JP2023025780A - Image forming apparatus and temperature control method - Google Patents

Abstract

To provide an image forming apparatus and a temperature control method that can prevent heat supply from a heater from becoming excessive and prevent the occurrence of fixing failure.SOLUTION: An image forming apparatus comprises: axing fi belt 41; a temperature sensor 45 that detects the temperature of a partial area 41A of the fixing belt 41 in an axial direction of the rotation axis of the fixing belt 41; a drive control unit that controls the drive of a heater that heats the fixing belt 41 on the basis of the difference between a temperature detected by the temperature sensor 45 and a target temperature; a toner amount acquisition unit that acquires the amount of toner brought into contact with the partial area 41A in a specific period; and a temperature changing unit that, after the beginning of the specific period, changes the target temperature to a specific temperature based on the amount of toner acquired by the toner amount acquisition unit.SELECTED DRAWING: Figure 4

Description

The present invention relates to an electrophotographic image forming apparatus and a temperature control method executed in the image forming apparatus.

An electrophotographic image forming apparatus includes a fixing device that fixes a toner image transferred to a sheet onto the sheet. The fixing device includes a fixing member such as a fixing belt, a temperature sensor, and a drive control section. The temperature sensor detects the temperature of a predetermined partial region of the fixing member in the axial direction of the rotation shaft of the fixing member. The drive control section controls the driving of the heater that heats the fixing member based on the difference between the temperature detected by the temperature sensor and a preset target temperature.

In this type of fixing device, when a large amount of toner is in contact with the partial area of the fixing member, heat may be excessively supplied by the heater to an area of the fixing member other than the partial area. On the other hand, an image forming apparatus is known as a related art that changes the target temperature so that the target temperature becomes lower within a predetermined specific range as the amount of toner contacting the partial area increases. (See Patent Document 1).

Japanese Patent Application Laid-Open No. 2018-13612

However, in the image forming apparatus according to the above-described related technology, before the sheet contacts the fixing member, the temperature of the fixing member changes based on the amount of toner in the contact area of the sheet that contacts the partial area. The target temperature is adjusted. Therefore, when the target temperature after the change is near the lower limit of the specific range, that is, when the amount of toner in the contact area is close to the upper limit, contact with the contact area causes the temperature of the partial area to rise to the specific range. It may fall below the lower limit of the range and cause poor fixing.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming apparatus and a temperature control method capable of suppressing excessive heat supply by a heater and suppressing the occurrence of poor fixing.

An image forming apparatus according to one aspect of the present invention includes a fixing member, a heater, a temperature sensor, a drive control section, a toner amount acquisition section, and a temperature change section. The fixing member is rotatably provided, contacts the sheet to which the toner image has been transferred, and heats the sheet. The heater heats the fixing member. The temperature sensor detects the temperature of a predetermined partial region of the fixing member in the axial direction of the rotation shaft of the fixing member. The drive control unit controls driving of the heater based on a difference between the temperature detected by the temperature sensor and a preset target temperature. The toner amount acquisition unit acquires the amount of toner that contacts the partial area during a predetermined specific period. The temperature change section changes the target temperature to a specific temperature based on the amount of toner acquired by the toner amount acquisition section after the beginning of the specific period.

A temperature adjusting method according to another aspect of the present invention includes a fixing member that is rotatably provided and contacts a sheet on which a toner image has been transferred to heat the sheet, a heater that heats the fixing member, and the fixing member. a temperature sensor for detecting the temperature of a predetermined partial region of the fixing member in the axial direction of the rotation shaft of the fixing member; a drive control unit for controlling drive, and includes a toner amount acquisition step and a temperature change step. In the toner amount acquisition step, the amount of toner contacting the partial area during a predetermined specific period is acquired. In the temperature changing step, the target temperature is changed to a specific temperature based on the toner amount acquired by the toner amount acquiring step after the start of the specific period.

According to the present invention, it is possible to suppress excessive heat supply from the heater and to suppress the occurrence of poor fixing.

FIG. 1 is a diagram showing the configuration of an image forming apparatus according to an embodiment of the invention. FIG. 2 is a block diagram showing the system configuration of the image forming apparatus according to the embodiment of the invention. FIG. 3 is a diagram showing the configuration of the fixing device of the image forming apparatus according to the embodiment of the invention. FIG. 4 is a diagram showing the positional relationship among the fixing belt, temperature sensor, and sheet of the image forming apparatus according to the embodiment of the invention. FIG. 5 is a flowchart showing an example of temperature control processing executed by the image forming apparatus according to the embodiment of the invention.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. It should be noted that the following embodiment is an example that embodies the present invention, and does not limit the technical scope of the present invention.

[Configuration of Image Forming Apparatus 100]
First, the configuration of an image forming apparatus 100 according to an embodiment of the present invention will be described with reference to FIGS. 1 and 2. FIG. Here, FIG. 1 is a sectional view showing the configuration of the image forming apparatus 100. As shown in FIG.

For convenience of explanation, the vertical direction in the installation state (the state shown in FIG. 1) in which the image forming apparatus 100 can be used is defined as the up-down direction D1. A front-rear direction D2 is defined with the left side of the image forming apparatus 100 shown in FIG. 1 as the front side. Further, the horizontal direction D3 is defined with reference to the front of the image forming apparatus 100 in the installed state.

The image forming apparatus 100 has multiple functions such as a scanning function for reading an image of a document, a printing function for forming an image on a sheet 200 (see FIG. 1) based on image data, a facsimile function, and a copying function. machine. The present invention can be applied to printers, facsimiles, copiers, and the like that form images by electrophotography.

As shown in FIGS. 1 and 2, the image forming apparatus 100 includes an ADF (Auto Document Feeder) 1, an image reading section 2, an image forming section 3, a paper feeding section 4, an operation display section 5, a storage section 6, and A control unit 7 is provided.

ADF 1 conveys a document whose image is to be read by image reading section 2 . The ADF 1 includes a document set section, a plurality of transport rollers, a document presser, and a paper discharge section.

The image reading section 2 realizes the scanning function. The image reading unit 2 reads an image from a document conveyed by the ADF 1 and outputs image data including the read image. Further, the image reading section 2 reads an image from a document placed on a document platen and outputs image data including the read image. The image reading unit 2 includes the document platen, a light source, a plurality of mirrors, an optical lens, and a CCD (Charge Coupled Device).

The image forming section 3 realizes the printing function. Specifically, the image forming unit 3 forms an image by electrophotography. The image forming section 3 forms an image based on the image data output by the image reading section 2 . Further, the image forming section 3 forms an image based on image data input from an external communication device.

The paper feeding section 4 supplies the sheet 200 (see FIG. 1) to the image forming section 3 . The paper feeding unit 4 includes a paper feeding cassette 31, a paper feeding unit 32, a sheet conveying path 33, a pair of registration rollers 34, and a pair of discharge rollers 35 shown in FIG. The sheet feeding unit 4 conveys the sheet 200 accommodated in the sheet feeding cassette 31 through the sheet conveying path 33 in the conveying direction D5 (see FIG. 1) toward the discharge tray 29 (see FIG. 1).

The operation display unit 5 is a user interface of the image forming apparatus 100 . The operation display unit 5 includes a display unit such as a liquid crystal display for displaying various information according to control instructions from the control unit 7, and operation keys or a touch panel for inputting various information to the control unit 7 according to user operations. It has an operation part such as

The storage unit 6 is a nonvolatile storage device. For example, the storage unit 6 is a storage device such as non-volatile memory such as flash memory and EEPROM (registered trademark), SSD (Solid State Drive), and HDD (Hard Disk Drive).

The control unit 7 controls the image forming apparatus 100 as a whole. As shown in FIG. 2, the control unit 7 includes a CPU 11, a ROM 12, and a RAM 13. The CPU 11 is a processor that executes various kinds of arithmetic processing. The ROM 12 is a non-volatile storage device in which information such as control programs for causing the CPU 11 to execute various processes is stored in advance. The RAM 13 is a volatile or nonvolatile storage device used as a temporary memory (work area) for various processes executed by the CPU 11 . In the control unit 7 , various control programs stored in advance in the ROM 12 are executed by the CPU 11 . Thereby, the control unit 7 controls the image forming apparatus 100 in an integrated manner. Note that the control unit 7 may be configured by an electronic circuit such as an integrated circuit (ASIC). Further, the control unit 7 may be a control unit provided separately from the main control unit that controls the image forming apparatus 100 in an integrated manner.

[Configuration of Image Forming Unit 3]
Next, the configuration of the image forming section 3 will be described with reference to FIG.

As shown in FIG. 1, the image forming section 3 includes a plurality of image forming units 21 to 24, an optical scanning device 25, an intermediate transfer belt 26, a secondary transfer roller 27, a fixing device 28, and a paper discharge tray 29. .

The image forming unit 21 forms a Y (yellow) toner image. The image forming unit 22 forms a C (cyan) toner image. The image forming unit 23 forms an M (magenta) toner image. The image forming unit 24 forms a K (black) toner image. As shown in FIG. 1, the image forming units 21 to 24 are arranged along the front-rear direction D2 of the image forming apparatus 100 in the order of yellow, cyan, magenta, and black from the front side of the image forming apparatus 100 .

The image forming unit 21 includes a photosensitive drum, a charging roller, a developing device, a primary transfer roller, and a drum cleaning section. Also, each of the image forming units 22 to 24 has the same configuration as the image forming unit 21 .

The photosensitive drum carries a toner image. The charging roller charges the surface of the photosensitive drum. The surface of the photosensitive drum charged by the charging roller is irradiated with light based on image data emitted from the optical scanning device 25 . As a result, an electrostatic latent image is formed on the surface of the photosensitive drum. The developing device visualizes (develops) the electrostatic latent image formed on the surface of the photosensitive drum using toner. A toner image is formed on the surface of the photosensitive drum by the developing device. The primary transfer roller transfers the toner image formed on the surface of the photosensitive drum by the developing device onto the intermediate transfer belt 26 . The drum cleaning section removes toner remaining on the surface of the photosensitive drum after the toner image is transferred by the primary transfer roller.

The optical scanning device 25 emits light based on image data toward the surface of each of the photosensitive drums of the image forming units 21-24.

The intermediate transfer belt 26 is an endless belt member onto which the toner images formed on the surfaces of the photosensitive drums of the image forming units 21-24 are transferred. The intermediate transfer belt 26 is stretched with a predetermined tension by a drive roller and a tension roller. The intermediate transfer belt 26 rotates in the rotation direction D4 shown in FIG. 1 by receiving a rotational driving force supplied from a motor (not shown) and rotating the drive roller.

The secondary transfer roller 27 transfers the toner image transferred on the surface of the intermediate transfer belt 26 to the sheet 200 supplied by the paper feeding unit 4 at the transfer position P1 shown in FIG.

The fixing device 28 fixes the toner image transferred onto the sheet 200 by the secondary transfer roller 27 onto the sheet 200 .

The sheet 200 on which the toner image is fixed by the fixing device 28 is discharged to the discharge tray 29 .

[Structure of Fixing Device 28]
Next, the configuration of the fixing device 28 will be described with reference to FIGS. 1 to 4. FIG. Here, FIG. 3 is a sectional view showing the configuration of the fixing device 28. As shown in FIG. 4 is a front view showing the positional relationship among the fixing belt 41, the temperature sensor 45, and the sheet 200 conveyed toward the nip portion P2 (see FIG. 3). A dashed line in FIG. 4 indicates a partial area 41A on the fixing belt 41. As shown in FIG. 4 indicates the contact area 201 on the seat 200. As shown in FIG. Also, dashed lines within the contact area 201 in FIG. 4 indicate divided areas 202 within the contact area 201 .

As shown in FIG. 3 , the fixing device 28 includes a fixing belt 41 , pressure roller 42 , pre-entry guide 43 , heater 44 , temperature sensor 45 , separation claw 46 , separation plate 47 , and discharge roller pair 48 . The fixing device 28 also includes a drive control section 49 (see FIG. 2).

The fixing belt 41 is an endless belt-like member that comes into contact with the sheet 200 onto which the toner image has been transferred and heats the sheet 200 . The fixing belt 41 is rotatable along a rotation direction D6 shown in FIG. 3 around a rotation axis extending in the left-right direction D3. The fixing belt 41 is an example of the fixing member of the invention. Note that the fixing member of the present invention may be a roller-shaped member or the like.

The fixing belt 41 has a base layer, an elastic layer, and a release layer. The base layer is made of a metal material such as nickel. The elastic layer is made of an elastic material such as silicone rubber. The release layer is made of a fluororesin material such as PFA.

A belt guide member that guides rotation of the fixing belt 41 along the rotation direction D6, a pressing member that presses the fixing belt 41 toward the pressure roller 42 side, and the like are provided inside the fixing belt 41 .

