Patent Description:
In a conventional sheet feeder, when continuously feeding a plurality of sheets, every time one sheet is fed, an operation of moving a pickup roller (for example, <NUM> in <FIG> to be described later) to a sheet take-in position, bringing it into contact with the sheet, and rotating it, and then moving it to a retreat position is repeated. However, if the sheet is thin paper or the like with low stiffness, jam may occur between a separation roller pair (for example, <NUM> and <NUM> in <FIG>) and the pickup roller.

As a jam measure for a sheet such as thin paper, <CIT> has been proposed. In <CIT>, a pre-registration sensor (for example, <NUM> in <FIG> to be described later) detects the trailing edge of a precedingly fed sheet. After that, if the pre-registration sensor does not detect the leading edge of the next sheet after the elapse of a specific time, the pickup roller is brought into contact with the sheet and rotated. There has been proposed a technique of feeding a sheet while minimizing use of the pickup roller in this way.

In <CIT>, there have been proposed a sheet feeder as specified in the preamble of claim <NUM> and a control method of a sheet feeder as specified in the preamble of claim <NUM>.

The technique of <CIT> has an effect to certain extent as a jam measure for a sheet such as thin paper with low rigidity (to be referred to as "stiffness" hereinafter). On the other hand, in some cases, the sheet may be caught by a feed roller that constitutes the separation roller pair to cause jam.

As described above, in the conventional technique, if a sheet to be fed is thin paper or the like with low stiffness, jam may occur on the feed roller.

The present invention has been made to solve the above-described problem. It is an object of the present invention to provide a mechanism capable of making jam less likely to occur in feeding even if a sheet to be fed is thin paper or the like with low stiffness.

The present invention has been made in consideration of the above-described problem, and provides a sheet feeder as specified in claim <NUM> and a control method of a sheet feeder as specified in claim <NUM>.

According to the present invention, it is possible to make jam less likely to occur in feeding even if a sheet to be fed is thin paper or the like with low stiffness.

A sheet conveyance apparatus including a sheet feeder according to the first embodiment of the present invention will be described first.

A case in which the sheet conveyance apparatus according to the present invention is applied to an image reading apparatus will be described here as an example. However, the sheet conveyance apparatus can also be applied to various kinds of sheet conveyance apparatuses such as an apparatus including a document conveyance system, such as a printing apparatus (printer or the like) for printing on a sheet and a multi-function peripheral that combines an image reading apparatus and a printing apparatus.

As shown in <FIG> and <FIG>, a sheet conveyance apparatus <NUM> according to this embodiment includes a sheet take-in device (sheet feeder) <NUM>.

A plurality of sheets are stacked on a sheet stacker (sheet placement table) <NUM>, and the sheet stacker <NUM> is configured to move up and down. A sheet stacker drive motor <NUM> moves the sheet stacker <NUM> up and down. A sheet detection sensor <NUM> detects that a sheet stacked on the sheet stacker <NUM> is located at a sheet take-in position. A sheet stacking detection sensor <NUM> detects that a sheet is stacked on a sheet stacking surface 1a of the sheet stacker <NUM>. A document jumping detection sensor <NUM> includes a plurality of sensors arranged in a direction orthogonal to the sheet stacking surface 1a, and detects jumping of a sheet stacked on the sheet stacker <NUM>. For example, the document jumping detection sensor <NUM> can detect jumping of a document, which occurs when, for example, a stapled document is stacked on the sheet stacker <NUM> and fed. This enables control of, for example, stopping feeding of the stapled document.

A pickup roller <NUM> (take-in means) as an example of a sheet pickup unit feeds a sheet on the sheet stacker <NUM> from the sheet stacker <NUM>. A pickup roller drive motor <NUM> rotates the pickup roller <NUM> in a direction (take-in direction) of taking in the sheet. The state shown in <FIG> is a state in which the sheet upper surface is located at the sheet take-in position, and the take-in of the sheet starts when the pickup roller <NUM> is rotated. In addition, the pickup roller <NUM> can be driven and moved by a driving unit (not shown) to the sheet take-in position shown in <FIG> and a retreat position (not shown) on the upper side of the sheet take-in position. The pickup roller <NUM> is moved to the sheet take-in position when taking a sheet in, and moved to the retreat position when the take-in is ended. In the example shown in <FIG>, the pickup roller <NUM> pivots about a rotation center <NUM> of the pickup roller, which is provided on the downstream side of the pickup roller <NUM> int the conveyance direction. Hence, when the pickup roller <NUM> comes into contact with the sheet, the sheet can readily be pushed in the conveyance direction.

A rotation instruction of the pickup roller <NUM> and a moving instruction to the sheet take-in position or the retreat position are issued by a control unit <NUM>. The control unit <NUM> includes a CPU, a ROM, a RAM, and the like (none are shown). The CPU executes programs stored in the ROM, thereby implementing various kinds of control. Additionally, the pickup roller <NUM> carries an auxiliary role to reliably perform separation/feeding by a separation roller pair <NUM> to be described later. When a sheet on the sheet stacker <NUM> is fed by the pickup roller <NUM> to the nip portion of the separation roller pair <NUM>, separation/feeding by the separation roller pair <NUM> can reliably be performed.

In the separation roller pair <NUM>, a feed roller <NUM> is driven by a feed motor <NUM> to rotate in a direction (feeding direction) of feeding the sheet to the downstream side in the conveyance direction. A separation roller <NUM> always receives a rotating force of rotating in a direction of pushing back the sheet to the upstream side in the conveyance direction from a separation motor <NUM> via a torque limiter (slip clutch) (not shown).

When one sheet exists between the feed roller <NUM> and the separation roller <NUM>, the rotating force in a direction of feeding the sheet to the downstream side by the frictional force between the separation roller <NUM> and the sheet fed to the downstream side by the feed roller <NUM> is larger than the upper limit value of the rotating force transmitted by the above-described torque limiter in the direction in which the separation roller <NUM> pushes back the sheet to the upstream side. For this reason, the separation roller <NUM> rotates following the feed roller <NUM> (rotates together).

On the other hand, if a plurality of sheets exist between the feed roller <NUM> and the separation roller <NUM>, the separation roller <NUM> receives, from the roller shaft, rotation in the direction of pushing back the sheets to the upstream side, thereby preventing sheets other than the sheet at the uppermost position from being conveyed to the downstream side.

In this way, by the function of the feed roller <NUM> to feed a sheet to the downstream side and the function of the separation roller <NUM> to prevent a sheet from being conveyed to the downstream side, even if sheets are fed in an overlapping state to the nip portion (the contact portion between the feed roller <NUM> and the separation roller <NUM>) formed between the feed roller <NUM> and the separation roller <NUM>, only the sheet at the uppermost position is fed to the downstream side, and the remaining sheets are not conveyed to the downstream side. Hence, the sheets in the overlapping state are separated and fed.

The feed roller <NUM> and the separation roller <NUM> form a pair of separation roller pairs <NUM> (sheet separation portion). Note that in this embodiment, the separation roller pair <NUM> is used. Instead of the separation roller pair <NUM>, a separation belt/roller pair formed by changing one of the separation roller and the feed roller to a belt may be used. Alternatively, the separation roller may be replaced with a separation pad, and the pad may be brought into contact with a sheet to prevent a plurality of sheets from being conveyed to the downstream side. Instead of rotating the separation roller <NUM>, it may be used in contact with the sheet, like a separation pad.

By the sheet pickup unit formed by the thus configured pickup roller <NUM>, feed roller <NUM>, separation roller <NUM>, and the like, the sheets stacked on the sheet stacker <NUM> are separated one by one and taken into the sheet conveyance apparatus <NUM>.

In addition, when a multiple feed detection sensor <NUM> is provided at a position where the separated sheet passes (that is, on the downstream side of the separation roller pair <NUM>), it can be detected whether the sheets are separated one by one by the sheet separation portion. In this embodiment, a detection device using ultrasonic wave transmitting and receiving portions is used as the multiple feed detection sensor <NUM>, and multiple feed can be detected based on the attenuation amount of an ultrasonic wave between the transmitting and receiving portions across the conveyance path. Note that the multiple feed detection sensor <NUM> can also be used as a sensor configured to detect a sheet that has reached a predetermined position (a position corresponding to between the ultrasonic wave transmitting and receiving portions) of the conveyance path.

A conveyance motor <NUM> drives other rollers (sheet conveyance unit) to convey the separated sheet to an image reading position where the image of the sheet is read by image reading sensors <NUM> and <NUM> and further convey the sheet to a discharge position. Also, the conveyance motor <NUM> drives the rollers to change the sheet conveyance speed in accordance with a speed optimum for sheet reading and settings such as the resolution of the sheet.

A nip gap adjusting motor <NUM> adjusts the gap between the feed roller <NUM> and the separation roller <NUM> or a contact force (nip pressure) of the feed roller <NUM> contacting the separation roller <NUM> via a sheet. This can adjust the gap adapted for the thickness of the sheet or the contact force and separate the sheet.

A registration clutch <NUM> transmits the rotation driving force of the conveyance motor <NUM> to a registration roller <NUM> (sheet conveyance unit) or blocks the transmission. By stopping the rotation of a first registration roller pair formed by the registration rollers <NUM> and <NUM>, the leading edge of the fed sheet is made to abut against the nip portion of the registration roller pair to correct skewing of the sheet.

A second registration roller pair formed by registration rollers <NUM> and <NUM>, a conveyance roller pair formed by conveyance rollers <NUM> and <NUM>, a conveyance roller pair formed by conveyance rollers <NUM> and <NUM>, and a discharge roller pair formed by discharge rollers <NUM> and <NUM> convey the sheet to a discharge stacking unit <NUM>. A discharge sensor <NUM> detects the passing of the conveyed sheet. After the discharge sensor <NUM> detects the trailing edge of the sheet, a discharge brake for reducing the rotation speed of the discharge roller pair (<NUM> and <NUM>) is applied, thereby preventing the discharged sheet from popping out and improving the discharge alignment property. Two guide plates including an upper guide plate <NUM> and a lower guide plate <NUM> guide the sheet conveyed by the separation roller pair, the registration roller pairs, the conveyance roller pairs, and the discharge roller pair.

Apre-registration sensor <NUM> (fourth sheet detection sensor) is arranged on the upstream side of the registration roller pair (<NUM> and <NUM>), and detects the fed sheet. A post-registration sensor <NUM> (first sheet detection sensor) is arranged on the downstream side of the registration roller pair (<NUM> and <NUM>), and detects the conveyed sheet. Furthermore, a middle-registration sensor <NUM> (third sheet detection sensor) is arranged on the downstream side of the registration roller pair (<NUM> and <NUM>) and on the upstream side of the registration roller pair (<NUM> and <NUM>), and detects the conveyed sheet.

When the post-registration sensor <NUM> detects the sheet, the control unit <NUM> issues an image reading instruction to the image reading sensors <NUM> and <NUM>, and the image of the conveyed sheet is read. Note that reference numerals 14a and 15a denote platen rollers. The image of the sheet read by the image reading sensors <NUM> and <NUM> is transmitted to an external apparatus such as an information processing apparatus via an interface unit (not shown).

An example of the control operation of the pickup roller <NUM> at the time of execution of a thin paper mode (predetermined specific mode), which is performed by the control unit <NUM> according to the first embodiment will be described next with reference to <FIG>.

<FIG> is a flowchart for explaining an example of the control operation in the thin paper mode (to be also referred to as a "thin paper conveyance mode" hereinafter), which is performed by the control unit <NUM> according to the first embodiment. That is, the processing shown in this flowchart is implemented when the CPU (not shown) of the control unit <NUM> executes a program stored in the ROM. Note that the thin paper mode can be set from an operation unit (not shown) or an information processing apparatus (personal computer or the like) communicably connected to the sheet conveyance apparatus <NUM>.

When a feeding operation in the thin paper mode is started, the control unit <NUM> drives the feed roller <NUM> and starts measuring time (measurement time (TIME) = <NUM>) (step S101).

Next, in step S102, the control unit <NUM> checks the pre-registration sensor <NUM> and determines whether the pre-registration sensor <NUM> detects a sheet leading edge.

Upon determining that the pre-registration sensor <NUM> does not detect a sheet leading edge (NO in step S102), the control unit <NUM> advances the process to step S103.

In step S103, the control unit <NUM> determines whether the measurement time (TIME) has exceeded a specific time (TS). Upon determining that the measurement time (TIME) has not exceeded the specific time (TS) (NO in step S103), the control unit <NUM> returns the process to step S102.

On the other hand, upon determining that the measurement time (TIME) has exceeded the specific time (TS) (YES in step S103), that is, if a sheet leading edge is not detected by the pre-registration sensor <NUM> even if the measurement time (TIME) has reached the specific time (TS), the control unit <NUM> advances the process to step S104.

In step S104, the control unit <NUM> moves the pickup roller <NUM> to the sheet take-in position and brings the pickup roller into contact with the sheet.

Further, in step S105, the control unit <NUM> rotates the pickup roller <NUM> after the elapse of a specific time (TD) to be described later. Hence, the pickup roller <NUM> feeds the sheet to the feed roller <NUM>.

Next, in step S106, the control unit <NUM> starts measuring time again (measurement time (TIME) = <NUM>).

In step S107, the control unit <NUM> checks the pre-registration sensor <NUM> and determines whether a sheet leading edge is detected by the pre-registration sensor <NUM>.

Upon determining that the pre-registration sensor <NUM> does not detect a sheet leading edge (NO in step S107), the control unit <NUM> advances the process to step S110.

In step S <NUM>, the control unit <NUM> determines whether the measurement time (TIME) has exceeded an error time (TOUT). Upon determining that the measurement time (TIME) has not exceeded the error time (TOUT) (NO in step S110), the control unit <NUM> returns the process to step S107.

On the other hand, upon determining that the measurement time (TIME) has exceeded the error time (TOUT) (YES in step S110), that is, if a sheet leading edge is not detected by the pre-registration sensor <NUM> even if the measurement time (TIME) has reached the error time (TOUT), the control unit <NUM> advances the process to step S111. That is, it is determined that although the pickup roller <NUM> is moved to the take-in position and rotated, a sheet leading edge is not detected even if reaching the error time, that is, a sheet feeding error has occurred (for example, jam has occurred).

The control unit <NUM> moves the pickup roller <NUM> to the retreat position (step <NUM>), stops the rotation of the pickup roller <NUM> (step <NUM>), and error-ends the processing of the flowchart.

On the other hand, upon determining in step S107 that the pre-registration sensor <NUM> detects a sheet leading edge (YES in step S107), the control unit <NUM> advances the process to step S108.

The control unit <NUM> moves the pickup roller <NUM> to the retreat position (step S108), stops the rotation of the pickup roller <NUM> (step S109), and advances to step S113.

In addition, upon determining in step S102 that the pre-registration sensor <NUM> detects a sheet leading edge (YES in step S102), the control unit <NUM> advances to step S113. In this case, the pickup roller <NUM> does not move to the contact position and remains at the retreat position. That is, in this situation, a sheet leading edge reaches the pre-registration sensor <NUM> even if the pickup roller <NUM> is not driven. This situation is a situation in which after a sheet has reached the feed roller <NUM> due to a friction or static electricity generated between the sheet and a precedingly fed sheet, the previously fed sheet passes through the feed roller <NUM>, is conveyed by the feed roller <NUM>, and reaches at least a point before the pre-registration sensor <NUM>. At this time, feed by the pickup roller <NUM> is unnecessary. To prevent damage caused by bringing the pickup roller <NUM> into contact with the sheet, the pickup roller <NUM> is kept at the retreat position.

Upon determining, in step S102 or S107, that the leading edge of a sheet is detected by the pre-registration sensor <NUM>, the control unit <NUM> advances the process to step S113. In step S113, the control unit <NUM> issues an image reading instruction to the image reading sensors <NUM> and <NUM> at a predetermined timing after the leading edge of the sheet is detected by the post-registration sensor <NUM>, and causes the image reading sensors <NUM> and <NUM> to perform a sheet reading operation. During this time, the control unit <NUM> monitors sheet trailing edge detection by the pre-registration sensor <NUM> (step S114). Upon determining that the pre-registration sensor <NUM> does not detect the sheet trailing edge (NO in step S114), the control unit <NUM> returns the process to step S113.

On the other hand, upon determining that the pre-registration sensor <NUM> detects the sheet trailing edge (YES in step S114), the control unit <NUM> advances the process to step S115. Note that the control unit <NUM> ends the reading operation in step S113 at a predetermined timing after the post-registration sensor <NUM> detects the leading edge of the sheet.

In step S115, the control unit <NUM> checks whether a sheet exists on the sheet stacker <NUM>. Upon determining that a sheet exists on the sheet stacker <NUM> (YES in step S115), that is, if a next sheet exists, the control unit <NUM> returns the process to step S101.

On the other hand, upon determining that no sheet exists on the sheet stacker <NUM> (NO in step S115), that is, if a next sheet does not exist, the control unit <NUM> ends the processing of the flowchart. Note that it is preferable that before the end, if a sheet is detected by the pre-registration sensor <NUM> after waiting for a time equal to or more than the specific time (TS), the process advances to step S113, and if no sheet is detected, the processing is ended.

<FIG> shows timing charts showing examples of the operations of the pre-registration sensor <NUM> and the pickup roller <NUM> according to the first embodiment.

<FIG> corresponds to an example in a case in which the pre-registration sensor <NUM> does not detect the leading edge of a sheet even if the measurement time (TIME) has exceeded the specific time (TS) (TIME > TS). In this case, the pickup roller <NUM> moves to the contact position, and after the specific time (TD), rotates to feed the sheet to the feed roller <NUM>. This prevents the occurrence of jam caused by the contact pressure of the pickup roller <NUM>.

<FIG> corresponds to an example in a case in which the pre-registration sensor <NUM> detects the leading edge of a sheet when the measurement time (TIME) is within the specific time (TS) (TIME < TS). In this case, the pickup roller <NUM> does not move to the contact position and remains at the retreat position. For this reason, jam caused by the contact pressure of the pickup roller <NUM> does not occur. Note that in <FIG>, the output of the pre-registration sensor <NUM> before counting of the measurement time (TIME) starts is OFF. This indicates that before counting of the measurement time (TIME) starts, the pre-registration sensor <NUM> itself is not driven, and the output is OFF. On the other hand, if the pre-registration sensor <NUM> is always driven, the next sheet may reach the pre-registration sensor <NUM> before counting of the measurement time (TIME) starts, and the output of the pre-registration sensor <NUM> is assumed to be ON. In this case, this may be confirmed before the start of counting of the measurement time (TIME), and it may be determined as YES in step S <NUM> of <FIG>. Note that the pre-registration sensor <NUM> detects a sheet by receiving, by a light receiving portion, irradiation light that is output from a light source arranged on one side (as an example, the lower guide plate <NUM>) of the conveyance path and returned to the one side again by a light guide member arranged on the facing other side (as an example, the upper guide plate <NUM>). Hence, if a sheet exists at the sensor position, the irradiation light is shielded. Hence, the light receiving level in the light receiving portion is L level. In this embodiment, the output becomes ON when the light receiving level is L level. On the other hand, if no sheet exists at the sensor position, the irradiation light returns without being shielded. Hence, the light receiving level in the light receiving portion is H level. In this embodiment, the output becomes OFF when the light receiving level is H level. This also applies to other sensors in this embodiment.

Note that in this embodiment, the specific time (TS) is set to, for example, <NUM> sec in consideration of shortening of the feed time in <FIG> and reliability of sheet detection in <FIG>. However, the specific time (TS) is not limited to <NUM> sec.

<FIG> is a graph showing a change in a contact pressure to a sheet after the pickup roller <NUM> is brought into contact with the sheet.

As shown in <FIG>, until a time TC elapses from the start of contact of the pickup roller <NUM> to the sheet, the contact pressure of the pickup roller <NUM> to the sheet changes. When the contact pressure is high, the frictional force between sheets also increases. Hence, if the rotation of the pickup roller <NUM> is started before the elapse of the time TC, a sheet is readily conveyed together, and feed jam readily occurs.

On the other hand, in this embodiment, as the specific time (TD) after the pickup roller is brought into contact with the sheet until the pickup roller is rotated, a time longer than the contact pressure change time (TC) shown in <FIG> is set, and rotation is started. The time is set to, for example, <NUM> sec. However, the specific time (TD) is not limited to <NUM> sec.

Note that in steps S108 and S109 or steps S111 and S112 in <FIG> and in <FIG>, control is done to move the pickup roller <NUM> to the retreat position and then stop rotation. However, the retreat operation and the rotation stop may be simultaneously performed. The order may be changed to stop rotation and then perform the retreat operation. However, during the time from the stop of rotation to the retreat, the frictional force between sheets is increased by the pressing pressure of the pickup roller <NUM>, and a sheet is readily conveyed together. Hence, the jam preventing effect becomes high when rotation is stopped after the retreat position, or the retreat and the rotation stop are simultaneously performed.

As described above, the first embodiment is characterized in that if the pre-registration sensor does not detect the leading edge of a next sheet after the elapse of the standby time (TS) after detecting the trailing edge of a previously separated and fed sheet, the pickup roller is moved to a position to contact a sheet stacked on the sheet stacker, after the elapse of TD, the pickup roller is rotated, and after the pre-registration sensor detects the leading edge of the sheet, the pickup roller is retreated to a position not to contact a sheet, and rotation is stopped. With this configuration, as a jam measure for a sheet such as thin paper, the timings of sheet contact and rotation start of the pickup roller are controlled, and a further jam measure is applied, thereby making jam less likely to occur in feeding even if the sheet to be fed is thin paper or the like with low stiffness.

Note that the movement and rotation of the pickup roller <NUM> may be controlled using the middle-registration sensor <NUM> in place of the pre-registration sensor <NUM>. That is, if the leading edge of the next sheet is not detected even after the elapse of the standby time (TS) after the middle-registration sensor <NUM> detects the trailing edge of the previously separated and fed sheet, the pickup roller <NUM> may be moved to the position to contact a sheet stacked on the sheet stacker, after the elapse of TD, the pickup roller <NUM> may be rotated, and after the middle-registration sensor <NUM> detects the leading edge of the sheet, the pickup roller <NUM> may be retreated to the position not to contact a sheet, and rotation may be stopped.

Note that the sheet conveyance apparatus <NUM> according to this embodiment has a normal paper mode (to be also referred to as a "normal conveyance mode" hereinafter) different from the above-described thin paper mode, and can selectively set these modes from an operation panel (not shown) or an information processing apparatus (for example, a personal computer) connected to the sheet conveyance apparatus <NUM>. When continuously feeding a plurality of sheet in a state in which the normal paper mode different from the thin paper mode is set, the control unit <NUM> controls to continuously feed the plurality of sheets by rotating and stopping the pickup roller <NUM> while keeping the pickup roller <NUM> in contact with the sheet stacked on the sheet stacker <NUM>.

If the conveyance of thin paper is started by the sheet feeder <NUM> described in this embodiment, a sheet may be caught by the feed roller <NUM> to cause jam of the sheet on the feed roller <NUM>. In particular, when the thin paper mode is applied, thin paper with low stiffness is readily caught by the feed roller <NUM>. Effective control for preventing this will be described below.

<FIG> shows schematic views showing an example of the positional relationship between the leading edge of a fed document and a feed roller pair according to the first embodiment.

<FIG> shows a state in which the document leading edge has reached a nip portion formed between the feed roller <NUM> and the separation roller <NUM>.

<FIG> shows a state in which the document leading edge has passed through the nip portion formed between the feed roller <NUM> and the separation roller <NUM>.

<FIG> is a flowchart for explaining an example of a feeding control operation in the thin paper mode, which is performed by the control unit <NUM> according to the first embodiment. This control aims at preventing the leading edge of a sheet from being caught by the feed roller <NUM> when thin paper with low stiffness has reached the feed roller <NUM>. The processing shown in this flowchart is implemented when the CPU (not shown) of the control unit <NUM> executes a program stored in the ROM. Note that the control shown in <FIG> and the control shown in <FIG> described above are performed in one feeding operation.

The control unit <NUM> drives the conveyance rollers when the feeding operation in the thin paper mode is started. The conveyance rollers are controlled to be continuously driven from then on.

Next, the control unit <NUM> starts measuring time (measurement time (TIME) = <NUM>) (step S201).

The control unit <NUM> drives the feed roller <NUM> at a first feeding speed V3 (low speed) at which the sheet is not caught by the feed roller <NUM> (step S202). The control unit <NUM> continuously drives the feed roller <NUM> at the first feeding speed V3 during the time after the leading edge of the sheet is fed from the sheet stacker <NUM> until a predetermined time T3 in which the leading edge passes through the nip portion formed between the feed roller <NUM> and the separation roller <NUM> elapses (TIME < T3).

The control unit <NUM> waits for the elapse of the predetermined time T3 (step S203).

Upon determining that the predetermined time T3 has elapsed (YES in step S203), the control unit <NUM> judges that the leading edge of the sheet has passed through the nip portion formed between the feed roller <NUM> and the separation roller <NUM>, and drives the feed roller <NUM> by switching the feeding speed to a second feeding speed V4 (high speed) (step S204). The second feeding speed V4 (high speed) is higher than the first feeding speed V3 (low speed). The second feeding speed V4 is, for example, a speed equal to the conveyance speed to drive the registration rollers <NUM>, <NUM>, <NUM>, and <NUM> or almost the same speed approximate to the conveyance speed.

After that, the control unit <NUM> monitors whether it is detected that the sheet leading edge has reached the middle-registration sensor <NUM> (step S205). Upon determining that it is not detected that the sheet leading edge has reached the middle-registration sensor <NUM> (NO in step S205), the control unit <NUM> continues monitoring in step S205. Upon determining that it is detected that the sheet leading edge has reached the middle-registration sensor <NUM> (YES in step S205), the control unit <NUM> advances the process to step S206.

The control unit <NUM> stops driving feed motor <NUM> (step S206), returns the count TIME for driving control of the feed roller <NUM> to "<NUM>", and stops measuring time (step S207).

Next, the control unit <NUM> monitors whether it is detected that the sheet leading edge has reached the post-registration sensor <NUM> (step S208). If the post-registration sensor <NUM> does not detect that the sheet leading edge has reached (NO in step S208), the control unit <NUM> continues monitoring in step S208.

If it is detected that the sheet leading edge has reached the post-registration sensor <NUM> (YES in step S208), the control unit <NUM> starts the image reading operation by the image reading sensors <NUM> and <NUM> at a predetermined timing (step S209).

After that, the control unit <NUM> monitors whether the sheet trailing edge has reached the post-registration sensor <NUM> (step S210). If the post-registration sensor <NUM> does not detect the reaching of the sheet trailing edge (NO in step S210), the control unit <NUM> continues the image reading operation in step S209.

If the post-registration sensor <NUM> detects the reaching of the sheet trailing edge (YES in step S210), the control unit <NUM> advances the process to step S211.

In step S211, the control unit <NUM> checks whether a sheet exists on the sheet stacker <NUM>. Upon determining that a sheet exists on the sheet stacker <NUM> (YES in step S211), that is, if the next sheet exists, the control unit <NUM> returns the process to step S201.

On the other hand, upon determining that no sheet exists on the sheet stacker <NUM> (NO in step S211), that is, if the next sheet does not exist, the control unit <NUM> ends the processing of the flowchart.

As described above, when resuming driving of the feed roller <NUM> after the reaching of the trailing edge of the sheet is detected by the post-registration sensor <NUM>, the feed roller <NUM> is controlled to the first feeding speed. Furthermore, upon determining that the leading edge of the sheet has passed through the nip between the feed roller <NUM> and the separation roller <NUM>, the feed roller <NUM> is controlled to the second feeding speed higher than the first feeding speed. With this control, even if the sheet to be fed is thin paper or the like with low stiffness, jam in which, for example, a sheet is caught by the feed roller in feeding can be made less likely to occur.

Note that in step S210, instead of detecting the reaching of the sheet trailing edge by the post-registration sensor <NUM>, when the middle-registration sensor <NUM> or the pre-registration sensor <NUM> detects the reaching of the sheet trailing edge, the process may advance to step S211. In these cases, the sheet interval can be made small as compared to a case in which the reaching of the sheet trailing edge is detected by the post-registration sensor <NUM>.

Additionally, in this embodiment, a configuration in which the middle-registration sensor <NUM> and the post-registration sensor <NUM> are provided, and the above-described control is performed using these has been described. However, the above-described control may be performed by one sensor. For example, the middle-registration sensor <NUM> may be omitted, and the above-described control may be done using the post-registration sensor <NUM>. In this case, in step S205, if the post-registration sensor <NUM> detects the sheet leading edge, the process advances to step S206, and the process of step S208 is omitted.

A method of deciding the time (T3) to drive the feed motor <NUM> such that the feed roller <NUM> is driven at the first feeding speed V3 (low speed) will be described below with reference to <FIG>.

<FIG> is a view for explaining the relationship between sheets (documents) on the sheet stacker <NUM>, the feed roller <NUM>, the positions of the leading edge portions of the documents, and the feeding speed of the pickup roller <NUM>.

When a document is fed at a feeding speed V5 by the pickup roller <NUM>, the maximum time of the predetermined time T3 corresponding to a time necessary for the leading edge portion (a portion of a length X from the leading edge of a document) of a document to pass through the nip portion formed between the feed roller <NUM> and the separation roller <NUM> is calculated as follows. Letting D be the distance from the leading edges of the documents stacked on the sheet stacker <NUM> to the feed roller <NUM>, as shown in <FIG>, the predetermined time T3 can be calculated by "T3 = (D + X)/V5". The length X of the leading edge portion of the document may be, for example, about <NUM>/<NUM> of the peripheral diameter of the feed roller <NUM>. Note that the position of the nip portion between the feed roller <NUM> and the separation roller <NUM> is set here as the center position of the shaft of the feed roller <NUM>.

In the above description, a configuration in which the driving speed of the feed roller <NUM> is changed from V3 to V4 at a timing at which it is detected that T3 has elapsed from detection of the trailing edge of a preceding sheet by the post-registration sensor <NUM> has been described. However, as another example of the elapse of the predetermined time T3, if driving pulses of the feed motor <NUM> to perform sheet conveyance by the feed roller <NUM> only in "D + X" shown in <FIG> are counted, it may be determined that the predetermined timing has elapsed, and the driving speed of the feed roller <NUM> may be changed from V3 to V4.

Note that the first feeding speed V3 (low speed) is, for example, a set speed at which the peripheral speed of the feed roller <NUM> becomes almost the second feeding speed V4 (high speed) even if an overshoot occurs at the rising of the feed motor <NUM> that rotationally drives the feed roller <NUM>. Note that the set speed is obtained in advance by experiments and the like.

In addition, the first feeding speed V3 and the feeding speed V5 by the pickup roller <NUM> may be set equal.

Note that in a state in which the normal paper mode is set, the control unit <NUM> controls the feed roller <NUM> to the second feeding speed V4 (high speed) at the start of driving of the feed roller <NUM>.

Note that in some cases, a plurality of stacked documents may simultaneously be fed due to friction between the documents and passed through the pickup roller <NUM>, resulting in a so-called "fed-together" state in which a document scheduled to be fed next already exists at a position close to the nip portion between the feed roller <NUM> and the separation roller <NUM>. In this case, if the speed change is executed with the predetermined time T3, as described above, the leading edge portion of the document immediately passes through the nip portion between the feed roller <NUM> and the separation roller <NUM>. That is, in this case, even if the leading edge portion of the document passes through the nip portion, and the speed can be switched to the speed V4, feeding may be continued at the speed V3 until the predetermined time T3 elapses, and throughput may lower.

Another aspect of this embodiment considering this point will be described below.

<FIG> shows views showing a configuration in which a thin paper conveyance registration sensor <NUM> (second sheet detection sensor) that is an optical sensor for the thin paper mode is arranged at a position parallel to the feed roller <NUM> in the conveyance direction of the document.

<FIG> shows a state in which the document leading edge has reached the nip portion formed between the feed roller <NUM> and the separation roller <NUM>.

<FIG> shows a state in which the document leading edge has passed through the nip portion formed between the feed roller <NUM> and the separation roller <NUM> and reached the thin paper conveyance registration sensor <NUM>.

A feeding control operation according to this aspect is shown in <FIG>.

<FIG> is a flowchart for explaining an example of a feeding control operation in the thin paper mode, which is performed by the control unit <NUM> in the other aspect of the first embodiment. The processing shown in this flowchart is implemented when the CPU (not shown) of the control unit <NUM> executes a program stored in the ROM. Note that the same step numbers as in <FIG> denote the same steps. Note that the control shown in <FIG> and the control shown in <FIG> described above are performed in one feeding operation.

In this aspect, the timing at which the document passes through the feed roller <NUM> can correctly be detected by the thin paper conveyance registration sensor <NUM>. In <FIG>, the control unit <NUM> drives the feed roller <NUM> at the first feeding speed V3 (low speed) (step S202), and then advances the process to step S212.

In step S212, the control unit <NUM> monitors whether the thin paper conveyance registration sensor <NUM> detects the leading edge of the document. Upon determining that the thin paper conveyance registration sensor <NUM> has not detected the leading edge of the document yet (NO in step S212), the control unit <NUM> continues monitoring in step S212.

On the other hand, upon determining that the thin paper conveyance registration sensor <NUM> has detected the leading edge of the document (YES in step S212), the control unit <NUM> advances the process to step S204. Processing from step S204 is the same as in <FIG>, and a description thereof will be omitted.

Based on the detection of the leading edge of the document by the thin paper conveyance registration sensor <NUM>, the control unit <NUM> changes the driving speed of the feed roller <NUM> from the first feeding speed V3 to the second feeding speed V4. With this configuration, speed control for thin paper conveyance can more effectively be executed. Note that preferably, to detect, by the optical sensor, that the leading edge portion of the document has passed through the normal paper mode formed by the feed roller <NUM> and the separation roller <NUM>, the detection position of the optical sensor is preferably located on the downstream side of the position of the nip portion formed by the feed roller <NUM> and the separation roller <NUM>.

In addition, the thin paper conveyance registration sensor <NUM> may be a detection sensor other than an optical sensor. For example, even if a tracking sensor (movement detection sensor) capable of detecting the moving amount of a document is arranged in the feeding unit to detect the leading edge of the document, the same effect as described above can be obtained.

Note that in step S212, the driving speed of the feed roller <NUM> may be changed from V3 to V4 in accordance with not the detection of the document leading edge by the thin paper conveyance registration sensor <NUM> but the detection of the document leading edge by the pre-registration sensor <NUM>.

Alternatively, the driving speed of the feed roller <NUM> may be changed from V3 to V4 in accordance with not the detection of the document leading edge by the thin paper conveyance registration sensor <NUM> but the detection of the document by the multiple feed detection sensor <NUM>.

In an apparatus including skew sensors (for example, formed by a plurality of optical sensors arranged in two lines in the document conveyance direction) on both sides of the conveyance path on the downstream side of the separation roller pair <NUM>, the feeding speed may be switched when a document is detected by the skew sensors.

That is, the feeding speed may be switched when a document is detected by one of the sensors provided on the downstream side of the separation roller pair <NUM>. As for the type of sensors, sensors of any detection type can be used.

The aspect shown in <FIG> and the other aspect shown in <FIG> and <FIG> may be combined. For example, the control unit <NUM> may change the driving speed of the feed roller <NUM> from the V3 to V4 at an earlier timing of the timing from the detection of the trailing edge of the preceding sheet by the post-registration sensor <NUM> to the elapse of T3 and the timing of the detection of the subsequent sheet by the thin paper conveyance registration sensor <NUM>.

The second embodiment of the present invention will be described next. In the second embodiment, an embodiment in which driving of a feed roller <NUM> (separation roller <NUM>) is turned on/off will be described. Note that driving of a registration roller pair (<NUM> and <NUM>) may be turned on/off at the timing of turning on/off driving of the feed roller <NUM> (separation roller <NUM>). Even concerning a case in which driving of the feed roller <NUM> and the separation roller <NUM> is turned on/off, this will be referred to as "driving of the feed roller <NUM> is turned on/off" hereinafter.

<FIG> is a partial sectional view schematically showing a part of the configuration of a sheet conveyance apparatus (image reading apparatus) to which a sheet feeder according to the second embodiment of the present invention can be applied. Note that the same reference numerals as in <FIG> and the like denote the same components.

Referring to <FIG>, a registration roller pair (<NUM> and <NUM>) is disposed on the downstream side of a registration roller pair (<NUM> and <NUM>). A middle-registration sensor <NUM> (third sheet detection sensor) is disposed on the downstream side of the registration roller pair (<NUM> and <NUM>) and on the upstream side of the registration roller pair (<NUM> and <NUM>), and detects a conveyed sheet. A post-registration sensor <NUM> is disposed on the downstream side of the conveyance path (<NUM> and <NUM>) and on the upstream side of image reading sensors <NUM> and <NUM>, and detects a conveyed sheet.

<FIG> is a timing chart showing an example of the relationship between the operations of a pickup roller, a feed roller (and the registration roller pairs) and the detection states of a pre-registration sensor and the middle-registration sensor according to the second embodiment.

<FIG> are schematic views showing an example of the relationship between the operations of the pickup roller, the feed roller, and the registration roller pairs and the detection states of the pre-registration sensor and the middle-registration sensor according to the second embodiment. Note that the same reference numerals as in (<NUM>) to (<NUM>) of <FIG> denote the same states. A series of procedures will be described below.

First, the feed roller <NUM> and the registration rollers (<NUM>, <NUM>, <NUM>, and <NUM>) are driven ((<NUM>) of <FIG>), and a pickup roller <NUM> is moved to the contact position ((<NUM>) of <FIG>) and rotated after the elapse of a specific time (TD) ((<NUM>) of <FIG>), thereby feeding a sheet to the feed roller <NUM>. When the sheet leading edge reaches a pre-registration sensor <NUM> ((<NUM>) of <FIG>), the pickup roller <NUM> is moved to the retreat position ((<NUM>) of <FIG>), and the rotation is stopped ((<NUM>)' of <FIG>). When the sheet leading edge reaches the middle-registration sensor <NUM> ((<NUM>) of <FIG>), the feed roller <NUM> is stopped ((<NUM>) of <FIG>). The sheet trailing edge passes through the pre-registration sensor <NUM> ((<NUM>) of <FIG>) (the time is defined as "t0"), and after the elapse of t1 ((<NUM>) of <FIG>), the feed roller <NUM> is rotated. After that, the sheet trailing edge passes through the middle-registration sensor <NUM> ((<NUM>)' of <FIG>). In addition, after the elapse of time t0 to t2 (preferably, t2 > t1 + L/V1) ((<NUM>) of <FIG>), the pickup roller <NUM> is moved to the contact position ((<NUM>) of <FIG>) and rotated after the elapse of the specific time (TD) ((<NUM>) of <FIG>), thereby feeding the next sheet to the feed roller <NUM>. Note that as shown in <FIG> to be described later, letting V1 be the sheet conveyance speed by the feed roller <NUM>, and L be the distance from the feed roller <NUM> to the pre-registration sensor <NUM>, the above-described time t2 is preferably "t2 > t1 + L/V1".

Note that if the pre-registration sensor <NUM> detects the leading edge of the next sheet during the time (from (<NUM>) to (<NUM>)) until t2 elapses after the elapse of t1 described above, the process waits until the sheet leading edge reaches the middle-registration sensor <NUM> as shown in ((<NUM>) of <FIG>) without moving the pickup roller <NUM> to the contact position. This example will be described below in detail with reference to <FIG>.

<FIG> are schematic views showing an example of the relationship between the operations of the pickup roller, the feed roller, and the registration roller pairs and the detection states of the pre-registration sensor and the middle-registration sensor according to the second embodiment. These drawings correspond to a case in which the leading edge of the next sheet is detected by the pre-registration sensor <NUM> before the elapse of t2.

As in the example shown in <FIG> described above, as shown in <FIG>, first, the feed roller <NUM> and the registration rollers (<NUM>, <NUM>, <NUM>, and <NUM>) are driven ((<NUM>) of <FIG>), and the pickup roller <NUM> is moved to the contact position ((<NUM>) of <FIG>) and rotated after the elapse of the specific time (TD) ((<NUM>) of <FIG>), thereby feeding the first sheet to the feed roller <NUM>. When the leading edge of the first sheet reaches the pre-registration sensor <NUM> ((<NUM>) of <FIG>), the pickup roller <NUM> is moved to the retreat position ((<NUM>) of <FIG>), and the rotation is stopped ((<NUM>)' of <FIG>). Note that this example corresponds to a case in which at the point of time of (<NUM>), the second sheet is fed together with the first sheet due to a friction or static electricity between the sheets, and reaches the nip portion of the feed roller <NUM>, as shown in <FIG>. However, the first sheet and the second sheet are separated by the separation roller <NUM> so multiple feed does not occur. After that, when the leading edge of the first sheet reaches the middle-registration sensor <NUM> ((<NUM>) of <FIG>), the feed roller <NUM> is stopped ((<NUM>) of <FIG>). Furthermore, the trailing edge of the first sheet passes through the pre-registration sensor <NUM> ((<NUM>) of <FIG>) (the time is defined as "t0"), and after the elapse of t1 ((<NUM>) of <FIG>), the feed roller <NUM> is rotated. Feeding of the second sheet is thus started by the feed roller <NUM>. After that, the trailing edge of the first sheet passes through the middle-registration sensor <NUM> ((<NUM>)' of <FIG>). Also, in this example, the leading edge of the second sheet is detected by the pre-registration sensor <NUM> before the elapse of time t0 to t2 ((<NUM>)" of <FIG>). In this case, operation control is performed such that the process waits until the leading edge of the second sheet reaches the middle-registration sensor <NUM> in ((<NUM>) of <FIG>) without moving the pickup roller <NUM> to the contact position.

As shown in <FIG>, <FIG>, and <FIG>, when the feed roller <NUM> is stopped until the predetermined time (t1) elapses after the sheet passes through the middle-registration sensor <NUM> and the sheet trailing edge passes through the pre-registration sensor <NUM>, the conveyance interval between the previously fed sheet and the sheet to be fed next can be ensured. Hence, even if the discharge speed of the previously fed sheet becomes low, a sheet interval to prevent the sheet from being hit by the sheet to be fed next can be ensured. In this case, this example is merely an example and, for example, as the timing of stopping the feed roller <NUM>, the feed roller <NUM> may be stopped after waiting for a predetermined timing from the time at which the sheet leading edge reaches d the middle-registration sensor <NUM>. That is, the feed roller <NUM> is stopped at a timing capable of obtaining a desired sheet interval.

Note that in a configuration in which the feed roller <NUM> is not stopped, the time t2 after the sheet trailing edge passes through the pre-registration sensor <NUM> until the movement of the pickup roller <NUM> to the contact position starts can be set to t2', for example, "t2' > (L - V1 × (L/V2))/V1". That is, the time can be made slightly shorter than "t2 > t1 + L/V1" in the above-described case in which the feed roller <NUM> is stopped.

<FIG> is a view for explaining the relationship between the positions of the feed roller <NUM>, the pre-registration sensor <NUM>, and the registration rollers <NUM> and <NUM>, the feeding speed of the feed roller <NUM>, and the conveyance speed of the registration rollers.

If the feed roller <NUM> is always rotating, the minimum condition of the wait time until the pickup roller <NUM> is lowered to the subsequent sheet is as follows.

If the second sheet reaches the feed roller <NUM> together with the feeding of the first sheet, the second sheet exists at a position ahead of the position of the feed roller <NUM> by "V1 × (L/V2)" at the point of time when the first sheet passes through the pre-registration sensor <NUM>. Hence, if the process waits for only the time "(L - V1 × (L/V2))/V1" in which the second sheet is fed from that position to the position of the pre-registration sensor <NUM> at the feeding speed V1, the above-described second sheet should reach the pre-registration sensor <NUM>. Hence, the time "(L - V1 × (L/V2))/V1" can be set as the minimum condition of the wait time until the pickup roller <NUM> is lowered to the subsequent sheet.

In the present invention, as indicated by step S206 in <FIG>, control is performed to stop the feed motor <NUM> when the leading edge of the sheet reaches the middle-registration sensor <NUM>.

Note that concerning the sheet feeder <NUM> shown in <FIG> and <FIG>, a configuration in which the pickup roller arranged above the sheet stacker comes, from the upper side, into contact with a sheet stacked on the sheet stacker capable of moving up and down, and supplies sheets sequentially from the upper side of the sheet bundle to the feed roller has been described. However, the present invention can also be applied even to a sheet feeder having a configuration in which, for example, a pickup roller arranged below a sheet stacker comes, from the lower side, into contact with a sheet stacked on the sheet stacker with a tilt, and supplies sheets sequentially from the lower side of the sheet bundle to a feed roller.

Claim 1:
A sheet feeder (<NUM>) comprising:
a feed roller (<NUM>) configured to feed a sheet along a conveyance path;
a separation roller (<NUM>) configured to form a nip with the feed roller (<NUM>) and separate the sheet fed by the feed roller (<NUM>) from other sheets;
a first sheet detection sensor (<NUM>) arranged on a downstream side of the conveyance path with respect to the feed roller (<NUM>) in the conveyance path, and configured to detect that the sheet has reached; and
a control unit (<NUM>) configured to control rotation of the feed roller (<NUM>),
wherein in a case where starting feeding of a subsequent sheet by the feed roller (<NUM>) after reaching of a trailing edge of a preceding sheet is detected by the first sheet detection sensor (<NUM>), the control unit (<NUM>) controls the feed roller (<NUM>) to rotate at a first feeding speed (V3), and upon determining that a leading edge of the subsequent sheet has passed through the nip, the control unit (<NUM>) further controls the feed roller (<NUM>) to rotate at a second feeding speed (V4) higher than the first feeding speed (V3),
characterized by
a first conveyance roller (<NUM>) located on the downstream side of the feed roller (<NUM>) in the conveyance path and on the upstream side of the first sheet detection sensor (<NUM>) in the conveyance path, and configured to convey the sheet;
a second conveyance roller (<NUM>) located on the downstream side of the first conveyance roller (<NUM>) in the conveyance path and on the upstream side of the first sheet detection sensor (<NUM>) in the conveyance path, and configured to convey the sheet; and
a third sheet detection sensor (<NUM>) located on the downstream side of the first conveyance roller (<NUM>) in the conveyance path and on the upstream side of the second conveyance roller (<NUM>) in the conveyance path, and configured to detect that the sheet has reached,
wherein in a case where reaching of a sheet leading edge is detected by the third sheet detection sensor (<NUM>), the control unit (<NUM>) stops the rotation of the feed roller (<NUM>).