DEVICE FOR LAYING DOWN A THIN METAL WIRE ON A SURFACE
A device for laying a thin metal wire taken from a coil of wire stock onto a surface, in particular onto the surface of a sheet, using a presser. The device includes a mechanism exerting mechanical tension in a region of the wire that lies between the rotary coil of wire stock and the presser, and a wire-guiding device provided in the region. The wire-guiding device includes a tensioning device that acts directly on the wire taken off the coil of wire stock. That makes it possible effectively and appreciably to compensate for changes in relative speeds at which the wire and the sheet progress.
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The invention relates to a device for laying down a thin metal wire onto a surface and in particular onto the surface of a sheet, which has the features of the preamble of claim 1. It relates in particular to the preparation of sheets for wire-heated laminated window panes.
Wire-heated laminated window panes are to be understood in particular as meaning panes for windows and the like which have a multilayer structure consisting of at least one rigid pane (made of glass or of a synthetic material) and of one layer or sheet of a synthetic material bonded to its surface, several resistive wires laid down by a machine being positioned in the surface that forms the boundary between the rigid pane and the layer or sheet of synthetic material. These wires are generally electrically connected in parallel and are powered with heating voltage using at least two collectors. The collectors generally extend along each exterior edge of the pane. In general, the sheets equipped with wires are sandwiched between two rigid panes.
European patent EP 0 443 691 describes a device of this type, for laying these wires down onto sheets. It comprises a mobile laying device to which the wires taken from a coil are led via an eyelet guide and two toothed wheels meshing with one another. Document DE 20 43 746 describes such a wire-laying device which has a wire-guiding tube positioned between the coil of wire stock and the laying location.
Document DE 41 01 984 A1 describes a similar device which has a simple guide between the coil of wire stock and the toothed wheels. Reduction gearing is provided between the toothed wheels and the constantly driven roll which pushes the wires onto the sheet. The toothed wheels turn slightly more slowly than the presser roll. It is thus contrived for the corrugated wire to remain always under a slight tensile load in its path between the toothed wheels and the presser roll. Uncontrolled movement of the laid-down wire is thus avoided.
In document DE 42 01 620 A1, for such a device designed to lay wires in straight lines, and which therefore does not have a wire-corrugating means, an electrical brake is provided on the coil of wire stock. This brake is designed to maintain constant tension in the wire paid out. In their path between the coil and the presser roll, the wires pass over deflection and guide rollers which have no braking function and are mounted on ball bearings.
Customarily, the sheets that are to be provided with the wires in these known devices are fixed on rotary drums which allow the substrate in sheet form to advance more or less continuously beneath the wire-laying devices. Depending on the local curvature intended for the wires, the rotational movement of the drum may also be set to different speeds so that braking or acceleration transitions are achieved.
When a device such as this is provided with a braking system and with mechanisms for corrugating the wire that is to be laid down, oscillations which arise out of the deformation of the wire and out of the relative inertia of the coil of wire stock interact and therefore cause uneven corrugations to be formed.
Furthermore, the ratio between the rotational speed of the coil of wire stock and the rotational speed of the drum to which the sheet of PVB that is to be equipped with the wires is fixed is not constant. What this means is that the tensile force with which the wire is taken off the coil is not constant. There is therefore a need to keep the tension in the wire constant.
The problem underlying the invention is therefore, for a device of the kind indicated at the start, to further improve the guidance of the wire before it is laid onto the sheet.
According to the invention, this problem is solved by the features of claim 1. The features of the dependent claims provide advantageous developments of the invention.
By inserting a tensioning device or tensioning element in the path of the wire between the coil of wire stock which may or may not be braked, the desired improvement can be achieved. The tensioning element ensures constant tension in the wire prior to the laying operation proper and possibly prior to its corrugation. The influence of relatively slow rotation of the coil of wire stock, particularly when the coil is full, on the subsequent corrugating and laying of the wire is thus greatly reduced.
In other words, the wire is passed through a “buffer region” (for example one provided with turn rollers) in order thus to compensate for the change in tensile force at the exit of the buffer region through a suitable compensation of the force and a compensation of the length of the wire within the buffer region.
This solution according to the invention has not hitherto been proposed in the state of the art because, fundamentally, with the known electrical brake, the problem of oscillations of the wire could be considered to have been resolved. The solution according to the document DE 20 43 746 mentioned above, which consists in passing the wire through a tube, gives no indication in this respect. The document does not disclose that it anticipates this guide tube exerting a braking function. On the contrary, in that document it is assumed that the wire slides through this tube with little friction.
