JPS63127266A - Xerographic apparatus - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an electrophotographic apparatus that can regulate the charging potential of a photoreceptor with high precision.

(Prior Art) In electrophotographic devices such as copying machines and printers, it is strongly required to strictly control the charging potential of the photoreceptor in order to maintain a constant image density and extend the life of the photoreceptor. There is.

As a method for regulating the charging potential of the photoreceptor, there is a method of charging the photoreceptor to a predetermined potential using a scorotron charger. This scorotron charger has a mesh-like grid with many openings arranged between the charger main body, which has a shield case and a corona wire that is connected to a high voltage source and emits corona ions, and a photoreceptor. A predetermined bias voltage is applied to the grid to control the amount of corona ions emitted toward the photoreceptor through the openings of the grid. Therefore, if a photoreceptor is charged using this scorotron charger, the charging potential of the photoreceptor can be controlled by controlling the glissode voltage, and the entire surface of the photoreceptor can be charged uniformly. Even if a so-called charge unevenness occurs in the corona wire, in which the amount of corona ions emitted is excessive or insufficient in some areas in the recording width direction, when the corona ions pass through the grid, the excessive or insufficient corona ions are uniformized by the grid. , a significant advantage is achieved that can effectively reduce charging unevenness. There are two types of scorotron chargers: one that connects the grid to a reference voltage source and applies a constant reference voltage at all times, and the other that connects the grid to a voltage drop element such as a Zener diode or varistor and uses a voltage drop device such as a Zener diode or varistor to ground the scorotron charger. There is a method that uses corona current to maintain the grid at a predetermined potential. In any type of scorotron charger, the grid effect cannot be achieved unless the grid is placed close to the surface of the photoreceptor, and the gap between the grid and the photoreceptor is, for example, 0.5 to 1. It is necessary to set it to about 5 fins. For this reason, if the distance between the grid and the surface of the photoreceptor changes, a disadvantage arises in that the charged potential of the photoreceptor changes significantly.

(Problem to be solved by the invention) The scorotron charger, which connects the grid to a reference voltage source and applies a constant reference voltage at all times, does not suffer from fluctuations in the amount of corona ions emitted due to changes in the environment such as temperature and humidity. This has the advantage that the grid can be maintained at a constant reference potential at all times. However, since the reference power source is expensive, the scorotron charger itself has the disadvantage of being expensive. Furthermore, there is a drawback that even if the distance from the grid to the surface of the photoreceptor deviates even slightly from a reference value, the charged potential of the photoreceptor changes. Particularly when replacing the photoconductor, for example, even a slight change in the meshing state of the drive gear can cause a change in the distance from the photoconductor to the grid, and this slight gap change can cause the inconvenience of changing the charged potential of the photoconductor. was. On the other hand, in order to precisely regulate the distance from the grid to the photoconductor surface, positioning must be performed using various highly precisely machined parts, which complicates the grid construction and increases manufacturing costs. I end up.

The scorotron charger uses a method in which the grid is grounded via a voltage drop element such as a Zener diode and uses corona current from a corona wire to maintain the grid at a reference potential.The configuration is simplified and the number of parts is reduced. Therefore, there is an advantage that manufacturing costs can be reduced. However, there is a problem in that the corona current emitted from the corona wire fluctuates as the environment changes, and the grid voltage fluctuates during use. Furthermore, the charging potential of the photoreceptor changes as the distance from the grid to the photoreceptor surface changes, and when the charging potential becomes low, the image density decreases, while when the charging potential increases, the photoreceptor deteriorates prematurely. This may cause inconvenience.

In particular, the charging potential tends to decrease during use, resulting in a decrease in image density.

On the other hand, the relationship between the charged potential of the photoreceptor and the distance to the grid reaches a saturation value as the grid approaches the surface of the photoreceptor, as shown in FIG. However, the closer the grid is to the photoreceptor, the more likely it is that toner scattered from an adjacently disposed developing device or cleaning device will adhere to the grid, and if toner adheres to the grid, the charging potential will change and uneven charging will occur. Therefore, it is necessary to place the grid at some distance from the photoreceptor and use it in transition areas affected by distance variations.

