DEVICE FOR AUTOMATICALLY SETTING UP THE MULTIPLE TOOL IN HOT-WIRE CUTTING MACHINES

This invention relates to a device for automa ically setting up the multiple tool in hot-wire cutting machines, particularly for sheets and blocks of polystyrene and the like. Hot-wire cutting machines for sheets and blocks of polystyrene and similar materials are known- They generally comprise a bench on which the blocks or sheets to be cut are rested, and a pair of side walls between which a plurality of metal wires are stretched transversely to said bench- When in operation, these wires are traversed by an electric current which heats them to a temperature sufficient to cause localized melting of the polystyrene. The polystyrene is cut into pieces of the required shape by the longitudinal and vertical movement of all the wires relative to the polystyrene. The movement of the metal wires relative to the bench and thus relative to the polystyrene can be obtained either by a double horizontal and vertical movement of the wire-supporting side walls relative to the fixed bench or by a double horizontal and vertical movement of said bench relative to fixed side walls, or again by a horizontal movement of the side walls and a vertical movement of the bench-

The number and arrangement of the wires between the two side walls and thus the configuration of the multiple tool to be used at any given time obviously varies according to the number of polystyrene pieces to be

*-* produced, their shape and their size. The preparation of the particular tool, ie the setting up of the machine, comprises arranging the wires between the two side walls in the number and arrangement corresponding to the particular work to be carried out. This preparation is

10 currently done manually, and this results in a series of drawbacks which the present invention proposes to eli inate-

One of these drawbacks is that this manual involvement results in a very slow operation, requiring

15 the simultaneous presence of two persons, one at each side wall on the one and other side of the bench, this slowness being more felt the greater the number of wires to be stretched, a number which can vary from a few tens to as many as one hundred-

20 A further drawback is that such manual setting is valid only for the particular work in hand, and must be reversed when finished, so that the machine can be used with a different wire arrangement for the subsequent ϊ

work- It is therefore necessary to re-set the cutting machine in the identical manner each time the same work is to be done, and this obviously multiplies the drawbacks which each manual setting operation involves- All these drawbacks and others which will be apparent from the following description are obviated according to the invention by a device for automa ically setting up the multiple tool in hot-wire cutting machines, particularly for sheets and blocks of polystyrene and the like, comprising a bench on which the material to be cut is rested, a pair of side walls between which a plurality of electrically heated wires are stretched, and means for longitudinally and vertically moving said side walls relative to said bench in such a manner that said wires hot-cut the material resting on said bench into the predetermined pattern, characterised in that each side wall comprises a longitudinal bar along which there are slidable a plurality of slides to which the ends of the wires are fixed and a carriage provided with a member for the removable engagement of each slide and driven under the control of an electronic control unit in order to position said slide along the respective longitudinal bar

in accordance with data acquired by said control unit -

A preferred embodiment of the present invention is described hereinafter with reference to the accompanying drawings in which: Figure 1 is a schematic plan view of a hot-wire cutting machine provided with the device according to the invention; Figure 2 is a partial longitudinal section therethrough on the line II-II of Figure 1; Figure 3 is an enlarged partial cross-section therethrough on the line III-III of Figure 1 in the non-operative condition; and Figure 4 is the same view as Figure 3 but in the operative condition- As can be seen .from the figures, the machine according to the invention comprises a bench or base 1 of substantially traditional type, to the side of which there are disposed two side walls 2 each comprising a longitudinal bar 3- The purpose of the bench 1 is to support the polystyrene sheets or blocks to be cut, whereas the purpose of the longitudinal bars 3 is to support a plurality of transverse wires 4 which hot-cut the polystyrene. For this purpose the side walls 2 are

mobile both axially and vertically relative to the bench 1 so as to cause the wires 4 to move relative to the polystyrene. This relative movement, which is obtained either by moving the bench 1 or by moving the side walls 2 or by moving both, is effected with traditional systems which do not form part of the invention and are not shown on the drawings for reasons of clarity.

Each longitudinal bar 3, which is constructed preferably of aluminium or another metal, is hinged to the corresponding side wall 2 by a horizontal hinge 5, the purpose of which will be apparent hereinafter, and is also provided with a longitudinal round rod 6 of conducting material such as brass, connected to the electrical power supply. Each longitudinal bar 3 has a rail profile along which a carriage indicated overall by

7 can slide, and a plurality of slides 8 to which the ends of the wires 4 are fixed.

More specifically, the carriage 7 is provided with a stepper motor or a direct current motor controlled by an electronic control unit, not shown on the drawings- It is also provided with a pin 9 operated by a pneumatic actuator 10 which moves it axially between an advanced position in which it engages a corresponding cavity 11 of

- ό -

each slide 8, and a retracted position of disengagement.

In addition to the cavity 11, each slide 8 comprises a further cavity 12 housing a coil spring 13 for tensioning the corresponding wire 4.

5 The opera ion of the machine according to the invention is as follows: with the tool "unset", all the pairs of slides 8 corresponding to the various wires 4 are side by side at one end 14 of the longitudinal bars. To set the tool, the

I*- ¹ number and arrangement of the wires 4 required for the particular work in hand are firstly established- These data can either be fed into the control unit for example via a keyboard, or can be called up from the memory if that number and arrangement have lredy been used and

¹ 5 memorized.

When the setting command has been given, the two motors of the carriages 7, which are operated synchronously, cause the respective carriage 7 to move up to the corresponding pack of slides 8 and halt at the

- ^Q last slide 8a defined by the particular chosen number of wires 4. A command is now fed to the actuators 10 to cause the respective pin 9 to emerge and engage the cavity 11a of said slide 8a, and a further command is fed

to the motors in the opposite sense to move those longitudinal bars 3 together with the slides 8 and thus the wires 4 required for the particular setting of the tool towards the end 15- When the slide 8a reaches its definitive position, which is also obtained by data either fed into the electronic control unit or previously memorised, the motors are stopped and the pins 9 are disengaged from the corresponding cavity 11, so that the last wire 4a is left in its definitive position along the bars 3. The motors are then advanced through a distance equal to the thickness of the slides 8 and the pins 9 of the two carriages are again advanced to engage the corresponding cavity 11 of the adjacent slide 8b- At this point a command is given for the carriages 7 to again move until the relative wire reaches its definitive position, and so on until all the wires 4 have been correctly positioned-

A subsequent command fed simultaneously to the two bars 3 causes them to rotate about the respective hinges 5 in the direction of the arrow 16 in Figure 3, so raising the round rods 6 and bringing them into contact with the wires 4 in the traditional manner- The multiple

It

tool is now ready to operate-

To change the arrangement of the wires 4 along the bars 3, the carriages 7, which still have their pin 9 engaged in the corresponding slide of the first wire 4, are caused to move towards the end 14 of the bars, to thus pack the various pairs of slides 8 at that end, after which the previous procedure can be carried out based on data for the new arrangement to be obtained-

From the aforegoing it is apparent that the setting device according to the invention offers numerous important advantages for the entire cutting machine, and in particular:

- possible total automation of the plant,

- considerable speed and accuracy of tool setting, _ reproducibi1ity of positioning-