U.S. patent application number 13/498110 was filed with the patent office on 2012-09-20 for welding head and method for joining a workpiece.
Invention is credited to Joachim Schwarz.
Application Number | 20120234805 13/498110 |
Document ID | / |
Family ID | 43502629 |
Filed Date | 2012-09-20 |
United States Patent
Application |
20120234805 |
Kind Code |
A1 |
Schwarz; Joachim |
September 20, 2012 |
WELDING HEAD AND METHOD FOR JOINING A WORKPIECE
Abstract
A method for joining a workpiece by means of a welding head, in
which at least one line of light is generated on a workpiece, which
crosses a joint line at a site to be joined and a joint seam
generated at a joined site after processing. The lines of light are
imaged at the site to be joined and at the joined site in order to
generate reference data relating to the geometry of the site to be
joined and measurement data relating to the geometry of the joined
sites. The reference data and the measurement data are then
compared at one and the same workpiece site before and after
processing, in order to determine the geometry of the joint seam
independently of the geometry of the site to be joined.
Inventors: |
Schwarz; Joachim;
(Kleinandelfingen, CH) |
Family ID: |
43502629 |
Appl. No.: |
13/498110 |
Filed: |
September 23, 2010 |
PCT Filed: |
September 23, 2010 |
PCT NO: |
PCT/EP2010/005832 |
371 Date: |
May 29, 2012 |
Current U.S.
Class: |
219/121.63 |
Current CPC
Class: |
B23K 26/044 20151001;
B23K 26/03 20130101; B23K 26/12 20130101; G01B 5/0037 20130101;
G01B 11/14 20130101; B23K 31/125 20130101; G01B 11/0608 20130101;
B23K 26/032 20130101; G01B 11/25 20130101 |
Class at
Publication: |
219/121.63 |
International
Class: |
B23K 26/14 20060101
B23K026/14 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 25, 2009 |
DE |
10 2009 042 986.7 |
Claims
1. A welding head for joining a workpiece, comprising: a welding
device which is adapted to weld a joint site of the workpiece to be
processed inside a working region, a light section device which is
attached to the welding device and has at least one light source
for generating at least one line of light inside the working region
on the workpiece, which crosses a joint line at a site to be joined
and a joint seam generated at a joined site after processing by the
welding device, at least one camera for observing the working
region of the workpiece to be processed, which images the line of
light at the site to be joined and the line of light at the joined
site at regular time intervals, in order to generate reference data
(DataR(t)) relating to the geometry of the site to be joined and
measurement data (DataM(t)) relating to the geometry of the joined
site with a joint seam, and a processing unit for receiving the
reference data (DataR(t)) and measurement data (DataM(t)) from the
at least one camera and for comparing the reference data (DataR(t))
and measurement data (DataM(t)) respectively at the same workpiece
site before and after processing by the welding device, so that the
geometry of the joint seam can be determined independently of the
geometry of the site to be joined.
2. The welding head as claimed in claim 1, wherein the welding
device is a metal shielding gas welding device.
3. The welding head as claimed in claim 2, wherein the at least one
camera is attached to an outer side of the welding device.
4. The welding head as claimed in claim 1, wherein the welding
device comprises a housing, through which a beam path for a laser
beam is formed and which has focusing optics for focusing the laser
beam onto the joint site of the workpiece to be processed inside
the working region.
5. The welding head as claimed claim 1, wherein the processing unit
comprises the following: a buffer memory for temporarily storing
the received reference data; a comparator for comparing the
measurement data (DataM(t)) at a respective first instant (t.sub.1)
with the reference data (DataR(t)) at a respective second instant
(t.sub.2), the respective first (t.sub.1) and second (t.sub.2)
instants respectively having a predetermined time difference
(.DELTA.t); and an integrator for determining the respective
predetermined time difference (.DELTA.t) by means of integration of
the joining speed (v(t)) with respect to time and comparing the
calculated joining displacement with the predetermined distance (d)
between the line of light sections.
6. The welding head as claimed in claim 1, wherein the light
section device comprises a first light fan device having a first
light source for generating a straight line of light, which crosses
the joint line at the site to be joined, and a second light fan
device having a second light source for generating a straight line
of light on the workpiece, which crosses the joint seam at the
joined site.
7. The welding head as claimed in claim 6, wherein the straight
lines of light of the first and second light fan devices, which are
generated on the workpiece, extend mutually parallel.
8. The welding head as claimed in claim 6, wherein the first and
second light fan devices are arranged with respect to one another
so that the light fan of the first light source and the light fan
of the second light source respectively strike the workpiece to be
processed obliquely with respect to the optical axis (L) of the
laser beam, so that a distance between the welding device and the
workpiece can be determined by means of triangulation.
