JP2020184018A - Image forming apparatus, image forming method, and program - Google Patents

Abstract

To provide an image forming apparatus that, even when forming an image on a recording medium in a condition where a curl easily occurs, can prevent the occurrence of a curl without reducing productivity.SOLUTION: An image forming apparatus comprises: transfer means that transfers a toner image to a recording medium; fixing means that heats the transferred toner image to fix the toner image to the recording medium; curl amount measuring means that measures the amount of a curl of the recording medium having passed through the fixing means; inversion means that performs an inversion operation for inverting the recording medium having passed through the fixing means and causing the recording medium to pass through the fixing means again; and a control unit that selects whether to instruct the inversion operation to the inversion means according to the amount of the curl of the recording medium having the toner image fixed to one side thereof.SELECTED DRAWING: Figure 1

Description

The present invention relates to an image forming apparatus, an image forming method and a program.

It is known that in an electrophotographic image forming apparatus, when an image is formed on a paper having a high water content, the paper is curled or curled. On the other hand, when paper having a high water content is fed, the surface of the paper is subjected to the fixing process while applying heat, and then the paper is passed through the fixing means again to remove the moisture of the paper. , A technique for equalizing the water content on the front and back surfaces of paper has been proposed.

For example, Patent Document 1 discloses a non-printing pass mode in which the paper is passed through the fixing means again while applying heat to the paper for the purpose of optimizing the moisture content of the paper at the time of transfer. ..

However, in the conventional technology, the water content is determined by using the temperature sensor and the humidity sensor provided in the device, and depending on the temperature and humidity conditions, double-sided transportation is always performed, which causes a problem that productivity is lowered. is there. Also, when paper with a high water content is fed from the outside (for example, when the paper is brought from another room such as the paper stock place, that is, a place different from the temperature and humidity environment where the device is placed). There is a problem that the temperature sensor and the humidity sensor in the device cannot detect that the paper having a high water content is fed, and the control technology for equalizing the water content on the front and back surfaces of the paper does not work.

An object of the present invention is to provide an image forming apparatus capable of suppressing curling generation without reducing productivity even when an image is formed on a recording medium under conditions in which curling is likely to occur.

In order to solve the above problems, the image forming apparatus of the present invention includes a transfer means for transferring a toner image to a recording medium, a fixing means for heating the transferred toner image and fixing it on the recording medium, and the fixing. A curl amount measuring means for measuring the curl amount of the recording medium that has passed through the means, a reversing means that reverses the recording medium that has passed through the fixing means, and causes the recording medium to pass through the fixing means again. It is characterized by including a control unit that selects whether or not to instruct the reversing means to perform a reversing operation according to the amount of curl of the recording medium on which the toner image is fixed.

According to the present invention, even when an image is formed on a recording medium under conditions where curl is likely to occur, curl generation can be suppressed without reducing productivity.

It is a schematic block diagram in the main part of the image forming apparatus which concerns on embodiment. It is a schematic block diagram of the whole image forming apparatus which concerns on embodiment. It is a block diagram of the image forming apparatus which concerns on embodiment. It is a flowchart of the image formation method which concerns on embodiment. It is a flowchart of the image formation method which concerns on other embodiment. It is a flowchart of the image formation method which concerns on other embodiment. It is a flowchart of the image formation method which concerns on other embodiment. It is a flowchart of the image formation method which concerns on other embodiment. It is a flowchart of the image formation method which concerns on other embodiment. It is a schematic block diagram in the main part of the image forming apparatus which concerns on another embodiment. It is a schematic block diagram in the main part of the image forming apparatus which concerns on another embodiment.

Hereinafter, the image forming apparatus, the image forming method, and the program according to the present invention will be described with reference to the drawings. The present invention is not limited to the embodiments shown below, and can be modified within the range conceivable by those skilled in the art, such as other embodiments, additions, modifications, and deletions. However, as long as the action and effect of the present invention are exhibited, it is included in the scope of the present invention.

(First Embodiment)
The image forming apparatus of the present embodiment includes a transfer means for transferring a toner image to a recording medium, a fixing means for heating the transferred toner image and fixing it on the recording medium, and the recording medium passing through the fixing means. A curl amount measuring means for measuring the curl amount of the above, an inversion means for performing an inversion operation of inverting the recording medium that has passed through the fixing means and passing the recording medium through the fixing means again, and the toner image fixed on one side. It is characterized by including a control unit for selecting whether or not to instruct the reversing means to perform a reversing operation according to the curl amount of the recording medium.

In the present embodiment, the curl amount of the recording medium that has passed through the fixing means is detected, and if curl occurs, the water content of the front surface and the back surface of the recording medium (for example, paper) is made uniform to prevent curl. In order to make it move to the reverse operation. As a result, double-sided transportation can be performed only when curl occurs regardless of the temperature and humidity conditions, and a decrease in productivity can be prevented. In addition, a recording medium under conditions that are prone to curl from the outside, such as when a recording medium stored in a place different from the temperature and humidity environment in which the device is placed, is supplied, for example, a recording medium having a high water content. Even when paper is used, the water content on the front and back surfaces of the recording medium can be made uniform, and curling can be prevented.

The curl in the above is generated by the following mechanism due to the difference in heating temperature of the recording medium in the fixing means.
(1) Moisture moves from the high temperature side to the low temperature side in the thickness direction of the recording medium by heating in the fixing means.
(2) The water content on the low temperature side increases.
(3) The amount of water evaporated after heating increases on the low temperature side.
(4) Since the recording medium shrinks as the amount of water evaporated increases, the low temperature side shrinks more than the high temperature side.
(5) The recording medium is curled in the direction from the high temperature side to the low temperature side, and curls are formed.
Considering the above, in order to prevent the occurrence of curl, it is sufficient to make the water content of the front surface and the back surface of the recording medium uniform.

In the conventional method, the water content is determined by a temperature sensor or a humidity sensor provided in the device, and depending on the temperature and humidity conditions, double-sided transportation is always performed to make the water content uniform.
However, in the conventional method, there is a problem that productivity is lowered because double-sided transportation is always performed depending on temperature and humidity conditions. In addition, when paper with a high water content is fed from the outside, it is not possible to judge the water content by the temperature sensor or humidity sensor, and double-sided transport to equalize the water content on the front and back surfaces of the paper. There is also a problem that curl occurs without doing.

On the other hand, in the present embodiment, as described above, the amount of curl of the recording medium that has passed through the fixing means is detected, and if curl occurs, the front surface and the back surface of the recording medium are curled to prevent curling. Shift to inversion operation to make the water content uniform. As a result, even when an image is formed on a recording medium under conditions where curl is likely to occur, curl generation can be suppressed without reducing productivity.

Next, the details of this embodiment will be described. FIG. 1 shows a schematic configuration diagram of a main part of the image forming apparatus of the present embodiment. In FIG. 1, a fixing means 9, a heating roller 21, a pressure roller 22, a distance measuring sensor 31, recording media 60a, 60b, a paper ejection unit 70, and a guide unit 71 are shown.

The fixing means 9 in the present embodiment has a heating roller 21 and a pressure roller 22, and the toner image on the recording medium is fixed by the heating roller 21 and the pressure roller 22, and the recording medium that has passed through the fixing means is guided. It is conveyed on the section 71 and discharged to the paper ejection section 70. The guide unit 71 is used to facilitate the transfer of the recording medium to the paper ejection unit 70, but it has an arbitrary configuration and may be used as needed.
In addition to the heating roller, a fixing belt or the like can also be used as the fixing means.

As the curl amount measuring means in the present embodiment, the distance from the recording medium that has passed through the fixing means to the recording medium is measured, and the distance measuring sensor 31 is used. The distance measuring sensor 31 of the present embodiment measures the distance to the recording medium in a non-contact manner, and can measure the distance by, for example, infrared rays.

In the present embodiment, when curl does not occur, the paper is ejected without curling as shown in FIG. 1A. On the other hand, when curl occurs, as shown in FIG. 1B, curls are formed downward from the paper ejection port and the paper is ejected. In FIG. 1B, the distance measured by the distance measuring sensor 31 is represented by d1.

In the present embodiment, it is determined whether or not curl is generated based on the distance d1 between the recording medium and the distance measuring sensor at the time of paper ejection, and when curl is not generated, the paper is ejected as it is as single-sided printing. On the other hand, when curl occurs, it is switched back (reversed operation) to switch to double-sided transfer, and the back surface of the recording medium is warmed by the heating mechanism in the fixing means to make the water content of the front surface and the back surface of the recording medium uniform.

Due to this difference in operation, when curl does not occur, the paper is ejected by single-sided printing to prevent productivity from dropping, and when curl occurs, both sides are conveyed and the back side is warmed by a heating mechanism to make the water content of the front and back sides uniform. Curling can be prevented by making it.

The presence or absence of curl is determined, for example, by comparing the measured value d1 with the threshold value. For example, FIG. 1 shows an example of the threshold LX. The threshold value lp can be the distance from the distance measuring sensor when curl does not occur as shown in FIG. 1 (A).

FIG. 2 shows a schematic configuration diagram of the entire image forming apparatus according to the embodiment.
The image forming apparatus 1 shown in FIG. 2 is also referred to as a digital multifunction device or the like, and has a copying function, a printer function, a facsimile function, and the like.
The image forming apparatus 1 may have an operation unit such as a touch panel, and the copying function, the printer function, and the facsimile function can be sequentially switched and selected by the application switching key of the operation unit. For example, when the copy function is selected, the copy mode is set, when the printer function is selected, the printer mode is set, and when the facsimile mode is selected, the facsimile mode is set.

The flow of image formation in the image forming apparatus will be described by taking a copying mode as an example.
In the copying mode, the document bundle is sequentially fed to the image reading device 3 by the automatic document feeding device (ADF) 2, and the image information is read by the image reading device 3. Then, the read image information is converted into optical information by the writing unit 4 as the writing means via the image processing means. The photoconductor drum 6 is uniformly charged by a charger and then exposed to light information from the writing unit 4 to form an electrostatic latent image.

Next, the electrostatic latent image on the photoconductor drum 6 is developed by the developing device 7 to become a toner image. The toner image is transferred from the paper feed unit 10 to the recording medium fed to the transport belt 8, and the toner image is fixed and discharged from the recording medium by the fixing device 9 (fixing means). At the time of double-sided printing, after the fixing device 9 completes the fixing of the toner image on the front surface, the double-sided transfer unit 12 reverses the printing, and the fixing device 9 fixes the toner image on the back surface. After the fixing of the toner image on the back surface is completed by the fixing device 9, the toner image is discharged.

In FIG. 2, the paper ejection unit 70 is not shown. Further, although the image forming apparatus of the present embodiment has a switchback type device configuration, the present invention is not limited to this as long as it can perform double-sided transfer.

In the present embodiment, a dehumidifying heater 11 (paper feeding unit heating means) for heating the recording medium stored in the paper feeding unit 10 and adjusting the humidity of the recording medium is provided. Although the details will be described later, it is preferable to control ON / OFF of the dehumidifying heater 11 according to the presence or absence of curl of the discharged recording medium.

FIG. 3 is an example of a block diagram in the image forming apparatus of the present embodiment.
The detection distance of the distance measuring sensor (f) 31 is transmitted as a signal to the CPU (e) 41. The detection distance of the CPU (e) 41 is compared with the threshold information stored in the ROM (c) 42 or the RAM (d) 43 in advance, and if it is equal to or less than the threshold, it is discharged as it is as single-sided printing.

If it matches above the threshold value, the control IC (W) 45 performs a reversing operation with the double-sided transfer unit control circuit (G) 41 and the double-sided transfer unit (W) 42, and then heats with the heating mechanism control circuit (G) 46. The mechanism (i) 21 heats the front surface and the back surface to make the water content uniform. As the heating mechanism, for example, the above-mentioned heating roller 21 can be mentioned.

Further, in order to make the water content in the paper feed unit uniform, the dehumidifying heater control circuit (H) 47 and the dehumidifying heater (N) 11 are used to heat the recording medium itself stored in the paper feed unit to reduce the water content. I do.

In the present embodiment, a control circuit is provided on the PSU (Power Supply Unit) 52 side, and the heating mechanism and the dehumidifying heater 11 are controlled by the control circuit. Further, DC / AC conversion is performed from the power supply 51, and power is supplied from the PSU 52 to the control board 48.

In the present embodiment, the control unit may be the control board 48, the CPU 41, the CPU 41, the ROM 42, and the RAM 43, or the double-sided transfer unit control circuit. It may include 44.

Hereinafter, an example of the present embodiment will be described.
FIG. 4 is a flowchart of the image forming method according to the embodiment.

First, in the present embodiment, after starting Job, the surface of the recording medium is heated by a heating mechanism (S101, S102). The heating mechanism includes the above-mentioned heating roller 21.
In the present embodiment, printing of one recording medium may be performed as one job, or printing of a plurality of recording media may be performed as one job.

Next, it is determined whether or not the double-sided printing operation is performed (S103).
Here, in addition to determining whether the image is formed on both sides, it is determined whether the double-sided transport setting is ON. In the double-sided transfer, an image is formed on only one side, and after the image is fixed by the fixing means, the recording medium is conveyed to the fixing means again in order to heat the back surface.

In the determination of S103, when the double-sided printing operation is in progress (when the double-sided transfer setting is ON), the reverse operation is performed and the double-sided transfer is performed (S108, S109). Further, the back surface of the recording medium is heated by the heating mechanism (S110).
As for the reverse operation and double-sided transfer, the control unit gives an instruction to the double-sided transfer unit control circuit 44 via the control IC 45, and the double-sided transfer unit control circuit 44 controls the double-sided transfer operation and double-sided transfer to the double-sided transfer unit 12.

When forming an image on both sides of the recording medium, for example, before S110, the toner image is transferred to the recording medium by a transfer means, and the toner image is fixed in S110. When an image is formed on both sides of a recording medium, it is considered that curling does not occur because heating is performed on both sides of the recording medium, and even if curling occurs, it is considered to be within an allowable range.

Next, the recording medium is ejected, and it is determined whether or not the job is finished (S111, S112). If Job is not finished, the processing after S102 is repeated.

In the determination of S103, if the double-sided printing operation is not in progress, it is determined whether or not it is the first printing sheet (S104).
In the present embodiment, the reason for determining S104, that is, determining whether or not it is the first print sheet will be described below.
In this embodiment, double-sided transport or single-sided transport is set for each Job. The presence or absence of curl is determined for the first printed sheet, and if curl is generated, it is determined that curl will be generated in subsequent printing, and double-sided transfer is performed. As a result, the processing of S105 to S110 can be omitted from the second and subsequent printing sheets, and delay in the processing can be prevented.
On the other hand, the presence or absence of curl is determined for the first printed sheet, and if no curl is generated, it is determined that no curl will be generated in the subsequent printing, and single-sided transfer is performed.

When it is determined that curl has occurred on the first printed sheet, it corresponds to the case where the determination of S103 is No and the determination of S104 to S107 is Yes in the flow. In this case, although the description is omitted in the flow, the setting of double-sided transport is turned ON. In the present embodiment, the initial value of the double-sided transport setting is set to OFF.

The number of prints in one Job is not particularly limited and can be changed as appropriate, and may be one or a plurality of prints. The number of sheets when there are a plurality of sheets is not particularly limited, and examples thereof include 100 sheets and 1000 sheets.

When an image is formed on both sides of the recording medium for the first sheet in the Job, it is considered that double-sided transfer is not performed in the Job because the determination after S104 is not made for the first sheet. For example, in the determination of S104, "1st sheet of printing?" Is displayed, for example, "1st sheet of printing? However, the determination of the 1st sheet of printing has never been performed." Is set to Yes even for the second and subsequent sheets. " That is, make sure that the determination of S104 is Yes at least once in Job.

In the determination of S104, if it is not the first sheet to be printed, the recording medium is ejected and it is determined whether or not the job is finished (S111, S112).
If No in the determination of S104, it means that curl did not occur on the first print sheet, and it was determined that curl did not occur on the second and subsequent print sheets in the Job, and double-sided transfer was performed. Do not do, and eject the paper.

In the determination of S104, when it is the first sheet to be printed, it is determined whether or not the recording medium is detected by the distance measuring sensor (S105).
The reason for making such a determination is that, depending on the measurement position of the distance measurement sensor, there is a time difference before the recording medium heated by the fixing means reaches the measurement position of the distance measurement sensor. By making the determination, it becomes easier to respond to changes in the position of the distance measuring sensor.
In the determination of S105, if the distance measuring sensor does not detect the recording medium, it waits until it is detected.

In the determination of S105, when the recording medium is detected by the distance measuring sensor, it is determined whether or not the time detected by the distance measuring sensor has elapsed the predetermined time Tx (S106).
If it is less than the specified time Tx, it is assumed that an object other than the recording medium is detected. Therefore, by determining whether or not the specified time Tx has elapsed, it can be determined that the distance measuring sensor has detected the recording medium, and the detection accuracy can be improved.

In the determination of S106, when the specified time Tx has elapsed, the detection distance d1 of the distance measuring sensor is compared with the threshold value lux (S107).
“Lx” is a threshold value for determining whether or not the product is curled. The threshold value LX can be appropriately changed depending on the type of recording medium and the like. As an example of LX, for example, as shown in FIG. 1, the distance from the distance measuring sensor to the recording medium when curl does not occur can be used.

In the determination of S107, when d1> lp, it is determined that curl has occurred, the reverse operation and double-sided transfer are performed, and the back surface of the recording medium is heated by the heating mechanism (S108 to S110). In this case, the double-sided transport setting is turned ON. When the double-sided transfer setting is turned ON, the determination of S103 is Yes for the subsequent recording media, and double-sided transfer is performed until Job is completed.

After the processing of S110, the recording medium in which curl is suppressed is discharged (S111).

In the determination of S107, if d1> lp is not satisfied, it is determined that no curl has occurred, and the recording medium is ejected without performing the reversing operation or double-sided transfer (S111). In this case, the double-sided transport setting is left OFF. When the double-sided transport setting is OFF, the determination of S103 is No for the subsequent recording media, and single-sided transport is performed until Job is completed, except when an image is formed on both sides.

Hereinafter, a supplementary explanation of the present embodiment will be given.
In the present embodiment, the distance measuring sensor is arranged above the ejected recording medium, but the present invention is not limited to this, and for example, the distance measuring sensor may be arranged below the ejected recording medium. In this case, it can be determined that curl has occurred when d1 <lux.

Further, in the present embodiment, as shown in FIG. 1, the heating roller is arranged on the upper side and the pressure roller is arranged on the lower side. It is preferable that the heating roller and the pressurizing roller are arranged in this way as in the present embodiment. In this case, it becomes easier to obtain the curl amount, and it is possible to accurately determine whether or not curl has occurred.

On the other hand, the heating roller and the pressure roller may be arranged in reverse, that is, the heating roller may be arranged on the lower side and the pressure roller may be arranged on the upper side. In this case, the curl amount can be obtained by arranging the distance measuring sensor under the ejected recording medium, but it should be noted that the weight of the recording medium acts downward.

Further, as shown in FIG. 1, it is preferable that the paper ejection portion 70 in the present embodiment has a region in which the recording medium hangs downward so that the curl amount can be measured. The paper ejection unit 70 in the present embodiment has a predetermined depth below the point where the recording medium is ejected from the fixing means, and the depth can be appropriately changed.

Further, the paper ejection unit 70 in the present embodiment has a predetermined height above the point where the recording medium is ejected from the fixing means, and the height can be appropriately changed. Having a predetermined height makes it easier for the curl amount measuring means to obtain the curl amount.

As described above, the present embodiment provides an image forming method and a program capable of suppressing curling without reducing productivity even when an image is formed on a recording medium under conditions where curling is likely to occur. can do.
The image forming method of the present embodiment has passed through a transfer step of transferring a toner image to a recording medium, a fixing step of heating the transferred toner image by a fixing means and fixing it on the recording medium, and the fixing means. A curl amount measuring step of measuring the curl amount of the recording medium, an inversion step of inverting the recording medium that has passed through the fixing means and passing the recording medium through the fixing means again, and the recording medium on which the toner image is fixed. A control step of instructing the reversing means to perform a reversing operation according to the amount of curl is included.

The program of this embodiment causes a computer to execute the image forming method of this embodiment. Further, in the program of the present embodiment, for an image forming apparatus including a transfer means, a fixing means, a curl amount measuring means, and a reversing means, the reversing means is provided according to the curl amount of the recording medium on which the toner image is fixed on one side. Is made to execute a control process for selecting whether or not to instruct the inversion operation.

(Second Embodiment)
Next, another embodiment of the image forming apparatus according to the present invention will be described.
Descriptions of matters common to the above embodiments will be omitted.

A flowchart for explaining the present embodiment is shown in FIG.
In the present embodiment, the control unit changes the heating temperature of the fixing means when reheating the inverted recording medium according to the curl amount.

First, in the present embodiment, after the start of printing, it is determined whether or not the double-sided printing operation is performed (S121, S122).
The determination of S122 in the present embodiment is the same as the determination of S103 in the first embodiment.

Here, in the present embodiment, as described as "printing start" in S121, the flow is for one recording medium. That is, in the first embodiment, the flow is for one Job, but in the present embodiment, the determination is made for each recording medium.

In the determination of S122, when performing the double-sided printing operation, the reverse-sided operation is performed and double-sided transfer is performed (S126, S127). Further, the back surface of the recording medium is heated by the heating mechanism (S128). In the present embodiment, the case where the double-sided printing operation is performed (the case where the determination in S122 is Yes) corresponds to the case where an image is formed on both sides of the recording medium.

Here, in S128 in the present embodiment, unlike the first embodiment, the heating temperature is changed according to Table A (Table 1).

In Table 1, lx represents the threshold value of the distance measuring sensor detection distance. In the example shown here, the heating temperature is increased as the range of lp increases. This is because it is judged that the amount of curl is large when LX is a large value, and it is considered preferable to heat at a higher temperature in order to prevent curl that becomes a large value. is there.

In this way, by changing the reheating temperature in the fixing means according to the threshold value of the curl amount, it is possible to heat at an appropriate temperature for preventing curling, and overheating can be prevented. Therefore, it is possible to suppress the power consumption while preventing the occurrence of curl.

In the present embodiment, it is preferable to have a storage means capable of holding a plurality of curl amount thresholds. The configuration of the storage means is not particularly limited and can be appropriately changed.

The values in Table A (Table 1) are examples, and are not limited to these, and can be changed as appropriate. For example, the threshold value LX is changed depending on the position where the distance measuring sensor is arranged, and the heating temperature is also changed depending on the type of recording medium, the contact area between the heating roller and the recording medium, the contact time, and the like. It will be changed. Further, in the case of lp ≧ 125 [mm], for example, the temperature may be uniformly set to 160 ° C., or in such a case, the error processing may be executed assuming that it is not expected.

In the determination of S122, when the double-sided printing operation is not performed (when the determination of S122 is No), the same determination as in S105 to S107 of the first embodiment is performed (S123 to S125).
In the determination of S125, when d1> lp, it is determined that curl has occurred, the reverse operation and double-sided transfer are performed, and the back surface of the recording medium is heated by the heating mechanism (S126 to S128). After that, the recording medium in which curl is suppressed is discharged (S129).
As described above, in the heating in S128, the reheating temperature in the fixing means is changed according to the threshold value of the curl amount.

In the determination of S125, if d1> lp is not satisfied, it is determined that no curl has occurred, and the recording medium is ejected without performing the reversing operation or double-sided transfer (S129).

In this embodiment, the end of Job is not determined. As described above, in the present embodiment, the determination is performed for each recording medium, and this makes it possible to optimally deal with cases where the curl amount differs depending on the recording medium.

(Third Embodiment)
Next, another embodiment of the image forming apparatus according to the present invention will be described.
Descriptions of matters common to the above embodiments will be omitted.
A flowchart for explaining the present embodiment is shown in FIG.

The image forming apparatus of the present embodiment includes a paper feeding unit in which the recording medium before the image is formed is stored, and a paper feeding unit heating means for heating the recording medium housed in the paper feeding unit. When the curl amount is equal to or more than a predetermined value, the control unit operates the paper feeding unit heating means.
In this embodiment, the dehumidifying heater 11 (paper feeding unit heating means) in FIG. 2 is preferably controlled.

First, as in the second embodiment, after the start of printing, it is determined whether or not the double-sided printing operation is performed (S131, S132).
Also in this embodiment, the determination is made for each recording medium as in the second embodiment.

Next, the determinations of S132 to S135 are performed in the same manner as in the second embodiment.
Here, in the present embodiment, the processing after the determination of S135 is different from that of the second embodiment.
In the present embodiment, in the determination of S135, when d1> lp, the paper feed unit heating means is operated, or when it is already in operation, the operation is continued (S136).

When d1> lx, curling is generated. Therefore, by operating the paper feeding unit heating means, the water content of the recording medium can be reduced in advance in the paper feeding unit, and the subsequent recording media are curled. Occurrence can be prevented. Further, in the present embodiment, an operation for preventing the occurrence of curl can be performed from the time of feeding the recording medium, and it is not necessary to switch the double-sided transport for making the water content uniform. This has the advantage of preventing curling, reducing power consumption, and preventing a decrease in productivity.

In the process after S136, the reverse operation is performed and the double-sided transfer is performed in the same manner as in the second embodiment (S138, S139). Further, the back surface of the recording medium is heated by the heating mechanism (S140).

On the other hand, in the determination of S135, if d1> lp is not satisfied, it is determined that no curl has occurred, the paper feeding unit heating means is stopped, and the recording medium is ejected (S137, S141).
As described above, when the curl does not occur, the power consumption can be suppressed by stopping the paper feeding unit heating means. When the curl disappears at a certain number of prints, it is considered that the recording medium stored in the paper feed unit is sufficiently dehumidified by heating the paper feed unit heating means.

The heating temperature of the paper feed unit heating means can be changed as appropriate. Further, the installation location of the dehumidifying heater 11 is not limited to that shown in FIG.

(Fourth Embodiment)
Next, another embodiment of the image forming apparatus according to the present invention will be described.
Descriptions of matters common to the above embodiments will be omitted.
A flowchart for explaining the present embodiment is shown in FIG.

In the present embodiment, the curl amount measuring means measures the curl amount for each number of prints of the recording medium, and the control unit obtains the difference of the curl amount for each print number of the recording medium, and responds to the difference. The reversing means is instructed or not instructed to perform the reversing operation.

First, in the present embodiment, after starting Job, the surface of the recording medium is heated by a heating mechanism (S101, S102). In the present embodiment, the processing is performed in Job units as in the first embodiment.
In the present embodiment, "for each number of prints" means that double-sided transfer or single-sided transfer is set for each Job.
Further, in the present embodiment, the curl amount is detected for each number of printed sheets, and the paper transport is switched between double-sided transport and single-sided transport from the middle of printing depending on whether the difference between the detection results is equal to or greater than the threshold value. After the temperature difference is reduced by the heat storage on the pressurizing roller side, it is not necessary to switch the double-sided transfer, so that it is possible to prevent curling and further improve the power consumption and the decrease in productivity from the middle of printing.

Next, the determination of S152 to S156 is performed in the same manner as in the second embodiment and the third embodiment.

Next, the difference in curl amount is obtained (S157).
The difference in the amount of curl is the difference between the value d1 of the distance measuring sensor obtained for the recording medium that determines whether the recording medium is double-sided or single-sided, and the value of the distance measuring sensor obtained for the recording medium immediately before the recording medium. Obtained by. As shown in the figure, it can be obtained as "d1 of d1-1 sheets before". It is preferable to have a recording means for recording the previous d1.

Next, the threshold value is determined for the obtained difference (S158).
When the above difference is a negative value and the absolute value is equal to or greater than the threshold value ly, the value d1 of the distance measuring sensor of the recording medium is smaller than the value d1 of the previous distance measuring sensor, so that the curl is small. It has become. It is considered that this is because the temperature difference in the recording medium is reduced by the heat storage on the pressure roller side and curl is less likely to occur. In this case, the double-sided transfer is changed to the single-sided transfer.

The threshold value ly is not particularly limited, but by setting a certain value, it can be reliably determined that curl is less likely to occur.

In the determination of S158, when it is determined that the curl is in the direction of occurrence (when the determination of S158 is No), the reverse operation and double-sided transfer are performed, and the back surface of the recording medium is heated by the heating mechanism (S159 to S161). .. Here, the setting of double-sided transport is left ON.

On the other hand, in the determination of S158, when it is determined that curl does not occur based on the difference (when the determination of S158 is Yes), the reverse operation and double-sided transfer are performed, and the back surface of the recording medium is heated by the heating mechanism. After that, the setting of double-sided transport is turned off (S162 to S165).

Next, the recording medium in which curl is suppressed is discharged (S166).
Next, it is determined whether or not the job is finished (S167). If Job is not completed, the processing after S152 is repeated.

(Fifth Embodiment)
Next, another embodiment of the image forming apparatus according to the present invention will be described.
Descriptions of matters common to the above embodiments will be omitted.
A flowchart for explaining the present embodiment is shown in FIG.

In the present embodiment, the control unit selects whether or not to instruct the reversing means to perform a reversing operation according to the curl amount and type of the recording medium.

In the present embodiment, after the start of printing, the paper type setting is read, and the threshold value LX according to the reading result of the paper type setting is set (S171 to S173).
As the paper type setting, for example, as shown in Table B (Table 2) below.

In Table 2, the thickness of the recording medium increases in the order of thin paper to OHP.
In Table 2, plain paper 1 and plain paper 2 have different thicknesses, and plain paper 1 is thinner than plain paper 2.

The threshold value lx in Table 2 is not particularly limited and can be appropriately changed. For example, it is changed depending on the position where the distance measuring sensor is arranged.
It is preferable to have a storage means for storing the settings of the table B.

After S173, the processes of S174 to S181 are performed in the same manner as in the second embodiment and the third embodiment.
In S177, the determination of d1> lx is performed as in the above embodiment, but here, lx used in lx set in S173. The method of grasping which paper type of the table B the recording medium corresponds to is not particularly limited, but for example, it may be specified by the user, or a sensor may be provided in the paper feed section or the like. It may be provided and judged.

The threshold value for curl detection is changed according to the type of paper used, and when the curl amount is equal to or greater than the threshold value, the paper transport is switched to double-sided paper transfer, and the fixing mechanism equalizes the water content on the front and back surfaces of the paper.
As a result, it is possible to more accurately determine whether the recording medium is hung down and curled due to its own weight, or whether it is curled and curled.
When it is determined that the recording medium is rounded by its own weight and no curl has occurred, the double-sided transfer can be switched to the single-sided transfer, which can suppress power consumption and further suppress productivity reduction.

(Sixth Embodiment)
Next, another embodiment of the image forming apparatus according to the present invention will be described.
Descriptions of matters common to the above embodiments will be omitted.
A flowchart for explaining the present embodiment is shown in FIG.

