Laser machining system with optical compensation assembly

Abstract

The invention relates to a laser machining system, comprising a focusing optical unit (12) for the laser beam (11) and comprising an optical compensation assembly (16) which counteracts a thermal change (Δf) in the focal length of the focusing optical unit (12), wherein the compensation assembly (16) is formed by a number (x) of identical, compensation elements (17) arranged in the path of the laser beam (11), each effecting an at least approximately identical thermal displacement (fkp) of the focal length of the laser beam (11) in the opposite direction to the thermal focal length (fth) of the focusing optical unit (12).

Description

[0001] Laser processing system with optical compensation arrangement

[0002] Background of the invention

[0003] The invention relates to a laser processing system with a laser source and a processing head for guiding the laser beam over a workpiece, wherein the processing head is equipped with a focusing optic for the laser beam, as well as with an optical compensation arrangement that counteracts a thermal change in the focal length of the focusing optic.

[0004] High-power laser beams cause the focusing optics of laser processing heads to heat up, as some of the laser power is absorbed by the material of the optical elements and / or their coating. This heating is inhomogeneous, which changes the refractive index of the focusing optics. Consequently, a shift in the focal point of the focusing optics can occur, negatively impacting the laser beam processing process.

[0005] To address this problem, DE 10 2013 021 151 B3, for example, proposes incorporating a thermal compensation arrangement into the focusing optics. The refractive index of this arrangement changes with temperature in the opposite direction to the change in the refractive index of the focusing optics. This allows the shift in the focal point of the focusing optics to be largely compensated for. However, the proposed solution requires the compensation arrangement to be custom-made to match the focusing optics and the laser used. If changes are made to the focusing optics or the laser used in the laser processing system, a new compensation arrangement must be provided each time.

[0006] Object of the invention

[0007] The invention is based on the objective of providing a thermal compensation for the focal point shift of the focusing optics in laser processing systems that can be easily adapted to changing circumstances.

[0008] Description of the invention

[0009] This problem is solved according to the invention by a laser processing system comprising a laser source and a processing head for guiding the laser beam over a workpiece, wherein the processing head is equipped with a focusing optic for the laser beam, and with an optical compensation arrangement that counteracts a thermal change in the focal length of the focusing optic, characterized in that the compensation arrangement is formed by a number of identical compensation elements arranged in the path of the laser beam, each of which causes an at least approximately identical thermal shift of the focal length of the laser beam in the opposite direction to the thermal focal length shift of the focusing optic, wherein the number of compensation elements is selected such thatthat the sum of the thermal shifts of the focal length caused by the compensation elements compensates for the thermal shift of the focal length of the focusing optics as effectively as possible.

[0010] By varying the number of compensation elements in the compensation arrangement, the thermal shift in the focal length of the focusing optics can be compensated incrementally. If changes are made to the focusing optics of the laser processing system or a different laser is used, the compensation arrangement can be easily adapted to the resulting new thermal shift in the focal length of the focusing optics by omitting one or more compensation elements or inserting additional compensation elements. Due to the modular design of the compensation arrangement of the laser processing system according to the invention, it is not necessary to manufacture a completely new compensation arrangement.

[0011] By maintaining a large number of identical compensation elements, modular compensation arrangements can be provided for a wide range of different laser processing systems. The absorption behavior and the thermal shift of the focal length of the compensation elements are known. By measuring or calculating the thermal shift of the focal point of the focusing optics of a laser processing system as a function of the laser power, the required number of compensation elements can be calculated to ensure optimal compensation of the focal point shift.

[0012] To easily adapt to the thermal focal length shift of the focusing optics, the compensation arrangement can be interchangeable. Several compensation arrangements with different numbers of compensation elements can be kept on hand, so that the thermal focal length shift of the focusing optics can be adjusted simply by replacing the entire arrangement.

[0013] The compensating elements can also be arranged in an interchangeable manner. In this case, the insertion of additional compensating elements or the removal of already installed elements can also be carried out directly in the laser processing machine.

[0014] In a preferred embodiment, the compensation elements are plane-parallel plates. The refractive index of these plates changes as desired with temperature without affecting the beam shaping. The compensation elements can be made, in particular, of crystalline quartz or calcite. These materials generate a negative thermal lens depending on the laser beam power absorbed by the compensation elements.

[0015] The degree of laser power absorption by the compensation elements, and thus the power-dependent change in their refractive index, can be significantly increased by coating them with an absorbing layer. Typically, the absorption of such a coating can range from 100 ppm to 400 ppm.

[0016] There are various options for arranging the compensation assembly. In a suitable design, the compensation assembly can be located within the machining head. It can therefore be positioned, for example, in front of, inside, or even after the focusing optics.

[0017] If, on the other hand, the processing head and the laser source in the laser processing system are connected via a laser light cable, the compensation arrangement can be located in a connector that allows the laser light cable to be connected to the processing head. These connectors are often equipped with a protective glass cover. This protective glass cover can be replaced by a compensation arrangement, whereby the required number of compensation elements in the compensation arrangement is determined beforehand by measuring or calculating the focal point shift of the focusing optics of the processing head.

[0018] The invention further relates to a processing head for a laser processing system with a focusing optic for a laser beam and with an optical compensation arrangement that counteracts a thermal change in the focal length of the focusing optic, characterized in that the compensation arrangement is formed by a number of identical compensation elements arranged in the path of the laser beam, each of which causes an identical thermal shift of the focal length of the laser beam in the opposite direction to the thermal focal length shift of the focusing optic, wherein the number of compensation elements is selected such that the sum of the thermal shifts of the focal length by the compensation elements compensates for the thermal shift of the focal length of the focusing optic as best as possible.

[0019] Another aspect of the invention relates to a laser light cable for connecting a laser source and a processing head of a laser processing system, wherein the processing head has a focusing optic for the laser beam and the laser light cable can be connected to the processing head by means of a connector, wherein the laser light cable is characterized in that a compensation arrangement, which counteracts a thermal change in the focal length of the focusing optic, is arranged in the connector, wherein the compensation arrangement is formed by a number of identical compensation elements arranged in the path of the laser beam, each of which causes an identical thermal shift of the focal length of the laser beam in the opposite direction to the thermal focal length shift of the focusing optic, wherein the number of compensation elements is selected such thatthat the sum of the thermal shifts of the focal length caused by the compensation elements compensates for the thermal shift of the focal length of the focusing optics as effectively as possible.

[0020] The invention further comprises a compensation arrangement for a thermal change in the focal length of a focusing optic for a laser beam of a laser processing system, characterized in that it is formed by a number of identical, arranged compensation elements, wherein the compensation elements are interchangeably arranged. The compensation arrangement can be positioned at a suitable location in the path of the laser beam of the laser processing system. The interchangeable arrangement of the compensation elements allows the compensation arrangement to be adapted to different focusing optics with varying degrees of thermal change in focal length by adding or removing individual compensation elements.

[0021] Further features and advantages of the invention will become apparent from the description, the claims, and the drawings. According to the invention, the features mentioned above and those further elaborated can each be used individually or in any suitable combination. The embodiments shown and described are not to be understood as an exhaustive list, but rather serve as examples for illustrating the invention.

[0022] Detailed description of the invention and drawing

[0023] Figs. aa-c schematically show a focusing optic of a laser processing system without thermal change of focal length, with a thermal change of focal length and with a compensated thermal change of focal length;

[0024] Fig. 2 shows a schematic representation of the processing head of a laser processing system with a compensation arrangement in its focusing optics according to Fig. 1c;

[0025] Fig. 3 shows a representation of a laser light cable of a laser processing system with a compensation arrangement for a thermal change in the focal length of the focusing optics of the system.

[0026] Fig. 1a shows a laser source 10 that emits a laser beam 11 and directs it to a focusing optic 12 of a laser processing system (not shown in further detail). The focusing optic 12 includes a collimation device 13 and a lens 14. At low and medium powers of the laser beam 11, the laser beam 11 is directed parallel after the collimation device 13 and is focused by the lens onto a focal point F in a focal plane 15. A workpiece (not shown) can be positioned in the focal plane 15, enabling processing of the workpiece with the focused laser beam 11.

[0027] Fig. 1b illustrates the effect of a high laser beam power 11. In this case, the collimation device 13 and the lens 14 heat up so much that their refractive index changes. After passing the collimation device 13, the laser beam 11' is no longer parallel but slightly converging. This effect is further amplified by the lens 14, causing the focal point F' of the entire focusing optics 12 to move out of the focal plane 15. The focal length of the focusing optics 12 has shortened. Consequently, a workpiece positioned in the focal plane 15 can no longer be processed with a precisely focused laser beam 11.

[0028] To remedy this problem, a compensation arrangement 16 is provided within the focusing optics 12 in Fig. 1c. This arrangement is modularly formed from three identical compensation elements 17 arranged one behind the other. The compensation elements 17 are plane-parallel plates, which may preferably be provided with an absorbing coating. The plates themselves can be made of crystalline quartz or calcite. These materials undergo a thermal change in their refractive index in the opposite direction to the change in the refractive index of the collimation device 13 and the lens 14.

[0029] Fig. 2 shows a processing head 18 with a focusing optic 12, which, in addition to the collimation device 13 and the lens 14 in the beam path of the laser beam 11 after the collimation device 13, has a thermal compensation arrangement 16 according to Fig. 1c. The laser beam 11 is supplied here by means of a laser light cable 19 from a laser source (not shown).

[0030] In the example shown, the thermal compensation arrangement 16 consists of three plane-parallel plates 17, each of which shifts the focal length by fk P This effect can be achieved. Due to its modular design, the compensation arrangement 16 could, for example, be equipped with fewer or more compensation elements 17 if the laser power changes. The required number x of compensation elements 17 for the most optimal compensation of the thermal displacement fth of the focusing optics 12 can be calculated according to the following formula:

[0031] 1 1, 1 r.

[0032] - = m - 1- x — = 0, f th, total fth f kp where fth, total is the thermal focal length of the entire arrangement consisting of the focusing optics 12, i.e., the collimation device 13 and the lens 14, as well as the compensation arrangement 16, and m is the number of optical elements 13, 14 that form an equally sized thermal lens. In the example shown, therefore, m = 2. Since x must be an integer, a corresponding number of compensation elements 17 can also lead to a slight overcompensation of the thermal focal length fth of the focusing optics 12.

[0033] In general, the thermal focal length fth of an optical element can be determined from the equation

[0034] 1 > y absorb fth K TT W? Calculate with y = (nl)a + ß, where n is the refractive index, a is the coefficient of thermal expansion, ß = dn / dT is the change in refractive index with temperature,

[0035] K is the thermal conductivity,

[0036] Where the beam radius and

[0037] Pabsorb is the absorbed power of the optical element. If these properties of the elements of the focusing optics 12 are known, the thermal focal length fth can also be calculated instead of measured. However, a thermal compensation arrangement does not necessarily have to be arranged within the focusing optics 12 of the processing head 18. As Fig. 3 illustrates, a thermal compensation arrangement 16' can also be integrated into a laser light cable 19 for connecting a laser source 10 to the processing head 18 of a laser processing system. The laser light cable 19 consists of a fiber optic cable 20 and two end connectors 21, 22, where connector 22 serves for the connection to the laser source 10 and connector 21 for the connection to the processing head 18. A thermal compensation arrangement 16' is integrated into connector 21, which in the illustrated example consists only of a compensation element 17', which is also designed here as a plane-parallel plate.

Claims

Patent claims 1. Laser processing system with a laser source (10) and a processing head (18) for guiding the laser beam (11) over a workpiece, wherein the processing head (19) is equipped with a focusing optic (12) for the laser beam (11), and with an optical compensation arrangement (16, 16') that counteracts a thermal change (Af) of the focal length (f) of the focusing optic (12), characterized in that the compensation arrangement (16, 16') is formed by a number (x) of identical compensation elements (17, 17') arranged in the path of the laser beam (11), each of which has an at least approximately identical thermal displacement (fk). P ) the focal length of the laser beam (11) in the opposite direction to the thermal focal length (fth ) of the focusing optics (12), wherein the number (x) of the compensation elements (17, 17') is chosen such that the sum of the thermal displacements (fk P) the focal length is compensated as best as possible by the compensation elements (17, 17') to compensate for the thermal displacement (Af ) of the focal length of the focusing optics (12).

2. Laser processing system according to claim 1, characterized in that the compensation arrangement (16, 16') is arranged interchangeably.

3. Laser processing system according to claim 1 or 2, characterized in that the compensation elements (17, 17') are arranged interchangeably.

4. Laser processing system according to one of the preceding claims, characterized in that the compensation elements (17, 17') are plane-parallel plates.

5. Laser processing system according to one of the preceding claims, characterized in that the compensation elements (17, 17') are made of crystalline quartz or calcite.

6. Laser processing system according to one of the preceding claims, characterized in that the compensation elements (17, 17') are provided with an absorbing coating.

7. Laser processing system according to claim 6, characterized in that the absorption of the coating is 100ppm - 400ppm.

8. Laser processing system according to one of the preceding claims, characterized in that the compensation arrangement (16) is arranged in the processing head.

9. Laser processing system according to one of claims 1 to 7, characterized in that the processing head (18) and the laser source (10) are connected to each other via a laser light cable (19) and the compensation arrangement (16') is arranged in a plug (21) with which the laser light cable (19) can be connected to the processing head (18).

10. Processing head for a laser processing system with a focusing optic (12) for a laser beam (11) and with an optical compensation arrangement (16) that counteracts a thermal change in the focal length (fth ) of the focusing optic (12), characterized in that the compensation arrangement (16) is formed by a number (x) of identical compensation elements (17) arranged in the path of the laser beam (11), each of which has an identical thermal displacement (fk ). P ) the focal length of the laser beam (11) in the opposite direction to the thermal focal length (fth ) of the focusing optics (12), wherein the number (x) of the compensation elements (17) is chosen such that the sum of the thermal displacements (fk P ) the focal length is compensated as best as possible by the compensation elements (17) to compensate for the thermal displacement (fth ) of the focal length of the focusing optics (12).

11. Laser light cable for connecting a laser source (10) and a processing head (18) of a laser processing system, wherein the processing head (18) has a focusing optic (12) for the laser beam (11) and the laser light cable (19) can be connected to the processing head (18) by means of a connector (21), characterized in that a compensation arrangement (16') is arranged in the connector (21), which counteracts a thermal change in the focal length (fth) of the focusing optic (12), wherein the compensation arrangement (16') is formed by a number (x) of identical compensation elements (17') arranged in the path of the laser beam (11), each of which has an identical thermal displacement (fk). P ) the focal length of the laser beam (11) in the opposite direction to the thermal focal length (fth ) of the focusing optics (12), wherein the number (x) of the compensation elements (17') is chosen such that the sum of the thermal displacements (fkP ) the focal length is compensated as best as possible by the compensation elements (17') to counteract the thermal displacement (fth ) of the focal length of the focusing optics (12).

12. Thermal compensation arrangement for a thermal change in the focal length (fth) of a focusing optic (12) for a laser beam (11) of a laser processing system, characterized in that it is formed by a number (x) of identical, arranged compensation elements (17, 17'), wherein the compensation elements (17, 17') are arranged interchangeably.

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