JP7318301B2 - Image forming apparatus and image forming method - Google Patents

Description

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

2. Description of the Related Art In an electrophotographic image forming apparatus, it is known that when an image is formed on paper having a high water content, the paper curls. On the other hand, when paper with a high water content is fed, after the fixing process is performed while applying heat to the surface of the paper, the water is removed from the paper by passing it through the fixing unit again. , a technique for equalizing the water content on the front and back sides of paper has been proposed.

For example, Japanese Patent Application Laid-Open No. 2002-200002 discloses performing a non-printing pass mode in which the paper is passed again through the fixing means while being heated, for the purpose of optimizing the moisture content of the paper at the time of transfer. .

However, in the conventional technology, the moisture content is determined using the temperature sensor and humidity sensor provided in the device, and depending on the temperature and humidity conditions, double-sided transportation is always required, which poses a problem of reduced productivity. be. Also, when paper with a high moisture content is fed from the outside (for example, when paper is brought from another room such as a paper stock room, i.e., a place different from the temperature and humidity environment where the device is placed) There is also the problem that the temperature sensor and humidity sensor in the device cannot detect that paper with a high water content has been fed, and the control technology that equalizes the water content on the front and back sides of the paper does not work.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming apparatus capable of suppressing curling without reducing productivity even when forming an image on a recording medium under conditions where curling is likely to occur.

In order to solve the above problems, the image forming apparatus of the present invention includes transfer means for transferring a toner image onto a recording medium, fixing means for heating and fixing the transferred toner image onto the recording medium, and the fixing means. curl amount measuring means for measuring the curl amount of the recording medium that has passed through the fixing means; reversing means for performing a reversing operation to reverse the recording medium that has passed through the fixing means and pass it through the fixing means again; a control section for selecting 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 , wherein the control section determines whether or not curling occurs for the first printed sheet. Whether or not to instruct the reversing means to perform the reversing operation for the first printed sheet is determined according to the amount of curl, and the reversing operation to instruct the reversing means for the second and subsequent printed sheets is performed according to the amount of curl. The reversing operation is the same as the reversing operation for the first sheet .

According to the present invention, even when an image is formed on a recording medium in which curling tends to occur, it is possible to suppress curling without reducing productivity.

1 is a schematic configuration diagram of a main part of an image forming apparatus according to an embodiment; FIG. 1 is a schematic configuration diagram of an entire image forming apparatus according to an embodiment; FIG. 1 is a block diagram of an image forming apparatus according to an embodiment; FIG. 4 is a flow chart of an image forming method according to the embodiment; 8 is a flowchart of an image forming method according to another embodiment; 8 is a flowchart of an image forming method according to another embodiment; 8 is a flowchart of an image forming method according to another embodiment; 8 is a flowchart of an image forming method according to another embodiment; 8 is a flowchart of an image forming method according to another embodiment; FIG. 3 is a schematic configuration diagram of a main part of an image forming apparatus according to another embodiment; FIG. 3 is a schematic configuration diagram of a main part of an image forming apparatus according to another embodiment;

An image forming apparatus, an image forming method, and a program according to the present invention will be described below with reference to the drawings. In addition, the present invention is not limited to the embodiments shown below, and can be changed within the scope of those skilled in the art, such as other embodiments, additions, modifications, deletions, etc. is also included in the scope of the present invention as long as the functions and effects of the present invention are exhibited.

(First embodiment)
The image forming apparatus of this embodiment includes transfer means for transferring a toner image onto a recording medium, fixing means for heating and fixing the transferred toner image onto the recording medium, and the recording medium that has passed through the fixing means. curl amount measuring means for measuring the curl amount of the toner image; reversing means for performing a reversing operation of reversing the recording medium that has passed through the fixing means and passing it through the fixing means again; and a control unit for selecting whether or not to instruct the reversing means to perform reversing operation according to the amount of curl of the recording medium.

In this embodiment, the amount of curling of the recording medium that has passed through the fixing unit is detected, and when curling occurs, the moisture content of the front and back surfaces of the recording medium (for example, paper) is made uniform to prevent curling. It shifts to the reversal operation in order to As a result, regardless of temperature and humidity conditions, double-sided conveyance can be performed only when curling occurs, and a decrease in productivity can be prevented. Also, if a recording medium is brought in that has been stored in a location different from the temperature and humidity environment where the device is placed, a recording medium with conditions that easily cause curling, such as a recording medium with a high water content, is supplied from the outside. 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 described above is caused by the following mechanism due to the heating temperature difference 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 due to heating in the fixing means.
(2) The moisture 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 moisture evaporated increases, the low temperature side shrinks more than the high temperature side.
(5) The recording medium curls in the direction from the high temperature side to the low temperature side, forming a curl.
Considering the above, in order to prevent the occurrence of curling, the water content of the front and back surfaces of the recording medium should be made uniform.

In the conventional method, the water content is determined by a temperature sensor and humidity sensor provided in the equipment, and depending on the temperature and humidity conditions, double-sided conveyance is always performed to equalize the water content.
However, in the conventional method, there is a problem that the double-sided conveyance is always carried out depending on the temperature and humidity conditions, resulting in a decrease in productivity. Also, when paper with a high moisture content is fed from the outside, the moisture content cannot be determined by the temperature sensor or humidity sensor. There is also the problem that curling occurs without

On the other hand, in the present embodiment, as described above, the amount of curling of the recording medium that has passed through the fixing unit is detected, and if curling occurs, the front and back surfaces of the recording medium are adjusted to prevent curling. In order to equalize the water content, it shifts to an inversion operation. Accordingly, even when an image is formed on a recording medium under conditions where curling is likely to occur, curling can be suppressed without reducing productivity.

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

The fixing means 9 in this embodiment has a heating roller 21 and a pressure roller 22. 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. The sheet is conveyed on the section 71 and discharged to the discharge section 70 . The guide portion 71 is used to facilitate transport of the recording medium to the paper ejection portion 70, but it is an arbitrary configuration and may be used as necessary.
As the fixing means, a fixing belt or the like can be used in addition to the heating roller.

As curl amount measuring means in this embodiment, a distance sensor 31 is used to measure the distance from above the recording medium that has passed through the fixing means. The distance measuring sensor 31 of the present embodiment measures the distance to the recording medium without contact, and can measure the distance using, for example, infrared rays.

In this embodiment, when no curl occurs, the sheet is discharged without curling, as shown in FIG. 1A. On the other hand, when curl occurs, as shown in FIG. 1B, the sheet is ejected with a curl formed downward from the ejection port. In FIG. 1B, the distance measured by the distance measuring sensor 31 is represented by d1.

In this embodiment, it is determined whether or not curling occurs based on the distance d1 between the recording medium and the distance measuring sensor at the time of paper ejection, and when curling does not occur, the paper is ejected as single-sided printing. On the other hand, when curling occurs, a switchback (reversal operation) is performed to switch to double-sided conveyance, and the heating mechanism of the fixing means heats the back surface of the recording medium to equalize the water content of the front and back surfaces of the recording medium.

Due to this difference in operation, when there is no curl, the paper is ejected with single-sided printing, which prevents productivity from dropping. curling can be prevented.

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

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 called a digital multi-function machine, 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 an application switching key of the operation unit can be used to sequentially switch and select a copying function, a printer function, and a facsimile function. For example, when the copy function is selected, the copy mode is selected, when the printer function is selected, the printer mode is selected, and when the facsimile mode is selected, the facsimile mode is selected.

The flow of image formation in the image forming apparatus will be described using a copy mode as an example.
In the copy mode, an automatic document feeder (ADF) 2 sequentially feeds a bundle of documents to an image reading device 3, which reads image information. Then, the read image information is converted into optical information by the writing unit 4 as writing means via the image processing means. After being uniformly charged by a charger, the photosensitive drum 6 is exposed to light information from the writing unit 4 to form an electrostatic latent image.

Next, the electrostatic latent image on the photosensitive drum 6 is developed by the developing device 7 into a toner image. The toner image is transferred onto the recording medium fed from the feeding unit 10 onto the conveying belt 8, and the recording medium is discharged after the toner image is fixed by a fixing device 9 (fixing means). During double-sided printing, after fixing of the toner image on the front side by the fixing device 9 is completed, the sheet is reversed by the double-sided conveying unit 12 and the toner image on the back side is fixed by the fixing device 9 . After fixing of the toner image on the back surface by the fixing device 9 is completed, the sheet is discharged.

Note that illustration of the paper discharge unit 70 is omitted in FIG. 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 carry out double-sided conveyance.

In this embodiment, a dehumidifying heater 11 (paper feeding unit heating means) is provided for heating the recording medium stored in the paper feeding unit 10 and for conditioning the humidity of the recording medium. 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 curling of the ejected recording medium.

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

If the values are equal to or greater than the threshold value, the double-sided conveying unit control circuit (g) 41 and the double-sided conveying unit (wa) 42 are operated by the control IC (o) 45, and then the heating mechanism control circuit (g) 46 performs heating. A mechanism (i) 21 heats the surface and the back surface to make the water content uniform. Note that the heating mechanism includes, for example, the heating roller 21 described above.

Further, in order to equalize the water content in the paper feeding unit, the dehumidifying heater control circuit (h) 47 and the dehumidifying heater (n) 11 heat the recording medium itself stored in the paper feeding unit to reduce the water content. I do.

In this embodiment, a control circuit is provided on the PSU (Power Supply Unit) 52 side, and the control circuit controls the heating mechanism and the dehumidifying heater 11 . 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 this embodiment, the control unit may be the control board 48, the CPU 41, the combination of the CPU 41, the ROM 42 and the RAM 43, or the double-sided transport unit control circuit. 44 may be included.

An example of this embodiment will be described below.
FIG. 4 is a flow chart of an image forming method according to the embodiment.

First, in this embodiment, after starting a job, the heating mechanism heats the surface of the recording medium (S101, S102). Note that the heating roller 21 described above can be used as the heating mechanism.
In this embodiment, printing on one recording medium may be performed as one job, or printing on a plurality of recording media may be performed as one job.

Next, it is determined whether or not it is a double-sided printing operation (S103).
Here, in addition to determining whether images are to be formed on both sides, it is determined whether the setting for double-sided conveyance is ON. Double-sided conveyance means that an image is formed only on one side, but after the image is fixed by the fixing means, the recording medium is again conveyed to the fixing means in order to heat the back side.

In the judgment of S103, if the double-sided printing operation is in progress (the double-sided conveyance setting is ON), the reversing operation is performed and the double-sided conveyance is performed (S108, S109). Further, the heating mechanism heats the back surface of the recording medium (S110).
As for the reversing operation and double-sided transport, the control section issues instructions to the double-sided transport unit control circuit 44 via the control IC 45 , and the double-sided transport unit control circuit 44 controls the double-sided transport unit 12 to perform the reverse operation and double-sided transport.

When images are formed on both sides of the recording medium, for example, prior to S110, the toner image is transferred to the recording medium by a transfer unit, and the toner image is fixed in S110. When images are formed on both sides of the recording medium, both sides of the recording medium are heated, so it is considered that curling does not occur, and even if curling occurs, it is considered to be within an allowable range.

Next, the recording medium is discharged, and it is determined whether or not the job is completed (S111, S112). If the Job has not ended, the processes after S102 are repeated.

If it is determined in S103 that double-sided printing is not in progress, it is determined whether or not it is the first sheet to be printed (S104).
In this embodiment, the reason why the determination in S104, that is, the determination as to whether or not it is the first printed sheet will be described below.
In this embodiment, double-sided conveyance or single-sided conveyance is set for each job. The presence or absence of curling is determined for the first printed sheet, and if curling occurs, it is determined that curling will occur in subsequent printing as well, and double-sided conveyance is performed. This makes it possible to omit the processes of S105 to S110 from the second printed sheet onward, thereby preventing delays in the processes.
On the other hand, the presence or absence of curling is determined for the first printed sheet, and if curling does not occur, it is determined that curling will not occur in subsequent printing, and single-sided conveyance is performed.

Note that when it is determined that curling has occurred on the first printed sheet, in the flow, this corresponds to the case where the determination in S103 is No and the determinations in S104 to S107 are Yes. In this case, although not described in the flow, the setting for double-sided conveyance is turned ON. In this embodiment, the initial value of the setting for double-sided conveyance is set to OFF.

The number of sheets to be printed in one job is not particularly limited and can be changed as appropriate, and may be one sheet or a plurality of sheets. The number of sheets in the case of a plurality of sheets is not particularly limited, but examples thereof include 100 sheets and 1000 sheets.

Note that when images are formed on both sides of the recording medium for the first sheet in a job, the judgments after S104 are not performed for the first sheet, so double-sided conveyance may not be performed in the job. For this, appropriate changes are made. For example, in the judgment of S104, "First printed sheet?" is set to Yes for the second and subsequent sheets." That is, the determination in S104 is made to be Yes at least once in the Job.

If it is determined in S104 that it is not the first printed sheet, the recording medium is discharged, and it is determined whether or not the job has ended (S111, S112).
If the determination in S104 is No, it means that it is determined that curling did not occur on the first printed sheet, and it is determined that curling will not occur on the second and subsequent printed sheets in the job, and double-sided conveyance is performed. paper is ejected.

In the judgment of S104, if it is the first printed sheet, it is judged whether or not the recording medium is detected by the distance measuring sensor (S105).
The reason for making such a determination is that there is a time difference until the recording medium heated by the fixing means reaches the measuring position of the distance measuring sensor, depending on the measuring position of the distance measuring sensor. By performing the determination, it becomes easier to cope with changes in the position of the distance measuring sensor.
In the determination of S105, if the recording medium is not detected by the distance measuring sensor, the process waits until it is detected.

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

In the determination of S106, if the specified time Tx has passed, the distance d1 detected by the distance measuring sensor is compared with the threshold value lx (S107).
lx is a threshold value for determining whether or not the image is curled. The threshold lx can be changed as appropriate depending on the type of recording medium. An example of lx is the distance from the range sensor to the recording medium when curl does not occur, as shown in FIG.

In the determination of S107, if d1>lx, it is determined that curling has occurred, reverse operation and double-sided conveyance are performed, and the back surface of the recording medium is heated by the heating mechanism (S108-S110). In this case, the setting for double-sided conveyance is turned ON. When the setting of double-sided conveyance is turned ON, the determination in S103 is YES for subsequent recording media, and double-sided conveyance is performed until the job is completed.

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

If d1>lx is not satisfied in the determination of S107, it is determined that curling has not occurred, and the recording medium is discharged without performing reversing operation or double-sided conveyance (S111). In this case, the setting of double-sided conveyance remains OFF. If the setting for double-sided transport is OFF, the determination in S103 will be No for subsequent recording media, and single-sided transport will be performed until the job ends, except when images are formed on both sides.

A supplementary description of this embodiment will be given below.
In the present embodiment, the distance measuring sensor is arranged above the ejected recording medium, but is not limited to this, and may be installed below the ejected recording medium, for example. In this case, it can be determined that curling occurs when d1<lx.

Further, in this 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 to arrange the heating roller and the pressure roller in such a manner as in the present embodiment. In this case, it becomes easier to obtain the amount of curl, and it is possible to accurately determine whether or not curl is occurring.

On the other hand, the heating roller and the pressure roller may be reversely arranged, 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 self weight of the recording medium acts downward.

In addition, as shown in FIG. 1, it is preferable that the paper ejection section 70 in the present embodiment secures a region where the recording medium hangs down so that the amount of curl can be measured. The discharge section 70 in this embodiment has a predetermined depth below the point where the recording medium is discharged from the fixing means, and the depth can be changed as appropriate.

Further, the paper discharge section 70 in this embodiment has a predetermined height above the point where the recording medium is discharged from the fixing means, and the height can be changed as appropriate. Having a predetermined height makes it easier for the curl amount measuring means to determine the curl amount.

As described above, the present embodiment provides an image forming method and 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 includes a transfer step of transferring a toner image onto a recording medium, a fixing step of heating the transferred toner image by a fixing means to fix it on the recording medium, and a toner image passing through the fixing means. a curl amount measuring step of measuring the curl amount of the recording medium; a reversing step of reversing the recording medium that has passed through the fixing means and passing through the fixing means again; and a control step of instructing the reversing means to perform a reversing operation according to the amount of curl.

The program of this embodiment causes a computer to execute the image forming method of this embodiment. In addition, the program of the present embodiment can be applied to an image forming apparatus having a transfer device, a fixing device, a curl amount measuring device, and a reversing device, according to the amount of curl of the recording medium having the toner image fixed on one side thereof. to execute a control process for selecting whether or not to instruct the reversing 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 embodiment are omitted.

FIG. 5 shows a flowchart for explaining this embodiment.
In this embodiment, the control unit changes the heating temperature of the fixing unit when reheating the reversed recording medium according to the curl amount.

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

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

In the determination of S122, if the double-sided printing operation is to be performed, the reverse operation is performed and the double-sided conveyance is performed (S126, S127). Further, the heating mechanism heats the back surface of the recording medium (S128). In the present embodiment, performing double-sided printing (Yes in S122) corresponds to forming images on both sides of the recording medium.

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

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

In this manner, by changing the reheating temperature in the fixing unit according to the curl amount threshold, it is possible to perform heating at a temperature suitable for preventing curling, thereby preventing overheating. Therefore, power consumption can be reduced while preventing curling.

In this embodiment, it is preferable to have storage means capable of holding a plurality of curl amount threshold values. The configuration of the storage means is not particularly limited, and can be changed as appropriate.

Note that the values in Table A (Table 1) are just an example, and the values are not limited to these, and can be changed as appropriate. For example, the threshold lx can be changed depending on the position of the distance measuring sensor, etc., and the heating temperature can be changed depending on the type of recording medium, the contact area and contact time between the heating roller and the recording medium, and the like. It is subject to change. In the case of lx≧125 [mm], for example, the temperature may be uniformly set to 160° C., and error processing may be performed assuming that such a case is not assumed.

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

If d1>lx is not satisfied in the determination of S125, it is determined that curling has not occurred, and the recording medium is discharged without performing reversing operation or double-sided conveyance (S129).

In this embodiment, it is not determined whether the Job has ended. As described above, in the present embodiment, the determination is made for each print medium, so that even when the amount of curl differs depending on the print medium, it is possible to optimally handle the situation.

(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 embodiment are omitted.
FIG. 6 shows a flow chart for explaining this embodiment.

The image forming apparatus according to the present embodiment includes a paper feeding unit that stores the recording medium before an image is formed, and a paper feeding unit heating unit that heats the recording medium accommodated in the paper feeding unit. The controller operates the paper feeding unit heating means when the amount of curl is equal to or greater than a predetermined value.
The present embodiment performs preferable control of the dehumidification heater 11 (paper feeding section heating means) in FIG.

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

Then, 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 in S135 is different from that in the second embodiment.
In the present embodiment, if d1>lx in the determination of S135, the paper feeding unit heating means is operated, or if already operating, the operation is continued (S136).

If d1>lx, curling occurs. 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 curling of subsequent recording media can be prevented. occurrence can be prevented. In addition, in the present embodiment, it is possible to perform an operation to prevent curling from the time the recording medium is fed, and there is no need to switch between double-sided conveyance to equalize the water content. As a result, it is possible to obtain the advantages of suppressing power consumption and preventing a decrease in productivity while preventing curling.

In the processing after S136, the reversing operation is performed and double-sided conveyance is performed (S138, S139) in the same manner as in the second embodiment. Further, the heating mechanism heats the back surface of the recording medium (S140).

On the other hand, if d1>lx is not satisfied in the determination of S135, it is determined that curling has not occurred, the paper feeding unit heating means is stopped, and the recording medium is discharged (S137, S141).
In this manner, power consumption can be suppressed by stopping the sheet feeding unit heating means when curling does not occur. When curling disappears when a certain number of sheets are printed, it can be considered that the recording medium stored in the paper feed unit is sufficiently dehumidified by the heating of the paper feed unit heating means.

Note that the heating temperature of the paper feed unit heating means can be changed as appropriate. Also, 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 embodiment are omitted.
FIG. 7 shows a flowchart for explaining this embodiment.

