JPH01187578A - Automatic toner concentration controller for recording device - Google Patents

Abstract

PURPOSE:To prevent image quality from lowering by properly adjusting the target toner concentration at the time of actual recording so that it is matched with the recording state. CONSTITUTION:The change of an output value from a toner concentration detecting means 20, caused by the change of the electrification quantity of toner which occurs from the difference of a stirring time every number of recorded sheets, is estimated based on the number of recorded sheets set by a recorded sheets number setting means 21. Based on said estimation, the target toner concentration which is the target value of control is altered to gradually approach the optimum value matched with the intended number of the recorded sheets so that the replenishment of the toner is controlled in a state where the change is diminished. Thus, the effects of the toner electrification quantity which is the cause of variation except the toner concentration in the toner concentration detecting means 20 are reduced and the proper replenishment of the toner is performed during the recording action regardless of the number of the recorded sheets. Thus, it is evaded that the actual toner concentration is drastically deviated from the target value, thereby obtaining the image of good quality.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention is a method for developing an electrostatic latent image formed on a photoreceptor in a recording apparatus such as a copying machine or a printer that records using electrophotography. The present invention relates to an automatic toner density control device for a recording apparatus that automatically controls the density of toner that changes.

More specifically, a developing device that develops an electrostatic latent image using a two-component developer consisting of toner and carrier is equipped with a toner concentration detection means that measures the carrier magnetic permeability and outputs it as toner concentration, thereby determining the target toner concentration. A toner concentration setting means for outputting is provided, and the developing process is performed so that the toner concentration becomes the target toner concentration based on a comparison between the toner concentration detected by the toner concentration detection means and the target toner concentration from the toner concentration setting means. The present invention relates to an automatic toner concentration control device for a recording apparatus, which is provided with a toner replenishing means for replenishing toner, and a target toner concentration adjusting means for adjusting the target toner concentration of the toner concentration setting means.

[Conventional technology]

In an automatic toner concentration control device that automatically controls the toner concentration, generally, when the detected toner concentration from the toner concentration detection means is lower than the target toner concentration, the toner replenishing means replenishes the developing device with toner; When the detected toner concentration exceeds the target toner concentration, the toner replenishing means stops replenishing toner to the developing device, and the toner replenishment operation is controlled so that the toner concentration reaches the target toner concentration. .

The automatic control of toner density described above is performed based on the recognition that the output value from the toner density detection means has a one-to-one correspondence with the actual toner density. and,
Although this type of toner concentration detection means is generally used to detect toner concentration using carrier magnetic permeability, it is possible to conveniently detect the toner concentration in the developing device, which cannot be detected directly. Since the output value is an indirect detection method, the output value varies depending not only on the toner concentration but also on other factors. Therefore, when comparing the detected toner concentration with the target toner concentration, the target toner concentration is changed so that the fluctuation in the output value of the toner concentration detection means due to the fluctuation of the aforementioned factors can be removed. A device equipped with a concentration adjustment means has been proposed.

As one type of automatic toner density control device for such a recording device, we focused on the fact that the output value from a toner density detection means that uses carrier magnetic permeability changes depending on the amount of charge on the toner. Since the amount of charge on the toner depends on the stirring time of the toner, which changes depending on the operating rate of the developing device, a counter is provided to count the cumulative number of recorded sheets, and when the counter counts the set number of recorded sheets, the developing device is There is a known system in which the operating rate is determined and the target toner density is changed according to the operating rate, so that the toner density in the developing device does not deviate significantly from the target regardless of the level of charge of the toner. (For example, see Japanese Patent Laid-Open No. 62-24286).

[Problem to be solved by the invention]

However, in the conventional automatic toner density control device described above, the adjustment of the target toner density by the target toner density adjustment means is performed after the recording of a predetermined number of sheets is completed, based on the operating rate of the developing device determined at that point. Therefore, although it was possible to adjust the target toner concentration to match the toner charge amount based on the understanding of the toner charge amount at that time, the subsequent The actual recording state during recording, which requires real-time toner density control, was not taken into consideration, that is, whether recording was performed on one sheet only or continuously on many sheets. Even though the target toner density has been adjusted, in subsequent recordings, if the recording state is different as described above, and the amount of charge on the toner changes significantly from when the target toner density was adjusted,
The amount of adjustment of the target toner density is insufficient, or the direction of adjustment is reversed, and due to this,
Deterioration in image quality may occur, such as fogging or staining of the background due to excessive toner concentration, or blurring or blurring due to insufficient toner concentration.

SUMMARY OF THE INVENTION In view of the above circumstances, an object of the present invention is to provide an automatic toner density control device for a printing apparatus that can appropriately adjust the target toner density during actual printing to match the printing state.

[Means to solve the problem]

A characteristic configuration of the automatic toner density control device of the recording apparatus according to the present invention is that recording number setting means is provided, and the target toner density of the toner density setting means is set in advance according to the number of recording sheets set by the recording number setting means. A control means for operating a target toner concentration adjusting means for adjusting the target toner concentration of the toner concentration setting means so that the target toner concentration of the toner concentration setting means gradually approaches the optimum target toner concentration according to the set number of recording sheets among a plurality of target toner concentrations for each number of sheets. This is because we have established

[For production]

In other words, if the number of sheets recorded in a -degree recording operation is one, in addition to the development process in which toner is actually consumed, stirring for preparation and post-processing is often performed before and after the development process.
On the other hand, if a plurality of sheets are recorded in the -degree recording operation, the stirring process other than the above-mentioned development process is often omitted and recording is performed continuously, so the stirring time per recording sheet is becomes shorter as the number of records increases. and,
The amount of charge on the toner depends on its stirring time, and whether the amount of charge on the toner increases or decreases as the stirring time increases depends on the composition of the toner, but in any case, the amount of charge on the toner increases or decreases as the stirring time changes. Accordingly, the amount of charge on the toner changes, and thereby the output value from the toner concentration detection means also changes.

Therefore, in advance, by the number of recorded sheets, that many sheets ′
The change in the output value from the above-mentioned toner concentration detection means while recording the number is predicted, and based on the prediction result, the toner concentration can be determined even if the toner concentration is the same and only the toner charge amount has changed. A plurality of target toner densities are determined for each number of recording sheets so that the comparison result between the output from the detection means and the target toner density is almost the same, and for example, in the case of a copying machine, a recording number setting means such as a copy number setting key is used. In accordance with the set number of recorded sheets, the optimum toner concentration is selected from among the plurality of target toner densities according to the set number of recorded sheets before starting the recording operation, and the target toner density of the toner concentration setting means is set. By adjusting the toner concentration so that it gradually approaches the optimum target toner concentration, toner replenishment by the toner replenishing means reduces as much as possible the change in the output value from the toner concentration detection means caused by the change in the amount of charge on the toner. This is done based on detection results that are close to changes in only the actual toner density.

Furthermore, the target toner density is not adjusted suddenly to the optimum target toner density according to the set number of sheets to be recorded, but is adjusted to gradually approach the optimum target toner density, so when recording a small number of sheets, By making adjustments gradually as the recording operation for multiple images progresses, it is possible to avoid deterioration in image quality due to too much adjustment in the initial stage. On the other hand, it is possible to prevent the target toner density from being adjusted in the opposite direction even when there is a transition from recording a large number of sheets to recording a small number of sheets.

Furthermore, if the target toner density is adjusted in stages, for example by dividing it into the same number of times as the set number of recorded sheets, even if the set number of recorded sheets increases from the previous number of recorded sheets, it may decrease. Similarly, it is possible to automatically control toner replenishment in an optimal state at all times during the recording operation for the set number of recording sheets.

In summary, the automatic toner density control device according to the present invention comprises:
In the carrier magnetic permeability measurement type toner concentration detection method, changes in the toner charge amount, which is a cause of detection output fluctuations other than toner concentration, are predicted before the start of recording operation, and based on the prediction, the changes are reduced. The target toner concentration, which is the target value for control, is set so that toner replenishment is controlled according to the
The change is made so as to gradually approach the optimum value that corresponds to the number of images to be recorded.

〔Example〕

Hereinafter, the present invention will be described in detail based on the drawings.

FIG. 1 schematically shows the area around a photoreceptor (1) of an electrophotographic copying machine which is an example of a recording device.

The photoreceptor (1) has a drum shape and is configured to be rotated at a constant speed clockwise in the figure by the drive of a DC motor (not shown). Around the photoconductor (1), along the direction of rotation, there are a charging device (2) for uniformly charging its surface, an exposure section (3) that receives image light from the document, and a developing device (4). ), a transfer device (5), a separation device (6), a cleaning device (7), an eraser lamp (8), etc. are provided.

