SHEET FEEDING APPARATUS

Abstract

A sheet feeding apparatus includes a sheet loading tray configured to be loaded with a sheet, an intake unit configured to take in the sheet loaded in the sheet loading tray to an apparatus body, a feeding unit configured to feed the sheet taken in by the intake unit, a separation unit configured to contact the feeding unit and separate a sheet to be fed from a plurality of sheets, and a sheet detection unit configured to emit light and detect presence or absence of a sheet between the feeding unit and the separation unit.

Claims

1. A sheet feeding apparatus comprising: a sheet loading tray configured to be loaded with a sheet; an intake unit configured to take in the sheet loaded in the sheet loading tray to an apparatus body; a feeding unit configured to feed the sheet taken in by the intake unit; a separation unit configured to contact the feeding unit and separate a sheet to be fed from a plurality of sheets; and a sheet detection unit configured to emit light and detect presence or absence of a sheet between the feeding unit and the separation unit.

2. The sheet feeding apparatus according to claim 1, wherein the feeding unit includes a first feed roller part and a second feed roller part that have a rotation axis extending in a sheet width direction, the separation unit includes a first separation roller part and a second separation roller part having a rotation axis extending in the sheet width direction, and the sheet detection unit is provided such that the light passes at least between the first feed roller part and the second feed roller part.

3. The sheet feeding apparatus according to claim 2, wherein the first feed roller part and the first separation roller part are configured to contact to each other to form a first nip range, the second feed roller part and the second separation roller part are configured to contact each other to form a second nip range, and a range over which the sheet detection unit detects presence or absence of the sheet is within a range of the first nip range and the second nip range in a conveyance direction of the sheet and between the first nip range and the second nip range in a sheet width direction.

4. The sheet feeding apparatus according to claim 3, wherein the sheet detection unit includes a light emitting unit and a light receiving unit, and the light emitted by the light emitting unit is obliquely incident on a surface of a sheet present in the first nip range and the second nip range.

5. The sheet feeding apparatus according to claim 2, wherein the sheet detection unit is provided such that the light passes between the first separation roller part and the second separation roller part and between the first feed roller part and the second feed roller part.

6. The sheet feeding apparatus according to claim 1, further comprising: a moving unit configured to move the intake unit between an intake position in contact with the sheet loaded in the sheet loading tray and a retracted position away from the sheet; and a control unit configured to control the feeding unit and the moving unit, wherein, in a case where a sheet is detected by the sheet detection unit when starting sheet feeding by the feeding unit, the control unit controls the moving unit such that the intake unit maintains the retracted position.

7. The sheet feeding apparatus according to claim 6, wherein, in a case where a sheet is not detected by the sheet detection unit when starting sheet feeding by the feeding unit, the control unit controls the moving unit such that the intake unit moves to the intake position.

8. The sheet feeding apparatus according to claim 3, wherein the sheet detection unit includes a light emitting unit and a light receiving unit, and the light emitted by the light emitting unit is perpendicularly incident on a surface of a sheet present in the first nip range and the second nip range.

9. The sheet feeding apparatus according to claim 4, further comprising: a light guide configured to change a direction of the light emitted from the light emitting unit.

10. The sheet feeding apparatus according to claim 4, wherein the sheet detection unit includes a reflective photoelectric sensor, and the light emitting unit and the light receiving unit are located downstream of a rotation center of the feeding unit in the conveyance direction of the sheet.

11. The sheet feeding apparatus according to claim 9, wherein the light receiving unit is located downstream of a rotation center of the feeding unit in the conveyance direction of the sheet, and the light emitting unit and the light guide are located upstream of a rotation center of the separation unit in the conveyance direction of the sheet.

12. The sheet feeding apparatus according to claim 11, wherein the light guide includes a first end portion that receives the light emitted from the light emitting unit, and a second end portion that is different from the first end portion and discharges the light, and the light guide has a curved shape such that the second end portion is oriented toward the light receiving unit.

13. The sheet feeding apparatus according to claim 12, wherein the second end portion is located between a rotation center of the separation unit and an upper end portion of the separation unit.

14. The sheet feeding apparatus according to claim 12, further comprising: a holding unit configured to cover the separation unit, such that the separation unit is partially exposed in a conveyance path of the sheet, wherein the holding unit includes a first holding part and a second holding part configured to be attached to and detached from the first holding part and to hold the light guide.

