JPS5930269B2 - toner supply device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a developing device in an electrophotographic copying machine, and more particularly to a device that controls the amount of toner supplied to the developing device to maintain a constant toner concentration in the developing device.

In general, developing methods for indirect type electrophotographic copying machines include liquid development, magnetic brush development, cascade development, and the like.

In these developing methods, it is not easy to always maintain the toner concentration in the developer (liquid) within an appropriate range.

However, if the toner concentration in the developer can be maintained within an appropriate range, the image quality of the copying machine can be maintained in a very good condition. Therefore, general users can operate the copying machine very easily. If the toner density becomes too high, the background of the copy becomes dirty, and if it becomes too low, the image density decreases, resulting in a copy with poor contrast. On the other hand, whether it is a direct or indirect electrophotographic copying machine,
2. Description of the Related Art In a copying machine using a liquid development method, an automatic toner concentration control method using the light transmittance of a developer is known.

However, this method can only be used with liquid development,
Regarding powder development methods or general development methods, there is no known method that automatically controls toner concentration to keep it constant. In view of the above points, the present invention is designed to maintain a constant toner concentration in a dry type copying machine, that is, a powder development method.

The present invention will be described in detail below with reference to Examples.

First, FIG. 1 shows the structure of an indirect electrophotographic copying machine, and is a diagram for explaining the process of copying.

In the figure, 1 is a document table, and 2 is an illumination device comprising a lamp 2a, a reflector 2b, etc. for irradiating light onto the document 1' on the document table 1. An illumination device 2 is configured to move along the document table 1. Reference numeral 4 denotes a photoconductor drum which rotates at a constant speed around a shaft 5 in synchronization with the movement of the document table 1 or illumination device 2, 6 a photoconductive layer formed on the surface of the photoconductor drum 4, and T. This is a charger for uniformly charging the photoconductive layer 6 on the drum 4, which rotates at a constant speed.

Now, as the photosensitive drum 4 rotates, the photoconductive layer 6, which has been uniformly charged by the charger T, is exposed by a reflected image of the original illuminated by the illumination device 2 being projected through the optical system 3. Here, an electrostatic latent image corresponding to the original is formed on the surface of the photoconductive layer 6 onto which the image is projected. Next, the electrostatic latent image formed on the surface of the photoconductive layer 6 is developed with toner in a developing device 8 and visualized. This visualized toner image is transferred to a plain paper 11 which is fed by a roller 10 at a transfer unit 9.
transcribed into. Thereafter, the plain paper 11 onto which the toner image has been transferred is sent to the fixing section 12, where the toner image is heated and fixed to complete the copy. On the other hand, the photosensitive drum 4 reaches the cleaning section 13, the surface of which is cleaned, and the same process is repeated again. Here, when developing with powder toner, such as magnetic brush development or cascade development, a toner supply device 14 is provided close to the development device 8, and the toner supply device 14 is connected to the development device 8. Powder toner is being replenished. This replenishment is accomplished by a mechanical mechanism. This replenishment amount is generally controlled by the user's judgment, and a fixed amount of powder toner is mechanically replenished according to the number of copies. For this reason, the toner density may sometimes become too high or too low.
Therefore, as described above, the present invention is to control the amount of toner supplied to the developing device 8 in order to keep the toner concentration constant at all times, and this will be explained with reference to FIG. FIG. 2 shows a developed view of the photosensitive drum 4. In the figure, reference numeral 15 indicates an effective image area, in which an electrostatic latent image corresponding to the original is formed. Reference numeral 16 designates an ineffective image area provided on a part of the extension of the effective image area 15, and 5 represents a drum rotating shaft.

The ineffective image area 16 is designed to be subjected to charging exposure development only for an original (image area) of a specific density provided in advance on a part of the original platen 1, etc., and the original is mainly Consideration is given to the original document so that a certain halftone between black and white or one with a stepwise difference in tone can be obtained. Light is irradiated from a light source 17 to the ineffective image area 16 on which such a specific toner image is formed, and the reflected light is received by a light receiving element 18, and photoelectric conversion is performed according to the amount of received light.

Now, for example, if the amount of light received by the light receiving element 18 is large, the amount of reflected light will be large, and the toner image will be thin.

Therefore, the toner image in the effective image area 15 is naturally thin, and if toner is replenished from the toner supply device 14 in accordance with the amount of light received at this time, a normal toner image can be revealed. Therefore, the photoelectric conversion signal output from the light-receiving element 18 is compared with a set value when the toner image density is a proper value, and the toner supply section is operated according to the signal of the comparison value to control the amount of toner supply. By doing so, the toner concentration can always be kept within an appropriate range. As a result, the toner image density of the obtained copy becomes stable, and a clear image with good contrast can be obtained. At this time,
If the photoelectric conversion signal outputted from the light-receiving element 18 is obtained by changing significantly and linearly in proportion to the toner concentration, conversion into a control signal will be easier and more accurate.

Therefore, as described above, in the present invention, a toner image that is a halftone between black and white is formed in the ineffective image area 16 for detecting toner density.

For example, FIG. 3 shows the toner concentration a in the developing section 8,
The resulting image density b is expressed using curve 1 when the original density (formed in the ineffective image area 16) is too high, curve 2 when it is appropriate, and curve 3 when it is too low.

Therefore, with respect to the original appropriate toner density range a' to a'', curve 1 is slightly saturated with almost no difference in image density, and curve 3 is linear, but the amount of change is too small, so curve 1,
While all three require extremely delicate detection capabilities,
In the present invention, the curve 2 changes substantially linearly with a large gradient over the entire range from a' to a'', so by utilizing this, a photoelectric conversion signal corresponding to b' or b can be obtained. Using this, it is easy to control the supply of toner.A document having an appropriate halftone in this way is provided in a part of the document table 1, and it is extremely easy to realize it. Further, the light source 17 and the light receiving element 18 can be installed in a process after the toner image is formed on the non-effective image area 16. After that, the cleaning section 13 removes the toner image formed on the non-effective image area 16. As described above, according to the toner supply device of the present invention, a region for toner density detection is provided on the photoreceptor separately from the image forming section, and the image forming section is located in this region. A half-tone toner image is formed using the same developing device as the toner, and by detecting this reflected light, the toner concentration is detected and toner replenishment is controlled, and it is possible to accurately detect changes in toner concentration. This makes it easy to keep the toner concentration in the developer tank constant.

[Brief explanation of drawings]

FIG. 1 is a diagram for explaining the structure of an indirect type electrophotographic copying machine according to the present invention, FIG. 2 is a developed view of a photosensitive drum as an embodiment of the present invention, and FIG. 3 is a diagram showing toner density and It is a characteristic curve showing the relationship with image density. 3...Optical system, 4...Photosensitive drum,
8...Developing device, 14...Toner supply device, 15...Effective image area, 16...
Ineffective image area, 17...Light source, 18...
·Light receiving element.

Claims (1)

[Claims] 1. A toner supply device that includes an area on the photoconductor for detecting the toner density of the developing device, separate from the image forming area, and controls toner supply to the developing device based on the image density formed in the area. means for forming a half-tone toner image in the area using the same developing device as the image forming area; density detecting means for detecting the density of the half-tone image formed by the means; A toner supply device comprising: supply means for controlling toner supply to the developing device based on an output signal from the density detection means.