JP2000089528A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device constituted so that the density target value of a density sensor can be quickly and accurately decided. SOLUTION: Processing that the patch images of a first to a third levels obtained by changing the light intensity of a laser exposure unit are formed on an image carrier by giving first resolution and processing that the patch images of the first to the third levels obtained by changing the light intensity of the laser exposure unit are formed on the image carrier by giving second resolution being lower than the first resolution (S101-S106) are executed. Besides, processing that the density of the patch images of the first to the third levels formed with the first resolution on the image carrier are detected by the density sensor and processing that the patch images of the first to the third levels formed with the second resolution on the image carrier are transferred and fixed on a paper (S106 and S107) are executed. Moreover, processing that the density of the patch images of the first to the third levels obtained after the fixing action thereof are executed are measured and processing that the density target value of the density sensor is decided based on density information obtained before and after the fixing action are executed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine and a printer using an electrophotographic system, and more particularly to an image forming apparatus having a density control function for appropriately controlling the density of an output image.

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus using an electrophotographic system, as a part of a function for controlling image density, the density of a patch image for density control formed on an image carrier is controlled. A device provided with a concentration sensor for detection is widely known. In the case of this type of image forming apparatus, it is necessary to determine the density target value of the density sensor for the patch image for each apparatus due to individual differences in the detection performance of the density sensor and variations in the attachment of the density sensor to the apparatus. .

The prior art is disclosed in, for example, Japanese Patent Laid-Open No. 4-2
No. 46672 discloses that a toner image is formed on an image carrier after a developing potential of a toner image for density control is made constant, and toner is supplied or consumed so that the density of a patch image on paper becomes constant. There is disclosed a technology in which the density of a patch image is measured by a density sensor and the measured value is used as a density target value.

In addition to this, for example, Japanese Patent Application Laid-Open No. 9-60
No. 69 discloses a method in which the density of a patch image formed on an image carrier is measured by a density sensor, and the patch image is fixed on paper to measure the image density. There is disclosed a technique in which a measurement value of a density sensor corresponding to an image density on a sheet to be targeted is predicted from a relationship between the density and a measurement value of the density sensor, and the predicted value is used as a density target value.

[0005]

However, in the technique disclosed in Japanese Patent Application Laid-Open No. Hei 4-246672, it is possible to determine an accurate density target value, but it is necessary to supply or consume toner to obtain an appropriate density. Takes a long time. Normally, the density target value is determined based on the adjustment process at the time of manufacturing the image forming apparatus or the density target value being used because the density sensor is replaced while the image forming apparatus is being used. This is when it is no longer possible. Therefore,
When supplying or consuming toner to obtain an appropriate density,
For the time spent on it, assembling and adjusting the device,
In addition, the repair time of the equipment in the customer market is lengthened.

On the other hand, in the technique disclosed in Japanese Patent Application Laid-Open No. 9-6069, although the time required for determining the density target value is shortened, the relationship between the image density on paper and the measurement value of the density sensor is as follows. Since it is necessary to make predictions using a relational expression that captures individual differences and variations in attachment of the density sensor on average, there is a problem that the concentration target value cannot be determined with high accuracy.

[0007]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and forms an electrostatic latent image by exposing an image carrier and developing a toner by developing the electrostatic latent image. In an image forming apparatus for forming an image, transferring the toner image to a transfer material, and fixing the toner image on the transfer material, an image forming apparatus forms the image on the image carrier with a first resolution and a density setting condition. A first patch forming means for forming a plurality of different patch images, and a second patch for forming a plurality of patch images on the image carrier each having a different density setting condition with a second resolution different from the first resolution. Forming means; density detecting means for detecting image densities of a plurality of patch images formed by the first patch forming means before fixing;
A plurality of patch images formed by the patch forming unit, a density obtaining unit that obtains an image density after fixing, and density information detected by the density detecting unit and density information obtained by the density obtaining unit based on the density information. And a target value determining means for determining a density target value of the density detecting means.

In the image forming apparatus having the above configuration, a plurality of patch images having different density setting conditions are respectively formed on the image carrier by the first and second patch forming means, and the patch images before fixing are formed. The density is detected by the density detecting means, the density of the patch image after fixing is obtained by the density obtaining means, and the density target value of the density detecting means is determined based on the density information before and after fixing. So, regardless of the individual difference of the concentration detection means and the dispersion of the mounting,
It is possible to quickly and accurately determine the concentration target value of the concentration detecting means. Further, a patch image serving as a density measurement image before fixing is formed with a first resolution, and a patch image serving as a density acquisition image after fixing is formed with a second resolution different from the first resolution. Thereby, the patch image for density measurement before and after fixing is optimized. This makes it possible to determine the density target value of the density detecting means with higher accuracy.

[0009]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a schematic configuration diagram showing an embodiment of an image forming apparatus according to the present invention. In the illustrated image forming apparatus, a platen (original table) 2 on which an original 1 is set
Below, an image reading system including an exposure lamp 3, a scanning optical system 4, and a CCD sensor 5 is provided. The CCD sensor 5 receives reflected light from the original 1 by the irradiation light from the exposure lamp 3 via the scanning optical system 4 and photoelectrically converts the light to generate image data corresponding to the original image. This image data is stored in the image memory 6.

An image processing unit (IPS) 7 includes an image memory 6
Is subjected to various types of image processing, and the image signals subjected to the image processing are supplied to the laser exposure device 8. The laser exposure device 8 includes a light emitting driver 8a and a semiconductor laser 8b, and emits a laser beam when the light emitting driver 2a drives the semiconductor laser 2b according to the image signal processed by the image processing unit 7. The rotating polygon mirror (polygon mirror) 9 scans the laser light emitted from the laser exposure device 8 in the axial direction of the image carrier (photosensitive drum) 10.

The image carrier 10 is provided so as to be rotatable in the direction of the arrow in FIG. Around the image carrier 10, a charger 11, a developing device 12, a transfer device 13, a density sensor 14, a cleaner 15, and a static eliminator 16 are sequentially arranged according to the rotation direction.

The developing unit 12 agitates and mixes the two-component developer charged in the developer stirring chamber to charge the developer.
And a developing roll 12 b rotatably arranged at a position facing the image carrier 10 and transporting the charged developer to a position facing the image carrier 10. For example, a DC of -500 V or a voltage obtained by superimposing AC on DC is applied from the developing bias voltage applying unit 17 to the developing roll 12b.

The density sensor 14 is an optical sensor composed of, for example, a combination of a light emitting diode and a photosensor. The photosensor receives reflected light of light emitted from the light emitting diode toward the image carrier 10 and receives the reflected light (reflected amount). Light intensity)
The density detection is performed according to the following.

On the other hand, a toner box 18 connected to the developing device 12 stores toner for development. The weight ratio (TC%) of the toner in the developer is maintained at a predetermined level by driving a dispense motor 20 controlled by a motor driver 19, and the toner is transferred to the developing device 1
2.

The paper feed roll 21 is for transporting the paper P as a material to be transferred, and a transport guide 22, a fixing device 23, a discharge roll 24, and a tray 25 are sequentially arranged downstream in the transport direction. I have. The fixing device 23 permanently fixes the toner image transferred onto the paper P by a heating / pressing action.

The control section 26 controls the processing operation of the entire image forming apparatus. For example, a ROM storing a control program or an RA storing various control data is provided.
M, and a CPU that performs processing operations in accordance with a control program stored in the ROM. The control unit 26 controls the image processing unit 7 and the bias voltage applying unit 1
7, a motor driver 19, a patch data memory 27, a light intensity determination unit 28, and the like. The processing operation of the control unit 26 will be described later in detail with reference to a flowchart.

The patch data memory 27 stores a line image (hereinafter, referred to as a line image) in which a large number of lines are arranged at a line pitch of 600 lines / inch as patch data which is a basis of a patch image related to density control.
It stores patch data corresponding to a 600-line image and a line image in which many lines are arranged at a line pitch of 200 lines / inch (hereinafter, a 200-line image). Among them, the 600-line image is a patch image corresponding to the first resolution in the present invention, and the 200-line image is a patch image corresponding to the second resolution in the present invention. The respective pieces of patch data stored in the patch data memory 27 are read out by the control unit 26 as needed. The light intensity determining unit 28 determines the intensity of the laser light according to the control signal from the control unit 26, and drives the light emission driver 8a.

Next, the basic operation of the image forming apparatus having the above configuration will be described. First, upon receiving an image formation start signal from the control unit 26, the laser exposure unit 8 emits laser light in accordance with the image signal processed by the image processing unit 7. The image signal in this case may correspond to electronic information transferred via a network, or may correspond to a document image read by an attached image reading system (3, 4, 5).

On the other hand, the surface of the image carrier 10 is previously charged at a predetermined voltage level (for example, -700 V) by the charger 11.
And moves to the exposure position by the rotating polygon mirror 9 in this state. At this time, the laser beam emitted from the laser exposure device 8 is irradiated on the image carrier 10 while being scanned by the rotating polygon mirror 9, so that an electrostatic latent image is formed on the image carrier 10.

The electrostatic latent image thus formed on the image carrier 10 is visualized by toner supplied from the developing device 12. On the other hand, the paper P serving as the transfer material is sent by the paper feed roll 21 to the portion where the image carrier 10 and the transfer device 13 are opposed to each other, that is, to the image transfer position 29. At the image transfer position 29, the toner image carried on the image carrier 10 is transferred onto the paper P by the electrostatic force of the transfer device 13. At this time, the residual toner not transferred from the image carrier 10 to the sheet P is removed by the cleaner 15. Unnecessary charges on the surface of the image carrier 10 after cleaning are removed by the charge remover 16.

Thereafter, the paper P on which the toner image has been transferred is
The toner image is transferred to a fixing device 23 while being guided by a transport guide 22, where the toner image is fixed by a heating / pressing action, and then discharged to a tray 25 by a discharge roller 24. Thus, a series of image forming operations is completed.

Next, a procedure for controlling the image density in the image forming apparatus will be described. First, it goes without saying that the so-called image density, such as the density of the toner image formed on the image carrier 10 and the density of the toner image transferred onto the paper P, depends on the image signal given from the image processing unit 7. However, even for the same image signal, the image density differs due to various factors. The determinants of the image density for the same image signal include the output of the charger 11, the light intensity of the laser exposure unit 8, the developing bias voltage, TC% and the dispense motor 20 for maintaining TC% at desired levels. Operating time, developing roll 12
b, the rotation speed ratio of the image carrier 10 and the transfer electric field.

In order to control the image density, the control unit 26 separates the patch data corresponding to the 600-line image stored for the density control, for example, from the patch data separately from the above-mentioned normal image formation. A patch latent image corresponding to the patch data is formed on the image carrier 10 by reading from the memory 27 and driving the laser exposure device 8 based on the read patch data. The formation of such a patch latent image is performed during a pre-rotation operation of the image carrier 10 before and after the start of image formation, or in a non-image area during image formation.

The patch latent image thus formed on the image carrier 10 moves to a position facing the density sensor 14 in a state where the patch latent image is visualized as a patch image by toner similarly to normal image formation. . Incidentally, in the apparatus configuration shown in FIG. 1, the density sensor 14 is arranged downstream of the image transfer position 29 in the rotation direction of the image carrier 10, but in such a case, unlike the normal image formation, 10 is not transferred to the sheet P, and the density sensor 14
Is sent to the position opposite to.

Then, the density sensor 14 measures the density of the patch image sent to the opposing position, that is, the density measurement area. This measured value is referred to as “VPATCH”.
At this time, it is preferable to measure the density of the patch image a plurality of times, average the results, and obtain a VPATCH, thereby reducing variation in the measurement by the density sensor 14. Further, the density sensor 14 is used to correct the contamination of the image carrier 10 and the sensor itself and the fluctuation of the sensor measurement value due to the surrounding environment (temperature or the like). The surface of the image carrier 10 is measured. This measured value is referred to as “VCLEAN”.

On the other hand, in the control unit 26, the above-mentioned VP
The ratio of ATCH to VCLEAN (VPATCH / VCLE
AN), and calculate the density of the patch image (patch density).
This is used for subsequent density control. The patch density used for this density control is defined as “Radc”. When the patch density Radc is calculated in this way, the control unit 26
The calculated Radc is compared with a preset Radc target value, and the image density determining factor is changed according to the comparison result (for example, a difference) to control the image density.

Here, a processing procedure for controlling the image density by changing the operation time of the dispense motor 20, which is one of the image density determining factors, will be described with reference to the flowchart of FIG.

First, the above-mentioned VCLEAN is obtained by measuring the surface of the image carrier (image carrier) 10 immediately after starting the image forming operation with the density sensor 14 (step S1). At this time, the surface of the image carrier is kept in a clean state because all the residual toner has been removed by the cleaner 15 in the preliminary rotation operation at the end of the previous image forming operation and before the new image forming operation is started. I'm dripping.

