JP2000227694A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect for each color an amount of a transfer material transferred to a recording medium and to estimate an amount of the occurrence of a curl in the paper from a value obtained by weighting an amount of transfer in each color. SOLUTION: The image processor comprises a transfer means 4 for transferring transfer materials of several colors to a recording medium P based on inputted image information, a curl correction means 6 for correcting a curl in the recording medium P subjected to transfer by the transfer means 4, a detection means 7 for detecting for each color an amount of the transfer material transferred by the transfer means 4, and a control means 8 for controlling curl correction by the curl correction means 6 based on the amount of the transfer material of each color detected by the detection means 7.

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 a printer, a copying machine, a facsimile, and the like, and more particularly to an improvement in an image forming apparatus for performing curl correction.

[0002]

2. Description of the Related Art In an image forming apparatus such as a laser printer or a color image copier using an electrophotographic system, generally, image data input from a personal computer or an image input device (IIT) is exposed to light by a laser or the like. An electrostatic latent image is formed on an image carrier such as a body drum, the toner is developed by a developing device, transferred to a sheet, and then the toner is melted on the sheet by a fixing device of a heating roller type to form an image. Is fixed and discharged. An apparatus for automating the operation by connecting an apparatus for performing post-processing such as stapling, punching, and sorting (collating) to such an image forming apparatus is also provided. When these post-processing devices are used, it has been known that the curl state of the paper is deeply related to the occurrence of a jam due to insufficient conveyance of the paper, the quality of the paper alignment in a sorter device, and the quality of the post-processing performance. Have been.

At this time, the curl of the paper depends on the type of the paper,
Because it changes with temperature and humidity, for example,
As disclosed in Japanese Patent Publication No.-251067, there is already a technique for adjusting the curl correction amount by detecting the humidity, the water content of the paper, the type of paper, and the paper thickness. Further, when the transferred toner is fixed, the toner is heated when it is fixed, and contracts when the toner is discharged to the post-processing device with a decrease in temperature. This contraction greatly affects the curl of the sheet. Kaihei 8-21731
Japanese Patent Application Laid-Open No. 3 (Kokai) No. 3 and Japanese Unexamined Patent Application Publication No. 9-30712 disclose a technique for adjusting the curl correction amount according to the detection results of the image density and toner amount. Here, JP-A-9-30712
Japanese Patent Application Laid-Open Publication No. H11-163873 discloses a technique for calculating the amount of toner from a potential sensor, a sensor for detecting the amount of light on a drum, and an image signal after gradation correction from a relational expression with the amount of toner obtained from an experiment.

[0004]

However, in an actual color image, the amount of toner to be developed is not always the same even if the laser writing amount is the same for the photosensitive member. For example, there is a large difference in the amount of toner to be developed between a single color black and a single color yellow even if the laser writing amount is the same. Therefore, the difference in the amount of toner causes a difference in the amount of toner transferred to the sheet, and as a result, a difference in the amount of curl. Therefore, if the control information of the curl correction is used by using the colors of the toner equally as in the technique described in the above-mentioned publication, the amount of curl generated cannot be accurately predicted.

In the prior art, paper type information such as paper thickness, size, material, rigidity, and gap direction, and the surrounding temperature and humidity environment are causes of curl. Although there is a disclosure of a technique for performing the curl correction, the amount of curl greatly differs depending on the front and back sides of the paper even in the same paper type and the same temperature and humidity environment. In such a case, if the curl correction is performed only with the paper type information or the temperature and humidity environment information, a large curl may be generated, which may cause a large trouble in post-processing such as stapling.

Further, since the stiffness, tensile strength, tensile elongation, moisture elongation and the like of the paper differ between the vertical and horizontal eyes, Japanese Patent Application Laid-Open No. 8-217313 discloses a curl in consideration of the paper gap. There is a proposal for a technique for performing correction. However,
Here, the proposal is merely to perform curl correction in consideration of the gap expected from the paper size, and although a certain degree of gap can be expected, for example, when special paper is not used such as printing paper, the gap is not adjusted. Eyes are not constant. Since the expected gap information in such a case is inaccurate, there is a risk of causing a secondary obstacle due to performing the curl correction.

Further, even in the same image forming apparatus, for example, the paper transport speed may differ between a monochrome image and a color image, or between a printer and a copying machine. In spite of the difference in the amount of curl generated due to the difference in the paper conveyance speed, conventionally, the difference in the paper conveyance speed has not been considered at all. Therefore, appropriate curl correction cannot be realized, and a conveyance failure to the post-processing device has occurred.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned technical problem. The present invention appropriately grasps the curl amount that will occur on a recording material and uses the curl correction amount by a curl correcting unit. Thus, for example, it is possible to provide an image forming apparatus capable of reliably preventing the occurrence of a jam in the post-processing device and the deterioration of the post-processing function by controlling the post-processing device.

[0009]

That is, as shown in FIG. 1, the image forming apparatus of the present invention forms an image on a recording material P by using transfer materials of a plurality of colors based on input image information. Image forming means for forming, curl correcting means 6 for performing curl correction on the recording material P on which an image is formed by the image forming means, and recording material P in the image forming means
Detecting means for detecting the amount of transfer material for forming an image for each color, and controlling the curl correction by the curl correcting means 6 based on the amount of transfer material for each color detected by the detection means. And a control unit 8.

The control means 8 calculates the amount of the transfer material of all colors in consideration of a predetermined weight for each color with respect to the amount of the transfer material of each color detected by the detection means 7. Then, based on the calculated amount, the curl correcting means 6
It is preferable to control the curl correction by the following.

Further, the image forming apparatus according to the present invention comprises: an image carrier 1 on which an electrostatic latent image is formed; and an image carrier 1 that is exposed to each color based on color image information input to the image carrier 1 and statically exposed. Exposure means 2 for forming an electrostatic latent image, developing means 3 for developing a toner image for each color on the electrostatic latent image formed by exposure by the exposure means 2, and toner developed by the development means Transfer means 4 for transferring the image to the recording material, fixing means 5 for fixing the toner image transferred to the recording material P by the transfer means 4, and recording on which the toner image is fixed by the fixing means 5 A curling correction unit 6 for performing curl correction on the material P; a lighting amount detecting unit 7 for detecting a lighting amount of the exposure unit 2 for each color; and a lighting amount detecting unit 7 for each color detected by the lighting amount detecting unit 7. Based on the amount of lighting, the curl correction means 6 It is characterized by comprising a control means 8 for controlling the curling.

Further, the control means 8 adds a predetermined weight for each color to the lighting amount for each color detected by the lighting amount detecting means 7 to predict the curl amount and perform the curl correction. It is preferable to control.

Further, the image forming apparatus of the present invention comprises an image forming means for forming an image on a recording material P by using a transfer material based on the input image information, and the recording material P by the image forming means. Front and back determining means 9 for determining the front and back of the surface of the recording material P before the image is formed on the recording material P
And a curl correction means 6 for correcting the curl of the recording material P based on the result of the determination by the front / back determination means 9.

Further, the image forming apparatus of the present invention has an image forming means for forming an image on a recording material P by using a transfer material based on the input image information, and an image forming means for forming an image on the recording material P by the image forming means. On the other hand, when the recording material P is being conveyed at a stage before an image is formed, a fiber direction determining unit 10 that determines a fiber direction with respect to a conveying direction of the recording material P, and recording is performed based on the determination result by the fiber direction determining unit 10. And a curl correcting means 6 for correcting the curl of the material P.

Further, according to the image forming apparatus of the present invention, based on the input image information, an image forming means for forming an image on the recording material P using a transfer material, and an image is formed by the image forming means. Transport speed recognition means 101 for recognizing the transport speed of the recording material P to be transported, and the transport speed recognition means 101
And a curl correction means 6 for correcting the curl of the recording material P based on the conveyance speed recognized by the control unit.

Here, in the present invention, the transfer material for forming an image on the recording material includes not only an electrophotographic toner material but also an ink jet ink material. However, when the recording material is pressed by a heating roll, as in a fixing device in an electrophotographic system, the effect of applying the present invention is large because curling of the recording material is further increased.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail based on an embodiment shown in the accompanying drawings. First Embodiment FIG. 2 shows a schematic configuration of a double-sided image forming apparatus (a color electrophotographic copying machine in the present embodiment) to which the present invention is applied. In the figure, reference numeral 66 denotes a document reading device (IIT), which converges the reflected light of the document illuminated by the lamp onto the CCD using an exposure optical system. This CCD is
The IIT 66 converts the reflected light of the original image into an electric signal as each color component image of yellow (Y), magenta (M), cyan (C) and black (K), and the IIT 66 adjusts the gain of the analog electric signal to convert the digital signal. To perform shading correction and the like. Reference numeral 67 denotes an image processing device (IPS) which performs data processing such as density correction, color conversion processing, enlargement / reduction, etc. on the image digital signal obtained from the IIT 66, and outputs color components of Y, M, C, and K. The image data is output to the image writing device (ROS) 13 every time. Where I
The data processing by the PS 67 is not limited to the input data from the IIT 66, and the same data processing is performed on image data from an externally connected device such as a personal computer.

Here, reference numeral 11 denotes a photosensitive drum (image carrier) which rotates in the direction of an arrow, for example, and reference numeral 12 denotes a charger such as a corotron which charges the photosensitive drum 11 in advance. Also, 13
Denotes an image writing device (ROS) such as a laser scanning device that writes a digital image input from the IPS 67 on the photosensitive drum 11 as an electrostatic latent image, and is modulated by a laser drive signal generated for each color component. The surface of the photosensitive drum 11 is irradiated with the laser beam. Reference numeral 14 denotes a developing device 14 corresponding to each color of Y, M, C, and K.
1 to 144 are rotary type developing devices,
The electrostatic latent image formed on the photosensitive drum 11 is
To 144 to form each color component toner image. Reference numeral 15 denotes the photosensitive drum 1
Reference numeral 16 denotes a transfer pre-processing device such as a corotron for aligning the polarity of each toner image on the photosensitive drum 1, and a drum cleaner 16 for removing residual toner on the photosensitive drum 11.

Reference numeral 20 denotes an intermediate transfer belt arranged so as to be in contact with the surface of the photosensitive drum 11;
Plural (for example, five in this embodiment) rolls 21 to 2
5 so as to rotate in the direction of the arrow.
In this embodiment, reference numeral 21 denotes a drive roll of the intermediate transfer belt 20, reference numerals 22 and 24 denote driven rolls, reference numeral 23 denotes a tension roll for controlling the tension of the intermediate transfer belt 20 to a constant value, and reference numeral 25 denotes a secondary roll. This is a transfer roll (backup roll) for transfer.

Further, at a portion (primary transfer position) of the intermediate transfer belt 20 facing the photosensitive drum 11, a primary transfer device (transfer roll in the present embodiment) 18 is disposed on the back side of the intermediate transfer belt 20. The toner image on the photosensitive drum 11 is electrostatically attracted to the intermediate transfer belt 20 by applying a voltage having a polarity opposite to the charge polarity of the toner to the transfer roll 18.

Further, a secondary transfer device 40 is provided at a secondary transfer position of the intermediate transfer belt 20 facing the conveyance path of the sheet P as a sheet. And a counter roll (backup roll) 25 serving as a counter electrode of the secondary transfer roll 26 disposed on the back side of the intermediate transfer belt 20. I have. In the present embodiment, the secondary transfer roll 26 is grounded, and a bias having the same polarity as the charged polarity of the toner is stably applied to the backup roll 25 via the power supply roll 27. Reference numeral 41 denotes a belt cleaner that removes residual toner on the intermediate transfer belt 20.

In this embodiment, the paper transport system 50 transports paper from a predetermined number (three in this embodiment) of paper trays 51 to 53 or a manual tray 55 via a predetermined paper path 56. I do. Here, reference numeral 130 denotes a conveyance sheet determination device including the moisture content detection device 96, the front and back determination device 110, the fiber direction determination device 120, and the like. Judgment is being implemented. The content determined by the transport paper determination device 130 is sent to the control unit 68. The sheet conveying system 50 further conveys the sheet to the secondary transfer position at a predetermined timing after the sheet is once stopped by the registration roll (registration roll) 57 in the sheet path 56, and after the secondary transfer, The sheet is guided to the transport belt 58, and the fixing device 4
2. The paper path 56 is provided with an appropriate number of transport rolls 59. In particular, in the present embodiment, when the duplex mode is selected, the sheet returning / conveying mechanism 60 for reversing the sheet fixed on one side by the fixing device 42 and returning the sheet to the secondary transfer position again is provided.

As shown in FIG. 2, the paper returning / conveying mechanism 60 is provided with a paper branch path 62 that branches downward from a paper discharge path 61 from the fixing device 42. Paper reversing path 63 toward the lower side
And a paper return path 64 returning from the paper reversing path 63 to the paper path 56 just before the secondary transfer position. An appropriate number of transport rolls 65 are provided in the paper branch path 62, the paper inversion path 63, and the paper return path 64. In particular, the transport rolls 65 provided in the paper inversion path 63 rotate forward and backward at appropriate timing. It has become. Further, a sheet switching gate (not shown) is provided between the sheet discharge path 61 and the sheet branch path 62 and between the sheet branch path 62, the sheet reversing path 63, and the sheet return path 64, respectively. The paper path is appropriately switched and selected according to the selected mode.

Here, in the case of single-sided printing, when the sheet P ejected from the fixing device 42 is ejected to the outside of the apparatus as it is, an image is printed on the upper surface of the sheet and ejected, that is, a so-called face-up ejection. On the other hand, on the other hand, the sheet P that is a one-sided printing and is discharged from the fixing device is transferred to the sheet discharging path 6.
When the sheet is inverted from 1 through the sheet reversing path 63 and discharged from the paper branch path 62 to the outside of the apparatus, a state in which an image is printed on the lower surface of the sheet and discharged, that is, a face-down discharge is performed.

Further, in the present embodiment, the fixing device 42 includes a heating fixing roll 70 having a built-in heater 71.
And a pressure fixing roll 72 which is disposed in pressure contact with the heat fixing roll 70 in a predetermined nip region and rolls therein and has a heater 73 incorporated therein.
An exit sensor 75 for detecting that the paper P has passed is disposed on the exit side of the nip area.

Further, reference numeral 80 denotes a curl removing device for removing the curl from the paper P discharged from the fixing device 42, and reference numeral 69 denotes a post-processing for the paper discharged from the curl removing device 80. The post-processing apparatus includes a sorter 79 for distributing a required number of sheets and a staple 78 for bundling the required number of sheets.

Here, reference numeral 68 denotes a control unit, which controls the paper conveyance and, in particular, recognizes that the curl removing device 80 and the post-processing device 69 are connected to the image forming apparatus main body,
Based on the image output signal from the PS 67, the adjustment of the curl correction amount of the curl removing device 80, the movement of the post-processing device 69, and the like are controlled. Further, the control device controls the paper tray 51
To 53 and the paper size of the paper P supplied from the manual feed tray 55, the humidity condition of the image forming apparatus and the humidity in the paper trays 51 to 53 are recognized, and the curl amount in the curl removing device 80 is determined. It is possible to make adjustments. Further, the control device receives the detection signal from the conveyance paper determination device 130 and
It also plays the role of controlling 0. Further, the control device
In addition to the exit sensor 75, based on a plurality of paper sensors (not shown) provided on a paper transport path in the image forming apparatus, and based on the timing at which the IPS 67 outputs data, paper transport is performed. The speed is accurately grasped, and the curl removing device 80 is adjusted based on the recognized transport speed.

Next, the configuration of the curl removing device 80 in the present embodiment will be described with reference to FIG. Code 9
Reference numeral 2 denotes a chute that forms the sheet transport path on which the sheet P fixed by the fixing device enters. 81a is a shot 9
Reference numeral 81b denotes an upper decurler device which has an operation mechanism at the lower part of the chute 2 and performs curl removal, and an upper decurler device 81b which has an operation mechanism at the upper part of the chute 92 and executes curl removal. The lower decurler device 81a and the upper decurler device 81b have the same mechanism, respectively.
a and 82b are drive rolls for transporting the paper;
Reference numeral 3b denotes a pressing roll that cuts into the drive rolls 82a and 82b and performs curl correction. When the sheet P enters, the pressing roll cuts into the drive roll, and the sheet is deformed by the arc of the drive roll at the portion sandwiched between the two, and the curl is corrected. Here, since the lower decurler device 81a performs the curl correction by making the pressing roll 83a bite into the drive roll 82a, the lower decurler device 81a is responsible for the correction in the downward convex direction. On the other hand, the upper decurler device 81b performs curl correction by making the pressing roll 83b bite into the drive roll 82b, and is responsible for correction in the upwardly convex direction.

Also, 85a and 85b are pressing rolls 83a,
A shaft 83b is located at the center of the shaft 83b, and is movable in a direction perpendicular to the sheet entering direction (a direction blocking the conveyance path) via slide bearings 84a and 84b. The slide bearings 84a, 84b are connected to shafts 85a, 85b.
Are provided at both ends (front and back sides) in a direction orthogonal to the paper transport direction, so that they slide without frictional resistance against sladders (not shown) at both ends of the main body of the curl removing device 80. It is configured. 86a and 86b are:
These cams are rotated by the camshafts 87a and 87b to press the slide bearings 84a and 84b, and are provided independently at both ends (front and back sides) in a direction orthogonal to the sheet conveyance direction. Also, 88a, 88
b denotes a pulley driven from a pulley 90 of the motor 89 via a belt 91.

The motor 89 rotates under the control of the control unit 68 provided in the main body of the image forming apparatus. The state shown in FIG. 3 is a state in which the cam 86a presses the slide bearing 84a by the rotation of the motor 89, and the pressing roll 83a bites into the drive roll 82a, that is, the lower decurler device 81a performs the curl correction. This is in the ON state, and in the present embodiment, the pressing roll 83a is designed to bite into the drive roll 82a by about 2 mm. This means that the maximum of the toner amount ratios of the four colors of YMCK is a theoretical total of 400%,
This is because, for an image having a substantially maximum toner amount ratio of about 150%, a bite amount of about 2 mm is required as curl correction. On the other hand, the upper decurler device 81b is in an OFF state in which the pressing roll 83b does not bite into the drive roll 82b, and in this case, in this embodiment, the pressing roll 83b bites by about 0.5 mm, and the minimum transport capacity Is secured.

Next, the motor 89 is controlled by the control unit 68.
Rotates, and the cams 86a provided at both ends on the near side and the far side
Then, when the cams 86b provided at both ends on the near side and the far side are respectively rotated half a turn, the upper decurler device 81b is turned on to execute the curl correction. On the other hand, in the lower decurler device 81a, the pressing roll 83a, which has been in the pressed state, is released by the rotation of the cam 86a and moves away from the drive roll 82a, and as a result, the lower decurler device 81a is in the OFF state. Becomes

Here, in the present embodiment, the lower decurler device 81a is turned off / on, and the upper decurler device 81a is turned off.
Although the example in which the rotation of the motor 89 is controlled based on the so-called two values of ON / OFF of b has been described, it is also possible to finely control the rotation of the motor 89 to change the curl correction amount.

Here, in this embodiment, SUS of Φ8 is used for the drive rolls 82a and 82b. Here, it is preferable to use a drive roll having a diameter as small as possible in order to enhance the decurling function, but in the present embodiment, φ8 is used in consideration of the deflection of the shaft. Further, the pressing rolls 83a, 83
For b, a urethane material of Φ26 (20 lb / ft ³ ) is used, and is configured to have a certain elasticity so as to be able to bite into the drive rolls 82a and 82b.

FIG. 4 schematically shows the drive system of the drive rolls 82a and 82b. 93 is a drive motor, 94 is a motor gear provided in the drive motor 93, and 95b and 95a are drive gears that obtain driving force from the motor gear 94 and drive the drive rolls 82b, 82a. Upon receiving the transmission of the driving force from the motor gear 94, the drive gear 95b rotates clockwise, and the drive roll 82b also rotates. The drive gear 95a rotates counterclockwise by receiving the transmission of the driving force from the drive gear 95b, and the drive roll 82a also rotates. The drive roll 8 which is the side to be bitten in this way
The reason why the driving rollers 2a and 82b are driven is that when the pressing rolls 83a and 83b having a biting function are used as driving rollers, the conveyance speed varies depending on the biting amount.

In the present embodiment, the pressing roll 83
a, 83b slide and drive rolls 82a, 82b
Does not slide. This is the drive roll 82
This is in consideration of the fact that the sheet conveyance path changes when a and 82b are slid, and the sheet conveyance may not be performed properly.

Next, the configuration of the water content detection device 96, which is one of the transport paper determination devices 130 in this embodiment, will be described with reference to FIG. Here, reference numeral 100 denotes a surface plate, and two surface plates are arranged at intervals so that sheets pass therethrough, and grooves 97 are formed in the two surface plates. Reference numeral 98 denotes a transmitting oscillator, and 99 denotes a receiving oscillator. The paper P fed from the paper trays 51 to 53 is conveyed by being sandwiched between two grooved surface plates 100 as shown in FIG. At that time, in the groove 97 carved in the surface plate 100,
A microwave with a low power and a high frequency flows from the transmitting oscillator 98 to the receiving oscillator 99. When the moisture content of the paper P is high, the attenuation of the microwave wave becomes large. Therefore, the moisture content can be calculated by measuring the attenuation. The detection result of the water content detection device 96 is sent to the control unit 68, and the control unit 68 receives the result and controls the movement of the curl removing device 80.

Next, the control of the curl correction amount performed by the control unit 68 in the present embodiment will be described with reference to FIGS.

First, a method 1 for measuring the amount of curl of a sheet is described.
One is to calculate the amount of an image to be printed on paper. Conventionally, as this method, a method has been adopted in which image information (for example, pixel: pixel) to be printed is counted as an amount of an image to be printed on a sheet, and the counted amount of the image is converted into a curl amount of the sheet.

FIG. 6 is a graph showing the relationship between the toner color (single color) and the amount of curl in a state where the image density ratio is kept constant. On the other hand, the image density ratio of 100% is set to the toner colors Y, M,
The four colors C and K are output on one side, and the added values obtained by measuring n sheets at four corners of the paper are shown. This figure 6
As shown in (1), even if the image density is the same, the amount of curling of the paper differs for each color of toner in a color image. For example, when black (K) is printed, curling occurs about twice as much as yellow (Y) having the same image density ratio. This is because even if the image density ratio is the same, that is, even if the amount of laser writing is the same, the amount of toner to be developed for each color is different, resulting in a difference in the amount of toner on the paper. This is because there is a difference.

Therefore, the present embodiment employs a method of determining the curl correction amount by obtaining the toner amount ratio Z (%) instead of the conventional image density ratio as the image amount. That is,
Xy, Xm, Xc, and Xk are the total pixel counts measured for each of the colors Y, M, C, and K, and the converted toner amount values (constants) obtained from FIG. 6 are Ty, Tm, Tc, and Tk. Then
XT = (Xy × Ty) + (Xm × Tm) + (Xc × Tc) + (Xk × T
k). On the other hand, the maximum paper image density in a state using A3 paper (297 mm × 420 mm) is set to XT _A3max ,
Assuming that the maximum pixel count in each color when three papers are used is X (Y), X (M), X (c), X (K), XT _A3max = [X (Y) × Ty] + ｛X (M) × Tm｝ + ｛X (c) × T
c｝ + {X (K) × Tk}, and the toner amount ratio Z (%) is as follows: Z (%) = XT / XT _A3max × (297 × 420 [mm ² ] / (paper size) [mm ² ]) Is obtained as

Next, curl correction is controlled based on the toner amount ratio Z (%) obtained here. FIG. 7 is a table showing the toner amount ratio on the A / B side (front and back) and the ON / OFF condition of the decurler. In each of (a), (b) and (c), the condition is determined by the “moisture content” of the paper or the “humidity” in the environment where the image forming apparatus is placed. In this embodiment, the “water content” is configured to be detected by the water content detection device 96. However, it is generally difficult to accurately measure the “water content”. Since the moisture content of the paper has a positive correlation, the measured humidity condition (preferably the humidity in the paper tray) can be substituted. In the present embodiment, the humidity M is 40%
Less than or less than 4% water content under the first condition, humidity M of 40
7 (a) and 7 (b), the second condition is that the water content is 4% or more and less than 6%, and the third condition is that the humidity M is 70% or more or the water content is 6% or more. , (C).

The surfaces A and B refer to the front and back surfaces of the discharged paper P. In the image forming apparatus of this embodiment, the paper P on which the image has been transferred by the intermediate transfer belt 20 is turned over. The image surface (upper surface) in the state discharged as it is without being processed is surface A (front surface), and the opposite surface is surface B (back surface)
And Therefore, when the one-sided printing is inverted and output, the image information exists on the B side (back side),
If the image is output without being inverted at the end in the double-sided printing, the first transfer image appears on the B side (back side), and the second transfer image appears on the A side (front side). In FIGS. 7A, 7B, and 7C, the numerical values in the table columns of the surfaces A and B indicate the toner amount ratio Z (%). Further, the numerical values “0”, “1”, and “−1” in the tables of FIGS. 7A, 7B, and 7C correspond to the lower decurler device 81a and the upper decurler device 81b in the curl removing device 80. The contents of ON / OFF are shown, and the lower decurler device 81a and the upper decurler device 81
"b" is OFF when both are "0", lower decurler device 8
"1" is when 1a is ON and the upper decurler device 81b is OFF, and "-1" when the lower decurler device 81a is OFF and the upper decurler device 81b is ON.

Here, for example, let us consider a case where the toner amount ratio on the surface A is 8% and the surface B is 35% in a state where the humidity M is less than 40%. In this case, since the toner amount on the side B is larger than that on the side A, the curl is applied downward (down curl). Next, the decurler condition in this case is examined from the table. As shown in FIG.
Looking at the fourth row of the surface () 40%), it can be seen that the decurler ON / OFF condition is “1”. This correction is performed in the ON state of the lower decurler device 81a, that is, in the direction in which the sheet is bent upward (both ends are jumped up and convex downward). In the case of single-sided printing, the column for the toner amount ratio in the first row or the first column of each table shown in FIG. What is necessary is just to determine ON / OFF of an apparatus.

As described above, the decurler conditions can be determined according to (a), (b), and (c) of FIG. 7. In these tables, "-1", that is, the state in which the upper decurler device 81b is ON is shown. Is set a lot. This is because the down curl whose end is bent downward is in the direction in which the curl is corrected by its own weight, but the up curl whose end bounces upward cannot be corrected by itself. Upper decurler device 81b for performing downward correction (correction for up-curl) for reasons such as weakness
Specific gravity.

ON / OFF of each of these decurler devices
Based on the conditions, the controller 68 controls the curl removing device 80 to remove the curl. Specifically, the control unit 68
Calculates the toner amount ratio for each side of the paper based on the image information from the IPS 67, the recognized paper size information, and the like, as described above. The ON / OFF condition of each decurler device is determined from the toner amount ratio based on the above-described condition. Next, in the image device shown in FIG. 2, the lower decurler device 81a and the upper decurler device 81 in the curl removing device 80 are checked while the paper conveyance state is checked by the exit sensor 75 and various paper sensors in the device (not shown). The timing at which the curl correction area of the sheet passes through 81b is checked. By controlling the rotation of the motor 89 in the curl removing device 80 and rotating the cams 86a and 86b in accordance with this timing, the lower decurler device 81a and the upper decurler device 81b are rotated.
Is turned on / off to execute the curl correction.

As described above, according to the present embodiment, the printing amount is detected for each color, the weighting is applied to each color, and the toner amount ratio Z (%) is converted to determine the curl generation state. By doing so, it is possible to reliably perform curl correction when a color image is printed.

Embodiment 2 FIG. 8 is a schematic explanatory view of Embodiment 2 in an image forming apparatus to which the present invention is applied. In the present embodiment, the calculation of the toner amount ratio Z (%) is performed for each of the divided portions in the direction orthogonal to the transport direction of the sheet P. Note that components similar to those of the first embodiment are denoted by the same reference numerals as those of the first embodiment, and detailed description thereof is omitted here.

In FIG. 8, the laser writing amount (for each color) in the ROS 13 is extracted from the image signal of the IPS 67 for each area by dividing the area into three parts in the direction orthogonal to the transport direction. Here, as described in the first embodiment, the extracted laser writing amount (pixel count number) for each color is added with the weight of each color obtained from FIG. Calculate Z (%). This toner amount ratio Z
By performing the calculation operation of (%) on the A surface and the B surface for each area, the curl occurrence state can be predicted in the direction orthogonal to the transport direction.

FIG. 9 is a diagram for explaining a method of performing curl correction on a predicted curl occurrence state. This state indicates a state in which an up-curl occurs on the near side in the sheet transport direction. In order to remove the curl in this state, it is preferable to turn on the lower decurler device 81a on the near side and turn off the lower decurler device 81a on the far side. In the present embodiment, the cams 86a,
As shown in FIG. 9, the rotation of the curl removing device 80 is controlled so that the operation of the curl removing device 80 is different between the front side and the rear side, instead of making the rotation of 86b the same at both ends of the front side and the rear side. . That is, in the present embodiment, the cam 8 is positioned between the front and the back.
6a is driven independently, the rear cam 86a is controlled so that the rear pressing roll 83a is OFF with respect to the drive roll 82a, and the front pressing roll 83a is ON.
The cam 86a on the front side is controlled so that In this way, by providing different bite amounts for the front and the back, curl correction in the direction perpendicular to the paper transport direction, which was impossible until now, can be performed, and curl correction more suited to actual curl occurrence can be performed Becomes

Further, in the present embodiment, the curl correction amounts on the front side and the back side are not two steps of ON / OFF, but free values according to the distribution of the image amount, that is, the curl correction amounts of the pressing rolls 83a and 83b. The bite amount is, for example, 0.5 mm
It is also possible to select freely between の 間 2 mm. With this control, it is possible to perform correction in accordance with the curl generation state.

Third Embodiment FIG. 10 is a schematic configuration diagram of a third embodiment illustrating a front / back determination device 110 in an image forming apparatus to which the present invention is applied. Generally, paper has a so-called wire side on the mesh side from which water is drained during refining and a so-called felt side on the opposite side on both sides. On the wire side, fine fibers are removed together with water, leaving only long fibers. On the other hand, on the felt side, fine fibers remain. As a result, the length of the fiber is different between the front and back sides of the paper. Here, the wire side with a long fiber has a small degree of shrinkage because the bonding area between the fibers is small. On the other hand, the short felt side of the fiber has a large degree of shrinkage. Therefore, if the degree of the contraction is different, a large difference occurs in the amount of curl depending on which of the front and the back of the sheet the toner is transferred. Therefore, in the present embodiment, the front and back determination device 110 in the transport paper determination device 130 determines the front and back of the transported paper, and determines whether the surface to which the paper P is transferred is the wire side or the felt side. We understand contents. The same components as those in the above-described embodiment are denoted by the same reference numerals, and a detailed description thereof will be omitted.

Here, reference numeral 113 denotes a chute that forms a paper transport path, 111 denotes a light emitting element made of infrared light or the like, and 112 denotes a light receiving element that receives light emitted from the light emitting element 111. A light emitting element 111 and a light receiving element 112 are provided on both sides of the sheet, respectively, and a difference in relative reflectance is determined. That is, the wire side having a longer fiber length is generally more uneven and rougher than the felt side. For this reason, the reflectance is generally lower than that of the felt side.
There is a difference in the light incident level on the sheet, and the front and back of the sheet can be determined.
According to this determination result, if the toner is transferred to the felt side, it is expected that the curl will be greatly generated by winding the felt side. Good.

As described above, according to the present embodiment, it is possible to determine the front and back sides of a sheet, which is a major cause of the occurrence of curl, and appropriate curl correction can be performed based on the result of the determination. .

Fourth Embodiment FIG. 11 is a schematic configuration diagram for explaining an image forming apparatus according to a fourth embodiment of the present invention. Generally, the orientation of the fibers in the paper is related to the tensile strength and the anisotropy of the expansion and contraction rate, and has a great influence on the curl generation. In the present embodiment, the content of the curl of the paper P is grasped by the determination result of the fiber direction determination device 120 in the transport paper determination device 130 provided during the transport. The same components as those in the above-described embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted.

In FIG. 11, reference numeral 121 denotes wavelengths 1 to 3.
Alternatively, a light emitting element made of infrared light of about 4 to 6.5 μm, and a light receiving element 122 for receiving infrared light emitted from the light emitting element. The light emitting element 121 and the light receiving element 122
A plurality of polarizing elements 12 having different polarization directions from each other.
3, 124 are provided. This fiber direction determination device 1
If the detection output of each light receiving element is measured in a state where the paper P is transported between the light emitting element 121 and the light receiving element 122 of 20
The fiber orientation of the paper P can be determined. In addition, this polarizing element 1
It is preferable that at least one of 23 and 124 has a polarization direction with respect to a direction perpendicular to the sheet conveyance direction and the other one has a polarization direction in that the degree of curling can be measured only by a difference in transmittance.

The fiber direction of the paper P is determined based on the result of the determination by the fiber direction determination device 120. The determined information and the ratio of the amount of toner transferred to the paper P, distribution, information on the surface to be transferred, and the like are taken into consideration. Thus, the amount of curl can be predicted.
That is, as generally expected, the degree of curl in the same direction as the fiber direction is low, and the degree of curl in the direction orthogonal to the fiber direction is high. Therefore, according to the present embodiment, the amount of curl can be determined in consideration of the degree of curl occurrence of the sheet itself, so that more precise curl correction can be performed.

Fifth Embodiment In this embodiment, attention is paid to the fact that the amount of curl is different depending on the paper transport speed, and the content of adjusting the curl correction amount in the curl removing device 80 in accordance with the paper transport speed is described. It is assumed that. The same components as those in the above-described embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted.

FIG. 12 is a graph showing the relationship between the paper speed and the amount of curl. Here, at three types of paper speeds, Lead / F, which is the front part of the leading edge in the paper transport direction,
ront, Lead / Rear which is the rear part of the front end, Tail / Front which is the front part of the rear end in the conveyance direction, and the curl amount at the four ends of the tail / Rear which is the rear part of the rear end are measured. The measured values are plotted. As can be seen from this graph, the curl amount is increased by about 30% when the paper speed is low as compared with when the paper speed is high. Therefore, in the present embodiment, the curl correction amount in the curl removing device 80 is adjusted according to the sheet conveyance speed based on the measurement result. That is, the lower decurler device 81a and the upper decurler device 81 of the curl removing device 80
At b, the movements of the cams 86a and 86b provided are finely controlled, and, for example, the bite amount of the pressing rolls 83a and 83b is increased by about 30% when the sheet conveying speed is low compared to when the sheet conveying speed is high. By controlling in this way, more accurate curl correction can be performed in response to a difference in curl amount based on a difference in sheet conveyance speed.

As described above, a plurality of embodiments of the present invention have been described. When the curl amount is detected, other factors causing the curl, such as the temperature condition, the heating temperature of the fixing device, and the paper thickness, are considered. It is naturally possible to predict the curl amount by further taking into account the paper type and the like. By taking these other curl generation factors into account, more accurate curl generation modes can be predicted, and based on them, more appropriate curl correction can be performed.

[0060]

As described above, according to the image forming apparatus of the present invention, the amount of curl that would actually occur can be more accurately predicted, and the curl correction can be performed without causing a problem in a post-processing device or the like. Can be applied.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram illustrating an outline of an image forming apparatus according to the present invention.

FIG. 2 is an explanatory diagram illustrating an outline of an image forming apparatus according to an embodiment.

FIG. 3 is an explanatory diagram illustrating a configuration of a curl removing device according to an embodiment.

FIG. 4 is an explanatory diagram for explaining a drive system of the curl removing device in the embodiment.

FIG. 5 is an explanatory diagram showing an outline of a moisture content detecting device in an embodiment.

FIG. 6 is an explanatory diagram illustrating a relationship between a toner color and a curl generation amount in the embodiment.

FIGS. 7A to 7C are tables showing a relationship between a toner amount ratio and a decurler in the embodiment.

FIG. 8 is an explanatory diagram of image amount detection according to the second embodiment.

FIG. 9 is an operation explanatory diagram according to the second embodiment.

FIG. 10 is an explanatory diagram illustrating an overview of a front / back determination device according to a third embodiment.

FIG. 11 is an explanatory diagram illustrating an outline of a fiber direction determination device according to a fourth embodiment.

FIG. 12 is a table showing a relationship between a sheet speed and a curl generation amount according to the fifth embodiment.

[Explanation of symbols]

P: recording material, 1: image carrier, 2: exposing means, 3: developing means, 4: transferring means, 5: fixing means, 6: curl correcting means, 7: detecting means, 8: control means, 9: front and back Judgment means,
DESCRIPTION OF SYMBOLS 10 ... Fiber direction determination means 101: Transport speed recognition means 11 ... Photoreceptor drum, 13 ... Image writing device (ROS), 1
4: rotary developing device, 20: intermediate transfer belt, 4
0: secondary transfer device 42: fixing device, 51, 52, 53: paper tray, 60:
Paper return / conveyance mechanism 67 Image processing device (IPS) 68
... Control unit, 69 ... Post-processing device, 80 ... Curl removing device,
96: moisture content detection device, 110: front / back determination device, 120
... Fiber direction determination device, 130 ... Conveyed paper determination device 82a, 82b ... Drive roll, 83a, 83b ... Press roll, 84a, 84b ... Slide bearing, 86a,
86b: cam, 89: motor

Claims (7)

[Claims] An image forming means for forming an image on a recording material using transfer materials of a plurality of colors based on input image information, and a recording material on which an image has been formed by the image forming means. Curl correction means for performing curl correction; detection means for detecting the amount of the transfer material for forming an image on a recording material in the image forming means for each color; transfer material for each color detected by the detection means An image forming apparatus comprising: a control unit that controls curl correction by the curl correction unit based on the amount of curl. 2. The control means calculates the amount of transfer material of all colors in consideration of a predetermined weighting of each color with respect to the amount of transfer material of each color detected by the detection means. 2. The image forming apparatus according to claim 1, wherein curl correction by the curl correction unit is controlled based on the calculated amount. 3. An image carrier on which an electrostatic latent image is formed, and an exposure unit for exposing each color based on color image information input to the image carrier to form an electrostatic latent image; Developing means for developing a toner image of each color with respect to the electrostatic latent image formed by exposure by the exposure means; transfer means for transferring the toner image developed by the developing means to a recording material; A fixing unit that fixes the toner image transferred to the recording material by the transfer unit; and a curl correction unit that performs curl correction on the recording material on which the toner image is fixed by the fixing unit. An image forming apparatus, comprising: a lighting amount detection unit that detects a lighting amount of the exposure unit for each color; and a curl compensation unit that performs curl correction based on the lighting amount of each color detected by the lighting amount detection unit. An image forming apparatus characterized by comprising a control means for controlling the. 4. The curl correction is performed by adding a predetermined weight for each color to the lighting amount of each color detected by the lighting amount detecting means and predicting the curl amount. The image forming apparatus according to claim 3, wherein: 5. An image forming means for forming an image on a recording material using a transfer material based on the input image information, and a step before the image is formed on the recording material by the image forming means. An image forming apparatus, comprising: a front / back determination unit that determines front and back of a surface of the recording material; and a curl correction unit that corrects curl of the recording material based on a determination result by the front / back determination unit. apparatus. 6. An image forming means for forming an image on a recording material using a transfer material based on the input image information, and a step before the image is formed on the recording material by the image forming means. During the conveyance of the recording material in
A fiber direction determining unit configured to determine a fiber direction with respect to a conveying direction of the recording material; and a curl correcting unit configured to correct curl of the recording material based on a determination result by the fiber direction determining unit. Image forming device. 7. An image forming means for forming an image on a recording material using a transfer material based on input image information, and a conveying speed of the recording material on which an image is formed by the image forming means is recognized. An image forming apparatus, comprising: a conveyance speed recognition unit that performs the operation; and a curl correction unit that corrects the curl of the recording material based on the conveyance speed recognized by the conveyance speed recognition unit.