the non-printed areas between the printed pages sent from 11) is used as valid data, and based on this data, the charging control means (10) controls the charging current flowing through the charging electrode (2).

Here, in order to find out whether there is a blank sheet suitable for measurement at the position corresponding to the surface potential sensor (8) within the printed page,
There is a function to check whether there is blank data in the address corresponding to the sensor detection position in the page buffer that temporarily stores print data, that is, a large range of several mm square of the measurement aperture of the surface potential sensor (8). is necessary. However, in the non-printing area between pages, regardless of the content of the print data, only the timing of the non-printing area, which is the non-exposed area of the photoconductor (1), is extracted and the photoconductor (1) corresponding to the non-printing area ( What is necessary is to control the charging potential of the part 1).

As described above, according to the present invention, the surface potential of the non-exposed area, that is, the white background area, of the photoreceptor (1) of the developing means (4) can be kept constant with a simple configuration, resulting in stable high print quality. You get quality.

In addition, in the above embodiment, an example was shown in which the surface potential of the non-exposed part of the photoreceptor (1) was controlled to a desired value, but in addition to this, the exposure means may be controlled by the surface potential of the exposed part. An example of this will be described below.

As shown in the above embodiment, when the surface potential of the non-exposed area of the photoreceptor (1) in the developing means (4) section is controlled to a constant value, the surface potential at the charging electrode (2) section changes, and therefore, The surface potential at the light emitting diode head (3) also changes. Therefore, the potential of the exposed portion of the photoreceptor (1) in the developing means (4) section changes, the latent image potential contrast of the photoreceptor (1) changes, and the contrast of print density changes accordingly.

4 to 6 show changes in the surface potential of the photoreceptor (1) during a printing cycle in various methods of controlling the surface potential of the photoreceptor (1). Figure 4 shows the transition of the surface potential of the photoreceptor in the conventional example, where the solid line represents the transition of the potential during the printing cycle at the beginning of use, and the - dotted line represents the transition of the potential during the printing cycle after continuous use. It shows the transition.

In the conventional example, the surface potential at the charging position is controlled to be constant, so at the developing position, the initial potential A on the exposed area, the initial potential B on the non-exposed area, and the potential C1 on the exposed area after continuous use. The potentials are different from those of the non-exposed areas, and the initial potential contrast CD is also different. On the other hand, in the above embodiment, as shown in FIG. 5, the potential of the non-exposed area at the development position is controlled to a constant value, so the potentials B and D match, but the potentials A and C of the exposed area are They are different, and therefore their potential contrasts are also different.

In another embodiment to be described next, as shown in FIG. 6, the potentials B and D are matched and then the potentials A and C are controlled to match, so the potential contrast is also constant and more stable. You can obtain high printing quality.

Further, the photosensitivity of the photoreceptor (1) changes depending on usage environmental conditions and edge fatigue, and the above-described embodiments are also effective in this regard.

In FIG. 3, (8), (10) and (11) are the same as in FIG. (12) is an exposure amount control means. At the end of the printer's job, a jeb end mark (not shown) with a length of CII+ is printed on the fold perforation between the pages of the recording paper (9) so that the feed can be recognized. This example utilizes this job end mark printing to
This method attempts to keep the potential of not only the non-exposed area (1) but also the exposed area constant. In other words, the exposure amount control means (12)
The surface potential data of the surface potential sensor (8) installed between the light emitting diode head (3) and the developing means (4) and immediately in front of the developing means (4) is transmitted to the printer control means (
11) It is detected intermittently at the timing of job end mark printing sent from 11). In order to set this value to a desired value, the above-mentioned surface potential sensor (
The surface potential data of step 8) is input manually to the exposure amount control means (12), and the output drive current controls the light amount of the light emitting diode head (3). Here, it is preferable that the surface potential sensor (8) is located close to the developing means (4), so that at least the charged surface potential of the photoreceptor (1) is exposed to light, and only the exposed part is insulated due to photoconductivity. changes from conductive to conductive,
It is necessary that the photoreceptor (1) is further away from the light emitting diode head (3) than the position at which the photoreceptor (1) rotates during the time required for so-called light attenuation, in which the charges of the exposed portion escape to the ground and disappear. Further, by performing detection not continuously but intermittently at a desired printing timing, the surface potential can be detected from a portion of the photoreceptor (1) corresponding to the portion used for actual printing. As a result, the surface potential of the developing means (4) portion of the photoreceptor (1) is controlled to a desired value in both exposed and non-exposed areas, and more stable and high quality can be obtained.

Furthermore, the dynamic resistance of the developer changes over time, so the optimum surface potential changes. Therefore, by actually measuring the number of sheets of developer used or the change in dynamic resistance, and changing the reference value of the optimum surface potential of the developing means in accordance with the measured value, even more constant high printing quality can be obtained. For this purpose, a table of the relationship between the number of printed sheets or the dynamic resistance value and the optimum surface potential may be stored in the memory, and the set value for one surface mold position may be adjusted by referring to this data. This example will be explained with reference to FIG.

