JP5240099B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus having a function of printing on both sides of a recording sheet, and more particularly to a technique for preventing the occurrence of condensation on rollers provided in a paper feed path used when reversing the front and back of a sheet.

2. Description of the Related Art Image forming apparatuses such as copiers are widely used that have a double-sided printing function for printing on both sides of a recording sheet by performing toner image transfer and thermal fixing on the first and second sides of the recording sheet. ing.
In an image forming apparatus having such a double-sided printing function, the front and back sides of the recording sheet on which the heat fixing of the toner image on the first surface is completed are reversed, and then the recording sheet is transferred to a fixing device in which the thermal fixing is performed. A refeed mechanism is provided.

FIG. 8A and FIG. 8B are diagrams showing a conventional configuration of such a refeed mechanism.
In the normal printing (single-sided printing), the image forming apparatus having the double-sided printing function heat-fixes the toner image formed on the first surface of the recording sheet S by the fixing device 1005, and then the image forming apparatus shown in FIG. In this manner, the recording sheet S is discharged onto the discharge tray 1072 via the discharge roller pair 1073 via the discharge conveyance path 1007a.

Above the pair of paper discharge rollers 1073, a switchback roller pair 1071 is disposed substantially in parallel with the pair of paper discharge rollers. When the tip of the switching guide plate 1074 is tilted upward, the pair of paper discharge rollers 1073 When inclined downward, the conveyance path is switched so that the recording sheet is guided to the switchback roller pair 1071.
In the case of duplex printing, as shown in FIG. 8B, by changing the inclination of the switching guide plate 1074 provided in the middle of the paper discharge conveyance path 1007a, The recording sheet S on which the thermal fixing of the toner image has been completed is guided to the switchback roller pair 1071, and the switchback roller pair 1071 sends out a predetermined length of the recording sheet to the outside, and then the rotation of the roller is reversed to switch Let me back.

The recording sheet S is re-fed to a transfer position (not shown) via the re-feed path 1008a in a state where the front and back sides are reversed, and the toner image is transferred to the second surface.
After that, heat fixing is performed by the fixing device 1005, and the recording sheet S is discharged onto the discharge tray 1072 by returning the switching guide plate 1074 to the original position as shown in FIG. Complete.

By the way, when the recording sheet S passes through the fixing device 1005, some of the moisture contained in the recording sheet S is released as water vapor by heating.
Since the switching guide plate 1074 is normally located at the position shown in FIG. 8A, most of the water vapor is discharged outside the apparatus through the discharge conveyance path 1007a together with the conveyance of the recording sheet S. The water vapor passes through the gap 1074d near the rotation shaft 1074c of the switching guide plate 1074 and reaches the switchback roller pair 1071.

Since the switchback roller pair 1071 is not used except during double-sided printing, the temperature is lower than that of the paper discharge transport path 1007a and the paper discharge roller pair 1073 through which the high-temperature recording sheet frequently passes. When water vapor comes into contact with the pair 1071, condensation occurs and adheres to the roller surface as shown in FIG.
When dew condensation occurs in this way, water droplets adhere to the recording sheet S when the switchback roller pair 1071 switches back during the next double-sided printing, and the fixing quality of the second side is degraded or re-feeding. This causes a jam in the paper path 1008a.

  Therefore, for example, by applying the technique disclosed in Patent Document 1, a plate-like elastic member 1075a extending in the direction perpendicular to the paper surface is provided on another member 1075 provided near the rotation shaft 1074c of the switching guide plate 1074. It is conceivable that the water vapor does not reach the switchback roller pair 1071 by providing the tip portion against the surface of the rotating shaft 1074c and closing the gap 1074d.

JP 2001-324885 A

However, when the above configuration is applied, since the elastic member 1075a is pressed against the rotation shaft 1074c, friction acts between them, and the switching guide plate 1074 cannot be rotated smoothly. Depending on the assembling error, the pressing force becomes too large, and a switching operation cannot be performed.
The present invention has been made in view of the above problems, and is an image that suppresses the inflow of water vapor into a refeed path, particularly a switchback roller pair, while ensuring a smooth operation of the switching guide plate. An object is to provide a forming apparatus.

  In order to achieve the above object, an image forming apparatus according to the present invention reverses the recording sheet on which an unfixed image on the first surface is fixed by a fixing device, and re-feeds the recording sheet to the image forming position. An image forming apparatus capable of forming an image on the surface, a discharge roller for discharging a recording sheet onto a discharge tray, and a part of the recording sheet are sent out of the apparatus, and then switched back to be re-feeded. A switchback roller that feeds the path, and a recording sheet that has passed through the fixing device by changing the posture thereof, a first transport path toward the discharge roller, and a second transport toward the switchback roller. A switching guide plate that switches to and guides the path, and a partition member that is interposed between the switching guide plate and the first transport path, and the opposing portion of the switching guide plate and the partition member includes: To each other When the extending shielding members are erected in a non-contact state and the switching guide plate is in a posture to guide the recording sheet to the first conveyance path, the switching guide plate and the partition member are shielded. The members are configured such that at least part of the members overlap each other when viewed from the upstream side in the conveyance direction of the recording sheet in the first conveyance path.

  By configuring the shielding member as described above, the flow of water vapor from the fixing device to the switchback roller is blocked. As a result, the amount of water vapor reaching the switchback roller can be reduced, and the amount of dew condensation that occurs can be significantly reduced as compared with the prior art. Further, since the shielding members are not in contact with each other, there is no problem in smooth switching of the conveyance path by the switching guide plate.

The switching guide plate may be pivotally supported by the apparatus main body, and the shielding member on the switching guide plate side may be provided closer to the rotating shaft of the switching guide plate.
By providing the shielding member closer to the rotation axis of the switching guide plate, it is possible to reduce the amount of movement of the shielding member accompanying the change in the posture of the switching guide plate, so even if the gap between the shielding members is set narrower, There is no contact between the two due to the turning operation. As a result, the amount of water vapor flowing from the fixing device to the switchback roller can be blocked more.

Furthermore, when the switching guide plate is in a first posture that is inclined to guide the first conveyance path, and is in a second posture that is inclined to be guided to the second conveyance path, The shielding member of the switching guide plate may be formed at a position where the distance from the partition member is reduced when the second posture is shifted to the first posture.
Furthermore, a refeed guide member for guiding the recording sheet switched back by the switchback roller to the refeed path is located at a position facing the switching guide plate across the second transport path. And the switching guide plate is inclined toward the second conveyance path to guide the recording sheet to the first conveyance path, and a part of the switching guide plate is the refeed guide member. And the shapes of the refeed guide member and the switching guide plate are determined so that the facing surfaces of the switching guide plate and the refeeding guide member at the proximity portion are substantially parallel to each other. Good.

As a result, the amount of water vapor flowing through the gap between the switching guide plate and the refeed guide member can be suppressed to a sufficiently low level.
Here, a refeed guide member for guiding the recording sheet switched back by the switchback roller to the refeed path is disposed at a position facing the switching guide plate across the second transport path. The switching guide plate is inclined toward the second conveying path to guide the recording sheet to the first conveying path, and a part of the switching guide plate is used as the re-feeding guide member. A cross-sectional shape of a portion of the facing surface of the switching guide plate and the refeeding guide member that is orthogonal to the rotation axis of the discharge roller in the proximity portion is a predetermined distance between the facing surfaces. It may be bent while maintaining the gap.

As a result, the flow path of the gap in the adjacent portion is bent, and the flow path resistance of the gap is increased accordingly, so that the amount of water vapor reaching the refeed path via the gap can be further reduced.
Further, when the switching guide plate is tilted toward the second conveyance path to guide the recording sheet to the first conveyance path, a part of the switching guide plate of the refeed guide member approaches. A sheet-like elastic member may be attached to the part, and a part of the switching guide plate may be in contact with the re-feeding guide member via the elastic member.

  As a result, it is possible to close a gap in a portion where the refeed guide member and a part of the switching guide plate are close to each other, and to reduce the collision noise between the refeed guide member and the switching guide plate.

1 is a diagram illustrating a schematic configuration of a tandem-type full-color printer according to an embodiment. (A) And (b) is a figure which shows the operation state of the conveyance path switching part in this Embodiment. It is a partial notch perspective view of the conveyance path switching part concerning this Embodiment. (A) And (b) is a figure which shows the operation state in the 1st modification of the conveyance path switching part which concerns on this Embodiment. (A) And (b) is a figure which shows the operation state in the 2nd modification of the conveyance path switching part which concerns on this Embodiment. (A) And (b) is a figure which shows the operation state in the 3rd modification of the conveyance path switching part which concerns on this Embodiment. (A) And (b) is a figure which shows the operation state in the 4th modification of the conveyance path switching part which concerns on this Embodiment. (A) And (b) is a figure which shows the operation state of the conventional conveyance path switching part.

Hereinafter, an image forming apparatus according to an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram illustrating a schematic configuration of a tandem type full-color printer according to the present embodiment.
As shown in FIG. 1, the printer 1 includes an image processing unit 3, a paper feeding unit 4, a fixing device 5, a conveyance path switching unit 7, a refeeding path 8, and a control unit 60. When a print job execution instruction is received from an external terminal device (not shown), a toner image composed of yellow, magenta, cyan, and black is formed based on the instruction, and these are transferred in multiples. Then, full-color image formation is executed.

Hereinafter, the reproduction colors of yellow, magenta, cyan, and black are represented as Y, M, C, and K, and Y, M, C, and K are added as subscripts to the numbers of the components related to the reproduction colors.
<Image process part>
The image processing unit 3 includes image forming units 3Y, 3M, 3C, and 3K corresponding to each of Y to K colors, an optical unit 10, an intermediate transfer belt 11, and the like.

The image forming unit 3Y includes a photosensitive drum 31Y, a charger 32Y, a developing unit 33Y, a primary transfer roller 34Y, a cleaner 35Y for cleaning the photosensitive drum 31Y, and the like disposed around the photosensitive drum 31Y. A Y-color toner image is formed on the drum 31Y.
The other image forming units 3M to 3K have the same configuration as the image forming unit 3Y, and the reference numerals are omitted in FIG.

The intermediate transfer belt 11 is an endless belt, is stretched around a driving roller 12 and a driven roller 13 and is rotationally driven in the direction of arrow C.
The optical unit 10 includes a light emitting element such as a laser diode, emits a laser beam L for forming an image of Y to K colors by a drive signal from the control unit 60, and exposes and scans the photosensitive drums 31Y to 31K.

By this exposure scanning, electrostatic latent images are formed on the photosensitive drums 31Y to 31K charged by the chargers 32Y to 32K.
The electrostatic latent images are developed by developing units 33Y to 33K, and Y to K color toner images are superimposed on the same positions on the intermediate transfer belt 11 and primarily transferred onto the photosensitive drums 31Y to 31K. It is executed at different timings.

The toner images of the respective colors are sequentially transferred onto the intermediate transfer belt 11 by the electrostatic force acting on the primary transfer rollers 34Y to 34K to form a full-color toner image, and further move toward the secondary transfer position 46.
On the other hand, the paper feed unit 4 includes a paper feed cassette 41 that stores the recording sheets S, a feed roller 42 that feeds the recording sheets S in the paper feed cassette 41 one by one onto the transport path 43, and a fed recording sheet S. Are provided with a timing roller pair 44 for taking the timing of feeding the toner to the secondary transfer position 46, and the recording sheet S is transferred from the paper feeding unit 4 to the secondary transfer position in accordance with the movement timing of the toner image on the intermediate transfer belt 11. The toner images on the intermediate transfer belt 11 are collectively transferred onto the recording sheet S by the action of the secondary transfer roller 45.

The recording sheet S that has passed the secondary transfer position 46 is conveyed to the fixing device 5, and the toner image (unfixed image) on the recording sheet S is fixed to the recording sheet S by heating and pressurization in the fixing device 5. After that, it is transported to the transport path switching unit 7.
The various rollers in the present embodiment are driven by a single or a plurality of driving sources via a predetermined driving mechanism, but these mechanisms are not shown because they are known.

<Fixing device>
The fixing device 5 includes a fixing roller, a pressure roller, and a casing 5a that accommodates both the rollers. The recording sheet S is passed through a fixing nip formed between the two rollers. The toner image is fixed.
At this time, moisture contained in the recording sheet S is heated and released as water vapor.

The water vapor flows into the conveyance path switching unit 7 through the recording sheet outlet hole 5b and the fixing unit outlet path 7b provided in the housing 5a.
Here, the fixing device outlet path 7b is a conveyance path of the recording sheet S from the recording sheet outlet hole 5b to a switching guide plate 74 described later.
<Refeed path>
The refeed path 8 is provided with conveyance roller pairs 81, 82, 83, and 84, which are guided to the timing roller pair 44 by these roller pairs.

Here, a portion existing around the transport path switching unit 7 of the refeed path 8 is indicated by reference numeral 8a.
<Conveyance path switching unit>
As shown in FIG. 1, the conveyance path switching unit 7 rotates the switching guide plate 74 within the range indicated by the arrow A to change the inclination, so that the recording sheet S that has passed through the fixing device 5 is discharged into the discharge roller pair 73. And a paper refeeding conveyance path 7c for guiding to a pair of switchback rollers (hereinafter abbreviated as “SB roller pair”) 71.

2A and 2B are cross-sectional views showing the operation of the transport path switching unit 7 according to the present embodiment. FIG. 3 shows only the transport path switching unit 7 in FIG. It is a partial notch perspective view when it sees from diagonally right above of FIG.
As shown in FIG. 2A, the transport path switching unit 7 includes a pair of SB rollers 71, a pair of discharge rollers 73 provided below the pair, a switching guide plate 74, a partition member 75, and a transport for discharge. A path guide 76, a refeed path guide member 80, and the like.

  As shown in FIG. 2B, the SB roller pair 71 sandwiches the recording sheet S2 on which the thermal fixing of the toner image on one side is completed and rotates forward (upward clockwise, lower counterclockwise) to obtain a predetermined Discharge out of the machine for the length. At the timing when the rear end of the recording sheet S2 passes through the gap between the re-feed path guide member 80 and the frame portion 74a, the recording sheet S2 is reversed (upper counterclockwise, lower clockwise) as shown in FIG. By executing a switchback operation and sending it out to the refeed path 8a, the front and back of the recording sheet S2 are reversed.

The discharge conveyance path guide 76 is a member that guides the recording sheet S1 from the fixing device outlet path 7b to the discharge roller pair 73.
The partition member 75 is located close to the discharge roller pair 73 and is provided between the discharge conveyance path 7a and the switching guide plate 74, and the heat flow or water vapor generated in the fixing device 5 flows upward. Is to prevent.

The partition member 75 has a deformed U shape whose cross section is widened upward, and is held by a body frame (not shown) in a state of being arranged in a direction substantially parallel to the shaft of the discharge roller pair 73.
Further, the partition member 75 includes a bottom surface portion 75b facing the main surface of the frame portion 74a of the switching guide plate 74, a curved portion 75c curved along a part of the peripheral surface of the upper roller of the discharge roller pair 73, and The first shielding member 75a extends toward the main surface of the switching guide plate 74.

The switching guide plate 74 is pivotally supported on a main body frame (not shown) by a turning shaft 74c, and is turned by a driving source (not shown) such as a solenoid, so that the tip on the fixing device 5 side. Can be switched between a first posture (FIG. 2 (a)) moved upward and a second posture (FIG. 2 (b)) moved downward.
The switching guide plate 74 includes a plate-like frame portion 74a and a plurality of guide panel portions 74b provided in a direction orthogonal to the plate-like frame portion 74a (see FIG. 3). The ridge line portions of the plurality of guide panel portions 74b serve to guide and contact the recording sheets S1 and S2.

When the switching guide plate 74 is in the first posture, the paper discharge transport path 7a extending from the fixing device outlet path 7b to the discharge roller pair 73 is formed, and is in the second posture. Then, a re-feeding conveyance path 7c extending from the fixing device outlet path 7b to the SB roller pair 71 is formed.
Further, the frame portion 74a of the switching guide plate 74 flows into the refeeding conveyance path 7c where the SB roller pair 71 is provided even if water vapor is discharged onto the fixing device outlet path 7b and the discharge conveyance path 7a. It also functions as a shielding plate that suppresses this.

A plate-like second shielding member 74 d and a third shielding member 74 e are erected on the surface of the frame portion 74 a facing the partition member 75 so as to extend toward the partition member 75. Both shielding members 74d and 74e extend in parallel to the roller axial direction.
Here, at least when the switching guide plate 74 is in the first posture (FIG. 2A), the second shielding member 74d is located between the curved portion 75c of the partition member 75 and the first shielding member 75a. The position and height of each member are set so that the first shielding member 75a of the partition member 75 enters between the second shielding member 74d and the third shielding member 74e.

As shown in FIG. 2A, when the switching guide plate 74 is in the first posture and is switched to the paper discharge transport path 7a, recording in the paper discharge transport path 7a is performed on the paper discharge transport path 7a. When viewed from the front side (upstream side) of the sheet S1, the length L1 of the portion where the second shielding member 74d and the first shielding member 75a overlap is set to a range of, for example, 3 mm or more and 8 mm. Yes.
At this time, the gap D1 between the second shielding member 74d and the first shielding member 75a in the overlapping portion is not interfered even in the second posture (see the gap D4 in FIG. 2B). ), It is necessary to take some allowance in consideration of component accuracy, assembly error, etc. On the other hand, if the gap D1 is too large, the effect of suppressing the inflow of water vapor is lost, so the range is set to 1 mm or more and 2 mm or less. It is desirable to do. Moreover, it is desirable to set the gap D2 in the range of 1 mm or more and 3 mm or less.

When the length L2 of the portion where the first shielding member 75a and the third shielding member 74e overlap when viewed from the front of the recording sheet S1 in the sheet discharge conveyance path 7a is also switched to the second posture. It is desirable to make it as large as possible without touching the other party.
In addition, convex portions (not shown) project at the positions of both ends of the lower surface of the refeed path guide member 80 in the roller axial direction, respectively, and when the switching guide plate 74 is rotated and the front end side is inclined upward, The convex portion comes into contact with the frame portion 74a and is positioned in the first posture.

Further, when the switching guide plate 74 is in the second posture, the distal end portion of the guide panel portion 74b that sandwiches the acute angle comes into contact with the bottom surface of the paper delivery path guide 76, and the stationary position is determined. It has become.
<Effects of the first to third shielding members>
As described above, the switching guide plate 74 and the partition member 75 are provided with the first shielding member 75a, the second shielding member 74d, and the third shielding member 74e that alternately extend toward the opposing surface of the other party. In the state where the switching guide plate 74 is in the first posture and is switched to the paper discharge transport path 7a (see FIG. 2A), the recording sheet S1 is transported forward in the paper discharge transport path 7a. Since the second shielding member 74d and the third shielding member 74e overlap with the first shielding member 75a when viewed from the (upstream side), water vapor generated in the vicinity of the fixing device 5 is used for discharging paper. There are many barriers between the flow along the conveyance path 7a and the SB roller pair 71, and the gaps between the second shielding member 74d and the third shielding member 74e and the first shielding member 75a are narrow and bent. The channel length is Therefore, the flow path resistance with respect to the water vapor passing through the gap between the frame portion 74a and the partition member 75 increases, and most of the water vapor passes through the paper discharge conveyance path 7a with a small flow path resistance. It flows out from the 73 side and does not reach the SB roller pair 71 side.

Therefore, as the gaps D1 and D2 are reduced and the lengths L1 and L2 are increased, the effect of reducing the amount of water vapor reaching the SB roller pair 71 and the refeed path 8a increases.
If the water vapor reaching the SB roller pair 71 and the refeed path 8a decreases, condensation does not occur, and even if condensation occurs, it is suppressed to such an extent that fixing quality is not deteriorated and jamming is not affected. be able to.

Further, according to this configuration, the second shielding member 74d, the third shielding member 74e, and the first shielding member 75a can prevent the inflow of water vapor toward the SB roller pair 71 in a non-contact state. Therefore, there is no problem in the smooth rotation operation of the switching guide plate 74.
<Modification>
The present invention is not limited to the above-described embodiment, and the following modifications can be implemented.

(1) In the above embodiment, the two plate-shaped members of the second shielding member 74d and the third shielding member 74e are erected from the switching guide plate 74. However, the present invention is not limited to this. There may be one.
In that case, it is desirable to leave the second shielding member 74d on the side closer to the rotation shaft 74c of the switching guide plate 74.

This is because the second shielding member 74d located closer to the rotation shaft 74c has a smaller movement amount due to the rotation, and thus the dimension between the first shielding member 75a and the second shielding member 74d. This is because the accuracy can be set high, and the gap D1 between the shielding members 74d and 75a can be easily reduced.
(2) In the above embodiment, both the second shielding member 74d and the third shielding member 74e of the switching guide plate 74 are provided closer to the fixing device 5 than the rotation shaft 74c. It is not limited.

For example, as shown in FIG. 4A, a fourth shielding member 174d is erected on a plate-like portion 174f closer to the SB roller pair 71 than the rotation shaft 174c of the switching guide plate 174, and the bottom surface of the partition member 175 is provided. The fifth shielding member 175a may be erected on the portion 175b toward the plate-like portion 174f.
In such a configuration, the fourth shielding member is used during single-sided printing in which it is necessary to suppress the inflow of water vapor to the refeeding path 8a side, that is, when the switching guide plate 174 is in the first posture. The opposing surfaces of 174d and the fifth shielding member 175a can be brought close to each other, and the effect of shielding water vapor flowing into the SB roller pair 71 during single-sided printing is greater.

(3) In the above embodiment, the inflow of water vapor from the gap between the switching guide plate 74 and the partition member 75 existing around the SB roller pair 71 when the switching guide plate 74 is in the first posture. Although there was a problem, since there is a gap between the tip of the switching guide plate 74 and the end of the refeed path guide member 80, water vapor may flow into the refeed path 8a also from the gap. .
FIG. 5A shows a conveyance path switch that suppresses the flow of water vapor into the refeed path 8a from the gap with the refeed path guide member 80 when the switching guide plate 74 is in the first posture. FIG. 4 is a diagram illustrating a configuration of a unit 27.

As shown in the figure, the switching guide plate 274 is obtained by changing the shape of the switching guide plate 74 in the above embodiment in the upstream side of the frame portion 74a in FIG. 4A (hereinafter referred to as “frame portion 274a”. The configuration is the same as that of the switching guide plate 74 except that it is used.
More specifically, a chevron-shaped projecting portion 274j is formed on the upper surface on the upstream side of the frame portion 274a. The slope 274k of the projecting portion 274j near the SB roller pair 71 and the end of the refeed path guide member 80 The partial lower surface 80b is provided so as to face almost in parallel over the length L3.

Further, it is desirable to set the gap D5 between the inclined surface 274k and the end lower surface 80b as small as possible in consideration of an actual assembly error.
Thereby, the flow resistance in the gap between the portions where the switching guide plate 274 inclined surface 274k and the end lower surface 80b face each other increases, and the amount of water vapor flowing into the refeed path 8a can be reduced.

FIG. 5B is a diagram illustrating a state in which the switching guide plate 274 is in the second posture.
In this example, the top portion of the protruding portion 274j slightly protrudes from the guide panel portion 74b and may come into contact with the recording sheet S3. However, the collision angle with the recording sheet S3 is shallow, and in some cases, it does not come into contact. In some cases, the recording sheet S3 is not adversely affected.
(4) Further, in the configuration of FIG. 5A, the value of the gap D5 is not 0, and the gap is allowed to be generated. However, as shown in FIG. A sheet-like elastic member 80c is adhered to the lower surface of the end portion 8a of the member 80, and water vapor flows into the refeed path 8a from between the inclined surface 274k and the end lower surface 80b so as not to generate a gap. It is also possible to reduce the collision noise between the refeed path guide member 80 and the protruding portion 274j.

As a material of the elastic member 80c, for example, urethane foam or silicone rubber is desirable.
FIG. 6B is a diagram illustrating a state in which the switching guide plate 274 is in the second posture in such a configuration.
As shown in the figure, in the state where the recording sheet S3 is being conveyed, the elastic member 80c is stuck at a position where it does not interfere with the recording sheet S3.
(5) Further, in the configuration of FIG. 5 (a), one ridge-shaped protrusion 274j is formed on the upper surface on the upstream side of the frame portion 274a, but as shown in FIG. 7 (a), the protrusion A refeed path guide member 80 is applied so that two 274j are formed continuously (hereinafter referred to as “frame portion 374a”), and further along the shape of the tip of the frame portion 374a. The configuration of the transport path switching unit 47 to which the shape of the end portion is reexamined (hereinafter referred to as “re-feed path guide member 280”) may be adopted.

Here, the configuration of the transport path switching unit 47 is the same as that of the transport path switching unit 27 except for the differences described above.
A switching guide member having a frame portion 374a is indicated by reference numeral 374.
In the conveyance path switching unit 47, the lower end surface 280b of the refeed path guide member 280 and the leading end portion 374g of the frame portion 374a meander, and the gap sandwiched therebetween also meanders. Since the road resistance increases, it becomes more difficult for water vapor to flow in.

FIG. 7B is a diagram illustrating a state where the tip of the switching guide plate 374 is in the second posture.
As shown in the figure, the two tops of the protruding portion 374f at the tip of the frame portion 374a protrude from the guide panel portion 374b and may come into contact with the recording sheet S3. The collision angle of the recording sheet S3 is shallow, and in some cases, there is a case where it passes through without being touched, so that the conveyance of the recording sheet S3 is not adversely affected.

  (6) In the above embodiment, the example in which the fixing device 5 and the image forming apparatus according to the present invention are applied to a tandem color digital printer has been described. However, the present invention is not limited to this. Regardless of color or monochrome image formation, the fixing roller arranged inside the rotation path of the substantially cylindrical fixing belt is pressed from the outer side of the rotation path with the pressure roller through the fixing belt, and the fixing nip. And an electromagnetic induction heating type fixing device 5 having a configuration in which a magnetic flux generating section for generating a magnetic flux for generating heat from the induction heat generating layer of the fixing belt is disposed outside the circulation path of the fixing belt, and image formation including the same Any apparatus can be applied to, for example, a copying machine, a FAX, and an MFP (Multiple Function Peripheral).

  The contents of the above embodiment and the above modification may be combined.

  The present invention can be widely applied to an image forming apparatus having a function of printing on both sides of a recording sheet.

DESCRIPTION OF SYMBOLS 1 Printer 3 Image process part 3Y, 3M, 3C, 3K Image creation part 4 Paper feed part 5 Fixing part 5a Case 5b Recording sheet exit hole 7 Conveyance path switching part 7a Discharge conveyance path 7b Fixer exit path 7c Refeed Paper transport path 8 Refeed path 8a Refeed path 10 Optical section 11 Intermediate transfer belt 12 Drive roller 13 Driven roller 31 Photoreceptor drum 32 Charger 33 Developer 34 Primary transfer roller 35 Cleaner 41 Paper feed cassette 42 Feeding roller 43 Conveying path 44 Timing roller pair 45 Secondary transfer roller 46 Secondary transfer position 47 Conveying path switching unit 60 Control unit 70 Branch point 71 Switchback roller pair 72 Discharge tray 73 Discharge roller pair 74 Switching guide plate 74a Frame unit 74b Guide Panel portion 74c Rotating shaft 74d Second shielding member 74e Third shielding member 75 Partition member 75a First shielding member 75b Bottom surface portion 75c Curved portion 76 Paper delivery path guide 80 Refeed path guide member 80c Elastic member 174 Switching guide plate 174d Fourth shielding member 175 Partition member 175a Fifth shielding member

Claims (6)

An image forming apparatus capable of forming an image on the second side of a recording sheet on which a non-fixed image on the first side is fixed by a fixing device, reversing the front and back, and re-feeding the recording sheet.
A discharge roller for discharging the recording sheet onto a discharge tray;
A switchback roller that sends a part of the recording sheet to the refeed path after being sent back to the outside of the apparatus;
A switching guide plate that switches and guides the recording sheet that has passed through the fixing device to a first conveyance path toward the discharge roller and a second conveyance path toward the switchback roller by changing the posture; ,
A partition member interposed between the switching guide plate and the first transport path,
The switching guide plate and the partitioning member are opposed to each other with shielding members extending toward the other side standing in a non-contact state with each other,
When the switching guide plate is in a posture to guide the recording sheet to the first conveyance path, the switching guide plate and the shielding member of the partition member are upstream of the recording sheet conveyance direction in the first conveyance path. An image forming apparatus, wherein the image forming apparatus is configured so that at least a part thereof overlaps each other when viewed from above. The switching guide plate is pivotally supported by the apparatus main body,
The image forming apparatus according to claim 1, wherein the switching guide plate-side shielding member is provided near the rotation shaft of the switching guide plate. When the switching guide plate is in a first posture that is inclined to guide the first conveyance path, and is in a second posture that is inclined to guide the second conveyance path,
The shielding member of the switching guide plate is formed at a position where the distance from the partition member is reduced when the second posture is shifted to the first posture. The image forming apparatus described. A refeeding guide member for guiding the recording sheet switched back by the switchback roller to the refeeding path is disposed at a position facing the switching guide plate across the second transport path. And
In a state where the switching guide plate is inclined toward the second conveyance path to guide the recording sheet to the first conveyance path, a part of the switching guide plate is close to the refeed guide member, and The shape of the re-feeding guide member and the switching guide plate is determined so that the opposing surfaces of the switching guide plate and the re-feeding guide member at the adjacent portions are substantially parallel to each other. 4. The image forming apparatus according to any one of items 1 to 3. A refeeding guide member for guiding the recording sheet switched back by the switchback roller to the refeeding path is disposed at a position facing the switching guide plate across the second transport path. And
The switching guide plate is configured such that a part of the switching guide plate is close to the re-feeding guide member in a state where the switching guide plate is inclined toward the second conveying path to guide the recording sheet to the first conveying path. And
A cross-sectional shape of a portion of the adjacent portion of the facing surface of the switching guide plate and the refeed guide member that is orthogonal to the rotation axis of the discharge roller is bent while maintaining a predetermined gap between the facing surfaces. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. When the switching guide plate is tilted toward the second conveyance path to guide the recording sheet to the first conveyance path, a part of the switching guide plate of the re-feeding guide member is close to the part. 5. A sheet-like elastic member is affixed, and a part of the switching guide plate is in contact with the re-feeding guide member via the elastic member. Or the image forming apparatus according to 5.

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