DEVICE FOR THERMAL CUTTING OF A FABRIC SHEET INTO RIBBONS

Technical Field The invention relates to a device of the type given in the pre- characterizing clause of claim 1. An important application of this device is the production of label ribbons.

As shown in EP 0853 697, a wide sheet of fabric is first woven on a loom, with several label ribbons, that are attached on the long edge, being produced in adjacent sheet zones. A group of knives is used, each of which is held between two clamping points through which electric current is passed through the knife, thus heating it. Both clamping points are carried by a common housing mounted on one side of the sheet of fabric. An arm that positions one of the two clamping points on the opposite side of the sheet of fabric, extends from the housing. In doing so, the arm passes through the slot between adjacent ribbons cut in the sheet of fabric. A group of such knives is used that are disposed at a specific distance apart and cut the sheet of fabric in the individual sheet zones into label ribbons. This thermal cutting of the textile sheet can still be carried out on the loom. The finished label ribbons then only have to be cut in sections into the individual labels.

With a different kind of device, according to DE 34 05 252 Al that is used for cutting foam pieces, a cutting system of two crossing cutting wires is used to cut foam sheets from a polystyrene block. The ends of the wires of the two cutting wires are disposed on two oscillating shafts at circumferential positions opposite each other, with the two cutting wires

executing opposing movements, in the manner of a saw, when cutting the polystyrene block. The ends of the cutting wires are connected to the oscillating shaft through a coil spring that tensions the wires. To heat the cutting wires, electric current is passed through the shafts and coil springs and, then, through the cutting wire. This means that not only is the cutting wire heated, the coil spring is heated too. Because the resilience of a coil spring depends on temperature, the flow of current through the coil spring adversely affects its resilience.

Disclosure of Invention

The object of the invention is therefore to develop a reliable device of the type named in the characterizing clause of claim 1 that improves the thermal cutting of the fabric sheet. This is achieved by the measures given in claim 1, of which the following are particularly important.

The knife is held between its two clamping points in the deenergised state, when it is still cold. When the knife is heated by electric current during subsequent use, the clamping length of the knife between the two clamping points usually increases. This is because the given length of the knife increases with temperature. The result of this increase in length is that the knife loses the required ideal tension between the two clamping points and curves uncontrollably. The heated, hot knife cannot be easily re-tensioned by slackening the clamping points and, also, this is awkward and time- consuming .

The invention overcomes this problem. To do this, the invention proposes to make at least the one clamping point adjustable with respect to its distance from the other one and to apply a preload force to it that attempts to increase the clamping length of the knife. This results in an automatic re-tensioning of the knife in the hot condition, and in fact regardless of the particular operating temperature. In accordance with the invention, slackening and tightening the clamping points during operation is unnecessary, apart from the initial stage when the knife is clamped between its two clamping points. Regardless of how high is the operating temperature, the knife always remains straight between its two clamping points. The one clamping point changes its distance from the other clamping point, but the knife still operates along its straight connection. The knife is always tensioned regardless of the temperature. This means that the precise position of the cut point in the sheet of fabric is accurately defined, i.e., the shortest connection between the two clamping points. Incorrect cuts are precluded.

Further measures and advantages of the invention are given in the subclaims, in the following description and using drawings. The drawings show only one example of an embodiment of the invention.

Brief Description of the Drawings

The accompanying figures, where like reference numerals refer to identical or functionally similar elements throughout the separate views and which together with the detailed description below are incorporated in and form part of the specification, serve to further illustrate various embodiments and to explain

various principles and advantages all in accordance with the present invention.

FIG. 1 is a side elevational view of a housing with a knife having a first exemplary embodiment of a tensioner according to the invention positioned between two clamping points in an at- rest position with the knife unheated and cold;

FIG. 2 is a side elevational view of the housing of FIG. 1 with the knife in a working position with an increased clamping length due to heating of the knife;

FIG. 3 is a side elevational view of the housing with a knife having a second exemplary embodiment of the tensioner according to the invention;

FIG. 4 is an enlarged side elevational view of a tensioning device of FIG. 3;

FIG. 5 is an enlarged side elevational view of a tensioner assembly of FIG. 3 without the sheet;

FIG. 6 is a side elevational view of the housing with a knife having a third exemplary embodiment of the tensioner according to the invention;

FIG. 7 is a side elevational view of the housing with a knife having a fourth exemplary embodiment of the tensioner according to the invention; and

FIG. 8 is a side elevational view of the housing with a knife having a fifth exemplary embodiment of the tensioner according to the invention.

Best Mode for Carrying Out the Invention

The device in accordance with the invention is illustrated being applied in a loom for the production of a fabric sheet 10, with the cutting taking place during the weaving. The device could also be used regardless of the loom, in order to cut the fabric sheet 10 into a number of ribbons 11.

In FIG. 2, the direction of movement of the sheet of fabric 10 or of the ribbons 11 is marked by an arrow 13. A carrier 12, on which a plurality of housings 15 are mounted, moves over the sheet of fabric 10 or the ribbons 11 transverse to the direction of movement 13. The housing 15 is located a distance from the top 14 of the sheet of fabric 10 or of the ribbons 11 and can be moved along the carrier up to a defined point. The housing 15 carries a knife 20 that can be electrically heated. The distance between two housings 15 determines the width of the ribbon 11 to be cut from the sheet of fabric 10. The sheet of fabric can be of fusible yarn and the knife 20 is heated by electric current to a temperature at which the yarn melts and, thus, creates the cut 16.

Each knife 20 moves between two clamping points 21, 22 disposed on opposite sides 14, 17 of the sheet of fabric 10. Each of the two clamping points 21, 22 is mounted on a holder 23, 24, seated on the housing 15. A first particular feature of the invention is that the one holder 23 disposed on the top 14 of the sheet of fabric 10 is stationery whereas the other holder

24 is movable and is, therefore, referred to as the "moving holder". {Of course, these features can be reversed to have the top holder 23 be movable.) The stationery holder 23 is referred to in the following as the "stationery holder". The moving holder 24 is connected to the housing 15 by a hinged joint 18 and has an arm 25 that projects through the slot 16 in the sheet of fabric with its end terminating at the bottom clamping point 22. In the present example, the moving holder 24 is configured as a bell crank lever that forms a lever arm of the arm 25, whereas the other arm 26 is loaded by a spring force 30 in the direction shown by the arrow 30 (see FIG. 1) . The spring loading 30 is provided by a spiral coil spring 31, disposed in a recess 27 of the housing 15 and with its free end 32 supported on the lever arm 26.

FIG. 1 shows the at-rest position of the moving holder 24, with the lever arm 26 resting against a stop 19 of the housing 15. This at-rest position is shown by an indicating line 24.1 in Fig 1. In this at-rest position 24.1, the knife 20 is positioned between the two holders 23, 24, In this exemplary embodiment, the knife 20 is a wire clamped at both ends to the clamping points 21, 22. Clamping screws can be used for this purpose. In the at-rest position 24.1, the lever arm 26 can also be a little distance from its stop 19. The decisive factor is that the wire forming the knife 20 runs tensioned between the two clamping points 21, 22. In the at-rest position, the knife 20 has a clamped length, marked by distance Ii between its two clamping points 21, 22. The spring loading 30 makes sure that the bottom clamping point 22 is kept under a preload P, that attempts to increase this clamping length li, by the moving

holder 24. In the at-rest position 24.1, a minimum clamping length Ii is present in this case.

Both holders 23, 24 are fitted in the housing 15, electrically insulated from each other and connected to electrical lines 28 by electrical components. The current flow is shown by a dotted line in FIG. 2. As can be seen, the coil spring 31 is outside the electrical circuit, i.e., the current does not flow through the coil spring 31. The electric current level is set relative to the material and the cross-section of the knife 20 so that the knife 20 is heated to an adequately high temperature to melt the yarn of the sheet of fabric 10. If the sheet of fabric 10 is moved in the direction of arrow 13 in FIG. 2, a cut 16 is made in the sheet of fabric 10. Thus, a sheet of fabric 10 is cut into ribbons 11.

FIG. 2 also shows what normally happens if metal materials, such as the knife 20, are heated, i.e., the length increases. The clamped length I ₂ of the knife 20 between the two clamping points 21, 22 increases by a differential δl . If both holders 23, 24 were at-rest, the excess length δl would lead to an uncontrolled curved run between both clamping points 21, 22. But, because the spring loading exerts a tensile force P on at least the one clamping point 22, the knife 20, being a fleπible wire, remains tensioned. The moving holder 24 is swiveled about an angle 34. The cutting point 33 of the knife 20 on the sheet of fabric 10, therefore, is always the shortest linear connection between the two clamping points 21, 22. The indicating line 24.2 in FIG. 2 shows the "working position" of the moving holder 24.

The tensile force P acting on the knife 20 automatically ensures that the knife is tensioned at any temperature. If the knife 20 in the initial condition is clamped to its two clamping points 21, 22, the operator does not have to worry further about the device during operation. The knife 20 always takes up a well-defined, tensioned position between both its holders 23, 24.

One or both of the holders 23, 24 can be provided with pressure faces or opposing pressure faces, not further illustrated, as for example are shown in DE 196 44 534 C2. They can be before or after the knife 20 as viewed in the direction of transport 13 of the sheet of fabric 10. The deciding factor in any case is that these pressure and opposing pressure faces are pressed against the top and/or bottom 17 of the sheet of fabric 10.

In this example of an embodiment, the moving holder 24 is designed as a lever. As an alternative it could be designed as a lengthwise moving slide connected to the housing 15 by a guide. Furthermore, the spring force 30 could be replaced by a weight acting on the moving holder 24.

A second exemplary embodiment of a tensioner according to the invention is shown in FIGS. 3 to 5. Instead of pivoting either of the arms 23, 24 holding the knife 20, both arms 37, 38 are fixed. To provide the variable tensioning of the wire of the knife 20, a spring loaded plunger assembly 50 is disposed at one of the arms 37, 38. FIG. 4 shows an enlarged view of the plunger assembly 50 with a plunger 51 inside a cavity of the arm 37, 38. The bias force is provided, for example, by a spring 57 moving the plunger 51 along the movement axis 58.

The tip 59 of the plunger 51 is provided with a groove 61 having a depth 60 sufficient to prevent the knife 20 from moving out of the groove 61 as the knife 20 heats up and expands. Over time, the knife 20 can obtain deposits thereon from the fusible yarn it cuts. Therefore, a length of the knife 20 is wrapped around a first spool 22 and is fed in a feeding direction 39 to a second spool 23, or vice-versa. A slit for a screwdriver, for example, shown in the second spool 23, can be used to tighten the knife 20 and, thereby cause movement of a used knife section out of the cutting area 44 and onto the second spool.

FIG. 6 illustrates another exemplary embodiment of the tensioner according to the invention. Instead of the plunger assembly 50, a plate spring assembly 60 including a rounded end 32 (with or without a groove for the knife 20) disposed away from the first spool 22 by a spring-like plate or rod 52 acts as a spring board that keeps tension on the knife 20 by resisting movement in the direction indicated by arrow 66. As the knife 20 is tightened, the rod 52 bends into the direction 66 and places a bias force on the knife 20.

FIG. 7 illustrates another exemplary embodiment of the tensioner according to the invention. Here, the plunger assembly 50 includes a distal plunger roller assembly 60, 63. The roller can be grooved in the center to accommodate the knife 20 therein and retain it from exiting the groove when tensioned thereon. The plunger 51 provides the bias force in the direction 55.3 and tensions the knife 20 over the extent 46.

FIG. 8 illustrates another exemplary embodiment of the tensioner according to the invention in the form of a tensioning pillow. A flexible band 53 is bent into a curved shape and attached to the arm 37 at connection points 53. The pillow of the band 53 can be provided with a groove if desired. The natural characteristics of the material forming the band 53 provides the bias force 55.4 that tensions the knife 20 as it changes length due to heating.

Reference character list

10 Sheet of fabric

11 Ribbon 12 Carrier for 15

13 Arrow showing the transport of 10 or 11, direction of movement

14 Top of 10

15 Housing 16 Cut in 10 for 11

17 Bottom of 10

18 Hinged joint

19 Stop of 15 for 26

20 Knife, wire 21 Top, at-rest clamping point of 20

22 Bottom, moving clamping point of 20

23 At-rest holder, stationery holder

24 Moving holder, moving holder 24.1 At-rest position of 24 (FIG. 1) 24.2 Working position of 24 (FIG. 2)

25 Arm, first arm of 24

26 Second arm of 24, lever arm

27 Recess for 31 in 15

28 Electrical leads 29 Dotted line showing path of electrical current

30 Arrow showing spring force, spring loading

31 Coil spring for 30

32 Contact point of 31 for 26

33 Effective cut point of 20 on 10 (FIG. 2) 34 Arrow showing the swivel movement of 26, push-away direction

11 Clamping length of 20 at 24.1

1 ₂ Clamping length of 24 at 24.2

δ Differential length between I ₁ and I ₂

P Preload force of 20, tensile force