JP3674704B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus such as a copying machine, a printer, and a fax machine using electrophotography.
[0002]
[Prior art]
In the image forming apparatus, an electrostatic latent image is formed on an image carrier such as a photoconductor, and the electrostatic latent image is developed with toner, and then the toner image is primarily transferred onto the intermediate transfer belt. There is a system in which the above process is repeated for each rotation of the image, and the respective color toner images are superimposed on an intermediate transfer belt, and then a four-color full-color image is secondarily transferred onto a sheet material.
[0003]
In this type of image forming apparatus, the sheet material that has entered the secondary transfer section is transferred to the toner image on the intermediate transfer belt by the bias applied to the secondary transfer roller, and sent to the fixing device. . At this time, if there is a charge on the sheet material that has passed through the secondary transfer portion, the toner will fly and adhere to the sheet material, causing image degradation. To prevent this, the sheet material may be neutralized with a neutralizing brush. In addition, a static elimination needle is disposed at a position immediately after transfer by a transfer roller to neutralize a sheet material (see Patent Document 2).
[0004]
[Patent Document 1]
Japanese Patent Publication No. 6-77170 [Patent Document 2]
Japanese Patent No. 2759487 (Fig. 7)
[0005]
[Problems to be solved by the invention]
By the way, when the sheet material after transfer is conveyed through the guide member in a state where charge removal is insufficient, the sheet material comes into contact with the ribs of the guide member, and streaky image disturbance occurs due to static electricity. Further, for example, in an image forming apparatus using an intermediate transfer belt, a sheet material conveyed in pressure contact with the secondary transfer roller and the intermediate transfer belt generates paper dust due to friction during nip. In particular, once the sheet material has passed through the fuser, it is damaged by the pressure and heat of the rollers, so more paper dust is generated, which accumulates on the static elimination members such as static elimination brushes and static elimination needles. This causes image distortion. In addition, in order to improve the charge removal capability, a reverse bias is applied to the charge removal member at the time of transfer, and thereby the charge removal member functions to collect dust such as paper dust floating in the machine. As a result, dirt is attached to the static elimination member and it is difficult to remove it, which causes image disturbance.
[0006]
Thus, although it is conceivable to dispose the charge eliminating member on the sheet material guide member, a new problem arises. That is, if the belt gap between the neutralization member and the intermediate transfer belt is large, the sheet material is not sufficiently neutralized and the toner image on the sheet material is disturbed. Conversely, there is a belt gap between the neutralization member and the intermediate transfer belt. If it is smaller, the distance between the sheet material and the charge removal member is reduced accordingly, and the toner image on the sheet material is directly disturbed by the bias applied to the charge removal member. The belt gap is generated for each product due to variations in individual parts.
[0007]
If the sheet material guide member is defined as a post-transfer sheet guide member, there is also a pre-fixing sheet guide member on the inlet side of the fixing device, and the parallelism in the width direction of the post-transfer sheet guide member and the pre-fixing sheet guide member is poor. The posture of the sheet material is disturbed at the joint from the post-transfer sheet guide member to the pre-fixing sheet guide member, and the posture of the sheet material when sandwiched between the fixing devices is uneven in the width direction or is sandwiched between the left and right Timing will shift. As a result, the length of the sheet material conveyed between the transfer and fixing is different in the width direction. In this case, the sheet material between the transfer unit and the fixing unit is closer to the static elimination member, and the shorter one is shorter. The unevenness of the static elimination state that leaves | separates from a static elimination member will arise.
[0008]
The present invention solves the above-described conventional problems, and ensures the parallelism in the width direction of the post-transfer sheet guide member and the pre-fixing sheet guide member, and the gap between the intermediate transfer belt and the post-transfer sheet guide member. An object of the present invention is to provide an image forming apparatus capable of managing the amount within a predetermined range.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, the image forming apparatus of the present invention includes a post-transfer sheet guide member and a pre-fixation sheet guide member between the intermediate transfer belt, the secondary transfer roller, and the fixing device, and the post-transfer sheet guide. The member is swingably disposed so as to be biased toward the pre-fixing sheet guide member, and the upper part of the post-transfer sheet guide member is positioned below the pre-fixing sheet guide member.
Further, a spacer having a contact protrusion protruding in the horizontal direction is detachably mounted on the upper part of the post-transfer sheet guide member.
Further, a charge eliminating member is disposed on the sheet material conveyance path of the post-transfer sheet guide member.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is an overall configuration diagram showing an example of an image forming apparatus to which the present invention is applied.
