JP3159047B2 - Transport guide device in image forming apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus for forming a toner image on a recording medium such as paper, such as a copying machine, a facsimile or a laser printer, and heating and fixing the toner image for recording. The present invention relates to a structure of a medium conveyance guide device.

[0002]

2. Description of the Related Art Conventionally, for example, an electrophotographic image forming apparatus is fired and scanned by a scanner unit disposed at a lower portion in a main body case as disclosed in Japanese Patent Application Laid-Open No. 8-44274. An electrostatic latent image is formed on the outer peripheral surface of the photoconductor drum by a laser beam, and a developer (toner) supplied from a toner cartridge is electrostatically attached to the electrostatic latent image to become visible. The toner image is transferred onto the surface of a recording medium such as paper that has passed through the transfer section of the drum, and then the recording medium is passed between the heating roller and the pressing roller in the fixing unit to cover the toner image. Generally, the sheet is heated and fixed on a recording medium and discharged outside the apparatus.

In this case, as disclosed in the prior art, a plurality of conveyance guide ribs for guiding a sheet to be discharged are provided on the discharge side of the heating roller (under the case) in the fixing unit case. Is provided.

[0004]

However, conventionally, since the upper end of the transport guide rib is flat, there is a problem that the curl at the leading end of the paper curled around the heating roller cannot be corrected. Was.

That is, since the pressing roller in the fixing unit is generally a heat-resistant rubber roller and the heating roller is made of metal, the pressing roller is surrounded by the heating fixing section (the nip portion of the paper by the pressing roller and the heating roller). The amount of deformation of the surface is increased, and a pressing force is applied to the sheet such that the sheet is wound around the circumferential surface of the heating roller, so that the curl (curl) is generated.

One method for eliminating this curl is as follows:
It is necessary to dispose a sharp peeling claw close to the circumferential surface of the heating roller in the vicinity of the nip portion, but this peeling claw must be made of a heat-resistant member, and Therefore, it is necessary to increase the manufacturing accuracy in order to dispose them close to each other, and there is a problem that the manufacturing cost increases.

According to the present invention, there is provided the above-mentioned structure without the peeling claw.
It is an object of the present invention to provide a transport guide device in an image forming apparatus in which the paper is prevented from curling with a simple configuration by devising the shape of the upper end surface of the transport guide rib.

[0008]

In order to achieve this object, a transport guide device in an image forming apparatus according to the present invention is provided with a toner image forming a toner image on a recording medium such as a transported sheet. A conveyance guide device for guiding the leading end of a heat-fixed recording medium in an image forming apparatus including a forming unit and a fixing unit having a heating roller and a pressing roller for heating and fixing the toner image on a recording medium. In the discharge side of the heating roller, a plurality of conveyance guide members for guiding the recording medium to be discharged are arranged at least at both ends in the conveyance width direction of the recording medium and at substantially the center thereof at appropriate intervals. The guide surface on which the leading end of the recording medium discharged from the heating roller is slidably contacted with the conveyance guide member is a nip between the heating roller and the pressing roller.
Direction opposite to the curl direction of the recording medium ejected from the
And the height position of the guide surface is closer to the discharge side from the heating roller, and the left and right ends of the recording medium in the conveying width direction are in the conveying width direction of the recording medium. It is set to be higher than the center.

[0009] The invention of claim 2, claim 1
The conveyance guide device in the image forming apparatus described in
The fixing unit includes the heating roller and the pressing roller.
A fixing unit case for accommodating the conveying unit;
Material is integrally formed with the fixing unit case.
is there.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment in which the present invention is embodied in a laser beam printer will be described with reference to the drawings. FIG. 1 is a perspective view of main components of a laser printer as an image forming apparatus, and FIG. 2 is a schematic side sectional view of the laser printer. As shown in FIG. 1, a main body case 1 made of a synthetic resin in a laser printer includes a scanner unit 2 as an exposure unit, a process unit 3 as a toner image forming unit, and a fixing unit 4 as a fixing unit from the top. It comprises a main frame 1a on which the paper feed unit 5 can be mounted, and a main cover 1b which covers the outer surfaces of the main frame 1a on four sides (front and rear and right and left sides). The main frame 1a and the main cover 1b are integrally formed. It is formed by injection molding or the like.

The drive system unit 6 including the drive motor and the gear train is housed in the main body case 1 in the storage recess 1d between the left inner surface of the main cover 1b in FIG. 1 and the left side of the main frame 1a adjacent thereto. Insert from below and secure. Further, the top cover 7 as a synthetic resin main body cover for covering the upper surfaces of the main frame 1a and the main cover body 1b has a hole through which an operation panel 1c projecting upward to the right side of the main frame 1a. 7a and a hole 7b for penetrating the base of the paper feed unit 5 are provided. The base of the paper discharge tray 8 is mounted on brackets 9 and 9 (only one of which is shown in FIG. 1) protruding from the left and right sides of the front end of the top cover 7 so as to be vertically rotatable. The paper discharge tray 8 can be folded and covered on the upper surface side of the top cover 7.

The leading end side of the sheets P set in the feeder unit case 5a in the sheet feeding unit 5 in the stacked state is connected to the feed roller 11 by a support plate 10 with a biasing spring 10a in the feeder unit case 5a. The sheet is separated one by one by the paper feed roller 11 and the separation pad 12, which are pressed toward each other and rotated by the power transmitted from the drive system unit 6.
The separated sheet P is placed on a pair of upper and lower registration rollers 13,
The paper P fed to the process unit 3 at 14 and having an image formed on its surface with toner by the process unit 3 is fixed by the heating roller 15 and the pressing roller 16 of the fixing unit 4 described in detail later. After that, the paper discharge rollers 17 disposed on the downstream side in the fixing unit case
The sheet is discharged to the sheet discharge tray 8 via a sheet discharge section including the sheet and the pinch roller 18.

An upper support plate 2a of the scanner unit 2 is provided below the process unit 3 which is disposed substantially at the center in plan view of the main frame 1a having an open top in the main body case 1 in a plan view. It is fixed with screws or the like to a stay portion integrally formed on the upper surface side of the bottom plate portion. And a scanner unit 2 as an exposure unit
On the lower surface side of the synthetic resin upper support plate 2a, a laser emitting unit, a polygon mirror 20, a lens 21, a reflection mirror 22 and the like are arranged, and on the upper support plate 2a along the axis of the photosensitive drum 23. The laser beam is applied to the outer peripheral surface of the photosensitive drum 23 in the process unit 3 through the glass plate 24 that covers the horizontally long scanner hole formed so as to extend and is exposed.

As shown in FIG. 2, the process unit 3 includes a photosensitive drum 23 and a transfer roller 25 in contact with the upper surface of the photosensitive drum 23, a scorotron type charger 26 disposed below the photosensitive drum 23, and a supply unit. A developing device having a developing roller 27 and a supply roller 28 disposed on the upstream side of the photosensitive drum 23 in the paper direction, and a developer (toner) supply unit, that is, a detachable toner cartridge 29 disposed on the upstream side thereof; The cleaning roller 30 includes a cleaning roller 30 disposed downstream of the body drum 23.
An electrostatic latent image is formed on the outer peripheral surface of the photosensitive drum 23 by scanning the charged layer formed by the charger 26 with a laser beam from the scanner unit 2. The developer (toner) in the toner cartridge 29 is agitated and released by the agitator 31, and then carried on the outer peripheral surface of the developing roller 27 via the supply roller 28.
2 regulates the thickness of the toner layer. Photoconductor drum 2
The electrostatic latent image of No. 3 is visualized by the developer adhering from the developing roller 27, and is transferred to the sheet P passing between the transfer roller 25 and the photosensitive drum 23. The toner remaining on the photosensitive drum 23 is removed by the cleaning roller 30.
Is returned to the photosensitive drum 23 at a predetermined timing and collected by the developing roller 27 into the process unit 3.

