JP2003280355A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To carry out a stable toner concentration control even when the linear velocity of a process is varied. <P>SOLUTION: Output value from a toner concentration sensor is adjusted to be a specified output value in standard toner concentration when warming up, action to store that adjusted value is carried out for each linear velocity of the process and toner replenishing control is carried out by calling the adjusted value from memory when printing operation is carried out. <P>COPYRIGHT: (C)2004,JPO

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 for forming an image on a recording material by an electrophotographic method, and more particularly to an image forming apparatus for developing using a two-component developer.

[0002]

2. Description of the Related Art In an example of an image forming process for forming an image by an electrophotographic method, an electrostatic latent image is formed on an image bearing member such as a photoconductor, and the formed electrostatic latent image is developed by a developing means. A toner image is formed on the image carrier, the formed toner image is transferred to a recording material by a transfer unit, and the transferred toner image is fixed on the recording material by a fixing unit to form an image on the recording material. In another example, a toner image on an image forming body such as a photoconductor is transferred to an intermediate transfer body as an image carrier, and then transferred from the intermediate transfer body to a recording material by a transfer means to be fixed, thereby recording the recording material. To form an image.

In the developing step in the image forming step,
Development using a two-component developer containing toner and carrier is often used, and a development bias voltage in which a DC bias is superimposed on an AC bias is often applied.

In the development using the two-component developer, only the toner is consumed by the development, so it is necessary to replenish the toner in an appropriate amount corresponding to the consumed amount. Toner replenishment is performed by detecting the ratio of toner to carrier in the developing device by means of toner concentration detecting means for detecting the magnetic permeability of the developer, and detecting that the toner ratio (toner concentration) has dropped below a predetermined ratio. Toner replenishment control for replenishment is performed. The toner and carrier in a predetermined ratio in the developing device are agitated and frictionally charged, the toner charged by mutual friction is electrostatically attached to the carrier, and the carrier electrostatically attached to the toner is developed by magnetic force. The latent image on the image carrier is attached to the peripheral surface of the roller, is conveyed to the developing nip portion, and a developing bias voltage is applied in the developing nip portion to develop the latent image on the opposing image carrier.

Since a color image is formed by superposing toner images of four colors of Y, M, C and K to form a color image, the fixing property is poor as compared with a single color image, and it is necessary to reduce the fixing speed for a color image. Especially, when a color image is formed on thick paper or the color image is made to retain glossiness, it is necessary to further reduce the linear velocity of the conveyed recording paper. In the color image forming apparatus, the linear velocity is switched to a plurality of stages according to the use.

[0006]

In the image forming apparatus, the drive means for the image carrier and the drive means for agitating the developer in the developing device and transporting the developer to the developing nip portion are common drive means. I often do it. When the image forming apparatus is driven by the same driving unit, the rotation speed of the driving unit of the developing device is changed as well as the speed of the image carrier for the purpose of changing the linear velocity of image formation.

In an image forming apparatus that controls the toner replenishment by detecting the magnetic permeability of the developer, the output also changes when the linear velocity of the stirring member in the developing device changes.
Correct toner supply control cannot be performed.

The object of the present invention is to properly control the toner density regardless of the operating condition such as the process linear velocity change of the image forming apparatus, the deterioration condition of the developer, the environmental change, and the like, thereby causing the fog and the toner scattering. An object of the present invention is to provide an image forming apparatus that prevents problems such as carrier adhesion.

[0009]

The above object of the present invention is achieved by the following image forming apparatus.

1. An image carrier that forms a latent image, a developing roller that conveys a developer that visualizes the latent image to a developing nip portion, a toner density detecting unit that detects the magnetic permeability of the developer, and the toner density. A toner replenishing means for replenishing the developer with toner according to the detection result of the detecting means, an agitating means for agitating the replenishment toner from the toner replenishing means, and a supplying means for supplying the developer to the developing roller. And a driving means for driving at least the image carrier, the supplying means and the stirring means of the image bearing member and the stirring means is a common driving means, and it is possible to switch the process linear velocities in a plurality of stages, In an image forming apparatus having a control unit for driving and controlling the driving unit and the toner replenishing unit, at the time of warming up, the process linear velocity is set to a standard linear velocity to obtain an appropriate toner density. An image forming apparatus characterized in that the sea urchin toner density control.

