DE102008048502A1 - Optical device for focusing laser beam in a laser processing head for material processing, comprises collimator, a first and second lens group movably arranged in axial direction, and front lens group stationary arranged to the collimator - Google Patents

Abstract

The optical device comprises a collimator (18), a first and second lens group (21, 22) movably arranged in axial direction, and a front lens group (23) that is stationary arranged relative to the collimator. The movably arranged lens groups are formed so that the axial position of the processing focus (16) relative to the front lens group is adjustable through its displacement without changing the magnification. The second movable lens group comprises a positive focal length while the first movable lens group and the front lens group posses a negative focal length. The optical device comprises a collimator (18), a first and second lens group (21, 22) movably arranged in axial direction, and a front lens group (23) that is stationary arranged relative to the collimator. The movably arranged lens groups are formed so that the axial position of the processing focus (16) relative to the front lens group is adjustable through its displacement without changing the magnification. The second movable lens group comprises a positive focal length while the first movable lens group and the front lens group posses a negative focal length. A servomotor is arranged for displacing the first and the second movable lens group. The actuating drive provided by the servo motor transmits one of the movable lens group over a drive arrangement to another movable lens group so that the movable lens groups are displaced relative to each other in displacement of the lens group relative to the front lens group. The servo motor is arranged between the movable lens groups and is controllable dependent upon the movement of other servo motor.

Description

The The invention relates to an optical device for focusing a Laser beam in a working focus, especially for focusing a laser beam in a laser processing head for material processing.

at the machining of workpieces by means of laser radiation Often it is necessary that the location of the work focus is relative changed to a laser processing head, as appropriate whether larger or smaller distances between Workpiece and laser processing head are required. When adjusting the focus position relative to the laser processing head should the diameter of the working focus does not change so with the same laser power, the power density in the working focus is constant.

From the DE 41 43 414 a laser processing head is known in which a focusing lens is displaceable in the direction of the optical axis, whereby the position of the working focus relative to the laser processing head can be changed without causing a change in the power density. Here, however, the adjustment range for the working focus is relatively small, since it corresponds to the mechanical adjustment path of the focusing lens.

In order to achieve a larger adjustment path for the working focus in a laser processing head, suggests the WO 2008/019681 A1 instead of using a single focusing lens, a lens system in which distances of the individual lens groups are variable relative to each other, thereby to shift the working focus along the optical axis of the system.

The known optical device for focusing a laser beam has a collimator that emits the laser light emerging from an optical fiber collimated into an expanded parallel laser beam. The device for focusing the collimated laser beam comprises a first Lens group with collecting effect, along the optical axis is displaceable, a second lens group with dissipative effect, So with negative refractive power and a fourth lens group, in turn collecting effect, that has a positive refractive power. The third and fourth lens group are relative to each other and to the laser processing head fixedly arranged.

Alternatively, in which from the WO 2008/019681 A1 known optical device for focusing a working laser beam and the first lens group to be fixed while the second lens group is axially displaceable relative to the first and third.

In order for the same distance between an object and a fixed image plane to be able to image the object with different image scales in each case sharply, it is known in photography to use zoom lenses. In such zoom lenses, as for example from the US 4,591,235 A or the US 4,846,562 A are known, four lens groups are provided, which have alternately negative and positive power. While the third lens group is stationary in these known zoom lenses, the first, second, and fourth lens groups can be moved along the optical axis, so that the air gaps between the individual lens groups are variable.

From that Based on the object of the invention, another optical device for focusing a laser beam into a Provide a work focus that will enable to shift the position of the working focus along the optical axis, without, assuming consistent laser power, the power density to change in the working focus.

These Task is achieved by the device according to claim 1 solved. Advantageous embodiments and developments The invention are described in the subclaims.

According to the invention so provided that between a collimator and a front lens group, which is fixed relative to the collimator, a first and a second axially displaceable lens group is, wherein the movably arranged lens groups are formed are that by their displacement, the axial position of the working focus relative to the front lens group is adjustable, without affecting it the magnification changed.

According to the invention So by the displacement of the two inner lens groups relative to each other and relative to the collimator and the front lens group on the one hand shifted the position of the working focus on the optical axis while on the other hand, the focus diameter and thus the power density in the work focus is kept constant, despite the shift the working focus the overall magnification of the system stays the same.

In an advantageous embodiment of the invention, it is provided that the second displaceable lens group has a positive focal length, while the first displaceable lens group and the front lens group each have a negative focal length. This not only ensures that aberrations of the overall system can be better compensated, but that the energy density within the Fo lowers kussiervorrichtung.

Appropriately Way is to shift the first and the second displaceable Lens group provided at least one servomotor.

in this connection It is possible that the actuator supplied by the servomotor for a sliding lens group over a Transmission arrangement is also transmitted to the other displaceable lens group, so that with a shift of the lens groups relative to the front lens group the displaceable lens groups are also displaced relative to each other. The use of a gear arrangement that makes it possible both lens groups not only relative to the front lens and the collimator, but also to shift relative to each other leads to a simple control of the invention Focusing system. As gear arrangement can each of the desired displacement enabling transmissions, such as B. cam mechanism can be used with cams. It but can also gear with corresponding guide grooves and groove successors are used.

ever after construction of the laser processing head for which the invention Device is provided, but it may also be appropriate be if for each of the two sliding lens groups a separate servo motor is provided, preferably one Actuator depending on the movement of the other Servomotor is controllable. This allows the mechanical Considerably simplify the construction of the device.

The Invention will be described below, for example, with reference to the drawing explained in more detail. Show it:

1 a greatly simplified schematic representation of a laser processing head for material processing with a device according to the invention for focusing the laser beam;

2 a simplified schematic representation of the individual lens groups of the device according to the invention; and

3 a not to scale diagram illustrating the lens positions along the optical axis with the associated position of the working focus.

In The various figures of the drawing are corresponding to each other Components provided with the same reference numerals.

As in 1 is shown purely schematically is in a laser processing head 10 as an optical device for focusing a laser beam 11 a lens arrangement 12 provided, which is a laser light source 14 on a workpiece 15 maps. The image of the laser light source 14 puts the working focus 16 in which the laser radiation with the workpiece 15 interacts.

As a laser light source 14 serves in the illustrated embodiment, the exit surface of an optical fiber 17 , by which the laser radiation from a laser (not shown) the laser processing head 10 is supplied.

The lens arrangement 12 includes as a basic objective a collimator 18 that's out of the optical fiber 17 emerging, divergent laser beam 11 in a parallel laser beam 11 '' collimated. Seen in the light direction behind the collimator 18 is in the parallel laser beam 11 '' a beam splitter 19 arranged to serve radiation from the area of the interaction zone around the working focus 16 comes around, decouple from the working beam path and a connection element 20 supply one or more sensor and / or observation modules.

Behind the beam splitter 19 is the first axially displaceably arranged in the lens group a correction element 21 provided with negative refractive power, the second axially displaceably arranged in the lens group a variator 20 with positive refractive power follows. The workpiece end of the lens assembly 12 is from a front lens group 23 formed with negative refractive power, in a manner not shown a the workpiece 15 may have opposite protective glass.

Instead of an optical fiber 17 Any other beam guiding system may be provided to move the laser beam from the laser to the laser processing head 10 respectively. If the beam delivery system used already provides a parallel laser beam, then the collimator can be used 18 be waived. Otherwise, the basic objective must be adapted accordingly to a parallel laser beam in the area of the laser processing head 11 '' to obtain.

While the collimator 18 and the front lens group 23 in the laser processing head 10 are fixed, are the correction member 21 and the variator 22 axially, ie in the direction of the optical axis, the objective arrangement 12 slidably mounted.

For shifting the correction element 21 and the variator 22 are two servomotors 24 . 25 provided, of which a servomotor is driven by a control device, not shown, to move one of the two movably arranged lens groups. The other Stellmo Tor is then controlled in response to the operation of the first servomotor. In the illustrated embodiment of the serves the variator 22 moving servomotor 25 as an immediately controlled servomotor (master), during which the correction element 21 shifting servomotor 24 depending on the servomotor 25 is controlled and thus works as a so-called slave. However, it is also conceivable that the master-slave function of the two servomotors is reversed.

Further It is possible to use only one servomotor for shifting provide for both lens groups. In this case, one of the two Lens groups are driven directly, while the other is displaceable Lens group via a gear arrangement (not shown) is moved.

To the work focus 16 from the in 2 To move laid intermediate layer P16 closer to the laser processing head or to move it further away, is initially the variator 22 according to the in 3 shown curve V in the -x direction, ie opposite to the direction of light or in the + x direction so to move in the direction of light. That's out in 3 the position P21 shown on the curve K in both cases in the -x direction to move.

In other words, when the work focus 16 from the near position N, in 3 lying on the x-axis is indicated to be moved over the intermediate position P16 in the remote position N, the variator 22 and the correction term 21 first shifted from its leftmost position in the drawing in the beam direction according to the curves V and K, wherein also the working focus corresponding to the curve AF in 3 shifts. For a further shift of the working focus in the direction of the remote position AF beyond the intermediate position P22 beyond the variator 22 moved further in the beam direction, while now the correction element 21 is returned according to the curve K in the direction of its initial position.

It should be noted that in 3 the scale on the x-axis is chosen differently for the displacement of the two lens groups and the working focus for drawing reasons. If, for example, the negative refractive power of the correction element 21 chosen so that its focal length is in the range of -700 mm to -750 mm, while the positive refractive power of the variator 22 a focal length of +300 mm to +350 mm supplies and the front lens group 23 has a focal length in the range of -670 to -720, a shift of the working focus by 800 to 900 mm can be achieved. The shift of the correction term 21 lies in the range between 25 and 30 mm, and the displacement of the variator 22 is in the range of 200 to 250 mm.

The use of a dissipating lens or dispersing lens group as a correction element 21 leads in the laser processing head to an extended beam cross-section, so that in the variator 22 a lower energy density is present, which leads to a lower thermal load. In addition, aberrations can be better corrected in this way.

The optical device according to the invention for focusing a laser beam thus makes it possible to adjust the distance between the laser light source 14 So to vary between the fiber end and the working focus over a wide range, thereby the working distances between the laser processing head 14 and workpiece 15 to be able to adapt to the respective processing tasks, workpiece shapes and the like, without thereby the magnification so the energy density changes in the working focus.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - DE 4143414 [0003]
• - WO 2008/019681 A1 [0004, 0006]
• - US 4591235 A [0007]
• - US 4846562 A [0007]

Claims (6)

Optical device for focusing a laser beam ( 11 ) into a working focus ( 16 ), in particular for focusing a laser beam ( 11 ) in a laser processing head ( 10 ) for material processing, with - a collimator ( 18 ), - a first and a second axially displaceably arranged lens group ( 21 . 22 ) and - with a front lens group ( 23 ) relative to the collimator ( 18 ) is arranged stationary, wherein the movably arranged lens groups ( 21 . 22 ) are formed so that by their displacement, the axial position of the working focus ( 16 ) relative to the front lens group ( 23 ) is adjustable without changing the magnification. Device according to claim 1, characterized in that the second displaceable lens group ( 22 ) has a positive focal length while the first displaceable lens group ( 21 ) and the front lens group ( 23 ) each have a negative focal length. Apparatus according to claim 1 or 2, characterized in that for the displacement of the first and the second displaceable lens group ( 21 . 22 ) at least one servomotor ( 24 . 25 ) is provided. Apparatus according to claim 3, characterized in that the of the servomotor ( 24 ) supplied actuator for the one displaceable lens group ( 21 . 22 ) via a gear arrangement to the other displaceable lens group ( 22 . 21 ) is transferred so that when a shift of the lens groups ( 21 . 22 ) relative to the front lens group ( 23 ) the displaceable lens groups ( 21 . 22 ) are also shifted relative to each other. Apparatus according to claim 3, characterized in that for each of the two displaceable lens groups ( 21 . 22 ) an own servomotor ( 24 . 25 ) is provided. Apparatus according to claim 5, characterized in that the one servomotor ( 24 . 25 ) in dependence on the movement of the other servomotor ( 25 . 24 ) is controllable.