JP2021110792A - Image forming apparatus - Google Patents

Abstract

To provide an image forming apparatus that controls the timing to start fixing so as to avoid the timing at which temperature is suddenly reduced.SOLUTION: An image forming apparatus comprises: a fixing belt 173 that sandwiches and conveys a sheet; driving means that rotates the fixing belt 173; a heat source 172a that heats the fixing belt 173; a pressure roller 174 that applies pressure to the fixing belt 173; a temperature sensor 70 that detects the temperature of the pressure roller 174; and a control unit that controls operations. When the fixing belt 173 starts rotation, the control unit calculates a temperature difference being the difference between a temperature set in advance for the fixing belt 173 and the temperature of the pressure roller 174, and executes timing control of controlling the timing to start fixing with the fixing belt 173 based on the temperature difference.SELECTED DRAWING: Figure 3

Description

The present invention relates to an image forming apparatus that pressurizes and heats a paper to fix an unfixed image formed on the paper.

Conventionally, in a fixing device used in an electrophotographic image forming apparatus such as a copier or a printer, the toner image is fixed by pressurizing and heating a paper on which an unfixed toner image is formed. By the way, in the image forming apparatus, each part such as a motor and a heater is stopped in a standby state in which image forming is not continuously performed to save power. When image formation is performed from such a standby state, it waits for the temperature to rise to a temperature suitable for image formation, so that the waiting time may become long or the temperature may not rise sufficiently and the image quality may deteriorate. there were. Therefore, a method of forming an image in a short time without deteriorating the image quality has been proposed.

Japanese Unexamined Patent Publication No. 2009-103748

The image forming apparatus described in Patent Document 1 detects a temperature related to image formation in an image forming portion, and when the detected temperature reaches a predetermined temperature, allows paper to be conveyed to the image forming portion. There is. In the image forming apparatus described above, the determination is made only by the temperature of the fuser, and the sudden temperature fluctuation of the fuser is not taken into consideration. In the standby state where each part is stopped, heat from the heat source is not transferred, and local temperature unevenness occurs. Then, when the image forming apparatus starts to move, heat is transferred without being sufficiently heated, which may cause a sudden temperature drop (undershoot), and at this timing, fixing may be poor.

The present invention has been made to solve the above problems, and an object of the present invention is to provide an image forming apparatus that controls the timing of starting fixing so as to avoid the timing of sudden temperature drop.

The image forming apparatus according to the present invention is an image forming apparatus that pressurizes and heats a paper to fix an unfixed image formed on the paper, and includes a fixing member that sandwiches and conveys the paper, and the above-mentioned fixing member. A driving means for rotating the fixing member, a heat source for heating the fixing member, a pressure member for pressurizing the fixing member, a temperature sensor for detecting the temperature of the pressure member, and a control unit for controlling the operation. The control unit is provided with a temperature difference which is a difference between a temperature preset for the fixing member and a temperature of the pressurizing member detected by the temperature sensor when the fixing member starts to rotate. Is calculated, and based on the temperature difference, timing control for controlling the timing at which the fixing on the fixing member is started is performed.

In the image forming apparatus according to the present invention, the control unit may be configured to perform the timing control based on the result of determining whether or not the temperature difference is equal to or higher than a preset threshold value.

In the image forming apparatus according to the present invention, the control unit has a first time until the temperature of the fixing member drops and a second time until the fixing member starts fixing based on the temperature difference. The second time may be set longer than the first time.

The image forming apparatus according to the present invention includes a storage means for storing a timing table in which the temperature difference is associated with the second time, and the control unit determines the second time based on the timing table. It may be configured.

In the image forming apparatus according to the present invention, a plurality of the timing tables may be provided, and the control unit may be configured to select the timing table according to the conditions set for fixing.

The image forming apparatus according to the present invention may include a paper transporting means for transporting paper to the fixing member, and the control unit may be configured to control the timing for driving the paper transporting means in the timing control.

In the image forming apparatus according to the present invention, the control unit may be configured to output a first signal for causing the fixing member to start rotation and a second signal for causing the paper conveying means to convey paper.

In the image forming apparatus according to the present invention, the control unit may be configured to change the timing at which the fixing member starts fixing based on the temperature difference calculated after the fixing member starts rotating.

In the image forming apparatus according to the present invention, the control unit may be configured to control the timing at which the fixing member starts rotation according to the image formed on the paper.

In the image forming apparatus according to the present invention, the control unit may be configured to perform the timing control when it is determined that the stopped fixing member has started rotation.

According to the present invention, by controlling the timing at which the fixing starts to be fixed so as to avoid the timing at which the fixing member starts to move and the temperature suddenly drops, it is possible to prevent the fixing failure due to insufficient temperature.

It is a schematic block diagram which shows the image forming apparatus which concerns on embodiment of this invention. It is a schematic plan view which shows by extracting the main part of the fixing device. It is a schematic side view which shows by extracting the main part of the fixing device. It is a characteristic diagram which shows the relationship between the timing at which each part operates and the transition of temperature in the conventional control. It is a characteristic figure which shows the relationship between the timing at which each part operates and the transition of temperature in the control in embodiment of this invention. It is a flow chart which shows the control flow at the time of image formation by the image forming apparatus which concerns on this embodiment.

Hereinafter, the image forming apparatus according to the embodiment of the present invention will be described with reference to the drawings.

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

The image forming apparatus 1 forms a multicolored and monochromatic image on a predetermined paper according to the image data transmitted from the outside, and exposes the exposure apparatus 11, the developing apparatus 12, the photoconductor drum 13, and the cleaner apparatus 14. It is configured to include a charger 15, an intermediate transfer belt device 16, a fixing device 17, a paper feed cassette 18, and a paper output tray 19.

The image data handled in this image forming apparatus corresponds to a color image using each color of black (K), cyan (C), magenta (M), and yellow (Y). Therefore, four developing devices 12, a photoconductor drum 13, a charging device 15, and a cleaner device 14 are provided so as to form four types of latent images corresponding to each color, and the colors are black, cyan, magenta, and yellow, respectively. It is set and these make up four image stations.

The photoconductor drum 13 is arranged substantially in the center of the image forming apparatus 1. The charger 15 uniformly charges the surface of the photoconductor drum 13 to a predetermined potential. The exposure apparatus 11 exposes the surface of the photoconductor drum 13 to form an electrostatic latent image. The developing device 12 develops an electrostatic latent image on the surface of the photoconductor drum 13 to form a toner image on the surface of the photoconductor drum 13. By the series of operations described above, toner images of each color are formed on the surface of each photoconductor drum 13. The cleaner device 14 removes and recovers residual toner on the surface of the photoconductor drum 13 after development and image transfer.

The intermediate transfer belt device 16 is arranged above the photoconductor drum 13, and includes an intermediate transfer belt 21, an intermediate transfer belt drive roller 22, an intermediate transfer belt driven roller 23, an intermediate transfer roller 24, an intermediate transfer belt cleaning device 25, and a tension. It is equipped with a roller 26. It should be noted that four intermediate transfer rollers 24 are provided corresponding to the image stations of each color for YMCK.

The intermediate transfer belt drive roller 22, the intermediate transfer belt driven roller 23, the intermediate transfer roller 24, and the tension roller 26 stretch the intermediate transfer belt 21 and set the surface of the intermediate transfer belt 21 in a predetermined direction (direction of arrow C in the drawing). ) Is configured to move.

The intermediate transfer belt 21 orbits in the direction of the arrow C, the residual toner is removed and recovered by the intermediate transfer belt cleaning device 25, and the toner images of each color formed on the surface of each photoconductor drum 13 are sequentially transferred. A color toner image is formed on the surface of the intermediate transfer belt 21.

The transfer roller 27a of the secondary transfer device 27 has a nip area formed between the transfer roller 27a and the intermediate transfer belt 21, and conveys the paper P conveyed through the sheet transfer path S by sandwiching it in the nip area. When the paper P passes through the nip area, the toner image on the surface of the intermediate transfer belt 21 is transferred.

The paper feed cassette 18 is a cassette for storing the paper P used for image formation, and is provided under the exposure apparatus 11. Further, the output tray 19 is provided on the upper side of the image forming portion 1a, and is a tray on which the image-formed paper P is placed.

Further, in the image forming apparatus 1, the paper P of the paper feed cassette 18 is sent to the output tray 19 via the secondary transfer device 27 and the fixing device 17 through the sheet transport path S. A paper feed roller 31, a resist roller 32 (an example of a paper transport means), a pre-resist roller 33, a fixing device 17, and a paper discharge roller 34 are arranged along the sheet transport path S.

