JPH0720711A - Image forming device - Google Patents

Abstract

PURPOSE:To perform steady toner replenishment irrespective of the position where a toner concentration sensor is attached and, also, even when toner concentration changes. CONSTITUTION:The image forming device is provided with a toner concentration control part 26 which determines the target value Vref of toner concentration based on the output value of an image density sensor 10, further determines a toner replenishment rate based on a difference (VT-Vref) between the target value Vref and the output value VT of the toner concentration sensor 10, and makes a toner replenishment device carry out toner replenishment at the toner replenishment rate, and, an altering means 26 which detects a difference between the output values of the image density sensor 10 before and after the toner replenishment, and alters a relation between the (VT-Vref) and the toner replenishment rate based on the difference.

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 copying machine, a facsimile or a printer having a developing device using a two-component developer.

[0002]

2. Description of the Related Art An image forming apparatus such as a copying machine forms an electrostatic latent image on an image carrier, develops the electrostatic latent image with a two-component developer by a developing device, and then transfers it to a transfer agent. There is something to fix. In such an image forming apparatus, there is an image forming apparatus in which various image forming density controls are performed in order to stabilize the image quality. For example, a reference density pattern image is formed on an image carrier, the density is detected by a reflection type photo sensor, the detected value is compared with the reference value, and the result is used to develop from the toner replenishing device to the developing device. Controls the toner replenishment to the developer, detects the mixture ratio of the toner and carrier of the developer in the developing device as an inductance change and feeds it back to the toner replenishing device, and detects the current flowing in the developer. Then, there are various types such as a type that feeds back to the toner replenishing device. Since each of them has advantages and disadvantages, many control methods are adopted.

In Japanese Patent Laid-Open No. 53-119051, a toner concentration in the developer is measured in an electrophotographic apparatus using a developer composed of at least a carrier and a toner, and the measured value is predetermined. When the signal becomes lower than the lower limit of the toner concentration range, a toner replenishment signal is generated, and when this signal is generated, a fixed amount of toner required to reach the upper limit of the toner concentration range is replenished in the developer. A method for controlling toner concentration is described in which the operation of the toner replenishment signal is stopped at least immediately after the generation of the signal until the completion of toner replenishment.

Further, there has been proposed an image forming apparatus in which image density control is performed by a combination of a toner density sensor and an image density sensor. In this image forming apparatus, a reference density pattern image is formed on the image carrier once per 100 images, and the output value V _SG of the image density sensor for only the image carrier and the image density on the image carrier. The reference voltage V _C is shifted according to the ratio of the output value V _SP of the image density sensor to the reference density pattern image of the toner image, and the toner is replenished with the difference (V ₀ −V _C ) between the output values V ₀ and V _C of the toner density sensor. Turns on / off toner supply by the device.

[0005]

In the toner density control method, since the operation of the toner replenishment signal is stopped immediately after the toner replenishment signal is generated until the toner replenishment is completed, the toner replenishment depends on the development in the high-speed image forming apparatus. Problems such as not following changes in toner density due to toner consumption occur. In the above image forming apparatus, since the relationship between (V ₀ −V _C ) and toner supply is fixed, for example, when a ripple occurs in the output value V ₀ of the toner density sensor due to toner supply, the toner supply is stabilized. Can not be done.

Further, in the above image forming apparatus, when the toner concentration sensor is installed near the toner replenishment position of the developing device at a position where the amount of developer is small, the toner concentration sensor for the toner replenished by the toner replenishment device is detected. the reaction is large, the output value V _T and the toner replenishment of the toner density sensor is as shown in FIG. 10, the output value V _T of the toner density sensor is highly variable. Amount of developer in the developing device
When (bulk) is sufficient, the output value V of the toner concentration sensor
_T and toner replenishment are as shown in FIG. 11, and the fluctuation of the output value V _T of the toner concentration sensor with respect to toner replenishment is small.

When toner is supplied to the developer in the developing device by the toner replenishing device based on the output value V _T of the toner concentration sensor, if the output value V _T of the toner concentration sensor fluctuates greatly as shown in FIG. Toner replenishment control varies greatly, and proper toner replenishment cannot be performed. Therefore, when the toner concentration sensor is attached to the developing device, the toner concentration sensor must be attached at a position where the bulk of the developer is sufficiently large, but it is unavoidable due to restrictions such as layout and the like. In some cases, it is not possible to properly supply toner because the sensor must be attached.

