JPH03252683A - Image forming device - Google Patents

Abstract

PURPOSE:To accomplish the control of image density in an AIDC method(Auto Image Density Control) for deciding toner concentration from a real image without wastefully consuming toner by forming a pattern image for detecting density by the use of a 1st developing device on the outer periphery of a photosensitive body and collecting the toner constituting the pattern image into a 2nd developing device after measuring the image density. CONSTITUTION:The surface of the photosensitive body 1 is uniformly electrostatically charged by an electrostatic charger 2 and a pattern latent image of a specified area is formed by flickering an interimage eraser 9. The pattern latent image is developed by the 1st developing device 10 to form the pattern image, and the image density thereof is read by a photosensor 17. Then, the pattern image which passes a detecting position by the photosensor 17 is collected in the 2nd developing device 11 in a succeeding 2nd developing area X5. Thus, the AIDC method is accomplished without consuming and exhausting the toner.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an image forming apparatus such as a copying machine or a printer using an electrophotographic copying process.

(Prior art and its problems) Conventionally, in Japanese Patent Application Laid-Open No. 1-307783, a first developing device and a second developing device are provided on the side of an electrostatic latent image carrier along the moving direction of the electrostatic latent image carrier. The developer filling rate of the developing area where the developing sleeve of these developing devices faces the electrostatic latent image carrier is set so that the first developing device has a higher developer filling rate than the second developing device. An image forming apparatus is provided in which an electrostatic latent image developed by a developing device is reproduced by a second developing device.

Here, the developer filling rate is the value obtained by dividing the amount of developer passing between the developing sleeve and the electrostatic latent image carrier per unit time by the distance between the developing sleeve and the electrostatic latent image carrier. .

According to the image forming apparatus, the electrostatic latent image is visualized with sufficient density in the first developer, and the fine line is visualized faithfully to the original in the second developer. In other words, an image with excellent density reproducibility and fine line reproducibility can be obtained.

By the way, in an image forming apparatus using a two-component developer consisting of toner and carrier, in order to ensure the necessary image density, the weight mixing ratio of toner to carrier (hereinafter referred to as "toner density") is kept constant. need to be maintained.

Therefore, two methods have been proposed so far.

One is to read the image density of the toner pattern image created on the photoreceptor with a reflective photosensor, and use the result to determine the image forming conditions of the developing device, such as toner density, developing bias voltage,
Control that feeds back to the charging voltage of the photoreceptor [hereinafter referred to as r
AIDc method (Auto Image Density C
ontrol)j. ”].

Another type of control is to measure the toner concentration in the developing device as a change in magnetic permeability using a magnetic sensor, etc., and feed the result back to the image forming conditions of the developing device [hereinafter referred to as rATDc].
(Auto Tonor Density Control)
ol)J].

When these methods are compared, the AIDC method has the advantage that the toner density is determined from the actual image formed on the photoreceptor, so the reliability of the detection results is higher.

Therefore, in the image forming apparatus, the density is poor.

(Function) According to the above configuration, the pattern forming means forms a pattern for density detection using the first developing device, and the image density is read by the density measuring means. When the reading of the image density is completed, the toner constituting the pattern is collected by the second developing device by the collecting means.

(Example) Hereinafter, an example of the present invention will be described with reference to FIG.

In the figure, a photoreceptor 1 is a cylindrical body having an organic photoreceptor layer on its outer periphery, and is rotated in the direction of arrow a at a circumferential speed of 150 mm/sec.

The charger 2 includes a charge stabilizing plate 3, a charge wire 4, and a grid mesh 5. charge wire 4
A voltage of about -6 KV is applied from the high voltage transformer 6 to discharge the battery. Further, a voltage of about -600V is applied to the grid mesh 5 from another high voltage transformer 7. As a result, it is preferable that the density control of the first developing device, which emphasizes transferability from the direction of arrow a, be performed by the AIDC method.

