MULTIPLE WIRE MACHINE FOR CUTTING STONE MATERIALS

Technical Field

The present invention relates to a machine for multiple wire cutting of stone materials, designed to obtain a plurality of slabs from blocks of materials such as marble, granite, etc.

Background Art

Such machines generally comprise a plurality of cutting devices positioned side by side in parallel planes and each consisting of a cutting wire wound in a loop around at least two flywheels, at least one of the flywheels being motor-driven.

The actual cutting operation is performed by causing relative motion between the block to be cut and the cutting wires..

Each cutting device also has a tensioning ^' system which guarantees tensioning of the individual cutting wire during the entire cutting operation.

An example of a tensioning device, which allows independent tensioning of all of the individual cutting wires, is described in patent EP 1 024 314 by the same Applicant.

In said patent, wire tensioning is guaranteed by a hydraulic cylinder connected between the flywheel and a fixed part relative to the flywheel, and which is fed with pressurised oil so as to cause it to extend and consequently move the flywheel relative to the fixed part in a direction such that it causes an extension of the path of the cutting wire. However, the machines for multiple wire cutting known today have several disadvantages.

During cutting operations the characteristics of the material cut (hardness) may vary considerably even in the same block. When, during the reciprocal movement of the cutting device and the block, the hardness of the material increases, the

sweepforward and therefore the tension to which the cutting wire is subjected increases and if the tension becomes excessive the wire may break.

In contrast, when the hardness of the material is reduced, the wire finds no obstacle to the cutting action (in particular the sweepforward is cancelled) , therefore wire tensioning could be too low, the result being that the cut obtained is not smooth and precise enough.

In both cases, the problem which arises is linked to the fact that the flywheel used for tensioning guarantees the correct tensioning only for as long as it can move freely relative to the other flywheel. However, when the flywheel reaches the end of its stroke (on one side or the other) it cannot move any further in that direction. As a result, if, depending on the case in question, there is a further increase or reduction in the tensioning, the known tensioning means are not able to compensate for it.

Disclosure of the Invention In this situation, the technical need which forms the basis of the present invention is to provide a machine for multiple wire cutting of stone materials which overcomes the above-mentioned disadvantages .

In particular, the technical need of the present invention is to provide a machine for multiple wire cutting of stone materials which can prevent excessive tensioning of the cutting wires under any operating condition.

Another technical need of the present invention is to provide a machine for multiple wire cutting of stone materials which prevents the cutting wires from breaking due to excessive tensioning.

Yet another technical need of the present invention is to provide a machine for multiple wire cutting of stone materials which prevents excessive slackening of the cutting wires and which therefore guarantees a precise and smooth cut under any operating condition.

The technical need specified and the aims indicated are

substantially achieved by a machine for multiple wire cutting of stone materials as described in the claims herein.

Brief Description of the Drawings Further features and advantages of the present invention are more apparent in the detailed description below, with reference to a preferred, non-limiting embodiment of a machine for multiple wire cutting of stone materials, illustrated in the accompanying drawings, in which: Figure 1 is a front view with some parts transparent of a machine for multiple wire cutting of stone materials in accordance with the present invention;

Figure 2 is a top view of the machine illustrated in Figure i; Figure 3 is a top view of an enlarged detail of the machine illustrated in Figure 1;

Figure 4 is a cross-section of the detail illustrated in Figure 3 according to line IV - IV;

Figure 5 is a front view of a group of first flywheels 6 of the machine illustrated in Figure 1;

Figure 6 is a cross-section of the group of first flywheels 6 illustrated in Figure 5;

Figure 7 is an axonometric rear view of the group of first flywheels 6 illustrated in Figure 5; Figure 8 is an axonometric front view of the group of first flywheels 6 illustrated in Figure 5;

Figure 9 is an axonometric view of a first flywheel made in accordance with the present invention;

Figure 10 is a front view of the central part of the flywheel illustrated in Figure 9;

Figure 11 is a cross-section of the flywheel illustrated in Figure 10 according to line XI - XI;

Figure 12 is a cross-section of the flywheel illustrated in Figure 10 according to line XII - XII; Figure 13 is a chart representing operation of the machine in accordance with the present invention;

Figures 14 to 17 illustrate other charts of further

operating conditions of the machine in accordance with the present invention.

Detailed Description of the Preferred Embodiments of the Invention With reference to the accompanying drawings, the numeral 1 denotes as a whole a machine for multiple wire cutting of stone materials in accordance with the present invention.

The machine 1 comprises a fixed supporting structure 2 on which a frame 3 mobile in a vertical direction is slidably mounted.

A plurality of cutting devices 4 is mounted on the frame 3, the devices arranged parallel with one another so that they can simultaneously make a plurality of cuts on the same block 5 of material. Each cutting device 4 in turn comprises at least one first flywheel 6 and one second flywheel 7 positioned in the same plane and distanced from one another. The flywheels 6, 7 are rotatably mounted on the frame 3 and at least one of them is motor-driven, whilst the other is preferably idle. At least one cutting wire 8 is wound in a loop around the two flywheels 6, 7. In the embodiment illustrated, each cutting device 4 also comprises a plurality of smaller additional flywheels 9 in the same plane as the first and second flywheels 6, 7 and designed to guide the cutting wire 8 in the best possible way.

In each cutting device 4, tensioning means 10 operate on the first flywheel 6 (which is preferably idle) to keep the cutting wire 8 taut. For this purpose, the tensioning means 10 move the first flywheel 6 relative to its supporting shaft 11, between a minimum tensioning position 12 (first flywheel 6 moved to the right in Figures 1 and 10) and a maximum tensioning position 13 (first flywheel 6 moved to the left in Figures 1 and 10) .

Since under operating conditions the tensioning applied to the wire by the tensioning means 10 is substantially constant, in this text the definition "minimum tensioning position" 12 indicates the condition in which the cutting wire 8 is subject to an external traction force such that it cannot compensate for the action of the tensioning means 10, so that the first flywheel 6 is pushed to the end of its stroke by the action of the tensioning

means 10 whose traction action is not balanced by external stresses. Similarly, hereinafter "maximum tensioning position" 13 refers to the condition in which the cutting wire 8 is subjected to an external traction force greater than the force exerted by the tensioning means 10 so that the first flywheel 6 is pulled to the end of its stroke by the external traction force.

Advantageously, the supporting shaft 11 is shared by all of the first flywheels 6, which may, however, be moved independently of one another (for the sake of clarity, Figures 5 to 8 illustrate the supporting shaft 11 with only some of the first flywheels 6 mounted on it ) .

A control unit (not illustrated) is also set up to control operation of the machine 1 as a whole; in particular it is designed to control the movement of all of the machine 1 moving parts.

In accordance with the present invention, the machine 1 also comprises, for each first flywheel 6, at least one sensor 14 for detecting the position of the first flywheel 6 relative to the supporting shaft 11. The sensor 14 preferably detects and sends to the control unit the position of the first flywheel 6 relative to the minimum tensioning position 12 and/or the maximum tensioning position 13.

Advantageously, each sensor 14 comprises a fixed reference part 15 integral with the supporting shaft 11 and a mobile part 16 integral with the relative first flywheel 6. The fixed part 15 / mobile part 16 is also fitted with an electromagnetic detector able to detect the position of the mobile part 16 / fixed part 15 and so identify the position of the first flywheel 6.

The signal indicating the position of each first flywheel 6 is then sent to the control unit which, in accordance with the present invention, is programmed to vary the speed of movement of the frame 3 relative to the supporting structure 2, depending on the position of the first flywheels 6 detected by the relative sensors 1*. In the embodiment illustrated, since blocks of stone material are cut by a vertical descent of the frame 3 so that the cutting wires act in the block 5 from the top down, the frame 3

movement speed is normally called the descent speed. Therefore, in this case the descent speed is determined according to the position of the individual first flywheels 6.

Advantageously, the control unit is programmed to increase the frame 3 movement (descent) speed when it receives from the sensors the indication that at least one of the first flywheels 6 is at a distance from the minimum tensioning position 12 that is less than a predetermined first safety distance 17.

A first flywheel 6 may move towards the minimum tensioning position 12 when the tensioning of the relative cutting wire 8 is insufficient. This is normally due to a wire descent speed that is too low relative to the hardness of the portion of material being cut.

As a result, increasing the descent speed under normal conditions successfully increases wire tensioning. The extent of the speed increase may be established on each occasion according to requirements. In particular, it may be varied either for discrete values or continuously. Moreover, it may be varied one or more times in succession as far as a predetermined limit. Whatever the case, the control unit is also preferably programmed to interrupt machine 1 operation when at least one first flywheel 6 remains at a distance from the minimum tensioning position 12 that is less than the predetermined first safety distance 17, for a time longer than a predetermined threshold time, despite the fact that the frame 3 movement speed has already been increased one or more times or as far as the predetermined limit.

The control unit is also preferably programmed to interrupt machine 1 operation when it receives from the sensors the indication that at least one of the first flywheels 6 is at a distance from the minimum tensioning position 12 that is less than a predetermined first threshold distance 18, where the first threshold distance 18 is less than the first safety distance 17.

By way of example, for an overall first flywheel 6 stroke of 65 mm, there may be a first safety distance 17 of 10 mm and a first threshold distance 18 of 4 mm. This means that if a first flywheel 6 is in a position less than 10 mm but more than 4 ram

from the minimum tensioning position 12, the control unit increases the frame 3 descent speed as described above, but if the distance is less than 4 mm the control unit stops machine 1 operation. Similarly, in accordance with the present invention, the control unit may be programmed to reduce the frame 3 movement speed when it receives from the sensors the indication that at least one of the first flywheels 6 is at a distance from the maximum tensioning position 13 that is less than a predetermined second safety distance 19.

In this case, a first flywheel 6 is forced to move towards the maximum tensioning position 13 when the tensioning of the relative cutting wire 8 is excessive. This is normally due to a wire descent speed that is too high relative to the hardness of the portion of material being cut, so that the cutting wire 8 feed speed in the material is less than the frame 3 movement speed.

As a result, by reducing the descent speed, under normal conditions the tensioning of the cutting wire 8 is successfully reduced. Again in this case the extent of the speed reduction may be established on each occasion according to requirements similarly to what is described relative to its increase. In particular, it may be varied either for discrete values or continuously. Moreover, it may be varied two or more times in succession as far as a predetermined limit. Again, the control unit is also preferably programmed to interrupt machine 1 operation when at least one first flywheel 6 remains at a distance from the maximum tensioning position 13 that is less than the predetermined second safety distance 19, for a time longer than a predetermined threshold time, despite the fact that the movement speed has already been reduced one or more times or as far as the predetermined limit.

Moreover, similarly to what is described above, the control unit is preferably programmed to interrupt machine 1 operation when it receives from the sensors the indication that at least one of the first flywheels 6 is at a distance from the maximum tensioning position 13 that is less than a predetermined second threshold distance 20, where the second threshold distance 20 is

less than the second safety distance 19.

With reference to the example above (overall first flywheel 6 stroke of 65 mm) , there may be a second safety distance 19 of 10 mm and a second threshold distance 20 of 4 mm. This means that if a first flywheel 6 is in a position less than 10 mm but more than 4 mm from the maximum tensioning position 13, the control unit reduces the frame 3 descent speed as described above, but if the distance is less than 4 mm the control unit stops machine 1 operation. As regards the structure of the tensioning means 10, they comprise, for each first flywheel 6, a bearing 21, integral with the first flywheel 6, slidably mounted on the supporting shaft 11 according to a sliding direction lying in a plane perpendicular to the direction in which the supporting shaft 11 extends. A first actuator 22 (such as a hydraulic cylinder as illustrated in the accompanying drawings, a pneumatic cylinder or an electrical device) is mounted between the supporting shaft 11 and the bearing 21, to move the bearing 21 relative to the supporting shaft 11 in the plane perpendicular to the axis of rotation of the first flywheel 6. To guide the movement of the bearing 21 (and therefore of the corresponding first flywheel 6), the tensioning means 10 have, for each first flywheel, 6, at least one guide 23 integral with the supporting shaft 11. In the accompanying drawings there are two guides 23, parallel and each consisting of a through-hole 24 made in a supporting shaft 11 projection 25. A bar 26 shaped to match the hole and integral with the bearing 21 is slidably mounted in each through-hole 24.

Advantageously, the machine 1 for multiple wire cutting according to the present invention also comprises means 27 for positioning the supporting shaft 11 designed to vary the distance of the supporting shaft 11 from the second flywheels 7, ^" between a minimum distance position (movement to the left relative to ^" the position in Figure 3) and a maximum distance position (movement to the right relative to the position in Figure 3) . In the embodiment illustrated, the positioning means 27 comprise a mobile element 28 slidably mounted on four parallel guide bars 29 integral with the frame 3, and which supports the

supporting shaft 11 of the first flywheels 6. A second actuator 30, mounted between the frame 3 and the mobile element 28, causes mobile element 28 sliding relative to the frame 3. In other embodiments there may be one or more guide bars 29. In the accompanying drawings, the second actuator 30 comprises a threaded bar 31 on which the mobile element 28 is mounted and means for driving the rotation of the threaded bar 31, which, advantageously, consist of an electric motor 32 connected to the threaded bar 31 either directly or via a transmission, for example using gears.

Activation of the positioning means 27 is also controlled by the control unit. In particular, the control unit is programmed to move the supporting shaft 11 by a predetermined distance after a command supplied by an operator, by activating the positioning means 27.

For this purpose the machine 1 also comprises an interface element (not illustrated) which can be activated by an operator and connected to the control unit to check and control its operation. In the preferred embodiment, the interface element provides an indication of the position of each of the first flywheels 6 relative to the supporting shaft 11. An example of said indication is schematically illustrated in Figures 13 to 17 (see below) .

The control unit may also be programmed to ignore one or more cutting devices 4 during a cutting operation. This is necessary when only some of the cutting devices 4 are used (for example, on a machine 1 with thirty cutting devices 4, only fifteen are used) . However, there may be a check which stops machine 1 operation if tensioning is detected on one of the excluded cutting devices 4, since this would imply the unwanted presence of the cutting wire 8.

The control unit may also be programmed to count the hours for which each cutting wire 8 is used and to interrupt machine 1 operation when the hours for which each cutting wire 8 has been used exceed a predetermined time limit.

Many aspects of operation of the machine 1 disclosed are derived from the structural description above.

As indicated, Figures 13 to 17 illustrate several operating situations of four cutting devices 4 in the machine 1 disclosed.

In each figure, the upper bar graphically represents the five zones into which the stroke of each first flywheel 6 is divided. The right end corresponds to the minimum tensioning position 12 (hydraulic cylinder 22 fully extended) , whilst the left end corresponds to the maximum tensioning position 13 (hydraulic cylinder 22 fully retracted) .

Consequently, in the stroke of each first flywheel 6, a central normal operation zone 33 may be identified, two critical operation zones 34 adjacent to it, and two unacceptable operation limit zones 35.

Vertical lines indicate the first and the second safety distances 17, 19 and the first and the second threshold distances 18, 20.

The four rectangles below indicate the position of four first flywheels 6 relative to the minimum tensioning position 12.

Figure 13 illustrates operation up to speed, where all four cutting devices 4 are in the normal operation 33 zone. Figure 14 illustrates the case in which a cutting device 4 is in the critical ^' operation zone 34 close to the maximum tensioning position 13. The other three devices 4 are also close to said zone. In this case, the control unit intervenes, reducing the frame 3 movement (descent) speed. Under normal conditions this causes all of the flywheels to move towards the minimum tensioning position 12 and to return within the normal operation zone 33.

Figure 16 illustrates the similar but opposite case in which a cutting device 4 is in the critical operation zone 34 close to the minimum tensioning position 12. In this case the control unit is programmed to increase the frame 3 movement (descent) speed.

Figures 15 and 17 illustrates the case of a cutting device 4 in the unacceptable operation zone 35 (Figure 17 also shows a first flywheel 6 in the critical operation zone 34). In this case the control unit is programmed to interrupt machine 1 operation. The operator is responsible for identifying the causes which resulted in the cutting device 4 being in the unacceptable operation zone 35.

For example, in the case in Figure 15, this may be due to excessive wear of the cutting wire 8 diamond coating which causes a considerable sweepforward. If this is the case, the operator substitutes the cutting wire 8. In the case in Figure 17, it may be enough to move the supporting shaft 11 towards the maximum distance position to return all of the cutting devices 4 to the normal operation position 33.

When a new cutting operation is started, the control unit is preferably programmed to perform several operating steps which guarantee correct machine 1 operation.

First, the control unit uses the positioning means 27 to move the supporting shaft 11 to the minimum distance position.

Then it applies a predetermined tensioning force to all of the first flywheels 6 using the tensioning means 10. In the embodiment illustrated this involves feeding all of the first actuators 22 with oil or another fluid at the same pressure. Since there are no external stresses, all of the first flywheels 6 move to the minimum tensioning position 12. At this point, the control unit preferably adopts the position of each first flywheel 6 as the reference position for subsequent movements.

Then, the control unit activates the positioning means 27 to move the supporting shaft 11 towards the maximum distance position (to the right in Figure 3) . Once each cutting wire 8 is fully extended, the action of the positioning means 27 overcomes the tensioning force applied by the relative first actuator 22, causing the first flywheel 6 to gradually move from the minimum tensioning position 12 towards the maximum tensioning position 13. This movement is controlled by the control unit using the sensors i4.

The control unit is programmed to stop operation of the positioning means 27 when all of the first flywheels 6 are in the normal operation zone 33. If necessary, before interrupting operation of the positioning means 27, the control unit waits until all of the first flywheels 6 are a predetermined distance from the critical operation zone 34 close to the minimum tensioning position 12.

1 ?

The present invention brings important advantages.

Firstly, the machine for multiple wire cutting disclosed can prevent excessive tensioning of the cutting wires under any operating condition. In this way it can prevent the cutting wires from breaking due to excessive tensioning, even if they are excessively worn.

Moreover, the machine disclosed prevents excessive slackening of the cutting wires and therefore guarantees a precise and smooth cut under any operating condition. It should also be noticed that the present invention is relatively easy to produce and even the cost linked to implementation of the invention is not very high.

The invention described may be modified and adapted without thereby departing from the scope of the inventive concept. All details of the invention may be substituted by other technically equivalent elements and, in practice, all of the materials used, as well as the shapes and dimensions of the various components, may be any according to requirements.