JP7806002B2 - Fixing device - Google Patents

Description

The present invention relates to a fixing device that fixes an image formed with ink onto a sheet.

As a fixing device that heats a sheet and an image to fix the image to the sheet, a configuration has been proposed in which multiple heating elements of different lengths are arranged inside a fixing roller, and the heating elements are selectively heated to match the width of the recording material (Patent Document 1).

Japanese Patent Application Publication No. 57-158866

One fixing device configuration uses a belt to heat the recording material. In a configuration where a non-cylindrical belt is heated by multiple heating elements, a reflective element can be used to reflect the radiant heat from the multiple heating elements and irradiate it toward a specific area of the belt. In this case, if one of the multiple heating elements with a high resistance per unit length is positioned close to the specific area of the belt, there is a risk that the belt's lifespan will be shortened due to localized temperature increases.

The present invention aims to provide a configuration that can prevent a reduction in belt lifespan.

One aspect of the present invention is a fixing device that heats a sheet on which an image has been formed by ejecting ink, thereby fixing the image to the sheet, and includes: a rotating endless belt; a nip forming member that forms a nip between the belt and the nip forming member to sandwich and transport the sheet; a plurality of halogen heaters that are arranged non-contact with the belt and along the width direction of the belt that intersects the rotation direction of the belt, and that heat the belt by radiating heat; and a reflective member that is arranged along the width direction and reflects the radiant heat of the plurality of halogen heaters toward a predetermined area of the belt, wherein the plurality of halogen heaters are arranged inside the reflective member, and among the plurality of halogen heaters , the halogen heater with the highest resistance per unit length in the width direction is arranged at a position farthest from the predetermined area , and the halogen heater with the smallest resistance per unit length in the width direction is arranged at a position closest to the predetermined area .

This invention can prevent the belt's lifespan from being shortened.

1 is a schematic cross-sectional view showing the configuration of an image forming system according to a first embodiment. FIG. 2 is a cross-sectional view showing the schematic configuration of a fixing module according to the first embodiment. FIG. 2 is a cross-sectional view showing the schematic configuration of a fixing belt unit according to the first embodiment. FIG. 2 is a perspective view showing the configuration of a steering portion of the fixing belt unit according to the first embodiment. FIG. 2 is a plan view showing the relationship between a belt and an edge sensor according to the first embodiment. FIG. 3 is a perspective view showing a second heating unit according to the first embodiment. FIG. 4 is a perspective view showing the second heating unit according to the first embodiment with the cable cover removed to expose the cable. FIG. 3 is a schematic cross-sectional view showing the configuration of a second heating unit according to the first embodiment. FIG. 10 is a cross-sectional view showing a schematic configuration of a fixing belt unit according to a second embodiment.

First Embodiment
The first embodiment will be described with reference to Figures 1 to 8. First, the schematic configuration of an image forming system according to this embodiment will be described with reference to Figure 1.

[Image forming system]
The image forming system 1 as the image forming apparatus of this embodiment is a so-called sheet-fed inkjet recording apparatus that uses an inkjet recording method in which ink is ejected to form an image on a sheet, and forms an ink image on the sheet using two liquids: a reaction liquid and ink. The sheet may be any recording material that can accept ink, such as paper such as plain paper or cardboard, plastic film such as an overhead projector sheet, specially shaped sheets such as envelopes or index paper, or cloth.

As shown in FIG. 1, the image forming system 1 of this embodiment includes a feeding module 1000, a printing module 2000, a drying module 3000, a fixing module 4000, a cooling module 5000, an inverting module 6000, and a stacking module 7000. The sheet S supplied from the feeding module 1000 undergoes various processes as it is transported along the transport path within each module, and is ultimately ejected onto the stacking module 7000.

The feeding module 1000, printing module 2000, drying module 3000, fixing module 4000, cooling module 5000, reversing module 6000, and stacking module 7000 may each have separate housings, and these housings may be connected to form the image forming system 1. Alternatively, the feeding module 1000, printing module 2000, drying module 3000, fixing module 4000, cooling module 5000, reversing module 6000, and stacking module 7000 may be arranged in a single housing.

The feeding module 1000 has storage cabinets 1500a, 1500b, and 1500c for storing sheets S, and storage cabinets 1500a-1500c are arranged so that they can be pulled out toward the front of the device to store sheets S. Sheets S are fed one by one in each storage cabinet 1500a-1500c by a separation belt and transport rollers, and transported to the print module 2000. Note that the number of storage cabinets 1500a-1500c is not limited to three, and there may be one, two, four, or more.

The print module 2000, which serves as the image forming unit, includes a pre-imaging registration correction unit (not shown), a print belt unit 2010, and a recording unit 2020. The sheet S transported from the feed module 1000 has its tilt and position corrected by the pre-imaging registration correction unit before being transported to the print belt unit 2010. The recording unit 2020 is positioned opposite the print belt unit 2010 with respect to the transport path. The recording unit 2020 is an inkjet recording unit that forms an image by ejecting ink onto the transported sheet S from above using a recording head. Multiple recording heads that eject ink are arranged along the transport direction. In this embodiment, in addition to the four colors of Y (yellow), M (magenta), C (cyan), and Bk (black), there are a total of five line-type recording heads corresponding to the reaction liquids. The sheet S is adsorbed and transported by the print belt unit 2010, ensuring clearance between the sheet S and the recording heads.

The number of ink colors and recording heads is not limited to the five mentioned above. Inkjet systems can use heating elements, piezoelectric elements, electrostatic elements, or MEMS (Micro Electro Mechanical Systems) elements, among others. Each color of ink is supplied to the recording head from an ink tank (not shown) via an ink tube. The ink contains 0.1% to 20.0% by mass of resin components, water, water-soluble organic solvents, colorants, wax, additives, etc., based on the total mass of the ink.

As the sheet S, on which an image has been formed by the recording unit 2020, is transported by the print belt unit 2010, the misalignment and color density of the image formed on the sheet S are detected by an inline scanner (not shown) located downstream of the recording unit 2020 in the transport direction of the sheet S. Based on this image misalignment and color density, the image formed on the sheet S, its density, etc. are corrected.

The drying module 3000 has a decoupling section 3200, a drying belt unit 3300, and a warm air blowing section 3400. The drying module 3000 reduces the liquid content of the ink and reaction liquid applied to the sheet S to improve the fixation of the ink to the sheet S by the subsequent fixing module 4000. The sheet S with an image formed thereon is transported to the decoupling section 3200 located within the drying module 3000. In the decoupling section 3200, frictional force is generated between the sheet S and the belt by the wind pressure of the air blown from above, causing the sheet S to be transported by the belt. In this way, the sheet S placed on the belt is transported by frictional force, preventing the sheet S from shifting as it is transported between the print belt unit 2010 and the decoupling section 3200. The sheet S conveyed from the decoupling unit 3200 is adsorbed and conveyed by the drying belt unit 3300, and hot air is blown onto it from the hot air blowing unit 3400 located above the belt, drying the ink and reaction liquid applied to the sheet S.

In this way, the drying module 3000 heats the ink and reaction liquid applied to the sheet S, promoting the evaporation of water, thereby preventing so-called cockling, in which ink splatters onto the sheet S and leaves a border-like line around the periphery. The drying module 3000 may be any device capable of heat drying, but a hot air dryer or heater is preferred. Heating using an electric heating wire or infrared heater is preferred from the standpoint of safety and energy efficiency.

The fixing module 4000, which serves as a fixing system, has a fixing belt unit 4100, which serves as a fixing device. The fixing belt unit 4100 fixes the ink onto the sheet S by passing the sheet S, which has been conveyed from the drying module 3000, between a heated upper belt unit and a lower belt unit. The fixing belt unit 4100 will be described in detail later.

The cooling module 5000 has multiple cooling units 5001, which cool the high-temperature sheet S transported from the fixing module 4000. The cooling units 5001, for example, use a fan to draw in outside air into a cooling box to increase the pressure inside the cooling box, and then cool the sheet S by blowing the air out of the cooling box through a nozzle due to the pressure against the sheet S. The cooling units 5001 are arranged on both sides of the transport path of the sheet S, and cool both sides of the sheet S.

The cooling module 5000 is provided with a transport path switching unit 5002. The transport path switching unit 5002 switches the transport path of the sheet S depending on whether the sheet S is being transported to the reversing module 6000 or to a double-sided transport path for double-sided printing, in which images are formed on both sides of the sheet S.

The inversion module 6000 has an inversion section 6400. The inversion section 6400 inverts the sheet S being conveyed, changing the orientation of the sheet S when it is discharged to the stacking module 7000. The stacking module 7000 has a top tray 7200 and a stacking section 7500, and stacks the sheet S conveyed from the inversion module 6000.

When double-sided printing is performed, the sheet S is transported by the transport path switching unit 5002 to a transport path below the cooling module 5000. The sheet S then passes through a double-sided transport path that includes the fixing module 4000, drying module 3000, print module 2000, and feeding module 1000, before being returned to the print module 2000. The double-sided transport section of the fixing module 4000 is provided with an inverting unit 4200 that inverts the sheet S. After the sheet S is returned to the print module 2000, an image is formed on the other side with ink, and the sheet S is ejected via the drying module 3000, fixing module 4000, cooling module 5000, and inverting module 6000 to the stacking module 7000.

[Fixing module]
Next, the fixing module 4000 will be described in detail with reference to FIG. 2 . In this embodiment, the fixing module 4000 is an example of a sheet conveying device that conveys a sheet. FIG. 2 is a schematic diagram showing the fixing module 4000. A fixing belt unit 4100 is provided above the fixing module 4000. The fixing belt unit 4100 has a substantially linear sheet conveying path 401 for receiving the sheet S discharged from the drying module 3000, performing fixing, and then delivering the sheet S to the cooling module 5000. In each drawing, the front side of the inkjet recording system 100 is referred to as the front direction F, the rear side as the rear direction B, the right side as the right direction R, the left side as the left direction L, the upper side as the upward direction U, and the lower side as the downward direction D. An operating unit (not shown) operated by an operator is provided at the front side of the inkjet recording system 100.

The fixing belt unit 4100 includes an upper belt unit 410 and a lower belt unit 420. The upper belt unit 410 is disposed vertically above the lower belt unit 420. The upper belt unit 410 includes an upper belt 411, which is an example of a fixing belt and a conveyor belt (first conveyor belt), and a tension roller 4011a that applies tension to the upper belt 411. In other words, the upper belt unit 410 is an example of a belt unit (first belt unit) and includes a detachable upper belt 411 that conveys the sheet S. The lower belt unit 420 is an example of a second belt unit and includes a lower belt 421, a tension roller 422 that applies tension to the lower belt 421, and a pad 423 with an arc-shaped curved surface. The pad 423 is disposed so as to form a nip with the upper belt 411 via the lower belt 421.

The sheet S is conveyed while being sandwiched in the nip between the upper belt unit 410 and the lower belt unit 420. That is, the lower belt 421 is an example of a rotating body and a second conveyor belt, and is positioned opposite the upper belt unit 410 when the upper door unit 43 is in the closed position and the upper belt unit 410 is in the upper storage position. At this time, the lower belt 421, together with the upper belt 411, sandwiches and conveys the sheet S. The nip pressure is determined by the tension and thickness of the upper belt 411 and the curvature of the pad 423. If the nip pressure is too high, ink on the sheet S may adhere to the upper belt unit 410, causing the ink to peel off from the sheet S. Therefore, the pressure is preferably 1 Pa to 2000 Pa, and more preferably 1 Pa to 200 Pa.

If the curvature of the pad 423 becomes larger, the difference in the transport path between the front and back of the sheet S becomes larger, which may result in friction between the sheet S and the belt. If the curvature of the pad 423 becomes larger, there is a risk that the sheet S itself may memorize the curved shape and curl, so it is desirable that the radius of curvature of the pad 423 be 50 mm or more. Furthermore, from the perspective of manufacturing precision, it is desirable that the curvature of the pad 423 be 100,000 mm or less. Due to these constraints, in this embodiment, the tension of the upper belt 411 is set to 200 N, the thickness is set to 0.3 mm, the curvature of the pad 423 is set to 30,000 mm, and the nip pressure is set to approximately 16 Pa.

By adopting this configuration, uniform pressure can be applied even in a wide nip. This allows sufficient heat transfer to the sheet S by increasing the contact time between the sheet S and the upper belt unit 410, even when the temperature of the upper belt unit 410 is set to the melting point of wax or the boiling point of water. However, if the nip continues to form after sufficient heat transfer, ink may adhere to the upper belt 411 and peel off from the sheet S, or the upper belt 411 may rub against the sheet S, causing image distortion. Therefore, a long contact time is not desirable. Therefore, the time required for the leading edge of the sheet S to enter the nip entrance and exit the nip exit is preferably 0.5 to 4 seconds. In this embodiment, a pad 423 with a length of 900 mm in the sheet transport direction is used, the sheet S is transported at 700 mm/s, and the time required for the leading edge of the sheet S to completely exit the nip entrance is approximately 1.3 seconds. Furthermore, moisture is necessary for ink to penetrate into the sheet S, so when the sheet becomes hot, the upper belt 411 and the lower belt 421 should preferably be impermeable to moisture so that the moisture evaporated from the surface of the sheet S does not escape through the upper belt 411 or the lower belt 421 that they come into contact with.

[Fusing belt unit]
Next, the fixing belt unit 4100 of this embodiment will be described with reference to FIG. 3. As shown in FIG. 3, the fixing belt unit 4100 as a fixing device includes an upper belt unit 410 and a lower belt unit 420. A nip N is formed by pressing an upper belt 411 of the upper belt unit 410 and a lower belt 421 of the lower belt unit 420 together. A sheet S1 is sandwiched and conveyed through the nip N, and pressure and heat are applied thereto, thereby fixing an image formed with ink to the sheet S1. Note that, since the nip N is formed by the upper belt 411 and the lower belt 421, the lower belt 421 corresponds to a nip-forming member with respect to the upper belt 411, and the upper belt 411 corresponds to a nip-forming member with respect to the lower belt 421.

The upper belt unit 410 includes an endless upper belt 411 serving as a belt and a first belt, multiple tension rollers that tension the upper belt 411, and a first heating unit 4060a serving as a heating device. The multiple tension rollers are an entrance roller 4110, an exit roller 4120, a drive roller 4031a, a tension roller 4011a, a guide roller 4051a, and a steering roller 4021a. These rollers are arranged in order from upstream of the nip N in the direction of rotation of the upper belt 411, thereby forming a rotational trajectory for the upper belt 411. The nip N is located between the entrance roller 4110 and the exit roller 4120. Each roller is supported by an upper frame 414, which serves as the housing of the upper belt unit 410.

The first heating unit 4060a is disposed inside the upper belt 411 and includes a first heater 4061a, a reflective member, and a reflective plate 4052a serving as the first reflective member. The first heating unit 4060a is detachable from the first belt unit main body 410a, which includes the upper belt 411. The first belt unit main body 410a includes the upper belt 411, multiple rollers that tension the upper belt 411, and an upper frame 414.

The first heater section 4061a has multiple heaters 4071a, 4072a, 4073a as multiple heating elements and multiple first heating elements (see Figure 8). The heaters 4071a, 4072a, 4073a are arranged in a non-contact manner with the upper belt 411 and along the width direction of the upper belt 411, which intersects with the direction of rotation of the upper belt 411, and heat the upper belt 411 by radiating heat. The reflector 4052a is arranged along the width direction and reflects the radiant heat from the multiple heaters 4071a, 4072a, 4073a toward specified areas of the upper belt 411.

In this embodiment, the first heating unit 4060a of the upper belt unit 410 is disposed inside the upper belt 411 and above the nip portion N, and heats the upper belt 411 from the inside. The first heating unit 4060a has multiple first heater portions 4061a. In this embodiment, three first heater portions 4061a are arranged side by side in the rotation direction of the upper belt 411. Furthermore, as shown in FIG. 8 described below, each first heater portion 4061a has heaters 4071a, 4072a, and 4073a, and a reflector 4052a is disposed to cover the periphery of the heaters 4071a, 4072a, and 4073a except for the side facing the upper belt 411.

The reflectors 4052a are arranged in the same number as the first heater units 4061a, corresponding to the first heater units 4061a. The reflectors 4052a are formed so that the nip N side of the first heater units 4061a is open, and so that they cover both widthwise ends of the heaters 4071a, 4072a, and 4073a of the first heater units 4061a. This allows the reflectors 4052a to efficiently irradiate the radiant heat from the heaters 4071a, 4072a, and 4073a toward the nip N.

That is, in the upper belt unit 410, the predetermined area is the area (first area) within the range of the nip portion N on the inner surface of the upper belt 411, and the nip portion N is directly heated by multiple first heater portions 4061a and multiple reflectors 4052a. This allows heat to be efficiently transferred to the sheet S passing through the nip portion N. In this embodiment, the area within the range of the nip portion N heated by the multiple first heater portions 4061a is the inner surface (lower surface portion) of the upper belt 411, and is the lower surface portion 411a located upstream of the center position of the nip portion N in the conveyance direction of the sheet S passing through the nip portion N. That is, in this embodiment, the predetermined area in the upper belt unit 410 is the lower surface portion 411a.

The lower surface portion 411a is positioned opposite the lower belt 421, which is stretched between the nip upstream roller 426 and the nip downstream roller 427, two of the tension rollers for the lower belt 421 described below, and is also positioned opposite the area where the lower belt 421 is supported by the pad 423 disposed between these rollers. This ensures that the distance between the lower surface portion 411a of the upper belt 411 and the first heating unit 4060a remains roughly constant regardless of the rotation of the upper belt 411.

The lower belt unit 420 includes an endless lower belt 421 serving as a belt and a second belt, multiple tension rollers that tension the lower belt 421, and a second heating unit 4060b serving as a heating device. The multiple tension rollers are a nip upstream guide roller 425, a nip upstream roller 426, a nip downstream roller 427, a drive roller 4031b, a tension roller 4011b, a guide roller 4051b, a guide roller 428, and a steering roller 4021b. These rollers are arranged in order from upstream of the nip portion N in the direction of rotation of the lower belt 421.

A nip portion N exists between the nip upstream roller 426 and the nip downstream roller 427, and a pad 423 is disposed therein. That is, the nip upstream roller 426 as the first roller and the nip downstream roller 427 as the second roller are disposed so as to sandwich the nip portion N in the direction of rotation of the lower belt 421. The pad 423 as a support member abuts against the inner circumferential surface of the lower belt 421 in the area of the nip portion N, thereby supporting the lower belt 421. A rotational trajectory of the lower belt 421 is formed by these rollers and pad 423. The rollers and pad 423 are supported by the lower frame 424, which is the housing of the lower belt unit 420.

The second heating unit 4060b is disposed inside the lower belt 421 and includes a second heater 4061b, a reflecting member, and a reflector 4052b serving as the second reflecting member. The second heating unit 4060b is detachable from the second belt unit main body 420a which includes the lower belt 421. The second belt unit main body 420a includes the lower belt 421, multiple rollers that tension the lower belt 421, a pad 423, and a lower frame 424.

Like the first heating unit 4060a, the second heater section 4061b has multiple heating elements and multiple heaters 4071b, 4072b, and 4073b as multiple second heating elements (see Figure 8). The heaters 4071b, 4072b, and 4073b are arranged in a non-contact manner with the lower belt 421 and along the width direction of the lower belt 421, which intersects with the direction of rotation of the lower belt 421, and heat the lower belt 421 by radiating heat. The reflector 4052b is arranged along the width direction and reflects the radiant heat of the multiple heaters 4071b, 4072b, and 4073b3 toward specified areas of the lower belt 421.

In this embodiment, the second heating unit 4060b of the lower belt unit 420 is disposed inside the lower belt 421 and below the nip portion N, and heats the lower belt 421 from the inside. The second heating unit 4060b has multiple second heater portions 4061b. In this embodiment, two second heater portions 4061b are disposed side by side in the rotation direction of the lower belt 421. Furthermore, as shown in FIG. 8 described below, each second heater portion 4061b has heaters 4071b, 4072b, and 4073b, and a reflector 4052b is disposed to cover the periphery of the heaters 4071b, 4072b, and 4073b except for the side facing the lower belt 421.

Reflectors 4052b are arranged in the same number as the second heater units 4061b, corresponding to the second heater units 4061b. Furthermore, the reflectors 4052b are formed so that the bottom of the second heater units 4061b is open, and so that they cover both widthwise ends of the heaters 4071b, 4072b, and 4073b of the second heater units 4061b. This allows the reflectors 4052b to efficiently irradiate the radiant heat from the heaters 4071b, 4072b, and 4073b toward the lower portion of the lower belt 421.

That is, in the lower belt unit 420, the predetermined region is a region (second region) of the inner circumferential surface of the lower belt 421 that is outside the nip portion N, and in this embodiment, this is the lower portion of the lower belt 421. Specifically, the region outside the nip portion N that is heated by the multiple second heaters 4061b is the inner circumferential surface (lower surface portion) of the lower belt 421 between the guide roller 4051b and the guide roller 428 in the direction of rotation of the lower belt 421. That is, the predetermined region in the lower belt unit 420 is the lower surface portion 421a of the lower belt 421, which is the surface on which the lower belt 421 is stretched in a substantially horizontal direction between the guide roller 4051b and the guide roller 428. As described above, the lower belt unit 420 has a pad 423 provided at a position corresponding to the nip portion N, and therefore cannot directly heat the nip portion N as in the upper belt unit 410. For this reason, by arranging multiple second heater units 4061b and multiple reflectors 4052b facing the lower surface 421a of the lower belt 421, the lower belt 421 is efficiently heated directly.

The lower surface portion 421a, which is the region of the lower belt 421 heated by the multiple second heaters 4061b and multiple reflectors 4052b, is located upstream of the nip upstream guide roller 425 at the entrance to the nip portion N and the steering roller 4021b in the direction of rotation of the lower belt 421. The lower surface portion 421a is also located downstream of the center position between the guide roller 428 and tension roller 4011b, which tension the lower portion of the lower belt 421, in the direction of rotation of the lower belt 421. Therefore, the multiple second heaters 4061b and multiple reflectors 4052b can heat the lower belt 421 at a position relatively close to the nip portion N, allowing heat to be efficiently transferred to the sheet S passing through the nip portion N. A detailed description of the first heating unit 4060a and second heating unit 4060b will be provided later.

In the upper belt unit 410, as described above, the pad 423 keeps the distance between the upper belt 411 and the first heating unit 4060a roughly constant regardless of the rotation of the upper belt 411. This stabilizes the thermal effect from the first heater unit 4061a on the upper belt 411. In the lower belt unit 420, the tension roller 4011b and guide roller 428 tension the lower belt 421 upstream and downstream of the second heating unit 4060b, so that the distance between the lower belt 421 and the second heating unit 4060b is kept roughly constant regardless of the rotation of the lower belt 421. This stabilizes the thermal effect from the second heater unit 4061b on the lower belt 421.

Furthermore, the heaters 4071a, 4072a, and 4073a of the first heater section 4061a and the heaters 4071b, 4072b, and 4073b of the second heater section 4061b may be heaters that heat the belt by radiating heat, such as halogen heaters. In this embodiment, these heaters are halogen heaters.

As mentioned above, reflectors 4052a and 4052b are arranged around the first heater section 4061a and the second heater section 4061b to efficiently focus light onto the upper belt 411 and the lower belt 421, respectively. The reflectors 4052a and 4052b are made of, for example, mirror-finished aluminum members to efficiently reflect light. The heater output of the multiple first heater sections 4061a and multiple second heater sections 4061b is controlled based on the temperature detected by a temperature detection section (not shown). This maintains the temperature of the upper belt 411 and the lower belt 421 at an appropriate level.

[About the tension rollers of each belt unit]
A description will be given of the tension rollers 4011a and 4011b, steering rollers 4021a and 4021b, and drive rollers 4031a and 4031b of the upper belt unit 410 and the lower belt unit 420. Note that the functions of these rollers are the same for the upper belt unit 410 and the lower belt unit 420, so the following description will be given taking the rollers of the lower belt unit 420 as an example.

[Tension roller]
First, the tension roller 4011b will be described with reference to FIG. 3. Of the multiple tension rollers provided in the lower belt unit 420, one roller is the tension roller 4011b, which applies tension to the lower belt 421. The tension roller 4011b is disposed on the surface (downward direction D) opposite to the surface (upward direction U) that forms the nip portion N, and tensions the lower belt 421. In this embodiment, of the nip upstream roller 426 and nip downstream roller 427 that form the nip portion N, the tension roller 4011b is disposed downstream of the nip downstream roller 427 in the rotation direction of the lower belt 421. Specifically, the tension roller 4011b is disposed further downstream of the drive roller 4031b, which is downstream of the nip downstream roller 427, in the rotation direction of the lower belt 421.

The tension roller 4011b is supported so that it can move in a predetermined direction (in this embodiment, the direction of the arrow shown in Figure 3) and is pressurized by a pressure member (e.g., a spring) not shown. For example, if the circumferential length of the lower belt 421 varies from the target length due to manufacturing variations or changes caused by usage conditions, the tension roller 4011b can be pressed by the pressure member to stabilize the tension state of the lower belt 421.

[Steering roller]
Next, the steering roller 4021b will be described with reference to Figs. 3 to 5. Fig. 4 is a schematic perspective view showing the vicinity of the steering roller of the fixing belt unit 4100. Fig. 5 is a plan view showing the relationship between the upper belt 411 (lower belt 421) and the edge sensor 4025a (4025b). Of the multiple tension rollers provided in the lower belt unit 420, one roller is the steering roller 4021b for controlling the position of the lower belt 421 in the front-to-rear direction (forward direction F and rear direction B, width direction of the lower belt 421).

The steering roller 4021b is a roller made of metal, such as aluminum or iron. One front-to-rear end of the steering roller 4021b is rotatably supported by a fixed plate 4026b. The fixed plate 4026b is fastened to the lower frame 424 with screws 4027b or the like. The other front-to-rear end of the steering roller 4021b is rotatably supported by a steering arm 4023b. The steering arm 4023b is supported on the lower frame 424 so that it can rotate around a rotation center 4024b. A steering cam 4022b with an eccentric radius abuts a portion of the steering arm 4023b, and the alignment of the steering roller 4021b can be changed by rotating the steering cam 4022b with a steering motor (not shown).

Furthermore, the fixed plate 4026b is configured so that the rotation center position of the steering roller 4021b can be moved by loosening the screws 4027b on the lower frame 424, and the alignment can be adjusted by refastening them. For example, this makes it possible to fine-tune the optimal alignment position of the steering roller 4021b to accommodate variations in the installation environment.

In addition, a nip upstream guide roller 425 is arranged downstream of the steering roller 4021b provided on the lower belt unit 420 in the direction of rotation of the lower belt 421. This is to stabilize the trajectory of the lower belt 421 immediately before the nip portion N, regardless of the position of the steering roller 4021b. When the conveyed sheet S enters the nip portion N, the sheet S is conveyed so that its position is aligned with the lower belt 421, thereby stabilizing its entry.

Next, the control of the front-to-rear position of the lower belt 421 by the steering roller 4021b will be described using Figures 4 and 5. Since the upper belt unit 410 and the lower belt unit 420 have slightly different configurations, each will be described separately.

First, at one end of the lower belt 421 in the front-to-rear direction (the end on the forward direction F side in this embodiment), on the downward direction D side of the lower belt 421, an edge sensor 4025b is provided in contact with the end face of the lower belt 421 to detect the position of the lower belt 421 in the forward direction F. In the lower belt unit 420, the guide roller 428 is positioned so that the surface of the lower belt 421, stretched between the tension roller 4011b and the guide roller 428, is approximately parallel to the direction of movement of the tension roller 4011b (horizontal direction). By providing the edge sensor 4025b between the tension roller 4011b and the guide roller 428, the effect on the edge sensor 4025b of the belt trajectory due to variations in the circumferential length of the lower belt 421 is reduced.

The rotation amount of the steering cam 4022b is controlled based on the detection value of the edge sensor 4025b. The center of rotation 4028b of the edge sensor 4025b is set so that when the lower belt 421 rotates, the edge sensor 4025b receives a force in a direction that moves it away from the lower belt 421 due to friction. As a result, the load acting between the edge sensor 4025b and the end face of the lower belt 421 can be reduced.

Meanwhile, at the other end of the upper belt 411 in the front-to-rear direction (the end on the rearward B side in this embodiment), on the upper U side of the upper belt 411, an edge sensor 4025a is provided that contacts the end surface of the upper belt 411 and detects the position of the upper belt 411 in the rearward B direction. In the upper belt unit 410, the guide roller 4051a is positioned so that the surface of the upper belt 411, stretched between the tension roller 4011a and the guide roller 4051a, is approximately parallel to the movement direction (horizontal direction) of the tension roller 4011a. By providing the edge sensor 4025a between the tension roller 4011a and the guide roller 4051a, the effect on the edge sensor 4025a of the belt trajectory due to variations in the circumferential length of the upper belt 411 is reduced.

The rotation amount of the steering cam 4022a is controlled based on the detection value of the edge sensor 4025a. The center of rotation 4028a of the edge sensor 4025a is set so that when the upper belt 411 rotates, the edge sensor 4025a receives a force in a direction that moves it away from the upper belt 411 due to friction. As a result, the load acting between the edge sensor 4025a and the end face of the upper belt 411 can be reduced.

As shown in Figure 5, by arranging edge sensor 4025b at the end of the lower belt 421 on the forward F side and the portion on the downward D side, and edge sensor 4025a at the end of the upper belt 411 on the rear B side and the portion on the upward U side, it is possible to use edge sensors of the same shape for the upper belt 411 and the lower belt 421.

In addition, while the steering roller in this embodiment is a metal roller, a roller with a heat-resistant rubber layer on the surface may also be used to increase friction and thereby improve steering performance. Also, while one end of the steering roller is fixed and the alignment is changed by moving the other end, both ends may be supported movably to allow the alignment to be changed.

[Drive roller]
Next, the drive roller 4031b will be described with reference to Fig. 3. Of the plurality of tension rollers provided in the lower belt unit 420, one roller is the drive roller 4031b for applying a driving force to the lower belt 421.

The drive roller 4031b is a roller made of metal, such as aluminum or iron. Both front and rear ends of the drive roller 4031b are rotatably supported relative to the lower frame 424, and rotates when drive is input using a drive transmission mechanism (not shown), such as a gear or timing belt, causing frictional force to rotate the lower belt 421 in a predetermined direction.

In this embodiment, the lower belt 421 and the upper belt 411 are rotated independently by the driving force applied by the drive rollers 4031a and 4031b. Note that while the drive rollers in this embodiment are made of metal, rollers with a rubber layer such as heat-resistant rubber on their surface may also be used to increase the driving force by increasing the frictional force.

[Heating unit]
Next, the first heating unit 4060a and the second heating unit 4060b will be described in detail using FIGS. 6 to 8 while also referring to FIG. 3. FIG. 6 is a schematic perspective view of the second heating unit 4060b. FIG. 7 is a schematic perspective view showing a state in which the cable cover 4069 of the second heating unit 4060 has been removed to expose the cable 4070. FIG. 8 is a schematic cross-sectional view of the second heating unit 4060b. The first heating unit 4060a and the second heating unit 4060b have the same basic configuration, except for the number of heater units. Therefore, only the second heating unit 4060b will be described below.

As shown in Figures 6 and 7, the second heating unit 4060b has a case 4062 formed into a box shape by a heating section front side plate 4063, a heating section rear side plate 4064, a heating section right side plate 4065, a heating section left side plate 4066, and a heating section upper side plate 4067. Cables 4070 are arranged on the top surface of the case 4062, which serves as a storage section, as shown in Figure 7, and the cables 4070 are covered by a cable cover 4069, as shown in Figure 6. As shown in Figure 8, a reflector 4052b and second heater sections 4061b are arranged inside the case 4062. Each of the multiple second heater sections 4061b is supported on both sides in the longitudinal direction (width direction) by the case 4062 via heater holders 4068.

As shown in FIG. 8, each of the multiple second heater sections 4061b has multiple heaters 4071b, 4072b, and 4073b. A pair of heater holding sections 4068 serving as holding members are arranged on both widthwise sides of each second heater section 4061b. The pair of heater holding sections 4068 respectively hold both widthwise ends of the multiple heaters 4071b, 4072b, and 4073b so as to regulate the relative positions of the multiple heaters 4071b, 4072b, and 4073b. By holding both ends in this way by the pair of heater holding sections 4068, the multiple heaters 4071b, 4072b, and 4073b are integrated. The pair of heater holders 4068 are supported by the heating unit front plate 4063 and the heating unit rear plate 4064, respectively, so that multiple heaters 4071b, 4072b, and 4073b are housed inside the case 4062.

The integrated heaters 4071b, 4072b, and 4073b and heater holder 4068 can be inserted and removed from the heating unit rear side plate 4064 side of the case 4062. This makes it easy to replace the heaters 4071b, 4072b, and 4073b.

As shown in FIG. 7 , the cable 4070 connected to the heaters 4071b, 4072b, and 4073b is arranged along the outer surface of the case 4062. Specifically, the cable 4070 of the heaters 4071b, 4072b, and 4073b is routed along the upper surface of the heating section upper plate 4067 of the case 4062. The cable 4070 of each heater 4071b, 4072b, and 4073b is arranged from the rear to the front of the second heating unit 4060b, with the connectors 4071 of each cable 4070 concentrated at the front. As described above, the second heating unit 4060b, which includes the second heater section 4061b, reflector 4052b, case 4062, and cable 4070, is detachable from the second belt unit main body 420a.

The second heating unit 4060b is inserted and removed from, for example, the front side of the second belt unit main body 420a. Therefore, by arranging the cable 4070 inside the second heating unit 4060, the second heating unit 4060b can be inserted and removed without having to worry about the wiring of the cable 4070, and by consolidating the connectors 4071 of the cable 4070 at the front side, the connectors 4071 can be easily connected to the connectors on the second belt unit main body 420a side. This improves the ease of assembling the second heating unit 4060b to the second belt unit main body 420a.

In this embodiment, at least one of the multiple heaters 4071b, 4072b, and 4073b has a higher resistance value per unit length in the width direction (longitudinal direction) than the other heaters. As described above, heat radiated from the multiple heaters 4071b, 4072b, and 4073b is reflected by the reflector 4052b and irradiated onto a predetermined area of the lower belt 421. In this case, if one of the multiple heaters 4071b, 4072b, and 4073b with a higher resistance value per unit length is positioned close to a predetermined area of the lower belt 421, there is a risk that the life of the lower belt 421 will be shortened due to localized temperature increases.

In this embodiment, the heater with the highest resistance per unit length in the width direction among the multiple heaters 4071b, 4072b, and 4073b is positioned farther from a predetermined region of the lower belt 421 than the heater with the lowest resistance per unit length in the width direction. In this embodiment, the heater with the highest resistance per unit length among the multiple heaters 4071b, 4072b, and 4073b is heater 4071b. Heater 4071b has a power of 2000 W and a heating element length of 400 mm. The heater with the next highest resistance per unit length is heater 4072b. Heater 4072b has a power of 1500 W and a heating element length of 360 mm. The heater with the lowest resistance per unit length is heater 4073b. Heater 4073b has a power of 1000 W and a heating element length of 260 mm. Note that the multiple heaters 4071b, 4072b, and 4073b mentioned here are arranged inside the reflector 4052b.

For this reason, in this embodiment, the heater 4071b, which has the highest resistance per unit length, is arranged in a predetermined region of the lower belt 421, i.e., at a position farther from the lower surface 421a of the lower belt 421 than the heater 4073b, which has the lowest resistance per unit length . In particular , the heater 4071a is arranged at a position farther from the lower surface 421a than the other heaters 4072b and 4073b.