Therefore, an object of the present invention is to eliminate the above-mentioned drawbacks, and to maintain the charged potential of the photoreceptor constant at all times without being affected by gap fluctuations even when the grid is used in a transition region where the grid is separated from the surface of the photoreceptor to some extent. The present invention provides an electrophotographic device that can perform

(Means for Solving the Problems) An electrophotographic apparatus according to the present invention includes a grid having a large number of openings arranged between a photoreceptor on which an electrostatic latent image is to be formed and a corona wire, and In an electrophotographic device that regulates the charged potential of a photoreceptor based on a grid voltage, there is a surface potential detector that detects the charged potential of the photoreceptor, and a detection output of this surface potential detector and a reference value corresponding to a reference surface potential. and a grid voltage generation circuit connected to the grid and generating a grid voltage based on the control signal from the comparison circuit.

(Function) As described above, when a scorotron charger is used in a transition region, there is a problem in that the charging potential changes due to a change in the gap from the surface of the photoreceptor to the grid. However, as a result of various experiments and studies, it has been found that the charged potential of the photoreceptor can be maintained at a constant reference value by appropriately changing the grid potential according to the change in the gap. That is, as the gap becomes larger, the grid potential is controlled to become higher, and as the gap becomes smaller, the grid voltage is controlled to become lower. By controlling the grid potential according to the gap variation in this way, the surface potential of the photoreceptor can be kept constant at all times. Therefore, in the present invention, the charged potential of the photoreceptor is detected by a surface potential detector,
This detection output is compared with a reference value corresponding to the reference surface potential to create a control signal, and the grid voltage is controlled based on this control signal. As a result, the charged potential of the photoreceptor can be automatically maintained at the reference value. In particular, if the grid is connected to a series branch of a constant voltage effect element and an electronic volume element, and the amount of corona current flowing through this series branch is controlled by the electronic volume element, the grid will be controlled by the amount of voltage drop occurring across the electronic volume. Voltage can be controlled, and grid voltage can be automatically controlled with a simple configuration.

(Embodiment) FIG. 1 is a diagram showing the configuration of an example of an electrophotographic apparatus according to the present invention. In this example, a copying machine will be explained as an example. The photosensitive drum 1 on which the electrostatic latent image is to be formed is rotated in the direction of arrow a, uniformly charged to a predetermined surface potential, and then exposed by the exposure device 2 to form the electrostatic latent image. This electrostatic latent image is developed by a developing device 3 to create a toner image. This toner image is transferred by a transfer charger 4 onto a recording paper 5 that is conveyed in synchronization with the photosensitive drum 1. The transferred recording paper 5 is separated from the surface of the photosensitive drum 1 by a separation charger 6, conveyed in the direction of the arrow, and discharged outside the machine via a fixing device (not shown).

The untransferred toner on the photosensitive drum 1 is cleaned by a cleaning device 7 and uniformly photostatically eliminated by an eraser device 8 before reaching a charging position. In the present invention, a scorotron charger 9 is used as a charging device. This scorotron charger 9 has a mesh-shaped grid 13 that is electrically insulated and supported by a shield case 10, a corona wire 11, and an electrically insulating support member 12.

