JP3023373B2 - Double-sided printing device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a double-sided printing apparatus for printing an image on both sides of a sheet in a copying machine, a printer, a facsimile, or the like.

2. Description of the Related Art In one-sided printing mode, printed sheets are discharged to a paper output tray. In two-sided printing mode, printed sheets are stacked on an intermediate stocker, and the sheets of the intermediate stocker are fed to an image forming unit. In a copying machine in which paper is re-fed by rollers, as shown in FIG. 4, a rotating paper feed roller 51 is brought into contact with a surface opposite to a printing surface of a paper 50 placed on an intermediate stocker. Some items need to be re-fed. In this case, the contact pressure between the sheets 50 on the vertical line 52 passing through the center of the sheet feeding roller 51 is the highest. Also, since only the lowermost sheet 50 is pulled out, a part of the second sheet 50 located immediately above the lowermost sheet 50 on the vertical line 52 depends on the printing surface of the lowermost sheet 50 to be drawn out. Rubbed. Therefore, the toner or ink peeled from the printed image 53 on the entire surface of the lowermost sheet 50 will adhere to only a part of the second sheet 50 on the vertical line 52 of the non-printing surface. Part of the second sheet 50 is stained in a line. This stain is extremely unsightly because it appears on the printing surface when printing on both sides.

The refeeding method shown in FIG. 4 is referred to as a lower feed refeeding method in which the sheets stacked on the intermediate tray are re-fed in order from the lowermost layer. Even if an upper feed re-feeding method in which sheets are re-supplied in order from the lower layer is adopted, when the printing surface is stacked on the intermediate tray with the printing surface facing downward, the paper is stained as described above.

For this reason, as described in JP-A-1-303236, printing is performed on the upper surface of a sheet in the process of conveying the sheet along the lower outer peripheral surface of the photoreceptor on which the toner image is formed. In the case of the feed re-feeding method, the paper is stored in the intermediate tray with the printed side facing up, and in the case of the down-feed re-feeding method, the paper is placed in the intermediate tray with the printing side facing down. There is an image forming apparatus that is configured to house the image forming apparatus.

Problems to be Solved by the Invention It can be seen that the invention described in JP-A-1-303236 can make the stain on the printed surface less noticeable.

However, when obtaining a plurality of printed materials to be printed on both sides, the upper feed re-feeding type image forming apparatus waits until all of the specified number of sheets printed on one side are stacked on the intermediate tray. Since the paper must be re-fed in order from the upper layer, the printing processing speed is reduced.

On the other hand, the image forming apparatus of the lower feed re-feeding method can re-feed the sheets in order from the lowest layer before all the specified number of sheets are stored in the intermediate tray. However, since the paper printed on the upper surface is reversed and stored in the intermediate tray with the print surface facing down, the paper in the intermediate tray is re-fed to the image forming unit with the print surface facing down during duplex printing. Must be reversed again by the switchback mechanism. The reversal operation by the switchback mechanism causes a reduction in the printing processing speed.

The present invention is based on the pre-feed re-feeding method, and prevents the paper from being stained at the time of re-feeding while satisfying the condition of increasing the print processing speed by re-feeding the paper in the intermediate tray without switching back. It is an object of the present invention to provide a double-sided printing apparatus that can perform the printing.

Means for Solving the Problems The present invention provides a paper transport path extended toward a paper discharge unit,
An intermediate stocker positioned below the paper transport path; a curved path having one end selectively connected to the paper discharge side of the paper transport path and the other end connected to one end of the intermediate stocker; A single paper re-feeding path directly connecting the end of the sheet and the supply side of the sheet conveying path, and a clamp roller having a claw for gripping a leading edge of the sheet to be conveyed; Sheet inverting means for inverting the sheet from the leading edge side and feeding the sheet backward on the intermediate stocker by feeding the sheet backward in the tip direction;
An image forming unit provided inside the paper transport path, the curved path, the intermediate stocker, and the paper re-feed path and opposed to the paper transport path; and a sheet stored in the intermediate stocker in a lowermost layer. A sheet re-feeding means for feeding the sheet to the sheet re-feeding path in order from the sheet feeding section.

According to the present invention, the paper transported by the paper transport path is printed on the lower surface by the image forming unit, and in the case of double-sided printing, the printed paper is inverted downward by the curved path and again inverted by the paper inverting means. Then, the sheet is stacked on the intermediate stocker with the printing surface facing down, and is further turned upside down by the re-feeding path so that the printing surface faces up and is re-fed to the upper part of the image forming unit. When re-feeding from the intermediate stocker, the sheets stacked with the print surface facing down are sent out by the re-feeding means in order from the lowest layer, so that the printed image of the second sheet is peeled off. Even if it adheres to the lowermost sheet, the print image peeled off from the second sheet is a part facing the re-feeding means, and
Since the minute amount of the peeled image is dispersed and adheres to the upper surface of the lowermost sheet, the stain on the printing surface during double-sided printing can be made inconspicuous.
Before the set number of sheets are all stored in the intermediate tray, it is possible to re-feed the sheets in order from the bottom layer, so that the printing processing speed can be increased, and moreover, the number of sheets Since the sheet is directly supplied from the intermediate stocker to the sheet conveying path by the re-feeding path, the structure of the re-feeding path is simplified and the time required for re-feeding is shortened.

Embodiment An embodiment of the present invention will be described with reference to FIGS. As shown in FIG. 1, an image forming section 1 is provided. The image forming unit 1 scans a rotatable photoconductor 2, a charger 3 for applying a voltage to the photoconductor 2 to charge the photoconductor 2, and scans a charged portion of the photoconductor 2 with an optical signal corresponding to image information. It is composed of main components such as an exposure section 3a for forming an electrostatic latent image, a developing section 4 for developing the electrostatic latent image, and a cleaning device 5 for cleaning the photosensitive member 2. Reference numeral 6 denotes a transfer charger for transferring a developed image formed on the photoconductor 2 to paper. Further, a linear paper transport path 7 is provided from the direction A to the paper discharge section (not shown) provided in the direction B through the upper part of the photosensitive member 2. A fixing roller 8 for fixing the transferred image is provided, and a separation claw 9 for switching the conveyance direction of the sheet after fixing to the B direction or the C direction below is rotatably provided downstream of the fixing roller 8. Is provided. A curved path 10 that is curved in the direction C from the separation claw 9 is connected to an intermediate stocker 11 provided below the paper transport path 7. The curved passage 10 is provided with two sets of conveying rollers 13 each of which has a pinch roller 12 resiliently contacted thereto. At an end of the curved passage 10, a pair of conveying rollers 13 are opposed to the upper portion of the intermediate stocker 11 in parallel. A clockwise driven belt conveyor 14 is provided.

Further, at the lower end of the curved passage 10, the curved passage 10
A clamp roller 16 which is a sheet reversing means having a claw (not shown) for gripping the leading edge of the sheet 15 conveyed along the outer periphery is provided rotatably. When the two-sided copy mode is selected, the clamp roller 16 is driven 180 ° clockwise by gripping the leading edge of the sheet 15 passing through the curved path 10 with a nail, releasing the nail from the sheet 15, and Driven 180 ° clockwise for 15 receptions. Therefore, the paper 15 guided to the paper transport path 7 with the printing surface facing downward is inverted by the curved passage 10 and further inverted by the clamp roller 16 and stacked on the intermediate stocker 11 with the printing surface facing downward. Is done. When the composite copy mode for performing multiple copies on the same surface is selected, the function of the clamp roller 16 is stopped, so that the paper 15 passing through the curved path 10 is transported by the transport roller 13 and the belt conveyor 14. And is stacked on the intermediate stocker 11 with the printing surface facing upward. Although not visible on the drawing, on the axis of the clamp roller 16, one of the transport rollers 13 provided at the lower end of the curved passage 10 is provided.
Are arranged.

Further, below the intermediate portion and the right end portion of the intermediate stocker 11, a delivery roller 17 as a paper re-feeding means driven in a clockwise direction is arranged at a predetermined interval, and the right end of the intermediate stocker 11 and the paper A re-feeding path 18 connecting the supply side of the transport path 7 is provided to be curved in the direction of arrow D,
The re-feeding path 18 includes a sheet separating unit 19 and a conveying roller 20.
And are arranged. The paper separating means 19 is a feed roller
And a reverse roller 22 which resiliently contacts the feed roller 21. A paper press 23 is provided above the feed roller 17 located on the right end side of the intermediate stocker 11. Further, a movable plate 24 is held along the bottom surface of the intermediate stocker 11 so as to be reciprocally movable.
Is fixed to a part of an annular wire 26 driven by a step motor 25. During the moving range of the moving plate 24,
A home position sensor 27 for optically detecting the moving plate 24 is provided.

In such a configuration, the toner image formed on the outer periphery of the photoconductor 2 is transferred to the lower surface of the sheet 15 in the process of conveying the sheet 15 along the sheet conveying path 7 and is fixed by the fixing roller 8.

When the two-sided copy mode is selected, the separation claw 9 is raised to guide the fixed sheet 15 to the curved path 10 toward the arrow C, and the sheet 15 is transported to the intermediate stocker 11 by the transport roller 13 and the belt conveyor 14. . In the two-sided copy mode, as described above, the leading edge of the sheet 15 is gripped by the clamp roller 16 which is arranged on the same axis as the rear transport roller 13 and is driven intermittently every 180 °. Paper 15
Are stacked in the intermediate stocker 11 with the print surface facing downward so as to draw an S-shape. Further, by rotating the wire 26 by the step motor 25 and moving the moving plate 24 to the right, the stacked paper 15 is pressed to the right reference position of the intermediate stocker 11. Then, step motor 25
The movable plate 24 is returned to the home position by reversing. This position is detected by the home position sensor 27. Then, the sheet 15 of the intermediate stocker 11
When the paper is supplied to the paper transport path 7 through the above, the previous printing surface is directed upward.

Next, the paper feeding operation from the intermediate stocker 11 will be described in detail. The paper feed roller 17 is rotated clockwise, and at this time, the paper 15 on the intermediate stocker 11 is pressed by the paper presser 23 in synchronization with the rotation of the paper feed roller 17, so that the paper 15 on the intermediate stocker 11 is changed from the bottom layer. Sent out in order. Further, the feed roller 21 and the reverse roller 22 are driven clockwise. Accordingly, when a plurality of sheets 15 are sent out between the feed roller 21 and the reverse roller 22, the friction coefficient between the feed roller 21 and the sheet 15 and the friction coefficient between the reverse roller 22 and the sheet 15 are increased. Since the coefficient of friction is larger than the coefficient of friction between the sheets 15, only the lowermost sheet 15 is pulled out by the feed roller 21, and the sheet 15 below the next layer is returned to the intermediate stocker 11 side by the reverse roller 22. When one sheet of paper 15 is fed out between the feed roller 21 and the reverse roller 22, the reverse roller
Due to the slip operation of the torque limiter connecting the motor 22 and the motor, the reverse roller 22 rotates counterclockwise due to the frictional force with the paper 15 being conveyed. The paper 15 thus separated by the paper separating means 19 is transported by the transport roller 20.
Is transported toward the paper transport path 7 by the

As described above, the paper 15 transported by the paper transport path 7
Is printed on its lower surface by the image forming unit 1, and in the case of double-sided printing, the printed paper 15 is inverted downward by the curved path 10 and again inverted by the clamp roller 16 so that the printing surface is directed downward. The sheet is stacked on the intermediate stocker 11 in the state, and is further turned upside down by the re-feeding path 18 so that the printing surface is turned upward and the sheet is fed again to the upper part of the image forming unit 1. At the time of paper feeding, since the paper 15 stacked with the printing surface facing downward is sent out by the feed roller 17 in order from the lowermost one, the printed image of the second paper 15 is peeled off and the lowermost paper 15 Even if it adheres, the printed image peeled from the second sheet 15 is a part facing the feed roller 17 and a small amount of the peeled image is dispersed over the entire upper surface of the lowermost sheet 15. Printing, double-sided printing Dirty printing surface can be obscured in. Furthermore, even in the case of double-sided printing, it is possible to re-feed the sheets 15 in the lowermost layer in order before the set number of sheets 15 are all stored in the intermediate tray 11, so that the printing processing speed is increased. Can be.
In addition, since the sheet 15 is directly supplied from the intermediate stocker 11 to the sheet conveying path 7 by the single sheet re-feeding path 18, the structure of the sheet re-feeding path 18 is simplified and the sheet re-feeding is required. Time is reduced.

When the composite copy mode is selected, the function of the clamp roller 16 is stopped, so that the paper 15 passing through the curved path 10 is converted into a U-shape by the transport roller 13 and the belt conveyor 14 and printed. It is sent to the intermediate stocker 11 with its surface facing up. Therefore, the intermediate stocker
In a state where the eleven sheets 15 are supplied to the sheet transport path 7 through the re-feeding path 18, the previous printing surface is turned downward, and the second image is printed on the previously printed surface. When the composite copy mode is selected, the sheets 15 are stacked on the intermediate stocker 11 with the printing surface facing upward, and sent out in order from the lowermost sheet 15 as in the conventional example shown in FIG. Therefore, the print image of the lowermost sheet 15 adheres to the rear surface of the second sheet 15, but in the composite copy mode, printing is performed only on one side, so there is no problem.

Next, another embodiment of the present invention will be described with reference to FIG. The same parts as those in the above embodiment are denoted by the same reference numerals, and the description is omitted. An intermediate stocker 11 is provided above the paper transport path 7, a curved path 10 curved upward from the paper transport path 7 is connected to the left end of the intermediate stocker 11, and the right end of the intermediate stocker 11 is curved downward. The paper transport path 7 by the paper feed path 18
Connected to the supply side. At the end of the curved passage 10, a clamp roller 16 is arranged.
A convey roller (not shown) on which the pinch roller 12 resiliently contacts is arranged coaxially with the reference numeral 16. The image forming section 1 is provided below the paper transport path 7.

In such a configuration, the paper 15 conveyed by the paper conveyance path 7 is printed on the lower surface by the image forming unit 1, and in the case of double-sided printing, the paper 15 is turned upward by the curved path 10 and clamped. The intermediate stocker 11 is turned upside down again by the rollers 16 so that the printing surface faces downward and the upper intermediate stocker 11
To be loaded. Subsequently, the sheet is re-fed to the upper portion of the image forming unit 1 with the printing surface turned upside down by being turned downward by the re-feeding path 18. Re-feeding from the intermediate stocker 11 is the same as in the first embodiment.

Advantageous Effects of the Invention As described above, the present invention provides a paper transport path extending toward a paper discharge section, an intermediate stocker located below the paper transport path, and one end on the paper discharge side of the paper transport path. A curved passage selectively connected and the other end connected to one end of the intermediate stocker, a single re-feeding passage directly connecting the other end of the intermediate stocker and the supply side of the paper transport path, A clamp roller provided with a claw for gripping a leading edge of a sheet to be conveyed, and by rotating the clamp roller, the sheet is reversed from the leading edge side and the rear of the sheet is fed in the leading direction, so that the intermediate stocker has A sheet reversing means for storing a sheet by reversing the sheet, an image forming unit provided inside the sheet transport path, the curved path, the intermediate stocker, and the re-feed path and opposed to the sheet transport path; Stored in the intermediate stocker And the re-feeding means for sequentially feeding the sheets from the lowermost layer to the re-feeding path, so that the sheet conveyed by the sheet conveying path is printed on the lower surface thereof by the image forming unit. The printed sheet is inverted downward by the curved path, is again inverted by the sheet inverting means, is stacked on the intermediate stocker with the printing surface facing down, and is further inverted upward by the re-feeding path. The paper is re-fed to the upper part of the image forming unit with the printing surface facing up.When re-feeding from the intermediate stocker, the paper stacked with the printing surface facing down Since the print image is sent out by the re-feeding unit, even if the print image on the second sheet is separated and adheres to the lowermost sheet, the print image separated from the second sheet is opposed to the re-feed unit. Some , The small amount of peeling picture for attaching dispersed on the upper surface of the lowermost sheet can be made less noticeable contamination of the printed surface during two-sided printing,
Further, even in the case of double-sided printing, it is possible to re-feed the sheets in order from the lowest layer before all the set number of sheets are stored in the intermediate tray, so that the printing processing speed can be increased. In addition, since the sheet is directly supplied from the intermediate stocker to the sheet transport path by a single re-feed path, the structure of the re-feed path is simplified, and the time required for re-feed is reduced. And the like.

[Brief description of the drawings]

FIG. 1 is a side view showing one embodiment of the present invention, FIG. 2 is a partial longitudinal sectional side view, FIG. 3 is a side view showing another embodiment of the present invention, and FIG. FIG. DESCRIPTION OF SYMBOLS 1 ... Image forming part, 7 ... Paper conveyance path, 10 ... Curved path, 11 ...
Intermediate stocker, 15: paper, 16: paper reversing means, 17: refeeding means, 18: refeeding passage

Continuation of the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) G03G 15/00 106 G03G 15/00 510-534 B65H 83/00-85/00

Claims (1)

(57) [Claims] A sheet conveying path extending toward a sheet discharging unit;
An intermediate stocker positioned below the paper transport path; a curved path having one end selectively connected to the paper discharge side of the paper transport path and the other end connected to one end of the intermediate stocker; A single paper re-feeding path directly connecting the end of the sheet and the supply side of the sheet conveying path, and a clamp roller having a claw for gripping a leading edge of the sheet to be conveyed; Sheet inverting means for inverting the sheet from the leading edge side and feeding the sheet backward on the intermediate stocker by feeding the sheet backward in the tip direction;
An image forming unit provided inside the paper transport path, the curved path, the intermediate stocker, and the paper re-feed path and opposed to the paper transport path; and a sheet stored in the intermediate stocker in a lowermost layer. A double-sided printing apparatus, comprising: a sheet re-feeding unit for feeding the sheet to the sheet re-feeding path in order from the sheet feeding unit.