2. An image carrier that forms a latent image, a developing roller that conveys a developer that visualizes the latent image to a developing nip portion, a toner density detecting unit that detects the magnetic permeability of the developer, and the toner density. A toner replenishing means for replenishing the developer with toner according to the detection result of the detecting means, an agitating means for agitating the replenishment toner from the toner replenishing means, and a supplying means for supplying the developer to the developing roller. And a driving means for driving at least the image carrier, the supplying means and the stirring means of the image bearing member and the stirring means is a common driving means, and it is possible to switch the process linear velocities in a plurality of stages, In an image forming apparatus having a control unit for driving and controlling the driving unit and the toner replenishing unit, the sensor output value from the toner concentration detecting unit is set to the standard toner concentration when warming up. At the time of print operation, the control unit adjusts the process linear velocity from the memory by adjusting the output value to a predetermined sensor output value and storing the adjusted value in the memory for each process linear velocity. An image forming apparatus characterized in that a toner replenishment control is performed by calling a value and using the called adjustment value.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (1) An image forming apparatus to which the present invention is applied will be described.

A color image forming apparatus shown as an embodiment of the present invention forms toner images composed of yellow (Y), magenta (M), cyan (C) and black (K) toners on a plurality of image carriers, respectively. A tandem type color image forming apparatus in which toner images formed and formed on a plurality of image bearing members are superposed on a transfer material via an intermediate transfer member or directly.

The color image forming apparatus shown in the cross-sectional view of FIG. 1 is a tandem system in which toner images formed on an image carrier are transferred to an intermediate transfer member in an overlapping manner, and the superimposed toner images are collectively transferred. Type color image forming apparatus, a plurality of sets of image forming units 10Y, 10M, 10C, 1
0K, an intermediate transfer unit 7, a sheet feeding / conveying unit and a fixing unit 24. A document image reading device SC is arranged above the image forming apparatus main body (hereinafter referred to as the apparatus main body) A.

Image forming unit 1 for forming a yellow image
0Y has a charging unit 2Y, an exposing unit 3Y, a developing unit 4Y, a primary transfer unit 5Y, and a cleaning unit 6Y arranged around an image carrier (photoconductor) 1Y. The image forming unit 10M that forms a magenta image includes an image carrier (photoconductor) 1M, a charging unit 2M, an exposing unit 3M, and a developing unit 4.
M, primary transfer means 5M, and cleaning means 6M. The image forming unit 10C that forms a cyan image includes an image carrier (photoconductor) 1C, a charging unit 2C, an exposing unit 3C,
Developing means 4C, primary transfer means 5C, cleaning means 6
Has C. The image forming unit 10K that forms a black image,
Image carrier (photoreceptor) 1K, charging means 2K, exposure means 3
K, developing means 4K, primary transfer means 5K, and cleaning means 6K. In each image forming unit 10, charging, exposure and development are performed to form an image of each color on the image carrier 1.

The intermediate transfer unit 7 has a semiconductive endless belt-shaped intermediate transfer member 70 which is wound by a plurality of rollers and is rotatably supported.

Image forming units 10Y, 10M, 10C, 10
The image of each color formed by K is transferred to the primary transfer means 5Y, 5
By M, 5C, and 5K, a superimposed color image is transferred onto the rotating intermediate transfer member 70 in synchronism with each other and sequentially superimposed and transferred. A recording medium (hereinafter, referred to as paper) P housed in the paper feeding cassette 20 is a paper feeding unit 21.
Is fed by a plurality of intermediate rollers 22A, 22B, 2
The color images superposed on the paper P are collectively transferred by being conveyed to the secondary transfer unit 5A via the 2C and 22D and the registration roller 23. Paper P on which a color image has been transferred
Is subjected to a fixing process by the fixing means 24, and the paper discharge roller 25
The sheet is sandwiched between the sheets and placed on the sheet discharge tray 26 outside the machine.

On the other hand, after the color image is transferred onto the paper P by the secondary transfer means 5A, the residual toner is removed by the cleaning means 6A from the intermediate transfer body 70 obtained by separating the curvature of the paper P.

During the image forming process, the primary transfer means 5K is constantly in pressure contact with the photoreceptor 1K. Other primary transfer means 5
Y, 5M and 5C are pressed against the corresponding photoconductors 1Y, 1M and 1C only when forming a color image.

The secondary transfer means 5A comes into pressure contact with the intermediate transfer member 70 only when the sheet P passes through the secondary transfer means 5 and secondary transfer is performed.

(2) FIG. 2 shows a set of image forming units 10 taken out. An OPC photosensitive member or the like is used as the drum-shaped photosensitive member 1 as an image bearing member that rotates in the arrow direction,
Uniform charging is performed by the charging means 2 using a scorotron charger or the like. As the exposure means 3, an exposure means for performing dot exposure such as a laser or a light emitting diode is used, and an electrostatic latent image is formed by the image exposure of the exposure means 3. Subsequent to the latent image forming step, development is performed by the developing unit 4 which will be described in detail below, and the electrostatic latent image becomes a toner image. The photoconductor 1 and the developing means 4 are driven by a motor which is the same driving means.

In the image forming apparatus of the present embodiment, the process linear velocity can be switched to a plurality of stages. For example, the process linear velocity is (1/2) velocity with respect to the standard linear velocity (1/1) velocity,
Switching drive to (1/3) speed is possible. When the standard linear velocity is 220 mm / s, the linear velocity is 110 mm / s,
The linear velocity is variable to 73 mm / s. In the following description, such a variable case will be described. Of course, the present invention can be applied to other multistage switching.

(3) The developing means 4 includes a developing device frame 40,
A developer carrier 41 composed of a developing roller, a magnetic field generating means (magnet roll) 42, a regulating means 43 composed of an ear cutting plate, a water wheel type supply means 44, a supply / conveyance means 45 composed of a screw, and an agitation / conveyance composed of a screw. Means 4
6, a conveying roller 47, a stripping plate 48, a collecting means 49 including a screw, and the like, and is driven by a motor that is the same driving means as the photoconductor 1.

The developer carrying member 41 is arranged so as to face the photoconductor 1 and is rotatably supported. The developer carrying member 41 rotates as indicated by an arrow to convey the developer to the developing nip portion DR, and the developing nip portion DR. In the DR, a developer is carried to form a layer of the developer necessary for development.

The supplying means 44 is a rotatable water wheel type conveying means for supplying the developer to the developer carrying body 41, and the developer carried from the supplying / conveying means 45 is supplied to the developer carrying body 4.
The developer is uniformly supplied in the vicinity of the developer receiving magnetic pole S3.
The supply means 44 may be a screw having a conveying function in the rotation axis direction.

The supplying / conveying means 45 is arranged in parallel with the supplying means 44, and conveys the developer conveyed from the stirring / conveying means 46 to the supplying means 44 while conveying the developer in the rotation axis direction thereof.

The stirring / conveying means 46 mixes the new toner to be replenished with the developer refluxed from the supplying / conveying means 45, agitates them, and conveys them to the upstream portion of the supplying / conveying means 45.

A conveying roller 47 is arranged near the developer stripping magnetic pole S2 of the developer carrier 41. The transport roller 47 is a rotatable rotating member (sleeve) 47.
A and the developing device frame 4 housed inside the rotating member 47A.
It is composed of a cylindrical magnet body 47B fixed to 0.

The collecting means 49 rotatably arranged in the collecting section 403 collects the developer which is peeled off by the conveying roller 47 and the peeling plate 48 and drops, and supplies it.
The developer is carried to the downstream side of the carrying means 45 in the carrying direction and to the outside of the image forming area of the developer carrying body 41. At the position where the developer does not return to the developer carrier 41, the collected developer is put in the developing region of the developer carrier 41 on the downstream side in the transport direction of the supply / transport means 45. Good. Alternatively,
The developer collected by the collecting means 49 may be returned to the upstream portion of the stirring / conveying unit 402.