15. The sheet feeding apparatus according to claim 12, wherein a shaft portion of the light guide is inclined from an upstream side in the conveyance direction of the sheet to a downstream side in the conveyance direction of the sheet.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention and, together with the description, serve to explain principles of the invention.

[0010] FIG. 1 is a cross-sectional view schematically showing the configuration of an image reading apparatus according to one embodiment of the present invention;

[0011] FIG. 2 is a schematic diagram schematically showing the configuration of a main part of the image reading apparatus in FIG. 1;

[0012] FIG. 3A is a cross-sectional view of the area around a pickup roller;

[0013] FIG. 3B is a cross-sectional view of the area around the pickup roller;

[0014] FIG. 4 is a partial cross-sectional view schematically showing the disposition of components around optical sensors;

[0015] FIG. 5 is a partial cross-sectional view of FIG. 4 as viewed from the upstream side in a conveyance direction;

[0016] FIG. 6 is a flowchart showing the procedure of a feeding operation;

[0017] FIG. 7 is a partial cross-sectional view schematically showing the disposition of components around optical sensors in a second embodiment;

[0018] FIG. 8 is a partial cross-sectional view schematically showing the disposition of components around optical sensors in a third embodiment;

[0019] FIG. 9 is a perspective view of a lower guide plate in a fourth embodiment;

[0020] FIG. 10 shows the lower guide plate in the fourth embodiment as viewed from above; and

[0021] FIG. 11 is a partial cross-sectional view schematically showing the disposition of components around optical sensors in the fourth embodiment.

DESCRIPTION OF THE EMBODIMENTS

[0022] Hereinafter, embodiments will be described in detail with reference to the attached drawings. Note, the following embodiments are not intended to limit the scope of the claimed invention. Multiple features are described in the embodiments, but limitation is not made to an invention that requires all such features, and multiple such features may be combined as appropriate. Furthermore, in the attached drawings, the same reference numerals are given to the same or similar configurations, and redundant description thereof is omitted.

First Embodiment

[0023] FIG. 1 is a partial cross-sectional view schematically showing the configuration of an image reading apparatus which is an example of a sheet feeding apparatus according to a first embodiment, and FIG. 2 is a schematic diagram schematically showing the configuration of a main part of the image reading apparatus in FIG. 1.

[0024] In FIGS. 1 and 2, an image reading apparatus 200 includes a sheet intake unit 101. A plurality of sheets are loaded in a sheet loading tray 1, and the sheet loading tray 1 is configured to be freely raised and lowered. A loading tray drive motor 2 raises and lowers the sheet loading tray 1. A sheet detection sensor 3 detects that a sheet loaded in the sheet loading tray 1 is in a sheet intake position. When a sheet loaded in the sheet loading tray 1 is not in the sheet intake position, the loading tray drive motor 2 is driven, and the sheet loading tray 1 is moved so that the uppermost sheet surface is in the intake position. A sheet loading detection sensor 4 detects that sheets are loaded on a sheet loading surface la of the sheet loading tray 1.

[0025] A pickup roller 5 is provided opposing the sheet loading tray 1, and functions as an intake unit configured to send sheets loaded in the sheet loading tray 1 to a feed roller 7 and taking the sheets into the apparatus body. A pickup motor 6 rotates the pickup roller 5. In FIG. 2, the upper sheet surface is in the sheet intake position, and sheets will start being taken in when the pickup roller 5 is rotated.

[0026] The feed roller 7 is provided downstream of the pickup roller 5 in the conveyance direction, is driven to rotate in the direction in which sheets are fed downstream in the conveyance direction by a feed motor 8, and functions as a feeding unit. The feed roller 7 is coupled to the feed motor 8 via a one-way clutch not shown, and the drive of the feed motor 8 is transmitted in only one direction. The drive force is transmitted to the feed roller 7 by the feed motor 8 at the time of feeding, but when the sheets are conveyed at a speed exceeding the speed of the feed roller 7 by conveyance rollers 14, 15, and the like, the rotation of the feed motor 8 is not transmitted by the one-way clutch and the feed roller 7 is turned around by the conveyance of the sheets and rotationally driven.