The paper feed roller 31 is provided near the end of the paper feed cassette 18, and supplies the paper P one by one from the paper feed cassette 18 to the sheet transport path S. The resist roller 32 temporarily holds the paper P conveyed from the paper feed cassette 18, and conveys the paper P to the transfer roller 27a at the timing of aligning the tip of the toner image on the photoconductor drum 13 with the tip of the paper P. .. The pre-resist roller 33 is a small roller for promoting and assisting the transport of the paper P.

The fixing device 17 is a belt fixing type fixing device, and a fixing belt 173 (an example of a fixing member) is wound around a plurality of rollers (here, a fixing roller 171 and a heating roller 172). The fixing belt 173 can transfer heat from the heating roller 172 to the fixing roller 171. In the fixing device 17, the pressure roller 174 (an example of the pressure member) is pressed against the fixing roller 171 via the fixing belt 173. The fixing device 17 is connected to a driving means such as a motor (not shown). The driving means rotates, for example, the fixing roller 171, and as the fixing roller 171 rotates, the fixing belt 173, the heating roller 172, and the pressure roller 174 are driven. The rotation by the driving means is not limited to the fixing roller 171. Other rollers may be rotated, or a plurality of rollers may be rotated in synchronization with each other. The fixing device 17 receives the paper P on which the unfixed toner image is formed, sandwiches the paper P between the fixing belt 173 and the pressure roller 174, and conveys the paper P. A first fixing sensor 50 and a second fixing sensor 60 are provided in the vicinity of the fixing belt 173. A temperature sensor 70 is provided in the vicinity of the pressure roller 174. The fixed paper P is discharged onto the output tray 19 by the output roller 34.

Next, the fixing device 17 in the image forming device 1 will be described with reference to the drawings.

FIG. 2 is a schematic plan view showing the main part of the fixing device extracted, and FIG. 3 is a schematic side view showing the main part of the fixing device extracted.

In FIGS. 2 and 3, the fixing roller 171, the heating roller 172, the fixing belt 173, the pressure roller 174, and the like are extracted from the fixing device 17 shown in FIG. A heat source 172a such as a heater is housed inside the heating roller 172. The heat generated by the heat source 172a warms the heating roller 172 and the fixing belt 173. The fixing belt 173 is moved by the fixing roller 171 and the heating roller 172, and the portion close to the heat source 172a is gradually displaced to warm the whole.

The first fixing sensor 50 and the second fixing sensor 60 are provided in the vicinity of the heating roller 172 and facing the fixing belt 173. The first fixing sensor 50 and the second fixing sensor 60 are separated from each other in the width direction along the rotation axis of the heating roller 172. Specifically, the first fixing sensor 50 faces the center of the heating roller 172 in the width direction, and detects the temperature at the center of the fixing belt 173. The second fixing sensor 60 faces the end portion of the heating roller 172 in the width direction, and detects the temperature of the end portion of the fixing belt 173. The temperature sensor 70 is provided facing the pressure roller 174 and detects the temperature of the pressure roller 174. The detection results of the first fixing sensor 50, the second fixing sensor 60, and the temperature sensor 70 are output to a control unit (for example, a CPU or the like, which is not shown) of the image forming apparatus 1.

In the image forming apparatus 1, the temperature of the fixing belt 173 changes depending on the timing at which each part operates, and the temperature is controlled to be the instructed temperature by switching the heat source 172a on and off. Further, in the image forming apparatus 1, if the time during which the image forming is not performed continues for a long time, the image forming apparatus 1 shifts to the standby state and stops the operation of each part to save power. Specifically, in the fixing belt 173, since the rotation is stopped, the temperature is kept relatively high in the portion close to the heat source 172a, but the temperature is lowered in the portion far from the heat source 172a, and a temperature difference occurs. There is. In the conventional control, when the fixing belt 173 is rotated when the image is formed from the standby state, the temperature may drop sharply due to the generated temperature difference.

FIG. 4 is a characteristic diagram showing the relationship between the timing at which each part operates and the transition of temperature in the conventional control.

In FIG. 4, the upper part shows the timing at which each part operates, and the lower part shows the transition of temperature, indicating that time elapses along the direction from left to right in the drawing. There is. The upper part of FIG. 4 shows the operations of image processing, MM (various motors), paper feed pickup, resist roller, laser, and FUM. In the lower part of FIG. 4, the temperature of the fixing belt 173 (fixing temperature UM) detected by the first fixing sensor 50 and the second fixing sensor 60 and the temperature of the pressurizing roller 174 detected by the temperature sensor 70 (pressurizing temperature LM). )It is shown.

The image processing indicates processing for the image data received by the image forming apparatus 1, and the control unit generates a signal to be output to each unit based on the image data. The control unit outputs a signal generated by image processing to each unit, and an image is formed on paper based on this signal. FIG. 4 shows a transition from the time when the image formation is instructed in the standby state in the initial stage, and the image processing is started when the image formation is instructed. Then, at the time T1 when a predetermined time has elapsed from the initial stage, the control unit outputs a first signal to start the rotation of the fixing belt 173. Further, the image processing is completed at the time T2 when a predetermined time has elapsed from the time T1, and the control unit outputs a second signal for conveying the paper to the resist roller 32. In the following, for the sake of explanation, the time from the time T1 to the time T2 may be referred to as the first time ST1.

The MM indicates a motor that operates each part, and each part operates by transmitting the power from this motor. A clutch or the like is provided between the motor and each part, and the timing of transmitting power can be appropriately controlled. The MM is initially turned off and stopped, and at time T1, it receives the first signal, turns on, and starts operating. After the time T1, the MM may be appropriately stopped after the image formation is completed, or may continue to operate in preparation for the next image formation.

The paper feed pickup corresponds to the paper feed roller 31 shown in FIG. 1, and when it operates, the paper is conveyed from the paper feed cassette 18 to the resist roller 32. The paper feed pickup is initially turned off and stopped, and at time T1, power from the motor is transmitted to turn it on and start operating. In FIG. 4, the paper feed pickup is turned off at time T2 after the paper is conveyed.

The resist roller corresponds to the resist roller 32 shown in FIG. 1, and when it operates, it conveys the paper to the transfer roller 27a. That is, by operating the resist roller 32, the toner image is transferred and fixed on the paper. The resist roller is initially turned off and stopped, and at time T2, the power from the motor is transmitted to turn it on and start operating, and after operating for a predetermined time until the paper is conveyed, it is turned off. ..

The laser corresponds to the exposure apparatus 11 shown in FIG. 1, and when it operates, it starts forming an electrostatic latent image based on image data. That is, the exposure apparatus 11 operates in synchronization with the resist roller 32 to form an image on paper. The laser is initially turned off and stopped, and at time T2 it is turned on and started operating, and is turned off after the exposure to the photoconductor drum 13 is complete.

The FUM corresponds to the fixing device 17 shown in FIG. 1, and when operated, the fixing belt 173 is rotationally driven. The drive means connected to the fixing device 17 may be a motor common to the paper feed roller 31 or the like, or a motor independent of other parts. The FUM is initially turned off and stopped, and at time T1, it is turned on and starts operating, and after time T2, it is turned off after operating for a predetermined time until the fixing to the paper is completed.

In the image forming apparatus 1, the first temperature TE1 is set in advance as the temperature of the fixing belt 173 in the standby state, and the heat source 172a is repeatedly turned on and off to maintain a temperature close to the first temperature TE1. It is controlled to. In the present embodiment, the first temperature TE1 is set to about 165 ° C. Further, when fixing, the second temperature TE2 is set in advance as the temperature of the fixing belt 173, and it is controlled to maintain a temperature close to the second temperature TE2 in the same manner as the first temperature TE1. .. The second temperature TE2 may be set to a temperature having a predetermined range, and in the present embodiment, the second temperature TE2 is set to a range of 5 ° C. in total before and after around 175 ° C. .. Further, during fixing, the temperature is likely to fluctuate due to contact between the fixing belt 173 and the paper, and therefore the temperature may be changed in a wider range than in the standby state.

Next, the transition between the fixing temperature UM and the pressurizing temperature LM will be described in detail. From the initial stage to the time T1, the fixing temperature UM has changed around the first temperature TE1, and the pressurizing temperature LM keeps a temperature lower than the first temperature TE1. That is, since the fixing belt 173 is not rotating until the time T1, the heat transfer to the pressure roller 174 is suppressed, and the pressure temperature LM does not fluctuate much.

Since the fixing belt 173 started to rotate from the time T1, the fixing temperature UM could not catch up with the heating in the heat source 172a and rapidly decreased to the lowest temperature in the time T2. Further, the pressurization temperature LM gradually rises from the time T1 to the time T2 by transferring the heat from the fixing belt 173.

After the time T2, the fixing temperature UM rapidly rises to reach the second temperature TE2, and is then controlled to maintain the vicinity of the second temperature TE2. The pressurization temperature LM is slightly lowered when the fixing is performed, but the heat from the fixing belt 173 is transferred, so that the temperature is maintained higher than that in the standby state.

In the conventional control shown in FIG. 4, the resist roller 32 passes the paper immediately after the time T2, and the fixing is performed at a temperature lower than the second temperature TE2. As a result, due to insufficient temperature, incomplete fixing may occur, resulting in poor fixing. In order to avoid such fixing defects, in the present embodiment, the timing at which each part operates is controlled so that the fixing is performed after the undershoot is exceeded.

FIG. 5 is a characteristic diagram showing the relationship between the timing at which each part operates and the transition of temperature in the control according to the embodiment of the present invention.

FIG. 5 shows substantially the same items as those in FIG. 4, and the timings at which the respective parts shown in the upper row operate are different. Therefore, items different from those in FIG. 4 will be described in detail, and description of the same items will be omitted.

Specifically, in FIG. 5, the timing at which the resist roller and the laser are turned on is different from that in FIG. The resist roller and the laser are turned on and started to operate at a time T3 when a predetermined time elapses from the time T2, and are turned off after operating for a time corresponding to image formation. That is, in the control of the present embodiment, the timing control for delaying the timing for starting the image formation is performed as compared with the conventional control. The fixing temperature UM was the lowest temperature at the time T2, but increased to a temperature close to the second temperature TE2 at the time T3 when the time elapsed. Therefore, when the image formation is started from the time T3, the temperature of the fixing belt 173 is stable, and the fixing can be performed without any problem. In the following, for the sake of explanation, the time from the time T1 to the time T3 may be referred to as the second time ST2.

The second time ST2 is longer than the first time ST1, and even if the image processing is completed and the image formation is ready, there is a time to wait without starting the image formation. During the time T2 to the time T3, the paper may be stopped and made to stand by, for example, immediately before the resist roller 32. In the present embodiment, the first time ST1 is set to about 4 seconds and the second time ST2 is set to about 6 seconds, but the present invention is not limited to this, and is appropriately adjusted according to the transition of the fixing temperature UM. Just do it. The image forming apparatus 1 has a storage means for storing a timing table in which the temperature difference and the second time ST2 are associated with each other, and the control unit refers to the timing table when performing the timing control, and the second Determine the time ST2. Therefore, the second time ST2 can be easily determined by referring to the timing table.

As described above, the control unit outputs a first signal for starting the rotation of the fixing belt 173 and a second signal for conveying the paper to the resist roller 32. In the timing control shown in FIG. 5, the first signal is output at time T1 and the second signal is output at time T3. Since the fixing belt 173 and the resist roller 32 are controlled by different signals in this way, the timing of outputting the signals can be easily adjusted.

FIG. 6 is a flow chart showing a control flow when an image is formed by the image forming apparatus according to the present embodiment.

In the control flow shown in FIG. 6, the execution of image formation is instructed at the start of processing.

In step S01, the temperature sensor 70 detects the temperature of the pressurizing roller 174.

In step S02, the control unit calculates the temperature difference. Here, the temperature difference indicates the difference between the temperature preset for the fixing belt 173 and the temperature of the pressure roller 174. Regarding the set temperature of the fixing belt 173, for example, when the image forming apparatus 1 is in the standby state, it corresponds to the first temperature TE1 shown in FIG. In the present embodiment, the temperature difference is calculated when the fixing belt 173 starts to rotate. For example, in the case shown in FIG. 5, the difference between the first temperature TE1 and the pressurizing temperature LM at time T1 is the temperature difference.

In step S03, the control unit determines whether or not the temperature difference exceeds the threshold value. Here, the threshold value is set in advance according to the transition of the fixing temperature UM and the pressurizing temperature LM, and is set to 40 ° C. in the present embodiment, but the threshold value is not limited to this and may be changed as appropriate. good. If the temperature difference exceeds the threshold value as a result of the determination by the control unit (step S03: Yes), the process proceeds to step S04. On the other hand, if the temperature difference does not exceed the threshold value (step S03: No), the process proceeds to step S05.

In step S04, the control unit controls the timing of the start of fixing. That is, the control unit performs the timing control described above, and determines the second time ST2 so as to avoid undershoot.

In step S05, the control unit causes the fixing device 17 to start fixing. When the fixing is completed, the process ends.

As described above, the control unit has a temperature that is the difference between the temperature preset for the fixing belt 173 and the temperature of the pressurizing roller 174 (pressurizing temperature LM) when the fixing belt 173 starts to rotate. The difference is calculated, and based on the temperature difference, timing control is performed to control the timing at which the fixing on the fixing belt 173 is started. According to this configuration, by controlling the timing of starting the fixing so as to avoid the timing when the fixing belt 173 starts to move and the temperature suddenly drops, it is possible to prevent the fixing failure due to insufficient temperature.

Further, the control unit performs timing control based on the result of determining whether or not the temperature difference is equal to or higher than a preset threshold value. That is, by setting a threshold value according to the temperature difference, timing control can be performed at an appropriate opportunity.

Further, the control unit determines, based on the temperature difference, the first time ST1 until the temperature of the fixing belt 173 drops and the second time ST2 until the fixing belt 173 starts fixing. For the first hour ST1, a value based on the previously detected transition of the fixing temperature UM may be attached to the timing table. In the timing table, the second time ST2 is set longer than the first time ST1. As a result, by starting the fixing after the timing when the temperature of the fixing belt 173 drops has passed, it is possible to more reliably prevent the fixing failure due to the insufficient temperature.

Further, the control unit is configured to control the timing for driving the resist roller 32 in the timing control. Therefore, by controlling the timing at which the paper reaches the fixing belt 173, it is possible to avoid a temperature shortage in the fixing belt 173.

Further, when the control unit determines that the stopped fixing belt 173 has started to rotate, the control unit performs timing control. Whether or not the fixing belt 173 is stopped can be determined by, for example, the temperature difference, and if the temperature difference is sufficiently large, it can be determined that the fixing belt 173 is in the stopped standby state. Further, not limited to this, it can be determined whether or not the fixing belt 173 is stopped by the instruction status to each part, and it is said that a sufficient time has passed since the instruction to stop the fixing belt 173 was issued. , The image forming apparatus 1 shifts to the standby state. In the image forming apparatus 1, undershoot is likely to occur at the start of rotation in which the temperature is not stable. Therefore, if timing control is performed accordingly, stable fixing can be performed.

In the timing control described above, the temperature of the pressure roller 174 is used when calculating the temperature difference, which is based on the positional relationship between the heat source 172a and the pressure roller 174. In the present embodiment, the temperature of the fixing belt 173 (particularly in the vicinity of the heating roller 172) changes significantly due to the on / off switching of the heat source 172a. On the other hand, the pressure roller 174 is indirectly heated by the heat source 172a, and the change in temperature is suppressed in response to the on / off switching of the heat source 172a. That is, since the temperature of the pressurizing roller 174 changes slowly, the longer the standby state, the easier it is to stay at a constant temperature, and the temperature difference becomes a constant value, which is suitable as a reference for comparison with the threshold value.

In the present invention, the present invention is not limited to the above-described configuration, and a plurality of timing tables may be provided, and the control unit may select the timing table according to the conditions set for fixing (image formation). .. Regarding the image formation conditions, for example, in the timing table according to the size of the paper, the second time ST2 may be set to become longer as the size of the paper increases. Further, the environmental temperature and humidity in which the image forming apparatus 1 is installed may be set as the image forming conditions, and a timing table in which the temperature difference and the second time ST2 are different may be provided according to the temperature and humidity. In this way, control can be optimized by preparing a timing table that takes into account various factors such as the size of the paper, the installation environment of the device, and the operating status of the device.

Further, in FIG. 5, the configuration for determining the second time ST2 at the time T1 has been described, but the present invention is not limited to this, and the control unit fixes the fixing belt 173 based on the temperature difference calculated after the fixing belt 173 starts rotating. The timing at which the fixing on the belt 173 is started may be changed. That is, even after the first signal is output, the temperature difference at that time may be calculated to adjust the second time ST2. In this way, by reflecting the change in the temperature difference while the fixing belt 173 is rotating in the timing control, fixing can be performed at the optimum timing according to the situation.