In the present embodiment, the control unit determines the frequency with which a curl-prone type is used as the recording medium based on the operating time of the paper feeding unit heating means and the curl amount, and is provided in the image forming apparatus. The frequency is displayed on the display unit.
In this embodiment, the processes of S201 to S205 are further performed with respect to the third embodiment (FIG. 6).

First, as in the third embodiment, the determinations S192 to S195 are performed after the start of printing.
In the determination of S195, as in the third embodiment, when d1> lp, the paper feed unit heating means is operated, or when the paper feed unit heating means is already in operation, the operation is continued. (S196).
When d1> lx, curling is generated, so that the water content of the recording medium can be reduced in advance in the paper feed unit by operating the paper feed unit heating means, and the water content can be made uniform. There is no need to switch double-sided paper for this purpose. This has the advantage of preventing curling, reducing power consumption, and preventing a decrease in productivity.

In the processing after S196, the processing of S198 to S200 is performed in the same manner as in the third embodiment.

Next, the operating time of the paper feeding unit heating means is obtained (S201).
The method of obtaining the operating time can be appropriately changed, but for example, it can be obtained by the difference between the current time and the time when the operation of the paper feeding unit heating means is started.
It is preferable to have a storage means for storing the time when the operation of the paper feed unit heating means is started.

Next, it is determined whether or not the operating time of the paper feeding unit heating means is equal to or longer than a predetermined time (S202).
In the figure, it is set to 5 hours, but it is not limited to this and can be changed as appropriate. When it is longer than a predetermined time, that is, when the determination of S202 is "Yes", it is determined that the recording medium having a high water content has been used, and the usage history of the recording medium having a high water content is counted up (S203). ..

Next, the number of counts of the usage history of the recording medium having a high water content is determined (S204).
In S204, it is determined whether or not the number of counts is equal to or greater than a predetermined number of times. In the example here, it is determined whether or not the number of times is 5 or more, but the present invention is not limited to this, and can be changed as appropriate.

In the determination of S204, when the number of counts is equal to or greater than a predetermined number, the number of times the recording medium on which curl is likely to occur is replenished is notified and displayed (S205).
The notification destination can be changed as appropriate, and examples thereof include a display unit provided in the image forming apparatus of the present embodiment. As the display unit, for example, a display, a touch panel, or the like can be used. In addition to this, a device other than the image forming device may be notified.
The display unit that receives the notification displays the number of times the paper that is prone to curl has been replenished.

The display form is not particularly limited, but it is preferable to perform a display that promotes improvement. For example, a message such as "Paper that is prone to curl is being replenished. It is recommended to replenish paper that is less likely to curl."
You may notify by logging information.

In the present embodiment, the fact that the curl generation rate is high despite the long operating time of the paper feed section heating means means that the paper is replenished by the user of the image forming apparatus, and the recording medium having a large water content is used. It can be said that the probability of being replenished is high. In such a case, it can be understood that the user often replenishes paper from the external environment, such as a user who often uses a recording medium stored in a place different from the temperature and humidity environment in which the device is placed. By performing such an understanding, it is possible to promote improvement of paper replenishment from an uncontrolled external environment, which is one of the causes of curl.

On the other hand, in the determination of S195, if d1> lp is not satisfied, it is determined that no curl has occurred, the paper feeding unit heating means is stopped, and the recording medium is ejected (S197, S206).
In this way, when it is determined that curl does not occur, the power consumption can be suppressed by stopping the paper feeding unit heating means.

(7th Embodiment)
Next, another embodiment of the image forming apparatus according to the present invention will be described.
Descriptions of matters common to the above embodiments will be omitted.

As shown in FIG. 1, the curl amount measuring means in the embodiment obtains the curl amount by measuring the distance from the recording medium that has passed through the fixing means to the recording medium. ..

On the other hand, also in the present embodiment, the curl amount measuring means measures the distance from the recording medium from above the recording medium, but the curl amount measuring means has a different configuration than the distance measuring sensor. A diagram for explaining this embodiment is shown in FIG. FIG. 10 is a diagram illustrating an example when the curl amount is detected by using the filler 36 as the curl amount measuring means.

Similar to the above embodiment, when curl does not occur, the paper is ejected without curling as shown in FIG. 10A. On the other hand, when curl occurs, a curl is formed downward from the paper ejection port as shown in FIG. 10B, and the paper is ejected.

In the present embodiment, the curl at the time of paper ejection is detected by the filler 36. If the recording medium comes into contact with the filler, the paper is discharged as single-sided printing as no curl occurs, and if the recording medium does not come into contact with the filler, the back side is switched back (reversed operation) as curl and switched to double-sided transfer. Warm to equalize the water content on the front and back surfaces of the recording medium.

In the present embodiment, the amount of curl can be determined not only by whether or not curl is generated, but also by appropriately changing the position where the filler is arranged, the size and length of the filler, and the like.

(8th Embodiment)
Next, another embodiment of the image forming apparatus according to the present invention will be described.
Descriptions of matters common to the above embodiments will be omitted.

In the present embodiment, the curl amount measuring means has a transmission sensor provided on the side surface of the recording medium that has passed through the fixing means, and is the recording medium curled by using the transmission sensor? Judge whether or not.

