JP2008083466A - Fixing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To allow low temperature and high speed and to satisfactorily transmit driving force to a pressure roller without causing deteriolation in image quality and damage to the electric system of a heat source. <P>SOLUTION: The fixing device 18 includes: a heat roller 41; the pressure roller 42 to be pressed to the heat roller 41; a frame 62 supporting the heat roller 41 so that the heat roller 41 is rotatable; a pressure arm 63, one part of which is rotatably supported by the frame 62 and the other part of which supports the pressure roller 42 so that the pressure roller 42 is rotatable; a driving gear 66 fixed to the end of the pressure roller 42 and rotated integrally with the pressure roller 42; and an input gear 64 engaged with an output gear 67 on the main body casing 2 side and rotated around the same swing rotation center of the pressure arm 63. The input gear 64 and drive gear 66 are connected via an intermediate gear 65 rotatably supported by the pressure arm 63. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a fixing device that thermally fixes a developer image on a sheet (recording sheet), and an image forming apparatus including the fixing device.

  Generally, an image forming apparatus such as a laser printer is provided with a fixing device for thermally fixing a developer image transferred from a photosensitive member to a sheet. The fixing device includes a heating roller that is heated by a heat source and supplied with a driving force, and a pressure roller that is disposed opposite to the heating roller and pressed toward the heating roller. It is known (see Patent Document 1).

JP-A-6-308847

  In such a fixing device, if the nip width between the pressure roller and the heating roller can be increased to increase the contact area between the paper and the heating roller, the temperature of the heating roller can be lowered or the heating roller can be rotated. Fixing is performed well even if it is early. That is, it is possible to reduce the temperature and speed of the fixing device.

Here, if the pressing force of the pressure roller to the heating roller is increased or the surface of the pressure roller is made of a soft member in order to increase the nip width, the portion of the pressure roller that faces the heating roller However, it will be in a depressed state.
However, when the pressure roller is deformed in this way (when the circularity is reduced), the force that the pressure roller impedes the conveyance of the paper is superior to the conveyance force that the heating roller applies to the paper, and the There is a possibility of slipping.

Therefore, the inventor of the present application has found that the slippage of the paper can be suppressed by the configuration in which the pressure roller having a large deformation is driven.
Conventionally, the pressure roller is driven by a heating roller in which a heat source is integrally fixed, a pressure roller disposed along the heating roller, and the heating roller to the pressure roller. There has been known one provided with a pressing spring to be pressed and a driving gear provided at an end of a pressure roller.

  In such a fixing device, the driving force from the driving source installed in the image forming apparatus is transmitted to the driving gear of the pressing roller through a plurality of gears, so that the pressing roller rotates. The heating roller is driven to rotate along with the rotation. In addition, the heating roller reciprocates in a direction toward and away from the pressure roller in order to absorb fluctuations in the outer diameter of the pressure roller. In a general fixing device, the paper conveyed from the upstream is first applied to a heating roller made of a material harder than the pressure roller, so that the paper is satisfactorily sent between the pressure roller and the heating roller. Is possible.

  However, in the structure in which the heating roller reciprocates as in the above-described technique, the paper entry position (the position where the sheet is first applied to the heating roller) is not fixed, and thus the image quality may be deteriorated. In the above-described technique, since the heat source is fixed to the heating roller, the heat source may reciprocate together with the heating roller, and the electric system of the heat source may be damaged.

  In order to avoid such a problem, the heating roller is supported by the frame of the fixing device so as to be able to rotate, and the pressure roller can be structured to reciprocate. It is done. However, in such a structure, the driving gear fixed to the pressure roller also reciprocates together with the pressure roller. Therefore, the driving gear is disengaged from the gear on the image forming apparatus side, and the pressure roller from the driving source. There is a possibility that the driving force is not transmitted to the vehicle properly.

  Accordingly, the present invention is capable of lowering the speed and increasing the speed, and can perform a good transmission of the driving force to the pressure roller without degrading the image quality and damaging the electrical system of the heat source. It is another object of the present invention to provide an image forming apparatus.

  The present invention for solving the above-described problems is provided in a main body of an image forming apparatus having a photosensitive member and a developing unit, and fixes the developer image on a recording sheet onto which the developer image is transferred from the photosensitive member. A heating roller heated by a heat source, a pressure roller pressed against the heating roller, a frame that rotatably supports the heating roller, and a part that is rotatably supported by the frame. In addition, a pressure arm that rotatably supports the pressure roller at another portion, a driving gear fixed to an end of the pressure roller and rotating integrally with the pressure roller, and connected to the drive gear And an input gear that meshes with an output gear rotatably provided in the main body of the image forming apparatus and that rotates coaxially with the swing center of the pressure arm.

  According to the present invention, since the pressure roller is driven, the nip width between the pressure roller and the heating roller can be increased. As a result, the fixing device can be reduced in temperature and speed. In addition, since the heating roller is supported by the frame and does not reciprocate, the recording sheet entry position is constant, and the image quality is improved. Further, since the heating roller does not reciprocate, an extra load is not applied to the electric system of the heat source, so that damage to the electric system can be reliably suppressed.

