Sheet feeding device, and document feeding device in image reading apparatus comprising the same

Abstract

A sheet feeding device, and a document feeding device including the sheet feeding device have a pickup roller which can elevate and lower between an operative position and a standby position, a sheet feeding rotating device that separably feeds each sheet from the roller, and a registration roller that registers the sheet from the sheet feeding rotating device. A carry-in roller conveys the sheet to a predetermined processing position, and a carry-out roller carries the sheet from the processing position. The pickup roller and sheet feeding rotating device are drivingly coupled to a first driving motor. The registration roller and carry-in roller are coupled to a second driving motor via a sliding friction clutch. The sliding friction clutch is configured so that the registration roller is rotated by rotating the second driving motor and transmission of a driving force is blocked by rotating the first driving motor.

Description

BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT

The present invention relates to sheet feeding devices that feed sheets to image forming apparatuses and various other instruments, and particularly, to improvements in a driving mechanism and its control mechanism for a document feeding device in an image reading apparatus.

Sheet feeding devices of this kind are commonly used in various instruments including image forming apparatuses such as copiers as well as scanner apparatuses, as sheet feeding mechanisms that sequentially deliver sheets housed in a stacker or feeder mechanisms, or sequentially feed sheets downstream which have been conveyed to a sheet guide or the like. These mechanisms comprise rotating members (hereinafter referred to as roller means) such as rollers or belts which feed sheets set in a sheet feeding stacker, downstream under a frictional force. In this case, a mechanism is also commonly used which, when the roller means feeds a sheet downstream, elevates and lowers the roller means between a position where the roller means contacts the sheet and a position where the roller means is separate from the sheet, in accordance with sheet feeding timing.

For example, according to Japanese Patent Laid-Open No. 10-338391, sheets placed on a sheet feeding tray are delivered by a pickup roller located above the tray, and a sheet feeding roller located at the tip of the tray separates a sheet from the others. The leading end of the sheet abuts against a registration roller for registration located at a downstream side. The sheet is then fed to a downstream reading section. The pickup roller, sheet feeding roller, and registration roller are coupled to the same driving motor. The driving motor rotates forward to drivingly move the pickup roller from a standby position located above to a delivery position on the tray, while rotating both rollers in the sheet feeding direction. The driving motor rotates backward to cause the registration roller to feed the sheet from the sheet feeding roller downstream. Thus, forward and backward rotations of the single motor allow the pickup and sheet feeding roller and the registration roller to be drivingly rotated in the opposite directions.

Japanese Patent Laid-Open No. 2002-182437 discloses a device having a sheet feeding tray and a sheet discharging tray both located above a reading platen and juxtaposed in a vertical direction, and a sheet from the sheet feeding tray is conveyed to the sheet feeding tray along a U-shaped conveying path via the reading platen. According to this document, a pickup roller, a sheet feeding roller, and a registration roller are coupled to a sheet feeding section motor as described above. A carry-in roller and a carry-out roller arranged upstream and downstream, respectively, of the reading platen are coupled to a conveying section motor different from the sheet feeding section motor. This configuration allows a pickup operation and a registration operation to be timely performed by switching the rotation of the single motor between a forward direction and a backward direction. This device is thus made by enabling a driving mechanism to be simply constructed without using any special control parts such as an electromagnetic clutch.

When a pickup operation and a registration operation are performed by switching the rotation of the single motor between the forward and backward directions as described above, the driving mechanism is simplified but the pickup roller repeats moving up and down whenever a sheet is delivered. Thus, disadvantageously, a whack noise may be made when the pickup roller beats the upper surface of the sheet, and upon contact with the sheet, the roller may beat only one side of the sheet, which may thus be wrinkled or skewed. Further, the sheet from which the image is being read may be vibrated, resulting in a blurred image. To solve these problems, attempts have been made to elevate and lower the pickup roller using an independent motor or a solenoid. However, this has increased the size and cost of the apparatus.

Thus, an object of the present invention is to provide a sheet feeding device that can perform a pickup operation and a registration operation using a simple driving mechanism that can be easily controlled, wherein the pickup operation involves elevating and lowering roller means for delivering sheets from a stacker or the like, between an operative position and a retracted position.

Another object of the present invention is to provide a document feeding device that minimizes possible vibration, noise, skewing, and the like during sheet delivery when each of the sheets in a sheet feeding stacker is separably fed to a predetermined reading position.

Further objects and advantages of the invention will be apparent from the following description of the invention.

SUMMARY OF THE INVENTION

The present invention employs a configuration described below in order to accomplish the above objects. In the present invention, the term “forward direction” of a first driving motor and a second driving motor refers to a direction in which a sheet moves from a sheet feeding tray to a predetermined processing position (first platen) and a direction in which the sheet moves from the processing position to a sheet discharging tray. The term “backward direction” refers to a direction in which the sheet moves in a direction opposite to the forward direction. Sliding friction clutch means refers to a friction clutch configured to slip at least a predetermined torque to prevent transmission of a driving force.

The present invention thus has pickup roller means located above a placement tray on which sheets are placed, the pickup roller means being able to elevate and lower between an operative position where the pickup roller means engages the sheets and a standby position located above the operative position, sheet feeding rotating means for separably feeding each sheet from the pickup means, and a registration roller that registers the sheet from the sheet feeding rotating means. A carry-in roller and a carry-out roller are arranged downstream of the registration roller, wherein the carry-in roller conveys the sheet to a predetermined processing position, and the carry-out roller carries the sheet out from the processing position. The pickup roller means and the sheet feeding rotating means are drivingly coupled to the first driving motor. The registration roller and the carry-in roller are coupled to the second driving motor.

The registration roller and the second driving motor are configured so that the second driving motor transmits a driving force to the registration roller via sliding friction clutch means. The sliding function clutch means is coupled to the registration roller so that the registration roller is rotated by rotating the second driving motor and so that the transmission of a driving force to the registration roller is blocked by rotating the first driving motor. In this case, for example, the sliding friction clutch means has a rotating shaft connected to the registration roller and around which a coil spring is wound so that rotation of the second driving motor is transmitted to the rotating shaft via the coil spring, while the transmission is cancelled by rotating the first driving motor, coupled to the coil spring, in a predetermined direction. More specifically, the coil spring is wound around the rotating shaft so that the spring can be compressed and loosened. The second and first driving motors are coupled to the coil spring so as to exert a rotating force in a direction in which the coil spring is compressed and in a direction in which the coil spring is loosened, respectively. The transmission of driving from the second driving motor to the rotating shaft is turned on and off on the basis of the difference in rotation speed between the first driving motor and the second driving motor.

A document feeding device in an image reading apparatus in accordance with the present invention comprises a placement tray on which sheets are placed, a sheet feeding path along which a sheet from the placement tray is guided to a reading position, a sheet discharging path along which the sheet from the reading position is guided to a sheet discharging tray, pickup roller means located above the placement tray and configured to elevate and lower freely between an operative position where the pickup roller means engages the sheet and a standby position located above the operative position, sheet feeding rotating means for separably feeding each sheet from the pickup roller means, a registration roller located on the sheet feeding path to register the sheet from the sheet feeding rotating means and a carry-in roller that conveys the sheet from the registration roller to the reading position, a carry-out roller located on the sheet discharging path to carry the sheet out from the reading position and a sheet discharging roller that carries the sheet from the carry-out roller out to the sheet discharging tray, a first driving motor that is able to rotate forward and backward to drivingly rotate the pickup roller means and the sheet feeding rotating means, and a second driving motor that is able to rotate forward and backward to drivingly rotate the registration roller, carry-in roller, carry-out roller, and sheet discharging roller.

The pickup roller means and sheet feeding rotating means are coupled to the first driving motor so as to be drivingly rotated in a sheet feeding direction by rotating the first driving motor forward. The pickup roller means is coupled to the first driving motor so as to be moved from the standby position to the operative position by rotating the first driving motor forward and to be moved from the operative position to the standby position by rotating the first driving motor backward. The registration roller, carry-in roller, carry-out roller, and sheet discharging roller are coupled to the second discharging motor so as to be drivingly rotated in the sheet feeding direction by rotating the second driving motor forward. The second driving motor transmits a driving force to the registration roller via sliding friction clutch means. The sliding friction clutch means is configured so that transmission of a driving force from the second driving motor to the registration roller is blocked by rotating the first driving motor forward.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating an entire document feeding device containing a sheet feeding device in accordance with the present invention;

FIG. 2 is an enlarged diagram illustrating an essential part of the device in FIG. 1;

FIG. 3 is a diagram illustrating a driving transmitting mechanism for a sheet feeding motor in the device in FIG. 1;

FIG. 4 is a diagram illustrating a driving transmitting mechanism for a conveying motor in the device in FIG. 1;

FIG. 5 is a diagram illustrating essential parts of the driving transmitting mechanisms in FIGS. 3 and 4;

FIG. 6 is an exploded perspective view showing a driving transmitting mechanism for a registration roller in FIG. 5;

FIG. 7(a) is a sectional view of an essential part of the driving transmitting mechanism for the registration roller in FIG. 5, and FIG. 7(b) is a sectional view of an essential part of the driving transmitting mechanism for the registration roller in FIG. 5; and

FIG. 8 is a timing chart showing the control of the motors in FIGS. 3 and 4.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

With reference to the drawings, description will be given below for a sheet feeding device and an image reading apparatus comprising the sheet feeding device. FIG. 1 is a diagram showing the general configuration of a document feeding device incorporated in an image reading apparatus such as a scanner or a copier. FIG. 2 is a diagram illustrating an essential part of a sheet feeding section of the document feeding device. FIG. 3 is a diagram illustrating a driving mechanism in the device in FIG. 2. First, with reference to FIGS. 1 and 2, description will be given for the configuration of the document feeding device in the image reading apparatus and then the sheet feeding device in accordance with the present invention.

In FIG. 1, reference numeral 10 denotes a document feeding device (hereinafter referred to as an “ADF”) incorporated into an image reading apparatus. The ADF 10 includes a U-shaped conveying path (a sheet feeding path 25 and a carry-out path 26 described below) along which a sheet is conveyed so as to pass over a top surface of a first platen 2 provided in the image reading apparatus 1. The image reading apparatus 1 has a light source 3 such as a lamp which is located below the first platen 2, a mirror 4 that polarizes reflected light resulting from irradiation of a sheet with light from the light source 3, and optical reading means (not shown) such as a CCD sensor (charge coupled device) which electrically reads an image from the sheet. The image reading apparatus 1 has a reading section provided on the top surface of the first platen 2. The image reading apparatus 1 includes a second platen 5 on which a sheet is stationarily set. The ADF 10, located above the second platen 5, is opened, and a light source unit (carriage) composed of the light source 3, the mirror 4, and the like is moved in a sub-scanning direction to read a sheet image from a book document or other sheets set on the second platen 5.

The ADF 10 includes a placement tray 15 on which a plurality of sheets are placed, a sheet feeding section 11 that separably feeds each of the sheets on the placement tray 15 toward the first platen 2, a conveying section 12 that passes the sheet along the top surface of the first platen 2 at a predetermined speed, a sheet discharging section 13 that receives and discharges the sheet having passed over the top surface of the first platen 2, and a sheet discharging tray 16 that houses the sheet from the sheet discharging section 13. The ADF 10 further includes a switchback section 14 that allows the sheet discharging section 13 to switch back the sheet carried out from the first platen 2 to return the sheet to the sheet feeding section 11 so that the first platen 2 can read a back surface of the sheet. The ADF 10 further includes a circulating path 30.

The sheet feeding section 11 is composed of the above placement tray 15, a pickup roller 18, sheet feeding rotating means 19, a registration roller 21, and a sheet feeding path 25. The placement tray 15 is composed of a tray member shaped so that sheets with a size preset in accordance with apparatus specifications are placed. Side guides 17 are located on the placement tray 15 so that the side edges of a sheet can be aligned with the side guides 17. A gate stopper 38 is located at a leading end of the placement tray 15 so that the leading end of a sheet can be abutted against and aligned with the gate stopper 38; the gate stopper 38 can be projected from and retracted onto the placement tray 15. The illustrated placement tray 15 is attached to a device frame so as to incline at a predetermined angle. The placement tray 15 can pivot around a supporting point at its leading end, shown at 15a in the figure.

The pickup roller 18 is located so as to be able to elevate and lower between a standby position (corresponding to the state shown in FIG. 2) located above the placement tray 15 and an operative position in which the pickup roller 18 engages the sheets on the tray. An elevating and lowering arm 18a is supported by a rotating support shaft 19b attached to the device frame, so as to be able to swing freely. The elevating and lowering arm 18a has the pickup roller 18 supported at its leading end. A first driving motor M1 described below is coupled to the rotating support shaft 19b to transmit its rotation to the pickup roller 18.

The sheet feeding rotating means 19 is composed of rotating members such as a belt and a roller in order to separably feed each sheet downstream; the illustrated sheet feeding rotating means 19 is composed of a sheet feeding roller supported by the rotating support shaft 19b. In the description below, the sheet feeding rotating means is the sheet feeding roller 19. Separating means 20 such as a separating pad (not shown) or a separating roller is brought into pressure contact with the sheet feeding roller 19 to separably feed each sheet delivered by the pickup roller 18, to the interior of the apparatus. The arrangement of the sheet feeding roller 19 will be described below. Since sheets are set in the placement tray 15 by centering, the sheet feeding roller 19 is located at a position corresponding to the center of the sheets.

The sheet feeding path 25 is curved like the letter U to guide a sheet from the placement tray 15 to a processing position (first platen 2 described above). The registration roller 21 is located on the sheet feeding path 25 and composed of a pair of rollers 21a and 21b that are in pressure contact with each other. One of the rollers 21a and 21b is coupled to a second driving motor M2 described below. The conveying section 12 is composed of a carry-in roller 22 located upstream of the first platen 2 and a carry-out roller 23 located downstream of the first platen 2. Each of these rollers 22 and 23 is composed of a pair of rollers that conveys a sheet nipped between them. A backup guide 26a is located above the first platen 2, and a scooping guide 6 is located downstream of the first platen 2. Reference numeral 26 in the figure denotes a conveying path along which a sheet from the first platen 2 is carried out and guided to a sheet discharging path described below 27.

The sheet discharging section 13 is composed of a sheet discharging path 27, a path switching flapper 29 located on the sheet discharging path 27, and a sheet discharging roller 24. A rear end of the sheet discharging path 27 constitutes a switchback path 28. The switchback path 28 continues into a circulating path 30. The sheet discharging roller 24 rotates reversely with the trailing end of a sheet nipped between the rollers to switch back and feed the sheet to the circulating path 30. Thus, a sheet discharging roller 24b is separated from a sheet discharging roller 24a when the end of a sheet passes by the rollers; the sheet discharging rollers 24a and 24b constitute the sheet discharging roller 24. Further, the path switching flapper 29 is always urged downward by an urging spring to switch the path by means of an electromagnetic solenoid.

The circulating path 30 is composed of an upper guide 28a and a lower guide 28b so as to guide the sheet having its conveying direction reversed by the switchback path 28. Reference numeral 28 in the figure denotes a Myler guide that guides the sheet from the circulating path 30 to a nip point of the registration roller 21. A plurality of sensors S1, S2, and S3 (FIG. 1) is located on the placement tray 15 to detect a sheet size. The placement tray 15 has an empty sensor S4 that detects the presence or absence of a sheet. The sheet feeding path 25 has a registration sensor S5 that detects the leading and trailing ends of a conveyed sheet. A lead sensor S6 is provided upstream of the first platen 2 to detect the leading end of the sheet. The carry-out path 26 has a carry-out sensor S7. The sheet discharging path 27 has a sheet discharging sensor S8. The sensors S1 to S8 are connected to a CPU that drivingly controls the whole device. On the basis of detection signals from the sensors, the driving motors M1 and M2 and electromagnetic solenoid, described below, are controlled.

In the present invention, the pickup roller 18, sheet feeding roller 19, registration roller 21, carry-in roller 22, carry-out roller 23, and sheet discharging roller 24 are coupled to the first and second driving motors. Driving mechanisms for the conveying rollers will be described with reference to FIGS. 3 and 4.

FIG. 3 shows a driving mechanism for the first driving motor M1 (hereinafter referred to as a sheet feeding motor) that drivingly rotates the pickup roller 18 and sheet feeding roller 19. The sheet feeding motor M1 can rotate forward and backward to drivingly rotate the pickup roller 18 and sheet feeding roller in the sheet feeding direction. Moreover, the sheet feeding motor M1 swings the elevating and lowering arm 18a in a vertical direction, which supports the pickup roller 18. Thus, the sheet feeding motor M1 is coupled to the rotating support shaft 19b via a pulley P16, a timing belt T16, a pulley P36, a gear Z17, a gear 19, and a gear 18. Consequently, the rotating support shaft 19b rotates forward and backward in conjunction with the sheet feeding motor M1. Rotation of the sheet feeding roller 19 is transmitted to the rotating support shaft 19b via a one-way clutch OW2 and then to the pickup roller 18 via the timing belt T2. The one-way clutch OW2 transmits only the forward rotation of the sheet feeding motor M1 to the pickup roller 18 and sheet feeding roller 19, which thus rotate in the sheet feeding direction.

On the other hand, a base end of the elevating and lowering arm 18a is fitted around the rotating support shaft 19b via spring clutches A and B. The spring clutches are set so as to be loosened when the rotating support shaft 19b rotates forward and so to be compressed when the rotating support shaft 19b rotates backward. Consequently, forward rotation of the rotating support shaft 19b loosens the spring clutches to swing the elevating and lowering arm 18a from the standby position, located above, to the operative position, located below, under its own weight. In contrast, backward rotation of the rotating support shaft 19b compresses the spring clutches to raise the elevating and lowering arm 18a from the operative position to the standby position under a rotating torque from the shaft. Although not shown, the elevating and lowering arm 18a has a stopper at its standby position. While being restricted by the stopper, the elevating and lowering arm 18a is held at the standby position through the action of a spring clutch C (torque limiter) located between the pulley P36 and the gear Z17.

Even after the sheet feeding motor M1 is stopped, the spring clutches A and B remain compressed to hold the elevating and lowering arm 18a at the standby position under the load of the driving system. Thus, forward rotation of the sheet feeding motor M1 lowers the pickup roller 18 from the standby position to the operative position. The pickup roller 18 then rotates in the sheet feeding direction to deliver the sheets on the placement tray 15 in conjunction with the sheet feeding roller 19. After all the sheets on the placement tray 15 are delivered, the sheet feeding motor M1 rotates backward to swing the elevating and lowering arm 18a to raise the pickup roller 18 from the operative position to the standby position. In FIG. 3, the driving force of the sheet feeding motor M1 is transmitted from a gear 61 to a gear 66. The action of the driving force will be described below.

Now, description will be given to a driving mechanism for the second driving motor (hereinafter referred to as the conveying motor) M2, which drivingly rotates the registration roller 21, carry-in roller 22, carry-out roller 23, and sheet discharging roller 24; the driving mechanism is shown in FIG. 4. The driving motor M2 can rotate forward and backward and is coupled to a driving roller 22a of the carry-in roller 22 through a pulley P31 via a pulley P26, a timing belt T4, a pulley P46, a pulley P33, and a timing belt T6. Similarly, the driving motor M2 is coupled to a driving roller 23a of the carry-out roller 23 through a pulley P32. A driving force is also transmitted to pinching rollers 22b and 23b that are in pressure contact with the above rollers; a driving force is transmitted to the pinching roller 22b via gears Z3 and Z4 and to the pinching roller 23b via gears Z1 and Z2. Illustrated spring clutches C and D serve as torque limiters that absorb the difference in peripheral speed.

On the other hand, the driving force of the conveying motor M2 is transmitted to the sheet discharging roller 24 through a pulley 42, a timing belt T5, and a pulley P48 shown in FIG. 4. The driving force is also transmitted to a driving roller 24a of the sheet discharging roller 24 via a spring clutch E and to a pinching roller 24b through gears Z5 and Z6. The peripheral speed of the driving roller 24a is set slightly higher than that of the pinching roller 24b. When one sheet is nipped or no sheet is present, the spring clutch E allows the driving roller 24a to follow the peripheral speed of the pinching roller 24b. The peripheral speed of the pinching roller 24b is set to the same as that of the driving roller 23a of the carry-out roller 23. Moreover, the sheet discharging roller 24 has an electromagnetic solenoid (not shown) that separates the driving roller 24a from the pinching roller 24b. The driving roller 24a is provided with a coaxial reverse preventing lever 35 via a spring clutch F.

Thus, rotation of the conveying motor M2 is transmitted to a timing belt T3 through the timing belt T5 via a pulley 63 and a pulley 67 that is coaxial with the pulley 63. The rotation is further transmitted to a driving roller 21a of the registration roller 21 via a one-way clutch OW1 provided on the pulley 28a. This transmission system has a sliding friction clutch means 60 described below. The sliding friction clutch means 60 is configured as shown in FIGS. 5 and 8 to transmit rotation of the conveying motor M2 to the registration roller 21 and to block the transmission of the driving force (turn off the driving operation) when the sheet feeding motor M1 is drivingly rotating under predetermined conditions.

As shown in FIGS. 4 and 5, the timing belt T 5 for the conveying motor M2 is coupled through the pulley 63 to a rotating shaft 62 that continues into the registration roller 21 (in the figure, via the timing belt T3). The pulley 63 is loosely fitted around the rotating shaft 62 so as to avoid the direct transmission of a driving force from the rotating shaft 62. As shown in FIG. 7(a), a coil spring 65 is wound between a driving sleeve 63a integrated with the pulley 63 and a driven sleeve 64 fixed to the rotating shaft 62. The driving sleeve 63a is loosely fitted around the rotating shaft 62, and the driven sleeve 64 is fixed to the rotating shaft 62. The driving and driven sleeves 63a and 64 have substantially the same diameter. A spring 65 is wound around the driving and driven sleeves 63a and 64. The spring 65 is set on the loosening side when the pulley 63 rotates clockwise (CW) in FIG. 6 and on the compressing side when the pulley 63 rotates counterclockwise (CCW) in FIG. 6. The CCW rotation of the pulley 63 is transmitted to the driving shaft 62 via the driven sleeve 64.

On the other hand, a driven sleeve-side end of the spring 65 is bent and fixed to the gear 66. The gear 66 is loosely fitted on and supported by flanges formed on the driving sleeve 63a and driven sleeve 64 so as to rotate freely regardless of rotation of the pulley 63 and rotating shaft 62. The gear 61, connected to the sheet feeding motor M1, meshes with the gear 66. The gear 61 is attached to the rotating shaft 61a (see FIG. 3) via the one-way clutch OW to transmit the rotation of the sheet feeding motor M1 to the rotating shaft 61a through the pulley P36 and timing belt T16. The one-way clutch OW is set so as to avoid transmitting forward rotation (CCW in FIG. 3) of the driving sleeve 63a to the rotating shaft 61a as shown in FIG. 7(b).

Now, the operation of the driving mechanism will be described with reference to the timing chart shown in FIG. 8.

“Leading Sheet (First Sheet) Feeding Operation (First Operation)”

The apparatus is powered on to turn on the empty sensor S4 on the placement tray 15 to rotate the sheet feeding motor M1 forward (sheet feeding direction). At this time, the conveying motor M2 is stopped. The forward rotation of the sheet feeding motor M1 rotates the pickup roller 18 and the sheet feeding roller 19 in the sheet feeding direction (rightward in the figure). At the same time, the spring clutches A and B between the rotating support shaft 19b and the elevating and lowering arm 18a holding the pickup roller 18 are compressed to swing the elevating and lowering arm 18a in conjunction with rotation of the rotating support shaft 19b to lower the elevating and lowering arm 18a from the standby position to the operative position. The rotation of the rotating support shaft 19b is similarly transmitted, via the timing belt T2, to the pickup roller 18 supported at a swinging end of the elevating and lowering arm 18a. The rotating operation of the pickup roller 18 delivers each of the sheets on the placement tray 15 to the sheet feeding roller 19. The separating means 20 then separably feeds the delivered sheet. The elevating and lowering arm 18a stops swinging when the pickup roller 18 moves to the operative position to press the leading sheet to loosen the spring clutches A and B to stop rotating the rotating support shaft 19b. Further, the elevating and lowering arm 18a moves to the standby position to abut against a stopper (not shown) to loosen the spring clutch C. This turns off the sheet feeding driving system.

This operation allows the leading end of the sheet carried out to the sheet feeding path 25 to be sensed by the registration sensor S5. Subsequently, the sheet abuts against the registration roller 21. At this time, the conveying motor M2 coupled to the registration roller 21 is at a stop, so that the leading end of the sheet abuts against the nip point of the registration roller 21 and is thus bent. The bending of the sheet allows the leading end of the sheet to be registered. At a predetermined delay time (registration time) after the issuance of a sensing signal from the registration sensor S5, the sheet feeding motor M1 is stopped. During this process, in the sliding friction clutch means 60, the gear 66 rotates in conjunction with the gear 61 coupled to the sheet feeding motor M1. However, since the spring 65 is set in an opening direction (loosening direction), the spring 65 and the driven sleeve 64 slip against each other to keep the rotating shaft 62 at a stop; the rotating shaft 62 is not driven by the sheet feeding motor M1. The registration roller is at a stop without being rotated.

“Conveyance by the Registration Roller (Second Operation)”

Then, a predetermined time after a processing operation such as image reading, a sheet feeding instruction signal is issued, and in response to the signal, the conveying motor M2 is rotated forward (sheet feeding direction). At this time, the sheet feeding motor M1 is at a stop as previously described. The forward rotation of the conveying motor M2 rotates the pulley 63 clockwise in FIG. 5 to compress the coil spring 65 wound around the driving sleeve 63a. The driven sleeve 64 is thus rotated clockwise in FIG. 6 to rotate the rotating shaft 62 in the same direction. Rotating the rotating shaft clockwise in FIG. 6 rotates the registration roller 21 coupled to the rotating shaft 62 in the sheet feeding direction.

The rotation of the registration roller 21 transfers the sheet downstream along the sheet feeding path 25. Simultaneously with the operation of the registration roller 21, the forward rotation of the conveying motor M2 is transmitted to the carry-in roller 22 and carry-out roller 23 via the pulley P33 and timing belts T6 and T7 as previously described. These rollers are thus rotated in the sheet feeding direction. The motor M2 also transmits rotation in a sheet discharging direction to the sheet discharging roller 24 via the timing belt T5 and pulley P48. During this process, the clockwise rotation (in FIG. 5) of the gear 61 meshed with the gear 66 of the rotating shaft 62 is not transmitted to the sheet feeding motor M1 by the built-in one-way clutch OW.

“Stopping the Registration Roller (Third Operation)”

The lead sensor S6, located upstream of the carry-in roller 22, senses the leading end of the sheet conveyed as described above to issue a cue signal in accordance with which the first platen 2 reads an image. Then, the registration sensor S5 senses the trailing end of the sheet, and after the time when the trailing end of the sheet is expected to pass through the registration sensor 21, the sheet feeding motor M1 at a stop is actuated to rotate forward (sheet feeding direction). At this time, the conveying motor M2 continuously rotates forward (sheet feeding direction). Rotating the sheet feeding motor M1 and the conveying motor M2 at the same time subjects the coil spring 65 around the rotating shaft 62 to both the rotating force of the conveying motor in a compressing direction (shown by arrow a in FIG. 7(b)) and the rotating force of the sheet feeding motor M1 in a loosening direction (shown by arrow b).

Thus, for the sliding friction clutch means 60, the relationship between the rotation speed V2 (angular speed) of the conveying motor M2 transmitted to the rotating shaft 62 by the pulley 63 and the rotation speed V1 (angular speed) of the sheet feeding motor M1 transmitted by the gear 66 is set to be V1>V2. That is, the rotation speed of the sheet feeding motor M1 in the loosening direction acts more significantly on the coil spring 65 than the rotation speed of the conveying motor M2 in the compressing direction.

Consequently, the driving sleeve 63a and the coil spring 65 slip against each other, preventing the driving force of the sheet feeding motor M1 from being transmitted to the rotating shaft 61a. This stops the registration roller 21. On the other hand, rotation of the conveying motor M2 is transmitted to the carry-in roller 22, carry-out roller 23, and sheet discharging roller 24, coupled to the conveying motor M2. These rollers continue to rotate in the above directions. Accordingly, the sheet conveyed by the registration roller has its trailing end carried out from the roller 21 and is then conveyed to the first platen 2 by the carry-in roller 22. The platen then executes a reading process. The sheet from the platen 2 is carried out to the sheet discharging tray 16 by the carry-out roller 23 and sheet discharging roller 24.

“Delivering and Conveying the Second Sheet (Fourth Operation)”

The simultaneous rotation of the sheet feeding motor M1 (forward rotating CW direction) and conveying motor M2 (forward rotating CCW direction) stop the registration roller 21 as described above. At the same time, the pickup roller 18 and sheet feeding roller 19, coupled to the sheet feeding motor M1, rotate in the sheet feeding direction to deliver the next sheet from the placement tray 15 for registration. On the basis of the timing when the next sheet is fed to the registration roller 21, for example, on the basis of a leading end sensing signal from the registration sensor S5, the sheet feeding motor M1 is stopped. The conveying motor M2 finishes carrying the sheet out to the sheet discharging tray 16 and stops before the sheet feeding motor M1 stops. Further, stopping and rotating the registration roller 21 does not necessarily require the stoppage of the conveying motor M2; the registration-roller 21 can be stopped and rotated with the conveying motor M2 rotating, by rotating and stopping the sheet feeding motor M1. Then, in this state, the sheet fed to the registration roller 21 waits for the next sheet feeding instruction signal. Subsequently, the process returns to the second operation, which is then repeated as described above.

“Circularly Conveying Sheets (Fifth Operation)”

On the other hand, the sheet from which the image has been read is fed to the carry-out path 26 and carry-out path 27. At this time, in a double-side reading mode in which the back surface of the sheet is also read, the carry-out sensor S7 detects the trailing end of the sheet during above second operation. A predetermined time later, the carry-out sensor S7 switches the rotation of the conveying motor M2 to the backward direction (CW direction). At this time, the sheet feeding motor M1 is kept at a stop. The backward rotation of the conveying motor M2 reverses the direction in which the sheet nipped by the sheet discharging roller 24 is conveyed. The sheet is then fed to the circulation circuit 30. When the sheet is fed along the circulating path 30 and the trailing end of the sheet reaches the registration roller 21, the registration roller 21 at a stop registers the leading end of the sheet. That is, the backward rotation (CW direction) of the conveying motor M2 is transmitted to the pulley 63. However, a rotating force in the loosening direction acts on the coil spring 65 to prevent the backward rotation from being transmitted to the rotating shaft 62, coupled to the registration roller 21. After the circulated sheet is registered by the registration roller 21, the conveying motor receives a sheet feeding instruction signal at a predetermined timing and is thus rotated forward (CCW direction). The process returns to the second operation, which is then sequentially repeated.

“Pickup Roller Returning Operation (Sixth Operation)”

Once all the sheets on the placement tray 15 are delivered, the empty sensor S4 is turned off to issue the corresponding signal. Then, when the final sheet is carried out to the sheet discharging tray 16, for example, after a predetermined delay time since the sheet discharging sensor S8 issues a sheet trailing end detection signal, the sheet feeding motor M1 is rotated backward (CCW rotation). The rotation compresses the spring clutches A and B, provided on the elevating and lowering arm 18a as described above, to raise the elevating and lowering arm 18a from the operative position to the standby position under the rotating torque from the support shaft. Even after the sheet feeding motor M1 is stopped, the spring clutches A and B remain compressed to hold the elevating and lowering arm 18a in its standby position under the load of the driving system.

As described above, according to the present invention, the first driving motor drivingly rotates the pickup roller and sheet feeding rotating means, which separates and feeds each of the sheets on the placement tray. The second driving motor drivingly rotates the registration roller and carry-in roller, located downstream of the pickup roller and sheet feeding rotating means. Further, the sliding friction clutch means is provided between the second driving motor and the registration roller. The transmission of a driving force through the sliding friction clutch means is blocked by the corresponding rotation of the first driving motor. Consequently, even while a sheet delivered from the tray is being conveyed by the downstream carry-in roller, the rotation of the first driving motor for delivering the following sheet blocks the transmission of a driving force to the registration roller. This enables the pickup roller and sheet feeding rotating member to deliver the next sheet to the registration roller at a stop, allowing the sheet with its leading end registered to stand by. Thus, sheets can be consecutively fed at a high speed.

Therefore, compared to the conventional technique with which a motor rotates forward to perform a pickup operation and backward to perform a registered feeding operation, the present invention can control the motor so that the pickup roller is lowered from the standby position before starting the operation and raised from the operative position after finishing the operation. This eliminates the need to elevate and lower the pickup roller between the standby position and the operative position whenever a sheet is to be delivered. A precise process can be executed at the downstream processing position without any noise or vibration. Moreover, the required configuration is such that, for example, the coil spring is wound around the rotating shaft, connected to the registration roller, so that the registration roller being rotated by the second driving motor can be stopped by appropriately rotating the first driving motor to loosen the coil spring. Thus, the required structure is simple and can be easily controlled. Therefore, the present invention exerts significant effects.

Therefore, the automatic sheet feeding device set forth in the present invention can controllably stop and rotate the registration roller by rotating the sheet feeding motor forward and stopping it. The device enables the sheet to be separated from the pickup roller to stand by by reversely rotating the sheet feeding motor. This allows the provision of an automatic sheet feeding device and an image processing apparatus which eliminate the need for an expensive electromagnetic clutch otherwise required to stop and rotate the registration roller, the device and apparatus also enabling the pickup roller to always abut against the sheet during the sequential separation and feeding of sheets, reducing the possibility of vibration or noise.

Further, the sheet feeding motor M1 can be driven at a low speed while the registration roller 21 is being driven. By rotating the motor at a driving speed appropriate to prevent a plurality of overlapping sheets from being simultaneously fed, it is possible to feed the sheet being conveyed by the conveyance driving system, in a trailing end-first position. This enables smooth conveyance with a reduced conveying load.

The disclosure of Japanese Patent Application No. 2006-103668 filed on Apr. 4, 2006, is incorporated as a reference.

While the invention has been explained with reference to the specific embodiments of the invention, the explanation is illustrative and the invention is limited only by the appended claims.

Claims

1. A sheet feeding device comprising:

a placement tray on which sheets are placed;

pickup roller means configured to move up and down between an operative position where the pickup roller means engages a sheet and a standby position located above the operative position;

sheet feeding rotating means for separably feeding each sheet from the pickup means;

a registration roller located downstream of the sheet feeding rotating means to register the sheet from the sheet feeding rotating means;

a carry-in roller located downstream of the sheet feeding rotating means to transfer the sheet to a predetermined processing position;

a carry-out roller for carrying the sheet out from the processing position;

a first driving motor for rotating the pickup roller means and the sheet feeding rotating means;

a second driving motor for rotating the registration roller and the carry-in roller; and

sliding friction clutch means situated between the second driving motor and the registration roller, the sliding friction clutch means being coupled to the registration roller so that the registration roller is drivingly rotated by operating the second driving motor, and transmission of a driving force to the registration roller is blocked by operating of the first driving motor.

2. The sheet feeding device according to claim 1, wherein the sliding friction clutch means comprises a rotating shaft connected to the registration roller; and a coil spring wound around the rotating shaft, and

rotation of the second driving motor is frictionally transmitted to the rotating shaft via the coil spring, and frictional transmission of rotation of the rotating shaft with the coil spring is cancelled by rotating the first driving motor in a predetermined direction.

3. The sheet feeding device according to claim 2, wherein the coil spring is wound around the rotating shaft so as to be freely compressed and loosened,

the second driving motor and the first driving motor are coupled to the coil spring so as to rotate in a compressing direction and in a loosening direction, respectively, and

transmission of a driving force from the second driving motor to the rotating shaft is controlled on a basis of a difference in rotation speed between the first driving motor and the second driving motor which act on the coil spring.

4. The sheet feeding device according to claim 1, wherein the pickup roller means is attached to a swinging arm member supported by a rotating support shaft,

the rotating support shaft is coupled to the first driving motor, and

the swinging arm member is coupled to the rotating support shaft so that the pickup roller means is moved from the standby position to the operative position by rotating the first driving motor forward and from the operative position to the standby position by rotating the first driving motor backward.

5. The sheet feeding device according to claim 1, wherein the first driving motor is configured to rotate forward and backward,

the pickup roller means and the sheet feeding rotating means are coupled together so as to be rotated by rotating the first driving motor forward,

the pickup roller means is coupled to the sheet feeding rotating means so as to be moved from the standby position to the operative position by rotating the first driving motor forward and from the operative position to the standby position by rotating the first driving motor backward, and

the sliding friction clutch means is configured so that transmission of a driving force from the second driving motor to the registration roller is blocked by rotating the first driving motor forward.

6. A document feeding device in an image reading apparatus, comprising:

a placement tray on which sheets are placed;

a sheet feeding path for guiding a sheet from the placement tray to a reading position;

a sheet discharging path for guiding the sheet from the reading position to a sheet discharging tray;

pickup roller means located above the placement tray and configured to move up and down between an operative position where the pickup roller means engages the sheet and a standby position located above the operative position;

sheet feeding rotating means for separably feeding each sheet from the pickup roller means;

a registration roller located on the sheet feeding path to register the sheet from the sheet feeding rotating means;

a carry-in roller located on the sheet feeding path for transferring the sheet from the registration roller to the reading position;

a carry-out roller located on the sheet discharging path to carry the sheet out from the reading position;

a sheet discharging roller located on the sheet discharging path, for carrying the sheet from the carry-out roller out to the sheet discharging tray;

a first driving motor configured to rotate forward and backward to drivingly rotate the pickup roller means and the sheet feeding rotating means, wherein the pickup roller means and sheet feeding rotating means are coupled to the first driving motor so as to be drivingly rotated in a sheet feeding direction by rotating the first driving motor forward, and the pickup roller means is coupled to the first driving motor so as to move from the standby position to the operative position by rotating the first driving motor forward and to move from the operative position to the standby position by rotating the first driving motor backward;

a second driving motor configured to rotate forward and backward to drivingly rotate the registration roller, carry-in roller, carry-out roller, and sheet discharging roller, wherein the registration roller, carry-in roller, carry-out roller, and sheet discharging roller are coupled to the second discharging motor so as to drivingly rotate in the sheet feeding direction by rotating the second driving motor forward; and

sliding friction clutch means situated between the second driving motor and the registration roller, for transmitting a driving force from the second driving motor to the registration roller, the sliding friction clutch means being configured so that transmission of the driving force from the second driving motor to the registration roller is blocked by rotating the first driving motor forward.

7. The document feeding device according to claim 6, wherein a circulation path for guiding the sheet from the sheet discharging roller to the sheet feeding path is connected to the sheet discharging path,

the sheet discharging roller is coupled to the second driving motor so that the sheet is carried out to the sheet discharging tray by rotating the second driving motor forward, and the sheet is reversed and conveyed to the circulation path by rotating the second driving motor backward, and

the registration roller is coupled to the second driving motor via a one-way clutch so as to be drivingly rotated in the sheet feeding direction by rotating the second driving motor forward.