[0027] A separation roller 9 is provided opposing the feed roller 7 across the conveyance path and is biased toward the feed roller 7. The separation roller 9 is subjected to a rotational force in a direction in which the sheets are pushed back upstream in the conveyance direction by a torque limiter not shown (counterclockwise direction in the diagram). When there is only one sheet between the feed roller 7 and the separation roller 9, the rotational force applied in the clockwise direction in the diagram by the friction force between the sheet that is fed and the separation roller 9 is greater than the upper limit of the rotational force applied in the counterclockwise direction in the diagram by the torque limiter, and thus the separation roller 9 follows the feed roller 7 and rotates (is turned) clockwise in the diagram. On the other hand, when there are a plurality of sheets between the feed roller 7 and the separation roller 9, the separation roller 9 functions as a separation unit, and is subjected to a rotational force by the torque limiter in a direction in which the sheets are pushed back upstream in the conveyance direction, and only the sheet to be fed that is in contact with the feed roller 7 is conveyed.

[0028] As described above, the feed roller 7 acts to feed the sheets downstream, and the separation roller 9 acts to prevent the sheets from being fed downstream. When a plurality of sheets stacked one on the other are sent to the contact portion (nip portion) between the feed roller 7 and the separation roller 9, the stacked sheets are separated, with only the uppermost sheet, which is the sheet to be fed, being fed downstream, and the other sheets are not fed downstream.

[0029] Note that a plurality of sheets may be prevented from being conveyed downstream by replacing the separation roller 9 with a separation pad and bringing the separation pad in contact with the sheets.

[0030] A multi-feed detection sensor 30 is provided downstream of the feed roller 7 in the conveyance direction. The multi-feed detection sensor 30 detects whether the sheets are being separated one by one by the separation roller 9. In the present embodiment, a detection device that uses ultrasonic transmitting/receiving units is used as the multi-feed detection sensor 30, and multi-feeding is detected by the attenuation amount of ultrasonic waves between the transmitting/receiving units on both sides of the conveyance path.

[0031] A conveyance motor 11 rotates conveyance rollers 14, 16, 18, and 20 to convey sheets to an image reading position where images of the sheets are read by image reading sensors 12 and 13. When the conveyance rollers 14, 16, 18, and 20 are rotated, conveyance rollers 15, 17, 19, and 21 respectively disposed opposite thereto are rotationally driven, enabling the sheets to be conveyed. Also, the conveyance motor 11 drives the rollers so as to be able to change the conveyance speed of the sheets according to the optimal speed for reading the sheets, and settings such as the resolution of the sheets. Note that a registration clutch 22 drives the conveyance roller 14 or stops the drive thereof, by transmitting the rotational drive force of the conveyance motor 11 to the conveyance roller 14 or interrupting transmission thereof.

[0032] A conveyance roller pair constituted by the conveyance rollers 16 and 17, a conveyance roller pair constituted by the conveyance rollers 18 and 19, and a roller pair constituted by the conveyance rollers 20 and 21 convey the sheets to a discharge roller pair constituted by discharge rollers 23 and 24 and a discharge stacking unit 42 that are further downstream. An upper guide plate 40 and a lower guide plate 41 guide the sheets that are conveyed by the pairs of rollers. Also, the lower guide plate 41 forms a wall surface between the sheets loaded in the sheet loading tray 1 and the separation roller 9, and covers the upstream and downstream sides of the separation roller 9 such that part of the separation roller 9 is exposed in the conveyance path.

[0033] An upstream sensor 31 and a downstream sensor 32 are respectively provided upstream and downstream of the conveyance roller 14 in the conveyance direction. The upstream sensor 31 and the downstream sensor 32 detect the arrival of the leading edge and the trailing edge of a sheet. At the timing at which the leading edge or trailing edge of a sheet arrives, rotation of the pickup roller 5, the feed roller 7 and the like is started or stopped. A detailed description will be given later when describing the sheet feeding flow.

[0034] Note that the image reading apparatus 200 includes a control unit 43 that controls the operations of the entire apparatus. The control unit 43 includes one or more processors (CPUs), and one or more storage devices such as memories in which programs to be executed by one or more processors are stored, for example.

Pickup Roller Lifting Mechanism

[0035] The pickup roller 5 is provided with a lifting mechanism and can be moved by a moving unit between an intake position where the pickup roller 5 can take in sheets by coming in contact with the sheets and a retracted position away from the sheets. FIGS. 3A and 3B are cross-sectional views of the area around the pickup roller 5, with FIG. 3A showing the state when the pickup roller 5 has been moved to the retracted position, and FIG. 3B showing the state when the pickup roller 5 has been moved to the intake position.

[0036] In FIGS. 3A and 3B, the drive force of the pickup motor 6 is transmitted to a pickup motor drive gear 51. The drive force from the pickup motor drive gear 51 is transmitted to the pickup roller 5 via a timing belt 54 and a gear 53. The pickup motor drive gear 51, the gear 53, and the pickup roller 5 are attached to a pickup roller frame 52. The pickup roller 5 is freely detachable from the pickup roller frame 52 so as to be replaceable. The pickup roller frame 52 swings freely with the center of the pickup motor drive gear 51 as the rotation axis. A pickup lifting motor 60 is a pulse motor that generates a force for swinging the pickup roller frame 52.

[0037] When the pickup roller 5 is in the retracted position shown in FIG. 3A, the pickup roller frame 52 is in an upper limit position, and a frame detection sensor 56 detects that the pickup roller frame 52 is in this position. The pickup roller 5 is moved to the intake position shown in FIG. 3B by driving the pickup lifting motor 60 for only a predetermined number of pulses, starting from the position where the frame detection sensor 56 detects the pickup roller frame 52.

[0038] A control unit executes control to move the pickup roller 5 to the sheet intake position when taking in a sheet from the sheet loading tray 1, and to move the pickup roller 5 to the retracted position away from the sheet intake position when the pickup roller 5 has finished taking in a sheet to the feed roller 7 and when sheets are being conveyed by downstream rollers, using the lifting mechanism of the pickup roller 5 described above.

Configuration for Detecting Sheets in the Vicinity of Feed Roller 7 and Separation Roller 9

[0039] FIG. 4 is a partial cross-sectional view schematically showing the disposition of components in the vicinity of the feed roller 7 and the separation roller 9, and is a cross-section taken at the position of an optical axis R described later. FIG. 5 is a partial cross-sectional view schematically showing the disposition of components when the vicinity of the feed roller 7 and the separation roller 9 is viewed from upstream in the conveyance direction (from the left side in FIG. 4).

[0040] In FIGS. 4 and 5, a light emitting sensor 33 that emits light including infrared light and a light receiving sensor 34 that received light, which are optical sensors that function as a sheet detection unit configured to detect the presence or absence of sheets, and a light guide 35 that changes the direction of light emitted from a light emitting sensor 33 and guides the light to the light receiving sensor 34 are shown, in addition to the feed roller 7, the separation roller 9, the upper guide plate 40, and the lower guide plate 41 out of the members shown in FIG. 1 being shown in an extracted manner. Furthermore, a separation roller holding member 44 that holds a rotation shaft portion of the separation roller 9 is shown. The sheets are fed from the left side to the right side of the diagram in FIG. 4, and from the near side to the far side of the surface of the diagram in FIG. 5.

[0041] In the feed roller 7, a first feed roller part 7a and a second feed roller part 7b formed of rubber material or the like are installed on a feed wheel part 7c. In the separation roller 9, a first separation roller part 9a and a second separation roller part 9b formed of a rubber material or the like are installed on a separation wheel part 9c. The first and second feed roller parts 7a and 7b and the first and second separation roller parts 9a and 9b each partially protrude into the conveyance path. Also, the first and second feed roller parts 7a and 7b and the first and second separation roller parts 9a and 9b are provided substantially symmetrically with respect to the center of a fed sheet in the width direction (left-right direction in FIG. 5). The interval between the first feed roller part 7a and the second feed roller part 7b and the interval between the first separation roller part 9a and the second separation roller part 9b are set to be narrower than the minimum feedable sheet width. A nip range 50 (illustrated with double-headed arrow) in FIG. 4 is the range over which the feed roller 7 and the separation roller 9 come in contact with each other. Note that, when the nip range 50 is viewed from the sheet feeding direction, a first nip range 50a and a second nip range 50b described later are observed (see FIG. 5).

[0042] The light emitting sensor 33 which is a light emitting unit and the light receiving sensor 34 which is a light receiving unit are respectively mounted on a light emitting substrate 36 and a light receiving substrate 37. The light emitting substrate 36 and the light guide 35 are provided on the separation roller 9 side (lower side in FIGS. 4 and 5) across the conveyance path, and the light receiving substrate 37 is provided on the feed roller 7 side (upper side in FIGS. 4 and 5) across the conveyance path.

[0043] Also, as shown in FIG. 4, the light emitting sensor 33 and the light guide 35 are provided upstream in the conveyance direction from the rotation center of the separation roller 9. The light receiving sensor 34 is provided downstream in the conveyance direction from the rotation center of the feed roller 7. Note that the light emitting sensor 33, the light guide 35, and the light receiving sensor 34 may be disposed at different positions from the positions shown in FIG. 4. For example, the light emitting sensor 33 and the light guide 35 may be provided downstream in the conveyance direction from the rotation center of the feed roller 7, and the light receiving sensor 34 may be provided upstream in the conveyance direction from the rotation center of the separation roller 9.

[0044] The light guide 35 is provided upward of the light emitting sensor 33 and the light emitting substrate 36. As shown in FIG. 4, the light guide 35 has a shaft portion extending vertically and a shaft portion inclined at an angle from the upstream side in the conveyance direction to the downstream side in the conveyance direction. The length of the light guide 35 is the combined length of the shaft portion extending vertically and the shaft portion inclined at the angle . At this time, the length of the light guide 35 is preferably a length at which the separation roller 9 and the light guide 35 do not interfere with each other when the user attaches and detaches the separation roller 9, but is not limited thereto. The position and angle of the light guide 35 are set such that the light emitted from the light emitting sensor 33 is incident at an angle so as to be not be blocked by the feed wheel part 7c, the separation wheel part 9c, and the nip range 50. Here, in FIG. 4, the light emitted from the light emitting sensor 33 passes along an optical path that does not overlap with the nip range 50 in a direction from the near side to the far side of the surface of the diagram (i.e., same range as first nip range 50a and second nip range 50b (i.e., same range as nip range 50) in the conveyance direction of the sheet described later and in a direction perpendicular to the sheet surface, and a detection range consisting of a range in an intermediate position between first nip range 50a and second nip range 50b in the sheet width direction). Note that the light reflected inside the light guide 35 is omitted, and the direction in which the light is guided is representatively indicated in a simplified manner by a dotted line (optical axis R).

[0045] Note that, when the light emitting sensor 33 is disposed such that the axis thereof is vertical, and the shaft portion of the light guide 35 that extends vertically is disposed between the lower guide plate 41 and the separation roller holding member 44, as in the present embodiment, the light emitting sensor 33, the light emitting substrate 36, and the light guide 35 can be disposed in a minimal space, and the entire apparatus can be made more compact.

[0046] The light receiving sensor 34 and the light receiving substrate 37 are provided such that the central axis of the light receiving sensor 34 substantially coincides with the optical axis R inclined at the angle 0 by the light guide 35.

[0047] As shown in FIG. 5, the light emitting sensor 33, the light guide 35, and the light receiving sensor 34 are provided such that the optical axis R passes between the first separation roller part 9a and the second separation roller part 9b, and between the first feed roller part 7a and the second feed roller part 7b.

[0048] Accordingly, when the range (nip range) over which the first feed roller part 7a and the first separation roller part 9a come in contact with each other is given as the first nip range 50a, and the range (nip range) over which the second feed roller part 7b and the second separation roller part 9b come in contact with each other is given as the second nip range 50b, the light emitted from the light emitting sensor 33 passes, as the detection range, through the same range as the first nip range 50a and the second nip range 50b (i.e., same range as the nip range 50) in the conveyance direction of the sheet and in a direction perpendicular to the sheet surface, and through a range in an intermediate position between the first nip range 50a and the second nip range 50b in the sheet width direction.

[0049] The interval between the first feed roller part 7a and the second feed roller part 7b and the interval between the first separation roller part 9a and the second separation roller part 9b are set narrower than the minimum feedable sheet width, and thus, when there is a sheet in the detection range, it may be determined that the sheet is being nipped by the feed roller 7 and the separation roller 9. When there is a sheet in the detection range, the light emitted from the light emitting sensor 33 is attenuated when passing through the sheet, and the amount of light detected by the light receiving sensor 34 is greatly reduced compared to when there is no sheet. Accordingly, by comparing the magnitude of the light amount detected by the light receiving sensor 34 with a predetermined threshold value, it can be determined whether or not a sheet is in the detection range (is being nipped).

[0050] If the following sheet is in the detection range when feeding of the following sheet is started, the following sheet does not need to be taken in by the pickup roller 5, and thus the feed motor 8 is immediately driven to rotate the feed roller 7 and the following sheet is fed. If the following sheet is not in the detection range when feeding the following sheet is started, the following sheet needs to be taken in by the pickup roller 5, and thus the pickup roller 5 is moved to the intake position and brought in contact with the following sheet, after which the pickup motor 6 is driven to rotate the pickup roller 5 and the following sheet is taken in.

Sheet Feeding Control Flow

[0051] Controls of the present embodiment will be described on the basis of the flowchart in FIG. 6. The flowchart starts from a state where sheets are loaded in the sheet loading tray 1 and the sheet loading detection sensor 4 has detected the sheets. Also, the sheet loading tray 1 actually rises such that the uppermost sheet is in the intake position whenever the number of loaded sheets decreases, but, in this flowchart, the rising operation of the sheet loading tray 1 is omitted. Also, this flowchart starts from a state in which the separation motor 10 is in a holding state.

[0052] First, the conveyance motor 11 is driven to rotate the conveyance rollers 14, 16, 18, and 20 (S101). Next, the feed motor 8 is driven to rotate the feed roller 7 (S102).

[0053] Next, in order to take in a sheet with the pickup roller 5, the pickup lifting motor 60 is driven to lower the pickup roller 5 to the intake position shown in FIG. 3B, after which the pickup motor 6 is driven to rotate the pickup roller 5 (step S103). When the pickup roller 5 is rotated after the pickup roller 5 comes in contact with the sheet and the posture of the sheet and the load on the sheet are stabilized, the sheet can be stably taken in.

[0054] When the sheet taken in by the pickup roller 5 reaches the nip range of the feed roller 7 and the separation roller 9, the sheet is fed by the feed roller 7. The peripheral speed of the feed roller 7 is set faster than the peripheral speed of the pickup roller 5, and the sheet is pulled out by the feed roller 7.

[0055] Next, the upstream sensor 31 provided upstream in the conveyance direction from the conveyance rollers 14 and 15 detects the presence or absence of a sheet, and it is determined whether the leading edge of a sheet is detected (step S104). When the upstream sensor 31 detects the leading edge of a sheet, the drive of the pickup motor 6 is stopped to stop the rotation of the pickup roller 5, and, thereafter, the pickup lifting motor 60 is driven to raise the pickup roller 5 to the retracted position shown in FIG. 3A, and the pickup roller 5 moves out of contact with the sheet (step S105).

[0056] When the sheet reaches the conveyance rollers 14 and 15, the sheet is conveyed by the conveyance rollers 14 and 15. The peripheral speed of the conveyance rollers 14 and 15 is set faster than the peripheral speed of the feed rollers 7, and the sheet is pulled out by the conveyance rollers 14 and 15.

[0057] Next, the downstream sensor 32 provided downstream in the conveyance direction from the conveyance rollers 14 and 15 detects the presence or absence of a sheet, and it is determined whether the leading edge of a sheet is detected (step S106). When the downstream sensor 32 detects the leading edge of a sheet, the drive of the feed motor 8 is stopped to stop the rotation of the feed roller 7 (step S107).

[0058] Next, the upstream sensor 31 detects the presence or absence of a sheet, and it is determined whether the trailing edge of a sheet is detected (step S108). When the upstream sensor 31 detects the trailing edge of a sheet, it is known that the trailing edge of the sheet has already passed through the nip range of the feed roller 7 and the separation roller 9, and taking in of the next sheet (following sheet) loaded in the sheet loading tray 1 is started.

[0059] In taking in the following sheet, the configuration consisting of the light emitting sensor 33, the light receiving sensor 34, and the light guide 35 detects whether the following sheet is in the nip range (step S109). Since the pickup roller 5 does not need to take in the following sheet when the following sheet is detected in the nip range, the feed motor 8 is driven to rotate the feed roller 7 while keeping the pickup roller 5 in the retracted position (step S110). The following sheet fed by the feed roller 7 passes through the detection position of the upstream sensor 31, reaches the conveyance rollers 14, 15 and is conveyed by the conveyance rollers 14, 15, and then reaches the detection position of the downstream sensor 32. When the downstream sensor 32 detects the leading edge of the following sheet (step S106), the subsequent feeding operation is the same as the operation performed when the preceding sheet was fed.

[0060] When the following sheet is not detected in the nip range in step S109, the presence or absence of sheets in the sheet loading tray 1 is detected (step S111). When there are no sheets on the sheet loading tray 1, the drive of the conveyance motor 11 is stopped to stop the rotation of the conveyance rollers 14, 16, 18, and 20 (step S112), and the feeding operation is stopped. Since the pickup roller 5 needs to take in the following sheet when there are sheets in the sheet loading tray 1, the feed roller 7 is rotated (step S102), after which the pickup lifting motor 60 is driven to lower the pickup roller 5 to the intake position and bring the pickup roller 5 in contact with the sheet, after which the pickup roller 5 is rotated (step S103). The subsequent feeding operation is similar to the operation when the preceding sheet is fed.

[0061] According to the above control flow, the pickup roller 5 is brought in contact with the following sheet only when the intake operation by the pickup roller 5 is necessary, by determining whether or not the sheet is in the nip range of the feed roller 7 and the separation roller 9 at the stage at which taking in of the following sheet is started. Detection of whether or not the following sheet is in the nip range can be performed immediately before the feed roller 7 is rotated to feed the sheet, and thus there is no chance for the following sheet that was in the nip range to move out of the nip range in the opposite direction to the conveyance direction from when the following sheet is detected until when the feed roller 7 is rotated. Therefore, following sheet can be reliably fed.

Second Embodiment

[0062] Next, a sheet feeding apparatus according to a second embodiment will be described. Parts common to the first embodiment will be omitted, and description will mainly focus on the differences from the first embodiment with reference to FIG. 7.

[0063] In the first embodiment, the lower guide plate 41 covers the separation roller 9 as shown in FIG. 4. In the present embodiment, in order to enable the separation roller 9 to be easily detached from the feed port side, a separation cover 45 is provided in a part of the lower guide plate 41, as shown in FIG. 7. The separation cover 45 is provided to be attachable and detachable with respect to the lower guide plate 41.

[0064] Also, the light guide 35 is assembled to the separation cover 45, and the separation cover 45 and the light guide 35 are integrated. The separation cover 45 and the light guide 35 are thereby attached and detached as one, and thus the user does not interfere with the separation roller 9 and the light guide 35 when attaching and detaching the separation roller 9. Also, the light guide 35 does not require wiring in order to be connected to another substrate compared to a sensor provided on an electrical board. Therefore, the user is able to attach and detach the separation cover 45 without needing to worry about wiring.

Third Embodiment

[0065] Next, a sheet feeding apparatus according to a third embodiment will be described. Parts common to the first embodiment will be omitted, and description will mainly focus on the differences from the first embodiment with reference to FIG. 8.

[0066] In the first embodiment, sheets are detected using a transmissive detection method consisting of the light emitting sensor 33 and the light receiving sensor 34, as shown in FIGS. 4 and 5. In the present embodiment, a reflective photoelectric sensor 38, which is a reflective detection method, is used, as shown in FIG. 8. In order to prevent dust from the sheets from accumulating on the reflective photoelectric sensor 38, the reflective photoelectric sensor 38 is provided on the feed roller 7 side (upper side in the diagram) across the conveyance path. The reflective photoelectric sensor 38 is provided downstream in the conveyance direction from the rotation center of the feed roller 7, but may be provided upstream in the conveyance direction.

[0067] The dotted line portion in the diagram represents the optical path along which light emitted from a light emitting unit of the reflective photoelectric sensor 38 passes between the first feed roller part and the second feed roller part and reaches a light receiving unit of the reflective photoelectric sensor 38 after being diffusely reflected by the sheet surface. Use of the reflective photoelectric sensor 38 means that the light guide 35 and the separate light receiving sensor 34 are no longer needed, enabling the number of components to be reduced and miniaturization to be achieved in a space-saving manner.

[0068] In the first to third embodiments, the optical sensors are provided in a YZ plane, such that the optical axis R indicating the direction of the light of the optical sensors is parallel to the YZ plane as shown in FIG. 5, for example, where the sheet width direction is the X direction, the conveyance direction is the Y direction, and the direction perpendicular to the conveyance direction is the Z direction, but the optical sensors may be shifted in the X direction such that the optical axis R is oblique to the YZ plane to an extent that the optical axis R is not blocked by the feed roller 7 or the separation roller 9. Adopting this configuration enables a layout in which the optical sensors are effectively placed in a limited space to also be realized.

Fourth Embodiment

[0069] Next, a sheet feeding apparatus according to a fourth embodiment will be described. Parts common to the first embodiment will be omitted, and description will mainly focus on the differences from the first embodiment with reference to FIGS. 9 to 11.

[0070] In the first embodiment, as shown in FIGS. 4 and 5, sheets are detected using a transmissive detection method consisting of the light emitting sensor 33, the light guide 35, and the light receiving sensor 34. In the present embodiment, the light guide 35 is provided in a position where the light emitted from the light emitting sensor 33 can be guided downstream in the conveyance direction, so as to not erroneously detect the sheet upstream in the conveyance direction. For example, due to variation in the positions in which the components constituting the sheet feeding apparatus are disposed, the sheet detection position is shifted upstream in the conveyance direction from the nip range 50, as shown in FIG. 11. Furthermore, since the light emitted from the light emitting sensor 33 diffuses rather than traveling straight through the end portion of the light guide 35 on the light emitting side, the amount of light received by the light receiving sensor 34 is reduced. Due to these factors, the pickup roller 5 is controlled to remain in the retracted position even though a sheet is not being nipped. Thus, problems such as not being able to smoothly feed the following sheet may occur. In order to solve this problem, the end portion of the light guide 35 on the light emitting side is located in the vicinity of the conveyance path as shown in FIG. 11. For example, the end portion of the light guide 35 on the light emitting side is located between the rotation center of the separation roller 9 and the upper end portion of the separation roller 9.

[0071] As shown in FIG. 9, a light guide 35 in which the length of the shaft portion extending vertically and the length of the shaft portion inclined at an angle 0 from the upstream side in the conveyance direction to the downstream side in the conveyance direction are both extended, such that the distance between the end portion of the light guide 35 on the light emitting side (end portion located on upper side in FIG. 9) and the conveyance path is shortened. The light guide 35 is attached to an upper part of the inner wall of the lower guide plate 41 on the downstream side in the conveyance direction. A mechanism that allows the light guide 35 to be attached and detached with respect to the lower guide plate 41 may be provided at any position on the inner wall of the lower guide plate 41. When the lower guide plate 41 in FIG. 9 is viewed from above, the end portion of the light guide 35 on the light emitting side is located between the two separation rollers 9, as shown in FIG. 10.

[0072] FIG. 11 is a partial cross-sectional view schematically showing the disposition of components around the optical sensors when the lower guide plate 41 in FIG. 9 is viewed from the side. A distance L (shown by dashed line) between the end portion of the light guide 35 on the light emitting side and the light receiving sensor 34 is shorter than a distance L (not shown) between the end portion of the light guide 35 on the light emitting side and the light receiving sensor 34 in FIG. 4. The present embodiment is thereby able to prevent a reduction in the amount of light received by the light receiving sensor 34 and deviation of the sheet detection position. Note that the light guide 35 is disposed upstream in the conveyance direction from the rotation center (separation wheel part 9c) of the separation roller 9, but may be disposed downstream in the conveyance direction from the rotation center (feed wheel part 7c) of the feed roller 7.

[0073] The position of the end portion of the light guide 35 on the light emitting side desirably protrudes into the conveyance path since the distance between the end portion and the conveyance path is preferably shorter, but need not protrude as long as the end portion is close to the conveyance path. At that time, the end portion of the light guide 35 on the light emitting side desirably does not protrude on the conveyance path side from the sheet contact surface of the separation roller 9 so that the sheets that are conveyed do not get caught thereon.

[0074] The present invention can be implemented by processing of supplying a program for implementing one or more functions of the above-described embodiments to a system or apparatus via a network or storage medium, and causing one or more processors in the computer of the system or apparatus to read out and execute the program. The present invention can also be implemented by a circuit (for example, an ASIC) for implementing one or more functions.

[0075] The present invention is not limited to the above embodiments and various changes and modifications can be made within the spirit and scope of the present invention. Therefore, to apprise the public of the scope of the present invention, the following claims are made.