JPH01303246A - Automatic document carrying equipment - Google Patents

Abstract

PURPOSE:To prevent a document once discharged from being carried again below a document carrying roller so as to prevent jamming, etc., by providing a discharge roller which is driven only in a direction to discharge the document and a floating roller which rotates in contact with the discharge roller. CONSTITUTION:By separately driving a document carrying roller 30 and a discharge roller 45 in rotation, documents are discharged by both rollers. At this juncture, the discharge roller 45 is supported by its shaft via a one-way- clutch 461, and at the same time, installed in a state in which it is in contact with a floating roller 35. For this reason, driving force is not transmitted by the one-way-clutch 461, to the discharge roller 45 while the document carrying roller 30 is rotating in the normal direction where the document is carried toward a plate on which the document is placed and the discharge roller 45 and the floating roller 35 are kept in a halt states. Thus, reverse carrying of the discharged document can be prevented from being taken in by the discharged roller 45.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Field of Application> The present invention relates to an automatic document feeder that carries in and ejects documents using rollers that are in contact with a document placement plate.

<Prior Art> In recent years, in image forming apparatuses such as electrostatic copying machines, automatic document feeders (A
DF) has become popular, and an example of this automatic document feeder is the one disclosed in Japanese Patent Application Laid-Open No. 118551/1983.

This automatic document feeder is equipped with a paper feeder that feeds the original placed on the document feeder, and the feeder transports the fed original to a predetermined position on the contact glass. After the scanning exposure for
A conveyance means is provided for discharging the document conveyed onto the contact glass onto the upper surface of the document presser.

However, this conveyance means consists of an endless conveyor belt attached to the bottom of the document holder, and the mechanism for driving this conveyor belt is complicated, which increases the manufacturing cost of the automatic document feeder. Additionally, there is a problem in that the device is too large to be applied to small-sized copying machines and the like.

Therefore, as a self-help document conveying device to solve these problems, as shown in FIG. The present applicant has proposed an original document conveyance roller (93) which is provided in contact with the upper surface of a contact glass (92) and is rotatable in forward and reverse directions. 83-81333). This document transport roller (93) is connected to the document holding portion (94).
) is attached to the recess (95) formed on the lower side surface of the
During forward rotation, the original (S) is conveyed to a predetermined position on the contact glass (92), and during reverse rotation, the original (S) being conveyed onto the contact glass (92) is reversely conveyed.

Then, the reversely fed original (S) is sent above the original transport roller (98) along the recess (95), and a driven discharge roller contacts directly above the original transport roller (93). (96) so that the document is discharged onto the upper surface of the document holding section (94).

<Problems to be Solved by the Invention> By the way, the automatic document feeder disclosed in the specification and drawings of Patent Application No. 61333 of 1988 has various drawbacks and inconveniences found in conventional automatic document feeders. Although this is an excellent product that includes various improvements that skillfully solved the problem, the following disadvantages have become clear. That is, when the automatic document feeder finishes copying the document (S),
The original document (S
) is discharged onto the original holding unit (94). However, in the automatic document feeder described above, when the document feed roller (93) rotates in the forward direction to convey the next document (S), the rear end of the discharged document (S) approaches the discharge roller (96). If the original (S) remains in the original position, the ejection roller (96) is driven by the document transport roller (93) and rotates in reverse, so the ejected original (S) is transported backwards by the ejection roller (9B) and is then transported again. The document is sent below the document transport roller (93), and a jam occurs.

Further, as described above, when the document conveyance roller (93) is reversed to discharge the copied document (S) onto the document presser (94), the discharge roller (96) is rotated by the document conveyance roller (
93), the rear end of the document (S) is rotated by the document transport roller (93) and the contact glass (92).
After passing the contact position with the document, the rotation of the document transport roller (93) and the rotation of the discharge roller (96) must be continued until the document passes the discharge roller (96).
The original document (S) cannot be completely ejected.

Therefore, the document transport roller (93) continues to rotate more than half a revolution even though there is no document (S) between it and the contact glass (92).
Each time the document S) is discharged, the document conveying roller (93) idles in direct contact with the contact glass (92).

The document conveyance roller (93) is made of a material with a high friction coefficient to ensure reliable conveyance of the document (S), so friction with the contact glass (92) due to idle rotation may cause abnormal noises such as chatter. Otherwise, the document transport roller (93) may wear out prematurely. Furthermore, since the document conveyance roller (93) does not rotate smoothly, there is a problem that a load is applied to the drive system and torque fluctuation becomes large.

SUMMARY OF THE INVENTION In view of the above-mentioned problems, an object of the present invention is to provide an automatic document feeder that can prevent reverse feeding of a document that has already been ejected. It is an object of the present invention to provide an automatic document conveying device that can be used without causing any abnormal noise from a document conveyance roller.

Means for Solving the Problems> In order to achieve the above object, the automatic document feeder of the present invention includes a paper feeding means for feeding the original on the original feeding table toward the original placing plate; It is provided in contact with the plate and is configured to be rotatable in forward and reverse directions to convey the original fed from the paper feeding means to a predetermined position on the original placing plate and to feed the conveyed original in the opposite direction. A document conveyance roller, a floating roller that is rotatably mounted coaxially with the document conveyance roller and provided in a non-contact state with respect to the document placement plate, and a document holding roller that holds the document reversely fed by the document conveyance roller. an ejection path for ejecting the document to the upper part of the document; an ejection roller that is rotatably supported via a one-way clutch that allows rotational drive in the document ejection direction and that is provided in contact with the idle roller within the ejection path; The present invention is characterized by comprising a drive means capable of driving each of the paper feed means, the document transport roller, and the ejection roller at predetermined timings.

Furthermore, when the trailing edge of the document to be reversely fed passes through a contact position between the document transport roller and the document placement plate, the driving means
The image forming apparatus may further include an electromagnetic clutch that stops rotation of the document transport roller.

<Function> According to the automatic document feeder having the above configuration, the document feed roller and the discharge roller can be driven to rotate individually, and the document can be discharged by both rollers.

In particular, the ejection roller is supported via a one-way clutch and is provided in contact with the idle roller, so it is always driven to rotate only in the direction of ejecting the original, without being driven by the rotation of the original transport roller. be able to.

Therefore, when the ejection roller does not need to rotate, in other words, when the original transport roller rotates normally when the original is sent toward the original plate, even if the original transport roller is driven, the ejection roller has a one-way No driving force is transmitted by the clutch, and the ejection roller and idle roller can be kept stationary, thereby preventing the ejected document from being taken in by the ejection roller and sent backwards.

Further, the driving means for driving the document conveyance roller can stop the rotation of the document conveyance roller when the trailing edge of the document being reversely fed passes through the contact position between the document conveyance roller and the document placement plate. If an electromagnetic clutch is installed,
By stopping the rotation of the document conveyance roller when the document passes between the document conveyance roller and the document placement plate,
Friction between the document transport roller and the document placement plate can be prevented.

<Example> Next, FIGS. 1 to 7 show an example of the present invention.
This will be explained below with reference to the figures.

As an image forming apparatus, for example, an electrostatic copying machine (1) is provided with an optical system, an image processing section, and a paper conveying section inside a housing (11) as is well known.
) and a contact glass (12) serving as a document placement plate for placing a document on top of the contact glass (12), which can be freely opened and closed between a closed position that covers the contact glass (12) and an open position that releases the contact glass (12). Formed document holding part (13)
is provided. In addition, on the right and left sides of the nozzle (11), there are a paper feed cassette (16) that supplies paper and a discharge tray (16) that receives copied paper.
[7) is provided.

A document supply table (18) for placing a plurality of sheet-like documents is provided on the side of the document presser (13), and there is a border between the document feeder table (18) and the document presser (13). An automatic document feeder (2) is attached to the section (see Fig. 2).

As shown in FIGS. 1 and 3, this automatic document feeder (2) is a paper feeder that sequentially feeds the documents on the document supply table (18) one by one toward the contact glass (12). means(
20) is provided in a recess (130) formed on the side of the original holding part (13), and conveys the original to the contact glass (12).
) and a document conveying roller (30) that can be rotated in forward and reverse directions and reversely conveys the document conveyed above the document conveying roller (30).
) is provided coaxially with the shaft (301) of the document feeder (301) and is sandwiched between the freely rotatable floating roller (35), the recess (130) on the paper feed means (20) side, and the document transport roller (30). A discharge path (40) is provided and opened toward the upper surface of the document holding part (13), and a discharge path is provided directly above the document transport roller (30) and in contact with the floating roller (35). It includes a roller (45), and a driving means (50) for driving the paper feeding means (20), each roller (aO), and the roller (45) at a predetermined timing.

The document supply table (18) has a contact glass (12)
It is arranged in an inclined state with the side lowered, and a detector (181) is arranged below near the lower end to check whether the original (S) is placed on the original supply table (18). It is set up. This detector (181) has a detection arm (
182) The leading end is exposed on the surface of the document supply table (18), and the presence or absence of the document is detected by being rotated downward by the weight of the document (S) placed thereon. Original supply table (
A document restraining member (185) for preventing the placed document (S) from moving forward until the feeding timing is reached is attached to the lower end of the device 18). This document restraining member (185) is made of a member with a cross section that is rotatable about the shaft (LH), and usually has a tension spring (
The original supply table (18) is in a state of being protruded upward due to the urging force of the original (187), and the solenoid (1
88), the leading edge is rotated below the document supply table (18) and the document (S) is allowed to advance.

The paper feeding means (20) feeds the original (S) on the original supply table (18).
) for initial feeding one by one, and a paper feed roller mechanism for feeding this original (S) toward the contact glass (12) and preventing double feeding of originals (S). (220).

The feed roller mechanism (210) has a pair of rollers whose base end is rotatably attached to a rotating shaft (221) on the paper feed roller mechanism (220) side, and whose tip end extends upstream of the document supply table (18). A support arm (211), a shaft (212) rotatably attached to the tip of the support arm (211), and a plurality of shafts arranged at appropriate intervals in the axial direction of the shaft (212). and a delivery roller (213) (see also FIG. 4). A stepped portion (214) is formed at the base end of the support arm (211).

The separation roller mechanism (220) includes a restraining member (185)
On the downstream side of the document (S), a shaft (221) and a shaft (2
22), a plurality of paper feed rollers (223) arranged at appropriate intervals in the axial direction of the shaft (221,), and a shaft (222).
), and leave an appropriate interval in the axial direction of the paper feed roller (
223) and a plurality of separation rollers (224) arranged alternately.
It is composed of. A substantially crescent-shaped notch (223a) is formed in a part of the outer peripheral surface of the paper feed slot (223). This notch (223a) is
is located on the separation roller (224) side except when feeding the document (S), and even if the document (S) is interposed between the paper feed roller (223) and the separation roller (224), the document transport (described later) The conveyance of the document (S) by the rollers (30) is not obstructed.

The separation roller (224) is rotated in synchronization with the paper feed roller (223) when the document (S) is fed by the paper feed roller (223), and rotates in the opposite direction to the feeding direction of the document (S). This is to prevent double feeding of documents (S).

A shaft (231) is rotatably disposed between the delivery roller (213) and the paper feed roller (223) in parallel to these shafts (212) and (221).
), a pair of cams (232) are fixed at positions corresponding to the pair of support arms (211). These cams (232) each have an actuation protrusion (234), which is connected to the support arm (211).
), the support arm (211>) can be restrained at a separate position above the document (S) (see FIG. 3).

The delivery roller (213) is supported by a shaft (212).
and the toothed pulleys (21, 5) (225) attached to the shaft (221) of the paper feed roller (223), respectively. The driving force is transmitted from (221).

Note that a document (S) is located downstream of the paper feed roller (223).
) to detect that the document feeding table (18
A detector (181) similar to the detector (181) attached to )
24,0) is provided.

The document conveying roller (30) is made of a synthetic resin material with a large friction coefficient and is provided at appropriate intervals in the longitudinal direction of a shaft (301) provided in the recess (130) of the document holding part (13). The lower end of each roller's circumferential surface is covered with contact glass (1
2) is placed in constant contact with (see Figure 3). The idle roller (35) is provided to be sandwiched between the two document conveyance rollers (30) in the center, and has a diameter smaller than that of the document conveyance rollers (30).
Although it is provided coaxially with the shaft (301) of 0), it is provided in a non-fixed state with the shaft (301) by inserting a bearing (351) etc., so that it can always rotate freely ( (See especially Figure 5).

The discharge roller (4) that is in contact with this idle roller (35)
5), as shown in FIG.
It is attached via a one-way clutch (481) and is rotationally driven only in the direction of ejecting the original (S) toward the original holding part (13) (counterclockwise in FIG. 3).

As shown in FIG. 3, the discharge path (40) has a curved shape sandwiched between the document transport roller (30) and the inner surface of a recess (130) formed along the circumferential surface of this roller. The upper end side is opened toward the upper part of the document holding part (13). At the lower end of this discharge path (40),
A guide means (41) is provided for guiding the reversely fed original (S) to the discharge path (40). This guide means (41
) is made of a flexible piece of synthetic resin such as polyester film with a thickness of about 0.075 mm, and allows the original (S) to enter from the original supply table (18) onto the contact glass (12). However, contact glass (12)
This prevents the original (S) from being fed backwards toward the original supply table (18) from above and deflects it upward.

As shown in FIGS. 4 and 6, the drive source of the drive means (50) is composed of a reversible C motor (510), and a gear (511) attached to this DC motor (510). A gear (242) provided through a one-way clutch (241) engages with the foot (222) of the separation roller (224), thereby transmitting the driving force for rotationally driving the paper feeding means (20). be done.

Further, as shown in FIGS. 4 to 6, a rotational drive transmission system (52) having a plurality of idle gears is connected to the gear (511) of the DC motor (510), and the rotational drive transmission system (52) is connected to the gear (511) of the DC motor (510). The shaft (
A gear (303) provided in the device (301) is rotationally driven.

The shaft (301) of this document transport roller (30) has a fifth
As shown in the figure, an electromagnetic clutch (32) is provided so that the rotation of the shaft (301,) can be stopped even though the gear (303) is rotating. The gear (303) is engaged with a gear (453) fixed to the shaft (451) of the discharge roller (45), and the discharge roller (45) is provided inside the discharge roller (45),
It is attached to the shaft (451) via a one-way clutch (481) that is driven only when the document conveyance roller (30) is reversed.

As shown in FIG. 7, the drive device (20) is driven by a gear (22B) provided at the other end of the shaft (222) of the separation roller (224), so that the paper feed roller (223) is moved in the same direction. A gear (227') provided on the shaft (221) of the paper feed roller (223) is engaged with the paper feed roller (223) via an idle gear (226a) so as to rotate the paper feed roller (223). This gear (227
) is interposed with a spring clutch (229) controlled by a solenoid (228). Spring clutch (229
) has one locked protrusion (229a) on the outer peripheral surface of the boss.
is provided, and when the solenoid (22g) is energized for a very short time, the solenoid pawl (228a) is disengaged from the locked projection (229a), and the spring clutch (229
) connections are made. At this time, the solenoid claw (228a
) to return to its original position in a short period of time, the spring clutch (229) rotates once, and then the solenoid claw (
228a) will be locked to the locked projection (229a), and the clutch (229) will be disconnected.

The gear (227) has a spring clutch (229) and a
The gear (23G) that has become a body is attached, and the gear (23G)
B), the shaft (232) on which the cam (232) is attached
The gear (238) of 231) is engaged with the idler gear (237). Therefore, when the spring clutch (229) is connected, the shaft (231) rotates, and the operating protrusion (234) of the cam (232) attached to this shaft (231) moves to the stepped portion of the support arm (211). (214
), the support arm (211) rotates downward, the feed roller (213) rotates and falls onto the original (S), and feeding of the original (S) begins.

The rotational drive transmission system (52), as shown in FIG.
Idle gears (522) (523) (52) are attached to the support plate (521) rotatably attached to the housing (11) side.
4) are arranged, and the support plate (521) is resiliently biased upward. Therefore, the document holding part (1
3), when the gear (303) of the document transport roller (30) engages with the rotational drive transmission system (52), the idle gear (3H) on the gear (303) side and the idle gear (524) If the tips of the teeth overlap with each other, remove the support plate (
521,) is slightly rotated downward, and when the idler gear (524) starts to rotate, the two engage and the support plate (521) is lifted to continue transmitting the driving force. It has become so.

Next, the operation of the automatic document feeder (2) will be described with reference to FIGS. 3 and 8 (ω to C1) and the timing chart of FIG. 9.

When a sheet-like original (S) is placed on the original supply table (18), the detector (181) on the side of the original supply table (18) is closed, and the original (S) to be copied is placed on the original supply table (18). ) is output. When this signal is output, operation of the print start button (PS) (see Figure 2) is permitted, and when this button (PS) is pressed, the DC motor (510) rotates in the normal direction (in Figure 6, the (direction indicated by F). After a short time tl (about 150ms) for the rotation of the DC motor (510) to stabilize,
A solenoid (18) rotates the document restraining member (185).
ft) is excited, and feeding of the original (S) is permitted.

Also, the gear (242) rotates from the gear (51, 1) of the DC motor (510), and the one-way clutch (241)
Together with the shaft (222), the separation roller (224) rotates. When this shaft (222) rotates, the gear (227) of the paper feed roller (221,) starts rotating from the gear (22B) fixed to the other end, and the button (PS
) is pressed, the time t2 (3
00is), the solenoid (228) briefly t3(
150ms), and the spring clutch (229) provided on the gear (227) is connected. When this spring clutch (229) is connected, as described above,
The cam (232) rotates, the feed roller (213) rotates and falls onto the document (S), and feeds one document (S) toward the paper feed roller (223).

The fed original (S) is continuously transported by the paper feeding roller (223) in the direction of the original transport roller (30), and
The detector (240) is turned on by this document (S) (see FIG. 8 (J). At this time, the separation roller (224)
is rotating in the opposite direction to the conveyance direction of the document (S), so
If the second or subsequent documents (S) are fed in duplicate, their movement can be prevented.

In this way, the paper feeding means (20) can feed the document (S) until the leading edge of the document (S) comes into contact with the document conveyance roller (30), and also allows the document (S) to come into contact with the document conveyance roller (30). The paper feed roller (223) continues to rotate slightly even when the original (S)
is directly facing the document transport roller (30), and the document (S)
The posture of the person is corrected correctly. Figure 8 shows a state in which the original (S) is in contact with the original transport roller (30). In addition, 14 indicates the time it takes for the leading edge of the document (S) to contact the document transport roller (3o) after the detector (240) is turned on, and after the DC motor (510) starts normal rotation. The time required for the original conveyance roller (30) to start rotating is indicated by the symbol A in FIG.

After the detector (240) is turned ON and a predetermined time t4 has elapsed, the electromagnetic clutch (32) for starting the rotation of the document transport roller (30) is activated, and the document is transferred onto the contact glass (12). Transport of (S) is started. At the same time, the pulse counter (33) provided on the shaft (301) of the document transport roller (30)
2) Count the number of pulses nl from the time of activation until the time of OFF of the detector (240). The length of the original (S) corresponding to this pulse number 01 corresponds to the length excluding the length from the detector (240) to the original transport roller (30).

The connection time of the electromagnetic clutch (32) is determined by the detector (24).
A predetermined number of pulses n2 (detector (24
0) to the document transport roller (30)) and to completely stop them against the rotational inertia of the rollers and gears. This is the time obtained by adding the extremely short time t5 required for reversing. Electromagnetic clutch (3
2) If the document (S) is cut off, the document (S) should be placed on the contact glass (
12) The rear end of the original (S) is placed at the lower end of the original transport roller (30), and this state is shown in FIG. 8 (C1). The time is indicated by the symbol B in Fig. 9. - When the original (S) is exposed and scanned and the copying is completed, the
At the same time as the C motor (510) starts reverse rotation, the electromagnetic clutch (32) is also connected again (however, the electromagnetic clutch (32) may also be connected during exposure scanning). D
When the C motor (510) rotates in the reverse direction, the document transport roller (
30) rotates in the opposite direction to the direction in which the original (S) was conveyed, and the ejection roller (45) is rotated by a one-way clutch (461) toward the original holding part (13), which is the ejection direction of the original (S). Start rotating.

Therefore, the original (S) is fed backwards, guided to the ejection path (40) by the guide member (41), and reaches between the ejection roller (45) and the idle roller (35) (see Fig. 8). ),
After the document is printed, the document is discharged onto the upper part of the document presser (13) by the discharge roller (45).

The electromagnetic clutch (32) is connected until the leading edge of the document (S) passes between the ejection roller (45) and the idle roller (35) (indicated by symbol C in FIG. 9), and then The connection is broken. The document transport roller (30) becomes freely rotatable when the electromagnetic clutch (32) is disconnected.
As the original (S) is discharged, it is rotated and the original (S) is rotated as it moves.
Stop when S) passes.

The DC motor (510) drives at least the discharge roller (35).
) is ejecting the original (S), that is, the period corresponding to the pulse n1 and pulse n2 plus the time for the original (S) to pass half a revolution around the original transport roller (30) is reversed. rotated (indicated by C and D in Figure 9)
.

Note that when ejecting this original (S), the paper feeding means (20)
are all stopped by a one-way clutch (241) provided on the shaft (222) of the separation roller (224).

The transport and ejection operations for one original (S) are as described above, but while the original (S) is placed on the original supply table (18), in other words, the detector (181) While the switch is ON, sheets are fed one by one, and conveyance, copying, and ejection are repeated.

<Effects of the Invention> As described above, according to the automatic document feeder of the present invention, the ejection roller that is driven only in the ejection direction of the original and the idle roller that rotates in contact with the ejection roller are provided. It is possible to prevent the original from being sent downward to the original transport roller again, thereby preventing the occurrence of a jam or the like.

In addition, by providing an electromagnetic clutch in the drive means, it is possible to stop the rotation of the document transport roller at a predetermined timing, so that abnormal noises such as chattering noises that are generated when the document transport roller rubs against the document placement plate can be avoided. It is possible to prevent premature wear of the document transport rollers. Furthermore, since the document conveyance roller rotates smoothly, no load is applied to the drive system, and torque fluctuations can be prevented.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of an automatic document feeder according to an embodiment of the present invention, FIG. 2 is a perspective view of an electrostatic copying machine equipped with an automatic document feeder, and FIG. 3 is a cross-section of the automatic document feeder. 4 is a plan view of the automatic document feeder, FIG. 5 is a sectional view of the document feed roller side, FIG. 6 is a partial rear view of the drive means, FIG. 7 is a partial front view of the drive means, 8 (ω to (d) are cross-sectional views each illustrating the operation of the automatic document feeder, FIG. 9 is a timing chart showing the operation of the automatic document feeder, and FIG. 10 is a conventional automatic document feeder. It is a schematic configuration diagram of (18)...document supply table, (20)...paper feeding means, (30)...document transport roller, (32)...electromagnetic clutch, (35)... ...Idle roller, (40)
...Discharge path, (45)...Discharge roller, (50
)...Driving means, (461)...One-way clutch, (S)...Document. Figure 3 Figure 5 Figure 6 Figure 7 Figure 8 (Q) Figure 8 (b) Figure 8 (C) Figure 8 (d)

Claims (1)

[Claims] 1. Move the original on the original supply table towards the original placing plate. A feeding means for feeding the paper to the from the paper feeding means. Place the fed document in the specified position on the document placement plate. At the same time, the transported raw materials are It is designed to be able to rotate in forward and reverse directions to feed the original in reverse. the original transport roller and the original transport roller. Coaxially and rotatably mounted, the original It is installed in a non-contact state with respect to the manuscript placement plate. the idle roller and the document transport roller above. Therefore, the document that has been sent backwards should be placed on the top of the document holder. the ejection path from which the document is ejected, and the direction in which the original is ejected. One-way clamp that allows rotational drive of The above-mentioned Set in contact with the idle roller in the discharge path. a cut-off ejection roller, the above-mentioned paper feeding means, the document transport roller and ejection roller respectively. drive hand that can be driven at a predetermined timing. A self-contained vehicle characterized by comprising steps and Automatic document feeder. 2. Move the original on the original supply table towards the original placing plate. A feeding means for feeding the paper to the from the paper feeding means. Place the fed document in the specified position on the document placement plate. At the same time, the transported raw materials are It is designed to be able to rotate in forward and reverse directions to feed the original in reverse. the original transport roller and the original transport roller. Coaxially and rotatably mounted, the original It is installed in a non-contact state with respect to the manuscript placement plate. the idle roller and the document transport roller above. Therefore, the document that has been sent backwards should be placed on the top of the document holder. the ejection path from which the document is ejected, and the direction in which the original is ejected. One-way clamp that allows rotational drive of The above-mentioned Set in contact with the idle roller in the discharge path. a cut-off ejection roller, the above-mentioned paper feeding means, the document transport roller and ejection roller respectively. is formed so that it can be driven at a predetermined timing. The trailing edge of the original that is being fed backwards is the contact between the document transport roller and the document placement plate. When passing the position, the document transport roller Equipped with an electromagnetic clutch that stops the rotation of A driving means is provided. Automatic document feeder.