In the present embodiment, the curl amount measuring unit measures the curl amount for each number of printed sheets of the recording medium, and the control unit obtains a difference in the curl amount for each number of printed sheets of the recording medium, and determines the curl amount according to the difference. to select whether or not to instruct the reversing means to perform the reversing operation.

First, in this embodiment, after starting a job, the heating mechanism heats the surface of the recording medium (S101, S102). In this embodiment, as in the first embodiment, processing is performed on a job-by-job basis.
In the present embodiment, "for each number of printed sheets" means setting whether double-sided or single-sided conveyance is performed for each job.
Further, in this embodiment, the amount of curl is detected for each number of printed sheets, and depending on whether the difference in the detection result is equal to or less than a threshold value, paper transport is switched between double-sided transport and single-sided transport during printing. After the temperature difference is reduced by heat accumulation on the pressure roller side, it is not necessary to switch to double-sided conveyance, so it is possible to prevent curling and further reduce power consumption and productivity from the middle of printing.

Then, determinations of S152 to S156 are performed in the same manner as in the second and third embodiments.

Next, the curl amount difference 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 for which it is determined whether it is to be conveyed on both sides or one side, and the value of the distance measuring sensor obtained for the recording medium one sheet before this recording medium. Calculated by As shown in the figure, it can be obtained as "d1 - d1 one page before". In addition, it is preferable to have recording means for recording d1 of the previous sheet.

Then, a threshold is determined for the obtained difference (S158).
If the 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 measurement sensor of the recording medium is smaller than the value d1 of the distance measurement sensor of the previous sheet, so the curl is small. It's becoming This is thought to be due to the fact that the temperature difference in the recording medium is reduced due to heat accumulation on the pressure roller side, and curling is less likely to occur. In this case, double-sided conveyance is changed to single-sided conveyance.

Although the threshold value ly is not particularly limited, by setting a certain value, it is possible to reliably determine that curling is less likely to occur.

When it is determined in S158 that curling is occurring (when the determination in S158 is No), reversing operation and double-sided conveyance are performed, and the back surface of the recording medium is heated by the heating mechanism (S159 to S161). . It should be noted that the setting of double-sided conveyance is left ON here.

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

Next, the recording medium whose curling is suppressed is discharged (S166).
Next, it is determined whether or not the Job has ended (S167). If the job has not ended, the processes after S152 are 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 embodiment are omitted.
FIG. 8 shows a flow chart for explaining this embodiment.

In this embodiment, the control section 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 this embodiment, after starting printing, the paper type setting is read, and the threshold lx is set according to the result of reading the paper type setting (S171 to S173).
The paper type is set, for example, as shown in Table B (Table 2) below.

In Table 2, the thickness of the recording medium increases in order from 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 lx in Table 2 is not particularly limited and can be changed as appropriate. For example, it can be changed depending on the position where the distance measuring sensor is arranged.
In addition, it is preferable that a storage means for storing the setting of the table B is provided.

After S173, the processes of S174 to S181 are performed as in the second and third embodiments.
In S177, similarly to the above embodiment, d1>lx is determined, but lx set in S173 is used here. The method for grasping which paper type in 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 installed in the paper feed unit or the like. You may make it provide and judge.

The curl detection threshold is changed according to the type of paper used, and when the amount of curl exceeds the threshold, paper conveyance is switched to double-sided paper feeding, and the moisture content of the front and back surfaces of the paper is equalized by the fixing mechanism.
As a result, it is possible to more accurately determine whether the print medium hangs down due to its own weight or curls due to curling.
When it is determined that the recording medium curls due to its own weight and that curling does not occur, double-sided conveyance can be switched to single-sided conveyance, power consumption can be reduced, and productivity can be prevented from decreasing.

(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 embodiment are omitted.
FIG. 9 shows a flowchart for explaining this embodiment.

In the present embodiment, the control unit obtains the frequency of use of the type of recording medium that tends to curl based on the operation time of the paper feed unit heating unit and the amount of curl, The frequency is displayed on the display unit.
This embodiment further performs the processes of S201 to S205 in contrast to the third embodiment (FIG. 6).

First, as in the third embodiment, the determinations of S192 to S195 are performed after printing is started.
In the determination of S195, if d1>lx, as in the third embodiment, the paper feeding unit heating means is operated, or if the paper feeding unit heating means is already operating, the operation is continued. (S196).
If d1>lx, curling occurs. 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 water content can be made uniform. Therefore, it is not necessary to switch between double-sided paper feeding. As a result, it is possible to obtain the advantages of suppressing power consumption and preventing a decrease in productivity while preventing curling.

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

Next, the operation time of the paper feeding section heating means is obtained (S201).
The method of obtaining the operating time can be changed as appropriate, but for example, it can be obtained from the difference between the current time and the time at which the operation of the paper feed unit heating means is started.
In addition, it is preferable to provide a storage means for storing the time when the operation of the paper feed section heating means is started.

Next, it is determined whether or not the operation time of the paper feed 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. If it is longer than the predetermined time, that is, if the determination in S202 is "Yes", it is determined that a recording medium with a high water content has been used, and the usage history of the recording medium with a high water content is counted up (S203). .

Next, the number of counts of the use history of the recording medium with a large water content is determined (S204).
In S204, it is determined whether or not the counted number of times 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 five or more, but the present invention is not limited to this and can be changed as appropriate.

If it is determined in S204 that the counted number of times is equal to or greater than the predetermined number of times, the number of times the recording medium that tends to curl is replenished is notified and displayed (S205).
The destination of notification can be changed as appropriate, and for example, the display unit provided in the image forming apparatus of the present embodiment can be used. As the display unit, for example, a form such as a display or a touch panel is possible. Alternatively, the notification may be sent to a device other than the image forming device.
Upon receipt of the notification, the display unit displays the number of times paper that tends to curl has been replenished.

The form of display is not particularly limited, but it is preferable to perform a display that encourages improvement. For example, a message such as "Paper that curls easily is being replenished. It is recommended that you replenish paper that does not easily curl."
You may make it notify by logging information.

In the present embodiment, the fact that the rate of curl occurrence is high despite the fact that the operation time of the paper feed unit heating means is long means that the user of the image forming apparatus (user) supplies the recording medium with a high water content. It can be said that the probability of being replenished is high. In such a case, it can be recognized that the user often uses recording media stored in a place different from the temperature and humidity environment in which the apparatus is placed, and that the user frequently replenishes paper from the external environment. By grasping such a situation, it is possible to improve the paper supply from the outside environment that is not humidity-conditioned, which is one of the causes of curling.

On the other hand, if d1>lx is not satisfied in the determination of S195, it is determined that curling has not occurred, the paper feeding section heating means is stopped, and the recording medium is discharged (S197, S206).
In this way, when it is determined that curling does not occur, power consumption can be suppressed by stopping the paper feeding section heating means.

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

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

On the other hand, in the present embodiment as well, the curl amount measuring means measures the distance to the recording medium from above the recording medium, but the curl amount measuring means is configured differently than the distance measuring sensor. FIG. 10 shows a diagram for explaining this embodiment. FIG. 10 is a diagram for explaining an example in which the curl amount is detected using the filler 36 as the curl amount measuring means.

As in the above embodiment, when no curl occurs, the sheet is discharged without being curled as shown in FIG. 10A. On the other hand, when curling occurs, the sheet is ejected with a curl formed downward from the ejection port as shown in FIG. 10B.

In this embodiment, the filler 36 detects the curl at the time of paper ejection. If the recording medium touches the filler, it is assumed that curl does not occur and the paper is ejected as single-sided printing. Warming equalizes the water content on the front and back sides of the recording medium.

In the present embodiment, the amount of curl can be obtained not only by determining whether or not curling occurs, but also by appropriately changing the position at which the filler is arranged, the size and length of the filler, and the like.

(Eighth embodiment)
Next, another embodiment of the image forming apparatus according to the present invention will be described.
Descriptions of matters common to the above embodiment are 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 whether or not the recording medium is curled by using the transmission sensor. determine whether or not

FIG. 11 shows a diagram for explaining this embodiment. FIG. 11 is a diagram illustrating an example of means for detecting the amount of curl using a transmission sensor as the means for measuring the amount of curl.

As in the above embodiment, when no curl occurs, the sheet is discharged without being curled as shown in FIG. 11A. On the other hand, when curling occurs, the sheet is ejected with a curl formed downward from the ejection port as shown in FIG. 11B.

In this embodiment, the transmission sensors 34 and 35 detect the curl at the time of sheet ejection. In this embodiment, the transmission sensor is provided on the side surface of the recording medium that has passed through the fixing means.
As transmission sensors in this embodiment, a sensor 34 on the light projecting side and a sensor 35 on the light receiving side are used. When the projected light from the transmission sensor is received without being blocked by the curled recording medium, it is determined that no curl occurs and the paper is discharged as single-sided printing. On the other hand, when the projected light from the transmission sensor is blocked by the curled recording medium and is not received, it is determined that curling has occurred, and a switchback (reversal operation) is performed to switch to double-sided conveyance. When the double-sided conveyance is switched, the heating mechanism heats the back surface of the recording medium to equalize the water content of the front surface and the back surface of the recording medium.

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

The arrangement of the curl amount measuring means can be changed in addition to the example shown above.
For example, the distance measurement sensor 31 is not limited to being arranged as in the example shown in FIG. Further, as described above, the curl amount may be measured from below the print medium.

Moreover, it may be in contact with the paper discharge section 70 or may be separated therefrom. In the case of arranging it apart from the paper discharge section 70, the curl amount measuring means can be arranged on the lower surface of the image reading device 3 or the writing unit 4, for example.

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

1 image forming device 2 automatic document feeder (ADF)
3 image reading device 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 pressure roller 31 range sensor 60a, 60b recording medium 70 paper ejection unit 71 Eject guide 72 Eject tray

JP 2006-301192 A

Claims (8)

a transfer means for transferring the toner image onto a recording medium;
a fixing unit that heats the transferred toner image to fix it on the recording medium;
curl amount measuring means for measuring the curl amount of the recording medium that has passed through the fixing means;
a reversing unit that reverses the recording medium that has passed through the fixing unit and performs a reversing operation to pass the recording medium through the fixing unit again;
a control unit that selects whether or not to instruct the reversing unit to perform a reversing operation according to the amount of curl of the recording medium having the toner image fixed on one side thereof;
The control unit determines whether or not curling occurs on the first printed sheet, selects whether or not to instruct the reversing unit to perform a reversing operation for the first printed sheet according to the amount of curl, and The image forming apparatus, wherein the reversing operation instructed to the reversing means is the same reversing operation as the reversing operation for the first printed sheet. 2. The image forming apparatus according to claim 1, wherein the control unit changes a heating temperature of the fixing unit when reheating the reversed recording medium according to the curl amount. a paper feeding unit in which the recording medium before an image is formed is stored;
a paper feed unit heating means for heating the recording medium accommodated in the paper feed unit;
3. The image forming apparatus according to claim 1, wherein, when the amount of curling is equal to or greater than a predetermined value, the control section activates the heating section of the sheet feeding section. 4. The image forming apparatus according to any one of claims 1 to 3, wherein the control unit selects whether or not to instruct the reversing operation to the reversing unit according to the curl amount and type of the recording medium. . Based on the operation time of the paper feed unit heating means and the amount of curl, the control unit obtains the frequency of use of the type of recording medium that tends to curl, and displays the above information on the display unit provided in the image forming apparatus. 4. The image forming apparatus according to claim 3, wherein the frequency is displayed. 6. The curl amount measuring device according to claim 1, wherein the curl amount measuring unit measures the curl amount by measuring a distance from above the recording medium that has passed through the fixing unit. 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 determines whether or not the recording medium is curled by using the transmission sensor. 6. The image forming apparatus according to claim 1, wherein: a transfer step of transferring the toner image onto a recording medium;
a fixing step of heating the transferred toner image by fixing means to fix it on the recording medium;
a curl amount measuring step of 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 device by a reversing device and passing through the fixing device again;
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;
The control step determines whether or not curling occurs on the first printed sheet, selects whether or not to instruct the reversing means to perform a reversing operation for the first printed sheet according to the curl amount, and The image forming method, wherein the reversing operation instructed to the reversing means is the same reversing operation as the reversing operation for the first printed sheet.

Images