JP2019056793A - Image forming apparatus and temperature control method - Google Patents

Abstract

To provide an image forming apparatus and a temperature control method with which even when conditions are changed during printing, the temperature of a fixing member can be returned to a preset temperature before a next sheet reaches a nip part.SOLUTION: An image forming apparatus acquires a first timing at which the temperature of a fixing member is decreased from a predetermined preset temperature in an initial sheet conveying period (step S12), acquires the amount of change in temperature of the fixing member detected by a temperature sensor at a predetermined acquisition time for every acquisition time from the first timing (step S13), acquires a second timing at which the reduction in temperature of the fixing member continuing from the first timing stops on the basis of each of the amounts of change (step S14), and sets the rate of increase in output from a heating unit for every acquisition time from a third timing to a fourth timing in the conveying period of each of the sheets to be conveyed in the second and subsequent order on the basis of each of the amounts of change (step S17).SELECTED DRAWING: Figure 3

Description

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

  An electrophotographic image forming apparatus includes a fixing unit that fixes a toner image transferred to a sheet to the sheet. The fixing unit includes a fixing member and a pressure member. The fixing member is heated to a preset temperature. The pressure member is in pressure contact with the fixing member. In the fixing unit, when the sheet passes through the nip formed between the fixing member and the pressure member, the toner image transferred to the sheet is heated and pressed and fixed to the sheet. The An image forming apparatus that detects the type of sheet on which an image is formed and can set the set temperature based on the detection result is known (see Patent Document 1).

JP 2004-277057 A

  Incidentally, when the sheet passes through the nip portion, the temperature of the fixing member may decrease. If the degree of this temperature decrease is large, the next sheet may reach the nip portion before the temperature of the fixing member returns to the set temperature, and the image quality of the printed matter output from the image forming apparatus may deteriorate. . On the other hand, while the sheet passes through the nip portion, feed-forward control is performed to increase the output of the heating unit that heats the fixing member in accordance with a preset amount of increase, and the temperature of the fixing member is decreased. Can be suppressed.

  Here, the amount of temperature decrease in the fixing member when the sheet passes through the nip portion varies depending on the ambient temperature during printing, the thickness of the sheet, and the like. Therefore, in the conventional feedforward control, a deviation may occur between the temperature decrease amount compensated by the increase amount and the actual temperature decrease amount in the fixing member. When this deviation is large, the temperature of the fixing member does not converge to the set temperature until the next sheet reaches the nip portion, thereby reducing the image quality of the printed matter output from the image forming apparatus. To do.

  An object of the present invention is to provide an image forming apparatus capable of converging the temperature of a fixing member to a set temperature until the next sheet reaches the nip portion even when various conditions during printing change, and the temperature It is to provide a control method.

  An image forming apparatus according to one aspect of the present invention includes a fixing unit, a heating unit, a temperature sensor, a print processing unit, a first acquisition processing unit, a second acquisition processing unit, and a third acquisition processing unit. And a setting processing unit and a power supply control unit. The fixing unit includes a fixing member heated to a predetermined set temperature, and a pressure member pressed against the fixing member, and a toner image is formed at a nip portion formed by the fixing member and the pressure member. Is fixed to the sheet. The heating unit heats the fixing member upon receiving driving power. The temperature sensor detects the temperature of the fixing member. The print processing unit executes a print process for forming an image based on image data on each of a plurality of sheets sequentially conveyed along a conveyance path passing through the nip portion. The first acquisition processing unit acquires a first timing at which the temperature of the fixing member decreases from the set temperature during a conveyance period of a sheet first conveyed in the printing process. The second acquisition processing unit acquires a change amount of the temperature of the fixing member detected by the temperature sensor at the acquisition time for each predetermined acquisition time from the first timing. The third acquisition processing unit acquires a second timing at which the temperature decrease of the fixing member that continues from the first timing stops based on each of the change amounts acquired by the second acquisition processing unit. The setting processing unit corresponds to the first timing during the conveyance period of each of the second and subsequent sheets conveyed in the printing process, based on each change amount acquired by the second acquisition processing unit. The amount of increase in the output of the heating unit for each acquisition time from 3 timings to the 4th timing corresponding to the second timing is set. The power supply control unit increases the driving power according to the increase amount for each acquisition time set by the setting processing unit every time the second and subsequent sheets are conveyed in the printing process.

  A temperature control method according to another aspect of the present invention includes a fixing member that is heated to a predetermined set temperature, and a pressure member that is in pressure contact with the fixing member. Image forming comprising: a fixing unit that fixes a toner image on a sheet at a nip portion to be formed; a heating unit that heats the fixing member by receiving driving power; and a temperature sensor that detects a temperature of the fixing member. It is executed by the apparatus and includes the following printing step, first acquisition step, second acquisition step, third acquisition step, setting step, and power feeding control step. In the printing step, a printing process for forming an image based on the image data on each of a plurality of sheets sequentially conveyed along a conveyance path passing through the nip portion is executed. In the first acquisition step, a first timing is acquired at which the temperature of the fixing member decreases from the set temperature during a conveyance period of a sheet first conveyed in the printing process. In the second acquisition step, the amount of change in the temperature of the fixing member detected by the temperature sensor at the acquisition time is acquired every predetermined acquisition time from the first timing. In the third acquisition step, a second timing at which the temperature decrease of the fixing member that continues from the first timing stops is acquired based on each of the change amounts acquired in the second acquisition step. In the setting step, a third timing corresponding to the first timing during the conveyance period of each of the second and subsequent sheets conveyed in the printing process based on each of the change amounts acquired in the second acquisition step. To the fourth timing corresponding to the second timing, an increase amount of the output of the heating unit for each acquisition time is set. In the power supply control step, every time the second and subsequent sheets are conveyed in the printing process, the drive power is increased according to the increase amount for each acquisition time set in the setting step.

  According to the present invention, even when various conditions during printing change, the temperature of the fixing member can be converged to the set temperature until the next sheet reaches the nip portion.

FIG. 1 is a diagram illustrating a configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a block diagram showing the configuration of the control unit of the image forming apparatus according to the embodiment of the present invention. FIG. 3 is a flowchart showing an example of a temperature control process executed by the image forming apparatus according to the embodiment of the present invention. FIG. 4 is a view showing a temperature change in the fixing member of the image forming apparatus according to the embodiment of the present invention. FIG. 5 is a diagram illustrating an increase rate of the output of the heating unit set by the control unit of the image forming apparatus according to the embodiment of the present invention. FIG. 6 is a diagram showing a temperature change in the fixing member of the image forming apparatus according to the embodiment of the present invention.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. The following embodiment is an example embodying the present invention, and does not limit the technical scope of the present invention.

[Schematic Configuration of Image Forming Apparatus 10]
First, a schematic configuration of an image forming apparatus 10 according to an embodiment of the present disclosure will be described with reference to FIGS. 1 and 2. Here, FIG. 1 is a schematic cross-sectional view showing the configuration of the image forming apparatus 10.

  The image forming apparatus 10 is a multifunction machine having a plurality of functions such as a facsimile function and a copy function, as well as a scan function for reading image data from a document and a print function for forming an image based on the image data. The present invention is also applicable to image forming apparatuses such as printers, facsimile machines, and copiers.

  As shown in FIGS. 1 and 2, the image forming apparatus 10 includes an ADF (automatic document conveying apparatus) 1, an image reading unit 2, an image forming unit 3, a sheet conveying unit 4, a control unit 5, and an operation display unit ( (Not shown).

  The ADF 1 includes a document setting unit, a plurality of conveyance rollers, a document pressing unit, and a paper discharge unit, and conveys a document read by the image reading unit 2. The image reading unit 2 includes a document table, a light source, a plurality of mirrors, an optical lens, and a CCD, and can read image data from the document. The operation display unit includes a display unit such as a liquid crystal display that displays various types of information in accordance with control instructions from the control unit 5, and an operation key or touch panel that inputs various types of information to the control unit 5 in accordance with user operations. And so on.

  The control unit 5 includes control devices such as a CPU, ROM, RAM, and EEPROM (registered trademark) (not shown). The CPU is a processor that executes various arithmetic processes. The ROM is a non-volatile storage device in which information such as a control program for causing the CPU to execute various processes is stored in advance. The RAM is a volatile storage device, and the EEPROM is a nonvolatile storage device. The RAM and the EEPROM are used as a temporary storage memory (working area) for various processes executed by the CPU. In the control unit 5, various control programs stored in advance in the ROM are executed by the CPU. As a result, the image forming apparatus 10 is comprehensively controlled by the control unit 5. The control unit 5 may be an electronic circuit such as an integrated circuit (ASIC), and is a control unit provided separately from the main control unit that controls the image forming apparatus 10 in an integrated manner. May be.

  The image forming unit 3 can form an image by electrophotography based on the image data read by the image reading unit 2. The image forming unit 3 can also form an image based on image data input from an information processing apparatus such as an external personal computer. Specifically, as shown in FIG. 1, the image forming unit 3 includes a photosensitive drum 31, a charging device 32, an optical scanning device 33, a developing device 34, a transfer device 35, a cleaning device 36, and a fixing device 37. .

  The sheet conveying unit 4 supplies the sheet to the image forming unit 3. Specifically, as shown in FIG. 1, the sheet transport unit 4 includes a paper feed cassette 41, a feed mechanism 42, a transport path 43, a registration roller 44, a discharge roller 45, a paper discharge tray 46, and a sheet sensor 47. Prepare.

  The paper feed cassette 41 accommodates a sheet on which an image is formed by the image forming unit 3. For example, the sheet cassette 41 contains sheet members such as paper, coated paper, postcards, envelopes, and OHP sheets. As shown in FIG. 1, the feeding mechanism 42 includes a pickup roller 421, a feed roller 422, and a retard roller 423, and feeds the sheet to the conveyance path 43. The conveyance path 43 is a sheet movement path formed between the paper feed cassette 41 and the paper discharge tray 46. As shown in FIG. 1, the conveyance path 43 is provided with a plurality of rollers including a registration roller 44 and a discharge roller 45. The plurality of rollers are rotated by a driving force generated by a motor (not shown), thereby conveying the sheet along the conveyance path 43 in the conveyance direction D1 shown in FIG. As shown in FIG. 1, the conveyance path 43 is provided with the photosensitive drum 31, the transfer device 35, and the fixing device 37 of the image forming unit 3. Here, the sheet conveyance path defined by the conveyance path 43 is an example of the conveyance path in the present invention. The sheet sensor 47 is provided upstream of the registration rollers 44 in the conveyance path 43 in the conveyance direction D1, and detects the passage of the sheet.

  Here, an image forming procedure by the image forming unit 3 will be described. First, the surface of the photosensitive drum 31 is uniformly charged to a predetermined potential by the charging device 32. Next, the light scanning device 33 irradiates the surface of the photosensitive drum 31 with light based on the image data. Thereby, an electrostatic latent image corresponding to the image data is formed on the surface of the photosensitive drum 31.

  The electrostatic latent image formed on the surface of the photosensitive drum 31 is developed (visualized) as a toner image by the developing device 34. The toner image formed on the surface of the photosensitive drum 31 is conveyed by the photosensitive drum 31 to a transfer position P1 (see FIG. 1) by the transfer device 35. The developing device 34 is supplied with toner from a toner container 34 </ b> A (see FIG. 1) that can be attached to and detached from the image forming unit 3.

  On the other hand, the sheet conveying unit 4 conveys the sheet to the transfer position P1 in parallel with the image forming operation by the image forming unit 3. Specifically, the sheet feeding cassette 41 uses a lift plate (not shown) provided at the bottom of the sheet feeding cassette 41 to transfer the sheets stored in the sheet feeding cassette 41 to the pickup roller 421 of the feeding mechanism 42. Lift to contact position. The feeding mechanism 42 feeds the sheet lifted by the lift plate to the conveyance path 43.

  The registration roller 44 conveys the sheet to the transfer position P1 in accordance with the timing at which the toner image is conveyed to the transfer position P1 by the photosensitive drum 31. Specifically, in the image forming apparatus 10, the sheet conveyance timing by the registration roller 44 is set based on the detection timing of the sheet passing by the sheet sensor 47. Then, the registration roller 44 conveys the sheet to the transfer position P1 based on the set conveyance timing. As a result, the toner image formed on the surface of the photosensitive drum 31 is transferred to the surface of the sheet, and an image is formed on the sheet. The toner remaining on the surface of the photosensitive drum 31 after the transfer of the toner image is removed by the cleaning device 36.

  The sheet on which the toner image is transferred at the transfer position P1 is conveyed to the fixing device 37. In the fixing device 37, the toner image transferred to the sheet is fixed to the sheet. The sheet on which the toner image is fixed by the fixing device 37 is discharged to the discharge tray 46 by the discharge roller 45.

[Configuration of Fixing Device 37]
Next, the fixing device 37 will be described with reference to FIGS. 1 and 2.

  As shown in FIGS. 1 and 2, the fixing device 37 includes a fixing member 371, a pressure member 372, a heating unit 373, a temperature sensor 374, and a power feeding unit 375.

  The fixing member 371 is rotatably provided. For example, the fixing member 371 is a roller-shaped member. The fixing member 371 is heated to a preset temperature X1 (see FIG. 4) by the heating unit 373. For example, the set temperature X1 is 180 degrees. Note that the fixing member 371 may be a belt-shaped member.

  The pressure member 372 is provided so as to be rotatable in contact with the fixing member 371. For example, the pressure member 372 is a roller-shaped member. The pressure member 372 is biased toward the fixing member 371 by a biasing member (not shown). Thereby, a nip portion P2 (see FIG. 1) having a predetermined pressure is formed between the fixing member 371 and the pressure member 372.

  In the fixing device 37, when the sheet on which the toner image is transferred passes through the nip portion P2, the toner image on the sheet is heated by the fixing member 371 and is also pressed by the fixing member 371 and the pressure member 372. The As a result, the toner image transferred to the sheet is fixed to the sheet. Here, the fixing member 371 and the pressure member 372 are examples of the fixing unit in the present invention.

  The heating unit 373 heats the fixing member 371 upon receiving the driving power. For example, the heating unit 373 is provided inside the fixing member 371 as shown in FIG. For example, the heating unit 373 is a halogen heater or an IH heater.

  The temperature sensor 374 detects the temperature of the surface of the fixing member 371. For example, the temperature sensor 374 is provided at a position separated from the surface of the fixing member 371 as shown in FIG. For example, the temperature sensor 374 includes an optical lens that collects infrared rays emitted from the surface of the fixing member 371, and a thermocouple that receives the infrared rays collected by the optical lens and outputs a voltage corresponding to the amount of received light. Etc. The temperature sensor 374 outputs an electric signal Sig1 (see FIG. 2) corresponding to the temperature of the surface of the fixing member 371.

  The power feeding unit 375 supplies the driving power to the heating unit 373. Specifically, the power feeding unit 375 is a power source that can output the driving power according to the electric signal Sig2 (see FIG. 2) input from the control unit 5. For example, the electrical signal Sig2 is a PWM signal.

  Here, based on the current temperature of the fixing member 371 detected by the temperature sensor 374, the control unit 5 outputs the output of the heating unit 373 so that the temperature of the fixing member 371 becomes the set temperature X1 that is the target temperature. Execute feedback control to control. For example, the control unit 5 generates the electric signal Sig2 having a duty ratio corresponding to the difference between the temperature of the fixing member 371 indicated by the electric signal Sig1 input from the temperature sensor 374 and the set temperature X1. The signal Sig2 is input to the power feeding unit 375.

  By the way, when the sheet passes through the nip portion P2, the temperature of the fixing member 371 may decrease. If the temperature decrease is large, the next sheet reaches the nip portion P2 before the temperature of the fixing member 371 returns to the set temperature X1 by the feedback control, and the image quality of the printed matter output from the image forming apparatus 10 is high. May decrease. On the other hand, while the sheet passes through the nip portion P2, feedforward control is performed to increase the output of the heating unit 373 in accordance with a preset amount of increase, thereby suppressing a temperature decrease in the fixing member 371. Is possible.

  Here, the amount of temperature decrease in the fixing member 371 when the sheet passes through the nip portion P2 varies depending on the ambient temperature during printing, the thickness of the sheet, and the like. Therefore, in the conventional feedforward control, a deviation may occur between the temperature decrease amount compensated by the increase amount and the actual temperature decrease amount in the fixing member 371. When this deviation is large, the temperature of the fixing member 371 does not converge to the set temperature X1 until the next sheet reaches the nip portion P2, and the image quality of the printed matter output from the image forming apparatus 10 is thereby increased. descend.

  On the other hand, in the image forming apparatus 10 according to the embodiment of the present invention, as described below, even when various conditions during printing are changed, the fixing is performed before the next sheet reaches the nip portion P2. It is possible to converge the temperature of the member 371 to the set temperature X1.

  Specifically, the ROM of the control unit 5 stores in advance a temperature control program for causing the CPU to execute a temperature control process (see a flowchart of FIG. 3) described later. The temperature control program may be recorded on a computer-readable recording medium such as a CD, a DVD, or a flash memory, and read from the recording medium and installed in a storage device such as the EEPROM. Good.

  As shown in FIG. 2, the control unit 5 includes the print processing unit 51, the first acquisition processing unit 52, the second acquisition processing unit 53, the third acquisition processing unit 54, the setting processing unit 55, and the determination processing unit 56. The change processing unit 57 and the power supply control unit 58 are included. Specifically, the control unit 5 executes the temperature control program stored in the ROM using the CPU. Thereby, the control unit 5 includes a print processing unit 51, a first acquisition processing unit 52, a second acquisition processing unit 53, a third acquisition processing unit 54, a setting processing unit 55, a determination processing unit 56, a change processing unit 57, and The power supply control unit 58 functions.

  The print processing unit 51 executes print processing for forming an image based on image data on each of a plurality of sheets sequentially conveyed along a conveyance path that passes through the nip portion P2.

  Specifically, the print processing unit 51 controls the operation of each of the image forming unit 3 and the sheet conveying unit 4 to execute the print process. That is, the print processing unit 51 controls the operation of each unit of the sheet conveying unit 4 to sequentially convey the sheets stored in the sheet feeding cassette 41 toward the sheet discharge tray 46. The print processing unit 51 controls the operation of each unit of the image forming unit 3 to form an image based on the image data on each sheet conveyed by the sheet conveying unit 4.

  For example, the print processing unit 51 determines whether the conveyance interval between the sheet first conveyed by the sheet conveying unit 4 and the second conveyed sheet after the start of execution of the printing process is between the second and subsequent conveyed sheets. Each sheet is conveyed to the sheet conveying unit 4 so as to be longer than the conveying interval.

  Further, the print processing unit 51 forms an image based on specific image data including only white pixels on the sheet conveyed first in the print processing. For example, when the print processing unit 51 executes the print processing for printing one side of each page image partly on the basis of image data including page images for 10 pages, the print processing unit 51 specifies the specified sheet as the first transported sheet. An image based on the image data is formed. Then, the print processing unit 51 prints each of the page images on each of the second and subsequent conveyed sheets.

  Note that the print processing unit 51 may convey each of the sheets including the first conveyed sheet in the printing process at a predetermined interval. In addition, the print processing unit 51 may form an image based on image data read by the image reading unit 2 or input from an external information processing apparatus on the first conveyed sheet in the printing process.

  The first acquisition processing unit 52 acquires a first timing A1 (see FIG. 4) at which the temperature of the fixing member 371 decreases from the set temperature X1 during the conveyance period of the sheet first conveyed in the printing process.

  For example, the first acquisition processing unit 52 acquires the arrival timing at which the first conveyed sheet in the printing process reaches the nip portion P2 as the first timing A1.

  For example, in the image forming apparatus 10, first timing information indicating the arrival timing is stored in advance in the ROM. For example, the first timing information is information indicating the moving time of the sheet conveyed by the sheet conveying unit 4 from the detection position of the sheet by the sheet sensor 47 to the nip part P2. The first timing information may be information indicating a moving time of the sheet conveyed by the sheet conveying unit 4 from the sheet feeding cassette 41 to the nip part P2.

  The first acquisition processing unit 52 acquires the arrival timing by reading the first timing information stored in the ROM.

  Here, FIG. 4 shows an example of a temperature change of the fixing member 371 that occurs when the sheet conveyed first in the printing process passes through the nip portion P2. The vertical axis in FIG. 4 indicates the temperature of the fixing member 371, and the horizontal axis indicates the passage of time. Further, X1 in FIG. 4 indicates the set temperature described above.

  As shown in FIG. 4, the temperature of the fixing member 371 is maintained at the set temperature X1 by the feedback control until the first timing A1 arrives. When the first timing A1 elapses, the temperature of the fixing member 371 decreases from the set temperature X1. The rate at which the temperature of the fixing member 371 decreases immediately after the first timing A1 changes, depending on the in-machine temperature and in-machine humidity of the image forming apparatus 10 and the material and thickness of the sheet that has reached the nip portion P2. For example, the lower the internal temperature of the image forming apparatus 10, the higher the rate of decrease in the temperature of the fixing member 371 immediately after the first timing A1 has elapsed. Further, as the in-machine humidity of the image forming apparatus 10 is higher, the rate of decrease in the temperature of the fixing member 371 immediately after the first timing A1 elapses becomes higher. Further, as the thickness of the sheet reaching the nip portion P2 is thicker, the rate of temperature decrease of the fixing member 371 immediately after the first timing A1 elapses becomes higher.

  The rate of temperature decrease of the fixing member 371 after the first timing A1 has elapsed is that the output of the heating unit 373 is increased according to the temperature decrease of the fixing member 371 by the feedback control, and the time from the first timing A1 is increased. It gradually decreases with the passage of time to zero. Thereafter, as the sheet passes through the nip portion P2, the temperature of the fixing member 371 increases, and the temperature of the fixing member 371 converges to the set temperature X1 as time passes.

  The second acquisition processing unit 53 is detected by the temperature sensor 374 at the acquisition time T1 for each predetermined acquisition time T1 (see FIG. 4) from the first timing A1 acquired by the first acquisition processing unit 52. The change amounts D11 to D16 of the temperature of the fixing member 371 are acquired.

  Here, the acquisition time T1 is shorter than the time from when the leading edge of the sheet conveyed by the sheet conveying unit 4 reaches the nip part P2 until the trailing edge of the sheet passes through the nip part P2. It is a fixed time. As the acquisition time T1 is shorter, the acquisition accuracy of the second timing A2 (see FIG. 4) described later can be improved. For example, the acquisition time T <b> 1 is set by a person in charge of manufacturing the image forming apparatus 10 when the image forming apparatus 10 is manufactured. The acquisition time T1 may be arbitrarily set by a user operation on the operation display unit 6. In FIG. 4, for the convenience of explanation, an acquisition time T1 that is set longer than the original is shown.

  For example, the second acquisition processing unit 53 acquires the temperature of the fixing member 371 using the temperature sensor 374 at the first timing A1. The second acquisition processing unit 53 receives the first timing A1 when the time indicated by the first timing information acquired by the first acquisition processing unit 52 has elapsed since the sheet sensor 47 detected the sheet. Judge that Further, the second acquisition processing unit 53 acquires the temperature of the fixing member 371 using the temperature sensor 374 at the timing when the acquisition time T1 has elapsed from the first timing A1. Then, the second acquisition processing unit 53 subtracts the temperature detected by the temperature sensor 374 acquired at the first timing A1 from the temperature detected by the temperature sensor 374 acquired when the acquisition time T1 has elapsed from the first timing A1. Then, the change amount D11 is acquired. Similarly, the second acquisition processing unit 53 acquires the change amounts D12 to D16. In the following description, the change amount acquired at an arbitrary timing by the second acquisition processing unit 53 may be referred to as a change amount D1X.

  The second acquisition processing unit 53 is detected by the temperature sensor 374 at the acquisition time T1 every acquisition time T1 from the time when the sheet is detected by the sheet sensor 47 or the time when the sheet conveyance unit 4 starts to convey the sheet. The amount of change in the temperature of the fixing member 371 may be acquired. In this case, the first acquisition processing unit 52 may acquire the first timing A1 based on the amount of change in the temperature of the fixing member 371 acquired by the second acquisition processing unit 53. For example, the first acquisition processing unit 52 acquires the time when the amount of change in the temperature of the fixing member 371 acquired by the second acquisition processing unit 53 changes from 0 to a negative value from when the sheet is detected by the sheet sensor 47. Information indicating the elapsed time up to the time before time T1 may be acquired as the first timing A1.

  The third acquisition processing unit 54, based on the change amount D1X acquired by the second acquisition processing unit 53, the second timing A2 at which the temperature decrease of the fixing member 371 that continues from the first timing A1 stops (see FIG. 4). To get.

  For example, every time the change amount D1X is acquired by the second acquisition processing unit 53, the third acquisition processing unit 54 determines whether or not the change amount D1X is 0 or a positive value. When the third acquisition processing unit 54 determines that the change amount D1X is either 0 or a positive value, the second acquisition timing T1 is set to a timing before the acquisition time T1 from the timing at which the change amount D1X is acquired. Obtain as A2.

  For example, in the example shown in FIG. 4, the change amounts D11 to D15 are negative values, whereas the change amount D16 is a positive value. Therefore, the third acquisition processing unit 54 acquires the timing before the acquisition time T1 as the second timing A2 from the timing A5 (see FIG. 4) at which the change amount D16 is acquired. For example, the third acquisition processing unit 54 acquires second timing information indicating the time from the first timing A1 to the second timing A2 as the second timing A2.

  Note that the third acquisition processing unit 54 may execute a process of acquiring the second timing A2 in parallel with the process of acquiring the amount of change in the temperature of the fixing member 371 by the second acquisition processing unit 53. In this case, the second acquisition processing unit 53 may not execute the process of acquiring the amount of change in the temperature of the fixing member 371 after the third acquisition processing unit 54 acquires the second timing A2.

  The setting processing unit 55 determines the third timing A3 (see FIG. 5) during the conveyance period of each of the second and subsequent sheets conveyed in the printing process based on the change amounts D11 to D16 acquired by the second acquisition processing unit 53. 5) to the fourth timing A4 (see FIG. 5), the rate of increase U11 to U15 (see FIG. 5) of the output of the heating unit 373 for each acquisition time T1 is set.

  Here, the third timing A3 is a timing corresponding to the first timing A1 during the conveyance period of each of the second and subsequent sheets conveyed in the printing process. For example, the third timing A3 is a timing at which the time indicated by the first timing information has elapsed since the detection by the sheet sensor 47 of each of the second and subsequent sheets conveyed in the printing process.

  The fourth timing A4 is a timing corresponding to the second timing A2 during the conveyance period of each of the second and subsequent sheets conveyed in the printing process. For example, the fourth timing A4 is a timing at which the time indicated by the second timing information has elapsed from the third timing A3.

  Specifically, the setting processing unit 55 determines the third timing based on each of the change amounts D11 to 15 acquired up to the second timing A2 among the change amounts D11 to 16 acquired by the second acquisition processing unit 53. The rate of increase U11 to U15 of the output of the heating unit 373 for each acquisition time T1 between A3 and the fourth timing A4 is set.

  Here, the increase rates U11 to U15 are values indicating an increase rate (percentage) with respect to the drive power immediately before the third timing A3 arrives. For example, the rate of increase U11 is 30%, the rate of increase U12 is 15%, the rate of increase U13 is 7%, the rate of increase U14 is 3%, and the rate of increase U15 is 1%. Here, the rate of increase U11 to U15 is an example of the amount of increase in the present invention. In the following description, any increase rate set by the setting processing unit 55 may be referred to as an increase rate U1X.

  For example, the setting processing unit 55 passes the acquisition time T1 from the third timing A3 (see FIG. 5) based on the change amount D11 from the first timing A1 (see FIG. 4) to the timing at which the acquisition time T1 has passed. The rate of increase U11 is set up to the timing.

  For example, in the image forming apparatus 10, first table data indicating a correspondence relationship between the change amount D1X acquired by the second acquisition processing unit 53 and the increase rate U1X set by the setting processing unit 55 is stored in the ROM in advance. Has been.

  The setting processing unit 55 acquires the increase rate U11 corresponding to the change amount D11 based on the first table data. For example, the setting processing unit 55 stores the acquired increase rate U11 in a predetermined storage area of the RAM, so that the period from the third timing A3 (see FIG. 5) to the timing when the acquisition time T1 has elapsed. The rate of increase U11 at is set. Similarly, the setting processing unit 55 sets the rate of increase U12 to U15 based on the change amounts D12 to D15.

  Note that the setting processing unit 55 may acquire the increase rate U11 corresponding to the change amount D11 from the change amount D11 using a predetermined calculation formula.

  The determination processing unit 56 determines the type of the sheet first conveyed in the printing process based on the change amount D11 from the first timing A1 acquired by the second acquisition processing unit 53 until the acquisition time T1 elapses. Determine.

  For example, in the image forming apparatus 10, second table data indicating a correspondence relationship between the change amount D <b> 11 acquired by the second acquisition processing unit 53 and the sheet type is stored in advance in the ROM.

  The determination processing unit 56 determines that the type of the sheet corresponding to the change amount D11 specified by the second table data is the type of the sheet first conveyed in the printing process.

  The change processing unit 57 changes the set temperature X <b> 1 based on the sheet type determined by the determination processing unit 56.

  For example, in the image forming apparatus 10, the third table data indicating the correspondence relationship between the sheet type and the temperature of the fixing member 371 optimal for the transfer of the toner image transferred to the sheet of the type is stored in the ROM in advance. ing.

  The change processing unit 57 sets the temperature corresponding to the sheet type determined by the determination processing unit 56 specified by the third table data as the set temperature X1.

  The power supply control unit 58 increases the driving power in accordance with the increase rate U1X for each acquisition time T1 set by the setting processing unit 55 every time the second and subsequent sheets are conveyed in the printing process.

  For example, the power supply control unit 58 increases the duty ratio of the electric signal Sig2 based on the increase rate U11 from the third timing A3 (see FIG. 5) to the timing at which the acquisition time T1 has elapsed. Specifically, the power feeding control unit 58 increases the output of the electric power Sig2 so that the output of the electric power Sig2 increases by an increase obtained by multiplying the driving electric power just before the third timing A3 arrives by the increase rate U11. Increase the duty ratio. Similarly, the power supply control unit 58 increases the duty ratio of the electric signal Sig2 based on each of the increase rates U12 to U15.

[Temperature control processing]
Hereinafter, an example of the procedure of the temperature control method according to the present invention will be described together with an example of the procedure of the temperature control process executed by the control unit 5 in the image forming apparatus 10 with reference to FIG. Here, steps S11, S12,... Represent the numbers of processing procedures (steps) executed by the control unit 5. The control unit 5 executes the temperature control process when a user operation for instructing execution of the print process is performed on the operation display unit or when a print job is transmitted from an external information processing apparatus. To do.

<Step S11>
First, in step S11, the control unit 5 starts the printing process. Here, the process of step S <b> 11 is an example of a printing step in the present invention, and is executed by the print processing unit 51 of the control unit 5.

  Specifically, the control unit 5 controls the operation of each unit of the sheet conveying unit 4 to sequentially convey the sheets stored in the sheet feeding cassette 41 toward the sheet discharge tray 46. Further, the control unit 5 controls the operation of each unit of the image forming unit 3 to form an image based on the image data on each sheet conveyed by the sheet conveying unit 4.

  Here, the control unit 5 causes the conveyance interval between the first conveyed sheet and the second conveyed sheet in the printing process to be longer than the conveyance interval between the second and subsequent sheets. Each of the sheets is conveyed. As a result, the temperature of the fixing member 371, which has decreased as a result of the first sheet passing through the nip portion P2, until the second conveyed sheet reaches the fixing device 37, is converged to the set temperature X1. It becomes possible.

  Further, the control unit 5 forms an image based on the specific image data including only white pixels on the sheet conveyed first in the printing process. As a result, due to the temperature difference of the fixing member 371 during fixing of the toner image, the image quality of the image printed on the sheet conveyed first in the printing process and the sheets conveyed on the second and subsequent sheets are printed. It is avoided that there is a difference between the quality of the image to be processed.

<Step S12>
In step S12, the controller 5 determines the first timing A1 when the temperature of the fixing member 371 decreases from the set temperature X1 during the conveyance period of the sheet first conveyed in the printing process started in step S11 (FIG. 4). Reference). Here, the process of step S <b> 12 is an example of a first acquisition step in the present invention, and is executed by the first acquisition processing unit 52 of the control unit 5.

  For example, the control unit 5 acquires the first timing information read from the ROM as the first timing A1. Accordingly, the processing is performed in comparison with the configuration in which the first timing A1 is acquired by monitoring the temperature detected by the temperature sensor 374 from the time when the sheet is detected by the sheet sensor 47 or the time when the sheet conveying unit 4 starts conveying the sheet. It can be simplified.

<Step S13>
In step S13, the control unit 5 changes the temperature of the fixing member 371 detected by the temperature sensor 374 at the acquisition time T1 for each acquisition time T1 (see FIG. 4) from the first timing A1 acquired in step S12. The quantities D11 to D16 are acquired. Here, the process of step S <b> 13 is an example of a second acquisition step in the present invention, and is executed by the second acquisition processing unit 53 of the control unit 5.

  For example, the control unit 5 obtains the change amount D11 by subtracting the temperature detected by the temperature sensor 374 at the first timing A1 from the temperature detected by the temperature sensor 374 at the timing when the acquisition time T1 has elapsed from the first timing A1. . Similarly, the control unit 5 acquires the change amounts D12 to D16.

<Step S14>
In step S14, the control unit 5 acquires a second timing A2 (see FIG. 4) at which the temperature decrease of the fixing member 371 that continues from the first timing A1 stops based on the change amount D1X acquired in step S13. . Here, the process of step S <b> 14 is an example of a third acquisition step in the present invention, and is executed by the third acquisition processing unit 54 of the control unit 5.

  For example, every time the change amount D1X is acquired in step S13, the control unit 5 determines whether the change amount D1X is one of 0 and a positive value. When the control unit 5 determines that the change amount D1X is either 0 or a positive value, the control unit 5 acquires the timing before the acquisition time T1 as the second timing A2 from the timing at which the change amount D1X is acquired. To do.

<Step S15>
In step S15, the control unit 5 determines the type of the sheet conveyed first in the printing process based on the change amount D11 from the first timing A1 acquired in step S13 until the acquisition time T1 elapses. judge. Here, the process of step S <b> 15 is executed by the determination processing unit 56 of the control unit 5.

  For example, the control unit 5 determines that the type of the sheet corresponding to the change amount D11 specified by the second table data is the type of the sheet first conveyed in the printing process.

<Step S16>
In step S16, the control unit 5 changes the set temperature X1 based on the sheet type determined in step S15. Here, the process of step S <b> 16 is executed by the change processing unit 57 of the control unit 5.

  For example, the control unit 5 sets the temperature corresponding to the sheet type determined in step S15, which is specified by the third table data, as the set temperature X1. Thereby, it is possible to set the temperature according to the sheet type as the set temperature X1 without providing a configuration for detecting the sheet type.

  In addition, the process of step S15 and step S16 may be abbreviate | omitted.

<Step S17>
In step S <b> 17, the control unit 5 determines the third timing A <b> 3 during the conveyance period of each of the second and subsequent sheets conveyed in the printing process based on the change amounts D <b> 11 to 16 acquired in step S <b> 13 (FIG. 5). The increase rate U11 to U15 of the output of the heating unit 373 for each acquisition time T1 from the reference) to the fourth timing A4 is set. Here, the process of step S <b> 17 is an example of a setting step in the present invention, and is executed by the setting processing unit 55 of the control unit 5.

  For example, the control unit 5 acquires the increase rate U11 corresponding to the change amount D11 based on the first table data. Then, the control unit 5 sets the increase rate U11 between the third timing A3 and the timing when the acquisition time T1 has elapsed by storing the acquired increase rate U11 in the storage area of the RAM. Similarly, the control unit 5 sets the rate of increase U12 to U15 based on the change amounts D12 to D15.

<Step S18>
In step S18, the control unit 5 determines whether or not the third timing A3 has arrived.

  For example, the control unit 5 determines that the third timing A3 has arrived when the time indicated by the first timing information has elapsed since the sheet sensor 47 detected the second or later conveyed sheet in the printing process. Judge that

  Here, if the control part 5 judges that the 3rd timing A3 has arrived (Yes side of S18), it will transfer a process to step S19. If the third timing A3 has not arrived (No side in S18), the control unit 5 waits for the arrival of the third timing A3 in step S18.

<Step S19>
In step S19, the control unit 5 increases the drive power according to the increase rate U1X for each acquisition time T1 set in step S17. Here, the process of step S19 is an example of a power supply control step in the present invention, and is executed by the power supply control unit 58 of the control unit 5.

  For example, the control unit 5 increases the duty ratio of the electric signal Sig2 based on the increase rate U11 from the third timing A3 (see FIG. 5) to the timing at which the acquisition time T1 has elapsed. Specifically, the control unit 5 determines the duty of the electric signal Sig2 so that the output of the drive power increases by an increase obtained by multiplying the drive power immediately before the third timing A3 arrives by the increase rate U11. Increase the ratio. Similarly, the control unit 5 increases the duty ratio of the electric signal Sig2 based on each of the increase rates U12 to U15.

  Here, FIG. 6 shows an example of a temperature change of the fixing member 371 when the process of step S19 is executed. D20 in FIG. 6 indicates a difference between the set temperature X1 and the lowest temperature of the fixing member 371 between the third timing A3 and the fourth timing A4. Note that the change amount D20 is smaller than the change amount D10 obtained by adding the change amounts D11 to D15 shown in FIG.

  As shown in FIG. 6, the temperature change of the fixing member 371 (see FIG. 4) during the first sheet conveyance period in the printing process in which the process of step S <b> 19 is not executed by executing the process of step S <b> 19. In comparison, the temperature change of the fixing member 371 is suppressed.

<Step S20>
In step S20, the control unit 5 determines whether or not the printing process has been completed.

  Here, if the control part 5 judges that the said printing process was complete | finished (Yes side of S20), it will complete | finish the said temperature control process. If the printing process has not been completed (No in S20), the control unit 5 shifts the process to step S18.

  As described above, in the image forming apparatus 10, the temperature of the fixing member 371 from the first timing A1 to the acquisition time T1 based on the detection result by the temperature sensor 374 during the conveyance period of the sheet conveyed first in the printing process. Change amounts D11 to D16 are acquired. And among the acquired temperature change amounts D11 to D16, based on the change amounts D11 to D15 up to the second timing A2, the third time during the transport period of each of the second and subsequent sheets transported in the printing process. Increase rates U11 to U15 of the output of the heating unit 373 for each acquisition time T1 between the timing A3 and the fourth timing A4 are set.

  That is, the image forming apparatus 10 acquires the temperature decrease amount of the fixing member 371 reflecting various conditions such as the ambient temperature at the time of execution of the printing process and the thickness of the sheet used for printing, and is based on the temperature decrease amount. The feedforward control is executed in accordance with the amount of increase in the driving power set as described above. Thereby, even when various conditions during printing are changed, the temperature of the fixing member 371 can be converged to the set temperature X1 until the next sheet reaches the nip portion P2.

1 ADF
2 image reading unit 3 image forming unit 4 sheet conveying unit 5 control unit 10 image forming apparatus 37 fixing device 51 print processing unit 52 first acquisition processing unit 53 second acquisition processing unit 54 third acquisition processing unit 55 setting processing unit 56 determination Processing unit 57 Change processing unit 58 Power supply control unit 371 Fixing member 372 Pressure member 373 Heating unit 374 Temperature sensor 375 Power supply unit

Claims (6)

A fixing member heated to a predetermined set temperature; and a pressure member pressed against the fixing member; and a toner image is fixed to the sheet at a nip formed by the fixing member and the pressure member. A fixing unit;
A heating unit that receives supply of driving power and heats the fixing member;
A temperature sensor for detecting the temperature of the fixing member;
A print processing unit that executes a printing process for forming an image based on image data on each of a plurality of sheets sequentially conveyed along a conveyance path that passes through the nip portion;
A first acquisition processing unit for acquiring a first timing at which the temperature of the fixing member decreases from the set temperature during a conveyance period of a sheet first conveyed in the printing process;
A second acquisition processing unit that acquires a change in temperature of the fixing member detected by the temperature sensor at the acquisition time for each predetermined acquisition time from the first timing;
A third acquisition processing unit that acquires a second timing at which the temperature decrease of the fixing member that continues from the first timing stops based on each of the change amounts acquired by the second acquisition processing unit;
Based on each change amount acquired by the second acquisition processing unit, the second timing from the third timing corresponding to the first timing during the conveyance period of each of the second and subsequent sheets conveyed in the printing process. A setting processing unit that sets an increase amount of the output of the heating unit for each acquisition time until the fourth timing corresponding to the timing;
A power supply control unit that increases the driving power according to the amount of increase for each acquisition time set by the setting processing unit each time the second and subsequent sheets are conveyed in the printing process,
An image forming apparatus comprising: The first acquisition processing unit acquires, as the first timing, an arrival timing at which a sheet conveyed first in the printing process reaches the nip portion.
The image forming apparatus according to claim 1. A determination processing unit that determines a type of a sheet first conveyed in the printing process based on the change amount from the first timing acquired by the second acquisition processing unit to the time when the acquisition time elapses. When,
Based on the type of sheet determined by the determination processing unit, a change processing unit that changes the set temperature,
The image forming apparatus according to claim 1, further comprising: The print processing unit is configured such that a conveyance interval between a first conveyed sheet and a second conveyed sheet in the printing process is longer than a conveyance interval between second and subsequent sheets. Transport each sheet,
The image forming apparatus according to claim 1. The print processing unit forms an image based on specific image data including only white pixels on a sheet conveyed first in the print processing;
The image forming apparatus according to claim 1. A fixing member heated to a predetermined set temperature; and a pressure member pressed against the fixing member; and a toner image is fixed to the sheet at a nip formed by the fixing member and the pressure member. A temperature control method executed in an image forming apparatus, comprising: a fixing unit; a heating unit that receives supply of driving power to heat the fixing member; and a temperature sensor that detects a temperature of the fixing member,
A printing step of executing a printing process for forming an image based on image data on each of a plurality of sheets sequentially conveyed along a conveyance path passing through the nip portion;
A first acquisition step of acquiring a first timing at which a temperature of the fixing member decreases from the set temperature during a conveyance period of a sheet conveyed first in the printing process;
A second acquisition step of acquiring a change amount of the temperature of the fixing member detected by the temperature sensor at the acquisition time for each predetermined acquisition time from the first timing;
A third acquisition step of acquiring a second timing at which the temperature decrease of the fixing member that continues from the first timing stops based on each of the change amounts acquired by the second acquisition step;
Based on each of the change amounts acquired in the second acquisition step, the second timing from the third timing corresponding to the first timing during the conveyance period of each of the second and subsequent sheets conveyed in the printing process. A setting step for setting an increase amount of the output of the heating unit for each acquisition time until the fourth timing corresponding to
A power supply control step of increasing the driving power according to the amount of increase for each acquisition time set by the setting step each time the second and subsequent sheets are conveyed in the printing process;
Including temperature control method.

Images