JPH05257369A - Image recorder - Google Patents

Abstract

PURPOSE:To make image density proper by altering the condition of development when the image density drops or rises although the concentration of toner is kept at almost a prescribed value. CONSTITUTION:When the reflection density (image density) of a standard toner image measured by an optical image density measuring means 61 drops/rises below/above a prescribed level, although the concentration of toner is kept at almost the prescribed value, a second CPU 60 controls a developing bias circuit 62 to alter a developing bias. Thereby, a sticking force between the sleeve 20c and the two-component developer, that is, a force by which toner in the two-component developer is moved to a photosensitive drum 1, is altered to make the image density proper.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image recording apparatus adopting a developing method for developing an electrostatic latent image by using a two-component developer composed of a toner and a carrier of a copying machine, and particularly suitable for the image recording apparatus. The present invention relates to an image recording apparatus that controls development conditions so as to obtain a high image density.

[0002]

2. Description of the Related Art In a developing device for developing an electrostatic latent image on an image bearing member by using a two-component developer composed of a toner and a carrier, the toner and the carrier in the two-component developer are mixed by weight. The ratio (hereinafter referred to as toner concentration T _C ) greatly affects the developability. For example, if the toner density of the two-component developer is lower than the proper value, the density of the developed image will be low. On the contrary, when the toner density becomes too high, the density of the developed image becomes too high and the so-called fog increases. Therefore, the recorded image on the transfer material transferred from the image carrier becomes unsuitable.

Therefore, in order to always obtain an image having a preferable density, the toner density of the two-component developer is set to an appropriate level,
At the same time, it is necessary to keep the appropriate level constant during development. Therefore, conventionally, there has been proposed a two-component developer concentration control system in which the toner concentration of the two-component developer is kept constant by controlling the toner supply amount. This density control method detects change events such as magnetic permeability change and volume change of two-component developer, change of image density after development, and color change of two-component developer due to toner and carrier having different colors. By doing so, the toner concentration is detected, and the toner replenishment amount is controlled based on the detected toner concentration to maintain the proper toner concentration.

However, in the method of detecting a change event as described above, stable operation for a long period of time has been difficult due to reasons such as erroneous detection and difficulty in compensating for deterioration of the surface of the photosensitive member over time.

As a solution to this problem, Japanese Patent Laid-Open No. 57-1366 has been proposed.
No. 69 “Two-component developer concentration control device” is introduced. This "two-component developer concentration control device" is a detection level that should detect the volume of the two-component developer in the developing device so that the developing effect in the recording device can be stably and appropriately maintained for a long period of time. With a plurality of, separately, by optically detecting the developed image of the reference image formed on the photosensitive surface to detect the developing performance, or the density of the recorded image,
In response to this, the plurality of detection levels are switched and set by the central processing unit so that the toner density of the two-component developer is controlled in order to avoid carrier replenishment as much as possible and to keep the developing performance as constant as possible. It is configured to. For the time being, the above-mentioned object was achieved.

[0006]

However, the contents of the original document to be image-recorded often have variations in blackening rate due to differences in image density and image density, and blackening of line drawings, character images, low-density originals, etc. When a developing operation is executed to continuously form an image of original contents having a low rate, a predetermined image density corresponding to the toner density cannot be obtained even though the toner density is constant, and the toner density is low. -The phenomenon that the correspondence between the density and the image density is broken has occurred. It was also found that this phenomenon is likely to occur in the case of a color electrostatic recording device in which a color image can be reproduced by using a two-component developer of various colors.

Then, when the cause of occurrence of such a phenomenon was considered, the following findings were found. That is, as a result of analyzing the phenomenon common to the above two examples, the developing sleeve and the agitating means in the developing device are continuously rotationally driven within the developing time during the image forming process in the electrostatic recording device. It has been found that this stirring time, in other words, the residence time of the two-component developer in the toner hopper, is commonly related. That is, in the former example, since the original is of low density, the toner consumption amount per unit time is smaller than usual, and the toner retention time becomes longer accordingly. In the latter example, the toner consumption amount of the two-component developer for each color is different, and the residence time of the toner is also different for each color. Considering that the phenomenon in the above example occurs even when the toner concentration is constant, it can be presumed that the toner component is attached around the carrier and the toner charge amount is reduced, that is, it is not due to a so-called spent toner. It is expected that the toner charge amount will continue to increase because it is related to the toner retention time, that is, as the toner retention time increases, the chances of friction between the toner and the carrier increase. It is considered that the toner charge amount that has become the influence on the image density. Therefore, the relationship between the toner charge amount and the image density was examined.