However, in AIDC, it is necessary to create a toner pattern image each time it is detected, and conventionally, the toner in the toner pattern image is collected and discarded with a cleaning device, etc., so each time a pattern image is created, The drawback is that the toner is consumed and runs out.

(Means for Solving the Problems) Therefore, the present invention includes a photoreceptor, a first developing device and a second developing device of magnetic brush type, and a developing area of the first developing device and the second developing device. The developer filling rate is set to be higher in the first developer than in the second developer, and
In an image forming apparatus in which electrostatic latent images developed by a developing device are superimposed and developed by a second developing device, a pattern forming means for forming a pattern image for density detection on the photoreceptor using the first developing device; a density detection means for measuring the image density of the pattern image; and a density detection means for measuring the image density of the pattern image;
A photoconductor 1 is set up with a collection means for collecting it in a developing device.
The surface of is charged to about 600V in charging region X.

The image light 8 is exposed at the exposure section X2 onto the surface of the photoreceptor 1 charged by the charger 2 as described above, and an electrostatic latent image corresponding to the original image is formed on the outer periphery of the photoreceptor 1.

The inter-image eraser 9 has light emitting diodes arranged in multiple stages in the axial direction of the photoreceptor 1, and blinks the light emitting diodes.
The surface potential of an unnecessary charged portion (inter-image portion) of the photoreceptor 1 passing through the static elimination region X3 is removed.

The first developing device 10 stores two-component developer consisting of toner and carrier in a front conveyance path 26 and a rear conveyance path 27 . The developer in the rear conveyance path 27 is transferred to the conveyor blade 3.
0 rotation, it is transported from the front side to the back side in the figure, and the wall 28
The front conveyance path 26 is connected via a communication path (not shown) provided in the
transported to.

On the other hand, the developer in the front conveyance path 26 is conveyed from the back side to the front side based on the rotation of the packet roller 29, and is transferred to the rear conveyance path 26 via a communication path (not shown) provided on the front side of the wall 28. transported to. In other words, the developer is transported through the transport path 26, 27.
The toner is circulated and conveyed in a certain direction, and mixed and stirred during the conveyance process, so that the toner is positively charged and the carrier is negatively charged.

Further, the developer transported through the front transport path 26 is supplied to the developing roller 22 by a packet roller 29 . The developer supplied to the developing roller 22 is attracted by the magnetic force of the magnet body 23 and held on the outer periphery of the sleeve 24.
As the developer rotates, it is transported in the direction indicated by the arrow and regulated by the regulation plate 25, and the developer that passes through the gap between the regulation plate 25 and the sleeve 24, that is, the regulation gap Dt++ (=o, 5 mm), is further transported in the direction indicated by the arrow. Ru. Regulatory gap D b
, the developer moves to the first development area X4 in a magnetic brush state along the lines of magnetic force generated from the magnetic poles.

The developer conveyed to the first development area
4 and the photoreceptor 1, that is, the development gap Ds+
(-0.6mm). At this time, the developer comes into contact with the outer circumferential surface of the photoreceptor 1, and a photo sensor 17 is provided opposite the photoreceptor 1, and a toner concentration detection sensor 36 is provided at the bottom of the front conveyance path 26. It is. These photosensor 17 and toner concentration detection sensor 36 will be described in detail later.

With the above configuration, the second developing device 11 operates in the same manner as the first developing device 10, and the electrostatic latent image that has passed through the first developing area X4 is developed again in the second developing area X5.

The transfer charger 12 and the separation charger 13 are arranged to face the photoreceptor 1 that has passed through the second development area X5, and the toner image visualized by the developer 10.11 is different from the toner image. The images are transferred onto the recording medium 16 that is synchronously conveyed to the transfer area x8.

The recording medium 16 onto which the toner image has been transferred is separated from the photoreceptor 1 by a separation charger 13, and the toner image is heated and fixed by a fixing device (not shown).

