JPH0642109B2 - Automatic toner concentration controller - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic toner concentration control device for always maintaining a constant toner concentration in a developer used in a copying machine, a printer or the like.

2. Description of the Related Art Generally, in an image forming apparatus such as a copying machine or a printer that develops an electrostatic latent image formed on a surface of a photoconductor using a developer containing toner, the electrostatic latent image The toner contained in the developer housed in the developing device is consumed, and therefore, in order to keep the density of the developed image constant at all times, a new amount of toner corresponding to the consumed amount is added to the developer. Toner must be replenished.

Therefore, in the past, attention was paid to the fact that the toner concentration in the developer and the development concentration (toner adhesion amount on the surface of the photoconductor) have a constant proportional relationship, and a constant concentration provided near the platen glass A reference chart having the following is exposed and developed on the photoconductor to form a reference development image for toner concentration detection (for example,
JP-A-54-97044 and JP-A-58-1909
No. 66), or an insulator region formed on a part of the surface of the photoconductor is charged and developed to form a reference developed image for toner concentration detection (see, for example, JP-A-59-12).
No. 466), these reference developed image densities are optically detected, and toner replenishment to the developer is controlled according to the detected value.

Specifically, the density of the reference developed image when the toner density in the developer is at a predetermined set value is compared with the density of the reference developed image detected for toner replenishment control, and the latter is If it is high, stop the toner supply or decrease the supply amount,
If it is low, the toner supply is restarted or the supply amount is increased.

On the other hand, in recent years, development of an image forming apparatus capable of obtaining not only black but also single color images of red, blue, yellow and the like has been advanced. In this type of image forming apparatus, the developing device containing the black toner and the developing device containing the color toner of a single color may be arbitrarily replaced, or both types of developing devices may be installed side by side to operate them arbitrarily. A switching control method is adopted.

Problems to be Solved by the Invention However, when the automatic toner density control device is used in an image forming apparatus capable of selectively developing with black toner and color toner, the following problems occur.

That is, the conventionally used optical means for detecting the density of the reference developed image is configured such that the light receiving element detects the directly (direct) reflected light of the light from the light emitting element. This is because when developing with black toner, the reflectance (absorption rate) between the photoconductor and the black toner is greatly different, so that the toner concentration (toner adhesion amount) and the light receiving element output are as shown by the solid line in FIG. 7a. This is because a sufficient correlation can be obtained between and.
However, during development with color toner, since the color toner causes diffused reflection, there is almost no difference in the reflectance between the photoconductor and the color toner, and the toner concentration (toner adhesion amount) as shown by the dotted line in FIG. 7a. However, it is impossible to detect the density of the reference developed image with color toner.

Therefore, when developing with color toner, it is conceivable that the light receiving element is configured to detect irregularly reflected light. In this case, as shown by the solid line in FIG. Can obtain a sufficient correlation.
However, when developing with black toner, as shown by the dotted line in FIG. 7b, a correlation cannot be obtained between the toner density and the output of the light receiving element, and the density of the reference developed image with black toner is detected. Is impossible.

On the other hand, as a method of detecting the reference developed image density by color toner, it is conceivable to use a light source having a wavelength absorbed by each toner, but a light emitting element of a wavelength light source corresponding to each wavelength and a light receiving element for receiving light are required And increase the cost.

It is also possible to use an incandescent light source to change the filter according to each color toner, but it is necessary to have a mechanism to switch the filter according to each toner as well as to decrease the light amount at the filter, and to detect the detection level. In order to obtain the difference, a light receiving element corresponding to each toner is required, which is not practical.

Therefore, as a result of various studies, the present inventor has set the reference developed image forming portion to, for example, black or the like, and when color toner adheres to the formed portion, the reflectance of the reference developed image is increased in accordance with the amount of the adhered toner. I have found that it changes.

Therefore, according to the present invention, by providing the low-density reference development image forming portion and the high-density reference development image forming portion on the photosensitive member, the toner density and the light receiving element for both the black toner and the color toner can be reduced. An object of the present invention is to provide an automatic toner concentration control device that can obtain a correlation with an output.

