Marc
Christiaan
Leon, Hermans
Wilhelmus
Adrianus
Henricus
Johanna
Van Dieren, Marc Christiaan Leon Hermans Wilhelmus Adrianus Henricus Johanna
The invention relates to a method of cutting a metal strip into separate sheets and depositing the sheets onto a stack, wherein the metal strip is cut at a speed V l f whereafter the cut sheet is further conveyed on a first conveyor and is then transferred to a second conveyor from which the sheet is suspended and conveyed further up to a stack where the sheet is released from the conveyor and is lowered to the stack.
The documents DE-A-1815651, EP-A-0 009 014 and GB 1477854 describe methods of cutting a metal strip into sheets, wherein the sheets are dropped on the stack while the second conveyor is being driven. As a result thereof, the sheet has a horizontal speed during deposition onto the stack which may lead to positioning inaccuracies on the one hand and to damages to the upper sheet of the stack on the other hand. Of course, in these prior art methods measures are taken to decrease the horizontal speed, but do not lead to satisfactory results.
A satisfactory result will be obtained without any doubt if the sheet is stationary in horizontal direction for deposition on the stack. However, this leads to problems when the conveyors are arranged behind a so-called "rotary shear" in which the metal strip is being transported during the cutting operation. Stopping the second conveyor may lead to an uncontrolled transfer of sheets from the first to the second conveyor resulting in a loss of indexation or in collision of successive sheets.
The object of the invention is to provide a method of the type mentioned in the preamble, in which this problem is removed in an effective way.
For this purpose the method according to the invention is characterized in that during cutting of each sheet the first conveyor is driven at the speed V 1 and the second conveyor is stopped for lowering the sheet onto the stack, and after cutting, and releasing, respectively, of each sheet, both conveyors being accelerated to a speed V 2 which is higher than said speed V χ , wherein each sheet is only
conveyors are driven with equal speeds.
Due to these measurements it is without any problems possible to deposit sheets on the stack at a standstill of the second conveyor. Then, due to the increase of the speed of the first conveyor after cutting each sheet there is created an interval to the next sheet which is still fixed to the metal strip and moves with a lower speed. Said interval may then be
"used" during the standstill period of the second conveyor.
Because both conveyors have the same speed during the transfer of the sheets the indexation of the sheets is not disturbed.
The speed of the conveyors does not have to be constant during the transfer of the sheets. Also during an - equal - acceleration or deceleration of the conveyors may a transfer take place. The invention will hereafter be elucidated with reference to the drawings showing embodiments of the invention by way of example.
Fig. 1 is a side view of an apparatus for cutting and stacking metal sheets with which the method according to the invention may be carried out.
Fig. 1A schematically shows the dimensional parameters of the apparatus of Fig. 1 which are important to the method according to the invention, together with metal sheets. Fig. 2 shows a speed-time diagram of the first conveyor belt of the apparatus of Fig. 1.
Fig. 3 is a speed-time diagram corresponding to that of Fig. 2 but of the second conveyor belt of the apparatus of
Fig. 1. Fig. 4 illustrates the displacement of the cut sheets during their transport by the conveyor belts as a function of time.
Fig. 5-7 are diagrams corresponding to those of Fig.
2-4 of a second exemplary embodiment of the method according to the invention.
Fig. 1 shows an exemplary embodiment of an apparatus or cutting a metal strip into separate sheets and for depositing the sheets onto one or more stacks. On the left hand side of Fig. 1, the metal strip is supplied at constant s s of a o the dischar e end of which a
rotary shear 2 is arranged which is indicated only very schematically. This rotary shear 2 is adapted to cut while the metal strip moves on with a constant speed so that the strip does not have to be stopped in order to be cut. The rotary shear may be of a conventional design and does not form part of the present invention so that a detailed description thereof is omitted. For the sake of completeness it is noted that instead of a single metal strip it is also possible to handle a plurality of narrow metal strips supplied side by side.
The apparatus comprises first of all a belt conveyor 4 supported by a frame 3 and including a plurality, for example 10, narrow conveyor belts 5 extending parallel with a small interspace. Of course a single conveyor belt may also be sufficient. The conveyor belts 5 extend along rollers 6, 7 and are driven by one or more indexing motors 8 controlled by a microprocessor. At the inlet end of the belt conveyor 4 there may be arranged short entrance belts 9 provided between the conveyor belts 5. The belt conveyor 4 is preferably equipped with magnet means (not shown) ensuring that the sheets cut by the rotary shear 2 remain properly positioned on the conveyor belts 5 and do not slide when the conveyor belts 5 are accelerated or decelerated. It is preferred to make the magnet means of the belt conveyor 4 adjustable at least in the area of the belt conveyor 4 directly after the shear 2 in order to reduce frictional forces on the sheet during the increased speed V 2 while the subsequent sheet of the metal strip moving at the speed V χ is not yet cut.
Behind the discharge end of the belt conveyor 4 is arranged a second belt conveyor 10 in this case consisting of two conveyor portions 11, 12 each of which may comprise a plurality, "for example five, parallel narrow conveyor belts 13, 14 respectively, extending at a small adjustable distance from each other. The conveyor belts 13 and 14 extend along rollers 15, 16 and 17, 18, respectively, and are driven by one or more indexation motors 19, 20, respectively, controlled by a microprocessor. Under the conveyor portions 11, 12 of the belt conveyor 10 are positioned four lifts 21-24 arranged behind each other and adjustable in vertical direction in order to maintain the upper side of a stack of sheets
supported thereon at a constant distance to the under side of the lower conveying part of the conveyor belts 13, 14. Transverse to the direction of conveyance of the belt conveyor 10 7 the lifts 21-24 have a device for supplying empty pallets on which sheets may be stacked and for discharging full pallets.
The belt conveyors 4 and 10 overlap some distance so that the sheets supplied by the belt conveyor 4 may be transferred to the belt conveyor 10 without the risk of falling off, the sheets being conveyed further, suspended from said belt conveyor 10. This suspended transport is enabled by the arrangement of magnets above the lower conveying parts of the conveyor belts 13 and 14 so that the sheets are magnetized through the conveyor belts 13, 14 and hence adhere to the belt conveyor 10. The release of the separate sheets from the belt conveyor 10 could be effected by making the magnets switchable so that the sheets fall down by gravity. Certainly in the case of a plurality of parallel spaced conveyor belts 13, 14 it is preferred however to use push off means of which a great number is distributed over the length of the belt conveyor 10 and also over the width thereof so that push off means are provided between all adjacent conveyor belts. These push off means are adapted to forcibly release the sheet or sheets suspended from the belt conveyor 10 so that both a quick and reliable operation is effected. Depending on the size of the sheets to be pushed off, a corresponding number of push off means is energized.
In order to obtain a stacking of sheets on the corresponding lifts 21-24 which is as accurate and cautious as possible, the belt conveyor 10 according to the invention is stopped for releasing the sheets so that the sheets may be pushed off vertically downwardly without any horizontal speed. Since the supply of sheets is taking place continuously, however, as a result of the supply conveyor " 1 supplying the metal strip 1 at constant speed, the belt conveyors 4 and 10 should be controlled such that the continuous supply at the inlet end of the belt conveyor 4 may be converted into a discontinuous discharge of sheets to the lifts 21-24. For this purpose, the invention proposes to drive the first belt
to the supply speed of the conveyor 1 and a higher speed V 2 , while the speed of the second belt conveyor 10 varies between the higher speed V« and a speed 0 when the sheets are pushed off. The speed of the first belt conveyor 4 should be equalled to V j^ when a sheet is cut, while the speeds of both belt conveyors 4 and 10 should be the same when the sheets are transferred between them. Example 1 In the embodiment shown in Fig. 1 and 1A and having discretely distributed push off means it is important for an accurate stacking operation to allow the push off means 25 to engage the sheet to be pushed off centrically or symmetrically. This is particularly true for shorter sheets. With a distance P between a joining push off means 25 and a sheet length B, the first push off point is under the first push off means if B < P. Because the distance between the transfer of the belt conveyors 4 and 10 and the first push off means 25 is 1% P and the first lift 21 starts at a distance P, it is possible to push off a sheet directly after the first belt conveyor 4. In this manner the systematic push off position of each sheet can be formulated. The centre distance of the sheets is L = n x P, with n = 1 + |B/P| , and the first stacking position (centre of the sheet) is at XI = 1.5 x n x P.
In this manner, the smallest distance II between the stacks is possible which is necessary for obtaining a high stacking speed. For larger sheet lengths, for example if n > 3, the distance between the sheets is less important. In this case, a large Xl-value would limit the use of the apparatus too much.
This is the reason that with larger plate lengths another approach is followed, that is that L = (n + 1) x P, if n > 3, and XI = 0.5 x (n + 2) x P, or even that L = B + P XI = 0.5 x B + P. Moreover the stacking position may be chosen freely and may depend from the osition on the lift.
Hereafter two examples of methods according to the invention will be described with reference to Fig. 2-7. Example 1
In the first example it is assumed that sheet length B = 1.833 , and line supply speed V χ = 100 m/min. or
V χ = 1.667 m/s. This results in a cycle time a stacking speed of 54.55 sheets/min.
For the sake of simplicity we assume an acceleration of a = 16.67 m/s 2 which results in a sheet acceleration time t. = 0.1 s. We assume a push off time t = 0.1 s.
(N.B. : in practice this means a push off time of approximately
0.2 s) .
With B = 1.833 and P = 0.5 m, n = 4 this results in XI = P + %B = 1.416 m
L = P + B = 2.333 m
L+I2 = L + (t a +t ) X V χ = 2. 666 m
II = P = 0.500 m
With these dimensions, the maximum conveyor belt - speed V 2 of 200 m/min. (3.333 m/s) is possible. The resulting speed-time diagrams of the first belt conveyor 4 and the second belt conveyor 10 are illustrated in Fig. 2 , 3 respectively.
Very illustrative for the result of the control for the speeds of the belt conveyors 4 and 10 is the diagram of
Fig. 4 showing the displacement of the separate sheets S after leaving the rotary shear 2.
After being cut the sheets on the first belt conveyor
4 are conveyed faster than the next sheet to be cut which is still fixed to the metal strip. As a result the interspace II
+ 12 is effected. Furthermore, it is shown in this Fig. 4 that during cutting of the sheet the speed of the first belt conveyor 4 is exactly equal to the speed of the supply line
each sheet is transferred from the first belt conveyor 4 to the second belt conveyor 10 both belt conveyors have the same speed so that no sliding movement between conveyor belts and sheet is caused and an exact indexation of the sheets is maintained. When each sheet is fully transferred to the second belt conveyor 10 it can be braked and be stopped in order to allow a sheet to be pushed off or to be accelerated again to the next push off position.
From Fig. 4 the very important conclusion may be drawn that the cutting action of the rotary shear, taking place during a displacement of the sheet of circa 0.10 m, should coincide with the period in which the supply line 1 and the first belt conveyor 4 have equal speeds. This is particularly important if a plurality of parallel strips should be cut because otherwise their would be a risk of the strips sliding with respect to each other. Furthermore, it is important to the method that during the push off period in which the belt conveyor 10 brakes, stops and accelerates, the belt conveyor 4 has the lowest speed, that is V 1 . This means that a whole number of sheet lengths and a whole number of interspaces (II + 12) should fit within the total length of the first belt conveyor 4 plus that length which is caused when the belt conveyor 4 has a speed equal to V χ and in which the cutting action takes place. If this is not the case, 12 should be increased.
The above mentioned can be illustrated in the following example in which a push off time t = 0.1 s is not possible and should be increased to 0.1375 s (longer 12) for the reason mentioned above. Example 2
12 = 0.15 m
L1+L2 = 0. 65 m
The corresponding speed-time diagrams of the first belt conveyor 4 and the second belt conveyor 10 are shown in Fig. 5 and 6, and the corresponding displacements of the sheets as a function of time are illustrated in Fig. 7.
The invention is not restricted to the embodiments shown in the drawing and described herein before, which may be varied in different manners within the scope of the invention. For example, the sheets may also be suspended from the second belt conveyor by suction means. The invention also includes both the simultaneous cutting and conveyance of a number of parallel sheets or strips and the treatment of a single metal sheet.
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