On the other hand, the photoconductor 1 that has passed through the part facing the separation charger 13 has residual toner removed by a cleaning device 14, and then a main eraser 15 supplies toner to the electrostatic latent image formed by the residual heavy exposure to form a toner image. Visualize it as.

The developer on the sleeve that has passed through the development area X4 is further conveyed in the direction indicated by the arrow, and is separated from the surface of the sleeve 24 at a portion facing the packet roller 29 and mixed with the developer in the front conveyance path 26.

The second developing device 11 has almost the same configuration as the first developing device 10. Therefore, the same members are given the same reference numerals. Note that the regulation gap Dゎ is the same as the regulation gap Db of the first developing device 10 (0.5 mm). On the other hand, the developing cap Ds2 is 1. omm and the first developer 10.
Therefore, the developer filling rate of the first developing area X4 is larger than the developer filling rate of the second developing area X. Further, the sleeve 24 is connected to a power source 35, and as will be described later, during normal development, the voltage is VB-i50V, and the AID of the first developing device 10 is
When forming a pattern image for toner density measurement using the C method, a voltage of V8° to -600V is applied. Further, the upper part of the second developing device 11 is removed.

As described above, the electrostatic latent image formed on the photoreceptor 1 is developed by the two developing devices to, 11, and the regulating gap D bl,
It is assumed that Db2 is the same and the amount of developer conveyed to the development area is the same. However, the developing gap D51 (=0, 5 mm) of the first developing device 10 is narrower than the developing cap D52 (-1,0 mm) of the second developing device 11. Therefore, in the first development area X4, the photoreceptor 1
The frequency of contact of the magnetic brush with the image is high, and solid images and ordinary character images are developed with sufficient density. Here, since the first developing device IO is set to conditions that can reproduce a solid image with sufficient density, it consumes a large amount of toner, and toner replenishment is performed in a manner that responds sharply to changes in toner concentration within the developing device. There is a need. On the other hand, the magnetic brush has a high scraping effect, and the toner adhering to the electrostatic latent image of the fine line is scraped off by the magnetic brush, resulting in poor reproducibility of the fine line.

On the other hand, in the second developing device 11, the developing gap DS2
By widening the area, the frequency of contact of the magnetic brush with the photoreceptor 1 is reduced, and the scraping effect of the magnetic brush is reduced, so that even fine lines can be developed with sufficient density. Also, the bias VB applied to the sleeve 24 = -150V
As a result, the toner adhering to the non-image area of the photoreceptor 1 is electrically attracted and collected into the sleeve 24.

Therefore, the image recorded on the recording medium 16 is not only a solid image or a normal character image, but also fine lines are clearly reproduced, and a high-quality image without background fog can be obtained.

Next, toner density control of the developing devices 10 and 11 will be explained.

First, in the toner density control of the first developing device (2) 0, the surface of the photoreceptor I is uniformly charged by the charging charger 2, and the inter-image eraser 9 is blinked to form a pattern latent image of a predetermined area.

Next, the pattern latent image is developed by the first developing device 10 to form a pattern image, and the image density is measured by the photosensor 17.
Read with.

The comparator 42 compares these inputs and inputs a corresponding signal to the control device CPU when the toner density is lower than the reference density. In the control device CPU, when a signal is input from the comparator 42, the first developer toner replenishment motor 34 is driven to replenish toner from the toner replenishing section 31 to the rear conveyance path 27.

As described above, in the first developing device 10, toner is replenished based on the AIDC method that can measure changes in toner density with high reliability. There is no need to worry about this.

The toner density control of the second developing device 11 will be explained.

In the second developing device 11, a change in magnetic permeability of the developer is measured by a toner concentration detection sensor 36 provided at the bottom of the front conveyance path 26.

The output of sensor 36 is input to a comparison input terminal of comparator 44 . On the other hand, the pattern image that has passed through the detection position of the photosensor 17 corresponding to the toner concentration to be controlled at the reference input terminal of the comparator 44 is collected by the second developing device 11 in the subsequent second developing area X5.