Furthermore, each heater 4071b, 4072b, and 4073b is arranged inside the reflector 4052b. Specifically, in FIG. 8, heater 4071b is located at the top, and heaters 4072b and 4072c are arranged below heater 4071b (toward the lower surface 421a) in a direction parallel to the lower surface 421a. The reflector 4052b is formed so that the width at a position where two heaters 4072b and 4073b are arranged is wider in a direction parallel to the lower surface 421a than the width at a position where one heater 4071b is arranged. In other words, the reflector 4052b is formed so that the greater the number of heaters in a position from the lower surface 421a, the wider its width in a direction parallel to the lower surface 421a.

Even if the heaters have the same power, there may be areas where the resistance per unit length is high due to factors such as the distribution of heating elements within the heater. In this case, if a heater with an area where the resistance per unit length is high is positioned closest to a predetermined area on the belt, there is a risk of the belt heating up locally. For this reason, in this embodiment, the heater with the highest resistance per unit length is positioned furthest from the predetermined area. Furthermore, if the resistance per unit length and power are different, the heater with the highest resistance per unit length and the highest power is positioned furthest from the predetermined area compared to the other heaters.

In this embodiment, the distance d1 between heater 4071b, which has the highest power consumption, and the underside 421a of the lower belt 421 is approximately 60 mm, and the distance d2 between the other two heaters 4072b and 4073b and the underside 421a of the lower belt 421 is approximately 40 mm. Heater 4071b, which has the highest power consumption, is positioned furthest from the underside 421a. If heaters 4071b and 4073b were positioned the same distance from the underside 421a of the lower belt 421, the thermal effect of heater 4071b on the lower belt 421 would be approximately twice that of heater 4073b. For this reason, heater 4071b is positioned farther from the underside 421a of the lower belt 421 than heater 4073b.

In this embodiment, heater 4071b, which has the highest resistance per unit length, is positioned farther from a predetermined region of lower belt 421, i.e., the lower surface portion (second region) 421a of lower belt 421, than the other heaters 4072b and 4073b. This prevents localized temperature increases in lower belt 421 and reduces the lifespan of lower belt 421. Note that the relationship between the multiple heaters 4071a, 4072a, and 4073a of first heating unit 4060a is the same as described above, except for the suffixes "a" and "b." In other words, heater 4071a, which has the highest resistance per unit length, is positioned farther from a predetermined region of upper belt 411, i.e., the lower surface portion (first region) 411a, which is the region of the inner circumferential surface of upper belt 411 within the range of nip portion N, than the other heaters 4072a and 4073a. This prevents localized temperature increases in the upper belt 411 and reduces the shortening of the upper belt 411's lifespan.

In this embodiment, for example, in the lower belt unit 420, the lower surface 421a of the lower belt 421, which is located below the second heating unit serving as a heating device, is heated, but the positional relationship between the heating device and the belt is not limited to this. For example, as long as the belt is located on the opposite side of the heating device (on the light-collecting side of the reflectors 4052a and 4052b), the same effect can be achieved by configuring the heating device in the same way as described above, regardless of the orientation of the heating device relative to the belt. Also, in the above embodiment, a halogen heater was used as the heating element to directly heat the belt from the inside, but the heating element may also be configured using a planar heating element, for example.

Second Embodiment
The second embodiment will be described with reference to FIG. 9 . In the first embodiment described above, the first heating unit 4060a and the second heating unit 4060b are respectively disposed inside the upper belt 411 and the lower belt 421. In contrast, in the fixing belt unit 4100A of this embodiment, the first heating unit 4060a and the second heating unit 4060b are respectively disposed outside the upper belt 411 and the lower belt 421. The other configurations and functions are the same as those of the first embodiment described above. For this reason, the same components as those of the first embodiment are denoted by the same reference numerals, and their description and illustration will be omitted or simplified. The following description will focus on the differences from the first embodiment.

In the upper belt unit 410B, the first heating unit 4060a is disposed outside the upper belt 411. Therefore, the predetermined area irradiated with heat from the heaters 4071a, 4072a, and 4073a of the first heating unit 4060a is the outer peripheral surface portion (third region) 411b of the outer peripheral surface of the upper belt 411, which is outside the nip portion N. The outer peripheral surface portion 411b is the area of the outer peripheral surface of the upper belt 411 that is located on the opposite side of the nip portion N in the vertical direction, and is the outer peripheral surface of a portion of the upper belt 411 that is stretched between the tension roller 4011a and the guide roller 4051a.

In the lower belt unit 420B, the second heating unit 4060b is disposed outside the lower belt 421. Therefore, the predetermined area irradiated with heat from the heaters 4071b, 4072b, and 4073b of the second heating unit 4060b is the outer peripheral surface portion (fourth region) 421b of the outer peripheral surface of the lower belt 421, which is outside the nip portion N. The outer peripheral surface portion 421b is the area of the outer peripheral surface of the lower belt 421 that is on the opposite side of the nip portion N in the vertical direction, and is the outer peripheral surface of the portion where the lower belt 421 is stretched approximately horizontally between the guide roller 4051b and the guide roller 428.

In this embodiment, too, for the upper belt unit 410B, heater 4071a, which has the highest resistance per unit length, is positioned farther from the outer peripheral surface 411b than the other heaters 4072a and 4073a in a predetermined region of the upper belt 411. Also, for the lower belt unit 420B, heater 4071b, which has the highest resistance per unit length, is positioned farther from the outer peripheral surface 421b than the other heaters 4072b and 4073b in a predetermined region of the lower belt 421. Therefore, in this embodiment as well, local temperature increases in the upper belt 411 and the lower belt 421 can be suppressed, and a reduction in the lifespan of the upper belt 411 and the lower belt 421 can be suppressed.

<Other Embodiments>
In the first embodiment described above, the first heating unit 4060a and the second heating unit 4060b are disposed inside the upper belt 411 and the lower belt 421, respectively. In the second embodiment, the first heating unit 4060a and the second heating unit 4060b are disposed outside the upper belt 411 and the lower belt 421, respectively. However, the present invention is not limited to these. For example, the first heating unit 4060a may be disposed inside the upper belt 411 and the second heating unit 4060b may be disposed outside the lower belt 421. Alternatively, the first heating unit 4060a may be disposed outside the upper belt 411 and the second heating unit 4060b may be disposed inside the lower belt 421. Furthermore, when the heating units are disposed inside the belts, they may heat the area within the nip portion or an area outside the nip portion.

1...Image forming system (image forming apparatus)
410a...first belt unit main body (belt unit main body)
411: Upper belt (belt, first belt, nip portion forming member)
411a...lower surface part (predetermined area, first area)
420a: Second belt unit main body (belt unit main body)
421: Lower belt (belt, second belt, nip portion forming member)
421a...lower surface part (predetermined area, second area)
423...Pad (support member)
426: Nip upstream roller (first roller)
427...nip downstream roller (second roller)
4052a...Reflector (reflector member, first reflector member)
4052b...Reflector (reflector member, second reflector member)
4062...Case (storage section)
4068...Heater holding part (holding member)
4060a...First heating unit (heating device)
4060b...Second heating unit (heating device)
4070... Wire bundle 4071a, 4072a, 4073a... Heater (heating element, first heating element)
4071b, 4072b, 4073b...Heaters (heating members, second heating members)
4100, 4100A... fixing belt unit (fixing device)
N: Nip section

Claims (13)

A fixing device that heats a sheet on which an image is formed by ejecting ink, thereby fixing the image to the sheet,
A rotating endless belt,
a nip portion forming member that forms a nip portion between the belt and the nip portion to nip and convey a sheet;
a plurality of halogen heaters arranged in a non-contact manner with the belt and along a width direction of the belt that intersects with a rotation direction of the belt, the halogen heaters radiating heat to heat the belt;
a reflecting member disposed along the width direction and reflecting radiant heat from the plurality of halogen heaters toward a predetermined area of the belt,
the plurality of halogen heaters are disposed inside the reflecting member,
a halogen heater having the largest resistance value per unit length in the width direction among the plurality of halogen heaters is arranged at a position farthest from the predetermined area , and a halogen heater having the smallest resistance value per unit length in the width direction is arranged at a position closest to the predetermined area . 2. The fixing device according to claim 1, wherein, among the plurality of halogen heaters , the halogen heater with the highest power is arranged at a position farthest from the predetermined area, and the halogen heater with the lowest power in the width direction is arranged at a position closest to the predetermined area . The fixing device described in claim 1, characterized in that the multiple halogen heaters are located at positions farther from the predetermined area of the belt than the portion of the reflective member closest to the predetermined area. the plurality of halogen heaters and the reflecting member are disposed inside the belt,
2. The fixing device according to claim 1, wherein the predetermined area is an area of the inner circumferential surface of the belt that is within the range of the nip portion. the belt is a first belt;
5. The fixing device according to claim 4, wherein the nip portion forming member is a rotating endless second belt. The fixing device described in claim 5, further comprising a first roller and a second roller that are arranged to sandwich the nip portion in the rotational direction of the second belt and tension the second belt. The fixing device described in claim 5, further comprising a support member that supports the second belt by contacting the inner circumferential surface of the second belt in the nip region. the plurality of halogen heaters and the reflecting member are disposed inside the belt,
2. The fixing device according to claim 1, wherein the predetermined area is an area of the inner circumferential surface of the belt that is outside the nip portion. the plurality of halogen heaters and the reflecting member are disposed outside the belt,
2. The fixing device according to claim 1, wherein the predetermined area is an area of the outer circumferential surface of the belt that is outside the nip portion. The fixing device of claim 1, further comprising a pair of holding members that hold both ends of the plurality of halogen heaters in the width direction, respectively, so as to regulate the relative positions of the plurality of halogen heaters. a belt unit main body having the belt;
2. The fixing device according to claim 1, further comprising a heating device detachable from the belt unit body, the heating device having a storage section that stores the plurality of halogen heaters and the reflective member, and a bundle of wires arranged along the outer surface of the storage section and connected to the plurality of halogen heaters. the belt is a first belt;
the nip portion forming member is a rotating endless second belt,
the plurality of halogen heaters are a plurality of first halogen heaters,
the reflecting member is a first reflecting member,
the plurality of first halogen heaters and the first reflecting member are disposed inside the first belt,
the predetermined region is a first region of the inner circumferential surface of the first belt that is within the range of the nip portion,
a plurality of second halogen heaters disposed inside the second belt in a non-contact manner with the second belt and along a width direction of the second belt that intersects with a rotation direction of the second belt, the second halogen heaters radiating heat to heat the second belt;
a second reflecting member that is disposed inside the second belt along the width direction and that reflects radiant heat from the plurality of second halogen heaters toward a second region of an inner circumferential surface of the second belt that is outside the nip portion,
the second halogen heater is disposed inside the second reflecting member,
2. The fixing device according to claim 1, wherein, among the plurality of second halogen heaters, the halogen heater having the highest resistance value per unit length in the width direction is arranged at a position farthest from the second region, and the halogen heater having the smallest resistance value per unit length in the width direction is arranged at a position closest to the second region . the belt is a first belt;
the nip portion forming member is a rotating endless second belt,
the plurality of halogen heaters are a plurality of first halogen heaters,
the reflecting member is a first reflecting member,
the plurality of first halogen heaters and the first reflecting member are disposed outside the first belt,
the predetermined region is a third region of the outer peripheral surface of the first belt that is outside the nip portion,
a plurality of second halogen heaters arranged outside the second belt in a non-contact manner with the second belt and along a width direction of the second belt that intersects with a rotation direction of the second belt, the second halogen heaters radiating heat to heat the second belt;
a second reflecting member that is disposed on the outer side of the second belt along the width direction and that reflects radiant heat from the plurality of second halogen heaters toward a fourth region of the outer circumferential surface of the second belt that is out of the nip portion,
the second halogen heater is disposed inside the second reflecting member,
2. The fixing device according to claim 1, wherein, among the plurality of second halogen heaters, the halogen heater having the highest resistance value per unit length in the width direction is arranged at a position farthest from the fourth region, and the halogen heater having the smallest resistance value per unit length in the width direction is arranged at a position closest to the fourth region .