JPH0241752B2 - - Google Patents

Description

[Detailed description of the invention]

This invention provides an image density control device for an electronic copying machine, which optically detects the image density from a reference image formed on a non-image area of a photoreceptor during copying, and controls the amount of toner supplied based on the obtained value. Regarding the improvement of Conventionally, this type of control device for electronic copying machines measures image density based on the amount of reflected light detected from the undeveloped surface of the photoreceptor and the amount of reflected light detected from the developed reference image formed on the non-image area of the photoreceptor. , a method in which the amount of toner replenishment is controlled based on the obtained control value is known, such as in Japanese Patent Laid-Open No. 103359/1983.
However, with such a control device, there is no problem if the toner transfer efficiency to the paper is always constant, but the toner transfer efficiency usually changes greatly due to toner deterioration, etc., and is affected by these factors. It has the disadvantage that it is difficult to obtain copies with consistently stable image density on paper. The present invention has been made for the purpose of improving such drawbacks, and provides an image density control device for an electronic copying machine that is capable of controlling image density without being affected by toner deterioration, etc., so that images are always stable. It is designed so that a copy of the density can be obtained. The present invention will be described in detail below. Generally, the developer used in electronic copying machines is formed by toner and additives adhering to the surface of a charged carrier.
During use, toner with reverse polarity or no polarity, ie, deteriorated toner, increases. These toners are uniformly developed and adhere to the photoreceptor regardless of the presence or absence of a latent image on the photoreceptor, but during transfer, the toner remains on the photoreceptor without being transferred to the paper, resulting in development. This results in a decrease in transfer efficiency, that is, the rate at which toner in the image area on the photoreceptor transfers to the paper side, which causes a decrease in image density on the paper. Therefore, in this invention, the photoreceptor 4 is used as the reference image 5.
a comparator 20 that compares the difference between the toner density after developing the image area potential formed in the non-image area of the reference image 5 and the toner density after developing the potential that erased the latent image of the reference image 5 with the reference density; The amount of toner replenishment is controlled based on the value obtained by the comparator 20, and as a result, true transfer toner is obtained by eliminating toner of opposite polarity and without charge that remains on the photoreceptor. The transfer efficiency is improved by controlling the amount of toner replenishment by detecting only the amount of toner, and the image density on the paper is made constant. That is, as mentioned above, toner having opposite polarity and no electric charge is uniformly developed regardless of the presence or absence of a latent image on the photoconductor, and the development that adheres to the photoconductor causes the development. From the density of the image developed as is,
The density of the developed image after erasing the reference latent image is subtracted and the value (value obtained by subtracting the density of deteriorated toner from the density including deteriorated toner) is compared with the reference density, and toner is replenished using the obtained control value. By controlling the amount, copies with constant image density can always be obtained. Next, one embodiment of the present invention will be described in detail with reference to the drawings. In the figure, 1 is the main body of an electronic copying machine, and 2 is a platen provided on the top of the main body 1, on which a document 3 to be copied can be placed. A target 6 forming a reference image 5 is provided in the image area. Reference numeral 7 denotes a light source that simultaneously irradiates the original 3 on the platen 2 and the target 6. The reflected light from the original 3 and the target 6 irradiated by the light source 7 is guided to the photoreceptor 4 by an optical system (not shown) and is exposed to the photoreceptor. A latent image of the original 3 is formed in the image area of the body 4, and a latent image of the target 6 is formed in the non-image area. On the other hand, around the photoconductor 4, a charger 8, an unnecessary image erasing light source 9, a developing device 10, a pre-transfer lamp 11, a transfer device 12, and a static eliminator 1 for removing paper are provided.
3. The density detector 14, the cleaning device 15, and the static eliminator 16 are arranged in this order along the rotational direction of the photoreceptor 4, and the density detector 14
is installed at a position where the density can be detected from the reference image 5 formed on the non-image area of the photoreceptor 4. Also, the concentration optically detected by the concentration detector 14 is the amount of light -
After being input to the voltage converter 18 and converted into a voltage, the density is measured by the density measuring circuit 19. Furthermore, the density before development and the density after development are compared in the next comparator 20, and the output of the comparator 20 is The toner replenishment motor 21 that drives the toner replenishment roll 10a of the developing device 10 is controlled as follows. However, when the copy start switch is turned on to make a copy, the unnecessary image erasing light source 9 turns on in the first empty cycle, erasing the latent image of the reference image 5 formed on the photoreceptor 4, and the potential of this part becomes It has almost the same potential as the margin area of the image area. Next, the image area and the non-image area of the photoreceptor 4 are developed by the developing device 10, so that the density of the reference image 5 becomes the same density as the so-called fogged surface of the margin area of the image area. This concentration is detected by the concentration detector 14.
After the light is detected and converted into a voltage by the light amount-to-voltage converter 18, the density is measured by the density measurement circuit 19 and held as the density of the blank area of the image area. Next, when entering the copying cycle after completing the empty cycle, a latent image of the original 3 is formed in the image area of the photoconductor 4, and a latent image of the target 6 is formed in the non-image area, respectively.
These latent images are developed by a developing device 10 to become a toner image and a reference image 5. The toner image is transferred to paper (not shown) in a transfer process, and the reference image reaches the density detector 14 without being transferred, where the density is detected. The density signal detected by the density detector 14 is converted into a voltage by a light amount-to-voltage converter 18, and then the density is measured by a density measurement circuit 19, and outputted to a comparator 20 together with the previously measured margin density. . The comparator 20 compares these value differences with a reference density, and if the detected value is higher than the reference value, the toner replenishment motor 21 is stopped, and if it is lower, the toner replenishment motor 21 is rotated to supply toner to the developing device 10. Toner replenishment roll 10a
control. As a result, the toner density can be controlled without being affected by untransferred toner that remains on the photoreceptor 4 without being transferred to the paper, so that copies with stable image density can always be obtained. The table below compares the control according to the present invention and the control using a conventional control device.As for the degree of deterioration of the developer, a developer that causes fog toner of about 0.3 in the margin area is used, and a developer that produces about 0.3 fog toner in the margin area is used. The reproduced contrast density shows the case where the control circuit is set to reproduce at 0.5 (reference density).

