JPS6180174A - Device for adjusting image density - Google Patents

Abstract

PURPOSE:To maintain the adequate image density in the stage of automatic setting and to improve the operability in the stage of manual density setting by making the number of the image density level by automatic setting larger than the manual setting level and decreasing the width of one kind of image density level in automatic adjustment. CONSTITUTION:The density levels in the automatic setting of an electrostatic recorder which permits the manual and automatic setting of a copy image are provided in the number larger than the number of the density levels for manual setting. Since there are fewer density levels to be set manually, the operator has no confusion in the manual setting and the probability of mis- copying decreases. On the other hand, the more density levels are provided in the case of automatic setting and therefore the width of the single image density level is narrower and more delicate image sensity setting is made possible. The record image having the preferable density is thus obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an image density adjusting device in an electrostatic recording device.

(Prior Art) An electrostatic recording device exposes a photoreceptor to a light image of a document to be recorded to form an electrostatic latent image on the photoreceptor, and then applies a developer to the portion of the electrostatic latent image. A developer image is formed by electrostatic adsorption, the developer image is transferred to recording paper, and then fixed, so that the image of the document is copied onto the recording paper.

By the way, with such an electrostatic recording device, it may not be possible to obtain a clear copy image depending on the density of the original image and the background color, so the appropriate sound is to adjust the image density to adjust the copy density. A regulating device i+," is provided.

This image density adjustment device is a device that adjusts, for example, a developing bias voltage applied between a developing device and a photoreceptor to adjust the amount of developer electrostatically attracted to the photoreceptor. Toner image based on the density of the recorded image (hereinafter referred to as
This is called image density. ) settings include manual settings performed by an operator by checking the density of the original, and automatic settings performed by automatically detecting the density of the original.

However, in the past, even if the image bk The number is selected from the following.

However, the number of manually set image density levels is not very large in consideration of ease of operation by the operator. On the other hand, when automatically setting image density for originals with images of various densities, the fewer the number of image density levels to be selected, the more the number of originals that must be covered by one type of image density level. increases.

Therefore, within one type of image density level, there is a high probability that although the image density level is appropriate for one document, it will be too dark or too light for another document.

(Object of the Invention) The present invention has been made in view of the above-mentioned problems, and its purpose is to enable a copy image with an appropriate density to be obtained when the image density is automatically set, and to provide a copy image with an appropriate density when the image density is set manually. An object of the present invention is to provide an image density adjusting device whose operability is not sacrificed.

(Structure of the Invention) For this purpose, in the image density adjusting device of the present invention, the number of image density levels is set to be greater during automatic setting than during manual setting, that is, the original density, The configuration is such that the range of image density levels of lIlj in automatic adjustment is reduced by increasing the number of image density correspondences.

(Example) The present invention will be described in detail below. FIG. 1 schematically shows an electrophotographic copying apparatus among electrostatic recording apparatuses.

When the original fg 2 is set on the surface of the platen glass l, the platen cover (not shown) is closed, and the copy start key is operated, the exposure light source 3 scans the original 2 for exposure in the direction of arrow a. The optical image of the original 2 is reflected by the mirror 4.6 and the lens 5.
The light is guided to the surface of the photosensitive drum 7 as an image forming photoreceptor through an image forming optical system such as . The photosensitive drum 7 is a grounded metal cylinder with a photoconductive layer made of selenium or the like provided on the outer peripheral surface thereof, and rotates in the direction indicated by the arrow in conjunction with the exposure scanning.

Before the arrival of the optical image on the photosensitive drum 7, the photoconductive layer is, for example, uniformly charged by a charging electrode 8 to which a DC high voltage is applied, and the photoconductive layer in this state receives the optical image. Then, the conductivity of the area that receives the light increases, and the electrical charge in that area escapes to the metal cylinder, and positive charges remain in the dark area depending on the degree of brightness, and this causes the photoconductive layer to An electrostatic latent image corresponding to the image of the original is formed on the surface of the document.

When the portion on which the electrostatic latent image is formed reaches the image sleeve 9a of the developing device 9, the negatively charged developer is applied to the remaining positively charged portion of the photosensitive drum 7. The developing sleeve 9a is attracted by the electrostatic force caused by the developing bias voltage applied between the developing sleeve 9a and the developing sleeve 9a. As a result, a developer image corresponding to the electrostatic latent image is formed on the surface of the photosensitive drum 7.

The transfer paper 11 in the paper feed force center 10 is sent out in the direction of the registration roller 13 by the feed roller 2 and once stopped, and the leading edge of the transfer paper and the leading edge of the developer image on the photosensitive drum 7 The transfer pole 1 is sent out again from the registration roller 13 at a timing such that the
4, the developer image on the surface of the photosensitive drum 7 is transferred.

Thereafter, the transfer paper is separated from the photosensitive drum 7 by the separation electrode 15 to which AC high voltage is applied, and is sent to the fixing device 17 by the conveyor belt 16, where the developer image is fixed, and the receiver is discharged onto the tray 18. .