The surface of the photoreceptor (1), whose surface is uniformly charged by the charging device (2), reaches the exposure section (3) as it rotates, and is charged depending on the brightness of the image light received at the exposure section (3). The surface charge at the portion corresponding to the bright area is attenuated.As a result, an electrostatic latent image corresponding to the image of the original is formed on the surface of the photoreceptor (1).

This electrostatic latent image is visualized by selective adhesion of toner in a developing device (4) through which the photoreceptor (1) successively passes as it rotates. After that, the photoconductor (1) further rotates and reaches the transfer device (5), and this transfer device (5)
, the paper feed guide (
Recording paper (P) fed into the transfer device (5) via 9)
The structure is such that a toner image visualized as described above is transferred thereon by electrostatic adsorption.

The recording paper (P) on which the toner image has been transferred is then peeled off from the surface of the photoreceptor (1) by a separating device (6), and is deposited on a fixing device (11) by a conveyor belt (10). After the toner image is melted and fixed on the surface by heating accompanied by pressure, the toner image is discharged outside the machine.

On the other hand, after the toner image has been transferred to the recording paper (P), the photoreceptor (
1), after the residual toner adhering to the surface is scraped off by the cleaning blade (12) of the cleaning device (7), the residual charge on the surface is erased by the eraser lamp (8), and the surface returns to its initial state. After that, it reaches the charging device (2) again and is newly charged, thereby preparing for the next copying operation.

The developing device (4) includes a hopper (1) containing toner.
3), a carrier reservoir (14) containing magnetic carrier to be mixed with toner, a stirring blade (15), a developing sleeve (16) containing a magnetic roller (16a), and a carrier reservoir (14) from the hopper (13); a shutter (17) that interrupts the flow of toner to the shutter (17);
) for driving the opening/closing motor (18).

The motor (18L) is configured to open and close the shutter (17) in response to a control signal from the microcomputer (19). When the shutter (17) is in the open state, the toner in the hopper (13) is The carrier reservoir (14) is replenished.Toner is supplied to the carrier reservoir (14).
4), the mixture is mixed with the magnetic carrier and stirred by a driven and rotated stirring blade (15), thereby being charged by contact friction with the magnetic carrier. On the other hand, the magnetic carrier is charged with a polarity opposite to that of the toner, and the toner adheres to the periphery of the magnetic carrier due to the attractive force of frictional charging.

A magnetic roller (
Along the lines of magnetic force formed between the different magnetic poles of 16a),
The magnetic carriers and rears to which the toner is attached are connected in a chain, forming ears of a two-component developer consisting of the magnetic carrier and toner. The developing sleeve (16) is provided in a fixed state, and the magnetic roller (16a) rotates counterclockwise in the figure at a speed that is faster (1.1 to 3.0 times) than the rotational speed of the photoreceptor (1). As the development sleeve (16) rotates, the spikes of developer on the surface of the developing sleeve (16) are also conveyed counterclockwise in the figure until they reach the area where they come into contact with the surface of the photoreceptor (1). .

The toner in the developer is absorbed by the electric field formed by the developing bias voltage applied to the developing sleeve (16) and the electrostatic latent image on the photoreceptor (1), and by the adsorption force due to triboelectric charging of the magnetic carrier. It is configured to be selectively attracted to the charge non-attenuated region of the electrostatic latent image by the electrostatic force relationship. Thereby, the electrostatic latent image is visualized.

On the other hand, the magnetic carrier is further conveyed by the developing sleeve (16) and reaches the carrier reservoir (14), where it is used again.

On the other hand, the carrier reservoir (14) is attached with a carrier magnetic permeability sensor (20) that measures the magnetic permeability of the magnetic carrier and outputs it as toner concentration.

In other words, in this type of developing device (4), toner and magnetic carrier coexist as described above, and although the toner concentration cannot be directly detected, the magnetic permeability of the magnetic carrier can be measured in real time. By doing this, it is possible to detect the amount of magnetic carrier in a predetermined volume of developer, which is then output as the toner density.

