The present invention relates to a laser cutting machine, as described in the preamble of the first claim.

Such a laser cutting machine is for example known from US-A1 -2006/0169681 . The laser cutting machine according to US- 5 A1 -2006/0169681 comprises a laser cutting machine for laser cutting of sheet metal workpieces. The laser cutting machine comprises a workpiece support with a support surface formed by a multiplicity of parallel longitudinal grid elements spaced from each other by recesses, a laser cutting unit having a laser cutting head movably mounted with respect to the workpiece support for

10 cutting workpieces from a metal sheet disposed on the support surface. The laser cutting machine further comprises an unloading unit comprising a fork assembly with a multiplicity of longitudinal fork elements correspondingly provided with the recesses such as to be respectively received in the recesses. Two opposed pair of fork elements are provided which can move from an open

15 position in which the pairs are distal from each other to a closed position in which the opposed end parts of the fork elements are adjacent. The unloading unit is provided to move the fork elements in and out of the recesses by moving them along a direction parallel to the grid elements from the open position into the closed position such that they become positioned under the

20 support surface. After workpieces are cut from the metal plate disposed on the support surface, the fork assembly is lifted in the closed position and therefore the fork elements are lifted from the recesses, lifting the workpieces from the support surface. Subsequently the workpieces are supported by the fork elements, and therefore the fork assembly, on a support plane of the fork

25 assembly defined by a carrying surface of the fork elements. The fork assembly is further moved to a discharge station where the workpieces are discharged from the fork assembly by sliding them off the fork elements by moving the fork elements to the open position while the workpiece retains its position with respect to the discharge station and, during support by the fork assembly, with respect to the support plane. The fork elements are usually made from metal.

However, by sliding the workpieces off the fork elements, the workpieces are often damaged by scratches. The occurrence of scratches on the workpieces is often undesired and leads to rejection of the workpieces, being a considerable cost.

There is thus a need for a laser cutting machine in which the risk for scratches on the workpieces is reduced.

This is achieved in the present invention with the technical features of the characterising part of the first claim.

Thereto, the at least one fork element comprises a rolling element for at least partly rollingly supporting the workpiece while discharging the workpiece of the fork assembly.

By removing the workpieces from the fork element in such a way, the risk for scratches to be created on the workpieces while being slid off the fork assembly at the discharge station is substantially reduced.

In preferred embodiments of the laser cutting machine according to the present invention, the rolling element comprises a wheel or more preferably is a wheel. It has been found that wheels offer a simple yet effective way of rollingly supporting the workpiece.

In preferred embodiments of the laser cutting machine according to the present invention, the rolling element is provided such that the workpiece during discharge of the workpiece off the fork assembly, during support by the fork assembly, substantially retains its position with respect to the support plane of the fork assembly. It has been found that in such laser cutting machines, the rolling element need not be driven to discharge the workpiece of the fork assembly as the inertia due to the mass of the workpiece, which is often relatively high, is sufficient to keep the workpiece on substantially the same, or even the same, position with respect to the support plane of the fork assembly during support by the fork assembly. Thereto, the inertia of the rolling element is preferably kept relatively low with respect to the inertia of the workpiece. When the rolling element, for example, is a wheel, the diameter of the wheel can be kept small, the mass of the wheel is kept small, etc. In further preferred embodiments of the laser cutting machine according to the present invention, the workpiece is discharged of the fork assembly by moving the at least one fork element with respect to the workpiece and to the remainder of the fork assembly.

In preferred embodiments of the laser cutting machine according to the present invention, the fork assembly comprises two fork elements movably provided to the fork assembly between an open position distal from each other and a closed position close to each other. After workpieces are cut from the metal plate disposed on the support surface and after the fork elements are moved into the closed position in the recesses, the fork assembly is lifted in the closed position and therefore the fork elements are lifted from the recesses, lifting the workpieces from the support surface. Subsequently the workpieces are supported by the fork elements, and therefore the fork assembly, on a support plane of the fork element.

In further preferred embodiments of the laser cutting machine according to the present invention opposed end parts of the fork elements are substantially adjacent in the closed position. Such a closed position has been found to offer improved support, for example to small workpieces.

In preferred embodiments of the laser cutting machine according to the present invention, the fork element is provided to move in and out of the recesses by moving the fork element along a moving direction substantially parallel to the support surface. It has been found that such a moving direction allows to put the fork element to be put under a workpiece located on the support surface.

In preferred embodiments of the laser cutting machine according to the present invention, the moving direction is along longitudinal direction of the fork element. It has been found that moving the fork element along such a direction allows putting the fork element under a workpiece under the support surface with an increased ease.

Other details and advantages of the device according to the invention will become apparent from the enclosed figures and description of preferred embodiments of the invention.

Figure 1 shows an overview of the laser cutting machine according to the present invention.

Figure 2a shows an overview of a fork element of the laser cutting machine according to the present invention.

Figure 2b shows a side view of the fork element of figure 2a.

Figure 2c shows a top view of the fork element of figure 2a.

Figure 2d shows a cross-section of the fork element of figure 2a along line A - A.

Figure 1 shows an overview of the laser cutting machine 1 according to the invention. The laser cutting machine 1 comprises a laser cutting unit 4. The laser cutting unit 4 is provided to cut sheet metal workpieces from a sheet of metal. Such laser cutting units 4 are known to the person skilled in the art and the specific laser cutting unit 4 used in the laser cutting machine 1 is not critical for the current invention. The details of the laser cutting unit 4 are therefore not shown in figure 1.

Such a laser cutting unit 4 comprises a laser cutting head which is movably mounted with respect to the workpiece support 2 for cutting workpieces from a metal sheet. However, the type of laser cutting head is not critical for the invention and is also not shown in the figures.

The workpiece support 2 has a support surface 3 formed by a multiplicity of parallel grid elements spaced from each other by at least one recess. The support surface 3 is only shown in an overview.

The laser cutting machine 1 further has an unloading unit 5. The unloading unit 5 is provided to unload workpieces present on the support surface 3 onto a discharge station 9. As such an unloading unit 5 allows to remove the workpiece from the support surface 3, a more continuous operation of the laser cutting machine 1 becomes possible. If the unloading unit 5 operates autonomously, continuous operation of the laser cutting machine 1 is even allowed without the presence of an operator being necessary.

The unloading unit 5 comprises a fork assembly 6. The fork assembly 6 comprises at least one longitudinal fork element 7 provided to be received in a corresponding recess of at least one of the recesses of the support surface 3. The unloading unit 4 is provided to move the at least one fork element 7 in and out of the corresponding recess.

A detail of the fork assembly 6 is for example shown in figure 1 , more in particular detail A.

Preferably, as shown in figure 1 , the fork assembly 6 comprises two fork elements 7, 1 1 movably provided to the fork assembly between an open position distal from each other and a closed position close to each other. In such case the fork elements 7, 1 1 preferably extend from opposing sides of the fork assembly 6, as shown in figure 1 . More preferably, opposed end parts 12, 13 of the fork elements 7, 1 1 are substantially adjacent in the closed position.

As shown in figure 1 , the fork assembly 6 can comprise a plurality of fork elements 7, 1 1 , for example extending from opposing sides of the fork assembly 6 and extending towards each other. For example, 10, 20, 30, 40 or even more fork elements 7, 1 1 can extend on each side. The number of fork elements 7, 1 1 is however not critical for the invention and can be determined in function of the workpiece to be supported by them by the person skilled in the art.

Preferably, the fork element 7 is provided to move in and out of the recesses by moving the fork element 7 along a moving direction substantially parallel to the support surface 3. This way the fork element 7 can for example be guided under the workpieces positioned on the support surface 3 without contacting the workpieces such that the workpieces keep their position with respect to the support surface 3 while the fork element 7 is guided under them. However this is not critical for the invention. The fork elements 7 can for example be provided below the support surface 3 before the workpiece is provided on the support surface 3. More preferably, the fork element 7 is provided to move along longitudinal direction of the fork element 7. The unloading unit 4 is provided to lift the at least one fork element 7 from the recess for lifting at least one workpiece cut out of the metal sheet and subsequently supporting the workpiece on a support plane of the fork assembly 6.

The unloading unit is further provided to transport the workpiece to a discharge station 9 by moving the fork assembly 6 to the discharge station 9 and to discharge the workpiece from the fork assembly 6 by sliding the workpiece off the fork assembly 6. The workpiece can for example be slid off the fork assembly 6 by moving the fork elements 7 supporting the workpiece from beneath the workpiece such that the workpiece moves with respect to the fork elements 7.

Preferably, the fork elements 7 are thereto provided to move along their longitudinal direction with respect to the remained of the fork assembly. This is however, not critical for the invention and the fork elements 7 can also be provided to, for example move sideways. In case the fork assembly 6 comprises at least two fork elements 7, 1 1 extending from opposing sides of the fork assembly towards each other, the fork elements 7, 1 1 are for example provided to move along longitudinal direction away from each other. In figure 1 , the fork assembly 6 is provided with opposing rows of fork elements 7 extending from opposing sides of the fork assembly 6 and is provided to move the fork elements 7, 1 1 of both opposing rows along their mutual longitudinal direction away from each other. A workpiece or workpieces positioned on top of the fork elements 7, 1 1 of the shown fork assembly are then moved with respect to the fork elements 7, 1 1 and eventually are no longer supported by the fork elements 7, 1 1 such that they fall from the support plane onto the discharge station 9.

To make sure that the workpiece moves with respect to the fork element 7 or the plurality of fork elements 7, 1 1 , the workpiece can be retained by a retaining member, not shown. It is however preferred that the workpiece moves with respect to the at least one fork element 7 because of its inertia, as explained above.

The at least one fork element comprises at least one rolling element 10 for at least partly rollingly supporting the workpiece while discharging the workpiece of the fork assembly 6. As explained above, such a rolling element 10 prevents the at least one fork element 7 from scratching the workpiece or workpieces present on the support plane.

The rolling element 10 is shown in more detail in detail A of figure 1 and more in particular in figures 2a, 2b, 2c and 2d. The rolling element 10 shown in the figures comprises, and in more in particular is, a wheel. However, also other rolling elements 10 can be used to at least partly rollingly support the workpiece or workpieces during discharge off the fork assembly 6, more in particular the fork elements 7. The rolling element 10 can for example also comprise, or be, in the form of an endless belt. However, it has been found that such rolling elements 10 have, in general, a larger inertia making it more difficult to slide the workpiece or workpieces off the fork elements 7.

The fork element 7 shown in figures 2a, 2b and 2c are provided with more than one rolling element 10, in particular 4 rolling elements, more in particular 4 wheels. This is however not critical for the invention and the fork element can also be provided with more or less rolling elements 10, such as wheels. Preferably, sufficient rolling elements 10 are provided for substantially, or even fully, supporting the workpiece or the workpieces. It has been found that when the workpiece or workpieces are substantially, or even fully, supported by the rolling elements 10, the risk for scratching to occur during discharge of the workpiece or the workpieces from the fork element 7 is further reduced.

Preferably, the surface of the rolling elements 10 contacting the workpiece or the workpieces during discharge of the workpiece or the workpieces is provided with a coating further preventing scratching of the workpieces. Such a coating can for example be a rubber layer at the circumference of the wheel.

The wheel preferably is mounted to the fork element 7 using bearings such as to decrease the resistance of the wheel. This offers the advantage of increasing the ease with which the workpiece or workpieces are discharged from the fork elements by sliding. Using the laser cutting machine 1 according to the present invention usually will consist of the steps described below.

First the laser cutting machine 1 is provided with a metal sheet. The metal sheet can for example be provided by a special unit for providing such plates or can be provided by the unloading unit 5. The metal sheet is then supported by the workpiece support 2 more in particular by the support surface 3 by the multiplicity of parallel grid elements.

After a metal sheet has been provided on the workpiece support 2, the laser cutting unit 4 cuts a workpiece or several workpieces from the metal sheet.

After the workpiece or the different workpieces have been cut from the metal sheet, the unloading unit 5 lifts the at least one fork element 7 from the corresponding recesses and therewith lifts the at least one workpiece cut out off the metal sheet. In most cases, the remainder of the metal sheet, left over after cutting the workpieces, is lifted by the at least one fork element 7 together with the workpiece or the workpieces.

The at least one fork element 7 is provided in the corresponding recesses before lifting the at least one workpiece. Thereto, the at least one fork element 7 may be provided inside the corresponding recess before the workpiece is provided or can be provided in the recess after the at least one workpiece has already been provided if the at least one fork element 7 can provided in and out of the recesses underneath the at least one workpiece, for example by moving the fork elements along their longitudinal direction in and out of the recesses.

When the at least one workpiece is supported by the support plane of the fork assembly 6, the at least one workpiece is transported to a discharge station 9 by moving the fork assembly 6 to the discharge station 9. As shown in figure 1 , this can be done by rotating the fork assembly 6 around an axis. This is however not critical for the invention and the fork assembly 6 can also be moved to the discharge station 9, by for example a translational movement. The movement of the fork assembly 6 is however not critical for the invention and can be determined by the person skilled in the art depending on the nature of the desired laser cutting machine 1 .

When the fork assembly 6 carrying the at least on workpiece reaches the discharge station 9, the at least one workpiece is discharged from the fork assembly 6 by sliding it off the at least one fork element 7. In the laser cutting machine according to figure 1 this is done by moving the two opposing rows of fork elements 7, 1 1 away from each other such that the at least one workpiece substantially retains its position with respect to the discharge station 9, preferably under influence of its own inertia, and is at the same time slid off the fork elements 7, 1 1 .

At the moment that the at least one workpiece is deposited at the discharge station 9, the fork assembly can for example be used to pick up a new metal sheet from a loading station 8, to start the process over.