Supply / transport means 45, stirring / transport means 46
Each of the collecting means 49 and the collecting means 49 is composed of a spiral screw, conveys the developer in the rotation axis direction while stirring, and discharges the developer in a direction substantially perpendicular to the rotation axis.

The developing device frame 40 includes a developer carrier 41,
A lower frame 40A that supports the transport roller 47, the supply unit 44, the supply / transport unit 45, and the stirring / transport unit 46, and an inner frame 40B that supports the stripping plate 48 and the recovery unit 49.
And an upper lid 40C that closes the upper opening of the middle frame 40B.

The lower frame 40A forms a supply section 401 for accommodating the supply means 44 and the supply / conveyance means 45, and a stirring / conveyance section 402 for accommodating the stirring / conveyance means 46. The supply unit 401 and the stirring / conveying unit 402 are formed on both sides with the first partition wall 404 standing upright from the bottom of the lower frame 40A.

The second partition wall 405 formed at the bottom of the middle frame 40B for rotatably supporting the collecting means 49 is provided by the supply section 4.
01 and the collection unit 403 are partitioned. Further, a part of the middle frame 40B closes the upper opening of the stirring / conveying unit 402.

The developer transport downstream side of the recovery section 403 and the developer transport downstream side of the supply section 401 communicate with each other through a first opening 406 formed near the end of the second partition 405.

Stirring with the developer conveying downstream side of the supply unit 401
The developer transport upstream side of the transport unit 402 means the first partition 404.
An opening (not shown) provided near one end of one of the two communicates with each other.

The developer stripped off by the transport roller 47 and the stripping plate 48 is collected in the collection unit 403, and the collected developer is transported to the downstream side of the developer transport by the collection unit 49, and further, the supply unit 401. Reflux to.

The developer in the supply section 401 is fed into the stirring / transfer section 402 by an arrow W from an opening (not shown) formed in one end of the first partition 404 by the supply / transfer means 45.
It is conveyed as indicated by 1. The developer conveyed into the stirring / conveying section 402 is mixed and stirred by the stirring / conveying means 46 with the toner discharged from the toner container 40T and replenished from the toner replenishing opening 409, and then conveyed. And is discharged from an opening (not shown) formed at the other end of the first partition 404, and the arrow W2 is drawn in the supply unit 401.
It is refluxed as shown in. In the supply unit 401, supply
The developer is discharged while being transported in the axial direction by the transport unit 45 and is supplied to the supply unit 44. The supply unit 44 radiates the developer while conveying the developer in the axial direction to supply the developer to the developer carrier 41.

B (DC) is a DC bias power source for applying a DC bias to the developer carrying member 41, and D (AC) is an AC bias power source for applying an AC bias to the developer carrying member 41, which is controlled by a control unit described later. Then, the AC bias is superimposed on the DC bias and applied, and the development is performed.

The developing means 4 of the image forming apparatus according to the present embodiment develops using a two-component developer containing toner and carrier.

The toner has a mass average particle diameter of 3 to 8 μm.
m polymerized toner is preferred. By using the polymerized toner, it is possible to form an image having a high resolution and a stable density and very little fog.

The polymerized toner is manufactured by the following manufacturing method. The formation of the binder resin for the toner and the shape of the toner are obtained by polymerizing the raw material monomer or prepolymer of the binder resin and the subsequent chemical treatment. More specifically, it is obtained through a polymerization reaction such as suspension polymerization or emulsion polymerization and, if necessary, a fusion step of particles to each other, and in a polymerized toner, a raw material monomer or a prepolymer is uniformly dispersed in an aqueous system. By polymerizing the toner later, a toner having a uniform particle size distribution and shape can be obtained.

In the present embodiment, the mass average particle size is 3
-8 μm toner is used. The mass average particle diameter is an average particle diameter on a mass basis, and is a value measured by a "Coulter Counter TA-II" or a "Coulter Multisizer" (both manufactured by Coulter, Inc.) equipped with a wet disperser.

If the mass average particle diameter is less than 3 μm, fogging and toner scattering are likely to occur. The upper limit of 8 μm is the upper limit of the particle size that enables formation of high image quality that is the target of the present embodiment.