While grounding the shield case 10, the corona wire 11
is connected to a high-voltage reference power source 14 to emit corona ions toward the photosensitive drum 1. A portion of the corona ions emitted from the corona wire 11 is captured by the shield case 10 and flows into the ground, and the remaining portion is captured by the grid 13.
The corona current is captured by the corona current and flows into the grid voltage generation circuit 15. Furthermore, the remaining corona ions pass through a large number of openings provided in the grid 13 and reach the photosensitive drum 1, charging the photosensitive drum 1 to a predetermined surface potential. The grid 13 is composed of a mesh member made of stainless steel having a large number of openings, and is arranged close to the surface of the photoreceptor. As a result, the photosensitive drum 1 is charged to a potential approximately equal to the bias voltage of the grid 13, and therefore the charging potential of the photosensitive drum 1 is controlled according to the grid voltage. A surface potential detection sensor 16 is disposed downstream of the scorotron charger 9 to detect the surface potential of the charged photosensitive drum 1 and output it to a comparison circuit 17 . As the surface potential detection sensor 16, various detection sensors such as a vibration type and a capacitance type can be used. The comparison circuit 17 compares the detected surface potential with a reference value and supplies this output to the grid voltage generation circuit 15 as a control signal. This reference value corresponds to a predetermined charging potential of the photosensitive drum 1, and a control signal is output in accordance with a change in the detected surface potential with respect to the reference surface potential. The grid voltage generating surface path 15 generates a grid voltage based on the control signal from the comparator 17 and the corona current from the grid 13.

FIG. 2 is a graph showing the relationship between the distance d between the grid and the photosensitive drum and the charged potential of the photosensitive drum. The horizontal axis indicates the distance d between the grid and the photosensitive drum (decreasing as it goes to the right), and the vertical axis indicates the charged potential of the photosensitive drum. The charged potential v0 of the photoreceptor asymptotically approaches the grid voltage v9 as the gear d becomes smaller, and becomes approximately equal to the grid voltage v9 when d becomes smaller than 1.5++n. However, when the gap d becomes 1.5+n or more, the charging potential v
0 is a sharp drop. Therefore, when the grid voltage V9 is fixed as in the conventional device, if the gap d becomes large, the charging potential of the photosensitive drum will decrease. Therefore, it is desirable to design the gap d to be extremely small, but there is a limit to making the gap d smaller due to mechanical design conditions, such as the amount of eccentricity of the photosensitive drum. On the other hand, in order to always obtain a constant charging potential even if the gap d changes, it is sufficient to change the grid voltage according to the change in the gap d. For example, the design conditions shown in Fig. 2, d = 1.5 mm, V, = -500
V, and when the charged potential v0 of the photoreceptor is maintained at -480V, when the gap d becomes larger than 1.5V, the grid voltage v9 is controlled so that the absolute value becomes larger than -500V, and the gap d is If the grid voltage v9 is controlled to be small when d is smaller than 1.5 mm, the photoreceptor charging potential can always be maintained at a constant value regardless of the gap change. The first and third generation systems are based on this recognition, and the detection signal from the surface potential detection sensor 16 is compared with a reference value, and the grid voltage is controlled according to the change in the reference surface potential to increase the charged potential of the photoreceptor. Configure it so that it remains constant at all times.

FIG. 3 is a circuit diagram showing the configuration of an example of a comparison circuit. A detection signal from the surface potential detection sensor 16 is amplified by an amplifier 20 and a high frequency component is removed by a low-pass filter 21 before being supplied to one input terminal of a comparator 22 . A reference voltage Vcc is connected to the series branch of the two resistors R,,R,, one end of the resistor R2 is grounded, and the resistor R
The connection point between R1 and R2 is connected to the other input terminal of the comparator 22, and a reference signal corresponding to the reference surface potential is input. Then, the detection signal from the surface potential detection sensor 16 is compared with the reference signal, a control signal is output, and the control signal is supplied to the grid voltage generation circuit 15.

FIG. 4 is a circuit diagram showing the configuration of an example of a grid voltage generating circuit. The grid 13 is connected to the drain of a field effect transistor (FET) 31 via a Zener diode 30 that acts as a constant voltage drop element, the source of the FET 31 is grounded, and a control signal from the comparator circuit 17 is supplied to the gate of the FET 31. do. As described above, a corona current flows from the corona wire 11 into the grid 13, and this corona current flows through the Zener diode 30 and the FET.
31 and flows into the ground.

