JP2008276133A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To control toner concentration to prescribed concentration even when deviation in detected concentration occurs. <P>SOLUTION: An image forming apparatus (U) includes: a toner concentration detecting means (C6D) for detecting the toner concentration (TC2) in developing units (Gy to Gk); a developer supply control means (C8) for controlling the developer supply device (Ug) on the basis of a toner concentration target value (Mb) as the target value of the toner concentration (TC2) and the detected toner concentration (TC2); and a toner concentration target value correcting means (C6) for correcting the toner concentration target value (Mb) to a value close to the detected toner concentration value (TC2) when the high or low level of a reference toner image density (TC1) to a condition calculation reference value (Ma) as the reference of an image forming condition is the same as the high or low level of the detected value of the toner concentration (TC2) to the toner concentration target value (Mb), and also, when the accumulated supply amount (t1) to the accumulated number of printed pixels (N1) exceeds a correction execution determination range. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image forming apparatus that forms an image.

In an electrophotographic image forming apparatus, an electrostatic latent image is formed on the surface of an image carrier, visualized as a toner image by a developing device, and transferred to a medium. As a developer accommodated in the developing device, one using a two-component developer composed of a toner and a carrier is known. When an image is formed using a two-component developer, the developer It is necessary to maintain the toner density, which is the ratio of the toner with respect to the total amount, within a predetermined range. Therefore, the toner density is detected, and the replenishment operation is controlled so that the detected toner density becomes a predetermined target value.
Also, depending on the deterioration over time and the environment such as temperature and humidity, the latent image is formed on the surface of the image carrier, and the image forming conditions such as applied voltage when developing and transferring are corrected to appropriate values. Therefore, a reference toner image serving as a reference, that is, a so-called patch image is formed, and the density of the reference toner image is read by the density detection sensor to correct the image forming conditions.

As such an image forming apparatus, techniques described in Patent Documents 1 to 3 are conventionally known.
Japanese Patent Application Laid-Open No. 10-39555 discloses a technique for adjusting a charging potential and a developing potential based on an image density detected by reading a test print from a platen glass. Further, in Patent Document 1, based on the image density detected by reading another test print from the platen glass, for example, with respect to the target value of the toner density of the developer due to deterioration over time, etc. A technique is also described in which when the detected toner density is low, the target value of the toner density is corrected to a high value and the image density is maintained at a desired value.

Patent Document 2 (Japanese Patent Laid-Open No. 2002-162895) describes a technique for adjusting the developing bias and the voltage applied to the charging device based on the density of the first test patch. In the technique described in Patent Document 2, the toner density of the developing device is estimated based on the detected density of the second test patch, and the toner is replenished based on the toner density. In the technique described in Patent Document 2, the difference between the density of the first test patch and the target value is greater than or equal to the threshold value, and the difference between the density of the second test patch and the target value is less than the threshold value. Is also described as a technique for determining that the toner concentration is excessive due to the deterioration of the developer and changing the target value of the second test patch for controlling the supply of the toner to a high value when the toner is continuously applied three or more times.
That is, based on the density of the second test patch, even when the developer is replenished, when the developer density remains low, it is determined that the toner density is excessive due to the deterioration of the developer, The toner supply (dispensing) is stopped for a certain period of time and the target value is set to a high value so that the developer is not replenished any more.

In Patent Document 3 (Japanese Patent Laid-Open No. 2006-17918), the density of the second reference toner image is adjusted by adjusting the DC of the developing bias, the charging potential, the exposure condition, and the like based on the density of the first reference toner image. Describes a technology for executing toner replenishment by detecting toner density based on the above.
In the technique described in Patent Document 3, when the average value of the developing bias set from the density of the first reference toner image exceeds the upper limit value of the target potential, the correction value is subtracted from the detected value of the toner density. Make corrections. At this time, since the technology described in Patent Document 3 uses a sensor that detects the density from the reflectance, the reflectance increases as the density decreases, and the detection value of the sensor increases. Therefore, when the correction value is subtracted from the detection value of the sensor, the correction is performed in the direction in which the density of the reference toner image read by the sensor increases.
Conversely, when the average value of the developing bias set from the density of the first reference toner image is less than the lower limit value of the target potential, the correction value is added to the detection value of the sensor, and the toner density is decreased. Correct in direction.
In the technique described in Patent Document 3, when the detection value of the sensor is not corrected, the target value of the toner density is corrected to be low when the density of the first reference toner image for setting the image forming condition is high. This corresponds to correcting the target value of the toner density to be high when the density of the first reference toner image is low.

JP-A-10-39555 (“0027” to “0037”, “0051” to “0078”, especially “0065”) JP 2002-162895 ("0047" to "0086", especially "0083" to "0084") JP 2006-17918 A (“0070” to “0074”, “0091” to “0094”, “0107” to “0113”)

  A sensor that detects the density of a toner image when creating a toner image, detecting the density of the toner image, and adjusting and correcting the image forming conditions such as the applied voltage and the toner density of the developing device as in the prior art. If there is a shift in the mounting position or mounting angle, or there is an individual difference in detection sensitivity, the detected concentration may shift. In a state where there is a deviation in the detected density, as in the conventional technique, when the toner density of the developing device exceeds the upper limit, the target value is decreased, and when the toner density is lower than the lower limit, the target value is increased. When correction is performed, the toner density of the developing device may cause an abnormal decrease or an abnormal increase. When the toner density is abnormally lowered, the carrier in the developer adheres to the image carrier and stains the printed image, or the image carrier is damaged to cause image defects such as streaks and black spots, or the image density is significantly reduced. There was a problem. In addition, when the toner density rises abnormally, there are problems that image defects such as fogging occur, the toner flies and stains the inside of the machine, or the image density rises remarkably.

  In view of the above circumstances, it is a technical object of the present invention to control the toner density to a predetermined density even if a detected density deviation occurs.

In order to solve the technical problem, an image forming apparatus according to claim 1 is provided.
An image carrier, a latent image forming device that forms a latent image on the surface of the image carrier, and a developing unit that develops the latent image on the surface of the image carrier into a visible image, the surface of the image carrier A toner image forming apparatus for forming a reference toner image having a predetermined density set in advance;
A developer supply device for supplying a new developer to the developer;
Reference toner image density detecting means for detecting the density of the reference toner image;
Based on a condition calculation reference value which is a reference for calculating an image forming condition for forming an image by the toner image forming apparatus, and a detected density of the reference toner image detected by the density detecting unit, the toner Condition calculating means for calculating an image forming condition for forming an image by the image forming apparatus;
Toner concentration detecting means for detecting the toner concentration of a two-component developer comprising toner and carrier contained in the developing device;
A developer replenishment control means for controlling the driving of the developer replenishing device based on a toner density target value that is a target value of the toner density of the developing device and a toner density detected by the toner density detection means;
A cumulative replenishment amount measuring means for measuring a cumulative replenishment amount that is a cumulative value of a developer replenishment amount replenished by the developer replenishing device;
A cumulative print pixel number measuring unit that measures a cumulative print pixel number that is a cumulative value of the number of pixels of the print image formed by the latent image forming device;
The high or low detection value of the reference toner image density with respect to the condition calculation reference value is the same as the high or low detection value of the toner density with respect to the toner density target value, and the cumulative print pixel Toner concentration target value correction means for correcting the toner density target value to a value close to the detected value of the toner density when the cumulative supply amount with respect to the number exceeds a preset correction execution determination range;
It is provided with.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect,
The toner density detecting means for detecting the toner density of the two-component developer contained in the developing device based on the density of a second reference toner image different from the reference toner image for calculating the image forming condition;
It is provided with.

According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect,
The cumulative replenishment with respect to the cumulative print pixel count when the detected value of the density of the reference toner image with respect to the condition calculation reference value is high and the detected value of the toner density with respect to the target toner density value is high. A toner density target that corrects the toner density target value to a value obtained by adding the density correction value to the toner density target value when the amount is equal to or lower than the correction execution judgment lower limit that is the lower limit of the correction execution determination range Value correction means,
It is provided with.

According to a fourth aspect of the present invention, in the image forming apparatus according to any one of the first to third aspects,
The cumulative replenishment for the cumulative print pixel count when the detected value of the density of the reference toner image with respect to the condition calculation reference value is low and the detected value of the toner density with respect to the target toner density value is low. A toner density target for correcting the toner density target value to a value obtained by subtracting the density correction value from the toner density target value when the amount is equal to or greater than the correction execution determination upper limit value that is the upper limit value of the correction execution determination range. Value correction means,
It is provided with.

According to a fifth aspect of the present invention, in the image forming apparatus according to the third or fourth aspect,
A density correction value calculating means for calculating the density correction value based on the cumulative correction amount with respect to the cumulative print pixel number and a difference between the toner density detection value with respect to the toner density target value;
It is provided with.

The invention according to claim 6 is the image forming apparatus according to claim 3 or 4,
Density correction value calculating means for calculating the density correction value based on the change amount of the cumulative correction amount with respect to the change amount of the cumulative print pixel number and the difference between the detected value of the toner density with respect to the toner density target value. ,
It is provided with.

According to a seventh aspect of the present invention, in the image forming apparatus according to any one of the first to sixth aspects,
The correction execution determination range that changes with a change in the cumulative print pixel number or the cumulative correction amount,
It is provided with.

The invention according to claim 8 is the image forming apparatus according to claim 7,
The correction execution determination range that changes based on the supply capability of the developer supply device;
It is provided with.

According to the first aspect of the present invention, even if a detection density shift occurs due to problems such as a mounting position shift or an individual difference in detection sensitivity in a sensor for detecting the density, the toner density target value is detected as the toner density. By correcting to a value close to the value, the toner density can be controlled to a predetermined density, and an abnormal increase or decrease in toner density can be prevented.
According to the second aspect of the present invention, it is possible to detect the image forming condition and the toner density using two reference toner images, and to detect the toner density compared to the case where the configuration of the present invention is not provided. The number of sensors can be omitted or the number of sensors that read the density of the reference toner image can be shared.
According to the third aspect of the present invention, since the cumulative replenishment amount with respect to the cumulative number of print pixels is equal to or less than the correction execution determination lower limit value, the detected value of the density of the reference toner image even though the actual toner density is low. When the toner density detection value is high and the detected value of the toner density is high, the toner density target value is corrected to the value obtained by adding the density correction value, so that the replenishment of the toner can be promoted and an abnormal decrease in the toner density can be prevented. it can.

According to the fourth aspect of the present invention, since the cumulative replenishment amount with respect to the cumulative number of print pixels is equal to or greater than the correction execution determination upper limit value, the detected value of the density of the reference toner image even though the actual toner density is high. When the toner density detection value is low and the toner density detection value is low, the toner density target value is corrected to a value obtained by subtracting the density correction value, so that toner replenishment can be suppressed and abnormal increase in toner density can be prevented. it can.
According to the fifth aspect of the present invention, the density correction value can be calculated based on the cumulative correction amount with respect to the cumulative number of print pixels and the difference between the detected toner density value with respect to the toner density target value. The density correction value can be set with higher accuracy than in the case where the configuration is not provided.
According to the sixth aspect of the present invention, the density correction value can be calculated based on the change amount of the cumulative correction amount with respect to the change amount of the cumulative number of print pixels.

According to the invention described in claim 7, since the correction execution determination range changes with the change in the cumulative number of print pixels or the cumulative correction amount, the correction execution determination range that changes according to the actual use situation can be adopted. Compared to the case without the configuration of the present invention, the toner density target value can be corrected with high accuracy.
According to the eighth aspect of the present invention, the correction execution determination range changes according to the replenishment ability that decreases as the toner amount decreases. Can be corrected.

Next, specific examples (examples) of the embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to the following examples.
In order to facilitate understanding of the following description, in the drawings, the front-rear direction is the X-axis direction, the left-right direction is the Y-axis direction, the up-down direction is the Z-axis direction, and arrows X, -X, Y, -Y, The direction indicated by Z and -Z or the indicated side is defined as front, rear, right, left, upper, lower, or front, rear, right, left, upper, and lower, respectively.
In the figure, “•” in “○” means an arrow heading from the back of the page to the front, and “×” in “○” is the front of the page. It means an arrow pointing from the back to the back.

1 is a perspective explanatory view of an image forming apparatus according to a first embodiment of the present invention.
FIG. 2 is an overall explanatory diagram of the image forming apparatus according to the first exemplary embodiment.
In FIG. 1, a printer U as an example of an image forming apparatus according to a first embodiment of the present invention includes an apparatus main body U1 and a front cover U2 as an example of an opening / closing part that can be opened and closed with respect to the apparatus main body. In the printer U, an image forming unit UP is detachably supported, and a paper feed cassette TR1 as an example of a paper feed container in which a recording paper S on which an image is recorded is housed is housed. A discharge tray TRh as an example of a paper discharge unit is provided on the upper surface.
In FIG. 2, the printer U includes a control unit C, an image processing unit GS whose operation is controlled by the control unit C, a laser driving circuit DL, a power supply device E, and the like. The power supply device E applies a bias voltage to charging rollers CRy to CRk, developing units Gy to Gk, a transfer roller Rt, and the like which will be described later.

  The image processing unit GS uses print information input from an external information processing apparatus or the like as latent images corresponding to images of four colors K (black), Y (yellow), M (magenta), and C (cyan). The image information is converted into image information for formation and output to a laser drive circuit DL as an example of a latent image writing device drive circuit at a predetermined timing. The laser drive circuit DL outputs a laser drive signal to the latent image forming apparatus ROS according to the input image information of each color. The latent image forming device ROS emits laser beams Ly, Lm, Lc, and Lk as an example of image writing light of each color in accordance with a laser drive signal.

A toner replenishing device Ug as an example of a developer replenishing device for replenishing toner is disposed above the latent image forming device ROS. In front of the latent image forming apparatus ROS (in the + X direction), drum-shaped photosensitive members Py, Pm, Pc, and Pk are disposed as an example of an image carrier that is rotationally driven.
Around the photosensitive body Pk for K color, there are a charging roll CRk as an example of a charger, a developing unit Gk in which a developing unit is unitized, and a cleaning brush for a photosensitive member as an example of an image carrier cleaner. CLk and the like are arranged. The image carrier Pk, the charging roll CRk, the photoconductor cleaning brush CLk, and the like constitute a photoconductor unit UK for K color.
Around the photoconductors Py, Pm, and Pc for other colors, charging rolls CRy, CRm, and CRc, developing units Gy, Gm, and Gc, and photoconductor cleaning brush CLy similar to those around the photoconductor Pk are provided. , CLm, CLc, etc. are arranged. Similarly to the photoconductor unit UK, the photoconductor units UY, UM, and UC of each color are configured by the photoconductors Py to Pc, the charging rolls CRy to CRc, the photoconductor cleaning brushes CLy to CLc, and the like. Yes. In addition, the toner image forming apparatus according to the first exemplary embodiment is configured by the photosensitive units UY to UK, the developing units Gk to Gk, the latent image forming apparatus ROS, and the like.

An intermediate transfer device Ut is disposed in front of the photoreceptor units UY, UM, UC, UK. The intermediate transfer device Ut includes three intermediate transfer drums DR1, DR2, and DR3 as intermediate transfer members. The first intermediate transfer drum DR1 faces and contacts the Y-color photoconductor Py in the primary transfer region Qy and contacts the M-color photoconductor Pm in the primary transfer region Qm. The second intermediate transfer drum DR2 is in contact with the C-color photoconductor Pc in the primary transfer region Qc and in contact with the K-color photoconductor Pk in the primary transfer region Qk. The third intermediate transfer drum DR3 is in contact with the intermediate transfer drums DR1 and DR2 in the intermediate transfer regions Q31 and Q32.
In front of the third intermediate transfer drum DR3, a secondary transfer roll Rt as an example of a secondary transfer device that is in contact with the secondary transfer region Q2 is disposed so as to face. A secondary transfer roll cleaner CLt as an example of a cleaning device for a secondary transfer device that cleans the toner on the surface of the secondary transfer roll Rt is in contact with the secondary transfer roll Rt. Further, the secondary transfer roll Rt detects the density of the image transferred to the surface of the secondary transfer roll Rt on the downstream side in the rotational direction of the secondary transfer area Q2 and upstream in the rotational direction of the secondary transfer roll cleaner CLt. A density sensor SN1 as an example of the density detection member is disposed to face the density sensor SN1.

Intermediate transfer drum cleaning brushes CL1 and CL2 as an example of an intermediate transfer body cleaner are arranged downstream of the intermediate transfer regions Q31 and Q32 in the rotational direction of the intermediate transfer drums DR1 and DR2. An intermediate transfer drum cleaning brush CL3 is disposed downstream of the secondary transfer region Q2 in the rotation direction of the third intermediate transfer drum DR3. A bias for toner image transfer is applied to each of the intermediate transfer drums DR1 to DR3 and the secondary transfer roll Rt.
The intermediate transfer drums DR1 to DR3 and the intermediate transfer drum cleaning brushes CL1 to CL3 constitute an intermediate transfer device Ut.

In FIG. 2, photoconductors Py, Pm, Pc, and Pk are uniformly charged by charging rolls CRy, CRm, CRc, and CRk, respectively, and then laser beams Ly, Lm, and Lc output from the latent image forming apparatus ROS. , Lk form an electrostatic latent image on the surface. When forming a full-color image, electrostatic latent images corresponding to four color images of Y, M, C, and K are formed on the respective photoreceptors Py, Pm, Pc, and Pk. Only the electrostatic latent image corresponding to the image of) is formed on the photosensitive member Pk.
The electrostatic latent images on the surfaces of the photoreceptors Py, Pm, Pc, and Pk are converted into Y (yellow), M ( Magenta), C (cyan), and K (black) toner images are developed. Each developing device Gy, Gm, Gc, Gk is supplied with toner from toner cartridges KTy, KTm, KTc, KTk of each color as an example of a developer supply container mounted on the toner supply device Ug.

Y (yellow) and M (magenta) toner images formed on the Y-color and M-color photoconductors Py and Pm are primarily transferred to the first intermediate transfer drum DR1 in the primary transfer areas Qy and Qm. After that, the image is transferred to the third intermediate transfer drum DR3 in the intermediate transfer region Q31. C (cyan) and K (black) toner images formed on the C-color and K-color photoconductors Pc and Pk are primary-transferred on the second intermediate transfer drum DR2 in the primary transfer areas Qc and Qk. Then, in the intermediate transfer region Q32, the toner is transferred onto the Y (yellow) and M (magenta) toners of the third intermediate transfer drum DR3.
The recording paper S as an example of the medium stored in the paper feed tray TR1 is taken out at a predetermined timing by a pickup roll Rp as an example of a take-out member, and separated one by one by a separation roll Rs as an example of a separating member. The The separated recording sheet S is conveyed to a registration roll Rr as an example of a transfer region conveyance timing adjustment member by a conveyance roller Ra as an example of a conveyance member in the sheet conveyance path SH1. Further, the recording sheet S on the manual feed tray TR0 as an example of a manual feed unit is fed by the manual feed roll Rp0 and conveyed to the registration roll Rr.

The recording sheet S transported to the registration roll Rr is transported to the secondary transfer area Q2 in time with the multiple toner image or single color toner image moving to the secondary transfer area Q2, and is then transported to the secondary transfer roll Rt. The toner image is secondarily transferred.
The toner remaining on the surface of each photoconductor Py, Pm, Pc, Pk after the primary transfer is temporarily adsorbed and held by the photoconductor cleaning brushes CLy, CLm, CLc, CLk, and the photoconductors Py, Pm, Pc. , Pk surface is cleaned. Similarly, residual toner adhering to the surface of the intermediate transfer drums DR1 to DR3 after intermediate transfer or secondary transfer is cleaned by the intermediate transfer drum cleaning brushes CL1 to CL3.
Waste toner removed by the cleaning brushes CLk, CLy, CLm, CLc, CL1 to CL3 is collected in a waste toner collection container Bt.

The recording sheet S on which the toner image is secondarily transferred in the secondary transfer area is conveyed to the fixing device F. When the recording sheet S passes through a fixing region Q5 where a heating roll Fh as an example of a heating fixing member of the fixing device F and a pressure roll Fp as an example of a pressure fixing member are pressed, the toner image is heated and fixed. Is done. The recording sheet S on which the toner image is heat-fixed is conveyed to a discharge roller Rh as an example of a discharge member, and is discharged to a discharge tray TRh.
When performing duplex printing, the recording paper S is switched back by the discharge roller Rh and conveyed to the paper reversing path SH2, and is retransmitted to the registration roll Rr with the front and back reversed.

(Description of control unit)
FIG. 3 is a block diagram of the control unit of the image forming apparatus according to the first exemplary embodiment of the present invention.
4 is a block diagram of the control unit of the image forming apparatus according to the first exemplary embodiment of the present invention, and is a continuation of FIG.
3 and 4, the control unit C includes an input / output interface for performing input / output of signals to / from the outside and adjustment of the input / output signal level, and a ROM storing programs and data for performing necessary processes. (Read-only memory), RAM (random access memory) for temporarily storing necessary data, a central processing unit (CPU) that performs processing according to a program stored in the ROM, a clock oscillator, etc. Various functions can be realized by executing a program stored in the ROM.

(Signal input element connected to the control unit C)
The control unit C receives signals from the operation unit UI, the concentration sensor SN1, and other signal input elements.
The operation unit UI includes a display unit UI1, an operation button UI2, and the like.
The density sensor SN1 detects the density of the reference toner image.

(Control element connected to the control unit C)
The control unit C is connected to the main motor drive circuit D1, the developing device motor drive circuit D2, the developer supply motor drive circuit D3, and other control elements, and outputs their operation control signals. .
The main motor drive circuit D1 rotationally drives the image carriers Py to Pk and the like via a main motor M1 which is an example of a main drive source.
The developing device motor drive circuit D2 rotationally drives the developer holding member and the circulating conveyance member in the developing devices Gy to Gk via the developing device motors M2y to M2k which are driving sources for the developing devices Gy to Gk. .
The toner replenishing motor drive circuit D3 drives the toner replenishing device Ug via the toner replenishing motor M3 which is a driving source of the toner replenishing device Ug, and the developing devices Gy to Gk from the toner cartridges KTy, KTm, KTc, KTk. Refill the toner.

The power supply circuit E includes a development power supply circuit E1, a charging power supply circuit E2, a transfer power supply circuit E3, a fixing power supply circuit E4, and the like.
The developing power supply circuit E1 applies a developing voltage to the developing rolls of the developing devices Gy to Gk. Note that the developing power supply circuit E1 of Example 1 applies a voltage in which an AC voltage is superimposed on a DC voltage to the developing roll.
The charging power supply circuit E2 applies a charging voltage to the charging rolls CRy to CRk.
The transfer power supply circuit E3 applies a transfer voltage to the intermediate transfer drums DR1 to DR3 and the secondary transfer roll Rt2.
The fixing power supply circuit E4 supplies a heating current to the heater of the heating roll Fh of the fixing device F.

(Function of the control unit C)
The control unit C has a function of executing processing according to an input signal from the signal output element and outputting a control signal to each control element.
That is, the control unit C has the following functions.
C1: Job control means The job control means C1 as an example of the image recording control means is configured to respond to a print request from the image information transmitting device, the latent image forming device ROS, the photoreceptors Py to Pk, the transfer devices DR1 to DR3, By controlling the operations of Rt, fixing device F, etc., a job which is an image forming operation is executed.

C2: Main motor rotation control means The main motor rotation control means C2 controls the main motor M1 via the main motor drive circuit D1 to control the driving of the photoreceptors Py to Pk and the like.
C3: Power supply circuit control means The power supply circuit control means C3 includes a development power supply control means C3A, a charging power supply control means C3B, a transfer power supply control means C3C, and a fixing power supply control means C3D, and controls the power supply circuit E. The power supply to each member of the image forming apparatus U is controlled.

C3A: Development power control means The development power control means C3A controls the development power supply circuit E1 to control the development voltage.
C3B: Charging power supply control means The charging power supply control means C3B controls the charging power supply circuit E2 to control the charging voltage.
C3C: Transfer power supply control means The transfer power supply control means C3C controls the transfer power supply circuit E3 to control the transfer voltage.
C3D: Fixing power supply control means The fixing power supply control means C3D controls the fixing power supply circuit E4 to control the fixing temperature of the fixing device F.

C4: Latent image forming device control means The latent image forming device control means C4 has a cumulative printing pixel number measuring means C4A, and controls the latent image forming device ROS via the laser drive circuit DL and the like, and the photoreceptors Py˜ An electrostatic latent image is formed on the Pk surface.
C4A: Cumulative Print Pixel Number Measuring Unit The cumulative print pixel number measuring unit C4A measures the number of pixels formed by the latent image forming apparatus ROS, that is, the cumulative print pixel number N1 that is a cumulative value of the pixel number. In Example 1, the cumulative print pixel number N1 is measured for each of Y, M, C, and K colors.
C5: Printed sheet number measuring means The printed sheet number measuring means C5 measures a cumulative printed sheet number N that is a cumulative value of the printed sheet number printed by the image forming apparatus U.

C6: Toner density target value correcting means The toner density target value correcting means C6 has means C6A to C6R described later, and is a toner that is a target value of the toner density of the two-component developer accommodated in the developing devices Gy to Gk. The density target value Mb is corrected. In the first embodiment, the toner density target value Mb is corrected for each color of Y, M, C, and K.
C6A: Target Value Correction Start Determination Unit The target value correction start determination unit C6A includes a density target value correction number storage unit C6A1, and determines whether or not to start correction of the toner density target value Mb. The target value correction start determination unit C6A according to the first exemplary embodiment determines whether the accumulated print sheet number N starts correction of the toner density target value Mb stored in the density target value correction sheet storage unit C6A1. When the density target correction sheet number Na, which is a reference threshold value, is reached, it is determined that it is time to start correcting the toner density target value Mb. The density target correction sheet number Na can be set to Na = 60 (sheets), for example, and can be changed to an arbitrary value according to the design or the like.

C6B: Reference toner image formation control means The reference toner image formation control means C6B includes a first reference toner image formation control means C6B1 and a second reference toner image formation control means C6B2, and the main motor rotation control means C2 A control signal is transmitted to the power supply circuit control means C3, the latent image forming apparatus control means C4, etc., a reference toner image is created, and the secondary paper is passed through the intermediate transfer drums DR1 to DR3 without conveying the recording paper S. Transfer to the transfer roll Rt.
C6B1: First reference toner image formation control means The first reference toner image formation control means C6B1 forms a first reference toner image for setting image forming conditions such as a developing voltage during an image forming operation. In the first reference toner image formation control unit C6B1 according to the first exemplary embodiment, a conventionally known so-called patch image can be used as the first reference toner image, and Y, M can be detected by one density sensor SN1. , C, K first reference toner images are formed at positions shifted from the rotation direction of the secondary transfer roll Rt. Note that the first reference toner image for setting image forming conditions is, for example, an image having a density of 33% (corresponding to a target value Ma described later) formed under the same conditions as in the image forming operation. it can.

C6B2: Second reference toner image formation control means The second reference toner image formation control means C6B2 forms a second reference toner image for detecting the toner density of the developer contained in the developing devices Gy to Gk. . In the second reference toner image formation control unit C6B2 according to the first exemplary embodiment, as the second reference toner image, a conventionally known so-called patch image can be used as in the case of the first reference toner image. Subsequent to the toner image, second reference toner images of Y, M, C, and K are formed at positions shifted in the rotation direction of the secondary transfer roll Rt. In order to detect the toner density, the second reference toner image can be, for example, a toner image developed by applying only a DC voltage as a development voltage at a density of 100%.

C6C: Reference toner image density detection means The reference toner image density detection means C6C detects the toner image density of the reference toner image based on the output signal of the density sensor SN1. The reference toner image density detection unit C6C according to the first exemplary embodiment detects the toner image density TC1 of the first reference toner image and the toner image density of the second reference toner image for each color.
C6D: Toner density detection means The toner density detection means C6D is configured to control the two-component developer of the developing units Gy to Gk based on the toner image density of the second reference toner image detected by the reference toner image density detection means C6C. The toner density TC2 is detected.

FIG. 5 is an explanatory diagram of numerical values used for control of the image forming apparatus according to the first exemplary embodiment. When it is determined that the densities of the first reference toner image and the second reference toner image are both higher than the target value, FIG. 5A is an explanatory diagram of a condition calculation reference value and a toner density target value, and FIG. 5B is an explanatory diagram of a change amount.
FIG. 6 is an explanatory diagram of each numerical value used for control of the image forming apparatus according to the first embodiment, in which it is determined that the densities of the first reference toner image and the second reference toner image are both lower than the target value. FIG. 6A is an explanatory diagram of a condition calculation reference value and a toner density target value, and FIG. 6B is an explanatory diagram of a change amount.

C6E: Condition Calculation Reference Value Storage Unit In FIGS. 3 to 6, the condition calculation reference value storage unit C6E includes an environment such as a development voltage, a charging voltage, a transfer voltage, and other environments such as temperature and humidity, and each of the photoreceptors Py to Pk. A condition setting density target value Ma is stored as an example of a condition calculation reference value that serves as a reference for calculating and setting an image forming condition that varies due to deterioration of the member over time.
C6F: Reference value upper limit width storage means The reference value upper limit width storage means C6F is a density for condition setting caused by an error of the density sensor SN1 when determining whether the density TC1 of the first reference toner image is high or low. A reference value upper limit width Ma1 that is an upper limit width of the allowable range of the target value Ma is stored.
C6G: Reference value lower limit width storage means The reference value lower limit width storage means C6G is a condition setting density generated by an error of the density sensor SN1 or the like when determining whether the density TC1 of the first reference toner image is high or low. The reference value upper limit width Ma2 that is the lower limit width of the allowable range of the target value Ma is stored. The reference value upper limit width Ma1 and the reference value lower limit width Ma2 can be the same value.

C6H: Toner density target value storage means The toner density target value storage means C6H stores a toner density target value Mb that is a target value of the toner density TC2 of the developer accommodated in the developing devices Gy to Gk.
C6I: Toner density upper limit width storage means The toner density upper limit width storage means C6I is a toner density that is an upper limit width of an allowable range caused by an error of the density sensor SN1 when determining whether the toner density TC2 is high or low. The upper limit width Mb1 is stored.
C6J: Toner density lower limit width storage means When the toner density lower limit width storage means C6J determines whether the toner density TC2 is high or low, the toner density is a lower limit width of an allowable range caused by an error of the density sensor SN1. The lower limit width Mb2 is stored. The toner density upper limit width Mb1 and the toner density lower limit width Mb2 can be set to the same value.

C6K: Condition Setting Density Level Discrimination Unit In FIG. 4, the condition setting density level discrimination unit C6K includes the density of the first reference toner image detected by the reference toner image density detection unit C6C and the condition setting density target value. Based on Ma, it is determined whether the density of the first reference toner image is higher or lower than the condition setting density target value Ma. The condition setting density high / low discrimination means C6K according to the first exemplary embodiment has the density TC1 of the first reference toner image higher than the reference value upper limit width Ma1 around the condition setting density target value Ma, that is, TC1 ≧ Ma + Ma1. Determine if it exists. Further, the condition setting density high / low discrimination means C6K determines whether the density TC1 of the first reference toner image is lower than the reference value lower limit width Ma2 around the condition setting density target value Ma, that is, TC1 ≦ Ma−Ma2. Determine if it exists.
C6L: Toner density high / low discrimination means The toner density high / low discrimination means C6L determines that the toner density TC2 is based on the toner density TC2 of the developing units Gy to GK detected by the toner density detection means C6D and the toner density target value Mb. It is determined whether it is higher or lower than the density target value Mb. The toner density high / low discrimination means C6L according to the first exemplary embodiment determines whether the toner density TC2 is higher than the toner density upper limit width Mb1 around the toner density target value Mb, that is, TC2 ≧ Mb + Mb1. The toner density high / low discrimination means C6L determines whether the toner density TC2 is lower than the toner density lower limit width Mb2 around the toner density target value Mb, that is, TC2 ≦ Mb−Mb2.

C6M: Change Amount Calculation Means The change amount calculation means C6M calculates a change amount H1 = t1 / N1 with respect to the cumulative print pixel number N1 of the accumulated value t1 of the replenishment amount by the toner replenishing device Ug.
C6N: Correction execution determination range storage means The correction execution determination range storage means C6N is a correction execution determination lower limit value storage means C6N1 that stores a correction execution determination lower limit value Ha, and a correction execution determination upper limit value that stores a correction execution determination upper limit value Hb. Storage means C6N2, and stores a correction execution determination range for determining whether or not to correct the toner density target value Mb based on the amount of change. As shown in FIGS. 5B and 6B, the correction execution determination range storage unit C6N according to the first embodiment has a straight line whose inclination is a correction execution determination lower limit Ha and an inclination is a correction execution determination upper limit value as shown in FIGS. The range sandwiched between the Hb straight line is stored. In the first embodiment, the correction execution determination range is set based on a range of values that the change amount H1 takes when the attachment position and the attachment angle of the density sensor SN1 are normal and the detection sensitivity is also normal. Yes.

C6P: Correction execution determining means The correction execution determining means C6P determines whether or not to correct the toner density target value Mb. The correction execution determination unit C6P according to the first exemplary embodiment determines that the toner density target value Mb is to be corrected in the following situations (1) to (4).
(1) The density TC1 of the first reference toner image is higher than the condition setting density target value Ma, the toner density TC2 is higher than the toner density target value Mb, and the change amount H1 is lower than the correction execution determination lower limit value Ha. If low. That is, when TC1 ≧ Ma + Ma1, TC2 ≧ Mb + Mb1, and H1 ≦ Ha.
(2) When the density TC1 of the first reference toner image is higher than the condition setting density target value Ma and the toner density TC2 is lower than the toner density target value Mb. That is, in Example 1, when TC1 ≧ Ma + Ma1 and TC2 ≦ Mb−Mb2.
(3) The density TC1 of the first reference toner image is lower than the condition setting density target value Ma and the toner density TC2 is higher than the toner density target value Mb. That is, when TC1 ≦ Ma−Ma2 and TC2 ≧ Mb + Mb1.
(4) The density TC1 of the first reference toner image is lower than the condition setting density target value Ma, the toner density TC2 is lower than the toner density target value Mb, and the change amount H1 is lower than the correction execution determination upper limit value Hb. If high. That is, when TC1 ≦ Ma−Ma2, TC2 ≦ Mb−Mb2, and H1 ≧ Hb.

C6Q: Density Correction Value Storage Unit The density correction value storage unit C6Q includes a density target addition correction value storage unit C6Q1 and a density target subtraction correction value storage unit C6Q2, and is a correction value for correcting the toner density target value Mb. The density correction value is stored.
C6Q1: Density target addition correction value storage means The density target addition correction value storage means C6Q1 stores a density target addition correction value Nh1 used when correcting the toner density target value Mb to a high value. In the first embodiment, it is used in the cases (1) and (3) determined by the correction execution determining means C6P.
C6Q2: Density Target Subtraction Correction Value Storage Unit The density target subtraction correction value storage unit C6Q2 stores a density target subtraction correction value Nh2 used when correcting the toner density target value Mb to a low value. In the first embodiment, it is used in the cases (2) and (4) determined by the correction execution determining means C6P.

C6R: Toner density target value setting means The toner density target value setting means C6R is based on the determination result by the correction execution determination means C6P and the density target correction values Nh1, Nh2 stored in the density correction value storage means C6Q. Then, a new toner density target value Mb is set, and the toner density target value Mb of the toner density target value storage means C6H is updated. That is, in the cases (1) and (3), a value obtained by adding the density target addition correction value Nh1 to the toner density target value Mb is set as a new toner density target value Mb, and the situations (2) and (4) ), A value obtained by adding the density target addition correction value Nh1 to the toner density target value Mb is set as a new toner density target value Mb.
C7: Condition Calculation Unit The condition calculation unit C7 calculates and sets an image forming condition such as a developing voltage when executing the image forming operation based on the first reference toner density TC1. For example, when the density TC1 is high, the DC component of the development voltage is set to a low value. The condition calculation means C7 is conventionally known (see, for example, Patent Documents 2 and 3), and various configurations can be adopted, and detailed description thereof is omitted.

C8: Developer replenishment control means The developer replenishment control means C8 has a developer replenishment time determination means C8A, a toner replenishment amount calculation means C8B, a replenishment time calculation means C8C, and a cumulative replenishment amount measurement means C8D. The toner supply motors M3y to M3k are driven via the toner supply motor drive circuit D3, and the supply of the developer to the developing devices Gy to Gk by the toner supply device Ug is controlled. In Example 1, the developer replenishment control is performed for each of Y, M, C, and K colors.
C8A: Developer replenishment time determination means The developer replenishment time determination means C8A has a previous replenishment pixel number storage means C8A1 and a replenishment interval pixel number storage means C8A2, and determines whether or not it is time to replenish the developer. Determine. The developer replenishment timing determination means C8A of Example 1 develops when the latent image forming device ROS writes the replenishment interval pixel number N0a and when the second reference toner image is created and the toner density TC2 is detected. It is determined that it is time to replenish the medicine.

C8A1: Previous replenishment pixel number storage means The previous replenishment pixel number storage means C8A1 stores the previous replenishment pixel number N0 which is the cumulative number of print pixels when the toner replenishment operation is executed by the previous toner replenishment device Ug.
C8A2: Replenishment Interval Pixel Number Storage Unit The replenishment interval pixel number storage unit C8A2 stores the replenishment interval pixel number N0a, which is an interval for executing replenishment. The replenishment interval pixel number N0a can be set to an arbitrary value according to design or the like, but can be set to 1000 (pixels), for example.
C8B: Toner replenishment amount calculation means The toner replenishment amount calculation means C8B calculates the toner replenishment amount based on the difference between the toner density TC2 and the toner density target value Mb.

C8C: Replenishment time calculation means The replenishment time calculation means C8C has unit replenishment time storage means C8C1 for storing a replenishment unit time ta that is a unit time for executing replenishment. A replenishment time tb for driving and executing developer replenishment is calculated. In the first embodiment, the replenishment time calculation means C8C calculates an integer n where the replenishment time tb is an integral multiple of the replenishment unit time ta, that is, tb = ta × n.
C8D: Cumulative Replenishment Amount Measuring Unit The cumulative replenishment amount measuring unit C8D measures a developer replenishment amount cumulative value t1 that is a cumulative value of the developer replenished by the toner replenishing device Ug. In the first embodiment, the replenishment times ta and tb are employed as the developer replenishment amount accumulated value t1, and the replenishment amount is indirectly measured by measuring the accumulated values of the replenishment times ta and tb.

FL1: Density detection execution flag The initial value of the density detection execution flag FL1 is “0”, which is “1” when the detection of the density of the reference toner image is executed, and “0” when the toner replenishment process is completed. Become.
FL2: Target value setting end flag The initial value of the target value setting end flag FL2 is “0”. When the setting of the toner density target value Mb is completed, the target value setting end flag FL2 is “1”. Become.

(Description of Flowchart of Example 1)
Next, the processing according to the first exemplary embodiment of the present invention will be described with reference to a flowchart. The processing for setting the image forming conditions based on the density TC1 of the first reference toner image is the same as a conventionally known method. Therefore, illustration and detailed description are omitted.
(Explanation of cumulative print pixel count measurement process)
FIG. 7 is a flowchart of the cumulative print pixel number measurement process in the image forming apparatus according to the first exemplary embodiment of the present invention.
The processing of each ST (step) in the flowchart of FIG. 7 is performed according to a program stored in the ROM of the control unit C. This process is executed in parallel with other various processes of the image forming apparatus U.
The cumulative print pixel number measurement process shown in FIG. 7 is started when the image forming apparatus U is turned on.

In ST1 of FIG. 7, it is determined whether or not a job that is an image forming operation is started. If yes (Y), the process proceeds to ST2. If no (N), ST1 is repeated.
In ST2, counting of the cumulative print pixel number N1, which is the cumulative value of the number of pixels of the printed image formed during the image forming operation, that is, measurement is started. Then, the process proceeds to ST3.
In ST3, it is determined whether or not single-sheet printing has been executed. If yes (Y), the process proceeds to ST4. If no (N), ST3 is repeated.
In ST4, 1 is added to the cumulative number of printed sheets N. That is, N = N + 1. Then, the process proceeds to ST5.

In ST5, it is determined whether or not the cumulative number N of printed sheets has reached the density target value correction number Na or more. If yes (Y), the process proceeds to ST6. If no (N), the process proceeds to ST8.
In ST6, a toner density target value correction process (see subroutines in FIGS. 8 and 9 described later) for correcting the toner density target value Mb is executed, and the process proceeds to ST7.
In ST7, the cumulative number N of prints is initialized to 0, and the process returns to ST5.
In ST8, it is determined whether or not the job is finished. If yes (Y), the process proceeds to ST9. If no (N), the process returns to ST3.
In ST9, the measurement of the cumulative print pixel number N1 is terminated. Then, the process returns to ST1.

(Description of toner density target value correction processing)
FIG. 8 is a flowchart of the toner density target value correction process according to the first exemplary embodiment, and is a flowchart of the subroutine of ST6 in FIG.
FIG. 9 is a flowchart of the toner density target value correction process according to the first exemplary embodiment, and is a flowchart subsequent to FIG.
Next, toner density target value correction processing will be described. In the first embodiment, the toner density target value correction processing is executed for each color of Y, M, C, and K. For simplification of description, only the toner density target value correction process for one color will be described.

In ST11 of FIG. 8, a first reference toner image and a second reference toner image are formed. Then, the process proceeds to ST12.
In ST12, the following processes (1) to (3) are executed, and the process proceeds to ST13.
(1) The first reference toner image density TC1 is detected.
(2) The toner density TC2 of the developing device is detected from the second reference toner image density.
(3) The density detection execution flag FL1 is set to “1”.
In ST13, it is determined whether or not the first reference toner image density TC1 is equal to or greater than (condition setting density target value Ma + reference value upper limit width Ma1). If yes (Y), the process proceeds to ST14. If no (N), the process proceeds to ST21.

In ST14, it is determined whether or not the toner density TC2 is equal to or greater than (toner density target value Mb + toner density upper limit width Mb1). If the answer is no (N) (that is, the situation (2)), the process proceeds to ST15, and if the answer is yes (Y), the process proceeds to ST16.
In ST15, the density target subtraction correction value Nh2 is subtracted from the toner density target value Mb, and the value after the subtraction is used as the corrected toner density target value Mb. That is, Mb = Mb−Nh2. Then, the process proceeds to ST20.
In ST16, the cumulative print pixel number N1 and the developer replenishment amount cumulative value t1 are read. Then, the process proceeds to ST17.
In ST17, the change amount H1 (= t1 / N1) is calculated, and the process proceeds to ST18.

In ST18, it is determined whether or not the change amount H1 is smaller than the correction execution determination lower limit value Ha. In the case of yes (Y) (that is, in the case of situation (1)), the process proceeds to ST19. If no (N), the process proceeds to ST20.
In ST19, as shown in FIG. 5, the density target addition correction value Nh1 is added to the toner density target value Mb, and the value after the addition is used as the corrected toner density target value Mb. That is, Mb = Mb + Nh1. Then, the process proceeds to ST20.
In ST20, the target setting end flag FL2 is set to “1”, the toner density target value correction process in FIG. 8 is ended, and the process returns to FIG.

In ST21 of FIG. 9, it is determined whether or not the first reference toner image density TC1 is equal to or less than (condition setting density target value Ma−reference value lower limit width Ma2). If yes (Y), the process proceeds to ST22, and, if no (N), the process proceeds to ST20.
In ST22, it is determined whether or not the toner density TC2 is equal to or less than (toner density target value Mb−toner density lower limit width Mb2). If the answer is no (N) (that is, the situation (3)), the process proceeds to ST23, and if the answer is yes (Y), the process proceeds to ST24.
In ST23, the density target addition correction value Nh1 is added to the toner density target value Mb, and the added value is used as the corrected toner density target value Mb. That is, Mb = Mb + Nh1. Then, the process proceeds to ST20.

In ST24, the cumulative print pixel number N1 and the developer replenishment amount cumulative value t1 are read. Then, the process proceeds to ST25.
In ST25, the change amount H1 (= t1 / N1) is calculated, and the process proceeds to ST26.
In ST26, it is determined whether or not the change amount H1 is larger than the correction execution determination upper limit value Hb. If yes (Y) (that is, situation (4)), the process proceeds to ST27, and if no (N), the process returns to ST20.
In ST27, the density target subtraction correction value Nh2 is subtracted from the toner density target value Mb, and the value after the subtraction is used as the corrected toner density target value Mb. That is, Mb = Mb−Nh2. Then, the process returns to ST20.

(Toner supply process)
FIG. 10 is a flowchart of toner supply processing in the image forming apparatus according to the first exemplary embodiment of the present invention.
Processing of each ST (step) in the flowchart of FIG. 10 is performed according to a program stored in the ROM of the control unit C. This process is executed in parallel with other various processes of the image forming apparatus U.
The toner supply process shown in FIG. 10 is started when the image forming apparatus U is powered on. The toner replenishing process of the first exemplary embodiment is executed for each color of Y, M, C, and K. However, since the process is similar, only the toner replenishing process for one color will be described for the sake of simplicity. Other explanations are omitted.

In ST31 of FIG. 10, it is determined whether or not the cumulative print pixel number N1 is equal to or greater than (previous supply pixel number N0 + supply interval pixel number N0a). If yes (Y), the process proceeds to ST32, and, if no (N), the process proceeds to ST35.
In ST32, the toner replenishing device Ug is driven for the unit replenishment time ta to replenish the toner. Then, the process proceeds to ST33.
In ST33, the unit supply time ta is added to the developer supply amount cumulative value t1. That is, t1 = t1 + ta. Then, the process proceeds to ST34.
In ST34, the previous replenishment pixel number N0 is updated to the cumulative print pixel number N1. That is, N0 = N1. Then, the process returns to ST31.

In ST35, it is determined whether or not the concentration detection execution flag FL1 is “1”. If yes (Y), the process proceeds to ST36, and, if no (N), the process returns to ST31.
In ST36, it is determined whether or not the target value setting end flag FL2 is “1”. If yes (Y), the process proceeds to ST37, and if no (N), ST36 is repeated.
In ST37, the toner replenishment amount is calculated based on the toner density TC2 and the toner density target value Mb. Then, the process proceeds to ST38.
In ST38, the replenishment time tb corresponding to the replenishment amount is calculated, and the toner replenishing device Ug is driven for the replenishment time tb to replenish the toner. Then, the process proceeds to ST39.
In ST39, the replenishment time tb corresponding to the replenishment amount is added to the developer replenishment amount cumulative value t1. That is, t1 = t1 + tb. Then, the process proceeds to ST40.
In ST40, the concentration detection execution flag FL1 and the target value setting end flag FL2 are set to “0”. Then, the process returns to ST31.

(Operation of Example 1)
In the image forming apparatus U according to the first embodiment having the above-described configuration, the first reference toner image and the second reference toner image each time the developer density target value correction sheet number Na printing is executed in the image forming operation. And the density is read by the density sensor SN1. An image forming condition is set based on the first reference toner image density TC1, and toner is replenished based on the toner density TC2 of the developing units Gy to Gk detected from the second reference toner image. The
In the image forming apparatus U according to the first exemplary embodiment, when the reference toner image is created and the density is read, the first reference toner image density TC1 is between Ma−Ma2 to Ma + Ma1, and the developing units Gy to Gk When the toner density TC2 is between Mb−Mb2 and Mb + Mb1, the toner density target value Mb is not corrected, and an image forming operation and a replenishing operation are performed based on the target values Ma and Mb. On the other hand, when the first reference toner image density TC1 and the toner density TC2 of the developing units Gy to Gk are far from the target values Ma and Mb, the toner density target value Mb may be corrected.

5 and 6, in the situation (2), that is, when the first reference toner image density TC1 is high and the toner density TC2 is low, the toner density target value Mb is corrected, and the density target subtraction correction value Nh2 is corrected. Only subtracted. That is, as in the technique described in Patent Document 3, the density difference between the low toner density TC2 and the corrected toner density target value Mb is reduced, the toner replenishing operation is suppressed, and the toner is added along with the image forming operation. Even if consumed, the toner is not replenished very much. As a result, even if the toner density is lowered, the toner density TC2 is kept between Mb−Mb2 and Mb + Mb1, and as the toner density is lowered, the higher first reference toner image density TC1 is lowered and Ma−Ma2− It falls within Ma + Ma1.
In the case of situation (3), that is, when the first reference toner image density TC1 is low and the toner density TC2 is high, the toner density target value Mb is corrected and added by the density target addition correction value Nh1. That is, as in the technique described in Patent Document 3, the density difference between the high toner density TC2 and the corrected toner density target value Mb is reduced, the toner replenishing operation is promoted, and the toner is added along with the image forming operation. It becomes easy to be replenished. As a result, even if the toner density increases due to replenishment, the toner density TC2 falls within the range of Mb−Mb2 to Mb + Mb1, and as the toner density increases, the first reference toner image density TC1 that has decreased increases to Ma−. It falls within Ma2-Ma + Ma1.

5A, in the case of the situation (1), that is, when the first reference toner image density TC1 is high and the toner density TC2 is also high, and the change amount H1 is smaller than the correction execution determination lower limit value Ha, The toner density target value Mb is corrected.
When there is no problem in the density sensor SN1, that is, when there is no displacement of the mounting position and the detection sensitivity is normal, the change amount H1 is a value between the correction execution determination lower limit value Ha and the correction execution determination upper limit value Hb. Should be. However, since the change amount H1 is below the correction execution determination lower limit value Ha, the cumulative print pixel number N1 is large and the toner is consumed, whereas the replenishment amount cumulative value t1 is small, so that the actual toner density TC2 should be low. Nevertheless, in the situation (1), it is detected that the concentrations TC1 and TC2 are both high. That is, in this case, there is a problem with the density sensor SN1, and it is determined that the densities TC1 and TC2 cannot be detected with high accuracy. Correction for adding the value Nh1 is performed.
Thereby, in the situation (1), the toner density target value Mb is corrected to be high, and the toner replenishing operation is promoted. Therefore, the toner is easily supplied to the developing devices Gy to Gk having the toner density TC2 that should be low, and an abnormal decrease in the toner density TC2 can be prevented.

  In the first embodiment, when the change amount H1 is equal to or greater than the correction execution determination lower limit value Ha, the high density TC1 and TC2 are detected in a state where the toner is sufficiently supplied, and thus there is a problem with the sensor. The toner density target value Mb is not corrected. However, when the change amount H1 is equal to or greater than the correction execution determination lower limit value Ha, the toner density target value Mb is corrected to a small value corresponding to the high densities TC1 and TC2, and toner replenishment is suppressed. It is also possible to do. That is, in FIG. 8, when the answer is no (N) in ST18, the process may advance to ST15 instead of ST20, or in FIG. 9, if the answer is no (N) in ST26, the process may advance to ST23 instead of ST20. Is possible.

In FIG. 6, in the case of the situation (4), that is, when the first reference toner image density TC2 is low and the toner density TC2 is low, the change amount H1 is larger than the correction execution determination lower limit Ha. The toner density target value Mb is corrected.
Contrary to the situation (1), since the change amount H1 exceeds the correction execution determination upper limit value Hb, the cumulative print pixel number N1 is small, and the toner is not consumed much, whereas the replenishment amount cumulative Since the value t1 is large, the actual toner density TC2 should be high. Nevertheless, in the situation (4), it is detected that the concentrations TC1 and TC2 are low. That is, in this case, there is a problem with the density sensor SN1, and it is determined that the densities TC1 and TC2 cannot be accurately detected. Correction for subtracting the value Nh2 is performed (see FIG. 6).
As a result, the toner density target value Mb is corrected to be low, and the toner supply operation is suppressed. Therefore, it becomes difficult to supply toner to the developing devices Gy to Gk having a toner density TC2 that should be high, and an abnormal increase in the toner density TC2 can be prevented.

Next, the second embodiment of the present invention will be described. In the description of the second embodiment, the same reference numerals are given to the components corresponding to the components of the first embodiment, and the detailed description thereof will be given. Omitted.
The second embodiment is different from the first embodiment in the following points, but is configured in the same manner as the first embodiment in other points.

(Description of control unit)
FIG. 11 is a block diagram of the control unit of the image forming apparatus according to the second exemplary embodiment of the present invention, and corresponds to FIG. 4 according to the first exemplary embodiment.
In FIG. 11, the control unit C of the image forming apparatus U according to the second embodiment replaces the correction execution determination range storage unit C6N and the correction execution determination unit C6P according to the first embodiment with the correction execution determination range storage unit C6N ′ and the correction execution. Since it is the same except that the determination means C6P ′ is provided, some illustrations and detailed descriptions of other means are omitted.

FIG. 12 is an explanatory diagram of the correction execution determination range of the second embodiment, FIG. 12A is a diagram for explaining the relationship between the cumulative number of print pixels and the developer replenishment amount cumulative value, and FIG. 12B is the cumulative print pixel number and toner replenishing device. It is a figure explaining the relationship of the developer supply capability by.
C6N ': Correction execution determination range storage means In FIG. 11, the correction execution determination range storage means C6N' includes an inflection determination value storage means C6N3, a correction execution determination lower limit value storage means C6N1 ', and a correction execution determination upper limit value storage means. As shown in FIG. 12, the correction execution determination upper limit value Ha and the correction execution determination lower limit value Hb are inflected at the inflection determination value Hc as shown in FIG. To do.

C6N3: Inflection discrimination value storage means The inflection discrimination value storage means C6N3 stores an inflection discrimination value Hc in which the correction execution discrimination upper limit value Ha and the correction execution discrimination lower limit value Hb change. In the second embodiment, the inflection determination value Hc is set in advance by experimentally determining the cumulative print pixel number N1 when the developer supply capability of the toner replenishing device Ug decreases.
C6N1 ': Correction execution determination lower limit value storage means The correction execution determination lower limit value storage means C6N1' includes a correction execution determination lower limit value Ha0 before inflection and a post-inflection correction execution determination lower limit value Ha1 as the correction execution determination lower limit value Ha. Remember. In the second embodiment, Ha0 <Ha1 is set.
C6N2 ': Correction execution determination upper limit value storage means The correction execution determination upper limit value storage means C6N2' includes a correction execution determination upper limit value Hb0 before inflection and a correction execution determination upper limit value Hb1 after inflection as the correction execution determination upper limit value Hb. Remember. In the second embodiment, Hb0 <Hb1 is set.

C6P ′: Correction execution determination means The correction execution determination means C6P ′ includes an inflection determination means C6P1, a correction execution determination lower limit value setting means C6P2, and a correction execution determination upper limit value setting means C6P3, and a toner density target value Mb. It is determined whether or not to execute the correction. As in the case of the first embodiment, the correction execution determination unit C6P ′ according to the second embodiment determines that the correction of the toner density target value Mb is performed in the cases (1) to (4).
C6P1: Inflection discrimination means The inflection discrimination means C6P1 determines whether or not the cumulative print pixel number N1 is greater than or equal to the inflection discrimination value Hc based on the cumulative print pixel number N1 and the inflection discrimination value Hc. It is determined whether it is before the inflection or after the inflection. Therefore, based on the cumulative print pixel number N1, it is determined whether the developer supply capability of the toner replenishing device Ug is before or after the decrease.

C6P2: Correction execution determination lower limit value setting means The correction execution determination lower limit value setting means C6P2 executes correction before inflection when it is determined before the inflection based on the determination result of the inflection determination means C6P1. The determination lower limit value Ha0 is set as the correction execution determination lower limit value Ha, and when it is determined that the inflection has occurred, the post-inflection correction execution determination lower limit value Ha1 is set as the correction execution determination lower limit value Ha. Therefore, the correction execution determination means C6P ′ determines the situation (1) using the correction execution determination lower limit value Ha set by the correction execution determination lower limit value setting means C6P2.
C6P3: Correction execution determination upper limit value setting means When the correction execution determination upper limit value setting means C6P3 is determined to be before the inflection based on the determination result of the inflection determination means C6P1, the correction execution before the inflection is executed. The determination upper limit value Hb0 is set as the correction execution determination upper limit value Hb, and when it is determined that the inflection is after inflection, the post-inflection correction execution determination upper limit value Hb1 is set as the correction execution determination upper limit value Hb. Therefore, the correction execution determination means C6P ′ determines the situation (4) using the correction execution determination upper limit value Hb set by the correction execution determination upper limit value setting means C6P3.

(Explanation of flowchart of embodiment 2)
Next, processing in the image forming apparatus U according to the second exemplary embodiment of the present invention will be described with reference to a flowchart. Detailed description will be omitted.
(Description of toner density target value correction processing)
FIG. 13 is a flowchart of the toner density target value correction process according to the second embodiment, and corresponds to FIG. 8 according to the first embodiment.
FIG. 14 is a flowchart of the toner density target value correction process of the second embodiment, which is a continuation of FIG. 13 and corresponds to FIG. 9 of the first embodiment.
Next, the toner density target value correction process of the second embodiment will be described. The same processes as those of the first embodiment are denoted by the same ST numbers, and detailed description thereof will be omitted.
13 and 14, in the toner density target value correction process according to the second exemplary embodiment, processes ST51 to ST53 are performed between ST17 and ST18, and processes ST61 to ST63 are performed between ST25 and ST26. Is the same as in the first embodiment.

In ST51 of FIG. 13, it is determined whether or not the cumulative print pixel number N1 is greater than or equal to the inflection determination value Hc. If yes (Y), the process proceeds to ST52, and, if no (N), the process proceeds to ST53.
In ST52, the post-inflection correction execution determination lower limit Ha1 is set as the correction execution determination lower limit Ha. Then, the process proceeds to ST18.
In ST53, the pre-inflection correction execution determination lower limit Ha0 is set as the correction execution determination lower limit Ha. Then, the process proceeds to ST18.
In ST61 of FIG. 14, it is determined whether or not the cumulative print pixel number N1 is equal to or greater than the inflection determination value Hc. If yes (Y), the process proceeds to ST62, and, if no (N), the process proceeds to ST63.
In ST62, the post-inflection correction execution determination upper limit value Hb1 is set as the correction execution determination upper limit value Hb. Then, the process proceeds to ST26.
In ST63, the pre-inflection correction execution determination upper limit value Hb0 is set as the correction execution determination upper limit value Hb. Then, the process proceeds to ST26.

(Operation of Example 2)
In the image forming apparatus U according to the second embodiment having the above-described configuration, when the toner cartridges KTy to KTk have a large amount of toner, a predetermined amount of toner can be replenished by one driving of the toner replenishing apparatus Ug. When the number is reduced, the amount of toner that can be replenished by one driving of the conveying member is reduced. That is, in order to reduce the developer supply capability and replenish a predetermined amount of toner, the replenishment time tb by the toner replenishing device Ug becomes long and the replenishment cumulative value t1 tends to increase. Correspondingly, in the image forming apparatus U according to the second embodiment, the timing at which the developer supply capacity changes is determined by the inflection determination value Hc, and the correction execution determination lower limit value Ha and the correction execution determination upper limit value Hb are changed. Therefore, it is possible to perform discrimination and correction with higher accuracy than in the first embodiment.

(Modification of Example 2)
FIG. 15 is an explanatory diagram of a correction execution determination range according to a modification of the second embodiment. FIG. 15A is a diagram for explaining the relationship between the cumulative number of print pixels and the developer replenishment amount accumulated value, and FIG. 15B is a developer replenishment amount accumulation. FIG. 6 is a diagram for explaining a relationship between a value and a developer supply capability by a toner supply device.
In the second embodiment, the inflection determination value Hc, which is the time when the developer supply capability starts to decrease, is set based on the cumulative print pixel number N1, but as shown in FIG. 15, instead of the cumulative print pixel number N1, It is also possible to set the inflection determination value Hc ′ based on the developer replenishment amount cumulative value t1. This case also has the same function and effect as the second embodiment.

Next, the third embodiment of the present invention will be described. In the description of the third embodiment, the same reference numerals are given to the components corresponding to the components of the first embodiment, and the detailed description thereof will be given. Omitted.
The third embodiment is different from the first embodiment in the following points, but is configured in the same manner as the first embodiment in other points.

(Description of control unit)
FIG. 16 is a block diagram of the control unit of the image forming apparatus according to the third embodiment of the present invention, and corresponds to FIG. 4 according to the first embodiment.
In FIG. 16, in the control unit C of the image forming apparatus U according to the third embodiment, a density correction curve storage unit C6S, a density difference calculation unit C6T, a correction curve selection unit C6U, and a density correction value calculation unit C6V are added. Since it is the same, some illustrations and detailed descriptions of other means are omitted.

FIG. 17 is an explanatory diagram of parameters used to control the image forming apparatus according to the third exemplary embodiment. Both the density of the first reference toner image and the second reference toner image are higher than the target value and the change amount is small. 17A is an explanatory diagram of a condition calculation reference value and a toner density target value, FIG. 17B is an explanatory diagram of a change amount, and FIG. 17C is an explanatory diagram of a density correction curve.
FIG. 18 is an explanatory diagram of parameters used to control the image forming apparatus according to the third embodiment. Both the density of the first reference toner image and the second reference toner image are smaller than the target value and the amount of change is large. 18A is an explanatory diagram of a condition calculation reference value and a toner density target value, FIG. 18B is an explanatory diagram of a change amount, and FIG. 18C is an explanatory diagram of a density correction curve.

C6S: Density Correction Curve Storage Unit The density correction curve storage unit C6S stores density correction curves Hk for setting density correction values Nh1 and Nh2 for correcting the toner density target value Mb based on the change amount H1. In FIG. 17C and FIG. 18C, the density correction curve storage means C6S of the third embodiment stores a large difference density correction curve Hk1, a medium difference density correction curve Hk2, and a small difference density correction curve Hk3. In each of the density correction curves Hk1 to Hk3, 0 is between the correction execution determination lower limit value Ha and the change correction execution determination upper limit value Hb, and the correction is subtracted as the change amount H1 becomes larger than the change correction execution determination upper limit value Hb. When the amount (density target subtraction correction value Nh2) increases and increases to some extent, the correction amount becomes constant. Similarly, as the change amount H1 becomes smaller than the change correction execution determination lower limit value Ha, the added correction amount (density target addition correction value Nh1) increases, and when the change amount H1 increases to some extent, the correction amount becomes constant.

C6T: Density Difference Calculation Unit The density difference calculation unit C6T calculates a density difference Sh that is a difference between the detected toner density TC2 and the toner density target value Mb. In the third embodiment, when the toner density TC2> the toner density target value Mb, the density difference Sh1 = TC2-Mb is calculated, and when the toner density TC2 <the toner density target value Mb, the density difference Sh2 = Mb-TC2 is calculated. .
C6U: Correction Curve Selection Unit The correction curve selection unit C6U selects the correction curves Hk1 to Hk3 to be used based on the calculated density difference Sh. In the third embodiment, when the density differences Sh1 and Sh2 are smaller than the preset small difference threshold, the small difference density correction curve Hk3 is selected, and when the density difference Sh is larger than the preset large difference threshold. The large difference density correction curve Hk1 is selected. Therefore, when the density differences Sh1 and Sh2 are between the small difference threshold value and the large difference threshold value, the medium difference density correction curve Hk2 is selected.

C6V: Density correction value calculation means The density correction value calculation means C6V calculates density target correction values Nh1, Nh2 based on the selected density correction curve Hk and the change amount H1, and calculates the calculated density target correction value Nh1. , Nh2 are stored in the density correction value storage means C6Q. As shown in FIGS. 17C and 18C, the density correction value setting unit C6V of Example 3 calculates density target correction values Nh1 and Nh2 from the intersections of the density correction curves Hk1 to Hk3 and the change amount H1. It should be noted that density target correction values Nh1 and Nh2 similar to those in the first and second embodiments are stored in the density correction value storage unit C6Q of the third embodiment as initial values.

(Description of Flowchart of Example 3)
Next, processing in the image forming apparatus according to the third exemplary embodiment of the present invention will be described with reference to a flowchart. Since the cumulative print pixel number measuring process and the toner replenishing process are the same as those in the first exemplary embodiment, Detailed description is omitted.
(Description of toner density target value correction processing)
FIG. 19 is a flowchart of the toner density target value correction process according to the third embodiment, and corresponds to FIG. 8 according to the first embodiment.
FIG. 20 is a flowchart of the toner density target value correction process according to the third embodiment, which is a continuation of FIG. 19 and corresponding to FIG. 9 according to the first embodiment.
Next, the toner density target value correction process of the third embodiment will be described. The same processes as those of the first embodiment are denoted by the same ST numbers, and detailed description thereof is omitted.
19 and 20, in the toner density target value correction process of the third embodiment, the processes of ST71 to ST73 are performed instead of ST19, and the processes of ST81 to ST83 are performed instead of ST27. The same as in the case of Example 1.

In ST71 of FIG. 19, a density difference Sh1 (= TC2-Mb) is calculated based on the detected toner density TC2 and the toner density target value Mb. Then, the process proceeds to ST72.
In ST72, the following processes (1) and (2) are executed, and the process proceeds to ST73.
(1) Based on the density difference Sh1, density correction curves Hk1 to Hk3 are set.
(2) The density target addition correction value Nh1 is calculated and set based on the selected density correction curves Hk1 to Hk3 and the change amount H1.
In ST73, the following processes (1) and (2) are executed, and the process proceeds to ST20.
(1) The density target addition correction value Nh1 is added to the toner density target value Mb. That is, Mb = Mb + Nh1.
(2) The density target addition correction value Nh1 is initialized (reset) to an initial value.

In ST81 of FIG. 20, the density difference Sh2 (= Mb−TC2) is calculated based on the detected toner density TC2 and the toner density target value Mb. Then, the process proceeds to ST82.
In ST82, the following processes (1) and (2) are executed, and the process proceeds to ST83.
(1) Based on the density difference Sh2, density correction curves Hk1 to Hk3 are set.
(2) The density target subtraction correction value Nh2 is calculated and set based on the selected density correction curves Hk1 to Hk3 and the change amount H1.
In ST83, the following processes (1) and (2) are executed, and the process proceeds to ST20.
(1) The density target subtraction correction value Nh2 is subtracted from the toner density target value Mb. That is, Mb = Mb−Nh2.
(2) The density target subtraction correction value Nh2 is initialized (reset) to an initial value.

(Operation of Example 3)
In the image forming apparatus U according to the third embodiment having the above-described configuration, the density target correction values Nh1 and Nh2 are calculated according to the difference between the detected toner density TC2 and the toner density target value Mb, and the toner density is calculated. The target value Mb is corrected. Therefore, the correction can be performed with higher accuracy than when the fixed density target correction values Nh1 and Nh2 are used, and the abnormal increase or decrease in the toner concentration TC2 can be prevented with high accuracy.

Next, a description will be given of a fourth embodiment of the present invention. In the description of the fourth embodiment, the same reference numerals are given to the components corresponding to the components of the first and third embodiments, and the details thereof are described. Description is omitted.
The fourth embodiment is different from the first and third embodiments in the following points, but is configured similarly to the first and third embodiments in other points.

(Description of control unit)
FIG. 21 is a block diagram of the control unit of the image forming apparatus according to the fourth embodiment of the present invention, and corresponds to FIG. 16 according to the third embodiment.
In FIG. 21, the control unit C of the image forming apparatus U according to the fourth embodiment is similar to the control unit C except that it includes a change amount calculation unit C6M ′ instead of the change amount calculation unit C6M of the third embodiment. Some illustrations and detailed descriptions of the means are omitted.

FIG. 22 is an explanatory diagram of parameters used to control the image forming apparatus according to the fourth embodiment. Both the density of the first reference toner image and the second reference toner image are higher than the target value and the change amount is small. 22A is an explanatory diagram of a condition calculation reference value and a toner density target value, FIG. 22B is an explanatory diagram of a change amount, and FIG. 22C is an explanatory diagram of a density correction curve.
FIG. 23 is an explanatory diagram of each parameter used for control of the image forming apparatus of the embodiment. When the densities of the first reference toner image and the second reference toner image are both smaller than the target value and the change amount is large. FIG. 23A is an explanatory diagram of a condition calculation reference value and a toner density target value, FIG. 23B is an explanatory diagram of a change amount, and FIG. 23C is an explanatory diagram of a density correction curve.

C6M ′: Change amount calculation means The change amount calculation means C6M ′ of FIG. 21 includes the previous supply pixel number storage means C6M1 that stores the cumulative number of print pixels when the previous supply operation is executed as the previous supply pixel number N0, and the previous time. And a previous supply amount storage means C6M2 for storing the accumulated amount of developer supply when the supply operation is performed as the previous supply amount t0. The change amount calculation means C6M ′ according to the fourth embodiment uses the change amount (N1 and the previous supply amount t0, the accumulated print pixel number N1 when the supply operation is performed, and the developer supply amount accumulated value t1 based on the change amount ( (Change amount ratio) H1 is calculated. That is, H1 = (t1-t0) / (N1-N0) is calculated.

(Description of Flowchart of Embodiment 4)
Next, processing in the image forming apparatus U according to the fourth exemplary embodiment of the present invention will be described with reference to a flowchart. However, the cumulative print pixel number measuring process and the toner replenishing process are the same as those in the first exemplary embodiment. Detailed description will be omitted.
(Description of toner density target value correction processing)
FIG. 24 is a flowchart of the toner density target value correction process according to the fourth embodiment, and corresponds to FIG. 19 according to the third embodiment.
FIG. 25 is a flowchart of the toner density target value correction process of the fourth embodiment, is a continuation flowchart of FIG. 24, and corresponds to FIG. 20 of the third embodiment.
Next, the toner density target value correction process according to the fourth embodiment will be described. The same processes as those according to the first and third embodiments are denoted by the same ST numbers, and detailed description thereof is omitted.
24 and 25, in the toner density target value correction process of the fourth embodiment, ST16 ', ST17', ST20 ', ST24', and ST25 'are executed in place of ST16, ST17, ST20, ST24, and ST25. Except for this, this is the same as in the third embodiment.

In ST16 ′ of FIG. 24, the following processes (1) and (2) are executed, and the process proceeds to ST17 ′.
(1) The cumulative print pixel number N1 and the developer replenishment amount cumulative value t1 are read.
(2) Read the previous supply pixel number N0 and the previous developer supply amount t0.
In ST17 ′, the change amount H1 = (t1−t0) / (N1−N0) is calculated, and the process proceeds to ST18.
In ST20 ′ of FIG. 24, the following processes (1) to (3) are executed, and the toner density target value correction process of FIG.
(1) The target value setting end flag FL2 is set to “1”.
(2) The accumulated print pixel number N1 is stored (updated) as the previous supply pixel number N0.
(3) The developer replenishment amount cumulative value t1 is stored (updated) as the previous replenishment amount t0.

In ST24 ′ of FIG. 25, the following processes (1) and (2) are executed, and the process proceeds to ST25 ′.
(1) The cumulative print pixel number N1 and the developer replenishment amount cumulative value t1 are read.
(2) Read the previous supply pixel number N0 and the previous developer supply amount t0.
In ST25 ′, change amount H1 = (t1−t0) / (N1−N0) is calculated, and the process proceeds to ST26.

(Operation of Example 4)
In the image forming apparatus U according to the fourth embodiment having the above-described configuration, not only the cumulative print pixel number N1 and the developer replenishment amount accumulated value t1 when the replenishment operation is performed, but also the previous replenishment pixel number N0 and the previous developer replenishment. The amount of change H1 is calculated using the amount t0, and it is determined whether or not to correct the toner density target value Mb based on the amount of change H1. Therefore, for example, even if the relationship between the cumulative print pixel number N1 at the time when the replenishment operation is performed and the developer replenishment amount accumulated value t1 is within the correction execution determination range, the change amount H1 of the fourth embodiment is corrected. If it is smaller than the execution determination lower limit value Ha or larger than the correction execution determination upper limit value Hb, correction is performed.
Therefore, the normal density sensor SN1 can correct the change amount H1 that is unlikely to occur, so that the toner density target value Mb can be corrected earlier than in the first to third embodiments.

(Example of change)
As mentioned above, although the Example of this invention was explained in full detail, this invention is not limited to the said Example, A various change is performed within the range of the summary of this invention described in the claim. It is possible. Examples of modifications of the present invention are illustrated below.
(H01) In each of the above embodiments, the present invention is not limited to a color image forming apparatus including a plurality of developing units Gy to Gk, and the present invention can also be applied to a monochrome image forming apparatus. The present invention can also be applied to image forming apparatuses such as copying machines and facsimile machines. Further, the configuration using the intermediate transfer drum as the intermediate transfer member has been exemplified, but the present invention is not limited to this. It is also possible to provide an image forming apparatus that directly transfers from an image carrier. Further, the image forming apparatus is not limited to a so-called tandem image forming apparatus in which an image holding member is provided for each color, and can be applied to a rotary type or retract type image forming apparatus.

(H02) In each of the above embodiments, the toner density TC2 is detected by reading the density of the second reference toner image. However, the present invention is not limited to this, and conventionally known magnetic sensors are arranged in the developing units Gy to Gk. Thus, it is possible to adopt a configuration for detecting the toner density. The order of forming the two reference toner images, the image forming method, the density, and the like can be arbitrarily changed according to the design and specifications.
(H03) In each of the above-described embodiments, the upper limit value Hb and the lower limit value Ha of the correction execution determination range are illustrated as changing in a straight line shape or a broken line shape. However, the present invention is not limited to this. is there. That is, Ha and Hb can be values that continuously change.

(H04) In each of the above embodiments, the embodiments 2 to 4 can be combined.
(H05) In each of the embodiments, the first reference toner image density TC1 and the toner density TC2 are derived. However, the present invention is not limited to this, and any parameter related to the first reference toner image density TC1 or the toner density TC2 (for example, And a configuration in which correction and control are performed indirectly based on the first reference toner image density TC1 and the toner density TC2 by using a DC component of the development voltage as in the technique described in Patent Document 3. Is also possible.

(H06) In each of the above embodiments, the configuration in which the timing for detecting and replenishing the toner density TC2 and the timing for correcting the toner density target value Mb is exemplified, but the present invention is not limited to this. It is also possible to shift the timing for correcting the value Mb and the timing for replenishment. For example, it is possible to employ a configuration in which the toner density target value Mb is corrected every time the second reference toner image is formed 10 times while the second reference toner image is frequently formed and replenished. In addition, it is possible to perform the toner replenishment and the correction of the toner density target value Mb as completely separate processes.
(H07) In the above-described embodiment, the configuration in which the target values Ma and Mb have the widths Ma1, Ma2, Mb1, and Mb2 is exemplified. However, the width can be arbitrarily changed, and the width can be eliminated. is there.
(H08) In the embodiment, the density sensor generally includes a reflected light type for sensing reflected light and a diffused light type for sensing diffused light, and any type of sensor can be used. is there. In the above embodiment, a reflected light type density sensor is used, and the reflected light type density sensor has a low output value when the density of the object to be detected is high, and a high output value when the density is low. Although there is a characteristic, it is not limited to this, and it is also possible to use a diffused light type concentration sensor. In this case, the output value is high when the concentration of the object to be detected is high, and the output is output when the concentration is low. The value becomes lower. Therefore, when a diffusion type density sensor is used, it is possible to perform correction and control by reversing the direction of density density.

1 is a perspective explanatory view of an image forming apparatus according to a first embodiment of the present invention. FIG. 2 is an overall explanatory diagram of the image forming apparatus according to the first exemplary embodiment. FIG. 3 is a block diagram of the control unit of the image forming apparatus according to the first exemplary embodiment of the present invention. 4 is a block diagram of the control unit of the image forming apparatus according to the first exemplary embodiment of the present invention, and is a continuation of FIG. FIG. 5 is an explanatory diagram of numerical values used for control of the image forming apparatus according to the first exemplary embodiment. When it is determined that the densities of the first reference toner image and the second reference toner image are both higher than the target value, FIG. 5A is an explanatory diagram of a condition calculation reference value and a toner density target value, and FIG. 5B is an explanatory diagram of a change amount. FIG. 6 is an explanatory diagram of each numerical value used for control of the image forming apparatus according to the first embodiment, in which it is determined that the densities of the first reference toner image and the second reference toner image are both lower than the target value. FIG. 6A is an explanatory diagram of a condition calculation reference value and a toner density target value, and FIG. 6B is an explanatory diagram of a change amount. FIG. 7 is a flowchart of the cumulative print pixel number measurement process in the image forming apparatus according to the first exemplary embodiment of the present invention. FIG. 8 is a flowchart of the toner density target value correction process of the first embodiment, and is a flowchart of the subroutine of ST6 of FIG. FIG. 9 is a flowchart of the toner density target value correction process according to the first exemplary embodiment, and is a flowchart subsequent to FIG. FIG. 10 is a flowchart of toner supply processing in the image forming apparatus according to the first exemplary embodiment of the present invention. FIG. 11 is a block diagram of the control unit of the image forming apparatus according to the second exemplary embodiment of the present invention, and corresponds to FIG. 4 according to the first exemplary embodiment. 12A and 12B are explanatory diagrams of the correction execution determination range of the second embodiment. FIG. 12A is a diagram for explaining the relationship between the cumulative number of printing pixels and the cumulative developer replenishment amount. FIG. 12B is the cumulative printing pixel number and the toner replenishing device. It is a figure explaining the relationship of the developer supply capability by. FIG. 13 is a flowchart of the toner density target value correction process according to the second embodiment, and corresponds to FIG. 8 according to the first embodiment. FIG. 14 is a flowchart of the toner density target value correction process according to the second embodiment, which is a continuation of FIG. 13 and corresponds to FIG. 9 according to the first embodiment. FIG. 15 is an explanatory diagram of a correction execution determination range according to a modification of the second embodiment. FIG. 15A is a diagram for explaining the relationship between the cumulative number of print pixels and the developer replenishment amount accumulated value, and FIG. 15B is a developer replenishment amount accumulation. FIG. 6 is a diagram for explaining a relationship between a value and a developer supply capability by a toner supply device. FIG. 16 is a block diagram of the control unit of the image forming apparatus according to the third embodiment of the present invention, and corresponds to FIG. 4 according to the first embodiment. FIG. 17 is an explanatory diagram of parameters used to control the image forming apparatus according to the third exemplary embodiment. Both the density of the first reference toner image and the second reference toner image are higher than the target value and the change amount is small. 17A is an explanatory diagram of a condition calculation reference value and a toner density target value, FIG. 17B is an explanatory diagram of a change amount, and FIG. 17C is an explanatory diagram of a density correction curve. FIG. 18 is an explanatory diagram of parameters used to control the image forming apparatus according to the third embodiment. Both the density of the first reference toner image and the second reference toner image are smaller than the target value and the amount of change is large. 18A is an explanatory diagram of a condition calculation reference value and a toner density target value, FIG. 18B is an explanatory diagram of a change amount, and FIG. 18C is an explanatory diagram of a density correction curve. FIG. 19 is a flowchart of the toner density target value correction process according to the third embodiment, and corresponds to FIG. 8 according to the first embodiment. FIG. 20 is a flowchart of the toner density target value correction process of the third embodiment, is a continuation flowchart of FIG. 19, and corresponds to FIG. 9 of the first embodiment. FIG. 21 is a block diagram of the control unit of the image forming apparatus according to the fourth embodiment of the present invention, and corresponds to FIG. 16 according to the third embodiment. FIG. 22 is an explanatory diagram of parameters used to control the image forming apparatus according to the fourth embodiment. Both the density of the first reference toner image and the second reference toner image are higher than the target value and the change amount is small. 22A is an explanatory diagram of the condition calculation reference value and the toner density target value, FIG. 22B is an explanatory diagram of the change amount, and FIG. 22C is an explanatory diagram of the density correction curve. FIG. 23 is an explanatory diagram of parameters used to control the image forming apparatus of the embodiment. When the densities of the first reference toner image and the second reference toner image are both smaller than the target value and the change amount is large. FIG. 23A is an explanatory diagram of a condition calculation reference value and a toner density target value, FIG. 23B is an explanatory diagram of a change amount, and FIG. 23C is an explanatory diagram of a density correction curve. FIG. 24 is a flowchart of the toner density target value correction process according to the fourth embodiment, and corresponds to FIG. 19 according to the third embodiment. FIG. 25 is a flowchart of the toner density target value correction process of the fourth embodiment, is a continuation flowchart of FIG. 24, and corresponds to FIG. 20 of the third embodiment.

Explanation of symbols

C4A: Cumulative printing pixel number measuring means,
C6: Toner density target value correcting means,
C6C: reference toner image density detecting means,
C6D: toner density detecting means,
C6V: Density correction value calculation means,
C7: Condition calculation means,
C8 ... developer replenishment control means,
C8D: Cumulative supply amount measuring means,
Gy, Gm, Gc, Gk ... developer,
Ha: Correction execution determination lower limit value,
Hb: Correction execution determination upper limit value,
Ma: Condition calculation reference value,
Mb: Toner density target value,
N1 ... Cumulative print pixel number,
N1-N0: Change amount of the cumulative number of print pixels,
Nh1, Nh2 ... density correction value,
Py, Pm, Pc, Pk ... image carrier,
ROS ... latent image forming device,
Sh1, Sh2 ... difference,
t1: Cumulative supply amount,
t1-t0: the amount of change in the cumulative correction amount,
TC1: density of the reference toner image,
TC2: toner density,
U: Image forming apparatus,
Ug: Developer supply device.

Claims (8)

An image carrier, a latent image forming device that forms a latent image on the surface of the image carrier, and a developing unit that develops the latent image on the surface of the image carrier into a visible image, the surface of the image carrier A toner image forming apparatus for forming a reference toner image having a predetermined density set in advance;
A developer supply device for supplying a new developer to the developer;
Reference toner image density detecting means for detecting the density of the reference toner image;
Based on a condition calculation reference value which is a reference for calculating an image forming condition for forming an image by the toner image forming apparatus, and a detected density of the reference toner image detected by the density detecting unit, the toner Condition calculating means for calculating an image forming condition for forming an image by the image forming apparatus;
Toner concentration detecting means for detecting the toner concentration of a two-component developer comprising toner and carrier contained in the developing device;
A developer replenishment control means for controlling the driving of the developer replenishing device based on a toner density target value that is a target value of the toner density of the developing device and a toner density detected by the toner density detection means;
A cumulative replenishment amount measuring means for measuring a cumulative replenishment amount that is a cumulative value of a developer replenishment amount replenished by the developer replenishing device;
A cumulative print pixel number measuring unit that measures a cumulative print pixel number that is a cumulative value of the number of pixels of the print image formed by the latent image forming device;
The high or low detection value of the reference toner image density with respect to the condition calculation reference value is the same as the high or low detection value of the toner density with respect to the toner density target value, and the cumulative print pixel Toner concentration target value correction means for correcting the toner density target value to a value close to the detected value of the toner density when the cumulative supply amount with respect to the number exceeds a preset correction execution determination range;
An image forming apparatus comprising: The toner density detecting means for detecting the toner density of the two-component developer contained in the developing device based on the density of a second reference toner image different from the reference toner image for calculating the image forming condition;
The image forming apparatus according to claim 1, further comprising: The cumulative replenishment with respect to the cumulative print pixel count when the detected value of the density of the reference toner image with respect to the condition calculation reference value is high and the detected value of the toner density with respect to the target toner density value is high. A toner density target that corrects the toner density target value to a value obtained by adding the density correction value to the toner density target value when the amount is equal to or lower than the correction execution judgment lower limit that is the lower limit of the correction execution determination range Value correction means,
The image forming apparatus according to claim 1, further comprising: The cumulative replenishment for the cumulative print pixel count when the detected value of the density of the reference toner image with respect to the condition calculation reference value is low and the detected value of the toner density with respect to the target toner density value is low. A toner density target for correcting the toner density target value to a value obtained by subtracting the density correction value from the toner density target value when the amount is equal to or greater than the correction execution determination upper limit value that is the upper limit value of the correction execution determination range. Value correction means,
The image forming apparatus according to claim 1, further comprising: A density correction value calculating means for calculating the density correction value based on the cumulative correction amount with respect to the cumulative print pixel number and a difference between the toner density detection value with respect to the toner density target value;
The image forming apparatus according to claim 3, further comprising: Density correction value calculating means for calculating the density correction value based on the change amount of the cumulative correction amount with respect to the change amount of the cumulative print pixel number and the difference between the detected value of the toner density with respect to the toner density target value. ,
The image forming apparatus according to claim 3, further comprising: The correction execution determination range that changes with a change in the cumulative print pixel number or the cumulative correction amount,
The image forming apparatus according to claim 1, further comprising: The correction execution determination range that changes based on the supply capability of the developer supply device;
The image forming apparatus according to claim 7, further comprising:

Images