Fixing device

Abstract

To suppress change in the shape of a second roll more than when the number of rotations of a fan for sending air to the second roll for pressing a recording medium in a fixation device is kept constant.SOLUTION: A pressure roll 46 is formed so that the diameter of end parts 46b, 46c in a longer axial direction Z is larger than the diameter of a center part 46a in the longer axial direction Z. A fan 48a sends air to the center part 46a, a fan 48b sends air to the end part 46b, and a fan 48c sends air to the end part 46c. A processor changes the number of rotations of the fans by the center part 46a of the pressure roll 46 and the end parts 46b, 46c.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a fixing device. [Background technology]

[0002] A fixing device that fixes an image formed on a recording medium such as paper to the recording medium is known. The fixing device includes a first roll and a second roll. The first roll and the second roll are arranged opposite each other in an area where the image is fixed to the recording medium. The first roll heats the recording medium, and the second roll presses the recording medium toward the first roll. The recording medium on which the image has been formed passes between the first roll and the second roll, and the fixing device applies heat and pressure to the recording medium to fix the image to the recording medium.

[0003] Patent Document 1 describes a fixing device that corrects the magnitude of pressure applied by a pressure roll based on a correction amount corresponding to the cumulative number of past fixing operations. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 10-142995 Summary of the Invention [Problem to be solved by the invention]

[0005] To prevent the occurrence of wrinkles and the like in the recording medium, the second roll may have a flared shape in which the diameter at the longitudinal end is larger than the diameter at the center in the longitudinal direction. By using a second roll with a flared shape, the recording medium is transported while pulling both ends of the recording medium, thereby preventing or suppressing the occurrence of wrinkles and the like. If the shape of the second roll changes, the function of transporting the recording medium while pulling both ends of the recording medium decreases, and wrinkles and the like may occur in the recording medium.

[0006] An object of the present invention is to suppress changes in the shape of the second roll in a fixing device compared to when the rotation speed of the fan that blows air onto the second roll that presses the recording medium is maintained constant. [Means for solving the problem]

[0007] The invention of claim 1 provides a fixing device comprising: a first roll disposed in an area where an image formed on a recording medium is fixed to the recording medium and heats the recording medium; a second roll disposed opposite the first roll in the area and pressurizing the recording medium toward the first roll; a fan blowing air onto the second roll; and a processor controlling the fan, wherein the second roll has a shape in which the diameter of the end portion in the longitudinal axis direction is larger than the diameter of the center portion in the longitudinal axis direction, the first roll and the second roll fix the image to the recording medium in the area, and the processor changes the rotation speed of the fan between the center and the end portion of the second roll. the processor executes a process of changing the rotation speed of the fan in accordance with the length of a total time during which the second roll presses the recording medium, the process of keeping the rotation speed of the fan for a center portion of the second roll unchanged between a first total time and a second total time longer than the first total time, and of decreasing the rotation speed of the fan for an end portion of the second roll in the second total time compared to the rotation speed of the fan for the end portion of the second roll in the first total time. is.

[0011] Claim 2 The invention according to claim 1 further comprises a step of changing the rotation speed of the fan in accordance with the temperature of the second roll. 1 to The fixing device is as described above.

[0012] Claim 3 The invention according to claim 1 further comprises a step of changing the rotation speed of the fan differently between the center and the end of the second roll depending on the temperature state of the second roll. 2 2. The fixing device according to claim 1, wherein the fixing device is a fixing device for fixing a printed circuit board.

[0013] Claim 4 The invention according to claim 1 to claim 2 is characterized in that, when priority is given to image quality, the processor controls the rotation speed of the fan so that the temperature difference between the center and the end of the second roll becomes smaller compared to when priority is not given to image quality. 3 10. The fixing device according to claim 9, wherein the fixing member is a fixing member having a fixing surface. [Effects of the Invention]

[0014] According to the invention of claim 1, it is possible to suppress changes in the shape of the second roll compared to when the rotation speed of the fan that blows air onto the second roll that pressurizes the recording medium in the fixing device is maintained constant.

[0015] moreover In the case where the shape of the second roll may change over time, this can suppress the change in the shape of the second roll.

[0016] Claim 2 , 3 According to the invention, when the temperature state of the second roll changes, the change in shape of the second roll can be suppressed.

[0017] Claim 4 According to the invention, degradation of image quality can be suppressed compared to when the temperature difference between the center and end portions of the second roll is increased. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a diagram illustrating an outline of a configuration of an image forming apparatus according to an embodiment. [Figure 2] 1 is a diagram illustrating an outline of a configuration of a fixing device according to an embodiment. [Figure 3] FIG. 2 is a diagram showing a pressure roll and a fan. [Figure 4] FIG. 2 is a block diagram showing a configuration related to fan control. [Figure 5] FIG. 10 is a diagram showing control of the temperature of the pressure roll. DETAILED DESCRIPTION OF THE INVENTION

[0019] An image forming apparatus according to an embodiment will be described with reference to FIG.

[0020] The image forming apparatus 10 according to the embodiment includes an image forming section 12, a storage section 14, a conveying section 16, and a control device 18.

[0021] The image forming unit 12 forms a toner image by, for example, electrophotography. The storage unit 14 stores a recording medium P such as paper. The transport unit 16 transports the recording medium P stored in the storage unit 14 along a transport path 20 toward the image forming unit 12. The transport unit 16 also transports the recording medium P transported along the transport path 20 along an inversion path 22 to invert the recording medium P and transport it again toward the image forming unit 12.

[0022] The toner image formed by the image forming unit 12 is formed on the surface of the recording medium P transported along the transport path 20. The recording medium P on which the toner image has been formed is discharged to the outside of the housing 10a of the image forming apparatus 10.

[0023] When a toner image is formed on the back surface of the recording medium P, the recording medium P with the toner image formed on the front surface is transported along the reversing path 22, and the toner image is again formed on the back surface of the recording medium P by the image forming unit 12. Thereafter, the recording medium P is ejected to the outside of the housing 10a. Note that, in the example shown in FIG. 1, the image forming apparatus 10 has the function of forming a toner image on both sides of the recording medium P, but it may also have the function of forming a toner image on only one side of the recording medium P.

[0024] The image forming unit 12 includes, for example, image forming units 24Y, 24M, 24C, and 24K, a transfer unit 26, and a fixing device 28, and forms a toner image for each color. The image forming unit 24Y forms a yellow (Y) toner image using yellow (Y) toner. The image forming unit 24M forms a magenta (M) toner image using magenta (M) toner. The image forming unit 24C forms a cyan (C) toner image using cyan (C) toner. The image forming unit 24K forms a black (K) toner image using black (K) toner. The transfer unit 26 transfers the toner images formed by the image forming units 24Y, 24M, 24C, and 24K to the recording medium P. The fixing device 28 fixes the toner images transferred to the recording medium P by the transfer unit 26 to the recording medium P. Although four colors of toner are used in the example shown in FIG. 1, this is merely an example, and five or more colors of toner may be used. For example, other spot colors may be used in addition to yellow, magenta, cyan, and black. Alternatively, only black toner may be used.

[0025] The image forming units 24Y, 24M, 24C, and 24K have basically the same configuration except for the toner used. For example, the image forming units 24Y, 24M, 24C, and 24K each include a rotating cylindrical image carrier, a charger that charges the image carrier, an exposure device, and a developing device. The exposure device irradiates the charged image carrier with light to form an electrostatic latent image. The developing device develops the electrostatic latent image into a toner image using a developer containing toner.

[0026] The transfer unit 26 includes a transfer belt 30, a primary transfer roll 32, a secondary transfer roll 34, and a roll 36. The transfer belt 30 is wound around multiple rolls including the roll 36 and rotates in the direction of the arrow in Figure 1. A secondary transfer unit NT that transfers a toner image to the recording medium P is formed between the secondary transfer roll 34 and the transfer belt 30.

[0027] The fixing device 28 is disposed downstream of the secondary transfer portion NT in the conveying direction of the recording medium P.

[0028] The storage section 14 includes a storage member 38 and a feed roll 40. The storage member 38 stores the recording medium P. The feed roll 40 sends the recording medium P stored in the storage member 38 to the transport path 20.

[0029] The conveying section 16 includes a plurality of conveying rolls and a belt unit 42. The recording medium P sent out from the storage section 14 is conveyed along the conveying path 20 by the plurality of conveying rolls. The belt unit 42 conveys the recording medium P onto which the toner image has been transferred, and delivers it to the fixing device 28.

[0030] The control device 18 controls each part of the image forming apparatus 10. The control by the control device 18 will be described in detail later.

[0031] According to the image forming apparatus 10, an image is formed on the recording medium P as will be described below.

[0032] First, in each of the image forming units 24Y, 24M, 24C, and 24K, the surface of the image carrier is charged by a charger, and the surface of the image carrier is exposed to light by an exposure device to form an electrostatic latent image. The electrostatic latent image is then developed by a development device. As a result, a toner image is formed on the surface of the image carrier. The toner images of each color are transferred sequentially to the transfer belt 30 by a primary transfer roll 32.

[0033] The recording medium P is sent out from the storage member 38 to the transport path 20 by the delivery roll 40, and is sent along the transport path 20 to the secondary transfer unit NT. At the secondary transfer unit NT, the recording medium P is transported between the transfer belt 30 and the secondary transfer roll 34, so that the toner image transferred to the transfer belt 30 is transferred onto the surface of the recording medium P.

[0034] The toner image transferred onto the surface of the recording medium P is fixed to the recording medium P by the fixing device 28. The recording medium P with the fixed toner image is discharged to the outside of the housing 10a.

[0035] When a toner image is also formed on the back side of the recording medium P, the conveying unit 16 conveys the recording medium P that has passed through the fixing device 28 along the reversing path 22 to invert the recording medium P, and then conveys the inverted recording medium P along the conveying path 20 to the secondary transfer unit NT. At the secondary transfer unit NT, the toner image is transferred to the back side of the recording medium P, and the toner image is fixed to the recording medium P by the fixing device 28. The recording medium P with the fixed toner image is discharged from the housing 10a to the outside.

[0036] The fixing device 28 will be described with reference to Fig. 2. Fig. 2 shows the configuration of the fixing device 28.

[0037] The fixing device 28 includes a fixing roll 44, a pressure roll 46, fans 48a, 48b, and 48c, and temperature sensors 50a, 50b, and 50c.

[0038] The fixing roll 44 and the pressure roll 46 are cylindrical rolls that rotate around an axis that intersects with the transport direction of the recording medium P. The fixing roll 44 and the pressure roll 46 are disposed in an area where an image is transferred to the recording medium P.

[0039] The fixing roll 44 is rotated by a motor (not shown) and has a built-in heater such as a halogen lamp, and heats the recording medium P.

[0040] The pressure roll 46 is provided at a position facing the fixing roll 44 across the transport path of the recording medium P, and is rotated by a motor (not shown). The pressure roll 46 applies pressure to the recording medium P. For example, the pressure roll 46 is pressed against the fixing roll 44 by an elastic member such as a spring, thereby applying pressure to the recording medium P toward the fixing roll 44. Note that the pressure roll 46 may be rotated by the rotation of the fixing roll 44 without using a motor to rotate the pressure roll 46.

[0041] The pressure roll 46 includes a cylindrical member made of metal such as aluminum, iron, or stainless steel, a heat-resistant elastic layer such as silicone rubber that covers the outer periphery of the member, and a release layer made of a fluorine-based resin that covers the outer periphery of the elastic layer.

[0042] A fixing section N (i.e., Nip section) that fixes the toner image to the recording medium P is formed between the fixing roll 44 and the pressure roll 46. The recording medium P transported to the fixing section N is heated by the fixing roll 44 and pressed toward the fixing roll 44 by the pressure roll 46. This fixes the toner image to the recording medium P. The fixing roll 44 is an example of a first roll, and the pressure roll 46 is an example of a second roll.

[0043] The fixing device 28 includes a cleaning roll (not shown) that removes toner and foreign matter adhering to the surface of the fixing roll 44.

[0044] Alternatively, a fixing belt wound around the fixing roll 44 may be used, and a fixing section N may be formed between the fixing belt and the pressure roll 46, whereby the toner image may be fixed onto the recording medium P.

[0045] The fans 48a, 48b, and 48c send cooling air ("air" in the figure) to the pressure roll 46. There are no particular limitations on the fans 48a, 48b, and 48c as long as they can send cooling air to the pressure roll 46. For example, a propeller fan, a blower, a cross-flow fan, or the like may be used.

[0046] 2, the fans 48a, 48b, and 48c are arranged upstream of the fixing unit N in the transport path of the recording medium P, and send cooling air from the upstream side to the pressure roll 46 (for example, the location where the fixing unit N is formed). This arrangement is merely one example, and the fans 48a, 48b, and 48c may be arranged downstream of the fixing unit N and send cooling air to the pressure roll 46 from the downstream side, or may be arranged below the pressure roll 46 and send cooling air to the pressure roll 46 from below.

[0047] The temperature sensors 50a, 50b, and 50c detect the temperature of the surface of the pressure roll 46. For example, the temperature sensors 50a, 50b, and 50c are sensors that detect temperature in a non-contact manner, such as infrared radiation temperature sensors.

[0048] 2, the temperature sensors 50a, 50b, and 50c are arranged upstream of the fixing unit N in the transport path of the recording medium P, and detect the temperature of the surface of the pressure roll 46 near the fixing unit N. This arrangement is merely an example, and the temperature sensors 50a, 50b, and 50c may be arranged downstream of the fixing unit N to detect the temperature of the surface of the pressure roll 46, or may be arranged below the pressure roll 46 to detect the temperature of the surface of the pressure roll 46.

[0049] The shape of the pressure roll 46 and the positional relationship between the pressure roll 46 and the fans 48a, 48b, and 48c will be described with reference to Fig. 3. Fig. 3 is a diagram showing the pressure roll 46 and the fans 48a, 48b, and 48c.

[0050] The direction in which the cylindrical pressure roll 46 extends is defined as the longitudinal axis direction Z of the pressure roll 46. The pressure roll 46 is broadly divided into a central portion 46a and end portions 46b, 46c along its longitudinal axis direction Z. The pressure roll 46 has a shape in which the diameters of the end portions 46b, 46c in the longitudinal axis direction Z are larger than the diameter of the central portion 46a in the longitudinal axis direction Z (i.e., a flared shape). In other words, the end portions 46b, 46c have a shape that widens outward more than the central portion 46a.

[0051] For example, the central portion 46a is a portion between the end portions 46b and 46c, and is a portion having a constant diameter along the longitudinal axis direction Z, or a portion having a substantially constant diameter to the extent that its effect on pressure is negligible. The end portions 46b and 46c are portions whose diameters increase with increasing distance from the central portion 46a along the longitudinal axis direction Z.

[0052] By using the pressure roll 46 having a flared shape, a force that pulls the recording medium P outward on both sides acts on the recording medium P, thereby suppressing the occurrence of paper wrinkles, etc. For example, even when thin paper (e.g., paper with a gms of 70 or less or 80 or less) is used as the recording medium P, the occurrence of paper wrinkles, etc. is suppressed. Of course, the occurrence of paper wrinkles, etc. is also suppressed when paper other than thin paper is used.

[0053] Fan 48a is positioned corresponding to center portion 46a and sends cooling air to center portion 46a. Fan 48b is positioned corresponding to end portion 46b and sends cooling air to end portion 46b. Fan 48c is positioned corresponding to end portion 46c and sends cooling air to end portion 46c.

[0054] Temperature sensor 50a is disposed at a position corresponding to center portion 46a and detects the surface temperature of center portion 46a. Temperature sensor 50b is disposed at a position corresponding to end portion 46b and detects the surface temperature of end portion 46b. Temperature sensor 50c is disposed at a position corresponding to end portion 46c and detects the surface temperature of end portion 46c. Temperature data detected by each of temperature sensors 50a, 50b, and 50c is output to control device 18.

[0055] The configuration relating to the control of the fans 48a, 48b, and 48c will be described with reference to Fig. 4. Fig. 4 is a block diagram showing the configuration.

[0056] For example, the control device 18 includes a processor 52 and a memory 54. The control device 18 controls the operation of each part of the image forming apparatus 10, and Fig. 4 shows the configuration related to the control of the fans 48a, 48b, and 48c.

[0057] The processor 52 controls the operation of each of the fans 48a, 48b, and 48c. For example, the processor 52 controls the rotation speed of each of the fans 48a, 48b, and 48c, thereby controlling the airflow of each of the fans.

[0058] The memory 54 is a device that configures one or more storage areas for storing data. The memory 54 is, for example, a hard disk drive (HDD), a solid state drive (SSD), various types of memory (e.g., RAM, DRAM, ROM, etc.), other storage devices (e.g., optical disks, etc.), or a combination thereof. One or more memories 54 are included in the control device 18. Note that the memory 54 may not be included in the control device 18 and may be installed in a location other than the control device 18 in the image forming apparatus 10.

[0059] The control of the fans 48a, 48b, and 48c will now be described.

[0060] The processor 52 controls the airflow rate of each of the fans 48a, 48b, and 48c by controlling the rotation speed of each of the fans 48a, 48b, and 48c, thereby controlling the temperature of the center 46a and the ends 46b and 46c of the pressure roll 46, respectively.

[0061] For example, the processor 52 changes the rotation speed of the fans at the center portion 46a and the end portions 46b, 46c of the pressure roll 46. Specifically, the processor 52 makes the rotation speed of the fan 48a that sends cooling air to the center portion 46a different from the rotation speed of the fans 48b, 48c that send cooling air to the end portions 46b, 46c. This causes the airflow rate of the fan 48a to differ from the airflow rate of the fans 48b, 48c, and as a result, the temperature control of the center portion 46a differs from the temperature control of the end portions 46b, 46c.

[0062] When cooling air is sent from the fan to the pressure roll 46, the temperature of the pressure roll 46 drops. However, when the fan rotation speed is low, the amount of cooling air sent to the pressure roll 46 is reduced, and therefore the drop in temperature of the pressure roll 46 is suppressed compared to when the fan rotation speed is high. The thermal expansion of the pressure roll 46 is controlled by controlling the temperature based on the control of the air volume. For example, the thermal expansion of the pressure roll 46 is controlled so as to maintain the flared shape of the pressure roll 46. Specifically, the rotation speeds of the fans 48a, 48b, and 48c are controlled so as to achieve thermal expansion that maintains the flared shape of the pressure roll 46.

[0063] For example, the processor 52 changes the rotation speed of each of the fans 48a, 48b, and 48c depending on the total length of time that the pressure roll 46 presses the recording medium P (hereinafter referred to as the "total Nip time"). That is, the processor 52 controls the temperature of each of the center portion 46a and the end portions 46b and 46c by changing the airflow rate of each of the fans 48a, 48b, and 48c depending on the total Nip time. The total Nip time corresponds to the total length of time that the pressure roll 46 is used for fixing in the fixing device 28 and corresponds to the change in the shape of the pressure roll 46 over time. Generally, the longer the total Nip time, i.e., the longer the time that the pressure roll 46 is used for fixing, the greater the change in the shape of the pressure roll 46 over time. Specifically, the longer the total Nip time, the smaller the diameter of the end portions 46b and 46c, making it more difficult to maintain the flared shape.

[0064] As another example, the processor 52 changes the rotation speed of each of the fans 48a, 48b, and 48c depending on the state of the pressure roll 46 (for example, the temperature state of the pressure roll 46). In other words, by changing the airflow rate of each of the fans 48a, 48b, and 48c depending on the state of the pressure roll 46, the temperatures of the center portion 46a and the ends 46b and 46c are controlled.

[0065] Hereinafter, the control of the fans 48a, 48b, and 48c, that is, the control of the temperature of the pressure roll 46, will be described with reference to Fig. 5. Fig. 5 shows the control of the temperature of the pressure roll 46. Specifically, the control of the temperature according to the total Nip time T and the control of the temperature according to the state of the pressure roll 46 are shown.

[0066] FIG. 5 shows the pressure roll 46 in an "unsteady" state and a "steady" state.

[0067] The "steady" state is, for example, a state when a predetermined time Ts or more has elapsed since the image forming apparatus 10 was turned on, or a state when images have been formed on a predetermined number Ns or more of recording media P after the image forming apparatus 10 was turned on. The time Ts is the time required for the pressure roll 46 to start heating when the image forming apparatus 10 is turned on and for the temperature of the pressure roll 46 to reach a predetermined temperature or higher, or the time required for the temperature of the pressure roll 46 to stabilize. The number Ns is a value corresponding to the time Ts.

[0068] The "unsteady" state is a state that does not reach the "steady" state. In other words, the "unsteady" state is a state in which time Ts or more has not elapsed since the image forming apparatus 10 was turned on (i.e., a state less than time Ts), or a state in which images have not been formed on several Ns or more recording media P after the image forming apparatus 10 was turned on. Generally, in the "unsteady" state, the pressure roll 46 is not heated as much as in the "steady" state, and therefore the temperature of the pressure roll 46 is lower than in the "steady" state.

[0069] First, we will explain the temperature control according to the total Nip time T, that is, the temperature control according to the change over time in the shape of the pressure roll 46. The processor 52 controls the temperatures of the central portion 46a and the end portions 46b and 46c by changing the rotation speed of each of the fans 48a, 48b, and 48c according to the length of the total Nip time T.

[0070] In the example shown in Fig. 5, the total Nip time T is classified into "short," "medium," and "long," as an example. Times Ta and Tb are thresholds for the total Nip time, and there is a relationship in which time Tb is greater than time Ta. Note that the classification of the total Nip time shown in Fig. 5 is merely an example, and the total Nip time may be classified more finely to control the fans 48a, 48b, and 48c.

[0071] When the total Nip time T is less than the time Ta, the total Nip time T corresponds to a "short time." When the total Nip time T is equal to or greater than the time Ta and less than the time Tb, the total Nip time T corresponds to a "medium" time. When the total Nip time T is equal to or greater than the time Tb, the total Nip time T corresponds to a "long time." A "short time" corresponds to a small change in the shape of the pressure roll 46 over time. A "medium" time corresponds to a medium change in the shape of the pressure roll 46 over time. A "long time" corresponds to a large change in the shape of the pressure roll 46 over time.

[0072] The processor 52 measures the time that the pressure roll 46 presses the recording medium P during each fixing operation, and measures the total nip time T from when the pressure roll 46 is installed in the image forming apparatus 10. The total nip time T is stored in the memory 54.

[0073] For example, processor 52 controls the rotation speed of each of fans 48b and 48c so that the temperatures of end portions 46b and 46c increase as total nip time T increases. Processor 52 also controls the rotation speed of fan 48a so that the temperature of center portion 46a remains constant regardless of total nip time T.

[0074] Generally, the longer the total Nip time T, the greater the change in the shape of the pressure roll 46 over time. That is, the diameters of the ends 46b, 46c become smaller, making it difficult to maintain the flared shape of the pressure roll 46. In such cases, by controlling the rotation speeds of the fans 48b, 48c so that the temperatures of the ends 46b, 46c become higher, the diameters of the ends 46b, 46c do not increase or decrease due to thermal expansion of the ends 46b, 46c. As a result, the flared shape of the pressure roll 46 is maintained.

[0075] Focusing on the "unsteady" state, processor 52 controls the rotation speed of fans 48b and 48c so that the temperatures of end portions 46b and 46c are "YY-5[°C]" when total nip time T is "short," "YY[°C]" when total nip time T is "medium," and "YY+5[°C]" when total nip time T is "long." Processor 52 also controls the rotation speed of fan 48a so that the temperature of center portion 46a is maintained at "XX-5[°C]" regardless of the length of total nip time. Temperature "YY[°C]" and temperature "XX[°C]" are predetermined temperatures.

[0076] Temperature data detected by each of the temperature sensors 50a, 50b, and 50c is output to the processor 52, and the processor 52 controls the rotation speed of each of the fans 48a, 48b, and 48c based on the temperatures detected by each of the temperature sensors 50a, 50b, and 50c.

[0077] For example, the processor 52 reduces the rotation speed of each of the fans 48b, 48c as the total Nip time T increases, thereby increasing the temperature of each of the ends 46b, 46c as the total Nip time T increases. More specifically, the processor 52 reduces the rotation speed of each of the fans 48b, 48c for each of the ends 46b, 46c during a second Nip total time T2, which is longer than the first Nip total time T1, compared to the rotation speed of each of the fans 48b, 48c for each of the ends 46b, 46c during a first Nip total time T1. The first Nip total time is an example of a first total time, and the second Nip total time is an example of a second total time. This control will be described in more detail below.

[0078] When the first Nip total time T1 is a "short" time and the second Nip total time is a "medium" time, the processor 52 controls the rotation speed of each of the fans 48b and 48c so that the temperatures of the ends 46b and 46c are higher during the "medium" time compared to the temperatures of the ends 46b and 46c during the "short" time. Specifically, the processor 52 reduces the rotation speed of each of the fans 48b and 48c during the "medium" time compared to the rotation speed of each of the fans 48b and 48c during the "short" time. By reducing the rotation speed of each of the fans 48b and 48c, the airflow to the ends 46b and 46c is reduced, making it more difficult for the temperatures of the ends 46b and 46c to decrease compared to when the rotation speed of each of the fans 48b and 48c is high. As a result, the temperatures of the ends 46b and 46c are higher during the "medium" time compared to the temperatures of the ends 46b and 46c during the "short" time. In the example shown in FIG. 5, the temperature of each of the ends 46b, 46c in the "medium" time is "+5[° C.]" higher than the temperature of each of the ends 46b, 46c in the "short" time.

[0079] Generally, the change in the shape of each of the ends 46b, 46c over time is greater during the "medium" period than during the "short" period. That is, the diameters of the ends 46b, 46c during the "medium" period are smaller than the diameters of the ends 46b, 46c during the "short" period. Therefore, it is more difficult to maintain the flared shape of the pressure roll 46 during the "medium" period than during the "short" period. Therefore, by increasing the temperatures of the ends 46b, 46c during the "medium" period compared to the temperatures of the ends 46b, 46c during the "short" period, the diameters of the ends 46b, 46c are prevented from increasing or decreasing due to thermal expansion of the ends 46b, 46c during the "medium" period. As a result, the flared shape of the pressure roll 46 is maintained.

[0080] Similarly, when the first Nip total time T1 is a "medium" time and the second Nip total time is a "long" time, the processor 52 controls the rotation speed of each of the fans 48b, 48c so that the temperatures of the ends 46b, 46c during the "long" time are higher than the temperatures of the ends 46b, 46c during the "medium" time. In the example shown in FIG. 5 , the temperatures of the ends 46b, 46c during the "long" time are "+5°C" higher than the temperatures of the ends 46b, 46c during the "medium" time. This prevents the diameters of the ends 46b, 46c from increasing or decreasing due to thermal expansion of the ends 46b, 46c during the "long" time, and as a result, the flared shape of the pressure roll 46 is maintained.

[0081] The processor 52 also controls the rotation speed of the fan 48a so that the temperature of the center portion 46a is maintained constant during each of the "short," "medium," and "long" periods. For example, the processor 52 does not change the rotation speed of the fan 48a. As a result, as the total nip time increases, the temperature of the center portion 46a is maintained constant while the temperatures of the end portions 46b and 46c increase. As a result, the difference between the temperature of the center portion 46a and the temperature of the end portions 46b and 46c increases. This temperature difference, i.e., the temperature distribution in the pressure roll 46, also maintains the flared shape of the pressure roll 46. In other words, while the temperature of the center portion 46a is maintained constant, the temperatures of the end portions 46b and 46c increase, causing each of the end portions 46b and 46c to expand, thereby maintaining a shape in which the diameters of the end portions 46b and 46c are larger than the diameter of the center portion 46a.

[0082] Note that as the total nip time increases, the temperature of the end portions 46b, 46c increases, and as long as the difference between the temperature of the center portion 46a and the temperature of the end portions 46b, 46c increases, the temperature of the center portion 46a does not have to be maintained constant. In other words, the rotation speed of the fan 48a does not have to be maintained constant. As long as the total nip time increases, the difference between the temperature of the center portion 46a and the temperature of the end portions 46b, 46c increases, and the flare shape is maintained, the temperature of the center portion 46a does not necessarily have to be maintained constant.

[0083] In the "steady" state, as in the "unsteady" state, the rotation speeds of the fans 48a, 48b, and 48c are controlled in accordance with the total Nip time.

[0084] Next, temperature control according to the state of the pressure roll 46 will be described. Here, as an example, the state of the pressure roll 46 is the temperature state of the pressure roll 46. The processor 52 controls the temperatures of the center portion 46a and the ends 46b and 46c by changing the rotation speed of each of the fans 48a, 48b, and 48c according to the temperature state of the pressure roll 46. The temperature state of the pressure roll 46 is either an "unsteady" state or a "steady" state, and the processor 52 changes the rotation speed of each of the fans 48a, 48b, and 48c according to whether the state of the pressure roll 46 is an "unsteady" state or a "steady" state.

[0085] Generally, in the "unsteady" state, the pressure roll 46 is not heated as much as in the "steady" state, and therefore the temperature of the pressure roll 46 is lower than in the "steady" state. In the example shown in FIG. 5, the temperature of the central portion 46a in the "unsteady" state is lower than the temperature of the central portion 46a in the "steady" state. Even in this case, the rotation speeds of the fans 48b and 48c are controlled so that the flared shapes are maintained at the end portions 46b and 46c, respectively. Specific control will be described below.

[0086] The processor 52 controls the rotation speed of each of the fans 48b and 48c so that the temperatures of the ends 46b and 46c in the "unsteady" state are the same as the temperatures of the ends 46b and 46c in the "steady" state. For example, in the "unsteady" state, the temperature of the pressure roll 46 is not as high as in the "steady" state. Therefore, if the rotation speeds of the fans 48b and 48c are the same in the "unsteady" state and the "steady" state, it is expected that the ends 46b and 46c will be overcooled in the "unsteady" state. Therefore, the processor 52 reduces the rotation speed of each of the fans 48b and 48c in the "unsteady" state compared to the rotation speed of each of the fans 48b and 48c in the "steady" state. This allows the flared shape of the ends 46b and 46c to be maintained even in the "unsteady" state, where the pressure roll 46 is not heated as much as in the "steady" state.

[0087] 5, in the "short time" period, the processor 52 controls the rotation speed of each of the fans 48b and 48c in both the "unsteady" state and the "steady" state so that the temperatures of the ends 46b and 46c become "YY-5[°C]." In the "medium" and "long" periods, the processor 52 also controls the rotation speed of each of the fans 48b and 48c in the same manner as in the "short time" period.

[0088] Even if the temperature of each of the ends 46b, 46c in the "unsteady" state is not the same as the temperature of each of the ends 46b, 46c in the "steady" state, the processor 52 may control the rotation speed of each of the fans 48b, 48c so that the difference between the temperature of each of the ends 46b, 46c in the "unsteady" state and the temperature of each of the ends 46b, 46c in the "steady" state falls within an acceptable range. The acceptable range is defined as the range within which a flare shape necessary to suppress the occurrence of wrinkles and the like is formed.

[0089] The processor 52 may change the rotation speed of the fans differently between the central portion 46a and the end portions 46b, 46c, depending on the temperature state of the pressure roll 46. In other words, the processor 52 may change the rotation speed of the fan 48a differently from the rotation speeds of the fans 48b, 48c, depending on the temperature state of the pressure roll 46. In the example shown in Fig. 5, the processor 52 changes the rotation speed of the fan 48a differently from the rotation speeds of the fans 48b, 48c when the state of the pressure roll 46 transitions from an "unsteady" state to a "steady" state.

[0090] For example, when transitioning from the "unsteady" state to the "steady" state, the processor 52 controls the rotation speed of the fan 48a so that the temperature of the center portion 46a increases, and controls the rotation speeds of the fans 48b and 48c so that the temperatures of the ends 46b and 46c remain constant.

[0091] In the example shown in FIG. 5, the processor 52 controls the rotation speed of the fan 48a (e.g., reduces the rotation speed) so that the temperature of the center portion 46a rises from "XX-5°C" to "XX°C." Focusing on the "short time," the processor 52 controls the rotation speed of each of the fans 48b and 48c so that the temperature of each of the end portions 46b and 46c is maintained at "YY-5°C." The same applies to the "medium" and "long" times. By performing such control, the flared shape of the pressure roll 46 is maintained even when the state of the pressure roll 46 transitions from an "unsteady" state to a "steady" state.

[0092] In addition, the processor 52 may control the rotation speed of each of the fans 48b, 48c so that the difference between the temperature of each of the ends 46b, 46c in the "unsteady" state and the temperature of each of the ends 46b, 46c in the "steady" state is within an acceptable range.

[0093] Furthermore, if the temperature of the central portion 46a is increased in an "unsteady" state in which the temperatures of the end portions 46b, 46c are not rising, the diameter of the central portion 46a increases due to thermal expansion of the central portion 46a, which may result in the flared shape of the pressure roll 46 not being maintained. Therefore, by not increasing the temperature of the central portion 46a as much as in the "steady" state in the "unsteady" state, the flared shape of the pressure roll 46 is maintained.

[0094] The following describes modified examples.

[0095] In a modified example, when the quality of the image formed on the recording medium P (i.e., image quality) is prioritized, the processor 52 controls the rotation speeds of the fans 48a, 48b, and 48c so that the difference in temperature between the center 46a and the ends 46b and 46c of the pressure roll 46 is smaller than when image quality is not prioritized. Depending on the magnitude of the difference in temperature between the center 46a and the ends 46b and 46c, the toner melts differently between the center and the ends of the recording medium P, resulting in a difference in gloss between the center and the ends (i.e., a larger gloss difference), which can degrade image quality. When image quality is prioritized, the processor 52 controls the rotation speeds of the fans 48a, 48b, and 48c so that the difference in temperature between the center 46a and the ends 46b and 46c is equal to or smaller than a threshold value. The threshold value is a value at which the gloss difference is deemed to be within an acceptable range. By performing such control, the difference in glossiness between the center and edges of the recording medium P is reduced, and deterioration of image quality is suppressed. Note that prioritizing image quality may be specified by the user or may be predetermined in the print job, etc.

[0096] The functions of the control device 18 are realized, for example, by a combination of hardware and software. For example, the functions of the control device 18 are realized by the processor 52 of the control device 18 reading and executing a program stored in the memory 54. The program is stored in the memory 54 via a recording medium such as a CD or a DVD, or via a communication path such as a network.

[0097] In the above embodiments, the term "processor" refers to a processor in a broad sense, and includes general-purpose processors (e.g., CPU: Central Processing Unit, etc.) and dedicated processors (e.g., GPU: Graphics Processing Unit, ASIC: Application Specific Integrated Circuit, FPGA: Field Programmable Gate Array, programmable logic device, etc.). Furthermore, the operations of the processor in each of the above embodiments may not only be performed by a single processor, but may also be performed by multiple processors located in physically separate locations working together. Furthermore, the order of each operation of the processor is not limited to the order described in each of the above embodiments, and may be changed as appropriate. [Explanation of symbols]

[0098] 10 image forming device, 28 fixing device, 44 fixing roll, 46 pressure roll, 46a center portion, 46b, 46c end portions, 48a, 48b, 48c fans, 52 processor.

Claims

1. a first roll disposed in an area where an image formed on a recording medium is fixed to the recording medium, and which heats the recording medium; a second roll disposed opposite the first roll in the region and pressing the recording medium toward the first roll; a fan that blows air onto the second roll; a processor for controlling the fan; and the second roll has a shape in which the diameter of an end portion in the longitudinal axis direction is larger than the diameter of a central portion in the longitudinal axis direction, the first roll and the second roll fix the image to the recording medium in the region; The processor: changing the rotation speed of the fan between the center and end portions of the second roll; A fixing device, The processor: a process of changing the rotation speed of the fan depending on the length of a total time during which the second roll presses the recording medium, wherein the rotation speed of the fan for the center portion of the second roll is not changed between a first total time and a second total time longer than the first total time, and the rotation speed of the fan for the end portion of the second roll for the second total time is reduced compared to the rotation speed of the fan for the end portion of the second roll for the first total time; A fixing device characterized by:

2. The processor: changing the rotation speed of the fan depending on the temperature state of the second roll; The fixing device according to claim 1 .

3. The processor: changing the rotation speed of the fan differently between the center and the end portions of the second roll depending on the temperature state of the second roll; The fixing device according to claim 2 .

4. The processor: When priority is given to image quality, the rotation speed of the fan is controlled so that the temperature difference between the center and the end of the second roll becomes smaller than when priority is not given to image quality. The fixing device according to claim 1 .

Images