Therefore, the automatic toner density control device according to the present invention is configured so that a non-image area on the surface of the photoconductor has a low-density reference development image forming portion having a low surface reflection density and a high-density reference development image. When two types of forming sections are provided and black toner is used for development, based on the reference development image formed in the low-density reference development image forming section, while using color toner for development Is characterized in that the toner density in the developer is detected based on the reference developed image formed in the high density reference developed image forming portion.

Action That is, when the black toner is used, the reference developed image is formed in the portion where the background has a low density, and therefore the reflected light has the maximum value when the black toner does not adhere, and the toner adhesion amount increases. Accordingly, the toner density is detected with a sufficient correlation shown by the solid line in FIG. 7a with the output of the light receiving element which is inversely proportional to the reflected light. On the other hand, when the color toner is used, the reference developed image is formed on the part where the background has a high density. Therefore, the reflected light has the minimum value when the color toner does not adhere, and as the toner adhesion amount increases, As a result, the toner density is increased and the toner density is detected in a sufficient correlation shown in FIG. 7b with the output of the light receiving element which is inversely proportional to the reflected light.

Basically, the detection light in the case of black toner is specular reflection light, and the detection light in the case of color toner is irregular reflection light.

Therefore, a reference value corresponding to the reference developed image when the toner concentration in the developer is at a predetermined setting value, and a toner concentration detection value (light receiving element output) of the reference developed image detected for toner concentration control When the black toner is used for development, the output of the light receiving element is lower than the reference value, and when the color toner is used for development, the output of the light receiving element is lower than the reference value. When they are high, it is determined that the toner density is insufficient, and the toner replenishment is controlled.

First Embodiment In FIG. 1, first, a schematic structure of an electrophotographic copying machine equipped with an automatic toner density control device according to the present invention will be described together with its operation.

A photoconductor drum (2) is rotatably driven in a direction indicated by an arrow (a) by a main motor (not shown) at approximately the center of the copying machine (1). Around the photosensitive drum (2), a charger (4) and a developing device are sequentially installed according to the rotation direction.
(5), a transfer charger (6), a separation charger (7), a cleaner device (8), and an eraser lamp (9) are arranged. Further, an optical system (10) is provided above the photosensitive drum (2) and its peripheral devices, a paper feeding section (30) is provided on the left side, and a fixing device (2 is provided on the right side.
3) are provided respectively.

The optical system (10) is of a slit exposure type and includes a light source (12) fixed to a holder (11), a first movable mirror (13), and a holder (1
Second and third movable mirrors (16) and (17) fixed to 5),
It is composed of a lens (18) and a fixed mirror (19).
Then, the surface of the photoconductor drum (2) is charged by the charger (4), the light source (12) is turned on, and then the light source (12) and the movable mirrors (13), (16) and (17) are not shown. Scan motor with arrow
The original image is scanned and exposed on the surface of the photoconductor drum (2) while moving in the direction (b) to form an electrostatic latent image corresponding to the original image.

If the peripheral speed of the photosensitive drum (2) is (V ₀ ), and the copy magnification is (m), the moving speed of the light source (12) and the first movable mirror (13) is (V
₀ / m) and the moving speeds of the second and third movable mirrors (16) and (17) are set to (V ₀ / 2m).

The electrostatic latent image is developed by passing through the developing device (5) to form a toner image corresponding to the original image.

On the other hand, the paper feed unit (30) is provided with the first paper feed unit (31) and the first paper feed unit (31).
It has the paper feed cassettes (32) and (33) of the manual feed unit (31)
The copy paper inserted from is conveyed to the timing roller pair (36) through the manual feed roller pair (34) and the intermediate roller pair (35), and is stored in the first and second paper feed cassettes (32) and (33). The copy paper is conveyed to the timing roller pair (36) via the first and second paper feed rollers (37) and (38) and the intermediate roller pair (35), respectively.

