JP7544584B2 - Document feeder and image reader - Google Patents

Description

The present invention relates to a document feeder capable of feeding documents.

There are known document feeders that sequentially separate and feed documents from the topmost surface of multiple documents loaded on a document tray that can be raised and lowered by driving a motor, and image reading devices that read images of the documents being fed. In such devices, when loading a small amount of documents compared to the maximum amount that can be loaded on the document tray, a method is known in which the document tray is made to wait at an intermediate position in the movable range in order to shorten the lift time.

In the above-mentioned device, a sensor is provided to detect when the platen is at its lowest home position, and the position of the platen is controlled by counting the motor pulses that accompany motor drive, with the sensor position as the origin. Therefore, to accurately position the platen, it is necessary to periodically lower the platen to its lowest home position and initialize the count value.

When performing such a position control operation of the platen while making the platen wait at the middle position of its movable range, the following problem occurs. In other words, if the platen is lowered to the home position and repositioned each time the feeding of a stack of documents loaded on the platen is completed, the platen will first be lowered to the lowest position and then raised to the middle position again, which takes time to raise and lower the platen and increases the user's waiting time.

Patent document 1 proposes a method of counting the number of motor pulses from when the platen starts to rise from the intermediate waiting position, and when lowering the platen to the intermediate waiting position, lowering it by the integrated value of the number of pulses, thereby returning the platen to the intermediate waiting position without lowering it to the home position.

In the device disclosed in Patent Document 1, an overload on the document table caused by a user's operation error or the like is dealt with by providing a torque limiter in the path of the driving force transmission from the motor to the document table. Therefore, an overload on the torque limiter is detected by a separately provided sensor, and when the sensor detects an overload, it is determined that the document table has shifted in position, and the document table is lowered to the lowest home position.

JP 2020-121878 A

However, the method disclosed in Patent Document 1 requires a dedicated sensor to be installed to detect overload on the platen.

The present invention was made in consideration of the above-mentioned problems, and its purpose is to correct the positional deviation of the document table caused by overload, etc., when performing document table position control that involves returning the document table to its home position, without increasing waiting time or adding a dedicated sensor.

The document feeder of the present invention comprises a lifting means for lifting and lowering a document table on which documents are placed, a first detection means arranged at the lowest position of the movable range for lifting and lowering the document table and detecting that the document table is at a home position which is the origin of the lifting and lowering operation of the document table, a second detection means for detecting whether or not a document is placed on the document table, a take-in means for taking in the topmost document loaded on the document table, a third detection means for detecting that the topmost document has risen to a position where it can be taken in by the take-in means, and a counting means for counting the amount of drive of the lifting means for lifting and lowering the document table and detecting when the document table has risen from the home position. and a control means for controlling the lifting operation of the lifting means based on the count value while retaining the amount of lift as a count value, the control means raising the document table by the lifting means while the third detection means does not detect a document while the document is being sequentially taken in and fed by the take-in means, stopping the document table when a document is detected, and controlling the lifting means to lower the document table to the home position based on the detection result of the first detection means when the second detection means no longer detects a document and the count value is outside a predetermined normal range.

According to the present invention, when controlling the position of the platen, which involves returning the platen to its home position, it is possible to correct misalignment of the platen due to overload or other reasons, without increasing waiting time or adding a dedicated sensor.

1 is a cross-sectional view illustrating a schematic configuration of an image reading apparatus according to an embodiment of the present invention. FIG. 2 is a schematic diagram illustrating a configuration of a main part of the image reading apparatus of FIG. 1 . 11 is a schematic diagram showing the vicinity of the paper feed unit when an upward overload is applied to the sheet stacking table; 11 is a schematic diagram showing the vicinity of the sheet feeding unit when an overload is applied downward to the sheet stacking table; 5 is a flowchart showing a procedure after power is turned on in the first embodiment. 5 is a flowchart showing a procedure for determining a home position in the first embodiment. 6 is a flowchart showing a procedure for moving to an intermediate standby position in the first embodiment. 5 is a flowchart showing a procedure of sheet stacking tray control in the first embodiment. 10 is a flowchart showing a procedure of sheet stacking tray control in the second embodiment.

The following describes in detail an embodiment of the present invention with reference to the accompanying drawings. Note that the following embodiment does not limit the scope of the present invention as claimed, and not all of the combinations of features described in the present embodiment are necessarily essential to the solution of the present invention.

[First embodiment]
First, a document feeder according to a first embodiment and an image reading apparatus including the document feeder will be described.

<Image reading device 200>
FIG. 1 is a partial cross-sectional view showing the configuration of an image reading device having a document feeding device according to a first embodiment, and FIG. 2 is a schematic diagram showing the configuration of a main part of the image reading device of FIG. 1.

In Figures 1 and 2, the image reading device 200 includes a sheet loading device 101. A plurality of sheets (originals) F are loaded (placed) on a sheet loading platform (original platform) 1, which is configured to be freely raised and lowered. A loading platform drive motor 2 is driven to rotate and raise and lower the sheet loading platform 1. A sheet detection sensor 3 detects that the sheets loaded on the sheet loading platform 1 are at the sheet loading position (position where they can be loaded). If the sheets F loaded on the sheet loading platform 1 are not at the sheet loading position, the loading platform drive motor 2 is driven to move the sheet loading platform 1 so that the top surface of the sheets is at the loading position. A sheet loading detection sensor 12 detects that the sheets F are loaded on the sheet loading surface 1a of the sheet loading platform 1.

The pickup roller 4 (take-in roller) sequentially takes in the sheets on the sheet stacking tray 1 and sends them to the feed roller 6. The pickup motor 5 rotates the pickup roller 4. In FIG. 2, the top surface of the sheet is in the sheet take-in position, and if the pickup roller 4 is rotated, the take-in of the sheet F will begin.

The feed roller 6 is provided downstream of the pickup roller 4 and is driven by the feed motor 8 to rotate in a direction to feed the sheet F downstream in the conveying direction. The feed roller 6 is connected to the feed motor 8 via a one-way clutch, and the drive of the feed motor 8 is transmitted in only one direction. When the sheet F is fed by the feed motor 8, the drive force is transmitted to the feed roller 6, but when the sheet F is conveyed by the registration rollers 17, 18, etc. at a speed faster than the feed motor 8, the rotation of the feed motor 8 is not transmitted by the one-way clutch, and the feed roller 6 rotates in response to the conveyance of the sheet F. The separation roller 7, which is provided opposite the feed roller 6 across the conveying path and forms a nip, constantly receives a rotational force from the separation motor 9 via a torque limiter (slip clutch) (not shown) that rotates in a direction to push the sheet F back upstream in the conveying direction. When one sheet F is present between the feed roller 6 and the separation roller 7, the torque transmitted by the torque limiter to the separation roller 7 in the direction of pushing the sheet F back upstream is exceeded by the torque in the direction of the feed roller 6 sending the sheet downstream, and the separation roller 7 rotates following the feed roller 6 (rotates together).

On the other hand, when there are multiple sheets F between the feed roller 6 and the separation roller 7, the rotational force of the separation roller 7 pushing the sheets F back upstream is greater than the force acting in the direction downstream in the conveying direction due to friction between the sheets F, so that only the topmost sheet is conveyed downstream.

In this way, when overlapping sheets F are fed into the nip between the feed roller 6 and the separation roller 7, due to the action of the feed roller 6 feeding the sheet F downstream and the action of the separation roller 7 preventing the sheet F from being transported downstream, only the topmost sheet F is fed downstream. The other sheets F are prevented from being transported downstream, so that the overlapping sheets F are separated and fed. In this way, the feed roller 6 and the separation roller 7 form a pair of separation rollers 42. The separation roller pair 42 functions as an example of a sheet separation section for separating and transporting the multiple sheets F to be transported one by one.

In this embodiment, the force with which the separation roller 7 separates the sheet F can be changed. The sheet F can be separated simply by holding the separation motor 9 without rotating it. An even stronger separation force can be obtained by driving the separation motor 9 so that the separation roller 7 rotates in a direction that returns the sheet F to the upstream side.

In this embodiment, a pair of separation rollers 42 is used, but a pair of separation belt rollers, in which either the separation roller or the feed roller is a belt, may be used instead of the pair of separation rollers 42. Also, the separation roller may be replaced with a separation pad that abuts against the sheet F to prevent multiple sheets F from being transported downstream.

In addition, by providing a double feed detection sensor 30 at the position where the separated sheets F pass, it is possible to detect whether the sheets F have been separated one by one by the sheet separation section. In this embodiment, a detection device using an ultrasonic transmission/reception section is used as the double feed detection sensor 30, and double feed can be detected by the amount of ultrasonic attenuation between the transmission/reception sections across the transport path.

The conveying motor 10 drives the registration roller 18 and conveying rollers 21 and 23 to convey the separated sheet F to an image reading position where the image of the sheet (original) F is read by the image reading sensors 14 and 15 (image reading section), and further to a discharge position. The driving of each roller drives the opposing rollers (registration roller 17, conveying rollers 20 and 22) that are configured as a roller pair, so that the sheet can be conveyed to the discharge position. The conveying motor 10 also drives each roller so that the conveying speed of the sheet F can be changed according to the optimal speed for reading the sheet F and the settings such as the resolution of the sheet F. The registration clutch 19 drives the registration roller 18 (original conveying section) by transmitting the rotational driving force of the conveying motor 10 to the registration roller 18 or by cutting off the transmission, thereby driving the registration roller 18 or stopping its driving.

The nip gap adjustment motor 11 adjusts the gap between the feed roller 6 and the separation roller 7, or the pressure with which the feed roller 6 is pressed against the separation roller 7 via the sheet. This adjusts the gap or pressure to suit the thickness of the sheet F, allowing the sheet F to be separated.

The conveying roller pair consisting of conveying rollers 20 and 21, the conveying roller pair consisting of conveying rollers 22 and 23, and the further downstream roller pair shown in FIG. 1 convey the sheet to the discharge stacking section 44. The two guide plates, the upper guide plate 40 and the lower guide plate 41, guide the sheet F conveyed by the separation roller pair, the registration roller pair, each conveying roller pair, and the downstream roller pair.

The image reading device 200 is equipped with a control unit 45 that controls the operation of the entire device. The control unit 45 is composed of, for example, one or more processors (CPUs).

<Sheet loading tray position control>
The sheet stacking platform 1 includes a home position detection sensor 13 disposed at the lowest position of the movable range of the lifting and lowering operation, and detects that the sheet stacking platform 1 is at the home position based on the detection result of the home position detection sensor 13. The stacking platform drive motor 2 is a stepping motor (pulse motor), and is driven by drive pulses from the control unit 45. The control unit 45 counts the drive pulses, which are the drive resolution (minimum unit) of the motor while driving the stacking platform drive motor 2, and holds the count value as a pulse counter. When driving the stacking platform drive motor 2 upward, the count is increased (the count is added) in the positive direction, and when driving the stacking platform drive motor 2 downward, the count is decreased (the count is subtracted) in the negative direction. In addition, the home position is set as the origin of the lifting and lowering operation of the sheet stacking platform 1, and the amount of lift from the home position is counted in the number of motor pulses, so that the current position of the sheet stacking platform 1 can be grasped.

The user can set the standby position of the sheet stacking tray 1 by selecting from multiple options according to the number of sheets to be stacked. If the maximum amount of sheets F that can be stacked is desired, the home position at the lowest position is set. For example, if the sheet stacking tray 1 can hold a maximum of 500 sheets, the home position is the 500-sheet stacking position. On the other hand, if only a small amount of sheets F is desired, an intermediate position set above the home position is set (can be set). If a position that can hold a predetermined number of sheets, for example, 300 sheets or 100 sheets, is set as the intermediate standby position, the 300-sheet stacking position or the 100-sheet stacking position is set as the intermediate standby position. The user can select one of these standby positions: 500 sheets, 300 sheets, or 100 sheets. If the standby position selected by the user is the intermediate standby position with 300 sheets or 100 sheets, the stacking tray drive motor 2 is driven in the upward direction by the number of pulses corresponding to the required lift distance from the home position.

In this embodiment, the loading platform drive motor 2 is configured as a stepping motor, but as long as the amount of drive by the motor is known, it is not limited to a stepping motor. For example, if a DC motor is used instead and an encoder is provided on the DC motor, the amount of drive can be counted.

<Sheet stacking tray position shift due to overload>
Based on the schematic diagram of FIG. 3, an operation will be described when the user mistakenly applies an overload to the sheet stacking tray 1 and the sheet stacking tray 1 shifts from its proper position.

In FIG. 3(a), the sheet stacking tray 1 is detected by the home position detection sensor 13 and is in the home position. FIG. 3(b) shows the state after it has been moved from this point to the intermediate standby position according to the user's settings. Here, the actual position of the sheet stacking tray 1 matches the position assumed by the pulse counter. Then, suppose that the user accidentally pushes up the sheet stacking tray 1 while loading a stack of sheets on the sheet stacking tray 1. Then, the actual position of the sheet stacking tray 1 moves above the position assumed by the pulse counter, causing a positional deviation. Because the sheet stacking tray 1 is located above the home position detection sensor 13, it is not possible to detect the positional deviation at this point. However, the sheets F that the user wants to load have been loaded, so feeding of the sheets F begins as is.

The sheet stacking table 1 is raised, and when the sheet detection sensor 3 detects that the top surface of the sheet has risen to the take-in position, the sheet stacking table 1 is stopped (Fig. 3(d)). The pickup roller 4 is below the sheet detection sensor 3 in Figs. 3(a)-(c), but is pushed up as the sheet stacking table 1 rises, and the pickup roller 4 is pressed against the top surface of the sheet by its own weight, as shown in Fig. 3(d), and the contact area between the top surface of the sheet and the pickup roller 4 is at the same height as the take-in position. In this state, the feed motor 8 is driven to rotate the feed roller 6, while the pickup motor 5 is driven to rotate the pickup roller 4, allowing the sheet F to be taken into the sheet separation section and separated (Fig. 3(e)).

The sheet F is fed in sequence, and while the sheet detection sensor 3 does not detect the sheet F, the control to raise the sheet stacking table 1 is repeated. The figure of the last sheet being fed is shown in FIG. 3(f). When the trailing edge of the sheet passes the sheet stacking detection sensor 12, it is determined that there are no sheets remaining on the sheet stacking table 1, sheet feeding is terminated, and the lifting of the sheet stacking table 1 is also stopped. At this time, the actual position of the sheet stacking table 1 is at the intake position. On the other hand, since the position assumed by the pulse counter in FIG. 3(c) is still displaced by the amount of the lift caused by the overload, if it is lowered to the intermediate waiting position in this state, it will wait in the displaced position in FIG. 3(g). In this way, only when there is a large difference between the actual sheet stacking table position and the position assumed by the pulse counter, the sheet stacking table 1 is lowered to the home position once, and then raised to the intermediate waiting position after the home position is set, so that it is moved to the correct position in FIG. 3(b).

In the example of FIG. 3, the sheet stacking tray 1 is moved upward due to overloading by the user, but FIG. 4 shows the case where it is moved downward. FIGS. 4(a) and (b) are the same as FIG. 3, and FIG. 4(c) shows the case where the sheet stacking tray 1 is pushed downward. The sheet stacking tray 1 is raised in this state, and feeding is performed sequentially (FIGS. 4(d) and (e)). When the last sheet F is fed (FIG. 4(f)), the actual sheet stacking tray position is the same as FIG. 3(f), but the assumed position by the pulse counter is different, and it is higher by the amount it was pushed down. If it is lowered to the intermediate waiting position in this state, it will become as shown in FIG. 4(g), and the position will be shifted as in FIG. 4(c). For this reason, it is first returned to the home position and then raised to the intermediate waiting position to move it to the correct position in FIG. 4(b).

<Flow of moving the sheet stacking tray to the intermediate standby position>
The operation of the sheet stacking tray 1 will be described with reference to the flow charts of FIGS. 5 to 7, from when the power supply of the image reading device 200 is turned on until the sheet stacking tray 1 moves to the intermediate standby position and waits there.

First, the image reading device 200 is powered on (S101). Then, the sheet stacking tray 1 is located at its home position (S102). The home positioning is performed as shown in the flowchart in FIG. 6 (S201).

In FIG. 6, the lowering operation of the sheet stacking tray 1 is started (S202), and the system waits until the home position detection sensor 13 detects the sheet stacking tray 1 and confirms that the sheet stacking tray 1 has been lowered to the home position (No in S203). When the sheet stacking tray 1 has been lowered to the home position (Yes in S203), the pulse counter is cleared to 0 (S204), and this position is set as the origin of the lifting operation. At the same time, the lowering operation of the sheet stacking tray 1 is stopped (S205), and the home position setting is completed (S206). At this point, the state is as shown in FIG. 3(a), and the sheet stacking tray 1 is stopped at the position detected by the home position detection sensor 13.

Next, the process returns to S103 in FIG. 5 to check whether the standby position set by the user is the home position or an intermediate position. If the setting is the home position (No in S103), the sheet stacking tray 1 is already in the home position, so the process ends (S105).

