EP0173959B1

EP0173959B1 - Sheet stacker

Info

Publication number: EP0173959B1
Application number: EP85110845A
Authority: EP
Inventors: Tadashi C/O Mihara Machinery Works Of Yano
Original assignee: Mitsubishi Heavy Industries Ltd
Current assignee: Mitsubishi Heavy Industries Ltd
Priority date: 1984-08-30
Filing date: 1985-08-28
Publication date: 1988-11-02
Also published as: EP0173959A1; DE173959T1; DE3565972D1; JPS6160560A

Description

The present invention relates to a sheet stacker for stacking various sheet-like products such as corrugated fiberboards, cardboards, plastic sheets, or the like.
Figures 6 and 7 of the accompanying drawings illustrate the principal arrangement of a conventional sheet stacker for stacking corrugated fiberboards to a prescribed height. As shown in Figure 6, corrugated fiberboards 2 (hereinafter referred to simply as "sheets") of prescribed dimensions and shape which have been produced by a corrugated fiberboard manufacturing machine 1 are transferred one by one upwardly by an inclined belt conveyor 3. The conveyor 3 is inclined at an angle of which is required to allow the sheets 2 to be stacked at a height A.
The inclined belt conveyor 3 is generally in the form of a suction conveyor having a conveyor belt 5 supporting the sheets 2 attracted to the surface thereof for preventing the sheets 2 from slipping with respect to each other as they are fed. The speed V1 of travel of the conveyor belt 5 is selected to be lower than the speed V2 of movement of the sheets 2 through the machine 1. Therefore, the sheets 2 on the inclined belt conveyor 3 are partly overlapped.
The speed V1 of travel of the conveyor belt 5 is adjustable so as to be an optimum speed dependent on the length L of each sheet 2 and the speed of the sheets 2 through the machine 1.
As illustrated in Figure 7, the sheets 2 are successively fed from the inclined belt conveyor 3 onto a horizontal belt conveyor 6 which comprises a suction conveyor for attracting the sheets 2 upwardly. Each sheet 2 transferred horizontally by the horizontal belt conveyor 6 is stopped by a sheet stopper 7. The sheet 2-a stopped by the sheet stopper 7 is separated from the horizontal belt conveyor 6 by the following sheet 2-b as it moves in the direction of the arrow. The separated sheet 2-a drops between the sheet stopper 7 and a confronting sheet guide 9 onto a vertically movable sheet table 8, which is successively lowered as the sheets 2 are successively stacked thereon.
The speed of descent of the sheet table 8 is automatically controlled dependent on the sheet thickness and the speed of travel of the sheets 2 on the belt conveyors so that the distance B between the lower run of the horizontal belt conveyor 6 and the upper surface of the uppermost sheet 2 of the stack will remain substantially constant. When the stack of the sheets 2 on the sheet table 8 reaches a prescribed height A, the supply of the sheets 2 from the machine 1 is stopped, and the stacked sheets 2 are fed rearwardly as shown in Figure 6. When the sheet table 8 is moved upwardly and stopped in a position just short of contact with the lower edge of the sheet stopper 7, the sheets 2 are supplied again from the machine 1. When the distance B between the lower run of the horizontal belt conveyor 6 and the upper surface of the uppermost sheet 2 of the stack on the sheet table 8 reaches the prescribed height, the sheet table 8 is lowered again to discharge the stacked sheets 2, thus repeating the above cycle of operation.
In the conventional sheet stacker, each sheet 2 attracted to the horizontal belt conveyor 6 is separated off the horizontal belt conveyor 6 by the next sheet 2 and is caused to fall. Where the sheets manufactured by the machine 1 is of a complex shape as shown in Figure 8, the sheets are apt to get caught by each other and jammed up as shown in Figure 9. When the sheet jam occurs, the involved sheets are damaged and a product loss takes place.
If the aforesaid trouble is caused frequently, then the sheet stacker and the machine 1 have to be shut off to remove the defective sheets, with the result that the operation efficiency of the system is much reduced. The conventional sheet stacker has therefore been limited in use since it is only effective in stacking those sheets which are simple in shape and will not get caught or jammed when overlapped and relatively slipped.
A sheet stacker of the kind defined in the preamble of Claim 1 is known from US-A-3 820 779. The sheets attracted and conveyed by the suction belt conveyor of this known sheet stacker are separated one by one by means of the up-and-down movement of tines, which is in synchronism with the driving of a rotary die cutter. The travel speed of the sheets is slowed down before they are separated by means of a Geneva wheel and the friction of a strip. All the tines act with the same timing against large and small sheets, therefore not allowing a truing-up of sheets of different lengths.
It is the object of the invention to control the sheet separation such a kind that sheets of different lengths may be trued up properly.
This object is solved by the characterizing features of Claim 1.
The invention allows for a control of the motion timing of the sheet separator of the sheet stacker in accordance with the length of the sheet, thereby enabling the sheets to be trued up properly independent of the sheet length.
In the following the invention is described in detail with respect to an illustrative example in conjunction with the accompanying drawing, wherein

Figure 1 is a sectional side elevation view of a sheet stacker according to the invention;
Figure 2 is a plan view of the sheet stacker shown in Figure 1;
Figure 3 is an enlarged cross-sectional view taken along line III-III of Figure 1;
Figure 4 is an enlarged cross-sectional view taken along line IV-IV of Figure 2;
Figure 5 is a view similar to Figure 4, but showing a different aspect of operation;
Figure 6 is a sectional side elevational view of a conventional sheet stacker;
Figure 7 is an enlarged cross-sectional view of a portion of the sheet stacker illustrated in Figure 6;
Figure 8 is a plan view of a sheet of a complex shape; and
Figure 9 is a side elevational view showing a sheet jam.

Figure 1 shows a corrugated fiberboard manufacturing machine 1, an inclined belt conveyor 3, a horizontal belt conveyor 6, a sheet table 8, a sheet stopper 7, and a sheet guide 9 which are of the same arrangement as those shown in Figures 6 and 7. The inclined belt conveyor 3 and the horizontal belt conveyor 6 are each composed of several independent suction belt conveyors, the number of which may vary dependent on the maximum width W (Figure 2) of sheets 2 supplied. The speeds. of travel of the belts of the belt conveyor 3, 6 are the same since their drive pulleys (as indicated at 11 in Figure 7) on a common drive shaft (as indicated at 10 in Figure 7) are of the same diameter. The belt conveyors 3, 6 operate at the same speed V1.
The aforesaid basic construction is identical to that of the conventional sheet stacker. The speed of operation of the belt conveyors 3, 6 is also variable to a desired speed dependent on the operation conditions. The sheet stacker according to the present invention, shown in Figures 1 through 5, has a sheet separator as described below.
The sheet separator, denoted at 12 in Figures 3 and 4, is installed on the horizontal belt conveyor 6. The sheet separator 12 comprises a photoelectric sensor 13 positioned at the inlet of the horizontal belt conveyor 6, a drive motor 14, a drive gear 15 fixed to the shaft of the drive motor 14, a drive shaft 16, a drive gear 17 fixed to one end of the drive shaft 16 and held in mesh with the drive gear 15, a pair of bearings 18, 19 on which the drive shaft 16 is rotatably supported, a plurality of sprockets 20 fixedly mounted on the drive shaft 16 and disposed between the horizontal conveyor belts, a driven shaft 22 rotatably supported by a pair of bearings 25, 26 a plurality of sprockets 23 fixedly mounted on the driven shaft 22, a plurality of chains 21 trained around the sprockets 20, 23, and a plurality of sheet separation cams 24 fixed at intervals to the driven shaft 22 closely to the horizontal belt conveyor 6. The drive motor 14 is controlled in its operation by a control device 27 in response to a signal from the photoelectric sensor 13. The sheet separation cams 24 have outer circumferential surfaces eccentric with respect to the center of rotation of the cams 24 which is concentric to the drive shaft 22.
As illustrated in Figures 4 and 5, the outer circumferential surface of each of the sheet separation cams 24 is movable below and above the lower run of the horizontal belt conveyor 6 as the cam 14 rotates.
Operation of the sheet stacker of the above construction is as follows: Corrugated fiberboards or sheets 2 of prescribed dimensions and shape which have been produced by the machine 1 are transferred at spaced intervals one by one upwardly by the inclined belt conveyor 3. The sheets 2 coming out of the machine 1 are fed toward the upper horizontal belt conveyor 6. The sheets 2 are attracted to the belts of the inclined and horizontal suction belt conveyors 3, 6 as with the conventional sheet stacker.
The sheets 2 transferred by the inclined and horizontal suction belt conveyors 3, 6 are not partly overlapped, but are spaced from each other, with distances I kept between the leading and trailing ends of adjacent sheets. More specifically, the speed V1 of travel of the belt conveyors 3, 6 is selected to be higher than that of the belt conveyors in the conventional sheet stacker. If the speed of travel of the sheets on the belt conveyors were low with respect to the speed of the sheets in the machine 1, then the sheets would be overlapped on the belt conveyors. The belt speed is adjusted dependent on the length L of each sheet 2 in order to optimize the intersheet distance I (normally in the range of from 50 to 100 mm) on the belt conveyors. The process of adjusting the belt speed will not be described as it has no direct bearing on the present invention. At any rate, it is important that the sheets be transferred separately at the distance I without being overlapped.
The sheets 2 are successively fed from the inclined belt conveyor 3 onto the horizontal belt conveyor 6. The photoelectric sensor 13 at the inlet of the horizontal belt conveyor 6 detects the leading end of each sheet 2 and transmits a detected signal to the control device 27. The sheet 2-a with its leading end having just passed the photoelectric sensor 13 is attracted upwardly and transferred by the horizontal belt conveyor 6. The sheet separation cams 24 in the sheet separator 12 are rotated so that, immediately before the leading end of the sheet 2-a reaches the sheet stopper 7, the outer circumferential surfaces of the cams 24 depress the sheet 2-a off the horizontal belt conveyor 6. The distance C between the sheet stopper 7 and the sheet guide 9 is selected in advance to be larger than the sheet length L by a certain clearance required to allow the sheets to drop freely.
The sheet separation cams 24 are rotated at all times by the drive motor 14 such that the cams 24 will make one revolution each time a sheet 2 is supplied to the horizontal belt conveyor 6. More specifically, upon detection of the leading end of the sheet 2-a by the photoelectric sensor 13, the sheet 2-a is separated from the horizontal belt conveyor 6 immediately before the leading end of the sheet 2-a reaches the sheet stopper 7. Just prior to arrival of the following sheet 2-b at the sheet separation cams 24, the sheet separation cams 24 are turned to an angular position in which they are held out of contact with the leading end of the sheet 2-b. Immediately before the leading end of the sheet 2-b fed by the horizontal belt conveyor 6 reaches the sheet stopper 7, the sheet 2-b is separated from the horizontal belt conveyor 6 by the sheet separation cams 24 and is caused to fall onto the sheet table 8.
The time it takes for the leading end of the sheet to reach the sheet stopper 7 after the leading sheet end has been detected by the photoelectric sensor 13 varies dependent on the operation speed or the speed of movement of the belt conveyors 3, 6. There is a sensor (not shown) for detecting the distance that the belt conveyors have moved, that is, the distance that the sheet has travelled. The drive motor 14 is controlled in its rotation by this sensor, the photoelectric sensor 13, and the control device for rotating the sheet separation cams 24 through the illustrated power transmission mechanism. The structure and operation of the sheet table 8 and the manner in which the sheets 2 falling on the sheet table 8 will be discharged remain the same as those of the conventional sheet stacker.
With the arrangement of the present invention, the sheets are depressed by the sheet separator at appropriate times so as to be separated from the suction belt conveyor and dropped downwardly. It is therefore not required to supply the sheets in overlapping relation to the horizontal belt conveyor. Accordingly, the sheets, even if they are of the complex as shown in Figure 8, are prevented from getting caught and jammed. For stacking sheets of simpler shape, the sheet separator may be inactivated with the sheet separation cams stopped in an angular position out of contact with the sheets, and the speeds of operation of the horizontal and inclined belt conveyors may be lowered, so that the sheet stacker will operate in the same manner as that of the prior sheet stacker.
According to the present invention, the sheets are forcibly separated from the upper or horizontal suction belt conveyor by the sheet separator in timed relation to the supply of the sheets to the upper suction belt conveyor. It is possible to drive the sheet separator from the machine 1, rather than the drive motor. Since the sheet separation cams should make one revolution each time a sheet is fed, the sheet separator may be coupled to the machine 1 through a suitable coupling means to enable the sheet separation cams to make one revolution each time a sheet is supplied from the machine 1. The rotatable sheet separation cams may be replaced with vertically repro- catable mechanisms. While only one sheet separator is employed in the foregoing embodiment, a plurality of sheet separators may be arranged in the direction of travel of the sheets dependent on the size, rigidity, and other qualities of the sheets to be stacked.

Claims

1. A sheet stacker comprising

a sheet table (8) supporting a stack of sheets (2) thereon,

a horizontal suction belt conveyor (6) disposed upwardly of said sheet table (8) and having a lower sheet attracting surface for transferring the sheets supplied from a previous processing station (1), and

a sheet separator (12) for separating the sheets (2) successively from said suction belt conveyor (6), characterized

by a detector (13) at the inlet of the horizontal suction belt conveyor (6) for detecting the leading end of each sheet (2),

by a sensor responsive to the speed of movement of the suction belt conveyor (6), and

by a control device (27) responsive to the signals from said detector (13) and said speed sensor for controlling the sheet separator (12) so that each sheet will be depressed from the horizontal suction belt conveyor (6) immediately before the leading end of said sheet (2) reaches a sheet stopper (7), which is positioned at the downstream end of said suction belt conveyor (6) in a distance (C) from an upstream sheet guide (9), said distance (C) being selected to be larger than the sheet length (L) by a certain clearance required to allow the sheets (2) to drop freely.

2. The sheet stacker according to Claim 1, characterized in that the sheet separator (12) comprises cams (24) having outer circumferential surfaces eccentric with respect to the center of rotation of said cams, which are rotated by drive means (20-23) for moving intermittently into and out of the sheet attracting surface of said suction belt conveyor (6), thereby separating the respective sheet (2) from said conveyor (6).