JPH11272061A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent an image deterioration by improving the precision of toner concentration controll at the drive restart early stage of a two component developing device. SOLUTION: In this device, whether or not the toner replenishment is necessary is judged by detecting the toner concentration by a magnetic sensor in the developing device, obtaining a difference Δx between the toner concentration detected at the first time after resuming the drive of the developing device and the toner concentration detected at the preceding drive completed time, setting the initial correction time tc based on a function ft(Δx) in the case this is larger than a threshold (h), and judging whether the detected toner concentration (x) at this time is smaller than the reference toner concentration shown by fs(Δx, t) (step S401 to S405). This function fs(Δx, t) is, preliminarily determined by experiments, and by making the reference toner concentration changed in accordance with the value of (t) for each Δx, curve gradually approaching the reference toner concentration A from the value smaller than the reference toner concentration A at the normal driving time.

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 having a two-component developing type developing device, and more particularly to an improvement in a technique for controlling a toner concentration of a developer.

[0002]

2. Description of the Related Art A two-component developer for developing an electrostatic latent image formed on the surface of a photosensitive drum using a two-component developer in which a carrier composed of magnetic powder and toner particles made of resin are mixed at an appropriate ratio. In the type developing device, it is necessary to control the amount of carrier and toner in the developing device to be a fixed ratio in order to maintain an appropriate image density.

For this reason, conventionally, a magnetic sensor has been used to detect the magnetic amount of developer in a toner storage section in a developing device, thereby obtaining the ratio between toner and carrier. By supplying an appropriate amount of toner, the toner concentration in the developer has been controlled. However, usually, the developing device is operated only during the image forming operation in order to avoid wasteful consumption, and the operation is stopped for other times, and the operation stop time until the next image formation is performed. If the length is long, the degree of tightness of the developer left unstirred during that time increases, and its bulk density (apparent density per unit volume: AD value (a
parent density)).

[0004] Such an increase in bulk density is caused by the weight of the developer itself, a decrease in repulsive force between the particles due to a decrease in the amount of charge of the developer particles with time, and the like.
When the bulk density increases, the output value of the magnetic sensor also increases because the amount of the carrier existing per unit volume increases even if the mixing ratio of the toner and the carrier is the same. As a result, the toner density is detected to be lower than the original density, so that extra toner is replenished in an attempt to restore the toner density, resulting in a state of excessive toner replenishment. If the toner is replenished excessively, problems such as fogging of the reproduced image and toner scattering occur, which is not preferable in image formation.

To avoid such inconveniences, Japanese Patent Application Laid-Open No.
Japanese Patent Application Laid-Open No. 4-76166 discloses a technique in which the detection result of the magnetic sensor is ignored and the toner density control is not executed for a predetermined time after the operation of the developing device is restarted. The predetermined time is determined according to the length of the immediately preceding operation suspension time (first conventional technique). Japanese Patent Application Laid-Open No. 1-222279 discloses a technique for correcting the toner supply amount by using a parameter (reference voltage) that changes with a constant time constant when the operation is restarted (second conventional technique).

[0006]

However, according to the first prior art, since the control of the toner concentration is not performed within a predetermined time when the operation is restarted, the toner consumed during this time cannot be supplied. As a result, not only does the toner amount actually become insufficient, but also the pause time of the toner concentration control is determined according to the length of the immediately preceding operation pause time, and such a determination method can increase the bulk density. It is questionable whether the degree of the criterion can be evaluated accurately. That is, the change in the bulk density is largely affected not only by the operation suspension time but also by the device environment such as humidity and temperature at that time, and cannot be uniformly evaluated only by the suspension time. Therefore, according to the first conventional technique, there still remains a problem that the toner concentration cannot be appropriately controlled at the initial stage of the operation restart.

Further, according to the second prior art, without considering the degree of increase in bulk density during the downtime,
Control is performed uniformly with only a constant time constant that changes with the lapse of time after the start of operation. In this case as well, proper control of the toner concentration cannot be expected. For example, the case where the next operation is restarted within 10 minutes after the end of the previous operation of the developing device, the case where the operation is performed for the first time after the end of the previous day, and It is also clear from the fact that the control is performed with the same time constant despite that the change amount of the bulk density is greatly different.

In view of the above problems, the present invention provides an image forming apparatus using a developing device of a two-component developing system, which evaluates the amount of change in the bulk density of the developer due to the suspension of operation and starts operation. An object of the present invention is to provide an image forming apparatus capable of correctly controlling the toner density of an initial developing unit.

[0009]

In order to solve the above-mentioned problems, the present invention provides a developing device using a two-component developer and developing by supplying an appropriate amount of toner from a toner replenishing means based on predetermined control parameters. An image forming apparatus comprising: a control unit configured to control a toner concentration in a developing device; a toner density detecting unit configured to detect a toner concentration in a developing device; Bulk density evaluation means for evaluating the amount of change in the bulk density of the developer in the developing device, the control means, within a predetermined initial time after restarting the operation of the developing device, the bulk density evaluation means The control parameter is corrected based on the evaluation result to control the toner density.

Further, according to the present invention, the bulk density estimating means includes:
The amount of change in the bulk density is evaluated based on the toner concentration detected at the end of or immediately after the previous operation of the developing device and the toner concentration detected at the time of restarting the operation of the developing device. Further, the present invention is configured such that the control means controls the toner density based on a comparison result between the detected value of the toner density and a predetermined reference density value, and the reference density is controlled within the predetermined initial time. The correction is made based on the evaluation result of the bulk density evaluation means using a value as a control parameter.

Further, according to the present invention, the control means preferably comprises:
When it is determined that toner replenishment is necessary based on a comparison result between the detected value of toner density and a predetermined reference density value, the toner density is controlled by operating the toner replenishing means for a predetermined time. And correcting the operation time of the toner replenishing means within the predetermined initial time as a control parameter based on the evaluation result of the bulk density evaluating means.

Further, according to the present invention, the control means includes:
It is characterized by further comprising a determining means for determining the length of the initial time based on the evaluation result of the bulk density evaluating means. Further, the present invention is an image forming apparatus including a developing device using a two-component developer and control means for controlling a toner density in the developing device, wherein the density of a document on which an image is to be formed is detected. The control means controls the toner density using a detection result of the document density detecting means as a control parameter within a predetermined initial time after the operation of the developing device is restarted. .

Further, the present invention comprises a developing device using a two-component developer, and control means for controlling a toner concentration in the developing device, and the developing device uses the developing device to form an electrostatic latent image on a photosensitive member. And an image forming apparatus for forming a toner image by developing a toner image density detecting means for detecting a density of the toner image formed on the photoconductor, wherein the control means restarts the operation of the developing device. In a later predetermined initial time, the toner density is controlled using the detection result of the toner image density detecting means as a control parameter.

Here, the present invention is based on the toner density detected at the end of or immediately after the last operation of the developing device and the toner density detected at the time of restarting the operation of the developing device. It is characterized by comprising a bulk density evaluation means for evaluating a change amount of the bulk density, and the control means further comprising a determination means for determining the length of the initial time based on the evaluation result of the bulk density evaluation means.

Further, according to the present invention, the control means preferably comprises:
The image forming apparatus further includes a correction unit configured to correct the control parameter or the initial time based on a usage time of the carrier in the developer.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. (1) Configuration of Copying Machine FIG. 1 is a schematic sectional view of a digital color copying machine (hereinafter, simply referred to as “copying machine”) according to the present embodiment. This copying machine is a so-called tandem-type copying machine that forms a color image by multiply transferring images transferred by a plurality of image forming units arranged along a transfer belt.

The copying machine shown in FIG. 1 has an image reader section 100 for reading a document image and an image reader section 100.
And a printer section 200 for reproducing the image read by the printer. The image reader unit 100 scans a document on the platen glass 21 and reads R, G, and B electric signals. The scanner 22 reads the electric signals obtained by the scanner 22 to perform processing such as conversion into gradation data. It comprises a signal processing unit 28. The scanner 22 is driven by a motor 27 to move in the direction of arrow A when reading an original, and scans the original on the platen glass 21 while irradiating the original with an exposure lamp 23. The reflected light of the irradiation light from the document surface is condensed by the rod lens array 24 and is brought into close contact C
Photoelectrically converted by the CD color image sensor 25,
It becomes an electrical signal of three colors of R, G and B. Read signal processing unit 2
8 converts this electric signal into 8-bit grayscale data of yellow (Y), magenta (M), cyan (C), and black (K).

The printer unit 200 includes a printer control unit 20
1. It is composed of a laser optical system 30, an image forming system 40, and a transport system 50. The printer control unit 201 generates laser diode drive signals for each gradation data of each color based on the signal output from the read signal processing unit 28, and the drive signals of the corresponding printer heads 3C to 3K of the laser optical system 30 are generated by the respective drive signals. The laser diode emits light. The photosensitive drums 1C to 1K that are rotationally driven by the laser beam generated thereby are exposed and scanned.

The photosensitive drums 1C to 1K are uniformly charged by charging chargers 2C to 2K, and an electrostatic latent image is formed by this exposure, and the developing units 4C to 4K are respectively used for cyan, magenta, yellow, and black. The electrostatic latent images on the photosensitive drums 1C to 1K are developed with the respective color toners.
On the other hand, the recording sheet fed from the paper cassette 13 or 14 is conveyed with a timing by the transfer belt 10 stretched by the driving roller 11 and the driven roller 12 and rotated at a constant speed. The toner images of each color formed on the photosensitive drums 1C to 1K are sequentially transferred so as to be superimposed on the recording sheet by receiving the transfer electric fields from the transfer brushes 5C to 5K. The recording sheet to which the toner image has been transferred is separated from the transfer belt 10 and fixed by the fixing device 15, and thereafter, the recording sheet is discharged onto the paper discharge tray 16.

Further, AIDC sensors 9C to 9K are provided downstream of the respective photosensitive drums 1C to 1K on the transfer belt 10 in the conveying direction to detect the amount of toner adhered on the belt immediately after the transfer. Each of the AIDC sensors 9C to 9K uses a reflection type sensor having a built-in light emitting diode and a photodiode inside, and transfers the transfer belt 10 from each of the photosensitive drums 1C to 1K.
The reference pattern (AIDC pattern) transferred above is detected. When the transfer belt 10 is transparent, it goes without saying that a transmission type sensor may be used.

Using a table in which the voltage value is associated with the toner adhesion amount, the toner adhesion amount can be obtained from the voltage value output from the AIDC sensor, and the grid potential VG and the developing bias potential can be obtained from the toner adhesion amount. VB and the like are determined so that the transfer density is kept constant. In addition, AI
The DC sensors 9C to 9K are arranged at positions where the detection ranges in the main scanning direction do not overlap each other, and do not detect a reference pattern of another color during control.

In order to detect the density of the reference pattern on the photosensitive drums 1C to 1K before transfer immediately below the developing units 4C to 4K, a pattern density comprising the same reflection type optical sensor as the AIDC sensor is used. Sensors 8C to 8K are provided. The detection results of these sensors are used in the AIDC sensor 9 described above.
Although the image density can be appropriately controlled instead of or in combination with the detection results of C to 9K, in a modified example of the present embodiment, the image density is used for toner density control in the early stage of operation of the developing device. ing. Details will be described later.

Each of the developing units 4C to 4K is of a two-component developer type, and has the same configuration except for the color of the supplied toner. FIG. 2 is a diagram showing the configuration of the developing unit 4C. As shown in the drawing, the developing device 4C includes a toner replenishing hopper 41C for storing toner, a toner replenishing roller 42C for replenishing toner in the hopper to a lower stirring chamber 46C, and a developer (carrier) in the stirring chamber. And the toner) and a developing roller 44C for supplying the stirred developer to the developing surface of the photosensitive drum 1C. As the developing roller 44C, a known roller in which a magnet roller is inserted into an aluminum developing sleeve and only the developing sleeve is rotated is used.

The stirring roller 43C and the developing roller 44C are driven to rotate by a driving device (not shown) during image formation. Further, the toner supply roller 42C
Is rotated by a driving unit (not shown) for a predetermined time only when toner supply is necessary. A magnetic sensor 45C is attached to the bottom near the right stirring roller 43C, so that the toner concentration of the developer in the stirring chamber 46C is detected. The printer control unit 201 (see FIG. 3) controls the rotation operation of the toner replenishing roller 42C based on the detection result, and adjusts the toner concentration in the stirring chamber to a constant ratio. Details will be described later.

An operation panel 60 is provided at a position on the front of the image reader unit 100 where it can be easily operated. The operation panel includes keys for inputting various copy modes, and a display unit for displaying settings and the like. (2) Configuration of Control System Next, the configuration of the control system installed inside the copying machine will be described with reference to the block diagram of FIG.

This control system includes an image reader 100
, An image reader control unit 101 for controlling the operation of the printer unit 200, a read signal processing unit 28 for performing necessary correction processing on image data obtained by the image reader control unit 101, and a printer control unit 201 for controlling the operation of the printer unit 200. Each control unit is configured around a CPU. The image reader control unit 101 receives a drive I / O 103 and a parallel I / O 104 based on a position signal from the position detection switch 26 indicating the position of the document on the platen glass 27.
The scanning motor driver 1 controls the lighting of the exposure lamp 23 via the
05 is scanned to scan the original image. The image signal read by the CCD color image sensor 25 by this scanning operation is subjected to gradation data conversion, shading correction, and the like in the read signal processing unit 28.

In this embodiment, the printer control unit 201
Is also used as the entire timing control unit, and the control ROM
The data stored in the data ROM 2
03 using various data stored in the drive I / O
206, the semiconductor laser driver 208 is controlled via the parallel I / O 207, and the semiconductor lasers in each of the printer heads 3C to 3K are driven based on the image signals processed by the read signal processing unit 28, to thereby control the photosensitive drums 1C to 1K. 1K is exposed and scanned, and the operations of the image forming system 40 and the transport system 50 are uniformly controlled via the copy control unit 230 while taking timing.

The printer controller 201 also stores pattern density sensors 8C to 8K for detecting the toner density of the reference pattern on each of the photosensitive drums 1C to 1K and the density of the reference pattern after being transferred to the transfer belt 10. AI to detect
Detection signals from the DC sensors 9C to 9K, the humidity sensor 209, the temperature sensor 210, and the like are input. And
Based on these detected values, automatic density control, transfer output control, exposure control, and the like are performed.

In the automatic density control, the AIDC sensors 9C to 9K
Based on the detected values, the VB generation units 232 and 232 provided for the respective colors are provided via the parallel I / O 222 and the drive I / O 223 using a table recorded in advance.
234, 236, 238 and VG generation unit 23
3, 235, 237 and 239, and the grid potential VG of the charging chargers 2C to 2K and the developing devices 4C to 4K.
The K developing bias potential VB is set. Thereby, the density of the toner image formed on the photosensitive drums 1C to 1K is controlled.

The voltages applied to the transfer brushes 5C to 5K can be controlled by the transfer HV units 251 to 254 via the drive I / O 242 and the parallel I / O 241. On the other hand, the detection signals of the magnetic sensors 45C to 45K installed in the developing units 4C to 4K are also input to the printer control unit 201, and the printer control unit 201
Samples the detection signal at regular intervals of sampling time, and controls the rotation of the toner supply roller via the toner supply roller driving unit 213 based on the detected signal, so that the toner concentration in the developer is always within the optimal range. Control so that

The RAM 211 has an operation panel 60.
, And the detected toner density value and other control variables are temporarily stored in the EEPROM.
M212 stores the toner density value at the end of the operation, the cumulative number of copies for maintenance, and the like. (3) Control Operation Next, the control operation of the copying machine by the above control system will be described with reference to FIG.
This will be described based on the flowcharts of FIG.

FIG. 4 is a flowchart showing a main routine of the control operation of the entire copying machine. When the power is turned on to the apparatus, the settings of the registers of the CPU in the image reader control unit 101, the printer control unit 201, the copy control unit 230, the RAM 211, and the like are initialized (step S1).

Next, an internal timer of the CPU in the printer control unit 201 is started (step S2), and the contents input from the operation panel 60 are set in the RAM 211, and the set contents and the state of the apparatus are checked. Operation panel 6
An input / output process for displaying on the display unit 0 is executed (step S3). Thereafter, based on the detection values of the magnetic sensors 45C to 45K and the like, while controlling the toner concentration in each of the developing devices 4C to 4K to be within a certain range (step S4), the image reader control unit 101 and the copy control unit 230. To execute a process of reading the original image and reproducing it on the recording sheet (copying process) (step S5).

Then, other processes, for example, a color shift correction process for forming a registration mark of each color on the transfer belt 10 and correcting an image writing position based on the relative position shift amount, and a process for controlling image density. After executing the processing for forming the reference pattern on the transfer belt or the like (Step S
6) After waiting for the end of the internal timer, the process returns to step S2 (step S7), and repeats the above steps S3 to S6 while managing the time.

FIG. 5 is a flowchart showing a subroutine of the toner density control process in step S4. In the toner density control processing, similar processing is executed independently for each of the developing devices 4C to 4K. Therefore, the toner density control in the developing device 4C will be described as a representative.

When the copy start key on the operation panel 60 is depressed, the copying process in step S5 starts, and the developing unit 4C also starts operating. The printer control unit 201 samples the detection signal of the magnetic sensor 45C after a certain sampling time, and obtains the toner concentration x (%) at each sampling (step S401). This toner concentration is determined by the toner amount (T) in the stirring chamber 46C.
Is a percentage (T / C) with respect to the total developer amount (C), and a table of toner density values associated with the output signal of the magnetic sensor 45C is a data ROM.
The toner density x is stored in the table 203 and the table is referred to to obtain the toner density x.

Next, it is determined whether or not the sampling is the first time since the start of the operation (step S4).
02) If it is the first time, the difference Δx (= xb−) between the toner density x obtained by the sampling and the toner density xb sampled at the end of the previous operation of the developing device.
x) is determined, and it is determined whether or not this is greater than a predetermined threshold h (step S403). The toner concentrations xb and x are
Since it means the toner concentration immediately before and immediately after the suspension of the operation of the developing device 4C, there should be no substantial difference between the two. However, as described above, the increase in the bulk density of the developer during the suspension period is not considered. As a result, the output of the magnetic sensor 45C increases, and the toner density apparently changes by Δx accordingly. Therefore, the amount of change in the bulk density can be properly evaluated based on the magnitude of the difference Δx.

In the present embodiment, the value of the threshold value h is set to approximately 0.5%, and the difference Δ
If x is large, it is determined that accurate control cannot be performed by toner density control during normal operation any more, and control (correction control) taking into account the difference Δx is executed. First, based on the difference Δx, a time tc at which the correction control is to be executed (hereinafter referred to as “initial correction time”) is calculated by a function ft (Δx).
(Step S404). The function ft is obtained by experimentally obtaining the relationship between the value of the difference Δx and the time required for the bulk density to recover to the bulk density during normal operation by stirring and plotting the relationship on a graph.

The curve G1 in FIG. 8 shows the difference Δx in the toner concentration when the carrier in the developer is still used for a short time, and the operation time (==) of the developing device required to recover the normal bulk density. (Initial correction time). A table indicating the correspondence between the apparent toner density difference Δx determined by such a curve G1 and the initial correction time tc is stored in the data ROM 203, and the printer control unit 201 refers to the data. hand,
An initial correction time tc is obtained.

Actually, a new amount of toner is replenished by the amount consumed for development, and the initial correction time tc corresponding to the amount is considered to fluctuate slightly depending on the magnitude thereof, but the difference is negligible. Note that while Δx changes continuously, the memory capacity of the data ROM 203 is limited. Therefore, in practice, ts is given to a typical value of Δx and stored in a table. Part 2
The CPU 01 obtains tc for Δx during this time by, for example, a two-dimensional interpolation method.

In addition, an equation of a curve approximating each graph may be obtained, the equation may be stored, and the calculation may be performed based on the equation. Other functions to be described later are stored in the data ROM 203 in a similar manner. After the initial correction time tc is obtained in this way, step S4
At 05, it is determined whether or not the toner density x is smaller than a correction reference value fs (Δx, t) which is a control parameter at that time.

FIG. 9 is a graph showing the function fs (Δx, t). A curve G3 indicated by a dashed line indicates a change in the reference toner density when the density difference is Δx1, and is indicated by a solid line. G4 has a density difference Δx2 (where Δx1 <Δx
The change of the reference toner density in the case of 2) is shown. As described above, the larger the difference Δx is, the larger the change amount of the bulk density is.
As a control parameter, a reference toner concentration A (about 5%) during normal operation (ie, when the operation is continued, the developer is sufficiently stirred, and the bulk density is constant)
It takes some time to adopt. In the figure, only the density differences Δx1 and Δx2 are disclosed.
It is needless to say that a graph that can correspond to each value is formed, and the value of the reference toner density corresponding to the value of Δx and t is stored in the data ROM 20 as a table.
3 is stored.

When the toner density x detected by the magnetic sensor 45C is smaller than the reference toner density fs (Δx, t), it is necessary to replenish the toner. Stir chamber 46C
(Steps S405 and S40)
6). As a value of the toner supply time T, an appropriate time equal to or less than the sampling time is set in advance, and the data ROM 2
For example, it is determined by the relationship between the toner supply amount per unit time due to the rotation of the toner supply roller 42C and the expected maximum toner consumption amount per unit time. In this case, the toner density is set to a value that maintains the toner density at a certain level or more.

On the other hand, if the detection of the toner density is not the first detection after the start of the operation in step S402, in step S407, it is determined whether or not t> tc, that is, whether or not the operation time has exceeded the initial correction time tc. Judge. If it has not elapsed yet, in step S405, it is determined whether or not toner supply is necessary by comparing it with the correction reference value fs (Δx, t). If the initial correction time tc has elapsed, there is no need for correction anymore. Then, the process proceeds to step S408, where the toner concentration is compared with the reference toner concentration A at the time of normal operation, and toner supply is performed only when the density is lower than the reference toner concentration A (step S40).
6).

Thereafter, it is determined whether or not the operation of the developing device 4C has been stopped after the image formation has been completed.
The final toner density x sampled by the AM 211 is overwritten and stored as the toner density xb in the EEPROM 212, and the process returns to the main routine. As described above, in the present embodiment, the reference toner density value, which is a parameter for determining whether or not toner replenishment is necessary, is changed in accordance with the initial bulk density change amount and the operation time, so that the actual Can be replenished while estimating the amount of toner replenishment necessary for the toner, and the problem of excessive replenishment of toner unlike the related art does not occur.

FIG. 6 is a flowchart showing a modified example of the toner density control process. In the control example of FIG.
The correction for changing the reference toner density value in accordance with the so-called degree of restoration of the bulk density of the developer is performed. In the present modification, the correction is performed by changing the toner supply time in accordance with the degree of restoration. That is, when the first toner concentration is detected after the restart of operation or within a predetermined initial correction time (“Y” in step S422 or “N” in step S427), the detected toner density x is smaller than the reference toner density value A. It is determined whether or not it is smaller, and if it is smaller, the toner supply roller 42C is driven for the supply time ts to supply toner (steps S425 and S426). The replenishment time ts is determined by a function fst (Δx, t) using the difference Δx and the elapsed time t after the start of operation as variables.

FIG. 10 is a graph showing the function fst (Δx, t), and the curves G5 and G6 respectively show the difference Δx
1, Δx2. The larger the density difference Δx is, the larger the bulk density is changed. Therefore, it takes time to reach the reference supply time T. Immediately after the resumption of operation, replenishment is performed with the minimum replenishment time Tm, and the toner replenishment time rapidly increases as the predetermined time elapses and the bulk density recovers, and eventually reaches the reference replenishment time T. .

As described above, Δx and the elapsed time t after the start of operation
The table corresponding to the graph formed for each is data R
The printer control unit 201 is stored in the OM 203
Determines the replenishment time when toner replenishment is required by the determination in step S425. If it is determined in step S427 that t> tc,
The detected toner density value x at that time is compared with the reference toner density value A. If the toner density x is smaller, the toner is supplied for the reference time T (step S429).

The other steps are the same as the corresponding steps in FIG. 5 and will not be described. According to this modification, it is possible to accurately estimate the toner replenishment time at the beginning of the operation according to the change in the bulk density, thereby realizing toner replenishment without excess and deficiency. FIG. 7 is a flowchart illustrating still another modified example of the toner density control process. In this modified example, at the beginning of the operation, the density data of the document is used as the parameter of the toner density control without using the detection result of the magnetic sensor 45C.

That is, the read signal processing section 28 has a density integration section 29 therein (see FIG. 3), and converts the R, G, B image data obtained by reading the original image by color correction processing. The obtained C, M, Y, and K density data are respectively integrated. Printer control unit 201
CPU obtains the B / W ratio (the ratio of the actual integrated density when the integrated density when the entire surface of one sheet is formed with the highest density is set to 1) from the density integrated value.

