Sheet Feeding Device

Abstract

To provide a sheet supply device capable of reducing sheet supply error.SOLUTION: A control part 13: controls a floating part 6 and a conveyance part 8 to convey paper P to a paper feed destination, and acquires a light receiving amount of a light receiving part 32 during floating of paper P floated by the floating part 6 for each sheet of paper conveyed by the conveyance part 8; and performs a follow-up control for raising a paper feeding table 2 when an acquired sensor value is less than a follow-up threshold value. And, the control part 13 controls the floating part 6 and the conveyance part 8 so as to retry paper feed when empty feed of paper P is performed by the conveyance part 8. Further, the control part 13 sets the follow-up threshold value so that a target position of the height position of an upper surface of a paper bundle PT in the follow-up control is a position where empty feed is more likely to occur than the double feed of paper P by the conveyance part 8.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a sheet feeding device for feeding sheets.

Background Art

[0002] As a sheet feeding device for feeding sheets, there is known a paper feeding device that blows air onto a stack of sheets loaded on a paper feed table to lift the sheets, and adsorbs and conveys the uppermost (topmost) sheet among the lifted sheets by an adsorption conveying means to feed the sheet to a printing device.

[0003] In this type of paper feeding device, following control is performed to raise the paper feed table in accordance with a decrease in the remaining amount of paper on the paper feed table and maintain the height position of the upper surface of the stack of sheets on the paper feed table at a target position (see Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the above-described paper feeding device, double feeding and air feeding of the sheets may occur. Double feeding is that a plurality of sheets overlap and are adsorbed by the adsorption conveying means and conveyed. Air feeding is that the sheet is not adsorbed by the adsorption conveying means and the sheet is not conveyed.

[0006] The higher the height position of the upper surface of the stack of sheets on the paper feed table, the more likely double feeding is to occur, and the lower the height position of the upper surface of the stack of sheets, the more likely air feeding is to occur. The target position of the upper surface of the stack of sheets in the above-described following control is set to a position where double feeding and air feeding are less likely to occur to the same extent.

[0007] Incidentally, when air feed occurs, by retrying paper feeding (redoing paper feeding), only a slight amount of time taken for feeding one sheet of paper is consumed, and it is possible to continue a series of paper feeding operations and printing operations in the printing apparatus at the paper feeding destination. That is, air feed can be remedied by paper feed retry.

[0008] On the other hand, when double feed occurs, in order to continue a series of paper feeding operations and printing operations in the printing apparatus at the paper feeding destination by paper feed retry, for example, it is necessary to return the double-fed sheet to the paper feed table and retry paper feeding, which cannot be achieved without a complicated mechanism and control. Therefore, in reality, double feed cannot be remedied by paper feed retry.

[0009] As described above, since the target position of the upper surface of the sheet bundle in the follow-up control is set at a position where double feed and air feed are equally unlikely to occur, double feed occurs at about the same frequency as air feed. When double feed occurs, since it cannot be remedied by paper feed retry, a paper feed error occurs and a series of paper feeding operations stop. When a paper feed error occurs, work by the user for error recovery occurs. Also, when a paper feed error occurs, the printing operation in the printing apparatus at the paper feeding destination stops, so the printing productivity decreases.

[0010] The present invention has been made in view of the above, and an object thereof is to provide a sheet supply apparatus capable of reducing a sheet supply error.

Means for Solving the Problems

[0011] According to one aspect of the present invention, there is provided a liftable loading platform on which a stack of sheets is loaded, a floating portion that blows air onto the stack of sheets to lift the sheets of the stack, a conveying portion that conveys the uppermost sheet among the sheets lifted by the floating portion to a supply destination, a detecting portion that detects an output signal obtained by inputting from the side of the stack of sheets, and a control portion that controls the floating portion and the conveying portion so as to convey the sheets to the supply destination, and for each sheet conveyed by the conveying portion, acquires a detection value of the detecting portion during the floating of the sheet lifted by the floating portion, and performs a follow-up control to raise the loading platform when the acquired detection value is less than a threshold value. When an air feed of the sheet by the conveying portion occurs, the control portion controls the floating portion and the conveying portion so as to perform a supply retry to re-convey the sheet to the supply destination, and the threshold value is set such that a target position of a height position of the upper surface of the stack of sheets in the follow-up control is a position where air feed is more likely to occur than double feeding of the sheet by the conveying portion. A sheet supply device is provided.

[0012] According to another aspect of the present invention, there is provided a liftable loading platform on which a stack of sheets is loaded, a floating portion that blows air onto the stack of sheets to lift the sheets of the stack, a conveying portion that conveys the uppermost sheet among the sheets lifted by the floating portion to a supply destination, a detecting portion that emits light from the side of the stack of sheets toward the stack of sheets side and receives the light from the stack of sheets side, and a control portion that controls the floating portion and the conveying portion so as to convey the sheets to the supply destination, and for each sheet conveyed by the conveying portion, acquires a light reception amount of the detecting portion during the floating of the sheet lifted by the floating portion, and performs a follow-up control to raise the loading platform when the acquired light reception amount is less than a threshold value. When an air feed of the sheet by the conveying portion occurs, the control portion controls the floating portion and the conveying portion so as to perform a supply retry to re-convey the sheet to the supply destination, and the threshold value is set such that a target position of a height position of the upper surface of the stack of sheets in the follow-up control is a position where air feed is more likely to occur than double feeding of the sheet by the conveying portion. A sheet supply device is provided.

[0013] According to another aspect of the present invention, there is provided a sheet feeding apparatus including: a liftable loading table on which a stack of sheets is loaded; a floating unit that blows air onto the stack of sheets to lift the sheets in the stack; a conveying unit that sucks and conveys the uppermost sheet among the sheets lifted by the floating unit to a supply destination; and a control unit that controls the floating unit and the conveying unit to convey the sheets to the supply destination and performs follow-up control to raise the loading table in response to a decrease in the number of sheets on the loading table. When air conveyance of the sheets by the conveying unit occurs, the control unit controls the floating unit and the conveying unit to perform a supply retry to re-convey the sheets to the supply destination, and controls the conveying unit such that the suction force of the conveying unit is a suction force at which air conveyance is more likely to occur than double feeding of the sheets when the height position of the upper surface of the stack of sheets is at a target position in the follow-up control.

Advantages of the Invention

[0014] According to the sheet feeding apparatus of the present invention, sheet supply errors can be reduced.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Embodiments for Carrying Out the Invention

[0016] Hereinafter, embodiments of the present invention will be described with reference to the drawings. The same or equivalent parts and components are denoted by the same or equivalent reference numerals throughout the drawings.

[0017] The embodiments shown below illustrate devices and the like for embodying the technical idea of this invention. The technical idea of this invention does not specify the materials, shapes, structures, arrangements, etc. of each component part as the following. The technical idea of this invention can be variously modified within the scope of the claims.

[0018] [First Embodiment] FIG. 1 is a schematic configuration diagram of a paper feeding device according to the first embodiment of the present invention. FIG. 2 is a control block diagram of the paper feeding device shown in FIG. 1. In the following description, the up, down, left, and right directions on the paper surface in FIG. 1 are taken as the up, down, left, and right directions.

[0019] As shown in FIGS. 1 and 2, a paper feeding device (corresponding to a sheet supply device) 1 according to the first embodiment includes a paper feed table (corresponding to a stacking table) 2, an end fence 3, a lifting motor 4, an encoder 5, a floating portion 6, a separating portion 7, a conveying portion 8, an upper limit sensor (corresponding to a detection portion) 9, a pair of paper feed rollers 10, a paper feed motor 11, a paper feed inlet sensor 12, and a control portion 13.

[0020] The paper feeding device 1 is a device that feeds paper (corresponding to a sheet) P to a printing device 100 which is a paper feeding destination (corresponding to a supply destination). The direction from left to right in FIG. 1 is the conveying direction of the paper P by the conveying portion 8 during the paper feeding operation (corresponding to the sheet supply operation). In the following description, upstream and downstream mean upstream and downstream in the conveying direction of the paper P by the conveying portion 8.

[0021] The paper feed table 2 is for loading the paper P used for printing. The paper feed table 2 is configured to be able to move up and down.

[0022] The end fence 3 is a member that regulates the position of the upstream end (left end) of the paper P on the paper feed table 2.

[0023] The lifting motor 4 moves the paper feed table 2 up and down.

[0024] The encoder 5 outputs a pulse signal for each predetermined rotation angle of the rotation shaft of the lifting motor 4.

[0025] The floating part 6 blows air from the downstream side to the side of a paper bundle PT (corresponding to a sheet bundle) composed of a plurality of papers P stacked on the paper feed table 2, and floats a plurality of papers P at the upper end of the paper bundle PT. The floating part 6 includes a floating fan 16 and a shutter 17.

[0026] The floating fan 16 generates a floating air flow A1 (see FIG. 3) for floating the paper P of the paper bundle PT on the paper feed table 2.

[0027] The shutter 17 switches the on / off of the blowing of the floating air flow A1 to the paper bundle PT.

[0028] Note that two floating parts 6 facing each other across the paper bundle PT on the paper feed table 2 in the width direction orthogonal to the conveyance direction of the paper P may be further provided.

[0029] The separating part 7 separates the uppermost paper P lifted by the floating part 6 and adsorbed by the conveying part 8 from the second and lower papers P from the top. The separating part 7 includes a separating fan 18.

[0030] The separating fan 18 generates a separating air flow A2 (see FIG. 3) for flowing air between the uppermost paper P adsorbed by the conveying part 8 and the second paper P from the top to separate the uppermost paper P from the second and lower papers P from the top.

[0031] Note that, in the width direction of the sheet P, two separating parts 7 facing each other across the sheet stack PT on the sheet feeding table 2 may be further provided.

[0032] The conveying unit 8 sucks and conveys the uppermost sheet P among the plurality of sheets P lifted by the floating part 6 by air suction. The conveying unit 8 includes a conveying belt 21, a driving roller 22, a driven roller 23, a conveying motor 24, and a suction mechanism part 25.

[0033] The conveying belt 21 is an annular belt spanned between the driving roller 22 and the driven roller 23. A plurality of belt holes (not shown) are formed over the entire circumference of the conveying belt 21. The conveying belt 21 adsorbs and holds the sheet P by the adsorption force generated in the belt holes by the driving of the suction mechanism part 25. With the sheet P adsorbed and held, the conveying belt 21 rotates (runs endlessly) by the driving of the driving roller 22, and thus the sheet P is conveyed.

[0034] The driving roller 22 rotates (runs endlessly) the conveying belt 21.

[0035] The driven roller 23 supports the conveying belt 21 together with the driving roller 22. The driven roller 23 rotates in a driven manner with respect to the rotating conveying belt 21.

[0036] The conveying motor 24 rotates the driving roller 22.

[0037] The suction mechanism part 25 sucks air through the belt holes of the conveying belt 21, thereby adsorbing the sheet P to the conveying belt 21. The suction mechanism part 25 includes a fan (not shown) that sucks air through the belt holes.

[0038] The upper limit sensor 9 monitors the end face on the downstream side (right side) of the paper P stacked on the paper feed table 2. The upper limit sensor 9 is arranged at a height position capable of detecting the floating paper P within the floating region F (see Fig. 3) on the downstream side of the paper feed table 2. The floating region F is a region where the floating portion 6 floats the paper P in the vertical direction. The upper limit sensor 9 is a reflection type photosensor and includes a light emitting part 31 and a light receiving part 32.

[0039] The light emitting part 31 emits light from the right side of the paper bundle PT on the paper feed table 2 toward the left side (toward the paper bundle PT).

[0040] The light receiving part 32 receives the light from the left side (toward the paper bundle PT).

[0041] A pair of paper feed rollers 10 nip the paper P conveyed by the conveying part 8 and convey it toward the printing device 100 arranged on the downstream side of the paper feeding device 1.

[0042] The paper feed motor 11 drives the paper feed rollers 10.

[0043] The paper feed entrance sensor 12 detects the conveyed paper P in the vicinity of the downstream side of the paper feed rollers 10.

[0044] The control part 13 controls the operation of the entire paper feeding device 1. The control part 13 is configured to include a CPU, a RAM, a ROM, a hard disk, etc.

[0045] The control part 13 controls the floating part 6 and the conveying part 8 so as to float the uppermost paper P of the upper end part of the paper bundle PT on the paper feed table 2 and adsorb it to the conveying belt 21, and convey the uppermost paper P to the printing device 100.

[0046] When the air feed of the paper P by the conveying part 8 occurs, the control part 13 controls the floating part 6 and the conveying part 8 to perform a paper feed retry (corresponding to a supply retry) until the number of consecutive air feed occurrences reaches a predetermined upper limit consecutive number (corresponding to a predetermined number) R described later. The paper feed retry is a process of re - conveying the paper P to the printing device 100.

[0047] Further, during the paper feeding operation, the control unit 13 acquires the amount of light received (sensor value) of the light receiving unit 32 of the paper P lifted by the lifting unit 6 for each sheet of paper P conveyed by the conveying unit 8, and when the acquired sensor value is less than the follow-up threshold value (corresponding to the threshold value), performs follow-up control to raise the paper feed tray 2. The follow-up control is for raising the paper feed tray 2 in response to the decrease in the remaining amount of the paper P on the paper feed tray 2 due to paper feeding, and maintaining the height position of the upper surface of the paper bundle PT on the paper feed tray 2 at the target position.

[0048] The control unit 13 sets the follow-up threshold value so that the target position of the height position of the upper surface of the paper bundle PT in the follow-up control during the paper feeding operation is a position where air feeding is more likely to occur than double feeding of the paper P by the conveying unit 8.

[0049] Here, the sensor value during the lifting of the paper P lifted by the lifting unit 6 is the amount of light received of the reflected light from the end face of the lifted paper P within the detection range of the upper limit sensor 9. Therefore, the sensor value during the lifting of the paper P becomes larger as the number of lifted paper P within the detection range of the upper limit sensor 9 is larger.

[0050] Also, the number of sheets of paper P that can be lifted by the blowing of air by the lifting unit 6 is the number of sheets of paper P within the lifting region F. Therefore, the lower the height position of the uppermost sheet of paper P (the upper surface of the paper bundle PT) on the paper feed tray 2 when the paper P on the paper feed tray 2 is not lifted, the smaller the number of sheets of paper P that can be lifted by the blowing of air by the lifting unit 6.

[0051] From this, the sensor value during the lifting of the paper P can be used quasi - as information indicating the height position of the upper surface of the paper bundle PT on the paper feed tray 2 when it is assumed that the paper P on the paper feed tray 2 is not lifted. If the height position of the paper feed tray 2 does not change, as the paper feeding progresses, the number of lifted paper P decreases, and the sensor value tends to decrease.

[0052] Therefore, in the paper feeding device 1, as described above, follow-up control during the paper feeding operation is performed using the sensor value during the lifting of the paper P.

[0053] Next, the process of determining the following threshold value in the paper feeding device 1 and the following control will be described.

[0054] The determination of the following threshold value is performed after the start of a series of paper feeding operations. Here, it will be described on the assumption that no air feeding or double feeding of the sheet P by the conveying unit 8 occurs.

[0055] When a paper feeding start is instructed, the control unit 13 starts raising the paper feed table 2 from a state where the upper surface of the paper stack PT on the paper feed table 2 is below the lower limit of the detection range of the upper limit sensor 9.

[0056] After the start of raising the paper feed table 2, when the upper end of the paper stack PT on the paper feed table 2 enters the detection range of the upper limit sensor 9, the reflected light from the side surface on the right side of the upper end of the paper stack PT starts to be received by the upper limit sensor 9. Thereafter, as the paper feed table 2 rises, the range of the paper stack PT on the paper feed table 2 that is within the detection range of the upper limit sensor 9 expands, so the sensor value of the upper limit sensor 9 increases.

[0057] When the control unit 13 determines that the sensor value has reached a predetermined non - floating threshold value, it stops raising the paper feed table 2. Here, the non - floating threshold value is set as the sensor value when the height position of the upper surface of the paper stack PT is at a predetermined sensor position within the detection range of the upper limit sensor 9. Therefore, by stopping the raising of the paper feed table 2 when the sensor value reaches the non - floating threshold value as described above, the paper feed table 2 stops at a height position where the upper surface of the paper stack PT is at the above - mentioned sensor position.

[0058] Next, the control unit 13 starts raising or lowering the paper feed table 2, and when the upper surface of the paper stack PT reaches a predetermined paper feeding start position, it stops the paper feed table 2. As a result, the height position of the upper surface of the paper stack PT is set to the paper feeding start position. Here, the control unit 13 determines whether the upper surface of the paper stack PT has reached the paper feeding start position based on the number of output pulses of the encoder 5 from the time when the raising or lowering of the paper feed table 2 is started.

[0059] The paper feed start position is higher than the target position in the follow-up control. Specifically, the paper feed start position is higher than the target position by the thickness of the sheet P for the total number of sheets obtained by adding the number of sampling exclusion sheets described later and half of the number of sampling sheets described later.

[0060] Here, in the paper feeding device 1, as described above, the control unit 13 sets the target position at a position where air feed is more likely to occur than double feeding of the sheet P by the conveying unit 8. Specifically, the control unit 13 sets the target position at a position below the appropriate position where both double feeding and air feed are less likely to occur by a predetermined offset amount. The offset amount is set based on experiments or the like so that the target position is a position where the occurrence of double feeding can be suppressed while suppressing an increase in air feed. The appropriate position and the offset amount are according to the paper type (thickness of the sheet). For this reason, the target position is set for each paper type (thickness of the sheet).

[0061] Next, the control unit 13 starts the paper feeding operation. Specifically, the control unit 13 opens the shutter 17 and starts driving the suction mechanism unit 25, the levitation fan 16, and the separation fan 18. Also, the control unit 13 controls the paper feed motor 11 to start driving the paper feed roller 10.

[0062] After starting the driving of the suction mechanism unit 25, the levitation fan 16, and the separation fan 18, as shown in FIG. 3, a plurality of sheets P in the levitation region F are levitated by the levitation air flow A1, and the topmost sheet P is adsorbed to the conveying belt 21.

[0063] Next, the control unit 13 closes the shutter 17. As a result, the levitation air flow A1 is stopped. As a result, as shown in FIG. 4, the topmost sheet P and the second and lower sheets P from the top are separated by the separation air flow A2, and the second and lower sheets P from the top fall.

[0064] Next, when the control unit 13 receives a paper feed signal from the printing apparatus 100, it starts driving the conveyance motor 24 and controls the conveyance unit 8 to convey the paper P. As a result, the paper P is conveyed to the printing apparatus 100 by the conveyance unit 8 and the paper feed roller 10. The control unit 13 stops the conveyance motor 24 after a predetermined driving time from the start of driving the conveyance motor 24.

[0065] Here, the paper feed signal is a signal for the printing apparatus 100 to instruct the start of conveyance of the paper P by the conveyance unit 8. The paper feed signal is transmitted from the printing apparatus 100 to the paper feeder 1 for each sheet of paper fed by the paper feeder 1.

[0066] Next, the control unit 13 opens the shutter 17 to lift the paper P for feeding the next sheet of paper P.

[0067] By repeating the above operations, the paper P is sequentially fed from the paper feeder 1 to the printing apparatus 100.

[0068] After the start of the paper feed operation, when the number of sheets fed reaches the sampling exclusion number, the control unit 13 starts sampling sensor values for determining the tracking threshold value.

[0069] Here, the sampling exclusion number is set in advance as the number of sheets of paper for which sampling of sensor values for determining the tracking threshold value is not performed immediately after the start of the paper feed operation. As will be described later, immediately after the start of the paper feed operation, the behavior of the paper P when it is lifted is unstable. Therefore, the sampling exclusion number is set so that sampling of sensor values is not performed until that number of sheets is fed. Since the behavior of the paper P at the time of lifting varies depending on the paper type (thickness of the paper), the sampling exclusion number is set according to the paper type (thickness of the paper). The sampling exclusion number may be one sheet or a plurality of sheets.

[0070] When the above sampling starts, while the sheet P lifted for feeding the next sheet P after the last sheet P for the sampling exclusion number is being lifted, the control unit 13 acquires the sensor value of the upper limit sensor 9. After that, for each sheet fed (paper-fed) by the conveying unit 8, the control unit 13 acquires the sensor value while the lifted sheet P is being lifted. As the sensor value while the sheet P is being lifted, the control unit 13 acquires, for example, the sensor value after a predetermined time from the opening time of the shutter 17.

[0071] When acquiring the sensor values for the sampling number, the control unit 13 determines a following threshold value and starts following control. Specifically, the control unit 13 calculates the average value of the acquired sensor values for the sampling number, and determines the calculated average value as the following threshold value.

[0072] Here, the sampling number is a number set in advance as the number of sheets fed for sampling the sensor values for determining the following threshold value. The sampling number can be a common value regardless of the paper type, etc., or can be changed according to the paper type (paper thickness).

[0073] Also, the sampling period, which is the period for acquiring the sensor values for the sampling number, is set so that the same number of sheets are fed before and after the time when the height position of the upper surface of the paper bundle PT reaches the target position.

[0074] When determining the following threshold value, the control unit 13 starts following control using the determined following threshold value. Until the following control starts, the height position of the paper feed tray 2 is fixed at the position set at the start time of the paper feed operation.

[0075] When starting the following control, for each sheet fed, if the acquired sensor value is less than the following threshold value, the control unit 13 raises the paper feed tray 2.

[0076] Specifically, when the acquired sensor value is less than the following threshold value, the control unit 13 drives the lifting motor 4 for a predetermined driving time to raise the paper feed table 2. At this time, the control unit 13 controls the driving voltage of the lifting motor 4 according to the difference between the acquired sensor value and the following threshold value.

[0077] Specifically, the greater the difference between the sensor value and the following threshold value, the greater the control unit 13 increases the driving voltage of the lifting motor 4 so that the rising amount of the paper feed table 2 increases. The greater the difference between the sensor value and the following threshold value, the fewer the sheets of paper P in the floating region F, and the lower the height position of the upper surface of the paper bundle PT on the paper feed table 2 when the paper P on the paper feed table 2 has not floated. For this reason, the control unit 13 controls so that the rising amount of the paper feed table 2 increases as the difference between the sensor value and the following threshold value increases. The relationship between the difference between the sensor value and the following threshold value and the driving voltage of the lifting motor 4 is preset based on experiments and the like for each paper type (paper thickness) so that the height position of the upper surface of the paper bundle PT reaches the target position as the paper feed table 2 rises.

[0078] Here, FIG. 5 shows an example of the transition of the sensor value acquired during the floating of the paper P for each sheet of paper fed in the paper feeding operation.

[0079] In a state where the height position of the paper feed table 2 is fixed, as the paper feeding progresses, the height position of the upper surface of the paper bundle PT becomes lower, and the paper P in the floating region F decreases. For this reason, as the number of sheets fed from the start of the paper feeding operation increases, the paper P lifted by the floating unit 6 decreases. Therefore, as the number of sheets fed from the start of the paper feeding operation increases, the sensor value acquired during the floating of the paper P for each sheet of paper fed becomes smaller.

[0080] However, immediately after the start of the paper feeding operation, the behavior of the sheet P when it is lifted is likely to become unstable. For example, air may not enter well between the sheets, and multiple sheets P may be lifted while remaining in close contact with each other. In such a case, the sensor value will be smaller than when each sheet P being lifted is separated from each other. For this reason, as shown in FIG. 5, immediately after the start of the paper feeding operation, it is likely to become unstable, such as the sensor value becoming smaller than the expected value. In particular, the sensor value is likely to become unstable during the first sheet feeding.

[0081] Therefore, as described above, in the paper feeding device 1, the above-described sampling exclusion number of sheets is set so as not to sample the sensor value immediately after the start of the paper feeding operation.

[0082] And in the paper feeding device 1, as shown in FIG. 5, a sampling period including the time point when the height position of the upper surface of the paper bundle PT reaches the target position is set. Also, as described above, the sampling period is set so that the same number of sheets are fed before and after the time point when the height position of the upper surface of the paper bundle PT reaches the target position.

[0083] The appropriate threshold value shown in FIG. 5 is, unlike this embodiment, a following threshold value in the case of performing following control to maintain the height position of the upper surface of the paper bundle PT at the above-described appropriate position. That is, the appropriate threshold value is a value at which double feeding or air feeding of the sheet P by the conveying unit 8 is equally unlikely to occur. When the following threshold value is larger than the appropriate threshold value, double feeding is more likely to occur than air feeding, and when the following threshold value is smaller than the appropriate threshold value, air feeding is more likely to occur than double feeding. As described above, in this embodiment, the target position is set lower than the appropriate position, and the following threshold value becomes smaller than the appropriate threshold value, resulting in a value at which air feeding is more likely to occur than double feeding.

[0084] Next, the operation of the paper feeding device 1 when air feeding occurs will be described with reference to the flowcharts of FIGS. 6 and 7.

[0085] The processing of the flowcharts in FIGS. 6 and 7 starts when the paper feeding operation is started.

[0086] In step S1 of FIG. 6, the control unit 13 determines whether it has received a paper feed end instruction from the printing apparatus 100. The paper feed end instruction is transmitted by the printing apparatus 100 to instruct the paper feeder 1 to end paper feeding. The paper feed end instruction is transmitted by the printing apparatus 100 to the paper feeder 1 when the paper feeding for the number of sheets to be fed in a series of paper feeding operations is completed and when an error notification from the paper feeder 1 is received.

[0087] If it is determined that the paper feed end instruction has been received (step S1: YES), the control unit 13 ends a series of paper feeding operations.

[0088] If it is determined that the paper feed end instruction has not been received (step S1: NO), in step S2, the control unit 13 determines whether it has acquired the sensor values for the aforementioned sampling number of sheets.

[0089] If it is determined that the sensor values for the sampling number of sheets have not been acquired (step S2: NO), in step S3, the control unit 13 determines whether it has received a paper feed signal from the printing apparatus 100. If it is determined that the paper feed signal has not been received (step S3: NO), the control unit 13 repeats step S3.

[0090] If it is determined that the paper feed signal has been received (step S3: YES), in step S4, the control unit 13 controls the transport unit 8 to transport the sheet P. Here, when the paper feeder 1 receives the paper feed signal, as described above, the uppermost sheet P among the plurality of sheets P lifted by the floating unit 6 is in a state of being adsorbed to the transport belt 21.

[0091] Next, in step S5, the control unit 13 determines whether air conveyance of the sheet P by the transport unit 8 has occurred. Here, the control unit 13 determines that air conveyance has occurred if the paper feed inlet sensor 12 does not detect the sheet P being transported from the transport unit 8 within a predetermined time after starting the transport of the sheet P by the transport unit 8 in step S4.

[0092] When it is determined that air feeding has occurred (step S5: YES), in step S6, the control unit 13 adds "1" to the continuous air feed count value Ca. The continuous air feed count value Ca indicates the number of occurrences of continuous air feeding of the sheet P by the conveying unit 8. Here, at the start of a series of paper feeding operations, the continuous air feed count value Ca = 0 is set.

[0093] Next, in step S7, the control unit 13 determines whether the continuous air feed count value Ca has reached the upper limit continuous count R (Ca = R). The upper limit continuous count R is set as a reference for the number of occurrences of continuous air feeding to determine whether to end the repetition of paper feeding retry and perform an error notification due to air feeding. The upper limit continuous count R may be once or a plurality of times. The upper limit continuous count R is set in advance based on experiments or the like.

[0094] When it is determined that the continuous air feed count value Ca has not reached the upper limit continuous count R (step S7: NO), the control unit 13 returns to step S1.

[0095] Here, in the paper feeding device 1, if air feeding of the sheet P by the conveying unit 8 occurs after the start of a series of paper feeding operations and before the tracking threshold value is determined, the control unit 13 does not adopt the sensor value sampled at the time of air feeding as the sensor value for determining the tracking threshold value. That is, the control unit 13 does not include the sensor value sampled at the time of air feeding in the sensor values for the number of sampled sheets.

[0096] Therefore, when it is determined as "NO" in step S7 and the process returns to step S1, and when a paper feed end instruction is not received (step S1: NO), in step S2, the control unit 13 determines that the sensor values for the sampling number of sheets have not been acquired (step S2: NO). Then, when a paper feed signal is received (step S3: YES), the control unit 13 causes the transport unit 8 to transport the sheet P (step S4). At this time, the control unit 13 releases the shutter 17 to float a plurality of sheets P of the sheet bundle PT by the floating unit 6 and adsorbs the uppermost sheet P to the transport belt 21, and transports the sheet P by the transport unit 8. In this way, a paper feed retry is performed.

[0097] In step S7, when it is determined that the continuous blank feed count value Ca has reached the upper limit continuous number R (step S7: YES), in step S8, the control unit 13 transmits an error notification due to blank feed to the printing apparatus 100. After that, the control unit 13 returns to step S1.

[0098] Here, the printing apparatus 100 that has received the error notification transmits a paper feed end instruction to the paper feed apparatus 1. Therefore, when returning from step S8 to step S1, the control unit 13 determines that a paper feed end instruction has been received (step S1: YES), and ends a series of paper feed operations as a paper feed error.

[0099] In step S5, when it is determined that no blank feed has occurred (step S5: NO), in step S9, the control unit 13 clears the continuous blank feed count value Ca (sets Ca = 0). After that, the control unit 13 returns to step S1.

[0100] In step S2, when it is determined that the sensor values for the sampling number of sheets have been acquired (step S2: YES), in step S10, the control unit 13 determines the follow - up threshold value as described above and starts the follow - up control. After that, the control unit 13 proceeds to step S11 in FIG. 7.

[0101] Here, as described above, in the paper feeding device 1, the sensor values sampled during the occurrence of air feeding are not included in the sensor values for the number of sampled sheets. Therefore, when the acquisition of the sensor values for the number of sampled sheets is completed, the last sheet P for the number of sampled sheets is conveyed without being air-fed. Thus, when determining the following threshold value and starting the following control in step S10, the continuous air-feeding count value Ca = 0.

[0102] The processes of steps S11 to S17 in FIG. 7 are the same as the processes of steps S1, S3 to S8 in FIG. 6 described above.

[0103] In step S16, when it is determined that the continuous air-feeding count value Ca has not reached the upper limit continuous number R (step S16: NO), in step S18, the control unit 13 determines whether the continuous air-feeding count value Ca = 1.

[0104] When it is determined that the continuous air-feeding count value Ca = 1 (step S18: YES), in step S19, the control unit 13 adds "1" to the intermittent air-feeding count value Cb. After that, the control unit 13 proceeds to step S20.

[0105] The intermittent air-feeding count value Cb indicates the number of occurrences of intermittent air-feeding of the sheet P by the conveying unit 8. At the start of a series of paper feeding operations, the intermittent air-feeding count value Cb = 0 is set.

[0106] In step S18, when it is determined that the continuous air-feeding count value Ca ≠ 1 (step S18: NO), the control unit 13 skips step S19 and proceeds to step S20.

[0107] In step S20, the control unit 13 forcibly raises the paper feed table 2 by a predetermined raising amount. Here, the control unit 13 can determine the raising amount of the paper feed table 2 based on the number of output pulses of the encoder 5.

[0108] The forced raising of the paper feed table 2 in step S20 is performed separately from the raising of the paper feed table 2 by follow-up control. This forced raising of the paper feed table 2 is performed to suppress the continuous occurrence of air feeding. The above-mentioned predetermined raising amount in the forced raising of the paper feed table 2 is preset based on experiments or the like as a value that can suppress the continuous occurrence of air feeding.

[0109] Performing the forced raising of the paper feed table 2 in step S20 means forcibly raising the paper feed table 2 by a predetermined raising amount when air feeding of the sheet P by the conveying unit 8 occurs during the implementation of the follow-up control.

[0110] Next, in step S21, the control unit 13 determines whether or not the intermittent air feed count value Cb has reached a predetermined upper limit intermittent count (corresponding to the intermittent count) D (Cb = D). The upper limit intermittent count D is set as a reference for the number of occurrences of intermittent air feeding to determine whether to increase the follow-up threshold value in order to suppress the occurrence of air feeding. The upper limit intermittent count D is set to a plurality of counts. The upper limit intermittent count D is preset based on experiments or the like.

[0111] If it is determined that the intermittent air feed count value Cb has not reached the upper limit intermittent count D (step S21: NO), the control unit 13 returns to step S11.

[0112] When it is determined as "NO" in step S21 and the process returns to step S11, and when a paper feed end instruction is not received (step S11: NO), when a paper feed signal is received (step S12: YES), the control unit 13 causes the conveying unit 8 to convey the sheet P (step S13). At this time, the control unit 13 opens the shutter 17 to float a plurality of sheets P of the sheet bundle PT by the floating portion 6 and adsorbs the uppermost sheet P to the conveying belt 21, and conveys the sheet P by the conveying unit 8. In this way, a paper feed retry is performed.

[0113] In step S21, when it is determined that the intermittent paper feed count value Cb has reached the upper limit of intermittent times D (step S21: YES), in step S22, the control unit 13 increases the tracking threshold value by a predetermined amount. Thereby, subsequent paper feed can be reduced. The amount by which the tracking threshold value is increased (the above-mentioned predetermined amount) is preset based on experiments or the like as a value that can reduce paper feed.

[0114] Next, in step S23, the control unit 13 clears the intermittent paper feed count value Cb (sets Cb = 0). After that, the control unit 13 returns to step S11.

[0115] In step S14, when it is determined that no paper feed has occurred (step S14: NO), in step S24, the control unit 13 clears the continuous paper feed count value Ca (sets Ca = 0). After that, the control unit 13 returns to step S11.

[0116] In addition, when double feeding of the paper P by the conveying unit 8 occurs during the paper feeding operation, the control unit 13 transmits an error notification due to double feeding to the printing apparatus 100. After that, the control unit 13 receives an instruction to end paper feeding from the printing apparatus 100 and ends a series of paper feeding operations as a paper feeding error.

[0117] Here, double feeding of the paper P by the conveying unit 8 is detected by, for example, a double feed sensor (not shown) provided near the paper feed roller 10. A configuration may be adopted in which the paper feed inlet sensor 12 functions as the double feed sensor.

[0118] As described above, in the paper feeding device 1, the control unit 13 sets the follow-up threshold value such that the target position of the height position of the upper surface of the paper bundle PT in the follow-up control is a position where air feed is more likely to occur than double feeding of the paper P by the conveying unit 8. Thereby, it is possible to reduce double feeding that cannot be recovered by paper feeding retry and results in a paper feeding error. On the other hand, although air feed is more likely to occur, when air feed occurs, the control unit 13 performs paper feeding retry until the number of consecutive occurrences of air feed reaches the upper limit consecutive number R. Thereby, by relieving air feed by paper feeding retry, it is possible to suppress the occurrence of a paper feeding error even when air feed occurs. As a result, according to the paper feeding device 1, it is possible to reduce the paper feeding error.

[0119] Further, in the paper feeding device 1, when the number of occurrences of consecutive air feed of the paper P by the conveying unit 8 (continuous air feed count value Ca) reaches the upper limit consecutive number R, the control unit 13 ends a series of paper feeding operations without performing paper feeding retry thereafter. Thereby, it is possible to suppress the wasteful repetition of air feed and paper feeding retry due to the follow-up threshold value being set such that the target position is a position where air feed is more likely to occur than double feeding. Also, it is possible to suppress the wasteful repetition of air feed and paper feeding retry due to some other cause (such as the paper P being caught by a member in the device, etc.). Even during the period from the start of a series of paper feeding operations until the follow-up threshold value is determined and the follow-up control is started, it is possible to suppress the wasteful repetition of air feed and paper feeding retry.

[0120] Further, in the paper feeding device 1, when air feed of the paper P by the conveying unit 8 occurs during the period from the start of a series of paper feeding operations until the follow-up threshold value is determined, the control unit 13 does not adopt the sensor value sampled at the time of the occurrence of air feed as the sensor value for determining the follow-up threshold value. Thereby, even if air feed occurs during the period until the follow-up threshold value is determined, it is possible to suppress a decrease in the accuracy of the follow-up threshold value.

[0121] Further, in the paper feeding device 1, when air feed of the paper P by the conveying unit 8 occurs during the execution of the follow-up control, the control unit 13 forcibly raises the paper feed table 2 by a predetermined amount of ascent. Thereby, it is possible to suppress the consecutive occurrence of air feed.

[0122] In the paper feeding device 1, during the implementation of the follow-up control, when the number of occurrences (intermittent air feed count value Cb) of the intermittent air feed of the paper P by the conveying unit 8 reaches the upper limit intermittent count D, the control unit 13 increases the follow-up threshold value by a predetermined amount. Thereby, when the situation is such that air feed is likely to occur because the follow-up threshold value is set too small, this situation can be improved.

[0123] In addition, when it is determined that the intermittent air feed count value Cb has reached the upper limit intermittent count D, the adsorption force of the paper P by the conveying unit 8 may be increased by a predetermined amount as in the fourth embodiment described later. Further, when it is determined that the intermittent air feed count value Cb has reached the upper limit intermittent count D, the process of increasing the follow-up threshold value by a predetermined amount and the process of increasing the adsorption force of the paper P by the conveying unit 8 by a predetermined amount may be combined. In the case of combining the process of increasing the follow-up threshold value and the process of increasing the adsorption force of the paper P by the conveying unit 8, how much each of the follow-up threshold value and the adsorption force of the paper P by the conveying unit 8 is increased may be determined based on, for example, experiments so as to reduce air feed.

[0124] [Second Embodiment] Next, a second embodiment in which a part of the operation of the paper feeding device 1 when air feed occurs in the above-described first embodiment is changed will be described.

[0125] FIG. 8 is a flowchart for explaining the operation of the paper feeding device 1 when air feed occurs in the second embodiment.

[0126] The processes of steps S31 to S35 in FIG. 8 are the same as the processes of steps S1 to S5 in FIG. 6 described above.

[0127] In step S35, when it is determined that air feed has not occurred (step S35: NO), the control unit 13 returns to step S31.

[0128] Here, when it is determined as "NO" in step S35 and the process returns to step S31, and if a paper feed end instruction has not been received (step S31: NO) and the sensor values for the sampling number of sheets have not yet been acquired (step S32: NO), when a paper feed signal is received (step S33: YES), the control unit 13 causes the transport unit 8 to transport the sheet P (step S34). At this time, the control unit 13 releases the shutter 17 to lift a plurality of sheets P of the sheet bundle PT by the floating unit 6 and adsorbs the topmost sheet P to the transport belt 21, and transports the sheet P by the transport unit 8. In this way, paper feed retry is performed.

[0129] When it is determined that air feed has occurred (step S35: YES), in step S36, the control unit 13 transmits an error notification due to air feed to the printing apparatus 100. After that, the control unit 13 returns to step S31.

[0130] Here, the printing apparatus 100 that has received the error notification transmits a paper feed end instruction to the paper feed apparatus 1. For this reason, when returning from step S36 to step S31, the control unit 13 determines that a paper feed end instruction has been received (step S31: YES), and ends a series of paper feed operations as a paper feed error. Thereby, when air feed of the sheet P by the transport unit 8 occurs between the start of a series of paper feed operations and the determination of the follow threshold value, the control unit 13 ends a series of sheet supply operations as a paper feed error without performing supply retry.

[0131] In step S32, when it is determined that the sensor values for the sampling number of sheets have been acquired (step S32: YES), in step S37, the control unit 13 determines the follow threshold value and starts follow control in the same manner as step S10 of FIG. 6 described above. After that, the control unit 13 proceeds to step S11 of FIG. 7 described above and executes subsequent processing.

[0132] As described above, in the second embodiment, when the conveyance unit 8 causes the blank conveyance of the sheet P before determining the follow-up threshold value, the control unit 13 ends a series of sheet supply operations without performing a supply retry. As a result, it is possible to avoid determining the follow-up threshold value in a state where there is some cause that easily causes blank conveyance. For this reason, it is possible to avoid repeating blank conveyance and paper feed retries after the paper feed operation has started, or causing a paper feed error when the continuous blank conveyance count value Ca reaches the upper limit continuous number R. That is, by setting a paper feed error at an early stage after the start of the paper feed operation, the user can take measures early.

[0133] [Third Embodiment] Next, a third embodiment in which a part of the operation of the paper feeding device 1 when blank conveyance occurs in the first embodiment described above is changed will be described.

[0134] FIG. 9 is a flowchart for explaining the operation of the paper feeding device 1 when blank conveyance occurs in the third embodiment.

[0135] In the third embodiment, when the paper feed operation is started, the processes of steps S1 to S10 in FIG. 6 described above are performed in the same manner as in the first embodiment. In the third embodiment, after step S10 in FIG. 6, the process proceeds to step S41 in FIG. 9. The processes of steps S31 to S37 in FIG. 8 described in the second embodiment may be performed, and after step S37 in FIG. 8, the process may proceed to step S41 in FIG. 9.

[0136] The processes of steps S41 to S49 in FIG. 9 are the same as the processes of steps S11 to S19 in FIG. 7 described above.

[0137] In step S50 of FIG. 9, the control unit 13 determines whether or not the continuous paper feed count value Ca has reached a predetermined specified continuous number of times K (Ca = K). The specified continuous number of times K is set as a reference for the number of occurrences of continuous paper feed for determining whether or not to forcibly raise the paper feed table 2 in order to suppress the occurrence of paper feed. The specified continuous number of times K is set to a plurality of times. The specified continuous number of times K is preset based on experiments or the like as a value that can suppress the occurrence of paper feed while avoiding excessive raising of the paper feed table 2. In the third embodiment, the upper limit continuous number of times R is set to a value larger than the specified continuous number of times K.

[0138] When it is determined that the continuous paper feed count value Ca has reached the specified continuous number of times K (step S50: YES), in step S51, the control unit 13 forcibly raises the paper feed table 2 by a predetermined amount of increase in the same manner as step S20 of FIG. 7 described above. After that, the control unit 13 proceeds to step S52.

[0139] When it is determined that the continuous paper feed count value Ca has not reached the specified continuous number of times K (step S50: NO), the control unit 13 skips step S51 and proceeds to step S52. Thereby, the control unit 13 does not forcibly raise the paper feed table 2 until the paper feed P by the transport unit 8 during the implementation of the follow-up control is repeated up to the specified continuous number of times K.

[0140] The processing of steps S52 to S55 is the same as the processing of steps S21 to S24 of FIG. 7 described above.

[0141] As described above, in the third embodiment, the control unit 13 does not forcibly raise the paper feed table 2 until the paper feed P by the transport unit 8 during the implementation of the follow-up control is repeated up to the specified continuous number of times K. Thereby, it is possible to suppress the occurrence of paper feed while suppressing an increase in the risk of double feed caused by excessively raising the paper feed table 2.

[0142] [Fourth Embodiment] Next, a fourth embodiment in which a part of the first embodiment described above is modified will be described.

[0143] In the fourth embodiment, the control unit 13 controls the conveying unit 8 such that the adsorption force of the sheet P by the conveying unit 8 becomes an adsorption force that is more likely to cause air conveyance of the sheet P than double feeding of the sheet P when the height position of the upper surface of the sheet stack PT is at the target position in the follow-up control. Specifically, the control unit 13 sets the suction air volume of the suction mechanism unit 25 of the conveying unit 8 during the paper feeding operation to a volume smaller than the appropriate volume. The appropriate volume is a suction air volume at which double feeding and air conveyance are equally unlikely to occur when the height position of the upper surface of the sheet stack PT is at the target position in the follow-up control.

[0144] Here, in the conveying unit 8, if the height position of the upper surface of the sheet stack PT is the same, the smaller the suction air volume of the suction mechanism unit 25, the smaller the adsorption force of the sheet P on the conveying belt 21, and the smaller the frictional force between the conveying belt 21 and the sheet P. Therefore, air conveyance of the sheet P is more likely to occur.

[0145] Also in the fourth embodiment, the process of determining the follow-up threshold value and the follow-up control are performed in the same manner as in the first embodiment described above.

[0146] That is, when paper feeding start is instructed, the control unit 13 adjusts the height position of the paper feed table 2 and sets the upper surface of the sheet stack PT to a paper feeding start position that is higher than the target position by the thickness of the sheet P corresponding to the total number of sheets obtained by adding the sampling exclusion number and half of the sampling number.

[0147] Next, the control unit 13 starts the paper feeding operation. At this time, the control unit 13 sets the suction air volume of the suction mechanism unit 25 to a volume smaller than the above-described appropriate volume and starts driving the suction mechanism unit 25. The suction air volume of the suction mechanism unit 25 is set to a suction air volume that can suppress the occurrence of double feeding while suppressing an increase in air conveyance during the implementation of the follow-up control according to the paper type and paper size. The suction air volume of the suction mechanism unit 25 corresponding to the paper type and paper size is obtained experimentally in advance, for example.

[0148] After the start of the paper feeding operation, when the number of sheets fed reaches the sampling exclusion number, the control unit 13 starts sampling sensor values for determining the tracking threshold. When the sensor values for the sampling number of sheets are acquired, the control unit 13 determines the tracking threshold and starts tracking control.

[0149] When the tracking threshold is determined, the control unit 13 starts tracking control using the determined tracking threshold. When starting the tracking control, for each sheet of paper being fed, if the acquired sensor value is less than the tracking threshold, the control unit 13 raises the paper feed tray 2.

[0150] Since the suction air volume of the suction mechanism unit 25 is set to a volume smaller than the appropriate air volume as described above, the paper feeding operation is performed in a situation where air feeding is more likely to occur than double feeding.

[0151] Next, the operation of the paper feeding device 1 when air feeding occurs in the fourth embodiment will be described.

[0152] The operation of the paper feeding device 1 when air feeding occurs in the fourth embodiment is the same as the operation described above in the first embodiment using the flowcharts of FIGS. 6 and 7, except for the process of step S22 in FIG. 7.

[0153] In the fourth embodiment, the process of increasing the tracking threshold in step S22 of FIG. 7 by a predetermined amount is replaced with the process of increasing the adsorption force of the sheet P by the conveying unit 8 by a predetermined amount. That is, when it is determined that the intermittent air feed count value Cb has reached the upper limit intermittent count D (step S21: YES), the control unit 13 increases the adsorption force of the sheet P by the conveying unit 8 by a predetermined amount.

[0154] Specifically, the control unit 13 increases the suction air volume of the suction mechanism unit 25 by a predetermined air volume. Thereby, subsequent air feeding can be reduced. How much to increase the adsorption force of the sheet P by the conveying unit 8, that is, how much to increase the suction air volume of the suction mechanism unit 25 (the above-mentioned predetermined air volume), is preset based on experiments and the like as a value that can reduce air feeding.

[0155] As described above, in the fourth embodiment, the control unit 13 controls the transport unit 8 such that the adsorption force of the sheet P by the transport unit 8 is an adsorption force that is more likely to cause air feed than double feed of the sheet P during the implementation of the follow-up control. Thereby, similar to the first embodiment, it is possible to reduce double feed that cannot be recovered by paper feed retry and results in a paper feed error. On the other hand, although air feed is more likely to occur, when air feed occurs, the control unit 13 performs paper feed retry until the number of consecutive occurrences of air feed reaches the upper limit consecutive number R. Thereby, by recovering air feed by paper feed retry, it is possible to suppress the occurrence of a paper feed error even when air feed occurs. As a result, the paper feed error can be reduced.

[0156] Also, similar to the first embodiment, in the fourth embodiment, when the number of consecutive occurrences of air feed of the sheet P by the transport unit 8 (continuous air feed count value Ca) reaches the upper limit consecutive number R, the control unit 13 ends a series of paper feed operations without performing paper feed retry thereafter. Thereby, it is possible to suppress the repeated wasteful air feed and paper feed retry.

[0157] Also, similar to the first embodiment, in the fourth embodiment, when air feed of the sheet P by the transport unit 8 occurs between the start of a series of paper feed operations and the determination of the follow-up threshold value, the control unit 13 does not adopt the sensor value sampled at the time of the occurrence of air feed as the sensor value for determining the follow-up threshold value. Thereby, even if air feed occurs before the follow-up threshold value is determined, it is possible to suppress a decrease in the accuracy of the follow-up threshold value.

[0158] Also, similar to the first embodiment, in the fourth embodiment, when air feed of the sheet P by the transport unit 8 occurs during the implementation of the follow-up control, the control unit 13 forcibly raises the paper feed tray 2 by a predetermined amount. Thereby, it is possible to suppress the continuous occurrence of air feed.

[0159] Also, in the fourth embodiment, during the implementation of the follow-up control, when the number of occurrences of the intermittent air conveyance of the sheet P by the conveyance unit 8 (intermittent air conveyance count value Cb) reaches the upper limit intermittent count D, the control unit 13 increases the adsorption force of the sheet P by the conveyance unit 8 by a predetermined amount. This can improve the situation when the adsorption force of the sheet P by the conveyance unit 8 is too small and it is easy for air conveyance to occur.

[0160] In addition, also in the fourth embodiment, as in the second embodiment, when air conveyance of the sheet P by the conveyance unit 8 occurs before the control unit 13 determines the follow-up threshold value, the control unit 13 may end a series of sheet supply operations without performing supply retry. This allows the user to take action earlier by setting a paper feed error at an early stage after the start of the paper feed operation.

[0161] Also, in the fourth embodiment, as in the third embodiment, during the implementation of the follow-up control, the control unit 13 may not forcibly raise the paper feed tray 2 until the air conveyance of the sheet P by the conveyance unit 8 is repeated up to the specified continuous count K. This can suppress the occurrence of air conveyance while suppressing an increase in the risk of double feeding caused by excessively raising the paper feed tray 2.

[0162] Also, when it is determined that the intermittent air conveyance count value Cb has reached the upper limit intermittent count D, as in the first embodiment, the follow-up threshold value may be increased by a predetermined amount. Also, when it is determined that the intermittent air conveyance count value Cb has reached the upper limit intermittent count D, a process of increasing the follow-up threshold value by a predetermined amount and a process of increasing the adsorption force of the sheet P by the conveyance unit 8 by a predetermined amount may be combined. When combining the process of increasing the follow-up threshold value and the process of increasing the adsorption force of the sheet P by the conveyance unit 8, how much to increase each of the follow-up threshold value and the adsorption force of the sheet P by the conveyance unit 8 may be determined based on, for example, experiments so as to reduce air conveyance.

[0163] [Other Embodiments] As described above, the present invention has been described according to the first to fourth embodiments. However, the discussion and drawings that form part of this disclosure should not be understood as limiting the invention. Various alternative embodiments, examples, and operating techniques will be apparent to those skilled in the art from this disclosure.

[0164] In the above-described first to fourth embodiments, the sampling period in the process of determining the following threshold is set such that the same number of sheets are fed before and after the time when the height position of the upper surface of the paper bundle PT reaches the target position, and the average value of a plurality of sampled sensor values is determined as the following threshold. However, the number of sheets fed before and after the time when the height position of the upper surface of the paper bundle PT reaches the target position during the sampling period may be different from each other. In this case, for example, the following threshold can be determined by adjusting the average value of the sensor values for the sampled number of samples according to the number of sheets fed before and after the time when the height position of the upper surface of the paper bundle PT reaches the target position during the sampling period.

[0165] Also, when the behavior of the lifted paper P is stable even immediately after the start of the paper feeding operation, it is possible to omit setting the sampling exclusion number immediately after the start of the paper feeding operation and start the sampling period together with the start of the paper feeding operation. For example, in a configuration in which air can be sent between the sheets P of the paper bundle PT before the start of the paper feeding operation to prevent a plurality of sheets P from floating while being in close contact and stabilize the behavior of the paper P, the sampling period may be started together with the start of the paper feeding operation.

[0166] Also, as described above, when the behavior of the lifted sheet P is stable even immediately after the start of the paper feeding operation, the sensor value sampled during the conveyance of the first sheet P in the paper feeding operation may be determined as the follow-up threshold value. In this case, the height position of the paper feed table 2 when starting the paper feeding operation is set so that the height position of the upper surface of the paper stack PT becomes the target position during the paper feeding operation. Then, the sensor value during the lifting of the sheet P lifted to convey the first sheet P in the paper feeding operation is sampled, and the follow-up control is started by determining the sensor value as the follow-up threshold value. The process of determining the follow-up threshold value may be any process that samples the sensor value during the lifting of the sheet P lifted by the floating portion 6 at least during the conveyance of one sheet of paper P after the start of the paper feeding operation and determines the follow-up threshold value using the sampled sensor value.

[0167] In the above-described first to fourth embodiments, the sensor value during the lifting of the sheet P is sampled after the start of the paper feeding operation to determine the follow-up threshold value, but the follow-up control may be performed using a preset follow-up threshold value.

[0168] In the above-described first to fourth embodiments, the upper limit sensor 9 is configured as an optical sensor, but the present invention is not limited to this, and the upper limit sensor 9 may be a sensor that detects the sheet P using electromagnetic waves, infrared rays, or the like. The upper limit sensor 9 only needs to be able to detect the output signal obtained by inputting from the side of the paper stack PT. Also, the follow-up control may be any control that, during the paper feeding operation, acquires the detection value of the upper limit sensor 9 during the lifting of the sheet P lifted by the floating portion 6 for each sheet of paper conveyed by the conveyance unit 8, and raises the paper feed table 2 when the acquired detection value is less than the threshold value.

[0169] In the above-described first to fourth embodiments, the conveyance unit 8 is shown to adsorb and convey the sheet P by the adsorption force due to air suction, but the present invention is not limited to this, and a configuration that adsorbs and conveys the sheet P by the adsorption force due to electrostatic force or magnetic force may also be used.

[0170] In the above-described first to fourth embodiments, the paper feeding device for feeding paper has been described, but the present invention is also applicable to a device for supplying sheets other than paper.

[0171] Thus, the present invention naturally includes various embodiments and the like not described herein. Therefore, the technical scope of the present invention is defined only by the invention specifying matters according to the scope of claims reasonable from the above description.

[0172] [Supplementary Note] This application discloses the following inventions.

[0173] (Supplementary Note 1) A liftable loading platform on which a stack of sheets is loaded, A floating part that blows air onto the stack of sheets to lift the sheets in the stack, A conveying part that conveys the uppermost sheet among the sheets lifted by the floating part to a supply destination, A detection part that detects an output signal obtained by inputting to the side of the stack of sheets, A control part that controls the floating part and the conveying part so as to convey the sheets to the supply destination, and for each sheet conveyed by the conveying part, acquires the detection value of the detection part during the floating of the sheets lifted by the floating part, and performs follow-up control to raise the loading platform when the acquired detection value is less than a threshold value. The control part, When air conveyance of the sheets by the conveying part occurs, controls the floating part and the conveying part so as to perform a supply retry to re-convey the sheets to the supply destination, A sheet supply device characterized in that the threshold value is set so that the target position of the height position of the upper surface of the stack of sheets in the follow-up control is a position where air conveyance is more likely to occur than double conveyance of the sheets by the conveying part.

[0174] (Supplementary Note 2) A liftable loading platform on which a stack of sheets is loaded, A floating part that blows air onto the stack of sheets to lift the sheets in the stack, A conveying part that conveys the uppermost sheet among the sheets lifted by the floating part to a supply destination, A detection unit that emits light from the side of the sheet bundle toward the sheet bundle side and receives the light from the sheet bundle side; The floating part and the conveying part are controlled to convey the sheet to the supply destination, and for each sheet conveyed by the conveying part, the light reception amount of the detection unit during the floating of the sheet floated by the floating part is acquired, and when the acquired light reception amount is less than a threshold value, a control unit that performs follow-up control to raise the stacking table is provided. The control unit When air conveyance of the sheet by the conveying part occurs, the floating part and the conveying part are controlled to perform a supply retry to re-convey the sheet to the supply destination. A sheet supply device, wherein the threshold value is set so that the target position of the height position of the upper surface of the sheet bundle in the follow-up control is a position where air conveyance is more likely to occur than double conveyance of the sheet by the conveying part.

[0175] (Appendix 3) The control unit During the conveyance of at least one sheet, the light reception amount of the detection unit during the floating of the sheet floated by the floating part is sampled, the threshold value is determined using the sampled light reception amount, and the follow-up control is started. When air conveyance of the sheet by the conveying part occurs before the threshold value is determined, the light reception amount sampled at the time of the occurrence of the air conveyance is not adopted as the light reception amount for determining the threshold value. The sheet supply device according to Appendix 2, characterized in that When air conveyance of the sheet by the conveying part occurs before the threshold value is determined, the series of sheet supply operations are terminated without performing the supply retry. The sheet supply device according to Appendix 2, characterized in that

[0176] (Appendix 4) The control unit During the conveyance of at least one sheet, the light reception amount of the detection unit during the floating of the sheet floated by the floating part is sampled, the threshold value is determined using the sampled light reception amount, and the follow-up control is started. When air conveyance of the sheet by the conveying part occurs before the threshold value is determined, the series of sheet supply operations are terminated without performing the supply retry. The sheet supply device according to Appendix 2, characterized in that

[0177] (Appendix 5) During the implementation of the follow-up control, when the number of occurrences of intermittent sheet air conveyance by the conveyance unit reaches a predetermined number of interruptions, the control unit increases the threshold value by a predetermined amount. The sheet feeding device according to any one of Appendices 2 to 4, characterized in that.

[0178] (Appendix 6) The conveyance unit adsorbs and conveys the sheet. During the implementation of the follow-up control, when the number of occurrences of intermittent sheet air conveyance by the conveyance unit reaches a predetermined number of interruptions, the control unit performs at least one of a process of increasing the threshold value by a predetermined amount and a process of increasing the adsorption force of the sheet by the conveyance unit by a predetermined amount. The sheet feeding device according to any one of Appendices 2 to 4, characterized in that.

[0179] (Appendix 7) A liftable loading table on which a stack of sheets is loaded. A floating part that blows air onto the stack of sheets to lift the sheets in the stack. A conveyance unit that adsorbs and conveys the uppermost sheet among the sheets lifted by the floating part to a supply destination. A control unit that controls the floating part and the conveyance unit to convey the sheet to the supply destination, and performs follow-up control to raise the loading table in response to a decrease in the sheets on the loading table. The control unit. When air conveyance of the sheet by the conveyance unit occurs, the floating part and the conveyance unit are controlled to perform a supply retry to re-convey the sheet to the supply destination. The sheet feeding device, characterized in that the conveyance unit is controlled such that the adsorption force of the sheet by the conveyance unit is an adsorption force at which air conveyance is more likely to occur than double conveyance of the sheet when the height position of the upper surface of the stack of sheets is at the target position in the follow-up control.

[0180] (Appendix 8) The sheet feeding device further includes a detection unit that emits light from the side of the sheet bundle toward the sheet bundle side and receives light from the sheet bundle side. The control unit As the follow-up control, for each sheet conveyed by the conveying unit, the light reception amount of the detection unit during the floating of the sheet floated by the floating unit is acquired, and when the acquired light reception amount is less than a threshold value, control is performed to raise the loading table. Before starting the follow-up control, during the conveyance of at least one sheet, the light reception amount of the detection unit during the floating of the sheet floated by the floating unit is sampled, and the threshold value is determined using the sampled light reception amount. When sheet empty feeding occurs by the conveying unit before the threshold value is determined, the light reception amount sampled at the time of the empty feeding is not adopted as the light reception amount for determining the threshold value, and the sheet feeding device according to appended note 7 is characterized in that.

[0181] (Appended note 9) The sheet feeding device further includes a detection unit that emits light from the side of the sheet bundle toward the sheet bundle side and receives light from the sheet bundle side. The control unit As the follow-up control, for each sheet conveyed by the conveying unit, the light reception amount of the detection unit during the floating of the sheet floated by the floating unit is acquired, and when the acquired light reception amount is less than a threshold value, control is performed to raise the loading table. Before starting the follow-up control, during the conveyance of at least one sheet, the light reception amount of the detection unit during the floating of the sheet floated by the floating unit is sampled, and the threshold value is determined using the sampled light reception amount. When sheet empty feeding occurs by the conveying unit before the threshold value is determined, the series of sheet feeding operations are terminated without performing the supply retry, and the sheet feeding device according to appended note 7 is characterized in that.

[0182] (Appended note 10) The sheet feeding device further includes a detection unit that emits light from the side of the sheet bundle toward the sheet bundle side and receives light from the sheet bundle side. The control unit As the follow-up control, for each sheet conveyed by the conveying unit, the light reception amount of the detection unit during the floating of the sheet floated by the floating unit is acquired, and when the acquired light reception amount is less than the threshold value, control is performed to raise the loading table. During the implementation of the follow-up control, when the number of occurrences of intermittent air feeding of the sheet by the conveying unit reaches a predetermined number of intermittent occurrences, at least one of the process of increasing the threshold value by a predetermined amount and the process of increasing the adsorption force of the sheet by the conveying unit by a predetermined amount is performed. The sheet feeding device according to any one of Appendices 7 to 9.

[0183] (Appendix 11) The control unit forcibly raises the loading table by a predetermined lifting amount when air feeding of the sheet by the conveying unit occurs during the implementation of the follow-up control. The sheet feeding device according to any one of Appendices 2 to 10.

[0184] (Appendix 12) The control unit does not forcibly raise the loading table until the air feeding of the sheet by the conveying unit during the implementation of the follow-up control is repeated a predetermined number of times. The sheet feeding device according to Appendix 11.

[0185] (Appendix 13) When the number of occurrences of continuous air feeding of the sheet by the conveying unit reaches a predetermined number, the control unit terminates a series of sheet feeding operations without performing the supply retry thereafter. The sheet feeding device according to any one of Appendices 2 to 12.

Explanation of Signs

[0186] 1 Paper feeding device 2 Paper feeding table 3 End fence 4 Lifting motor 5 Encoder 6 Floating unit 7 Separation unit 8 Conveying unit 9 Upper limit sensor 10 Sheet feeding roller 11 Sheet feeding motor 12 Sheet feeding entrance sensor 13 Control unit 16 Lift fan 17 Shutter 18 Separation fan 21 Conveyor belt 22 Driving roller 23 Driven roller 24 Conveyor motor 25 Suction mechanism unit 31 Light emitting unit 32 Light receiving unit 100 Printing device P paper PT paper bundle

Claims

1. A liftable loading platform on which a stack of sheets is loaded, a floating part that blows air onto the stack of sheets to lift the sheets in the stack, a conveying part that conveys the topmost sheet among the sheets lifted by the floating part to a supply destination, a detection part that detects an output signal obtained by inputting to the side of the stack of sheets, a control part that controls the floating part and the conveying part so as to convey the sheets to the supply destination, and for each sheet conveyed by the conveying part, obtains the detection value of the detection part during the floating of the sheets lifted by the floating part, and performs follow-up control to raise the loading platform when the obtained detection value is less than a threshold value, The control part is when air conveyance of the sheets by the conveying part occurs, controls the floating part and the conveying part so as to perform a supply retry to re-convey the sheets to the supply destination, A sheet supply device, characterized in that the threshold value is set so that the target position of the height position of the upper surface of the stack of sheets in the follow-up control is a position below a proper position where double feeding and air conveyance are equally unlikely to occur according to the paper type by a predetermined offset amount, and is a position where air conveyance is more likely to occur than double feeding of the sheets by the conveying part.

2. A liftable loading platform on which a stack of sheets is loaded, a floating part that blows air onto the stack of sheets to lift the sheets in the stack, a conveying part that conveys the topmost sheet among the sheets lifted by the floating part to a supply destination, a detection part that emits light from the side of the stack of sheets toward the stack of sheets side and receives the light from the stack of sheets side, a control part that controls the floating part and the conveying part so as to convey the sheets to the supply destination, and for each sheet conveyed by the conveying part, obtains the light reception amount of the detection part during the floating of the sheets lifted by the floating part, and performs follow-up control to raise the loading platform when the obtained light reception amount is less than a threshold value, The control part is when air conveyance of the sheets by the conveying part occurs, controls the floating part and the conveying part so as to perform a supply retry to re-convey the sheets to the supply destination, A sheet supply device, characterized in that the threshold value is set so that the target position of the height position of the upper surface of the stack of sheets in the follow-up control is a position below a proper position where double feeding and air conveyance are equally unlikely to occur according to the paper type by a predetermined offset amount, and is a position where air conveyance is more likely to occur than double feeding of the sheets by the conveying part. Claim 3. A liftable loading platform on which a stack of sheets is loaded, a floating part that blows air onto the stack of sheets to lift the sheets in the stack, a conveying part that conveys the topmost sheet among the sheets lifted by the floating part to a supply destination, a detection part that emits light from the side of the stack of sheets toward the stack of sheets and receives the light from the stack of sheets side, a control part that controls the floating part and the conveying part so as to convey the sheet to the supply destination, and for each sheet conveyed by the conveying part, acquires the amount of light received by the detection part during the floating of the sheet lifted by the floating part, and performs follow-up control to raise the loading platform when the acquired amount of light received is less than a threshold value, wherein the control part controls the floating part and the conveying part so as to perform a supply retry to re-convey the sheet to the supply destination when an air conveyance of the sheet by the conveying part occurs, sets the threshold value so that a target position of the height position of the upper surface of the stack of sheets in the follow-up control becomes a position where air conveyance is more likely to occur than double conveyance of the sheet by the conveying part, and further, the control part samples the amount of light received by the detection part during the floating of the sheet lifted by the floating part at least during the conveyance of one sheet, determines the threshold value using the sampled amount of light received, and starts the follow-up control, and a sheet supply device characterized in that when an air conveyance of the sheet by the conveying part occurs before the threshold value is determined, the amount of light received sampled at the time of the occurrence of the air conveyance is not adopted as the amount of light received for determining the threshold value. Claim 4. A liftable loading platform on which a stack of sheets is loaded, a floating part that blows air onto the stack of sheets to lift the sheets in the stack, a conveying part that conveys the topmost sheet among the sheets lifted by the floating part to a supply destination, a detection part that emits light from the side of the stack of sheets toward the stack of sheets and receives the light from the stack of sheets side, a control part that controls the floating part and the conveying part so as to convey the sheet to the supply destination, and for each sheet conveyed by the conveying part, acquires the amount of light received by the detection part during the floating of the sheet lifted by the floating part, and performs follow-up control to raise the loading platform when the acquired amount of light received is less than a threshold value, wherein the control part When sheet air conveyance occurs by the conveyance unit, the floating unit and the conveyance unit are controlled to perform a supply retry to re-convey the sheet to the supply destination. The threshold value is set so that the target position of the height position of the upper surface of the sheet bundle in the follow-up control is a position where air conveyance of the sheet is more likely to occur than double conveyance of the sheet by the conveyance unit. Also, the control unit During conveyance of at least one sheet, the light reception amount of the detection unit during floating of the sheet floated by the floating unit is sampled, and the threshold value is determined using the sampled light reception amount to start the follow-up control. When sheet air conveyance occurs by the conveyance unit before the threshold value is determined, a sheet supply device characterized by ending a series of sheet supply operations without performing the supply retry.

5. During implementation of the follow-up control, when the number of occurrences of intermittent sheet air conveyance by the conveyance unit reaches a predetermined number of interruptions, the control unit increases the threshold value by a predetermined amount. The sheet supply device according to any one of claims 2 to 4.

6. The conveyance unit adsorbs and conveys the sheet. During implementation of the follow-up control, when the number of occurrences of intermittent sheet air conveyance by the conveyance unit reaches a predetermined number of interruptions, the control unit performs at least one of a process of increasing the threshold value by a predetermined amount and a process of increasing the adsorption force of the sheet by the conveyance unit by a predetermined amount. The sheet supply device according to any one of claims 2 to 4.

7. A liftable loading table on which a sheet bundle is loaded; A floating unit that blows air onto the sheet bundle to float the sheets of the sheet bundle; A conveyance unit that adsorbs and conveys the uppermost sheet among the sheets floated by the floating unit to a supply destination; A control unit that controls the floating unit and the conveyance unit to convey the sheet to the supply destination and performs follow-up control to raise the loading table in response to a decrease in the sheets on the loading table. The control unit When sheet air conveyance occurs by the conveyance unit, the floating unit and the conveyance unit are controlled to perform a supply retry to re-convey the sheet to the supply destination. The sheet feeding device is characterized in that the conveying unit is controlled so that the suction force of the sheet by the conveying unit is smaller than the suction force at which double feeding and air feeding of the sheet are equally unlikely to occur when the height position of the upper surface of the sheet bundle is at the target position in the follow-up control according to the paper type and paper size, and air feeding of the sheet is more likely to occur than double feeding of the sheet.

8. A liftable loading table on which a sheet bundle is loaded, A floating unit that blows air onto the sheet bundle to lift the sheets of the sheet bundle, A conveying unit that adsorbs the uppermost sheet among the sheets lifted by the floating unit and conveys it to a supply destination, A detection unit that emits light from the side of the sheet bundle toward the sheet bundle side and receives the light from the sheet bundle side, A control unit that controls the floating unit and the conveying unit to convey the sheet to the supply destination, and performs follow-up control to raise the loading table in response to a decrease in the sheets on the loading table, The control unit, When air feeding of the sheet by the conveying unit occurs, controls the floating unit and the conveying unit to perform a supply retry to re-convey the sheet to the supply destination, Controls the conveying unit so that the suction force of the sheet by the conveying unit is a suction force at which air feeding of the sheet is more likely to occur than double feeding of the sheet when the height position of the upper surface of the sheet bundle is at the target position in the follow-up control, Also, the control unit, As the follow-up control, for each sheet conveyed by the conveying unit, acquires the light reception amount of the detection unit during the floating of the sheet lifted by the floating unit, and performs control to raise the loading table when the acquired light reception amount is less than a threshold value, Before starting the follow-up control, samples the light reception amount of the detection unit during the floating of the sheet lifted by the floating unit at least during the conveyance of one sheet, and determines the threshold value using the sampled light reception amount, The sheet feeding device is characterized in that when air feeding of the sheet by the conveying unit occurs before the threshold value is determined, the light reception amount sampled at the time of the occurrence of air feeding is not adopted as the light reception amount for determining the threshold value.

9. A liftable loading table on which a sheet bundle is loaded, A floating unit that blows air onto the sheet bundle to lift the sheets of the sheet bundle, A conveying unit that adsorbs the uppermost sheet among the sheets lifted by the floating unit and conveys it to a supply destination, A detection unit that emits light from the side of the sheet bundle toward the sheet bundle side and receives light from the sheet bundle side; A control unit that controls the floating unit and the conveying unit to convey the sheet to the supply destination, and performs follow-up control to raise the stacking table in response to a decrease in the sheets on the stacking table; The control unit: When air conveyance of the sheet by the conveying unit occurs, controls the floating unit and the conveying unit to perform a supply retry to re-convey the sheet to the supply destination; Controls the conveying unit such that when the height position of the upper surface of the sheet bundle is at the target position in the follow-up control, the adsorption force of the conveying unit is such that air conveyance is more likely to occur than double conveyance of the sheet; Also, the control unit: As the follow-up control, for each sheet conveyed by the conveying unit, obtains the light reception amount of the detection unit during the floating of the sheet floated by the floating unit, and performs control to raise the stacking table when the obtained light reception amount is less than a threshold value; Before starting the follow-up control, during the conveyance of at least one sheet, samples the light reception amount of the detection unit during the floating of the sheet floated by the floating unit, and determines the threshold value using the sampled light reception amount; A sheet supply device characterized in that when air conveyance of the sheet by the conveying unit occurs before the threshold value is determined, a series of sheet supply operations are terminated without performing the supply retry.

10. Further comprising a detection unit that emits light from the side of the sheet bundle toward the sheet bundle side and receives light from the sheet bundle side; The control unit: As the follow-up control, for each sheet conveyed by the conveying unit, obtains the light reception amount of the detection unit during the floating of the sheet floated by the floating unit, and performs control to raise the stacking table when the obtained light reception amount is less than a threshold value; During the implementation of the follow-up control, when the number of occurrences of intermittent air conveyance of the sheet by the conveying unit reaches a predetermined number of intermittent occurrences, at least one of a process of increasing the threshold value by a predetermined amount and a process of increasing the adsorption force of the sheet by the conveying unit by a predetermined amount is performed. The sheet supply device according to any one of claims 7 to 9.

11. The control unit according to any one of claims 2 to 10, characterized in that when sheet air conveyance by the conveyance unit occurs during implementation of the follow-up control, the loading table is forcibly raised by a predetermined upward amount.

12. The sheet feeding device according to claim 11, characterized in that the control unit does not forcibly raise the loading table until air conveyance of the sheet by the conveyance unit during implementation of the follow-up control is repeated a predetermined number of times.

13. The sheet feeding device according to any one of claims 2 to 12, characterized in that when the number of occurrences of continuous air conveyance of the sheet by the conveyance unit reaches a predetermined number, a series of sheet feeding operations are terminated without performing the supply retry thereafter.

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