The pressure roller 42 is a roller-shaped member that is provided in contact with the fixing belt 41 and presses the sheet 200 passing between the fixing belt 41 and the fixing belt 41 . The pressure roller 42 is rotatably provided along the rotation direction D7 shown in FIG. Between the fixing belt 41 pressed by the pressing member and the pressure roller 42, a nip portion P2 (see FIG. 3) is formed to sandwich the sheet 200 passing between the fixing belt 41 and the pressure roller 42. be.

The pressure roller 42 has a metal core, an elastic layer, and a release layer. The core bar is made of a metal material such as aluminum. The elastic layer is made of an elastic material such as silicon sponge. The release layer is made of a fluororesin material such as PFA.

The pressure roller 42 is rotatably supported by the housing of the fixing device 28 . The pressure roller 42 rotates in the rotation direction D7 (see FIG. 3) by receiving a rotational driving force supplied from a drive section (not shown). As a result, the fixing belt 41 is driven to rotate in the rotation direction D6 (see FIG. 3). In addition, a driving force to the downstream side in the transport direction D5 is applied to the sheet 200 passing through the nip portion P2 (see FIG. 3).

The sheet 200 to which the toner image has been transferred is heated and pressed by the fixing belt 41 and the pressure roller 42 when passing through the nip portion P2. Thereby, the toner image transferred to the sheet 200 is fixed on the sheet 200 .

The pre-entry guide 43 guides the sheet 200 conveyed from the secondary transfer roller 27 to the nip portion P2.

A heater 44 heats the fixing belt 41 . As shown in FIG. 3, the heater 44 is provided facing the surface of the fixing belt 41 . For example, the heater 44 is an IH fixing unit that induction-heats the fixing belt 41 by the action of a magnetic field generated by applying a high-frequency alternating current to a coil. Note that the heater 44 may be a halogen heater or the like.

The temperature sensor 45 detects the temperature of a predetermined partial area 41A (see FIG. 4) of the fixing belt 41 in the axial direction (horizontal direction D3) of the rotation shaft of the fixing belt 41 .

Specifically, the temperature sensor 45 is a non-contact thermistor provided outside the fixing belt 41 so as to face the partial area 41A. The temperature sensor 45 outputs an electrical signal corresponding to the detected temperature of the partial area 41A. The temperature sensor 45 may be a contact-type or non-contact-type thermistor provided inside the fixing belt 41 so as to face the partial area 41A. Also, the temperature sensor 45 may be a thermopile or the like.

Separation claw 46 separates sheet 200 that has passed through nip portion P<b>2 from pressure roller 42 .

The separation plate 47 separates the sheet 200 that has passed through the nip portion P2 from the fixing belt 41 .

The discharge roller pair 48 discharges the sheet 200 that has passed through the nip portion P<b>2 toward the paper discharge roller pair 35 .

The drive control unit 49 controls driving of the heater 44 so that the temperature detected by the temperature sensor 45 becomes a preset target temperature. Specifically, the drive control unit 49 controls driving of the heater 44 based on the difference between the detected temperature and the target temperature. For example, the drive control unit 49 is an electronic circuit such as an integrated circuit (ASIC). Note that the controller 7 may function as the drive controller 49 .

For example, a power supply path between the heater 44 and a power supply (not shown) that supplies power to the heater 44 is provided with a semiconductor switch (not shown) such as an IGBT or triac. The drive control unit 49 controls power supplied to the heater 44 by inputting a PWM signal generated based on the difference between the detected temperature and the target temperature to the semiconductor switch. The drive control unit 49 may control the driving of the heater 44 by switching on/off the semiconductor switch depending on whether the detected temperature is less than the target temperature.

By the way, when a large amount of toner contacts the partial area 41A (see FIG. 4) of the fixing belt 41, the heater 44 may excessively supply heat to an area of the fixing belt 41 other than the partial area 41A. On the other hand, an image forming apparatus is known as a related art that changes the target temperature so that the target temperature becomes lower within a predetermined specific range as the amount of toner in contact with the partial area 41A increases. .

However, in the image forming apparatus according to the related art described above, before the sheet 200 contacts the fixing belt 41, the temperature of the partial area 41A (see FIG. FIG. 4) is adjusted to the target temperature after the change based on the amount of toner. Therefore, when the target temperature after the change is near the lower limit of the specific range, that is, when the amount of toner in the contact area 201 is close to the upper limit, contact with the contact area 201 causes the temperature of the partial area 41A to rise to the specific range. It may fall below the lower limit of the range and cause poor fixing.

On the other hand, in the image forming apparatus 100 according to the embodiment of the present invention, as described below, it is possible to suppress excessive heat supply by the heater 44 and to suppress the occurrence of poor fixing. be.

[Configuration of control unit 7]
Next, the configuration of the control unit 7 will be described with reference to FIG.

As shown in FIG. 2 , the control section 7 includes a toner amount acquisition section 61 and a temperature change section 62 .

Specifically, the ROM 12 of the control unit 7 stores in advance a temperature control program for causing the CPU 11 to function as each unit described above. The CPU 11 functions as a toner amount acquiring section 61 and a temperature changing section 62 by executing the temperature control program stored in the ROM 12 .

The temperature control program is recorded on a computer-readable recording medium such as a CD, DVD, and flash memory, and may be read from the recording medium and stored in the storage section 6 . Also, the toner amount acquisition unit 61 and the temperature change unit 62 may be configured by an electronic circuit such as an integrated circuit (ASIC).

The toner amount acquisition unit 61 acquires the amount of toner that contacts the partial area 41A (see FIG. 4) during a predetermined specific period.

Here, the specific period is a period having the same length as the rotation period of the fixing belt 41 . For example, the specific period is a period that starts (starts) for each rotation cycle of the fixing belt 41 from the timing when the fixing belt 41 contacts the leading edge of the sheet 200 . In this case, the amount of toner contacting the partial area 41A (see FIG. 4) during the specific period is the amount of toner transferred to the divided area 202 (see FIG. 4) of the sheet 200 passing through the nip portion P2. A divided area 202 is an area obtained by dividing the contact area 201 based on the circumferential length of the fixing belt 41, and is an area whose length in the conveying direction D5 is the same as the circumferential length.

For example, the toner amount acquisition unit 61 acquires the amount of toner that contacts the partial area 41A during the specific period based on the image data to be printed.

Note that the toner amount acquisition unit 61 may acquire the amount of toner that contacts the partial area 41</b>A during the specific period based on the captured image of the sheet 200 . For example, the captured image can be acquired by providing an imaging device at a position facing the pre-entry guide 43 .

The temperature changing section 62 changes the target temperature to a post-change temperature (an example of a specific temperature in the present invention) based on the amount of toner acquired by the toner amount acquiring section 61 after the beginning of the specific period.

Specifically, the temperature changer 62 changes the target temperature at the end of the specific period.

Further, the temperature changing section 62 changes the target temperature to the post-change temperature based on the toner amount acquired by the toner amount acquiring section 61 and the current target temperature each time the fixing belt 41 rotates once. That is, the temperature changing section 62 changes the target temperature with the rotation period of the fixing belt 41 .

For example, the temperature changing unit 62 calculates the post-change temperature T _n each time the specific period starts, using the following formulas (1) and (2). Then, the temperature changing section 62 changes the target temperature to the calculated post-change temperature _Tn . In equation (1), n indicates the number of arrivals of the beginning of the specific period. Also, in equation (1), T _n-1 indicates the current target temperature (temperature before change). In equations (1) and (2), T ₀ represents the initial value of the target temperature. Moreover, in Formula (2), β represents a constant. Also, in equation (2), X _n-1 is the amount of toner that contacts the partial area 41A during the preceding specific period, and indicates the amount of toner acquired by the toner amount acquisition unit 61 . Note that the toner amount _X0 becomes zero. For example, the constant β is such that when a toner amount X _n-1 is attached to the divided area 202 (see FIG. 4), (β·X _n-1 ) is the portion due to contact with the divided area 202 It is defined to indicate the amount of temperature drop in region 41A. Moreover, in Formula (2), τ indicates a time constant.

_Tn = Tn _-1 + _ΔTn (1)

ΔT _n = (T ₀ - β X _n-1 - T _n-1 ) (1-e ^(- τ ⁾ ) (2)

Note that in equation (2), instead of the current target temperature Tn _-1 , the current detected temperature or an average value of the detected temperatures over a predetermined period up to the current time may be used.

Further, the temperature changing section 62 may change the target temperature at a timing after the start of the specific period and at a timing different from the end of the specific period.

[Temperature control process]
Hereinafter, the temperature control method of the present invention will be described together with an example of the procedure of temperature control processing executed by the control unit 7 in the image forming apparatus 100, with reference to FIG. Here, steps S11, S12, . For example, the temperature control process is executed each time the sheet 200 passes through the nip portion P2.

<Step S11>
First, in step S11, the control unit 7 sets the initial value T ₀ as the target temperature.

<Step S12>
In step S12, the control unit 7 determines whether or not the start time of the first specific period has arrived.

Specifically, the control unit 7 determines that the start timing of the first specific period has arrived at the timing when the leading edge of the sheet 200 reaches the nip portion P2.

Here, when the control unit 7 determines that the start time of the first specific period has arrived (Yes side of S12), the process proceeds to step S13. If the start time of the first specific period has not arrived (No side of S12), the control unit 7 waits for the start time of the first specific period in step S12.

<Step S13>
In step S13, the control unit 7 acquires the amount of toner contacting the partial area 41A during the previous specific period. Here, the process of step S13 is an example of the toner amount acquisition step of the present invention, and is executed by the toner amount acquisition section 61 of the control section 7. FIG.

Specifically, based on the image data to be printed, the control unit 7 acquires the amount of toner contacting the partial area 41A during the preceding specific period. It should be noted that the toner amount acquired when the first step S13 is executed is zero.

<Step S14>
At step S14, the controller 7 changes the target temperature. Here, the process of step S14 is an example of the temperature change step of the present invention, and is executed by the temperature change section 62 of the control section 7. FIG.

Specifically, the control unit 7 calculates the post-change temperature T _n using the equations (1) and (2). Then, the control unit 7 changes the target temperature to the calculated post-change temperature _Tn . Note that the post-change temperature T _n calculated based on the equations (1) and (2) when the first step S14 is executed becomes the initial value _T0 . That is, the target temperature is not changed when the first step S14 is executed.

<Step S15>
In step S15, the control unit 7 determines whether or not the specific period has started.

Specifically, the control unit 7 determines that the specific period has started when a period of time equal to the rotation period of the fixing belt 41 has elapsed since the previous specific period started.

Here, when the control unit 7 determines that the start time of the specific period has arrived (Yes side of S15), the process proceeds to step S13. Moreover, if the start time of the specific period has not arrived (No side of S15), the control unit 7 shifts the process to step S16.

<Step S16>
In step S16, the controller 7 determines whether or not the trailing edge of the sheet 200 has passed through the nip portion P2.

Specifically, the control unit 7 controls the trailing edge of the sheet 200 when a predetermined period of time corresponding to the length of the sheet 200 in the conveying direction D5 has elapsed since it was determined that the start of the specific period has arrived. has passed through the nip portion P2.

Here, when the controller 7 determines that the trailing edge of the sheet 200 has passed through the nip portion P2 (Yes side of S16), it terminates the temperature control process. If the trailing edge of the sheet 200 has not passed through the nip portion P2 (No side of S16), the control section 7 shifts the process to step S15.

Thus, in the image forming apparatus 100, the target temperature is changed to the post-change temperature based on the amount of toner that contacts the partial area 41A of the fixing belt 41 during the specific period. As a result, it is possible to suppress excessive heat supply by the heater 44 . Further, in the image forming apparatus 100, the target temperature is changed to the post-change temperature after the beginning of the specific period. As a result, when the partial region 41A and the sheet 200 first come into contact with each other, the temperature of the partial region 41A is prevented from dropping to the post-change temperature before contact with the sheet 200 . Therefore, compared to a configuration in which the target temperature is changed to the post-change temperature before the beginning of the specific period, the temperature of the partial region 41A is suppressed from falling below the post-change temperature. Therefore, it is possible to suppress the occurrence of poor fixing.

Further, in the image forming apparatus 100, the target temperature is changed to the post-change temperature at the end of the specific period. This prevents the temperature of the partial area 41A from dropping from the initial value of the target temperature before contact with the sheet 200 when the partial area 41A and the sheet 200 first come into contact with each other. Therefore, it is possible to more effectively suppress the occurrence of poor fixing.

Further, in the image forming apparatus 100, the target temperature is changed to the post-change temperature based on the toner amount acquired by the toner amount acquisition unit 61 and the current target temperature each time the fixing belt 41 rotates once. . As a result, the target temperature is changed to the post-change temperature obtained without being based on the current target temperature every time the fixing belt 41 rotates once. It is possible to suppress the decrease. Therefore, it is possible to suppress the occurrence of poor fixing due to a rapid decrease in the target temperature.

[Other embodiments]
Note that the specific period may be a period during which one sheet 200 is in contact with the fixing belt 41 .

