WO2005016587A1

WO2005016587A1 - Method for determining the position of the surface of a workpiece inside a laser machining unit

Info

Publication number: WO2005016587A1
Application number: PCT/EP2004/050535
Authority: WO
Inventors: Uwe Metka
Original assignee: Hitachi Via Mechanics, Ltd.
Priority date: 2003-08-11
Filing date: 2004-04-16
Publication date: 2005-02-24
Also published as: DE10336861B3

Abstract

The invention relates to a method for determining the height of the surface of a workpiece (6) inside a laser machining unit, in which a laser beam (2) is directed by a focusing lens (4) onto the workpiece (6) that is located on a support (5). According to said method, at least one mark (9) that is placed on the surface of the support is measured by means of a camera, when the support is at several predetermined heights (z-3 to z3). A measuring distance (B) that is predetermined by the mark produces different measured values at the different heights, said values enabling a calibration curve to be derived. A mark (9*) that is provided on the workpiece (6) is measured in the same way, when the support (5) is at a specific height. The exact height of the workpiece is obtained by comparing the measured value from the workpiece with the calibration curve.

Description

200310317

description

Method for determining the surface position of a workpiece within a laser processing machine

The invention relates to a method for determining the surface-height position of a workpiece within a laser processing machine, a laser beam being directed via an optical deflection unit and focusing optics onto the workpiece, which is arranged on a carrier and can be moved three-dimensionally therewith.

Laser processing machines for drilling, structuring and labeling workpieces are used in a wide variety of technical fields. Among other things, such machines are used for processing electrical circuit carriers, such as printed circuit boards, especially where miniaturized circuit carriers with high packing density require very fine bores and conductor structures in the range of 100 μ and less and where high processing speed is also required , Since the accuracy of the machining depends on the focus of the laser beam on the surface to be machined, it is important to know or set the working distance between the focusing optics and the workpiece surface to be machined as precisely as possible.

In known laser processing machines, the distance is entered manually and kept constant over the entire travel range of the carrier, that is to say the processing table. Mechanical tolerances of the machining table and the

Workpieces mean that processing takes place at different points in the travel area with different laser beam spot diameters and thus with different energy or power densities. In addition, these tolerances lead to a deterioration in the maximum achievable accuracy. For these reasons, it is difficult with conventional machines to provide consistently good drilling or 200310317

2 To achieve structuring quality on substrates with the required accuracy.

It would be possible to continuously measure the distance using additional sensors, which are expensive to use, and then to keep this distance between the workpiece and the focusing optics constant by means of an active control. Such a solution would be very complex and expensive.

The aim of the invention is to provide a simple method for determining the high position of the workpiece surface within the machine and thus also the distance between the workpiece surface and the focusing optics, which uses the optical properties of the systems present in such a machine, so that none of them are complex Additional instruments are required.

According to the invention, this aim is achieved in that at least one mark arranged on the surface of the wearer is measured by means of a camera in a plurality of predetermined height positions of the wearer, a predetermined measurement distance formed by the mark resulting in different measured values depending on the respective height position from which a calibration curve is derived and stored, that the predetermined measuring distance is then also formed with at least one mark arranged on the surface of the workpiece and measured by means of the camera at a certain height position of the wearer, and that the height position is compared by comparing a measurement value obtained in this way with the calibration curve the workpiece surface is determined.

In the method according to the invention, a camera is used to determine the height of the workpiece, which is present in any case in such laser machines since, among other things, it records markings for the horizontal orientation of the workpiece. According to the invention, a calibration curve is now directly on the surface of the carrier or processing ti 200310317

3 sches recorded, then one or more marks are measured on the surface of the workpiece to be machined, the thickness of the workpiece can be determined from the comparison of the results. This result can then be saved and taken into account in an active control during the subsequent machining of the workpiece.

In a first embodiment of the invention, a camera is provided, the beam path of which is guided separately from the laser beam and the focusing optics of which is guided via a separate imaging unit. In this case, the measuring distance is determined by the extent of the mark in a predetermined horizontal direction, that is, for example, by a line width of the mark. The calibration curve recorded in this way, like a measurement curve recorded with the brand of the workpiece, each has a minimum which corresponds to the focus distance of the brand from the imaging unit. The difference between the minima of these two curves is then directly the height or thickness of the workpiece. This method is preferably used for lasers with a longer wavelength, for example for CO ₂ lasers.

In another advantageous method, which is preferably used for short-wave lasers, such as UV lasers, the marks on the carrier and on the workpiece are observed by the camera via the focusing optics of the laser, and the measuring distance is determined by the distance between two horizontally displaced positions of the mark are determined, ie in each height position the carrier is horizontally displaced horizontally by the predetermined measuring distance, the mark being recorded by the camera in each of the two horizontally displaced positions. The virtual distance between the two measuring positions measured in each height position of the carrier then results in the calibration curve, and a measuring distance is determined by two image recordings of a mark located on the surface of the workpiece in likewise two horizontal positions offset by the measuring distance 200310317

Calibration curve immediately gives the high value for the surface of the workpiece. With the aid of the method according to the invention, the distance between the focusing optics and the processing plane in laser processing machines can thus be measured at almost any point on the workpiece and can be optimized by means of an active control, without the need for additional equipment, which would also mean increased financial expenditure. The method can be used several times, for example for measuring the flatness of the machining table, for measuring the tolerances of the workpieces, both the tolerances within the workpiece and the tolerances between two workpieces.

The invention is explained in more detail below using exemplary embodiments with reference to the drawing. It shows

1 shows a schematic arrangement for carrying out a first embodiment of the method according to the invention, FIG. 2 shows a calibration curve obtained with the structure of FIG. 1 on the surface of a processing table in comparison with a measurement curve obtained on a workpiece,

3a and 3b show the apparatus structure for a second embodiment of the method according to the invention, the beam path of the camera running over the focusing optics of the laser and the processing table being shown in two horizontally offset positions and

4 shows a calibration curve obtained with the arrangement according to FIGS. 3a and 3b.

FIG. 1 shows a possible apparatus construction for carrying out a method according to the invention with separate ones

Beam paths for the laser beam and the camera. A laser beam 2 emitted by a laser 1 is shown schematically, which is directed via a deflection device 3 and a focusing optics 4 in the form of an f-θ lens to a work table 5 or a workpiece 6 arranged thereon. By means of a camera 7 and an imaging unit arranged in front and formed by lenses 8, the 200310317

5 processing table and the workpiece can be observed and measured. This camera 7 is usually used to determine the horizontal position of the workpiece on the processing table in two directions x and y.

According to the invention, the camera 7 also determines the vertical position of the processing table 5 with respect to the z axis. For this purpose, the processing table 5 can be adjusted to different height positions, for example from z _-3 to z ₀ to z ₃ . For the measurement, a mark 9 is attached to the work table, which in the example of FIG. 1 has the shape of an indicated cross, whereby a mark property, for example the line width B or the bar length, is determined as the measuring distance. A 9 * mark is also provided on the workpiece at least once.

To create a calibration curve, the processing table 5 is first measured without a workpiece, the mark 9 being recorded by the camera at different z positions, for example z _-3 to Z ₃ . In this case, the predetermined measuring distance, for example the line width B, is plotted as a function of the respective height position or 7 position, so that a curve profile as shown in FIG. 2 is obtained on the basis of the imaging properties of the imaging optics 8. A b-value is thus assigned to each z-position, with which the measuring distance, ie the line width B, is measured at this corresponding height position. The measurement values obtained in this way are plotted as calibration points EP _-3 to EP ₃ over the corresponding z values and thus form a calibration curve EK1.

If the workpiece 6 is then placed on the processing table, the mark 9 * attached to the workpiece can be measured in the same way. For the different z positions, B measured values are again obtained, which are shown in FIG. 2 as measuring points MP _-3 to MP ₃ and together one 200310317

6 measurement curve MK1 result. Both curves, the calibration curve EK1 and the measurement curve MK1 have a minimum EP ₀ or MPi, which corresponds in each case to the focus distance of the mark 9 on the processing table 5 or on the workpiece 6. The difference Δz between the two minima is directly the workpiece height.

