JP2022034773A - Paper placing apparatus and image formation apparatus - Google Patents

Abstract

To detect a height position of an uppermost surface of plural pieces of paper placed on a paper tray with space saving, low cost, and high accuracy.SOLUTION: A paper placing apparatus includes paper feeding means that feeds transported paper onto a paper tray, paper surface detection means that detects a height position of an uppermost surface of the plural pieces of paper placed on the paper tray, and lifting means that lifts the paper tray according to the height position detected by the paper surface detection means. A photosensor is used as the paper surface detection means.SELECTED DRAWING: Figure 2

Description

The present invention relates to a paper placing device and an image forming device.

In Patent Document 1 below, the height of the top surface of the paper loaded on the output tray is detected by bringing the tip of the paper detection lever into contact with the top surface of the paper loaded on the output tray. , A technique for raising and lowering the output tray according to the height is disclosed.

However, in the technique of Patent Document 1, it is necessary to provide a relatively large and high-cost paper detection lever above the plurality of papers placed on the paper tray. Therefore, in the technique of Patent Document 1, it is not possible to detect the height position of the uppermost surface of a plurality of papers placed on a paper tray in a space-saving manner, at low cost, and with high accuracy.

In order to solve the above-mentioned problems, the paper loading device according to the embodiment includes a paper ejecting means for ejecting the conveyed paper onto a paper tray, and a plurality of papers placed on the paper tray. A paper surface detecting means for detecting the height position of the upper surface and an elevating means for raising and lowering the paper tray according to the height position detected by the paper surface detecting means were provided, and a photo sensor was used as the paper surface detecting means.

According to one embodiment, it is possible to detect the height position of the uppermost surface of a plurality of sheets placed on the paper tray with high accuracy, space saving, and low cost.

The figure which shows the whole structure of the image forming apparatus which concerns on one Embodiment. The figure which shows the specific structure of the paper discharge part provided with the image forming apparatus which concerns on one Embodiment. A plan view showing a configuration around a paper tray in a paper ejection unit according to an embodiment. The figure which shows the installation position of the paper surface detection sensor in the paper discharge part which concerns on one Embodiment. The figure which shows the installation position of the paper surface detection sensor in the paper discharge part which concerns on one Embodiment. The figure which shows the functional structure of the image forming apparatus which concerns on one Embodiment. An activity diagram relating to paper detection by a paper surface detection sensor and lowering control of a paper tray by a tray control unit in an image forming apparatus according to an embodiment. A sequence diagram showing a processing sequence by the image forming apparatus according to an embodiment. The figure which shows the modification of the arrangement of the paper surface detection sensor in the image forming apparatus which concerns on one Embodiment. The figure which shows the modification of the arrangement of the paper surface detection sensor in the image forming apparatus which concerns on one Embodiment. The figure which shows the modification of the arrangement of the paper surface detection sensor in the image forming apparatus which concerns on one Embodiment. The figure which shows the modification of the arrangement of the paper surface detection sensor in the image forming apparatus which concerns on one Embodiment.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

(Structure of image forming apparatus 100)
FIG. 1 is a diagram showing an overall configuration of an image forming apparatus 100 according to an embodiment. FIG. 2 is a diagram showing a specific configuration of a paper ejection unit 130 included in the image forming apparatus 100 according to the embodiment.

The image forming apparatus 100 shown in FIG. 1 is an example of a “paper placing apparatus” and an “image forming apparatus”, and at least has a function of forming an image on the paper P and a paper P on which an image is formed. It is a device having a function of discharging onto a tray 136. Examples of the image forming apparatus 100 include an MFP (Multifunction Peripheral / Product / Printer) having a scanning function, a printer function, a FAX function, and the like.

As shown in FIG. 1, the image forming apparatus 100 includes a paper feeding unit 110, a printing unit 120, and a paper ejection unit 130.

The paper feed unit 110 holds a plurality of sheets P. Further, the paper feeding unit 110 supplies the paper P to be printed to the printing unit 120. The paper feeding unit 110 can hold and supply a plurality of types of paper P having different sizes and the like.

The printing unit 120 forms an image corresponding to the print data on the surface of the paper P supplied from the paper feeding unit 110. For example, the printing unit 120 has a liquid ejection head (not shown) capable of ejecting ink by an inkjet method, and the liquid ejection head ejects ink of a plurality of colors onto the surface of the paper P. , A color image is formed on the surface of the paper P. The printing unit 120 sends the paper P on which the image is formed to the paper ejection unit 130.