The upper support plate 2a of the scanner unit 2
Is provided with a toner sensor 33 protruding upward, and a toner sensor 33 composed of a pair of a light emitting unit and a light receiving unit faces a lower surface recess of the toner cartridge 24 in the process unit 3 and detects whether or not toner is present in the toner cartridge 29. Can be detected. Process unit 3
Is made into a cartridge by being incorporated into a case 34 made of synthetic resin, and the process unit 3 made into a cartridge is detachably mounted on the main frame 1a.

A cooling fan 3 is provided on the lower surface side of the continuous portion between the front portion of the main frame 1a and the front portion of the main cover 1b.
The storage section 36 for storing the sheet 5 and a ventilation duct 37 extending in the left-right direction perpendicular to the direction in which the sheet P passes are formed to communicate with each other. Then, the upper surface plate portion 37a of the ventilation duct 37
Is formed in a downward V-shaped cross section, and the upper surface plate portion 37a is located between the process unit 3 and the fixing unit 4 so that heat generated from the heating roller 15 in the fixing unit 4 is directly directed to the process unit 3 side. Blocked from transmitting. The cooling air generated by the cooling fan 35 passes through the ventilation duct 37, travels along the lower surface on one side of the main frame 1a, and a rear power supply unit 39 (see FIG. 2) and a drive motor (not shown) of the drive system unit 6. The cooling air is blown out from a plurality of slit holes 38 of the upper surface plate portion 37a opened to the process unit 3 side, and the cooling air passes between the process unit 3 and the fixing unit 4 and rises. A plurality of exhaust holes 4 formed in the top cover 7
It is discharged out of the apparatus from 0.

Next, the detailed structure of the fixing unit 4 as fixing means will be described with reference to FIGS. 1 to 3 and FIGS. The case made of heat-resistant synthetic resin in the fixing unit 4 is separated into an upper case 41 and a lower case 42, which can be freely disengaged at engaging claw (not shown) portions on both left and right sides of the two cases 41, 42. It is fitted according to.

In the lower case 42, on the upstream side of the paper P, a heat roller 15 made of a synthetic resin and made of a metal having good heat conductivity, such as aluminum, in which a halogen lamp 43 having a small tube shape is provided on the inner diameter portion. A pair of paper discharge rollers including a paper discharge roller (upper roller) 17 and a pinch roller (lower roller) 18 are rotatably supported on the downstream side through ring-shaped bearings 44, 44. Then, power is transmitted from a transmission gear (not shown) on the downstream side of the transmission of the drive system unit 6 to a synthetic resin gear 45 fitted and mounted on one side of the heating roller 15, and two intermediate gears 47 (FIG. 5, only one of which is shown), is transmitted to a driven gear 46 attached to the paper discharge roller 17, and the heating roller 15 and the paper discharge roller 17 are rotationally driven in synchronization.

The paper discharge roller 17 is formed integrally with a support shaft portion 17a, while the plurality of pinch rollers 18 are elastically and rotatably supported by a shaft 48 made of a coil spring. . As shown in FIG. 8, one side of each of the pinch rollers 18 made of rubber has a large diameter, and the trailing edge of the sheet P to be discharged is hooked by a plurality of cut grooves 49 formed on the outer periphery thereof. The pinch roller 18
Releases the trailing edge of the sheet P with the sheet discharging roller 17 and smoothes the sheet discharging.

On the lower surface side of the upper case 41, right and left end shafts 52 of the pressing roller 16 in which a core metal 50 is covered with an elastic layer 51 such as a soft heat-resistant rubber are respectively biased by springs 53.
In addition, it is supported via a synthetic resin bearing 54 that can move up and down and cannot fall into mounting holes 55 on both the left and right sides of the upper case 41, and the lower side of the circumferential surface of the pressing roller 16 is the circumferential surface of the heating roller 15. It is constantly biased upward (see FIG. 7).