  Further, since the input gear meshing with the output gear on the image forming apparatus side is coaxial with the swing center of the pressure arm, the distance between the output gear and the input gear is not changed by the swing of the pressure arm. . In addition, since the drive gear is configured to turn by the swing of the pressure arm, the distance between the input gear and the drive gear that is coaxial with the swing center of the pressure arm does not change. Therefore, for example, when the input gear and the driving gear are directly connected, the distance between the shafts between the adjacent gears of the output gear, the input gear, and the driving gear does not change. Since it is in a meshed state, the driving force is transmitted to the pressure roller satisfactorily. Even if a predetermined number of gears supported by the pressure arm are provided between the input gear and the driving gear, the inter-shaft distance between the gears does not change. it can.

  The present invention also provides a fixing device that is provided in a main body of an image forming apparatus having a photoreceptor and developing means, and that thermally fixes the developer image onto a recording sheet onto which the developer image has been transferred from the photoreceptor. A heating roller heated by a heat source, a pressure roller pressed against the heating roller, a frame that rotatably supports the heating roller, a part of which is rotatably supported by the frame, and others A pressure arm that rotatably supports the pressure roller, a driving gear that is fixed to an end of the pressure roller and rotates integrally with the pressure roller, and is rotatably supported by the frame. An input gear meshing with an output gear rotatably provided in the image forming apparatus main body, a swing arm swinging coaxially with the rotation center of the input gear, the input gear and the drive gear And a planetary gear that is rotatably supported by the swing arm, and a gear biasing unit that biases the planetary gear toward the drive gear via the swing arm. It may be.

  Even in such a structure, since the pressure roller is driven, the nip width between the pressure roller and the heating roller can be increased. As a result, the fixing device can be lowered in temperature and speeded up. Become. Further, since the input gear that meshes with the output gear on the image forming apparatus side is supported by the frame, the distance between the shafts of the output gear and the input gear is not changed by the swing of the pressure arm. Further, even if the planetary gear is pushed by the driving gear due to the swinging of the pressure arm, the planetary gear rolls around the input gear while being supported by the swinging arm. The distance is not changed. Further, since the planetary gear is pressed to the driving gear side by the gear urging means via the swing arm, the distance between the planetary gear and the driving gear is not changed. Therefore, since the distance between the shafts between the adjacent gears among the output gear, the input gear, the planetary gear, and the driving gear does not change, each gear is always meshed, so that the driving force to the pressure roller Is transmitted well. Each fixing device as described above is provided in the image forming apparatus.

  According to the present invention, since the pressure roller is driven, the nip width between the pressure roller and the heating roller can be increased. As a result, the fixing device can be reduced in temperature and speed. In addition, the heating roller has a structure that does not reciprocate, and the distance between the adjacent gears from the output gear to the driving gear does not change, so there is no deterioration in image quality or damage to the electrical system of the heat source. The driving force can be transmitted to the pressure roller satisfactorily.

[First Embodiment]
<Overall configuration of laser printer>
First, the overall configuration of a laser printer as an example of the image forming apparatus of the present invention will be briefly described. In the drawings to be referred to, FIG. 1 is a side sectional view showing a first embodiment of a laser printer as an example of an image forming apparatus of the present invention.
As shown in FIG. 1, the laser printer 1 includes a feeder unit 4 for feeding a sheet 3 into a main body casing 2, an image forming unit 5 for forming an image on the fed sheet 3, and the like. ing.

<Configuration of feeder section>
The feeder unit 4 includes a paper feed tray 6 that is detachably attached to the bottom of the main casing 2 and a paper pressing plate 7 provided in the paper feed tray 6. The feeder unit 4 includes a sheet feeding roller 8 and a sheet feeding pad 9 provided above one end of the sheet feeding tray 6, and a sheet provided downstream of the sheet feeding roller 8 in the conveying direction of the sheet 3. Powder removing rollers 10 and 11 are provided. Further, the feeder unit 4 includes a registration roller 12 provided on the downstream side with respect to the paper dust removing rollers 10 and 11. In the following description, the downstream side or the upstream side in the conveyance direction of the paper 3 may be simply referred to as the downstream side or the upstream side.

  In the feeder section 4 configured as described above, the paper 3 in the paper feed tray 6 is brought close to the paper feed roller 8 side by the paper pressing plate 7 and sent out by the paper feed roller 8 and the paper feed pad 9. Then, after passing through the various rollers 10 to 12, they are conveyed one by one to the image forming unit 5.

<Configuration of image forming unit>
The image forming unit 5 includes a scanner unit 16, a process cartridge 17, a fixing device 18, and the like.

<Configuration of scanner unit>
The scanner unit 16 is provided at an upper portion in the main body casing 2 and includes a laser light emitting unit (not shown), a polygon mirror 19 that is rotationally driven, lenses 20, 21 and reflecting mirrors 22, 23, 24, and the like. . As indicated by the chain line, the laser beam based on the image data emitted from the laser emission unit passes or reflects in the order of the polygon mirror 19, the lens 20, the reflecting mirrors 22, 23, the lens 21, and the reflecting mirror 24, and the process cartridge. The surface of the 17 photosensitive drums 27 is irradiated by high-speed scanning.

<Process cartridge configuration>
The process cartridge 17 is disposed below the scanner unit 16 and is configured to be detachably attached to the main body casing 2. A developing cartridge 28, a photosensitive drum 27, a scorotron charger 29, and a transfer roller 30 are mainly provided in a hollow casing 51 that constitutes the outer frame of the process cartridge 17.

  The developing cartridge 28 is detachably attached to the housing 51 and includes a developing roller 31, a layer thickness regulating blade 32, a supply roller 33, and a toner hopper 34. The toner in the toner hopper 34 is supplied to the developing roller 31 by the rotation of the supply roller 33 in the arrow direction (counterclockwise direction). At this time, the toner is positively frictionally charged between the supply roller 33 and the developing roller 31. Is done. The toner supplied onto the developing roller 31 enters between the layer thickness regulating blade 32 and the developing roller 31 as the developing roller 31 rotates in the arrow direction (counterclockwise), and has a constant thickness. It is carried on the developing roller 31 as a thin layer.

  The photosensitive drum 27 is supported by the housing 51 so as to be rotatable in the arrow direction (clockwise). The photosensitive drum 27 is formed of a positively chargeable photosensitive layer made of polycarbonate, while the drum body is grounded.

  The scorotron charger 29 is disposed above the photosensitive drum 27 so as to face the photosensitive drum 27 with a predetermined interval therebetween. The scorotron charger 29 is a positively charged scorotron charger that generates corona discharge from a charging wire such as tungsten, and is configured to uniformly charge the surface of the photosensitive drum 27 to a positive polarity. ing.

  The transfer roller 30 is disposed below the photosensitive drum 27 so as to face the photosensitive drum 27 and is supported by the housing 51 so as to be able to rotate counterclockwise. The transfer roller 30 is configured by covering a metal roller shaft with a conductive rubber material. A transfer bias is applied to the transfer roller 30 at the time of transfer.

  The surface of the photosensitive drum 27 is uniformly positively charged by the scorotron charger 29 and then exposed by high-speed scanning of the laser beam from the scanner unit 16. Thereby, the potential of the exposed part is lowered, and an electrostatic latent image based on the image data is formed. Here, the “electrostatic latent image” refers to an exposed portion of the surface of the photosensitive drum 27 that is uniformly positively charged and exposed to a laser beam to have a lowered potential. Next, the rotation of the developing roller 31 causes the toner carried on the developing roller 31 to be supplied to an electrostatic latent image formed on the surface of the photosensitive drum 27 when it contacts and faces the photosensitive drum 27. The The toner is visualized by being selectively carried on the surface of the photosensitive drum 27, whereby a toner image is formed by reversal development.

  Thereafter, the photosensitive drum 27 and the transfer roller 30 are rotationally driven so as to sandwich and convey the sheet 3 between them, and the sheet 3 is conveyed between the photosensitive drum 27 and the transfer roller 30, so that the photosensitive drum 27 and the transfer roller 30 are photosensitive. The toner image carried on the surface of the drum 27 is transferred onto the paper 3.

<Configuration of fixing device>
The fixing device 18 is disposed on the downstream side of the process cartridge 17, and is provided on the downstream side of the heating roller 41, the pressure roller 42 pressed against the heating roller 41, and the heating roller 41 and the pressure roller 42. A pair of transport rollers 43 is provided. In the fixing device 18 configured as described above, the toner image transferred onto the sheet 3 is thermally fixed while the sheet 3 passes between the heating roller 41 and the pressure roller 42. Thereafter, the sheet 3 is transported to the paper discharge path 44 by the transport roller 43. The paper 3 sent to the paper discharge path 44 is discharged onto a paper discharge tray 46 by a paper discharge roller 45.

<Details of fixing device structure>
Next, details of the structure of the fixing device, which is a characteristic part of the present invention, will be described. 2 is a side view (a) showing a state before the fixing device shown in FIG. 1 is attached to a laser printer, and a side view (b) showing a state after the fixing device is attached to the laser printer. FIG. 6 is a schematic side view (c) showing the relationship between the diameter of the pressure roller of the fixing device and the nip width.

  As shown in FIG. 2A, the fixing device 18 mainly includes the heating roller 41 and the pressure roller 42 described above, a frame 62, a pressure arm 63, an input gear 64, and an intermediate gear 65. And a driving gear 66. The fixing device 18 is mounted in the vicinity of an output gear 67 that is rotatably provided in the main body casing 2 of the laser printer 1. It should be noted that a driving force from a driving source (not shown) disposed at an appropriate position in the main body casing 2 is transmitted to the output gear 67 through a plurality of gears.

  The heating roller 41 is a part formed in a hollow cylindrical shape, and is heated by a halogen heater HH disposed therein. The both ends of the heating roller 41 are rotatably supported by the frame 62 via bearings (not shown). Note that both ends of the halogen heater HH are fixed to the frame 62. As the heating roller 41, for example, a roller having a diameter of 25 mm can be used as shown in FIG. Further, the heating roller 41 may be formed of aluminum and the surface thereof may be coated with Teflon (registered trademark, PTFE).

  The pressure roller 42 is a part formed in a columnar shape, and a rotating shaft 42a protruding axially outward from both ends thereof is rotatably supported by a pressure arm 63 via a bearing (not shown). A driving gear 66 is fixed to the tip of the rotating shaft 42a protruding from the pressure arm 63.

  As the pressure roller 42, for example, a roller having a diameter of 25 mm can be used as shown in FIG. Further, as the configuration of the pressure roller 42, a urethane rubber having a thickness of 6 to 7 mm is provided around a core bar provided in the center portion thereof, and the surface of the urethane rubber is made of Teflon (registered trademark, registered trademark, 20 to 50 μm). You may make it cover with a PTFE) tube. In addition, since it will become easy to deform | transform if urethane rubber is a foaming thing, nip width | variety can be enlarged more.

As shown in FIG. 2C, the relationship between the diameter Dp of the pressure roller 42 and the nip width (contact width) N in the circumferential direction between the heating roller 41 and the pressure roller 42 is expressed by the following equation (1). It is set to satisfy.
0.24 <N / Dp <0.6 (1)
Here, the nip width N is the length along the curved surface of the concave portion generated on the surface of the pressure roller 42 by pressing the pressure roller 42 against the heating roller 41 (or the concave portion of the heating roller 41). The circumferential length of the part that touches.

  As a method for measuring the nip width N, for example, there is a method using a paper (hereinafter referred to as “black paper”) on which the entire surface is printed black as shown below. Specifically, in this method, the black paper is held between the heating roller 41 and the pressure roller 42 for a predetermined time and then taken out, so that the portion of the black paper held by the two rollers 41 and 42 is changed to the other. Glossy compared to the part. Then, the nip width N is measured by measuring the width of the glossy portion (the length in the paper transport direction) with calipers or the like.

  As shown in FIG. 2A, the pressure arm 63 is a long part formed by punching a metal plate, and one end thereof is rotated by a support shaft 62 a provided on the frame 62. By being supported as possible, the entire structure is rocked. Further, the pressure arm 63 rotatably supports the pressure roller 42 at a predetermined distance from one end portion thereof, and a tension spring S is attached at a proper position separated from the support portion by a predetermined distance.

  One end of the tension spring S is attached to the pressure arm 63, and the other end is attached to the frame 62. Accordingly, the pressure arm 63 is urged toward the heating roller 41 by the pulling spring S, and the pressure roller 42 is pressed (biased) toward the heating roller 41 by the pressure arm 63.

  As shown in FIG. 2B, the input gear 64 is disposed at a position that meshes with the output gear 67 in the main body casing 2 when the fixing device 18 is mounted in the main body casing 2. The input gear 64 is rotatably supported by a support shaft 62 a provided on the frame 62, so that the input gear 64 rotates coaxially with the swing center of the pressure arm 63. That is, the center position of the input gear 64 is stationary with respect to the frame 62. Therefore, when the fixing device 18 is mounted in the main casing 2, the meshing state between the input gear 64 and the output gear 67 in the main casing 2 is always maintained.

  The intermediate gear 65 meshes with the input gear 64 and the drive gear 66 and is rotatably supported by a support shaft 63 a provided on the pressure arm 63. Therefore, the intermediate gear 65 swings as the pressure arm 63 swings and rolls around the input gear 64.

  The driving gear 66 is fixed to the end of the rotating shaft 42 a of the pressure roller 42. Therefore, the driving gear 66 rotates integrally with the pressure roller 42 and swings as the pressure arm 63 swings. Furthermore, since the input gear 64 is coupled to the drive gear 66 via the intermediate gear 65, the driving force from the output gear 67 in the main body casing 2 is transmitted via the input gear 64 and the intermediate gear 65. Communicated.

  Next, referring to FIG. 3, the meshing state of the gears 67 and 64 to 66 when the pressing arm 63 swings when the driving force is transmitted from the output gear 67 to the driving gear 66. explain. In the drawings to be referred to, FIG. 3 is a side view (a) showing a state where the pressure roller is pressed against the heating arm with a predetermined nip width, and a side view (FIG. 3) showing a state where the pressure arm swings downward. b). FIG. 3 shows a state in which the pressure roller 42 is crushed by a predetermined amount and a state in which the pressure roller 42 is hardly crushed in order to emphasize the swinging of the pressure arm 63. The pressure arm 63 swings very little, and the pressure roller 42 is crushed by a substantially predetermined amount.

  As shown in FIG. 3A, during normal operation, the pressure roller 42 is pressed against the heating roller 41 so as to ensure a predetermined nip width N, and the gears 67 and 64 to 66 are They are engaged with each other. The driving force transmitted from a driving source (not shown) to the output gear 67 through a plurality of gears is transmitted to the pressure roller 42 through the input gear 64, the intermediate gear 65, and the driving gear 66. As a result, the heating roller 41 is driven and rotated, and the developer image is satisfactorily fixed on the sheet 3 while the sheet 3 is conveyed between the two rollers 41 and 42.

  Incidentally, since the outer periphery of the pressure roller 42 is made of soft rubber or the like, the outer shape accuracy (circularity) is lower than that of the heating roller 41. Therefore, during the operation as described above, the pressure arm 63 may swing downward as shown in FIG. 3B due to the outer diameter accuracy of the pressure roller 42, for example. Even in such a case, since the position of the input gear 64 does not shift with respect to the fixing device 18, and consequently the main body casing 2, the input gear 64 does not come off from the output gear 67.

  Further, since the positional relationship among the input gear 64, the intermediate gear 65, and the driving gear 66 does not shift on the pressurizing arm 63, the input gear 64, the intermediate gear 65, and the driving gear 66 do not deviate from each other. Therefore, even when the pressure arm 63 swings downward as described above, the driving force from the output gear 67 is transmitted to the pressure roller 42 via the input gear 64, the intermediate gear 65 and the driving gear 66. Good transmission.

Here, assuming that the pressure roller 42 is rotatably supported by the frame 62 and cannot swing, the outer diameter accuracy of the pressure roller 42 is low, so that the heating roller 41 and the pressure roller 42 are The contact area (nip width) varies. Therefore, there is a possibility that the conveyance force applied to the paper fluctuates between the heating roller 41 and the pressure roller 42 and the paper is wrinkled.
However, in the present invention, since the pressure arm 63 swings up and down, the pressure roller 42 is displaced in a direction toward and away from the heating roller 41. Fluctuation is suppressed. As a result, wrinkles on the paper are suppressed.

According to the above, the following effects can be obtained in the present embodiment.
By adopting a structure in which the heating roller 41 does not reciprocate, the entry position of the paper 3 can be fixed, so that the image quality can be improved. Further, since the load applied to the halogen heater HH can be suppressed by adopting a structure in which the heating roller 41 does not reciprocate, it is possible to suppress damage to the electrical system (terminal HI) fixed to the frame of the halogen heater HH. it can.

  Regardless of the swing of the pressurizing arm 63, the positional relationship between the output gear 67 and the input gear 64 (distance between the axes) and the positional relationship between the input gear 64, the intermediate gear 65 and the driving gear 66 (distance between the axes). Can always be kept constant. Therefore, the gears 67 and 64 to 66 are always meshed, so that the driving force can be transmitted to the pressure roller 42 satisfactorily.

  Since the relationship between the nip width N and the diameter Dp of the pressure roller 42 satisfies the formula (1) “0.24 <N / Dp <0.6”, the nip width N with respect to the size of the pressure roller 42. Can be as large as possible. Therefore, the contact time and contact range between the sheet 3 passing between the two rollers 41 and 42 and the heating roller 41 can be increased, and the temperature of the heating roller 41 can be lowered and the printing speed can be improved. Further, since N / Dp <0.6, the driving torque of the pressure roller 42 is increased due to an excessively large nip width, and a load on the fixing device is suppressed. Further, since N / Dp <0.6, it is possible to suppress an excessive burden on the sheet 3 passing between the pressure roller 42 and the heating roller 41.

  Incidentally, when the nip width N satisfying the formula (1) is adopted in a fixing device of a heating roller driving system (a system in which the heating roller is driven and the pressure roller is driven) different from the present embodiment, A phenomenon occurs in which the heating roller slips with respect to the pressure roller. Therefore, the nip width N satisfying the formula (1) is effective only for the pressure roller driving type as in this embodiment.

The present invention is not limited to the first embodiment described above, and can be used in various forms as exemplified below.
In the first embodiment, only one intermediate gear 65 is provided. However, the present invention is not limited to this, and two or more intermediate gears 65 may be provided. Further, the input gear 64 and the driving gear 66 may be directly meshed without providing the intermediate gear 65.

  In the first embodiment, the tension spring S is used as an example of the roller urging means for pressing the pressure roller 42 against the heating roller 41. However, the present invention is not limited to this, and for example, a pressing spring, a torsion spring, or the like. It may be.

[Second Embodiment]
Next, a second embodiment of the present invention will be described in detail with reference to the drawings as appropriate. Note that, in the present embodiment, a part of the structure of the fixing device 18 according to the first embodiment described above is changed. Therefore, the same components as those in the first embodiment are denoted by the same reference numerals. The description will be omitted. In the drawings to be referred to, FIG. 4A is a side view showing a state before the fixing device according to the second embodiment is attached to the laser printer, and FIG. 4B is a side view showing the state after the fixing device is attached to the laser printer. (B).

  As shown in FIG. 4A, the fixing device 18 ′ according to the second embodiment includes a pressure arm 63, a driving gear 66, and the like similar to those of the first embodiment, and the first embodiment. Different from the input gear 68, the swing arm 69, and the planetary gear 70.

  The input gear 68 is rotatably supported by a support shaft 62 b provided at a position different from the swing center of the pressure arm 63 in the frame 62. The input gear 68 is disposed at a position where the input gear 68 meshes with the output gear 67 in the main casing 2 when the fixing device 18 'is mounted in the main casing 2, as shown in FIG. ing.