Figure 3 shows a slightly modified arrangement compared to Figure. In this case, the beam path of the camera 7 is directed directly through the focusing optics 4 of the laser beam, which is not shown in this picture, so that the observation of the mark 9 on the processing table 5 or 9 * on the workpiece 6 is carried out via the Focusing optics 4 takes place. According to the second embodiment of the invention, two image recordings according to FIGS. 3a and 3b are now carried out in each of the possible z positions (z_ ₃ to z ₃ ), the processing table being horizontally one between the positions of FIGS. 3a and 3b exactly defined value Dx is moved, whereby a measuring distance Dx is fixed. This measuring distance Dx between the two image recordings is measured with a different virtual value in each height position. If one plots these virtual measured values A of the measuring distance Dx as a function of the height positions z, a calibration curve EK2 results. This has a linear course as a result of the non-optimal telecentricity of the f-θ object, since the beam path in the edge region of the f-θ objective is not parallel to the optical axis, but at a certain angle.

When measuring the workpiece 6, two image recordings are now again carried out on the mark 9 * on the workpiece, the machining table 5 also being moved horizontally by the measuring distance Dx between the positions of FIGS. 3a and 3b in this case too. The virtual distance determined is a direct measure of the height of the workpiece. For the illustration in FIG. 4, this means, for example, that the measuring point MA is determined at a high position zo of the table 5, the measurement in the two positions of the 200310317

7 Figures 3a and 3b gives a virtual distance that the height position z. equivalent. The height or thickness of the workpiece thus corresponds to the difference Δz between the height positions z ₀ and zi.

Claims

200310317Patentansprüche

1. A method for determining the surface high position of a workpiece (6) within a laser processing machine, wherein a laser beam (2) is directed via a focusing lens (4) onto the workpiece (6), which is arranged on a carrier (5) and with it can be moved three-dimensionally, characterized in that at least one mark (9) arranged on the surface of the carrier (6) is measured by means of a camera in several predetermined height positions (z_ ₃ ... z ₀ ... z ₃ ) of the carrier (5) , a predetermined measuring distance (B; Dx) formed by the mark (9) depending on the respective height position (z _-3 to z ₃ ) leading to different measured values (EP_ ₃ to EP ₃ ; A _-3 to A ₃ ) , from which a calibration curve (EK1) is derived and stored, that then with at least one mark (9 *) arranged on the surface of the workpiece (6) also forms the predetermined measuring distance (B; Dx) and by means of the camera (7) a certain high position is measured on the carrier (5) and that by comparing a measurement value (MP.MA) obtained in this way with the calibration curve (F.K1; EK2) the height position of the workpiece surface is determined.

2. The method according to claim 1, characterized in that the measuring distance is determined by the extent (B) of the mark (9) in a predetermined horizontal direction that the camera (7) one of the focusing optics (4) of the laser (1) separated Mapping unit (8) and that both the calibration curve (EK1) and a measurement curve (MK1) recorded with the mark (9 *) of the workpiece (6) have a focus distance of the carrier (5) or the workpiece (6) from the Imaging unit (8) has a corresponding minimum (EP ₀ ; MPj, the height position of the workpiece surface being determined from the comparison of the minima. 200310317

9

3. The method according to claim 1, characterized in that the measuring distance is determined by the distance (Dx) of two horizontally offset positions (Figure 3a, Figure 3b) of the mark (9), which in each height position (z_ ₃ to z ₃ ) by a predetermined horizontal offset of the carrier (5) is formed so that in each height position (z _-3 to z ₃ ) two pictures are taken with the camera via an f-θ lens forming the focusing optics (4) of the laser system, that from the measured virtual Distance (A _-3 to A ₃ ) between the two positions of the mark (9) in each height position (z _-3 to z ₃ ) the calibration curve (EK2) is formed and that two images of a mark located on the surface of the workpiece (9 *) A virtual measuring distance (MA) is determined in two horizontal positions offset by the measuring distance (Dx), which directly gives the high value for the surface of the workpiece (6) by comparison with the calibration curve (EK2).