JPS6148711B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electrostatic recording device, and more particularly to an electrostatic recording device that includes a step of developing an electrostatic latent image using a developer comprising a mixture of carrier and toner.

In electrostatic recording technology, an electrostatic latent image is developed and visualized using a developer. Developers are often liquids or powders consisting of a mixture of carrier and toner. These developers are used for recording (development)
The toner (toner concentration) decreases as the process is repeated. On the other hand, in such an electrostatic recording device,
The density of the final recorded image changes due to various changes in conditions. Therefore, in order to stably obtain a recorded image with a desired density, it is necessary to be able to detect the density of the recorded image and correct the operating conditions.

An object of the present invention is to provide an electrostatic recording device that can output a signal suitable for image density correction.

A feature of the present invention is that it determines whether the toner concentration in the developer is within a predetermined range that can exhibit a normal developing effect and whether the recorded image density is the desired density. Toner is replenished into the developer when it is outputting that the image density is below the desired value, on the condition that the toner density is below the upper limit of the toner density that provides normal development. be.

Generally, the recorded image deteriorates as the toner concentration in the developer decreases. Therefore, if the density of the recorded image is lower than the desired value, it can be corrected by increasing the toner density in the developer. If the recorded image density decreases, toner can be replenished into the developer, but if the toner concentration in the developer exceeds the upper limit for normal development, the image may become smudged or the exposure to light may deteriorate. There are disadvantages such as a thin film of toner that cannot be removed on the surface of the drum, a rapid increase in the amount of dirt on the device due to toner scattering, and a deterioration in the performance of the developer, making it impossible to perform normal development. Therefore, according to the apparatus of the present invention, it is possible to correct image density by toner density correction without causing such inconveniences.

Although the present invention can be carried out regardless of whether a liquid developer or a powder developer is used, and whether transfer recording or direct recording is performed, the following describes a toner image developed using a powder developer. An electrostatic recording device that transfers and fixes images onto plain paper as a recording medium will be explained as an example.

In FIG. 1, 1 is a photoconductive drum for electrophotography. As this drum rotates in the direction of the arrow, it is uniformly charged by a charger 2 and exposed to a light image 3 to form an electrostatic latent image. and is developed in the developing device 4.
The developing device 4 includes a developer container 4a, a developer 4b made of a magnetic carrier and toner, a magnetic roller 4c that absorbs the developer 4b to form a magnetic brush and slides on the surface of the photoconductive drum 1, and a magnetic roller 4c that slides on the surface of the photoconductive drum 1. It has a scraper 4d for scraping off the developer 4b from the roller 4c, a toner concentration detector 4e for detecting the toner concentration in the scraped off developer 4b, and a toner replenishing means 4f.
The toner concentration detector 4e has a detection coil whose inductance changes in response to the magnetic permeability of the developer 4b, thereby changing the terminal voltage. The surface of the photoconductive drum 1 then comes into contact with the recording paper 6, and by applying a bias voltage by the transfer device 7, the toner image formed on the drum surface is transferred to the recording paper 6, which is a recording medium. Thereafter, the surface of the photoconductive drum 1 is cleaned with a cleaner 8 and reused. An image density detector 9 photoelectrically detects the density of the image transferred to the recording paper 6. The light image 3 is exposed in the same manner as the information image in order to record a detection mark 10 for density detection outside the information image area, as shown in FIG. Then, as shown in FIG. 2, a detection mark 10 is recorded on the recording paper 6.
The image density detector 9 detects the density of the image.

FIG. 3 is a block diagram of the judgment circuit of the apparatus of the present invention. The output voltage obtained from the toner concentration detector 4e is sent to a comparison circuit 12 for determining toner concentration.
Enter. This comparison circuit 12 outputs "1" when the toner concentration in the developer is below the upper limit value, and outputs "0" when it is above the upper limit value. Incidentally, the upper limit value herein means the upper limit value at which a normal developing action can be performed without the above-mentioned defects. Reference numeral 13 denotes a timer whose output is given to an AND gate 14 to invalidate the unstable output from the comparator circuit 12 that is output at the initial stage of operation of the developing device. The output voltage obtained from the image density detector 9 is sent to a comparison circuit 17 for determining image density.
Enter. This comparison circuit 17 is set to output "0" when the image density is above the desired density, and to output "1" when it is below. Reference numeral 15 denotes an image density detection timing pulse generation circuit which outputs an output when the detection mark 10 faces the image density detector 9, and controls an AND gate 18 to allow the output of the comparison circuit 17 to pass. 19
inputs the outputs of AND gates 14 and 18 using an AND gate, and when the toner concentration in the developer is below the upper limit value and the image density is below the desired value, it outputs "1" and the image density is low. It notifies that it is in the recording state and energizes the toner replenishing means 4f.

