DEVICE FOR STACKING SHEETS

Abstract: A device for piling up such sheets as conveyed after cut by a cutting machine on a stacking table. The sheets cut by the cutting machine are conveyed at fixed intervals, clamped during the running by a clamping unit at reference positions of the rear ends of the sheets, and the running speeds of the sheets are reduced to an optimum ones required for neatly piling up the sheets. The clamping unit is provided with a rotating part having a free roller and a speed reduction roller at the tip thereof, in which, with each rotation of the rotating part, the free roller comes into contact with the speed reduction roller for clamping the sheets.

Description: Technical Field This invention relates to a sheet stacker to be used in the field of cutting corrugated cardboard, paper, plastic film, foil and the like, for slowing down sheet travelling speed to an optimum speed needed for stacking sheets cut by a sheet cutter orderly into stacking zone by clamping tails of sheets during transferring sheets, and for stacking the sheets directly and orderly into the stacking zone. Background Technologies Conventionally as shown in Figs.7A and Fig.7B, in order to stack sheets of corrugated cardboard, paper, plastic film, foil and other various material cut by a sheet cutting machine 82 into the stacking zone, sheets 86 are transferred by a high speed conveyor 84 and their transfer speed is reduced by an overlap conveyor 88 (a low speed conveyor) having a speed difference from the high speed conveyor. The sheets, whose speed is reduced, are then overlapped on the overlap conveyor one after another, are transferred by the overlap conveyor, and are stacked into the stacking zone, lot by lot overlapped. Many kinds of overlap conveyors are used. For example, sheets travelling on the high speed conveyor are nipped, slowed down and overlapped on the over lap conveyor by "pressing whiskers" of the overlap conveyor, with vacuum or the like, and are then transferred on the overlap conveyor. Or, sheets transferred by the high speed conveyor are slowed down and overlapped by "catching belt", "pressing belt", "low speed conveyor" or the like. Fig.7A shows an example where pressing whiskers 90 are used, and Fig.7B shows an example where a catching belt 92 is used. However, a system using such an overlap conveyor has various problems such that grazes are produced on surface of a sheet travelling at a high speed due to friction of "pressing whiskers", "catching belt", "pressing belt" or the like, the leading edge of sheet is folded or damaged because of high speed sheet transfer by the conveyor, and a sheet is normally because the leading edge of a sheet droops down or bumps against preceding sheet, especially when sheet stiffness is low. Because cutting performance of cutting machine has recently been improved remarkably, it is required to transfer cut sheets at a high speed. Therefore, it becomes necessary to install another higher speed conveyor upstream of said high speed conveyor, resulting in lengthening a line by said higher speed conveyor, in necessity of a larger installation space, and in increase of installation cost. Furthermore, because materials to be cut by a sheet cutting machine are various including thicker and thinner corrugated cardboard, paper, plastic film, foil and the like, it becomes impossible to dissolve said various problems for such various materials by said conventional sheet stacker, namely by a stacker for transferring cut sheets by a high speed conveyor, reduction sheet speed by an overlap conveyor, overlapping the sheets, sending the sheets to the stacking zone and stacking the sheets into the stacking zone, lot by lot overlapped. A means to dissolve such problems was disclosed in EP-A-150 655 having an US priority No.557,439, "Tail Stopping and Knockdown Device". As shown in Fig.8, this device has a slowing down device comprising a brush roll 103 and a low speed roll 104 between a conveyor 101 and a stacking station 102. The rolls 103 and 104 are driven by a motor 106 through appropriate gearings 105. In this conventional technology, sheets are slowed down and sent to the stacking station 102, their portions near the tails ends being contacted by either one of two brushes 108 of the brush roll 103 and being pressed to the roll 104 rotating at a low speed, when sheets pass between two rolls 103 and 104. But with this type of brush roll 103, the action of brush 108 to press sheets to the roll 104 is unstable, and sheets could be damaged by the brushes in case of paper sheets or the like. Furthermore, the pressing positions of sheets cannot be accurately controlled, and therefore, when the pressing positions of sheets are shifted, sheets might not be stacked into the stacking orderly. Document JP-B2-53 111 000 discloses a slowdown device, according to the preamble of Claim 1 enabling to dissolve said various problems without using conventional overlap conveyor. Disclosure of the Invention According to the present invention therefore there is provided a device for slowing down sheets cut by a sheet cutter and transferred and stacking into a stacking station, comprising; a conveyor for transferring sheets cut off by the sheet cutter, keeping a fixed sheet interval, a clamping device for clamping a base position near the tail end of the sheet transferred from the conveyor and slowing down sheet travelling speed to an optimum speed needed for stacking the sheet into the stacking station orderly, the clamping device having a rotating device including a rotating shaft, arms fixed to the rotating shaft and free rolls each thereof is supported to each end of the arms so as to rotate freely, and a slowdown roll installed opposite to the rotating device, the rotating speed of the slowdown roll being set based on the kind of material of sheet, the base position of the sheet being pressed by the free rolls onto the slowdown roll every one revolution of the free rolls about the rotating shaft, a servo motor coupled to the rotating shaft for driving the rotating device, a servo amplifier connected to the servo motor for controlling the rotating speed of the servo motor, a sheet tail end position sensor installed over the conveyor for detecting the tail end of the sheet being transferred by the conveyor, a first speed sensor for detecting the speed of the conveyor, a second speed sensor for detecting the rotating speed of the servo motor, and an origin sensor for detecting the origin of the rotating device, the origin of the rotating device being used for determining a slowdown starting position of the rotating device, characterized in that the device further comprises; a phase setter for setting the value of (L-X)-Bo after converting to pulse, where L is the distance between the lower reference point of the rotating device and the sheet tail end position sensor, X is the distance between the tail end position and the base position of the sheet, and Bo is a circumferential length of the circle drawn by the farmost point of the free rolls from the rotating shaft when the free rolls of the rotating device revolves about the rotating shaft, a gate circuit for gating the output of the first speed sensor, the gate circuit being opened when the tail end of the sheet is detected by the sheet tail end position sensor, and being closed when the origin of the rotating device is detected by the origin sensor, a first adder for calculating the value of R=((L-X)- Bo)-AA+BB , where AA is the pulse of sheet transfer length obtained through the gate circuit from the output of the first speed sensor, and BB is the count value of pulse which is obtained from the output of the second speed sensor, a first digital/analog converter for converting the value of R to an analog voltage value V C , a frequency/voltage converter for converting the output of the first speed sensor to an analog voltage V A , a second adder for calculating a speed command (V A -V C ), a subtracter for subtracting the output of the second speed sensor from a length along the circle up to the upper reference point from the slowdown starting position of the rotating device, the length being preset when the origin of the rotating device is detected by the origin sensor, a second digital/analog converter for converting the output of the subtracter to a speed command V B , and a speed command selecting circuit for selecting either the speed command (V A -V C ) or V B based on the voltage thereof and outputting a speed command to the servo amplifier. Preferably when R=O , the revolution speed of the free rolls about the rotating shaft is equalized to the sheet travelling speed. Preferably upper reference point determining control of the rotating device is performed to have the free rolls wait for arrival of the sheet from the conveyor at the upper reference point of the rotating device, based on the speed command V B . Brief Description of Drawings Fig.1 shows the construction of an embodiment of this invention. Fig.2 is an perspective view of the rotating device. Fig. 3 is a control diagram of the sheet stacker shown in Fig.1. Fig.4 is a drawing showing position relationship of the rotating device. Fig.5 shows speed patterns of the rotating device. Fig.6 is a drawing describing movement of the rotating device. Figs.7A and Fig.7B are drawings to describe conventional technologies. Fig.8 is a drawing to describe another conventional technology. Best Mode for Executing the Invention Fig.1 is a drawing illustrating an embodiment of this invention where two sets of stacking zones are provided for changing skids and order. This sheet stacker comprises a sheet cutting machine 10, a conveyor system 12 to transfer sheets from the sheet cutting machine, first and second clamping devices 14a and 14b to clamp sheet tail ends, and first and second stacking zones 16a and 16b to stack sheets. The cutting machine 10 has a sheet cutter 18 which cuts corrugated cardboard, paper, plastic film, foil and the like to a specified length. The conveyor system 12 is disposed downstream of the cutting machine 10 and has a conveyor 20 for transferring sheets, its length being set to longer than maximum cutting length of sheets. Pressing belts 22 consisting of several belts are installed on the conveyor 20, and pressing rolls 24a are disposed on the tail end of conveyor 20. These pressing rolls 24a are moved up and down by a diverter 26. Also, above the conveyor 20, a sheet tail end position sensor 34a is provided to detect the tail end of a sheet travelling on the conveyor 20. The speed of conveyor 20 is set at a few percent higher than web feeding speed to the cutting machine 10 so that the interval of cut sheets can be expanded. The first clamping device 14a is a device to clamp tail ends of cut sheets. Under it, a slowdown roll 28a is installed to slow down sheet speed to an optimum speed and to send out sheets to the first stacking zone 16a. At an upper position of the first clamping device 14a, there is provided a rotating device 32a having free rolls 30a at its end to press the cut sheet onto the slowdown roll via intervals of the pressing belts 22 and to equalize the speed of cut sheet to the speed of slowdown roll. For the slowdown roll 28a, high-friction rubber roll or the like is used depending on the kind of sheet material. Fig.2 is a perspective view of the slowdown roll 28a and the rotating device 32a. The rotating device 32a comprises arms 302 fixed to rotating shafts 301, shafts 303 fixed to ends of these arms and free rolls 30a supported by these shafts 303 enabling to rotate freely. Though the figure shows only two free roll 30a in order to simplify the figure, an actual sheet stacker has a plurality of the free rolls. The rotating speed of the slowdown roll 29a is set based on the kind of material of sheet 11, the line speed and the cutting length of sheets. AC servo motor is controlled so that the arms 302 of the rotating device 32a can start tracking at the time when the sheet tail end position sensor 34a detects the tail end of a sheet, and that the free rolls 30a can press the sheet to the slowdown roll 28a via intervals of the pressing belts 22 and can clamp the sheet by equalizing the revolution speed of the free rolls 30a about the shafts 301 at a fixed position present from the base position near the tail end of sheet. The first stacking zone has a first stacking station 38a installed on a first lifter 36a which moves up and down, and sheets are stacked to the stacking station. At the first stacking zone 16a, a guide belt 40 to guide sheets to the first stacking station 38a and a sheet transfer belt 42 to send sheets to the second clamping device 14b are provided. On the tail end of sheet transfer belt 42, pressing rolls 24b are provided. Also, above the sheet transfer belt 42, a sheet tail end position sensor 34b is installed to detect the tail end of a cut sheet being transferred by the sheet transfer belt 42. The pressing belts 22 of the conveyor system 12 are provided so that they can run through the first clamping device 14a, the first stacking zone 16a, the second clamping device 14b and the second stacking zone 16b via the pressing rolls 24a. A sheet sent out from the conveyor 20 at a high speed travels along the lower surface of guide belt 40 running at the same speed as the pressing belt 22, and when the leading edge of sheet reaches at a certain position before a stopper 44a of the stacking station 38a, the sheet is clamped by the function of the clamping device 14a, is slowed down to an optimum speed, is stopped by the stopper 44a and is stacked into the first stacking station 38a. In the first stacking station, the sheet is aligned by side jogging and front jogging and is stacked orderly. Moving down of the lifter is controlled so that the uppermost surface of the stacking pile is always kept at a fixed level by a sensor. In the above-mentioned stacking operation where sheets are stacked into the first stacking station 38a of the first stacking zone 16a, the sheets sent out from the conveyor system 12 at a high speed are sent to the stacking station 38a through the first clamping device 14a and along the lower surface of the guide belt 40. In case that skid change or order change is to be performed without changing operating speed, the diverter 26 is actuated by a signal of skid change and moves the pressing rolls 24 up (as shown in the figure), the sheets sent out from the conveyor system 12 at a high speed travel on the upper surface of the sheet transfer belt 42 running at the same speed as the conveyor 20, and are sent to the second clamping device 14b, being pressed by the pressing belt 22. The second clamping device 14b is a device to clamp the tail end of a cut sheet, has at a lower position of the device a slowdown roll 28b to slow down the sheet to an optimum speed and to send out the sheet to the second stacking zone 16b, and has at an upper position of the device a rotating device 32b having free rollers 30b to press the sheet tail end to the slowdown roll via the intervals of the pressing belts 22 and to equalize the speed of sheets to the speed of slowdown roll. Because the functions of second clamping device are same as those of first clamping device, the description of the second clamping device is omitted here. The second stacking zone 16b has a second stacking station 38b placed on a second lifter 36b movable up and down and a stopper 44b. A sheet sent out from the sheet transfer belt 42 at a high speed travels along the lower surface of the pressing belt 22 in the stacking zone 16b, and when the leading edge of sheet reaches at a certain position before the stopper 44b of the stacking station 38b, the sheet is clamped by the actions of the second clamping device 14b, is slowed down to an optimum speed, is stopped by the stopper, and is stacked into the second stacking station 38b. In the second stacking station 38b, the sheet is aligned by side jogging and is stacked orderly. Moving down of the lifter is controlled so that the uppermost surface of the stacking pile is kept at a certain level by sensor. Now, the control system of the sheet stacker of this embodiment is explained with reference to Fig.3. Fig.3 shows a control system for the first conveyor system 12, the first clamping device 14a and the first stacking zone shown in Fig.1. Because the control system for the second clamping device 14b and the second stacking zone 16b is same as that for the first clamping device 14a and the first stacking zone 16a, only the control system for the first clamping device 14a and the first stacking zone 16a is described here as representative. The control is divided into phase speed equalizing control and upper reference point determining control. The phase speed equalizing control is to control to equalize the revolution speed of free rolls 30a about the shafts 301 to the sheet transfer speed by clamping a sheet at a specific position from the sheet tail end by the free rolls, when the rotating device 32a clamps the sheet 11. The phase control is performed as follows. Phase setter 58 is preset at the value of (L-X) which is obtained by subtracting the distance (X) between the tail end position of the sheet 11 and the clamping position from the distance (L) between the lower reference point of the rotating device 32a and the sheet tail end position sensor 34a. This is the phase setting that is to set the phase setter 58 to the value of (L-X)-B₀ after converting to pulse, based on the slowdown position signal A (the signal showing slowdown starting position located at an angle of 90° from the lower reference point of the rotating device) obtained from the origin detected by the origin sensor 60 installed near the rotating device 32a. The value of B₀ is a circumferential length of the circle drawn by the farmost point from the revolution center when the free rolls 30a of the rotating device 32a revolves about the shafts 301. The sheet transfer length is obtained by opening the gate 66 by the signal C generated when the sheet tail end position sensor 34a detects the tail end of a sheet, by inputting to the adder 76 the pulse from the pulse generator (PG) 50 as a subtracting input, and by closing the gate 66 by the slowdown position signal A. The adder 76 subtracts the pulse AA of sheet transfer length passed through the gate 66. When the free rolls 30a of the rotating device 32a reach at the target clamping position which is the position to start acceleration, the rotating device starts acceleration, and then, before the free rolls 30a contact the sheet 11, speed equalization is performed by the speed equalizing functions described later and simultaneously, phase adjustment is performed by the following equation. The value B of position deviation counter 64 is expressed by the following equation. R = ((L-X)-B₀)-AA+BB where BB is the count value of pulse of the pulse generator (PG) 68 installed at the AC servo motor to drive the clamping device (count-base slowdown start point). This calculation is performed by the adder 76, and the position deviation counter 64 keeps the value R. Because the phase control aims to make the deviation zero, the value of R in the above equation finally becomes zero. Because the value of BB finally corresponds to one revolution of the rotating device, the value of BB becomes equal to the value of B₀. From this relation and the relation of R=0, therefore, the relation of AA=(L-X) is obtained, and it becomes possible to set the value of AA, i.e. the clamping position to a position X from the sheet tail end. The speed equalizing control is performed as follows. The deviation R is converted to an analog signal V c . Furthermore, the frequency of pulse generated by the pulse generator 50 installed at the conveyor system 20 is converted to voltage signal by frequency/voltage (F/V) converter 52, and thus, the line speed i.e. the travelling speed of sheet 11 is detected and is sent to the adder 80 as an adding input. The output of adder 80 (V A -V C ) is sent to the servo amplifier 57 of the AC servo motor 56 for driving the rotating device 32a as a command for phase equalization through speed command selecting circuit 54 described later. When R=0, V C becomes zero and the speed command (V A -V C ) becomes equal to V A , and thus, the revolution speed of the free rolls about the shafts 301 is equalized to the sheet travelling speed. The upper reference point determining control is a function required to have the free rolls 30a of the rotating device 32a wait for arrival of a sheet as shown in Fig.4 when sheets are not supplied continuously. By the slowdown position signal A from the origin sensor 60, the upper reference point deviation counter 70 is to set a circumferential length up to the upper reference point, and after subtracting the pulse from the pulse generator 68, produces a speed command V B through a D/A converter 72 and a speed command clamp circuit 74. The position at zero count is determined, and the rotating device 32a is stopped at the upper reference point. The above-mentioned speed command (V A -V C ) for the phase speed equalizing control and the speed command V B for the upper reference point determining control are sent to the speed command selecting circuit (higher voltage selecting circuit) 54, which selects a higher voltage of command and outputs a speed command B to the servo amplifier 57. The speed pattern of the rotating device is either pattern 1, 2 or 3 shown in Fig.5 depending on the sheet interval. The pattern 1 is for a longer sheet interval. when the sheet tail end position sensor 34a detects a sheet tail end at time t1, the rotating speed of the rotating device is accelerated by the speed command (V A -V C ) and reaches at the line speed at time t2, and the rotating device keeps this speed until time t3. After the time t3, the speed command is switched to the speed command V B and slows down the rotating device, which arrives at the upper reference point at time t4 and stops at the upper reference point until time t5 when the tail end of the next sheet is detected. The pattern 2 shows the case that the next sheet arrives before the rotating device stops at the upper reference point. In this case, when the tail end of a sheet is detected, the rotating device is controlled by the speed command (V B -V C ) until time t6, and is controlled by the speed command V B from time t6 to time t7. The pattern 3 shows the case that sheet interval is shorter than the set length of (L-X). In this case, the rotating device is controlled by the speed command (V A -V C ), starts to be accelerated from the line speed at time t8, starts to be slowed down at time t9, and is equalized to the line speed at time t10. Now, the behavior of the pattern 1 explained, with reference to Fig.6, which shows the revolution of the free rolls 30a of the rotating device 32a. A sheet 11 cut by a sheet cutter is transferred by the conveyor 20 towards the first stacking zone 16a. When the sheet tail end position sensor detects the tail end of sheet 11, the gate 66 is opened, the pulse AA generated by the pulse generator 50 is sent to the adder 76, the free rolls 30a, which were stopping at the upper reference point as shown in the upper figure of Fig.6, start to be accelerated by the speed command (V A -V C ) as shown in the middle figure of Fig.6, and the speed equalization is performed. When the deviation R of the deviation counter 64 becomes zero, the free rolls 30a clamp the sheet at the clamping position located at a position X from the sheet tail end, slow down the sheet and send it to the stacking station 38a. When the free rolls 30a arrive at the slowdown point, the speed command is switched to the speed command V B , and the free rolls 30a start to be slowed down and stop at the upper reference point. In the above, the case of the pattern 1 in Fig.5 was described. The behaviors of the remaining patterns 2 and 3 could be understood easily by persons skilled in the art. INDUSTRIAL APPLICABILITY Because a sheet stacker of this invention can slow down sheet transfer speed to an optimum speed regardless of cutting length of sheet cut off by a cutter, by clamping a base position near the tail end of a travelling cut sheet and can stack the sheet directly without overlapping sheets, production or grazes caused by friction of sheet surfaces due to overlapping can be eliminated, and also length of sheet transfer conveyor downstream of the cutter can be shortened. Furthermore, a sheet stacker of this invention has an effect to enable to send sheets to be stacking station normally, even if various kinds of sheet materials are handled.

Claims: A device for slowing down sheets cut by a sheet cutter (18) and transferred and stacking into a stacking station (38a), comprising; a conveyor (20) for transferring sheets (11) cut off by the sheet cutter, keeping a fixed sheet interval, a clamping device (32a) for clamping a base position near the tail end of the sheet transferred from the conveyor and slowing down sheet travelling speed to an optimum speed needed for stacking the sheet into the stacking station orderly, the clamping device having a rotating device including a rotating shaft (301), arms (302) fixed to the rotating shaft and free rolls (30a) each thereof is supported to each end of the arms so as to rotate freely, and a slowdown roll (28a) installed opposite to the rotating device, the rotating speed of the slowdown roll being set based on the kind of material of sheet, the base position of the sheet being pressed by the free rolls onto the slowdown roll every one revolution of the free rolls about the rotating shaft, a servo motor (56) coupled to the rotating shaft for driving the rotating device, a servo amplifier (57) connected to the servo motor for controlling the rotating speed of the servo motor, a sheet tail end position sensor (34a) installed over the conveyor for detecting the tail end of the sheet being transferred by the conveyor, a first speed sensor (50) for detecting the speed of the conveyor, a second speed sensor (68) for detecting the rotating speed of the servo motor, and an origin sensor (60) for detecting the origin of the rotating device, the origin of the rotating device being used for determining a slowdown starting position of the rotating device, characterized in that the device further comprises; a phase setter (58) for setting the value of (L-X)-Bo after converting to pulse, where L is the distance between the lower reference point of the rotating device and the sheet tail end position sensor, X is the distance between the tail end position and the base position of the sheet, and Bo is a circumferential length of the circle drawn by the farmost point of the free rolls from the rotating shaft when the free rolls of the rotating device revolves about the rotating shaft, a gate circuit (66) for gating the output of the first speed sensor, the gate circuit being opened when the tail end of the sheet is detected by the sheet tail end position sensor, and being closed when the origin of the rotating device is detected by the origin sensor, a first adder (76) for calculating the value of R=((L- X)-Bo)-AA+BB , where AA is the pulse of sheet transfer length obtained through the gate circuit from the output of the first speed sensor, and BB is the count value of pulse which is obtained from the output of the second speed sensor, a first digital/analog converter (78) for converting the value of R to an analog voltage value V C , a frequency/voltage converter (52) for converting the output of the first speed sensor to an analog voltage V A , a second adder (80) for calculating a speed command (V A -V C ), a subtracter (70) for subtracting the output of the second speed sensor from a length along the circle up to the upper reference point from the slowdown starting position of the rotating device, the length being preset when the origin of the rotating device is detected by the origin sensor, a second digital/analog converter (72) for converting the output of the subtracter to a speed command V B, and a speed command selecting circuit (54) for selecting either the speed command (V A -V C ) or V B based on the voltage thereof and outputting a speed command to the servo amplifier. A device for slowing down sheet as set forth in claim 1, characterized in that when R=O , the revolution speed of the free rolls about the rotating shaft is equalized to the sheet travelling speed. A device for slowing down sheet as set forth in claim 2, characterized in that upper reference point determining control of the rotating device is performed to have the free rolls wait for arrival of the sheet from the conveyor at the upper reference point of the rotating device, based on the speed command V B .

Inventors: MIYAGAWA TATSUYUKI C O RELIANC, TOKUNO MASATERU C O SK ENGINEE, MIYAGAWA, TATSUYUKI, C/O RELIANCE ELECTRIC LTD., TOKUNO, MASATERU, C/O SK ENGINEERING, LTD.
Applicants: RELIANCE ELECTRIC LTD, SK ENG CO LTD, RELIANCE ELECTRIC LIMITED, SK ENGINEERING LTD
Application year: 1991
Main classification: B65H29
IPC codes: B65H31, B65H29