The B / W of the resulting cyan (C)
Since the ratio has a substantially linear relationship with the cyan toner adhesion amount (that is, toner consumption amount) required at the time of image reproduction (see FIG. 11), the toner consumption amount is predicted based on the B / W ratio, and the current It is possible to calculate the toner density xd (step S445). Now, the calculated B /
If the W ratio is k, the toner consumption at that time is mt from FIG. Here, assuming that the toner density before toner consumption is the reference value A (%), and assuming that the amount of the developer (carrier + toner) in the developing device 4C at that time is mc, the original is one page. After copying is (mc ·
A / 100) -mt, while the developer amount is (mc-
mt), the former is divided by the latter and multiplied by 100 to determine the toner density xd (%) at that time.

That is, xd = [(mc · A / 100)
−mt] · 100 / (mc−mt). The calculation of the toner density xd based on the document density in step S445 may be performed each time image formation is performed, or may be performed in accordance with the toner density detection timing by the number of times of image formation (fraction) performed during that time. (Included), the density data may be integrated and then calculated. In the flowchart of FIG. 7, the latter example is shown.

The toner density x obtained as described above
By comparing d with the reference toner density value A, it is determined whether toner replenishment is necessary, and toner replenishment is performed based on this (steps S446, S447).
The rotation of the toner replenishing roller 42C is controlled so as to directly compensate for the toner consumption amount without calculating the toner concentration xd based on the toner consumption amount obtained from the integrated value of the image density and comparing it with the reference value A. In this case, substantially the same effect can be obtained.

In this way, the toner density is controlled based on the original density to be formed within the initial correction time, and when it is determined that the initial correction time has elapsed (step S44).
8 "Y"), it is no longer necessary to calculate the toner density xd from the document density, and the toner density x detected by the magnetic sensor 45C is compared with the reference density value A and controlled (steps S449 and S447).

The other steps have the same contents as the corresponding steps in FIG. 5 and will not be described. As a method of controlling the toner density without depending on the detected value of the toner density at the time of the initial correction as described above, another method is to detect the density of the pattern formed on the photosensitive drum and control based on the detection result. A method is conceivable.

That is, as described above, in this copying machine, a reference pattern (AIDC pattern) of each color is formed on the transfer belt 10 in order to appropriately control the image density.
This is detected by the AIDC sensors 9C to 9K to control image forming conditions such as charging voltage. At this time, the density of the reference pattern before transfer on each of the photosensitive drums 1C to 1K is detected by the pattern density sensors 8C to 8K, whereby the toner density can be directly obtained.

The pattern density on the photosensitive drum should be the same if other image forming conditions such as charging voltage, exposure intensity, and developing device bias voltage are the same. , Is considered to be caused by a change in toner density. FIG. 12 is a graph showing the correlation between the pattern density of the cyan reference pattern and the toner density in this case. Since the toner density xp is uniquely determined with respect to the pattern density dp by this correlation, this relationship is stored in a table in the data ROM 203, and instead of step S445 in FIG.
The toner density xd may be obtained based on the pattern density dp.

The graphs showing the functions shown in FIGS. 11 and 12 actually vary slightly due to environmental changes such as temperature and humidity and other image forming conditions. Although an error may occur, appropriate control that reflects the actual toner density value can be performed far more than the conventional control method at the beginning of operation. In order to further improve the control accuracy in this case, a correction coefficient corresponding to a change in temperature and humidity is obtained by an experiment,
9. Based on the detection signal from the temperature sensor 210 (FIG. 3), the toner density value obtained from FIGS. 11 and 12 may be corrected.

In the above control example, the control of the toner density of the cyan developing unit 4C has been described. Of course, the same control is executed independently in the other developing units 4M, 4Y, and 4K. (4) Modifications Although the image forming apparatus according to the present invention has been described based on the embodiments, the present invention is not limited thereto, and the following modifications can be considered.

(4-1) In each of the toner density control processes, first, an initial correction time tc is determined based on a difference between the toner density xb at the time of the previous stop of the operation and the toner density at the time of the restart of the operation. Although the special density control different from the control during normal operation is executed only for the time, since the density control within the initial correction period described above reflects the actual toner density value quite accurately, this initial correction time is used. As tc, a value sufficiently longer than the originally required correction time may be set as a fixed value. Further, the operator may be able to select and set an appropriate initial correction time by using the operation panel according to the use situation.

(4-2) The last operation of the developing device is
If the process is completed before the initial correction time tc is reached, the toner density at the end is defined as xb, and the next initial correction time and other control parameters are determined from the difference between this value and the toner density x after the restart of operation. , There is a possibility that a slight error may occur as compared with the case where the operation was stopped after the previous recovery to the normal bulk density.

To cope with such a case, a correction coefficient corresponding to the degree of bulk density recovery by the previous operation time is obtained in advance, and the values obtained by the above functions are appropriately corrected based on the correction coefficient. You should be able to do so. Alternatively, even when the previous image forming operation is completed before the initial correction time elapses, only the stirring operation of the developing device is continued until the initial correction time elapses, and the detected toner concentration when the stirring operation is stopped is reduced. It may be configured to be set as xb.

(4-3) For more accurate control,
Each control parameter may be further corrected according to the usage time of the carrier in the developer. That is,
In the two-component development, only the toner is supplied and the carrier remains in the developing device and is used for a long time, so that the carrier is deformed by abrasion, and the deformation causes a change in bulk density, a toner conveying force, and the like. Has a subtle effect. For example, in the function ft (Δx) for obtaining the initial correction time tc,
The curve changes from the solid curve G1 in FIG. 8 to the curve G2 indicated by the dashed line.

The function fs (Δx, t) showing the change in the reference toner density shown in FIG. 9 is also the same as Δx, the longer it takes to adopt the reference toner density A as the use time of the carrier becomes longer. Tends to be longer. FIG. 13 shows, in a slightly exaggerated manner, how the function fs (Δx, t) changes with the use time of the carrier, and shows a curve G7.
Indicates the initial use, and curve G8 indicates the result after long-term use, and the time to reach the reference toner density value is t.
It can be seen that the delay is from 1 to t3.

Therefore, it is desirable to perform correction using a different function according to the elapse of a certain carrier use time. The correction based on the carrier usage time is performed by, for example, accumulating and counting the number of copies in a non-volatile memory such as an EEPROM, and when the number of copies exceeds a predetermined number (for example, 50,000), FIG. In other words, the control is executed based on the table corresponding to the curve G8. At this time, the accumulated number of copies may be reset when a serviceman or the like replaces the carrier with a new carrier. Of course, finer control is possible by further dividing the carrier use time further and preparing a plurality of correction functions corresponding to the respective use times.

(4-4) In the above embodiment, the amount of change in the bulk density of the developer when the operation of the developing device is stopped is determined by the difference between the toner density detected when the operation was stopped last time and the toner density detected when the operation was restarted. As for the former toner concentration detection time, there is no problem if the toner concentration is detected immediately after the operation is stopped, and it is detected at two specific times (or more than two or more times) during the operation stop even if it is other than that. It would also be possible to analyze the rate of change of the bulk density from the toner concentration obtained, and evaluate the change in the bulk density during the stoppage of the operation from this and the value of the toner concentration at the time of restarting the operation.

In the above embodiment, the output signal of the magnetic sensor is temporarily converted to a specific toner density value (%) and then controlled for easy understanding, but the output signal of the magnetic sensor is controlled. Since the value directly reflects the toner density, the control is actually executed with the signal value. (4-5) In the above embodiment, an example in which the present invention is applied to a tandem type full-color digital copying machine has been described.
A monochromatic copying machine may be used, or an analog copying machine may be used except for the control based on the image density and the density of the reference pattern shown in FIGS. Further, the present invention is not limited to a copying machine, and can be applied to a laser printer using a two-component developing device, a plain paper facsimile, and the like.

[0068]

As described above, according to the present invention, the bulk density evaluation for evaluating the amount of change in the bulk density of the developer in the developing device based on the toner concentration detected at two or more specific points in time. Means for controlling the toner concentration by correcting the control parameter based on the evaluation result within a predetermined initial time after the operation of the developing device is restarted, so that the amount of change in the bulk density particularly during the operation suspension time can be correctly corrected. As a result of the evaluation, it is possible to appropriately control the toner concentration in the initial stage of the restart of the operation.
As a result, it is possible to prevent image deterioration due to excessive toner replenishment or toner shortage at the beginning of operation.

Further, according to the present invention, the bulk density evaluating means determines the toner density based on the toner density detected at the end of or immediately after the previous operation of the developing device and the toner density detected at the time of restarting the operation of the developing device. Since the change amount of the bulk density is evaluated, the change amount of the bulk density before and after the suspension of the operation of the developing device can be accurately evaluated. Further, in the present invention, within the predetermined initial time, a reference density value for specifically determining the necessity of toner replenishment or a toner replenishment amount per one time is used as a control parameter based on the evaluation result of the bulk density evaluation means. The toner concentration can be controlled by executing the correct toner supply.

Further, the present invention is provided with a density detecting means for detecting the density of a document on which an operation image is to be formed. The toner density is controlled using the detection result of the document density as a control parameter.
In particular, since the integrated value of the document density and the toner consumption amount have a fixed correlation, more accurate toner density control can be performed based on the density data.

The present invention further comprises a density detecting means for detecting the density of the toner image formed on the photoreceptor, and the detection result of the density detecting means within a predetermined initial time after the restart of the operation of the developing device. Is used as a control parameter to control the toner density. Since the density of the toner image formed on the photoreceptor and the toner density have a certain correlation, the current toner density can be estimated based on the density of the toner image and the toner density can be controlled.

Further, according to the present invention, since the initial time itself for executing the correction of the control parameter is also determined based on the evaluation result by the bulk density evaluation means, the bulk density of the developing device returns to the state at the time of normal operation. After the correction due to the change in the bulk density becomes unnecessary, the toner density can be accurately controlled by ordinary toner density control. Also,
Further, the present invention includes a correction unit that corrects the control parameter or the initial time based on a use time of the carrier in the developer, and a variation amount of the bulk density and a toner conveyance force due to the difference in the use time of the carrier. With change in mind,
Further, highly accurate toner density control can be executed.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a digital color copying machine according to an embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of a developing unit in the copying machine.

FIG. 3 is a block diagram showing a configuration of a control system installed in the copying machine.

FIG. 4 is a flowchart showing an overall control operation of the copying machine.