[0011]
The image forming apparatus 1 includes a main body case 2 and includes a front cover 2 a that is attached to the front surface of the apparatus 1 so as to be opened and closed. An image carrier 3 made of a photosensitive drum is disposed in the main body case 2 and is driven to rotate in the direction indicated by the arrow by a driving means (not shown). Around the image carrier 3, a charging device 4 for uniformly charging the image carrier 3 along the rotation direction, and an exposure device for forming an electrostatic latent image on the image carrier 3 5. A rotary developing device 6 for developing an electrostatic latent image, and an intermediate transfer device 7 for primary transfer of a monochromatic toner image formed on the image carrier 3 are provided.
[0012]
In the rotary developing device 6, a yellow developing device 6Y, a magenta developing device 6M, a cyan developing device 6C, and a black developing device 6K are mounted on a support frame 9, and the support frame 9 is rotationally driven by a drive motor (not shown). It is configured. The plurality of developing devices 6Y, 6M, 6C, and 6K rotate and move so that the developing roller 6a of a certain developing device selectively faces the image carrier 3 every time the image carrier 3 rotates by a predetermined amount. Has been. Each of the developing devices 6Y, 6M, 6C, and 6K has a toner storage portion that stores toner of each color.
[0013]
The intermediate transfer device 7 includes a driving roller 10 and a driven roller 11, an intermediate transfer belt 12 that is wound around the rollers 10 and 11 and driven in the direction indicated by the arrow, and is opposed to the image carrier 3 on the back surface of the belt 12. A four-color full-color image formed on the intermediate transfer belt 12 is disposed opposite to the primary transfer roller 13, the transfer belt cleaner 14 that removes residual toner on the belt 12, and the driving roller 10. It comprises a secondary transfer roller 15 for transferring onto a sheet material (paper or the like).
[0014]
A power supply device 16 is disposed below the exposure device 5, and a sheet feed cassette 17 is disposed at the bottom of the main body case 2. A sheet material in the sheet feed cassette 17 is a pickup roller 18, a sheet material conveyance path. 19, the secondary transfer roller 15, and the fixing device 20 are conveyed to the paper discharge tray 21. The paper feed cassette 17 is attached to the front of the apparatus by a handle 17b so that it can be pulled out, and an auxiliary cassette 17a is attached so that it can be pulled out so as to protrude toward the rear of the apparatus so as to cope with a large paper size. Yes.
[0015]
The operation of the image forming apparatus having the above configuration will be described. When an image forming signal is input from a computer (not shown), the image carrier 3, the developing roller 6 a of the developing device 6 and the intermediate transfer belt 12 are driven to rotate. First, the outer peripheral surface of the image carrier 3 is charged by the charging device 4. The exposure device 5 selectively exposes the outer peripheral surface of the uniformly charged image carrier 3 according to the image information of the first color (for example, yellow) so that the electrostatic latent image of yellow An image is formed.
[0016]
At the latent image position formed on the image carrier 3, the yellow developing device 6 </ b> Y rotates and the developing roller 6 a comes into contact therewith, whereby the yellow electrostatic latent image toner image is transferred to the image carrier 3. Next, the toner image formed on the image carrier 3 is transferred onto the intermediate transfer belt 12 by the primary transfer roller 13. At this time, the secondary transfer roller 15 is separated from the intermediate transfer belt 12.
[0017]
In accordance with the second color, the third color, and the fourth color of the image formation signal, the above processing is repeated to form a latent image, develop, and transfer by one rotation of the image carrier 3 and the intermediate transfer belt 12, thereby forming an image. Four color toner images corresponding to the contents of the signals are superimposed and transferred on the intermediate transfer belt 12. When the full color image reaches the secondary transfer roller 15, the sheet material is supplied from the conveyance path 19 to the secondary transfer roller 15. At this time, the secondary transfer roller 15 is pressed against the intermediate transfer belt 12. A secondary transfer voltage is applied, and the full-color toner image on the intermediate transfer belt 12 is transferred onto the sheet material. The toner image transferred onto the sheet material is heated and pressed by the fixing device 20 and fixed. The toner remaining on the intermediate transfer belt 12 is removed by the transfer belt cleaner 14.
[0018]
In the case of double-sided printing, the sheet material that has exited the fixing device 20 is switched back so that the trailing edge is the leading edge, and is supplied again to the secondary transfer roller 15 via the double-sided printing conveyance path 22. The full-color toner image on the intermediate transfer belt 12 is transferred onto the sheet material, and is again heated and pressed by the fixing device 20 to be fixed.
[0019]
Next, features of the image forming apparatus of the present invention will be described. In FIG. 1, the fixing device 20 has a fixing housing 23, and a pre-fixing sheet guide member 24 is disposed on the sheet material entry side below the fixing housing 23, and the pre-fixing sheet guide member 24 and the secondary transfer roller 15. A post-transfer sheet guide member 25 is disposed therebetween.
[0020]
In the present embodiment, the post-transfer sheet guide member 25 is a mixed material of polycarbonate and ABS resin. Since this material is neither positively charged nor strongly negatively charged even when it is rubbed with the charged sheet material (paper) after transfer, the unfixed toner before transfer and after fixing is a rib (25a in FIG. 3). Will not be disturbed by the charging. In the case of a strong positive charge, the guide attracts and accumulates the toner, and dirt corresponding to the shape of the guide adheres to the back surface of the sheet material. In the case of a strong negative charge, the toner on the sheet material is repelled by charging and becomes white. A streaky print defect occurs.
[0021]
2 to 8 show an embodiment of the image forming apparatus of the present invention, and FIG. 2 is a perspective view showing the fixing device 20, the pre-fixing sheet guide member 24, and the post-transfer sheet guide member 25 of FIG. 4 is a schematic diagram of a secondary transfer unit, FIG. 4 is an enlarged view of a main part of FIG. 3, FIG. 5 is a diagram for explaining the operation of the sensor lever of FIG. 3, and FIG. 7A and 7B are perspective views of the spacer viewed from different directions, and FIGS. 8A and 8B are perspective views of the spacer viewed from different directions after mounting the spacer.
[0022]
2 and 3, the intermediate transfer belt 12 described in FIG. 1, the driving roller 10 as a backup roller of the secondary transfer portion, the secondary transfer roller 15, the fixing housing 23, the pre-fixing sheet guide member 24, the post-transfer A sheet guide member 25 is shown. In FIG. 3, reference numeral 20a denotes a fixing roller pair. The post-transfer sheet guide member 25 and the pre-fixing sheet guide member 24 constitute a transport path for transporting the post-transfer sheet material upward to the fixing roller pair 20a. The post-transfer sheet guide member 25 is a fulcrum shaft. 26 is swingably mounted and is urged in the X direction in FIG. 3 by a spring (not shown).
[0023]
On the other hand, the secondary transfer roller 15 is rotatably mounted on a fulcrum shaft 26 via left and right side plates 27 and 29, and the fulcrum shaft 26 is rotatably mounted on a main body frame (not shown). Two spacers 30 are engaged with the upper portion of the post-transfer sheet guide member 25, and the upper portion of the spacer 30 is brought into contact with a positioning portion 24a formed at the lower portion of the pre-fixing sheet guide member 24, thereby allowing the post-transfer. Positioning of the sheet guide member 25 with respect to the pre-fixing sheet guide member 24 is performed to ensure parallelism in the width direction therebetween.
[0024]
As shown in FIGS. 3 and 4, the post-transfer sheet guide member 25 is provided with a neutralizing cloth 31 at a position close to the secondary transfer portion T2 of the sheet material conveyance path 25a, and a bias is applied to the neutralizing cloth 31. Has been. The post-transfer sheet guide member 25 is formed with a plurality of ribs 25b in the conveying direction in order to prevent the sheet material from coming into contact with the charge removal cloth 31.
[0025]
In the sheet material conveyance path 25a, a sensor lever 28 for detecting a paper jam of the sheet material is rotatably disposed around a shaft 28b. When the sheet material passes, the sensor lever 28 rotates as shown in FIG. 5, and the lower part of the sensor lever 28 moves from the photosensor 28c, whereby the photosensor 28c detects the passage of the sheet material. When the sheet material passes, the sensor lever 28 returns to the original position shown in FIG. 3 by the weight 28d. Since the sensor lever 28 is also made of the same material as the post-transfer sheet guide member 25, the sheet material contact portion of the sensor lever 28 is made of a material that is neither strongly positively charged nor strongly negatively charged. A good image can be obtained without disturbing the upper unfixed toner.
[0026]
As shown in FIG. 6, an engagement protrusion 25 b is formed on the upper end of the post-transfer sheet guide member 25. As shown in FIG. 7, the spacer 30 has a rectangular frame main body 30a, an engagement hook 30b formed at the lower part of the frame main body 30a, and a contact member formed on the sheet material conveying side at the upper part of the frame main body 30a. A contact piece 30c and an engagement recess 30d formed on the opposite side of the contact piece 30c are provided.