Here, in the second developing device 11, the bias voltage V8 or -60
The voltage is switched to 0V, and the attraction force for positively charged toner is increased. Therefore, the positively charged toner constituting the pattern image that has entered the second development area X5 is separated from the photoreceptor 1 by the electric field force based on the bias voltage V11.
The developer is collected on the sleeve 24. Therefore, the second
No pattern image exists on the surface of the photoreceptor 1 that has passed through the development area X5, and no toner is wasted.

By the way, the photosensor 17 consists of a light emitting element and a light receiving element, and the light emitting element illuminates the pattern image, and the light receiving element detects the reflected light. The photosensor 17 is the second
As shown in the figure, a signal having a strength corresponding to the strength of the amount of reflected light is input to a comparison input terminal of a comparator 42, which is a comparator. On the other hand, a reference voltage corresponding to the image density to be controlled is input from the power supply 41 to the reference input terminal of the comparator 42, and a reference voltage is input from the power supply 43 to the reference input terminal, and the measured toner density is lower than the reference density. If the controller CPU
Outputs a signal to. In the control device CPU, when the signal is input from the comparator 44, the second developer toner replenishment motor 34 is driven, and the toner replenishment section 31 is supplied with the rear conveyance path 2.
7. Replenish toner.

As described above, in the second developing device 11, toner is replenished based on the AIDC method, so the responsiveness to toner density changes is inferior to that in the AIDC method. In order to improve the chargeability, it is necessary to sufficiently stir the developer to increase the chargeability, and it is more suitable to control the toner concentration by ATDC.

In the above embodiment, the pattern image is formed by illuminating the surface of the photoreceptor 1 charged by the charger 2 with the inter-image eraser 9 to form a pattern latent image, and then developing the pattern latent image with the first developing device 10. However, a voltage having the same polarity as the toner charging polarity is applied to the sleeve 24 of the first developing device 10 while the photoreceptor 1 remains uncharged, thereby causing the charged toner to be electrically connected to the sleeve 24. The photoreceptor l
A pattern image may also be formed by flying the pattern image.

Further, in the embodiment described above, an image forming apparatus was described in which two developing devices 10 and 11 were provided on the side of the photoreceptor 1.
The present invention is applicable even to an image forming apparatus having three or more developing devices. For example, in the case of an image forming apparatus equipped with three developing devices, the toner of the pattern image created by the first and second developing devices is scraped off by the third developing device.

Furthermore, in the embodiment, in order to make the developer filling rate of the developing area facing the developing sleeve or the electrostatic latent image carrier of the developing device higher in the first developing device 10 than in the second developing device 11,
The developing cap Ds of the first developing device 10 is replaced by the developing cap Ds of the first developing device 10.
An example has been described in which the developing gap Ds of the first developing device 10 is made smaller than the developing gap Ds of the first developing device 10.
1 development gap Db2, or
The circumferential speed of the sleeve 24 of the first developing device 10 is set to the second developing device 11.
Figure 1 is a cross-sectional view of the main parts of the image forming apparatus, and Figure 2 is a cross-sectional view of the main parts of the image forming apparatus.
FIG. 3 is a circuit diagram related to image density control of a developing device.

(2)... Photoreceptor, 2... Charger, 9... Inter-image eraser, 10... First developer, 11... Second developer, 17... Photo sensor.

Claims (1)

[Claims] (1) A photoreceptor, a magnetic brush type first developing device and a second developing device, and the developer filling rate in the developing area of the first developing device and the second developing device is set to be lower than that of the first developing device. In the image forming apparatus, the electrostatic latent image developed by the first developing device is superimposed and developed by the second developing device, with the first developing device being set higher than the second developing device. a pattern forming means for forming a pattern image for density detection using a pattern image; a density detecting means for measuring the image density of the pattern image; and a collecting means for collecting toner constituting the pattern image into the second developing device. An image forming apparatus comprising: