JP7735089B2 - image heating device - Google Patents

Description

The present invention relates to an image heating device for heating an image on a recording material.

A fixing device, which is an image heating device, is known to have a configuration equipped with a cam that displaces the pressure at the nip formed by the heating roller and pressure roller. Also proposed is a configuration in which a drive transmission device that transmits drive from the drive source to the cam is provided with a clutch that blocks the reaction force from the cam from being transmitted to the drive source (Patent Document 1).

JP 2009-198949 A

However, in the configuration described in Patent Document 1, a clutch is provided to prevent the reaction force from the cam from being transmitted to the drive source. This increases the cost of the drive transmission device and increases the size of the device due to the clutch.

The present invention aims to provide a configuration that can prevent the reaction force from the cam from being transmitted to the drive source while minimizing increases in size and cost.

One aspect of the present invention is an image heating device comprising: a first rotating member that heats a recording material; a second rotating member that contacts the first rotating member and, together with the first rotating member, sandwiches and transports the recording material to form a nip portion where a toner image is fixed to the recording material; a pair of side plates that support the second rotating member; and a switching mechanism that changes the position of the second rotating member relative to the first rotating member to switch the pressure force at the nip portion, wherein the switching mechanism has: a motor; a worm that is driven to rotate by the motor; a worm wheel that meshes with the worm and to which driving force is transmitted from the worm; a cam that rotates as the rotation of the worm wheel is transmitted; a pair of bearings that rotatably support the worm; and a displacement mechanism that contacts the cam and displaces the second rotating member relative to the first rotating member as the cam rotates, wherein each support plate that constitutes the pair of bearings is fixed to one of the pair of side plates .

One aspect of the present invention is an image heating device comprising: a first rotating member that heats a recording material; a second rotating member that contacts the first rotating member and, together with the first rotating member, sandwiches and transports the recording material to form a nip portion where a toner image is fixed to the recording material; a pair of side plates that support the second rotating member; and a switching mechanism that changes the position of the second rotating member relative to the first rotating member to switch between applying pressure and releasing the pressure at the nip portion, wherein the switching mechanism has: a motor; a worm that is driven to rotate by the motor; a worm wheel that meshes with the worm and to which driving force is transmitted from the worm; a cam that rotates as the rotation of the worm wheel is transmitted; a pair of bearings that rotatably support the worm; and a displacement mechanism that contacts the cam and displaces the second rotating member relative to the first rotating member as the cam rotates, wherein each support plate that constitutes the pair of bearings is fixed to one of the pair of side plates.
One aspect of the present invention is a recording medium conveying device including a first rotating member that heats a recording material, a second rotating member that contacts the first rotating member and nip-conveys the recording material together with the first rotating member to form a nip portion where a toner image is fixed to the recording material, a pair of side plates that support the second rotating member, and a switching mechanism that changes the position of the second rotating member relative to the first rotating member to switch the pressure force at the nip portion, the switching mechanism including a motor, a worm that is driven to rotate by the motor, and a worm that engages with the worm and to which driving force is transmitted from the worm. the cam is fixed to one of the pair of side plates .

This invention makes it possible to prevent the reaction force from the cam from being transmitted to the drive source while minimizing increases in size and cost.

1 is a cross-sectional view showing a schematic configuration of an image forming apparatus according to an embodiment. FIG. 2 is a perspective view of a fixing device according to the embodiment. 3 is a cross-sectional view taken along the line AA in FIG. 2; 3 is a cross-sectional view taken along the line B-B in FIG. 2; FIG. 2 is a cross-sectional view showing a schematic configuration of a drive transmission mechanism to a heating roller according to the embodiment. FIG. 2 is a front view of the fixing device according to the embodiment, showing the drive transmission device exposed. (a) A graph showing the relationship between the cam rotation angle and the cam radius, (b) A schematic diagram of the cam showing each point in (a), (c) A graph showing the relationship between the cam rotation angle and the cam axial torque. 3 is a cross-sectional view taken along the line CC in FIG. 2 in a separated state. 3 is a cross-sectional view taken along the line CC in FIG. 2 in a state where the pressure is applied to an envelope. 3 is a cross-sectional view taken along the line CC in FIG. 2 in a state where a pressure is applied to a letter other than an envelope. FIG. 7 is a view similar to FIG. 6 of a fixing device according to Comparative Example 1. FIG. 2 is a perspective view of the fixing device according to the embodiment, seen from the front side in a state where the fixing device is pulled out from the device main body. FIG. 11 is a perspective view of a fixing device according to Comparative Example 2, seen from the rear side, in a state where the fixing device is pulled out from the device main body.

This embodiment will be described using Figures 1 to 13. First, the general configuration of the image forming apparatus of this embodiment will be described using Figure 1.

[Image forming apparatus]
The image forming apparatus 1 is an electrophotographic full-color printer having four image forming units Pa, Pb, Pc, and Pd corresponding to the four colors of yellow, magenta, cyan, and black. In this embodiment, the image forming units Pa, Pb, Pc, and Pd are arranged in tandem along the rotation direction of an intermediate transfer belt 204 (described later). The image forming apparatus 1 forms a toner image (image) on a recording material in response to an image signal from an image reading unit (document reading device) 2 connected to the image forming apparatus main body 3 or from a host device such as a personal computer connected to the image forming apparatus main body 3 so as to be able to communicate with the image forming apparatus main body 3. Examples of the recording material include sheet materials such as paper, plastic film, and cloth.

Image forming device 1 comprises an image reading unit 2 and an image forming device main body 3. Image reading unit 2 reads an original placed on a platen glass 21. Light emitted from a light source 22 is reflected by the original and forms an image on a CCD sensor 24 via optical components 23 such as lenses. This optical unit scans in the direction of the arrow, converting the original into a line-by-line electrical signal data stream. The image signal obtained by CCD sensor 24 is sent to image forming device main body 3, where it is processed in a control unit 30 according to the image forming units described below. Control unit 30 also receives external inputs as image signals from external host devices such as print servers.

The image forming device main body 3 has multiple image forming units Pa, Pb, Pc, and Pd, and each image forming unit forms an image based on the image signal described above. That is, the image signal is converted into a laser beam that is PWM (pulse width modulation) controlled by the control unit 30. A polygon scanner 31, which serves as an exposure device, scans the laser beam in accordance with the image signal. The laser beam is then irradiated onto the photosensitive drums 200a-200d, which serve as image carriers for each image forming unit Pa-Pd.

Note that Pa is the yellow (Y) image forming unit, Pb is the magenta (M) image forming unit, Pc is the cyan (C) image forming unit, and Pd is the black (Bk) image forming unit, and each forms an image of the corresponding color. Since image forming units Pa to Pd are substantially identical, the Y image forming unit Pa will be described in detail below, and a description of the other image forming units will be omitted. In image forming unit Pa, a toner image is formed on the surface of photosensitive drum 200a based on an image signal, as described below.

The charging roller 201a, which serves as a primary charger, charges the surface of the photosensitive drum 200a to a predetermined potential to prepare for the formation of an electrostatic latent image. A laser beam from the polygon scanner 31 forms an electrostatic latent image on the surface of the photosensitive drum 200a, which has been charged to a predetermined potential. The developing unit 202a develops the electrostatic latent image on the photosensitive drum 200a to form a toner image. The primary transfer roller 203a discharges from the back of the intermediate transfer belt 204 and applies a primary transfer bias of opposite polarity to the toner, transferring the toner image on the photosensitive drum 200a onto the intermediate transfer belt 204. After transfer, the surface of the photosensitive drum 200a is cleaned by the cleaner 207a.

The toner image on intermediate transfer belt 204 is then transported to the next image forming unit, where the toner images of each color formed at each image forming unit are transferred in the order of Y, M, C, and Bk, forming a four-color image on its surface. The toner image that passes through Bk image forming unit Pd, which is located at the most downstream position in the rotation direction of intermediate transfer belt 204, is then transported to a secondary transfer unit comprised of a pair of secondary transfer rollers 205 and 206. At the secondary transfer unit, a secondary transfer electric field of opposite polarity to the toner image on intermediate transfer belt 204 is applied, causing the toner image to be secondarily transferred to the recording material.

The recording material is stored in a cassette 9. The recording material fed from the cassette 9 is transported to a registration unit 208, which is composed of, for example, a pair of registration rollers, and waits there. The registration unit 208 then controls the timing to align the toner image on the intermediate transfer belt 204 with the paper, and transports the recording material to the secondary transfer unit.

The recording material onto which the toner image has been transferred in the secondary transfer section is transported to the fixing device 8, where it is heated and pressurized to fix the toner image carried on the recording material to the recording material. After passing through the fixing device 8, the recording material is discharged onto the discharge tray 7. When forming images on both sides of the recording material, once the toner image has been transferred and fixed onto the first side (front side) of the recording material, the recording material is turned over via the reversing conveyance section 10, and the toner image is transferred and fixed onto the second side (back side) of the recording material, and then stacked on the discharge tray 7.

As described above, the control unit 30 controls the entire image forming apparatus 1. The control unit 30 can also perform various settings based on input from the operation unit 4 and display unit 5 of the image forming apparatus 1. The operation unit 4 and display unit 5 are provided on the image forming apparatus 1 and are, for example, a touch panel or buttons that can be operated by touch.

Such a control unit 30 has a CPU (Central Processing Unit), ROM (Read Only Memory), and RAM (Random Access Memory). The CPU controls each part by reading programs corresponding to control procedures stored in the ROM. In addition, working data and input data are stored in the RAM, and the CPU performs control by referencing the data stored in the RAM based on the aforementioned programs, etc.

[Fixing device]
Next, a schematic configuration of the fixing device 8 in this embodiment will be described with reference to FIGS. 2 to 5. FIG. 2 is a perspective view of the fixing device 8, with the lower left side of FIG. 2 being the front side and the upper right side being the rear side. Here, the front side refers to the front side of the image forming apparatus 1, the side from which an operator operates the image forming apparatus 1. The rear side refers to the rear side of the image forming apparatus 1. In this embodiment, the fixing device 8 is movable relative to the housing 3a (see FIG. 1) of the image forming apparatus 1. By pulling the fixing device 8 out from the housing 3a to the front side, the fixing device 8 is exposed from the housing 3a, allowing replacement of the fixing belt 310, which will be described below, and the like. On the other hand, the fixing device 8 can be stored in the housing 3a by pushing the fixing device 8 into the housing 3a.

Figure 3 is a view of the fixing device 8 in Figure 2 cut at section F1, viewed from the direction of arrow A. Section F1 is a cross section perpendicular to the rotation axis of the pressure roller 330 of the fixing device 8, which will be described below, and Figure 3 is a view of the fixing device 8 taken from the front at section F1. Figure 4 is a view of the fixing device 8 in Figure 2 cut at section F1, viewed from the direction of arrow A, and is a view of the fixing device 8 taken from the rear at section F1. Figure 5 is a cross-sectional view showing the drive configuration of the heating roller 340, which will be described below.

The fixing device 8 of this embodiment employs a belt heating method using an endless belt. In Figure 3, the recording material is transported from right to left, as indicated by the arrow α. The fixing device 8 has a heating unit 300 having a fixing belt 310, which is an endless, rotatable belt, and a pressure roller 330, which is a pressure rotating body that contacts the fixing belt 310 and forms a nip N with the fixing belt 310.

The heating unit 300 has a fixing belt 310 as a first rotating member, a fixing pad 390 as a nip forming member and pad member, a heating roller 340 as a tension member, and a steering roller 350.

The endless fixing belt 310 has thermal conductivity, heat resistance, and other properties, and is a thin, cylindrical shape. In this embodiment, it has a three-layer structure consisting of a base layer, an elastic layer around the outer periphery of the base layer, and a release layer around the outer periphery of the elastic layer. The base layer is 60 μm thick and made of polyimide resin (PI), the elastic layer is 300 μm thick and made of silicone rubber, and the release layer is 30 μm thick and made of PFA (tetrafluoroethylene-perfluoroalkoxyethylene copolymer resin) as a fluororesin. The fixing belt 310 is stretched by the fixing pad 390, heating roller 340, and steering roller 350.

The fixing pad 390, which serves as a nip portion forming member, is positioned inside the fixing belt 310 so as to face the pressure roller 330 across the fixing belt 310, and forms a nip portion N between the fixing belt 310 and the pressure roller 330, which sandwiches and transports the recording material. In this embodiment, the fixing pad 390 is a generally plate-shaped member that is long along the width direction of the fixing belt 310 (the longitudinal direction intersecting the rotation direction of the fixing belt 310, the direction of the rotation axis of the heating roller 340). When the fixing pad 390 is pressed against the pressure roller 330 across the fixing belt 310, a nip portion N having a predetermined width in the transport direction of the recording material is formed. The fixing pad 390 is made of LCP (liquid crystal polymer) resin.

At least a portion of the fixing pad 390 that forms the nip portion N is formed flat. In other words, the portion that comes into contact with the inner surface of the fixing belt 310 via a lubricating sheet (not shown) is formed in a substantially flat shape, making the nip portion approximately flat. This configuration can prevent wrinkles and image misalignment from occurring on the envelope, particularly when fixing a toner image to an envelope as a recording material.

The fixing pad 390 is supported by a stay 360, which serves as a support member and is located inside the fixing belt 310. That is, the stay 360 is located on the opposite side of the fixing pad 390 from the pressure roller 330, and supports the fixing pad 390. Such a stay 360 is a reinforcing member that has long rigidity along the longitudinal direction of the fixing belt 310, and abuts against the fixing pad 390 to back it up. That is, the stay 360 provides strength to the fixing pad 390 when it is pressed by the pressure roller 330, ensuring the pressure at the nip N.

The stay 360 is made of metal such as stainless steel, and has a substantially rectangular cross section (transverse cross section) perpendicular to the longitudinal direction of the stay 360, which intersects with the rotation direction of the fixing belt 310. Both ends of the stay 360 are supported by the fixing frame (frame, housing) 380 of the fixing device 8. As shown in FIG. 2 , the fixing frame 380 is made up of a front side plate 320, a rear side plate 321, a right stay 322, a left stay 323, and a bottom plate 324.

A lubricating sheet (not shown) is interposed between the fixing pad 390 and the fixing belt 310. In this embodiment, a PI (polyimide) sheet coated with PTFE (polytetrafluoroethylene) is used as the lubricating sheet, with a thickness of 100 μm. The PI sheet has 100 μm protrusions formed at 1 mm intervals, which reduces the contact area with the fixing belt 310 and thereby reduces sliding resistance.

A lubricant is pre-applied to the contact surface of the lubricating sheet with the fixing belt 310 to improve sliding properties. In this embodiment, oil is used as the lubricant. Silicone oil is preferably used for its heat resistance, and oils of various viscosities are used depending on the conditions of use.

As shown in Figures 3 and 4, the heating roller 340 is disposed inside the fixing belt 310 and tensions the fixing belt 310 together with the fixing pad 390 and steering roller 350. As described above, a lubricant is applied to the inner surface of the fixing belt 310, and the heating roller 340 tensions the fixing belt 310 via this lubricant. The heating roller 340 is also disposed downstream of the fixing pad 390 and upstream of the steering roller 350 in terms of the rotation direction of the fixing belt 310. This allows the driving force of the heating roller 340 to directly tension the fixing belt 310 that has passed through the nip portion N, without using a tension roller in between.

The heating roller 340 is cylindrical and made of metal such as aluminum or stainless steel, and has multiple halogen heaters 341 disposed inside it to heat the fixing belt 310 (Figure 3). The heating roller 340 is heated to a predetermined temperature by the halogen heaters 341.

In this embodiment, the heating roller 340 is formed from a 1 mm thick stainless steel pipe, with multiple halogen heaters 341 arranged inside. It is desirable to have multiple halogen heaters, considering temperature distribution control in the longitudinal direction (rotational axis direction) of the heating roller 340. The multiple halogen heaters 341 have different light distributions in the longitudinal direction, and the lighting ratio is controlled according to the size of the recording material. The heater is not limited to a halogen heater, and other heaters capable of heating the heating roller 340, such as a carbon heater, may also be used. The fixing belt 310 is heated by the heating roller 340 heated by the halogen heaters 341, and is controlled to a predetermined target temperature according to the type of recording material based on temperature detection by a thermistor (not shown).

The heating roller 340 is rotatably supported by the fixing frame 380. As shown in FIG. 5, a gear 385a is fixed to one end (rear end) of the heating roller 340 in the direction of its rotation axis, and is connected to a motor M1, which serves as a heating roller drive source, via an idler gear 385b and a motor gear 385c, for rotational drive. The idler gear 385b is rotatably supported on a heating roller drive support plate 325 fixed to the rear side plate 321, and transmits rotational drive force to the heating roller 340 by meshing with the motor gear 385c and gear 385a. These gears 385a, 385b, and 385c constitute a gear train 385, which serves as a drive transmission mechanism from the motor M1 to the heating roller 340.

In this way, the heating roller 340 is connected to the motor M1 via the gear train 385 and is driven to rotate. The rotation of the heating roller 340 then applies a driving force to the fixing belt 310. Note that the drive transmission mechanism from the motor may be other mechanisms than gears, such as a pulley and belt, or a mechanism that presses a roller driven by the motor from the outside.

The steering roller 350 is positioned inside the fixing belt 310 and, together with the fixing pad 390 and heating roller 340, stretches the fixing belt 310 and rotates in response to the fixing belt 310. The steering roller 350 tilts relative to the rotational axis (longitudinal direction) of the heating roller 340, thereby controlling the position (offset position) of the fixing belt 310 relative to this rotational axis. In other words, the steering roller 350 has a rotation center at the center of the rotational axis (longitudinal direction) of the steering roller 350, and tilts relative to the longitudinal direction of the heating roller 340 by swinging around this rotation center. This generates a tension difference between one side and the other of the fixing belt 310 in the longitudinal direction, causing the fixing belt 310 to move in the longitudinal direction.

The steering roller 350 may be oscillated by a drive source such as a motor, or may be configured to oscillate by automatic centering. The center of rotation may be the center in the longitudinal direction, as in this embodiment, or it may be at one of the longitudinal ends. In this embodiment, a motor M3 is provided to tilt the steering roller 350.

In addition, in this embodiment, the steering roller 350 is biased by a spring supported by the frame of the heating unit 300, and also serves as a tension roller that applies a predetermined tension to the fixing belt 310. By applying tension to the fixing belt 310 using the steering roller 350 in this way, the fixing belt 310 is caused to follow the fixing pad 390.

The pressure roller 330, which serves as the second rotating member, is a roller with an elastic layer formed on the outer periphery of the shaft and a release layer formed on the outer periphery of the elastic layer. The shaft is made of stainless steel, the elastic layer is 5 mm thick and made of conductive silicone rubber, and the release layer is 50 μm thick and made of PFA (tetrafluoroethylene-perfluoroalkoxyethylene copolymer resin) fluororesin.

As described above, the fixing frame 380 has a front side plate 320 and a rear side plate 321. As shown in Figures 3 and 4, the front side plate 320 and the rear side plate 321 each have heating unit positioning portions 381 and 382. The heating unit positioning portions 381 and 382 have pressure direction regulating surfaces 381a and 382a that face the pressure roller 330, and transport direction regulating surfaces 381b and 382b that are abutting surfaces in the insertion direction of the heating unit 300.

The heating unit 300 is positioned on the fixing frame 380 by inserting the stay 360 into the heating unit positioning portions 381, 382 and fixing the stay 360 to the heating unit positioning portions 381, 382 using a fixing means (not shown). At this time, the stay 360 is fixed in a state where its movement is restricted by the pressure direction restricting surfaces 381a, 382a and the transport direction restricting surfaces 381b, 382b.

A pressure arm support plate 326 (Figure 3) is fixed to the rear plate 321, and a pressure arm support plate 327 (Figure 4) is fixed to the front plate 320 by welding. The pressure arm support plate 326 is a component for rotatably supporting the pressure arm 328, and the pressure arm 328 rotatably supports the pressure roller 330. Similarly, the pressure arm support plate 327 is a component for rotatably supporting the pressure arm 334, and the pressure arm 334 is a component for rotatably supporting the pressure roller 330. In other words, both ends of the pressure roller 330 are rotatably supported by the front and rear pressure arms 328, 334.

The front and rear pressure arms 328, 334 are connected to motor M2, which serves as a pressure drive source, around front and rear rotation shafts 333, 335, and are raised by front and rear pressure cams (pressure cams) 329, 336. The front and rear cams 329, 336 are connected to cam shaft 338, which serves as a rotation shaft. Specifically, cams 329, 336 are fixed to both ends of cam shaft 338, respectively, and can rotate in phase with each other. When the front and rear pressure arms 328, 334 are raised by cams 329, 336, the pressure roller 330 presses against the fixing pad 390 via the fixing belt 310, and a predetermined pressure force is applied by pressure springs 331, 337. In other words, the pressure arms 328, 334, which function as a displacement mechanism, abut against the cams 329, 336, and displace the pressure roller 330 relative to the fixing belt 310 as the cams 329, 336 rotate.

As described above, the pressure roller 330 is supported at both ends by the front and rear pressure arms 328, 334, and when the pressure arms 328, 334 are lifted by the cams 329, 336, a nip N is formed between the fixing belt 310 and the pressure roller 330. In the nip N, the recording material P carrying the toner image is sandwiched and heated while being transported, thereby fixing the toner image to the recording material P.

On the other hand, when the fixing process on the recording material P is not being performed, the pressure arms 328, 334 can be moved in the separation direction by the cams 329, 336 connected to the motor M2, thereby separating the fixing belt 310 and the pressure roller 330, releasing the nip, and allowing the device to wait. In other words, the cams 329, 336 can move the pressure roller 330 toward and away from the fixing belt 310 by rotating.

[Drive transmission device]
Next, referring to FIG. 6 , a description will be given of the pressure drive device 391, which serves as a switching mechanism and includes a drive transmission device 400 that transmits drive from the motor M2, which serves as a drive source, to the front and rear cams 329 and 336 (see FIGS. 3 and 4 ). The pressure drive device 391 includes a pressure drive support plate 389, the motor M2, and the drive transmission device 400, and is fixed as a unit to the front plate 320 of the fixing device 8. Therefore, when removing the fixing device 8 from the image forming apparatus, the motor M2 and the drive transmission device 400 are removed together with the fixing belt 310 and the pressure roller 330. Meanwhile, the motors M1 and M3 are attached to the rear plate 321. As a result, in this embodiment, when removing the fixing device 8 from the image forming apparatus, the motors M1 to M3 and the drive transmission device 400 are removed together with the fixing belt 310 and the pressure roller 330.

The drive transmission device 400 includes a worm gear 401, a pair of bearings 399, a pressure drive gear 395 as a first drive transmission member, and a gear 394 as a second drive transmission member. The worm gear 401 is composed of a worm wheel 392 and a worm 393. The worm wheel 392 is fixed to one end of the cam shaft 338, which is the rotation axis of the cams 329 and 336. The worm 393 is mounted on a rotation axis 393a (on the rotation axis) that rotates when driven by the motor M2, and meshes with the worm wheel 392. In this embodiment, the worm 393 is made of metal, specifically stainless steel. It is preferable that the worm wheel 392 be made of the same metal as the worm 393. It is also preferable that the pressure drive gear 395 and gear 394 be made of metal. The pair of bearings 399 support the rotating shaft 393a on both ends of the worm 393 in the direction of the rotation axis of the worm 393. In other words, the pair of bearings 399 are arranged to sandwich the worm 393 from both sides, and rotatably support the rotating shaft 393a.

The pressure drive gear 395 is mounted on the drive shaft 395a of the motor M2. That is, the pressure drive gear 395 is fixed to the drive shaft 395a and rotates together with the drive shaft 395a. The gear 394 is mounted on the rotation shaft 393a at one end of the worm 393 in the direction of the rotation axis of the worm 393, and receives drive from the pressure drive gear 395. Specifically, the gear 394 is fixed to the end of the rotation shaft 393a on one side of the bearing 399 on one side of the pair of bearings 399, and meshes with the pressure drive gear 395, so that it rotates together with the rotation shaft 393a and worm 393 when driven by the motor M2. The pressure drive gear 395 and gear 394 are spur gears that mesh with each other.

In this embodiment, this configuration allows the cams 329 and 336 to rotate when the motor M2 is driven. That is, when the drive shaft 395a and pressure drive gear 395 rotate when the motor M2 is driven, the gear 394 meshing with the pressure drive gear 395 rotates, and the worm 393 rotates along with the gear 394. Furthermore, the worm wheel 392 meshing with the worm 393 rotates, causing the cams 329 and 336 to rotate via the cam shaft 338 to which the worm wheel 392 is fixed. This changes the positions of the pressure arms 328 and 334 (Figures 3 and 4), and as described above, brings the fixing belt 310 and the pressure roller 330 into contact with or separates them. The following describes their placement. In the vertical direction, the motor M2 is positioned above the worm 393. When viewed from above, the motor M2 overlaps with the worm 393. Furthermore, the motor M2 is positioned above the worm wheel 392 in the vertical direction.

[How to change pressure]
In this embodiment, the fixing belt 310 and the pressure roller 330 are brought into contact with and separated from each other by rotating the cams 329 and 336 as described above. In addition to bringing them into contact with and separating them, the pressure applied by the pressure roller 330 can be changed to change the nip pressure between the fixing belt 310 and the pressure roller 330. That is, by changing the position of the pressure roller 330 relative to the fixing belt 310, it is possible to switch between applying and removing pressure at the nip. With the increasing diversification of media supported by image forming devices in recent years, fixing devices are required to perform optimal fixing processes for a variety of recording materials, from plain paper to special paper such as envelopes. For this reason, in this embodiment, the pressure applied to the nip (nip pressure) can be changed to accommodate a variety of media.

This method of changing the pressure force will be explained using Figures 7(a) to 10. Figure 7(a) shows a cam diagram of the front and rear cams 329, 336, Figure 7(b) shows a schematic diagram of the corresponding cams 329, 336, and Figure 7(c) shows the axial torque of the cams 329, 336. Figures 8 to 10 are views of the fixing device 8 in Figure 2, cut at section F2 and viewed from the direction of arrow C. Section F1 is a cross section perpendicular to the rotation axis of the pressure roller 330 of the fixing device 8, and Figures 8 to 10 are views of the fixing device 8 taken at section F2 as viewed from the front. Figures 8 to 10 also show the pressure states resulting from the transitions in the front and rear cams 329, 336.

The cams 329 and 336 are configured to be able to move the fixing belt 310 and pressure roller 330 closer to and farther from each other, and to change the pressure acting on the nip N in multiple stages when the fixing belt 310 and pressure roller 330 are in contact with each other. First, Figure 7(a) shows the relationship (cam diagram) between the rotation angle (phase) of the cams 329 and 336 and the cam radius when the front and rear cams 329 and 336 start at point D in Figure 7(b) and rotate counterclockwise to point E. Note that Figure 7(a) shows the cam radius with point D as the reference point (0 mm).

The cam surface 370 of the cams 329 and 336 consists of a cam flat surface 371a, which is the separation phase range including point A where the pressure roller 330 and the fixing belt 310 are separated, and a cam slope surface 371b, which is the pressure phase range of the pressure roller 330 that forms the nip portion N. The cam surface 370 is the surface that comes into contact with the cam follower 372 (Figures 8 to 10), which will be described later. The cam flat surface 371a is a flat surface that is approximately perpendicular to the direction of the reaction force acting from the cam follower 372 when in contact with the cam follower 372.

The cam slope surface 371b is the surface where the pressure roller 330 contacts the fixing belt 310 within this phase range, and is the surface that changes the pressure applied by the pressure roller 330. In the counterclockwise direction in Figure 7(b), a cam transition surface 371c is formed between the cam flat surface 371a and the cam slope surface 371b, which moves the pressure roller 330 from a position separated from the fixing belt 310 to a position where it contacts the fixing belt 310.

Cam gradient surface 371b and cam transition surface 371c are formed so that the distance (cam radius) from the center of rotation O of cams 329 and 336 gradually increases in the counterclockwise direction in Figure 7(b). Furthermore, the rate of increase in cam radius is smaller for cam gradient surface 371b than for cam transition surface 371c.

Furthermore, point B on cam slope surface 371b is the point at which pressure is applied when fixing envelopes. Point C on cam slope surface 371b is the point at which pressure is applied when fixing recording materials other than envelopes. For this reason, in this embodiment, cams 329 and 336 are capable of changing the pressure acting on the nip portion in two stages. However, the cams may also be capable of changing the pressure in three or more stages. For example, for recording materials with a high basis weight, such as cardboard, it may be possible to set a pressure greater than the pressure at point C described above.

Figure 7(c) shows the axial torque of cams 329, 336 when pressure is applied to nip portion N by cam slope surface 371b including points B and C shown in Figures 7(a) and (b). Figure 7(c) also shows the amount by which pressure arms 328, 334 are moved by cams 329, 336 (cam lift amount). Figure 7(c) shows that the axial torque increases as the rotation angle of cams 329, 336 increases on cam slope surface 371b, i.e., as the cam radius increases.

Figure 8 shows the pressure roller 330 in a separated state from the fixing belt 310. Note that Figure 8 is a view of cross section F in Figure 2 as seen from the direction of arrow C, so the front pressure arm 334 and cam 336 are visible. However, the rear pressure arm 328 and cam 329 are similar, so in the following explanation they will be described as the front and rear pressure arms 328, 334 and cams 329, 336, as described above. The same applies to Figures 9 and 10.

As shown in Figure 8, the front and rear pressure arms 328, 334 (see Figures 3 and 4) are composed of upper arm portions 328U, 334U, lower arm portions 328L, 334L, cam follower 372, pressure screw 373, and pressure springs 331, 337. The base ends of the upper arm portions 328U, 334U and the lower arm portions 328L, 334L are supported so as to be relatively rotatable about front and rear rotation shafts 333, 335, respectively.

Pressure springs 331 and 337 are arranged in an elastically compressed state between the tips of upper arm portions 328U and 334U and lower arm portions 328L and 334L, respectively. Pressure springs 331 and 337 bias the tips of upper arm portions 328U and 334U and lower arm portions 328L and 334L in a direction that widens the gap between the tips. Furthermore, pressure screws 373 restrict the relative movement of the tips of upper arm portions 328U and 334U and lower arm portions 328L and 334L so that the gap does not widen beyond a predetermined distance. However, relative movement in a direction that narrows the gap between the tips of upper arm portions 328U and 334U and lower arm portions 328L and 334L is permitted. The cam follower 372 is rotatably supported on the lower arm portions 328L and 334L so as to come into contact with the front and rear cams 329 and 336, respectively.

First, when the fixing process is not being performed on the recording material, the fixing belt 310 and pressure roller 330 are separated, the nip is released, and they are on standby. At this time, as shown in Figure 8, the cam follower 372 and the front and rear cams 329 and 336 are in contact at point A shown in Figures 7(a) and 7(b). Also, at this time, the distance between the tips of the upper arm portions 328U and 334U and the lower arm portions 328L and 334L is regulated by the pressure screw 373.

Next, when performing the fixing process on an envelope, as shown in Figure 9, motor M2 is driven to rotate cams 329 and 336 in the direction of the arrow. When cams 329 and 336 rotate, lower arm portions 328L and 334L are pushed up via cam follower 372, and upper arm portions 328U and 334U are further pushed up via pressure springs 331 and 337. Then, pressure roller 330 supported by upper arm portions 328U and 334U contacts fixing belt 310. When cams 329 and 336 rotate until they contact cam follower 372 at point B, a nip is formed between fixing belt 310 and pressure roller 330 that applies pressure for an envelope.

At this time, the pressure roller 330 comes into contact with the fixing belt 310, restricting the movement of the upper arm portions 328U and 334U, while the lower arm portions 328L and 334L move upward relative to each other, compressing the pressure springs 331 and 337 by W1. This causes the upper arm portions 328U and 334U to be biased against the pressure springs 331 and 337, applying a pressure of, for example, 1000 N, which is the pressure for an envelope, to the nip portion N.

Finally, when fixing recording materials other than envelopes, as shown in FIG. 10, motor M2 is driven to further rotate cams 329 and 336 in the direction of the arrow from the state shown in FIG. 9. This further pushes up lower arm portions 328L and 334L, further compressing pressure springs 331 and 337. When cams 329 and 336 rotate until they abut cam follower 372 at point C, the compression amount of pressure springs 331 and 337 becomes W2, which is larger than W1, the compression amount for envelopes. This causes upper arm portions 328U and 334U to be biased against pressure springs 331 and 337, applying a pressure of, for example, 1500 N to nip portion N, which is the pressure for recording materials other than envelopes. Of course, the pressure for recording materials other than envelopes is greater than the pressure for envelopes.

In this way, when fixing is performed on the recording material, the cams 329 and 336 abut against the cam follower 372 at points B or C. As shown in Figures 7(a) to (c), at points B and C, the cam shaft 338 receives a reaction force from the cams 329 and 336 in the form of axial torque. Because the cam shaft 338 is driven by the motor M2, there is a risk that the reaction force may also act on the motor M2 depending on the drive transmission device from the motor M2 to the cam shaft 338.

In this embodiment, a worm gear 401 is used in the drive transmission path from motor M2 to camshaft 338. The worm gear 401 achieves a large reduction ratio without using many gears. Furthermore, the worm gear 401 has a so-called self-locking function that makes it difficult for drive to be transmitted from worm wheel 392 to worm 393. As described above, the worm wheel 392 is fixed to one end of camshaft 338, and the worm wheel 392 is drivingly connected to worm 393. Therefore, in this embodiment, the self-locking function of the worm gear 401 itself locks the reaction force from cams 329 and 336, preventing the reaction force from being transmitted to motor M2.

As a result, even when the cams 329 and 336 are stopped at any point on the cam slope surface 371b, including points B and C, to change the pressure, it is possible to maintain the cam phase while preventing the transmission of a reaction force to the motor M2 via the drive transmission device 400. This eliminates the need to supply a drive force to the motor M2 to maintain the cam phase, making it possible to change the pressure at the nip N with less energy. In other words, it becomes possible to adjust the pressure steplessly to suit a variety of recording materials, including envelopes, with less energy.

Furthermore, while it is possible to provide a clutch in the drive transmission path to prevent the reaction force from the camshaft 338 from being transmitted to the motor M2, this embodiment does not require such a clutch. This makes it possible to prevent the reaction force from the cams 329, 336 from being transmitted to the motor M2 while suppressing increases in size and cost.

On the other hand, a load (thrust force) acts on the worm 393 in the direction of the rotation axis due to reaction forces from the cams 329 and 336. This point will be explained using Comparative Example 1 in Figure 11. In Comparative Example 1, compared to the configuration of this embodiment shown in Figure 6, the worm 393 is mounted on the drive shaft 393b of motor M2, and both sides of the worm 393 are not supported by bearings.

As shown in Figure 11, if the worm 393 is placed on the drive shaft 393b of the motor M2, the drive shaft 393b will receive a thrust force in direction A due to the reaction force from the cam. This will increase the load on the internal components of the motor M2, which could reduce the durability of the motor M2.

However, in this embodiment, as shown in FIG. 6, the rotation shaft 393a of the worm 393 and the drive shaft 395a of the motor M2 are separate bodies and are drive-coupled by gears. In this embodiment, the rotation shaft 393a is located off the drive shaft 395a and approximately parallel to it. A gear 394 is fixed to the end of the rotation shaft 393a, and a pressure drive gear 395 fixed to the drive shaft 395a is meshed with the gear 394. The gear 394 and the pressure drive gear 395 are spur gears. Therefore, even if a thrust force acts on the worm 393 and the rotation shaft 393a due to the reaction force from the cam, the thrust force can be reduced from acting on the internal components of the motor M2, preventing a decrease in the durability of the motor M2.

Furthermore, because the worm 393 is supported on both sides by a pair of bearings 399, the thrust force acting on the worm 393 and rotating shaft 393a can be received by the pair of bearings 399. This also reduces the thrust force acting on the internal components of the motor M2. Furthermore, when the motor M2 is running, the reaction force acting on the worm 393 from the worm wheel 392, which meshes with the worm 393, makes it difficult for the worm 393 to separate from the worm wheel 392, thereby improving drive transmission efficiency.

In addition, in this embodiment, the rotational speed of the drive shaft 395a of the motor M2 is reduced by the worm gear 401, so the reduction ratio can be increased without using multiple gears. For example, it is possible to place multiple idler gears between the gear 394 and the pressure drive gear 395 to achieve the reduction ratio, but this would result in the device becoming larger. In contrast, in this embodiment, the reduction ratio can be increased without providing multiple idler gears, allowing the device to be made more compact. As described above, this embodiment makes it possible to provide a drive transmission device 400 and pressure drive device 391 that can change the pressure force applied to the nip portion while achieving energy savings and compactness.

[Durability of Fixing Device During Maintenance]
Next, the durability of the fixing device 8 during maintenance will be described with reference to Figures 12 and 13. As shown in Figure 12, in this embodiment, the fixing device 8 is detachably unitized from the housing 3a of the image forming apparatus 1 (see Figure 1), taking into consideration the ease of maintenance of the pressure drive device 391, the heating unit 300, the pressure roller 330, etc.

To this end, the fixing device 8 is placed on the fixing drawer 501, which is designed to be removable from within the housing 3a to a predetermined position outside. A support rail 502 is provided between the fixing drawer 501 and the housing 3a, and a guide member 503 is attached to the back or side of the fixing drawer 501. The guide member 503 has a driven wheel that engages with the support rail 502. To remove the fixing device 8 from the housing 3a, open the front door (not shown) of the image forming apparatus 1, operate the lock lever 504, and then grasp the lock lever 504 to remove the fixing drawer 501 toward you (in the direction of the arrow in Figure 12). At this time, the fixing drawer 501 is guided by the guide member 503, and the driven wheel rotates on the support rail 502, allowing it to be removed forward. In this state, the fixing device 8 can be attached to or detached from the fixing drawer 501 for maintenance, for example, by holding a handle (not shown).

Here, comparative example 2 in Figure 13 will be used to examine the durability of the fixing device 8 during maintenance. In comparative example 2, of the pressure drive device 391A that transmits drive from motor M2 to the cam, the components downstream of the worm wheel 392 in the drive transmission direction, including the worm wheel 392, are fixed to the fixing device 8A, and the rest are provided in the housing 3a. In comparative example 2, when the fixing device 8A is pulled out and inserted, the worm wheel 392 provided on the fixing device 8A side and the worm 393 provided on the housing 3a side are engaged and disengaged. For this reason, the pressure drive device 391A is located on the rear side plate 321 side of the fixing frame 380.

In the case of Comparative Example 2, when the pulled-out fixing device 8A is inserted into the housing 3a during maintenance, the worm wheel 392 provided on the fixing device 8A side meshes with the worm 393 provided on the housing 3a side. At this time, the phases of the worm wheel 392 and the worm 393 become misaligned, which could cause the tooth surfaces to collide and be damaged.

In contrast, in this embodiment, the pressure drive device 391 is fixed to the fixing frame 380. That is, the drive transmission device 400, including the worm wheel 392 and worm 393, and the motor M2 are fixed to the fixing frame 380. Specifically, they are fixed to the front side plate 320 of the fixing frame 380. Therefore, even when the fixing device 8 is attached to or detached from the housing 3a, the worm wheel 392 and worm 393 move together with the fixing device 8. Therefore, when the fixing device 8 is inserted into the housing 3a, the tooth surfaces of the worm wheel 392 and the worm 393 do not collide with each other. This ensures durability during maintenance of the fixing device 8.

<Other Embodiments>
In the above embodiment, the drive force is transmitted between the drive shaft 395a of the motor M2 and the rotary shaft 393a of the worm 393 by means of gears, but it may also be configured using, for example, a pulley and a belt.

The pressure roller 330, which forms a nip with the fixing belt 310, may be a drive roller that rotates in contact with the outer surface of the fixing belt 310 and applies a driving force to the fixing belt 310. For example, the pressure roller 330 may have a gear fixed to one end and be connected to a motor serving as a pressure roller drive source via the gear, thereby being driven to rotate. In this case, it is preferable to set the peripheral speed of the heating roller 340 faster than that of the pressure roller 330. The heating roller 340 may also be connected to a motor that drives the pressure roller 330, thereby being driven to rotate.

Furthermore, in the above-described embodiment, the heating roller 340 is positioned downstream of the fixing pad 390 and upstream of the steering roller 350 in relation to the rotation direction of the fixing belt 310. However, the positions of the heating roller 340 and the steering roller 350 may be interchanged. That is, the heating roller 340 may be positioned downstream of the steering roller 350 and upstream of the fixing pad 390 in relation to the rotation direction of the fixing belt 310.

In addition, in the above-described embodiments, the fixing pad 390 was used as the member (nip portion forming member) that forms a nip portion on the fixing belt 310 between itself and the pressure roller 330, but the nip portion forming member may also be a rotating body such as a roller. In addition, in the above-described embodiments, the pressure roller 330 was used as the driving rotating member, but the driving rotating member may also be a belt that is driven to rotate. That is, in the above-described embodiments, the first rotating member was the fixing belt 310 and the second rotating member was the pressure roller 330, but both the first rotating member and the second rotating member may also be belts. Furthermore, both the first rotating member and the second rotating member may also be rollers.

In addition, in the above embodiment, a configuration in which the drive transmission device 400 is applied to a fixing device has been described, but the drive transmission device 400 can also be applied to other configurations as long as it is configured to be provided in the drive transmission path from the motor to the cam. For example, it can also be applied to a mechanism that raises and lowers recording materials loaded on a stacking tray of an image forming device.

8... Fixing device / 310... Fixing belt (first rotating member) / 328, 334... Pressure arm (displacement mechanism) / 329, 336... Cam / 330... Pressure roller (second rotating member) / 338... Cam shaft / 380... Fixing frame / 391... Pressure drive unit (switching mechanism) / 392... Worm wheel / 393... Worm / 393a... Rotating shaft / 394... Gear (second drive transmission member) / 395... Pressure drive gear (first drive transmission member) / 395a... Drive shaft / 399... Bearing / 400... Drive transmission unit / M2... Motor (drive source)

Claims (18)

a first rotating member that heats the recording material;
a second rotating member that contacts the first rotating member and nip-conveys a recording material together with the first rotating member to form a nip portion where a toner image is fixed onto the recording material;
A pair of side plates supporting the second rotary member;
a switching mechanism that changes the position of the second rotating member relative to the first rotating member to switch the pressure force at the nip portion,
The switching mechanism includes:
A motor;
a worm that is driven to rotate by the motor;
a worm wheel that meshes with the worm and to which a driving force is transmitted from the worm;
a cam that rotates when rotation of the worm wheel is transmitted to it;
a pair of bearings that rotatably support the worm;
a displacement mechanism that abuts against the cam and displaces the second rotary member relative to the first rotary member as the cam rotates,
an image heating apparatus, wherein support plates constituting the pair of bearings are fixed to one of the pair of side plates; a first drive transmission member attached to a shaft of the motor;
a second drive transmission member attached to one end of the worm in the rotational axis direction of the worm, to which driving force is transmitted from the first drive transmission member,
the first drive transmission member and the second drive transmission member are each spur gears;
2. An image heating apparatus according to claim 1, wherein the first drive transmission member meshes with the second drive transmission member. An image heating device according to claim 1 or 2, wherein when the image heating device is removed from the image forming apparatus that supports it, the motor and the worm are removed together with the image heating device. An image heating apparatus according to any one of claims 1 to 3, wherein the motor and the worm are supported by one of the pair of side plates. When the motor is a first motor, the motor has a second motor that rotates at least the first rotating member or the second rotating member,
5. An image heating apparatus according to claim 4, wherein the second motor is supported by the other side plate. a first drive transmission member attached to a shaft of the motor;
a second drive transmission member attached to one end of the worm in the rotational axis direction of the worm, to which driving force is transmitted from the first drive transmission member,
2. An image heating apparatus according to claim 1, wherein the first drive transmission member, the second drive transmission member, the worm, and the worm wheel are each made of metal. the first rotating member is a belt;
7. The image heating apparatus according to claim 1, further comprising: a steering roller that can be tilted and that stretches the belt; a pad that presses the second rotating member via the belt; and a heating roller that stretches the belt and heats the belt. the motor and the worm are supported by one of the pair of side plates;
8. An image heating apparatus according to claim 7, wherein a steering motor for tilting said steering roller is supported on the other side plate. An image heating apparatus according to any one of claims 1 to 8, wherein the motor is positioned above the worm wheel in the vertical direction. a first rotating member that heats the recording material;
a second rotating member that contacts the first rotating member and nip-conveys a recording material together with the first rotating member to form a nip portion where a toner image is fixed onto the recording material;
A pair of side plates supporting the second rotary member;
a switching mechanism that switches between applying pressure and releasing the pressure at the nip portion by changing the position of the second rotating member relative to the first rotating member,
The switching mechanism includes:
A motor;
a worm that is driven to rotate by the motor;
a worm wheel that meshes with the worm and to which a driving force is transmitted from the worm;
a cam that rotates when rotation of the worm wheel is transmitted to it;
a pair of bearings that rotatably support the worm;
a displacement mechanism that abuts against the cam and displaces the second rotary member relative to the first rotary member as the cam rotates,
an image heating apparatus, wherein support plates constituting the pair of bearings are fixed to one of the pair of side plates; a first drive transmission member attached to a shaft of the motor;
a second drive transmission member attached to one end of the worm in the rotational axis direction of the worm, to which driving force is transmitted from the first drive transmission member,
the first drive transmission member and the second drive transmission member are each spur gears;
11. An image heating apparatus according to claim 10, wherein the first drive transmission member meshes with the second drive transmission member. An image heating device according to claim 10 or 11, wherein when the image heating device is removed from the image forming apparatus that supports it, the motor and the worm are removed together with the image heating device. An image heating apparatus according to any one of claims 10 to 12, wherein the motor and the worm are supported by one of the pair of side plates. When the motor is a first motor, the motor has a second motor that rotates at least the first rotating member or the second rotating member,
14. An image heating apparatus according to claim 13, wherein the second motor is supported by the other side plate. a first drive transmission member attached to a shaft of the motor;
a second drive transmission member attached to one end of the worm in the rotational axis direction of the worm, to which driving force is transmitted from the first drive transmission member,
11. An image heating apparatus according to claim 10, wherein the first drive transmission member, the second drive transmission member, the worm, and the worm wheel are each made of metal. An image heating apparatus according to any one of claims 1 to 15, wherein the worm wheel meshes with the worm between the pair of bearings. a first drive transmission member attached to a shaft of the motor;
11. The image heating apparatus according to claim 1, further comprising: a second drive transmission member attached to one end of the worm in the direction of the rotation axis of the worm, and receiving a drive force from the first drive transmission member. a first rotating member that heats the recording material;
a second rotating member that contacts the first rotating member and nip-conveys a recording material together with the first rotating member to form a nip portion where a toner image is fixed onto the recording material;
A pair of side plates supporting the second rotary member;
a switching mechanism that changes the position of the second rotating member relative to the first rotating member to switch the pressure force at the nip portion,
The switching mechanism includes:
A motor;
a worm that is driven to rotate by the motor;
a worm wheel that meshes with the worm and to which a driving force is transmitted from the worm;
a cam that rotates when rotation of the worm wheel is transmitted to it;
a bearing that rotatably supports the worm at a position farther from the motor than an engagement position where the worm engages with the worm wheel in a rotational axis direction of the worm;
a displacement mechanism that abuts against the cam and displaces the second rotary member relative to the first rotary member as the cam rotates,
an image heating apparatus, wherein a support plate constituting the bearing is fixed to one of the pair of side plates;