Figure 7 shows a table showing the relationship between the number of sheets of developer used and the optimum surface potential, which changes over time due to the number of sheets of developer used, and the set value of the surface potential is corrected by referring to this data. It is something. This is because the dynamic resistance of the developer changes depending on how the developer is used, and the optimum surface potential of the photoreceptor (1) changes accordingly. Therefore, by counting the number of sheets of developer used and changing the reference value of the surface potential of the developing section to the optimum potential in accordance with that value, even more constant printing quality can be obtained. For this purpose, a table showing the relationship between the number of printed sheets and the optimum surface potential may be stored in the memory, and the set value of the surface potential may be corrected by referring to this data.

In FIG. 7, (8), (10) to (12) are the same as in FIG. 3. (13) is a surface potential setting means for supplying a surface potential control value to be set to the charge control means (10) based on the number of sheets of developer used and data in a surface potential setting table to be described later;
14) is a surface potential setting table.

The surface potential setting table (14) contains a database of the optimum surface potential of the photoreceptor (1) for the number of sheets of developer used. The surface potential setting means (13) obtains data on the number of sheets of developer used from the printer control means (11), reads out surface potential data to be set from the surface potential setting table (4), and sets the surface potential data to the charging control means (10). ) gives the surface potential control value to This makes it possible to control the deterioration of the developer depending on the number of sheets used.

In each of the first embodiments, the surface potential is detected at the timing between pages, but the kneading may also be carried out at the blank or black areas within the page. However, in this case,
Since it is necessary to search for an area of the document where at least the measurement range is entirely blank or solid black, a high-resolution surface potential sensor (8) is required. In addition to this, the print pattern in the page buffer is examined, and the surface potential sensor (
8) It is necessary to have a function of finding a point where a blank sheet or a solid black sheet appears in the calibration area and transmitting the timing to the printer control means (11).

Even if the effect of controlling the surface potential of the photoconductor (1) is somewhat weak, if you want to use it for a simpler purpose, install a surface potential sensor (8) at the end of the photoconductor (]) where there is no document. The surface potential of that portion may also be measured. In this case, the part to be measured is not exposed to light, so fatigue due to it cannot be detected, but the potential of the non-exposed part can be continuously measured without detecting inter-page timing.

[Effects of the Invention] As described above, according to the present invention, a surface potential sensor is provided between the exposing means and the developing means, closely facing the photoreceptor,
By detecting the surface potential of the photoconductor and controlling the surface potential of the photoconductor to a desired value using a charging control means, changes and variations in print quality are reduced, and stable high print quality is achieved with a simple configuration. There are benefits to be gained.

In addition, by intermittently detecting the surface potential of the photoreceptor at desired printing timing and controlling the exposure means with the exposure amount control means, variations in the surface potential of the exposed portion of the photoreceptor can be reduced, resulting in stable This has the effect of providing high print quality.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing a charging control device for an electrophotographic apparatus according to an embodiment of the present invention, FIG. 2 is a block diagram showing a charging control device for an electrophotographic apparatus according to an embodiment of the invention, and FIG. A block diagram showing a charge control device for an electrophotographic apparatus according to another embodiment of the present invention, FIG. 4 is a diagram showing the surface potential of a conventional photoreceptor, and FIG. FIG. 6 is a diagram showing the surface potential of a photoreceptor according to another embodiment of the present invention, and FIG. 7 is a diagram showing a charge control device for an electrophotographic apparatus according to another embodiment of the present invention. FIG. 8 is a block diagram schematically showing a charge control device for a conventional electrophotographic apparatus. (1) is a photoreceptor, (2) is a charging electrode, (3) is a light emitting diode head, (4) is a developing means, (8) is a surface potential sensor, (10) is a charging control means, (]2) is an exposure control means. In addition, the same symbols in the figures indicate the same or equivalent parts.

Claims (2)

[Claims] (1) A photoreceptor, a charging means that applies an electrostatic charge to the photoreceptor, an exposure means that exposes the photoreceptor, and a developing means that attaches colored particles corresponding to the electrostatic charge pattern on the photoreceptor. A surface potential sensor is provided between an exposure means and a developing means in close opposition to the photoreceptor, the surface potential sensor detects the surface potential of the photoreceptor, and the surface potential of the photoreceptor is measured. A charge control device for an electrophotographic apparatus, comprising a charge control means for controlling the value to a desired value by controlling the above-mentioned charging means. (2) By providing an exposure amount control means that intermittently detects the surface potential of the photoreceptor at desired printing timing and controls the exposure amount to a desired value, the value of the photoreceptor surface potential can be adjusted to a desired value. 2. The charging control device for an electrophotographic apparatus according to claim 1, wherein the charging control device controls the charging of an electrophotographic device.