Further, in a place near the toner replenishment position where the developer bulk is not sufficiently large, the developer bulk is apt to change depending on the toner concentration, so that the output value V _T of the toner concentration sensor and the toner replenishment amount are If the relationship is uniquely determined, the output value V _T of the toner concentration sensor fluctuates greatly as shown in FIG. 10 on the side where the toner concentration is low, and proper toner supply cannot be performed.

The present invention solves the above-mentioned drawbacks and enables stable toner supply regardless of the mounting position of the toner density sensor, and image formation capable of stable toner supply even if the toner density changes. The purpose is to provide a device.

[0010]

To achieve the above object, the invention according to claim 1 forms an electrostatic latent image on an image carrier and develops the electrostatic latent image with a developer by a developing device. And a toner replenishing device for replenishing the developer in the developing device with toner, and a toner concentration of the developer in the developing device. A toner density sensor for detecting, an image density sensor for detecting the density of the reference density pattern image formed on the image carrier, and a target value Vref of the toner density is determined based on the output value of the image density sensor. the difference between the target value Vref and the output value V _T of the toner density sensor (V _T -Vref)
And a toner density control unit for causing the toner replenishing device to replenish the toner at the toner replenishing rate based on the above-mentioned, the output of the image density sensor before and after the toner replenishing by the toner replenishing device. by detecting the difference between the values it is obtained comprising a changing means for changing the relationship between the (V _T -Vref) and the toner replenishment rate by this difference.

[0011] According to a second aspect of the invention, in the image forming apparatus according to claim 1, the toner supply and the (V _T -Vref) in accordance with the absolute value of the output value V _T of the changing means the toner density sensor It changes the relationship with the rate.

[0012]

In the invention described in claim 1, the toner replenishing device is presently used.
Toner is replenished to the developer in the image device to develop in the developing device.
The toner concentration of the agent is detected by the toner concentration sensor.
The density of the reference density pattern image formed on the image carrier is
It is detected by the image density sensor. The toner concentration control unit
Target value of toner density based on the output value of the image density sensor
Vref is determined, and this target value Vref and the toner density sensor output
Force value V_TDifference with (V _T-Vref) based on the toner replenishment rate
Determine the toner replenishment rate with this toner replenishment rate
Let it be done. The changing means is the toner supplied by the toner replenishing device.
Detects the difference in output value of the image density sensor before and after replenishment
However, due to this difference (V_T-Vref) and toner replenishment rate
To change.

[0013] In the present invention of claim 2, wherein, in the image forming apparatus according to claim 1, the changing means in accordance with the absolute value of the output value V _T of the toner density sensor and (V _T -Vref) and the toner replenishment rate Change the relationship.

[0014]

FIG. 2 shows the outline of one embodiment of the present invention. The image carrier 11 composed of a photosensitive drum is rotationally driven by a driving unit and uniformly charged by a charging device 12, and then an optical image is exposed by an exposure device to form an electrostatic latent image, and an unnecessary portion is erased by the eraser 13. Is discharged. The electrostatic latent image on the photosensitive drum is developed into a toner image by the developing device 14 with a two-component developer including toner and carrier. The transfer belt 15 is pressed against the photoconductor drum 11 at the time of copying operation by a contacting / separating device (not shown), and at the same time, a transfer bias is applied from the transfer bias power source. Away from the photosensitive drum 11.

The transfer paper fed from the paper feeding device is conveyed by the transfer belt 15 and passes through the nip portion between the photoconductor drum 11 and the transfer belt 15 so as to pass through the photoconductor drum 1.
The toner image on 1 is transferred, and the toner image is fixed by a fixing device (not shown). The residual toner is removed from the photosensitive drum 11 by the cleaning device 16 after the toner image is transferred.

