JPH08254760A - Image reader - Google Patents

Abstract

PURPOSE: To provide an image reader equipped with a small-sized inexpensive automatic document feeder capable of feeding a both-side document in a short longitudinal length and which can be installed in a small space, as for an image forming device. CONSTITUTION: After a document P which is fed to a reading position and read is picked up from a contact glass 4 by scooping up an endless belt 46 on which non-uniform electric field is impressed and separating it from the contact glass 4 through a solenoid 41, the document P is fed while switching a feeding path by a switching pawl 19 to either of the path on a paper ejecting means 16 side, or a switchback means 18 side.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image reading device,
More specifically, a reading unit configured to move when reading a document that is stationary on the contact glass and stop at a predetermined reading position when reading a document conveyed on the contact glass; The present invention relates to an image reading apparatus having an automatic document feeder capable of feeding a document to a reading position and discharging the read document.

[0002]

2. Description of the Related Art Conventionally, there are various methods for reading an original by an image reading apparatus such as a copying machine or a scanner, and various automatic original feeding apparatuses corresponding to the reading method have been developed. For example, when the reading optical system is moved (scanned) to read a document, the document is conveyed to the contact glass by the automatic document feeder and stopped on the contact glass, and the reading optical system is moved in this state to move the document. After reading the document, there is a device in which the sheet is discharged to the outside (for example, Japanese Utility Model Laid-Open No. 62-63255, JP-A-33040).
(See the official gazette). With this, when reading a book document, etc., after opening the automatic document feeder from the contact glass and placing the document on the contact glass, the automatic document feeder covers the contact glass and reads it. The original is read by moving the optical system.

However, in the image reading apparatus equipped with such an automatic document feeder, a long conveyor belt for conveying the entire surface of the original onto the contact glass is required, so that the conveyor becomes large and Since the reversing path of the original and the stack area have to be installed beside the contact glass, there is a problem that the apparatus becomes even larger. Further, since the document is conveyed to the contact glass and then read by resting the document, the document reading performance is very poor.

As a solution to such a problem, there is a so-called sheet-through type automatic document feeder for reading a document while feeding it to a fixed reading optical system (for example, Japanese Utility Model Laid-Open No. Sho 58-180828). Japanese Patent Laid-Open Publication No. 2-112642 and Japanese Laid-Open Patent Publication No. 2-198941). This one can read the original surface by the reading optical system fixed through the slit glass by conveying the original to the narrow slit glass without keeping the original still on the contact glass. Since the reading performance is improved and a long conveyor belt is not necessary, the device can be downsized.

However, in the image reading apparatus equipped with such an automatic document feeder, since there is no contact glass, it is impossible to read a book document or the like, and there is a problem that it lacks versatility. Will end up. Therefore, recently, various image reading apparatuses capable of reading both book originals and sheet through originals have been developed. This device moves when reading a document that is stationary on the contact glass, and a reading unit that is configured to stop on the slit glass when reading the document that is being conveyed, and a reading unit that is located at the predetermined reading position. It is provided with an automatic document feeder that can convey a document and discharge the read document (see, for example, Japanese Patent Laid-Open No. 2-48679).
However, in this case, a slit glass for reading a sheet-through document is required in addition to the contact glass, so that the apparatus becomes large and costly.

On the other hand, there is one in which a book original and a sheet-through original are read by one contact glass (Japanese Unexamined Patent Publication No. 2-77075), and this one reads an original that is stationary on the contact glass. It has a reading optical system that moves during reading and stops at the edge of the contact glass when reading a conveyed document.When reading a sheet-through original, the original placed on the original table is contacted. The document is conveyed toward the edge of the glass, and the original after being read at the edge of the contact glass is carried out from the edge of the contact glass by the transport rollers and discharged onto the discharge tray on the side of the machine. Has become. In this case, the apparatus can be made compact and low in cost because the book original and the sheet through original can be read by one contact glass.

[0007]

However, in the image reading apparatus having such a conventional automatic document feeder, the document after being read at the edge of the contact glass is fed from the edge of the contact glass. Since it is carried out by rollers and discharged onto the discharge tray on the side of the main body of the device, it is possible to install a discharge tray on the side of the main body or to pick up documents on the discharge tray on the side of the main body. There is a problem in that the automatic document feeder is lengthened in the longitudinal direction by the area required for the mechanism, which increases the installation space of the image reading apparatus.

Further, when reading a book original, since there is no pressing cover for pressing the original above the contact glass used for reading the sheet-through original, the entire contact glass is effectively used. In order to read a large-sized original, a contact glass having an area for reading a large-sized original is required in addition to the area of the contact glass required for reading a sheet-through original. There is also a problem that the image reading device becomes large.

Therefore, according to the first aspect of the present invention, the sheet-through original is scooped up on the pressing cover above the contact glass and discharged, and the scooped original is switched back to be returned to the contact glass reading position. Thus, it is an object of the present invention to provide an image reading apparatus that has a small-sized and low-cost automatic document feeder capable of feeding a double-sided original with a short length in the longitudinal direction and can be installed in a small space. .

It is an object of the present invention to provide an image reading apparatus capable of surely picking up an original document and conveying it to a paper discharge means or a switchback means. In the invention according to claim 3, the space above the contact glass can be effectively utilized, and
Provided is an image reading apparatus having an automatic document feeding device capable of feeding a double-sided document with a compact and low-cost configuration by making it possible to configure the document placing table and the switchback passage with the same member. Is intended.

According to a fourth aspect of the present invention, an image reading apparatus having an automatic document feeder capable of shortening the carrying time by making it possible to return the switched back document to the carrying means through a short carrying path. Is intended to provide. According to a fifth aspect of the present invention, the drive roller forming the paper discharge means and the switchback means is formed of the same member, and the image is provided with an automatic document feeder capable of simplifying the structure and reducing the cost. It is intended to provide a reader.

According to a sixth aspect of the invention, the size of the original is large, the leading edge of the original is sandwiched between the first pressure roller and the drive roller, and the rear edge of the original is sandwiched between the second pressure roller and the drive roller. In such a case, the document is firmly clamped by the second pressure roller and the drive roller, and is clamped by the first pressure roller and the drive roller with a relatively small clamping force, so that the load at the time of conveying the document is reduced. Can be reduced,
An object of the present invention is to provide an image reading apparatus having an automatic document feeder which can sufficiently protect a document and improve the transport performance.

