JP2003270868A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of stably reproducing colors at any time by correcting a gradation correction curve based on the density measurement result of a gradation correction patch formed by the same screen as a screen set by a printing control part side, even in the case the gradation characteristics are fluctuated due to the change with time and environmental change. <P>SOLUTION: In the image forming apparatus provided with a printing control part and an image forming part, the image forming part is provided with a 1st gradation correcting means for correcting the gradation of image data received from the printing control part based on a prescribed 1st gradation curve, a patch forming part for forming the gradation correction patch, a density sensor, and a 1st correcting means for comparing the density of the gradation correction patch with a prescribed target value and then correcting the 1st gradation correction curve, and the patch forming part receives information on the screen set by the printing control part, and forms the gradation correction patch by the same screen as the screen set by the printing control part. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus used in copying machines, printers and the like.

[0002]

2. Description of the Related Art Conventionally, for example, an electrophotographic image forming apparatus used in both a copying machine and a printer converts image data obtained by scanning light along a document surface, or converts externally input data. A toner image is formed based on any of the obtained image data, and the toner image is transferred to a recording medium,
The image is formed by fixing. The supply of the toner consumed by the image formation is controlled by the ICDC (Image) which predicts the toner consumption amount from the image data and controls the supply amount.
A count dispersion control method is used, and a density measuring toner image is formed in a non-image area of a photosensitive drum, the density is measured by a density sensor, and the toner amount is controlled based on a deviation from a target value.
The density control) method is used.

Further, the toner image of each color is formed after a predetermined gradation correction is applied to the gradation of the image data, and a color image is formed on the recording medium. Since the color tone changes with the aging of each component of the forming unit, a plurality of gradation correction patches with different gradations are automatically formed on each photoconductor at predetermined intervals, and the patches are applied to an intermediate transfer belt or the like. A gradation correction lookup table provided in the gradation control unit of the IOT (image forming unit) by transferring and measuring the density of the gradation correction patch with a density sensor and comparing it with a predetermined target value. Has been modified to maintain color reproducibility. Furthermore, if necessary, the gradation correction patches formed on each photoconductor are printed out on paper, the density of the print is measured manually, and the gradation correction look provided in the printer control unit is also measured. The up table is modified and the color tone is modified according to the user's preference.

FIG. 1 is a diagram showing an example of an electrophotographic image forming apparatus used in both a copying machine and a printer which have been conventionally used.

The image forming apparatus shown in FIG. 1 has a printer control section 200 in which input character or graphic data is set together with a screen of image data.
And a toner image formed on the photosensitive drum 110 based on image data set by the printer control unit 200 or image data read by an image reading unit (not shown), and the toner image formed on the photosensitive drum 110. And an image forming unit 100 that forms an image of the toner image fixed on the sheet P by finally transferring and fixing the sheet onto the sheet P.

The image forming unit 100 has Y (yellow), M
Four photosensitive drums 110 that form toner images of respective colors (magenta), C (cyan), and K (black) are arranged in series, and a charging unit 111 and an exposing unit are provided around each photosensitive drum 110. Each developing machine 13 includes a toner cartridge 114 for supplying color toner. In addition, the drive roll 13
1, an intermediate transfer belt 130, which is circulated around the driven roll 132 and the opposing roll 133 and circulates to transfer the toner images of the respective colors formed on the photoconductor drum 110, and the intermediate transfer belt 130 is sandwiched therebetween. A primary transfer roll 134 and a counter roll 1 are provided at positions where they come into contact with the photosensitive drum 110.
Secondary transfer rolls 135 are arranged at positions where they contact 33. Further, a sheet feeding unit 140 is arranged on the upstream side of the secondary transfer roll 135, and a fixing device 145 is arranged on the downstream side of the secondary transfer roll 135.

In the image forming section 100, a tone correction patch formed of a plurality of toner images having different densities on the photoconductor drum 110 and a density control patch formed of a toner image of a predetermined density are respectively provided in a predetermined manner. Patch forming section 170 formed at the timing of
Alternatively, the density sensor 180 that measures the density of the density control patch on the intermediate transfer belt, the image data received from the print control unit 200, and the image data read by an image reading unit (not shown) are subjected to a predetermined gradation correction. The tonality control unit 160 and the tone detection signal processing means 161 for obtaining the relative density of the density of the tone correction patch measured by the density sensor 180 and the relative density are compared with the tone density target value 162. First correction means 164 for correcting the first gradation correction curve provided in the first gradation correction means 163.
It has and. Further, the density detection signal processing means 151 for obtaining the relative density of the density of the density control patch measured by the density sensor 180 and the relative density of the density target value 15
Compared with No. 2, a density control unit 150 for controlling the rotation time of the toner supply motor is provided, and the density control unit issues a signal 154 for connecting / disconnecting the power supply of the toner supply motor. Between the timings when the density control patches are formed, an image count unit 153 that predicts the toner consumption amount based on the image data is provided, and the density control unit 150 is also provided with the image count unit 153. Adjusting the connection / disconnection of the power supply. The patch forming unit 170 separates the screen for forming the gradation correction patch from the screen for forming the density control patch by, for example, 150 dp.
i, 200dpi, 200L, 300L, 600L 5
The screen has different types of screens, and the same screen as the screen set on the print control unit 200 side forms the tone correction patch. The density of the gradation correction patch is measured by the density sensor 180, and based on the measurement result, the gradation detection signal processing unit 161 calculates the relative density with the background of the intermediate transfer belt 130 as a reference,
The correction means 164 compares the target density value 162 with the calculated relative density, and corrects the first gradation correction curve based on the comparison result.

The print control unit 200 stores the character or graphic data input from the computer and the set screen information in the image forming unit 100.
Hand over to. The screens that can be set are the same as the screens that can be set for the image data read by the reading unit (not shown). Further, the printer control unit 200 includes a second gradation correction unit 221 that corrects the image data based on a predetermined second gradation correction curve, and the gradation-corrected image is set by the set screen. The data is delivered to the image forming unit 100.

Since the screen of the image data of the print control unit 200 is set by the print control unit 200 side, a toner image by the screen is formed on the photoconductor drum 110, and the toner thus formed is formed. Since the color tone of the image also changes with changes in the environment and changes with time, it is necessary to modify the first gradation correction curve and the second gradation correction curve so as to obtain a target gradation density. .

In such a case, for example, the operator sees the color tone of the image formed on the paper P, issues an instruction from the operation panel, causes the patch forming section 170 to form a gradation correction patch, and forms the patch on the paper P. After the transfer and fixing, the fixed tone correction patch is formed on the paper P, and the paper P is fixed.
The density of the upper gradation correction patch 201 is measured by a density sensor 202 provided separately from the image forming apparatus, and the measured value is input to the print control unit 200. The tonality detection signal processing means 203 calculates the relative density based on the paper P, and the second correction means 222 provided in the tonality control section 220 calculates the relative density based on the calculated relative density. Correct the gradation correction curve.

However, since there is no link between the patch forming section 170 and the print control section 200, the patch forming section 170 does not screen the image data received from the print control section 200. Is set, and a gradation correction patch is formed by the screen. In addition, the patch forming unit forms on the intermediate transfer belt at predetermined intervals,
Even in the case of the periodical correction in which the first correction means corrects the first gradation correction curve in accordance with the environmental change or the like, the second correction means irregularly corrects the second gradation correction curve. Similar to the case of the above correction, the correction is performed based on the density measurement result of the gradation correction patch for which the screen is set regardless of the screen of the image data received from the print control unit 200. For example, even if the screen of the image data received from the print control unit is 200 dpi, the patch formation unit forms the gradation correction patch of 300 L, and therefore the correction is performed based on the density of the gradation correction patch of 300 lines. The applied image is formed, and 3
A 200-dpi image that has been subjected to gradation correction using the second gradation correction curve possessed by the print control unit, which has been corrected based on the density of the gradation correction patch that was formed and printed out on a 00L screen. Image data
A toner image is formed from the print control unit to the image forming unit.

On the other hand, since the amount of change in gradation due to changes with time or changes in environment is subtly different depending on the screen, it is said that the demand cannot be sufficiently satisfied in an image forming apparatus that requires stable color reproduction. There's a problem.

[0013]

SUMMARY OF THE INVENTION In view of the above circumstances, the present invention is formed by the same screen as the screen set on the print control side even if the gradation characteristics change due to aging or environmental changes. An object of the present invention is to provide an image forming apparatus in which a gradation correction curve is corrected on the basis of a density measurement result of a gradation correction patch, and stable color reproduction is always possible.

[0014]

SUMMARY OF THE INVENTION An image forming apparatus of the present invention that achieves the above object has a screen for image data, a printer control section in which input character or graphic data is set, and an image carrier. An image forming unit for forming a toner image according to image data, and finally transferring and fixing the toner image on a recording medium to form an image composed of the fixed toner image on the recording medium. In the image forming apparatus, the image forming unit includes a first gradation correction unit that performs gradation correction processing on the image data received from the print control unit based on a predetermined first gradation correction curve; A patch forming unit that forms a gradation correction patch composed of a plurality of toner images having different densities on the image carrier at a predetermined timing, and a density of the gradation correction patch. And a first correction unit that compares the density of the gradation correction patch measured by the density sensor with a predetermined target value and corrects the first gradation correction curve. The patch forming unit receives the screen information set by the print control unit and forms the gradation correction patch on the same screen as the screen.

Here, the image forming unit sets a predetermined density control patch in the patch forming unit, the density control patch including a toner image of a predetermined density by a screen that is set independently of the screen set by the print control unit. And the density of the density control patch is measured by the density sensor. The density control patch is formed on the image carrier based on the density of the density control patch measured by the density sensor. It is preferable to include density control means for controlling the density of the toner image.

Further, when the screen of the printer control section is changed, the patch forming section preferably forms the gradation correction patch on the same screen as the screen after the change.

Further, the image forming section causes the patch forming section to form the gradation correction patch and causes the first correction means to correct the first gradation correction curve, and then again the floor. A tone correction patch is formed, and the tone correction patch is transferred to and fixed on a recording medium to form a fixed tone correction patch on the recording medium. Second gradation correction means for performing gradation correction processing on the image data before being transferred to the image forming section based on a predetermined second gradation correction curve, and gradation correction fixed on the recording medium. It is also a preferable aspect that a second correction means for correcting the second gradation correction curve based on the density measurement result of the patch for use is provided.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the image forming apparatus of the present invention will be described below.

FIG. 2 is a block diagram showing an image forming apparatus used in both the copying machine and the printer of this embodiment.

The image forming apparatus shown in FIG. 2 has a printer control unit 200 in which input character or graphic data is set together with a screen of image data.
And a toner image formed on the photosensitive drum 110 based on the image data converted by the printer control unit 200 or the image data read by an image reading unit (not shown), and the toner formed on the photosensitive drum 110. By finally transferring and fixing the image on the paper P,
An image forming unit 100 that forms an image composed of a toner image fixed on the paper P is provided.

The image forming unit 100 has Y (yellow), M
Four photosensitive drums 110 that form toner images of respective colors (magenta), C (cyan), and K (black) are arranged in series, and the photosensitive drums 110 are uniformly arranged around each photosensitive drum 110. Charging means 111 for electrically charging to
An exposure unit 112 that forms an electrostatic latent image according to image data by irradiating the charged photosensitive drum 110 with a laser beam driven by a signal whose pulse width is modulated based on the image data is formed. A developing device 113 for developing the electrostatic latent image with each color toner to form a toner image for each color on the photosensitive drum 110 is provided. Each developing device 13 is provided with a toner cartridge 114 for supplying color toner. ing. Further, each color toner image formed on the photosensitive drum 110 by being circulated around the driving roll 131, the driven roll 132, and the facing roll 133, and contacting each of the four photosensitive drums 110 arranged in series. The intermediate transfer belt 130 for transferring the toner images is provided. The intermediate transfer belt 130 is sandwiched between the primary transfer roll 134 at a position in contact with each photoconductor drum 110 and the secondary transfer roll 135 at a position in contact with the counter roll 133. Are arranged respectively. Further, a sheet feeding unit 140 that feeds a sheet to the upstream side of the secondary transfer roll 135, and a fixing unit 145 that fixes each color toner image transferred onto the sheet to the sheet at the downstream side of the secondary transfer roll 135. Are arranged respectively.

In the image forming section 100, a tone correction patch formed of a plurality of toner images having different densities on the photoconductor drum 110 and a density control patch formed of a toner image of a predetermined density are provided in a predetermined manner. Patch forming section 170 formed at the timing of
Alternatively, the density sensor 180 that measures the density of the density control patch at a predetermined measurement position on the intermediate transfer belt, the image data received from the print control unit 200, and the image data read by an image reading unit (not shown) First gradation correction means 163 provided in the gradation control unit 160, which performs gradation correction processing based on the gradation correction curve;
A gradation detection signal processing unit 161 that obtains a relative density from the ratio of the density of the gradation correction patch measured by the density sensor 180 to the background density of the intermediate transfer belt 130, and the relative density of the gradation density target value. First correction means 164 provided in the gradation control unit 160, which compares the first gradation correction curve provided by the first gradation correction means 163 with the correction curve 162.
And have. Further, the density detection signal processing means 151 for obtaining the relative density from the ratio of the density of the density control patch measured by the density sensor 180 to the density of the background of the intermediate transfer belt 130, and the relative density is compared with the density target value 152. Then, a density control unit 150 that adjusts the density of the toner image by determining whether the toner mixing ratio is high or low and controlling the rotation time of the toner supply motor is provided. Signal 1 to connect / disconnect the motor power supply
Issue 54.

An image count unit 153 for predicting the toner consumption amount from the image data is provided, and the density control unit 15 is provided.
With respect to 0, between the timings when the density control patches are formed, the connection / disconnection time of the power supply of the toner replenishment motor is adjusted according to the predicted toner consumption amount.

The image data converted by the printer control unit 200 or the image data read by an image reading unit (not shown) has a gradation for each color based on a first gradation correction curve provided in the gradation control unit 160. After the correction processing is performed, pulse width modulation is performed by the pulse width modulation circuit 121, and the laser driver 122 is driven by the pulse width modulated signal. The exposure means 1 driven by the laser driver 122
The laser light emitted from 12 irradiates the photoconductor drum 110 for each YMCK color to form an electrostatic latent image. The electrostatic latent image on each photoconductor drum 110 is YMCK stored in each developing machine 113. Each photosensitive drum 1 is developed with each color toner
A toner image of each color is formed on 10. The toner images of the respective colors on the respective photoconductor drums 110 are sequentially transferred and superposed on the intermediate transfer belt 130 by the primary transfer roll 134,
Toner images of respective colors are formed on the intermediate transfer belt 130. The toner images of the respective colors on the intermediate transfer belt 130 are secondarily transferred onto the paper P by the secondary transfer roll 135. Paper P
The toner images of the respective colors transferred on are further heated and pressed by the fixing device 145 to be fixed, and an image composed of the fixed toner images is formed on the paper P.

When the intermediate transfer belt 130 circulates once, for example, about ten prints are formed and the toner is consumed to some extent. Therefore, the patch forming section 170 of the intermediate transfer belt 130 circulates once, for example, the screen 300L.
The density control patch set to
The density control patch is formed on the intermediate transfer belt 1.
The density is measured by a density sensor 180 located downstream of the four photosensitive drums 110 arranged in the circulating movement direction of the intermediate transfer belt 130.

Here, the density control patch has a screen set in advance so that the sensitivity detected by the density sensor is in a good state. Further, since the sensitivity of the density sensor 180 changes due to environmental changes and toner stains, the density detection signal processing unit 151 cancels the measurement error. Therefore, the density detection signal processing unit 151 causes the background of the intermediate transfer belt 130 to have the density detected by the density sensor. The ratio (relative concentration) to the concentration of is determined.

The density control unit 150 compares the relative density obtained by the density detection signal processing means 151 with a predetermined density target value 152. For example, when the measured density is lower than the target value, the toner replenishing motor is powered on. The connection / disconnection of signal 154
By adjusting the disconnection interval and lengthening the rotation time of the toner replenishing motor, a large amount of toner is supplied to control the supply amount to increase the toner concentration. Note that the toner consumption amount between the timings when the density control patches are formed is predicted by the image counting unit 153 based on the image data,
The concentration control unit 150 adjusts the supply amount according to the predicted consumption amount.

The patch forming section 170 further forms, for each color toner, a plurality of gradation correction patches having different densities each time the number of image formations reaches 1200, or every four hours elapse. At this time, the patch forming unit 170 changes the screen on which the gradation correction patch is formed,
Independently of the screen for forming the density control patch, for example, 150 dpi, 200 dpi, 200L, 300
It has five types of screens of L and 600L, receives the screen information set on the print control unit 200 side via a link 210 formed between the screen and the print control unit, and is the same screen as that screen. To form a gradation correction patch. The density of the gradation correction patch is measured by the density sensor 180, and based on the measurement result, the gradation detection signal processing means 161 calculates the relative density with the background of the intermediate transfer belt 130 as a reference, Correction means 164 compares the calculated relative density for each gradation with the density target value 162 for each gradation, thereby correcting the first gradation correction curve provided in the first gradation correction means 163. .

Here, the first gradation correction curve is stored, for example, as a look-up table (LUT) in which the correspondence between each image data and the corrected image data is tabulated, and the image data is input. Then, the corrected image data may be output.

When the density of the gradation correction patch is measured by the density sensor 180 and the relative density calculated by the gradation detection signal processing means 161 is input to the first correction means 164, the first correction means 164 compares the relative density of the gradation correction patch with the gradation density target value 162, and when the relative density deviates from the gradation density target value 162, the image data for correcting the deviation is provided. The shift amount is obtained, and the first tone correction curve is corrected according to the obtained shift amount. In addition, with respect to the densities other than the measured densities, interpolation is performed by, for example, an extrapolation method. Then, the subsequent image data is subjected to the gradation correction processing by the corrected first correction curve.

The print control unit 200 delivers the character or graphic data input from the computer and the screen information to the image forming unit 100. The screens that can be set include a screen that can be set for image data read by an image reading unit (not shown) and a plurality of screens that are the same as the screen that can be set by the patch forming unit 170. A link 210 is provided between the print control unit 200 and the patch forming unit 170, and the patch forming unit 170 is configured to be able to receive the screen information set by the print control unit 200. Therefore, the screen is set in the print control unit 200,
When changed, the screen of the patch forming unit 170 is set to the same screen accordingly. The printer control unit 200 also includes a second gradation correction unit 221 that performs gradation correction processing on image data of character data or graphic data input from a computer based on a second gradation correction curve. The image data that has been subjected to gradation correction by the set screen is delivered to the image forming unit 100. Further, the printer control unit 200 causes the patch forming unit 170 to form a tone correction patch, transfers and fixes the patch on the paper P, and forms the fixed tone correction patch on the paper P. When the density of the gradation correction patch 201 on the paper P is measured by the density sensor 202 provided separately from the image forming apparatus and the measured value is input to the print control unit 200, the gradation detection signal processing unit 203 causes the paper to be detected. The relative density based on P is calculated, and the second correction means 222 provided in the gradation control unit 220 corrects the second gradation correction curve based on the calculated relative density. The method of correcting the second gradation correction curve can be performed in the same manner as the method of correcting the first gradation correction curve by the first correction means.

Here, the second gradation correction curve is stored as a look-up table (LUT) in which, for example, the correspondence between each image data and the image data after the correction is tabulated, and the image data is input. Then, the corrected image data may be output.

When an operator issues a gradation correction correction command from a panel (not shown) of the print control unit 200, when the operator sees the color tone of the formed image and determines that the color reproducibility is defective, the image is first corrected. The patch forming unit 170 of the forming unit 100 forms a gradation correction patch, the density sensor 180 measures the density, and the gradation detection signal processing unit 161 calculates the relative density. First correction means 1
Reference numeral 64 compares the relative density with the gradation density target value 162, and corrects the first gradation correction curve if a deviation occurs. Next, a tone correction patch that has been subjected to tone correction processing using the corrected first tone correction curve is formed by the patch forming unit 170 of the image forming unit 100, and the tone correction patch is formed. Transfer the paper to the paper P and fix it
The upper gradation correction patch 201 is formed. The density of the gradation correction patch 201 on the paper P is measured by a density sensor 202 provided separately, and the measured value is input to the gradation detection signal processing unit 203. Gradation detection signal processing means 20
3 calculates the relative density based on the paper, and the calculated relative density is input to the second correction means 222. The second correction unit 222 compares the relative density of the gradation correction patch with a predetermined density target value, and when the relative density deviates from the density target value, corrects the second gradation correction curve. .
In addition, for concentrations other than those for which the concentration measurement has been performed, interpolation is performed by, for example, an extrapolation method.

FIG. 3 is a flow chart showing the control procedure of the density control section and the gradation control section of the image forming section.

In FIG. 3, when the print operation in the image forming section is started (S-1) and the number of prints reaches a predetermined number, the patch forming section of the image forming section will form a patch according to the number of prints. It is determined whether the type is a density control patch or a gradation correction patch (S-2). As a result of the judgment, when the density control patch is to be formed, the density control patch is formed on the photosensitive drum with a predetermined screen, for example, 300 L, and is transferred to the intermediate transfer belt (S-3). The density of the density control patch formed on the intermediate transfer belt is detected by the density sensor when passing through a predetermined measurement position (S-4). The density detection signal processing means obtains a relative density of the detected density with reference to the background density of the intermediate transfer belt (S).
-5). The obtained relative density is compared with the density target value in the density control unit. For example, when the measured density is lower than the target value, the signal for connecting / disconnecting the power supply of the toner replenishment motor
A signal with a longer break interval is sent (S-7).
In response to the signal, the toner replenishing motor is turned on for a predetermined time to rotate, a predetermined amount of toner is supplied to the developing machine (S-8), and one cycle of density control is completed (S-).
8).

As a result of the judgment, when the gradation correction patch is to be formed, the patch forming section receives the screen information set by the print control section through the link (S-11). Owned by the forming unit, for example, 150 dpi, 200 dpi, 200L, 300
The same screen as the screen set by the print control unit is selected from L and 600L, and a gradation correction patch is formed on the photosensitive drum (S-12). The gradation correction patch formed on the photosensitive drum is transferred to the intermediate transfer belt, and the density is measured by the density sensor when passing through a predetermined density measuring position (S-13). The gradation detection signal processing means obtains the relative density of the measurement value measured by the density sensor with reference to the background of the intermediate transfer belt (S-14). The calculated relative density is compared with the gradation density target value by the first correction means provided in the gradation control unit, and the first gradation correction curve is corrected based on the comparison result (S-15). . Then, thereafter, the gradation correction processing is performed on the image data according to the modified first gradation correction curve (S-16).

As described above, a link is established between the printer control section and the patch forming section, and the patch forming section receives the screen information set by the printer control section and recognizes the set screen. Therefore, when an image is formed by the image data received from the printer control unit, a gradation correction patch is formed on the same screen as the screen set by the printer control unit, and the density measurement result is displayed. Since the first gradation correction curve is modified based on
The color tone of the formed image can always be maintained.

FIG. 4 is a flowchart showing a control procedure in the gradation control section of the image forming section when the screen is changed in the printer control section.

In FIG. 4, when the print operation is being performed in the image forming section (S-21) and the screen set in the print control section is changed (S-22), the patch forming section is , The information of the changed screen is immediately received via the link, so that a gradation correction patch having the same screen as the changed screen is formed on the photosensitive drum (S-
23). The gradation correction patch formed on the photosensitive drum is transferred to the intermediate transfer belt, and the density is measured by the density sensor when passing through a predetermined density measuring position (S-2).
4). The gradation detection signal processing means obtains the relative density with reference to the background of the intermediate transfer belt, based on the measurement value measured by the density sensor (S-25). The obtained relative density is compared with the gradation density target value by the first correction means provided in the gradation control unit, and the first gradation correction curve is corrected based on the comparison result (S-26). . Then, thereafter, the gradation correction processing is performed on the image data by the corrected first gradation correction curve (S-27).

FIG. 5 is a flow chart showing the control procedure in the gradation control section of the print control section.

In FIG. 5, when the image forming unit is performing the printing operation (S-31), the operator looks at the color tone of the image formed on the sheet and operates the operation panel to operate the print control unit. When a command to modify the second gradation correction curve is issued (S-31), the patch forming unit receives the information via the link and is exposed by the same screen as the screen set in the print control unit. A tone correction patch is formed on the body drum (S
-33). The gradation correction patch formed on the photosensitive drum is transferred to the intermediate transfer belt, and the density is measured by the density sensor when passing through a predetermined density measuring position (S-3).
4). The gradation detection signal processing means obtains the relative density of the measurement value measured by the density sensor with reference to the background of the intermediate transfer belt (S-35). The obtained relative density is compared with the gradation density target value by the first correction means provided in the gradation control section of the image forming section, and the first gradation correction curve is corrected based on the comparison result ( S-36). Next, the patch forming unit forms a gradation correction patch, which has been subjected to gradation correction processing based on the corrected first gradation correction curve, on the photosensitive drum on the same screen again, and The image is transferred to a transfer belt, further transferred and fixed on a sheet, and a tone correction patch is printed on the sheet (S-37).
Then, the density of the printed tone correction patch is measured by a density sensor provided separately from the image forming apparatus,
The measured value is input to the gradation detection signal processing unit of the print control unit to obtain a relative density with reference to the background of the paper, and the relative density is compared with a predetermined target density by the second correction means. , And the second gradation correction curve is corrected based on the comparison result (S-38). After that, this modified second
The gradation correction curve is used to perform gradation correction processing on the image data transferred from the print control unit to the image forming unit (S-39).

As described above, when the second gradation correction curve is modified, the first gradation correction curve is first modified to adapt to the environmental change, and the modified first gradation correction curve is obtained. Based on the density measurement result of measuring the density of the gradation correction patch formed on the photosensitive drum by forming the gradation correction patch on which the gradation correction processing has been performed on the photosensitive drum. Therefore, it can be corrected more accurately.

Although the present embodiment has been described based on the tandem type image forming apparatus, the image forming apparatus is not necessarily limited to the tandem type and is also applicable to a direct transfer type or a 4-cycle type image forming apparatus. To be done. Although the density of the gradation correction patch is measured on the intermediate transfer belt, it may be measured on each photoconductor drum. Further, although the print control side is also provided with a gradation correction curve correction means, the print control side does not necessarily need to be provided with a gradation correction curve correction means, and the gradation correction curve correction means provided in the image forming unit is corrected. It may be provided with only means.

[0044]

As described above, according to the image forming apparatus of the present invention, a link is set up between the print control section and the patch forming section, and the image data transferred from the print control section to the image forming section. Is subjected to gradation correction processing based on the gradation correction curve currently maintained by the gradation correction patch formed on the same screen as the print control unit screen, so gradation characteristics may change due to aging and environmental changes. It is possible to always realize stable color reproduction even when the value fluctuates.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of an electrophotographic image forming apparatus used in both a copying machine and a printer which have been conventionally used.

FIG. 2 is a configuration diagram showing an image forming apparatus used in both the copying machine and the printer of the present embodiment.

FIG. 3 is a flowchart showing a control procedure of a density control unit and a gradation control unit of an image forming unit.

FIG. 4 is a flowchart showing a control procedure in the gradation control unit of the image forming unit when the screen is changed in the printer control unit.

FIG. 5 is a flowchart showing a control procedure in a gradation control unit of the print control unit.

[Explanation of symbols]

100 Image forming unit 110 photoconductor drum 111 charging means 112 exposure means 113 developing machine 114 toner cartridge 121 Pulse width modulation circuit 122 Laser driver 130 Intermediate transfer belt 131 drive roll 132 Follower roll 133 Opposite roll 134 Primary transfer roll 135 Secondary transfer roll 140 Paper feed section 145 fixing device 150 Concentration control unit 151 Concentration detection signal processing means 152 Concentration target value 153 Image counting section 154 Signal to connect / disconnect power 160,220 Gradation control section 161,203 Gradation detection signal processing means 162 gradation density target value 163 First gradation correcting means 164 First correction means 170 patch forming unit 180,202 Concentration sensor 200 Print control section 201 tone correction patch on paper P 221 Second tone correcting means 222 Second correction means

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Shino Yokoyama             Fuji Zero, 2274 Hongo, Ebina City, Kanagawa Prefecture             Co., Ltd. Ebina Office F term (reference) 2C061 AP04 AQ06 KK18 KK25 KK28                       KK32                 2C262 AA04 AA24 AA26 AB07 BB01                       BB27 BB36 FA13 GA02                 2H027 DA09 DE02 DE07 EA06 EB04                       EC03 EC06 EC20                 2H077 DA05 DA10 DA47 DA49 DA63                       DB02 DB22 GA03 GA13                 5C074 AA05 BB02 BB26 DD03 DD24                       EE08 EE20 FF05 FF07

Claims (4)

[Claims] 1. A screen for image data, a printer control section in which input character or graphic data is set, a toner image corresponding to the image data is formed on an image carrier, and the toner image is finally formed. An image forming apparatus comprising: an image forming unit that forms an image of a toner image fixed on the recording medium by transferring and fixing the image on the recording medium; First tone correction means for performing tone correction processing on the received image data based on a predetermined first tone correction curve, and tone correction comprising a plurality of toner images with different densities on the image carrier. Forming unit for forming a patch for a predetermined timing, a density sensor for measuring the density of the gradation correction patch, and a density sensor for measuring the density of the gradation correction patch. A first correction unit that compares the density of the gradation correction patch with a predetermined target value and corrects the first gradation correction curve; and the patch forming unit is a screen set by the print control unit. Image forming apparatus, which receives the information of 1. and forms the gradation correction patch on the same screen as the screen. 2. The image forming unit, the patch forming unit,
A density control patch consisting of a toner image of a predetermined density is formed at a predetermined timing by a screen set independently of the screen set by the print control unit, and the density of the density control patch is determined by the density sensor. And a density control means for controlling the density of the toner image formed on the image carrier based on the density of the density control patch measured by the density sensor. The image forming apparatus according to claim 1. 3. When the screen of the printer control unit is changed, the patch forming unit forms the gradation correction patch on the same screen as the screen after the change. The image forming apparatus according to claim 1. 4. The image forming section causes the patch forming section to form the gradation correction patch and causes the first correction means to correct the first gradation correction curve, and then again the floor. A tone correction patch is formed, and the tone correction patch is transferred and fixed on a recording medium to form a tone correction patch fixed on the recording medium. Second gradation correction means for performing gradation correction processing on the image data before being transferred to the image forming section based on a predetermined second gradation correction curve, and gradation correction fixed on the recording medium. The image forming apparatus according to claim 1, further comprising: a second correction unit that corrects the second gradation correction curve based on a density measurement result of the patch for use.