The carrier has a mass average particle diameter of 30 to
A carrier composed of magnetic particles having a magnetization amount of 65 μm and a magnetization amount of 20 to 70 emu / g is preferable. Carriers having a particle size smaller than 30 μm easily cause carrier adhesion. Also,
With a carrier having a particle size larger than 65 μm, a uniform density image may not be formed in some cases.

(4) A toner concentration sensor SD for detecting the magnetic permeability of the developer to detect the toner concentration in the developer is provided inside the developing means 4, and when the sensor output exceeds the threshold value. The toner is supplied from the toner container 40T. When the linear velocity in the developing means 4 changes, the sensor output of the toner concentration sensor SD changes with the change in the linear velocity,
Correct toner supply control is not performed.

In FIG. 3, the control voltage Vc value for the toner density sensor SD is kept constant, and the process linear velocities are standard linear velocity (220 mm / s) and (1/2) velocity (110 mm /).
s) and (1/3) speed (73 mm / s), the sensor output value changes and the sensor output transition depending on the copy number are shown. FIG. 3 shows that the output value of the toner density sensor SD increases when the linear velocity is decreased.

In order to perform the correct toner supply control, the sensor output for each linear velocity is corrected so as to have a correct output value during the initial adjustment. The details will be described below.

When the initial developer is charged, the linear velocity of the drum is 220 m for the toner density sensors SD for each of Y, M, C and K colors.
A control voltage Vc value at which the sensor output becomes a threshold value of 2.5 V is determined for a predetermined toner density (for example, toner density Tc = 8 mass%) for each linear velocity of m / s, 110 mm / s, and 73 mm / s. There is. (Table 1)

[0049]

[Table 1]

The determined control voltage Vc value is stored in the non-volatile memory, and when the toner density is detected, the control voltage Vc value stored in the non-volatile memory is called and applied to the toner density sensor SD to obtain the sensor output.

Table 2 shows the sensor output for each linear velocity and the control toner density at that time in the initial stage.

[0052]

[Table 2]

As is clear from Table 2, the toner concentration is initially controlled to be about 8% by mass. The control voltage Vc for each linear velocity as shown in Table 1
If the correction is not performed, the toner concentration Tc will be increased by the increase in the sensor output.

In the initial adjustment, good toner is replenished, but if the temperature / humidity environment changes or the deterioration of the developer progresses, the sensor output will move and the toner will not be replenished satisfactorily.

(5) The invention of claim 1 will be described.
In the present invention, the process linear velocity is set to the standard linear velocity (220 mm / s) at the time of warming up, and the toner concentration is controlled so that the toner concentration is appropriate at the standard linear velocity (Tc = 8 mass%). 4 shows a control block diagram of the present invention.

When the power switch C12 is turned on, the control section C11 detects the temperature of the fixing temperature sensor C13 provided in the fixing roller portion of the fixing means 24. When the detected sensor temperature is below a predetermined temperature, the temperature sensor is detected. During the warm-up time until the temperature detected by C13 rises to a predetermined temperature at which fixing is possible, the image adjustment program C14 recorded in the memory is called to perform image adjustment.

In the image adjusting step, the surface potential is measured by a potential sensor (not shown) which measures the surface potential of the photoconductor 1, and the voltage applied by the charging means 2 is adjusted based on the measured surface potential. Further, solid and non-solid patches (measurement plates) are formed on the photoconductor by the exposure unit 3, and the reflection density of the patch portion is measured by a reflection density sensor (not shown). Adjustment processing such as maximum density correction and γ correction is performed.

The developing means 4 consumes a large amount of toner by developing the patch portion.

In the present invention, the image adjusting program C
Toner density adjustment program C141
Is provided, the control unit C11 sends a clock for changing the rotation speed to the drive unit M so that the process linear velocity is the standard linear velocity (22
0 mm / s), the toner concentration in the developer is measured by the toner concentration sensor SD in the standard linear velocity state, and toner replenishment control C15 is performed so that the sensor output becomes a threshold value (2.5 V in this embodiment). I do. When the toner density is higher than the appropriate value, the toner is consumed by developing the patch image.