The copy paper is then resumed from the timing roller pair (36) to the right in FIG. 1 in synchronism with the toner image on the surface of the photoconductor drum (2), and the toner is discharged by discharging the transfer charger (6). The image is transferred. Immediately after being transferred, it is separated from the photoconductor drum (2) by AC discharge of the separation charger (7),
Conveyor belt with air suction means (not shown)
It is sent to the fixing device (23) at (22). The copy paper is heated and fixed on the toner image by the fixing device (23), and then the tray is transferred to the tray.
(24) Discharge on top.

The photoconductor drum (2) continues to rotate in the direction of arrow (a) after that,
The residual toner is removed by the cleaner device (8) and the residual charge is erased by the main racer (9) to prepare for the next copying.

Next, an automatic donor concentration control device provided in this copying machine will be described.

This automatic toner density control device comprises reference developing image forming sections (3a) and (3b) (see FIG. 2) provided on the surface of a photoconductor drum (2), a developing device (5) and a transfer charger (6). ) And a reflective photo sensor facing the surface of the photoconductor drum (2)
(26) and a control circuit for comparing the output of the sensor (26) with a reference value to control ON / OFF of toner supply.

The reference developed image forming portions (3a) and (3b) are insulating portions provided in the non-image area (Z) which is one end portion of the photosensitive drum (2), and the forming portion (3a) has a low density (white ), Another forming part (3
b) has a high concentration (black). This forming part (3a), (3
In b), charging and development are performed for each copying operation, and toner adheres to form a reference developed image. When black toner is used for development, the density of the developed image formed in the low density formation part (3a) is set, and when color toner is used for development, the high density formation part (3b) is set. The density of the formed developed image is detected.

By the way, in the present copying machine, the developing device (5) is replaceable with respect to the main body of the copying machine, and in addition to the one filled with black toner, the developing device of the same constitution filled with monochromatic color toners such as red, blue, and yellow, respectively. Preliminarily provided for the vessel (5). Two reed switches (not shown) are installed in the main body of the copying machine in which each developing device (5) is installed, and magnets (25a) and (25b) are provided on the top plate of the corresponding developing device (5). For example, two for black toner, only the right side for red toner, only the left side for blue toner, and not for yellow toner. Therefore, the color of the toner filled in the developing device (5) depends on the reed switch and the magnets (25a), (25b).
It is automatically detected by the signal from the reed switch in combination with.

As shown in FIGS. 5 and 6, the reflection type photo sensor (26) includes a light emitting element (26a) formed of a light emitting diode and a light receiving element (26b) formed of a phototransistor. 26b) receives the light of the light emitting element (26a) reflected by the surface of the photosensitive drum (2).

The color of the toner in the currently installed developing device (5) is detected by the signal from the reed switch, and if it is black toner, the reference developed image formed on the forming unit (3a) reaches the detection position. When the photosensor (26) is activated, when the color toner is used, the photosensor (26) is activated when the reference developed image formed on the forming unit (3b) reaches the detection position. The reflection density of is detected. The detection signal of the reed switch is also input to the display unit of the operation panel (not shown) via the microcomputer to display the color of the toner on the operation panel.

FIG. 5 illustrates the toner density detection when black toner is used, and the reference developed image, which is the object to be detected, is formed against the background of the low density (white) forming portion (3a). Therefore, as shown in (a), the amount of reflected light is maximum and the output of the light receiving element (26b) is minimum when black toner does not adhere to the forming portion (3a). Then, as shown in (b), black toner (T ₁ )
The amount of reflected light decreases as the amount of adhered light increases, and the output of the light receiving element (26b) rises along the curve shown by the solid line in FIG. 7a. Therefore, the control circuit compares the output value of the light receiving element (26b) and the density (reference value) of the reference developed image when the toner density in the developer in the developing device (5) is at a predetermined set value, If the former is lower, it is determined that the toner density is insufficient and toner supply is started.

FIG. 6 is for explaining the toner density detection when color toner is used for development. The reference developed image, which is the object to be detected, is formed against the background of the high density (black) forming portion (3b). Has been done. Therefore, as shown in FIG.
When the color toner is not attached to b), the amount of reflected light is minimum and the output of the light receiving element (26b) is maximum. Then, as shown in (b), as shown in the color toner (b), the amount of (random) reflected light increases as the adhesion amount of the color toner (T ₂ ) increases, and the output of the light receiving element (26b) becomes The curve shown by the solid line in FIG. Therefore, the control circuit compares the reference value of the output value of the light receiving element (26b), and if the former is higher, it is determined that the toner density is insufficient and toner supply is started.

It should be noted that the black toner and the color toner cause a difference in the output of the light receiving element (26b) with respect to the toner concentration, and even the color toner causes a slight difference in the output of the light receiving element (26b) for each color. Therefore, in the present embodiment, two types of comparison circuits are provided, one for black toner and one for color toner. In the case of color toner, the reference value voltage of the comparator in the comparison circuit is automatically set based on the detection signal for each color of the reed switch. Are being switched.

Further, as shown in FIG. 3, the reference developed image forming sections (3a) and (3b) are the same as those of the photoconductor drum (2) if the photoconductor drum (2) is a one-copy one-rotation type. The non-image area (Z) may be provided as a conductive area insulated from the photoreceptor. In this case, the forming unit (3a) has a low density for detecting the density of the black toner,
The forming portion (3b) has a high density for detecting the density of the color toner. The forming portions (3a) and (3b) are not charged, and the toner is attached by applying a developing bias having the same polarity as the toner to the developing sleeve during development. The toner concentration is detected by providing two sets of reflective photosensors (26) and selectively operating one of them according to the black toner or color toner to be used. Even when the detection mode shown in FIG. 2 is adopted, the reflection type photo sensor (26) is used for black toner and color toner.
Of course, a set may be provided.

On the other hand, in the main body of the copier (1), a plurality of developing devices filled with different colors of toner are provided, and the developing device to be used is selected by the selection switch on the operation panel, that is, a model in which the toner color is selected. If there is a selection signal from the selection switch or the operation of the selected developing device (5), the photo sensor
It suffices to match the detection timing of (26) and the setting of the reference value.

EFFECTS OF THE INVENTION As is clear from the above description, according to the present invention, when black toner is used for development, the density of the reference developed image formed in the low density portion of the background is detected, and development is performed. When the color toner is used for the background, the density of the reference developed image formed in the high density portion of the background is detected, so that the toner density and the output of the light receiving element are different for the black toner and the color toner, respectively. The relative relationship can be sufficiently taken, and the density (toner density) of the reference developed image formed on the surface of the photoconductor can be accurately detected with any toner. It is possible to accurately control the toner concentration of the toner.

[Brief description of drawings]

1 to 6 show an embodiment of an automatic toner density control device according to the present invention, and FIG. 1 is a schematic configuration diagram of a copying machine,
2 is a perspective view of the photosensitive drum, FIG. 3 is a perspective view showing another example of the photosensitive drum, FIG. 4 is a perspective view of a developing device, and FIG.
FIG. 6 is an explanatory diagram of toner concentration detection of black toner, and FIG. 6 is an explanatory diagram of toner concentration detection of color toner. Figures 7a and 7
FIG. 6B is a graph showing the change in the light receiving element output with respect to the toner concentration. (2) …… photosensitive drum, (3a), (3b) …… reference development image forming unit, (5) …… developing device, (26) …… reflection type photo sensor,
(26a) …… Light emitting element, (26b) …… Light receiving element.

Claims (1)

[Claims] 1. A black or monochromatic image can be produced, a reference development image for toner density detection formed on the surface of a photoconductor is irradiated with light from a light emitting element, and the reflected light is detected by a light receiving element. In the image forming device that detects the toner concentration in the developer and controls the toner replenishment from the toner container to the developing unit according to the detected value, the surface of the non-image area on the surface of the photoreceptor is Two types of reference development image forming portion having a low reflection density and a reference development image forming portion having a high reflection density are provided, and when black toner is used for development, the reference development image forming portion having a low density is formed. On the other hand, based on the reference developed image, on the other hand, when color toner is used for development, the toner density in the developer is detected based on the reference developed image formed in the high density reference developed image forming portion. Automatic toner density control characterized by Your device.