According to the seventh aspect of the present invention, the front and rear edges of the original are detected, and the switching means and the switchback means are controlled based on the detected information, so that the double-sided original can be reliably printed regardless of the size of the double-sided original. An object of the present invention is to provide an image reading apparatus having a highly reliable automatic document feeder which can be switched back and returned to the reading position again. According to the invention described in claim 8, a sheet through document and a book document can be reliably read by one contact glass, and an automatic document feeder having a short length in the longitudinal direction is placed on the contact glass. Therefore, it is an object of the present invention to provide an image reading apparatus that can be further downsized.

It is an object of the present invention to provide an image reading apparatus capable of reading a large-sized original by using the entire surface of the contact glass. According to the invention of claim 10, when a book document or the like is stationary on a contact glass and the document is read, a high-quality image of the document can be read without changing the background color and density of the entire document. It is an object of the present invention to provide an image reading device that can be used.

[0015]

According to the first aspect of the present invention,
In order to solve the above-mentioned problem, a reading configured to move when reading a document that is stationary on the contact glass, and to stop at a predetermined reading position when reading a document conveyed on the contact glass And an automatic document feeder that can convey the document to the predetermined reading position and discharge the read document, wherein the automatic document feeder is mounted on a contact glass. A pressing cover that presses the original onto the contact glass, an original placing table that is provided above the pressing cover and on which a plurality of originals can be placed, and an original feed port is formed on the edge of the contact glass. The document stack placed on the document table is fed from the paper feed port, the documents are separated from the document stack one by one, and the separated documents are inverted to move toward a predetermined reading position. And separating and conveying means for feeding, the separation and
A conveyance unit having a scooping mechanism that conveys the document conveyed toward a predetermined reading position by the conveyance unit to the reading position, and scoops the document read at the reading position to separate it from the contact glass; and the scooping unit. A sheet discharging unit that discharges the document picked up by the mechanism onto the pressing cover, and a document that is provided adjacent to the sheet discharging unit and that is picked up by the scooping mechanism is conveyed to the switchback passage, and then the contact glass is predetermined. Of the switchback means for reversing and returning to the reading position of the document and the upstream of the switchback means and the discharge means in the document conveying direction, and the document picked up by the scooping mechanism is either the switchback means or the discharge means. Switching means for switching the carrying direction so that the paper is carried to one side or the other. It is characterized by a door.

According to a second aspect of the present invention, in order to solve the above-mentioned problems, in the first aspect of the invention, the conveying means is an endless belt made of a dielectric material, and the front and rear of the endless belt in the conveying direction of a document. An endless belt, which comprises a pair of belt conveying rollers provided at an end portion, wherein the scooping mechanism moves the roller on the downstream side in the original conveying direction of the rollers toward and away from the contact glass, and an endless belt. And an application member for applying a voltage alternating with the.

In order to solve the above-mentioned problems, the invention according to claim 3 is characterized in that, in the invention according to claim 1 or 2, the switchback passage is provided in a lower portion of the document placing table. According to a fourth aspect of the invention, in order to solve the above-mentioned problems, in the invention according to any one of the first to third aspects, the original returned from the switchback passage by the switchback means is conveyed toward the conveying means. It is characterized by having a transport path.

According to a fifth aspect of the invention, in order to solve the above-mentioned problems, in the invention according to any one of the first to fourth aspects,
The switchback means is composed of a drive roller that is driven to rotate in forward and reverse directions, and a first pressure roller that is pressed by the drive roller and that can sandwich an original document together with the drive roller. It is characterized in that it is composed of a second pressure roller which is pressed by the roller and which can hold the document together with the driving roller.

In order to solve the above-mentioned problems, the invention according to claim 6 is the invention according to claim 5, wherein the contact pressure between the first pressure roller and the drive roller is the same as the second pressure roller. It is characterized in that it is smaller than the contact pressure with the roller. According to a seventh aspect of the invention, in order to solve the above-mentioned problems, in the invention according to any one of the first to sixth aspects, a document which is provided upstream of a direction in which the document is conveyed with respect to the conveying means and which is conveyed is provided. A front and rear edge detection sensor for detecting the front and rear edges, and a control means for controlling the switching means and the switchback means based on the front and rear edge detection information output from the front and rear edge detection sensor are provided. I am trying.

In order to solve the above-mentioned problems, the invention according to claim 8 is the invention according to any one of claims 1 to 7,
The stop position of the reading unit at the predetermined reading position is set within the range of the reading region of the reading unit when the document is stationary on the contact glass. Claim 9
In order to solve the above problems, the invention described in claims 1 to
8. The invention according to any one of claims 8 to 9, wherein the pressing cover is composed of a pressure contact pad in which a sheet is attached to a resin foam member, and the roller of the endless belt on the downstream side in the document conveying direction is an end of the pressure contact pad. When the original is placed on the contact glass and the stationary original is read by the reading means, the endless belt is brought into contact with the contact glass so that the original is attached by the endless belt and the pressure contact pad. The feature is that it is pressed onto the contact glass.

[0021] In order to solve the above-mentioned problems, the invention of claim 10 is the invention of claim 9, wherein the color of the sheet surface of the endless belt is the same as the color of the pressure contact pad surface facing the contact glass. It is characterized by having done.

[0022]

According to the first aspect of the present invention, the automatic document feeder conveys the document, which is separated by the separating / conveying means and then conveyed toward the predetermined reading position, to the reading position and reads at the reading position. Conveying means having a scooping mechanism for picking up the picked-up original and separating it from the contact glass, paper discharging means for discharging the picked-up original by the scooping mechanism onto the pressing cover, and provided adjacent to the paper discharging means. , A switchback means for transporting the document picked up by the scooping mechanism to the switchback passage, and then inverting and returning it toward a predetermined reading position of the contact glass, and an upstream side of the switchback means and the discharging means in the document transport direction. Switchback means and paper discharge means for the originals that are picked up by the scooping mechanism. And switching means for switching the conveying direction to convey either one, and a.

Therefore, after the original document which has been conveyed to the reading position and whose reading has been completed is scooped up above the contact glass by the scooping mechanism, the conveying path is switched to the sheet discharging means side by the switching means and the original is placed on the contact glass. When the two-sided original is ejected and the one-sided original is read, the original that has been read on one side is scooped up above the contact glass by the scooping mechanism, and then the transport path is switched to the switchback means by the switching means. After being transported to the switchback passage, it is switched back and returned to the reading position of the contact glass again.

Therefore, since the original is picked up and discharged to the discharge means or the switchback means,
The structure between the transport means, the paper discharge means, and the switchback means is simplified to reduce the space of the document transport path, and the document is discharged to the discharge tray on the side of the image reading apparatus body as in the conventional case. Since the paper is not printed, the length of the automatic document feeder in the longitudinal direction is shortened, and the double-sided document can be transported in a small space. As a result, the automatic document feeder can be downsized, the cost thereof can be reduced, and the installation space of the image reading apparatus can be reduced.

According to a second aspect of the present invention, the conveying means is composed of an endless belt made of a dielectric material, and a pair of belt conveying rollers provided at the front and rear portions of the endless belt in the original conveying direction. The scooping mechanism is composed of a proximity separating member that separates the roller on the downstream side of the original conveyance direction from the contact glass, and an applying member that applies an alternating voltage to the endless belt.

As a result, the document is attracted to the endless belt by a strong suction force, and in this state, the document is picked up from the contact glass and separated from the contact glass, so that the document can be reliably conveyed by either the conveying means or the switchback means. Be transported to. In the present invention, an alternating voltage is applied to the endless belt when, for example, the endless belt is uniformly charged with a direct current (for example, as such a conventional example, JP-A-63-63). 288843),
This is because a sufficient suction force cannot be obtained, and if an alternating voltage is applied to the endless belt, the charge densities + σ and −σ are alternately formed on the surface of the belt, so that a large suction force is applied to the endless document. Is sucked into the belt.

According to the third aspect of the present invention, since the switchback passage is provided in the lower portion of the document placing table, the space above the contact glass is effectively used, and
The switchback passage is formed of the same member as the document placing table, and the double-sided document is transported while further downsizing and cost reduction of the automatic document feeder. Claim 4
In the invention described above, since the transport path for transporting the document returned from the switchback path by the switchback means toward the transport means is provided, the switched-back document is returned to the transport means through the short transport path, and the transport time is reduced. Is shortened.

According to another aspect of the invention, the switchback means comprises a driving roller which is driven to rotate in the forward and reverse directions, and a first pressure roller which is pressed by the driving roller and can pinch the original with the driving roller. At the same time, the paper discharge means is composed of a second pressure roller that is pressed by the drive roller and can hold the document together with the drive roller. Therefore, the driving roller forming the paper discharging means and the switchback means are made of the same member, the structure of the automatic document feeder is simplified, and the size and cost are further reduced.

According to the sixth aspect of the invention, the contact pressure between the first pressure roller of the switchback means and the drive roller is smaller than the contact pressure between the second pressure roller of the paper discharge means and the drive roller. There is. Therefore, when the size of the document is large and the leading edge of the document is sandwiched between the second pressure roller and the driving roller, and the trailing edge of the document is sandwiched between the first pressure roller and the driving roller, the second pressure is applied. The document is firmly sandwiched by the rollers and the drive roller, and is sandwiched by the first pressure roller and the drive roller with a relatively small sandwiching force, so that the load at the time of transporting the document is reduced. As a result, the document is sufficiently protected and the conveyance performance is improved.

According to a seventh aspect of the present invention, a front and rear end detection sensor which is provided upstream of the conveying means in the conveying direction of the original and detects the front and rear ends of the conveyed original, and the front and rear end detecting sensor outputs the front and rear end detecting sensors. Since it has a control means for controlling the switching means and the switchback means based on the detection information of the front and rear edges of the original, the double-sided original is surely switched back and read again regardless of the size of the double-sided original. Will be returned to the location.

In the eighth aspect of the invention, the stop position of the reading means at the predetermined reading position is set within the reading area of the reading means when the document stands still on the contact glass. Sheet-through originals and book originals can be reliably read by the glass, and the image reading apparatus can be made even smaller by mounting the automatic original feeding device having a short length in the longitudinal direction on the contact glass. Planned.

According to a ninth aspect of the present invention, the pressing cover is composed of a pressure contact pad in which a sheet is attached to a resin foam member, and the roller of the endless belt roller on the downstream side in the document conveying direction is the pressure contact pad. The endless belt is provided close to the end portion, and when the original is stationary on the contact glass and the stationary original is read by the reading unit, the endless belt is brought into contact with the contact glass to press-contact the endless belt. The original is pressed against the contact glass by the pad. Therefore, when reading a book document or the like, the entire contact glass is used to read a large size document.

According to the tenth aspect of the invention, since the color of the sheet surface of the endless belt and the color of the pressure-contact pad surface facing the contact glass are the same, the book original or the like is kept still on the contact glass and the original is fixed. When the document is read, the background color and density of the entire document do not change, and the image of the document is read with high quality.

[0034]

Embodiments of the present invention will be described below with reference to the drawings. 1 to 10 are views showing a first embodiment of an image reading apparatus according to the invention described in any one of claims 1 to 10. First, the configuration will be described. In FIGS. 1 to 3, 1 is a scanner device as an image reading device, and this scanner device is composed of a reading unit 2 and an automatic document feeder 3.

The reading unit 2 has a main body 2a having a contact glass 4 on its upper surface, a light source 5 housed in the main body 2a, which is a fluorescent lamp or a halogen lamp for irradiating the original through the contact glass 4, and a light source. A plurality of mirrors 6 to 8 that reflect the light applied to the document, a lens 9 that collects the reflected light, a light that is collected by the lens 9 is read, and an analog signal is converted into a digital signal, which is not shown. The image pickup device 10 is composed of a CCD or the like for outputting to an image forming device.

The light source 5 and the mirrors 6 to 8 move in the left-right direction in FIG. 1 along the extending direction of the contact glass 4 to read a stationary book original on the contact glass 4, and at the same time, in FIG. A sheet-through document, which will be described later, is read by stopping at the left end, and the stop position is the contact glass 4 as shown by the one-dot chain line in FIG.
Is set in the reading area S of. The light source 5, the plurality of mirrors 6 to 8, the lens 9 and the image pickup device 10 described above constitute a reading unit.

Further, an automatic document feeder 3 is provided on the main body 2a of the reading section 2 so as to open and close with respect to the contact glass 4 so as to cover the contact glass 4. The automatic document feeder 3 has a holding cover 11 for holding the document placed on the contact glass 4 against the contact glass 4.
And a document tray 12 as a document placing table on which a plurality of sheet documents can be placed, and the document stacks placed on the document tray 12 are separated one by one, and the separated documents are inverted to perform a predetermined reading. Separating / conveying means 13 for conveying toward the position, and the original conveyed by the separating / conveying means 13 toward the predetermined reading position is conveyed to the reading position, and the original read at the reading position is conveyed. Scoop up the contact glass 4
Conveying means 15 having a scooping mechanism 14 for separating from the
And a discharge means for discharging the originals picked up by the scooping mechanism 14 to the discharge tray 11a on the pressing cover 11.
16 and a switchback means which is provided adjacent to the paper discharge means 16 and which conveys the original scooped up by the scooping mechanism 14 to the switchback passage 17 and then reverses it toward the reading position of the contact glass 4 and returns it. 18 and the switchback means 18 and the paper discharge means 16 are provided on the upstream side in the original conveyance direction, and the original picked up by the scooping mechanism 14 is conveyed so as to be conveyed to either the switchback means 18 or the paper discharge means 16. And a switching claw 19 as switching means for switching the direction.

The presser cover 11 is composed of a pressure contact pad in which a sheet 21 is attached to the surface of the resin foam member 20,
The sheet 21 has a surface and a material made of a coloring material that exhibits a uniform spectral response over the visible wavelength region, and is provided over the region showing most of the contact glass 4. Further, the document tray 12 is provided above the pressing cover 11, and a document stack made of a plurality of sheet documents is placed on the document tray 12.

The separating / feeding means 13 is a pickup roller 2
2, a document set sensor 23, separation rollers 24a and 24b, pressure rollers 25 and 26, a paper feed drive roller 27, a registration sensor 28, and a guide plate 29. Pickup roller 22
Is configured to feed the document stack placed on the document tray 12 through a paper feed port 30 formed on the end side of the contact glass 4, and is driven by a paper feed clutch 31. There is. The document set sensor 23 detects that a document is set on the document tray 12 and outputs a signal to the control means 34.

Separation rollers 24a and 24b are pickup rollers 22.
The uppermost document is separated from the bundle of documents fed by the separation clutch when separating.
Only the upper separating roller 24a is driven in the clockwise direction by 32, the lower separating roller 24b is stopped, and the separating clutch 31 is disengaged after separating the originals so that both rollers 24a and 24b idle. There is.

The paper feed drive roller 27 is driven by a main motor 33, and guides the separated document to the end of the contact glass 4 along a curved guide plate 29 so as to form a reversing path. It is designed to be transported. Further, the pressure rollers 25 and 26 are pressed against the reversing drive roller 27 with a predetermined pressing force, and the document is nipped and conveyed together with the reversing drive roller 27. Therefore, the original on the paper feed tray 12 is reversed and conveyed toward the end of the contact glass 4.

The registration sensor (front and rear edge detection sensor) 28 detects the front and rear edges of the document conveyed along the guide plate 29 and outputs detection information to the control means 34. The control means is a CPU (Central Processing Unit),
RAM (Random Access Memory), ROM (Read Only M
emory) and the like, and controls the entire automatic document feeder 3 according to a predetermined program stored in the ROM.

When the start key is pressed and the document set sensor 23 detects that a document is set on the document tray 12, the control means 34 drives the paper feed clutch 31, the separation clutch 32 and the main motor 33. When the front edge of the document is detected by the registration sensor 28, the separation rollers 24a and 24b are made to idle based on the detection information. Further, the control means 34 is adapted to detect the length of the original in the conveyance direction based on the detection information of the front and rear edges of the original.

The conveying means 15 includes an endless belt 36, a belt driving roller 37 (belt conveying roller), and this driving roller.
37, a stretching roller (belt conveying roller) 38 provided on the downstream side of the original in the conveying direction (rear end in the conveying direction). The endless belt 36 has a double-layered structure in which the front surface is made of a dielectric material and the back surface is made of a low-resistance layer. The surface dielectric material is made of a coloring material that shows an even spectral response over the visible wavelength range. And the material are used, and the surface has the same color as the sheet 21.

One end of the endless belt 36 is wound around the belt driving roller 37, and the roller 37 is driven in the counterclockwise direction by the main motor 33 to form an endless belt.
It is designed to move 36. Further, a predetermined tension is applied to the belt drive roller 37 to press the endless belt 36 against the contact glass 4 with a constant pressure.

In this embodiment, the belt driving roller 37
And the contact glass 4 which comes into contact with the driving roller 37 via the endless belt 36 constitutes a predetermined reading position. This reading position is set when the end of the document on the contact glass 4 is positioned on the reference scale 40. Also, it corresponds to the reading start position of the document. In addition, the stretch roller 38 has an endless belt 36.
The other end of is stretched and the stretch roller 38 is moved vertically by a scooping solenoid 41 with the belt drive roller 37 as a fulcrum. Further, when the stretch roller 38 is moved downward by the scooping solenoid 41 so as to bring the endless belt 36 into contact with the contact glass 4, the stretch roller 38 comes close to the end of the presser cover 11 (see FIG. 2).

Further, as shown in FIG.
An electrode roller 42 for forming a non-uniform electric field is provided in a portion which comes into contact with the outer peripheral surface of the endless belt 36 through 37, and an AC voltage (alternating voltage) is applied to this electrode roller 42 from an AC power supply 43. It has become so. The electrode roller 42 can move together with the stretching roller 38. The endless belt 36 is moved at a constant speed vmm / s in the direction of arrow A in FIG. 4A by the belt driving roller 37, and the document feeding position is the electrode roller with respect to the moving direction of the endless belt 36.
The area is in contact with the electrode roller 42 as a counter electrode on the downstream side of the contact position of 42.

For this reason, an AC voltage is applied to the endless belt 36 via the electrode roller 42 by the AC power source 43 before the original is fed to the surface thereof, whereby the surface of the endless belt 36 is applied. , Charge density + σ, −σ are alternately v
An electric field density pattern arranged at a pitch of / Amm is formed. A similar charge density pattern is also formed on the back surface of the endless belt 36 with a 180 ° shift. Due to the charge density pattern thus formed, an unequal electric field is formed near the surface of the endless belt 36 as shown in FIG. 4B.
Due to this electric field, the document P is electrostatically attracted to the endless belt 36 by the component of Fx of the derivative of the endless belt 36 and held without being displaced, and is conveyed along with the endless belt 36. The scooping solenoid 41, the electrode roller 42, and the AC power source 43 described above constitute a scooping mechanism that scoops the document read at the scanning position and separates it from the contact glass 4, and among them, the scooping solenoid.
Reference numeral 41 constitutes a proximity separating member, and an electrode roller 42 and an AC power source 43
Constitutes an application member.

The guide plates 39a and 39b are endless belts.
The guide plates 39a, 39b are provided above the 36, and form a conveyance path for conveying the document switched back from the switchback passage 17 toward the conveyance means 15.
The paper discharge means 16 includes a drive roller 44, a pressure roller (second pressure roller) 45 pressed by the drive roller 44, a paper discharge sensor 46,
It consists of The drive roller 44 is a reverse drive motor 47.
It is designed to rotate forward and backward by the tension roller.
When the 38 is moved upward by the scooping solenoid 41 so as to be separated from the contact glass 4, the drive roller
Reference numeral 44 is driven in the counterclockwise direction to hold the original document together with the pressure roller 45, and eject the scooped-up original document onto the paper ejection tray 11a through the paper ejection port 48. The paper discharge sensor 46 is provided in the vicinity of the paper discharge port 48, and the paper discharge tray 11a.
A signal is output to the control means 34 by detecting the trailing edge of the document discharged above.

The switchback means 18 is provided adjacent to the paper discharge means 16 and includes a drive roller 44 and this drive roller.
When the tension roller 38 is moved upward by the scooping solenoid 41 so as to be separated from the contact glass 4, the driving roller 44 is reversed. The original is nipped together with the pressure roller 49 by being driven in the clockwise direction by the drive motor 47, and the scooped original is conveyed to the switchback passage 17. This switchback passage 17 is provided integrally with the document tray 12 below the document tray 12.
It is composed of a space.

When the document is conveyed to the switchback passage 17, the reversing drive motor 47 is driven in the counterclockwise direction, and the document is switched back from the switchback passage 17 to be conveyed through the guide plates 39b and 39a. It is designed to be flipped over to the reading position and returned. In this example,
The members forming the above-mentioned conveying means 15 also form the switchback means.

On the other hand, the switching claw 19 is provided on the upstream side of the switchback means 18 and the paper discharge means 16 in the original conveying direction, and the original picked up by the endless belt 36 is placed between the drive roller 44 and the pressure roller 45. Further, it is driven by the switching solenoid 51 so as to switch the carrying direction so as to carry it to one side between the drive roller 44 and the pressure roller 49. The switching solenoid 51, together with the switching claw 19, constitutes a switching means.

This switching solenoid 51 switches the switching claw 19 based on a signal from the control means 34.
When the double-sided mode is designated by the mode selection unit 50 and the registration sensor 28 detects the leading edge of the document, the control means 34 controls the switching solenoid 51 to drive the switching claw 19 to drive the roller.
The drive roller 44 is driven in the clockwise direction while being set to a switching position so as to form a communication path communicating between the 44 and the pressure roller 49.

Further, the control means 34 operates when the number of rotations of the main motor 33 reaches a predetermined pulse or when a predetermined time elapses after the registration sensor 28 detects the trailing edge of the document (this pulse or time is a switch. The number of pulses or the time is set so that the document is surely stored in the back passage 17), the switching claw 19 is set to the drive roller 44 and the pressure roller.
The switching solenoid 51 is controlled so that the switching position is such that a communication path is formed between 49 and the guide plate 39a, and the drive roller 44 is driven in the counterclockwise direction to drive the document in the switchback path 17. Is reversed through the guide plates 39b and 39a and returned.

Further, when the single-sided mode is designated by the mode selection unit 50 and when the back side is read in the double-sided mode, the control means 34 determines the rotation speed of the main motor 33 after the registration sensor 28 detects the leading edge of the document. When the specified pulse is reached or the specified time has elapsed, the switching solenoid
51 to control the switching pawl 19 so that the endless belt 36 and the drive roller 44
Further, the drive roller 44 is driven in the counterclockwise direction while being set to a switching position so as to form a communication path that communicates between the pressure rollers 45. Further, the control means 34 is a reading control means provided in the reading section 2 when the number of rotations of the main motor 33 reaches a predetermined pulse or a predetermined time elapses after the registration sensor 28 detects the leading edge of the document. When a signal is output to 52 and the reading unit 2 starts reading the original and the registration sensor 28 detects the trailing edge of the original, the number of rotations of the main motor 33 reaches a predetermined pulse, or a predetermined time elapses. In this case, a signal is output to the reading control means 52 so that the reading of the original by the reading unit 2 is completed. In this embodiment, the contact pressure between the pressure roller 49 and the drive roller 44 is set to be smaller than the contact pressure between the pressure roller 45 and the drive roller 44.

Next, the operation will be described with reference to FIGS. 5 to 7 are views for explaining the carrying operation, and FIG. 8 is a timing chart at the time of carrying the carrying operation, showing a timing chart at the time of carrying a double-sided original. First, when reading only one document P such as a book document, the automatic document feeder 3 is opened from the contact glass 4, the document is placed on the contact glass 4, and the automatic document feeder 3 is closed. At this time, as shown in FIG. 2, since the stretch roller 38 is moved to the position where it comes into contact with the contact glass 4 by the scooping solenoid 41, and a predetermined tension is applied to the belt drive roller 37, the presser cover is held. Along with 12, the endless belt 36 presses the document against the contact glass 4. Therefore, the pressing cover 11 and the endless belt 36, which have the same color, do not lift the document from the contact glass 4 and stably press the contact glass 4.

When the start switch is pressed in this state, the light source 5 and the mirrors 6 to 8 move below the contact glass 4 from the left end to the right end in FIG. Scan the original with 10. On the other hand, in the case of reading a sheet-through document, FIG.
When the document stack Pn is placed on the document tray 12 as shown in FIG.
Is detected. When the start switch is pressed in this state, the main motor 33 is driven, and the paper feed clutch 31 and the separation clutch 32 are driven so that the pickup roller 22 feeds the document bundle Pn through the paper feed port 30. Next, after the uppermost original P is separated from the original bundle Pn by the separation rollers 24a and 24b, the original P is nipped by the sheet feeding drive roller 27 and the pressure rollers 25 and 26 and is guided along the guide plate 29. Be transported. When the leading edge of the original P is detected by the registration sensor 28, the control means 34 stops driving the separating clutch 32 to prevent the succeeding original P from being separated (the paper feeding clutch 31 is separated by the separating clutch 32). Has stopped before). At the start of separation, an alternating voltage is applied to the endless belt 36 by the electrode roller 42 to form an unequal electric field (see the high voltage power pack in the time chart of FIG. 8).

Next, the original P is conveyed between the belt driving roller 37, which is the reading position, and the contact glass 4. At this time, the number of pulses of the main motor 33 is counted by an amount corresponding to the distance from the registration sensor 28 to this reading position, and when this number of pulses is reached, or a predetermined time elapses until reaching the reading position from the registration sensor 28. Then, the reading control means 52 is controlled to stop the light source 5 and the like below the reading position to start reading the document P.

Further, when the document P is conveyed to the reading position, the belt driving roller 37 is pressed against the contact glass 4 with a predetermined tension, so that the document P is prevented from being skewed. Next, when the number of pulses of the main motor 33 reaches a predetermined number of pulses after the leading edge of the document P is detected by the registration sensor 28,
When a predetermined time elapses after the leading edge of the document P is detected on the document 28, the document P advances on the contact glass 4 by a certain distance, so that the control means 34 drives the scooping solenoid 41 to move the stretch roller 38 to the contact glass 4. Then, the glass roller 4 is brought into contact with the glass 4, and the stretching roller 38 is moved upward. Therefore, the original P is sucked by the endless belt 36 and scooped up from the contact glass 4 (see FIGS. 5B and 5C).

Further, when the one-sided mode is designated based on the signal from the mode selection unit 50, the control means 34 causes the switching solenoid 51 to switch the switching claw 19 when the leading edge of the document P is detected by the registration sensor 28. Switch the switching position,
The downstream side of the endless belt 36 in the document conveying direction is made to communicate between the drive roller 44 and the pressure roller 45, and the drive roller 44 is driven in the counterclockwise rotation direction. Therefore, the endless belt 36
The document P conveyed by the drive roller 44 and the pressure roller 45.
Output tray 11 through output outlet 48 while being pinched by
The sheet is discharged onto the sheet a (see FIG. 6A). Incidentally, after the registration sensor 28 detects the rear end of the document P, the main motor 33
When the number of pulses has reached a predetermined number of pulses, or when a predetermined time has elapsed, the control means 34 outputs a signal to the reading control section 52 and finishes reading the document P.

Here, when the document P is picked up, the contact glass 4 of the belt driving roller 37 and the stretching roller 38
On the side, that is, on the contact glass 4 side surface of the endless belt 36, the angle formed by the contact glass 4 is larger than the line connecting the tangent line between the driving roller 44 and the pressure roller 45 and the belt driving roller 38. The ability to convey the original P to the paper ejection port 48 is improved.

On the other hand, when the double-sided mode is designated based on the signal from the mode selecting section 50, the control means 34 detects the leading edge of the document P by the registration sensor 28 and detects the direction in which the endless belt 36 conveys the document. The downstream side is made to communicate between the drive roller 44 and the pressure roller 49, and the drive roller 44 is driven in the clockwise direction. Therefore, the document P conveyed by the endless belt 36 is nipped by the driving roller 44 and the pressure roller 49 and conveyed to the switchback passage 17 (see FIG. 6B).

Next, when the registration sensor 28 detects the trailing edge of the document P and when the number of pulses of the main motor 33 is counted enough to accommodate the document P in the switchback passage 17, or when a predetermined time elapses. When the control means
34 controls the switching solenoid 51 to drive the switching claw 19 to drive the roller.
The switching position is such that a communication path is formed between 44 and the pressure roller 49 and the guide plate 39a, and the drive roller 44 is driven in the counterclockwise direction to guide the document P in the switchback path 17. It is inverted through the plates 39b and 39a and returned to the reading position (see FIG. 6C).

Then, the control means 34 operates from the detection of the trailing edge of the original P by the registration sensor 28 to the main motor 33 from the time when the original P being reversed and returned to the reading position again.
The number of pulses is counted, and when the count value is reached, or when a predetermined time has elapsed after the trailing edge of the document P was detected by the registration sensor 28, the reading unit 2 starts reading the document P.

Further, when the number of pulses of the main motor 33 reaches a predetermined number of pulses after the registration sensor 28 detects the trailing edge of the document P, or after the registration sensor 28 detects the trailing edge of the document P. When the document P advances on the contact glass 4 by a predetermined distance after a lapse of a predetermined time, the control means 34 drives the scooping solenoid 41 to move the stretching roller 38 toward the contact glass 4 and hit the glass 4. After the contact, the stretching roller 38 is moved upward. Therefore, the document P is sucked by the endless belt 36 and is picked up again from the contact glass 4 (see FIGS. 7A and 7B).

Then, the control means 34 switches the switching position of the switching pawl 19 by the switching solenoid 51 at the time of outputting the scooping signal, and the downstream side of the endless belt 36 in the document conveying direction is driven by the drive roller 44 and the pressure roller 45. While communicating between
The drive roller 44 is driven counterclockwise. For this reason,
The document P conveyed by the endless belt 36 is a driving roller.
The paper is ejected onto the paper ejection tray 11a through the paper ejection port 48 while being sandwiched by the 44 and the pressure roller 45 (see FIG. 7B).
Next, when the trailing edge of the document P is detected by the paper discharge sensor 46, the paper feed clutch 31 and the separation clutch 32 are driven again to start feeding the subsequent document P. Then, when the conveyance of the final document P is completed, the document P is detected by the paper discharge sensor 46.
When the rear end is detected, the driving of the main motor 33, the reverse drive motor 47, and the AC power supply 43 is stopped, as shown in FIG.

As described above, in the present embodiment, the original P, which has been conveyed to the reading position and has been read, is separated from the contact glass 4 by the scooping solenoid 41 of the endless belt 36 to which an AC voltage is applied. After being picked up from the contact glass 4, the switching claw 19 switches the transport path to the sheet discharge means 16 side to discharge the sheet onto the sheet discharge tray 11a, and at the time of reading a double-sided original, the original P whose one side has been read is After the endless belt 36 and the scooping solenoid 41 scoop up above the contact glass 4, the switching claw 19 switches the transport path to the switchback means 18 side, transports it to the switchback passage 17, and then switches it back to contact it again. It is returned to the reading position on the glass 4.

For this reason, the document P is scooped up and discharged.
Since the paper can be discharged to the 16 or switchback means 18, the structure between the endless belt 36 and the paper discharge means 16 and the switchback means 18 can be simplified to reduce the space of the conveyance path of the document P. You can Further, unlike the conventional case, since the original P is not discharged to the discharge tray on the side of the image reading apparatus main body, the length in the longitudinal direction of the automatic document feeder 3 can be shortened and the space is small. The double-sided original can be conveyed with. As a result, the automatic document feeder 3 can be downsized, and
The cost can be reduced, and the installation space of the image reading device 1 can also be reduced.

Further, an endless belt 36 made of a dielectric material,
Stretching roller 38 wound around the other end of endless belt 36
Since it has a scooping solenoid 41 for moving the contact glass 4 close to and away from the contact glass 4, an electrode roller 42 for applying an AC voltage to the endless belt 36, and an AC power supply 43, the document P is strongly supported on the endless belt 36. The original P can be picked up from the contact glass and separated from the contact glass while being sucked by the suction force, and the original P can be reliably conveyed to either one of the conveying unit 16 and the switchback unit 18. .

Further, the switchback passage 17 is provided in the original tray.
Since it is provided in the lower part of 12, the space above the contact glass 4 can be effectively used, and the switchback passage 17 can be formed from the same member as the document tray 12, so that the automatic document feeder 3 It is possible to convey a double-sided original while further reducing the size and cost.

Further, the original P returned from the switchback passage 17 by the switchback means 18 is fed to the endless belt.
Since the guide plates 39a and 39b for conveying toward the 36 are provided, the switched back document P can be returned to the endless belt 36 through a short conveying path, and the conveying time can be shortened. Further, since the switchback means 18 and a part of the paper discharge means 16 are composed of a common drive drive roller 44, and the drive rollers 44 press the pressure rollers 45, 49,
The configuration of the automatic document feeder 3 can be simplified,
Further cost reduction can be achieved.

A registration sensor 28 is provided on the upstream side of the endless belt 36 in the conveying direction of the original P, and the switching claw 19 and the switching claw 19 are provided based on the detection information of the front and rear ends of the original P output from the registration sensor 28. Since the control means 34 for controlling the drive roller 44 is provided, the double-sided original can be reliably switched back and returned to the reading position regardless of the size of the double-sided original.

The light source 5 when the original is stopped on the contact glass 4 at the stop position of the light source 5 or the like at the reading position.
Since the contact glass 4 is set within the range of the reading area, it is possible to reliably read the sheet-through original P, the book original, and the like with one contact glass 4, and the length in the longitudinal direction on the contact glass 4. By mounting the short automatic document feeder 3, the image reading apparatus 1 can be further downsized.

Further, the pressing cover 11 is composed of a pressure contact pad in which the sheet 21 is attached to the resin foam member 20, and
A stretch roller 38 around which the endless belt 36 is wound is provided in the vicinity of the end of the pressure contact pad, and when the manuscript is kept stationary on the contact glass 4 and a still manuscript is read by the light source 5 or the like, the endless belt 36 is When the original is pressed against the contact glass 4 by the endless belt 36 and the pressing cover 11 by bringing the contact glass 4 into contact with the contact glass 4, the entire surface of the contact glass 4 is used when reading a book original or the like. The original can be read.

Further, since the color of the surface of the endless belt 36 and the color of the surface of the sheet 21 of the pressure contact pad facing the contact glass 4 are the same, the book original or the like is kept still on the contact glass 4 and It is possible to read an image of a document with high quality without changing the background color and density of the entire document when reading the document. In addition, as shown in FIG.
When a large-sized document P is reversed and returned from the switchback passage 17 to the reading position, the front end of the document P is pressed by the pressure roller 45.
And the driving roller 44, and the trailing edge of the document P is a pressure roller 49.
It may be pinched by the drive roller 44. In this embodiment, the contact pressure between the pressure roller 49 and the drive roller 44 is set to be smaller than the contact pressure between the pressure roller 45 and the drive roller 44. Drive roller 44
The document P can be firmly clamped by the pressure roller 49 and the driving roller 44 can be clamped by a relatively small force, so that the load when the document P is conveyed can be reduced. As a result, it is possible to sufficiently protect the document P and improve the transport performance.

In this embodiment, the switchback passage is also used.
The original P that is switched back from 17 is guided by the guide plates 39b, 39
Although the sheet is returned to the endless belt 36 side via a, the present invention is not limited to this, and as shown in FIG. 10, a guide plate 55 that forms a conveyance path is provided between the switchback path 17 and the sheet feeding drive roller 27. The document P in the switchback passage 17 may be returned to the guide plate 29 side. In this way, the registration sensor 28 provided in the guide plate 29 can detect the original P again, so that the conveyance state of the original P can be detected with high accuracy.

11 to 13 are views showing a second embodiment of the image reading apparatus according to the invention as claimed in any one of claims 1 to 10. In this embodiment, the pick-up solenoid 41 is used to switch the document feeding path. An example of controlling is shown, and since the configuration is the same as that of the above-mentioned embodiment, only the carrying method will be described. In the above-described embodiment, the document P picked up by the endless belt 36 is conveyed only by the switching claw 19 between the drive roller 44 and the pressure roller 45 and between the drive roller 44 and the pressure roller 49. Although the directions are switched, in this embodiment, FIG. 11 (c), FIG. 12 (a) (b), and FIG. 13 (b).
, The position of the stretch roller 38 is finely controlled by the scooping solenoid 41, and between the drive roller 44 and the pressure roller 45 and between the drive roller 44 and the pressure roller 49 in the respective conveying directions. By connecting the endless belt 36 to the stretch roller 38 side, the conveyance path of the document P is switched. In addition to this control, the conveyance path is switched by the switching claw 19, so that the document P is different from that in the above embodiment.
The transfer route can be switched with higher accuracy. Further, by performing the control as in this embodiment,
The switching claw 19 may be omitted. Although the image reading apparatus is applied to the scanner apparatus in the present embodiment, it may be applied to a copying machine or the like.

[0078]

According to the first aspect of the invention, since the original is picked up and conveyed to either one of the paper discharging means or the switchback means, the space between the conveying means and the paper discharging means and the switchback means is increased. This simplifies the configuration to reduce the space for the document transport path, and since documents are not ejected to the paper ejection tray on the side of the main body of the image reading device as in the conventional art, automatic document conveyance is possible. By shortening the length of the apparatus in the longitudinal direction, it is possible to convey a double-sided original in a small space. As a result, the size of the automatic document feeder can be reduced, its cost can be reduced, and the installation space of the image reading device can be reduced.

According to the second aspect of the present invention, the document can be attracted to the endless belt with a strong suction force, and in this state, the document can be picked up from the contact glass and separated from the contact glass, so that the document is surely secured. It can be transported to either one of the transport means and the switchback means. According to the third aspect of the present invention, the space above the contact glass can be effectively used, and the switchback passage can be formed from the same member as the document placing table, and the space of the automatic document feeder can be improved. It is possible to carry a double-sided document while further reducing the size and cost.

According to the fourth aspect of the present invention, the switched back original can be returned to the conveying means through the short conveying path, and the conveying time can be shortened. Claim 5
According to the invention described above, the drive roller forming the paper discharge unit and the switchback unit can be formed of the same member, so that the structure of the automatic document feeder is simplified to further reduce the size and cost. Can be planned.

According to the invention of claim 6, the size of the original is large, the leading edge of the original is sandwiched between the second pressure roller and the drive roller, and the rear edge of the original is sandwiched between the first pressure roller and the drive roller. In such a case, the document can be firmly clamped by the second pressure roller and the drive roller, and can be clamped by the first pressure roller and the drive roller with a relatively small clamping force. The load during transportation can be reduced. As a result, it is possible to sufficiently protect the document and improve the transport performance.

According to the seventh aspect of the present invention, the double-sided original can be reliably switched back and returned to the reading position regardless of the size of the double-sided original. According to the invention described in claim 8, it is possible to reliably read a sheet-through document, a book document and the like with one contact glass, and an automatic document feeder having a short length in the longitudinal direction is mounted on the contact glass. By arranging it, the size of the image reading device can be further reduced.

According to the ninth aspect of the present invention, when reading a book document or the like, a large size document can be read using the entire contact glass. According to the invention of claim 10, when a book document or the like is kept stationary on the contact glass and the document is read, the background color and the density of the entire document are prevented from changing, and the image of the document is provided with high quality. Can be read.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a first embodiment of an image reading apparatus according to any one of claims 1 to 10.

FIG. 2 is a state diagram of an automatic document feeder when one document is read while stationary on a contact glass.

FIG. 3 is a block diagram of a control system of the automatic document feeder.

FIG. 4A is a diagram showing a configuration of an applying member that applies an AC voltage to the endless belt, and FIG. 4B shows an uneven electric field formed on the endless belt and a document feeding state by the electric field. FIG.

5A to 5C are diagrams showing a document transport state by an automatic document transport device.

6A to 6C are diagrams showing a document conveyance state following FIG.

7A and 7B are diagrams showing a document conveyance state following FIG.

FIG. 8 is a timing chart when a double-sided original is conveyed.

FIG. 9 is a diagram showing a state in which the front and rear ends of a document are nipped by a drive roller and a pressure roller. It

FIG. 10 is a diagram showing another aspect of the automatic document feeder in which a document feeding path is formed between the switchback means and the separating / feeding means.

FIG. 11 is a configuration diagram of a second embodiment of the image reading device according to any one of claims 1 to 10, wherein (a) to (c) show a document conveyance state by the automatic document feeder. FIG.

12 (a) and 12 (b) are diagrams showing a document conveyance state following FIG. 11.

13 (a) and 13 (b) are diagrams showing a document conveyance state following FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Scanner device (original reading device) 3 Automatic document feeder 4 Contact glass 5 Light source (reading means) 6-8 Mirror (reading means) 9 Lens (reading means) 10 Imaging element (reading means) 11 Presser cover 12 Original tray ( Document placing table) 13 Separation / feeding means 14 Scooping mechanism 15 Conveying means 16 Paper discharging means 17 Switchback passage 18 Switchback means 19 Switching claw (switching means) 20 Resin foam member 21 Sheet 28 Registration sensor (front and rear edge detection sensor) 36 Endless belt (conveyance means, switchback means) 37 Belt drive roller (belt conveyance roller, conveyance means, switchback means) 38 Stretching roller (belt conveyance roller, conveyance means, switchback means) 39a, 39b Guide plate ( Conveyance path) 41 Scooping solenoid 42 Electrode roller (application member) 43 AC power supply (application member) 44 Drive roller 45 Pressure roller (second pressure roller) 49 pressure roller (first pressing roller) 51 switching claw solenoid (toward and away from member)

Claims (10)

[Claims] 1. A reading unit configured to move when reading a document that is stationary on the contact glass and to stop at a predetermined reading position when reading a document conveyed on the contact glass, In an image reading apparatus having an automatic document feeder capable of transporting a document to the predetermined reading position and ejecting the document after reading, the automatic document feeder may detect the document placed on the contact glass. A pressing cover that presses against the contact glass, an original placing table that is provided above the pressing cover and on which a plurality of originals can be placed, and an original feeding port are formed on the edge side of the contact glass.
A bundle of originals placed on the original placing table is fed from the paper feed port, originals are separated from the original bundle one by one, and the separated originals are inverted and conveyed toward a predetermined reading position. Separating / conveying means and a document conveyed by the separating / conveying means toward a predetermined reading position are conveyed to the reading position, and the document read at the reading position is scooped up to be separated from the contact glass. A transporting means having a mechanism, a discharging means for discharging the document picked up by the scooping mechanism onto the pressing cover, and a switchback passage for the document picked up by the scooping mechanism provided adjacent to the discharging means. Switchback means for reversing and returning the contact glass toward a predetermined reading position on the contact glass, and the switchback means and paper discharge. And a switching unit which is provided on the upstream side of the document transporting direction and switches the transporting direction so that the document picked up by the scooping mechanism is transported to either one of the switchback unit and the sheet discharging unit. Image reading device. 2. The conveying means comprises an endless belt made of a derivative, and a pair of belt conveying rollers provided at front and rear ends of the endless belt in the conveying direction of a document, wherein the scooping mechanism comprises: 2. A proximity separating member for moving a roller on the downstream side of the original in the conveying direction of the roller toward and away from the contact glass, and an applying member for applying an alternating voltage to the endless belt. Image reading device. 3. The image reading apparatus according to claim 1, wherein the switchback passage is provided in a lower portion of the document placing table. 4. The image reading apparatus according to claim 1, further comprising a conveyance path that conveys the document returned from the switchback passage by the switchback means toward the conveyance means. 5. The switchback means is composed of a drive roller that is driven to rotate normally and reversely, and a first pressure roller that is pressed by the drive roller and is capable of sandwiching a document with the drive roller. 5. The image reading apparatus according to claim 1, wherein the means comprises a second pressure roller that is pressed by the drive roller and can hold an original with the drive roller. 6. The image reading apparatus according to claim 5, wherein the contact pressure between the first pressure roller and the drive roller is smaller than the contact pressure between the second pressure roller and the drive roller. 7. A front / rear edge detection sensor which is provided on the upstream side in the document conveyance direction with respect to the conveyance means and detects a front / rear edge of the conveyed document, and a front / rear edge of the document output from the front / rear edge detection sensor. 7. The image reading device according to claim 1, further comprising: a control unit that controls the switching unit and the switchback unit based on the detection information of. 8. The stop position of the reading means at the predetermined reading position is set within the range of the reading area of the reading means when the document stands still on the contact glass. The image reading device according to any one of claims. 9. The pressing cover is composed of a pressure contact pad in which a sheet is attached to a resin foam member, and a roller of the rollers of the endless belt on the downstream side in the document conveying direction is close to the end of the pressure contact pad. When the document is stationary on the contact glass and the stationary document is read by the reading means, the endless belt is brought into contact with the contact glass so that the document is pressed against the contact glass by the endless belt and the pressure contact pad. The image reading apparatus according to claim 1, wherein the image reading apparatus is attached. 10. The image reading apparatus according to claim 9, wherein the color of the sheet surface of the endless belt and the color of the pressure contact pad surface facing the contact glass are the same.