JPH02281279A - Image forming device - Google Patents

Abstract

PURPOSE:To prevent a change in image density, which results from the potential fluctuation of an image part by providing a means which sets the latent image potential of a reference image at the inbetween of the potential of a base part and that of the image part and a means which adjusts a developer supply amount based on a detecting signal from a reflected density detecting means. CONSTITUTION:The image forming device is provided with a latent image forming means 12 forming a latent image for a detecting reference image on a photosensitive body 1, the potential setting means which sets the latent image potential for the reference image at the inbetween of the potential of the base part and that of the image part, the reflected image detecting means 20 which optically detects the density of a visible picture obtained by developing the latent image formed by the latent image forming means 12, and the developer adjusting means which adjusts the developer supply amount based on the detecting signal from the reflected density detecting means 10. Since the potential of the reference image for a latent image is set at the inbetween of the potential of the base part and that of the image part when the reference image is formed, its potential is secured sufficiently even if the potential of the image part rises. Consequently, the fluctuation of toner concentration resulting from the potential fluctuation of the photosensitive drum can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an image forming apparatus, and particularly to an image forming apparatus for recording on paper using an electrophotographic method.

[Prior Art] Image forming devices using electrophotography, such as copying machines, facsimiles, and printers, expose the surface of a photoreceptor by irradiating a light beam according to image information, and create a latent image by the exposure. The toner is developed by a developing device, a toner image resulting from the toner development is transferred onto paper, and the transferred image is further fixed on the surface of the paper by a fixing device.

In such an image forming apparatus, in order to maintain constant image quality at all times, it is necessary to control the potential of the electrostatic latent image on the photoreceptor, which is an image carrier.

Various control methods for performing this control have been proposed and put into practical use. One of them is a method of controlling toner density by forming a reference image for toner density control on an image carrier and detecting the optical density thereof (Japanese Patent Laid-Open No. 14/1645/1989).

In this case, in order to ensure the responsiveness of toner replenishment, a halftone density below the saturation density is generally used as a reference image for toner density control. That is, stable image quality can be obtained by controlling toner replenishment so as to keep the reflection density of the reference image consisting of halftone density constant.

[Problems to be Solved by the Invention] However, in the above-mentioned conventional technology, the electrostatic characteristics of the image carrier can be controlled in the same manner even when environmental changes and deterioration over time occur. As a result, the toner density may decrease significantly, or conversely may increase. When the toner concentration is below the appropriate range, carrier deterioration is accelerated,
On the other hand, if the value is exceeded, the charging ability of the toner decreases, toner adheres to the background, impairing image quality, and causes toner scattering, contaminating the inside of the apparatus.

Furthermore, if the toner density is significantly reduced, the resulting image density will be low even if the reflection density of the reference image consisting of halftone density is controlled to be constant. Also, conversely, 1~
If the density increases significantly, even if the reflection density of the reference image consisting of halftone density is controlled to be constant, the resulting image density will be poor in sharpness and good image quality will not be obtained. do not have.

Furthermore, in the above-mentioned image forming apparatus that performs recording by scanning and exposing an image carrier with a light beam such as a laser beam, in order to form a reference image having a halftone density below the saturation density, it is necessary to remove the latent image. It was necessary to change the developing bias potential or charging potential during development.

In this way, with conventional technology, it is possible to control variations in image density caused by toner density, but the reality is that it is nearly impossible to control changes in image density caused by potential variations in the image area. It is.

An object of the present invention has been made in view of the above-described actual state of the prior art, and it is an object of the present invention to provide an image forming apparatus that can obtain sharpness and resolution as well as stable image density.

[Means for Solving the Problems] In order to achieve the above object, the present invention exposes a photoreceptor using a light beam signal that is modulated according to image information, and develops a latent image resulting from this exposure using a developer. In an image forming apparatus that develops a visible image and records the visible image by transferring it to paper, a latent image forming means forms a latent image of a reference image for detection on the photoreceptor, and the reference image potential setting means for setting the latent image potential to be between the background potential and the image potential; and reflection density detection for optically detecting the image density of a developed image obtained by developing the latent image by the latent image forming means. and a developer adjusting means for adjusting the amount of developer supplied based on the detection signal of the reflection density detecting means.

[Operation] According to the above means, when forming a reference image latent image, the potential is set between the background potential and the image potential, so even if the image potential increases, the potential of the reference image does not change. A necessary value of the potential is ensured, and fluctuations in toner density due to fluctuations in the potential of the photoreceptor drum can be prevented.

[Example] Hereinafter, one embodiment of the present invention will be described based on the drawings.

FIG. 1 is a front view showing the configuration of main parts of an embodiment of an image forming apparatus according to the present invention.

The photosensitive drum 1, which is an image carrier, is rotated at a constant speed in the direction of the arrow shown in the figure by a drive unit using a motor as a drive source. A charger 2 for charging the surface of the photoreceptor is installed above the photoreceptor drum 1 just before the exposure position. The exposure position of the photosensitive drum 1 is irradiated with a laser beam 3 emitted from a laser generator 12 and subjected to processing such as modulation according to image recording information.