As shown in FIGS. 7, 9 and 10, a thermistor (temperature sensor means) mounted on a metal elastic support 61 extending from a socket 60 screwed to the left and right substantially central portions of the lower case 42. ) 62 to heating roller 1
5, a cover 63 made of synthetic resin or the like having electrical insulation is provided near one side of the lower case 42, and the surface of the cover 63 is The temperature fuse 64 is fixedly mounted on the rear surface of the cover piece 63 via a pair of gripping claws 65 integrally projecting from the rear surface of the cover piece 63. Lead wires 64a, 64 connected to the left and right ends of the
b is fixed to a base 66 provided on the lower case 42 via external terminals (metal pieces) 67a, 67b and stop screws 68, 68 (see FIGS. 11A and 11B). (Metal piece) 67a, 67b through the power supply unit 39
Then, the thermal fuse 64 is connected in series to the halogen lamp 43.

Next, a description will be given of a processing structure of heat generated during the heat fixing operation in the case of the fixing unit 4 and steam generated by evaporating moisture contained in the sheet P.
In the first embodiment, the heating roller 15 and the pressing roller 1
6 and a transport path 7 between a fixing unit consisting of a paper discharge roller 17 and a pinch roller 18 on the downstream side thereof.
In order to narrow at least the upper space of the upper case 41, the lower surface of the upper side wall of the upper case 41 is formed so as to approach the upper side of the transport path 70. As an example thereof, as shown in FIGS. 3, 5, 6, and 8, a fixing portion including a heating roller 15 and a pressing roller 16, Discharge roller 17 on the downstream side
It is formed in a downwardly convex shape so as to narrow the upper space of the transport path 70 between the paper discharge unit including the pinch roller 18 and the paper discharge unit.

As described above, if the upper space of the transport path 70 is narrowed as appropriate, the air heated by the heat from the heating roller during the heat fixing operation or the paper P
The volume of the space above the transport path 70 in the fixing unit case in which the steam generated from the toner accumulates is reduced, and the transport path 7
0 is not exposed to the high-temperature and high-humidity atmosphere in the space. As a result, the paper P does not become swollen or absorb excess water vapor again. The occurrence of curling and the like when cooled is eliminated.

If the upper side wall of the middle part of the upper case 41 is formed in a downwardly convex shape as described above, the inconvenience described above is solved and the rigidity of the upper case 41 is increased. Since the thickness of the wall can be set to be thin, the weight can be reduced and the material cost can be reduced. Then, of the downwardly protruding portions, the substantially vertical wall body 41a is moved to the pressing roller 16 above the fixing portion.
It is formed so as to approach the outer peripheral surface of. With this configuration, the volume of the space in which high-temperature and high-humidity air should be stored can be reduced as much as possible in the outer peripheral portion of the pressing roller 16. Further, as described above, the upper wall body in the middle part of the upper case 41 is formed to be curved downwardly convexly,
A steam release hole 71 for allowing steam generated in the fixing portion to escape to the outside is formed in a portion near the upper portion of the substantially vertical wall 41a on the side close to the outer peripheral surface of the pressing roller 16.
Are provided in the width direction. With this configuration, the volume of the space in which the high-temperature and high-humidity air is to be stored can be reduced as much as possible in the outer peripheral portion of the pressing roller 16 and the thickness of the wall 41a is small.
The length of the path is also shortened, and the generated high-temperature and high-humidity air can be quickly discharged to the outside through the vapor escape hole. As a result, the paper P is not burned by the high-temperature and high-humidity air, and does not absorb the excess water vapor again. In addition, it is possible to more efficiently eliminate the occurrence of curl or the like when the discharged paper P is cooled by the discharge.

In the illustrated embodiment, the upper case 41
The downwardly protruding portion in the middle part is a water droplet reservoir 73, and the water droplet reservoir 7 on the lower surface of the top cover 7.
The guide ribs 74 are provided so as to protrude downward substantially above and below the right and left sides (see FIG. 3). With this configuration, even if water that has condensed and formed on the lower surface of the top cover 7 flows along the lower surface of the top cover 7, it is blocked by the guide ribs 74 and does not hang down to the paper discharge side. It is possible to guide the water drops to drop and accumulate at the portion 73 without fail. Since the location of the water drop reservoir 73 is close to the upper surface of the heating roller 15 and has a high temperature, the effect of evaporating water in the water droplet reservoir 73 can be promoted. Further, the weakening of the strength at the discharge holes 72 formed in the top cover 7 can be reinforced by the guide ribs 74.

The top cover 7 as an openable / closable main body cover that covers the upper part of the process unit 3 and the fixing unit 4 also has a discharge hole for discharging the vapor discharged from the vapor release hole 71 to the outside of the printer. 72 for paper P
(Many) are pierced along the width direction of FIG.
See). According to this structure, the steam generated in the fixing section of the fixing unit 4 rides on the rising airflow to the wall 41.
Since the air is immediately exhausted from the fixing unit 4 through the vapor release hole 71 a and then discharged out of the apparatus through the discharge hole 72, no vapor is accumulated in the case of the fixing unit 4 and no dew is formed on the inner surface of the upper case 41. In addition, it is possible to eliminate inconveniences such as excess moisture being re-absorbed in the sheet P reaching the sheet discharging section from the fixing section through the transport path 70, and water droplets falling on the surface of the sheet P and getting wet.

As another embodiment, the direction of the opening of the steam release hole 71 formed at the upper portion of the wall 41a which is close to the outer peripheral surface of the pressing roller 16 at the upper position in the downward convex portion is exhausted. The opening direction of the discharge hole 72 in the top cover 7, such as the paper direction, is different from the opening direction (upward). Alternatively, the flow path of the steam from the steam release hole 71 to the discharge hole 72 is curved. With this configuration, when the sheet P is heated and pressed while being nipped and conveyed by the heating roller 15 and the pressing roller 16, steam generated from the steam release hole 71 and directed to the exhaust hole 72 is once directed in a horizontal direction or the like. As a result, the passage temperature increases, and the steam temperature decreases during that time. Therefore, as in the case where the steam passes through the shortest distance and is discharged from the discharge hole 72, high-temperature steam is urged from the discharge hole 72 of the top cover 7. Steam or mist when it comes out well
There is nothing that looks like.

As another embodiment, as shown in FIG. 3, a long exhaust hole 75 is formed on the wide surface of the paper discharge tray 8 along the width direction of the paper P. With this configuration, even when an image is formed and discharged so that the paper discharge tray 8 covers the upper part of the top cover 7, vapor is accumulated in the space between the paper discharge tray 8 and the top cover 7. It can be prevented.

Further, as shown in FIG. 3, at a position above the case 34 of the process unit 3, that is, on the downstream side of the sheet feeding unit 5 with respect to the sheet conveyance, a moisture absorbing member 76 such as a sponge material is widened on the lower surface of the top cover 7. It is arranged over a range, or longer in the width direction of the paper P, and appropriately over the width in the transport direction of the paper P. According to this configuration, the vapor flowing toward the sheet feeding unit 5 along the lower surface of the top cover 7 can be captured by the moisture absorbing member 76 such as a sponge material, and water droplets are formed on the surface of the sheet P fed from the sheet feeding unit 5. It can be prevented from falling.

Further, when the cooling air from the ventilation duct 37 is raised between the process unit 3 and the fixing unit 4 and is guided to be discharged out of the apparatus through the exhaust hole 40 of the top cover 7, the cooling air exits from the fixing unit. The function of an air curtain that prevents steam from flowing in the direction of the process unit 3 (the direction of the sheet feeding unit 5) can also be exhibited. Next, with reference to FIGS. 9, 12, and 13, a description will be given of a curl removing mechanism of the leading end portion of the sheet P discharged from the fixing unit in the fixing unit 4. FIG.

When a pressing roller 16 covered with a rubber layer is pressed against a heating roller 15 of a metal cylinder, both rollers 1
Pressed portions of paper P by nips 5 and 16 (nip portion 80)
Then, the circumferential surface of the pressing roller is deformed, and the paper P curls along the circumferential surface of the heating roller 15. However,
Due to the stiffness (elasticity of the paper) of each paper P, the leading end of the paper P separates from the circumferential surface of the heating roller 15 at a predetermined position protruding from the nip 80 to the discharge side. Such peeling is called spontaneous peeling or elastic peeling, and a peeling claw is arranged near the nip 80, and the leading end of the paper P wound around the circumferential surface of the heating roller 15 at the leading end of the peeling claw. It is distinguished from one that forcibly peels off the edge (forced peeling).

As described above, the heat roller 1 extends along the transport direction of the sheet P on the leading end of the sheet P that has been spontaneously peeled off.
The curl having a concavely curved shape on the fifth side is discharged. Therefore, a plurality of guide ribs 82 as transport guide members are arranged on the discharge side, and each of the guide ribs 82
When guiding the leading end of the paper P discharged from the upper end surfaces (guide surfaces) 82a and 82b of the paper P to the paper discharge portion including the paper discharge roller 17 and the pinch roller 18 while slidingly supporting the same,
In the section on the heating roller 15 side and at a predetermined distance L from the nip portion 80, the guide surfaces 82a and 82b, which are the upper end surfaces of the guide ribs 82, are bent in the first curl direction of the leading end of the sheet P in a side view ( (In the embodiment, the shape is convex upward)
The sheet P is formed on a curved surface (a downwardly convex curved shape) in the direction opposite to that of the sheet P so as to intersect with the transport direction of the sheet P (see FIG. 9).

With this configuration, the nip 80
The leading edge of the paper P pushed out from the guide ribs is a free end, and when sliding on the guide surfaces 82a and 82b of the respective guide ribs 82, the paper P tends to bend due to strong frictional resistance. In this case, the bending direction is opposite to the initial curl direction of the sheet P, so that the curled portion at the leading end of the sheet P is in a solid line state (initial curl state, spontaneous peeling) in FIG. State), the curling radius of the curl increases as indicated by a two-dot chain line, and is finally repaired (corrected) so as to be substantially linear as indicated by a one-dot chain line. That is, the guide rib 8
Forming the guide surfaces 82a, 82b on the curved surface of the leading end of the sheet P in a direction opposite to the curl direction of the first curl at the leading end of the sheet P is better than the case where the second guide surfaces 82a, 82b are linear. This is because the effect of setting the bending direction of the leading end portion in a direction opposite to the bending direction of the first curl of the leading end portion of the sheet P becomes stronger.

The second embodiment of the curl removing mechanism for the leading end of the sheet P has a guide surface (upper end surface) with which the leading edge of the sheet P as a recording medium slides on the discharge side of the heating roller 15. Guide rib 82 as a conveyance guide member
Are arranged at appropriate intervals in the conveying width direction of the paper P (many). At this time, as shown in FIG. 9, the height position of the guide surface (upper end surface) 82a of the guide rib 82 at the left and right end positions in the transport width direction of the paper P is set to the discharge side (nip portion 80) from the heating roller 15. On the near side, the height is set to be higher than the height position of the guide surface (upper end surface) 82b of the guide rib 82 near the center in the conveyance width direction of the paper P.

The reason is as follows. That is, in the illustrated embodiment, for example, if both rollers 15 and 16 have the same diameter from both left and right ends to the center (there is no crown), both rollers 15 and 16 are supported at both ends (pressurized). , The paper P by both rollers 15 and 16
As shown in FIG. 13, the width of the nip 80 is narrow at the center in the longitudinal direction of the rollers 15 and 16 and wide at both left and right ends. Then, as shown in FIG. 12, in the state where the paper P is naturally separated, the curvature radius R2 of the upward convex curl along the circumferential surface of the heating roller 15 at the central portion in the width direction of the paper P is large, and The curvature radius R1 of the curl having the upward convex curl along the circumferential surface of the heating roller 15 at both left and right ends in the width direction becomes smaller.
Thereby, the radius of curvature R3 of the curl at the leading end along the width direction of the paper P can also be obtained.

