JP6747409B2 - Image forming apparatus and temperature control method - Google Patents

Description

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

The electrophotographic image forming apparatus includes a fixing unit that fixes the toner image transferred on the 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 portion formed between the fixing member and the pressure member, the toner image transferred to the sheet is heated and pressed to be fixed on the sheet. It There is known an image forming apparatus capable of detecting the type of a sheet on which an image is formed and setting the set temperature based on the detection result (see Patent Document 1).

JP, 2004-277057, A

By the way, the temperature of the fixing member may decrease when the sheet passes through the nip portion. 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 by the image forming apparatus may deteriorate. .. On the other hand, while the sheet passes through the nip portion, feedforward control is performed to increase the output of the heating unit that heats the fixing member in accordance with a preset amount of increase, thereby lowering the temperature of the fixing member. Can be suppressed.

Here, the amount of temperature decrease in the fixing member when the sheet passes through the nip portion changes 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 of 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, which deteriorates the image quality of the printed matter output by 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 before the next sheet reaches the nip portion, even when various conditions during printing are changed, and a temperature. It is to provide a control method.

An image forming apparatus according to an 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. , A setting processing unit and a power supply control unit. The fixing unit includes a fixing member that is heated to a predetermined set temperature and a pressure member that is pressed against the fixing member, and a toner image is formed at a nip portion formed by the fixing member and the pressure member. To the sheet. The heating unit heats the fixing member by receiving driving power. The temperature sensor detects the temperature of the fixing member. The print processing unit performs a print process of forming an image based on image data on each of a plurality of sheets that are sequentially transported along a transport path that passes 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 the conveyance period of the sheet that is first conveyed in the printing process. The second acquisition processing unit acquires the amount of change in the temperature of the fixing member detected by the temperature sensor at each acquisition time set in advance from the first timing. The third acquisition processing unit acquires, based on each of the change amounts acquired by the second acquisition processing unit, a second timing at which the temperature decrease of the fixing member, which continues from the first timing, stops. The setting processing unit, based on each of the change amounts acquired by the second acquisition processing unit, corresponds to the first timing corresponding to the first timing during the transportation period of each of the second and subsequent sheets transported in the printing process. An increase amount of the output of the heating unit is set for each acquisition time from the third timing to the fourth timing corresponding to the second timing. The power supply control unit increases the drive power every time the second and subsequent sheets are conveyed in the printing process, according to the increase amount for each acquisition time set by the setting processing unit.

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 brought into pressure contact with the fixing member. Image formation including a fixing unit that fixes the toner image on the sheet at the nip portion that is formed, a heating unit that heats the fixing member by receiving driving power, and a temperature sensor that detects the 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 supply control step. In the printing step, a printing process is performed to form an image based on the image data on each of a plurality of sheets that are sequentially transported along the transport path that passes through the nip portion. In the first acquisition step, a first timing at which the temperature of the fixing member drops from the set temperature during the transportation period of the sheet that is first transported in the printing process is acquired. In the second acquisition step, the amount of change in the temperature of the fixing member detected by the temperature sensor during the acquisition time is acquired for each predetermined acquisition time from the first timing. In the third acquisition step, the second timing at which the temperature decrease of the fixing member, which continues from the first timing, stops is acquired based on each of the amounts of change acquired in the second acquisition step. In the setting step, a third timing corresponding to the first timing in the transport period of each of the second and subsequent sheets transported in the printing process based on each of the change amounts obtained in the second obtaining step. To the fourth timing corresponding to the second timing, the increase amount of the output of the heating unit for each of the acquisition times is set. In the power feeding control step, the drive power is increased every time the second and subsequent sheets are conveyed in the printing process, according to the increase amount for each acquisition time set in the setting step.

According to the present invention, even when various conditions at the time of printing change, it is possible to make the temperature of the fixing member converge to the set temperature before the next sheet reaches the nip portion.

FIG. 1 is a diagram showing 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 temperature control processing executed by the image forming apparatus according to the embodiment of the present invention. FIG. 4 is a diagram 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 showing 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 embodiments are examples of embodying the present invention and do 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 exemplary embodiment of the present invention 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 multi-function peripheral having a scan function for reading image data from a document, a print function for forming an image based on the image data, and a plurality of functions such as a facsimile function and a copy function. Further, the present invention can be applied to an image forming apparatus such as a printer device, a facsimile device, and a copying machine.

As shown in FIGS. 1 and 2, the image forming apparatus 10 includes an ADF (automatic document feeder) 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 transport rollers, a document retainer, and a paper discharge unit, and transports 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 a document. The operation display unit is a display unit such as a liquid crystal display that displays various kinds of information according to a control instruction from the control unit 5, and an operation key or a touch panel that inputs various kinds of information to the control unit 5 according to a user's operation. Has an operation unit such as.

The control unit 5 includes control devices such as a CPU, a ROM, a RAM, and an EEPROM (registered trademark), which are 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 non-volatile storage device. The RAM and the EEPROM are used as a temporary storage memory (work area) for various processes executed by the CPU. In the control unit 5, the CPU executes various control programs stored in advance in the ROM. As a result, the image forming apparatus 10 is comprehensively controlled by the control unit 5. The control unit 5 may be composed of an electronic circuit such as an integrated circuit (ASIC), and is a control unit provided separately from the main control unit that integrally controls the image forming apparatus 10. May be.

The image forming unit 3 can form an image by an electrophotographic method 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 device 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 conveying unit 4 includes a sheet feeding cassette 41, a feeding mechanism 42, a conveying path 43, a registration roller 44, a discharging roller 45, a discharging 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 paper feed cassette 41 accommodates 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 a 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 transport path 43 is provided with a plurality of rollers including a registration roller 44 and a discharge roller 45. The plurality of rollers conveys the sheet along the conveyance path 43 in the conveyance direction D1 shown in FIG. 1 by being rotated by a driving force generated by a motor (not shown) being transmitted. Further, 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. The sheet transport path defined by the transport path 43 is an example of the transport path in the invention. The sheet sensor 47 is provided on the upstream side of the registration roller 44 in the transport path 43 in the transport 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 charging device 32 uniformly charges the surface of the photosensitive drum 31 to a predetermined potential. Then, the optical scanning device 33 irradiates the surface of the photosensitive drum 31 with light based on the image data. As a result, an electrostatic latent image corresponding to the image data is formed on the surface of the photosensitive drum 31.

Then, 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 photoconductor drum 31 is conveyed by the photoconductor drum 31 to the transfer position P1 (see FIG. 1) by the transfer device 35. It should be noted that the developing device 34 is replenished with toner from a toner container 34A (see FIG. 1) that is detachable 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 paper feed cassette 41 uses a lift plate (not shown) provided at the bottom of the paper feed cassette 41 to connect the sheets stored in the paper feed cassette 41 to the pickup roller 421 of the feeding mechanism 42. Lift to the 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 at the timing when 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 rollers 44 is set based on the sheet passage detection timing of 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 the 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 on the sheet is fixed on the sheet. The sheet on which the toner image has been fixed by the fixing device 37 is discharged to the paper 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. The fixing member 371 may be a belt-shaped member.

The pressure member 372 is provided rotatably in contact with the fixing member 371. For example, the pressing member 372 is a roller-shaped member. The pressure member 372 is biased toward the fixing member 371 by a biasing member (not shown). As a result, 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 pressing member 372. It As a result, the toner image transferred to the sheet is fixed on the sheet. Here, the fixing member 371 and the pressing member 372 are examples of the fixing unit in the present invention.

The heating unit 373 receives the driving power and heats the fixing member 371. 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 apart 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 according to the amount of received light. And so on. The temperature sensor 374 outputs an electric signal Sig1 (see FIG. 2) according to the temperature of the surface of the fixing member 371.

The power supply unit 375 supplies the drive power to the heating unit 373. Specifically, the power feeding unit 375 is a power source capable of outputting the drive power according to the electric signal Sig2 (see FIG. 2) input from the control unit 5. For example, the electric signal Sig2 is a PWM signal.

Here, the control unit 5 controls the output of the heating unit 373 so that the temperature of the fixing member 371 becomes the target temperature set temperature X1 based on the current temperature of the fixing member 371 detected by the temperature sensor 374. Perform feedback 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, and the generated electric signal Sig2 is generated. The signal Sig2 is input to the power feeding unit 375.

By the way, the temperature of the fixing member 371 may decrease when the sheet passes through the nip portion P2. If the degree of this temperature decrease is large, the next sheet reaches the nip 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 by the image forming apparatus 10 is improved. It may decrease. On the other hand, while the sheet passes through the nip portion P2, feedforward control for increasing the output of the heating unit 373 according to a preset amount of increase is executed to suppress the temperature decrease in the fixing member 371. It is possible.

Here, the amount of temperature decrease in the fixing member 371 when the sheet passes through the nip portion P2 changes depending on the ambient temperature during printing, the thickness of the sheet, and the like. Therefore, in the conventional feedforward control, there may be a difference between the temperature decrease amount compensated by the increase amount and the actual temperature decrease amount of 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 thus the image quality of the printed matter output by the image forming apparatus 10 is improved. descend.

On the other hand, in the image forming apparatus 10 according to the exemplary embodiment of the present invention, as described below, even when various conditions during printing are changed, fixing is performed before the next sheet reaches the nip portion P2. It is possible to make the temperature of the member 371 converge 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 the temperature control process (see the flowchart of FIG. 3) described later. The temperature control program may be recorded in a computer-readable recording medium such as a CD, a DVD, or a flash memory, and may be read from the recording medium and installed in a storage device such as the EEPROM. Good.

Then, the control unit 5, as shown in FIG. 2, 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. , A change processing unit 57, and a power feeding control unit 58. Specifically, the control unit 5 uses the CPU to execute the temperature control program stored in the ROM. Accordingly, the control unit 5 causes 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, the determination processing unit 56, the change processing unit 57, and The power supply controller 58 functions.

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

Specifically, the print processing unit 51 controls the operation of each unit 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 transport unit 4 to sequentially transport the sheets contained in the paper feed cassette 41 toward the paper discharge tray 46. The print processing unit 51 also 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 is configured such that the conveyance interval between the sheet first conveyed by the sheet conveyance unit 4 and the second conveyed sheet after the start of execution of the print processing is between the sheets conveyed second or later. Each of the sheets is conveyed by the sheet conveying unit 4 so as to be longer than the conveyance interval of.

Further, the print processing unit 51 forms an image based on the specific image data including only white pixels on the first sheet conveyed in the print processing. For example, in the case where the print processing unit 51 executes the above-described print processing for printing one part of each page image on the basis of image data including page images for 10 pages, the print processing unit 51 specifies the sheet to be conveyed first as the specific image. 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.

The print processing unit 51 may convey each of the sheets including the first sheet to be conveyed in the print processing 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 device on the first sheet conveyed in the print processing.

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

For example, in the image forming apparatus 10, the first timing information indicating the arrival timing is stored in the ROM in advance. For example, the first timing information is information indicating the movement time of the sheet conveyed by the sheet conveying section 4 from the sheet detection position of the sheet sensor 47 to the nip portion P2. The first timing information may be information indicating the moving time of the sheet conveyed by the sheet conveying section 4 from the sheet feeding cassette 41 to the nip portion 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 first conveyed in the printing process passes through the nip portion P2. The vertical axis in FIG. 4 represents the temperature of the fixing member 371, and the horizontal axis represents the passage of time. Further, X1 in FIG. 4 indicates the above-mentioned set temperature.

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. After the lapse of the first timing A1, the temperature of the fixing member 371 decreases from the set temperature X1. The rate of decrease of the temperature of the fixing member 371 immediately after the passage of the first timing A1 changes depending on the temperature inside the apparatus and the humidity inside the apparatus, the material and thickness of the sheet reaching the nip P2, and the like. For example, the lower the temperature inside 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, the higher the humidity inside the image forming apparatus 10, the higher the rate of decrease of the temperature of the fixing member 371 immediately after the passage of the first timing A1. Further, the thicker the sheet that has reached the nip portion P2, the higher the rate of decrease in the temperature of the fixing member 371 immediately after the passage of the first timing A1.

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

The second acquisition processing unit 53 is detected by the temperature sensor 374 at the acquisition time T1 at 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 portion P2 to when the trailing end of the sheet passes through the nip portion P2. It is a fixed time. The shorter the acquisition time T1, the more the acquisition accuracy of the second timing A2 (see FIG. 4) described later can be improved. For example, the acquisition time T1 is set by the person in charge of manufacturing the image forming apparatus 10 when the image forming apparatus 10 is manufactured. Further, the acquisition time T1 may be arbitrarily set by a user operation on the operation display unit 6. For convenience of description, FIG. 4 shows the acquisition time T1 that is set to be longer than the original one.

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 arrives at 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. I judge that I did. In addition, 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 at the timing 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 amount of change acquired by the second acquisition processing unit 53 at arbitrary timing may be referred to as the amount of change D1X.

The second acquisition processing unit 53 is detected by the temperature sensor 374 at the acquisition time T1 for each acquisition time T1 from the time when the sheet sensor 47 detects the sheet or the time when the sheet conveyance unit 4 starts to convey the sheet. The change amount of 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 from the time when the sheet sensor 47 detects a sheet and 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. Information indicating the elapsed time until the time before the 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 (see FIG. 4) at which the temperature decrease of the fixing member 371 continued from the first timing A1 is stopped. To get.

For example, the third acquisition processing unit 54 determines whether or not the change amount D1X is either 0 or a positive value each time the change amount D1X is acquired by the second acquisition processing unit 53. Then, when the third acquisition processing unit 54 determines that the change amount D1X is either 0 or a positive value, the third acquisition processing unit 54 sets the timing before the acquisition time T1 to the timing when the change amount D1X is acquired as the second timing. Acquire as A2.

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

The third acquisition processing unit 54 may execute the 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 does not have to execute the process of acquiring the amount of change in the temperature of the fixing member 371 after the second timing A2 is acquired by the third acquisition processing unit 54.

The setting processing unit 55, based on the respective change amounts D11 to 16 acquired by the second acquisition processing unit 53, the third timing A3 (FIG. 5) to the fourth timing A4 (see FIG. 5), the increase rates U11 to U15 (see FIG. 5) of the output of the heating unit 373 for each acquisition time T1 are set.

Here, the third timing A3 is a timing corresponding to the first timing A1 during the transport period of each of the second and subsequent sheets transported 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 from the time of 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 transport period of each of the second and subsequent sheets transported in the printing process. For example, the fourth timing A4 is timing when the time indicated by the second timing information has elapsed from the third timing A3.

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

Here, the increase rates U11 to U15 are values indicating an increase rate (percentage) with respect to the drive power immediately before the arrival of the third timing A3. 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, one of the increasing rates set by the setting processing unit 55 may be referred to as an increasing rate U1X.

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

For example, in the image forming apparatus 10, the first table data indicating the 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 advance in the ROM. Has been done.

The setting processing unit 55 acquires the rate of increase U11 corresponding to the amount of change D11 based on the first table data. For example, the setting processing unit 55 stores the obtained rate of increase 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 elapses. The rate of increase U11 is set. Similarly, the setting processing unit 55 sets the rate of increase U12 to U15 based on the change amounts D12 to D15.

The setting processing unit 55 may acquire the rate of increase 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 sheet first conveyed in the printing process based on the amount of change D11 acquired by the second acquisition processing unit 53 from the first timing A1 until the acquisition time T1 elapses. To judge.

For example, in the image forming apparatus 10, the second table data indicating the correspondence between the change amount D11 acquired by the second acquisition processing unit 53 and the sheet type is stored in the ROM in advance.

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

The change processing unit 57 changes the set temperature X1 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 most suitable for transferring 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 type of sheet determined by the determination processing unit 56, which is specified by the third table data, as the set temperature X1.

The power supply control unit 58 increases the drive power according to 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 feeding 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 when the acquisition time T1 has elapsed. Specifically, the power feeding control unit 58 outputs 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 arrival of the third timing A3 by the increase rate U11. Increase the duty ratio. Similarly, the power feeding control unit 58 increases the duty ratio of the electric signal Sig2 based on each of the increasing rates U12 to U15.

[Temperature control processing]
Hereinafter, with reference to FIG. 3, an example of the procedure of the temperature control method in 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. Here, steps S11, S12,... Show numbers of processing procedures (steps) executed by the control unit 5. The control unit 5 executes the temperature control process when a user operation instructing the execution of the print process is performed on the operation display unit or when a print job is transmitted from an external information processing device. To do.

<Step S11>
First, in step S11, the control unit 5 starts the printing process. Here, the process of step S11 is an example of the 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 accommodated in the sheet feeding cassette 41 toward the sheet ejection tray 46. The control unit 5 also controls the operation of each unit of the image forming unit 3 to form an image based on the image data on each of the sheets conveyed by the sheet conveying unit 4.

Here, the control unit 5 sets 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 conveyed sheets. Then, each sheet is conveyed. As a result, the temperature of the fixing member 371 lowered by the passage of the first sheet through the nip portion P2 can be converged to the set temperature X1 until the second sheet conveyed reaches the fixing device 37. It will be possible.

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

<Step S12>
In step S12, the control unit 5 controls the first timing A1 (FIG. 4) 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. Get reference). The process of step S12 is an example of the first acquisition step of 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. As a result, the process is performed in comparison with the configuration in which the temperature detected by the temperature sensor 374 is monitored and the first timing A1 is acquired when the sheet sensor 47 detects the sheet or when the sheet conveying unit 4 starts the sheet conveyance. 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 at 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 S13 is an example of the 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 acquires the amount of change 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 the second timing A2 (see FIG. 4) at which the temperature decrease of the fixing member 371, which continues from the first timing A1, stops, based on the change amount D1X acquired in step S13. .. Here, the process of step S14 is an example of the third acquisition step in the present invention, and is executed by the third acquisition processing unit 54 of the control unit 5.

For example, the control unit 5 determines whether or not the variation D1X is either 0 or a positive value every time the variation D1X is acquired in step S13. Then, 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 from the timing when the change amount D1X is acquired as the second timing A2. To do.

<Step S15>
In step S15, the control unit 5 determines the type of sheet first conveyed 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 S15 is executed by the determination processing unit 56 of the control unit 5.

For example, the control unit 5 determines that the type of sheet identified by the second table data and corresponding to the change amount D11 is the type of the sheet that was 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 S16 is executed by the change processing unit 57 of the control unit 5.

For example, the control unit 5 sets, as the set temperature X1, the temperature identified by the third table data and corresponding to the type of sheet determined in step S15. This makes it possible to set the temperature according to the type of sheet as the set temperature X1 without providing a configuration for detecting the type of sheet.

The processes of steps S15 and S16 may be omitted.

<Step S17>
In step S17, the control unit 5 determines the third timing A3 (FIG. 5) during the transport period of each of the second and subsequent sheets transported in the printing process, based on the change amounts D11 to 16 obtained in step S13. (Refer to) to the fourth timing A4, the rate of increase U11 to U15 of the output of the heating unit 373 for each acquisition time T1 is set. Here, the process of step S17 is an example of the 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 rate of increase U11 corresponding to the change amount D11 based on the first table data. Then, the control unit 5 stores the obtained increase rate U11 in the storage area of the RAM to set the increase rate U11 from the third timing A3 to the timing when the acquisition time T1 has elapsed. 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 arrives at the third timing A3 when the time indicated by the first timing information elapses from the time when the sheet sensor 47 detects the second and subsequent sheets conveyed in the printing process. I judge that I did.

Here, when the control unit 5 determines that the third timing A3 has arrived (Yes side of S18), the control unit 5 shifts the processing to step S19. If the third timing A3 has not arrived (No side of 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 the power feeding control step in the present invention, and is performed by the power feeding 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 when the acquisition time T1 has elapsed. Specifically, the control unit 5 sets 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 arrival of the third timing A3 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 increasing rates U12 to U15.

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

As shown in FIG. 6, the temperature change of the fixing member 371 during the conveyance period of the first sheet in the printing process in which the process of step S19 is not performed by performing the process of step S19 (see FIG. 4). 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 is completed.

Here, when the control unit 5 determines that the printing process is finished (Yes in S20), the temperature control process is finished. If the printing process is not 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 for each acquisition time T1 from the first timing A1 based on the detection result of the temperature sensor 374 during the conveyance period of the sheet first conveyed in the printing process. Change amounts D11 to D16 are acquired. Then, based on the change amounts D11 to D15 up to the second timing A2 among the acquired change amounts D11 to D16 of the temperature, the third sheet in the transport period of each of the second and subsequent sheets transported in the printing process. The 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 that reflects various conditions such as the ambient temperature during the execution of the print process and the thickness of the sheet used for printing, and based on the temperature decrease amount. Feedforward control is executed in accordance with the amount of increase in the drive power set as above. As a result, even when various conditions during printing change, the temperature of the fixing member 371 can be converged to the set temperature X1 before 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 feeding control unit 371 Fixing member 372 Pressure member 373 Heating unit 374 Temperature sensor 375 Power feeding unit

Claims (6)

A fixing member that is heated to a predetermined set temperature and a pressure member that is in pressure contact with the fixing member are provided, and the toner image is fixed to the sheet at a nip portion formed by the fixing member and the pressure member. The fixing unit,
A heating unit that receives the supply of driving power to heat the fixing member;
A temperature sensor for detecting the temperature of the fixing member,
A print processing unit that executes a print process that forms an image based on image data on each of a plurality of sheets that are sequentially transported along a transport path that passes through the nip portion;
A first acquisition processing unit that acquires a first timing at which the temperature of the fixing member decreases from the set temperature during the conveyance period of the sheet that is first conveyed in the printing process;
A second acquisition processing unit that acquires the amount of change in the temperature of the fixing member detected by the temperature sensor at each acquisition time that is predetermined from the first timing;
A third acquisition processing unit that acquires, based on each of the change amounts acquired by the second acquisition processing unit, 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, from the third timing corresponding to the first timing during the transportation period of each of the second and subsequent sheets transported in the printing process to the second timing. A setting processing unit that sets an increase amount of the output of the heating unit for each acquisition time up to a fourth timing corresponding to the timing;
Every time the second and subsequent sheets are conveyed in the printing process, a power supply control unit that increases the drive power according to the increase amount for each acquisition time set by the setting processing unit,
An image forming apparatus including. The first acquisition processing unit acquires, as the first timing, an arrival timing at which a sheet first conveyed in the printing process reaches the nip portion.
The image forming apparatus according to claim 1. A determination processing unit that determines the type of the sheet first conveyed in the printing process based on the amount of change from the first timing acquired by the second acquisition processing unit until 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, so that the transport interval between the first transported sheet and the second transported sheet in the print processing is longer than the transport interval between the second and subsequent transported 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 that is first conveyed in the print processing,
The image forming apparatus according to claim 1. A fixing member that is heated to a predetermined set temperature and a pressure member that is in pressure contact with the fixing member are provided, and the toner image is fixed to the sheet at a nip portion formed by the fixing member and the pressure member. A temperature control method executed by 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 transported along a transport path passing through the nip portion;
A first acquisition step of acquiring a first timing at which the temperature of the fixing member decreases from the set temperature during the transportation period of the sheet that is first transported in the printing process;
A second acquisition step of acquiring the amount of change in the temperature of the fixing member detected by the temperature sensor at each acquisition time, which is predetermined from the first timing.
A third acquisition step of acquiring a second timing at which the temperature decrease of the fixing member continues from the first timing is stopped, based on each of the change amounts acquired in the second acquisition step,
Based on each of the change amounts acquired in the second acquisition step, from the third timing to the second timing corresponding to the first timing during the transportation period of each of the second and subsequent sheets transported in the printing process. Setting step for setting the amount of increase in the output of the heating unit for each acquisition time up to the fourth timing corresponding to
Every time the second and subsequent sheets are conveyed in the printing process, a power supply control step of increasing the drive power according to the increase amount for each acquisition time set by the setting step,
A temperature control method including.

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