EP3347157A1

EP3347157A1 - Laser machining apparatus and method for forming a pattern comprising a plurality of marks on a workpiece

Info

Publication number: EP3347157A1
Application number: EP16763061.5A
Authority: EP
Inventors: Ettore Fustinoni
Original assignee: SEI SpA
Current assignee: SEI SpA
Priority date: 2015-09-09
Filing date: 2016-09-09
Publication date: 2018-07-18
Also published as: WO2017042357A1

Abstract

It is disclosed alaser machining apparatus (1) for forming on a sheet workpiece (50) a predetermined pattern (P) comprising a plurality of marks (D) arranged in a plurality of pattern lines (L), the apparatus comprising a support table (2) on which the sheet workpiece to be machined is arranged, a laser source (3) for emitting a laser beam (B) and mounted fixed with respect to the support table, and a machining head (10) movable with respect to the support table and with respect to the sheet workpiece arranged thereon. The apparatus further comprisesa laser beam deflection device (15) arranged on said movable machining head (10) to receive said laser beam (B); and a control unit (100) configured to control: the laser source (3) for emitting a laser beam (B), the movable machining head (10) for positioning it with respect to said sheet workpiece (50), and the laser beam deflection device (15)for deflecting said laser beam into a plurality of paths (B') forming a group (G) of marks (D) arranged along a pattern line (L) on said sheet workpiece (50).

Description

"Laser machining apparatus and method for forming a pattern comprising a plurality of marks on a workpiece"

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The present inventions relates to a laser machining apparatus and method using a laser beam for forming a pattern comprising a plurality of marks on a workpiece. More in detail, the present invention relates to a laser machining apparatus and method for forming a pattern of marks, preferably in the form of dots, on a sheet workpiece, e.g. a light guide plate.

It has to be noted that, even if the in the following specific reference will be made to the laser machining of a sheet workpiece used as light guide plate, the apparatus and the method according to the present invention are not limited to this application, but can be applied to any field wherein a laser beam is used to form a pattern of marks on a sheet workpiece.

Nowadays, in different fields there is the need of forming a predetermined pattern of marks, having small dimensions, on a sheet workpiece.

For example, sheet workpiece are used to provide a uniform light diffusion from a light source by means of a plurality of marks arranged according to a predetermined pattern, the marks being preferably in the form of dots, formed on a surface of the sheet workpiece, known as light guide plate.

Light guide plates are used for the production of liquid crystal displays widely used in different devices, such as computers, televisions, portable video devices, mobile phones, etc.. The liquid crystal displays are not able to emit light but need to be provided with a backlight source.

In particular, a light guide plate receives light from a light source, for example arranged in correspondence of an edge of the light guide plate, and uniformly emits light from an emitting surface which in turn illuminates the liquid crystal panel.

The light guide plate, generally made of a transparent plastic material, is provided on its emitting surface with a pattern of marks, preferably in the form of dots, intended to provide a uniform diffusion of the light through the light guide plate. Similarly, light guide plates are also used in luminous display for signs and in general for illumination and advertising functions. Also in this case, a predetermined pattern of a plurality of marks is used to increase the uniformity of the light emitted.

In view of above, the pattern of marks which has to be formed on a surface of a sheet workpiece, e.g. a light guide plate used for example in backlight applications, plays an important role in the quality of the final product and therefore has to be formed with high precision and restricted tolerances.

Different production methods have been proposed to form a predetermined pattern of marks on a sheet workpiece. For example, is known a "hot stamping" process using a cylinder having on its lateral surface the negative image of the pattern to be produced on the sheet workpiece.

However, this technology involves high costs for the design and the production of the cylinder having its lateral surface shaped with the pattern. Additionally, a specific cylinder has to be designed for a specific dimension of the sheet workpiece, and due to the necessity of producing light guide plates having different dimensions (and also different patterns of marks), for a large range of correspondent liquid crystal displays, the production costs are very high.

In general, the cylinders cannot be rapidly adapted or used for different dimensions of the sheet workpiece on which a specific pattern has to be formed.

Also, laser machining apparatus are known, in which a laser beam is used to form patterns, and in particular a plurality of marks, on the surface of the sheet workpiece. In this apparatus the laser beam is directed towards a movable machining head on which a focalising lens is provided to direct the laser beam towards the surface of the sheet workpiece arranged below the machining head.

However, in this type of apparatus, the laser beam is used to form a single mark of the pattern in a position of the sheet workpiece and the machine has to wait the movement of machining head in a different position, before another single mark of the pattern can be produced. Therefore, in the known apparatuses the production process of a single sheet workpiece is long. Additionally, the laser beam has to be controlled with high accuracy and precision, in fact, the energy provided by the laser beam on the workpiece determines the shape and the dimension of the formed marks which, as already discussed above, have to be controlled and have to be realized according to predetermined values.

For example, in the production of light guide plates, the dimension and the shape of the marks, and in particular the diameter and the circular shape of the dots of the pattern affect the diffusion of the light through the light guide plate. To this regard it has to be noted that dimension and shape of the marks are affected by on/off transitory of the laser source to provide a plurality of pulses each intended to form a mark.

Therefore, there is the need of an accurate control of both the shape and the dimension of the dots of the pattern. More in detail, oval or oblong shape, and in general not perfectly circular shape of the dots, have to be avoided in order to provide a high quality light guide plate.

In known apparatuses, when a great number of marks has to be provided in a short time, i.e. when the apparatus production speed is high to increase productivity, an undesired oblong shape of the marks (e.g. an oval dot) is formed.