Concrete options for evening out the tension in the wire in the compensation portion concerned comprise passive compensation using mechanisms actuated by gravity and active compensation by means of elastic elements, pneumatic actuators or regulating motors.
A wire-laying device thus equipped is as suitable for laying wires uniformly, in the conventional manner, with or without corrugation, in even paths as it is for laying the wire in the recently proposed paths involving all kinds of curves, divergent paths, non-circular paths of variable radius, with local increases and/or reductions in the wire-laying density, etc. The tensioning device according to the invention displays its advantages particularly in the last-mentioned laying formats because in these instances it is often necessary to operate the sheet support at variable speeds. It is even possible (in a way known per se) that the direction of travel may need to be reversed.
Other details and advantages of the subject matter of the invention will emerge from the drawing of one exemplary embodiment of a wire-laying device according to the present invention and of its description given hereinafter.
In simplified depictions which are not drawn to scale:
The device according to the invention depicted in
The cylindrical drum 1 advantageously has a large diameter and a large circumference, so that several sheets 3 can be set on its cylindrical wall. Here, we can see two sheets 3 of the same size. They are fixed to the envelope surface of the drum, preferably by suction or pressure difference. To these ends, the envelope surface is equipped in the known way with a great many bores through which air is sucked. Atmospheric pressure presses the sheets onto the envelope surface.
Positioned above the drum 1 is a wire-laying device 4 (also known as a laying head). By virtue of a drive mechanism that has not been depicted in detail, this device can be moved back and forth parallel to the axis of rotation of the drum (and therefore parallel to the direction in which the figure is viewed) along a straight guide 5. A wire 7 is taken off a coil 6 of wire stock and ultimately laid using a presser roll 8 (preferably one that can be heated) onto the sheet 3 or incorporated into the surface thereof.
The coil 6 of wire stock may, in the known way, be equipped with an adjustable brake, for example an electric brake. The presser roll 8 is preferably elastically preloaded against the envelope surface of the drum 1 and runs along the sheet 3 without its own drive mechanism.
In the path between the coil 6 of wire stock and the presser roll 8, the wire 7 passes through a guide device denoted in its entirety by 9 in
In addition, the guide device 9 presents the wire 7 passing through it with another tensioning device more details of which are given in
For simplicity, this
Some lines of wire 7′ have already been laid onto the sheet 3 in earlier rotations of the drum 1 and the presser roll 8 has therefore to be situated in such a way as to be able to lay another line of wire 7′ to their right. In an embodiment known per se, the presser roll 8 has a planar and domed presser surface. The wire 7 passes over the line of its crown. In this way, the wire 7 is pushed into the surface of the sheet 3 without the lateral edges of the presser roll 8 penetrating the sheet 3.
The guide device 9 comprises, in the way known per se, two toothed wheels 10 which mesh in one another and which give the wire 7 guided between them the desired corrugation immediately upstream of the presser roll 8. In order to simplify matters, the corrugation of the wires laid onto the sheet 3 has not been depicted. As far as the relative speeds of the toothed wheels and of the presser roll are concerned, reference can be made to the prior art described above.
According to the invention, on leaving the coil 6 of wire stock and before infiltrating between the toothed wheels 10, the wire 7 passes through a tensioning device denoted in its entirety by 11. In its exemplary embodiment depicted here, this tensioning device comprises two fixed guide rolls 12 and, between these, a mobile and elastically preloaded tensioning roll 13. The latter roll is mounted to rotate in the tensioning device 11 and/or in the guide device 9 on an oscillating or pivoting lever 14 which is itself preloaded by means of a pressure spring 15. A broken line has been used to represent various possible positions of deployment of the pivoting lever 14 away from the central position depicted in solid line.
The guide rollers and the tensioning roller may also just as easily be replaced by sliding guides if the wire is able to slide over these with negligible friction. These are not therefore excluded, even though the text which follows refers always to rolls.
On the whole, the invention makes it possible to obtain a reaction that is as sensitive and immediate as possible of the tensioning device 11 to variations in the instantaneous tension of the wire. A particularly low mass of the moving parts of the tensioning device and low friction in all the mountings and anywhere that sliding might occur make a particularly strong contribution to this aspect.
It can be seen that, between the two guide rolls 10, the wire 7 forms a U-shaped loop of which the depth with respect to the guide rolls 12 is defined by the effective position of the moving tensioning roll 13 which is kept under load by the spring 15. This loop allows for fairly substantial compensation for the length, measuring several centimeters, in that part of the wire that at any moment lies between the coil 6 of wire stock and the presser roll 8.
If an even greater variation in length needs to be compensated, the tensioning roller 13 (which is elastically preloaded) can also be guided in a straight line in a readily accessible sliding guide, against the action of an elastic force or the like, rather than being so by the pivoting lever depicted, so as to be able to extend over a greater length without any angular shift.
On the whole it is possible very simply and with low inertia to compensate for variations in the rotational speed of the drum 1 which variations cause the rotation of the presser roll 8 to accelerate or decelerate and therefore generally also lead to uneven wire consumption. In particular, the mass of the coil 6 of wire stock which varies greatly according to how much wire stock still remains, and the relative inertia of the brake 6B play no part in this compensation, which is therefore able to react quite sensitively.
After the guide roll 12 situated downstream with respect to the direction of travel of the wire, the wire 7 again passes through two guide rolls 16 which lead it exactly centrally between the toothed wheels 10. The latter can obviously also be replaced by the sliding guide or even be completely omitted if, after the second guide roll 12, the wire 7 can be inserted between the toothed wheels 10 with sufficient precision.
Obviously it is possible to use many other ways of maintaining a defined tension in the wire, even at these points, as long as the aforementioned conditions (and the bulkiness data and the possibility of adjusting the tension in the wire) provide the same effect. Thus, in concrete terms, it might be possible to provide a sliding moving rail rather than the tensioning roll, if it is anticipated that it will be necessary to compensate for an excessive difference in length. These sliding rails are known in chain drives or belt drives. They run longitudinally in a curve the radius of curvature of which changes according to the tension in the wire passing through them.
Furthermore, in place of the helical pushing spring 15 depicted diagrammatically here, it would also be possible to use other means of adjusting the tensioning roll 13, for example, a pneumatic spring, or a pneumatic, electrical or similar adjustment drive mechanism.
The tensioning device may optionally also comprise a measurement unit (not depicted here) which determines the actual tension in the wire and then dictates the tensioning force needed at any moment to an associated adjustment drive mechanism. A measurement unit such as this might be able, for example, to detect the force exerted on its bearing by one of the turn rollers 12, which force increases as the drum 1 accelerates and decreases as the drum 1 slows down. When the force on the wire is small, it would then be necessary to provide additional tensioning, whereas if the tensile force increased, the tension could be reduced.
15. A device for laying onto a surface a thin metal wire taken from a coil of wire stock, using a presser, the device comprising:
- means for exerting mechanical tension in a region of the wire that lies between the coil of wire stock and the presser,
- a wire-guiding device provided in the region, and
- wherein the wire-guiding device comprises a tensioning device that acts directly on the wire taken off the coil of wire stock.
16. The device as claimed in claim 15, wherein the wire is guided in the region of the tensioning device over a portion of variable length.
17. The device as claimed in claim 16, wherein the variable length of the portion can be defined using at least one mobile tensioning roll or a sliding part that has an equivalent function.
18. The device as claimed in claim 15, wherein the wire is guided through the tensioning device by, in turn, a first turn roll, a mobile tensioning roll, and another turn roll, or by corresponding sliding parts.
19. The device as claimed in claim 15, wherein the tensioning device comprises a tensioning roll or a sliding part that has an equivalent function and that is mounted on an elastically urged pivoting lever.
20. The device as claimed in claim 15, wherein the wire is guided through the tensioning device by a mobile and/or curved sliding rail.
21. The device as claimed in claim 17, wherein the tensioning roll or the sliding part that has an equivalent function are mounted in a sliding guide.
22. The device as claimed in claim 15, wherein the tensioning device comprises at least one spring and/or a drive mechanism that is feedback controlled.
23. The device as claimed in claim 15, wherein the tensioning device comprises a device for measuring the tension in the wire at any moment.
24. The device as claimed in claim 15, further comprising a brake, braking force of which is feedback controlled, so as to damp rotational movement of the coil of wire stock.
25. The device as claimed in claim 15, further comprising means for mechanically corrugating the wire between the tensioning device and the pusher.
26. The device as claimed in claim 15, comprising plural laying devices.
27. The device as claimed in claim 15, wherein the surface that is to have the wire laid thereon is a sheet fixed to a flat or curved laying surface, and the wire is laid down by relative movement of the pusher and/or of the sheet, one relative to the other.
28. The device as claimed in claim 15, wherein a support element for supporting the sheet can be moved reversibly with respect to the pusher.