JPH0546041Y2 - - Google Patents

Description

[Detailed explanation of the idea] [Industrial application field]

The present invention relates to a transfer paper guide plate of a fixing device that guides a transferred transfer paper separated from the surface of a photoreceptor and conveyed to an inlet of fixing rollers rotating in pressure contact with each other.

[Conventional technology]

In general, image forming apparatuses such as electrophotographic copying machines use a rotating drum-type photoreceptor having a photoconductive photosensitive layer on the outer peripheral surface, and an electrostatic latent image is formed on the photosensitive layer while rotating the photoreceptor. Then, the image is developed with toner, and the resulting toner image is transferred to transfer paper. After completing the transfer, the transfer paper is separated from the surface of the photoreceptor and is transported by a transport mechanism to reach a fixing device. The fixing device includes an upper fixing roller and a lower roller that rotate in pressure contact with each other, a transfer paper guide plate that guides the transfer paper to the pressure contact portions of the upper and lower rollers, and the like. The transferred transfer paper is guided from the transfer paper guide plate to the upper and lower roller pressure contact portions, and is nipped by the upper and lower rollers and sent downstream. At this time, the transferred image on the transfer paper is heated and fixed by a heater provided on the fixing roller. FIG. 4 is a perspective view of the vicinity of the fixing roller entrance according to the conventional example, and FIG. 5 is a side sectional view of the vicinity of the fixing roller entrance according to the conventional example. In these figures, 1 is an upper fixing roller, 2 is a lower fixing roller, 3 is a transfer paper guide plate, 4 is a conveyance mechanism, 5 is a photoreceptor, 6 is a separation pole, H is a postcard, and P is a transfer paper. The upper fixing roller 1 is a drive-side roller, and is driven to rotate by receiving rotational driving force from a driving section (not shown) of the main body of the apparatus through a transmission member. The upper fixing roller 1 is formed of a hard member, and has an hourglass shape that is narrow at the center in the direction of the rotation axis and thick at both ends. The lower fixing roller 2 is a driven roller, and is in pressure contact with the upper fixing roller 1 and rotates as a driven roller. The roll portion of the lower fixing roller 2 is formed of a soft material, and when it comes into pressure contact with the upper fixing roller, the pressure side follows the shape of the upper fixing roller, and has a drum-shape that is thick at the center and narrow at both ends in the direction of the rotation axis. become. The transfer paper guide plate 3 is made of a hard member such as synthetic resin or metal. The transferred transfer paper is guided by the transfer paper guide plate 3 from the conveyance mechanism 4 to the pressure contact portions of the upper and lower fixing rollers. A conventional transfer paper guide plate has a convex portion 3a formed at the center of the transfer paper guide plate on the fixing roller side in accordance with the outer shape of the upper fixing roller 1. Immediately before the transfer paper P is fed into the pressure contact portion of the upper and lower fixing rollers, the transfer paper P is pressed against the convex portion 3 of the transfer paper guide plate.
The central part of the paper width is lifted by a, and the image is transferred in a state that approximates the shape formed by the depression in the central part of the upper fixing roller 1 and the bulge in the central part of the surface of the lower fixing roller 2 mentioned above. The paper is guided.
The transfer paper P advances as it is, is held between the upper and lower fixing rollers under the same conditions over the entire width of the paper, and is sent downstream as both rollers rotate. At this time, the transfer paper P is attached to the upper fixing roller 1 on the drive side.
According to the shape of the paper, the entire surface of the paper is subjected to a force that is spread out to prevent wrinkles from forming. On the other hand, when the postcard H is used as a transfer paper, it is known that the convex portion 3a provided on the transfer paper guide plate 3 becomes an obstacle to feeding the postcard to the pressure contact portion of the upper and lower fixing rollers. That is, as shown in FIG. 5, in the case of normal transfer paper P, when the leading edge of the transfer paper P reaches the pressure contact portion of the upper and lower fixing rollers, the rear end is in close contact with the surface of the photoreceptor 5, and the photoreceptor The rotational force of the body 5 urges the transfer paper P toward the fixing roller. However, since the postcard H has a short overall length, it is completely separated from the photoreceptor 5, and is transported toward the fixing roller only by the transport force from the transport mechanism 4. Moreover, the postcard enters between the upper and lower fixing rollers in a curved and warped state along the curved surface of the photoreceptor surface, and even if the postcard is pushed up by the convex portion 3a of the transfer paper guide plate 3, the postcard H The leading end of the fixing roller tends to separate from the pressure contact portion of the upper and lower fixing rollers, resulting in poor conveyance. As a countermeasure against such postcard conveyance defects, when forming a transfer image on a postcard, there is a method of switching the height of the transfer paper guide plate 3 into two levels by manual operation or automatic switching using a paper size detection sensor. This has been used in the past, but it results in high costs.

[Problem that the invention attempts to solve]

The present invention was devised in view of the above-mentioned shortcomings of the prior art, and provides a fixing device that can simultaneously guide both postcards and transfer paper other than postcards to the pressure contact portions of the upper and lower fixing rollers. The purpose of the present invention is to provide a transfer paper guide plate.

[Means to solve the problem]

The above purpose is to convey the transfer paper separated from the surface of the photoreceptor and conveyed via the conveyance path so that it is fixed by a pair of fixing rollers that rotate under pressure, and to change the shape of the upper roller of this fixing roller. In a transfer paper guide plate of a fixing device, the diameter of the center part is formed slightly smaller than the diameter of both ends, and the lower roller has a diameter of the center part slightly larger than the diameter of both ends. A concave portion having a step slightly lower than the pressure contact position of the pair of fixing rollers by the width of a postcard is provided, and protrusions located near both outer ends of the recess portion are located slightly higher than the pressure contact position. The fixing device is characterized in that it guides the leading edge of the sheet-like transfer paper in substantially the same shape as the pressure-contact shape formed by the pair of fixing rollers, and can also smoothly guide the postcard. This is achieved by the transfer paper guide plate of the device.

【Example】

FIG. 3 is a schematic diagram showing the internal structure of an electrophotographic copying machine provided with the transfer paper guide plate of this embodiment. First, an outline of each process up to the fixing device having the transfer paper guide plate of this embodiment will be explained using the same figure. An electrophotographic copying machine is provided with a photoreceptor 10 having a photoconductive photosensitive layer on its outer peripheral surface. An image is formed on the transfer paper through a plurality of steps while rotating the photoreceptor 10. First, the photosensitive layer is uniformly charged by the corona charger 11. Thereafter, the photosensitive layer is subjected to imagewise exposure by the exposure mechanism 12 to form an electrostatic latent image. This electrostatic latent image is developed with toner by a developing device 13 to form a toner image on the surface of the photosensitive layer. On the other hand, the transfer paper P supplied from the paper feed section 14 by the paper feed roller 15 and timing roller 16 is brought into close contact with the surface of the photoreceptor 10 on which the toner image is formed. In this state, transfer electrode 1
7 to transfer the toner image onto the transfer paper P. Then, the transfer paper P is separated from the photoreceptor 10 by the separation electrode 18. The separated transfer paper P is
The paper is transported by a transport mechanism 19, passed through a transfer paper guide plate 20 according to the present invention, and sent to a fixing device 21 where it is fixed. In the figure, the dashed line indicates the conveyance path of the transfer paper P. FIG. 1 is a perspective view of a transfer paper guide plate showing an embodiment of the present invention, and FIG. 2 is a sectional view of the transfer paper guide plate showing this embodiment. In these figures, 20 is a transfer paper guide plate, 20a is a postcard recess, 20b and 20c are guide projections, 22 is an upper fixing roller, and 23 is a lower fixing roller. The transfer paper guide plate 20 is made of a hard material such as synthetic resin or metal. A postcard recess 20a is provided near the longitudinal center of the transfer paper guide plate 20. The postcard recess 20a is a dedicated guide path for postcards when the postcard is used as transfer paper.
The bottom surface of the postcard recess 20a is positioned lower than the center pressure contact position of the upper fixing roller 22 and the lower fixing roller 23 by A (3 to 5 mm). The transfer paper guide plate 20 is provided with guide protrusions 20b and 20c for guiding the general transfer paper P at locations other than the postcard recess. The guide projections 20b, 2
For example, 0c is provided on both sides close to the postcard recess 20a, and is B (3 to 5 mm) from the center pressure contact position of the upper fixing roller 22 and the lower fixing roller 23.
position it higher. The upper fixing roller 22 is a drive-side roller, and is rotationally driven by receiving rotational driving force from a device main body driving section (not shown) through a transmission member. The upper fixing roller 22 is made of a hard material, and has a drum shape that is narrow at the center in the longitudinal direction of the rotating shaft and gradually becomes thicker toward both ends. The lower fixing roller 23 is a driven roller, and is in pressure contact with the upper fixing roller 22 to rotate as a driven roller. The roll portion of the lower fixing roller 23 is formed of a soft material, and when it comes into pressure contact with the upper fixing roller 22, the pressed side follows the shape of the upper fixing roller 22, and the center part in the longitudinal direction of the rotating shaft is thicker and the roll part is thicker in the direction of both ends. It becomes a drum shape that gradually becomes thinner. The toner image formed on the photoreceptor surface is transferred,
Postcard H separated by separation electrodes and transported
is transported by the transport mechanism 19, and when the leading edge of the postcard H reaches the transfer paper guide plate 20, it passes through the postcard recess 20a. Transfer paper guide plate 2 for postcard H
The conveyance path at 0 is indicated by a dotted line in FIGS. 2 and 3. The postcard recess 20a is formed by the upper fixing roller 2.
2 and the lower fixing roller 23 from the center pressure contact position A.
Since the leading edge of the postcard H is sent to the pressure contact portion of the upper and lower fixing rollers, no conveyance failure occurs.

[Effect of the idea]

According to the present invention, a postcard dedicated guide path having an entrance height slightly lower than the pressure contact position of the transfer paper upper and lower rollers is provided on the transfer paper guide plate that guides the transfer paper to the entrance portions of the upper and lower fixing rollers; A guide protrusion for preventing wrinkles for general transfer paper is provided in a location other than the guide path, so the transfer paper guide of the fixing device is capable of guiding both postcards and transfer paper other than postcards. We are now able to provide boards.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of a transfer paper guide plate showing an embodiment of the present invention, FIG. 2 is a side sectional view of the transfer paper guide plate,
Figure 3 is a schematic diagram showing the internal structure of an electrophotographic copying machine, Figure 4 is a perspective view of a conventional transfer paper guide plate, and Figure 5 is a schematic diagram showing the internal structure of an electrophotographic copying machine.
The figure is a schematic diagram of the vicinity of a conventional transfer paper guide plate. 10...Photoconductor, 14...Paper feeding unit, 15...Paper feeding roller, 16...Timing roller, 17...
Transfer electrode, 18... Separation electrode, 19... Transport mechanism, 20... Transfer paper guide plate, 20a... Postcard recess (recess), 20b, 20c... Guide protrusion (protrusion), 21... Fixing device, 22...Upper fixing roller,
23... lower fixing roller, H... postcard, P... transfer paper.

Claims (1)

[Scope of utility model registration request] The transfer paper that has been separated from the surface of the photoreceptor and conveyed via the conveyance path is conveyed so that it is fixed by a pair of rotating fixing rollers that are in contact with pressure, and the shape of the upper roller of this fixing roller is In the transfer paper guide plate of the fixing device, the lower roller is formed to have a diameter slightly thicker at the center than the diameter at both ends.
A recessed portion having a step slightly lower than the pressure contact position of the pair of fixing rollers by 2 to 3 mm with the width of a postcard is provided, and protrusions located slightly higher than the pressure contact position are provided near both outer ends of the recessed portion. It has been established,
A transfer paper guide plate for a fixing device, characterized in that it guides the leading edge of a sheet of transfer paper in substantially the same shape as the pressure contact formed by the pair of fixing rollers, and can also smoothly guide postcards. .