FIG. 4 is a diagram showing a change in image density CD with respect to a change in toner charge amount Q / m (μC / g) when the toner density in the two-component developer is constant.

FIG. 4 shows that the image density CD decreases as the toner charge amount Q / m increases. Specifically, when the toner charge amount Q / m is about 10 (μC / g), the image density CD is about 1.4, and the toner charge amount Q / m is about 30 (μC / g). In the case of, the image density CD is about 0.5.

Such image density CD and toner charge amount Q
The relationship with / m is that the toner in the two-component developer magnetically carried by the developing sleeve containing a permanent magnet receives the force in the developing area for developing the electrostatic latent image (hereinafter referred to as developing force). I can explain.

That is, when the developing force is F _t , the developing force F _t is approximately

[0012]

[Number 1] _{F t = q t · E -} k (q t · q c / r 2) - q t (V B / R) { However, _{q t} is the toner charge amount, E is the electric field by the electrostatic latent image (Hereinafter referred to as latent image electric field), q _c is the carrier charge amount,
r is the distance between the toner and the carrier, V _B is the voltage applied to the developing sleeve (hereinafter referred to as developing bias), and R is the distance between the photosensitive drum surface and the developing sleeve surface}. .

In Formula 1, the developing force F _t is the force resulting from the latent image electric field E, and is the adhesion force between the toner and the carrier (this is called Coulomb force) and the developing bias force acting on the toner. It shows that it has been reduced. Here, it should be noted that the force that determines the developing force F _t is the toner charge amount q.
_Although it is proportional to _t (Q / m), the Coulomb force, which is a force that reduces the developing force F _t , increases the carrier charge amount q _c as the toner charge amount q _t (Q / m) increases. Therefore, it tends to increase more than other forces. Therefore,
Increase in the toner charge amount q _t (Q / m) is appears as a decrease in the developing force F _t, toner - of reduced charge amount q _t (Q / m) appears as a rise in the developing force F _t It is a point.

FIG. 5 is a graph showing changes in the image density CD with respect to the toner concentration (wt%: weight mixing ratio) in the two-component developer loaded in the developing device.

Here, the two-component developer has an average particle size of 20 to
100 μm insulating magnetic carrier (resin coating,
Magnetic particle resin dispersion type) and a toner having an average particle diameter of 5 to 15 μm.

In FIG. 5, the solid line A indicates the developing bias V.
The case where _B is 200 V is shown, and the toner concentration is 1
The image density CD is about 0.4 at about wt%, and the image density CD is about 1.0 at the toner concentration of 5 wt%. When the toner concentration exceeds 5 wt%, the image density CD is about 1.2. It shows that it saturates in the vicinity. This solid line A
The image density CD is about 0.4 to about 1.2, the contrast is sufficiently wide, and the adhesion between the photosensitive drum, which is the latent image carrier, and the toner is good, and the image during the image forming process is Since the deviation is reduced, it is usually desired to control the image density CD on the locus of the solid line A.

The alternate long and short dash line B is, as in the above two examples,
The two-component developer time increases to stir, in the case where the toner charge amount q _t (Q / m) is too large as compared with the solid line A toner - density T _C (wt%) and the relationship between the image density CD Is shown. The other conditions such as the developing bias V _B are all the same as the solid line A. In this case, as is clear from Equation 1, the Coulomb force increases as compared with the other electrostatic forces, so that the force of attracting the toner to the photosensitive drum is relatively reduced, and the image density is reduced. ing. Specifically, the alternate long and short dash line B indicates that the toner density is saturated from 5 wt% to around image density 0.5. Therefore, there is a problem that a sufficient image density CD corresponding to the original image on the locus B cannot be obtained, and further a sufficient contrast cannot be obtained.

The dotted line C indicates the toner density T _C (wt%) and the image density CD when the toner charge amount becomes smaller than the solid line A due to environmental fluctuations such as an increase in relative humidity. Shows the relationship with. In this case, it is shown that the adhesive force (Coulomb force) between the toner and the carrier becomes insufficient and the image density CD rises as compared with the solid line A. Specifically, the image density CD is a toner density of 1 wt /
%, It reaches about 0.7, and as the toner concentration (wt%) rises, it is saturated at about 1.4. Therefore, in the development on the dotted line C, the contrast width has a sufficient width, but a large amount of toner is scattered and too much toner adheres to the latent image, so that the original image is faithfully reproduced. There is a problem that it cannot be put to practical use in terms of reproduction. Further, since the adhesive force between the photoconductor drum and the toner is not sufficient, there is a problem that image shift easily occurs.

The present invention has been made in view of the above problems, and an object thereof is to reduce or increase the image density even if the toner density is kept substantially constant at a predetermined value. First, it is to provide an image recording apparatus capable of reproducing an image with an appropriate image density by detecting this and controlling a developing condition to a predetermined value.

[0020]

To achieve the above object, an image recording apparatus according to the present invention is a two-component developer comprising a carrier and a toner to form an electrostatic latent image on an image carrier by applying a developing bias. And a toner replenishment control unit that performs toner replenishment control based on the toner concentration from the toner concentration detection unit. In an image recording apparatus, a reflection density detecting means for detecting a reflection density of a reference toner image formed on the image carrier, and a reflection density of the reference toner image detected by the reflection density detecting means is lower than a predetermined level. , Or rises and the toner concentration detected by the toner concentration detecting means is substantially constant, the developing bias is changed, and then the reference toner image is reflected. Degree is a developing bias control means for returning the developing bias to a predetermined value when it returns to a predetermined level.

[0021]

The two-component developing means applies a developing bias to develop the electrostatic latent image on the image carrier with a two-component developer consisting of carrier and toner. The toner concentration detecting means detects the toner concentration of the two-component developer. Toner supply control means
Toner replenishment control is performed based on the toner concentration from the toner concentration detecting means. Further, the reflection density detecting means detects the reflection density of the reference toner image formed on the image carrier.

Then, the developing bias control means, although the toner density detected by the toner density detecting means is substantially constant, the reflection density of the reference toner image detected by the reflection density detecting means, That is, when the actual image density is lower or higher than the predetermined level, the developing bias is changed to return the image density to the predetermined level, and then,
The developing bias is returned to a predetermined value.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An image recording apparatus according to an embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of an image recording apparatus according to an embodiment of the present invention. The image recording apparatus 100 includes a photosensitive drum 1 and a photosensitive drum 1 which are latent image carriers.
Motor driver 10 for controlling the rotation of the developing device, the developing device 2
0, high-voltage power supply 40, transfer device 42, charger 41, scanning optical system 54, first CPU 50, second CPU 60, optical density measuring means 61, developing bias circuit 62 and toner density detecting means 63. Then, when a copy button (not shown) is pressed, the light source emits light based on the image signal corresponding to the image density of the original image from the scanning optical system 54 under the control of the first CPU 50 to irradiate the photosensitive drum 1 with light. An electrostatic latent image is formed on the photosensitive surface of the photosensitive drum 1, and the electrostatic latent image is developed by the developing device 20 to be visualized as a toner image, and the transfer device 42 is discharge-driven based on the registration signal. Thus, the toner image is transferred onto a transfer paper. After that, the transfer paper is fixed to form a reproducible image that can be stored.

As the photosensitive drum 1, an aluminum drum-shaped conductive support having a diameter of 80 mm is used. An intermediate layer of ethylene vinyl acetate copolymer having a thickness of 0.1 μm and a thickness of 35 μm are used on the support. OP formed by stacking a photosensitive layer
It is a C photoconductor, and when the photosensitive layer is irradiated with light, the surface potential drops. Therefore, if the photosensitive drum 1 is previously charged uniformly to a predetermined potential and then light based on the density of the original image is irradiated, the surface potential of the photosensitive drum 1 becomes uneven.
It is possible to form a portion where the potential is lowered. This is what is called an electrostatic latent image. Photosensitive drum 1
The present invention is not limited to this, and may have another structure such as a photoconductor made of amorphous silicon. Here, for convenience of description, the OPC photosensitive member described above will be described.

The first motor driver 10 is a circuit that mainly controls the drive of a main motor (not shown) that rotates the photosensitive drum 1, and controls the rotation speed and rotation of the main motor based on a control signal from the first CPU 50. It is on / off controlled.

The encoder 11 generates a pulse signal of a predetermined width corresponding to the rotation phase of the photosensitive drum 1, and the first CPU
Output to 50. As a result, the first CPU 50 detects the rotation phase of the photosensitive drum 1.

When the scanning optical system 54 is an analog type,
A known scanning system is used. For example, although not shown, an illumination lamp integrally formed with the first scanning mirror, a second scanning mirror (V mirror) that moves at a speed ratio of 1/2 of the first scanning mirror, and the like, and an optical path in front of the lens The original is scanned while the length is always kept constant. A standard density plate corresponding to, for example, an optical reflection density of 1.0 is provided at one lower end of the platen glass, and this is irradiated by an irradiation lamp so that a standard latent image is formed on the photosensitive drum 1 and then developed with toner. There is.

As a so-called digital scanning optical system, a method using a similar reading scanning system and a method of storing image data forming a standard density portion in a memory and forming a standard latent image based on this data There is. In the case of the digital method, the scanning optical system 54 as an image exposing means for forming an electrostatic latent image is a laser scanning provided with a polygon mirror or the like for rotating and scanning a laser from a semiconductor laser modulated by an image signal. A fixed scanning system using a system, an LED array, or liquid crystal may be used. Here, for convenience of description, an analog scanning optical system will be described below.

The developing device 20 includes a sleeve 20c containing a magnet roller 20b having an N pole and an S pole in a developing tank 20a formed by a lower casing and an upper casing, and is in pressure contact with the sleeve 20c. A regulating member 20d made of a rigid member provided in the lower casing, screw-shaped first and second stirring rollers 20e and 20f, and a scraper 20 for scraping the two-component developer from the sleeve 20c.
and g. The two-component developer is composed of toner and carrier, and the toner is attached to the carrier and is conveyed to the position of the sleeve 20c, and is conveyed by the sleeve 20c to the developing area which is a position facing the photosensitive drum 1.
Further, since new toner is supplied into the developing tank 20a,
The internal pipe communicates with the toner hopper 20h and includes a conveying screw 20i which is driven according to a toner replenishment signal. In addition, instead of the regulating member 20d, a thin layer forming means including a magnetic rod or a magnetic plate may be provided.

The first stirring roller 20e has a shape that conveys the two-component developer toward the front side of the recording paper, and the second stirring roller 20f has a shape that conveys the two-component developer toward the back side of the recording paper. ing. In addition, the first and second stirring rollers 2
By providing a partition wall between 0e and 20f, the two-component developer can be smoothly circulated and locally retained. As a result, the two-component developer conveyed to the developing area can be replaced, and the developing conditions are stabilized.

The scraper 20g is rotatably supported by rollers and is provided so as to come into pressure contact with / separate from the sleeve 20c. At the time of pressure contact, the two-component developer which has passed through the developing area and consumed toner is scraped from the sleeve 20c. ..

The sleeve 20c is provided with a developing bias circuit 62 for applying a voltage having an AC bias component and a DC bias component via a protective resistor in order to prevent image fogging. The developing bias circuit 62 moves the toner in the two-component developer conveyed to the developing area by the sleeve 20c by receiving an electrostatic force by the electric field created by the electrostatic latent image formed on the surface of the photosensitive drum 1. It is provided with an AC power supply for applying an AC bias for causing the toner to vibrate between the sleeve 20c and the photoconductor 1 in the developing area, and a high voltage DC power supply for applying a DC bias. The developing bias circuit 62 can change the developing bias according to a control signal from the second CPU 60.
If the toner concentration is 5.0 (wt%), the developing bias has a DC component _VDC = -250 (V), and an AC component peaks.
Peak voltage V _PP = 1500 (V), AC frequency f _AC =
It has initialized set as 3KH _Z. In this way, the developing bias circuit 62 includes the sleeve 20c and the photosensitive drum 1
Since an oscillating electric field is generated between the toner particles and the toner particles, the toner particles vibrate between the sleeve 20c and the photosensitive drum 1, so that the two-component developer and the photosensitive drum 1 do not come into contact with each other efficiently and clearly. A toner image can be formed on the drum 1 by toner particles.

The high voltage power supply circuit 40 is a circuit for applying a predetermined high voltage to the transfer device 42 and the charging device 41.

The optical density measuring means 61 uses LE as a light source.
By using D, the light from the LED is reflected by the reference toner image on the photosensitive drum 1 and is received by the photodiode.

The toner concentration detecting means 63 is a means for detecting a change in the magnetic permeability of the two-component developer, and detects the toner concentration in the two-component developer loaded in the developing device 20. The means for detecting the volume level of the two-component developer in the developing device 20 may be used. Although not limited to these, here, for convenience of explanation, a toner density detecting means for detecting the toner density based on a change in magnetic permeability will be described.

The first CPU 50 controls the image forming process in sequence and has an image forming program for executing the image forming process. The first CPU 50 forms the image by a start signal issued in response to the pressing of the copy button. The program is started to execute the image forming process.

The second CPU 60 associates the data of the image density CD and the toner density _Tc on the loci of the solid line A, the chain line B and the broken line C shown in FIG. A so-called look-up table T, and a ROM 60 that incorporates an image density control program including a toner density determination program and a developing bias control program
It is stored on a. The toner density determination program determines whether or not the toner density detected by the toner density detecting means 63 is below a predetermined value, and when the toner density is below a predetermined value, the toner density NG signal is sent. This is a program for transmitting an toner density OK signal to the first CPU 50 when the density is not lower than a predetermined value. The first CPU 50 has a toner concentration determination result register R1 for setting the toner concentration OK signal or the toner concentration NG signal received from the second CPU 60. The signal in the toner concentration determination result register R1 is the toner concentration. In the case of the NG signal, the toner is supplied from the toner hopper 20h to the developing tank 20a in order to keep the toner density constant.
Although the developing bias control program keeps the toner density substantially constant at a predetermined value, the optical density detecting means 6
When the detection signal from 1 indicates a decrease / increase in image density, this program detects it and controls the developing bias to maintain the image density at a predetermined value. Here, the image density decrease / increase is detected by detecting the reflected image density of the toner image on the photosensitive drum 1 corresponding to the standard density plate, and the image density CD as a comparison reference read from the look-up table T = 1. 0.0 [toner concentration T _C = 5 (wt%)] for detection. At this time, the reference image density is set in the reference image density register R2.

The first CPU 50 has a first counter CT1 for counting the number of copies and a second counter CT2.
And a third counter CT3 are built-in. The first counter CT1 counts the number of continuous copies at the time of continuous copying, and the second counter CT2 executes a developing bias control program in response to a detection signal from a paper discharge sensor or the like. The number of copies indicating the timing of execution, that is, the total number of copies after the previous development bias control is performed is counted. Specifically, the developing bias control program is executed every time 1000 copies are made. Also, the third
The counter CT3, after executing the developing bias control program, counts the number of copies of the bias restoration judgment indicating the timing of judging whether or not the image density has returned to the predetermined level by the control, that is, the timing of the bias restoration judgment. Specifically, after executing the developing bias control program, it is determined whether or not the image density has recovered to a predetermined level at the time of copying 50 sheets, and the developing bias is returned to the initial value based on the determination. There is. In addition,
These first counter CT1, second counter CT2, third counter
The counter CT3 is a down counter, and the number of continuous copies, the total number of copies, and the number of copies for judgment of bias return are set, and these are counted down,
When the countdown value becomes “0”, it is assumed that the set number of copies have been made.

Next, the image recording operation of the image recording apparatus will be described with reference to the flowcharts of FIGS. In addition,
2 is a main flow executed by the first CPU 50, and FIG. 3 is a developing bias control flow executed by the first CPU 50.

The power is turned on by pressing the main switch (not shown). As a result, the first CPU 5
0 and the second CPU 60 are activated (step F-1 in FIG. 2).

The first CPU 50 is the first motor driver 1
By driving 0, the main motor is started, and the drive system is connected to the first and second agitating rollers 20e, 2 of the developing device 20.
0f is connected to stir the two-component developer. Further, the heater of the fixing device is heated to a predetermined temperature. Also, the first CPU
Reference numeral 50 denotes an image forming process condition in which the photosensitive drum 1 is connected to the drive system of the main motor to be rotationally driven, and the photosensitive drum 1 is charged by a charger 41 and a static eliminator (not shown) and the static elimination is repeated. Pre-processing such as adjustment is performed. Further, in the pre-processing, the continuous copy number A set by the user by operating a predetermined button is set to the first counter CT.
Set to 1 (step F-2). By the way, as described above, the second CPU 60 constantly determines whether or not the toner concentration detection signal from the toner concentration detection means 63 is equal to or lower than the set value 5 (wt%) based on the toner concentration determination program. If the result is 5 (wt%) or less, the toner density NG signal is sent to the toner density determination result register R1 of the first CPU 50 if it is not 5 (wt%) or less. .. Therefore, 1C
The PU 50 reads the signal set in the toner concentration determination result register R1 (step F-3) and determines whether it is the toner concentration NG signal (step F-).
4). As a result, if the toner density signal is NG, toner is replenished (step F-5) and step (F-6).
Proceed to. On the other hand, if it is the toner density OK signal, the process immediately proceeds to step (F-6) to determine whether the countdown value in the second counter CT2 is "0", thereby counting the total number of copies. It is determined whether or not the value has reached the total copy number of 1000 sheets related to the setting.
As a result, if the total number of copies has not reached 1000, the process proceeds to step (F-9). Total number of copies is 1
If the number has reached 000, the first CPU 50 causes the second counter CT2 to set the total number of copies to "1000".
"Sheet" (step F-7), an image density control interrupt is generated, and an image density control command signal is sent to the second CPU 60.
(Step F-8).

Therefore, the second CPU 60 is connected to the first CPU 5
In response to the image density control command signal from 0, the scanning optical system 54 is activated to turn on the light source, and the standard density plate is irradiated with light to reflect the reflected light from the first and second mirrors. A standard electrostatic latent image is formed by forming an image on the photosensitive drum 1 via the (step F-8 in FIG. 3).
1). Then, the developing device 20 is driven to visualize the standard electrostatic latent image as a toner image to form a standard toner image (step F-82). Next, the second CPU 60 reads out the reference image density CD corresponding to the toner density detection signal from the toner density detecting means 63 from the lookup table T and sets it in the reference image density register R2 (step F-83).

Then, the actual optical image density is fetched from the optical image density measuring means 61, and the reference image density register R2.
Then, it is determined whether or not they match with each other by comparing with the reference image density held in (step F-84). As a result, if they do not match, it is judged whether or not the developing bias of the developing bias circuit 62 is the initial value (step F-85). If it is the initial value, that is, if the developing bias is not changed,
The developing bias circuit 62 is adjusted to change the developing bias (step F-86), and the process returns. A specific example of changing the developing bias will be described in detail later. On the other hand, when the developing bias is not the initial value, as will be apparent from the explanation below, the developing bias was changed, but it means that the actual optical image density has not been restored to the reference image density due to the change. , In this case return immediately.

If it is determined in step (F-84) that the actual optical image darkness and the reference image darkness match, it is checked whether the developing bias of the developing bias circuit 62 is the initial value. It is determined (step F-87). as a result,
If the developing bias is not the initial value, it means that the actual optical image density is restored to the reference image density as a result of changing the developing bias. Therefore, the developing bias circuit 62 is adjusted to restore the developing bias to the initial value. Let me (Step F-
88) and return. On the other hand, if the developing bias is the initial value, the actual optical image density matches the reference image density from the beginning, and there is no need to change the developing bias.
It returns as it is.

Therefore, the first CPU 50 executes the image forming process based on the image forming program (FIG. 2).
Step F-9). Then, the countdown value of the continuous copy number of the first counter CT1, the second counter CT2
Then, the countdown value of the total number of copies is subtracted by 1 (step F-10), and it is determined whether the developing bias is the initial value (step F-11). As a result, if the developing bias is the initial value, the first counter CT
By determining whether or not the countdown value of the continuous copy number of 1 is "0", it is determined whether or not the continuous copy number A according to the setting has been reached (step F-12), and the first counter CT1. When the countdown value of is 0 and the continuous copy number A is reached, the process is ended. On the other hand, if the number of continuous copies A has not been reached, the process returns to step (F-3) to make continuous copies for that number.

In step (F-11), when it is determined that the developing bias is not the initial value, that is, the second CP
If the developing bias is changed in U60 and the initial value has not been restored thereafter, the bias return determination copy number B of the third counter CT3 is decremented by 1 (step F-13). Next, the countdown value (A) of the continuous copy number A of the first counter CT1 is set to the third counter C.
Bias recovery judgment at T3 It is judged whether or not it is equal to or more than the countdown value (B) of the number of copies B (step F-1).
4). As a result, if the countdown value (A) of the continuous copy number A is equal to or larger than the countdown value (B) of the bias recovery determination copy number B, the countdown value (B) of the bias recovery determination copy number B of the third counter CT3 is determined. By determining whether or not it is "0", it is determined whether or not the bias recovery determination copy number B related to the setting has been reached (step F-15). As a result, if the number of copies B for judgment of bias recovery has not been reached, it is clear that the set number of continuous copies A has not been completed, and therefore, in order to continue continuous copying, step (F-9)
Return to.

On the other hand, when the countdown value (B) of the third counter CT3 is "0", which indicates that the number of copies B for the bias recovery judgment relating to the setting has been reached,
The bias recovery judgment copy number B is set in the third counter CT3 (step F-16). Then, in order to return the changed developing bias to the initial value, step (F-
Return to 8).

When it is determined in step (F-14) that the countdown value (A) of the number of continuous copies A is smaller than the countdown value (B) of the number of copies B for determining the bias recovery, the first counter CT1 is set. Continuous copy number A
By determining whether or not the countdown value (A) of is 0, it is determined whether or not the continuous copy number A related to the setting has been reached (step F-17). As a result, if the continuous copy number A is not reached, the continuous copy number A
Return to step (F-9) to perform continuous copying for minutes.
On the other hand, when the countdown value (A) of the first counter CT1 is “0” and the continuous copy of the set continuous copy number A is completed, the process ends. In this case,
The developing bias will not be returned to the initial value and will end with being changed, but when performing the next continuous copy, the processing after step (F-13) is executed via step (F-11). Therefore, the developing bias is returned to the initial value at that time.

Returning the developing bias to the initial value in step (F-88) of FIG. 3 has the following significance.
That is, as described above, the first CPU 50 causes the second CP
The image forming process is executed after the developing bias is changed by U60. However, if the copying is continued for a while while the developing bias is being changed low, the developability may become too high. In this state, the toner having a high toner charge amount in the two-component developer is consumed and new toner supply is started. Therefore, after the development bias is changed, the standard toner image is created by executing the image density control program again when the copy number of the predetermined number (for example, 50 sheets) is completed, and the optical image density is indicated by the solid line A.
Alternatively, when returning to the vicinity of A, the developing bias is returned to the original proper value.

As is clear from the above description, the toner concentration is constantly monitored and the toner concentration control is performed immediately when the toner concentration decreases, but the developing bias control is 1000 times.
I do it every time I make a copy. This is because the developing bias can be adequately dealt with practically by intermittent control, and the toner forming the reference toner image is removed by the cleaner for cleaning the photosensitive drum 1 and cannot be used for normal copying. This is to save toner.

Next, the developing bias control operation of FIG. 3 by the second CPU 60 will be specifically described. Here, the developing bias is an example in which an AC bias is superimposed on a DC bias, the AC frequency is fixed, and the DC component and the effective value of the AC component are adjusted. The initial charging potential of the photosensitive drum 1 is constant.

In the comparison calculation in step (F-84), if the reference image density held in the reference density register R and the actual image density from the optical image density measuring means 61 substantially match, the developing device 20 The toner charge amount of the loaded two-component developer is appropriate, and the image density CD and the toner density T _C are on the locus of the solid line A shown in FIG. 5 or in the vicinity of the solid line A. In this case, it is possible to efficiently and clearly form a toner image on the photosensitive drum 1 with the toner particles. That is, the image density is about 0.4 to about 1.
At 2, the contrast is sufficiently wide and the adhesive force between the photosensitive drum 1 and the toner is appropriate, so that clear image reproduction without image deviation in the image forming process can be performed, and thus it is not necessary to adjust the developing bias. Therefore, as mentioned above,
DC component V _DC = −250 (V), AC component peak-to-peak voltage V _PP = 1500 (V), AC frequency f _AC = 3
It remains KH _Z.

However, in the comparison operation in step (F-84), if the actual image density is much lower than the reference image density, the toner charge amount becomes larger than the appropriate value, and for example, the chain line shown in FIG. Since it is on the miracle of B, sufficient image density and contrast cannot be obtained.

Therefore, the second CPU 60 controls the developing bias circuit 62 to lower the DC component V _DC of the developing bias and increase the _AC component V _AC to enhance the developing power. Specifically, DC component V _DC = −100 (V), AC component peak-to-peak voltage V _PP = 2000 (V),
Adjust to _AC frequency f _AC = −3 KH _Z. This allows
Since the developing power can be increased, it is as if the dashed-dotted line B in FIG. Therefore, it is possible to obtain sufficient image density and contrast according to the original image. As described above, when the toner charge amount becomes excessively larger than the specified range and the developing force is lowered, the developing force is quickly recovered by simultaneously increasing the AC bias. This is because by increasing the peak-to-peak voltage V _PP of the AC component, the toner behavior can be improved more efficiently than the mere displacement of the DC component.

Further, in the comparison calculation of step (F-84), if the actual image density greatly exceeds the reference image density, the toner charge amount becomes smaller than an appropriate value. For example, one point shown in FIG. Since the image is on the locus of the chain line C, the image density is too high, and the image cannot be reproduced faithfully.

Therefore, the second CPU 60 controls the developing bias circuit 62 to increase the DC component V _DC of the developing bias and decrease the _AC component V _AC to decrease the developing power. Specifically DC component V _DC = -350 (V), the peak of the AC component-to-peak voltage V _PP = 1200 (V), adjusted to AC frequency f _AC = 3KH _Z. As a result, the developing power can be reduced, and it is as if the broken line C in FIG. Therefore, it is possible to obtain sufficient image density and contrast according to the original image. However, in this case, problems such as image repellency and image misregistration occur in the processes of developing, transferring, and fixing. Therefore, the second CPU 60 makes sure that the developing device 20 is sufficiently stirred. Alternatively, the above-mentioned developing bias control may be executed again after the 1CPU 50 is instructed to sufficiently stir the inside of the developing device 20 under the control of the first CPU 50.

As described above, in this embodiment, when the toner density is maintained at a predetermined value substantially constant, when the image density is decreased or increased, this is detected and the developing condition is set. Since the strength of the developing force can be adjusted by performing the predetermined control, it is as if the straight line A in FIG. 2 is corrected. Therefore, it is possible to obtain sufficient image density and contrast according to the original image.

Also in the reversal development using another two-component developer, the initial charging potential V _H = −600 (V), the AC frequency 5.0 KH _Z , and the peak-to-peak voltage V _PP = 2.
Even under the appropriate conditions of 500 (V), developing bias _VDC = -500 (V), and toner concentration of 3.0 (wt%) ± 0.2 (wt%), the same control as above is applied, If the image density is lowered, the AC frequency 4.0KH _Z, the peak-to-peak voltage V _PP = 2800 (V), the developing bias V _DC =
Controls to -550 (V), when the image density is too high, AC frequency 5.0KH _Z, the peak-to-peak voltage V _PP =
The same effect as described above was obtained by controlling the developing bias to 2000 (V) and the developing bias V _DC = -450 (V).

Further, the initial charging potential V _H = −800
(V), AC frequency 3.0KH _Z, the peak-to-peak voltage V _PP = 2200 (V), the developing bias V _DC = -60
0 (V), toner concentration 5.0 (wt%) ± 0.3 (wt
%), The control similar to the above is applied, and the peak-to-peak voltage V _PP = 3000 (V), the developing bias V _DC = −700, or the peak-to-peak voltage V
_PP = 2000 (V), development bias _VDC = -500
The effect similar to the above was obtained also by adjusting to (V).

Further, in a color developing device having a plurality of similar developing devices, there may be a large difference in the consumption amount of each color toner. Therefore, the two components using the insulating carrier resin coated on the ferrite core as described above are used. The present invention can be preferably applied to the case where a developing agent is incorporated and development is performed under an AC electric field.

The present invention is not limited to the above embodiment, but can be modified in various ways, for example, the toner density control and the developing bias control are performed by one CPU.

[0062]

As described above, according to the image recording apparatus of the present invention, when the toner density is lowered or increased even though the toner density is maintained substantially constant at a predetermined value, By detecting this and controlling the developing condition to a predetermined value, an image can be reproduced with an appropriate image density.

[Brief description of drawings]

FIG. 1 is a block diagram of an image recording apparatus according to an embodiment of the present invention.

FIG. 2 is a flowchart showing an image recording operation in the image recording apparatus of this embodiment.

FIG. 3 is a flowchart showing an image density control operation in the image recording apparatus of this embodiment.

FIG. 4 is a toner in a two-component developer loaded in a developing device.
It is a figure which shows the change of the image density with respect to a density (wt%: weight mixing ratio).

FIG. 5 is a toner in a two-component developer loaded in a developing device.
Density C for changes in the charge amount Q / m (μc / g) of
It is a figure which shows the change of D.

[Explanation of reference numerals] 1 photosensitive drum 20 developing device 50 first CPU 60 second CPU 61 optical density measuring means 62 developing bias circuit 63 toner density detecting means

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kunihisa Yoshino 2970 Ishikawa-cho, Hachioji-shi, Tokyo Konica Stock Company

Claims (5)

[Claims] 1. A two-component developing means for applying a developing bias to develop an electrostatic latent image on an image bearing member with a two-component developer consisting of carrier and toner, and detecting the toner concentration of the two-component developer. And a toner replenishment control unit that performs toner replenishment control based on the toner concentration from the toner concentration detection unit,
A reflection density detecting means for detecting a reflection density of the reference toner image formed on the image carrier, and a reflection density of the reference toner image detected by the reflection density detecting means lowers or rises below a predetermined level, Further, when the toner density detected by the toner density detecting means is substantially constant, the developing bias is changed, and then the developing bias is set to a predetermined value when the reflection density of the reference toner image returns to a predetermined level. An image recording apparatus comprising: a developing bias control unit for returning the value to a value. 2. The image recording apparatus according to claim 1, wherein the toner concentration detecting unit detects a change in magnetic permeability or a change in volume level of the two-component developer. 3. The image recording apparatus according to claim 1, wherein the developing bias includes an alternating bias component. 4. The image recording apparatus according to claim 1, wherein the developing unit is a reversal developing unit, and the developing bias control is control of a DC component. 5. The image recording apparatus according to claim 1, wherein the developing bias control is to increase the amplitude of the alternating bias or to increase the DC component.