  One end of the swing arm 69 is rotatably supported by the support shaft 62 b described above, whereby the entire swing arm 69 swings coaxially with the rotation center of the input gear 68. A support shaft 69 a is provided at the other end of the swing arm 69, and a tension spring S ′ is provided between the support shaft 69 a and one end of the swing arm 69. One end of the tension spring S ′ is attached to the swing arm 69, and the other end is attached to the frame 62.

  The planetary gear 70 is rotatably supported on a support shaft 69 a of the swing arm 69. The planetary gear 70 meshes with the input gear 68 while being supported by the support shaft 69a. Further, the other end portion of the swing arm 69 is urged toward the pressure roller 42 by the above-described pulling spring S ′, so that the planetary gear 70 disposed on the other end portion of the swing arm 69 is driven. The gear 66 is pressed and meshed. Further, when the driving gear 66 is pressed by the planetary gear 70, the pressure arm 63 swings and the pressure roller 42 is pressed against the heating roller 41.

  Next, see FIG. 5 for the meshing state of the gears 67, 68, 70, 66 when the pressure arm 63 swings when the driving force is transmitted from the output gear 67 to the driving gear 66. To explain. In the drawings to be referred to, FIG. 5 is a side view (a) showing a state where the pressure roller is pressed against the heating arm with a predetermined nip width, and a side view (FIG. 5) showing a state where the pressure arm swings downward. b). In FIG. 5, as in FIG. 3, in order to emphasize the oscillation of the pressure arm 63, a state where the pressure roller 42 is crushed by a predetermined amount and a state where the pressure roller 42 is almost crushed are shown. To do.

  As shown in FIG. 5A, during normal operation, the pressure roller 42 is pressed against the heating roller 41 so as to ensure a predetermined nip width N, and the gears 67, 68, 70, 66 are in mesh with each other. The driving force transmitted from the driving source (not shown) to the output gear 67 through a plurality of gears is transmitted to the pressure roller 42 through the input gear 68, the planetary gear 70, and the driving gear 66. As a result, the heating roller 41 is driven and rotated, and the developer image is satisfactorily fixed on the sheet 3 while the sheet 3 is conveyed between the two rollers 41 and 42.

  Incidentally, since the outer periphery of the pressure roller 42 is made of soft rubber or the like, the outer shape accuracy (circularity) is lower than that of the heating roller 41. Therefore, during operation as described above, for example, due to the outer diameter accuracy of the pressure roller 42, the pressure arm 63 may swing downward as shown in FIG. 5B. Even in such a case, the position of the input gear 68 does not shift with respect to the fixing device 18 ′, and hence the main casing 2, so that the input gear 68 does not come off from the output gear 67.

  When the planetary gear 70 is pressed downward by the drive gear 66 that moves downward by the downward swing of the pressure arm 63, the planetary gear 70 meshes with the input gear 68 and the drive gear 66. However, it will roll around the input gear 68. As described above, since the distance between the axes between the adjacent gears 67, 68, 70, 66 does not change, the gears 67, 68, 70, 66 do not deviate from each other. Therefore, even when the pressure arm 63 swings downward as described above, the driving force from the output gear 67 is transmitted to the pressure roller 42 via the input gear 68, the planetary gear 70 and the driving gear 66. Good transmission.

Here, assuming that the pressure roller 42 is rotatably supported by the frame 62 and cannot swing, the outer diameter accuracy of the pressure roller 42 is low, so that the heating roller 41 and the pressure roller 42 are The contact area (nip width) varies. Therefore, there is a possibility that the conveyance force applied to the paper fluctuates between the heating roller 41 and the pressure roller 42 and the paper is wrinkled.
However, in the present invention, since the pressure arm 63 swings up and down, the pressure roller 42 is displaced in a direction toward and away from the heating roller 41. Fluctuation is suppressed. As a result, wrinkles on the paper are suppressed.

According to the above, the following effects can be obtained in the second embodiment.
Regardless of the swing of the pressurizing arm 63, the distance between the axes between the adjacent gears 67, 68, 70, 66 can always be kept constant. For this reason, the gears 67, 68, 70, 66 are always meshed with each other, so that the driving force can be transmitted to the pressure roller 42 satisfactorily.

The present invention is not limited to the above-described second embodiment, and can be used in various forms as exemplified below.
In the second embodiment, the tension spring S ′ is employed as an example of the gear urging means. However, the present invention is not limited to this, and may be, for example, a push spring, a torsion spring, or the like.
In the second embodiment, the planetary gear 70 is directly meshed with (connected to) the driving gear 66. However, the planetary gear 70 is interposed via a predetermined number of gears rotatably supported by the pressure arm 63. Indirectly, the driving gear 66 may be connected.
In the second embodiment, the planetary gear 70 is directly meshed with (connected to) the input gear 68. However, the planetary gear 70 is rotatably supported by a swing arm 69 via a predetermined number of gears. It is good also as a structure connected with the input gear 68 indirectly.

The present invention is not limited to the above-described embodiments, and can be used in various forms as exemplified below.
In each of the above embodiments, the present invention is applied to the laser printer 1, but the present invention is not limited to this, and the present invention may be applied to other image forming apparatuses such as a copying machine and a multifunction machine.

In each of the above embodiments, the transfer roller 30 is used as an example of the transfer unit. However, the present invention is not limited to this, and a non-contact type, for example, may be used.
In each of the embodiments, the paper 3 such as a thick paper, a postcard, and a thin paper is used as an example of the recording sheet. However, the present invention is not limited to this, and may be an OHP sheet, for example.

  In each of the above embodiments, the halogen heater HH is adopted as an example of the heat source. However, the present invention is not limited to this, and for example, an induction heating type IH (Induction Heating) heater or a heating resistor may be adopted.

  In each of the embodiments, the toner is used as an example of the developer, the developing cartridge 28 is used as an example of the developing unit, the scanner unit 16 is used as an example of the exposure device, and the photosensitive drum 27 is used as an example of the photoconductor. Is not to be done. That is, it goes without saying that materials and structures can be changed as appropriate without departing from the spirit of the present invention.

  In each of the embodiments described above, the structure in which one end portion of the pressure arm 63 is rotatably supported by the frame 62 and the pressure roller 42 is supported by the other end portion of the pressure arm 63 has been adopted. Is not limited to this. That is, any structure may be used as long as a part of the pressure arm 63 is rotatably supported by the frame 62 and the pressure roller 42 is supported by the other part of the pressure arm 63. For example, a structure in which the center portion of the pressure arm is rotatably supported by the frame and the pressure roller is supported by one end portion of the pressure arm may be employed.

Further, the nip width N is preferably about 6 to 10 mm in consideration of the relationship between the rollers 41 and 42 in FIGS.
Furthermore, the diameter of the pressure roller 42 is preferably about the diameter shown in FIG. 6B, that is, about 20 to 40 mm.
The thickness (diameter direction) of the rubber layer of the pressure roller 42 is preferably about the thickness shown in FIG. 6B, that is, about 5 to 15 mm. Further, the thickness of the rubber layer is preferably 6 to 8 mm, more preferably about 7.5 mm when the diameter of the pressure roller 42 is 25 mm.

  Examples of the above embodiment will be described below. Specifically, Example 1 showing the experimental result of examining the relationship between the nip width N and slip, and Example 2 showing the experimental result of examining the relationship between the nip width and the reflection density reduction rate (the degree of toner peeling). Will be explained.

<Example 1>
Various conditions of the experiment in Example 1 are as follows.
(A) Evaluation fixing device: fixing device mounted on Brother Industries, Ltd. HL-5250 (heating roller driving method, pressure roller driving method)
(B) Paper: A4 plain paper [Density; 80 g / m ² (gram / square meter)]
(C) Fixing temperature (heating roller surface temperature): 193 ° C. (degrees)
(D) Room temperature: Room temperature (e) Pressure roller diameter Dp: 25 mm

  Under the above conditions, an experiment was conducted to examine whether or not slip occurs between the two rollers that sandwich the sheet by sequentially changing the nip width N. In this experiment, the heating roller driving method was adopted by applying a predetermined driving force only to the heating roller in the fixing device of HL-5250. On the contrary, the pressure roller driving method is adopted by applying a predetermined driving force only to the pressure roller in the fixing device of the same model HL-5250.

  As a result, experimental results as shown in Table 1 below were obtained. In Table 1, “◯” indicates a normal state where no slip occurs, and “X” indicates an abnormal state where a slip occurs. That is, “◯” indicates a state in which the other roller is driven with respect to one roller to which the driving force is applied, and “X” indicates that the other roller is applied to the one roller to which the driving force is applied. It shows a state of not being driven. In addition, “-” indicates that no experiment was performed.

  More specifically, “◯” indicates that the slip test was not confirmed even after 1000 times of printing test, and “×” indicates that the slip was confirmed after 1000 times of printing test. Show. Slip determination was performed by a skilled person determining that slipping occurred when the printed image was disturbed.

  As described above, according to Example 1, when N / Dp is 0.24, it is confirmed that the nip width cannot be further increased because the heating roller driving method causes slip.

<Example 2>
Various conditions of the experiment in Example 2 are as follows.
(A) Evaluation fixing device: fixing device mounted on Brother Industries, Ltd. HL-5250 (only pressure roller drive system)
(B) Paper transport speed: 28 ppm (page / minute)
(C) Paper: A4 plain paper [density: 80 g / m ² (gram / square meter)]
(D) Fixing temperature (temperature of heating roller surface): 193 ° C. (degrees)
(E) Room temperature: 10 ° C. (degrees)
(F) Humidity: 10% (percent)
(G) Reflection densitometer: [GretagMacbeth D19C] is used.
(H) Reflection density: measured under the following two conditions.
Condition 1: The density of the developer image fixed on the paper is measured as it is.
Condition 2: A developer image (condition 1) formed on a sheet is rubbed with a cloth for a predetermined time at a predetermined pressure (rub fastness test) and then measured.
(I) Reflection density reduction rate:
100 × (reflection density measured under condition 1−reflection density measured under condition 2) / (reflection density measured under condition 1)

  Under the above conditions, an experiment was conducted to examine how much the reduction rate of the reflection density indicating the degree of toner peeling varies with the size of the nip width N by sequentially changing the nip width N. Here, the reflection density reduction rate is a numerical value indicating the degree of peeling of the toner after drying, and indicates that the fixing property is better as the value becomes lower. In this experiment, data with a nip width of 5.0 mm was obtained using the heating roller driving method, and other data was obtained using the pressure roller driving method. . However, in this experiment, it is predicted that the same result can be obtained even if all the data is acquired using the pressure roller driving method.

As a result, experimental results as shown in Table 2 and FIG. 7 were obtained.

  As described above, according to Example 2, it was confirmed that it is preferable to satisfy N / Dp> 0.24 in order to maintain good fixability. Therefore, based on the experimental results of Examples 1 and 2, it was confirmed that N / Dp> 0.24 is desirable.

1 is a side cross-sectional view showing a first embodiment of a laser printer as an example of an image forming apparatus of the present invention. A side view (a) showing a state before the fixing device shown in FIG. 1 is attached to the laser printer, a side view (b) showing a state after the fixing device is attached to the laser printer, and a pressure roller of the fixing device. It is a schematic side view (c) which shows the relationship between a diameter and nip width. In the fixing device according to the first embodiment, a side view (a) showing a state where the pressure roller is pressed against the heating arm with a predetermined nip width, and a side view showing a state where the pressure arm swings downward. FIG. FIG. 6 is a side view (a) showing a state before the fixing device according to the second embodiment is attached to a laser printer, and a side view (b) showing a state after the fixing device is attached to the laser printer. In the fixing device according to the second embodiment, a side view (a) showing a state where the pressure roller is pressed against the heating arm with a predetermined nip width, and a side view showing a state where the pressure arm swings downward. FIG. It is the side view (a) which shows an example of a heating roller, and the side view (b) which shows an example of a pressure roller. It is a graph which shows the relationship between N / Dp and a reflection density fall rate.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Laser printer 2 Main body casing (Image forming apparatus main body)
3 paper (recording sheet)
18 Fixing Device 41 Heating Roller 42 Pressure Roller 42a Rotating Shaft 62 Frame 62a Support Shaft 62b Support Shaft 63 Pressing Arm 63a Support Shaft 64 Input Gear 65 Intermediate Gear 66 Driving Gear 67 Output Gear 68 Input Gear 69 Oscillating Arm 69a Support Shaft 70 Planetary gear Dp diameter HH Halogen heater (heat source)
N Nip width S Pull spring

Claims (6)

Provided in an image forming apparatus main body having a photoreceptor and developing means,
A fixing device that heat-fixes the developer image on a recording sheet onto which the developer image is transferred from the photoreceptor;
A heating roller heated by a heat source;
A pressure roller pressed against the heating roller;
A frame that rotatably supports the heating roller;
A pressure arm that is rotatably supported by the frame and rotatably supports the pressure roller in the other part;
A driving gear fixed to an end of the pressure roller and rotating integrally with the pressure roller;
And an input gear that is coupled to the drive gear and meshes with an output gear that is rotatably provided in the main body of the image forming apparatus, and rotates coaxially with the swing center of the pressure arm. Fixing device to do.   The fixing device according to claim 1, wherein the input gear and the driving gear are connected via a predetermined number of gears rotatably supported by the pressure arm. Provided in an image forming apparatus main body having a photoreceptor and developing means,
A fixing device that heat-fixes the developer image on a recording sheet onto which the developer image is transferred from the photoreceptor;
A heating roller heated by a heat source;
A pressure roller pressed against the heating roller;
A frame that rotatably supports the heating roller;
A pressure arm that is rotatably supported by the frame and rotatably supports the pressure roller in the other part;
A driving gear fixed to an end of the pressure roller and rotating integrally with the pressure roller;
An input gear that is rotatably supported by the frame and meshes with an output gear that is rotatably provided to the image forming apparatus body;
A swing arm swinging coaxially with the rotation center of the input gear;
A planetary gear coupled to the input gear and the driving gear and rotatably supported by the swing arm;
A fixing device comprising: a gear urging unit that urges the planetary gear toward the driving gear via the swing arm.   The fixing device according to claim 3, wherein the planetary gear and the input gear are directly connected, and the planetary gear and the driving gear are directly connected. The relationship between the diameter Dp of the pressure roller and the nip width N in the circumferential direction between the heating roller and the pressure roller is expressed by the following equation: 0.24 <N / Dp <0.6
The fixing device according to claim 1, wherein the fixing device satisfies the following conditions. An image forming apparatus for forming an image on a recording sheet,
An exposure device that scans a laser beam in accordance with the input image signal;
A photoconductor on which an electrostatic latent image is formed by scanning laser light with the exposure device;
Developing means for supplying a developer to the photoreceptor;
Transfer means for transferring a developer image formed with the developer onto the recording sheet;
A fixing device according to any one of claims 1 to 5,
An image forming apparatus comprising: an output gear that meshes with the input gear of the fixing device.

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