This carrier magnetic permeability sensor (
The output of 20) is input to the microcomputer (19). The toner replenishing means (19a) of the microcomputer (19) includes a carrier magnetic permeability sensor (20
Based on the comparison between the detected toner concentration input from the hopper (13) and the target toner output from the built-in toner concentration setting means (19b), if the detected toner concentration is lower than the target toner concentration, the carrier is removed from the hopper (13). On the other hand, if the detected toner concentration exceeds the target toner concentration, the carrier reservoir (14) is replenished from the hopper (13).
A control signal is output to each motor (18) to stop toner replenishment to the developing device (4) so that the toner concentration in the developing device (4) reaches the target toner concentration.
) automatically controls toner replenishment.

Furthermore, the above-mentioned toner density setting means (19b) includes:
A target toner density adjusting means (19c) is provided for adjusting the target toner density outputted from the device. In other words, the automatic control of toner replenishment with the above-described configuration is performed using the carrier magnetic permeability sensor (20) which is the toner concentration detection means.
This is done based on the recognition that the output value of changes only depending on the concentration of toner in the developing device (4), but in reality, the output value of the carrier magnetic permeability sensor (20) is It is known that the change depends not only on the density of the toner but also on the amount of charge on the toner.

The graphs in FIGS. 2 and 3 show that the output value [E] of the carrier magnetic permeability sensor (20) has a one-to-one relationship with the carrier amount [C], which increases as the toner concentration decreases, and the toner concentration is constant. The relationship with the toner charge amount [Q] is shown below. The output value from the carrier magnetic permeability sensor (20) [E
] is specifically a voltage signal, and the larger the amount of carrier per predetermined volume and the lower the toner concentration, the larger the output value [E] becomes. Further, even if the toner concentration is the same, the lower the toner charge amount, the larger the output value [E] becomes.

Furthermore, the graph in FIG. 6 shows the relationship between the output value [E] of the carrier magnetic permeability sensor (20) and the toner charge amount [Q] using the actual toner concentration [D] as a parameter.

That is, as can be seen from these graphs, even if the actual toner concentration [D] is the same, the output value [E] from the carrier magnetic permeability sensor (20) also changes depending on the toner charge amount [Q]. The reason for this is that when the toner charge amount is low, the adsorption force between the toner and the magnetic carrier is small, so the toner can move relatively freely, and as shown in Figure 4 (a), the toner is surrounded by the magnetic carrier. Because the bulk density of magnetic carriers increases due to their presence in large numbers in the
The output value from the carrier magnetic permeability sensor (20) indicates a change in the direction of change when the toner concentration decreases.On the other hand, when the toner charge amount is high, the adsorption force between the toner and the magnetic carrier is large, so the toner concentration decreases. As shown in FIG. 4(b), the bulk density of the magnetic carriers is reduced because the toner is present in a bound state between the magnetic carriers, so the carrier magnetic permeability sensor (20) It is considered that the output value from . . . indicates a change in the direction of change when the toner concentration increases.

Therefore, the output value from the carrier magnetic permeability sensor (20) [
If toner replenishment is controlled based on the result of always comparing E] with the same target toner density, the control target value will differ from the actual target value, resulting in image fogging and background due to oversupply of toner. The image may become blurred or blurred due to insufficient toner supply.

Therefore, by appropriately changing and adjusting the target toner concentration using the target toner concentration adjusting means (19c), it is possible to eliminate factors other than toner concentration that occur because the carrier magnetic permeability sensor (20) is an indirect toner concentration detecting means. The structure is such that automatic control of toner replenishment by the toner replenishing means (19a) is performed without significantly deviating from the desired toner concentration.

Specifically, the amount of charge of the toner changes depending on the stirring time of the toner and the magnetic carrier in the developing device (4). The direction of the change depends on the composition of the toner, etc.
As shown in FIG. 5(a), the amount of charge increases as the stirring time increases, and as shown in FIG. 5(b), the amount of charge decreases as the stirring time increases. In the following explanation, a toner whose charge amount increases with stirring time will be explained as an example, but the same concept can be applied to a toner having the opposite characteristics.

Now, in FIG. 6, the lines [Dal to [Dal] represent the toner charge amount [Q] and the output [E] of the carrier magnetic permeability sensor (20) at four different toner concentrations.
] and each toner density [Dal, [Db
], [Dcl, [Dal, Da>Db>
It is assumed that there is a relationship of Dc > Dcl.

The reference voltage corresponding to the target toner density, which is compared with the output [E] from the carrier magnetic permeability sensor (20), which is the detected toner density, is set to [11] in the figure, and the toner in the developing device (4) is When trying to control the concentration to the standard concentration [Db] that intersects this line [11] at point [b], if the stirring time becomes longer and the amount of charge on the toner increases, the actual toner concentration will change. becomes [Dal], which intersects this line [11] at point [d], making it easy for blurring and the like to occur due to insufficient toner concentration.

Therefore, when the stirring time is expected to be long, the reference voltage corresponding to the target toner concentration is set in advance in [11].
By setting [I2] smaller than ],
The target toner density is set high, and the actual toner density is controlled to [Dc], which intersects this "I2" line at point [C], so it is possible to avoid insufficient toner density. .

Specifically, the target toner density is adjusted based on the operation of a plurality of sheets number setting key (21), which is a recording sheet number setting means.

In other words, when the number of copies is one, in addition to the agitation in the developing device during the copying operation, agitation is also performed before and after the copying operation, but when the number of copies is multiple, the series of copying operations is continuous. Since the agitation is performed by the amount of copying operation for each copy and is omitted, the more copies are made, the shorter the agitation time per copy is. The amount of change in the stirring time decreases as the number of copies increases.

Therefore, the carrier magnetic permeability sensor (20), which is a voltage signal,
As shown in FIG. 7, the reference voltage [I] corresponding to the target toner density compared with the output from The target toner density control means (1) is adjusted in accordance with the number of copies set by the number of copies setting key (21) so that the number of copies gradually approaches the optimum target toner density.
9C) is provided, and is configured to optimize automatic control of toner replenishment by the toner replenishment means (19a).

In other words, the target toner density is not suddenly changed to the optimal target toner density according to the set number of sheets to be recorded, but it is changed gradually to approach the optimal target toner density, and the target toner density is changed from when recording a small number of sheets to when recording a large number of sheets. In some cases, by making the adjustment gradually as the recording operation progresses for a large number of sheets, it is possible to avoid degrading the image quality due to too much adjustment at the initial stage. This structure is configured to prevent the adjustment direction of the target toner density from becoming reversed even when transitioning from the time to the recording of a small number of sheets.

This will be explained using drawings. First, to explain the actual change in toner density in a configuration in which the target toner density is changed to the optimal target toner density at once, for example, when copying only one sheet after continuous use, the toner density after continuous use is [ As a result of the control based on the reference voltage of (1), standard [Db] is obtained. After that, the number of copies is set to 1, the reference voltage is adjusted to [I2], and it is determined that the toner density is low, so control is performed to replenish toner, but the copying operation As a result of the long-time stirring, the amount of charge on the toner increases, and the actual toner concentration is indicated by the broken line [1] and [j
It is controlled to be [Dc] along the broken line of l.

After that, when a large number of copies, such as 50 or 100, is set again and the reference voltage is adjusted to [11], it is determined that the toner density is high, so toner replenishment is stopped. However, as the toner is consumed during the copying operation and the stirring time is shortened, the amount of charge on the toner decreases, and the actual toner concentration is
Along the dashed line [k] and the dashed line [A] in the figure,
b].

However, in the above-mentioned configuration, there is a possibility of passing through an under-density area hatched in the upper right corner of the figure or an over-density area hatched in the lower left corner of the figure, and in the initial state of the recording operation, some There is a risk of blurring or fogging. On the other hand, the control according to the present invention described above adjusts the target toner density so that it gradually approaches the optimal target density, so the actual toner density is indicated by the broken lines [m] and [T1] in the figure. Along [D
b] or [Dc], and as a result, the toner density is maintained more appropriately during the recording operation for the set number of sheets, making it possible to always obtain high-quality recordings. .

[Another example]

Next, other embodiments of the present invention will be listed.

<1> In the previous embodiment, the toner charge amount increases as the stirring time increases.
When using a toner in which the toner charge amount decreases as the stirring time increases, as shown in Figure (B), the toner should have a change characteristic opposite to that shown in Figure 7, as shown in Figure 8. What is necessary is to change the reference voltage [1] corresponding to the optimum target toner concentration.

<2> The change characteristic of the reference voltage [1] corresponding to the optimum target toner concentration corresponding to the change in stirring time does not necessarily have to be such that the amount of change gradually becomes smaller as shown in FIG. 7 or FIG. , it may be linear depending on the form of agitation in the developing device (4).

3) The automatic toner density control device according to the present invention predicts the change in toner charge amount due to the difference in the form of the recording operation on the front side before starting the recording operation, and adjusts the target toner based on the prediction result. In addition to adjusting the density, the toner density may also be provided with a function of adjusting the toner density according to the cumulative number of recorded sheets.

4) The automatic toner density control device according to the present invention can be applied to various types of printers using electrophotography, such as laser beam printers and LED printers, in addition to the copier described in the previous embodiment, and are collectively called recording devices.

5> The following various methods can be considered for bringing the target toner concentration closer to the optimum target toner concentration by operating the target toner concentration adjusting means (19C) by the control means (19d).

<5-1> Adjust the target toner density for each recording operation. In this case, there are two methods: one method to adjust the difference between the current target toner density and the optimal target toner density, one method to adjust the difference between the current target toner density and the optimal target toner density by weighting the difference proportionally, A possible method is to predict the change in the output of the carrier magnetic permeability sensor (20) due to the change in the toner charge amount when one recording operation is performed from the state of , and adjust the output to be smaller than the predicted change. .

<5-2> Adjust the target toner density every time a plurality of sheets are recorded. In this case as well, it is possible to set the adjustment amount in the same way as in (5-1> above).

<5-2> Instead of adjusting the target toner density every time the same number of sheets is recorded as described above, the target toner density may be adjusted every time a different number of sheets are recorded, for example, every time the number of sheets gradually increases.

6) The automatic toner density control device according to the present invention may be built into the developing device main body, or a part thereof may be provided on the recording device side, depending on the developing device and developer used. The change characteristics of the reference voltage [I] may be selected.

〔Effect of the invention〕

As described above, the automatic toner concentration control device of the recording apparatus according to the present invention can suppress the change in the output value of the toner concentration detection means caused only by the change in the amount of charge of the toner due to the difference in stirring time for each number of sheets to be recorded. , the target value for toner replenishment control, which is predicted from the set number of recording sheets and is performed to keep the toner concentration almost constant before starting the recording operation, is set so as to reduce the predicted change in the output value of the toner concentration detection means. By changing the toner concentration in advance, it is possible to always perform toner replenishment that better corresponds to actual toner concentration changes, so it is possible to perform toner replenishment that better corresponds to actual toner concentration changes. By reducing the influence of the toner charge amount and replenishing toner appropriately throughout the recording operation regardless of the number of sheets recorded, it is possible to avoid the actual toner density from deviating greatly from the target, and as a result, It is now possible to obtain high-quality images with less under- or over-density.

[Brief explanation of the drawing]

The drawings show an embodiment of an automatic toner concentration control device for a recording apparatus according to the present invention, in which FIG. 1 is a schematic configuration diagram, FIG. 2 is a graph showing the relationship between the amount of carrier and the output of the carrier magnetic permeability sensor, and FIG. The figure is a graph showing the relationship between the toner charge amount and the output of the carrier magnetic permeability sensor, Figures 4 (a) and (b) are conceptual diagrams showing the mixed state of toner and carrier, and Figure 5 (
A) and (B) are graphs showing the relationship between stirring time and toner charge amount, Figure 6 is a graph showing the relationship between toner charge amount and carrier magnetic permeability sensor output using toner concentration as a parameter, and Figure 7 and FIG. 8 is a graph showing the relationship between the set number of copies and the reference voltage. (4)...Developing device, (19a)...
Toner replenishing means, (19b)...Toner concentration setting means, (19C)...Target toner concentration adjusting means, (19d)...Controlling means, (20)...・
. . . Toner density detection means, (21) . . . Number of recording sheets setting means.

Claims (1)

[Claims] A developing device that develops an electrostatic latent image using a two-component developer is provided with toner concentration detection means for measuring carrier magnetic permeability and outputting it as a toner concentration, and a toner concentration setting means for outputting a target toner concentration. toner replenishing means for replenishing toner to the developing device so that the toner concentration becomes the target toner concentration based on a comparison between the toner concentration detected by the toner concentration detection means and the target toner concentration from the toner concentration setting means; In the automatic toner density control device of the recording apparatus, which is provided with a target toner density adjustment means for adjusting the target toner density of the toner density setting means, a number of recording sheets setting means is provided, and the number of recording sheets set by the number of recording sheets setting means is adjusted. Accordingly, the target toner concentration is adjusted so that the target toner concentration of the toner concentration setting means gradually approaches the optimum target toner concentration according to the set number of recording sheets among a plurality of target toner concentrations for each preset number of recording sheets. An automatic toner concentration control device for a recording device, comprising control means for activating the means.