By performing such toner concentration adjustment during the warm-up time, the toner concentration in the developer is at a predetermined toner concentration (Tc = 8 mass%), and fog and toner scattering from the beginning of the printing operation. It is possible to stably obtain a good print image.

(6) The invention of claim 2 will be described.
In the present invention, the toner concentration sensor SD is used during warming up.
Sensor output value from the standard toner density (8 in this embodiment).
The control voltage (Vc) is adjusted so that a predetermined sensor output value (2.5 V in this embodiment) is obtained at (mass%), and the adjusted control voltage value is stored in the memory for each linear velocity. During the printing operation, the control unit calls the control voltage value, which is the adjustment value of the process linear velocity, from the memory, and performs toner replenishment control using the called control voltage value. FIG. 5 is a control block diagram of the present invention. Is shown. The present invention is in a preferable state to be carried out subsequent to the invention of claim 1.

When the power switch C22 is turned on, the control section C21 detects the temperature of the fixing temperature sensor C23 provided in the fixing roller portion of the fixing means 24. If the detected sensor temperature is below a predetermined temperature, the fixing temperature is lowered. Sensor C2
The image adjustment program C24 stored in the memory is called during the warm-up time until the detected temperature of No. 3 rises to a predetermined temperature that enables fixing, and image adjustment is performed.

In the image adjusting step, the surface potential is measured by a potential sensor (not shown) which measures the surface potential of the photoconductor 1, and the voltage applied by the charging means 2 is adjusted based on the measured surface potential. Further, solid and non-solid patches are formed on the photoconductor by the exposure unit 3, and the reflection density of the patch portion is measured by a reflection density sensor (not shown), and the control unit C21 corrects the maximum density and the γ correction. And the like are adjusted.

In the present invention, the image adjustment program C
A toner concentration detection condition setting program C241 is provided in the image adjustment process of No. 24, and the control unit C21 follows the program to first provide the drive unit M with a clock for changing the rotation speed when the process linear velocity is the standard linear velocity (220 mm). / S) and the toner density sensor SD at the standard linear velocity state.
Then, the toner concentration in the developer is measured, and the toner replenishment control C26 is performed so that the sensor output becomes the threshold value (2.5 V in this embodiment).

Next, with respect to the toner density sensors SD for Y, M, C, and K colors, the process linear velocity is 220 mm / s, 1
The control voltage Vc value at which the sensor output becomes a threshold value of 2.5 V is adjusted and determined for a predetermined toner concentration (Tc = 8 mass%) for each linear velocity of 10 mm / s and 73 mm / s. (Table 3)

[0066]

[Table 3]

The determined control voltage Vc value is stored in the (non-volatile) memory C25, and when the toner density is detected, the corresponding control voltage Vc stored in the memory C25 is detected.
The value is called and applied to the toner density sensor SD to obtain the sensor output.

The process linear velocity can be changed manually or automatically. In the case of the manual, the operation panel is provided with a selection button displaying "glossy", "thick paper", or the process linear velocity, and the push linear button switches the process linear velocity to 110 mm / s, for example (C
27). In the case of the automatic mode, a switching instruction is given by detecting the thickness of the paper P to be used (C27).

The control section C21 outputs a pulse CLK corresponding to the determined process linear velocity to the control section M to record an image. Further, the control section C21 controls the control voltage Vc corresponding to the process linear velocity determined for each of Y, M, C and K colors.
Toner concentration sensor SD by calling the value from memory C25
To obtain the sensor output. The detected sensor output is compared with a threshold value (2.5 V), and toner replenishment control C26 is performed.

The control voltage Vc value as shown in Table 3 is set in the image adjusting step during the warm-up time, and 8 hours after the printing operation is performed, the sensor output for each linear velocity and the control toner density at that time are shown. Table 4 shows

[0071]

[Table 4]

The toner concentration Tc was controlled to be about 8% by mass, indicating that a good print image without fog or toner scattering was obtained.

Further, as a toner density control according to the present invention as an effect confirmation test, a toner density stability test up to 10000 prints was carried out, and a process linear velocity was standard (1/1)
FIG. 6 shows results obtained by incorporating (1/2) speed and (1/3) speed modes in addition to the speed.

Before the measures according to the present invention, the toner concentration Tc at the time of start was 8% by mass, but a large variation was observed due to deviation during 100,000 printing, and stable toner concentration control was not performed. In the case of, the toner concentrations Tc of the four colors Y, M, C, and K are controlled within ± 0.1% with respect to the target value of 8% by mass.
The average value of the toner density Tc of M, C, K colors is ± 0.05.
It was confirmed that it was maintained within%.

[0075]

According to the first aspect of the present invention, since the target toner density is reached immediately after warming up, good image recording conditions are set from the initial stage of printing, and printing without fog or toner scattering is achieved. An image is obtained.

According to the second aspect of the present invention, the toner concentration is adjusted during the warming-up time, and the target toner concentration is maintained in good condition from start to finish regardless of changes in the process speed, and fog and toner scattering. A good image with no image will be continuously obtained.

[Brief description of drawings]

FIG. 1 is a sectional view of a color image forming apparatus.

FIG. 2 is a cross-sectional configuration diagram of an image forming unit.

FIG. 3 is a graph showing the sensor output and its transition when the process linear velocity is changed.

FIG. 4 is a control block diagram of the present invention (claim 1).

FIG. 5 is a control block diagram of the present invention (claim 2).

FIG. 6 is a graph showing the results of the effect confirmation test of the present invention.

[Explanation of symbols]

1 photoconductor 2 charging means 3 exposure means 4 developing means 41 developer carrier SD toner concentration sensor

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Nobuyasu Tamura             2970 Ishikawa-cho, Hachioji-shi, Tokyo Konica stock             In the company F-term (reference) 2H005 AA21 BA02 EA05                 2H077 AB02 AB14 AC03 AC04 AD02                       AD06 AD13 AD18 AD31 BA01                       BA02 BA03 BA08 DA04 DA05                       DA10 DA42 DA47 DA54 DA63                       DA81 DA83 DB03 DB14 DB22                       DB25 EA01 FA19 GA13

Claims (3)

[Claims] 1. An image carrier that forms a latent image, a developing roller that conveys a developer that visualizes the latent image to a developing nip portion, and a toner density detecting unit that detects the magnetic permeability of the developer. A toner replenishing means for replenishing the developer with toner according to the detection result of the toner concentration detecting means, an agitating means for agitating the replenishment toner from the toner replenishing means, and the developing roller with the developer. And a driving unit for driving the feeding unit and the stirring unit of the image bearing member and the stirring unit is a common driving unit, and a plurality of process linear velocities In an image forming apparatus capable of switching and having a control unit for driving and controlling the driving unit and the toner replenishing unit,
An image forming apparatus characterized in that, during warming up, the process linear velocity is set to a standard linear velocity, and toner concentration control is performed so that an appropriate toner concentration is obtained. 2. An image carrier that forms a latent image, a developing roller that conveys a developer that visualizes the latent image to a developing nip portion, and a toner concentration detecting unit that detects the magnetic permeability of the developer. A toner replenishing means for replenishing the developer with toner according to the detection result of the toner concentration detecting means, an agitating means for agitating the replenishment toner from the toner replenishing means, and the developing roller with the developer. And a driving unit for driving the feeding unit and the stirring unit of the image bearing member and the stirring unit is a common driving unit, and a plurality of process linear velocities In an image forming apparatus capable of switching and having a control unit for driving and controlling the driving unit and the toner replenishing unit,
At the time of warming up, the sensor output value from the toner concentration detecting means is adjusted so as to be a predetermined sensor output value at the standard toner concentration, and the adjustment value is stored in the memory so as to be controlled for each process linear velocity. The image forming apparatus is characterized in that during the printing operation, the control unit calls the adjustment value of the process linear velocity from the memory and performs toner supply control using the called adjustment value. 3. The developer has a mass average particle diameter of 3 to 8 μm.
3. The image forming apparatus according to claim 1, wherein the two-component developer comprising the toner of 1. and a carrier having a mass average particle diameter of 30 to 65 μm is used.