A developing device 4 for developing a latent image formed on the surface of the photosensitive drum 1 is installed on the side of the photosensitive drum 1, and a developing device 4 for transferring a toner image onto a fed transfer paper 6 is installed below the photosensitive drum 1. A transfer charger 5 is installed, and a separation charge eliminator 7 for separating the transfer paper 6 from the photosensitive drum 1 is installed adjacent to the transfer charger 5.

Further, on the opposite side of the developing device 4, a cleaning device 8 is provided for removing residual toner adhering to the surface of the photoreceptor upon completion of the transfer. Furthermore, a charge eliminating lamp 9 is provided immediately before the charger 2 to eliminate charges remaining on the surface of the photoreceptor. Furthermore, a reflection density sensor 10 is installed downstream of the developing device 4, and detects the reflection density of a reference image A or B, which will be described later. Also,
The developing device 4 is provided with a 1-toner replenisher 70-ra 11 that is controlled by the present invention.

Next, the operation of the image forming apparatus with the above configuration will be explained.

When the recording execution mode is set, the photoconductor drum 111 rotates, and the surface that has been neutralized by the static elimination lamp 9 is transferred to the charger 2.
charged by. At the same time, a paper feed mechanism (not shown) operates to transport the transfer paper 6 to the registration position. Then,
A laser generator 12 generates a laser beam according to image information, and the surface of the photoreceptor is sequentially exposed.

The latent image resulting from this exposure is developed by the developing device 4 when it rotates and reaches the developing device 4, where it is reversely developed by a two-component developer mixed with charged toner. be done. The developed visible toner image moves to the transfer position as the photosensitive drum 1 rotates, and the waiting transfer paper 6 is sent out to the transfer position at the timing of arrival at the transfer position. At the transfer position, the visible toner image on the surface of the photoreceptor is transferred onto the transfer paper 6 by the transfer charger 5, and the transfer paper 6 is peeled off from the surface of the photoreceptor by the separation static eliminator 7 in order from the portion where the transfer has been completed.

The peeled transfer paper 6 is conveyed to a fixing device (not shown),
The toner image is fixed on the surface of the transfer paper 6.

Since toner remains on the surface of the photoreceptor after the transfer is completed, it is removed by the cleaning device 8. Furthermore, the charges remaining on the surface of the photoreceptor are removed from the cleaned surface using a charge removal lamp 9. The discharged surface of the photoreceptor is charged by the charger 2, and exposure, development, transfer, and fixing are performed again.

At this time, the surface potential of the photoreceptor drum 1 is the background potential (
The dark area potential) VD is set to approximately -800V, and the image area potential (light area potential) VL is set to approximately 50V.

And these and development bias potential V8 (-600V)
Development is performed by the potential difference between the two. However, as the usage time (the number of times of image formation) progresses, the photosensitive drum 1 deteriorates, and as shown in FIG. 2, the image portion potential (2) gradually increases. For this reason, (■.

-VB) gradually decreases, causing fluctuations in image density and image quality.

To deal with this, conventional countermeasures have been to change the developing bias when developing the reference image latent image when performing toner replenishment control, and to ensure responsiveness of toner replenishment. The purpose was to form a reference image using a smaller developing electric field than when forming the image. However, as described above, when the image portion potential VL increases, the potential difference when forming the reference image becomes smaller than necessary. As a result, the toner concentration increases excessively, leading to rough skin and toner scattering.

Therefore, in the present invention, when forming the reference image latent image, the latent image is formed with a smaller amount of light than the amount of light used when forming the original image latent image, and as shown in FIG. and V
The potential VM is set midway between L and L. By doing so, fluctuations in the potential of the latent reference image can be minimized, and fluctuations in toner density caused by fluctuations in the potential of the photoreceptor drum can be prevented.

FIG. 4 is a flowchart showing the flow of the control procedure using the reference image.

First, in step 31, a detection signal voltage VSC corresponding to the optical density of the surface of the photoreceptor drum 1 without a toner image is detected.
), it is determined whether this is appropriate (step 32). If it is not appropriate, there is a high possibility that there is an abnormality in the reflection density sensor 10 or the photosensitive drum 1, so an abnormality is displayed (
Step 33).

On the other hand, if the detection signal voltage Vgc is appropriate, the detection signal voltage VGP of the reference image is detected (step 34) and compared with the preset comparison signal R1 [(Vgp/Vgc)
> RP] (step 35). If this inequality does not hold, it is determined that the toner content in the developer is appropriate, the process shown here is completed, and the process moves to the next mode. If it is true, it is determined whether the remaining amount of toner is sufficient (step 3G).

If the remaining amount of toner is sufficient, the toner replenishing roller 11 is rotated for a certain period of time to replenish an appropriate amount of toner (step 38). If the remaining amount of toner is insufficient, "Toner End" is displayed and the process ends (step 37).
).

Next, a method for detecting a reference image will be explained.

As mentioned above, the reference latent image formed outside the image area has a latent image potential set to a potential VH between VD and VL, and the exposure amount for the image latent image that should be formed in the original image area. (laser power) to emit a lower exposure amount. As means for varying the laser power, there are conventionally known methods such as varying the driving voltage of the laser and varying the emission time of the laser by pulse width modulation. The latent image thus formed is visualized by the means described above. The image forming conditions at this time are desirably such that the amount of toner adhering to the photoreceptor drum 1 after development is 0.3 to 0.7+.
This is to set the image so that the solid image has an optical density between .ng and .ng.

The visualized reference image 20 is detected by a reflection density sensor 10 comprising a light emitting element 21 and a light receiving element 22, as shown in FIG. That is, the light emitted by the light emitting element 21 is irradiated onto the reference image 20, and the reflected light is received by the light receiving element 22, whereby the optical density of the reference image 20 is detected. Note that it is not necessary to perform this detection every time, and it is sufficient to perform this detection every time, for example, every certain number of sheets or every certain period of use, if necessary.

FIG. 6 is a circuit diagram showing details of the reflection density detection circuit.

The light emitting element 21 is connected to a power supply line via a resistor 23 and continuously emits light. A phototransistor is used as the light receiving element 22, and its output is amplified by an NPN type transistor 24.

The collector of this transistor 24 is connected to a power supply,
The emitter is grounded via a resistor 25. Further, resistors 26 and 27 are connected in series and inserted between the power supply line and the ground, and the output of the connection point thereof and the emitter output of the transistor 24 are connected to each of the two outputs of the operational amplifier 28. An output resistor 29 is connected between the output terminal of the operational amplifier 28 and the power supply, and the output of the operational amplifier 28 is applied to the toner replenishment control section 30.

In this circuit, the voltage at the connection point of resistors 26 and 27 is the reference voltage, and this voltage and transistors 1 to 24
The configuration is such that the operational amplifier 28 compares the emitter voltage of . When the output voltage of the emitter voltage of the transistor 24 (that is, the output of the light receiving element 22) becomes higher than the reference voltage, an output signal is generated in the operational amplifier 28 and applied to the toner replenishment control section 30. The toner replenishment control unit 30 controls the rotation time of the toner replenishment roller 11 to optimize the amount of toner replenishment.

Further, in the above embodiment, the case of a two-component magnetic brush reversal phenomenon system using laser beam scanning has been described, but the present invention can be similarly applied to the case of regular development.

[Effects of the Invention] As explained above, the present invention exposes a photoreceptor to light using a light beam signal modulated according to image information, develops a latent image resulting from this exposure into a visible image using a developer, In an image forming apparatus that transfers and records this visible image onto paper, a latent image forming means forms a latent image of a reference image for detection on the photoreceptor, and a latent image potential of the reference image is transferred to a background portion. a potential setting means for setting the potential to an intermediate value between the potential and the image area potential; a reflection density detection means for optically detecting the image density of a developed image obtained by developing the latent image by the latent image forming means; and the reflection density detection means. Since a developer adjustment means is provided to adjust the amount of developer replenishment based on the detection signal of the means, it is possible to minimize potential fluctuations of the reference image latent image, and stable toner replenishment control is possible. , it is possible to prevent the occurrence of toner scattering, etc.

[Brief explanation of drawings]

FIG. 1 is a front view showing the configuration of the main parts of an embodiment of an image forming apparatus according to the present invention, FIG. 2 is a characteristic diagram showing the relationship between the number of image formations and surface potential, and FIG. 3 is a standard according to the present invention. FIG. 4 is a flowchart showing the flow of control procedures using a reference image; FIG. 5 is a perspective view showing an overview of the density detection circuit; and FIG. 6 shows details of the density detection circuit. FIG. 1... Photosensitive drum, 4... Developing device, 5
...Transfer charger, 6...Transfer paper, 10.
... Reflection density sensor, 11 ... Toner supply roller, 12 ... Laser generator, 20 ...
...Reference image, 30... Toner supply control section, R
p...comparison signal, VD...ground potential, VL...light potential, v, c, y,...
・Detection signal voltage. □School-9 Figure H-j

Claims (1)

[Claims] A photoreceptor is exposed to light using a light beam signal that is modulated according to image information, a latent image resulting from this exposure is developed into a visible image using a developer, and this visible image is transferred to paper for recording. In the image forming apparatus, a latent image forming means forms a latent image of a reference image for detection on the photoconductor, and a potential setting sets the latent image potential of the reference image to an intermediate potential between a background part potential and an image part potential. means, a reflection density detection means for optically detecting the image density of a developed image obtained by developing the latent image by the latent image forming means, and a replenishment amount of developer based on a detection signal of the reflection density detection means. An image forming apparatus comprising: a developer adjusting means for adjusting the developer.