Therefore, the correction of the tight curl at the left and right ends in the width direction of the sheet P, which is the one having the smaller curvature radius R1 of the curl, is compared with the correction of the loose curl at the central portion in the width direction of the sheet P. The height position of the guide surface 82a in the guide ribs 82 at the left and right ends in the transport width direction of the paper P is determined by the transport of the paper P in order to start early after the leading edge of the paper P is pushed out from the nip portion 80. The height is set so as to be higher than the height position of the guide surface 82b of the guide rib 82 at the position near the center in the width direction (see FIGS. 9 and 12).

Although only three guide ribs 82 are shown in FIG. 12 for simplicity, the paper P
A large number of guide ribs 82 are formed integrally with the lower case 42 at intervals of about 1 cm along the conveying width direction. Further, when the dimension from the center position in the transport width direction of the paper P to the left and right end positions is 10 cm, the guide surface 82a of the guide rib 82 at the left and right end positions in the transport width direction of the paper P, and the guide rib near the center portion 1 to 2 m at the largest portion due to the difference in height from the guide surface (upper surface) 82b at 82
m. It is also desirable that the height of the guide ribs 82 be gradually increased from the center position in the transport direction of the paper P to the left and right ends.

With this configuration, the leading edge of the sheet P at both left and right sides in the width direction starts sliding first at a position close to the guide surface 82a of the guide rib 82 at the left and right end positions at a position close to the nip portion 80. The paper P is subjected to the curl removal (curl correction) action over a section longer than the distance at which the leading edge at the left and right central portion in the width direction of the P slides on the guide surface 82b of the guide rib 82 at the left and right central portion. Correction of tight winding habits on both left and right sides in the width direction can be surely executed. At this time, the guide surfaces 82a, 82 of the respective guide ribs 82
Since b is formed on the curved surface in the direction opposite to the curl direction of the paper P, the above-described bending action can be received at the leading edge of the paper P along the width direction of the paper P, and the curl of the paper P Can be corrected.

In each of the above embodiments, the heating roller 1
5 is disposed below the pressing roller 16. Therefore, each guide rib 82 is disposed below the nip portion 80. However, when the heating roller 15 is disposed above the pressing roller 16, the guide rib 82 Of course, the guide surfaces 82a, 8a of the guide ribs 82 as in the above-described embodiments.
2b.

The toner image forming means of the present invention transfers the toner image from the photoreceptor drum 23, and also has a back electrode which faces a number of openings in a direction intersecting the sheet conveying direction in the electrode array. Is disposed, and the toner is selectively applied to the surface of the recording medium passing between the opening and the back electrode by applying a voltage to the aperture electrode body associated with each opening based on image data. There is a type in which a toner image is formed by directly moving through an opening.

[0041]

As described above, the transport guide device in the image forming apparatus according to the first aspect of the present invention includes a toner image forming means for forming a toner image on a recording medium such as a sheet to be transported, A conveyance guide device for guiding a leading end of a heat-fixed recording medium in an image forming apparatus including a fixing unit having a heating roller and a pressing roller for heating and fixing the toner image on a recording medium, On the discharge side of the heating roller, a plurality of conveyance guide members for guiding the recording medium discharged are arranged at least at both ends and substantially at the center in the conveyance width direction of the recording medium at appropriate intervals, and the conveyance is performed. The guide surface of the guide member, at which the leading end of the recording medium discharged from the heating roller is in sliding contact , is
An object to be discharged from the nip between the heating roller and the pressing roller
Formed on the curved surface in the direction opposite to the curl direction of the recording medium,
The height position of the guide surface, on the side closer to the discharge side of the heating roller, so towards the left and right end side of the conveying width direction of the recording medium is higher than the central portion side of the conveying width direction of the recording medium It is set.

