# US 11,027,364 B2 · Method and device for measuring the depth of the vapor capillary during a machining process with a high-energy beam

> Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt

- Number: US 11,027,364 B2
- Document ID: US11027364B2
- Status: Granted
- Kind: B2
- Application number: 16/095,299
- Filed: 2016-10-19
- Published: 2019-03-28
- Granted: 2021-06-08
- Earliest claimed: 2016-04-22
- Assignees: Precitec Optronik GmbH
- Applicants: Precitec Optronik GmbH
- Inventors: Martin Schönleber; Christoph Dietz
- Web page: https://patentgrep.com/patent/US11027364B2

## CPC

- B23K 26/032: {using optical means}
- B23K 26/03: Observing, e.g. monitoring, the workpiece
- B23K 26/048: {by controlling the distance between laser head and workpiece}
- B23K 26/0643: {comprising mirrors}
- B23K 26/0648: {comprising lenses}
- B23K 26/0665: {by beam condensation on the workpiece, e.g. for focusing}
- B23K 26/0884: {in at least three axial directions, e.g. manipulators, robots}
- B23K 26/21: by welding
- G01B 9/02019: {contacting different points on same face of object}
- G01B 9/02044: {Imaging in the frequency domain, e.g. by using a spectrometer}
- G01B 9/02083: {characterised by particular signal processing and presentation}
- G01B 9/02091: Tomographic interferometers, e.g. based on optical coherence
- G01B 11/22: for measuring depth
- G01B 2290/65: Spatial scanning object beam
- B23K: SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- G01B: MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS

## Abstract

A method for measuring the depth of the vapour cavity during an industrial machining process employs a high-energy beam. An optical measuring beam is directed towards the base of a vapour cavity. An optical coherence tomograph generates interference factors or other raw measurement data from reflections of the measurement beam. An evaluation device generates undisturbed measurement data, wherein raw measurement data that is generated at different times is processed together in the course of a mathematical operation. This operation can be a subtraction or a division. Slowly changing interference factors can thus be eliminated. An end value for the distance to the base of the vapour cavity is calculated from the undisturbed measurement data using a filter. As a result, the depth of the vapour cavity can be determined, in the knowledge of the distance at a part of the surface of the work piece that is not exposed to the high-energy beam.

## Claims

### Claim 1

Method of measuring a depth of a vapor capillary during a high energy beam machining process, wherein the method comprises the steps of:
a) directing an optical measuring beam to the bottom of the vapor capillary, which arises in an area of interaction between a workpiece and a high energy beam;
b) detecting reflections of the measuring beam in an optical coherence tomograph;
c) generating raw measurement data from the reflections detected in the optical coherence tomograph;
d) repeating the steps a) to c) at several times ti, where i=1, 2, 3, . . . , during the machining process, wherein a set of raw measurement data for a first distance (a1) to the bottom of the vapor capillary is obtained for each time ti;
e) calculating a set of undisturbed measurement data for a time tn by commonly processing in a mathematical operation a first set of raw measurement data generated at the time tn and a second set of raw measurement data generated at an earlier time tm, where m<n;
f) calculating a final value for the first distance (a1) at time tn from the set of undisturbed measurement data calculated in step e);
g) measuring a second distance (a2) to a portion of the surface of the workpiece that is not exposed to the high energy beam; and
h) calculating the depth of the vapor capillary by subtracting the second distance (a2) from the final value for the first distance (a1) calculated in step f).

### Claim 2 (depends on 1)

Method according to claim 1, wherein, with the mathematical operation in step e), the set of raw measurement data generated at the earlier time tm is at least partially subtracted from the quantity of raw measurement data generated at time tn.

### Claim 3 (depends on 2)

Method according to claim 2, wherein at least part of the set of raw measurement data generated at an immediately preceding time tn-1 is subtracted from the quantity of raw measurement data generated at time tn.

### Claim 4 (depends on 2)

Method according to claim 2, wherein, through the mathematical operation in step e), the set of raw measurement data generated at the earlier time tm was completely subtracted from the set of raw measurement data generated at time tn.

### Claim 5 (depends on 1)

Method according to claim 1, wherein, through the mathematical operation in step e), a moving average is at least partially subtracted from the set of raw measurement data generated at time tn, which is calculated from sets of raw measurement data which were generated at several earlier times tj, where j≤m.

### Claim 6 (depends on 5)

Method according to claim 5, wherein the moving average is a weighted average having at least the order 2.

### Claim 7 (depends on 5)

Method according to claim 5, wherein the moving average is an exponentially smoothed average.

### Claim 8 (depends on 1)

Method according to claim 1, wherein the optical coherence tomograph is a spectral domain coherence tomograph, and wherein each set of raw measurement data represents an interference spectrum, which is generated by the optical coherence tomograph.

### Claim 9 (depends on 8)

Method according to claim 8, wherein, through the mathematical operation in step e), the interference spectrum generated at the time tn is divided by an averaged spectrum representing an average of a plurality of interference spectra which were generated at earlier times tj, where j≤m.

### Claim 10 (depends on 9)

Method according to claim 9, wherein the interference spectra of 50 to 200 earlier time points contribute to the moving average.

### Claim 11 (depends on 8)

Method according to claim 8, wherein a plurality of distance values is derived from the interference spectrums by Fourier transform, and wherein the final value for the first distance (a1) at time tn is calculated from the distance values according to a predetermined criterion.

### Claim 12 (depends on 11)

Method according to claim 11, wherein the criterion is a quantile criterion.

### Claim 13 (depends on 1)

Method according to claim 1, wherein in step g) the second distance (a2) is measured by a further measuring beam on the part of the surface of the workpiece that is not exposed to the high-energy beam, wherein reflections are detected by the other measuring beam in the same or another coherence tomograph, and wherein they are derived from the reflections of the distance values of the other measuring beam from which an final value for the second distance (a2) according to a predetermined criterion is calculated at time tn.

### Claim 14 (depends on 13)

Method according to claim 13, wherein an original measuring beam is divided into the measuring beam and the further measuring beam with the aid of a beam splitter.

### Claim 15

Apparatus for measuring a depth of a vapor capillary during a high energy beam machining process, wherein the apparatus comprises:
an optical coherence tomograph configured to perform the following steps:
a) directing an optical measuring beam to the bottom of the vapor capillary formed in an area of interaction between a workpiece and a high energy beam;
b) detecting reflections of the measuring beam in the optical coherence tomograph;
c) generating raw measurement data from the reflections detected in the optical coherence tomograph; and
d) repeating steps a) to c) at several times ti, where i=1, 2, 3, . . . , during the machining process, wherein a set of raw measurement data for a first distance (a1) to the bottom of the vapor capillary is obtained for each time ti, and
an evaluation device, which is configured to carry out the following steps:
e) calculating a set of undisturbed measurement data for a time tn by commonly processing in a mathematical operation a first set of raw measurement data generated at the time tn and a second set of raw measurement data generated at an earlier time tm, where m<n;
f) calculating a final value for the first distance (a1) at time tn from the set of undisturbed measurement data calculated in step e); and
g) calculating the depth of the vapor capillary wherein a measured second distance (a2) to a portion of the surface of the workpiece that is not exposed to the high energy beam is subtracted from the final value for the first distance (a1) calculated in step f).

### Claim 16 (depends on 15)

Apparatus according to claim 15, wherein, with the mathematical operation in step f), the set of raw measurement data generated at the earlier time tm is at least partially subtracted from the quantity of raw measurement data generated at time tn.

### Claim 17 (depends on 15)

Apparatus according to claim 15, wherein, through the mathematical operation in step f), a moving average is at least partially subtracted from the set of raw measurement data generated at time tn, which is calculated from sets of raw measurement data which were generated at several earlier times tj, where j≤m.

### Claim 18 (depends on 15)

Apparatus according to claim 15, wherein the optical coherence tomograph is a spectral domain coherence tomograph, and wherein each set of raw measurement data represents an interference spectrum, which is generated by the optical coherence tomograph.

### Claim 19 (depends on 15)

Apparatus according to claim 15, in step h) the second distance (a2) is measured by a further measuring beam on the part of the surface of the workpiece that is not exposed to the high-energy beam, wherein reflections are detected by the other measuring beam in the same or another coherence tomograph, and wherein they are derived from the reflections of the distance values of the other measuring beam from which a final value for the second distance (a2) according to a predetermined criterion is calculated at time tn.

### Claim 20

Apparatus for measuring a depth of a vapor capillary during a high energy beam machining process, wherein the apparatus comprises:
a spectral domain optical coherence tomograph configured to perform the following steps:
a) directing an optical measuring beam to the bottom of the vapor capillary formed in an area of interaction between a workpiece and the high energy beam;
b) detecting reflections of the measuring beam in the spectral domain optical coherence tomograph;
c) generating raw measurement data from the reflections detected in the spectral domain optical coherence tomograph; and
d) repeating steps a) to c) at several times ti, where i=1, 2, 3, . . . , during the machining process, wherein a set of raw measurement data for a first distance (a1) to the bottom of the vapor capillary is obtained for each time ti, wherein each set of raw measurement data represents an interference spectrum, which is generated by the spectral domain optical coherence tomograph, and
an evaluation device, which is configured to carry out the following steps:
e) calculating a set of undisturbed measurement data for a time tn by commonly processing in a mathematical operation a first set of raw measurement data generated at the time tn and a second set of raw measurement data generated at an earlier time tm, where m<n, wherein in the mathematical operation the interference spectrum generated at the time tn is divided by an averaged spectrum representing an average of a plurality of interference spectra which were generated at earlier times tj, where j≤m;
f) calculating a final value for the first distance (a1) at time tn from the set of undisturbed measurement data calculated in step e); and
g) calculating the depth of the vapor capillary wherein a measured second distance (a2) to a portion of the surface of the workpiece that is not exposed to the high energy beam is subtracted from the final value for the first distance (a1) calculated in step f).