JP2010030693A - Paper feeding device and image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a paper feeding device capable of detecting the number of remaining paper accurately, in particular, without requiring many members, and to provide an image forming device provided with the paper feeding device. <P>SOLUTION: This paper feeding device is provided with a paper feeding cassette provided to be freely inserted and pulled out in and out of an image forming device body to store bundles of paper, a loading plate arranged in the paper feeding cassette to elevate and lower freely while being loaded with bundles of paper on its upper face, an elevating means for elevating the loading plate when feeding paper, and a means for detecting the number of remaining paper. The means for detecting the number of remaining paper has parts to be detected provided in the paper feeding cassette, operating in accordance with the elevation of the loading plate, and having a predetermined arrangement and a plurality of sensors provided in the device body to detect the parts to be detected. The sensor is a means for detecting the number of remaining paper by recognizing positions of the loading plate at many steps owing to the combination of on/off-states of all the sensors when the on/off-states are switched in accordance with the elevation of the loading plate and the switching manner of the sensors switched when reaching the on/off-state by the means for detecting the number of remaining paper. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a paper feed device that includes a paper feed cassette that can be moved up and down and that can be inserted into and removed from the apparatus body, and that can detect the remaining amount of paper, and an image forming apparatus that includes the paper feed device.

  In general, an image forming apparatus such as a copying machine or a printer using an electrophotographic developing method is provided with a paper feeding device for supplying a sheet such as recording paper (hereinafter simply referred to as paper) to an image forming unit. This paper feeding device includes a paper feeding cassette for loading paper, a pickup roller, and the like. The uppermost surface of the loaded paper bundle is raised to the paper feeding position, and one sheet at a time from the paper feeding cassette by the pickup roller. Take it out and convey it to the image forming unit.

  Conventional paper cassettes are mainly used to exchange multiple types of paper with different sizes, but they are used depending on the paper size, such as A4 size paper is often used in general paperwork. In particular, the frequency of using paper of A3 size or larger is extremely low compared to the frequency of using A4 size paper, and in recent years, the frequency of replenishing paper that uses limited space effectively and is frequently used In order to reduce this, large-capacity paper feed cassettes that accommodate a large amount of paper of a certain size have been widely adopted.

  Such a large-capacity paper feed cassette is provided with a stacking plate for stacking and lifting paper in the paper feed cassette, and in order to detect the remaining amount of paper, for example, a stack in which the paper runs out using a detection sensor. There are means for detecting the plate, and means for detecting the remaining amount of paper by attaching an encoder to the motor or rotating shaft for raising the stacking plate and grasping the rising amount of the stacking plate.

  However, the former can only know that the paper has run out, and the latter has a problem in that the amount of movement is unknown unless it is continuously monitored, so that a dedicated electric circuit is required, which increases the number of parts and increases costs. .

In order to solve such a problem, Patent Document 1 discloses seven stages without particularly increasing the number of parts by detecting the fan-shaped detected portion engaged with the rotating shaft for raising the stacking plate with three sensors. The remaining amount of paper is detected.
However, for large-capacity paper cassettes with a long stacking distance, the 7-step detection is not accurate and sufficient, and in order to be able to detect more stages, the number of parts, such as the addition of sensors, can be reduced. There is a problem that an increase is necessary.

Japanese Patent No. 4015860

  SUMMARY OF THE INVENTION Problems to be solved by the present invention include a sheet feeding device that can detect the remaining amount of paper more accurately even in a large-capacity sheet feeding cassette, and an image forming apparatus including the sheet feeding device. Is to provide a device.

  The invention according to claim 1 is provided so as to be detachable with respect to the apparatus main body, and is provided in the inside of the paper feed cassette that can store the paper bundle, and can be moved up and down by stacking the paper bundle on the upper surface. A sheet stacking device, a lifting device that raises the stacking plate during sheet feeding, and a sheet remaining amount detecting unit that detects a remaining sheet amount, wherein the sheet remaining amount detecting unit includes the sheet cassette. And a plurality of sensors installed in the apparatus main body for detecting the detected parts, wherein the sensors are arranged as described above. The on / off state is switched according to the rise of the stacking plate, and the sheet remaining amount detecting means is a combination of the on / off state of all the sensors and the switching mode of the sensor switched when reaching the on / off state. By the position of the loading plate Recognized in multiple stages, to the sheet feeding apparatus, characterized in that the means for detecting the remaining sheets.