Further, after the copying operation is completed, the transfer belt 1
The reference numeral 5 is released from the photosensitive drum 11 by releasing the pressure contact with the photosensitive drum 11 by a contacting / separating device (not shown), and a reference density pattern image is formed on the photosensitive drum 11. That is, the photoconductor drum 11 is rotationally driven by the driving unit and uniformly charged by the charging device 12, and then the light image of the reference density pattern image is exposed by the exposure device to form an electrostatic latent image. The unnecessary parts are eliminated. The electrostatic latent image on the photosensitive drum is developed with a two-component developer by the developing device 14 to become a toner image of the reference density pattern image, and the density thereof is optically transferred by the image density sensor 10 without being transferred to the transfer paper. It is detected and removed by the cleaning device 16.

In the developing device 14, the two-component developer 1 composed of toner and carrier in the developing tank 17 is used.
8 is stirred by the stirrer 19 and conveyed to the developing roller 20, and the developing roller 20 magnetically attracts the developer to form a magnetic brush. The agitator 19 and the developing roller 20 are rotationally driven by a driving unit, and the developer on the developing roller 20 is
The (magnetic brush) is conveyed along with the rotation of the developing roller 20 and is partially scraped off by the doctor member 21 so that the magnetic brush is regulated to a certain amount, and then the developing area between the photosensitive drum 11 and the developing roller 20. And the electrostatic latent image on the photosensitive drum 11 is developed.

The developer scraped off from the developing roller 20 by the doctor member 21 falls into the developing tank 17 through the separator 22, and the developer on the developing roller 20 passes into the developing tank 17 after passing through the developing area. Return. As described above, the developer in the developing tank 17 is used for developing the electrostatic latent image on the photosensitive drum 11 while circulating. Further, the toner replenishing device 23 replenishes the toner in the toner tank 17 onto the developer 18 in the developing tank 17 by the rotation of the toner replenishing roller 24, and the toner is mixed with the developer 18 by the agitator 19. To be done. The toner concentration sensor 25 is attached to the developing tank 17 and detects the toner concentration of the developer in the developing tank 17.

FIG. 1 shows a part of the circuit configuration of this embodiment.
Control unit 26 configured using a microcomputer
Takes in the input signals from the toner density sensor 25 and the image density sensor 10 and performs A / D conversion, and controls the toner replenishment motor 28 via the driver 27. Also, the control unit 2
Reference numeral 6 captures an input signal from the operation unit or the like and controls each unit of the present embodiment to control the copying operation and the like.

FIG. 4 shows a part of the processing flow of the control unit 26. Immediately after the copying operation is completed, the control unit 26 controls the contact / separation mechanism to release the pressure contact of the transfer belt 15 with respect to the photoconductor drum 11 to separate the transfer belt 15 from the photoconductor drum 11, and the exposure device is exposed. Standard density pattern image (P
The sensor pattern) is exposed on the transfer belt 15. In this case, the photosensitive drum 11 is rotationally driven by the driving unit and uniformly charged by the charging device 12, and then an electrostatic latent image is formed by the exposure of the reference density pattern image by the exposure device, and the eraser 13 eliminates unnecessary portions. To be done. The electrostatic latent image on the photosensitive drum is developed with a two-component developer by the developing device 14 to obtain a toner image of a reference density pattern image.

This reference density pattern image is transferred to the transfer belt 15
The image density sensor 10 optically detects the density of the reference density pattern image on the photoconductor drum 11. Further, the reference density pattern image on the photosensitive drum 11 is removed by the cleaning device 16. Control unit 26
Takes in the output value V _SP of the image density sensor 10 with respect to the reference density pattern image on the photosensitive drum 11, the V _SP
The toner concentration target value Vref is shifted based on
The relationship between V _SP and V ref is table L, as shown in FIG.
It is stored in the non-volatile memory as N, H, HH,
The control unit 26 refers to the table and shifts the toner concentration target value Vref based on V _SP . For example, when the table N is selected and set, V _SP is 0.55.
If it is V, Vref is changed by -0.1V.

The control unit 26 controls the contact / separation mechanism to move the transfer belt 15 to the photosensitive drum 11 during the copying operation.
And the output value V _T with respect to the toner concentration of the developer 18 in the developing device 14 detected by the toner concentration sensor 25 is fetched. Next, the control unit 26 sets the toner supply rate based on the difference (V _T -Vref) with Vref set immediately after the copying operation ends and its V _T, controls the toner supply motor 28 via the driver 27 Then, the toner supply by the toner supply roller 24 of the toner supply device 23 is controlled.

The relationship between (V _T -Vref) and the toner replenishment rate table L as shown in FIG. 6, N, H, is stored in nonvolatile memory as HH, control unit 26 refers to the table Te (V _T -Vref) on the basis to control the toner supply, for example Vref when the table N is set is selected = 2.50 V, V _T = at 2.65V (V _T -
Vref) = 0.15V, the toner replenishment rate is set to 45% and the toner replenishment rate by the toner replenishing roller 24 is 45%.
The toner replenishment motor 28 is controlled so as to become%. The control unit 26 repeatedly performs such processing during the copying operation until the copying operation for the set number of sheets is completed.

FIG. 3 shows another processing flow of the control unit 26. In this embodiment, a fixed amount supply mode is provided,
This quantitative supply mode is executed when the machine is installed. In the fixed amount replenishment mode, the control unit 26 starts detecting the output value V _T from the toner concentration sensor 25, controls the toner replenishment motor 28 via the driver 27, and replenishes 60% of the toner three times. After that, the output value V from the toner density sensor 25
End detection of _T. In this case, V _T changes as the toner is replenished as shown in FIG.

[0025] Then, the control unit 26, the difference between the upper limit value V _Tmax and the lower limit value V _Tmin of V _T has been detected just the (V _Tmax -V _Tmin) determined, table based on the (V _Tmax -V _Tmin) L,
Set N, H, HH (setting of toner replenishment rate). (V
The relationship between _Tmax- V _Tmin ) and the tables L, N, H, HH is stored in the nonvolatile memory as a table as shown in FIG. 7, and the control unit 26 refers to the table (V
_{One of} the tables L, N, H, and HH is selected and set based on ( _Tmax− V _Tmin ). This setting table is used for controlling toner supply as described above. At this time, V
ref remains the same.

By the way, since the toner density sensor 25 is installed near the toner replenishment position, for example, when the machine is installed tilted, the developer in the developing device 14 tilts and the toner density sensor 25 is placed on the toner density sensor 25. The bulk of the developer changes,
When the developer on the toner concentration sensor 25 is low, when the toner is replenished by the toner replenishing roller 24, V _T
Change becomes large, and the variation in toner concentration control is shown in Fig. 1.
It becomes large as shown in 0.

That is, when a large amount of toner is replenished by the toner replenishing roller 24 as shown by * 1 in FIG. 10, the influence thereof appears in the output value V _T of the toner concentration sensor 25 with a time lag. Therefore, the toner density is detected as if the toner density is very high at the time of V _T detection by the control unit 26 next time, and the toner density control using the table shown in FIG. The amount of toner replenishment required will be selected. When a small amount of toner continues to be supplied, V _T rises with a time lag as shown by * 2 and * 3 in FIG. 10, and the control unit 26 detects that the toner concentration is low and supplies more toner than necessary. will have to go.

[0028] However, in the present embodiment, changes the relationship by selecting and setting the table when the machine installation when the developer on the toner density sensor 25 is small and (V _T -Vref) and the toner replenishment rate As a result, stable toner supply can be performed even if V _T changes significantly due to toner supply.
Since changing the relationship between the toner supply rate table N, by selecting and setting H or HH and (V _T -Vref) when the machine installation when the developer on the toner density sensor 25 is not low, developing The toner can be replenished properly according to the toner consumption. Therefore, stable toner supply can be performed regardless of the mounting position of the toner concentration sensor.

In another embodiment of the present invention, in the above embodiment, the control unit 26 sets a table according to the absolute value of V _T when performing V _T detection as described above during the copying operation. the change to change the relationship between the toner replenishment rate (V _T -Vref). The relationship between V _T and the tables L, N, H and HH is stored in the non-volatile memory as a table as shown in FIG. 8, and the control unit 26 refers to the table and based on V _T the table L, Change the N, H, HH settings. For example, when V _T is V _T <1.0 V, the control unit 26
Selects and sets table L. This setting table is used for controlling toner supply as described above.