Additionally, dimension and shape of the marks are also affected by the stability of the energy associated to each pulse of the laser beam, depending on the timing and energy of previous laser beam emissions, on power oscillation of the laser beam source, and on the energy distribution of the laser beam pulse. In view of above, it is an object of the present invention to provide a laser machining apparatus and method able to solve the above discussed problems of known apparatuses. More in detail, it is an object of the present invention to provide a laser machining apparatus and method allowing a simple and rapid formation of a predetermined pattern comprising a plurality of marks on a sheet workpiece which at the same time provide an high quality final product due to an high accuracy of the shape and dimension of the formed marks. The marks are obtained by contacting a portion of the surface material of the sheet whit a laser's beam. Each time the laser beam contacts the sheet's surface, a mark is obtained. In other words, a mark is an alteration of the surface of the sheet in a predefined area, operated by the laser beam.

Another object of the present invention is to provide an apparatus and a method for the formation of a pattern on a sheet workpiece which can be easily adapted to provide different patterns, and/or different shapes and dimension of the marks of the pattern, and which can be adapted according to the dimension of the sheet workpiece to be machined.

Another object of the present invention is to provide an apparatus and a method for the formation of a pattern on a sheet workpiece by which an increased productivity, i.e. an increased production speed, with respect to known apparatuses, may be reached. These and other objects are achieved by a laser machining apparatus and the method according to the independent claims. Further aspects of the present invention are set out in the dependent claims.

The laser machining apparatus for forming a predetermined pattern on a sheet workpiece, according to an embodiment of the invention comprises a support table on which the sheet workpiece to be machined is arranged, a laser source for emitting a laser beam and mounted fixed with respect to the support table, and a machining head movable with respect to the support table and with respect to the sheet workpiece arranged thereon. The apparatus comprises a laser beam deflection device arranged on the movable machining head and a control unit configured to control said laser source for emitting a laser beam, the movable machining head for positioning it with respect to the sheet workpiece and the laser beam deflection device to receive said laser beam and to deflect it into a plurality of paths forming a group of the plurality of marks along a pattern line on the sheet workpiece. A predetermined pattern is a pattern of marks designed to provide a required distribution of the marks on the surface of a sheet workpiece. In the case of a light guide plate, the predetermined pattern is designed to provide the required effect to the light traveling in the plate.

Advantageously, the use of laser beam deflection device arranged on the machining head allows to provide different paths of the laser beam which are used to form a group of marks along a pattern line. In fact, the pattern to be formed on the sheet workpiece comprises a plurality of marks arranged in a plurality of pattern lines; for a position of the machining with respect to the sheet workpiece the laser beam is deflected along different paths, thus allowing a rapid and accurate formation of a plurality of marks, i.e. a group of marks, along a line of the pattern.

Thanks to this, the productivity of the apparatus according to the invention is increased compared to the known devices wherein a single mark is formed for a position of the machining head with respect to the sheet workpiece and there is the need of waiting the advance of the machining head before forming another single mark. On the contrary, according to the invention, the deflection device arranged on the machining head allows to easily and rapidly deflect the laser beam along a plurality of paths corresponding to a plurality of marks which are formed on the sheet workpiece, i.e. to form a group of marks on the sheet workpiece.

This advantageously allows to increase the productivity, with respect to known apparatuses. For example, the apparatus according to the invention allows to obtain a productivity up to 16 times higher than a known apparatus.

According to an aspect of the invention, the pattern to be formed on the sheet workpiece comprises a plurality of marks arranged in a plurality of substantially straight pattern lines and, advantageously, the laser beam deflection device allows to form a group of the plurality of marks on a straight line by deflecting the laser beam, with high velocity and high accuracy. In other words, the control unit is configured so that the pattern formed on the sheet workpiece comprises a plurality of marks arranged in a plurality of substantially straight pattern lines. According to an aspect, the control unit is configured to control the laser beam deflection device to form a group of the plurality of marks on a straight line.

According to an aspect of the invention, the pattern line of the group of marks formed by the laser beam deflection along different paths by means of the laser beam deflection device is incident, and preferably substantially perpendicular, to the at least one direction of movement of the machining head. By doing so, during the advancing movement of the machining head along at least one direction, groups of marks on each pattern line incident to the direction of movement of the machining head are formed. Therefore, instead of forming a single mark for each position a group of marks is formed during the movement of the machining head along at least one direction.

Therefore the area of the sheet workpiece provided with pattern marks is larger than in the prior art technique.

According to an aspect of the invention, the laser beam deflection device comprises a modulator (e.g. an optical modulator), preferably an acousto-optic modulator. An advantage of this embodiment is that the modulator, and in particular the acousto-optic modulator can be controlled, for example by a radiofrequency driver, to provide a quick and accurate deflection of the laser beam thus allowing the formation of a group of the plurality of marks of the pattern, for a position of the machining head with respect to the sheet workpiece.

According to a possible embodiment, the use of acousto-optic modulator allows to deflect the laser beam in a plurality of paths, for example up to sixteen paths, and thus forming a correspondent group of marks, in 10 microseconds.

According to an aspect of the invention, the laser beam emitted by the laser source is selected from a pulsed laser beam, or a quasi-continuous laser beam, or a continuous laser beam. As known in the art, the quasi continuous laser beam is typically formed by a pulsed laser source controlled at high frequency values, so that a substantially continuous laser beam is emitted.

These types of laser beams can be advantageously used in the apparatus according to the invention, wherein the deflection device arranged on the machining head allows to easily and rapidly deflect the laser beam along a plurality of paths to form a group of marks on the sheet workpiece.

According to an aspect of the invention the laser source is controlled to provide a pulsed laser beam, or is controlled to provide a continuous laser beam, or a substantially continuous, i.e. known in the field as quasi-continuous laser beam. According to an aspect of the invention, the apparatus comprises at least one pulses selection device to provide a selected pulsed laser beam, i.e. to provide a train of selected fractions (pulses) of the laser beam. Said selected pulses correspond to the energy (power) need for forming each mark.

Advantageously, the provision of a pulses selection device allows to obtain a more accurate selection of the laser beam fractions (pulses). In particular, an accurate definition of the pulses (and thus of the energy associated thereto) can be obtained. In particular, on-off transitory effects can be eliminated, in fact, the pulses selection device allows to define an accurate square-waveform, forming an accurate selected pulsed laser beam.

If the laser beam emitted by the laser source is continuous or a quasi- continuous laser beam, the pulses selection device allows to form the desired pulses (fractions) of the laser beam and thus obtain a selected pulsed laser beam.

When the laser beam emitted by the laser source is a pulsed laser beam, also in this case, the presence of a pulses selection device allows to better define the fractions (pulses) of the laser beam, for example by eliminating on-off transitory effects due to the on-off control of the pulsed laser source to provide the pulsed laser beam.

According to a possible embodiment, the pulses selection device may correspond to the laser beam deflection device, i.e. the same device is able to perform both deflections and the functions of pulses selection and the laser beam deflection device is controlled for selecting pulses from the laser beam); in another embodiment, the device for pulses selection can be a separate device with respect to the laser beam deflection device. According to an aspect of the invention, the pulses selection device comprises a modulator (e.g. an optical modulator), preferably an acousto-optic modulator.

The use of a modulator, preferably of the acousto-optic type, allows to obtain an accurate control of the energy associated to the pulses which are intended to form the marks on the sheet workpiece. Therefore, high accuracy of the shape and dimension of the marks can be obtained. Additionally, the acousto- optic modulator is easy to control, for example by a radiofrequency driver, so that the energy (power) of the selected laser beam fractions, i.e. of the pulses of the laser beam, can be easily and effectively controlled.

As already mentioned above, according to an embodiment of the invention, the pulses selection device corresponds to the deflection device arranged on the movable machining head. In other words, according to a possible embodiment, the function of the pulses selection device, i.e. the selection of laser beam fractions (pulses of the laser beam), is carried out by the deflection device. More in detail, according to a possible embodiment a single modulator, and in particular a single acousto-optic modulator, arranged on the machining head is controlled to provide both a selection of laser beam fractions (pulses) and a deflection of the laser beam thus allowing the formation of a group of the plurality of marks of the pattern on the workpiece.

It has to be noted that according to another exemplary embodiment of the invention, the pulses selection device and the deflection device are two distinct components, and in particular a first modulator (e.g. a first acousto-optic modulator) and a second modulator (e.g. a second acousto-optic modulator) are provided.

The first acousto-optic modulator intended to provide the selected pulsed laser beam allows to control the selection of the pulses and thus the energy (power) associated with each pulse. In fact, the pulses correspond to the laser beam fraction intended to form the marks. The deflection device (and in particular the second acousto-optic modulator) allows to deflect the pulses along different paths so as to provide the formation of a group of marks.

According to an aspect of the invention, the laser machining apparatus comprises at least one laser beam directing element, i.e. an element for directing the laser beam, that is arranged on the movable machining head and is configured to receive the laser beam deflected along said plurality of paths by the laser beam deflection device and to direct the deflected laser beam towards said workpiece.

Advantageously, the directing element allows to shift the laser beam deflected in a plurality of paths to the sheet workpiece.

According to an aspect of the invention, the laser beam directing element comprises at least one mirror. The mirror is shaped and arranged so that the laser beam deflected along the possible paths by the laser beam deflection device can be effectively directed towards the sheet workpiece.

According to an aspect of the invention, the laser beam directing element is configured to align along a pattern line the group of marks formed by said laser beam deflected along said plurality of paths, preferably as a function of the movement of said the movable machining head. An advantage of this aspect is that the laser beam deflected by the deflection device along a plurality of paths can be effectively aligned along a pattern line according to the predetermined pattern of marks to be formed. In fact, the deflection along a plurality of paths could case misalignment with respect to the desired pattern, and in particular misalignment of the formed group of marks along a pattern line.

Additionally, according to a possible embodiment, the deflection of the laser beam by means of the laser beam deflection device is carried out while the machining head is moving. In this case the directing element is configured to compensate the movement of the machining head and to align the marks along the pattern line formed by the deflected laser beam by means of the deflection device.

According to an aspect of the invention, the laser beam directing element, and in particular the at least one mirror is inclined of an angle with respect to said pattern line along which a group of marks is formed by the laser beam deflected into said plurality of paths by said laser beam deflection device. The inclination angle advantageously allows to align the deflected laser beam and thus the marks of the group formed along a predetermined pattern line.

According to an aspect of the invention, the inclination angle of the laser beam directing element is selected as a function of the number of marks of the group to be formed on the same pattern line. By doing so, it is possible to provide an effective alignment of the formed group of marks, depending on the number of marks to be provided in a pattern line, and therefore depending on the paths into which the laser beam is deflected by the deflection device.

According to a possible embodiment, the inclination angle of the laser beam directing element can be calculated as the ratio 1/n, wherein n is the number marks to be formed on the same pattern line.

The present invention also relates to a laser machining method of forming a predetermined pattern comprising a plurality of marks and arranged in a plurality of pattern lines on a sheet workpiece. The method is preferably carried out by a laser machining apparatus according to the invention and having one or more of the features and/or aspects herein disclosed and/or claimed.

Other features, advantages and details appear, by way of example, in the following detailed description, the detailed description referring to the drawings, in which:

· Figure 1 is a schematic top view of an embodiment of the laser machining apparatus according to the present invention the laser beam deflection device can be used also for performing the pulses selection;

• Figure 1 a shows a possible schematic function diagram of the embodiment shown in figure 1 ;

· Figure 2 is a schematic top view of another embodiment of the laser machining apparatus according to the present invention further comprising a pulses selection device separate from the laser beam deflection device;

• Figure 2a shows a possible schematic function diagram of the embodiment shown in figure 2;

• Figure 3 is perspective view of a possible embodiment of the machining head of the apparatus according to the invention, where is also shown the sheet workpiece arranged on the support table;

• Figure 3a is a top view of figure 3;

· Figure 3b is a detailed view of a possible embodiment of the directing element according to figure 3a. With reference to the attached figures, possible embodiments of the laser machining apparatus 1 for forming a predetermined pattern P on a sheet workpiece 50 and the relative method, according to the invention will be now disclosed.

It has to be noted that the term "sheet workpiece" is used herein to indicate an object to be machined by the apparatus 1 according to the invention that is substantially planar, i.e. having two dimensions greater than a third dimension. More in detail, the term sheet workpiece is used to indicate a workpiece in the form of a plate having an extension in two dimensions much greater than the extension in a third dimension, i.e. the thickness.

In figures 1 , 2, 3a, 3b, the sheet workpiece 50 is shown in view from the top, so that its extension in two dimensions (X-Y coordinates) is shown. In the perspective view of figure 3, the thickness of the sheet workpiece (along the Z coordinate) is also shown.

According to different possible embodiments, the sheet workpiece can be made of different materials able to be machined by a laser beam in order to form a predetermined pattern P of marks D thereon.

According to a preferred embodiment, as already mentioned above, the sheet workpiece 50 is a light guide plate, preferably made of transparent material. As known in the art, light guide plates are used for example in the production of liquid crystal display or are used to produce advertising panel, or in lighting devices, to distribute the light beam from a light source by means of a pattern of marks provided thereon.

Light guide plates are for example made of plastic material, such as for example acrylic resin, polycarbonate, etc.

In general, according to a possible embodiment, the sheet workpiece 50 to be machined in the apparatus 1 is made of plastic material.

Even if specific reference has been made to a back light plate, the apparatus and the method according to the invention are not limited to the laser machining of these objects, but in general can be used for the production of a predetermined pattern of marks on a sheet workpiece. The pattern P comprising a plurality of marks D can be formed by the apparatus 1 according to the invention on the surface of the sheet workpiece, preferably on a predominant surface of the sheet workpiece.

The mark D formed by the energy provided by the laser beam B can be formed with a predetermined depth (preferably in the thickness of the sheet workpiece 50), depending for example on the use of the sheet workpiece after the formation of the pattern P.

According to a possible embodiment, for example when the sheet workpiece is a light guide plate, the pattern P of marks D is formed on the surface of the sheet workpiece and the depth of the pattern is selected to not extend to the opposite surface of the sheet workpiece. In other words, the formed marks are not connecting two surfaces of the sheet workpiece.

The pattern P to be formed on the sheet workpiece 50 comprises a plurality of marks D arranged in a plurality of pattern lines L. Having regards to the shape of the mark D of the pattern, it can be different and can comprises for example a circular shape (to form dots), or polygonal shape, including a number of sides, for example square-shaped marks, etc.

According to a preferred embodiment, the pattern comprises a plurality of dots, i.e. marks, having a circular shape (as for example shown in the figures 1 , 2, 3, 3a, 3b). It has to be noted that in the production of light guide plate the shape of the circular marks, i.e. the circular shape of the dots, determines the quality of the light guide plate. In fact, oval or oblong dots (i.e. not perfectly circular) negatively affects the transmission of the light thorough the light guide plate. The apparatus 1 and the method according to the invention allow to increase the precision and accuracy of the marks shape, and in particular allow to form circular marks, i.e. dots, with high precision thus providing high quality machined workpieces and in particular high quality machined light guide plates. It has to be also noted that the marks D are arranged in group G along a pattern line L, that is preferably a straight line L.

In other words, according to a possible embodiment, the marks D, of the pattern P to be formed, are arranged along a plurality of lines L, preferably along a plurality of straight lines. The straight lines L are preferably parallel one to another.

Marks D formed by the apparatus 1 according to the invention, and in particular circular dots, can for example be provided with a diameter between 30 to 500 micrometre, depth between 5 micrometre to 1 millimetre, and resolution (i.e. the spatial marks density) between 5 to 500 dpi.

According to a possible embodiment, the pattern P that has to be formed on the workpiece may comprise marks D (e.g dots) having different dimensions and shape, e.g. different diameter and/or depth. In other words, according to a possible embodiment, the pattern P is not "uniform" and one or more marks D can be different from one or more other marks D of the pattern P.

It has to be noted that even if in figures marks D (e.g. dots) having the same dimension (e.g. the same diameter) are shown, the marks D can be provided with different diameter and/or depth. The apparatus according to the invention allows to control the shape and dimension of the marks D of the pattern by modifying the energy associated to a pulse of the laser beam intended to form each mark. However, according to another possible embodiment, the energy associated to each mark (the energy associated to each pulse) is not changed, and therefore only the position of the marks is selected, thus for example allowing to modify the density of the marks of the pattern.

As it will appear clear in the following description, the desired pattern P, and in particular information about the position on the workpiece, the dimension and the shape of marks D, is provided to a control unit of the apparatus (as input data, see for example figures 1 a and 2a) and the apparatus is controlled to provide the desired pattern P.

Returning now to the laser machining apparatus 1 , it comprises a support table 2 on which the sheet workpiece 50 to be machined is arranged. The support table is schematically shown in the attached figures as a plane 2 on which the sheet workpiece 50 is laying.

The apparatus 1 comprises a laser source 3 for emitting a laser beam B that is mounted fixed with respect to the support table, and a machining head 10 that is movable with respect to the support table and with respect to the sheet workpiece arranged thereon. It has to be noted that a detailed view of a possible embodiment of the machining head 10 is provided in the perspective view of figure 3.

The apparatus is also provided with suitable elements, such as for example one or more mirror, intended to guide the laser beam B emitted by the fixed laser source 3 towards the movable machining head 10. In other words, mirrors or other suitable means can be provided to guide the laser beam B form the fix laser source to each position with respect to the support table 2 in which the machining head 10 can be moved.

The apparatus 1 further comprises a laser beam deflection device 15 arranged on the movable machining head 10, which will be disclosed in greater detail later.

The apparatus 1 further comprises a control unit (or CPU) 100 configured to control the laser source 3 for emitting a laser beam B, the movable machining head 10 for positioning it with respect to the sheet workpiece 50 and the laser beam deflection device 15 to receive the laser beam B and to deflect it into a plurality of paths B' forming a group G of marks D along a pattern line L on the sheet workpiece 50.