If the setting is the intermediate waiting position (Yes in S103), it moves to the intermediate waiting position (S104). Figure 7 is a flowchart showing the operation of moving to the intermediate waiting position. When entering S104 in Figure 5, the sheet stacking tray 1 is in the home position, so only lifting is required, but the process in Figure 7 allows it to move to the intermediate position no matter where it is.

In FIG. 7, first, to determine whether the sheet stacking tray 1 is already at the intermediate position, the pulse counter is compared with the number of pulses corresponding to the intermediate position (S302). If the pulse counter matches the number of pulses at the intermediate position (Yes in S302), the sheet stacking tray 1 is at the intermediate position, and the process ends (S308).

If they do not match (No in S302), it is determined whether the sheet stacking tray 1 is above or below the intermediate position (S303). If the pulse counter is greater than the number of pulses corresponding to the intermediate position (Yes in S303), the sheet stacking tray 1 is above the intermediate position, so the sheet stacking tray 1 starts to descend (S304). If the pulse counter is smaller than the number of pulses corresponding to the intermediate position (No in S303), the sheet stacking tray 1 is below the intermediate position, so the sheet stacking tray 1 starts to ascend (S305). The pulse counter is constantly updated as the stacking tray drive motor 2 is driven, and the drive continues until the pulse counter matches the number of pulses corresponding to the intermediate position (No in S306). If the pulse counter matches the number of pulses corresponding to the intermediate position (Yes in S306), the operation of the sheet stacking tray 1 is stopped (S307), and the movement process to the intermediate waiting position is completed (S308). This completes the process when the power is turned on in FIG. 5 (S105). At this time, the state is as shown in FIG. 3(b), and the sheet stacking tray 1 waits at an intermediate position above the home position.

<Operation flow of sheet stacking tray during feeding>
Next, the operation of the sheet stacking tray 1 when feeding a sheet and reading an image by a user operation will be described with reference to the flowchart of FIG.

The process starts when the image reading device 200 enters a standby state (S401). At this time, the user loads a sheet F onto the sheet stacking tray 1. During this time, the process waits until a feeding start instruction is issued by the user (No in S402).

If there is an instruction to start feeding (Yes in S402), it is checked whether the sheet F to be fed is present on the sheet stacking tray 1 (S403). If there is no sheet F (No in S403), the instruction to start feeding is canceled and the system waits until another instruction is given and sheet F is loaded. If it is possible to detect the presence of sheet F on the sheet stacking tray 1 (Yes in S403), the sheet stacking tray 1 is raised (S404) and continues to rise until the sheet detection sensor 3 detects sheet F at the intake position (No in S405). If it is possible to detect sheet F at the intake position (Yes in S405), the raising of the sheet stacking tray 1 is stopped (S406).

Now that the sheet feeding preparation is complete, feeding of sheet F begins (S407), and the sheets F stacked on the sheet stacking tray 1 are fed one by one. From this point on, the operation of the sheet stacking tray 1 is controlled so that the top surface of the sheet F on the sheet stacking tray 1 always coincides with the intake position.

The sheet detection sensor 3 detects whether or not there is a sheet F at the take-in position. If a sheet F is detected at the take-in position (Yes in S408), the sheet stacking tray 1 stops operating (S410), and if a sheet F is not detected (No in S408), the sheet stacking tray 1 is raised (S409). When the sheet stacking tray 1 is rising, if the pulse count has not reached the upper limit position (No in S411), the sheet stacking tray 1 continues to rise.

If the sheet stacking detection sensor 12 detects the stacking of sheet F (Yes in S414), feeding can be continued, so the process returns to S408. If the stacking of sheet F is no longer detected (No in S414), the sheet stacking tray 1 is stopped (S415).

In S411, if the pulse count reaches the upper limit position (Yes in S411), the sheet stacking tray 1 may be at the upper limit of its movable range. For example, if there is a foreign object on the sheet stacking detection sensor 12 and the sensor is constantly detecting sheets, the sheet stacking tray 1 may be raised indefinitely, which may lead to damage to the device, and therefore a limit must be set. If the pulse count value indicates that the upper limit position has been reached, the feeding of the sheet F is temporarily stopped (S412), and the sheet stacking tray 1 is moved to the home position (S413), the home position is returned to, and the pulse count is cleared (reset). The sheet stacking tray 1 is then raised again (S404), and sheet feeding is resumed.

After the sheet stacking tray 1 is stopped in S415 in FIG. 8, it is determined whether the pulse count value is normal (whether it is within the normal range) (S416). If the user accidentally pushes down or up the sheet stacking tray 1 while the sheet stacking tray 1 is waiting at the intermediate waiting position or while it is rising from the home position, the position of the sheet stacking tray 1 will deviate from the expected position corresponding to the pulse count value. To determine whether a positional deviation has occurred, it is determined whether the pulse counter is within a predetermined normal range (S416). If it is within the normal range, it is determined that no positional deviation has occurred, and the sheet stacking tray 1 is moved to the intermediate waiting position without returning to the home position (S418). If the pulse counter is outside the normal range, there is a possibility that a positional deviation has occurred, so the sheet stacking tray 1 is moved to the home position and returned to the home position (S417), and then moved to the intermediate waiting position (S418). When the movement is completed, the process ends (S419).

In S416 in FIG. 8, it is determined whether the pulse counter is within the normal range. The maximum value of this normal range is the number of pulses that corresponds to the upper limit position of the movable range in which the sheet stacking tray 1 can be raised and lowered. In this embodiment, S411 prevents the pulse count from exceeding the upper limit position, but if the device is configured so that it will not be damaged even if the sheet stacking tray 1 is raised beyond the upper limit position, the processes of S411, S412, and S413 may be omitted. In that case, the determination in S416 of whether the maximum value of the normal range has been exceeded is always valid.

The minimum value of the normal range is the number of pulses corresponding to the take-in position minus the number of pulses for the maximum thickness of one sheet (one document) that can be fed. The reason for this is that when the sheet stacking tray 1 is overloaded upward and displaced as shown in FIG. 3, the assumed position by the pulse counter will be lower than the take-in position when the sheet stacking tray 1 is at the same height as the take-in position as shown in FIG. 3(f). At this time, if the sheet stacking detection sensor 12 detects a foreign object or the like even though there is no sheet, the sheet stacking tray 1 will be raised up to the upper limit position of the pulse counter. At this time, if the minimum value of the normal range is set significantly lower than the take-in position, the sheet stacking tray 1 will be raised far beyond the upper limit position. In this embodiment, taking this situation into consideration, the range is set so that it is reliably within the normal range when there is no overload, but does not greatly exceed the upper limit position of the movable range even when an overload occurs.

If the result of S416 in FIG. 8 is No, the user may be notified that there is an abnormality in the position of the sheet stacking tray 1. In an image reading device equipped with a display unit or a buzzer, the abnormality in the sheet stacking tray 1 is displayed on the display unit or a buzzer is sounded to notify the user. If the user overloads the sheet stacking tray 1 and does not notice it, this may be repeated many times, which may result in damage to the device. If the user is notified and given a warning, the frequency of overloading can be reduced, preventing damage to the device.

If the home position detection sensor 13 detects the sheet stacking platform 1 while waiting at the intermediate position or during a feeding operation, it may be determined that the position of the sheet stacking platform 1 is abnormal. When the sheet stacking platform 1 is not detected by the home position detection sensor 13 while waiting at the intermediate position or during a feeding operation, and furthermore, the sheet stacking platform 1 is stopped or raised, it can be determined that the detection of the sheet stacking platform 1 by the home position detection sensor 13 is an abnormal state. In this case, the user may be notified by the display unit or a buzzer. If the sheet stacking platform 1 is pushed down to the home position, it is assumed that an extremely large overload has been applied due to a sheet stack that greatly exceeds the specifications or a user operation error. In that case, an even stronger warning may be given than the above-mentioned notification.

Second Embodiment
Next, a document feeder according to a second embodiment and an image reading apparatus including the document feeder will be described. Note that the description of the parts common to the first embodiment will be omitted, and the description will be focused mainly on the differences from the first embodiment.

The flowchart in FIG. 9 adds the process of S502 to FIG. 8 shown in the first embodiment, and the same processes as in FIG. 8 are given the same reference numerals. In FIG. 9, when the sheet stacking detection sensor 12 no longer detects a sheet during sheet feeding (S415), sheet feeding ends, but if the pulse counter is within the normal range at that time (Yes in S416), the number of pulses required to raise the sheet stacking tray 1 from the home position to the pick-up position is set (updated) in the pulse counter at this point (S502). When the sheet stacking tray 1 is subsequently raised or lowered, the count up/down is performed based on the value set here.

By processing S502, even if the pulse counter is within the normal range, any slight positional deviation is corrected.

Explaining with reference to Figures 3 and 4, the assumed position by the pulse counter is shifted in the state of Figures 3(f) and 4(f), but since the position of the sheet stacking tray 1 at this time is the take-in position, the number of pulses corresponding to the take-in position is set in the pulse counter. This allows the assumed position by the pulse counter to match the actual position of the sheet stacking tray 1. Then, when the sheet stacking tray 1 is lowered to the intermediate waiting position, it can be moved to the correct position of Figures 3(b) and 4(b), respectively. Therefore, even if the sheet stacking tray 1 is overloaded due to an erroneous operation by the user and rises or falls, it can be moved to the correct position without returning to the home position. Also, if all the sheets remaining on the sheet stacking tray 1 are pulled out during feeding, the pulse counter is determined to be out of the normal range in S416 of Figure 9 (No in S416), and in that case, the home position is returned, so no positional deviation occurs.

F: sheet, 1: sheet stacking tray, 1a: sheet stacking surface, 2: stacking tray drive motor, 3: sheet detection sensor, 4: pickup roller, 5: pickup motor, 6: feed roller, 7: separation roller, 8: feed motor, 9: separation motor, 10: transport motor, 11: nip gap adjustment motor, 12: sheet stacking detection sensor, 13: home position detection sensor, 14, 15: image reading sensor, 42: separation roller pair, 45: control unit, 101: sheet intake device, 200: image reading device

Claims (7)

a lifting means for lifting and lowering a document table on which documents are placed;
a first detection means arranged at a lowermost position of a movable range of the document table for lifting and lowering, for detecting that the document table is at a home position which is a starting point of the lifting and lowering operation of the document table;
a second detection means for detecting whether or not an original is placed on the original table;
a take-in means for taking in a topmost document loaded on the document table;
a third detection means for detecting that the uppermost document has risen to a position where the document can be taken in by the take-in means;
a control means for counting a drive amount of the lifting means for lifting and lowering the document table, and controlling the lifting and lowering operation of the lifting means based on the count value while retaining a lifting amount of the document table from the home position as a count value;
the control means causes the elevation means to raise the document table while the third detection means does not detect an original while the originals are being sequentially taken in and fed by the take-in means, and causes the control means to stop the document table when the third detection means detects an original;
A document feeding device characterized in that, when the second detection means no longer detects a document, if the count value is outside a predetermined normal range, the lifting means is controlled to lower the document table to the home position based on the detection result of the first detection means. The document feeder according to claim 1, characterized in that an intermediate standby position of the document table can be set, and the control means moves the document table to the intermediate standby position when the second detection means no longer detects the document and the count value is within a normal range. The document feeder according to claim 1 or 2, characterized in that, if the second detection means detects a document even when the count value reaches a value corresponding to the amount of lift from the home position to the upper limit position of the range in which the document table can be raised and lowered while the document is being sequentially taken in by the take-in means, the control means stops the take-in of the document by the take-in means, lowers the document table to the home position, and then controls the lifting means to lift the document table to resume the take-in of the document by the take-in means. The document feeder according to any one of claims 1 to 3, characterized in that, if the count value is within the normal range when the second detection means no longer detects the document, the control means sets the count value to a value corresponding to the amount of lift of the document table from the home position to the position where the document can be taken in. The document feeder according to any one of claims 1 to 4, characterized in that the maximum value of the normal range is a value equivalent to the amount of lift of the document table from the home position to the upper limit position of the range in which the document table can be raised and lowered, and the minimum value of the normal range is a value equivalent to the amount of lift of the document table from the home position to a position that is the maximum thickness of one document sheet lower than the position in which the document table can be taken in. The document feeder according to any one of claims 1 to 5, characterized in that the lifting means is a motor driven by a drive pulse, the count value is incremented according to the number of pulses when the motor rotates in a direction to lift the document table, the count value is decremented according to the number of pulses when the motor rotates in a direction to lower the document table, and the count value is reset to 0 when the first detection means detects the document table. A document feeder according to any one of claims 1 to 6,
a reading means for reading an image of the document fed by the document feeder;
An image reading device comprising:

Images