JPS6382275A - Sheet conveying method - Google Patents

Abstract

PURPOSE:To sharply shorten the time required for forming each image on both sides, by conveying a sheet at high speed when conveying it through a reconveying route with a roller pair to form the image again. CONSTITUTION:Conveying speed of a sheet S in a sheet conveying route ranging from an image forming part to a roller pair 33, is set to first speed, and conveying speed of the sheet S in a reconveying route 36 is set to second at high speed, respectively. A sheet detecting device 35, detecting whether there is the sheet S or not, is set up in the sheet conveying route, while there is provided with a speed selecting device A which selectively changes each revolving speed of these paired rollers 33 to the first and second ones, and the sheet S being conveyed at the first first speed by clockwise rotation of the roller pair 33 is detected by the sheet detecting device 35, operating the speed selecting device A, and thereby the roller pair 33 are reversed at the second speed. When each image is formed on both sides of the sheet S, or at the time of image formation being performed, the sheet S is conveyed at the normal conveying speed that the image formation takes place optimally.

Description

Detailed Description of the Invention (a) Industrial Application Field The present invention relates to a sheet conveying method in an image forming apparatus such as a copying machine or a laser beam printer. It relates to a sheet conveyance method when carrying out

(B) Conventional Technology Conventionally, as an example of a sheet conveyance method when performing double-sided copying, first, a sheet that has been copied on one side at a constant speed within the main body of the copying machine is transferred to a bin tray outside the main body of the copying machine by a pair of forward-rotating discharge rollers. After being conveyed at the same constant speed with the copied side facing up, it is then conveyed again into the copying machine main body at the same constant speed by the reverse rotation of the pair of discharge rollers, and then again through the same conveying path. A feeding method is adopted in which sheets are conveyed at a constant speed, so that copies are made even on the uncopied back side of the sheet, resulting in double-sided copying.

←→ Problems to be Solved by the Invention However, in the above-mentioned conventional sheet conveyance method, the sheet (well, even when forming an image or being conveyed through a re-conveying path for double-sided copying) Since the paper is transported at a high speed, there is a drawback that the time required for double-sided copying is longer.

2) Means for Solving the Problems The present invention aims to solve the above-mentioned problems, and it is an object of the present invention to reduce the sheet conveyance speed in the sheet conveyance path from the image forming section to the discharge roller pair to the normal speed. 1 speed, and then set the sheet transport speed on the re-transport path to the high speed 2nd speed.
A sheet detecting means for detecting the presence or absence of a sheet is arranged facing the sheet conveyance path, and the rotational speed of the discharge roller pair is selectively switched between the first speed and the second speed. A switching means is provided, and the sheet detecting means detects a sheet conveyed at the first speed by the forward rotation of the pair of discharge rollers, and operates the speed switching means, thereby switching the pair of discharge rollers to the first speed. Its feature is that it rotates in the opposite direction in second gear.

(e) Operation Based on the above-mentioned configuration, the sheet on which an image has been formed on one side at the first speed in the image forming section is transported, for example, to the outside of the main body of the image forming apparatus by the forward rotation of the discharge roller pair based on the forward rotation of the forward/reverse rotation driving means. When the sheet is conveyed at the first speed with the image-formed side facing up, and the sheet detection means detects the sheet, the speed switching means is actuated by the detection signal from the sheet detection means, and the ejection roller The pair is rotated in the opposite direction while holding the rear end of the sheet, and the rotation speed is increased to the second
can be switched quickly. As a result, the sheet is again transported into the main body of the image forming apparatus, which is equipped with a re-conveyance path that also conveys the sheet at the second speed, by a pair of ejection rollers that rotate in the opposite direction at the second speed. After being conveyed at the second speed, the sheet is conveyed to an image forming section to form an image again on the other side of the sheet on which the image has been formed.

(F) Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings.

As shown in FIG. 2, the copying machine U includes a document table 7, a light source 9,
The copying machine includes a lens system 10, two cassettes 11 and 12, and a cylindrical photoreceptor 13 disposed within the main body of the copying machine. Further, near the periphery of the photoconductor 13, there are two developing units 15 and 16 each containing toner of a different color, a cleaner 17, and a primary charger 19, and a transfer charger 21 is provided at the tip of the conveying device 20. and a separation charger 22 are provided. Further, paper feed rollers 23 and 25 are arranged in the cassettes 11 and 12, and the sheets S stored in the cassettes 11 and 12 are guided to a pair of registration rollers 29 via paths 26 and 27, respectively.

Further, a fixing device 30 is disposed at the rear end portion of the beam feeding device 20, and a flapper 31 is disposed downstream of the fixing device 30, and is displaced to a position shown by a solid line or a position shown by a chain line. ing. Further, an upper guide plate 34a and front and rear lower guides 34b and 34c are fixedly installed around the flapper 31, and when the flapper 31 is displaced to the solid line position, a sheet is formed between the flapper 31 and the upper guide plate 34a. A sheet ejection path 3 that guides S to the outside of the main body of the copying machine U is configured, and is a sheet transport path from the image forming section to the ejection roller pair, from the photoreceptor 13 to the transport device 20, the fixing device 30, and the sheet ejection path 3. A sheet conveyance path for conveying the sheet to the discharge roller pair 33 is formed. Furthermore, as shown in detail in FIG. 3, the flapper 31 has a shaft 31a that penetrates the flapper 31 and fixes and supports the flapper 31, which is attached to the side plate 3.
8 and is rotatably supported. An arm 40 is fixed to one end of the shaft 31a, a spring 41 is tensioned at one end of the arm 40, and a flapper 31
is biased to the solid line position shown in FIG.

A solenoid 42 is connected to the other end of the arm 40, and the excitation of the solenoid 42 switches the flapper 31 to the chain line position shown in FIG. Further, a large number of auxiliary guide members 32 are disposed in the upper part of the upper guide plate 34a in a comb-teeth shape so as to be rotatable around a shaft 32a extending between both side plates 38. It protrudes into the sheet discharge path 3 through the notch, allows the sheet to flow toward the discharge roller pair 33, and guides the sheet returned from the discharge roller pair 33 to the sheet conveyance path 36.

Further, the discharge roller pair 33 consists of an upper roller 33a and a lower roller 33b, and the lower roller 33b is fixed and the side plate 38
A forward/reverse DC motor 43 is connected to the lower roller shaft 33b', which is rotatably supported by the lower roller shaft 33b'. It is linked via. Further, the forward/reverse DC motor 43 is controlled to rotate forward and reverse by a signal from the control section C (FIG. 1), and is controlled to rotate normally by the operation of the speed switching means A built in the control section C. The speed is changed from the first speed to the second speed.

Further, as shown in FIG. 2, near the discharge roller pair 33, a sheet trailing edge detection sensor 35 consisting of an optical sensor 35a and a sheet detection lever 35b is installed. Grabbed by vs. 33,
When the rear end of the sheet discharged outward from the sheet discharge path 3 is detected, a detection signal is input to the control section C.

Further, a sheet re-feeding path 36 is formed below the flapper 31, and the sheet re-feeding path 36 is connected to the high-speed second
A pair of conveyance rollers 37° 39 and a pair of lateral registration rollers 1 which are rotated at a high speed are arranged, and the registration rollers 29
is communicated with.

Note that in FIG. 2, reference numeral 45 is a pin tray on which the sheets discharged from the pair of discharge rollers 33 are stacked.

Since this embodiment has a hypothetical configuration, when the light source 9 moves, the original M placed on the original platen 7 is irradiated by the light source 9, and the reflected light passes through the lens system 10 and is first An image is formed on the surface of the photoreceptor 13 that is uniformly charged by the charger 19 to form an electrostatic latent image, and then, based on the rotation of the photoreceptor 13 in the direction of the arrow, the electrostatic latent image is transferred to the developer 15 or A toner image is formed at 16 positions. On the other hand, cassette 11 or 1
The sheets S stacked on the paper feed roller 23 or 25
and is aligned with the toner image on the surface of the photoreceptor 13 by the registration roller 29, and then transferred to the transfer charger 2.
The toner image is transferred to the sheet surface at one location. Further, the sheet S carrying the toner image is separated from the photoreceptor 13 by a separation charger 22 and transferred to a fixing device 30 by a conveyance device 20.
and is fixed at the fixing unit @s30.

When the double-sided copy mode is selected, the sheet S fixed by the fixing device 30 is guided by the flapper 31 at the solid line position shown in FIG.
The discharge roller pair 33 is rotated by the forward rotation of the forward/reverse DC motor 43.
is rotated forward, brought into focus, and conveyed onto the file 5. At this time, the auxiliary guide member 32 is blocking the sheet ejection path 3, but since the auxiliary guide member 32 is made of a light member and is supported rotatably in the direction of arrow F, the sheet S As it passes, it is pushed up by the leading edge of the sheet and is retracted from the sheet S, so that it does not interfere with the passage of the sheet S. Furthermore, when the sheet 1-S is conveyed by the forward rotation of the ejection roller pair 33 and the trailing edge of the sheet S is detected by the sheet trailing edge detection sensor 35, the detection signal causes the controller C and its internal speed to be switched. Means A is activated, and the forward and reverse DC motor 43 is rotated in the reverse direction, and its rotational speed is switched from the first speed to the high speed second speed. As a result, the sheet S is reversely rotated at the second speed and guided by the pair of discharge rollers 33 to the auxiliary guide member 32 and the flapper 31, and guided to the sheet re-conveying path 36.

Furthermore, the sheet S is conveyed at second speed in front of the stopped horizontal registration roller pair 1 by the rotation of the conveyance roller pair 37 and 39, and after the tip of the sheet S hits the registration roller pair 1, the conveyance roller vs. 37.39 has been suspended,
The sheet S is stopped in front of the pair of lateral registration rollers 1 without forming a loop. Then, when a copy signal for the other side is transmitted from the copying machine main body, the structural registration roller pair 1 is rotated, and the horizontal registration roller pair 1 bites into the sheet S. The sheet S is moved in a direction perpendicular to the sheet conveyance direction until the end is detected by an optical sensor (not shown), and the position of the sheet S with respect to the conveyance direction is adjusted. Further, the sheet S is conveyed by the register 1-roller pair 29, and the toner image is transferred to the back surface (the non-copied surface) of the sheet by the photoreceptor 13, the transfer charger 21, etc., in the same manner as described above. After being further fixed by the fixing device 30, the sheet copied on both sides is discharged to the outside of the copying machine main body by a pair of discharge rollers 33.

(g) As described in detail, according to the present invention, the conveying speed of the sheet S in the sheet conveying path from the image forming section to the roller pair 33 is set to the first speed, and the conveying speed of the sheet S in the re-conveying path 36 is set to the first speed. Sheet detection means 3 that sets the conveyance speed to a high second speed and detects the presence or absence of sheet ]-3 on the sheet conveyance path.
5, and a speed switching means A for selectively switching the rotational speed of the roller pair 33 between the first speed and the second speed, and by forward rotation of the roller pair 33, the conveyance is carried out at the first speed. The sheet S detected by the sheet detecting means 35 is actuated to operate the speed switching means A, thereby causing the pair of rollers 33 to rotate in the reverse direction during the second pass, so that images can be formed on both sides of the sheet S. When performing image formation, the sheet S is conveyed at a normal conveyance speed at which image formation is optimally performed, and at the same time, the sheet S is conveyed at a normal conveyance speed at which image formation is performed optimally.
Since the sheet S is conveyed at high speed when being conveyed through the re-conveyance route Fe136 by No. 3, it is possible to form images on both sides despite the simple means and without any adverse effect on the formed images. It has become possible to significantly shorten the time required to do so.

[Brief explanation of the drawing]

Fig. 1 is a functional block diagram showing the configuration of the present invention, Fig. 2 is a side view showing a copying machine to which the sheet conveying method according to the invention is applied, and Fig. 3 shows its ejection roller pair and surrounding parts. FIG. 13. 20, 30, 3, 33... sheet conveyance path (photoreceptor, feeding device, fixing device, sheet ejection path, ejection roller pair), 33... roller pair (ejection roller pair),
35... Sheet detection means (sheet trailing edge detection sensor), 36... Re-conveyance path (sheet re-conveyance path),
43... Forward and reverse drive means (forward and reverse DC motor),
A...speed switching means, C...control unit, U...image forming apparatus (copying machine).

Claims (1)

[Claims] (1) In a sheet conveyance method in which a sheet is conveyed by forward rotation of a pair of rollers, and then the sheet is conveyed again to an image forming section by reverse rotation of a pair of rollers, the sheet is on a sheet conveyance path from the image forming section to the pair of rollers. The conveyance speed of the sheet is set to the first speed, and the conveyance speed of the sheet in the re-conveyance path is set to the high speed second speed. A speed switching means is provided for selectively switching the rotation speed between the first speed and the second speed, and the sheet detecting means detects the sheet conveyed at the first speed by the forward rotation of the pair of rollers. A sheet conveying method characterized in that the speed switching means is operated, thereby causing the pair of ejection rollers to rotate in reverse at the second speed.