The control unit (or CPU) 100, for example schematically shown in the figures 1 , 1 a, 2, 2a can be directly or indirectly connected to the components to be controlled, such as for example, the laser source 3, the movable machining head 10 and the laser beam deflection device 15. The control unit can be provided with a memory, or it can be connect to an external memory, wherein a computer program able to control the apparatus, for example to carry out the laser machining method according to the invention, can be stored.

Returning now to the laser source 3 of the apparatus 1 according to the invention, it may comprise any source of electro-magnetic radiation to provide a laser beam B. The laser source 3 may include, but is not limited to, gas lasers (e.g. a CO2 laser), solid state laser (e.g. YAG laser), etc..

As for example shown in figures 1 a, 2a, the apparatus 1 can be provided with a laser source control device 3a arranged in a feedback line for stabilize the laser power. As also for example shown in figures 1 a and 2a, the laser source can be controlled at a constant frequency.

According to different possible embodiments, the laser beam B emitted by the laser source 3 can be a pulsed laser beam, or a quasi-continuous laser beam, or a continuous laser beam.

More in detail, the laser source 3 can be a pulsed laser source or a continuous laser source. As known in the art a quasi-continuous laser source can be obtained by controlling a pulsed laser source at high frequency.

The pulsed laser beam can be generated for example by controlling the laser source by a control signal between two logic values, e.g. a 0 logic value and 1 logic value.

The frequency value of the control signal can be selected to provide the required pulsed output signal.

According to the invention the machining of the pattern P on the workpiece, and in particular the formation of each mark D is carried out by means of a pulse, i.e. a (fraction) of the laser beam, schematically shown in the figures by means of a dashed line.

In particular, according to an aspect of the invention, the apparatus comprises at least one pulses selection device 1 1 to provide a selected pulsed laser beam, i.e. to provide a train of selected fractions (pulses) of the laser beam. Said selected pulses correspond to the energy (power) need for forming each mark.

In the case the laser source provides a continuous, or substantially continuous laser beam, the pulses selection device allows to form the desired pulses (fractions) of the laser beam and thus to obtain a selected pulsed laser beam. In other words, the pulses selection device 1 1 selects a plurality of pulses from the laser beam which have to be directed to the workpiece in order to form the marks D thereon (see for example the embodiment shown in figure 2).

If the laser beam emitted by the laser source is a pulsed laser beam, the pulses selection device 1 1 allows to better define the fractions (pulses) of the laser beam, for example by eliminating on-off transitory effects due to the on-off control of the pulsed laser source to provide the pulsed laser beam.

According to different possible embodiments, the pulses selection device 1 1 can correspond to the laser beam deflection device 15 (i.e. the same device is able to perform both deflections and pulses selection functions), as for example in the embodiment shown in figures 1 and 1 a, or the pulses selection device 1 1 can be a separate device with respect to the laser beam deflection device 15, as for example in the embodiment shown in figures 2 and 2a.

A laser beam dump, of the type known in the art, and indicated in the attached figures with the reference "dump" or "beam dump", can be also provided and used as a target element of the laser beam when it is not directed towards the machining head 10 and thus towards the workpiece 50.

According to a possible embodiment, the pulses selection device 1 1 comprises a modulator, preferably an acousto-optic modulator.

As known in the art, the acousto-optic modulator is an optical element which can be excited with pressure waves, and in particular acoustic waves, to deflect the laser beam passing therethrough.

A control signal is used to control the acousto-optic modulator. For example, a radiofrequency control signal, generated by a control radiofrequency driver 1 1 a, can be used.

According to a possible embodiment, the power (amplitude) of the radiofrequency control signal is used to control the acousto-optic modulator 1 1 to select the pulses to be directed towards the machining head 10 and thus towards the sheet workpiece 50, to control the fractions (pulses) of laser beam B that is deflected towards the machining head 10.

The pulses selection device 1 1 , and in particular the radiofrequency driver 1 1 a of the acousto-optic modulator 1 1 is also connected to the control unit 100 (see reference "select dot (pulses) in figures 1 a and 2a").

It has to be noted that in the embodiment shown in figures 1 and 1 a, wherein the functions of the pulses selection device, i.e. the selection of laser beam fractions (pulses of the laser beam), is carried out by the deflection device 15, a single modulator, and in particular a single acousto-optic modulator, arranged on the machining head is controlled to provide both a selection of laser beam fractions (pulses) and a deflection of the laser beam thus allowing the formation of a group of the plurality of marks of the pattern on the workpiece.

According to this configuration a single radiofrequency driver 15 can be used to control the single acousto-optic modulator performing both functions of laser beam deflection and pulses selection.

It has to be also noted that the fractions of the laser beam B not deflected by the acousto-optic modulator 1 1 , shown for example in the attached figure 2 with the reference BO, and thus not directed towards the workpiece 50, can be used to stabilize the mean power output of the laser source 3.

As mentioned above, the apparatus 1 comprises a machining head 10, that is movable with respect to the support table 2 and, thus, with respect to the sheet workpiece 50 arranged thereon.

The machining head 10 is movable in at least one direction (for example at least one of the coordinates X, Y) with respect to the support table 2, so that it can be controlled to reach the desired position with respect to the support table 2, and thus with respect to the sheet workpiece arranged thereon.

By doing so, the laser beam B deflected by the laser beam deflection device 15 arranged on the machining head 10 are directed towards the sheet workpiece 50.

More in detail, the laser beam deflection device 15 arranged on the movable machining head 10 is configured to receive the laser beam B provided by the laser source 3 and to deflect it into a plurality of paths B' forming a group G of marks D along a pattern line L on said sheet workpiece 50.

More in detail, the laser beam received by the deflection device 15 can be deflected into the desired paths B' intended to form a group of marks D, and in particular a group G of dots, along a pattern line L.

The laser beam deflection device 15 provides different paths B' of the laser beam and in particular of the pulses.

It has to be noted that if the deflection device 15 is controlled to also perform the function of the pulses selection device, as for example shown in figures 1 and 1 a, the pulses of the laser beam intended to form the marks D are provided at the output of the deflection device 15.

However, if the pulses selection device 1 1 is separate from the deflection device 15, as for example shown in the embodiment of figures 2, 2a, the pulses of the laser beam intended to form the marks D are provided upstream of the deflection device 15 and the latter is controlled to only deflects already selected pulses.

The different paths B' along which the laser beam is deflected form a group of marks D along a pattern line L of the predetermined pattern P.

More in detail, the number of paths B' along which the laser beam deflection device 15 deflects the laser beam B corresponds to the number of marks D (i.e. the marks of the group G) which has to be provided for a pattern line L.

In the embodiment shown in the figures, a group G of four marks D is provided for a pattern line L (generated by four paths B' along which the laser beam is deflected by the laser beam deflection device 15). However, it has to be noted that the number of deflection paths B' and thus the number of marks D can be selected according to different possible embodiments, and could comprise for example up to sixteen paths B', forming a group G of sixteen marks D along a pattern line L.

Advantageously, higher the number of paths B' along which the laser beam is deflected by the laser beam deflection device 15, lower is the time needed to form the complete pattern P on the workpiece.

According to a possible embodiment, in the laser machining apparatus 1 the laser beam deflection device 15 comprises a modulator, preferably an acousto- optic modulator. The use of a modulator 15 allows to provide high accuracy of the deflection of the laser beam B and also a high speed of the deflection, so that a higher number of deflection corresponding to an higher number of formed marks D can be provided, thus reducing the overall time needed for the pattern P formation.

As already mentioned above, and as known in the art, the acousto-optic modulator is an optical element which can be excited with pressure waves, and in particular acoustic waves, to deflect the laser beam passing therethrough. As already mentioned above, if the function of the pulses selection device, i.e. the selection of laser beam fractions (pulses of the laser beam), is carried out by the deflection device, a single modulator and in particular a single acousto- optic modulator is provided on the machining head (see for example the embodiment of figures 1 , 1 a).

A control signal, for example a radiofrequency control signal provided by a radiofrequency driver 15a can be used. The laser beam deflection device 15 and in particular the acousto-optic modulator, and a radiofrequency driver 15a which can be used to control it, are also connected to the control unit 100.

According to a possible embodiment, the power (amplitude) and/or the frequency of the radiofrequency control signal is used to control the acousto- optic modulator 15 to select the angles of deflection of the laser beam exiting the acousto-optic modulator 15, i.e. the deflection angles of the different paths B' provided by the acousto-optic modulator 15. More in detail, according to a possible embodiment, to control the deflection angle, the frequency of the radiofrequency control signal is modified. However, it has to be noted that the energy associated to each pulse deflected by the acousto-optic modulator is dependent on the deflection angle. In other words different efficiency values are obtained depending on the control frequency and thus depending on the deflection angle. In order to compensate this undesired effect, the power (amplitude) of the radiofrequency control signal is used.

It has to be noted that the laser beam B can be deflected along a path in which the pulses are directed towards a laser beam dump, shown for example in the detailed view of figures 3, 3a, 3b. This deflection is used when there is no need to direct the deflected laser beam exiting the laser beam deflection device 15 towards the workpiece 50.

As mentioned above, the apparatus according to the invention allows to control the shape and dimension of the marks D of the pattern by modifying the energy associated to a pulse of the laser beam intended to form each mark. According to a possible embodiment, the modification (modulation) of energy associated to each pulse of the laser beam can be obtained by modifying the power (amplitude) of the radiofrequency control signal used to control the acousto- optic modulator to select the pulses and thus energy associated to them. It has to be noted that the control of the pulse energy by means of the power of the radiofrequency control signal can be used in both possible embodiments in which only one acousto-optic modulator 15 is used (see for example figure 1 ) or two acousto-optic modulator 1 1 , 15 are used (see for example figure 2). The laser machining apparatus 1 , and in particular its machining head 10, is also provided with at least one laser beam directing element 12 configured to receive the laser beam B deflected into said plurality of paths B' by said laser beam deflection device 15 and to direct it towards the workpiece 50.

The directing element 12 is used for example in the case the laser beam is deflected by the deflection device 15 into paths B' which are not directed towards the workpiece, so there is the need of shifting the deflected pulsed laser beam towards a surface of the workpiece.

According to a possible embodiment, the laser beam deflection device 15 deflects the laser beam into paths B' which are arranged substantially on a plane that is parallel to the supporting table 2, and thus to the upper surface of the sheet workpiece arranged thereon.

The directing element 12 is used to direct the deflect laser beam towards the workpiece, by substantially providing a change of direction of substantially 90° (see for example figures 3, 3a, 3b).

According to a possible embodiment, as for example shown in the figures, the laser beam directing element 12 comprises at least one mirror.

The mirror can be inclined of substantially 45° with respect to the X and Z directions, i.e. at 45° between a plane on which are ranged the paths B' along which the laser beam is deflected by the deflection device (modulator) 15, and a plane perpendicular to it.

According to a possible embodiment, the machining head 10 also comprises at least one focusing lens 13 arranged downstream of the deflection device 15, and in a particular downstream of the acousto-optic modulator 15 arranged on the machining head 10 (see for example figures 3, 3a, 3b). More in detail the focusing lens 13 is arranged downstream of the directing element 12, and in particular downstream of the mirror.

Returning now to the movement of the machining head 10, and thus of the component arranged on it, according to a possible embodiment, as for example shown in the figures, the machining head 10 is movable along a direction X (e.g. the axis X of the reference system shown in the figures).

The pattern lines L of the pattern P are arranged incident, and preferably perpendicular, with respect to the direction X of movement of the machining head.

In other words, according to a possible embodiment the movable machining head is movable along a direction and the lines L of the pattern P to be formed is arranged perpendicular with respect to the at movement direction X of the machining head 10.

By doing so, a group of marks D of a pattern line L is formed by the deflection of the laser beam into a plurality of paths B' corresponding to the marks D to be formed along the same pattern line L.

After a group of marks D is formed along a pattern line L, the movable machining head is advanced along the movement direction X for the formation of another group G of marks D along another pattern line L.

After, the groups G of marks D of the pattern lines L along the entire direction X have been formed, the sheet workpiece 50 can be moved along a direction Y perpendicular to the direction X of movement of the machining head 10 to allow the formation of other groups G of marks D along pattern lines L.

According to another possible embodiment, not sown in the figures, the movable machining head 10 is also movable along a second direction Y, perpendicular to the first direction X, so that the machining head 10 can be moved in a plane (X-Y).

According to this embodiment, when the plurality of pattern lines L each comprising a group G of marks D is competed, other groups G of marks D can be formed by the moving the machining head 10 along a second direction Y, preferably of a distance equal to the distance of the group G of marks deflected by the laser deflection means 15.

The movement of the machining head 10 is provided by suitable moving means 30. In fact, the apparatus 1 is provided with moving means of the machining head in at least one direction X, Y.

Moving means 30 can comprise a linear motor to provide and quick and accurate control of the position of the machining head 10 (as schematically shown in the figures 1 , 2).

According to an aspect of the invention, the laser beam directing element 12, e.g. at least one mirror, is configured to align the plurality of marks D formed by said plurality of paths B' along a pattern line L of the predetermined pattern P. In other words, the directing element 12 is arranged to shift the deflected laser beam exiting the deflection device 15 (e.g. the acousto-optic modulator) along the deflection paths B', in order to align it along a pattern line L.

As mentioned above, according to a possible embodiment, the pattern line L along which the marks D formed by the deflected laser beam according to the paths B', is a straight line L. In this case, the directing element 12, and in particular the at least one mirror 12, is configured to align the laser beam pulses exiting the deflection device 15, and thus the marks D along a straight pattern line L.

Even if a specific reference has been made to an alignment along a straight pattern line L, it has to be noted that the line along which the marks D of the pattern and generated by the deflected laser beam along the deflection paths B' of the deflection device (modulator) 15 may have different shapes.

According to an aspect of the invention, the laser beam directing element 12, e.g. at least one mirror, is configured to align the plurality of marks D formed by said plurality of paths B' along a pattern line L of the predetermined pattern P, as a function of the movement of the movable machining head 10. More in detail, the directing element 12 is configured to compensate possible misalignment of group G of marks D in a pattern line L, with respect to a predetermined alignment along the line L, caused by the movement of the machining head 10 while the deflection device 15 is controlled to deflects the laser beam B along the paths B' to form the group G of marks D of a pattern line L.

In other words, according to a possible embodiment, in order to advantageously reducing the time needed for the pattern formation, the marks D are formed by the deflection of the laser beam by the deflection device (modulator) 15 while the machining head 10 is moving along at least one direction, for example along the direction X (as for example shown in the figures 1 , 2).

The movement of the machining head 10, in conjunction with the high speed deflection of the laser beam by the modulator 15, may cause a misalignment of the marks D, which could result to be not aligned along the pattern line L, for example along a straight pattern line L. possible misalignment can be compensated by the directing element 12.

According to an aspect of the invention, the laser beam directing element 12, e.g. the at least one mirror, is inclined of an angle β with respect to the pattern line L along which group G of marks D is formed by the laser beam B deflected into the plurality of paths B' by the laser beam deflection device 15, e.g. the acousto-optic modulator.

Figures 3a and 3b show the inclination angle β. As for example shown in these figures, the inclination angle is measured on a plane, that is preferably parallel to plane defined by the support table 2 on which the workpiece is arranged. The angle β can be measured between the surface of the mirror (preferably in correspondence of the incidence line of the plurality of paths B' with the surface of the mirror) and a pattern line L, projected on said plane.

The inclination angle β of the laser beam directing element 12 is selected as a function of the number of marks D to be formed on the same pattern line L. Therefore, according to a possible embodiment the inclination angle of the laser beam directing element 12 is selected as a function of the number of deflection paths B'. According to a possible embodiment, the inclination angle β (in radiant) can be calculated as the ratio 1/n, i.e. 1 divided by n, wherein the n is the number marks D (number of the marks D of the group G) to be formed on the same pattern line L, which can be also seen as the number of deflection paths B' along which the laser beam B is deflected by the deflection device 15.

For example for a number of marks D per pattern line L equal to 4, the angle β (in radiant) is equal to 1/4=0,25. The result can be converted in degrees, from the well-known radiant-degree conversion formula, providing a result of about 14,33 degree. The same applies to the embodiment wherein the pattern line L to be formed comprises a different number of marks D. For example, having a number of 16 marks D, the inclination angle β of the directing element 12 with respect to the pattern line L is equal to 1/16=0,0625 radiant, substantially corresponding to 3,58 degree.

The present invention also relates to a method of forming a predetermined pattern P comprising a plurality of marks D arranged in a plurality of pattern lines L on a sheet workpiece 50 by a laser machining apparatus 1 according to the invention.

It has to be noted that features and aspects disclosed and/or claimed herein with reference to the apparatus 1 can be also applied to the method, and viceversa.

According to an aspect of the invention, the method comprises the steps of arranging a sheet workpiece 50 to be machined on a support table 2, operating a laser source 3 for emitting a laser beam B, moving a machining head 10 with respect to the support table for positioning it with respect to the sheet workpiece 50, and operating a laser beam deflection device 15 to deflect the received laser beam B into a plurality of paths B' for forming a group of marks D along a pattern line L on the sheet workpiece 50.

It has to be noted that the steps of the method can be carried out by means of a control unit 100 and a computer program comprising instruction for performing the method steps.

According to an aspect of the invention, the step of operating the laser beam deflection device 15 to deflect the received laser beam B into a plurality of paths B' for forming a group G of marks D along a pattern line L on the sheet workpiece 50 is carried out during the movement of the machining head 10. By doing so, it is possible to further increase the velocity of the pattern P formation. Additionally, as already discussed above in connection to the apparatus 1 , it is possible to provide a step of aligning along a pattern line L the group G of marks D formed by the plurality of paths B' exiting said laser beam deflection device 15. In the case, the deflection of the laser beam is carried out during the movement of the machining head 10, the alignment of the marks D along a pattern line L is advantageously carried pout as a function of the movement of said the movable machining head 10, to compensate possible misalignment caused by the movement of the machining head.

Claims

1 . A laser machining apparatus (1 ) for forming on a sheet workpiece (50) a predetermined pattern (P) comprising a plurality of marks (D) arranged in a plurality of pattern lines (L), the apparatus comprising a support table (2) on which the sheet workpiece to be machined is arranged, a laser source (3) for emitting a laser beam (B) and mounted fixed with respect to the support table, and a machining head (10) movable with respect to the support table and with respect to the sheet workpiece arranged thereon, the apparatus further comprising a laser beam deflection device (15) arranged on said movable machining head (10) to receive said laser beam (B); and a control unit (100) configured to control:

- the laser source (3) for emitting a laser beam (B),

- the movable machining head (10) for positioning it with respect to said sheet workpiece (50), and

- the laser beam deflection device (15) for deflecting said laser beam into a plurality of paths (Β') forming a group (G) of marks (D) arranged along a pattern line (L) on said sheet workpiece (50).

2. The laser machining apparatus according to claim 1 , wherein the laser beam deflection device (15) comprises a modulator, preferably an acousto-optic modulator.

3. The laser machining apparatus according to claim 1 or 2, wherein the control unit is configured so that the pattern (P) formed on the sheet workpiece comprises a plurality of marks (D) arranged in a plurality of substantially straight lines (L), preferably said straight lines (L) being parallel one to another.

4. The laser machining apparatus according to any previous claim, wherein the pattern (P) comprises a plurality of dots.

5. The laser machining apparatus according to any previous claim, wherein the laser beam (B) emitted by said laser source (3) is selected from a pulsed laser beam, or a quasi-continuous laser beam, or a continuous

1 laser beam.

6. The laser machining apparatus according to any previous claim, comprising at least one pulses selection device (1 1 ) to provide a selected pulsed laser beam, the pulses selection device (1 1 ) being said laser beam deflection device (15) controlled for selecting pulses or being a separate device with respect to said laser beam deflection device (15).

7. The laser machining apparatus according to claim 6, wherein the pulses selection device (1 1 ) comprises a modulator, preferably an acousto- optic modulator.

8. The laser machining apparatus according to claim 6 or 7, wherein the pulses selection device (1 1 ) is controlled to provide a train of selected fractions of the laser beam, preferably the pulses selection device (1 1 ) define an accurate square-waveform.

9. The laser machining apparatus according to any previous claim, further comprising at least one laser beam directing element (12) arranged on said movable machining head (10) and configured to receive said laser beam (B) deflected into said plurality of paths (Β') by said laser beam deflection device (15) and to direct the deflected laser beam towards said workpiece (50).

10. The laser machining apparatus according to claim 9, wherein said laser beam directing element (12) is configured to align said group (G) of marks (D) formed by said plurality of paths (Β'), along a pattern line (L), preferably as a function of the movement of said the movable machining head (10).

1 1 . The laser machining apparatus according to claim 10, wherein the directing element is configured to compensate the movement of the machining head (10) and to align the marks (D) along the pattern line (L) to be formed by the deflected laser beam by said laser beam deflection device (15).

12. The laser machining apparatus according to any claim 9 to 1 1 , wherein said laser beam directing element (12) is inclined of an angle (β) with

2 respect to said pattern line (L) along which a group (G) of marks (D) is formed by the laser beam (B) deflected into said plurality of paths (Β') by said laser beam deflection device (15).

13. The laser machining apparatus according to claim 12, wherein the inclination angle (β) of said laser beam directing element (12) is selected as a function of the number of marks (D) of said group (G) to be formed on the same pattern line (L).

14. The laser machining apparatus according to claim 13, wherein the inclination angle (β) is calculated as the ratio 1/n, wherein n is the number marks (D) to be formed on the same pattern line (L).

15. The laser machining apparatus according to any claim from 9 to 14, wherein said laser beam directing element (12) comprises at least one mirror.

16. The laser machining apparatus according to any previous claim, wherein said sheet workpiece (50) comprises a light guide plate, preferably made of transparent material.

17. A laser machining method of forming a predetermined pattern (P) comprising a plurality of marks (D) arranged in a plurality of pattern lines (L) on a sheet workpiece (50) by a laser machining apparatus (1 ) according to any previous claim, the method comprising the step of: a) arranging a sheet workpiece to be machined on a support table (2);

b) operating a laser source (3) for emitting a laser beam (B);

c) moving a machining head (10) with respect to the support table for positioning it with respect to said sheet workpiece (50);

d) operating a laser beam deflection device (15) arranged on the movable machining head (10) for deflecting the received laser beam (B) into a plurality of paths (Β') for forming a group (G) of marks (D) arranged along a pattern line (L) on said sheet workpiece (50).

18. The method according to claim 17, wherein said step d) of operating a

3 laser beam deflection device (15) to deflect the received laser beam (B) into a plurality of paths (Β') for forming a group (G) of said plurality of marks (D) arranged along a pattern line (L) on said sheet workpiece (50) is carried out during the movement of said machining head (10).

19. The method according to claim 17 or 18, further comprising the step of aligning along a pattern line (L) said group (G) of marks (D) formed by said plurality of paths (Β') exiting said laser beam deflection device (15) by a laser beam directing element (12), preferably as a function of the movement of said the movable machining head (10).

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