FIG. 5 is a flowchart illustrating a subroutine of a toner density control process in the flowchart of FIG. 4;

FIG. 6 is a flowchart illustrating a modified example of the subroutine of the toner density control process in the flowchart of FIG. 4;

FIG. 7 is a flowchart illustrating another modified example of the subroutine of the toner density control process in the flowchart of FIG. 4;

FIG. 8 is a diagram illustrating a relationship between a difference Δx in the detected toner concentration and a developing device operation time required to return to a normal bulk density.

FIG. 9 is a diagram illustrating a state of a change in the operation time of the developing device and a reference toner density for each difference Δx.

FIG. 10 is a diagram showing the relationship between the operation time of the developing device and the time of one toner supply for each difference Δx.

FIG. 11 is a diagram illustrating a relationship between a B / W ratio calculated from density data of a document and a toner consumption amount.

FIG. 12 is a diagram illustrating the relationship between the density of a reference pattern formed on a photosensitive drum and the toner density.

FIG. 13 is a diagram illustrating how the degree of change in the reference toner concentration changes depending on the usage time of the carrier in the developer.

[Explanation of symbols]

 1C-1K Photoconductor 10 Transfer belt 4C-4K Developing device 8C-8K Pattern density sensor 9C-9K AIDC sensor 28 Read signal processing unit 29 Density integrating unit 41C Toner supply hopper 42C Toner supply roller 43C Stirring roller 44C Developing roller 45C Magnetic sensor 46C Stirring chamber 50 Transport system 60 Operation panel 100 Image reader unit 101 Image reader control unit 200 Printer unit 201 Printer control unit 213 Toner supply roller drive unit

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Futama Hamada 2-3-113 Azuchicho, Chuo-ku, Osaka-shi, Osaka Inside Osaka International Building Minolta Co., Ltd. (72) Inventor: Yu Hamada, Azuchi, Chuo-ku, Osaka-shi, Osaka Osaka International Building Minolta Co., Ltd. (72) Inventor Yasuyuki 2-3-1, Azuchicho, Chuo-ku, Osaka-shi, Osaka

Claims (9)

[Claims] 1. An image forming apparatus comprising: a developing device using a two-component developer; and control means for controlling a toner concentration in the developing device by replenishing an appropriate amount of toner from a toner replenishing means based on predetermined control parameters. A toner density detecting means for detecting a toner density in a developing device; and a change amount of a bulk density of the developer in the developing device based on the toner density detected at two or more specific times. And a control unit that controls the toner density by correcting the control parameter based on the evaluation result of the bulk density evaluation unit within a predetermined initial time after the operation of the developing device is restarted. An image forming apparatus, comprising: 2. The method according to claim 1, wherein the bulk density evaluation unit determines the bulk density based on a toner density detected at the end of the previous operation of the developing device or immediately thereafter, and a toner density detected at the time of restarting the operation of the developing device. The image forming apparatus according to claim 1, wherein the amount of change is evaluated. 3. The control unit controls the toner density based on a comparison result between the detected toner density value and a predetermined reference density value, and the control unit controls the toner density within the predetermined initial time. 3. The image forming apparatus according to claim 1, wherein the correction is performed based on an evaluation result of the bulk density evaluation unit as a control parameter. 4. When the toner replenishment unit determines that toner replenishment is necessary based on a comparison result between the detected toner density value and a predetermined reference density value, the control unit operates the toner replenishment unit for a predetermined time. 2. The image forming apparatus according to claim 1, wherein the density is controlled, and the operation time of the toner supply unit is corrected as a control parameter within the predetermined initial time based on the evaluation result of the bulk density evaluation unit. Or the image forming apparatus according to 2. 5. The image forming apparatus according to claim 1, wherein the control unit further includes a determination unit that determines the length of the initial time based on an evaluation result of the bulk density evaluation unit. . 6. An image forming apparatus comprising: a developing device using a two-component developer; and control means for controlling a toner density in the developing device, wherein the density of a document on which an image is to be formed is detected. An image comprising document density detection means, wherein the control means controls toner density using a detection result of the document density detection means as a control parameter within a predetermined initial time after restarting operation of the developing device. Forming equipment. 7. A developing device using a two-component developer, and control means for controlling a toner concentration in the developing device, wherein the developing device develops an electrostatic latent image on a photoreceptor to form a toner image. A toner image density detecting means for detecting a density of a toner image formed on the photoconductor, wherein the control means comprises a predetermined initial time after resuming operation of the developing device. Wherein the toner density is controlled using the detection result of the toner image density detecting means as a control parameter. 8. The amount of change in the bulk density of the developer in the developing device based on the toner concentration detected immediately before or immediately after the end of the operation of the developing device and the toner concentration detected when the operation of the developing device is restarted. 8. The method according to claim 6, further comprising: a bulk density estimating unit that evaluates the following. The control unit further includes a determining unit that determines the length of the initial time based on an evaluation result of the bulk density estimating unit. The image forming apparatus as described in the above. 9. The method according to claim 1, wherein the control unit further includes a correction unit configured to correct the control parameter or the initial time based on a usage time of the carrier in the developer. The image forming apparatus as described in the above.