  According to a second aspect of the present invention, there is provided the stacking plate until any one of the sensors is switched after the on / off state of any one of the sensors is switched in accordance with the rising of the stacking plate. The paper feeding device according to claim 1, wherein the ascent distance is shorter than the distance from the uppermost surface of the paper bundle to the paper feeding position when the paper feeding cassette is fully loaded.

  According to a third aspect of the invention, there is provided the paper feeding device according to the first or second aspect, wherein at least one of the sensors is in an ON state when the paper feeding cassette is inserted.

According to a fourth aspect of the present invention, any one of the sensors is switched on / off, and the detected portion is in a state where the number of sensors is n until the sheet feeding cassette is full to empty. 4. An array according to any one of claims 1 to 3, characterized in that the on / off state switching of all the sensors is possible in total up to ²ⁿ times ( ²ⁿ × n-2 × n) times. The present invention relates to a sheet feeding device.

  According to a fifth aspect of the present invention, the ascending means is a means utilizing the rotation of a motor, and the detected portion is a disk that is engaged with a rotating shaft that is rotated by the motor. 5. The sheet feeding device according to claim 1, wherein a plurality of arcs are formed on n rows of concentric circles.

  The invention according to claim 6 has a storage means for storing a position of the stacking plate before the power is turned off even after the apparatus is turned off. Relates to the device.

  According to a seventh aspect of the present invention, after the on / off state of any one of the sensors is switched according to the rise of the stacking plate, the next sensor that is switched on / off is switched immediately before. The sheet feeding device according to claim 6, wherein the sheet feeding device is a sensor different from the sensor.

  The invention according to claim 8 is the paper feed according to any one of claims 1 to 7, wherein the paper feed cassette is a large-capacity paper feed cassette capable of storing a bundle of sheets made up of a large number of sheets. Relates to the device.

  A ninth aspect of the invention includes the paper feeding device according to any one of the first to eighth aspects, and an image forming unit that performs an image forming process on paper fed from the paper feeding device. The present invention relates to an image forming apparatus.

  According to the first aspect of the present invention, all the remaining amount detecting means having a predetermined array of detected portions that operate in response to the rising of the stacking plate and a plurality of sensors for detecting the detected portions are provided. This is a means for detecting the remaining amount of paper by recognizing the position of the stacking plate in multiple stages by determining the combination of the on / off state of the sensor and the mode of which sensor on / off state has been switched. As a result, the position of the stacking plate can be recognized in more stages than in the conventional paper feeding device using the same number of sensors, so that the remaining amount of paper can be detected with high accuracy even in a large capacity paper feeding cassette.

  According to the invention of claim 2, after the on / off state of any one of the sensors is switched according to the rising of the stacking plate, the stacking plate until any one of the sensors is switched next. Is lower than the distance from the top surface of the paper bundle to the paper feed position when the paper cassette is fully loaded, so that when the stacking plate rises after the paper cassette is inserted, the top surface of the paper bundle is at the paper feed position. Since the sensor is switched on / off at least once before reaching, the remaining amount of paper can be detected before feeding.

  According to the third aspect of the present invention, when the paper feed cassette is inserted, at least one of the plurality of sensors is in an on state, so that the sensor can also serve as the paper feed cassette insertion confirmation sensor. Therefore, it is not necessary to provide a separate sensor for confirmation of insertion, and the number of members can be reduced.

According to the fourth aspect of the present invention, any one of the sensors is switched on / off, and the detected part is not fully loaded when the number of sensors is n until the paper feeding cassette is full to empty. By having an arrangement in which the ON / OFF state of the sensor can be switched more than ²ⁿ times in total ( ²ⁿ × n−2 × n) times, it is possible to use other sensors using the same n sensors. Compared with the remaining paper amount detecting means, the remaining amount of paper can be detected in more stages, so that high accuracy can be obtained.

  According to the fifth aspect of the present invention, the ascending means is a means utilizing the rotation of the motor, and the detected portion is n with respect to n sensors in the disc meshed with the rotating shaft rotated by the motor. By forming a plurality of arcs on the concentric circles of the row, the parts can be reduced in size and installed in a limited space in the paper feeder.

  According to the sixth aspect of the present invention, even after the apparatus power is turned off, by having the storage means for storing the position of the stacking plate before the power is turned off, the sheet feeding device is not operated when the power is turned on again. Both can detect the remaining amount of paper.

  According to the seventh aspect of the present invention, after the on / off state of any one of the sensors is switched according to the rise of the loading plate, the sensor that is next switched on / off is the immediately preceding sensor. Because the sensor is different from the switched sensor, the on / off status of all sensors is not the same before and after the previous switching, so even if the sensor on / off status is switched before and after the power is turned off. The remaining amount of paper can be detected without operating the paper feeder when the power is turned on.

  According to the eighth aspect of the invention, it is possible to accurately detect the remaining amount of paper in the large-capacity paper feed cassette by combining the on / off state of a plurality of sensors and the switching mode thereof.

  According to the ninth aspect of the invention, since the image forming apparatus includes the paper feeding device according to any one of the first to eighth aspects, the position of the stacking plate can be recognized in multiple stages. It can detect the remaining amount of paper with high accuracy.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of a paper feeding device according to the invention and an image forming apparatus including the paper feeding device will be described with reference to the drawings.
FIG. 1 is a schematic diagram showing an internal structure of an embodiment of an image forming apparatus to which a paper feeding device according to the present invention is applied. FIG. 2 is an external perspective view of an embodiment of an image forming apparatus to which the paper feeding device according to the present invention is applied. In the specification, the front direction of the image forming apparatus in FIG.

In this embodiment, as an example of the image forming apparatus (1) according to the present invention, a copying machine is shown as shown in FIGS.
The image forming apparatus (1) mainly includes a paper feeding device (11), an image reading unit (12), an image forming unit (13), a fixing unit (14), and a paper discharge unit (15). .
The paper is supplied from the paper feeding device (11) to the image forming unit (13), and the image data read by the image reading unit (12) is formed on the paper as a toner image by the image forming unit (13). In (14), the toner is fixed on the sheet. The paper on which the image is formed is discharged to the paper discharge unit (15).

The sheet feeding device (11) according to the present invention is located at the lower part of the image forming apparatus (1) as shown in FIGS. 1 and 2, and includes a sheet feeding cassette (2) and (3), and a sheet feeding mechanism. (4) and a conveyance roller pair (5) are provided.
The paper feed cassette (2) is a large-capacity paper feed cassette (2) that can accommodate a large amount of small size paper such as A4 size that is frequently used, and is arranged side by side. The paper feed cassette (3) Is a large size paper feed cassette (3) arranged in the upper and lower stages, which accommodates large size paper such as B4 size and A3 size.
The paper feed mechanism (4) includes a pickup roller (41), a paper feed roller (42), and a separation roller (43).
The large-capacity paper feed cassette (2) is detachably installed on the apparatus main body as shown in FIG.

The paper feeding device (11) takes out the paper (S) from either the large capacity paper feeding cassette (2) or the large size paper feeding cassette (3) according to the paper size selected in the image forming operation, and forms an image. Send to part (13).
The paper (S) accommodated in the large-capacity paper feed cassette (2) or the large-size paper feed cassette (3) is picked up from the top surface by the pickup roller (41) and sent out by the paper feed roller (42). It is. When a plurality of sheets (S) are picked up, the separation roller (43) rotates reversely to prevent double feeding and the sheets (S) are sent out one by one.

FIG. 3 is a perspective view showing the structure of the large-capacity paper feed cassette (2), as seen from the rear right side of the apparatus and slightly above.
As shown in FIG. 3, the large-capacity paper feed cassette (2) is a box with a bottom having an open top surface, and has a stacking plate (21) in which a bundle of sheets (S) can be stacked and moved up and down. Externally, a wire (22) connected to the stacking plate (21), a reel (23) for winding and unwinding the wire (22), and a rotating shaft (24) for rotating the reel (23) The sheet remaining amount detecting means (25) is provided.

Further, the paper feeding device (11) is provided with a motor (not shown) for rotating the rotating shaft (24) inside the device main body into which the paper feeding cassette is inserted and removed, and the rotating shaft (24) has a large capacity. When the paper feed cassette (2) is inserted and connected, it is connected to the motor, and when it is pulled out, it is removed.
In this embodiment, the motor, the wire (22), the reel (23), and the rotating shaft (24) are used as the lifting means for the stacking plate (21), but the lifting means is not limited to this. .

FIG. 4 is a rear view structural view of the large-capacity paper feed cassette (2).
As shown in FIG. 4, the sheet remaining amount detecting means (25) is rotatably attached to the back surface of the three sensors (251a), (251b) and (251c) and the large capacity sheet feeding cassette (2). It has a detection member (252).

FIG. 5 is a diagram showing the detection member (252).
As shown in FIG. 5, the detection member (252) has a plurality of detected portions (253a), (253b), and (253c) formed in an arc shape on three rows of concentric circles.
Here, the three sensors (251a), (251b), and (251c) are collectively referred to as the sensor (251), and the three rows of detected portions (253a), (253b), and (253c) are collectively referred to. Let it be a detected part (253).

The three sensors (251) are fixed inside the main body of the paper feeding device (11), and when the large-capacity paper feeding cassette (2) is removed, the detected part (253) cannot be detected. When inserted, it becomes a position where the detected part (253) can be detected.
Sensors (251a), (251b), and (251c) detect detected parts (253a), (253b), and (253c), respectively.
Each sensor (251a), (251b), (251c) is turned on when the detected parts (253a), (253b), (253c) are detected, and is turned off when not detected.

The detection member (252) is a disc having a gear (254) on the outer periphery, and the gear (254) meshes with the gear (26) of the rotating shaft (24).
The gear ratio between the gear (254) and the gear (26) is such that the detection member (252) makes one round when the stacking plate (21) moves from when the paper is fully loaded to empty, that is, from the lowest position to the highest position. Is set to

Although there are three sensors (251), it is sufficient that there are a plurality of sensors. The detected part (253) has three rows when there are three sensors (251) and four rows when there are four sensors (251). However, the present invention is not limited to this.
In the present embodiment, the sensor (251) and the detected part (253) are a photosensor and an arc-shaped protrusion that can shield the photosensor as shown in FIG. 3, but the present invention is not limited to this. And an arc-shaped slit that can transmit light to the disc may be provided as the detected portion.
Although the shape of the detection member (252) is a disk, it is not limited to this. For example, the detection member is arranged on a plurality of rows of parallel straight lines as a rectangular plate, and a rack is formed on one side. You may make it mesh with a gear (26) by a rack.

When the sheet (S) is loaded into the large-capacity sheet cassette (2) and inserted into the body of the sheet feeder (11), the stacking plate (21) is raised, and the uppermost surface of the sheet (S) is a predetermined sheet. Reach the paper feed position.
The distance from the top surface of the sheet (S) to the sheet feeding position when the large-capacity sheet cassette (2) is fully loaded is not particularly limited, but is 10 mm in this embodiment.

  The paper feeding device (11) feeds the paper (S) to the image forming unit (13), and the motor (not shown) is reduced as the paper (S) in the large capacity paper feeding cassette (2) decreases. ), The rotating shaft (24) and the reel (23) are rotated to wind the wire (22), the stacking plate (21) is raised, and the uppermost surface of the sheet (S) is sequentially aligned with a predetermined sheet supply position. .

The sensors (251) are sequentially turned on / off one by one as the loading plate (21) rises.
The remaining paper amount detection means (25) is switched to the on / off state at that point in time according to all the on / off states of the three sensors (251) (hereinafter referred to as switching mode). Is called).
Since the position of the stacking plate (21) is recognized by a combination of all on / off states of the sensor (251) and the switching mode, the remaining amount of paper is detected in more stages.

  By having the remaining paper amount detecting means (25), the paper feeding device (11) is more accurate than a paper feeding device having a detecting means that uses only the on / off state of the sensor as a judgment material. The remaining amount can be detected.

  When any one of the sensors (251) is switched on / off in accordance with the rise of the loading plate (21), it further rises from the position of the loading plate (21). The distance (rising distance) from the top of the sheet (S) to the position of the stacking plate (21) when switching (hereinafter simply referred to as the section) is the sheet feeding position from the top surface of the sheet (S) when the large capacity sheet feeding cassette (2) is fully loaded. It is preferable that the distance is shorter than 10 mm (10 mm in this embodiment). In the present embodiment, the distance between each section is 9 mm.

As described above, when the large-capacity paper feed cassette (2) is inserted from the removed state, the uppermost surface of the paper (S) is raised to the paper feed position. The rising distance of the loading plate (21) at that time is 10 mm when fully loaded, and is 10 mm or more when not fully loaded.
Accordingly, if the distance between each section is shorter than 10 mm, the sensor (251) is used at least once when the top surface of the sheet (S) is raised to the sheet feeding position after the large capacity sheet cassette (2) is inserted. Since the on / off state is switched, the remaining amount of paper can be detected before the paper feeding operation.

When the large-capacity paper feed cassette (2) is inserted in the main body of the paper feed device (11), it is preferable that at least one of the three sensors (251) is in an on state.
When the large-capacity paper cassette (2) is removed from the paper feeder (11), all the sensors (251) are in an off state, and at least one of them is in an on state when being inserted. As a result, the remaining paper amount detection means (25) can also serve as confirmation of insertion of the large capacity paper feed cassette (2), so that it is not necessary to provide detection means such as a sensor for confirmation of insertion. This is because the number of members can be reduced.

Table 1 shows an example of combinations of on / off states and switching modes of the sensor (251).
In Table 1, A, B, and C mean the sensors (251a), (251b), and (251c), respectively, “◯” means an on state, and “x” means an off state.
Section 0 is a section in which the large-capacity paper cassette (2) is fully loaded, that is, the stacking plate (21) is located from the lowest position to 9 mm, and section 18 is empty in the large-capacity paper cassette (2). That is, it is a section where the loading plate (21) is located at the highest position.
The switching mode indicates switching in the sections 0 to 1, switching in the sections 1 to 2,..., Switching in the sections 17 to 18 in order from the bottom of Table 1.

Considering that at least one of the three sensors (251) is in the on state, combining the on / off states and switching modes of all the sensors, as shown in Table 1, the maximum 18 times can be switched.
Although the number of sections may be set to be small and the number of possible switching times may be less than 18, it is preferable that the maximum is 18 in order to detect the remaining amount of paper with higher accuracy.
In the present embodiment, the number of sensors (251) is three, but when the number of sensors is four, the switching can be performed up to 56 times, and when the number of sensors is n, the number of sensors (251) is maximum (2 ⁿ × n-2 × n). Can be switched.

Tables 2, 3, and 4 show examples of combinations of the on / off states and switching modes of the sensors A, B, C, and D when there are four sensors.
As in Table 1, “◯” means an on state, “x” means an off state, and the switching mode is switched in the sections 0 to 1 in order from the bottom of Table 4 to the top of Table 2, and in the sections 1 and 2. Switching,... Indicates switching in sections 55-56.

In order to be able to switch 18 times when there are three sensors (251), as shown in FIG. 5, when the detected part (253) is formed on three rows of concentric circles, It is necessary to arrange 3 pieces each.
When four sensors are formed on four rows of concentric circles, seven pieces are arranged in each row, and when n sensors are formed on n rows of concentric circles, {(2 ⁿ × n −2 × n) / (2 × n)} pieces, that is, {2 ⁽ⁿ⁻¹⁾ −1} pieces need to be arranged.
In addition, in the case where the number of sensors is a detected portion of an array of {(2 ⁿ × n−2 × n) / (2 × n)} pieces on n rows of concentric circles, each piece has a central angle Becomes a circular arc of [{360 / (2 ⁿ × n−2 × n)} × m] °. Here, “m” indicates the number of sections in which the ON state of the sensor continues.
Note that the arrangement of the detected parts is not limited to this. For example, when the number of sensors is n, the arrangement of the sensors may be devised to arrange the detected parts on concentric circles having fewer than n columns. Is possible.

The paper feeding device (11) preferably has storage means such as a memory.
Since the position of the stacking plate (21) before the power is turned off can be stored even after the apparatus power is turned off, the stacking plate (21) is raised in order to detect the remaining amount of paper when the power is turned on again. This is because the remaining amount of paper can be recognized without checking the switching of the sensor (251).

Further, after the on / off state of the sensor (251a) is switched in accordance with the rise of the stacking plate (21), the next sensor to be switched on / off is the sensor (251b) or (251c), and the sensor (251b) It is preferable that the sensor (251a) or (251c) is switched next after the switching of (), and the sensor (251a) or (251b) is switched next after the switching of the sensor (251c).
Hereinafter, this reason will be described.

  If the position of the loading plate (21) before the power is turned off is near the boundary of any section, it can be re-established before and after the power is turned off due to external impact during power-off, power-off, sensor chattering at the time of power-on, etc. After loading, the section where the loading plate (21) is located may be shifted, and the sensor (251) may be switched on / off.

If the on / off state of the sensor (251) is switched when the power is turned off and then turned on again when the loading plate (21) is located in a certain section, the same sensor operates by switching before and after a certain section. In this case, the on / off state of the sensor (251) is the same in the section before and after the certain section.
In this case, even if the position of the loading plate (21) before the power is cut off is stored, it is not known in which section it is shifted, and the loading plate (21) is raised to check the switching of the sensor (251). Otherwise, the remaining amount of paper cannot be detected.
However, if different sensors are operating before and after a certain section, the ON / OFF state of the sensor (251) is different between the previous section and the subsequent section of the certain section. Based on the position, it is clear which section has shifted, and the remaining amount of paper can be detected without raising the stacking plate (21).

  The present invention is not limited to the above embodiment, and includes the following contents.

  In the above embodiment, the remaining sheet amount detecting means (25) according to the present invention is applied to the large capacity sheet feeding cassette (2). However, the remaining sheet amount detecting means (25) is a large capacity sheet feeding cassette (2). The present invention is not limited to 2), but may be applied to a small-capacity paper feed cassette such as the large-size paper feed cassette (3).

  In the above embodiment, a copying machine has been described as an example of the image forming apparatus (1) to which the paper feeding device (11) according to the present invention is applied. However, the paper feeding device (11) according to the present invention is applicable. The apparatus to be used is not limited to a copying machine, but may be another image forming apparatus such as a printer or a facsimile machine, and each sheet is fed from a sheet bundle such as a normal printing machine or sorting machine. The present invention can also be applied to an apparatus configured to send out and perform predetermined processing.

  INDUSTRIAL APPLICABILITY The present invention is applied to an image forming apparatus such as a copying machine, a printer, and a facsimile machine, an apparatus configured to send out sheets one by one from a sheet bundle such as a normal printing machine and a sorting machine and perform predetermined processing. It is what is done.

1 is a schematic diagram illustrating an internal structure of an embodiment of an image forming apparatus to which a paper feeding device according to the present invention is applied. 1 is an external perspective view of an embodiment of an image forming apparatus to which a paper feeding device according to the present invention is applied. It is a perspective view of a sheet feeding cassette in the sheet feeding apparatus according to the present invention. It is a rear view structural drawing of the paper feed cassette in the paper feeder concerning the present invention. It is a figure which shows the detection member of the paper remaining amount detection means in the paper feeder which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 11 Paper feeder 2 Large capacity paper cassette 21 Stacking plate 24 Rotating shaft 25 Paper remaining amount detection means 251 Sensor 252 Detection member 253 Detected part 254 Gear 26 Gear S Paper

Claims (9)

A paper feed cassette that can be inserted into and removed from the apparatus main body and can store paper bundles, a stacking plate that is disposed inside the paper feed cassette and that can stack paper bundles on the upper surface and can be moved up and down, A paper feeding device comprising a raising means for raising the stacking plate and a paper remaining amount detecting means for detecting the remaining amount of paper;
The sheet remaining amount detecting means includes a plurality of detected portions attached to the sheet feeding cassette and operating in response to the rising of the stacking plate, and a plurality of detected portions installed in the apparatus main body for detecting the detected portions. Have a sensor,
The sensor is switched on / off according to the rise of the loading plate,
The paper remaining amount detecting means recognizes the position of the stacking plate in multiple stages by combining the on / off state of all the sensors and the switching mode of the sensor that is switched when reaching the on / off state, A paper feeding device which is means for detecting a remaining amount of paper.   After the on / off state of any one of the sensors is switched in accordance with the rising of the stacking plate, the rising distance of the stacking plate until the next switch of any sensor is the paper feed The paper feeding device according to claim 1, wherein the paper feeding device is shorter than a distance from a top surface of the paper bundle to a paper feeding position when the cassette is fully loaded.   3. The sheet feeding device according to claim 1, wherein at least one of the sensors is in an on state when the sheet feeding cassette is inserted. Each of the sensors is turned on / off one by one,
The detected section has a total of more than 2 ⁿ times (2 ⁿ × n) of on / off state switching in all sensors when the number of sensors is n until the paper feeding cassette is full to empty. The sheet feeding device according to claim 1, wherein the sheet feeding device has an arrangement that can be performed up to −2 × n) times. The raising means is means utilizing the rotation of a motor,
2. The detected portion is formed by forming a plurality of circular arcs on n rows of concentric circles with respect to the n sensors in a disc meshed with a rotating shaft rotated by the motor. 5. The paper feeding device according to any one of 4 to 4.   The sheet feeding device according to claim 1, further comprising a storage unit that stores a position of the stacking plate before the power is turned off even after the device is turned off.   After the on / off state of any one of the sensors is switched according to the rise of the loading plate, the next sensor that is switched on / off is a sensor different from the sensor that was switched immediately before. The sheet feeding device according to claim 6.   The sheet feeding device according to claim 1, wherein the sheet feeding cassette is a large capacity sheet feeding cassette capable of storing a sheet bundle composed of a large number of sheets.   9. An image forming apparatus comprising: the sheet feeding device according to claim 1; and an image forming unit that performs an image forming process on a sheet fed from the sheet feeding device.

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