In this case, the drain-source current can be controlled by the control signal supplied to the gate of the FET 31,
Therefore, the amount of voltage drop between the drain and the sheath is controlled by the control signal. In this case, if the grid voltage is controlled to be low when the charged potential of the photosensitive drum 1 is higher than the reference potential, and the grid voltage is controlled to be high when the charged potential of the photosensitive drum 1 is lower than the reference potential, The charging potential of the photosensitive drum can be maintained at a constant reference value at all times. With this configuration, the FET acts as an electronic volume element, and the grid voltage can be controlled at high speed. In particular, responsiveness can be further improved compared to the case where the control signal from the comparison circuit is used to control the output voltage of the high voltage power supply connected to the corona wire.

The present invention is not limited to the embodiments described above, and various modifications are possible. For example, although the above-mentioned embodiment has been explained using a copying machine as an example, it is not limited to copying machines only.
It can also be applied to electrophotographic devices such as printer devices.

In the above-described embodiment, the grid voltage is controlled using an FET, but the present invention is not limited to the FET, and any other device can be used as long as it can function as an electronic volume.

Furthermore, in the above-described embodiment, the grid voltage generation circuit was configured with a Zener diode that acts as a constant voltage drop element and one FET, but it is also possible to widen the grid voltage control range by connecting a plurality of FETs in series. can.

(Effects of the Invention) As explained above, according to the present invention, the charged potential of the photoreceptor is detected, and compared with a reference value corresponding to the reference surface potential to create a control signal, and based on this control signal, the scorotron Because it is configured to control the grid voltage of the charger,
Even if the distance between the photoreceptor and the grid changes or the output of the corona charger fluctuates during operation, the charged potential of the photoreceptor can be automatically maintained at a predetermined reference value at all times. especially,
Even if the distance between the grid and the surface of the photoreceptor is set to be relatively large, it can be automatically charged to the reference value at all times without being affected by changes in distance.

If the configuration is such that the grid voltage is maintained constant using the corona current flowing into the grid of the scorotron charger,
The structure can be simplified and manufacturing costs can be reduced.

Furthermore, the scorotron charger can stabilize the charging potential and effectively reduce the occurrence of charging unevenness, thereby further improving image quality.

Further, since the configuration uses an electronic volume to control the amount of corona current, the grid voltage can be controlled extremely quickly, and as a result, the charged potential of the photoreceptor can be quickly maintained at a constant value.

Furthermore, even if the distance from the grid to the photosensitive drum changes, it can be charged to the reference surface potential, so there is no need to position the grid with high precision with respect to the photosensitive drum, making the grid positioning work easier. , machining precision of positioning members is not required.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of an example of an electrophotographic apparatus according to the present invention, FIG. 2 is a graph showing the relationship between the charged potential of the photoreceptor and the distance between the grid and the surface of the photoreceptor, and FIG. FIG. 4 is a circuit diagram showing the configuration of an example of the comparison circuit. FIG. 4 is a circuit diagram showing the configuration of an example of the grid voltage generation circuit. FIG. 5 is a graph showing the relationship between the distance from the grid to the surface of the photoreceptor and the charged potential. be. 9... Scorotron charger 10... Shield case 11... Corona wire 12... Support member 13... Grid 14... High voltage power supply 1
5...Grid voltage generation circuit 16...Surface potential detection sensor 17...Comparison circuit 22...Comparator 30...Zener diode 31...FET patent applicant Nisobon Kentick Caixa Limited Figure 2 Figure 3

Claims (1)

[Claims] 1. A grid having a large number of openings is arranged between the photoreceptor on which an electrostatic latent image is to be formed and the corona wire, and the charging potential of the photoreceptor is determined based on the grid voltage generated in the grid. In an electrophotographic device that regulates electrophotography, there is a surface potential detector that detects the charged potential of the photoreceptor, and a comparison that outputs a control signal by comparing the detection output of this surface potential detector with a reference value corresponding to a reference surface potential. An electrophotographic apparatus comprising: a circuit; and a grid voltage generation circuit connected to the grid and generating a grid voltage based on a control signal from a comparison circuit. 2. The grid voltage generation circuit includes a constant voltage drop element;
An electrophotographic apparatus according to claim 1, characterized in that the electrophotographic apparatus is constructed with a series branch line with at least one electronic volumetric element.