[0027]
8, the engagement hook 30b of the spacer 30 is engaged with the surface of the post-transfer sheet guide member 25, and the engagement recess 30d is engaged with the engagement protrusion 25b of the post-transfer sheet guide member 25. I am doing so. In this state, the contact protrusion 30c of the spacer 30 is positioned on the upper surface of the post-transfer sheet guide member 25, and the contact protrusion 30c of the spacer 30 is formed on the sheet guide member 24 before fixing as shown in FIG. The post-transfer sheet guide member 25 is positioned by contacting the positioning portion 24a.
[0028]
The sheet material that has entered the secondary transfer portion T2 is transferred to the toner image on the intermediate transfer belt 12 by the bias applied to the secondary transfer roller 15, and is sent to the fixing device 20. The sheet material that has passed through the secondary transfer portion T2 needs to be neutralized (for example, −1000 V) in order to stabilize the toner image. For this reason, the neutralizing cloth 31 is disposed in the sheet material conveyance path 25a.
However, as shown in FIG. 4, if the belt gap D between the neutralizing cloth 31 and the intermediate transfer belt 12 is large, the sheet material is not sufficiently neutralized and the toner image on the sheet material is disturbed. If the belt gap D between the cloth 31 and the intermediate transfer belt 12 is small, the distance between the sheet material and the neutralizing cloth 31 approaches accordingly, and the toner image on the sheet material is directly disturbed by the bias applied to the neutralizing cloth 31. End up. This belt gap problem occurs for each product due to variations in individual parts.
[0029]
Therefore, in the present invention, a plurality of spacers 30 (for example, six types) having different projection amounts of the contact pieces 30c shown by hatching in FIG. 7A are prepared, and the spacers 31 are made detachable and replaced. Thus, the position of the post-transfer sheet guide member 25 is changed to change the belt gap amount.
[0030]
For example, an attempt is made to manage the belt gap amount in the range of 4.3 to 4.9 mm. If there is only one type of spacer, the belt gap amount varies from 3.8 to 5.5 mm. If a certain machine is 3.8 mm, it can be set to 4.3 mm by mounting the spacer 30 having the contact protrusion 30c having the largest protrusion amount in FIG. On the other hand, for a 5.5 mm-thick one, the spacer 30 having the smallest protrusion 30c can be attached to be 4.9 mm.
[0031]
The embodiment of the present invention has been described above, but the present invention is not limited to this, and various modifications are possible. The present invention may be applied to a conventionally known technique or a conventionally known technique. May be combined. For example, in the said embodiment, although the static elimination cloth is used as a static elimination member, you may make it employ | adopt a static elimination brush and a static elimination needle.
[0032]
【The invention's effect】
As apparent from the above description, according to the present invention, the post-transfer sheet guide member and the pre-fixing sheet guide member are secured in parallel in the width direction, and the gap amount between the intermediate transfer belt and the post-transfer sheet guide member. Can be managed within a predetermined range.
[Brief description of the drawings]
FIG. 1 is an overall configuration diagram illustrating an example of an image forming apparatus to which the present invention is applied.
FIG. 2 is a diagram for explaining an embodiment of an image forming apparatus of the present invention.
FIG. 3 is a view for explaining an embodiment of the image forming apparatus of the present invention.
FIG. 4 is a view for explaining an embodiment of the image forming apparatus of the present invention.
FIG. 5 is a diagram for explaining the operation of the sensor lever of FIG. 3;
FIG. 6 is a view for explaining an embodiment of the image forming apparatus of the present invention.
FIG. 7 is a view for explaining an embodiment of the image forming apparatus of the present invention.
FIG. 8 is a view for explaining an embodiment of the image forming apparatus of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 12 ... Intermediate transfer belt, 15 ... Secondary transfer roller, 24 ... Sheet guide member 25 before fixing 25 ... Sheet guide member after transfer, 30 ... Spacer, 30c ... Contact protrusion 31 ... Static elimination member

Claims (3)

A post-transfer sheet guide member and a pre-fixation sheet guide member are provided between the intermediate transfer belt and the secondary transfer roller and the fixing device, and swing to urge the post-transfer sheet guide member toward the pre-fixation sheet guide member. An image forming apparatus, wherein the image forming apparatus is arranged so that an upper portion of a post-transfer sheet guide member is positioned below a pre-fixing sheet guide member. The image forming apparatus according to claim 1, wherein a spacer having a contact protrusion protruding in a horizontal direction is detachably attached to an upper portion of the post-transfer sheet guide member. The image forming apparatus according to claim 1, wherein a charge eliminating member is disposed on a sheet material conveyance path of the post-transfer sheet guide member.

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