JP2002348023A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device of high reliability capable of detecting and correcting the curling state of a paper sheet with high accuracy. SOLUTION: The image forming device 20 having a photosensitive body 1, a charger 2, an exposure device 4, a developer 5, an intermediate transfer belt 7, a primary transfer unit T1, a cleaning device 6, a paper feed tray 9, a secondary transfer unit T2, a fixing device 8, and a discharge tray 16, comprises a curl shape measurement unit 101 for measuring the curl shape of the reference paper, a curl shape storage unit 102 for storing the measured curl shape of the reference paper, a curl correction calculation unit 103 for calculating the curl correction of the paper sheet based on the image area ratio of the image formed on the paper sheet and the curl shape of the reference paper, and a curl correction unit 104 for correcting the curl of the paper sheet based on the calculated curl correction.

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 used for an electrophotographic copying machine, a printer, and the like.

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus used for an electrophotographic copying machine or a printer, a toner image is formed on a photosensitive drum, and the toner image is finally transferred onto a predetermined sheet. A method in which the above toner image is heated and pressed by a fixing device including a heating roll and a pressure roll to fix the toner image to form a fixed toner image on a sheet is often used. In such an image forming apparatus, there is a problem that the paper is curled because heat and pressure are applied to the paper when the paper passes through the fixing device.

The curl generated on the paper varies in the strength and direction of the curl depending on the type of the paper and the characteristics of the fixing device, and the curl strength often changes depending on the moisture content of the paper.

[0004]

When such a curl occurs, a paper jam may occur in the paper transport path from the fixing device to the discharge tray.
Further, when a strongly curled sheet is discharged to the discharge tray, there may be a problem that the sheet is curled or broken on the discharge tray.

Further, when making a two-sided copy with a two-sided copying machine or the like, the positioning of the sheet printed on one side becomes unstable, and the operation of feeding the sheet toward the backside copy cannot be performed accurately. Problems can occur.

Therefore, in a conventional copying machine or the like, various curl correction devices for eliminating curl generated during copying have been proposed.

[0007] For example, Japanese Patent Application Laid-Open No. Hei 8-198477 discloses an electrophotographic apparatus provided with a mechanism for detecting the arrival time and the passage time of a sheet by a sheet position detection sensor provided on a sheet conveyance path. At least one of the paths
An electrophotographic apparatus having a paper curl detection mechanism using an optical distance sensor at more than one location is disclosed. However, the curl of the paper occurs due to various factors and in various shapes and various strengths. Therefore, as in this electrophotographic apparatus, the presence or absence of a curl of a certain size is determined by an optical distance sensor. It is almost impossible to perform a proper curl correction because it is not possible to determine how to correct the paper only by the detection.

Further, Japanese Patent No. 579636 discloses a means for measuring the amount of curl of a sheet on a sheet transport path, and generates a signal for exceeding a curl amount limit when the measured value exceeds a predetermined limit. A signal generating means, a warning display device for displaying a dangerous state based on the signal, and a control device for controlling the post-processing device of the copier to receive the signal and the jam occurrence signal so as to disable the post-processing device. A copying machine is disclosed in which the means for measuring the amount of curl measures the distance of a sheet rising from a conveying surface and moves the sheet in a direction perpendicular to the conveying direction according to the measurement result. However, in this method, since the control mechanism has a complicated configuration, the cost of the apparatus is likely to increase, and a considerable installation space is required. Further, there is a difficulty in the reliability of the apparatus.

In Japanese Patent Application Laid-Open No. Hei 5-221574, a contact-type curl detection sensor and a curl correction device are arranged on a paper transport path, and the curl direction and intensity are detected by the curl detection sensor, and the paper curl is detected. There is disclosed a curl correction device that adjusts the intensity of a curl correcting action in a curl correction device according to information on the direction and strength of a curl.

However, if a contact-type curl detection sensor such as that used in this curl correction device attempts to detect the direction and strength of the curl, a considerable load is imposed on the conveyance of the sheet, and the image forming apparatus has a problem. There is a risk that reliability will be impaired.

In addition to the above-described method, the curl correction amount is measured from the image area ratio of the developed image of the image information and the temperature and humidity in the apparatus based on the curl prediction table for each paper type prepared in advance. There is a way to do this.

FIG. 16 is a flowchart of a conventional curl correction method using a curl prediction table.

As shown in FIG. 16, at the setup stage, it is determined whether or not the paper has been replaced by the user (step S21). If it is determined that the paper has been replaced, the process proceeds to step S22. The curl is predicted from the paper basis weight, the paper gloss, the paper size, and the like with reference to the paper type curl prediction table created in advance (step S22). The curl correction amount is measured from the image area ratio and the temperature and humidity in the apparatus (step S23), and the curl correction is performed (step S24). On the other hand, step S
If it is determined in step 21 that the paper has not been replaced, step S22 is skipped and step S2 is performed.
Proceed to 3.

However, this method has the following various problems when creating a curl prediction table, and it is desired to solve it. That is, (1). It is difficult to pre-evaluate the curl at the time of developing the image forming apparatus, and the number of steps for creating the prediction table is large.

(2). Variations in various parameters during development of the image forming apparatus are large, and variations in initial parameters cannot be suppressed.

(3). There is a large curl control error depending on the type of paper, and there is a limit to grouping, so that curl cannot be corrected with high accuracy.

In view of the above circumstances, it is an object of the present invention to provide a highly reliable image forming apparatus capable of detecting and correcting the curl state of a sheet with high accuracy.

[0018]

An image forming apparatus according to the present invention, which achieves the above object, forms a toner image on an image carrier, transfers the toner image onto a predetermined sheet, and forms a toner image on the sheet. A curling shape measuring unit for measuring the curling shape of a reference sheet made of white paper, or a reference image formed with a reference image, in an image forming apparatus for fixing a fixed toner image on a sheet by forming a fixed toner image on the sheet; A curl shape storage unit that stores the curl shape of the reference paper measured by the curl shape measurement unit; and a curl of the paper based on the image area ratio of an image formed on the paper and the curl shape of the reference paper. A curl correction amount calculation unit for calculating a correction amount,
A curl correction unit configured to correct the curl of the sheet based on the curl correction amount calculated by the curl correction amount calculation unit.

Here, the image forming apparatus detects a temperature change information during transport which indicates a temperature change of the paper being transported while the paper on which the fixed toner image is formed is discharged from the fixing device. Preferably, the curl shape measurement unit measures the curl shape of the sheet based on the temperature change information during conveyance detected by the temperature change information detection unit.

Further, it is preferable that the temperature change information detecting section detects the temperature change information during conveyance by using a non-contact temperature sensor.

The temperature change information detecting section also detects post-discharge temperature change information indicating a temperature change of the sheet after the sheet is discharged to the discharge tray. A paper size detection unit that detects the size of the paper used for forming, a paper size detected by the paper size detection unit, and a paper basis weight from the post-ejection temperature change information detected by the temperature change information detection unit. It is also one of the preferable embodiments to have a paper basis weight measuring unit to be measured, and that the curl correction unit corrects the curl of the paper according to the curl shape and the paper basis weight.

Further, the image forming apparatus has a paper gloss detecting section for detecting glossiness of the paper used for image formation, and the paper basis weight measuring section detects the paper gloss detected by the paper size detecting section. One of the preferable embodiments is to measure the paper basis weight from the size, the paper glossiness detected by the paper glossiness detection unit, and the post-discharge temperature change information detected by the temperature change information detection unit. It is.

[0023]

Embodiments of the present invention will be described below.

FIG. 1 is a schematic configuration diagram showing a first embodiment of the image forming apparatus of the present invention.

The image forming apparatus 20 is an image forming apparatus used as an electrophotographic copying machine. As shown in FIG. 1, a photoreceptor 1 having a surface on which a toner image is formed,
A charging device 2 for uniformly charging the surface of the photoreceptor 1 and an exposure for irradiating the uniformly charged surface of the photoreceptor 1 with exposure light 3 according to image information to form an electrostatic latent image on the surface of the photoreceptor 1 Device 4,
A developing device 5 for developing the electrostatic latent image formed on the surface of the photoconductor 1 with toner to form a toner image on the surface of the photoconductor 1; An intermediate transfer belt 7 that conveys to the secondary transfer portion T2, a primary transfer portion T1 that transfers the toner image on the photoreceptor 1 to the intermediate transfer belt 7, and remains on the photoreceptor 1 downstream of the primary transfer portion T1. The cleaning device 6 for removing the removed toner, the paper feed tray 9 for storing the paper P used for image formation, and the toner image formed on the intermediate transfer belt 7 by the primary transfer are supplied from the paper feed tray 9. A secondary transfer portion T2 for transferring to the sheet P, and a pair of fixing rolls 8_1 and 8_2 which have a heat source 8a inside and rotate while forming a nip portion N by being in contact with each other, are transported to the nip portion N. A fixing device 8 that heats and pressurizes a sheet carrying an unfixed toner image on its surface to fix the unfixed toner image to the sheet, and a discharge tray from which the sheet P on which the fixed toner image is formed is discharged 16 and
A curl shape measuring unit 101 for measuring the curl shape of a reference sheet made of a blank sheet or a reference image formed thereon,
A curl shape storage unit 102 for storing the curl shape of the reference paper measured by the curl shape measuring unit 101; and a curl of the paper based on the image area ratio of the image formed on the paper and the curl shape of the reference paper. The apparatus includes a curl correction amount calculation unit 103 that calculates a correction amount, and a curl correction unit 104 that corrects paper curl based on the curl correction amount calculated by the curl correction amount calculation unit.

The image forming apparatus 20 further includes a curl shape measuring unit 101, a curl shape storage unit 102,
A control unit 100 that comprehensively controls the entire image forming apparatus 20 including the curl correction amount calculation unit 103 and the curl correction unit 104
Is provided.

The intermediate transfer belt 7 in the first embodiment corresponds to the image carrier according to the present invention.

Next, a normal image forming operation by the image forming apparatus 20 will be described.

After the surface of the photoconductor 1 rotating in the direction of the arrow A is uniformly charged by the charging device 2, the exposure device 4 irradiates the surface of the photoconductor 1 with exposure light 3 according to image information,
An electrostatic latent image is formed on the surface of the photoconductor 1. The electrostatic latent image formed on the surface of the photoconductor 1 is developed with toner by the developing device 5 to form a toner image on the surface of the photoconductor 1. The toner image on the photoreceptor 1 is indicated by an arrow B in the primary transfer portion T1.
The image is transferred to the intermediate transfer belt 7 rotating in the direction, and is conveyed to the secondary transfer portion T2. In the secondary transfer section T2, the toner image on the intermediate transfer belt 7 is transferred onto a sheet conveyed from the sheet feeding tray 9 via the sheet conveying path R1.
The unfixed toner image transferred onto the sheet is conveyed to the fixing device 8 and a pair of fixing rolls 8_1 and 8_ of the fixing device 8 are provided.
2 is heated and pressurized in a nip portion N formed by the fixing member 2 to be fixed on a sheet. The sheet P after the fixing is discharged to the discharge tray 16 via the sheet conveyance path R2.

Next, curl correction in the image forming apparatus according to the first embodiment will be described.

FIG. 2 is a diagram showing the configuration of each unit for performing curl correction according to the first embodiment of the present invention, and FIG.
5 is a flowchart of curl correction according to the first embodiment of the present invention.

As shown in FIG. 2, a control section 100 for controlling each section of the image forming apparatus includes a curl shape measuring section 101 for measuring the curl shape of a reference sheet formed of a blank sheet or a reference image. And the curl shape measuring unit 10
A curl shape storage unit 102 for storing the curl shape of the reference paper measured in Step 1 and a curl correction amount of the paper based on the image area ratio of an image formed on the paper and the curl shape of the reference paper. Curl correction amount calculation unit 103 to be calculated
And a curl correction unit 1 that corrects paper curl based on the curl correction amount calculated by the curl correction amount calculation unit 103
04 is provided.

As shown in FIG. 3, this image forming apparatus 20
First, at the setup stage, it is determined whether or not the paper has been replaced by the user (step S1). If it is determined that the paper has been replaced, the process skips step S2 and proceeds to step S3. Step S1
If it is determined that the paper has not been replaced, the process proceeds to step S3, where an environmental change in the image forming apparatus is checked to determine whether the temperature change is 5 ° C. or more and the humidity change is 10% or more. Is determined (step S2),
As a result of the judgment, the temperature change is 5 ° C. or more and the humidity change is 10
If it is not less than%, the flow proceeds to step S3 to execute simplex traveling. That is, reference paper, for example, a reference paper made of, for example, blank paper or a reference image formed thereon is fed to the image forming apparatus 20, and the image forming apparatus 20 travels in the image forming apparatus (step S3). Next, the aforementioned curl shape measuring unit 10
1 (see FIG. 2), the curl shape of the reference paper is measured.

For the measurement of the curl shape, for example, an optical measuring means can be used. That is, the LED (L
The running reference paper is irradiated by a light emitting device (PS) or the like, and the PSD (Position) is used.
A curl shape of the reference paper is measured by detecting a change in the position of the paper based on a change in the amount of light reflected from the reference paper by a position detecting device such as a sensing detector (step S4). The curl shape of the reference paper measured by the curl shape measuring unit is stored in the curl shape storage unit 102 (FIG. 2).
(See step S5). Thus, the setup phase is completed.

As a result of the determination in step S2,
If the temperature change is not more than 5 ° C. and the humidity change is not more than 10%, the setup stage is ended.

In the job stage, the curl correction amount calculation unit 10
Reference numeral 3 (see FIG. 2) indicates the curl shape obtained in the set-up step, the image area ratio of the developed image of the image information on both the front and back sides of the paper, the distinction between double-sided printing / single-sided printing, and the discharging method, that is, the printing surface. The curl correction amount is calculated based on whether upward discharge / print surface downward discharge (step S6).

The calculation of the curl correction amount is specifically performed, for example, as follows.

Table 1 is a table showing the basic curl correction amount based on the curl amount measured by the curl shape measuring unit. Table 1 is a table corresponding to a nip amount N1 described later.

[0039]

[Table 1]

As shown in Table 1, the basic curl correction amount is set to a different value depending on the type of paper (plain paper and thick paper). The basic curl correction amount for the environment at that time is obtained from Table 1 and then the curl correction amount is calculated from Table 2.

Table 2 is a table for calculating the amount of correction based on the image area ratio, and the method of double-sided printing / single-sided printing and the discharge method.

[0042]

[Table 2]

The image area ratio shown in Table 2 and the double-sided printing /
Correction amount (unit m
m) is obtained, and the final curl correction amount is calculated by adding the correction amount according to Table 2 to the basic curl correction amount according to Table 1 described above. Note that plus (+) and minus (-) in Table 2 indicate which of the first correction unit and the second correction unit shown in FIG. 4 performs curl correction.

FIG. 4 is a schematic configuration diagram of the curl correction device used in the first embodiment.

As shown in FIG. 4, the curl correcting device 3
0 denotes a first correction unit 31 that corrects the curl by curling the curled sheet in a direction opposite to the curl when the supplied sheet P is curled upward toward the paper surface. The second correction unit 32 that corrects the curl by curving the curled sheet in a direction opposite to the curl when the sheet P curled downward toward the paper surface, It comprises a guide device 33 for guiding one of the first correction unit 31 and the second correction unit 32.

The first correction unit 31 and the second correction unit 32 are composed of rolls 34 and 35 and endless belts 36 and 37 which are arranged to face each other and correct the curl of the sheet by pressing the sheet. .

Returning to FIG. 3, the description of the flowchart will be continued.

As described above, the curl correction amount calculation unit 1
When the curl correction amount is calculated by 03, the curl correction unit 104 (see FIG. 2) corrects the curl of the sheet based on the calculated curl correction amount (step S7). That is, based on the value of the curl correction amount, the nip amount N1 of the first correction unit 31 of the curl correction device 30 shown in FIG.
The nip amount N2 of the correction unit 32 is set to correct the curl of the sheet P.

Next, a second embodiment of the present invention will be described.

The configuration of the image forming apparatus according to the second embodiment is substantially the same as that of the image forming apparatus according to the first embodiment shown in FIG. Hereinafter, differences from the first embodiment will be mainly described.

FIG. 5 is a diagram showing the configuration of each unit for performing curl correction according to the second embodiment of the present invention, and FIG.
9 is a flowchart of curl correction according to the second embodiment of the present invention.

As shown in FIG. 5, in the image forming apparatus of the second embodiment, the sheet P on which the fixed toner image is formed is being conveyed and discharged from the fixing device 8 (see FIG. 1).
A temperature change information detecting section 111 for detecting temperature change information during transport indicating a temperature change of the sheet;
Is configured to measure the curl shape of the sheet based on the temperature change information during conveyance detected by the temperature change information detection unit 111.

In the present embodiment, the temperature change information detecting section 111 is configured to detect the temperature change information during transport using a non-contact temperature sensor. The apparatus is also configured to detect post-discharge temperature change information indicating a temperature change of the sheet P after the sheet P is discharged to the discharge tray 16.

The image forming apparatus according to the second embodiment includes a sheet size detecting unit 114 for detecting the size of a sheet used for image formation, a sheet size detected by the sheet size detecting unit 114, and a temperature change. Information detector 11
A paper basis weight measuring unit 115 for measuring the paper basis weight from the post-discharge temperature change information detected by step 1; and a curl correction unit 113 that corrects the paper curl according to the curl shape and the paper basis weight. It is configured to be.

To control each part of the image forming apparatus,
While the temperature of the sheet P is being conveyed from the fixing device 8 to the discharge tray 16, the temperature change information is detected while the sheet P is being conveyed, and the temperature change of the sheet after the sheet P is discharged to the discharge tray 16 is detected. A temperature change information detecting unit 111 that also detects post-discharge temperature change information indicating the following; a curl shape measuring unit 112 that measures the curl shape of the sheet based on the temperature change information during conveyance detected by the temperature change information detecting unit 111;
Curl correction unit 11 that corrects the curl of the paper according to the curl shape of the paper obtained by the curl shape measuring unit 112
3. A paper size detection unit 114 that detects the size of paper used for image formation, and a paper basis weight measurement unit 115 that measures the paper basis weight from the post-discharge temperature change information detected by the temperature change information detection unit 111 are provided. ing.

The temperature change information detecting section 11 of the second embodiment
As 1, a thermopile type non-contact temperature sensor is used as a temperature sensor, and is configured to detect the above-described temperature change information during conveyance. The temperature change information detecting unit 111 also detects post-discharge temperature change information indicating a change in the temperature of the sheet after the sheet P is discharged to the discharge tray 16. A paper size detection unit 114 that detects the size of the paper used in the printing, and a paper basis weight is measured from the paper size detected by the paper size detection unit 114 and the post-ejection temperature change information detected by the temperature change information detection unit 111. The paper curl correction unit 113 is configured to correct the curl of the paper according to the curl shape and the paper grammage.

As shown in FIG. 6, in the image forming apparatus according to the second embodiment, first, at the setup stage, it is determined whether or not the user has exchanged paper (step S1).
1) If it is determined that the sheet has been replaced, the process skips step S12 and proceeds to step S13. As a result of the determination in step S11, when it is determined that the sheet has not been replaced, the process proceeds to step S13, where the environmental change in the image forming apparatus is checked, and the temperature change is 5 ° C.
Then, it is determined whether or not the change in humidity is 10% or more (step S12). If the result of the determination is that the temperature change is 5 ° C. or more and the humidity change is 10% or more, step S12 is performed.
Proceed to 13 to execute simplex running. That is,
Either a blank sheet is supplied to the image forming apparatus and the image forming apparatus is driven inside the apparatus without forming an image, or the image forming apparatus forms an image of a specified image and runs inside the apparatus (step S13). Next, the sheet P (see FIG. 1) is transferred from the fixing device 8 to the discharge tray 1 by the temperature change information detecting unit 111 (see FIG. 5).
During conveyance, temperature change information indicating a temperature change of the paper being conveyed toward No. 6 is detected (step S14). The curl shape measuring unit 112 (see FIG. 5) measures the curl shape of the paper based on the temperature change information during conveyance detected in step S14 (step S15). Next, the temperature change information detecting unit 111 (see FIG. 5) detects post-discharge temperature change information indicating a temperature change of the sheet after the sheet P is discharged to the discharge tray 16 (Step S16). The paper basis weight measurement unit 115 (see FIG. 5) measures the paper basis weight from the post-discharge temperature change information detected in step S16 and the paper size detected by the paper size detection unit 114 (step S17).

When the set-up stage is completed and the curl shape and the basis weight of the paper are obtained, the process can shift to the job stage.

On the other hand, as a result of the determination in step S12, the temperature change is not 5 ° C. or more and the humidity change is 10%
If not, the setup stage ends.

In the job stage, the curl correction unit 113 (see FIG. 5) determines the curl shape and paper basis weight obtained in the above-described setup stage, the image area ratio of the image information developed on both sides of the paper, The curl correction amount is measured according to the single-sided printing and the discharging method, that is, the upward discharging of the printing surface / the downward discharging of the printing surface (step S1).
8) The curl correction is performed on the paper actually used for image formation (step S19).

Next, the principle of curl correction by the image forming apparatus will be described.

In general, when a thermopile type non-contact temperature sensor is used, the radiant energy P of a black body at a temperature T is calculated by the Boltzmann's law as the fourth power of the absolute temperature T as shown in the following equation (1). Is known to be proportional to

P = σT ⁴ [W · cm ² ] (1) Here, an area A [cm ² ] at a place vertically separated by a distance A (cm) from a heat source having an absolute temperature T ゜ K. incident energy P to the thermopile ^{sensor, P = σ (T 4 -T0} 4) (a · a S) / πL 2 a [W] ··· (2), the sensor output is inversely proportional to the square of the distance You can see that. The distance from the sensor output to the sheet can be detected by using the equation (2), so that the curl shape of the sheet can be detected.

FIG. 7 is a graph showing the time-dependent temperature change detected by the temperature change information detecting section according to the second embodiment of the present invention.

As described above, the temperature change information detecting unit 111 of the present embodiment uses the thermopile type non-contact temperature sensor to measure the temperature during the conveyance of the paper being conveyed from the fixing device 8 to the discharge tray 16. It is configured to detect change information.

Up to the point P1 shown in FIG. 7, that is, while the sheet does not reach the temperature sensor of the temperature change information detecting unit 111, the sensor temperature is slightly lower than about 29 ° C., and the toner image is fixed at the point P1. When the discharged sheet reaches the temperature change information detecting unit 111, the sensor temperature rises rapidly and reaches about 37 ° C. at a point P2.

If there is no curl on the sheet, the sensor temperature reaches the point P2, and while the sheet is conveyed in front of the sensor, the temperature is substantially the same. Then the temperature starts to drop.

FIG. 8 is a schematic diagram showing a temperature change when a sheet is curled.

As shown in FIG. 8, when there is no curl on the sheet, as shown by the solid line A1, the point P2
A flat level a is shown up to the point, but if there is an upcurl at the leading end of the sheet, that is, a curl that faces upward, the temperature changes in a shape as indicated by a broken line B1.

FIG. 9 is a distance characteristic curve of the thermopile type temperature sensor.

FIG. 9 shows that the level a shown in FIG.
And a distance characteristic curve B when the level a is 50 ° C. are shown.

The output of the temperature sensor is converted into a distance variation based on the distance characteristic curve. In this example, the nominal detection distance is set to 30 mm.

FIG. 10 is a diagram showing a temperature change curve when the curl of the sheet is detected using two sensors.

FIG. 10 shows an example of the temperature change information detecting section.
The temperature change when two thermopile non-contact temperature sensors A and B are arranged in parallel in the paper width direction is shown.

Curves A1 and B1 shown by solid lines in FIG. 10 are temperature changes when the paper has no curl. Curves A2 and B2 shown by broken lines in FIG. Curves A3 and B3 indicated by dashed lines in FIG. 10 indicate a temperature change when there is a down-curl, that is, a curl directed downward at the leading end of the sheet. In FIG. 10, since both A and B show the same shape, it can be seen that the curl shape of this sheet is the same shape in the width direction. By arranging the two sensors in parallel in the paper width direction in this way, it is possible to detect not only the curl shape in the paper length direction but also the curl shape in the paper width direction.

FIG. 11 is a partially enlarged view of the temperature change curve shown in FIG. 10 and a temperature change curve obtained by the sensor A ′ disposed on the back side symmetrical to the sensor A with the sheet interposed.

As shown in FIG. 11, curves A1, A
The presence or absence of curl and the distinction of up-curl and down-curl can be determined from the front side of the paper from the shape of A2 and A3, and the sensor A 'is also arranged on the back side of the paper to more accurately curl the paper. The presence or absence of up-curl and the distinction of up-curl and down-curl can be detected.

Next, the operation of the paper basis weight measuring unit provided in the image forming apparatus according to the second embodiment will be described.

The temperature change information detecting section 1 of the image forming apparatus
Reference numeral 11 (see FIG. 5) is also configured to detect post-discharge temperature change information indicating a change in the temperature of the sheet after the sheet is discharged to the discharge tray 16 and becomes stationary, and is provided in the image forming apparatus. The measured paper basis weight measurement unit 115 measures the paper basis weight from the post-ejection temperature change information detected by the temperature change information detection unit 111 and the paper size detected by the paper size detection unit 114, and performs a curl correction unit. 113 is a curl shape measured by the curl shape measuring unit 112,
The paper curl is corrected in accordance with the paper basis weight measured by the paper basis weight measurement unit 115.

FIG. 12 is a schematic diagram showing a method of measuring the paper basis weight in the second embodiment, and FIG. 13 is a graph showing a difference in sensor temperature change depending on the paper type.

As shown in FIG. 12, in the present embodiment, after the sheet is stopped in the discharge tray 16, the sensor temperature decrease amount for about seconds after the point P 4 at which the temperature starts to drop at a substantially constant gradient is obtained. The paper basis weight is measured. However, the degree of this temperature drop differs depending on the paper basis weight (paper type), and as shown in FIG.
The temperature of the coated paper of 0 g / m ² falls almost gently as shown by curve A, whereas the plain paper of 82 g / m ² has a sharply reduced temperature at the beginning like curve B and draws a gentle curve. Temperature. Furthermore, 55 g of paper basis weight
/ M ² , the temperature of the thin paper decreases more rapidly, as indicated by curve C, and then decreases in a gentle curve.

Assuming that the basis weight of the sheet is m, the specific heat of the sheet is c, and the temperature is t, the heat capacity Q of the sheet can be expressed by the following equation.

Q = m · ct · t Therefore, the paper basis weight (paper type) can be measured from the sensor temperature drop curve of FIG.

In the second embodiment, the temperature change information detecting section 111 also detects post-discharge temperature change information indicating the temperature change of the sheet after the sheet is discharged to the discharge tray 16. Further, the image forming apparatus detects the size of a sheet used for image formation by a sheet size detecting unit 114, a sheet size detected by the sheet size detecting unit 114, and a temperature change information detecting unit 111. A paper basis weight measurement unit 115 that measures the paper basis weight from the temperature change information after discharge, and the curl correction unit 113
Although it is configured to correct the curl of the paper according to the curl shape and the basis weight of the paper, the image forming apparatus of the present invention does not use the post-discharge temperature change information. The curl correction unit 113 may be configured to correct the curl of the paper according to the curl shape without including the paper basis weight measurement unit 115.

Next, a third embodiment of the present invention will be described.

FIG. 14 is a diagram showing the configuration of each unit for performing curl correction according to the third embodiment of the present invention.
11 is a flowchart of curl correction according to the third embodiment of the present invention.

Hereinafter, the curl correction by the image forming apparatus according to the third embodiment will be described with reference to FIGS.

As shown in FIG. 14, a control unit 110 'for controlling each unit of the image forming apparatus according to the third embodiment includes:
In addition to the components of the control unit 110 in the image forming apparatus according to the second embodiment illustrated in FIG. 5, the image forming apparatus includes a sheet gloss detection unit 118 that detects the gloss of a sheet used for image formation. The paper basis weight measurement unit 115 ′ is configured to control the paper size detected by the paper size detection unit 114, the paper glossiness detected by the paper glossiness detection unit 118, and the temperature change after discharge detected by the temperature change information detection unit 111. It is configured to measure the paper basis weight from the information.

As shown in FIG. 15, in the image forming apparatus of the third embodiment, the paper basis weight measuring unit 115 '(FIG. 14)
) Is the post-discharge temperature change information detected in step S16, the paper glossiness detected by the paper glossiness detection unit 118 (see FIG. 14), and the paper size detection unit 1.
The paper basis weight is measured from the paper size detected by 14 (step S17).

As described above, the image forming apparatus of the third embodiment is provided with the paper gloss detecting section 118, and the detected paper gloss is used for measuring the paper basis weight by the paper basis weight measuring section 115 '. In this case, the curl correction can be performed with higher accuracy than in the image forming apparatus according to the second embodiment.

[0091]

As described above, according to the image forming apparatus of the present invention, the curl shape measuring section for measuring the curl shape of the reference paper made of white paper or the reference image formed thereon, and the curl shape measurement section A curl shape storage unit that stores the curl shape of the reference paper measured by the unit, and calculates a curl correction amount of the paper based on the image area ratio of an image formed on the paper and the curl shape of the reference paper. By providing a curl correction amount calculation unit and a curl correction unit that corrects the paper curl based on the curl correction amount calculated by the curl correction amount calculation unit, the state of the paper curl is detected and corrected with high accuracy. And a highly reliable image forming apparatus capable of performing such operations.

Further, a temperature change information detecting section for detecting temperature change information during conveyance indicating a temperature change of the sheet being conveyed while the sheet on which the fixed toner image is formed is discharged from the fixing device; If a curl shape measuring unit that measures the curl shape of the paper based on the change information, and a curl correction unit that corrects the curl of the paper according to the curl shape of the paper obtained by the curl shape measuring unit, the reliability is further improved. It is possible to realize an image forming apparatus having high reliability.

[Brief description of the drawings]

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

FIG. 2 is a diagram illustrating a configuration of each unit that performs curl correction according to the first embodiment of the present invention.

FIG. 3 is a flowchart of curl correction according to the first embodiment of the present invention.

FIG. 4 is a schematic configuration diagram of a curl correction device used in the first embodiment.

FIG. 5 is a diagram illustrating a configuration of each unit that performs curl correction according to a second embodiment of the present invention.

FIG. 6 is a flowchart of curl correction according to the second embodiment of the present invention.

FIG. 7 is a graph showing a time-dependent temperature change detected by a temperature change information detection unit according to a second embodiment of the present invention. .

FIG. 8 is a schematic diagram illustrating a temperature change when a sheet has curl.

FIG. 9 is a distance characteristic curve of a thermopile type temperature sensor.

FIG. 10 is a diagram illustrating a temperature change curve when detecting curl of a sheet using two sensors. .

11 is a partially enlarged view of the temperature change curve shown in FIG. 10 and a temperature change curve obtained by a sensor A ′ disposed on the back surface side symmetrical to the sensor A across the sheet.

FIG. 12 is a schematic diagram illustrating a method for measuring the paper basis weight according to the second embodiment.

FIG. 13 is a graph showing a difference in sensor temperature change depending on a paper type.

FIG. 14 is a diagram illustrating a configuration of each unit that performs curl correction according to a third embodiment of the present invention.

FIG. 15 is a flowchart of curl correction according to the third embodiment of the present invention.

FIG. 16 is a flowchart of a conventional curl correction method using a curl prediction table.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 photoconductor 2 charging device 3 exposure light 4 exposure device 5 developing device 6 cleaning device 7 intermediate transfer belt 8 fixing device 8a heat source 8_1, 8_2 fixing roll 9 paper feed tray 16 discharge tray 20 image forming device 30 curl correction device 31, 32 First correction unit 33 Guide device 34, 35 Roll 36, 37 Endless belt 100, 110, 110 'Control unit 101 Curl shape measurement unit 102, 112 Curl shape storage unit 103 Curl correction amount calculation unit 104, 113 Curl correction unit 111 Temperature change information detecting section 114 Paper size detecting section 115, 115 'Paper basis weight measuring section 118 Paper gloss detecting section N1, N2 Nip amount P Paper R1, R2 Paper transport path T1 Primary transfer section T2 Secondary transfer section

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (reference) G03G 21/00 370 G03G 21/00 370 F term (reference) 2H027 DA11 DC02 DC10 DE01 DE07 DE09 ED29 EE08 2H033 AA15 BA25 BA59 BB17 BB28 CA09 CA16 CA17 CA39 2H072 AA07 AA16 AA17 AA23 AA26 AA30 CA01 CA05 HB05 JA02 JA03 3F048 AA02 AA05 AB01 BA07 BA11 BB02 BD07 DA06 DA09 DB01 DC00 EB24 3F053 HA03 HB01 HB09 HB22 LA

Claims (5)

[Claims] 1. A toner image is formed on an image carrier, the toner image is transferred onto a predetermined sheet, and the toner image on the sheet is fixed by a predetermined fixing device to fix the toner image on the sheet. In the image forming apparatus for forming the curl shape, a curl shape measuring unit for measuring the curl shape of the reference paper formed of a blank sheet or a reference image formed thereon, and the curl shape of the reference paper measured by the curl shape measuring unit are stored. A curl shape storage section to be stored; a curl correction amount calculating section for calculating a curl correction amount of the sheet based on an image area ratio of an image formed on the sheet and a curl shape of the reference sheet; An image forming apparatus comprising: a curl correction unit configured to correct the curl of the sheet based on the curl correction amount calculated by the amount calculation unit. 2. A temperature change information detecting section for detecting temperature change information during conveyance indicating a temperature change of a sheet being conveyed while the sheet on which the fixed toner image is formed is discharged from the fixing device. 2. The image forming apparatus according to claim 1, wherein the curl shape measuring unit measures the curl shape of the sheet based on the temperature change information during conveyance detected by the temperature change information detecting unit. apparatus. 3. The image forming apparatus according to claim 2, wherein the temperature change information detecting section detects the temperature change information during conveyance using a non-contact temperature sensor. 4. The temperature change information detecting section also detects post-discharge temperature change information indicating a temperature change of the sheet after the sheet is discharged to the discharge tray. A paper size detection unit for detecting the size of the paper used for forming, a paper size detected by the paper size detection unit, and a paper basis weight from the post-ejection temperature change information detected by the temperature change information detection unit. 3. The paper basis weight measurement unit to be measured, wherein the curl correction unit corrects the curl of the paper according to the curl shape and the paper basis weight. Image forming device. 5. An image forming apparatus according to claim 1, further comprising a sheet gloss detecting section for detecting a gloss level of a sheet used for image formation, wherein said sheet basis weight measuring section detects a sheet detected by said sheet size detecting section. The paper basis weight is measured from a size, a paper glossiness detected by the paper glossiness detection unit, and the post-discharge temperature change information detected by the temperature change information detection unit. 5. The image forming apparatus according to 4.