With this configuration, the heating roller and the fixing
Tip of recording medium pushed out from nip with roller
The edge is a free end, and it is on the side near the discharge side from the heating roller.
When sliding on the guide surface of each transport guide member
And tends to bend under strong frictional resistance. Deflection in that case
Is the first curl of the leading end of the recording medium
Curl) in the opposite direction to the direction of curvature.
The curved portion of the curl in the transport direction at the leading end of the recording medium is
The radius of curvature gradually increases from the initial curled state,
Is corrected so that it is almost linear,
This has the effect that the curl in the transport direction can be reliably removed.
Because

Further , the height position of the guide surface is determined by
The left and right sides of the recording medium in the transport width direction
Is set higher than the center of the transport width direction.
Therefore, by this, the left side in the width direction of the recording medium is
The degree of curl at the end on the right side is the recording medium
Of the curl at the tip of the center part in the width direction
In some cases, the leading edge at both left and right ends in the width direction of the recording medium
Are the transport guides at the left and right ends of the recording medium in the transport direction.
Slides first on the guide surface of the
It can be affected by the section bending action longer than the center edge.
As a result, the entire width of the leading end of the recording
This has the effect that the curl removal can be performed reliably.
I do.

Further, the invention described in claim 2 is the same as that in claim 1
Wherein the fixing means has a fixing unit case that houses the heating roller and the pressing roller, and the conveyance guide member is formed integrally with the fixing unit case. It is. Therefore, by forming the conveyance guide member integrally with the fixing unit case, the manufacturing process can be simplified, and since the heating roller and the pressing roller may be housed in the fixing unit case, the assembly process can be simplified. It works.

[Brief description of the drawings]

FIG. 1 is a perspective view of main components of a laser printer.

FIG. 2 is a schematic sectional view of a laser printer.

FIG. 3 is a sectional side view of a main part of the fixing unit.

FIG. 4 is a sectional view taken along line IV-IV of FIG.

FIG. 5 is a partially cutaway plan view of the fixing unit.

FIG. 6 is a sectional view taken along line VI-VI of FIG. 5;

7 is a sectional view taken along the line VII-VII in FIG. 5;

FIG. 8 is a partially cutaway perspective view of a fixing unit case.

FIG. 9 is an enlarged sectional view taken on line IX-IX of FIG. 5;

FIG. 10 is an enlarged sectional view taken on line XX of FIG. 5;

11A is an enlarged plan view of a mounting portion of a thermal fuse, and FIG. 11B is an enlarged sectional view of a mounting portion of a thermal fuse.

FIG. 12 is a perspective view illustrating a curl removing operation of a guide rib.

FIG. 13 is a plan view illustrating a width dimension of a nip portion formed by a heating roller and a pressing roller.

[Explanation of symbols]

 P paper 1 Laser printer main body case 2 Scanner unit 3 Process unit 4 Fixing unit 5 Feed unit 6 Drive system unit 7 Top cover 8 Discharge tray 15 Heat roller 16 Press roller 17 Discharge roller 18 Pinch roller 23 Photoconductor drum 41 Upper case 41a Wall 42 Lower case 43 Halogen lamp 70 Transport path 71 Vapor escape hole 72 Exhaust hole 73 Water drop part 80 Nip part 82 Guide rib 82a, 82b Guide surface

Continuation of front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G03G 15/20

Claims (2)

(57) [Claims] An image forming apparatus includes: a toner image forming unit configured to form a toner image on a recording medium such as a sheet of paper conveyed; and a fixing unit including a heating roller and a pressing roller configured to heat and fix the toner image on the recording medium. A conveyance guide device for guiding a leading end of a recording medium heated and fixed in the image forming apparatus, wherein a conveyance guide member for guiding a recording medium discharged on a discharge side of the heating roller. A plurality of recording media are disposed at least at both ends and a substantially central portion in the conveying width direction of the recording medium at appropriate intervals, and the guide surface of the conveyance guide member, on which the leading end of the recording medium discharged from the heating roller slides , is heated. B
Recording medium discharged from the nip between the roller and the pressing roller
Of forming the curved surface of the bending direction opposite to the direction of curl, the height position of the guide surface, on the side closer to the discharge side of the heating roller, is towards the left and right end side of the conveying width direction of the recording medium, the A conveyance guide device in an image forming apparatus, wherein the conveyance guide device is set to be higher than a position near a central portion in a conveyance width direction of a recording medium. 2. A fixing device comprising :
A fixing unit case for accommodating the rollers and
A feeding guide member is formed integrally with the fixing unit case.
The conveyance guide device in the image forming apparatus according to claim 1, wherein: