Sheet alignment device

A sheet alignment device includes a first alignment arm, a second alignment arm, a first sensor and a controller. The first alignment arm includes a first blocking piece and a second blocking piece. During the sheet-aligning action of each sheet, the first alignment arm is moved for a preset distance from a standby position. Then, the first alignment arm is moved back to the standby position, and a waiting time is required to introduce a next sheet into the sheet placement tray. When the first sensor is no longer interrupted by the second blocking piece of the first alignment arm, the controller starts to calculate the moving distance of the first alignment arm. Since the moving distance of the first alignment arm is calculated at the same start point during the sheet-aligning action of each sheet is performed, the possibility of resulting in the moving distance error is minimized.

FIELD OF THE INVENTION

The present invention relates to a sheet alignment device, and more particularly to a sheet alignment device for use in an office machine.

BACKGROUND OF THE INVENTION

An office machine such as a printer or a scanner is widely used in the office. For achieving diversified functions and integrating more functions, the office machine is usually equipped with a post-processing device (e.g. a stapler). By the stapler, a plurality of documents outputted from the printer or the scanner can be automatically stapled in order to enhance the working efficiency. The operations of the post-processing device (e.g. a stapler) will be illustrated as follows. Firstly, the documents are placed on a sheet placement tray. Then, the edges of these documents are aligned with each other by a sheet alignment device. Then, a stapling operation is performed by the stapler, so that the same parts of these documents are combined together.

Please refer toFIGS. 1A and 1B.FIG. 1Ais a schematic planar view illustrating a conventional sheet alignment device.FIG. 1Bis a schematic cross-sectional view illustrating the conventional sheet alignment device. The conventional sheet alignment device as shown inFIGS. 1A and 1Bis disclosed in for example U.S. Pat. No. 7,134,659.

The sheet alignment device1comprises a first alignment arm11, a second alignment arm12, a sensor13and a sheet placement tray14. The first alignment arm11comprises a first platform11a, a first sidewall11band a protrusion structure11c. The second alignment arm12comprises a second platform12aand a second sidewall12b.

The first sidewall11bof the first alignment arm11is extended from an end of the first platform11aand perpendicular to the first platform11a. The protrusion structure11cis extended from the first sidewall11b. The second sidewall12bof the second alignment arm12is extended from an end of the second platform12aand perpendicular to the second platform12a. The sensor13is arranged beside the protrusion structure11c. The sheet placement tray14is disposed under the first alignment arm11and the second alignment arm12. Moreover, the first platform11aof the first alignment arm11and the second platform12aof the second alignment arm12are coplanar.

Hereinafter, the operations of the conventional sheet alignment device1will be illustrated with reference toFIGS. 1A and 1B. In a case that no sheet is introduced to the sheet alignment device1, the first alignment arm11and the second alignment arm12are respectively located at a first home positional and a second home position a2. Meanwhile, the sensor13is interrupted by the protrusion structure11cof the first alignment arm11, and thus a first sensing signal is issued by the sensor13.

After the sheet is introduced into the sheet alignment device1, the power device (not shown) is controlled by a controller (not shown) to drive both of the first alignment arm11and the second alignment arm12to be inwardly moved by a preset distance d1. Consequently, the first alignment arm11and the second alignment arm12are moved to a first standby position b1and a second standby position b2so as to carry the sheet S. Meanwhile, the protrusion structure11cof the first alignment arm11is distant from the sensor13, and thus a second sensing signal is issued by the sensor13.

When the sheet-aligning action starts, according to the size of the sheet S and under control of the controller (not shown), the first alignment arm11is moved toward the second alignment arm12by an alignment distance d2to an alignment position c. Meanwhile, the edge of the sheet S is nestled against the second sidewall12b.

If another sheet is ready to be introduced into the sheet alignment device1, the power device (not shown) is controlled by the controller (not shown) to drive the first alignment arm11to be distant from the second alignment arm12by the alignment distance d2. Consequently, the first alignment arm11is returned to the first standby position b1. Similarly, the first alignment arm11is moved between the first standby position b1and the alignment position c in a reciprocating manner until the rest of the sheets implement the sheet-aligning actions.

After the sheet-aligning actions of all sheets have been implemented, a stapling operation is performed by a post-processing device (e.g. a stapler), so that the same parts of these sheets are combined together. Then, the power device (not shown) is controlled by the controller (not shown) to drive both of the first alignment arm11and the second alignment arm12to be outwardly moved until the sensor13is interrupted by the protrusion structure11cof the first alignment arm11again and the first sensing signal is issued by the sensor13. That is, the first alignment arm11and the second alignment arm12are respectively returned to the first home position a1and the second home position a2. Afterwards, the stapled sheets are introduced to the sheet placement tray14and ejected to the outer portion of the office machine.

From the above discussions, a plurality of sheets are aligned with each other by moving the first alignment arm11and the second alignment arm12of the conventional sheet alignment device1. In addition, the use of the sensor13can detect the positions of the first alignment arm11and the second alignment arm12.

The conventional sheet alignment device, however, still has some drawbacks. For example, during the process of performing the sheet-aligning actions of the sheets, the power device (not shown) drives the first alignment arm11to be moved between the first standby position b1and the alignment position c in a reciprocating manner. In addition, the sensor13is only able to detect whether the first alignment arm11and the second alignment arm12are respectively located at the first home position a1and the second home position a2. On the other hand, the sensor13fails to judge whether the first alignment arm11is really moved to the first standby position b1. If the first alignment arm11is moved by a distance shorter than the alignment distance d2after the sheet-aligning action of the first sheet is completed, the first alignment arm11fails to be moved to the actual first standby position b1. Under this circumstance, the real position of the first alignment arm11is separated from the first standby position b1by an error distance. After the sheet-aligning action of the second sheet is completed, the edges of the second sheet and the first sheet are separated from each other by the error distance. In other words, the second sheet fails to be precisely aligned with the first sheet. If the error distance is generated again during the subsequent sheet-aligning actions are performed, the total error distances will be largely increased. After the sheet-aligning actions of all sheets have been implemented and the sheets are combined together, the stapled parts of these sheets are not at the same position.

Therefore, there is a need of providing an improved sheet alignment device so as to obviate the drawbacks encountered from the prior art.

SUMMARY OF THE INVENTION

The present invention relates to a sheet alignment device with reduced moving distance error, and thus the sheet-aligning precision is enhanced.

In accordance with an aspect of the present invention, there is provided a sheet alignment device for aligning a plurality of sheets on a sheet placement tray with each other. The sheet alignment device includes a first alignment arm, a second alignment arm, a power device, a transmission device, a first sensor and a second sensor. The first alignment arm is used for carrying first ends of the sheets. The first alignment arm includes a first platform, a first sidewall, a first blocking piece and a second blocking piece. The first platform is parallel with the sheet placement tray. The first sidewall is perpendicular to the first platform. The first blocking piece and the second blocking piece are disposed over the first platform. The second alignment arm is used for carrying second ends of the sheets. The second alignment arm includes a second platform, a second sidewall and a third blocking piece. The second platform is parallel with the sheet placement tray. The second sidewall is perpendicular to the second platform, and the third blocking piece is disposed over the second platform. The transmission device is connected with the power device, the first alignment arm and the second alignment arm. Through the transmission device, the first alignment arm is driven by the power device to be moved to a first home position, a first standby position and an alignment position, and the second alignment arm is driven by the power device to be moved to a second home position and a second standby position. The first sensor is disposed over the first alignment arm for detecting a position of the first alignment arm. The second sensor is disposed over the second alignment arm for detecting a position of the second alignment arm.

In an embodiment, the power device includes a first driving element and a second driving element. The transmission device comprises a first transmission element and a second transmission element. The first transmission element is connected with the first driving element and the first alignment arm. The second transmission element is connected with the second driving element and the second alignment arm.

In an embodiment, the first alignment arm further includes a third platform, and the second alignment arm further includes a fourth platform. The third platform is extended from the first sidewall and parallel with the first platform. The fourth platform is extended from the second sidewall and parallel with the second platform.

In an embodiment, the sheet alignment device includes a first roller, a second roller and a first elastic element. The first roller is disposed on the first driving element. The second roller is disposed on the third platform of the first alignment arm. The outer peripheries of the first roller and the second roller are enclosed by the first transmission element. The first elastic element is disposed on the first transmission element for maintaining a tension force of the first transmission element

In an embodiment, the sheet alignment device further includes a third roller, a fourth roller and a second elastic element. The third roller is disposed on the second driving element. The fourth roller is disposed on the fourth platform of the second alignment arm. The outer peripheries of the third roller and the fourth roller are enclosed by the second transmission element. The second elastic element is disposed on the second transmission element for maintaining a tension force of the second transmission element.

In an embodiment, the first blocking piece and the second blocking piece are disposed on the third platform. The third blocking piece is disposed on the fourth platform.

In an embodiment, the sheet alignment device further includes a supporting shaft. Both ends of the supporting shafts are disposed on the third platform and the fourth platform to be connected with the first alignment arm and the second alignment arm, respectively. The first alignment arm and the second alignment arm are movable toward each other or distant from each other along the supporting shaft.

In an embodiment, the first alignment arm further includes a first fixing part, and the second alignment arm further includes a second fixing part. The first fixing part is disposed on the third platform for fixing the first alignment arm on the first transmission element. The second fixing part is disposed on the fourth platform for fixing the second alignment arm on the second transmission element.

In an embodiment, the sheet alignment device further includes a controller for controlling movement of the first alignment arm and the second alignment arm. If no sheet is placed on the sheet placement tray, the first alignment arm and the second alignment arm are controlled by the controller to be moved to the first home position and the second home position. If the first sensor and the second sensor are respectively interrupted by the first blocking piece and the third blocking piece, the controller stops moving the first alignment arm and the second alignment arm.

In an embodiment, when a first sheet is introduced into the sheet placement tray, the first alignment arm and the second alignment arm are controlled by the controller to be moved to the first standby position and the second standby position, respectively. Whereas, when the first sensor is interrupted by the second blocking piece, the controller stops moving the first alignment arm and the second alignment arm.

In an embodiment, when a sheet-aligning action of the first sheet starts, the first alignment arm is controlled by the controller to be moved to the alignment position according to a size of the first sheet. After the sheet-aligning action of the first sheet is completed, if there is any sheet to be aligned, the first alignment arm is moved to the first standby position. When the first sensor is interrupted by the second blocking piece, the controller stops moving the first alignment arm.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention provides a sheet alignment device. The sheet alignment device may be applied to an office machine.

FIG. 2is a schematic exploded view illustrating a sheet alignment device according to an embodiment of the present invention. As shown inFIG. 2, the sheet alignment device2comprises a first alignment arm21, a second alignment arm22, a first sensor23, a second sensor24, two supporting shafts25, a power device26, a transmission device27, a first roller28, a second roller29, a third roller30, a fourth roller31, a first elastic element32, a second elastic element33and a controller34(seeFIG. 5).

The first alignment arm21comprises a first platform21a, a first sidewall21b, a third platform21c, a first blocking piece21d, a second blocking piece21eand a first fixing part21f. The second alignment arm22comprises a second platform22a, a second sidewall22b, a fourth platform22c, a third blocking piece22dand a second fixing part22e. The power device26comprises a first driving element26aand a second driving element26b. The transmission device27comprises a first transmission element27aand a second transmission element27b.

Hereinafter, a process of assembling the sheet alignment device will be illustrated with reference toFIGS. 2 and 3.FIG. 3is a schematic assembled view illustrating the sheet alignment device according to the embodiment of the present invention. The first sidewall21bof the first alignment arm21is extended from an end of the first platform21aand perpendicular to the first alignment arm21. The third platform21cis extended from a top edge of the first sidewall21band parallel with the first platform21a. The first blocking piece21d, the second blocking piece21eand the first fixing part21fare disposed on the third platform21c. The second sidewall22bof the second alignment arm22is extended from the second platform22aand perpendicular to the second platform22a. The fourth platform22cis extended from the second sidewall22band parallel with the second platform22a. The third blocking piece22dand the second fixing part22eare disposed on the fourth platform22c. The first sensor23is disposed over the third platform21cof the first alignment arm21. The second sensor24is disposed over the fourth platform22cof the second alignment arm22. The two supporting shafts25are parallel with each other. The both ends of each supporting shaft25are respectively penetrated through the top surfaces of the third platform21cand the fourth platform22c, so that the both ends of each supporting shaft25are connected with the first alignment arm21and the second alignment arm22. Moreover, as the first alignment arm21and the second alignment arm22are horizontally moved along the two supporting shafts25, the first alignment arm21and the second alignment arm22are moved toward each other or distant from each other. The first driving element26aand the second driving element26bof the power device26are arranged between the first alignment arm21and the second alignment arm22. The first roller28is disposed under the first driving element26a. The second roller29is disposed on the third platform21cof the first alignment arm21. The outer peripheries of the first roller28and the second roller29are enclosed by the first transmission element27aof the transmission device27. In addition, the first transmission element27ais fixed on the first fixing part21fof the first alignment arm21for connecting the first driving element26awith the first alignment arm21. The first elastic element32is disposed on the first transmission element27afor maintaining the tension force of the first transmission element27a. The third roller30is disposed under the second driving element26b. The fourth roller31is disposed on the fourth platform22cof the second alignment arm22. The third roller30and the fourth roller31are enclosed by the second transmission element27bof the transmission device27. In addition, the second transmission element27bis fixed on the second fixing part22eof the second alignment arm22for connecting the second driving element26bwith the second alignment arm22. The second elastic element33is disposed on the second transmission element27bfor maintaining the tension force of the second transmission element27b.

Hereinafter, the operating principle of the present invention will be illustrated with reference toFIG. 4.FIG. 4is a schematic perspective view illustrating the sheet alignment device applied to an office machine according to an embodiment of the present invention. As shown inFIG. 4, the first alignment arm21and the second alignment arm22of the sheet alignment device2are respectively located at bilateral sides of the rear end of the sheet placement tray4. In addition, the first alignment arm21and the second alignment arm22are parallel with the sheet placement tray4. Please refer toFIG. 4. Firstly, a plurality of sheets printed by the office machine (e.g. a printer) are outputted and introduced to the sheet placement tray4through a sheet advancing path5. Then, by a short side alignment device6, the short sides of these sheets are nestled against a front end of the sheet placement tray4. Then, by the first alignment arm21and the second alignment arm22of the sheet alignment device2, the long sides of these sheets are aligned with each other. Then, a stapling operation is performed by a post-processing device (e.g. a stapler), so that the same parts of these sheets are combined together. Afterwards, the stapled sheets are ejected from the sheet placement tray4to the outer portion of the office machine.

Hereinafter, the operations of the sheet alignment device2will be illustrated with reference toFIG. 5.FIG. 5is a schematic block diagram illustrating a sheet alignment device according to an embodiment of the present invention. The sheet alignment device comprises a controller34for controlling the operations of the sheet alignment device2. As shown inFIG. 5, the rotations of the first driving element26aand the second driving element26bof the power device26are controlled by the controller34. As the first driving element26ais rotated, the first roller28is synchronously rotated to drive the first transmission element27aof the transmission device27. At the same time, the second roller29is driven by the first transmission element27ato rotate, so that the first transmission element27ais moved more smoothly. Under this circumstance, since the first alignment arm21is connected with the first transmission element27a, the first alignment arm21is simultaneously moved with the first transmission element27a.

As the second driving element26bis rotated, the third roller30is synchronously rotated to drive the second transmission element27bof the transmission device27. At the same time, the fourth roller31is driven by the second transmission element27bto rotate, so that the second transmission element27bis moved more smoothly. Under this circumstance, since the second alignment arm22is connected with the second transmission element27b, the second alignment arm22is simultaneously moved with the second transmission element27b.

Please refer toFIGS. 6A-6EandFIG. 7.FIG. 6Ais a schematic side view illustrating a sheet alignment device according to an embodiment of the present invention, in which the first alignment arm and the second alignment arm are respectively located at a first home position and a second home position.FIG. 6Bis a schematic side view illustrating a sheet alignment device according to an embodiment of the present invention, in which the first alignment arm and the second alignment arm are respectively located at a first standby position and a second standby position.FIG. 6Cis a schematic side view illustrating a sheet alignment device according to an embodiment of the present invention, in which the first alignment arm is located at a sheet alignment position.FIG. 6Dis a schematic side view illustrating a sheet alignment device according to an embodiment of the present invention, in which a second sheet is introduced into the sheet placement tray.FIG. 6Eis a schematic side view illustrating a sheet alignment device according to an embodiment of the present invention, in which the sheet-aligning actions of a first sheet and a second sheet are completed.FIG. 7is a schematic timing waveform diagram illustrating an output signal from a first sensor of a sheet alignment device according to an embodiment of the present invention. The X axis denotes the time T. The Y axis denotes the output signal Si issued by the first sensor23.

In a case that no sheet is introduced to the sheet placement tray4, the first alignment arm21and the second alignment arm22are respectively located at a first home position a1and a second home position a2(seeFIG. 6A). Meanwhile, the first sensor23is interrupted by the first blocking piece21dof the first alignment arm21, and thus the first sensor23issues a high-level signal H. As shown inFIG. 7, the high-level signal H is generated at the time spot T0. At the same time, the second sensor22dis interrupted by the third blocking piece22d.

Please also refer toFIG. 3. When a first sheet S1is ready to be introduced to the sheet placement tray4, the first driving element26ais controlled by the controller34to be rotated in an anti-clockwise direction, and thus the first transmission element27ais driven to be rotated in the anti-clockwise direction. At the same time, the second driving element26bof the power device26is controlled by the controller34to be rotated in a clockwise direction. Correspondingly, the second transmission element27bof the transmission device27is rotated in the clockwise direction. As the first transmission element27ais rotated in the anti-clockwise direction, the first alignment arm21is moved toward the second alignment arm22. Similarly, as the second transmission element27bis rotated in the clockwise direction, the second alignment arm22is moved toward the first alignment arm21. After the first alignment arm21has moved for a certain time period, the first sensor23is no longer interrupted by the first blocking piece21dof the first alignment arm21, and thus the first sensor23issues a low-level signal L. As shown inFIG. 7, the low-level signal L is generated at the time spot T1. When the first alignment arm21is moved to a position where the first sensor23is interrupted by the first end21eaof the second blocking piece21e, the first sensor23issues the high-level signal H again. As shown inFIG. 7, the high-level signal H is generated at the time spot T2. According to the repeated interrupted status of the first sensor23, the controller34will stop driving the first driving element26aand the second driving element26b. Under this circumstance, the first alignment arm21and the second alignment arm22are no longer moved. As shown inFIG. 6B, the first alignment arm21is located at a first standby position b1to carry an side of the first sheet S1, and the second alignment arm is located at a second standby position b2to carry another side of the first sheet S1.

Please also refer toFIG. 3. When the sheet-aligning action of the first sheet S1starts, the first driving element26ais controlled by the controller34to be rotated in the anti-clockwise direction. Correspondingly, the first transmission element27ais transmitted and rotated in the anti-clockwise direction. As the first transmission element27ais rotated in the clockwise direction, the first alignment arm21is continuously moved toward the second alignment arm22. Due to the width of the second blocking piece21e, the controller34does not immediately calculate the moving distance of the first alignment arm21. Until the first sensor23is no longer interrupted by the second end21ebof the second blocking piece21eand the first sensor23issues a low-level signal L at the time spot T3(seeFIG. 7), the controller34starts to calculate the moving distance of the first alignment arm21. Until the moving distance of the first alignment arm21is equal to a preset distance d, the controller34stops driving the first driving element26a, wherein the preset distance d is determined according to the size of the sheet. Consequently, the movement of the first alignment arm21is stopped. Under this circumstance, the first alignment arm21is located at an alignment position c (seeFIG. 6C). During the movement of the first alignment arm21, the first side of the first sheet S1is pushed by the first sidewall21bof the first alignment arm21, and thus the first sheet S1is moved toward the second sidewall22bof the second alignment arm22. When the first alignment arm21is moved to the alignment position c, the second side of the first sheet S1is nestled against the second sidewall22bof the second alignment arm22and the first side of the first sheet S1is nestled against the first sidewall21bof the first alignment arm21.

After the sheet-aligning action of the first sheet S1is completed, if a second sheet S2is ready to be aligned, the first alignment arm21needs to be removed back to the first standby position b1and a waiting time is required to introduce the second sheet S2into the sheet placement tray4. Under control of the controller34, the first transmission element27ais transmitted by the first driving element26ato be rotated in the clockwise direction. Please also refer toFIG. 3. As the first transmission element27ais rotated in the clockwise direction, the first alignment arm21is moved in the direction distant from the second alignment arm22. Until the first sensor23is interrupted by the second end21ebof the second blocking piece21e, the first sensor23issues the high-level signal H. In response to the high-level signal H, the controller34stops driving movement of the first alignment arm21. Since the first sensor23is interrupted by the second end21ebof the second blocking piece21e(rather than the first end21eaof the second blocking piece21e) at this moment, as shown inFIG. 6D, the first alignment arm21is located at a third standby position b3(rather than the first standby position b1).

During the sheet-aligning action of the second sheet S2is performed, the controller34will calculate the moving distance of the first alignment arm21. Similarly, until the first sensor23is no longer interrupted by the second end21ebof the second blocking piece21eand the first sensor23issues a low-level signal L, the controller34starts to calculate the moving distance of the first alignment arm21. The timing of starting calculating the moving distance is identical to that described above. Moreover, the first alignment arm21is also stopped at the alignment position c.

During the sheet-aligning action of the second sheet S2is performed, the first side of the second sheet S2is pushed by the first sidewall21bof the first alignment arm21, and thus the second sheet S2is moved toward the second sidewall22bof the second alignment arm22. After the sheet-aligning action of the second sheet S2is completed, the second side and the first side of the second sheet S2are nestled against the second sidewall22bof the second alignment arm22and the first sidewall21bof the first alignment arm21, respectively (seeFIG. 6E). So the first sheet S1and the second sheet S2are aligned with each other.

After the sheet-aligning action of the second sheet S2is completed, if another sheet is ready to be aligned, the controller34will drive the first driving element26aagain, so that the first alignment arm21is moved to the third standby position b3and a waiting time is required to introduce the sheet into the sheet placement tray4.

If no additional sheet is needed to be aligned, a stapling operation is performed by a post-processing device (e.g. a stapler), so that the same parts of the first sheet S1and the second sheet S2are combined together. Then, the stapled sheets S1and S2are ejected out of the sheet placement tray4. Then, under control of the controller34, the first alignment arm21and the second alignment arm22are moved in the directions distant from each other, so that the stapled sheets S1and S2fall down to the outer portion of the office machine. Until the first sensor23and the second sensor24are respectively interrupted by the first blocking piece21dof the first alignment arm21and the third blocking piece22dof the second alignment arm22(i.e. the first alignment arm21and the second alignment arm22are respectively moved back to the first home positional and the second home position a2), the controller34will stop moving the first alignment arm21and the second alignment arm22. Meanwhile, the sheet-aligning action of the sheet alignment device2is finished.

Please refer toFIG. 8.FIG. 8is a flowchart illustrating the operations of a sheet alignment device according to an embodiment of the present invention. The sheet alignment device2performs the sheet-aligning action according to the steps S11to S25. Firstly, in the step S11, if no sheet is introduced into the sheet placement tray4, the first alignment arm21and the second alignment arm22are respectively located at the first home position a1and the second home position a2. When the sheet is ready to be introduced into the sheet placement tray4, the first alignment arm21and the second alignment arm22are simultaneously moved toward each other (in the step S12). After the first alignment arm21and the second alignment arm22have been moved for a certain time period, the step S13is performed to judge whether the first sensor23is interrupted or not. If the first sensor23is not interrupted, the steps S12and S13are repeatedly done. Whereas, if the first sensor23is interrupted, the step of the step S14is performed to stop moving the first alignment arm21and the second alignment arm22. Meanwhile, the first alignment arm21and the second alignment arm22are respectively located at the first standby position b1and the second standby position b2. When the sheet-aligning action starts, the step S15is performed to move the first alignment arm21toward the second alignment arm22. Immediately after the movement of the first alignment arm21starts, the step S16is performed to judge whether the first sensor23is no longer interrupted. If the judging condition of the Step S16is not satisfied, the steps S15and S16are repeatedly done. If the first sensor23is no longer interrupted, the step S17is performed to continuously move the first alignment arm21toward the second alignment arm22and start calculating the moving distance of the first alignment arm21. After the step S17is done, the step S18is performed to judge whether the moving distance of the first alignment arm21is equal to a preset distance d. If the moving distance of the first alignment arm21is not equal to a preset distance d, the first alignment arm21is continuously moved and the step S18is performed again. Whereas, if the moving distance of the first alignment arm21is equal to a preset distance d, the step S20is performed to stop moving the first alignment arm21. Meanwhile, the first alignment arm21is located at the alignment position c. Next, the step S21is performed to check whether there is any sheet to be aligned. If there is no sheet to be aligned, the sheet-aligning action is completed (in the step S25). If there is any sheet to be aligned, the step S22is performed to move the first alignment arm21in the direction distant from the second alignment arm22. After the first alignment arm21has been moved for a certain time period, the step S23is performed to judge whether the first sensor23is interrupted or not. If the judging condition of the Step S23is not satisfied, the steps S22and S23are repeatedly done. If the first sensor23is no longer interrupted, the step S24is performed to stop moving the first alignment arm21. Meanwhile, the first alignment arm21is located at the third standby position b3. The steps S15to S21are repeated done until there in no sheet to be aligned.

From the above description, the second blocking piece21eof the first alignment arm21and the first sensor23are collectively operated to determine the timing of calculating the moving distance of the first alignment arm21. During the sheet-aligning action of each sheet is performed, if the first sensor23is no longer interrupted by the second end21ebof the second blocking piece21eand the first sensor23issues a low-level signal L, the controller34starts to calculate the moving distance of the first alignment arm21. Since the moving distance of the first alignment arm21is calculated at the same start point for each sheet during the sheet-aligning action of each sheet is performed, the possibility of resulting in the moving distance error will be minimized. Consequently, the possibility of accumulating the moving distance error will be reduced. Since these sheets can be precisely aligned with each other, after a stapling operation is performed by a post-processing device (i.e. the stapler), the same parts of these sheets can be accurately combined together.