[Table] As is clear from the table above, when using a conventional device, the reproduced density is significantly lower than the set density when using deteriorated developer, but with the device of this invention, it is always stable regardless of the deterioration of the developer. Image density can now be obtained. Further, in the above embodiment, a density detector 14 was used to detect the density based on the amount of light reflected from the photoreceptor 4, but as shown in FIG. A concentration detector 14 is provided on the rear side of the transparent body 22, and a bias power source 2 is connected to the transparent body 22 by a switch element 23.
4 may be applied selectively. In this case, the density of the reference image 5 is determined with the transmitting body 22 grounded by the switch element 23, and during development, a bias power source 24 is applied to perform development. Further, in the above embodiment, the unnecessary image erasing light source 9 was used to form a portion having the same potential as the image margin, but a dedicated erasing light source is provided, and this erasing power is used to form a latent image of the reference image 5. may be deleted. In addition, the toner density in the area with the same potential as the image margin area is detected during the empty cycle, and the toner density in the image area is detected during the copying cycle after the empty cycle is completed. Detection of both concentrations is possible even when not in cycle. As described in detail above, the present invention allows the use of a portion of the image on the photoconductor corresponding to the image margin even when deteriorated toner develops and adheres to the photoconductor but is not transferred onto the paper due to toner deterioration. Detects the density of deteriorated toner attached to the photoreceptor, corrects the toner density on the image area on the photoreceptor accordingly, and controls the amount of toner replenishment by comparing this value with a reference value. The density of the toner image on the photoreceptor transferred to the transfer paper becomes constant, and the effect is that it can be stably obtained. In addition, since the same reference image is used to detect the toner density in the image area and the toner density in the image margin area, the toner density in the image area and the image margin area is detected using the same reference image. can be faithfully reproduced, and by controlling the amount of toner replenishment based on the difference between the two toner densities, it is possible to control the toner density with high precision, and the density detector is installed in one location. It is more economical than detection with conventional compound detectors.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing one embodiment of the present invention, and FIG. 2 is an explanatory diagram showing another embodiment of the detection section. 4 is a photoreceptor, 20 is a comparator.

Claims (1)

[Claims] 1 The toner density after developing the image area potential formed on the non-image area of the photoreceptor 4 as the reference image 5;
A comparator 20 is provided to compare the difference between the potential of the latent image of the reference image 5 and the toner density after development with the reference density, and the amount of toner replenishment is controlled based on the value obtained by the comparator 20. Image density control device for electronic copying machines.