Further, the control unit may control the timing at which the fixing belt 173 starts rotating according to the image formed on the paper. That is, the processing time in the image processing changes depending on the image, and the timing at which the fixing can be performed changes. Therefore, by reflecting this in the control, the operation can be optimized. The image processing time varies depending on, for example, the number of images, the amount of data, the printing rate, the presence or absence of photographs, and the like. The timing of outputting the first signal may be determined according to the image data in consideration of the above-mentioned matters. For example, whether to output at the time of 50% processing or at the time of 80% processing of the entire image data. It may be adjusted dynamically, such as by selecting.

Further, the control may be such that the timing at which the fixing is started differs depending on the size of the paper on which the image is formed. For example, when using a large size paper, the temperature difference according to the paper size is calculated, and the second time ST2 is lengthened to delay the start of fixing until the timing at which stable fixability can be ensured. Further, the timing may be adjusted in consideration of the printing rate, and when the printing rate is low, the second time ST2 may be shortened so that the fixing may be performed without a delay.

In the present embodiment, the fixing device 17 which is a belt fixing method has been described, but the present invention is not limited to this, and other fixing methods such as a configuration in which the pressure roller 174 is directly pressed against the fixing roller 171 can also be used. It can be applied in common.

It should be noted that the embodiments disclosed this time are examples in all respects and do not serve as a basis for limited interpretation. Therefore, the technical scope of the present invention is not construed solely by the embodiments described above, but is defined based on the description of the claims. It also includes all changes within the meaning and scope of the claims.

1 Image forming device 17 Fixing device 171 Fixing roller 172 Heating roller 172a Heat source 173 Fixing belt (an example of fixing member)
174 Pressurizing roller (an example of pressurizing member)
32 Resist roller 70 Temperature sensor

Claims (10)

An image forming apparatus for fixing an unfixed image formed on the paper by pressurizing and heating the paper.
A fixing member that holds and conveys paper,
A driving means for rotating the fixing member and
A heat source for heating the fixing member and
A pressure member that pressurizes the fixing member and
A temperature sensor that detects the temperature of the pressure member and
Equipped with a control unit to control the operation
The control unit calculates a temperature difference, which is the difference between the temperature preset for the fixing member and the temperature of the pressurizing member detected by the temperature sensor when the fixing member starts rotating. An image forming apparatus, characterized in that, based on the temperature difference, timing control for controlling the timing at which fixing on the fixing member is started is performed. The image forming apparatus according to claim 1.
The control unit is an image forming apparatus, characterized in that the timing control is performed based on the result of determining whether or not the temperature difference is equal to or higher than a preset threshold value. The image forming apparatus according to claim 1 or 2.
Based on the temperature difference, the control unit determines a first time until the temperature of the fixing member drops and a second time until the fixing member starts fixing.
An image forming apparatus characterized in that the second time is set longer than the first time. The image forming apparatus according to claim 3.
A storage means for storing a timing table in which the temperature difference is associated with the second time is provided.
The control unit is an image forming apparatus, characterized in that the second time is determined based on the timing table. The image forming apparatus according to claim 4.
A plurality of the timing tables are provided.
The control unit is an image forming apparatus characterized in that the timing table is selected according to the conditions set for fixing. The image forming apparatus according to any one of claims 1 to 5.
A paper transporting means for transporting paper to the fixing member is provided.
The control unit is an image forming apparatus characterized in that, in the timing control, the timing for driving the paper transport means is controlled. The image forming apparatus according to claim 6.
The control unit is an image forming apparatus characterized in that it outputs a first signal for causing the fixing member to start rotation and a second signal for causing the paper conveying means to convey paper. The image forming apparatus according to any one of claims 1 to 7.
The control unit is an image forming apparatus, characterized in that the timing at which the fixing member starts fixing is changed based on the temperature difference calculated after the fixing member starts rotating. The image forming apparatus according to any one of claims 1 to 8.
The control unit is an image forming apparatus characterized in that it controls the timing at which the fixing member starts rotation according to the image formed on the paper. The image forming apparatus according to any one of claims 1 to 9.
The control unit is an image forming apparatus characterized in that when it is determined that the stopped fixing member has started to rotate, the timing control is performed.

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