A diagram for explaining the present embodiment is shown in FIG. FIG. 11 is a diagram illustrating an example of a means for detecting a curl amount using a transmission sensor as a curl amount measuring means.

Similar to the above embodiment, when curl does not occur, the paper is discharged without curling as shown in FIG. 11A. On the other hand, when curl occurs, a curl is formed downward from the paper ejection port as shown in FIG. 11B, and the paper is ejected.

In the present embodiment, the curl at the time of paper ejection is detected by the transmission sensors 34 and 35. In the present embodiment, the transmission sensor is provided on the side surface of the recording medium that has passed through the fixing means.
As the transmission sensor in this embodiment, a sensor 34 on the light emitting side and a sensor 35 on the light receiving side are used. When the light projected from the transmission sensor is received without being blocked by the curled recording medium, the paper is discharged as single-sided printing without curling. On the other hand, when the light projected by the transmission sensor is blocked by the curled recording medium and is not received, it is determined that curl has occurred and the switchback (reversal operation) is performed to switch to double-sided transfer. When switching to double-sided transport, the heating mechanism warms the back surface of the recording medium to equalize the water content of the front and back surfaces of the recording medium.

(9th embodiment)
Next, another embodiment of the image forming apparatus according to the present invention will be described.
Descriptions of matters common to the above embodiments will be omitted.

The curl amount measuring means can be rearranged in addition to the examples shown above.
For example, the distance measuring sensor 31 is not limited to the arrangement as in the example shown in FIG. 1, but can be arranged in other places of the paper ejection unit 70. Further, as described above, the curl amount may be measured from below the recording medium.

Further, it may be in contact with or away from the paper ejection portion 70. When the paper ejection unit 70 is arranged away from the paper ejection unit 70, for example, the curl amount measuring means can be arranged on the lower surface of the image reading device 3 or the writing unit 4.

In addition to the above, for example, it may be arranged on the printer unit 5 side of the output tray 72 in FIG. In this case, for example, the curl amount is measured by a distance measuring sensor from below the ejected recording medium. Further, in addition to the above, for example, it may be arranged in the transport path between the fixing means 9 and the paper output tray 72 in FIG. In this case, it is preferable to provide a configuration such as the paper ejection unit 70 in the transport path.

1 Image forming device 2 Automatic document feeder (ADF)
3 Image reader 4 Writing unit 5 Printer unit 6 Photoreceptor drum 7 Developing device 8 Conveying belt 9 Fixing means 10 Paper feeding unit 11 Dehumidifying heater 21 Heating roller 22 Pressurizing roller 31 Distance measuring sensor 60a, 60b Recording medium 70 Paper ejection unit 71 Paper ejection guide 72 Paper ejection tray

Japanese Unexamined Patent Publication No. 2006-301192

Claims (10)

A transfer means for transferring a toner image to a recording medium,
A fixing means for heating the transferred toner image and fixing it on the recording medium,
A curl amount measuring means for measuring the curl amount of the recording medium that has passed through the fixing means,
A reversing means that reverses the recording medium that has passed through the fixing means and causes the fixing means to pass through again.
An image forming apparatus including a control unit that selects whether or not to instruct the reversing means to perform a reversing operation according to the curl amount of the recording medium on which the toner image is fixed on one side. The image forming apparatus according to claim 1, wherein the control unit changes the heating temperature of the fixing means when the inverted recording medium is reheated according to the curl amount. A paper feed unit in which the recording medium before the image is formed is stored, and
A paper feed unit heating means for heating the recording medium housed in the paper feed unit is provided.
The image forming apparatus according to claim 1 or 2, wherein the control unit operates the paper feeding unit heating means when the curl amount is equal to or more than a predetermined value. The curl amount measuring means measures the curl amount for each number of prints on the recording medium.
The control unit obtains a difference in the amount of curl for each number of printed sheets of the recording medium, and selects whether or not to instruct the reversing means to perform a reversing operation according to the difference. The image forming apparatus according to any one of. The image forming apparatus according to any one of claims 1 to 4, wherein the control unit selects whether or not to instruct the reversing means to perform a reversing operation according to the curl amount and type of the recording medium. .. The control unit determines the frequency with which a curl-prone type is used as the recording medium based on the operating time of the paper feeding unit heating means and the curl amount, and displays the image on the display unit provided in the image forming apparatus. The image forming apparatus according to any one of claims 1 to 5, wherein the frequency is displayed. The curl amount measuring means according to any one of claims 1 to 6, wherein the curl amount is obtained by measuring the distance from the upper part of the recording medium that has passed through the fixing means to the recording medium. Image forming device. The curl amount measuring means has a transmission sensor provided on the side surface of the recording medium that has passed through the fixing means, and by using the transmission sensor, it is determined whether or not curl is generated in the recording medium. The image forming apparatus according to any one of claims 1 to 6. The transfer process of transferring the toner image to the recording medium,
A fixing step of heating the transferred toner image by a fixing means and fixing it on the recording medium,
A curl amount measuring step for measuring the curl amount of the recording medium that has passed through the fixing means,
A reversing step of reversing the recording medium that has passed through the fixing means and passing the recording medium through the fixing means again.
An image forming method comprising a control step of instructing the reversing means to perform a reversing operation according to the amount of curl of the recording medium on which the toner image is fixed. A program comprising causing a computer to execute the image forming method according to claim 9.