Next, it is repeatedly determined whether or not it is time to create a patch image for density control, and when the creation timing has come, a patch image for density control is formed on the surface of the image carrier 10 ( Steps S2 and S3). The timing of the patch creation is instructed, for example, at a rate of once while normal image formation is performed 20 times, and patch creation is performed based on this instruction. Then, the above-mentioned VPATCH is obtained by measuring the density of the patch image formed on the image carrier 10 by the density sensor 14 (step S4).

Subsequently, the ratio of the previously acquired VCLEAN to the subsequently acquired VPATCH (VPATCH /
VCLEAN × 200), the patch density Radc is calculated (step S5). It should be noted that here, for convenience of concentration calculation, the ratio of the actual measured concentration values (VPATCH / VCL
EAN) is multiplied by 200 to calculate the patch density Radc.

Next, the patch density Radc determined earlier
And the difference (ΔRad
After calculating c), the dispense motor operating time corresponding to the calculated ΔRadc is obtained with reference to a correspondence table between ΔRadc and the dispense motor operating time prepared in advance (steps S6 and S7).

Incidentally, the above-mentioned correspondence table between ΔRadc and the dispense motor operating time shows the relationship between ΔRadc (density difference from the target value) and the amount of toner excess or deficiency, and the dispense motor necessary to supply the insufficient toner amount. The operation time is set appropriately after experimentally grasping the operation time in advance.

Next, an instruction is given to the motor driver 19 to operate the dispense motor 20 for the dispense motor operation time obtained earlier (step S).
8). Thereafter, it is determined whether or not the image forming operation has been completed. If the image forming operation has not been completed, the process returns to step S2 to repeat the same processing. If completed, the process exits a series of processes (step S9).

In such image density control processing, the patch densities Radc and Rad calculated from the actual measured density values are used.
Since the image density determining factor (such as the operation time of the dispense motor 20) is set by the difference (ΔRadc) from the c target value, if the Radc target value (the density target value of the density sensor 14) is inappropriate, a desired value is obtained. Image density cannot be obtained.

Therefore, in the image forming apparatus of this embodiment, the Radc target value is determined by the following processing function.

First, FIG. 3 shows an operator operation procedure for determining a density target value (Radc target value). At first,
The operator executes a “PG copy” program (step S10). The “PG copy” program includes a process of forming a patch image related to density control, a process of fixing and outputting a patch image on a sheet, and a process of measuring the density of a patch image before fixing with the density sensor 14. It is a control program including:

Next, the operator sets the output PG copy on the platen 2 (step S20),
Execute the “IIT measurement” program (step S3
0). The “ITT measurement” program measures the image density of a PG copy (paper on which a patch image is formed) set on the platen 2 by using the CCD sensor 5, and measures the CCD density.
Using the measurement value of the sensor 5 and the measurement value of the density sensor 14 in the “PG copy” program, Rad
This is a control program for calculating a target value c.

Here, it is assumed that the density after fixing is obtained by measuring the image density of the PG copy using the original reading system (3, 4, 5) attached to the image forming apparatus. . However, the original purpose of the density adjustment is to correlate (match) the density measurement value of the patch image before fixing measured by the density sensor 14 with the density level of the patch image actually fixed on the paper. For this reason, the density acquisition unit for acquiring the image density after fixing is not necessarily limited to one using an attached image reading system. For example,
In the case of an image forming apparatus such as a printer that does not have an image reading system, the operator measures the image density after fixing using another density measuring device or scanner, and inputs the measurement result by key input or a network or communication interface. The image density after fixing may be obtained by inputting the image density to the image forming apparatus via the image forming apparatus.

Next, a specific processing procedure based on the "PG copy" program will be described. First, prior to the description of the processing procedure of the “PG copy” program, the correlation between the resolution of the patch image and the density measurement will be described.
Conventionally, in order to measure the image density on paper, an image of a half tone such as a low-resolution and 60% image density such as a 200-line parallel image has been used. The low resolution is selected firstly because it has excellent gradation reproducibility and is often used in a mode that emphasizes image quality such as a photographic image recording mode. (Transfer return), banding due to mechanical vibration, white spots, and the like, and are less susceptible to various disturbances. The reason for selecting the intermediate gradation is that the density on the paper is saturated at a certain gradation or higher, and the density cannot be measured correctly.

On the other hand, when a low-resolution image such as a 200-line image is selected as the patch image, the patch image before fixing (the patch image 9 on the image carrier is the toner accumulation structure on the image carrier). The density sensor 1 is strongly affected by, for example, an image formed by a new developer and an image formed by a deteriorated developer, even though the patch is visualized with the same amount of toner.
There is a drawback that the measured values at 4 are different.

More specifically, the change in the toner accumulation structure on the image carrier is caused by the deterioration of the developer, which causes toner particles to adhere to the carrier surface (toner impaction). The main reason seems to be that the value rises. For this reason, as shown in FIG. 4A, when the toner is deposited on the image carrier in a predetermined area with the new developer, when the developer becomes old and deteriorates, as shown in FIG. As shown, the toner accumulates higher in a smaller area than before. On the other hand, the density sensor 14 detects the density based on the area occupied by the toner on the image carrier, so that even if the same amount of toner is deposited on the image carrier, the area occupied by the toner is large. 4A, that is, the higher density is detected.

On the other hand, when a high-resolution image such as a solid image or a 600-line image is selected as a patch image, the effect of the toner accumulation structure on the image carrier is hardly affected. In a solid image, the toner is deposited not linearly but uniformly, so that the area occupied by the toner is substantially proportional to the amount of the toner. When a high-resolution image is developed with toner, it is not faithfully developed, and uniform toner adhesion close to a solid image is obtained (see FIG. 4C). Therefore, the amount of toner on the image carrier can be accurately measured by the density sensor 14. However, in the case of a solid image or a 600-line image, when the image is actually transferred to a sheet, the transferability is poor and the image is easily affected by various disturbances such as retransfer, banding, and white spots. Therefore, there is a problem that it is difficult to obtain accurate density information from the patch image after fixing.

Focusing on these points, the present embodiment adopts a high-resolution 600-line parallel image (35% image density) as a patch image formed for density detection before fixing, and acquires density after fixing. A low-resolution 200-line parallel image (60% image density) is adopted as the patch image formed for the image. Here, the reason why the image densities are different is that the densities of the two are made substantially constant. The reason why the solid image is not used as the density detection patch image before fixing is that image forming conditions having a substantially constant density cannot be obtained with the density acquisition patch image after fixing. Hereinafter, the processing procedure of the “PG copy” program based on such patch formation conditions will be described with reference to the flowcharts of FIGS.

First, the surface of the image carrier 10 kept in a clean state is measured by the density sensor 14 to obtain VCLEAN (step S100). Next, as a first level of patch formation, the light intensity of the laser exposure device 8 is set to a low level (for example, 150 μW) (Step S101). The setting of the light intensity level is performed by giving a control command to the light intensity determination unit 28 to that effect. Next, the patch data of the 200-line parallel image corresponding to the second resolution is read out from the patch data memory 27, and the light emission driver 8a is controlled based on the read-out patch data, whereby the second resolution (200
A first-level patch image is formed on the image carrier 10 using the line image, and at the same time, a timer for controlling the position of the patch is reset to 0 (step S10).
2).

Subsequently, as the second level of patch formation, the light intensity of the laser exposure unit 8 is set to an intermediate level (for example, 220 μm).
W) (step S103). After that, when the timer value reaches a predetermined value (Tmsec), the second-level patch image is imaged at the second resolution (200-line image) in the same manner as described above. Formed on carrier 10 (step S
104).

Next, as a third level of patch formation, the light intensity of the laser exposure unit 8 is set to a high level (for example, 290 μW).
(Step S105), and when the timer value reaches a predetermined value (2 × Tmsec), a third-level patch image is imaged at the second resolution (200-line image) in the same manner as described above. Formed on carrier 10 (step S
106).

As a result, three patch images composed of 200-line parallel images are formed on the image carrier 10 at regular intervals along the rotation direction. The densities of the patch images formed at the first to third levels correspond to the light intensity of the laser exposure device 8, which is one of the density setting conditions.
The third level patch image is the darkest, then the second level patch image, and the first level patch image is the lightest.

Next, the first to third level patches are
The transferred patch image is transferred onto a sheet of paper P, and the transferred patch image is fixed on the sheet P by the fixing device 23 (steps S107 and S1).
08). As a result, as shown in FIG.
Three patch images 30a, 30b, and 30c are sequentially formed from the sheet feeding direction (the direction of the arrow). The sheet P is discharged to a tray as a “PG copy”. FIG.
, The hatched pattern of each of the patch images 30a, 30b, and 30c is simply a difference in image density (low, medium, and high).
Is a visual representation of the patch image, and does not indicate the resolution of the patch image.

Next, the light intensity of the laser exposure device 8 is again increased to the first intensity.
After setting to the level (weak) (step S109), it is repeatedly determined whether or not the timer measures the time required for one rotation of the image carrier 10 (step S110). Next, when the timer measures one rotation of the image carrier 10, this time the patch data of the 600-line parallel image corresponding to the first resolution is read from the patch data memory 27, and the light emission driver 8a is controlled based on this. By doing, the first
A first-level patch image is formed on the image carrier 10 with a resolution of (600 lines per line image), and at the same time, a timer for controlling the position of the patch is reset to 0 (step S111).

Thereafter, the light intensity of the laser exposure device 8 is changed to the second
While changing to the third level (medium, strong), patch images of the second and third levels are placed on the image carrier 10 at the first resolution (600-line image) in the same manner as described above while referring to the timer value. It is formed (steps S112 to S115).

As a result, in the rotation direction of the image carrier 10, the image is transferred to the sheet P in steps S107 and S108.
The first to third level patch images are formed again with the same light intensity at the same positions as the fixed first to third level patch images. However, while the patch image formed later was a 600-line image, the patch image formed earlier was a 200-line image having a lower resolution.

After the first to third level patch images are formed on the image carrier 10 in this manner, the density of the first to third level patch images is determined by the density sensor in accordance with the rotation of the image carrier 10. The measurement is sequentially performed at 14, and thereby, a density measurement value VPATCH1 corresponding to the first level, a density measurement value VPATCH2 corresponding to the second level, and a density measurement value VPATCH3 corresponding to the third level are detected (step S1).
16 to S118).

Further, each of the measured concentration values VPATCH
1, VPATCH2, VPATCH3 and the ratio of VCLEAN obtained in advance in step S100 to 20 respectively.
By multiplying by 0, Radc1, Radc2, and Radc3 are calculated, and the calculation result is stored in the RAM or the like as a measured value of the density sensor 14 for each patch image (step S119).

Here, the electrical characteristics of the image carrier 10 slightly change in the outer peripheral surface thereof. Therefore, even if the surface of the image carrier 10 is charged at the same voltage level and then exposed at the same light intensity, the resulting surface potential remains within one round of the image carrier 10 as shown in FIG. Will fluctuate. Therefore, even if the patch images are formed under the same density setting conditions, if the formation positions in the rotation direction of the image carrier 10 are different, they appear as a density difference, which may adversely affect the density measurement. I am concerned.

On the other hand, in the case of the present embodiment, in the series of processes described above, the first to first transfer and fixation on the paper P are performed.
Since the third level patch image and the first to third level patch images for which density measurement is performed by the density sensor 14 are formed at the same position in the rotation direction of the image carrier 10, respectively.
The influence of a change in the electrical characteristics of the surface of the image carrier 10 can be avoided.

Next, a specific processing procedure based on the "IIT measurement" program will be described with reference to the flowchart of FIG. First, a PG copy (paper P shown in FIG. 7) placed on a platen 2 by an operator is scanned by an exposure lamp 3 and a scanning optical system 4 while a CCD sensor 5 is scanned.
The photoelectric conversion is performed on the light received in step (1) to obtain image data corresponding to the PG copy image (step S300).

Next, based on the image data corresponding to the PG copy patch formation position, first to third level patch images 30a to 30a-3 corresponding to the second resolution (200-line parallel image).
0c (see FIG. 7), and the density measurement value “IIT” corresponding to the first-level patch image 30a is thereby obtained.
1 ", a density measurement value" IIT2 "corresponding to the second level patch image 30b, and a density measurement value" IIT3 "corresponding to the third level patch image 30c (step S301).

The measurement of the density in this case is performed by the CCD sensor 5
Is converted into continuous 256 × 2
It is obtained by calculating the average value of the density levels of 56 pixels. Therefore, IIT1 to IIT3 are numerical values meaning that the larger the value is, the darker the image is.

Subsequently, the previously measured measured value IIT2 is compared with a preset IIT target value (step S).
302). The IIT target value is a standard image density desired in an output image transferred and fixed on a sheet P as a transfer material.

Here, when the measured concentration value IIT2 is larger than the IIT target value (Yes in step S302), as shown in FIG. 10A, the IIT target value exists between IIT1 and IIT2. Therefore, the density target value (Radc) of the density sensor 14 corresponding to the IIT target value
The target value) exists between Radc1 and Radc2 measured during the processing of the “PG copy” program.

Therefore, in step S303, Radc
"ΔRadc target value" which is the difference between the target value and Radc2
Is obtained by the following equation (1). ΔRadc target value = (Radc1−Radc2) × (IIT target value−IIT2) ÷ (IIT1−IIT2) (1) Incidentally, ΔRadc obtained by the equation (1)
The target value is (Radc1-Radc2) is a plus value,
(IIT target value-IIT2) is a negative value, (IIT1
Since −IIT2) is a negative value, it becomes a positive value.

On the other hand, the measured concentration value IIT2 is II
If it is smaller than the T target value (N in step S302
In the case of o), the IIT target value exists between IIT2 and IIT3 as shown in FIG.
The density target value (Ra) of the density sensor 14 corresponding to the T target value
dc target value) exists between Radc2 and Radc3.

Therefore, in step S304, Radc
The difference “ΔRadc target value” between the target value and Radc2 is obtained by the following equation (2). ΔRadc target value = (Radc3−Radc2) × (IIT target value−IIT2) ÷ (IIT3−IIT2) (2) Incidentally, ΔRadc obtained by the equation (2)
For the target value, (Radc3-Radc2) is a negative value,
(IIT target value-IIT2) is a plus value, (IIT3-
Since IIT2) is a plus value, it becomes a minus value.

Subsequently, in step S305, using the ΔRadc target value obtained in step S303 or S304, a density target value (Radc target value) of the density sensor 14 is obtained by the following equation (3). Radc target value = ΔRadc target value + Radc2 (3)

Finally, the Rad obtained in step S305
The target value c is stored in a memory such as a RAM (step S3).
06). Thus, the “IIT measurement” program is completed, and thereafter, the image density control processing (the flowchart of FIG. 2) is performed using the Radc target value stored in step S306.

Here, in the normal image density control process, an allowable range is provided for the density measured value measured by the density sensor 14, and if the allowable value is out of the allowable range, a failure of the sensor or the like is suspected. Concentration measurements are often invalidated. On the other hand, in the case of the present embodiment, since the laser light amount (exposure amount) is intentionally changed in order to determine the density target value, there is a possibility that the density measurement value by the density sensor 14 may be out of the allowable range. It is higher than the image density control process. In such a case, the concentration sensor 14
If the failure is immediately detected when the measured value of the density is out of the allowable range, the frequency of occurrence of the failure increases, and the processing efficiency may be significantly reduced. Therefore, in the present embodiment, a density measurement value other than the two sets of density measurement values (Radc3 in FIG. 10A or Radc in FIG. 10B) other than the two sets of density measurement values used for calculating the density target value (Radc target value).
If 1) is out of the permissible range, a failure is not determined, and a density target value (Radc target value) is calculated as it is. This makes it possible to increase the processing efficiency by suppressing the frequency of occurrence of a failure without affecting the calculation of the density target value (Radc target value), which is more preferable.

Further, the above-mentioned step S303 or S304
, When the difference between the IIT target value and IIT2 was calculated, the calculated value was outside the allowable range in which it was determined that the density could be adjusted, that is, the IIT target value was lower than IIT1 in FIG. In the case shown in FIG. 10B, if the IIT target value exceeds IIT3, the operator is warned to that effect or a separately prepared toner density adjustment program (the difference between the IIT target value and IIT2 can be adjusted. By executing a program for forcibly performing toner replenishment or toner consumption until the allowable range is determined, it is possible to appropriately cope with the problem.

As described above, in the image forming apparatus of the present embodiment, the first to third level patch images are formed on the image carrier 10 while changing the light intensity of the laser exposure device 8 which is the density setting condition in order. At the same time, the density of the patch image before fixing is detected by the density sensor 14, while the density of the patch image after fixing is obtained by the image reading system (3, 4, 5). Since the target density value of the density sensor 14 is obtained, it is possible to determine the target density value of the density sensor 14 more quickly and appropriately than before.

Further, the density of the first to third level patch images formed at the first resolution (600 lines) (before fixing)
Is detected by the density sensor 14, and the density (after fixing) of the first to third patch images formed at the second resolution (200 lines) is acquired by the image reading system (3, 4, 5). In the measurement of density before and after fixing, retransfer,
It is possible to minimize the effects of banding and changes in the deposited structure due to deterioration of the developer. As a result, accurate density information can be obtained both before and after fixing, so that the density target value of the density sensor 14 can be determined with higher accuracy.

In the above embodiment, a 600-line image is adopted as the patch image corresponding to the first resolution, and 200-line image is adopted as the patch image corresponding to the second resolution.
Although the line line image is adopted, the present invention is not limited to this. For example, a solid image is adopted as a patch image corresponding to the first resolution, and a 150 line image is adopted as a patch image corresponding to the second resolution. Various combinations are conceivable, such as employing a line image. Further, as a patch image other than the line image, for example, a patch image composed of a dot pattern can be adopted.

Further, in the above embodiment, three patch images for determining the density target value are formed on the image carrier 10, but the present invention is not limited to this. It is possible to grasp the characteristics of the density sensor even when the number of patches is two.
If the number is more than one, it is possible to grasp the characteristics of the density sensor more precisely.

[0073]

As described above, according to the image forming apparatus of the present invention, a plurality of patch images each having different density setting conditions are formed on an image carrier, and based on density information before and after fixing. Since the concentration target value of the concentration detecting means is determined, regardless of the individual difference of the concentration detecting means and the dispersion of the mounting,
The concentration target value of the concentration detecting means can be determined quickly and accurately. Furthermore, the resolution (first resolution) of the patch image for density detection before fixing is different from the resolution (second resolution) of the patch image for density acquisition after fixing. In the subsequent concentration measurement, influences such as retransfer, banding, and changes in the deposited structure due to deterioration of the developer can be minimized. As a result, accurate density information can be obtained both before and after fixing, so that the density target value of the density detecting means can be determined with higher accuracy.

[Brief description of the drawings]

FIG. 1 is a configuration diagram illustrating an embodiment of an image forming apparatus according to the present invention.

FIG. 2 is a flowchart illustrating a control procedure of an image density.

FIG. 3 is a flowchart illustrating an operator operation procedure for determining a density target value.

FIG. 4 is a diagram illustrating a structure of toner accumulation on an image carrier.

FIG. 5 is a flowchart (part 1) illustrating a processing procedure based on a “PG copy” program in the embodiment.

FIG. 6 is a flowchart (part 2) illustrating a processing procedure based on a “PG copy” program in the embodiment.

FIG. 7 is a diagram illustrating an output state of a patch image.

FIG. 8 is a diagram showing how the surface potential of the image carrier fluctuates.

FIG. 9 is a flowchart illustrating a processing procedure based on a “IIT measurement” program in the embodiment.

FIG. 10 is a diagram illustrating a specific method of determining a density target value.

[Explanation of symbols]

3 exposure lamp 4 scanning optical system 5 CCD sensor
8 laser exposure device, 10 image carrier, 12 developing device, 1
3 ... Transfer unit, 14 ... Density sensor, 20 ... Dispense motor, 23 ... Fixing unit, 26 ... Control unit, 27 ... Patch data memory, 28 ... Light intensity determination unit, 30a, 30b, 30
c: patch image, P: paper

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2C362 AA03 CB14 CB73 2H027 DA09 DE02 EC03 EC06 EC07 HB09 2H077 DA03 DA49 DA63

Claims (3)

[Claims] An image carrier that is exposed to form an electrostatic latent image, and the electrostatic latent image is developed to form a toner image;
In an image forming apparatus that forms an image on the transfer material by transferring and fixing the toner image to the transfer material, a plurality of images having different density setting conditions with a first resolution are formed on the image carrier. A first patch forming unit for forming a patch image, and a second patch forming unit for forming a plurality of patch images on the image carrier having different density setting conditions with a second resolution different from the first resolution. Means, density detection means for detecting image densities of a plurality of patch images formed by the first patch formation means before fixing, and a plurality of patch images formed by the second patch formation means. Density acquisition means for acquiring an image density after fixing; and density information based on density information detected by the density detection means and density information acquired by the density acquisition means. An image forming apparatus characterized by comprising a target value determining means for determining a density target value of the unit out. 2. The patch image according to claim 1, wherein the patch image is formed by arranging a large number of lines at a predetermined pitch, and wherein the second patch forming unit has a larger line pitch than the first patch forming unit. The image forming apparatus according to claim 1, wherein the image forming apparatus is formed. 3. The first patch forming means forms a patch image at a line pitch of 600 lines / inch, and the second patch forming means forms a patch image at a line pitch of 200 lines / inch. 3. The method according to claim 2, wherein
The image forming apparatus as described in the above.