JP2002068561A - Sheet loader and sheet processor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sheet loader and a sheet processor capable of simplifying and miniaturizing the constitution, capable of improving productivity and capable of coping with required various loading capacity. SOLUTION: A control means can lift a sheet loading tray 2 by a lifting means when a position of the sheet loading tray 2 detected by a position detecting means is above the prescribed detecting reference height, and can only lower the sheet loading tray 2 by the lifting means when the position of the sheet loading tray 2 is below the detecting reference height.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a copying machine having a function of forming an image on a recording medium such as a sheet.
The present invention relates to a sheet processing apparatus such as a printer or a facsimile apparatus, and particularly to a sheet stacking apparatus provided in these apparatuses.

[0002]

2. Description of the Related Art Heretofore, in this type of sheet processing apparatus, in a sheet discharge stacking apparatus for stacking sheets connected to an image forming apparatus or the like, a sheet on which an image is formed by the image forming apparatus is sequentially discharged. , And are sequentially stacked on a paper stack tray in a face-up or face-down state. The paper discharge stacker device has variously devised to improve the alignment of the paper discharge stacked state. As one of the methods, there is a method of reducing the sheet drop height when the sheet is discharged. The paper loading tray is sequentially lowered according to the amount of paper loaded, so that the height position of the uppermost loaded paper is always at a predetermined height with respect to the discharge roller (so that the distance between the discharge roller and the uppermost paper is constant. ), There is a device that adjusts the height of the loading tray.

In order to control the elevation of the paper stacking tray of the above apparatus, a paper height sensor for detecting the height position of the uppermost paper is provided. When the uppermost sheet height becomes higher, the stacking tray is lowered by a predetermined amount by the stacking tray elevating mechanism. In addition, when the user removes an arbitrary number of sheets on the output stacking tray, the height of the uppermost sheet of the stacked sheets is set to a predetermined height so that the discharge alignment of the next sheet to be output does not deteriorate. The paper stacking tray is raised by the lifting mechanism until the height reaches the height. By performing such control, it is configured as one method of improving the discharge stacking alignment of the paper discharged to the discharge stacker device.

[0004]

However, in the case of the above-described prior art, the following problems have occurred.

(1) When a user removes a sheet near the uppermost sheet by a user when the user has removed a sheet near the uppermost sheet even when the stacking amount of sheets is large, or even when the sheet is almost full, the uppermost sheet is raised. It is necessary for the height to maintain a predetermined height so that the alignment is not deteriorated. For this reason, as the amount of stacked paper increases, the load of the sheets stacked on the stacking tray increases, and it is necessary to have an elevating mechanism that raises the stacking tray even at the maximum stacking amount. In order to satisfy the above conditions, a drive system that supports high torque and high torque of
There are problems, such as a large power supply and an increase in the size of the device.

(2) There is a problem that the size and cost of the apparatus are increased due to the problem (1).

(3) In consideration of the case where the amount of loaded paper is large, restrictions are imposed on a lifting motor, a driving system, a power supply, and the like, and it is necessary to set the lifting speed of the paper loading tray relatively slowly. For this reason, the time required for the paper stacking tray to move from the lowermost position to the uppermost position becomes extremely long. Accordingly, the waiting time of the image forming apparatus is lengthened, and the state in which the next job cannot be received continues for a long time.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art, and it is an object of the present invention to achieve simplification of the configuration, downsizing, and improvement in productivity.
An object of the present invention is to provide a sheet stacking apparatus and a sheet processing apparatus that can cope with various required stacking capacities.

[0009]

In order to achieve the above object, according to the present invention, there is provided a sheet stacking means for stacking a conveyed sheet, and provided at a predetermined height on the sheet stacking means. Sheet height detecting means for detecting, at the predetermined height, an uppermost sheet stacked on the sheet stacking means; and a top sheet stacked on the sheet stacking means, wherein the sheet height detecting means detects the uppermost sheet. Control means for moving the sheet stacking means up and down by means of elevating means so as to be detected at the height of the sheet stacking apparatus, comprising: a position detecting means for detecting a position of the sheet stacking means in the height direction, When the position of the sheet stacking means detected by the position detecting means is higher than a predetermined detection reference height, the control means can move the sheet stacking means up and down by the elevating means. And then, when the position of the sheet stacking means is equal to or less than the reference height The detectable, characterized in that to allow only the lowering of the sheet stacking means by said lifting means.

When the sheet height detecting means detects that the uppermost sheet loaded on the sheet loading means is in a state of existence or nonexistence, the control means includes the sheet loading means by the position detecting means. When the position of the sheet stacking means detected by the position detecting means is higher than the detection reference height, the sheet stacking means can be moved up and down by the elevating means. When the position of the stacking means is equal to or lower than the detection reference height, it is also preferable that the sheet stacking means is lowered by the elevating means, or the elevating means is stopped.

It is also preferable that the detection reference height is set at a plurality of positions in accordance with the type of sheets stacked on the sheet stacking means.

When the position of the sheet stacking means detected by the position detecting means is higher than a first detection reference height, the control means enables the sheet stacking means to be lifted and lowered by the elevating means. If the position of the sheet stacking means is between the first detection reference height and a second detection reference height provided below the first detection reference height, Accordingly, the sheet stacking means can be moved up and down by the elevating means, or
The elevating means only allows the sheet stacking means to be lowered, and when the position of the sheet stacking means is below the second detection reference height, the elevating means only allows the sheet stacking means to be lowered. It is also suitable.

When a plurality of types of sheets are stacked on the sheet stacking means, the control means sets a third one of the plurality of types of sheets corresponding to a sheet having the largest unit weight. Only when the position of the sheet stacking means is higher than the detection reference height, the sheet stacking means can be moved up and down by the elevating means, and when the position of the sheet stacking means is equal to or less than the third detection reference height. It is also preferable that the sheet stacking means can only be lowered by the lifting means.

[0014] The position detecting means may be configured such that the sheet stacking means has a height equal to a half of the maximum stacking height of the sheet stacking means and 1
It is also preferable to detect the sheet stacking means when the sheet stacking means is substantially located at a height of / 4.

Preferably, the position detecting means is provided so as to be located at the detection reference height, and detects that the sheet stacking means has passed the detection reference height.

A sheet detecting means for detecting whether or not a sheet is loaded on the sheet loading means, wherein the control means detects by the sheet detecting means that no sheet is loaded on the sheet loading means. In this case, it is also preferable that the sheet stacking means is raised by the elevating means regardless of the position of the sheet stacking means.

A sheet processing apparatus includes the sheet stacking apparatus described above, and sheet processing means for discharging a sheet on which an image has been formed by the image forming means to the sheet stacking apparatus.

[0018]

Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. However, the dimensions of the components described in this embodiment,
The material, the shape, and the relative arrangement thereof should be appropriately changed depending on the configuration of the apparatus to which the invention is applied and various conditions, and are not intended to limit the scope of the invention to the following embodiments.

(Embodiment 1) Referring to FIGS. 1 to 7,
A sheet discharging device as a sheet stacking device according to the first embodiment will be described.

In FIGS. 1 and 2, reference numeral 1 denotes a main body of a sheet discharging apparatus which receives sheets discharged from an image forming apparatus constituting a sheet processing apparatus at a predetermined conveying speed and sequentially stacks the sheets, and P denotes an image forming apparatus. Sheet conveyed by
Reference numeral 2 denotes a sheet stacking tray serving as a sheet stacking unit of the sheet discharging device 1, reference numeral 3 denotes an entrance guide for receiving the sheet P conveyed by the image forming apparatus, and reference numeral 4 denotes a sheet P to be discharged to the sheet stacking tray 2. Discharge rollers for 5 pairs
Is a sheet height sensor flag as a sheet height detecting means for detecting the height of the uppermost sheet on the sheet stacking tray 2, and detects the position by shielding a sensor (not shown) from light.

Describing the lifting / lowering means, reference numeral 6 denotes a pulley for driving the drive belt 7, which is arranged in front of and behind the sheet discharging device 1 so as to span a sheet. Reference numeral 7 denotes a drive belt, and reference numeral 8 denotes a drive unit for driving the pulley 6. The drive unit is configured to be able to change the moving direction of the belt 7 by forward and reverse rotation of the drive unit. Reference numeral 9 denotes a pulley for holding the tension of the belt 7, which is disposed across the sheet in front of and behind the sheet discharging device 1 like the pulley 6. Reference numeral 10 denotes an elevating roller for maintaining a tray angle when the sheet stacking tray 2 is moved up and down, and is arranged on a side surface of the sheet stacking tray 2 at a predetermined distance. The elevating roller 10 is similarly provided on the side surface of the sheet stacking tray 2 on the opposing surface portion across the sheet. Numeral 11 denotes an elevating guide which is provided with a parallel portion so as to sandwich the elevating roller 10 and guides the elevating roller in the elevating direction. The elevating guide 11 is provided at an opposing portion across the sheet, and has a function of smoothly guiding the elevating of the sheet stacking tray 2.

A sensor flag 12 provided on a side surface of the sheet stacking tray 2 and a photo sensor 13 serving as a first sensor unit for detecting the sensor flag 12
a constitutes a position detecting means, and the photo sensor 1
Reference numeral 3a denotes a first detection reference height (a predetermined detection reference height, which can detect that the sheet stacking tray 2 has reached a predetermined height.
(A third detection reference height). Further, the sensor flag 12 and the photo sensor 13b as the second sensor unit also constitute a position detecting unit,
The photo sensor 13b is disposed at a predetermined position as a second detection reference height that can detect that the sheet stacking tray 2 has reached a predetermined height.

Reference numeral 14 denotes a belt fixing portion provided upstream of the sheet stacking tray 2 in the sheet conveying direction and connected to both the front and rear of the belt 7. Reference numeral 15 denotes a sheet presence / absence sensor as sheet detection means provided on the sheet stacking surface of the sheet stacking tray 2, which can detect that a sheet is present on the sheet stacking tray 2. FIG. 5 is a drawing showing two sheet stacking trays, and is a drawing showing each configuration in an easily understandable manner.

The operation of the control unit of the paper discharge device 1 according to the present embodiment having the above configuration will be described below. FIG. 10 is a diagram for explaining the operation of the paper discharge device 1.

When the power is turned on, the control means of the sheet discharging device 1 first checks whether the sheet height sensor flag 5 has detected the sheet height. When the sheet height is detected, the sheet stacking tray 2 is not moved up and down, and the sheet discharge stacking is enabled.

If the sheet height is not detected by the sheet height sensor flag 5, the sheet presence / absence sensor 15 detects whether or not sheets are stacked on the sheet stacking tray 2. When it is detected that there is no sheet on the sheet stacking tray 2, the lifting motor in the driving unit 8 is rotationally driven in the direction in which the sheet stacking tray 2 is lifted to rotate the pulley 6. As a result, the belt 7 starts lifting the sheet stacking tray 2 upward. Sheet loading tray 2
Does not rise until it is detected by the sheet height sensor flag 5 because no sheet is loaded on the tray, that is, the home position where there is no sheet on the sheet loading tray 2 and stops.

Next, when the sheet P is conveyed by an image forming apparatus (not shown), the leading end of the sheet P is guided by the entrance guide 3, and the sheet P is guided to the discharge roller pair 4.
The sheet P is sequentially discharged onto the sheet stacking tray 2 by the roller pair 4. When the sheet height sensor flag 5 detects that a predetermined number or more sheets on the sheet stacking tray 2 are stacked, the sheet stacking tray 2 is lowered by the driving unit 8 by a predetermined amount.

As described above, the sheets P are successively conveyed from the image forming apparatus, and the sheet discharging apparatus 1 stacks the sheets P on the sheet stacking tray 2 by repeating the above sequence. go.

Next, the operator extracts only the required number of sheets from the stacked sheet bundle. Extraction of this sheet
It is detected by the seat height sensor flag 5. The paper discharge device 1 is provided with a sheet stacking tray 2 for the image forming apparatus.
Since the upper sheet has been removed, a signal is sent to stop the conveyance of the sheet from the image forming apparatus. The paper discharge device 1 performs the following while the image forming apparatus stops conveying the sheet.

First, when the size of the discharged sheets is small (A4, letter size, etc.), (1) In the sheet loading state shown in FIG. , Photo sensor 13b
Is not detected, that is, the sheet stacking amount on the sheet stacking tray 2 is small, and the sheet stacking tray 2
The falling position of the photo sensor 13b sets the sensor flag 1
If the height is just before cutting at 2, the driving unit 8 rotates in the direction to raise the sheet stacking tray 2, and the sheet height that the uppermost sheet surface of the stacked sheets has reached the predetermined height is determined. The height is raised until it is detected by the height sensor 5. If the position of the sensor flag 12 of the sheet stacking tray 2 is at the height position before the photo sensor 13b detects the position,
The operation is the same as the operation described above. That is, in the “upward / downward range” shown in FIG. 3, when the stacked sheets are removed during the sheet stacking, the sheet stacking tray 2
Can rise to a predetermined height.

(2) In the sheet loaded state shown in FIG.
This is the case after the sensor flag 12 on the sheet stacking tray 2 is detected by the photo sensor 13b, that is, when the amount of sheets on the sheet stacking tray 2 is large.
When the stacked sheets are removed from the tray in this state, the removal of the sheets is detected by the sheet height sensor 5, and the conveyance of the sheets to the image forming apparatus is stopped in the same manner as in the above-described mode. Since the sensor flag 12 of the sheet stacking tray 2 has been detected by passing through the photosensor 13b, the driving unit 8 does not operate even if the sheet on the sheet stacking tray 2 is removed.

That is, after the sensor flag 12 of the sheet stacking tray 2 is detected by passing through the photosensor 13b, the sheet stacking tray 2 is not raised even if it is detected that the sheet on the tray has been removed. Since a large number of sheets are stacked on the sheet stacking tray 2, in the above-described state, the discharge device is kept stopped or the sheet stacking tray 2 is lowered. In order to cancel the above state, it is necessary to remove all the sheets on the sheet stacking tray 2.

When the sheet presence sensor 15 detects that all of the sheets on the sheet stacking tray have been removed, the driving unit 8 starts driving the sheet stacking tray 2 so that the sheet stacking tray 2 is raised. When the sheet height sensor 5 detects that the sheet stacking tray 2 has risen to a predetermined height, the driving unit 8 stops lifting the sheet stacking tray 2,
The paper discharge device 1 becomes ready. Then, a signal indicating that the sheet from the image forming apparatus can be received is sent to the image forming apparatus.

Next, in the case where the size of the discharged sheets is large (A3, leisure size, etc.), (3) In the sheet loading state shown in FIG. Is the photo sensor 13a
Is not detected, that is, the sheet stacking amount on the sheet stacking tray 2 is small, and the sheet stacking tray 2
The falling position of the photo sensor 13a sets the sensor flag 1
If the height is just before cutting at 2, the driving unit 8 rotates in the direction to raise the sheet stacking tray 2, and the sheet height that the uppermost sheet surface of the stacked sheets has reached the predetermined height is determined. The height is raised until it is detected by the height sensor 5. If the position of the sensor flag 12 of the sheet stacking tray 2 is at the height position before the photo sensor 13a detects the position,
The operation is the same as the operation described above. That is, in the “large size descending range” shown in FIG. 6, if the loaded sheets are removed during the sheet loading, the sheet loading tray 2 can be raised to a predetermined height by the driving unit 8.

(4) In the sheet loading state shown in FIG.
This is the case after the sensor flag 12 on the sheet stacking tray 2 is detected by the photo sensor 13a, that is, when the amount of sheets stacked on the sheet stacking tray 2 is large.
When the stacked sheets are removed from the tray in this state, the removal of the sheets is detected by the sheet height sensor 5, and the conveyance of the sheets to the sheet image forming apparatus is stopped in the same manner as in the above-described mode. Since the sensor flag 12 of the sheet stacking tray 2 has been detected by passing through the photosensor 13a, the driving unit 8 does not operate even if the sheet on the sheet stacking tray 2 is removed.

That is, after the sensor flag 12 of the sheet stacking tray 2 is detected by passing through the photosensor 13a, the sheet stacking tray 2 is not raised even if it is detected that the sheet on the tray is removed. Since a large amount of sheets are stacked on the sheet stacking tray 2, in the above state, the discharge device 1 is kept stopped or the sheet stacking tray 2 is lowered. In order to cancel the above state, it is necessary to remove all the sheets on the sheet stacking tray 2.

When the sheet presence sensor 15 detects that all the sheets on the sheet stacking tray have been removed, the drive unit 8 starts driving the sheet stacking tray 2 so as to move up. When the sheet height sensor detects that the sheet stacking tray 2 has risen to a predetermined height, the drive unit 8 prevents the sheet stacking tray 2 from rising, and the sheet discharging device 1 becomes ready. Then, a signal indicating that the sheet from the image forming apparatus can be received is sent to the image forming apparatus.

When sheets are continuously discharged onto the sheet stacking tray 2 and the sheets are fully loaded, the full loading state detection sensor (not shown) detects the full loading state of the sheet loading tray, and forms an image. A full load signal is output to the apparatus, and the conveyance of the sheet P is stopped. Then, the user removes the sheet. When the sheet presence sensor 15 detects that all the sheets have been removed,
The sheet stacking tray 2 is raised in the same manner as in (2) and (4) described above, and the sheet discharging device 1 becomes ready.

Here, the predetermined height at which the sensor unit is provided depends on the type (size, material, etc.) of the sheet and the sheet discharging device 1.
Are set in accordance with the specifications of.

When sheets of different types are mixed on the sheet stacking tray 2, control is performed using only the detection reference height set corresponding to the sheet having the largest unit weight among the sheets of different sizes. Good.

Further, the determination of the sheet size is performed by the sheet size detecting means, and the sheet size detecting means may be provided in the image forming apparatus or in the sheet discharging device 1.

According to the present embodiment, since the lifting force required to raise and lower the sheet stacking tray 2 can be made very small as compared with the conventional sheet discharging device, the lifting mechanism, the lifting motor, the power supply and the like are simplified. Can be realized.

Accordingly, it is possible to avoid an increase in the size of the apparatus and an increase in cost due to an increase in the number of sheets that can be stacked, which has been conventionally performed in a sheet discharge stacking apparatus for stacking a large number of sheets. The same sheet tray elevating mechanism can be used even in a sheet discharging stacking device having a different stacking amount. The discharge stacking device connected to the image forming apparatus has a low connection rate and requires a different discharge stacking device according to the discharge capacity. However, according to the present embodiment, the lifting mechanism This makes it possible to use common parts, thereby improving reliability, cost, and productivity, and improving development efficiency.

(Second Embodiment) FIGS. 8 and 9 show a second embodiment. The same components as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

Reference numeral 22 denotes a sensor flag provided on the belt 7, and a photo sensor 23 for detecting the position of the sensor flag 22 is moved to a position corresponding to a load corresponding to about half of the maximum load of the sheet load tray 2 ( That is, the photo sensor 24 is disposed at a position corresponding to a load of about １ ／ of the maximum stacking amount of the sheet stacking tray 2 (that is, the sheet is placed at a position of about の of the maximum movement range of the sheet stacking tray 2). (1/4 position of the maximum movement range of the loading tray 2).

With the above configuration, the same operation as the operation described in the first embodiment can be performed.

By standardizing to the configuration of the present embodiment, it is possible to provide a sheet stacking apparatus that can be commonly used in various discharge stacking apparatuses having different sheet stacking amounts, and reliability and cost can be provided. It is possible to improve surface and productivity and improve the efficiency of development.

Also, as compared with the first embodiment, the provision of the sensor flag 22 on the belt 7 allows the position of the sheet stacking tray 2 to be accurately defined.
That is, it is possible to eliminate the fluttering of the sheet stacking tray 2 up and down and the variation of the sensor flag position due to a change in the sheet stacking amount (removal of the sheet by the user). As a result, the sheet stacking tray 2
Can be detected stably, and the sheet stacking tray can be stably moved up and down.

[0049]

As described above, according to the present invention,
When the position of the sheet stacking means detected by the position detecting means is higher than a predetermined detection reference height, the control means enables the sheet stacking means to be able to move up and down by the elevating means, and the position of the sheet stacking means is When the height is equal to or less than the detection reference height, the lifting / lowering means enables only the lowering of the sheet stacking means. Since the size can be reduced, the elevating mechanism, the elevating motor, the power supply, and the like can be simplified, and the device can be downsized.

Therefore, it is possible to avoid an increase in the size of the apparatus and an increase in cost due to an increase in the number of sheets that can be stacked, which is conventionally performed in a sheet discharge stacking apparatus for stacking a large number of sheets.

Further, the standby time of the image forming apparatus, which has been long in the past, can be shortened, and the productivity can be improved.

Further, conventionally, a different paper output stacking device was required according to the paper output capacity. However, it is possible to use a common paper stacking apparatus and to cope with various required paper storage capacities.
It is possible to improve cost and productivity and improve development efficiency.

[Brief description of the drawings]

FIG. 1 is a schematic perspective view of a sheet stacking apparatus according to a first embodiment.

FIG. 2 is a schematic sectional view of the sheet stacking apparatus according to the first embodiment.

FIG. 3 is an operation explanatory view of the sheet stacking apparatus according to the first embodiment.

FIG. 4 is an operation explanatory diagram of the sheet stacking apparatus according to the first embodiment.

FIG. 5 is a schematic perspective view of the sheet stacking tray according to the first embodiment.

FIG. 6 is an operation explanatory diagram of the sheet stacking apparatus according to the first embodiment.

FIG. 7 is an operation explanatory diagram of the sheet stacking apparatus according to the first embodiment.

FIG. 8 is a schematic sectional view of a sheet stacking apparatus according to the second embodiment.

FIG. 9 is a schematic perspective view of a main part of the sheet stacking apparatus according to the second embodiment.

FIG. 10 is a diagram illustrating the operation of the sheet stacking apparatus according to the embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Paper discharge device 2 Sheet loading tray 3 Entrance guide part 4 Discharge roller pair 5 Sheet height sensor flag 6, 9 Pulley 7 Drive belt 8 Drive part 10 Lifting roller 11 Lifting guide 12, 22 Sensor flag 13a, 13b, 23, 24 Photo sensor 14 Belt fixing part 15 Sheet existence sensor

 ────────────────────────────────────────────────── ─── Continued on front page (72) Inventor Masayoshi Fukatsu 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Atsushi Ogata 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon (72) Inventor Tomoyuki Araki 3-30-2 Shimomaruko, Ota-ku, Tokyo F-term (reference) 3F054 AA01 AC02 AC03 AC05 BA04 BD02 CA02 CA10 CA11 DA12

Claims (9)

[Claims] A sheet stacking means for stacking the conveyed sheets; a sheet stacking means provided at a predetermined height on the sheet stacking means; and a top sheet stacked on the sheet stacking means at the predetermined height. The sheet height detecting means to be detected, and the sheet stacking means is moved up and down by the elevating means so that the uppermost sheet stacked on the sheet stacking means is detected at the predetermined height by the sheet height detecting means. And a position detecting means for detecting a position of the sheet stacking means in a height direction, wherein the control means detects the position of the sheet stacking means detected by the position detecting means. When the position is above a predetermined detection reference height, the sheet stacking means can be moved up and down by the elevating means, and the position of the sheet stacking means is not more than the detection reference height. In this case, the sheet stacking apparatus characterized by allowing only descent of the sheet stacking means by said lifting means. 2. The control means according to claim 1, wherein said sheet height detection means detects the uppermost sheet stacked on said sheet stacking means from the presence or absence of said sheet to said sheet detection means. Detecting the position of the stacking means, and if the position of the sheet stacking means detected by the position detecting means is above the detection reference height,
The sheet stacking means can be moved up and down by the elevating means,
2. The apparatus according to claim 1, wherein when the position of the sheet stacking unit is equal to or less than the detection reference height, the sheet stacking unit is lowered by the lifting unit, or the lifting unit is stopped. A sheet stacking apparatus according to claim 1. 3. The sheet stacking device according to claim 1, wherein the detection reference height is set at a plurality of positions in accordance with the type of sheets stacked on the sheet stacking unit. 4. When the position of the sheet stacking means detected by the position detecting means is higher than a first detection reference height, the control means raises and lowers the sheet stacking means by the elevating means. The position of the sheet stacking means is lower than the first detection reference height, and the second position is lower than the first detection reference height.
In the case where the sheet stacking means is located between the detection reference height and the sheet stacking means, the sheet stacking means can be moved up and down by the elevating means, or the sheet stacking means can be lowered only by the elevating means. 4. The sheet stacking device according to claim 3, wherein when the position of the sheet stacking device is lower than the second detection reference height, the sheet stacking device can be lowered only by the lifting / lowering device. apparatus. 5. When a plurality of types of sheets are stacked on the sheet stacking means, the control means sets a value corresponding to a sheet having the largest unit weight among the plurality of types of sheets. 3. Only when the position of the sheet stacking means is higher than the detection reference height of No.3, the lifting and lowering means can move the sheet stacking means up and down, and the position of the sheet stacking means is equal to or less than the third detection reference height. 5. The sheet stacking device according to claim 1, wherein the sheet stacking unit can only be lowered by the lifting unit. 6. The position detecting means, wherein the sheet stacking means has a height equal to one half of a maximum stacking height of the sheet stacking means.
6. The sheet stacking apparatus according to claim 3, wherein the sheet stacking unit is detected when the sheet stacking unit is substantially located at a height of / 4. 7. The apparatus according to claim 1, wherein said position detecting means is provided so as to be positioned at said detection reference height, and detects that said sheet stacking means has passed said detection reference height. 7. The sheet stacking apparatus according to any one of claims 1 to 6. 8. A sheet detecting means for detecting whether or not a sheet is loaded on the sheet loading means, wherein the control means determines that the sheet is not loaded on the sheet loading means by the sheet detecting means. 8. The sheet stacking apparatus according to claim 1, wherein when detecting that the sheet stacking unit is lifted, the sheet stacking unit is raised by the lifting unit regardless of the position of the sheet stacking unit. 9. 9. A sheet stacking apparatus according to claim 1, further comprising: sheet processing means for discharging a sheet on which an image has been formed by an image forming means to said sheet stacking apparatus. Characteristic sheet processing device.