JP2688038B2 - Sheet transport device - Google Patents

Description

The present invention relates to a sheet conveying device in an image forming apparatus such as an electrophotographic copying machine, and more specifically, an image is formed at an accurate position on a sheet. Sheet conveying device for conveying a sheet. (B) Prior Art Generally, in this type of sheet conveying apparatus, in order to align the position of the transfer sheet sent from the paper feeding unit with the original image formed on the photoconductor by optically scanning the original, After temporarily stopping the transfer sheet at the timing roller, the timing roller is controlled to convey the sheet again in time with the position of the original image on the photoconductor to transfer the image on the photoconductor onto the sheet. It is like this. Such a conventional sheet conveying device will be described with reference to FIG. Reference numeral 30 denotes a timing roller pair that positions and conveys the transfer sheet 20, and a sheet detection unit 31 that detects the sheet fed from the sheet supply unit is provided on the upstream side in the sheet conveyance direction. This sheet detecting means 31
Is composed of a lever 32 and a photo sensor 33. The tip of the fed sheet pushes the lever 32, and when the lever 32 is rotated in the direction of the arrow, the lever 32 blocks the photo sensor 33, thereby detecting the passage of the sheet. Has been done. A photosensitive drum 12 that rotates clockwise in the drawing is installed on the downstream side of the timing roller pair 30, and an original image is formed on the photosensitive drum 12 by an optical system (not shown) at a point A. The original image is transferred onto the conveyed sheet at a transfer point B which is opposite to the original image. In the sheet conveying device having such a configuration, the sheet 20 fed out by the sheet feeding roller (not shown) from the sheet feeding portion provided with the cassette or the like reaches the timing roller pair 30 while being guided by the guides 26 and 53, and at the same time. The sheet detecting means 31 detects it. At this time, the timing roller pair 30 is stopped, and the leading end of the sheet 20 is stopped at the position of the nip C which is the contact point of the roller. On the other hand, the paper feed roller provided in the sheet supply unit is still
The sheet 20 continues to be fed, so that the sheet 20 forms a loop on the upstream side of the timing roller pair 30. The restoring force generated on the sheet 20 by this loop formation is transmitted to the sheet front end, and the sheet front end further enters the nip C by this force and is positioned. After a lapse of a predetermined time after the sheet detection unit 31 detects the sheet, that is, after a predetermined amount of loop of the sheet is formed, the sheet feeding roller is stopped and the sheet conveying device is in a standby state. While the sheet conveying device is operating as described above, the photosensitive drum 12 is rotating at the speed v while the original image is formed by the optical system of the copying machine at the point A, and the original image on the photosensitive drum 12 is transferred. Move toward position B. Therefore,
The timing roller pair 30 starts rotating so that the leading edge of the sheet coincides with the image at the leading edge of the document at point B, and feeds the sheet 20 through between the guides 37 and 39. Here, since the distance ▲ ▼ between the nip C and the transfer position B is known in advance, assuming that the peripheral speed of the timing roller pair is rotated at the same speed as the peripheral speed v of the photosensitive drum, the leading edge of the formed image is obtained. Is ▲
When the timing roller pair 30 is rotated when the position D on the surface of the photosensitive drum where ▼ = ▲ ▼ is reached, the leading edge of the original image and the leading edge of the sheet coincide with each other.
Actually, after the signal called the image destination signal indicating when the beginning of the original is started to be formed on the photosensitive drum is issued,
The timing roller pair 30 is adjusted so as to start rotating after ▼ / v time, and the paper feed roller is also restarted at the same time so that an unnecessary load is not applied to the timing roller pair. (C) Problems to be Solved by the Invention By the way, in the above-described sheet conveying apparatus, it is premised that the sheet leading edge reaches the nip C due to the restoring force of the loop formed on the sheet as described above. There is no problem with a so-called stiff sheet with strong wind, but depending on the type of sheet, the upstream guide of the timing roller pair 30
Due to the influence of 26 or the like, the leading edge of the sheet 20 may be caught and stopped at a position like C'shown by the broken line in FIG. 4, and it is difficult to perform accurate positioning particularly on a normal sheet having a weak waist. was there. Further, even if the leading edge of the sheet enters the nip C, the position of the sheet may change subtly depending on the thickness of the sheet, and the leading edge of the sheet may not be straight but may be deformed such as wavy. However, there is a drawback that it is very difficult to position the leading edge of the sheet at an accurate position. (D) Means for Solving the Problem The present invention aims to solve the above-mentioned problems, and a sheet leading edge detecting unit that detects the leading edge of a sheet fed from a sheet feeding unit; and the sheet feeding unit. The timing roller that conveys the sheet fed from the sheet to the transfer position of the image forming unit, and the sheet leading edge comes to a predetermined position between the timing roller and the image forming unit according to the detection signal of the sheet leading edge detecting unit. Stop the timing roller when
Next, the timing roller is driven at a timing corresponding to the image forming operation of the image forming unit to feed the sheet to the image forming unit, and the sheet feeding unit is provided in the stopped nip of the timing roller. The leading edge of the sheet sent from the above is abutted to position the leading edge of the sheet, and then the timing roller is driven at a timing according to the image forming operation of the image forming means without stopping the sheet midway. According to another aspect of the present invention, there is provided a sheet conveying apparatus including: a second mode for sending to an image forming unit; and a switching unit for switching between the first mode and the second mode. (E) Operation By adopting the above means, when the sheet fed from the sheet feeding section is a sheet that does not fit in the conventional positioning means, the timing roller rotates and is fed in synchronization with the sheet feeding. The sent sheet is sent as it is. or,
The leading edge of the sheet fed from the sheet feeding unit is detected by the sheet leading edge detection unit. Then, when the leading edge of the sheet reaches a predetermined position between the timing roller and the image forming means, the timing roller is stopped according to the detection signal of the sheet leading edge detecting means, the sheet is positioned at that position, and the next sheet feeding is performed. Wait for delivery. Then, the timing roller is re-driven at a timing according to the image forming operation of the image forming unit, the sheet is accurately fed to the transfer position of the image forming unit, and the image is transferred to the accurate position on the sheet by the image forming unit. It On the other hand, when the sheet to be fed is a sheet that fits in the conventional positioning means, the driving mode of the timing roller is switched, and the sheet fed from the sheet feeding section is fed by the nip of the timing roller that is stopped. Once positioned. After that, the timing roller is driven at a timing corresponding to the image forming operation of the image forming unit, and the sheet is sent to the transfer position of the image forming unit without being stopped halfway. At this time, even if the sheet leading edge detecting unit detects the leading edge of the sheet, the timing roller continues to rotate regardless of the sheet detecting operation of the sheet leading edge detecting unit, and sends the sheet to the transfer position as described above. A desired image is formed on the sheet sent to the transfer position by the image forming unit. (F) Example Hereinafter, examples embodying the present invention will be described with reference to the drawings. A copying machine 1 equipped with the sheet conveying apparatus of the present invention has a structure as shown in FIG. 1, and an original 3 is placed on an original platen glass 2 for placing an original, and a copy (not shown) is made. When the start button is pressed, the original 3 is displayed on the lamp 4 and the mirror.
5, 6 and 7 are exposed and scanned in the direction of the arrow, and the image is formed at a point A on the photosensitive drum 12 rotating clockwise in the figure via the lens 8 and the mirrors 9, 10 and 11. In this exposure scanning process, when the scanning point a by the lamp 4 passes the end reference position where the leading edge 3'of the original 3 is located, an image tip signal indicating the start of the scanning is issued, and the inside of the copying machine main body 1 is issued. This signal is sent to a controller (not shown) provided, and the controller thereafter controls each operation timing inside the copying machine with reference to the time of receiving this signal. The image tip signal is generated, for example, when a base provided with the mirror 4 passes through a photosensor installed at a predetermined position of the apparatus main body. The surface of the photosensitive drum 12 is uniformly charged by a charger 13 provided in front of the image forming position A point, and the original image projected at the point A is formed on the surface as an electrostatic latent image.
A color developing device 14 containing a toner of a desired color and a black developing device 15 containing a black toner are provided on the downstream side of the photosensitive drum 12 in the rotational direction, the color developing device 14 containing a toner of a desired color that can move toward and away from the photosensitive drum. Therefore, by selecting either of the developing devices, the electrostatic latent image on the photosensitive drum 12 is developed into an image of a desired color. On the other hand, the sheet feeding unit 16 of the copying machine 1 includes an upper cassette 17, a lower cassette 18, and a manual feed guide for manual feeding.
19 are installed. Separation rollers are provided on the upper parts of both cassettes to feed out the individually stored sheets 20.
21 and 22 are provided, and the fed sheet 20 is conveyed toward the timing roller 30 by the pair of paper feed rollers 23 and 24, respectively. In contrast to this, the manual feed guide 19 is configured to be rotated in the arrow direction so as to be in a substantially horizontal position when used, and the manual feed table 25 of the sheet 20 and the separation roller 21 is interlocked with this rotation. Enter the space and guide surface 19 '
By inserting a sheet along the sheet, it is possible to manually feed the sheet from the outside of the copying machine. Such manual feeding is usually used when a special transfer sheet such as an OHP sheet made of a polyester sheet that cannot be fed by being housed in the cassette 17 or 18 is used. These papers are very liable to be triboelectrically charged, and when many sheets are stacked and fed like a cassette paper feed, they are stuck to each other due to the electrostatic force generated by friction.
This is because it is difficult to separate and feed the sheets one by one, and the manual feeding is used to feed one by one or a small number of sheets on the manual guide surface 19 '. The sheet sent out from the paper feed roller pair 23 or 24 of the sheet supply unit 16 passes between the guides 26 and 27 or between the guides 28 and 29 and is sent to the timing roller pair 30. As shown in FIG. 2, on the upstream side of the timing roller pair 30 in the sheet conveying direction, a sheet front end detecting means 31 having the same structure as that of the conventional sheet conveying device is provided, and the lever 32 is rotated by the sheet 20. The photo sensor 33 detects the movement and detects that the leading edge of the sheet has been conveyed. In addition, at the point E on the downstream side of the timing roller pair 30 in the sheet conveying direction, a light emitting unit is provided.
A sheet leading edge detecting means 34 including a light receiving portion 36 and a light receiving portion 36 is provided, and the light emitted from the light emitting portion 35 passes through a hole 38 provided in a sheet guide 37 and a hole 40 provided in the guide 39. The light is transmitted to the light receiving unit 36. The light emitting unit 35 and the light receiving unit 36
Slits 41, 42 for narrowing the light flux on the light incident surface of
Is provided. Further, in the sheet conveying apparatus of the present embodiment, the cassette sheet feeding is selected for feeding a sheet which is not suitable for the conventional positioning means due to its weakness, and the sheet is strong and suitable for the conventional positioning means. In this case, manual feeding is selected. Then, as shown in FIG. 3, when the manual sheet feeding is selected, the sheet 20 fed from the sheet feeding unit 16 is fed.
Is positioned at the nip C of the timing roller pair 30 and waits (second mode), as in the conventional conveying device. On the other hand, when the cassette sheet feeding is selected, the fed sheet 20 passes through the rotating timing roller pair 30 as it is, and advances to a position where the sheet leading edge detecting means 34 detects the sheet leading edge, and this detection position is detected. Stop at and wait. And
The sheet 20 is conveyed by the timing roller pair 30 at the same timing as the original image formed on the photosensitive drum 12 reaches the transfer position B facing the transfer charger 43.
The original image is transferred onto the sheet 20 (first mode).
A separation charger 44 for peeling the sheet 20 from the photosensitive drum 12 is provided on the downstream side of the transfer charger 43, and the image-formed sheet 20 peeled from the photosensitive drum 12 has a conveyance unit 46. An image formed by being sent through the fixing device 47 is fixed. On the downstream side of the fixing device 47, a first discharge roller pair 48 for discharging the image-formed sheet to the discharge tray 52,
The guides 49 and 50 and the second discharge roller pair 51 are provided,
A cleaner 45 for removing the developer remaining on the surface of the photosensitive drum 12 is provided downstream of the separation charger 44 along the circumference of the photosensitive drum 12. The present embodiment is configured as described above, and its operation will be described next. First, when cassette feeding is selected and a weak ordinary sheet placed on a cassette is fed, the timing roller pair 30 rotates in synchronization with the feeding roller pair 23 or 24 of the sheet feeding unit. Seats 20 started and fed
The detection signal of the sheet leading edge detecting means operated by is ignored. Therefore, the sheet 20 is a pair of timing rollers.
The sheet is nipped by the sheet 30, conveyed as it is, and reaches the position of the sheet leading edge detecting means 34. Then, at the moment when the leading edge of the sheet intercepts the light flux of the sheet leading edge detecting means 34, the timing roller pair 30 and the feeding roller pair 23 or 24 are stopped by the signal emitted from the detecting means 34. The sheet is positioned at this position and stands by, and when the leading edge 3'of the original image formed on the photosensitive drum 12 reaches the point F where ▲ ▼ = ▲ ▼, that is, the image-destination signal of the copying machine main body 1 is sent. ▲ ▼ / V time after entering the controller, the controller outputs the timing roller rotation re-start signal. In response to this signal, the timing roller 30 is redriven at the same speed as the drum peripheral speed, and the sheet 20
Are sent to the transfer position B, and the transfer is performed by accurately aligning the leading edge of the transfer sheet with the leading edge of the original image (first mode).
In this embodiment, since the positioning is performed on the side closer to the transfer position than the conventional regulation position, the movement path from the stop position of the sheet front end to the transfer position becomes clearer and more accurate. It is possible to match the leading edge of the transfer sheet with the leading edge of the image. On the other hand, when manual feed is selected and a special strong sheet such as transparent OHP paper is fed,
The driving mode of the timing roller pair 30 is switched, and the sheet is positioned by using the nip portion C of the timing roller pair 30 which is stopped by the same operation as the conventional apparatus. Then, even if the sheet 20 sent out in accordance with the position of the original image formed on the photosensitive drum 12 is detected by the sheet leading edge detecting means 34, this detection signal is ignored in this mode and the timing roller pair 30 is used. Continues to be driven at a constant speed, and the sheet 20 receives the transfer of the original image at the transfer position B (second mode). At this time, the OHP paper is considerably stiffer than a normal transfer sheet, and the restoring force of the loop is strong, so that it is easy to surely enter the nip portion C of the timing roller pair 30 and the misalignment with the original image may occur. Very few. In the above embodiment, the drive mode (first mode and second mode) of the timing roller is switched between cassette sheet feeding and manual sheet feeding depending on the sheet feeding mode. Regardless of the above, the operation control of the timing roller may be selected on the operation unit of the copying machine so that the operation control of the timing roller is performed only for OHP paper. (G) Effect of the Invention As described above, according to the present invention, the sheet leading edge is set to the timing roller according to the detection signal of the sheet leading edge detecting means for detecting the leading edge of the sheet fed from the sheet feeding section. When the predetermined position between the image forming means is reached, the timing roller is stopped, and then the timing roller is driven at a timing according to the image forming operation of the image forming means to feed the sheet to the image forming means. In the first mode, the leading edge of the sheet sent from the sheet feeding unit is abutted against the nip of the pair of timing rollers that are stopped to position the leading edge of the sheet, and then the image of the image forming unit is imaged. A second mode in which the timing roller is driven at a timing according to the forming operation and the sheet is sent to the image forming unit without being stopped halfway; Since it is configured to switch between, the original image can be formed at an accurate position on any type of sheet. Further, in the mode in which the timing roller is stopped and re-driven in response to the detection signal of the sheet leading edge detecting means, the sheet is positioned by the leading edge detecting means, so that the thickness of the sheet or the deformation of the sheet leading edge such as waviness is deformed. By this, the position does not vary, and it is possible to position at an accurate position.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side view of an image forming apparatus equipped with a sheet conveying apparatus according to the present invention, FIG. 2 is an enlarged view of a main portion of the sheet conveying apparatus, and FIG. 3 is the sheet conveying apparatus. And FIG. 4 is an enlarged view of a main part of a conventional sheet conveying device. 1 ... Image forming apparatus (copier), 12 ... Photosensitive drum, 16
…… Sheet supply unit, 17,18 …… Cassette, 19 …… Manual feed guide, 20 …… Sheet, 30 …… Timing roller,
31: Sheet leading edge detecting means, 34: Sheet leading edge detecting means.

   ────────────────────────────────────────────────── ─── Continuation of front page    (56) References JP-A-58-14159 (JP, A)                 JP-A-56-39562 (JP, A)                 JP 60-87360 (JP, A)                 JP 60-216359 (JP, A)

Claims (1)

(57) [Claims] A sheet leading edge detecting unit that detects the leading edge of the sheet fed from the sheet feeding unit, a timing roller that conveys the sheet fed from the sheet feeding unit to the transfer position of the image forming unit, and a sheet leading edge detecting unit The timing roller is stopped when the leading edge of the sheet reaches a predetermined position between the timing roller and the image forming unit according to the detection signal, and then the timing is set at a timing corresponding to the image forming operation of the image forming unit. The first mode in which the roller is driven to feed the sheet to the image forming unit and the leading edge of the sheet sent from the sheet feeding unit is abutted against the nip of the timing roller that is stopped After positioning, the timing roller is driven at a timing according to the image forming operation of the image forming means to move the sheet. In the sheet conveying apparatus characterized by comprising: a second mode for sending the image forming means without stopping, and a switching means for switching between the first mode and the second mode. 2. The sheet conveying apparatus according to claim 1, wherein the switching unit is a sheet feeding switching unit that switches between manual sheet feeding and cassette sheet feeding. 3. On the upstream side of the timing roller in the sheet conveying direction,
The sheet conveying device according to claim 1 or 2, wherein the sheet leading edge detecting means is provided.