Picture image forming device

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Technical field to which the invention belongs]

The present invention relates to an image forming apparatus having a so-called automatic double-sided mode in which an image is automatically formed on both sides of a transfer paper.

【0002】

[Conventional technology]

As a conventional method of an automatic double-sided printing (image forming) mechanism of an image forming apparatus, a stacking portion (intermediate tray) is provided in a transport path after single-sided printing to temporarily stack a predetermined number of transfer papers, and then re-stacking. There is a method of feeding paper and printing on the back side.

【0003】

Here, when re-feeding the stacked transfer paper, a lower transfer method (for example, Japanese Patent Application Laid-Open No. 3-174169) in which a pickup roller and a feed roller are arranged under the transfer paper capable of first-in first-out and a stack. There is also an upper transfer method in which a bottom plate raising mechanism is provided in the part to perform first-in and first-out.

【0004】

[Problems to be Solved by the Invention]

However, in the former method, first-in first-out is possible, but as the number of stacks increases, the frictional force between the transfer papers increases, and parameter setting for double feeding and the like becomes strict. The latter is less affected by the weight of the transfer paper, but is mechanically complicated because it requires a bottom plate raising mechanism.

【0005】

In addition, the method using an intermediate tray uses the drop of the transfer paper's own weight, so in terms of productivity when outputting a large amount of double-sided prints, such as when a paper alignment mechanism is required and the number of stacks cannot be increased. There's a problem.

【0006】

An object of the present invention is to provide an image forming apparatus equipped with an automatic double-sided mechanism having high productivity and reliability that can be applied to a new field such as short run color printing or on-demand printing.

【0007】

[Means for solving problems]

In order to achieve the above object, the first invention comprises a first transport path for feeding transfer paper from a paper feed unit in an image forming apparatus having an automatic double-sided mode in which images are automatically formed on both sides of the transfer paper. , The transfer paper with the image formed on one side merges with the second transport path, which is transported in an inverted state, and the first and second transport paths, and is sent from the first and second transport paths. A second device having a switchback mechanism that conveys the transferred paper to the vicinity of the transfer position of the image-forming portion and switches back the inverted single-sided image-formed transfer paper so that the non-image-forming surface faces the image-forming portion. It is characterized by having 3 transport routes.

【0008】

Further, in the first invention, the second invention includes four image forming portions for each color, a transfer belt provided in the vertical direction facing each image forming portion, and a vertical so as to be parallel to the transfer belt. The first and second transfer paths provided in the direction and the transfer paper after the confluence are horizontally conveyed, and the switchback mechanism switches back to the upstream end of the transfer belt. It is characterized by having 3 transport routes.

【0009】

Further, in the third invention, in the first invention, a paper feeding section dedicated to thick paper is provided so that paper can be fed from the third transport path, and a paper ejection section having a large curvature dedicated to thick paper is provided at the paper ejection port. It is characterized by that.

【0010】

The fourth invention is characterized in that, in the first invention, a paper tip detection sensor for temporarily stopping the transfer paper is provided in the vicinity of the confluence of the first and second transport paths, respectively. ..

【0011】

A fifth aspect of the present invention is the fourth aspect of the present invention, wherein the paper tip detection sensor is provided at an equal distance from the confluence.

【0012】

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention is characterized in realizing the automatic double-sided mode function without an intermediate tray. That is, if the intermediate tray is eliminated, the transfer paper passes through the closed loop-shaped transport path in the double-sided mode, but in the normal closed loop, the image may be transferred twice to the same surface of the transfer paper. Therefore, in the present invention, the transfer paper on which the single-sided image is formed is first inverted, and the non-image surface is conveyed so as to face the image-forming portion while being in this state (without being inverted again) by the switchback mechanism. It was done. Lateral resist adjustment is also performed at the same time as switchback.

【0013】

Hereinafter, a specific description will be given with reference to the attached drawings. FIG. 1 is a configuration diagram of an image forming apparatus showing an embodiment of the present invention. This image forming apparatus shows a 4-drum type color image forming apparatus. That is, four image-forming units 1 for each color of Y, M, C, and Bk, which are composed of the photoconductor drum and well-known electrophotographic process means arranged around the drum, are provided, and all the image-forming units are provided. It has a transfer belt 2 common to 1.

【0014】

In addition, it is parallel to the first transport path 5 and the first transport path 5 that vertically and downwardly transport the transfer paper fed from the large-capacity two-stage paper feed units 3 and 4, and the paper feed units 3 and 4. , The second transport path 6 which is a double-sided transport path that merges with the first transport path 5, the horizontal third transport path 7 which is a common transport path after merging, and the third transport path 7 It is equipped with a switchback provided in the above, a horizontal resist mechanism, a thick paper feeding unit 8 provided on the downstream side thereof, a paper ejection unit 9, and the like.

【0015】

FIG. 2 is a plan view of the switchback and lateral resist mechanism. In the third transfer path 7 shown in FIG. 1, a long cylindrical transfer roller 10 is provided on the upstream side in the transfer paper transfer direction before the switchback, and three rubbers are provided on the downstream side at intervals. Two sets of transfer rollers 11 and 12 are provided in which the transfer rollers of the above are provided on the same axis. The balls 13 and 14 are in contact with the transfer rollers 11a and 12a of the transfer rollers 11 and 12, and the transfer paper passes between them. Further, between the transfer rollers 11 and 12, there is provided a gathering roller 15 for performing lateral resist by abutting the transfer paper after switchback against the side fence 17. This gathering roller 15 comes into contact with the transfer paper only at the time of switchback, and retracts at other times. Further, a paper tip detection sensor 16 for detecting the tip of the transfer paper entering the switchback portion is provided.

【0016】

Here, returning to FIG. 1, in the third transport path 7, a vertical resist sensor 18 is provided in a portion where the transfer paper after switchback can be turned vertically, that is, in the vicinity of the upstream side of the transfer belt 2. There is. In addition, switching claws 19, 20, and 21 are appropriately provided in the transport path. Further, a fixing roller pair 22 is provided in the vicinity of the paper ejection portion. Further, paper tip detection sensors 23 and 24 are provided in the vicinity of the confluence of the first transport path 5 and the second transport path 6 at the same distance from the confluence, respectively. The thick paper is discharged to the upper surface of the main body by the paper ejection guide 25 forming the transport path having a large curvature.

【0017】

Next, the operation will be described. The transfer paper fed from the paper feed unit 3 or 4 is conveyed to the switchback unit through the first transfer path 5 and the third transfer path 7. Here, when the paper tip detection sensor 16 detects the tip of the transfer paper, the transfer rollers 10, 11 and 12 rotate in the reverse direction according to the signal to switch back the transfer paper. At this time, the transfer paper is abutted against the side fence 17 by the action of the gathering roller 15, and the lateral resist is adjusted.

【0018】

The transfer paper is then transferred to the transfer belt touchdown point through a portion of the third transfer path 7 that branches upward by the action of the switching claw 19. After the vertical resist sensor 18 detects the passage of the tip of the transfer paper, image is drawn at a predetermined timing according to the position of each image forming unit 1, so that each color toner image and the tip of the transfer paper match at each transfer position. The transfer paper is conveyed by the transfer belt 2. The transfer paper on which the full-color image is formed in this way is heat-fixed by the fixing rollers vs. 22.

【0019】

After the fixing is completed, the transfer paths are switched between the case of discharging paper on only one side and the case of printing on both sides by the switching claws 20 and 21.

【0020】

When performing double-sided printing, it is turned about 180 degrees at the top of the main body and transported to the second vertical transport path 6. The second transport path 6 is dedicated to double-sided printing, and the drive source is provided independently. The paper tip detection sensor 24 enables the paper tip detection sensor 24 to temporarily stop after detecting the tip. The transfer paper conveyed through the first transfer path 5 can also be temporarily stopped on the front side of the confluence by the paper tip detection sensor 23.

【0021】

At the time of double-sided printing, the transfer paper from the paper feed units 3 and 4 and the transfer paper with single-sided printing are alternately conveyed by the sequence control, and after merging, the transfer paper is passed through a common switchback and resist adjustment mechanism.

【0022】

The single-sided image-formed transfer paper that can be turned at right angles to the second transport path 6 to the third transport path 7 is switched back with the image side facing down, and the non-image-forming surface becomes the image-forming unit 1. It is conveyed by the transfer belt 2 so as to face each other, and an image is formed on this surface as well.

【0023】

A transport path for printing on thick paper with a large ream will be described. For example, in the case of thick paper with a ream weight of 180 kg or more, it is so-called stiff and the curvature of the transport path must be made very large to avoid jams, and the transport path and the outer shape of the main body must be large, which is not efficient. , The thick paper feeding unit 8 is provided at the above-mentioned position.

【0024】

The thick paper fed from the thick paper paper feed section 8 passes through the switchback transport mechanism section to form a full-color image in the same manner as normal transfer paper, but due to the action of the switching claw 20, the paper ejection guide 25 is removed from the machine. It is guided to (dedicated tray on the top of the main body).

【0025】

When adjusting the horizontal resist, the gathering roller 15 swings and comes into contact with the transfer paper, and the resist alignment is performed while abutting the side surface of the transfer paper against the side fence 17, but at this time, the rear end of the transfer paper is driven. Since the upper roller is a spherical ball 14 and the lower roller is a rubber roller 12a, the left and right movement with respect to the traveling direction cannot be regulated. Therefore, resist matching is performed smoothly.

【0026】

[Effect of the invention]

According to the invention of claim 1, since the transfer paper in which the inverted single-sided image has been formed can be sent to the transfer position by the switchback mechanism, the intermediate tray is eliminated and the configuration of the automatic double-sided mechanism is simplified and the cost is reduced. Can be planned. In addition, since an intermediate tray is not required, it is possible to print the front and back alternately, and at least the amount of paper feed capacity can be output continuously, so image data replacement and collating work can be performed efficiently. it can. Further, since a mechanism for stacking and re-feeding is not required, it is possible to improve the reliability of jams and the like at the time of re-feeding and reduce the number of parts.

【0027】

According to the invention of claim 2, the productivity and reliability of the automatic double-sided mode can be improved in the color copier.

【0028】

According to the invention of claim 3, the thick paper is ejected from the dedicated ejection portion having a large curvature. Therefore, for example, if the thick paper is ejected to the outer surface of the apparatus, the dead space can be effectively utilized. Damage to thick paper can also be prevented.

【0029】

According to the invention of claim 4, the reliability of single-sided paper feeding and double-sided paper feeding can be improved.

【0030】

According to the invention of claim 5, in addition to the above effects, it is possible to standardize the operation sequence (timing) after the confluence, and make the print speed on one side and the print speed on both sides substantially equal. Has the effect of making it possible.

[Simple explanation of drawings]

[Figure 1]

It is a block diagram of the image forming apparatus which shows one Embodiment of this invention.

[Figure 2]

It is a top view of the switchback and the horizontal resist mechanism.

[Explanation of symbols]

3,4 Paper feed unit 5 First transport route 6 Second transport route 7 Third transport route 10 ~ 15 Switchback mechanism components