JPS6224286A - Picture density controlling system in electrophotographic device - Google Patents

Abstract

PURPOSE:To obtain a copied picture at a certain density level without fail, irrespective of a change in the output characteristic of a toner density sensor, which is caused by a change in copy attitudes such as single printout and continuous printouts, by adjusting a picture density in accordance with the operation rate of a developing unit. CONSTITUTION:A picture area developing time counter 12 counts the product of a set time necessary for development and the number of copies, while a developing unit drive time counter 10 integrates the time when the developing unit is driven based on the number of copies. When the number of copies attains the set value, a developing unit operation rate calculating circuit 14 calculates the ratio of the developing time to the total operating time of the developing unit, that is, the operation rate of the developing unit, and outputs data on the charged situation of toner in the developing unit to a reference voltage adjuster 5, which corrects the hourly fluctuation of the level of a signal from the toner density sensor 2 based on a change in toner's charged amount.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a technique for controlling image density in an electrophotographic apparatus using a two-component developer.

(Prior Art) Image density in an electrophotographic apparatus using a two-component developer consisting of toner and carrier is determined based on a signal from a toner density sensor provided in a developing unit. This toner concentration sensor winds a coil near the discharge port of a funnel-shaped bobbin whose upper part is expanded and has a toner intake port, and captures the developer flowing down from the separator in the development unit to increase the toner concentration. The inductance of the coil is configured to detect the falling velocity of the developer, which changes in response to the change in velocity.

Incidentally, the developer is stirred and charged within the developing unit in order to promote adsorption of toner to the latent image formed on the photoreceptor drum, but the average charge amount of the toner present in the developing unit is Depends on unit operating time and amount of toner being replenished.

That is, in the copying operation, as shown in FIG. 4, the developing unit operates from the time when the copy start button is pressed, pre-stirs the developer for a certain period of time, and then enters the developing process to remove the toner. After consumption, the operation is stopped after rotating for a certain period of time T2 in preparation for the next copy operation.

On the other hand, in a continuous copy mode in which a plurality of copies are made continuously, toner is consumed and new toner is replenished with almost no idle time between the developing steps. Therefore, there is a difference in the amount of charge of the toner in the developing unit between single-sheet copying and continuous copying.

On the other hand, it goes without saying that the flow rate of the developer passing through the bobbin is proportional to the toner concentration, but it also depends on the degree of bonding of particles with each other depending on the amount of charge of the toner.

Therefore, the output of the toner density sensor changes over time not only due to the toner density but also due to the copy mode.
As a result, there was a problem in that the image density fluctuated.

(Objective) In view of these problems, the present invention makes it possible to always obtain copies with a constant image density by adjusting the image density in accordance with the time during which the developing unit is actually used for development. The purpose is to provide an image density control method that can

(Structure) Therefore, details of the present invention will be described below based on illustrated embodiments.

FIG. 1 shows an embodiment of the present invention, and reference numeral 1 in the figure indicates a toner concentration detection circuit, and a toner concentration sensor 2 detects the toner concentration of the developer as an inductance.
It is composed of an oscillator 3 that converts a signal from the oscillator into a frequency, and a frequency-voltage converter 4 that converts this frequency into a voltage level.

5 is a reference voltage regulator that adjusts the reference voltage output from the reference voltage generator 6 in accordance with a signal from an image density correction signal generation circuit 9, which will be described later, and outputs a corrected reference level signal. . Reference numeral 7 denotes a toner replenishment determination circuit, into which signals from the toner concentration detection circuit 1 and reference voltage regulator 5 are input, and the toner concentration detection signal from the toner concentration detection circuit 1 is used as a correction reference level signal from the reference voltage regulator 5. A signal is output to the toner replenishment drive circuit 8 at the time when the value falls below . Reference numeral 9 denotes the above-mentioned image density correction signal generation circuit, which is activated by a signal from the copy counter 11 of the main body of the electrophotographic apparatus, and is stopped by a developing unit stop signal to integrate the total operating time of the developing unit. ) An image in which the total time that the developing unit is actually used for developing work is integrated by adding the product of the driving time counter 10, the developing time for one sheet determined by the copy size, and the number of copies from the copy counter 11. It consists of an area development time counter 12 and a developing unit operating rate calculator 14 that calculates the ratio of the values of the counter 10 and the counter 12, that is, the operating rate, when the copy counter 11 counts a certain number of sheets. Note that reference numeral 13 in FIG. 1 indicates a document size detector that detects the size of the document.

In this embodiment, when the developing unit is filled with new developer and the apparatus is operated, since the counts of the counters 10 and 12 are zero, no signal is output from the image density correction signal generating circuit 9. The signal from the reference voltage generator 6 is directly input to the toner replenishment determining circuit 7 without being subjected to level change by the reference voltage regulator 5, and causes the developing unit to replenish toner until the initially set density is reached.

Now, when a sheet of paper corresponding to the original size is selected to make a copy, the unit time required to develop the original of this size is set in the image area development time counter 12.

If the copy start button is pressed at this point, the developing unit and exposure optical system start operating. This results in
The image area development time counter 12 counts the product of the set unit time and the number of copies, that is, the time when development is actually performed, and also counts the development unit drive time measurement time.
゛The counter 10 outputs a developing unit based on the number of copies.
) is driven.

When the number of copies per copy reaches the set value in this way, the development unit operation rate calculation circuit 14 receives signals from the development unit drive time counter 10 and the image area development time counter 12, and then The ratio of the developing time to the operating time, that is, the operating rate of the developing unit, is calculated, and data regarding the charging state of the toner in the developing image unit is output to the reference voltage regulator 5.

In other words, when the operating rate of the developing unit is high, the toner in the developing unit is consumed and the replacement rate with new toner is high, and when it is low, the toner replacement rate in the developing unit is low, so the toner in the developing unit is consumed. The operating rate represents the average amount of charge on the toner.

The reference voltage regulator 5 corrects the comparison reference level of the toner replenishment judgment circuit 7 based on the toner replacement rate output from the image density correction signal generation circuit 9, that is, the total number of times of agitation, and adjusts the toner charge amount change. The time-dependent fluctuation in the level of the signal from the toner concentration sensor 2 based on the toner concentration sensor 2 is corrected. As a result, the copy image is maintained at the initially set density regardless of the output fluctuations of the toner density sensor 2 over time (the third
figure).

FIG. 2 shows a second embodiment of the present invention, in which the reference signal from the reference voltage generator 6 is input to the toner replenishment judgment circuit 7 regardless of the operating rate of the developing unit, and the image density is corrected. The signal from the signal generation circuit 9 is input to the developing sleeve rotation speed control circuit 15.

According to this embodiment, toner is replenished while allowing the output from the toner concentration sensor to change over time, so the toner concentration in the developing unit gradually changes. Since the sleeve rotation speed is gradually adjusted in response to the signal from the image density correction signal generation circuit 9, that is, the operating rate of the developing unit, and the amount of toner supplied to the latent image is corrected, the copy image is initially set. Image density is maintained.

In the above-described embodiment, the image density is adjusted by changing the toner supply reference level and the rotation speed of the developing sleeve, but other image density adjusting means, such as adjusting the developing bias voltage, can also be used. Needless to say, the same effect can be obtained even if the method is done in this way.

(Effects) As explained above, according to the present invention, the image density is adjusted in accordance with the operating rate of the developing unit, so that it is possible to adjust the image density depending on the operating rate of the developing unit. Copy images with a constant density can always be obtained regardless of changes in the output characteristics of the toner density sensor.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a device showing one embodiment of the present invention, FIG. 2 is a block diagram of a device showing another embodiment of the present invention, FIG. 3 is an explanatory diagram showing the operation of the same device, and FIG. FIG. 4 is an explanatory diagram showing changes in the operating WA rate of the developing unit depending on the copy mode. l...Toner concentration detection circuit 2...Toner concentration sensor

Claims (1)

[Claims] Toner concentration detection means for detecting the concentration of toner contained in a developer consisting of two components of toner and carrier as a change in inductance is disposed in the development unit, and the electronic system controls toner replenishment based on a signal from the detection means. In a photographic device, detecting the realized image time rate of the developing unit,
An image density control method for an electrophotographic apparatus, characterized in that an image density adjustment means is controlled based on the realized image time rate.