Therefore, since toner is replenished into the developer based on this notification signal, the image density can be corrected without making the toner density of the developer excessive.

4 and 5 show other embodiments, and the configuration shown in FIG. 4 includes a drum surface potential measuring device 21, a developing density measuring device 22, a transfer voltage detector 23,
This configuration differs from the configuration shown in FIG. 1 in that .
In FIG. 5, the output of the surface potential measuring device 21 is input to a comparison circuit 26, which outputs "1" when the drum surface is within the normal range. The developed density measuring device 22 compares the output related to the density of the toner image of the detection mark on the drum surface with a comparison circuit 28.
and outputs "1" when the image density on the drum surface is below a predetermined value. 33 is an AND gate that inputs the outputs of the comparison circuits 26 and 28. The output of the transfer voltage detector 23 is input to a comparison circuit 32, which outputs "1" when the transfer voltage applied from the transfer device 7 is normal. 34 is an AND gate into which the outputs of the comparison circuit 32 and the AND gate 33 are input. The output of the image density detector 9 is compared by a comparison circuit 17, and if the image density is lower than the desired value, "1" is outputted, and is inputted to the AND gate 35 together with the output of the AND gate 34. The output of the toner concentration detector 4e is input to the comparison circuit 12, and when it is less than a predetermined value, "1" is output. The AND gate 36 inputs the output of the comparison circuit 12 and the output of the AND gate 35, and provides the output to the toner replenishing means 4f. Note that the timer 13 and timing circuit 15 shown in FIG.
Although not shown in FIG. 5, they are similarly provided.

According to the above-described circuit configuration, the image on the recording paper is generated when the drum surface potential and transfer voltage are normal, the developing density on the drum is low, and the toner density does not exceed the upper limit. Since a determination signal is output when the density is low, the toner replenishing means 4f is activated by this determination signal to replenish toner into the developer, thereby correcting the recording density.

In this case, toner density can be controlled more precisely than in the embodiment shown in FIG. That is,
In the embodiment shown in FIG. 1, for example, even if the drum surface voltage decreases and the image density decreases, toner is replenished, so that the toner in the developer becomes higher than the desired toner concentration when the drum surface voltage is normal. Put it away. Therefore, when the drum surface potential returns to normal, there is a problem that the image density becomes too high or fog occurs, but according to the embodiment shown in Fig. 4, such problems do not occur and a more stable image can be obtained. .

As described above, according to the electrostatic recording device of the present invention,
Image density can be increased by replenishing toner in the developer, and excess toner density can be prevented, so reliability of high-speed electrostatic recording devices can be improved and maintenance can be facilitated. .

[Brief explanation of the drawing]

The drawings show an embodiment of the present invention; FIG. 1 is a schematic diagram of the configuration of a recording device, FIG. 2 is a plan view of a recording sheet, FIG. 3 is a block diagram of its judgment circuit, and FIG. 4 is a diagram of the recording device. FIG. 5 is a block diagram of the judgment circuit. DESCRIPTION OF SYMBOLS 1... Photoconductive drum, 4... Developing device, 4e... Toner density detector, 6... Recording paper, 9... Image density detector, 10... Detection mark, 12... Comparison circuit for toner density judgment, 17... Image density judgment Comparison circuit for
14, 18, 19...and gate.

Claims (1)

[Claims] 1. Developing an electrostatic latent image using a developer containing a mixture of carrier and toner, recording a toner image on a recording medium, and controlling the density of the toner image to a desired density. In an electrostatic recording device, there is provided a toner concentration detection means for detecting the toner concentration in a developer, and a toner concentration detection output value from the toner concentration detection means is greater than or equal to an upper limit value of toner concentration that allows normal development action. an image density detection means for detecting the density of the toner image recorded on the recording medium; and an image density detection means for detecting the density of the toner image recorded on the recording medium; an image density determining means for determining whether the density is above or below a density value; and an image density determining means when the toner density determining means outputs that the toner density is below the upper limit value for the normal developing action. a state determining means for outputting a determination result; and a toner replenishing means for replenishing toner into the developer when the image density determining means outputs that the density of the desired toner image is below the desired toner image density value; An electrostatic recording device comprising: 2. The electrostatic recording apparatus according to claim 1, wherein the state determining means is an AND circuit inputting the output of the toner density determining means and the output of the image density determining means.