Reference numeral 19 denotes a removing electrode for removing charges remaining on the photosensitive drum 7, and reference numeral 20 denotes a cleaning device for removing developer remaining on the surface of the photosensitive drum 7.

Now, in this embodiment, in a copying apparatus as described above,
For example, a photodiode 21 as an optical sensor placed next to the lens 5 automatically detects the concentration of I, J fAfi2.

FIG. 2 shows a sensor circuit that processes the signal obtained by the photodiode 21 and detects the original density to generate an image density control signal. The photodiode 21 receives the light reflected from the surface of the document, and flows a photocurrent (2) corresponding to the amount of the received light. The amplifier 22 constitutes an I/V conversion circuit together with the feedback resistor R1, and converts the photocurrent I into a voltage signal V+ (-I
xR1). The amplifier 23 constitutes a voltage amplification circuit together with resistors R2 and R3, and outputs a voltage output (2). This voltage (2) is V2=I-R1·R3/R2. This voltage (2) has a value proportional to the reflectance of the original (inversely proportional to the density of the original).

Figures 3 and 4 show the characteristics of the above sensor circuit, where the horizontal axis is the original density (reflectance) (this may be the current I), and the vertical axis is the output voltage 2. .

First, FIG. 3 shows the density levels when manually setting the image density, and shows an example in which the density levels are divided into three levels. That is, image density 1 (dark) corresponds to the range of original fg + density Do - Di, image density 2 (medium dark) corresponds to the range of original density D1 to D2, and image density 3 (light) corresponds to the range of original density D2 to D3. By doing so, you can obtain good recorded images. Therefore, when setting manually, if the density of the original is high, set the image density to level 3 to produce a light copy image, and if the original is light, set it to the image density level 1 to produce a dark copy image. do.

FIG. 4 shows density levels when image density is automatically set, and does not include an example of five levels. Here, 1.5.2.5 is added to the manual image density level 1.2.3 shown in FIG. 3 above to narrow the document density range covered by one type of image density level. When the document density is D1', the voltage (2) is J2 when it is Jl, Dl, 5, J3 when it is D2', J4 when it is D2.5, and J5 when it is D3.

When automatic setting is selected, the voltage value J1~
Using each of J5 as a comparison reference value, the output voltage ■2 corresponding to the actual original density is compared with the comparison reference value using a comparator.
Depending on the comparison result, the developing bias is set and the density is set. For example, if the output of the sensor circuit is J1 or less, the original density is the highest, so select image density 3 and set the bias voltage to reduce the amount of toner adhesion, resulting in a copied image with an appropriate density. Do it like this. Further, if the output is between J2 and J3, image density 2.5 is selected.

From the above, the density level is set to a small number as before so as not to confuse the operator when it comes to manual settings, so the probability of miscopying is low (on the other hand,
In the case of automatic setting, the number is increased, so that the width of a single image density level becomes narrower, and more detailed image density settings can be made, thereby making it possible to obtain a recorded image with a preferable density.

In the above embodiment, the means for detecting the density of the original is, in addition to arranging a photodiode next to the lens 5 of the image forming optical system, a special means for detecting the density of the original prior to the exposure scanning of the light tA3. A part of the document is scanned using a light source,
It is also possible to use means for detecting the reflected light using a separately provided light receiving element. In addition to adjusting the developing bias voltage, the image h5 degree adjustment means can also adjust the phase of the exposure light source 3 to adjust its light amount, and further adjust the charging voltage of the charging electrode 8. You can also adjust the density by

(Effects of the Invention) As described above, according to the present invention, the number of 'b〉 degree levels to be selected during automatic setting is the same as in the past, so there is no risk of the operator making a mistake in the setting operation, and there is no risk of the operator making a mistake in setting operation. Since the width of one density level is narrow, fine density settings can be made, and variations in the density of copied images produced within a specific density level range are reduced.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram of the electronic copying machine, Fig. 2 is a circuit diagram of the sensor circuit of this embodiment, and Figs. 3 and 4 show the relationship between the output of the sensor circuit and the original fg'&% degree. FIG. 1...Platen glass, 2...Original, 3...Light source for exposure, 4.6...Mirror, 5...Lens, 7...
・Photosensitive drum, 8...Charging electrode, 9...Developing device, 1
0...Paper feed cassette, 11...Transfer paper, 12...
Feeding roller, 13... Registration roller, 1
4... Transfer pole, 15... Separation pole, 16... 1 general conveyance belt, 17... Fixing device, 18... Receiver is plate, 19
... Electrode removal, 20 ... Cleaning device, 21.2
2...Amplifier.

Claims (1)

[Claims] (1) In an image density adjustment device that allows the density of a copied image in an electrostatic recording device to be set manually or automatically, the number of density levels for automatic setting is greater than the number of density levels for manual setting. An image density adjustment device characterized by: