JP2003043838A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device capable of preventing a recording medium from being wrinkled at a nip part between a heating unit and a pressure roller even when the carrying speed of the recording medium is changed between a photoreceptor drum and the heating unit. SOLUTION: An intersection Q is formed by crossing a tangent 142 of an outer peripheral surface 112a of a photoreceptor drum 112 at a nip part 140 where the photoreceptor drum 112 and a transfer roller 122 hold the recording medium in between with a tangent 152 of an outer peripheral surface 126c of a heating unit 126a at a nip part 150 where the heating unit 126a and a pressure roller 126b hold the recording medium in between. The intersection Q is formed lower than two nip parts 140 and 150. The almost half of a guide surface 124a on an upstream side in a carrying direction is positioned at the same height as that of the tangent 152 or at the higher height.

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 an image on a recording medium such as recording paper.

[0002]

2. Description of the Related Art As an output device of a computer or a workstation, an electrophotographic image forming apparatus for forming an image on a recording medium using a powdery developer (toner) is known.

An example of an electrophotographic image forming apparatus is shown in FIG.
Will be described with reference to.

FIG. 6 is a schematic view showing a part of a conventional image forming apparatus.

In the image forming apparatus 10, for example, light (for example, laser) 12 carrying image information is applied to an image carrier such as a photosensitive drum 14 to form an electrostatic latent image, and the electrostatic latent image is developed. The roller 16 is used to supply toner to form a developed image, and the transfer roller 18 or the like is used to transfer the developed image to a recording medium to form a transferred image. In the image forming apparatus 10 that uses the transfer roller 18 to transfer the developed image formed on the photosensitive drum 14 to the recording medium,
While the recording medium is nipped and conveyed by the transfer roller 18, the developed image is transferred onto the recording medium to form a transferred image on the recording medium.

The recording medium on which the transferred image is formed is conveyed to the fixing device 20 while being guided by the conveying guide 19. The fixing device 20 fixes the transferred image on the recording medium. The fixing device 20 is provided with a heating unit 22 having an endless belt-shaped film on the outer periphery thereof and a built-in heater, and a pressure roller 24 that is in pressure contact with the heating unit 22. When fixing the transferred image to the recording medium, the transferred image is heated at a predetermined fixing temperature and simultaneously pressed while the recording medium is sandwiched and conveyed by the heating unit 22 and the pressure roller 24. The transfer image is fixed on the recording medium by the heating and pressing. The recording medium on which the transferred image is fixed is ejected while being sandwiched by the pair of ejection rollers 26.

As described above, since the photosensitive drum 14 and the transfer roller 18 convey the recording medium while sandwiching it, they also function as a conveying means. Similarly, the heating unit 22
Since the pressure roller 24 and the pressure roller 24 also convey the recording medium while sandwiching the recording medium, these also function as a conveying means.

By the way, in order to prevent the conveyance speed of the recording medium on the upstream side in the conveyance direction from affecting the conveyance speed of the recording medium on the downstream side in the conveyance direction, the photosensitive drum 14 and the transfer roller 18 convey the recording medium. The transport speed of the heating unit 22 and the pressure roller 24 is usually higher than the transport speed of the recording medium. As a result, the recording medium is conveyed between the photosensitive drum 14 and the heating unit 22 while forming a gentle loop protruding slightly downward. Therefore, the transport guide 19 having the guide surface 19 a matching the shape of the loop is arranged between the photosensitive drum 14 and the heating unit 22.

[0009]

By the way, the pressure roller 24 may expand due to the heat of the heating unit 22 to increase its outer diameter. When the outer diameter of the pressure roller 24 is increased, the conveyance speed when the recording medium is conveyed by being nipped by the heating unit 22 and the pressure roller 24 is increased. The behavior of the recording medium caused by such a change in the transport speed will be described with reference to FIGS. 6 and 7.

In a normal state in which the pressure roller 24 has not expanded so much, the recording medium 30 (shown by the chain double-dashed line) is conveyed while contacting the guide surface 19a of the conveying guide 19. However, when the outer diameter of the pressure roller 24 becomes large, the conveyance speed for conveying the recording medium 30 by being nipped by the heating unit 22 and the pressure roller 24 increases, so that the recording medium 30 (shown by the solid line) is exposed. The recording medium is pulled between the drum 14 and the heating unit 22 and floats from the guide surface 19a.

As described above, the recording medium 30 has the guide surface 19a.
The heating unit 2 is transported while being lifted from the
When sandwiched between the pressure roller 24 and the pressure roller 24, as shown in FIG. 7, the recording medium 30 is not straight but curved and wavy in the direction in which the roller shaft 24a of the pressure roller 24 extends. Such a phenomenon is likely to occur when the recording medium 30 absorbs moisture and has a “low waist”, which is affected by alignment of the photosensitive drum 14, the heating unit 22, and the like. When the recording medium 30 is sandwiched between the heating unit 22 and the pressure roller 24 while being wavy, wrinkles occur at the nip portion between the heating unit 22 and the pressure roller 24, and the image quality is degraded.

In view of the above circumstances, the present invention provides an image forming apparatus which does not cause wrinkles at the nip portion between the heating unit and the pressure roller even when the recording medium conveyance speed changes between the photosensitive drum and the heating unit. The purpose is to

[0013]

SUMMARY OF THE INVENTION An image forming apparatus of the present invention for achieving the above-mentioned object is a photosensitive drum on which a developed image is formed, and a recording medium is sandwiched between the photosensitive drum and conveyed. A transfer roller for transferring a developed image onto the recording medium, a conveyance guide for guiding the recording medium on which the developed image is transferred by the transfer roller in a predetermined conveying direction, and a recording medium guided by the conveyance guide are nipped. In an image forming apparatus equipped with a heating unit and a pressure roller for fixing a developed image on the recording medium while being conveyed, (1) the photosensitive drum in a nip portion where the recording medium is sandwiched between the photosensitive drum and the heating unit. The tangent line of the outer peripheral surface of the heating unit and the tangent line of the outer peripheral surface of the heating unit at the nip portion where the heating unit and the pressure roller sandwich the recording medium intersect with each other. It is formed below the nip portion, and (2) a portion of the transport guide on the downstream side of the intersection in the transport direction is located at substantially the same height as the tangent line of the outer peripheral surface of the heating unit. It is characterized by being a thing.

Here, (3) the heating unit is (3
-1) An endless belt made of resin, and (3-2) a heater arranged inside the endless belt,
(4) The pressure roller may (4-1) have an outer peripheral layer made of an elastic body, and may be rotationally driven by a predetermined drive source.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of an image forming apparatus of the present invention will be described with reference to FIG.

FIG. 1 is a schematic view showing a digital copying machine which is an embodiment of the image forming apparatus of the present invention.

The copying machine 50 includes a first housing 60 in which a plurality of parts for reading an image recorded on a document are incorporated.
And a second housing 100 in which a plurality of parts for forming an image on a recording medium are incorporated. Second housing 100
Are arranged under the first housing 60, as shown in the figure. Therefore, the first housing 60 is mounted on the second housing 100.

On the top surface of the copying machine 50, a rectangular parallelepiped original document pressing plate 62 that can be opened and closed is arranged. An image reading device 64 for reading an image recorded on a document is arranged below the document pressure plate 62. The upper surface (upper wall) of the image reading device 64 is a document table glass (not shown) on which a document is placed. The original pressing plate 62 and the image reading device 64 form a first housing 60.

An operation panel (not shown) for inputting the number of copies and the like is arranged on the front side of the second housing 100 with respect to the first housing 60. Second housing 10
A cassette 104, which accommodates a plurality of cut sheets, is provided in the lower part of 0 so that it can be inserted into and taken out of the second housing 100. The right side wall of the second housing 100 is provided with a rectangular manual feed tray 106 capable of feeding a small-sized recording sheet such as a postcard. The manual feed tray 106 has a lower side 10
6a is rotated in the direction of arrow C about the center and opened to a position where the recording medium can be placed. A space is formed in the left side portion of the second housing 100, and a paper discharge tray 108 on which discharged recording paper is stacked is formed.

A procedure for forming an image with the copying machine 50 will be described.

In order to form the image recorded on the original on the recording medium, the original pressure plate 62 is opened, and the original is placed on the upper surface of the original table glass (not shown) with the image side down. Then, the original is pressed and fixed by the original pressure plate 62. Next, by pressing a predetermined operation button or the like, the image recorded on the document is read by the image reading device 64. The read image is converted into a digital signal, and this digital signal is transmitted to the laser scanner 110.

The signal transmitted to the laser scanner 110 is converted into laser light, and this laser light is applied to the photosensitive drum 112 via the scanner mirror 110a and the folding mirror 110b which rotate at high speed. Photosensitive drum 1
12 is uniformly charged by the charger 111, and an electrostatic latent image is formed on the photosensitive drum 112 irradiated with laser light. This electrostatic latent image is developed with the developer supplied from the developing roller 114 to form a developed image.

On the other hand, a recording medium such as recording paper is fed from the cassette 104 by the feed roller 116 in the direction of arrow D (feed direction), and is conveyed to the transfer roller 122 by the conveying roller 118 and the registration roller 120. The transfer roller 122 holds the recording medium together with the photosensitive drum 112, and transfers the developed image of the photosensitive drum 112 onto the recording medium. The recording medium on which the developed image is transferred is the conveyance guide 12
4 to the fixing device 126. The fixing unit 126 is provided with a heating unit 126a and a pressure roller 126b, and the recording medium is conveyed while being sandwiched by these two rollers 126a and 126b, and the developed image is fixed on the recording medium. The recording medium on which the developed image has been fixed in this manner is discharged by the paper discharge rollers 128 and stacked on the paper discharge tray 108.

The recording medium can be fed from the manual feed tray 106, and the procedure for forming an image on the recording medium fed from the manual feed tray 106 is the same as above. Further, the copying machine 50 also has a built-in electric component board 129 on which a power source for driving various components and electric components are mounted.

As described above, the copying machine 50 incorporates various parts and members. Among these parts, the charger 111, the photosensitive drum 112, the developing roller 114, and the like are incorporated in the process cartridge 130.
The process cartridge 130 is detachably attached to the copying machine 50.

The above-mentioned transport guide 124 will be described with reference to FIGS. 2 and 3.

FIG. 2 is an enlarged schematic view showing the periphery from the photosensitive drum to the fixing device. FIG. 3 is a perspective view showing the heating unit and the transport guide. In these figures, FIG.
The same reference numerals are given to the same components as those shown in FIG.

A conveyance guide 124 is arranged between the photosensitive drum 112 and the fixing device 126 to guide the recording medium conveyed while being sandwiched between the photosensitive drum 112 and the transfer roller 122 to the fixing device 126. Transport guide 124
Of the upper surface of the guide surface is a guide surface 124a on the downstream side of a point Q, which will be described later, in the transport direction.
It is guided while touching 24a. The features of the transport guide 124 will be described.

First, the above-mentioned point Q will be described.

The photosensitive drum 1 in the nip portion 140 where the photosensitive drum 112 and the transfer roller 122 sandwich the recording medium.
12 and the tangent line 142 of the outer peripheral surface 112a of the heating unit 1
26a and the pressure roller 126b sandwich the recording medium, the outer peripheral surface 1 of the heating unit 126a in the nip portion 150.
The tangent line 152 of 26c intersects to form an intersection point Q. This intersection Q is formed below the two nip portions 140 and 150.

The transport guide 124 is formed with guide surfaces 124a and 124b which are gently curved downward. The guide surface 124b is a surface slightly inclined downward from the downstream side in the transport direction (direction of arrow E) with respect to the nip portion 140. Further, the guide surface 124a is the guide surface 12
It is a surface which is continuously inclined in the direction of arrow C from the lowest portion of 4b and is inclined upward. Guide surface 124a and guide surface 1
The portion where 24b is connected is located slightly upstream of the point Q in the transport direction. Therefore, a part of the guide surface 124a (upstream side portion in the transport direction) is located upstream of the point Q in the transport direction.

The guide surface 124a is, as shown in FIG.
It is formed from the top surfaces of the plurality of ribs 125. The same applies to the guide surface 124b (see FIG. 2). The guide surface 1
The recording medium guided by the guide surface 124a is provided on the downstream side of the transport direction 24a in the nip portion 15 of the fixing device 126.
An inlet guide 160 leading to 0 is arranged.

A portion of the guide surface 124a on the downstream side of the point Q in the transport direction is located at substantially the same height as the tangent line 152. Here, about half of the guide surface 124a on the upstream side in the transport direction is positioned at the same height as the tangent line 152 or higher. Therefore, the portion of the transport guide 124 downstream of the intersection Q in the transport direction is tangential line 1
It is located at substantially the same height as 52.

Now, referring to FIG. 4, the heating unit 1
The structure of 26a will be described.

FIG. 4 is a schematic diagram showing the internal structure of the heating unit.

The heating unit 126a has a thin film-shaped endless belt 172 made of resin. Endless belt 17
A heater 174 is arranged inside the heater 2.
74 is in contact with the inner peripheral surface of the endless belt 172. The endless belt 172 is heated by the heater 174.
The heater 174 is fixed to a resin fixture 176. In the fixture 176, the heater 174 has an endless belt 172.
Is pressed against the metal plate 178 so as to come into contact with. The endless belt 172, the heater 174, and the fixture 17 described above.
6. The sheet metal 178 extends in a direction orthogonal to the transport direction. In addition, the endless belt 172 is used for the pressure roller 12
The heater 174, the fixing member 176, and the sheet metal 178 do not rotate although they rotate following the rotation of the 6b.

On the other hand, the pressure roller 126b has an outer peripheral layer made of an elastic body (for example, hard rubber), and is driven by a drive motor (not shown). The pressure roller 126b is easily expanded by heat to increase its outer diameter, which increases the speed at which the recording medium is conveyed while being sandwiched between the heating unit 126a and the pressure roller 126b. The behavior of the recording medium guided by the transport guide 124 when the outer diameter of the pressure roller 126b is thus increased will be described with reference to FIG.

FIG. 5 is a schematic diagram showing the behavior of the recording medium.

As described above, the recording medium is the heating unit 12
When the speed at which the recording medium 30 is nipped by 6a and the pressure roller 126b and conveyed increases, the recording medium 30 (shown by the solid line) easily separates from the guide surface 124a of the conveyance guide 124 (easily rises). On the other hand, when the above speed is the normal speed, the recording medium 30 (shown by the alternate long and short dash line) does not float above the guide surface 124a.

However, even when the speed is increased, as described above, about half of the guide surface 124a on the upstream side in the conveying direction has the same height as the tangent line 152 (see FIG. 2) or more. Since it is located at the height of, the portion of the recording medium 30 that passes the intersection Q (see FIG. 2) is
It is guided from the guide surface 124a in the conveying direction in a stable and flat posture without waving and rising. Therefore, the recording medium 30 that has passed through the heating unit 126a and the pressure roller 126b has no wrinkles or the like, and the image quality does not deteriorate. It should be noted that such a transport guide 124 is particularly effective for an image forming apparatus in which the distance between the two nip portions 140 and 150 is relatively short.

[0041]

As described above, in the image forming apparatus of the present invention, the recording medium passing through the photosensitive drum and the transfer roller advances downward toward the intersection while passing through the intersection while being guided by the conveying guide. Further, it is nipped by the heating unit and the pressure roller while being guided by the conveyance guide. Since the portion of the transport guide downstream of the intersection in the transport direction is located at substantially the same height as the tangent line of the outer peripheral surface of the heating unit, the portion of the recording medium that has passed the intersection rises from the transport guide and undulates. It is guided in the transport direction with a stable and flat posture without hitting. In this way, the recording medium is conveyed while being guided in a stable and flat posture, so that the recording medium is sandwiched between the heating unit and the pressure roller in this stable and flat posture. Therefore, the recording medium that has passed through the heating unit and the pressure roller has no wrinkles,
Image quality does not deteriorate.

Here, the heating unit includes an endless belt made of resin and a heater disposed inside the endless belt, and the pressure roller has an outer peripheral layer made of an elastic body. When the pressure roller is driven to rotate by a predetermined driving source, the pressure roller expands due to the heat from the heating unit and its outer diameter tends to increase, whereby the recording medium and the heating unit are The speed at which the recording medium is nipped by the pressure roller and conveyed increases, and the recording medium easily separates from the conveyance guide (is easily lifted up). Since it is located at almost the same height as the above, the part of the recording medium that has passed the above intersection is guided in the transport direction with a stable flat posture without rising from the transport guide and waviness. . Therefore, the recording medium that has passed through the heating unit including the endless belt made of resin does not have wrinkles, and the image quality does not deteriorate.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a digital copying machine which is an embodiment of an image forming apparatus of the present invention.

FIG. 2 is an enlarged schematic view of the periphery from a photosensitive drum to a fixing device.

FIG. 3 is a perspective view showing a heating unit and a conveyance guide.

FIG. 4 is a schematic diagram showing an internal structure of a heating unit.

FIG. 5 is a schematic diagram showing the behavior of a recording medium.

FIG. 6 is a schematic view showing a part of a conventional image forming apparatus.

7 is a perspective view schematically showing the behavior of a recording medium in the image forming apparatus of FIG.

[Explanation of symbols]

112 photosensitive drum 122 transfer roller 124 Transport guide 126 Fixer 126a heating unit 126b Pressure roller 140,150 Nip part 142,152 tangent 172 endless belt 174 heater

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 2H033 AA15 BA02 BA09 BA11 BA12                       BA25 BB29 BB30 BB37 BE03                 2H071 DA09 DA12 DA23 EA04                 2H072 AB03 AB07 AB19 BA03 BA12                       CA01                 3F101 FB05 FB07 LA02 LA07 LB03

Claims (2)

[Claims] 1. A photosensitive drum on which a developed image is formed, a transfer roller for transferring the developed image to the recording medium while nipping and conveying the recording medium between the photosensitive drum, and the developed image by the transfer roller. A conveyance guide that guides the recording medium onto which the image has been transferred in a predetermined conveyance direction, and a heating unit and a pressure roller that fix the developed image on the recording medium while nipping and conveying the recording medium guided by the conveyance guide. In the image forming apparatus, the tangent line of the outer peripheral surface of the photosensitive drum in the nip portion where the photosensitive drum and the heating unit sandwich the recording medium, and the heating unit and the pressure roller sandwich the recording medium. An intersection of the nip portion with the tangent line of the outer peripheral surface of the heating unit is formed below the two nip portions, and the intersection of the conveyance guides is formed. Remote the downstream side portion, an image forming apparatus, wherein the tangential line of the outer circumferential surface of the heating unit in which is located at substantially the same height. 2. The heating unit includes an endless belt made of resin, and a heater disposed inside the endless belt, and the pressure roller has an outer peripheral layer made of an elastic body. The image forming apparatus according to claim 1, wherein the image forming apparatus is rotationally driven by a predetermined drive source.