JPH06118795A - Image forming device - Google Patents

Abstract

PURPOSE:To change over resolution without raising cost, in an image forming device capable of forming the image of different resolution corresponding to the selection of a printing mode. CONSTITUTION:A printing head 9 is a laser optical unit and as the printing mode, a normal resolution mode or a high resolution mode is selected to change the resolution (a laser spot diameter). A developing unit 10 has a unit constitution that it is freely attached/detached to/from a device main body and as the developing unit 10, a developing unit 10a housing normal grain diameter toner T1 and a developing unit 10b housing small grain diameter toner T2 can be selectively used. A toner concentration when the high resolution mode is selected and the developing unit 10b of the small diameter toner T2 is fitted is controlled lower than that when the developing unit 10a of the normal grain diameter toner T1 is fitted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a printer, a copying machine and a facsimile which adopts an electrophotographic method, and in particular, it is capable of forming images with different resolutions according to the selection of a print mode. The present invention relates to an image forming apparatus that employs a two-component developing method.

[0002]

2. Description of the Related Art In recent years, page printers typified by laser printers have become widespread, and more and more sophisticated printers have been desired and put on the market. Among them, in terms of resolution, for example, products such as 240 dpi to 300 dpi, 400 dpi to 600 dpi, and 1000 dpi have come out. In the case of a laser printer, since 1 dot is formed by scanning a laser beam, the resolution can be easily changed in the main scanning direction by beam shaping, that is, laser control. Some can be switched in stages. From the point of view of image quality, it seems that it may be better to always set the high resolution without switching the resolution in this way. For example, when the high resolution is set, the print information Therefore, it is desirable to set the normal print mode that does not normally require high image quality and switch to the high resolution mode only when high image quality is required.

By the way, as the resolution becomes higher, it is desired to use a finer toner having a finer particle size in order to develop the latent image thus formed with the toner. Conventionally used toner has an average particle size of 1
It is about 0 to 20 μm, and although there is no definition of a small particle size toner, it is 10 μm such as 5 μm.
It can be said that a toner having a particle size of less than m is a toner having a small particle diameter as compared with a conventional toner. When the above-mentioned resolution exceeds approximately 400 dpi, the above-mentioned small particle size toner is used for development. Of course,
It is possible to use small particle size toner even in dpi without considering cost. However, it goes without saying that the higher the resolution, the higher the cost of the printing means and the cost of the toner itself.

Under such circumstances, in the conventional one capable of switching the resolution as described above, since a high resolution toner is used as the toner, there is a problem that the running cost is extremely increased. . And
Conventionally, no device has been made to reduce the cost in connection with such resolution switching.

[0005]

SUMMARY OF THE INVENTION In view of the above problems, it is an object of the present invention to provide an image forming apparatus capable of switching resolution without increasing costs.

[0006]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention is provided with a printing unit capable of forming a latent image with different resolutions by selecting a printing mode, and includes a toner and a carrier to maintain a predetermined toner concentration target value. In an image forming apparatus that contains a two-component developer containing
Development mode selecting means for selectively enabling development with a toner having a predetermined particle size among toner particles having different average particle sizes corresponding to the resolution according to the selection of the print mode, and the predetermined toner to be maintained. And a means for changing the density target value according to the selected developer.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is an overall view of an image forming apparatus (here, a laser printer apparatus is shown as an example) according to an embodiment of the present invention. This apparatus includes a paper feed cassette 1 that is detachably attached to the apparatus main body, a paper feed roll 2 that feeds the sheets P stacked and stored in the paper feed cassette 1 one by one, and a toner image on the fed paper. An image forming unit 3 for forming, a fixing device 4 for fixing a toner image on a sheet, a sheet discharge roll 5 for discharging the fixed sheet to the outside of the apparatus, a sheet discharge tray section 6 for storing the discharged sheet, and the like. ing. The image forming unit 3 is uniformly charged by a photosensitive drum 7 rotatable in the direction of arrow A, a charger 8 arranged around the photosensitive drum 7 for uniformly charging the surface of the photosensitive drum 7, and a charger 8. A print head 9 as a printing unit that forms an electrostatic latent image by exposing the surface of the photosensitive drum 7 according to image information, a developing device 10 that develops the electrostatic latent image with toner, and a toner obtained by development. Transfer device 1 for transferring the image onto the fed paper
1. A cleaner 12 for collecting the toner remaining on the surface of the photosensitive drum 7 after the transfer, and the like. Further, the main body of the image forming apparatus is divided into a lower machine body M ₁ and an upper machine body M _2, and the upper machine body M ₂ can freely open and close in the arrow B direction with respect to the lower machine body M ₁ with a hinge shaft 13 at one end as a fulcrum. The print head 9 is integrated with the upper machine body M ₂ and moves together with the opening / closing operation of the upper machine body M ₂ .

Here, the print head 9 is a laser optical unit composed of a scanning device 9a, reflection mirrors 9b and 9c, a correction lens 9d, etc., and a laser modulated according to an electric signal from an image processing unit (not shown). By irradiating the surface of the photoconductor drum 7 with the light beam L, an electrostatic latent image is formed. The print head 9 can change the resolution (that is, the laser spot diameter in this case) in both the main scanning direction and the sub scanning direction by selecting the normal resolution mode or the high resolution mode as the printing mode. When the normal resolution mode is selected, it is switched to 300 dpi, for example, and when the high resolution mode is selected, it is switched to 600 dpi, for example.

Further, the developing device 10, as shown in detail in FIG. 2, stores a developer storage tank 14 for storing a two-component developer D composed of toner and carrier, and a developer D in the developer storage layer 14. An agitating member 15 for agitating, a developing sleeve 16 for rubbing the electrostatic latent image into a toner image by rubbing against the photosensitive drum 7 (FIG. 1) while carrying the developer D on the peripheral surface, and a replenishment toner T are stored. A toner storage tank 17, a replenishment roll 18 for replenishing the toner T in the toner storage tank 17 into the developer storage tank 14, and a toner concentration sensor 19 for detecting the toner concentration of the developer D in the developer storage layer 14. And so on. As shown in FIG. 3, the toner concentration sensor 19 includes an oscillator 19a.
The AC signal output from the developer D is passed through a differential transformer 19b provided in contact with the developer D, and a phase difference detection circuit 19c detects a phase difference signal which differs depending on the ratio of the toner and the carrier forming the developer D. The voltage value (analog signal) obtained by smoothing this with the smoothing circuit 19d is applied to the transistor 19
It is a circuit for supplying an analog signal indicating the toner concentration appearing at the connection point between the emitter (E) and the resistor 19f to the e. Here, as for the relationship between the output voltage of the toner concentration sensor 19 and the actual toner concentration, as shown in FIG. 4, when the toner concentration is low, the above phase becomes large, and therefore the output voltage becomes high and the toner concentration is high. Since the phase becomes smaller, the output voltage becomes lower. The output voltage of the toner concentration sensor 19 thus obtained is sent to the printer controller (see FIG. 5) on the apparatus main body side, and in accordance with the toner replenishment signal output from the printer controller, a replenishment roll control unit 20 (a solenoid or the like) ( By appropriately rotating the replenishment roll 18 in FIG. 2), the developer D is controlled to be maintained at a predetermined toner concentration target value according to the toner particle size. Details of this control will be described later.

The developing device 10 having such a structure is shown in FIG.
Unit configuration that can be attached to and detached from the device body as shown in 1.
(Hereinafter, it is called a developing unit.)
Body M ₂The operator can attach / detach with the open
Noh. Further, as the developing device unit 10, a plurality of developing devices are provided.
Unit units 10a and 10b (here, there are two types)
Can be used in each developing unit 10a, 10b
Is toner T with different particle size₁, T₂Each get
Has been paid. For example, toner T₁Has a particle size of 12 μm
Toner T is a particle size toner₂Has a small particle size of 8 μm
I'm Na.

Next, FIG. 5 shows a circuit configuration of the printer controller 21 provided in the image forming apparatus of this embodiment,
The printer controller 21 and the developing device unit 1
FIG. 3 is a diagram showing a connection configuration with a toner density sensor 19 within 0.

In the figure, the printer controller 21
Includes a microcomputer 22 configured by one chip, and the microcomputer 22 determines whether or not the developing device unit 10 is mounted, in addition to controlling the toner density.
Various processes such as determination of the type of developer therein and control of image forming operation are performed. In the microcomputer 22,
The CPU 23 performs the above processing according to the system program stored in the ROM 24, and stores the data generated during this processing in the RAM 25. In addition, the EEPROM 26
Will be described later in detail, but the attached developing device unit 1
The memory stores a toner replenishment reference value (reference voltage value corresponding to a toner concentration target value) according to a toner particle size of 0. In addition, the microcomputer 22 is an analog /
A digital converter (hereinafter referred to as A / D converter) 27 and an input / output circuit (hereinafter referred to as I / O circuit) 28 are provided.

The toner concentration sensor 19 and printer controller 21 described above are provided with a power line L ₁ , an output line L ₂ and a ground line L _3.
The toner density sensor 1 is connected by three lines
Power is supplied to 9 from the printer controller 21 side via the power supply line L _1, and the ground terminal G of the toner concentration sensor 19 is grounded to the printer controller 21 side via the ground line L ₃ . The toner concentration data (analog voltage signal) of the toner concentration sensor 19 is sent to the printer controller 21 via the output line L _2, and the voltage generated across the pull-down resistor R _D is the microcomputer 2 here.
It is input to the A / D converter 27 via the two input terminals AN ₁ . The analog voltage signal input to the A / D converter 27 is converted into digital data and then stored in the RAM 25 under the control of the CPU 23. The detection output of the toner concentration sensor 19 is also used as a signal for detecting the presence / absence of mounting of the developing device unit 10 as described later.

Based on the control of the CPU 23, the I / O circuit 28 supplies the replenishment roll controller 20 (see FIG. 2) via the output port P ₂ and the buffer 29 when toner replenishment is required.
By outputting a toner replenishment signal to, the replenishment roll 18 is rotated for a predetermined time to replenish the toner in constant amounts. In addition, the photosensitive drum 7 (see FIG. 1) and the developing device unit 10
When it is necessary to rotate each rotating member such as the developing sleeve 16 (see FIG. 2) in the inside, a motor rotation start signal is sent to the main motor rotation control circuit 31 via the output port P ₃ and the buffer 30 and not shown. The rotating member is rotated by driving the main motor. Further, display data is output to the display device 32 via the output port P ₄ , and, for example, the presence / absence of mounting of the developing device unit 10 or the presence / absence of toner is displayed.

Next, a processing operation for controlling the toner density by the printer controller 21 will be described with reference to FIG. First, in step S ₁ , it is detected whether or not the developing device unit 10 is attached. This detection is performed based on the output voltage of the toner concentration sensor 19 shown in FIG. 5, for example. That is, when the developing device unit 10 is not attached, the voltage at the ground level is completely applied to the input terminal AN by the pull-down resistor R _D.
Since it is input to ₁ , the presence / absence of the developing unit 10 is determined by comparing the digital data output from the A / D converter 27 with predetermined digital data. Here, if it is determined that the developing device unit 10 is attached, a motor rotation start signal is sent to the main motor rotation control circuit 31 in step S ₂ to drive the main motor to drive the stirring member 15 ( The developer is stirred by rotating (see FIG. 2).

Next, in step S ₃ , toner density data obtained by digitizing the detection output of the toner density sensor 19 by the A / D converter 27 is sampled, and subsequently, in steps S ₄ and S ₅ , It is determined which one of two predetermined reference ranges (that is, the range of the first reference value ± α and the range of the second reference value ± α) in which the toner density data are different from each other. Here, the first reference value corresponds to the toner concentration target value of the developer in the developing device unit 10a that accommodates the normal particle size toner T ₁ , and the second reference value is the small particle size toner T _2.
Corresponding to the toner concentration target value of the developer in the developing device unit 10b in which each of the reference values is EE.
It is stored in the PROM 26 in advance. Therefore, it is possible to determine which of the two developing device units 10a and 10b the currently installed developing device unit is by determining which of the reference ranges the toner density data is within. . Here, the toner concentration target value is made different between the developer containing the normal particle size toner T ₁ and the developer containing the small particle size toner T ₂ because the toner density is constant regardless of the size of the toner particle size. This is because the following problems will occur if this is done.

The charging of the toner is carried out by friction with the carrier, but for that purpose there must be many opportunities for contact with the carrier, and the contact between the toner and the carrier is the first step of the toner on the carrier surface. However, it depends on how the toner is coated on and brought into contact with the carrier. However, in general, the mass of the particles is proportional to the cube of the size of the particles (radius if the particles are spherical) and the surface area is proportional to the square of the particle. Therefore, when comparing the small particle size toner and the normal particle size toner, Even with the same volume (same weight), the small particle size toner has a larger surface area than the normal particle size toner. Therefore, the smaller the particle size, the smaller the holding power for the carrier of the same particle size. Therefore, even if the small particle size toner is controlled to have the same toner concentration as that of the normal particle size toner, the toner is not charged as a result. The amount of toner not retained in the carrier increases, and if the toner is continuously used as it is, the toner with a small particle size scatters in the image forming apparatus, and further, there is a problem that the output image on the paper is contaminated with toner. However, it becomes impossible to perform stable image formation for a long period of time. It can be said that the mechanism in which the small particle diameter toner is scattered in this way is the same as in the case of so-called overtoner in which the toner concentration greatly exceeds the normal range. That is, the target value of the toner density is determined by various conditions such as the properties of each of the carrier and the toner, stirring conditions, etc., and there exists an optimum density value that does not cause toner scattering or overtoner. It can be said that there is an optimum density value corresponding to different cases.

Therefore, in this embodiment, in order to make it possible to use toners having different toner particle sizes for the same device without causing toner scattering, the developer of each developer in the developing unit 10a, 10b is originally used. The toner density is slightly changed, and as a result, the reference values for the toner density control are correspondingly changed to the first reference value,
The second reference value is changed to use different values. Specifically, as shown in FIG. 7, the toner concentration target value C ₂ for the small particle size toner T ₂ is set lower than the toner concentration target value C ₁ for the normal particle size toner T ₁ , and Accordingly, the second reference value V _S2 which is the sensor output corresponding to the toner concentration target value C ₂ is set higher than the first reference value V _S1 which is the sensor output corresponding to the toner concentration target value C ₁ . For example, if the toner density target values C ₁ and C ₂ are 9
% And 7%, the first and second reference values V _S1 and V _S2 are set to 2.0 V and 2.4 V, respectively.

The first and second reference values V set in this way
_S1, V_S2Is previously stored in the EEPROM 26,
Step S_Four, S_FiveIn these, the first and second criteria
Value V _S1, V_S2To read the toner density data and
Compare and compare the first and second reference values V _S1, V_S2Which standard range
Determine whether it is within the range (± α). In addition, these criteria
The ranges are set so that they do not overlap with each other.
ing. Based on this determination, if the first reference value V_S1of
If it is within the range, a developing unit 10 for normal particle size toner
It can be determined that a is attached, while the second reference value V_S2
If it is within the range, the developing unit 10 for small particle size toner
It can be determined that b is attached. And step S
₆Then, if the first reference value V_S1of
If within the range, the first reference value V_S1To EEPROM 26
The second reference value V_S2Second reference value V if within the range
_S2Is written in the EEPROM 26.

After that, the above step S₆At EEPRO
Normal toner density based on the reference value written in M26
Control processing (step S₈~ S₁₁) Is executed. Sanawa
First, step S₈At the toner concentration sensor 19
The intelligent output is digitized by the A / D converter 27
Sampling the concentration data, then step S ₉
Then, the toner density data is obtained in the above step S.₆At EEPR
The reference value stored in the OM 26 (first reference value V_S1Or first
2 reference value V_S2) Above and below a predetermined range (that is, normal toner
-Within the standard range where it is judged that concentration control is performed)
Check if there is. Here, it is determined that it is within the reference range.
If not, step S_Ten, Toner density data
Is lower than the above reference value, and if higher
Is step S again₈Move to, and if low then the next step
S₁₁To actually replenish the toner. This toner supply is
The supply roll 18 shown in FIG.
The amount shall be replenished. Such toner density control
By the control, the developing unit 10a for normal particle size toner is
The first reference value V if attached_S1Based on toner density
Degree C₁(See FIG. 7) and also small particle size toner
Second when the developing device unit 10b for use is installed
Reference value V_S2Based on the toner density C₂(<C ₁)
To be done.

If it is determined in step S ₁ that the developing device unit 10 is not mounted, the toner density data falls within the reference range of both the first and second reference values in steps S ₄ and S ₅ . If it is determined that the toner density data is not within the reference range in step S ₉ , the process proceeds to step S ₇ .
An error is displayed on the display 32 (see FIG. 5).

Therefore, according to this embodiment, by selecting the high resolution mode, even when the developing unit 10b containing the small particle size toner T ₂ is mounted and the image formation is repeated, the normal particle size toner T _{Since the} toner density control is performed based on the second reference value that is larger than the first reference value for 1,
An appropriate toner concentration target value C ₂ (<C ₁ ) is maintained without the risk of toner scattering. As a result, it is possible to prevent the occurrence of toner contamination in the apparatus and the contamination of the output image as much as possible, and it is possible to perform stable image formation for a long period of time. As a result, it is possible to realize a device in which the developing device unit corresponding to each resolution can be exchanged with respect to the device in which the resolution can be switched, and it is expensive for high resolution when the normal resolution mode is executed in the above-mentioned switchable device. It is possible to eliminate waste such as using a small particle size toner.

In the above embodiment, the toner concentration sensor 1
Although the type of the developing device unit is determined based on the output voltage of 9 (see steps S ₄ and S _{5 of} FIG. 6), in addition to this,
For example, by providing a developer type detection switch 33 shown by a broken line in FIG. 5 and sending the detection output to the I / O circuit 28 via the input port P ₁ , the type of the developing unit based on the detection output. It is also possible to discriminate. As such a switch, for example, a mark, a color, a protrusion or the like that can identify the type of toner (toner particle size) contained in each developing device unit is provided, and this switch is provided with a plurality of optical sensors or micro switches. It is possible to adopt a configuration in which it is detected by such as. In such a case, if there are two types of developing device units, only one developer type detecting switch is provided by combining with the presence / absence detection of the developing device unit based on the detection output of the toner concentration sensor 19. Just enough. That is, it is possible to determine which unit is attached by setting the switch that is turned on and off as, for example, the first developing device unit 10a. In addition,
In the case of three types of developing device units, for example, two switches can be provided for detection.
Then, the processing of the toner density control when such a developer type detection switch 33 is provided is performed as shown in FIG. 8, for example. That is, first, in step S ₁ , whether or not the developing device unit 10 is mounted is determined based on the detection output of the toner concentration sensor 19 or the detection output of the developer type detection switch 33. When any one of the developing device units is installed, the developer type detecting switch 33 detects which of the two developing device units 10a and 10b is installed. determine on the basis of the output, followed by step S _3, the toner supply reference value corresponding to the determination result, that is, the development unit 1 for a normal particle size toner T ₁
If it is 0a, the first reference value V _{S1 is set} to the small particle size toner T
_In the case of the developing device unit 10b for ₂ , the second reference value V _S2 is written in the EEPROM 26. Thereafter, at step S ₅ to S _8, based on the reference value written in the above EEPROM 26, performs a normal toner supply processing similar to FIG. Incidentally, in the toner replenishing process in step S ₅ to S _8, although not shown in this figure, it goes without saying that the developer is agitated by the rotation of the main motor.

Further, FIG. 1 shows an example in which the upper machine body M ₂ is opened and the two types of developing device units 10a and 10b are manually replaced by the operator. It is also possible to automatically replace the developing device unit. For example, as shown in FIG. 9, a plurality of developing device units 10A that are movable in an elevator manner in the direction of arrow D at a position separated from the photosensitive drum 7,
10B, 10C, etc. are provided inside the apparatus main body, and for example, one unit corresponding to the resolution mode selected by the mode selection switch provided in the operation section can be horizontally separated from and contacted with the photosensitive drum 7 as shown by the broken line. With such a configuration, the units can be automatically replaced. By doing so, it is possible to realize a very convenient device that does not disturb the operator's hand.

Further, as the image forming apparatus whose resolution can be changed, a laser printer is shown as an example in the above embodiment, but the present invention can be applied to an apparatus which can change the resolution in the sub-scanning direction. In addition to the laser optical means, means using an LED array or the like can be adopted as means.

[0026]

According to the present invention, the toner density target value is changed according to the developer selected by switching the resolution, so that image formation is repeated with a small particle size toner for high resolution. However, since the target toner concentration target value that does not cause toner scattering is maintained, it is possible to prevent the occurrence of toner contamination in the apparatus and stains on the output image as much as possible, and to achieve stable image formation for a long period of time. It becomes possible to do. As a result, it is possible to realize a device capable of developing with toner having a particle size corresponding to each resolution, as compared with a device capable of switching resolution, and a device for high resolution when executing the normal resolution mode in the above-mentioned switchable device. It is possible to eliminate the waste of using expensive small particle size toner.

[Brief description of drawings]

FIG. 1 is an overall view of an image forming apparatus according to an exemplary embodiment of the present invention.

FIG. 2 is a sectional view of the developing device 10 in FIG.

3 is a circuit diagram of a toner concentration sensor 19 shown in FIG.

FIG. 4 is a diagram showing a relationship between an output voltage of a toner concentration sensor and an actual toner concentration.

FIG. 5 is a diagram showing a circuit configuration of a printer controller 21 provided in the image forming apparatus of the above embodiment and a connection configuration of the printer controller 21 and the toner density sensor 19.

6 is a flowchart showing a processing operation of toner density control by the printer controller 21 shown in FIG.

FIG. 7 is a diagram showing an example of a toner density target value set according to a toner particle size and a toner replenishment reference value corresponding to the toner density target value.

FIG. 8 is a flowchart showing a processing operation of toner density control in another embodiment of the present invention.

FIG. 9 is a diagram showing a configuration for automatic switching of a developing unit according to another embodiment of the present invention.

[Explanation of symbols]

7 Photoreceptor Drum 9 Print Head 10, 10a, 10b, 10A, 10B, 10C Developer Unit 18 Replenishing Roll 19 Toner Density Sensor 20 Replenishing Roll Controller 21 Printer Controller 23 CPU 24 ROM 25 RAM 26 EEPROM 27 A / D Converter 28 I / O circuit 33 Developer type detection switch

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Reference number within the agency FI Technical display location B41J 2/22 G03G 15/00 302 H04N 1/29 E 9186-5C (72) Inventor Shigeki Okawa Tokyo 2-229 Sakuragaoka, Yamato-shi, Tokyo Casio Electronics Industry Co., Ltd.

Claims (2)

[Claims] 1. A latent image containing a two-component developer, comprising a toner and a carrier, which is capable of forming a latent image with different resolutions by selecting a print mode, and which maintains a predetermined toner concentration target value. In the image forming apparatus for developing with a toner, a development mode selection that selectively enables development with a toner having a predetermined particle size among toners having different average particle sizes corresponding to the resolution according to the selection of the print mode. An image forming apparatus comprising: a unit and a unit for changing the predetermined toner concentration target value to be maintained according to a selected developer. 2. When the selected developer is selected from a plurality of developers having different toner average particle diameters, the toner density target value is changed to a smaller density value as the toner average particle diameter is smaller. The image forming apparatus according to claim 1.