In this case, the toner amount acquisition unit 61 determines the amount of toner that contacts the partial area 41A (see FIG. 4) during the period in which one sheet 200 contacts the fixing belt 41, that is, the contact amount of the sheet 200 passing through the nip portion P2. The amount of toner transferred to the area 201 (see FIG. 4) may be obtained.

Further, the temperature changing section 62 may change the target temperature to the post-change temperature based on the toner amount acquired by the toner amount acquiring section 61 after the timing when the leading edge of the sheet 200 reaches the nip portion P2. . For example, the temperature changing section 62 changes the target temperature at an arbitrary timing after the trailing edge of the sheet 200 passes through the nip portion P2 and before the leading edge of the next sheet 200 reaches the nip portion P2. The temperature should be changed.

Further, the temperature change unit 62 sets the target temperature to the target temperature using the toner amount acquisition unit 61 each time the sheet 200 passes through the nip portion P2 (an example of the contact position of the present invention) where the sheet 200 and the fixing belt 41 contact each other. The post-change temperature may be changed based on the obtained toner amount and the current target temperature. As a result, when the target temperature is changed for each rotation cycle of the fixing belt 41, the change interval is too fast to allow the detected temperature to follow the target temperature. is possible.

Further, the temperature changing unit 62 may initialize the target temperature when a delay exceeding a predetermined allowable time occurs in conveying the sheet 200 . Specifically, the temperature changing unit 62 may reset the target temperature to the initial value _T0 . As a result, the temperature control of the fixing belt 41 can be reset when the sheet runs out during the execution of the printing process, or when the conveyance of the sheet 200 is delayed due to the execution of calibration, or the like. It is possible. The allowable time may be a time set arbitrarily.

1 ADF
2 Image reading unit 3 Image forming unit 4 Paper feed unit 5 Operation display unit 6 Storage unit 7 Control unit 28 Fixing device 41 Fixing belt 41A Partial region 42 Pressure roller 43 Pre-entry guide 44 Heater 45 Temperature sensor 46 Separation claw 47 Separation plate 48 discharge roller pair 49 drive control unit 61 toner amount acquisition unit 62 temperature change unit 100 image forming apparatus 200 sheet 201 contact area

Claims (8)

a fixing member that is rotatably provided and contacts the sheet to which the toner image has been transferred to heat the sheet;
a heater for heating the fixing member;
a temperature sensor that detects the temperature of a predetermined partial region of the fixing member in the axial direction of the rotation shaft of the fixing member;
a drive control unit that controls driving of the heater based on the difference between the temperature detected by the temperature sensor and a preset target temperature;
a toner amount acquisition unit that acquires an amount of toner that contacts the partial area during a predetermined specific period;
a temperature change unit that changes the target temperature to a specific temperature based on the amount of toner acquired by the toner amount acquisition unit after the start of the specific period;
An image forming apparatus comprising: The temperature changing unit changes the target temperature after the end of the specific period.
The image forming apparatus according to claim 1. The specific period is the same period as the rotation period of the fixing member.
The image forming apparatus according to claim 1 or 2. The temperature changing unit changes the target temperature to the specific temperature based on the toner amount acquired by the toner amount acquisition unit and the current target temperature each time the fixing member rotates once.
The image forming apparatus according to claim 3. the specific period is a period during which one sheet is in contact with the fixing member;
The image forming apparatus according to claim 1 or 2. The temperature change unit adjusts the target temperature to the specific temperature based on the toner amount acquired by the toner amount acquiring unit and the current target temperature each time the sheet passes the contact position between the sheet and the fixing member. change to
The image forming apparatus according to claim 5. The temperature changing unit initializes the target temperature when a delay exceeding a predetermined allowable time occurs in conveying the sheet.
The image forming apparatus according to claim 5 or 6. a rotatably provided fixing member that comes into contact with a sheet on which a toner image has been transferred and heats the sheet; a heater that heats the fixing member; An image forming apparatus comprising: a temperature sensor that detects the temperature of a predetermined partial area; and a drive control unit that controls the driving of the heater based on the difference between the temperature detected by the temperature sensor and a preset target temperature. A temperature control method implemented in an apparatus, comprising:
a toner amount obtaining step of obtaining an amount of toner contacting the partial area during a predetermined specific period;
a temperature changing step of changing the target temperature to a specific temperature based on the toner amount obtained by the toner amount obtaining step after the start of the specific period;
temperature control methods including;

Images