Since the toner concentration sensor 25 is installed near the toner supply position, the toner concentration sensor 25
When the amount of the upper developer is small, the bulk of the developer on the toner concentration sensor 25 changes depending on the toner concentration, which easily affects V _T. For example, the toner concentration is low and the toner concentration sensor 2
When the bulk of the developer on No. 5 is reduced, the toner replenishment rate varies in the above-described embodiment as in the case where the amount of the developer is reduced. However, in this embodiment, since changing the relationship between the change the settings of the table (V _T -Vref) and the toner replenishment rate according to V _T, to perform stable toner replenishment even Hen' toner concentration You can

[0031]

As described above, according to the first aspect of the invention, an electrostatic latent image is formed on the image bearing member, and the electrostatic latent image is developed with a developer by a developing device to form a toner image. An image forming apparatus for transferring this toner image onto a transfer material, which comprises a toner replenishing device for replenishing the developer in the developing device with toner, and a toner concentration sensor for detecting the toner concentration of the developer in the developing device. And an image density sensor for detecting the density of the reference density pattern image formed on the image carrier, and a target value Vref of the toner density is determined based on the output value of the image density sensor. in those having a toner concentration control unit to perform the toner replenishing apparatus toner supply in the toner replenishment rate determined toner replenishment rate based on the difference between the output value V _T of the toner density sensor (V _T -Vref) , The toner supply Because with a changing means for changing the relationship between the this difference by detecting a difference between the output value of the image density sensor before and after the toner supply (V _T -Vref) and the toner replenishment rate by the device, the toner density sensor The toner can be replenished more stably regardless of the mounting position.

According to the second aspect of the present invention, in the image forming apparatus according to claim 1, wherein the changing means in accordance with the absolute value of the output value V _T of the toner density sensor (V _T -V
Since the relationship between ref) and the toner replenishment rate is changed, stable toner replenishment can be performed even if the toner concentration changes.

[Brief description of drawings]

FIG. 1 is a block diagram showing a part of a circuit configuration of an embodiment of the present invention.

FIG. 2 is a sectional view showing the outline of the embodiment.

FIG. 3 is a flowchart showing a part of a processing flow of a control unit in the embodiment.

FIG. 4 is a flowchart showing another part of the processing flow of the control unit in the embodiment.

FIG. 5 is a diagram showing a table used in the embodiment.

FIG. 6 is a diagram showing another table used in the embodiment.

FIG. 7 is a diagram showing another table used in the embodiment.

FIG. 8 is a diagram showing another table used in the embodiment.

FIG. 9 is a timing chart showing the operation timing of the embodiment.

FIG. 10 is a timing chart showing operation timings of the conventional device and the above-described embodiment.

FIG. 11 is a timing chart showing another operation timing of the conventional device.

[Explanation of symbols]

 10 Image Density Sensor 25 Toner Density Sensor 26 Control Unit 27 Driver 28 Toner Supply Motor

Claims (2)

[Claims] 1. An electrostatic latent image is formed on an image carrier, and the electrostatic latent image is developed with a developer by a developing device to form a toner image,
An image forming apparatus for transferring this toner image onto a transfer material, comprising a toner replenishing device for replenishing the developer in the developing device with toner, and a toner concentration sensor for detecting the toner concentration of the developer in the developing device. , An image density sensor that detects the density of a reference density pattern image formed on the image carrier, and a target value Vref of the toner density is determined based on the output value of the image density sensor. The target value Vref and the toner in those having a toner concentration control unit to perform the toner replenishing apparatus toner supply in the toner replenishment rate determined toner replenishment rate based on the difference between the output value V _T of the density sensor (V _T -Vref), changing means for changing the relationship between the toner supply device wherein the difference by detecting a difference between the output value of the image density sensor before and after the toner supply according to (V _T -Vref) and the toner replenishment rate An image forming apparatus characterized by comprising. 2. An image forming apparatus according to claim 1, changes the relationship between the (V _T -Vref) and the toner replenishment rate the changing means in accordance with the absolute value of the output value V _T of the toner density sensor An image forming apparatus comprising: