Image forming device

Abstract

To provide a fixing device that, when a recording medium is ordinary paper, can accurately adjust a fixing nip pressure to a plurality of pressure application settings according to the type of the ordinary paper, and an image forming apparatus including the fixing device.SOLUTION: An image forming apparatus comprises an image forming unit, a fixing device, an input unit, and a control unit. The fixing device includes a rotating body to be heated, a pressure rotating body, a heating unit, a pressure mechanism, and a reference position detection mechanism. When a recording medium is ordinary paper, the control unit arranges the pressure rotating body to any one of a plurality of pressure positions different in fixing nip pressure, and when the recording medium is special paper, arranges the pressure rotating body to any one of the plurality of pressure positions and a decompression position to perform fixing processing. After positively rotating a pressure drive motor, when a predetermined time elapses from the timing when a reference position detection sensor enters an on-state or the amount of rotation of a shaft reaches a predetermined amount, the control unit stops the pressure drive motor to arrange the pressure rotating body to any one of the plurality of pressure positions.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus equipped with a fixing device, such as a copying machine, a printer, a facsimile, or a combination machine thereof, and more particularly to a method for achieving both good fixing performance and paper transportability. [Background technology]

[0002] In order to fix a toner image on paper in an image forming apparatus, a fixing device equipped with a fixing member formed by pressing a fixing roller or fixing belt (a heated rotating body) and a pressure roller (a pressure rotating body) is widely used. In this fixing device, a recording material such as paper is passed through a fixing nip formed by a heating roller and a pressure roller, and heat and pressure are applied to the toner image to melt and fix the toner image on the recording material.

[0003] In the fixing device described above, the temperature of the fixing roller or fixing belt and the nip pressure of the fixing nip are set in consideration of the fixability of the toner to the recording material. However, for example, when a toner image is fixed to a type of special paper different from plain paper under heat and pressure conditions set in consideration of the fixability of the toner to plain paper, wrinkles are likely to occur on the recording material.

[0004] In view of this, a fixing device has been proposed that suppresses the occurrence of wrinkles without impairing the fixability of a toner image on special paper such as an envelope. For example, Patent Document 1 discloses a fixing device that includes a recognition means for recognizing the thickness of a member to be fixed, and a pressure contact force switching means for switching the pressure contact force of a pressing member to a smaller pressure than that used for fixing plain paper when the thickness of the member to be fixed recognized by the recognition means is thicker than that of plain paper.

[0005] Patent document 2 also discloses an image forming apparatus that includes a heating section that heats the recording paper onto which a toner image has been transferred, a pressure section that pressurizes the heating section to form a predetermined nip section, a transport drive means that drives at least one of the heating section and the pressure section to transport the recording paper in a predetermined direction through the nip section at a predetermined transport speed, and a pressure amount control means that controls the amount of pressure applied by the pressure section, wherein the pressure amount control means controls the amount of pressure applied by the pressure section depending on the type of recording paper.

[0006] Patent document 3 discloses a fixing device having a depressurization mode in which the fixing nip is set to a first pressure and a pressurization mode in which the pressure of the fixing nip is set to a second pressure greater than the first pressure, and which goes into a standby state for the fixing operation in the depressurization mode and performs paper feed and fixing for a specific brand of recording medium in the depressurization mode, while performing paper feed and fixing for brands other than the specific brand in the pressurization mode. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 201078903 A [Patent Document 2] JP 2010-181728 A [Patent Document 3] JP 2019-159247 A Summary of the Invention [Problem to be solved by the invention]

[0008] Incidentally, the appropriate fixing conditions differ depending on the basis weight and thickness not only when the recording medium is special paper such as an envelope, but also when the recording medium is normal paper such as thin paper or plain paper. Therefore, it is considered to set multiple fixing nip pressures even for normal paper. In this case, since the difference between the multiple fixing nip pressures that are set is very small, a highly accurate setting method is required.

[0009] In Patent Document 2, a pressure cam position sensor detects the cam position and drives a cam motor to change the fixing nip pressure, but the relationship between the cam position sensor and the cam position is not clear. In terms of cam position accuracy, the most important thing is the pressure position during printing, and in order to control the pressure position with higher accuracy according to the paper type, it was necessary to devise settings for the cam position detection mechanism and pressure mechanism.

[0010] In view of the above problems, the present invention aims to provide a fixing device and an image forming apparatus equipped with the same, which can set the detection position of the pressure position sensor to a position close to the pressure position where positional accuracy is required, and when the recording medium is regular paper, can accurately adjust the fixing nip pressure to one of multiple pressure settings depending on the type of regular paper. [Means for solving the problem]

[0011] In order to achieve the above object, the first configuration of the present invention is an image forming apparatus including an image forming section, a fixing device, an input section, and a control section. The image forming section forms a toner image on a recording medium. The fixing device includes a heated rotating body, a pressure rotating body that is pressed against the heated rotating body at a predetermined fixing nip pressure to form a fixing nip section, a heating section that heats the heated rotating body, a pressure mechanism, and a reference position detection mechanism, and performs a fixing process in which a toner image is fixed to the recording medium by heating and pressurizing the recording medium passing through the fixing nip section. The pressure mechanism includes a pressure lever that moves the pressure rotating body in a direction approaching or separating from the heated rotating body, a pressure cam that varies the pressure force applied by the pressure lever, and a pressure drive motor that rotates a shaft to which the pressure cam is fixed. The reference position detection mechanism includes a light shielding plate fixed to the shaft and a reference position detection sensor that is turned on or off by the light shielding plate, and detects that the pressure rotating body is at a reference position. The input section is capable of inputting information regarding the type of recording medium. The control unit adjusts the pressure position by controlling the pressure mechanism based on information about the type of recording medium input from the input unit. The pressure mechanism selectively positions the pressure rotor at a plurality of pressure positions with different fixing nip pressures, including a first pressure position and a second pressure position with a fixing nip pressure lower than that at the first pressure position, and at a reduced pressure position with a fixing nip pressure lower than that at the pressure position. When the recording medium is normal paper, the control unit positions the pressure rotor at one of the plurality of pressure positions to perform the fixing process, and when the recording medium is special paper, the control unit positions the pressure rotor at one of the plurality of pressure positions and the reduced pressure position to perform the fixing process. The light shielding plate is disposed so that the reference position detection sensor is turned on when the rotation position of the pressing cam reaches the vicinity of the pressure position. After rotating the pressure drive motor in the forward direction, the control unit stops the pressure drive motor when a predetermined time has elapsed since the reference position detection sensor was turned on or when the amount of rotation of the shaft reaches a predetermined amount, thereby positioning the pressure rotor at one of the plurality of pressure positions. Effect of the Invention

[0012] According to the first configuration of the present invention, by providing a plurality of pressure positions including a first pressure position and a second pressure position for normal paper, the plurality of pressure positions can be appropriately used according to the basis weight and thickness of all paper including special paper such as envelopes and normal paper such as thin paper, plain paper, and thick paper, and both conveying performance and fixing performance can be achieved with a simple mechanism and control. Also, by controlling the time or the amount of rotation (rotation angle) after the reference position detection sensor turns on and stopping the pressure drive motor to position the pressure rotor at the target pressure position, the pressure rotor can be accurately positioned at the specified pressure position. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a schematic cross-sectional view showing an internal structure of an image forming apparatus 100 according to an embodiment of the present invention. [Diagram 2] A side cross-sectional view of a fixing device 13 mounted in an image forming apparatus 100. [Diagram 3] 1 is a side view of a pressure mechanism 30 and a reference position detection mechanism 40 of a fixing device 13. [Figure 4] FIG. 4 is a front view of the reference position detection mechanism 40 as seen from the left side of FIG. [Diagram 5] A block diagram showing an example of a control path of the image forming apparatus 100. [Figure 6] 1 is a timing chart showing an example of control of the fixing device 13 during warm-up and standby modes in the image forming apparatus 100 of this embodiment. [Figure 7] FIG. 1 is a timing chart showing an example of control of the fixing device 13 during image formation in the image forming apparatus 100 of this embodiment, showing an example of control in the case where the sheet S is thin plain paper. [Figure 8] FIG. 1 is a timing chart showing an example of control of the fixing device 13 during image formation in the image forming apparatus 100 of this embodiment, showing an example of control in the case where the sheet S is thick plain paper. [Figure 9] FIG. 11 is a timing chart showing an example of control of the fixing device 13 during image formation in the image forming apparatus 100 of the present embodiment, showing another example of control when the sheet S is thick plain paper. [Figure 10] FIG. 11 is a timing chart showing an example of control of the fixing device 13 during image formation in the image forming apparatus 100 of the present embodiment, showing an example of control when the sheet S is an envelope. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a schematic cross-sectional view showing the internal structure of an image forming apparatus 100 according to one embodiment of the present invention. Inside the main body of the image forming apparatus 100 (here, a color printer), four image forming sections Pa, Pb, Pc, and Pd are arranged in order from the upstream side in the transport direction (the right side in Fig. 1). These image forming sections Pa to Pd are provided corresponding to images of four different colors (cyan, magenta, yellow, and black), and sequentially form images of cyan, magenta, yellow, and black through the respective processes of charging, exposure, development, and transfer.

[0015] These image forming units Pa to Pd are provided with photoconductor drums (image carriers) 1a, 1b, 1c, and 1d that carry visible images (toner images) of each color. Furthermore, an intermediate transfer belt 8 that rotates in a clockwise direction in FIG. 1 is provided adjacent to each image forming unit Pa to Pd. The toner images formed on these photoconductor drums 1a to 1d are sequentially primarily transferred and superimposed on the intermediate transfer belt 8 that moves while abutting against each of the photoconductor drums 1a to 1d. Thereafter, the toner images primarily transferred onto the intermediate transfer belt 8 are secondarily transferred onto a sheet S, which is an example of a recording medium, by a secondary transfer roller 9. Furthermore, the sheet S onto which the toner image has been secondarily transferred is discharged from the main body of the image forming apparatus 100 after the toner image is fixed by a fixing device 13. An image forming process is performed on each of the photoconductor drums 1a to 1d while the photoconductor drums 1a to 1d are rotated counterclockwise in FIG. 1 by a main motor 50 (see FIG. 5).

[0016] The paper S onto which the toner image is secondarily transferred is stored in a paper cassette 16 arranged at the bottom of the main body of the image forming apparatus 100, and is transported to a nip between a secondary transfer roller 9 and a drive roller 11 of the intermediate transfer belt 8 via a paper feed roller 12a and a pair of registration rollers 12b. A sheet made of a dielectric resin is used for the intermediate transfer belt 8, and a seamless belt is mainly used. In addition, a blade-shaped belt cleaner 19 is arranged downstream of the secondary transfer roller 9 to remove toner and the like remaining on the surface of the intermediate transfer belt 8.

[0017] Next, the image forming units Pa to Pd will be described. Around and below the rotatably arranged photoconductor drums 1a to 1d, there are provided charging devices 2a, 2b, 2c, and 2d that charge the photoconductor drums 1a to 1d, an exposure device 5 that exposes image information onto each of the photoconductor drums 1a to 1d, developing devices 3a, 3b, 3c, and 3d that form toner images on the photoconductor drums 1a to 1d, and cleaning devices 7a, 7b, 7c, and 7d that remove developer (toner) and the like remaining on the photoconductor drums 1a to 1d.

[0018] When image data is input from a host device such as a personal computer, first, the surfaces of the photoconductor drums 1a-1d are uniformly charged by the charging devices 2a-2d. Next, the exposure device 5 irradiates light according to the image data, and electrostatic latent images corresponding to the image data are formed on the photoconductor drums 1a-1d. The developing devices 3a-3d are filled with a predetermined amount of two-component developer containing toner of each color of cyan, magenta, yellow, and black. When the ratio of toner in the two-component developer filled in each developing device 3a-3d falls below a specified value due to the formation of a toner image described later, toner is replenished from the toner containers 4a-4d to each developing device 3a-3d. The toner in the developer is supplied onto the photoconductor drums 1a-1d by the developing devices 3a-3d and electrostatically adheres to them. As a result, a toner image corresponding to the electrostatic latent image formed by exposure from the exposure device 5 is formed.

[0019] Then, an electric field is applied between the primary transfer rollers 6a-6d and the photoconductor drums 1a-1d by the primary transfer rollers 6a-6d at a predetermined transfer voltage, and the cyan, magenta, yellow and black toner images on the photoconductor drums 1a-1d are primarily transferred onto the intermediate transfer belt 8. These four color images are formed with a predetermined positional relationship for forming a predetermined full-color image. After that, in preparation for the subsequent formation of a new electrostatic latent image, the toner and the like remaining on the surfaces of the photoconductor drums 1a-1d after the primary transfer are removed by the cleaning devices 7a-7d.

[0020] The intermediate transfer belt 8 is stretched over a driven roller 10 on the upstream side and a driving roller 11 on the downstream side, and when the intermediate transfer belt 8 starts to rotate clockwise with the rotation of the driving roller 11 by a belt driving motor (not shown), the paper S is transported at a predetermined timing from the registration roller pair 12b to a nip portion (secondary transfer nip portion) between the driving roller 11 and a secondary transfer roller 9 provided adjacent thereto, and the full-color image on the intermediate transfer belt 8 is secondarily transferred onto the paper S. The paper S to which the toner image has been secondarily transferred is transported to a fixing device 13.

[0021] The paper S conveyed to the fixing device 13 is heated and pressurized by a fixing belt 21 and a pressure roller 22 (see FIG. 2) to fix the toner image onto the surface of the paper S, and a predetermined full-color image is formed. The paper S on which the full-color image has been formed is then redirected by a branching section 14 that branches into multiple directions, and is discharged directly to a discharge tray 17 by a pair of discharge rollers 15 (or after being sent to a double-sided conveying path 18 and having images formed on both sides).

[0022] Fig. 2 is a side cross-sectional view of fixing device 13 mounted on image forming apparatus 100. The upper side in Fig. 2 is the downstream side in the paper insertion direction (transport direction) relative to fixing device 13, and the lower side is the upstream side in the paper insertion direction relative to fixing device 13. As shown in Fig. 2, fixing device 13 includes fixing belt 21 (heated rotatable member), pressure roller 22 (pressurizing rotatable member), heating section 23, nip forming member 24, belt guide 25, and frame member 26.

[0023] Fixing belt 21 is supported rotatably about a horizontal axis by a housing (not shown) of fixing device 13. Fixing belt 21 is endless and configured in a cylindrical shape with an outer diameter of 20 mm to 50 mm, for example, and has approximately the same axial length (width direction length of paper S) as pressure roller 22. Fixing belt 21 rotates in the clockwise direction in FIG. 2 along the insertion direction of paper S, which is a recording medium.

[0024] The fixing belt 21 has a laminated structure in which an elastic layer and a release layer are laminated on the outer periphery of a heat generating layer, which is a base layer. The heat generating layer is made of a metal film such as nickel having a thickness of 30 μm to 50 μm, or a polyimide film having a thickness of 50 μm to 100 μm containing metal powder such as copper, silver, or aluminum. The elastic layer is made of silicone rubber having a thickness of 100 μm to 500 μm. The release layer is made of a fluorine-based resin such as PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer) having a thickness of 30 μm to 50 μm.

[0025] Pressure roller 22 is supported on the housing of fixing device 13 so as to be rotatable about a horizontal axis. Pressure roller 22 is cylindrical, and has approximately the same axial length (widthwise length of paper S) as fixing belt 21. A predetermined pressure is applied to pressure roller 22 by pressure mechanism 30 (see FIG. 3) toward fixing belt 21. The outer circumferential surface of pressure roller 22 is pressed against the outer circumferential surface of fixing belt 21 by pressing nip forming member 24 through fixing belt 21, thereby forming fixing nip portion N.

[0026] The pressure roller 22 is connected to a fixing drive motor 45 (see FIG. 5) and rotates in a counterclockwise direction in FIG. 2. The pressure roller 22 contacts the outer peripheral surface of the fixing belt 21 and applies a rotational drive force to the fixing belt 21 in the clockwise direction.

[0027] The pressure roller 22 has a laminated structure in which an elastic layer 22b is laminated on the outer periphery of a core metal 22a, and a release layer (not shown) is laminated on the surface of the elastic layer 22b. The core metal 22a is made of a metal such as aluminum with a diameter of about 20 mm. The elastic layer 22b is made of silicone rubber with a thickness of about 8 mm. The release layer is made of a fluorine-based resin such as PFA with a thickness of about 10 μm to 50 μm.

[0028] Heating unit 23 is disposed opposite the outer circumferential surface of fixing belt 21 across a predetermined gap in an area of ​​fixing belt 21 opposite the side where pressure roller 22 is disposed. Heating unit 23 extends slightly longer than fixing belt 21 along the axial direction of fixing belt 21 (the width direction of paper S, the direction perpendicular to the paper surface of FIG. 2). Heating unit 23 heats fixing belt 21 by generating heat in a heat generating layer of fixing belt 21 through induction heating.

[0029] The heating unit 23 includes an exciting coil 23a, and a holding member, a core, etc. (not shown). The exciting coil 23a and the core are held in place by the holding member. The exciting coil 23a is made of a Litz wire made of a bundle of multiple conductive wires, and is wound so as to extend along the axial direction of the fixing belt 21. The exciting coil 23a is configured in an arc shape along the outer circumferential surface of the fixing belt 21 in the circumferential direction of the fixing belt 21.

[0030] The nip forming member 24 is disposed on the inside of the fixing belt 21, facing the pressure roller 22 across the fixing belt 21. The nip forming member 24 contacts the inner circumferential surface of the fixing belt 21, and forms a fixing nip portion N between the fixing belt 21 and the pressure roller 22.

[0031] The nip forming member 24 has a generally rectangular parallelepiped shape that extends along the axial direction of the fixing belt 21 with substantially the same length as the fixing belt 21. The nip forming member 24 has a base material made of a metal such as aluminum or a heat-resistant resin such as a liquid crystal polymer.

[0032] The belt guide 25 is disposed on the inside of the fixing belt 21, facing the heating unit 23 across the fixing belt 21. The belt guide 25 contacts the inner peripheral surface of the fixing belt 21 except for the fixing nip portion N, and supports the fixing belt 21 from the inside. The belt guide 25 is made of a metal plate that extends along the axial direction of the fixing belt 21 and has substantially the same length as the fixing belt 21. The belt guide 25 is made of an elastic magnetic metal such as SUS430 having a thickness of 0.1 mm to 0.5 mm.

[0033] The frame member 26 is supported by a housing portion of the fixing device 13, and holds the nip forming member 24 and the belt guide 25. The frame member 26 is disposed at approximately the center in the radial direction of the fixing belt 21, between the belt guide 25 and the nip forming member 24. The frame member 26 extends slightly longer than the fixing belt 21 along the axial direction of the fixing belt 21.

[0034] A fixing entrance guide 27 is disposed upstream of the fixing nip N in the paper insertion direction (lower side in FIG. 2). The fixing entrance guide 27 guides the paper S that has passed through the secondary transfer nip (see FIG. 1) to the fixing nip N.

[0035] A separation claw 29 is disposed downstream of the fixing nip N in the paper insertion direction (upper side in FIG. 2). The separation claw 29 separates the paper S after fixing processing from the surface of the fixing belt 21. The separation claw 29 is disposed at a predetermined angle such that its tip faces upstream with respect to the rotation direction of the fixing belt 21 (counter direction) and its tip approaches the outer circumferential surface of the fixing belt 21.

[0036] Fig. 3 is a side view of the pressure mechanism 30 and the reference position detection mechanism 40 of the fixing device 13. Fig. 4 is a front view of the reference position detection mechanism 40 as viewed from the left side of Fig. 3. Note that in Fig. 3, the nip forming member 24, the belt guide 25, and the frame member 26 arranged on the inside of the fixing belt 21 are omitted.

[0037] The pressure mechanism 30 has a pressure lever 31, a coil spring 32, and a pressing cam 33. The pressure lever 31 is rotatably supported on a fulcrum 31a, and contacts the core metal 22a of the pressure roller 22. The coil spring 32 biases the pressure lever 31 in a direction away from the pressure roller 22 (counterclockwise direction in FIG. 3). The pressing cam 33 is fixed to a shaft 35, and is an eccentric cam whose outer diameter from the shaft 35 to the outer circumferential surface changes. The pressure lever 31 and the pressing cam 33 are arranged in pairs at both ends of the pressure roller 22 in the axial direction.

[0038] The shaft 35 is connected to a pressure drive motor 47 (see FIG. 5), and as the shaft 35 is driven to rotate, the outer diameter of the pressure cam 33 at the contact portion between the pressure cam 33 and the pressure lever 31 changes. When the outer diameter of the pressure cam 33 at the contact portion increases, the pressure lever 31 presses the core metal 22a in a direction toward the fixing belt 21 against the biasing force of the coil spring 32, so the fixing nip pressure increases. When the outer diameter of the pressure cam 33 decreases, the pressure lever 31 moves in a direction away from the core metal 22a due to the biasing force of the coil spring 32, so the fixing nip pressure decreases.

[0039] The reference position detection mechanism 40 has a reference position detection sensor 41 and a light blocking plate 43. The reference position detection sensor 41 is a photointerrupter (PI) sensor equipped with a detection unit having a light emitting unit and a light receiving unit. The light blocking plate 43 is fixed to the shaft 35, and passes through the optical path of the detection unit of the reference position detection sensor 41 as the shaft 35 rotates.

[0040] Next, a method for detecting the pressurized position by the reference position detection mechanism 40 will be described. For example, the light blocking plate 43 is arranged so that the reference position detection sensor 41 is turned on (light blocking state) at the timing when the rotational position of the pressing cam 33 reaches approximately the pressurized position. Then, the shaft 35 is rotated forward (counterclockwise in FIG. 3) so that the target pressurized position is reached when a predetermined time has elapsed since the reference position detection sensor 41 was turned on (when the pressing cam 33 has rotated a predetermined amount).

[0041] Furthermore, during warm-up, which is executed when image forming apparatus 100 is turned on or when returning from a power saving mode (sleep mode), and during standby mode after warm-up, pressure roller 22 is placed in a reduced pressure position where the nip pressure is smaller than that at the pressurized position, and fixing belt 21 is driven to rotate. The reason for this is to reduce physical stress on fixing belt 21 to extend its life, reduce quirks when fixing belt 21 stops rotating, reduce the drive torque of pressure drive motor 47, reduce noise, etc.

[0042] Specifically, the shaft 35 is rotated in the reverse direction (clockwise direction in FIG. 3) so that the target pressure reduction position is reached when a predetermined time has elapsed since the reference position detection sensor 41 changed from an on state to an off state (translucent state) (when the pressure cam 33 has rotated a predetermined amount).

[0043] The amount of rotation of the pressure cam 33 caused by the pressure drive motor 47 varies slightly due to fluctuations in motor torque and load torque even if the drive time is constant. However, if the amount of variation is within an allowable range, the amount of rotation can be detected with a predetermined accuracy by control using a timer. To control the amount of rotation of the pressure cam 33 more accurately, an encoder (pulse plate) can be attached to the shaft 35 and the number of pulses passing through the reference position detection sensor 41 can be detected to further improve the accuracy of detection of the amount of rotation.

[0044] 5 is a block diagram showing an example of a control path of the image forming apparatus 100. Since various controls are performed on each part of the image forming apparatus 100 when it is used, the following description will focus on the parts of the control path that are necessary for implementing the present invention. Also, the description of the parts that have already been described will be omitted.

[0045] The voltage control circuit 51 is connected to the charging voltage power supply 52, the developing voltage power supply 53, the transfer voltage power supply 54, and the fixing voltage power supply 55, and operates each of these power supplies according to an output signal from the control unit 90. Each of these power supplies applies a predetermined voltage according to a control signal from the voltage control circuit 51: the charging voltage power supply 52 applies a predetermined voltage to the charging devices 2a-2d, the developing voltage power supply 53 applies a predetermined voltage to the developing devices 3a-3d, the transfer voltage power supply 54 applies a predetermined voltage to the primary transfer rollers 6a-6d and the secondary transfer roller 9, and the fixing voltage power supply 55 applies a predetermined voltage to the heating unit 23 in the fixing device 13.

[0046] The image input unit 70 is a receiving unit that receives image data transmitted from a personal computer or the like to the image forming apparatus 100. The image signal input from the image input unit 70 is converted into a digital signal and then sent to the temporary storage unit 94.

[0047] The operation unit 80 is provided with a liquid crystal display unit 81 and LEDs 82 that indicate various states, and is configured to indicate the state of the image forming apparatus 100, the image formation status, and the number of copies to be printed. In addition, the type and size of the paper S can be input by specifying the paper cassette 16 or manual paper feed tray (not shown) from which the paper S is fed from the operation unit 80. Various settings of the image forming apparatus 100 are made from the printer driver of the personal computer.

[0048] The control unit 90 at least includes a CPU (Central Processing Unit) 91 as a central processing unit, a ROM (Read Only Memory) 92 which is a read-only memory unit, a RAM (Random Access Memory) 93 which is a readable and writable memory unit, a temporary memory unit 94 which temporarily stores image data, etc., a timer 95, and multiple (here, two) I / Fs (interfaces) 96 which send control signals to each device within the image forming apparatus 100 and receive input signals from the operation unit 70.

[0049] The ROM 92 stores data such as a control program for the image forming apparatus 100, numerical values ​​necessary for control, and data that will not be changed during use of the image forming apparatus 100. The RAM 93 stores necessary data generated during the control of the image forming apparatus 100, data temporarily required for the control of the image forming apparatus 100, and the like.

[0050] The temporary storage unit 94 temporarily stores the image signal input from the image input unit 70 and converted into a digital signal. The timer 95 measures the driving time of the pressure drive motor 47 from the timing when the reference position detection sensor 41 of the pressure level detection mechanism 40 is turned on or off.

[0051] Next, adjustment control of the fixing nip pressure of the fixing device 13 in the image forming apparatus 100 of this embodiment will be described. In this embodiment, the pressure position of the pressure roller 22 can be set to two stages, a first pressure position and a second pressure position. Then, by changing the pressure position of the pressure roller 22 depending on whether the paper S passing through the fixing nip portion N is normal paper or special paper, or depending on the basis weight (basis weight) of the normal paper, it is possible to achieve both transportability and fixability of the paper S.

[0052] In this specification, "normal paper" refers to a single-layer sheet made of plant fiber (thin paper, regular paper, thick paper, etc.), while "specialty paper" refers to a single-layer sheet made of a material other than plant fiber, or a multi-layer sheet made of plant fiber (envelopes, labels, transparencies, etc.).

[0053] Table 1 shows an example of the pressure application position of pressure roller 22 in this embodiment. As shown in Table 1, in this embodiment, the pressure application position of pressure roller 22 can be set to a first pressure application position where the fixing nip pressure is a reference pressure, and a second pressure application position where the nip pressure is lower than that of the first pressure application position. In addition to the pressure application position, the pressure application position can also be set to a decompression position and a jam processing position.

[0054] [Table 1]

[0055] The jam processing position is set to the position where 3000 ms has elapsed since the drive time of the pressure drive motor 47 from the timing when the reference position detection sensor 41 becomes off when the shaft 35 is rotated in the reverse direction (clockwise direction in FIG. 3). The jam processing position is set when removing the jammed (paper jammed) paper S from the fixing nip portion N.

[0056] The depressurization position is set to the position where 1500 ms has elapsed since the drive time of the pressure drive motor 47 from the timing when the reference position detection sensor 41 becomes off when the shaft 35 is rotated in the reverse direction (clockwise direction in FIG. 3). The depressurization position is set during warm-up or standby mode, or when printing on special paper such as envelopes.

[0057] The first pressurization position is set to the position where 400 ms has elapsed since the drive time of the pressure drive motor 47 from the timing when the reference position detection sensor 41 becomes on when the shaft 35 is rotated in the forward direction (counterclockwise direction in FIG. 3). The first pressurization position is for printing on relatively thick plain paper (basis weight 76 - 105 g / m 2 ) or cardboard (basis weight 106 - 300 g / m 2 ) etc.

[0058] The second pressurization position is set to the position where 100 ms has elapsed since the drive time of the pressure drive motor 47 from the timing when the reference position detection sensor 41 becomes on. That is, the first pressurization position is the position where the pressure drive motor 47 is driven for an additional 300 ms from the second pressurization position. The second pressurization position is for printing on thin paper (basis weight 52 - 59 g / m 2 ) or relatively thin plain paper (basis weight 60 - 75 g / m 2 ) etc.

[0059] When the range of the fixing nip pressure at the first pressurization position and the second pressurization position is based on the fixing nip pressure P2 at the second pressurization position with a lower fixing nip pressure (=1), it is preferable that the fixing nip pressure P1 at the first pressurization position is in the range of 1 < P1 < 1.2.

[0060] Figure 6 is a timing chart showing a control example of the fixing device 13 during warm-up and in the standby mode in the image forming apparatus 100 of the present embodiment. As shown in Figure 6, during warm-up, the pressure roller 22 is arranged at the depressurized position, and the reference position detection sensor 41 is in the off state. In this state, while rotating the linear speed of the pressure roller 22 at half speed (1 / 2 of the full speed) by the fixing drive motor 45, a voltage is applied from the fixing voltage power supply 55 to the heating unit 23 to raise the fixing temperature to the standby temperature (warm-up).

[0061] After that, when the time T2 has elapsed from the start of temperature rise and the fixing temperature reaches the standby temperature, while controlling the voltage applied to the heating unit 23 to maintain the fixing temperature at the standby temperature, the rotation is continued at half speed with the pressure roller 22 arranged at the depressurized position (standby mode).

[0062] During the warm-up operation, when the time T1 (<T2) has elapsed and the fixing temperature reaches the T1 temperature (<standby temperature), as shown by the broken line in Figure 6, the linear speed of the pressure roller 22 is increased (here, from half speed to full speed), and the fixing nip pressure is increased (here, changed from the depressurized position to the second pressurized position) in some cases.

[0063] The purpose of this control is to increase the amount of heat supplied from the fixing belt 21 to the pressure roller 22 in a configuration where the pressure roller 22 does not have a heat source as in the present embodiment, and to ensure the temperature of the pressure roller 22 at the end of warm-up. Whether to execute such control depends on the specifications and required performance of the fixing device 13. For example, the temperature rise rate of the fixing belt 21 is faster under the depressurized and low-speed conditions where the amount of heat supplied to the pressure roller 22 is small. Therefore, for example, when the pressure roller 22 has a heat source and it is preferable to prioritize the temperature rise of the fixing belt 21, it is preferably not executed.

[0064] Furthermore, if a print command is input while the pressure roller 22 is in the second pressure position during warm-up, it is preferable to continue printing by leaving the pressure roller 22 in the second pressure position or by changing the pressure roller 22 to the first pressure position rather than returning it to the depressurization position. This can reduce the waiting time that occurs with the movement of the pressure roller 22.

[0065] Furthermore, depending on the configuration of the pressure mechanism 30 and the reference position detection mechanism 40, the position of the pressure roller 22 may be unclear at the start of warm-up, and it may not be possible to determine the position of the pressure roller 22. In such a case, as shown by the dotted line in Fig. 6, the pressure drive motor 47 is rotated forward at the start of warm-up, and the pressure drive motor 47 is driven for 100 ms after the reference position detection sensor 41 is turned on to perform a pressure operation to move the pressure roller 22 to the second pressure position. Then, after the on state of the reference position detection sensor 41 is detected, the pressure roller 22 is moved to the decompression position, so that the position of the pressure roller 22 can be determined.

[0066] FIG. 7 is a timing chart showing an example of control of the fixing device 13 during image formation in the image forming apparatus 100 of this embodiment, in which the sheet S is a thin plain paper (basis weight 60 to 75 g / m 2 7 is a diagram showing a control example in the case where the print command is input at time T3 as shown in Fig. 7. When a print command is input at time T3, the pressure drive motor 47 is rotated forward. Then, the pressure drive motor 47 is driven for 100 ms after the reference position detection sensor 41 is turned on to move the pressure roller 22 to the second pressure position. At the same time, the linear speed of the pressure roller 22 is increased from half speed to full speed, and the fixing temperature is increased from the standby temperature to the reference temperature.

[0067] Then, when the image forming operation ends at time T4, the pressure driving motor 47 is rotated in reverse. Then, the pressure driving motor 47 is driven for 1500 ms after the reference position detection sensor 41 turns off to move the pressure roller 22 to the decompression position. At the same time, the linear speed of the pressure roller 22 is reduced from full speed to half speed, and the fixing temperature is reduced from the reference temperature to the standby temperature, thereby putting the image forming apparatus 100 back into the standby mode.

[0068] FIG. 8 is a timing chart showing an example of control of the fixing device 13 during image formation in the image forming apparatus 100 of this embodiment. 2 7. When the paper S is thick plain paper, when a print command is input at time T3, the pressure drive motor 47 is rotated forward. Then, the pressure drive motor 47 is driven for 400 ms after the reference position detection sensor 41 is turned on to move the pressure roller 22 to the first pressure position. In addition, the fixing temperature is raised to a temperature higher than the reference temperature (reference temperature + correction temperature). Other operations are the same as those in FIG. 7.

[0069] 9 is a timing chart showing an example of control of the fixing device 13 during image formation in the image forming apparatus 100 of this embodiment, and shows another example of control when the paper S is thick plain paper. In FIG. 9, when a print command is input, if the information on the type of paper input from the operation unit 80 has not been determined, the control is divided so that the paper does not move from the depressurization position to the pressurization position (here, the first pressurization position) according to the paper type in one step, but moves to the second pressurization position once, and moves to the first pressurization position when the type of paper S is determined (time T5).

[0070] In this way, by moving the pressure roller 22 stepwise from the depressurization position to the second pressure position and the first pressure position, the fixing conditions can be set with the same control even in cases where information about the paper S is not known, such as when the paper type input from the operation unit 80 has not been determined when a print command is input. This simplifies the control of the image forming apparatus 100. The reason why the pressure roller 22 starts moving to the second pressure position when the print command is input is to complete the movement of the pressure roller 22 to the pressure position according to the type of paper S by the time the paper S reaches the fixing device 13.

[0071] There are two possible methods for moving the pressure roller 22 from the second pressure position to the first pressure position. One is a method (first method) in which, since the pressure roller 22 stops at the second pressure position 100 ms after the reference position detection sensor 41 turns on, the pressure roller 22 is driven in the pressure direction for a further 300 ms to move to the first pressure position. The other is a method (second method) in which the pressure roller 22 moves from the second pressure position in the decompression direction until the reference position detection sensor 41 turns off, then reverses to the pressure direction, and moves to the first pressure position by driving in the pressure direction for 400 ms from the reference position detection sensor 41 turns on.

[0072] The first method has the advantage of a short movement time, while the second method has the advantage of higher positional accuracy of the pressure roller 22 because the first pressure position is always determined by the elapsed time from the ON state of the reference position detection sensor 41. The method to be selected can be determined by considering the relationship between the required positional accuracy and the movement time.

[0073] 10 is a timing chart showing an example of control of the fixing device 13 during image formation in the image forming apparatus 100 of this embodiment, and shows an example of control when the paper S is special paper (envelope). When the paper S is an envelope, when a print command is input at time T3, the pressure roller 22 is kept in the reduced pressure position and the linear speed is kept at half speed to prevent wrinkles. Then, the fixing temperature is raised from the standby temperature to the reference temperature to execute printing.

[0074] If the fixing nip pressure is still high even at the reduced pressure position, printing may be performed by placing the pressure roller 22 in a jam processing position where the fixing nip pressure is even lower, as shown by the dashed line in Fig. 10. Table 2 summarizes examples of settings for the type of paper S, the pressure position of the pressure roller 22, the linear speed, and the fixing temperature.

[0075] [Table 2]

[0076] The setting examples shown in Table 2 show general setting trends, and may vary depending on the configuration of the fixing device 13, the strength of the fixing nip pressure by the pressure mechanism 30, the linear speed range, etc. Also, since a large change in the fixing temperature can cause waiting times when changing the paper type, it is desirable to control the fixing temperature so that it does not change significantly.

[0077] As described above, according to the configuration of this embodiment, two pressure positions, a first pressure position and a second pressure position, are provided as pressure positions for normal paper such as thin paper, plain paper, and thick paper, and the two pressure positions are appropriately used. This makes it possible to provide an image forming apparatus that can achieve both transportability and fixability with a simple mechanism and control when changing the fixing nip pressure according to the basis weight and thickness of paper including normal paper as well as special paper such as envelopes.

[0078] In this embodiment, a reference position detection mechanism 40 is used that reaches the target pressurized position when a predetermined time has elapsed since the reference position detection sensor 41 turned on (when the pressure cam 33 has rotated a predetermined amount), and reaches the target depressurized position when a predetermined time has elapsed since the reference position detection sensor 41 turned off (when the pressure cam 33 has rotated a predetermined amount). This allows the pressure roller 22 to be accurately positioned at a predetermined pressurized position (or depressurized position).

[0079] In addition, the present invention is not limited to the above embodiment, and various modifications are possible within the scope of the present invention. For example, in the above embodiment, two pressure positions, the first pressure position and the second pressure position, are set as the pressure positions of the pressure roller 22, but three or more pressure positions may be set. In this case, the fixing nip pressure can be set more finely according to the type of paper S. The fixing nip pressure at three or more pressure positions is preferably in the range of 1 to 1.2, assuming that the pressure position with the lowest fixing nip pressure is 1. Table 3 shows an example of setting the pressure positions in three stages. In the example shown in Table 3, in addition to the first pressure position and the second pressure position, a third pressure position with a fixing nip pressure lower than that of the second pressure position is provided.

[0080] [Table 3]

[0081] In the above embodiment, the fixing device 13 is of a sliding belt type in which the endless fixing belt 21 slides against the nip forming member 24 as the heated rotating body, but it goes without saying that the present invention can be applied in exactly the same way to a fixing device of a uniaxial belt type in which the fixing belt 21 is wound around a fixing roller, a biaxial belt type in which the fixing belt 21 is stretched between a fixing roller and a heating roller, or a fixing device equipped with a heated rotating body other than the fixing belt 21. In addition, the heating unit 23 is not limited to an induction heating type equipped with an excitation coil and a core, and can be, for example, a halogen heater.

[0082] Furthermore, the present invention is not limited to a vertical conveying type fixing device 13 in which the paper S passes through the fixing nip portion N from bottom to top as shown in each of the above embodiments, but can also be applied to a horizontal conveying type fixing device in which the paper S passes through the fixing nip portion N horizontally.

[0083] Furthermore, image forming apparatus 100 is not limited to a tandem color printer as shown in FIG. 1, but can be applied to various image forming apparatuses equipped with a fixing device, such as monochrome copying machines, digital multifunction machines, facsimiles, and laser printers. [Industrial Applicability]

[0084] The present invention can be used in an image forming apparatus equipped with a fixing device that applies heat and pressure to a toner image by inserting the recording medium into a fixing nip formed by a heated rotating body and a pressure member to melt and fix the toner image on the recording medium. By using the present invention, it is possible to provide an image forming apparatus that can precisely adjust the fixing nip pressure to one of a plurality of pressure settings according to the type of normal paper. [Explanation of symbols]

[0085] Pa~Pd Image forming section 13 Fixing device 21 Fixing belt (heated rotating body) 22 Pressure roller (pressure rotating body) 23 Heating section 24 Nip forming member 25 Belt guide 26 Frame members 30 Pressurizing mechanism 31 Pressure lever 32 Coil spring 33 Pressing Cam 35 Shaft 40 Reference position detection mechanism 41 Reference position detection sensor 43 Shading plate 47 Pressure drive motor 80 Operation section (input section) 90 Control section 95 Timer 100 Image forming device N Fixing nip S Paper (recording medium)

Claims

1. an image forming unit that forms a toner image on a recording medium; A heated rotating body; a pressure rotating body that is pressed against the heated rotating body at a predetermined fixing nip pressure to form a fixing nip portion; A heating unit that heats the heated rotating body; a pressure mechanism including a pressure lever that moves the pressure rotor in a direction approaching or separating from the heated rotor, a pressure cam that varies the pressure applied by the pressure lever, and a pressure drive motor that rotates a shaft to which the pressure cam is fixed; a reference position detection mechanism that detects that the pressurizing rotor is at a reference position, the reference position detection mechanism having a light-shielding plate fixed to the shaft and a reference position detection sensor that is turned on or off by the light-shielding plate; a fixing device that performs a fixing process of fixing the toner image onto the recording medium by applying heat and pressure to the recording medium passing through the fixing nip portion; an input unit capable of inputting information regarding the type of the recording medium; a control unit that adjusts a pressure position by controlling the pressure mechanism based on information regarding the type of the recording medium input from the input unit; In an image forming apparatus comprising: the pressure mechanism selectively disposes the pressure rotating body at a plurality of pressure positions having different fixing nip pressures, including a first pressure position and a second pressure position at which the fixing nip pressure is smaller than that at the first pressure position, and at a reduced pressure position at which the fixing nip pressure is smaller than that at the pressure positions; When the recording medium is normal paper, the control unit performs the fixing process by placing the pressure rotating body at one of the plurality of pressure positions, and when the recording medium is special paper, the control unit performs the fixing process by placing the pressure rotating body at one of the plurality of pressure positions and the decompression position, the light blocking plate is disposed so that the reference position detection sensor is turned on when the rotation position of the pressing cam reaches the vicinity of the pressing position, after rotating the pressure drive motor in the forward direction, when a predetermined time has elapsed since the reference position detection sensor was turned on, or when the amount of rotation of the shaft has reached a predetermined amount, the pressure drive motor is stopped to position the pressure rotor at any one of the pressure positions; the pressure mechanism selectively disposes the pressure rotating body at a plurality of pressure reduction positions where the fixing nip pressure is different; an image forming apparatus characterized in that after the pressure drive motor is rotated in reverse, the pressure drive motor is stopped when a predetermined time has elapsed since the reference position detection sensor was turned off, or when the amount of rotation of the shaft has reached a predetermined amount, thereby positioning the pressure rotor at one of the multiple decompression positions.

2. An image forming apparatus as described in claim 1, characterized in that the fixing nip pressure at the multiple pressure positions is in the range of 1 to 1.2, when the pressure position at which the fixing nip pressure is lowest is defined as 1.

3. An image forming unit that forms a toner image on a recording medium; A heated rotating body; a pressure rotating body that is pressed against the heated rotating body at a predetermined fixing nip pressure to form a fixing nip portion; A heating unit that heats the heated rotating body; a pressure mechanism including a pressure lever that moves the pressure rotor in a direction approaching or separating from the heated rotor, a pressure cam that varies the pressure applied by the pressure lever, and a pressure drive motor that rotates a shaft to which the pressure cam is fixed; a reference position detection mechanism that detects that the pressurizing rotor is at a reference position, the reference position detection mechanism having a light-shielding plate fixed to the shaft and a reference position detection sensor that is turned on or off by the light-shielding plate; a fixing device that performs a fixing process of fixing the toner image onto the recording medium by applying heat and pressure to the recording medium passing through the fixing nip portion; an input unit capable of inputting information regarding the type of the recording medium; a control unit that adjusts a pressure position by controlling the pressure mechanism based on information regarding the type of the recording medium input from the input unit; In an image forming apparatus comprising: the pressure mechanism selectively disposes the pressure rotating body at a plurality of pressure positions having different fixing nip pressures, including a first pressure position and a second pressure position at which the fixing nip pressure is smaller than that at the first pressure position, and at a reduced pressure position at which the fixing nip pressure is smaller than that at the pressure positions; When the recording medium is normal paper, the control unit performs the fixing process by placing the pressure rotating body at one of the plurality of pressure positions, and when the recording medium is special paper, the control unit performs the fixing process by placing the pressure rotating body at one of the plurality of pressure positions and the decompression position, the light blocking plate is disposed so that the reference position detection sensor is turned on when the rotation position of the pressing cam reaches the vicinity of the pressing position, after rotating the pressure drive motor in the forward direction, when a predetermined time has elapsed since the reference position detection sensor was turned on, or when the amount of rotation of the shaft has reached a predetermined amount, the pressure drive motor is stopped to position the pressure rotor at any one of the pressure positions; The control unit drives the pressure applying rotor to rotate at a predetermined linear speed while the pressure applying rotor is positioned at the reduced pressure position at the start of warm-up to raise the fixing temperature, which is the temperature of the heated rotating body, to a standby temperature, and when the fixing temperature reaches a predetermined temperature lower than the standby temperature during warm-up, increases the linear speed of the pressure applying rotor and moves the pressure applying rotor from the reduced pressure position to the second pressure applying position, and when the fixing temperature reaches the standby temperature, returns the linear speed of the pressure applying rotor to its original value and moves the pressure applying rotor from the second pressure applying position to the reduced pressure position.

4. The image forming apparatus according to claim 3, characterized in that when a print command is input while the pressure rotating body is positioned at the second pressure position during the warm-up, the control unit either maintains the pressure rotating body at the second pressure position or positions the pressure rotating body at either the pressure position different from the second pressure position or the decompression position based on the type of the recording medium.

5. An image forming unit that forms a toner image on a recording medium; A heated rotating body; a pressure rotating body that is pressed against the heated rotating body at a predetermined fixing nip pressure to form a fixing nip portion; A heating unit that heats the heated rotating body; a pressure mechanism including a pressure lever that moves the pressure rotor in a direction approaching or separating from the heated rotor, a pressure cam that varies the pressure applied by the pressure lever, and a pressure drive motor that rotates a shaft to which the pressure cam is fixed; a reference position detection mechanism that detects that the pressurizing rotor is at a reference position, the reference position detection mechanism having a light-shielding plate fixed to the shaft and a reference position detection sensor that is turned on or off by the light-shielding plate; a fixing device that performs a fixing process of fixing the toner image onto the recording medium by applying heat and pressure to the recording medium passing through the fixing nip portion; an input unit capable of inputting information regarding the type of the recording medium; a control unit that adjusts a pressure position by controlling the pressure mechanism based on information regarding the type of the recording medium input from the input unit; In an image forming apparatus comprising: the pressure mechanism selectively disposes the pressure rotating body at a plurality of pressure positions having different fixing nip pressures, including a first pressure position and a second pressure position at which the fixing nip pressure is smaller than that at the first pressure position, and at a reduced pressure position at which the fixing nip pressure is smaller than that at the pressure positions; When the recording medium is normal paper, the control unit performs the fixing process by placing the pressure rotating body at one of the plurality of pressure positions, and when the recording medium is special paper, the control unit performs the fixing process by placing the pressure rotating body at one of the plurality of pressure positions and the decompression position, the light blocking plate is disposed so that the reference position detection sensor is turned on when the rotation position of the pressing cam reaches the vicinity of the pressing position, after rotating the pressure drive motor in the forward direction, when a predetermined time has elapsed since the reference position detection sensor was turned on, or when the amount of rotation of the shaft has reached a predetermined amount, the pressure drive motor is stopped to position the pressure rotor at any one of the pressure positions; The control unit of this image forming apparatus is characterized in that when information regarding the type of the recording medium has not been determined at the time a print command is input, it places the pressure rotating body at the second pressure position, and when the type of the recording medium is determined, it either maintains the pressure rotating body at the second pressure position or places the pressure rotating body at either the pressure position or the decompression position which is different from the second pressure position.

6. An image forming unit that forms a toner image on a recording medium; A heated rotating body; a pressure rotating body that is pressed against the heated rotating body at a predetermined fixing nip pressure to form a fixing nip portion; A heating unit that heats the heated rotating body; a pressure mechanism including a pressure lever that moves the pressure rotor in a direction approaching or separating from the heated rotor, a pressure cam that varies the pressure applied by the pressure lever, and a pressure drive motor that rotates a shaft to which the pressure cam is fixed; a reference position detection mechanism that detects that the pressurizing rotor is at a reference position, the reference position detection mechanism having a light-shielding plate fixed to the shaft and a reference position detection sensor that is turned on or off by the light-shielding plate; a fixing device that performs a fixing process of fixing the toner image onto the recording medium by applying heat and pressure to the recording medium passing through the fixing nip portion; an input unit capable of inputting information regarding the type of the recording medium; a control unit that adjusts a pressure position by controlling the pressure mechanism based on information regarding the type of the recording medium input from the input unit; In an image forming apparatus comprising: the pressure mechanism selectively disposes the pressure rotating body at a plurality of pressure positions having different fixing nip pressures, including a first pressure position and a second pressure position at which the fixing nip pressure is smaller than that at the first pressure position, and at a reduced pressure position at which the fixing nip pressure is smaller than that at the pressure positions; When the recording medium is normal paper, the control unit performs the fixing process by placing the pressure rotating body at one of the plurality of pressure positions, and when the recording medium is special paper, the control unit performs the fixing process by placing the pressure rotating body at one of the plurality of pressure positions and the decompression position, the light blocking plate is disposed so that the reference position detection sensor is turned on when the rotation position of the pressing cam reaches the vicinity of the pressing position, after rotating the pressure drive motor in the forward direction, when a predetermined time has elapsed since the reference position detection sensor was turned on, or when the amount of rotation of the shaft has reached a predetermined amount, the pressure drive motor is stopped to position the pressure rotor at any one of the pressure positions; The control unit positions the pressure rotating body at the second pressure position when a print command is input, and, based on the type of recording medium input from the input unit, either maintains the pressure rotating body at the second pressure position or positions the pressure rotating body at either the pressure position or the decompression position which is different from the second pressure position.

7. 7. The image forming apparatus according to claim 4, wherein the control unit rotates the pressure drive motor forward or reverse for a predetermined period of time from the second pressure position when the pressure rotating body is moved from the second pressure position to either the pressure position or the decompression position different from the second pressure position.

8. The image forming apparatus according to any one of claims 4 to 6, characterized in that when the pressure rotating body is moved from the second pressure position to either the pressure position or the decompression position different from the second pressure position, the control unit rotates the pressure driving motor to turn on or off the reference position detection sensor, and rotates the pressure driving motor forward or reverse for a predetermined period of time after detecting that the pressure rotating body is at the reference position.

Images