The paper ejection unit 130 ejects the paper P conveyed from the printing unit 120. As shown in FIGS. 1 and 2, the paper ejection unit 130 includes a transport roller 131, a clip 133, a belt 134, a stack unit 135, a paper tray 136, a paper surface detection sensor 137, an elevating mechanism 138, and a pair of left and right side plates 139R. , 139L.

The transport roller 131 transports the paper P conveyed from the printing unit 120 to a position where it can be held by the clip 133.

The clip 133 and the belt 134 are examples of "paper ejection means". The clip 133 and the belt 134 are provided above the stack portion 135. The clip 133 holds the tip of the paper P conveyed by the transfer roller 131. The belt 134 conveys the paper P to the upper side of the stack portion 135 by moving the clip 133 holding the paper P to the downstream side. The clip 133 releases the paper P above the stack portion 135. As a result, the clip 133 ejects the paper P to the stack portion 135. The paper P discharged to the stack portion 135 is placed on a paper tray 136 provided on the lower side of the stack portion 135.

The paper surface detection sensor 137 is an example of “paper surface detection means”. The paper surface detection sensor 137 detects the height position of the uppermost surface of a plurality of sheets P placed on the paper tray 136. The elevating mechanism 138 is an example of "elevating means". The elevating mechanism 138 raises and lowers the paper tray 136 according to the height position detected by the paper surface detection sensor 137.

Further, as shown in FIG. 2, the stack portion 135 is provided with a tip alignment member 135A and a rear edge alignment member 135B at a target paper surface height position. The tip alignment member 135A moves rearward to bring the rear end of the paper P into contact with the rear edge alignment member 135B, so that the front end and the rear end of the plurality of sheets P mounted on the paper tray 136 are brought into contact with each other. Align.

Further, as shown in FIG. 2, a vertical flat plate-shaped side plate 139 extending linearly in a direction parallel to the transport direction A of the paper P above the paper tray 136 and at a predetermined height position H1. Is provided. As shown in FIG. 2, on the side plate 139, two sets of paper surface detection sensors 137 (paper surface detection sensor 137-1, paper surface detection sensor 137-2) are arranged in the front-rear direction (direction parallel to the transport direction A of the paper P). ) Are provided side by side. The side plate 139 may be provided with another sensor (for example, a temperature sensor that detects the temperature of the paper tray 136).

FIG. 3 is a plan view showing the peripheral configuration of the paper tray 136 in the paper ejection unit 130 according to the embodiment. As shown in FIG. 3, the paper ejection unit 130 is provided with a pair of left and right side plates 139R and 139L above the left and right end portions of the paper tray 136. Further, as shown in FIG. 3, the paper ejection unit 130 includes two sets of paper surface detection sensors 137 (paper surface detection sensor 137-1 and paper surface detection sensor 137-2). Each paper surface detection sensor 137 includes a light emitting unit 137A and a light receiving unit 137B so that the light emitting unit 137A and the light receiving unit 137B face each other with respect to the pair of left and right side plates 139R and 139L. It is provided. As a result, each paper surface detection sensor 137 is placed on the paper tray 136 with the direction orthogonal to the transport direction A of the paper P (that is, the height direction of the paper P) (that is, the width direction of the paper P) as the detection direction. It is possible to detect the height position of the uppermost surface of the plurality of sheets P.

Specifically, when the light receiving unit 137B does not receive the light emitted from the light emitting unit 137A, each paper surface detection sensor 137 assumes that the light emitted from the light emitting unit 137A is blocked by the paper P and displays the paper P. Can be detected. The elevating mechanism 138 lowers the paper tray 136 until the paper P is not detected by the paper surface detection sensor 137, so that the height position of the uppermost surface of the plurality of paper P placed on the paper tray 136 is always determined. It can be controlled to the height position H1 of.

As shown in FIG. 3, the pair of left and right side plates 139 and the two sets of paper surface detection sensors 137 are in the left-right direction (direction orthogonal to the transport direction A) with respect to the tip alignment member 135A and the rear edge alignment member 135B. It is provided on the outside. As a result, the pair of left and right side plates 139 and the two sets of paper surface detection sensors 137 do not interfere with the tip alignment member 135A and the rear edge alignment member 135B.

The image forming apparatus 100 of the present embodiment uses a photo sensor as the paper surface detection sensor 137. Thereby, as shown in FIGS. 3 and 4, the image forming apparatus 100 of the present embodiment can arrange the paper surface detection sensor 137 on the side of the plurality of papers P placed on the paper tray 136. .. Therefore, in the image forming apparatus 100 of the present embodiment, a paper detecting member (for example, a paper detecting lever of Patent Document 1) is relatively arranged above a plurality of papers P placed on the paper tray 136. There is no need to provide a large space. Further, the image forming apparatus 100 of the present embodiment does not require a paper detecting member (for example, a paper detecting lever of Patent Document 1) that comes into contact with the uppermost surfaces of a plurality of papers P placed on the paper tray 136. Therefore, the image forming apparatus 100 of the present embodiment can detect the height position of the uppermost surface of the plurality of papers P placed on the paper tray 136 in a space-saving manner, at low cost, and with high accuracy.

Further, since the image forming apparatus 100 of the present embodiment can detect the paper P from the side of the paper P by the paper surface detection sensor 137, it can detect the paper P having various paper widths.

4 and 5 are views showing the installation positions of the paper surface detection sensors 137-1 and 137-2 in the paper ejection unit 130 according to the embodiment. FIG. 4 shows a state in which the B2 size paper P is placed on the paper tray 136. FIG. 5 shows a state in which the A3 size paper P is placed on the paper tray 136.

As shown in FIGS. 4 and 5, the paper ejection unit 130 according to the embodiment has paper surface detection sensors 137-1 and 137-2. Each of the paper surface detection sensors 137-1 and 137-2 has a light emitting unit 137A and a light receiving unit 137B arranged to face each other, and is orthogonal to the transport direction A of the paper P (that is, the height direction of the paper P). The direction (that is, the width direction of the paper P) is defined as the detection direction.

The paper surface detection sensor 137-1 is an example of the “first photo sensor”, and is provided in the vicinity of the rear end portion of the paper P placed on the paper tray 136. The paper surface detection sensor 137-1 can detect the height position of the rear end portion of the paper P, which is most likely to be curled (that is, the height position is most likely to be high). As a result, the image forming apparatus 100 according to the embodiment can prevent the height position of the rear end portion of the paper P from being overlooked, so that the rear end portion of the paper P is transferred by the transport roller 131. It is possible to prevent the paper P from colliding with other paper to be conveyed.

The paper surface detection sensor 137-2 is an example of the “second photo sensor”, and is provided in the vicinity of the central portion of the paper tray 136 in the transport direction A. As a result, as shown in FIG. 5, the paper surface detection sensor 137-2 tends to curl when the paper size of the paper P is relatively small and the tip of the paper P is located near the center of the paper tray 136 (the paper surface detection sensor 137-2). That is, the height position tends to be high), and the height position of the tip of the paper P can be detected. Further, as shown in FIG. 4, in the paper surface detection sensor 137-2, when the paper size of the paper P is relatively large and the central portion of the paper P is located near the center of the paper tray 136, the paper P is the paper tray 136. It is possible to detect the height position of the central portion of the paper P, which is likely to be lifted by the air layer remaining when the paper is dropped (that is, the height position is likely to be high).

As shown in FIGS. 4 and 5, in the paper surface detection sensor 137-1, the light emitting unit 137A is provided on the left side (that is, the left side plate 139L), and the light receiving unit 137B is provided on the right side (that is, the right side plate 139R). It is provided. On the other hand, in the paper surface detection sensor 137-2, the light emitting unit 137A is provided on the right side (that is, the right side plate 139R), and the light receiving unit 137B is provided on the left side (that is, the left side surface plate 139L). That is, in the paper surface detection sensor 137-1 and the paper surface detection sensor 137-2, the light emitting directions of the light emitting unit 137A are opposite to each other. As a result, in the image forming apparatus 100 of the present embodiment, the light emitted from one of the paper surface detection sensors 137-1 and 137-2 is erroneously detected by the other paper surface detection sensor 137. Can be suppressed. Further, in the image forming apparatus 100 of the present embodiment, one of the paper surface detection sensors 137-1 and 137-2, the paper surface detection sensor 137, receives ambient light and cannot normally detect the paper P. Even in this case, the other paper surface detection sensor 137 does not receive the ambient light and can normally detect the paper P.

The image forming apparatus 100 of the present embodiment has two paper surface detection sensors 137-1 and 137-2, but is not limited to this. For example, the image forming apparatus 100 may have any one of the two paper surface detection sensors 137-1 and 137-2 (for example, only the paper surface detection sensor 137-1 that detects the rear end portion of the paper P). good. In this case, the image forming apparatus 100 can reduce the cost as compared with the case where the image forming apparatus 100 has two paper surface detection sensors 137-1 and 137-2.

FIG. 6 is a diagram showing a functional configuration of the image forming apparatus 100 according to the embodiment. As shown in FIG. 6, the printing unit 120 includes an image printing unit 721, a paper transport unit 722, and a communication unit 723. The image printing unit 721 forms an image corresponding to the print data on the surface of the paper P. In the paper transport unit 722, the printing unit 120 transports the paper P on which the image is formed to the paper ejection unit 130. The communication unit 723 transmits and receives various information (for example, the transport status of the paper P) to and from the paper ejection unit 130 by communicating with the paper ejection unit 130.

Further, as shown in FIG. 6, the paper ejection unit 130 includes a communication unit 731, a sensor monitoring unit 732, a tray control unit 733, a clip control unit 734, and a paper alignment member control unit 735. By communicating with the printing unit 120, the communication unit 731 transmits and receives various information (for example, the transport status of the paper P) to and from the printing unit 120. The sensor monitoring unit 732 monitors changes in the detected values of various sensors related to the paper ejection unit 130, and notifies each control unit of the changes. The tray control unit 733 controls the elevating operation of the paper tray 136 by the elevating mechanism 138. The clip control unit 734 controls the ejection operation of the paper P by the clip 133 and the belt 134. The paper alignment member control unit 735 controls the operation of aligning the front end portion and the rear end portion of the paper P by the tip alignment member 135A.

The printing unit 120 does not participate in the control content of the paper ejection unit 130, and notifies the paper ejection unit 130 of the start and end of the paper ejection operation period. The paper ejection unit 130 starts and ends the paper ejection operation in response to the notification from the printing unit 120.

Each control unit of the image forming apparatus 100 described above can be realized by one or a plurality of processing circuits. Here, the "processing circuit" in the present specification is a processor programmed to execute each function by software such as a processor implemented by an electronic circuit, or each control unit of the image forming apparatus 100 described above. It shall include devices such as ASICs (Application Specific Integrated Circuits), DSPs (digital signal processors), FPGAs (field programmable gate arrays) and conventional circuit modules designed to be used.

FIG. 7 is an activity diagram relating to the detection of the paper P by the paper surface detection sensor 137 and the lowering control of the paper tray 136 by the tray control unit 733 in the image forming apparatus 100 according to the embodiment.

Immediately after the power is turned on, the paper tray 136 lowering control is invalid for the paper ejection unit 130, and when the printing start notification is received, the paper tray 136 lowering control is enabled by detecting the paper P by the paper surface detection sensor 137. Become.

After the start of printing, the tray control unit 733 of the paper ejection unit 130 lowers the paper tray 136 according to the change in the detection value of the paper surface detection sensor 137. For example, the tray control unit 733 lowers the paper tray 136 by a certain amount when any one of the paper surface detection sensors 137 detects the paper P.

However, the tray control unit 733 includes "the paper surface detection sensor 137 remains in the state of detecting the paper P for T seconds" as a condition for lowering the paper tray 136. Note that T may be any time, for example, 5 seconds. As a result, in the image forming apparatus 100 according to the embodiment, when the paper P falls from the clip 133, the paper P is instantaneously detected by the paper surface detection sensor 137, and the paper tray 136 is detected by this detection. It is possible to prevent accidental lowering.

FIG. 8 is a sequence diagram showing a processing sequence by the image forming apparatus 100 according to the embodiment.

(1.) First, the power of the printing unit 120 is turned on. (2.) Next, the power of the paper ejection unit 130 is turned on. (3.) Next, in the paper ejection unit 130, the sensor monitoring unit 732 monitors the sensor detection value of the paper surface detection sensor 137 by polling. (4.) Then, when printing is started in the printing unit 120, the communication unit 723 notifies the printing unit 130 of the printing start.

(5.) Next, in the paper ejection unit 130, when the communication unit 731 receives the notification of the start of printing from the printing unit 120, it notifies the tray control unit 733 of the start of printing. (6.) When the tray control unit 733 receives the notification of the start of printing, the tray control unit 733 starts listening for the notification from the sensor monitoring unit 732.

(7.) After that, when the paper surface detection sensor 137 detects the paper P, the sensor monitoring unit 732 notifies the tray control unit 733 that the paper P has been detected. (8) Upon receiving the notification of the detection of the paper P, the tray control unit 733 starts measuring the duration of the state in which the paper P is detected.

(9.) Then, when the sensor monitoring unit 732 notifies that the paper P is no longer detected before the duration reaches T seconds, the tray control unit 733 (10.) Tray control unit 733. Inquires the sensor monitoring unit 732 about the detection value of each paper surface detection sensor 137. (11.) As a result, when the detection values of all the paper surface detection sensors 137 do not detect the paper P, the tray control unit 733 performs the sequence 6. Return the process to. (12.) On the other hand, when the detection value of at least one of the paper surface detection sensors 137 detects the paper P, the tray control unit 733 continues to measure the duration.

(13.) Then, when the duration reaches T seconds, the tray control unit 733 lowers the paper tray 136 by X mm. However, X is a predetermined amount of descent. For example, the optimum value of X is obtained in advance based on the threshold value T, the ejection interval of the paper P, the thickness of the paper P, and the like. (14.) After that, the tray control unit 733 inquires the sensor monitoring unit 732 about the detection value of each paper surface detection sensor 137. (15.) As a result, when the detection values of all the paper surface detection sensors 137 do not detect the paper P, the tray control unit 733 performs the sequence 6. Return the process to. (16.) On the other hand, when the detection value of at least one of the paper surface detection sensors 137 detects the paper P, the tray control unit 733 performs the sequence 8. Return the process to.

When the printing is completed in the printing unit 120, the communication unit 723 notifies the paper ejection unit 130 of the printing completion. (17.) Then, when the communication unit 731 receives the notification of the end of printing from the printing unit 120 in the paper ejection unit 130, it notifies the tray control unit 733 of the end of printing. (18.) When the tray control unit 733 receives the notification of the end of printing, the tray control unit 733 ends the standby for the notification from the sensor monitoring unit 732.

(Modified example of arrangement of paper surface detection sensor 137)
9 to 12 are views showing a modified example of the arrangement of the paper surface detection sensor 137 in the image forming apparatus 100 according to the embodiment.

For example, as shown in FIG. 9, the paper ejection unit 130 of the image forming apparatus 100 is provided with three or more paper surface detection sensors 137 arranged side by side in a direction parallel to the transport direction A (that is, in the height direction of the paper P). May be done. For example, in the example shown in FIG. 9, the paper ejection unit 130 is provided on both the left and right sides of the paper P placed on the paper tray 136, in addition to the paper surface detection sensors 137-1 and 137-2 described so far. Further, the paper surface detection sensors 137-3 and 137-4 are provided. As a result, the image forming apparatus 100 can detect the paper P in more places, so that the detection accuracy of the paper P can be improved.

Further, for example, as shown in FIG. 10, the paper ejection unit 130 of the image forming apparatus 100 is provided on both the left and right sides of the paper P placed on the paper tray 136, and the paper surface detection sensors 137-1 and 137-2 are provided. In addition, the paper P is provided in front of and behind the paper P placed on the paper tray 136, in a direction parallel to the transport direction A of the paper P (that is, in the height direction of the paper P), and on the right side of the paper P and on the right side of the paper P. Further, a paper surface detection sensor 137-5, 137-6 (an example of a "third photo sensor" and a "fourth photo sensor") may be further provided, in which the direction along the left side is the detection direction. As a result, the image forming apparatus 100 can detect the paper P over the entire outer circumference of the paper P where curling is likely to occur, so that the detection accuracy of the paper P can be improved.

Further, for example, as shown in FIGS. 11 and 12, the paper ejection unit 130 of the image forming apparatus 100 intersects two paper surface detection sensors 137-7 and 137-8 in the detection directions of both on the paper P. It may be provided as such. In this case, as shown in FIGS. 11 and 12, each paper surface detection sensor 137-7, 137-8 is a paper surface detection sensor so that the height positions of the diagonal portion and the central portion of the paper P can be detected. 137-7 (an example of the "fifth photo sensor") is arranged on an extension of one of the diagonal lines of the paper P so as to be in the detection direction along one of the diagonal lines of the paper P, and the paper surface detection sensor 137-8 is arranged. (An example of the "sixth photosensor") is preferably arranged on an extension of the other diagonal of the paper P so as to be in the detection direction along the other diagonal of the paper P. As a result, the image forming apparatus 100 detects the height positions of the four corners and the center of the paper P, whose height positions are easily changed by curling, by two relatively small number of paper surface detection sensors 137. Can be done. Further, in this case, as shown in FIGS. 11 and 12, it is preferable that the arrangement positions of the paper surface detection sensors 137-7 and 137-8 are different depending on the size of the paper P to be detected. Further, in this case, by making the light emission timing of the paper surface detection sensor 137-7 different from the light emission timing of the paper surface detection sensor 137-8, the light emission of the paper surface detection sensor 137-7 and the light emission of the paper surface detection sensor 137-8 are different. The emitted light may not interfere with each other.

Although the preferred embodiments of the present invention have been described in detail above, the present invention is not limited to these embodiments, and various modifications or modifications are made within the scope of the gist of the present invention described in the claims. It can be changed.

100 Image forming device 110 Feeding unit 120 Printing unit 130 Paper ejection unit 131 Transport roller 133 Clip 134 Belt 135 Stacking unit 135A Tip aligning member 135B Rear edge aligning member 136 Paper tray 137 Paper surface detection sensor 137-1 Paper surface detection sensor (1st) Photo sensor)
137-2 Paper surface detection sensor (second photo sensor)
137-3 Paper surface detection sensor 137-4 Paper surface detection sensor 137-5 Paper surface detection sensor (third photo sensor)
137-6 Paper surface detection sensor (4th photo sensor)
137-7 Paper surface detection sensor (fifth photo sensor)
137-8 Paper surface detection sensor (sixth photo sensor)
137A Light emitting part 137B Light receiving part 138 Elevating mechanism 139R Right side plate 139L Left side plate P Paper H1 Height position

Japanese Unexamined Patent Publication No. 2000-86055

Claims (10)

Paper ejection means for ejecting the conveyed paper onto the paper tray,
A paper surface detecting means for detecting the height position of the uppermost surface of a plurality of the sheets placed on the paper tray, and a paper surface detecting means.
A means for raising and lowering the paper tray according to the height position detected by the paper surface detecting means is provided.
A paper placing device characterized by using a photo sensor as a paper surface detecting means. The paper according to claim 1, wherein the photo sensor is provided at a position on the side of the paper placed on the paper tray so that the detection direction is a direction orthogonal to the transport direction of the paper. Mounting device. The second aspect of claim 2, wherein a plurality of the photosensors are provided side by side in a direction parallel to the transport direction of the paper at a position on the side of the paper placed on the paper tray. Paper loading device. A claim characterized in that a first photosensor is provided at a position on the side of the paper placed on the paper tray and in the vicinity of the rear end portion of the paper placed on the paper tray. Item 3. The paper placing device according to Item 3. The fourth aspect of claim 4, wherein a second photosensor is provided at a position on the side of the paper placed on the paper tray and in the vicinity of the central portion of the paper tray in the transport direction. Paper loading device. The paper placement according to claim 5, wherein the first photosensor and the second photosensor have a light emitting portion and a light receiving portion facing each other, and the light emitting directions of the light emitting portions are different from each other. Device. The paper loading device according to any one of claims 2 to 6, further comprising one or a plurality of the photosensors whose detection direction is a direction parallel to the paper transport direction. A third photosensor whose detection direction is parallel to the paper transport direction and along the right side of the paper.
A fourth photosensor whose detection direction is parallel to the paper transport direction and along the left side of the paper.
7. The paper placing device according to claim 7. A fifth photosensor whose detection direction is a direction along one diagonal of the paper,
A sixth photosensor whose detection direction is the direction along the other diagonal of the paper,
The paper placing device according to claim 1, wherein the paper placing device is provided. Paper ejection means for ejecting the conveyed paper onto the paper tray,
A paper surface detecting means for detecting the height position of the uppermost surface of a plurality of the sheets placed on the paper tray, and a paper surface detecting means.
A means for raising and lowering the paper tray according to the height position detected by the paper surface detecting means is provided.
An image forming apparatus characterized in that a photo sensor is used as a paper surface detecting means.

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