9. The welding head as claimed in claim 8, wherein the light fans
of the first light source and of the second light source are
arranged with respect to one another so that they converge with one
another starting from the respective light sources.
10. The welding head as claimed in claim 7, further comprising a
control unit which regulates the distance between the welding
device and the workpiece to a constant value by determining the
distance (d) between the mutually parallel lines of light of the
first and second light fan devices.
11. The welding head as claimed in claim 1, wherein the at least
one camera is a CMOS camera.
12. The welding head as claimed in claim 4, having a beam splitter
by which an observation beam path of the camera can be coupled
coaxially into the laser beam path.
13. The welding head as claimed in claim 6, wherein the first and
second light sources are lasers, in particular semiconductor
lasers.
14. The welding head as claimed in claim 6, wherein an optical
bandpass filter, which is tuned to the wavelengths of the first and
second light sources, is arranged in front of the at least one
camera.
15. A method for joining a workpiece by means of a welding head as
claimed in claim 1, having the steps: generating at least one line
of light inside a working region of the workpiece, which crosses a
joint line at a site to be joined and a joint seam generated at a
joined site after processing by means of the welding device at a
predetermined distance (d), imaging the lines of light at the site
to be joined and at the joined site at regular time intervals by
means of at least one camera, in order to generate reference data
(DataR(t)) relating to the geometry of the site to be joined and
measurement data (DataM(t)) relating to the geometry of the joined
sites, and processing the reference data (DataR(t)) and measurement
data (DataM(t)) generated by the at least one camera by means of a
processing unit, the processing comprising the comparison of the
reference data (DataR(t)) and measurement data (DataM(t))
respectively at one and the same workpiece site before and after
processing by the laser beam, in order to determine the geometry of
the joint seam independently of the geometry of the site to be
joined.
16. The method as claimed in claim 15, the processing step further
comprising: temporary storage of the received reference data
(DataR(t)); comparison of the measurement data (DataM(t)) at a
respective first instant (t.sub.1) with the reference data
(DataR(t)) at a respective second instant (t.sub.2), the respective
first (t.sub.1) and second (t.sub.2) instants respectively having a
predetermined time difference (.DELTA.t); and determining the
respective predetermined time difference (.DELTA.t) by means of
integration of the joining speed (v(t)) with respect to time and
comparison of the calculated joining displacement with the
predetermined distance (d) between the line of light sections.
17. The method as claimed in claim 15, further comprising the step
of regulating the distance between the welding device and the
workpiece by means of triangulation.
Description
[0001] The invention relates to a welding head, in particular a
laser welding head, and to a method for joining a workpiece, in
particular by means of a laser beam, by welding or by
soldering.
[0002] With the aid of a laser welding head, a workpiece can be
processed by using a laser beam, in which case, for example,
welding or soldering work may be carried out in order to join a gap
in a workpiece or between two workpieces. In this process, it is
necessary to monitor the quality of the weld or solder seams
produced by the laser welding head by means of the laser beam. The
inspection of the weld or solder seams is carried out by means of
image processing, the geometrical properties of the weld seams such
as concavity, convexity, seam width or seam thickness inter alia
being determined. In order to record these properties, the seam
region must be known exactly in the three-dimensional
representation, since otherwise irregularities in the workpiece in
the region of the seam to be joined will also possibly be included
when recording the geometry of the joint seam. The welding process
described above is not, however, restricted to laser welding, and
for example welding by means of a metal shielding gas welding head
likewise requires weld seam monitoring.
[0003] The most common evaluation of the three-dimensional
geometrical structure of joint sites is carried out by means of
laser triangulation. In this method, during a welding process, a
light section device is used which is attached to the laser welding
or metal shielding gas welding head. The light section device
projects a light fan by means of a laser beam onto the workpiece,
in order to generate a line of light thereon. From observation of
the light section, i.e. the line of light, the geometries of the
site to be joined and the joined site after processing by means of
the laser beam, i.e. the weld or solder seam, can be determined by
means of the shape of the line of light in the processing
region.
[0004] In known methods for determining the geometry of the joint
site for quality monitoring, optionally the sheet metal geometry
without a weld or solder seam is stored beforehand and subsequently
compared with the measurement data after joining the workpiece.
This, however, either requires full knowledge of the sheet metal
geometry without a weld seam beforehand or conduct of a reference
run before the welding process, in order to record the geometrical
data of the joint site without a weld seam. During the inspection,
these data are compared with the current measurement data and
discrepancies are thus identified. In this method, however, in the
event of path changes between the reference and measurement runs,
elaborate manual modification of the reference data is necessary.
Furthermore, component deviations and modifications of the
component during the joining process are not able to be recorded
and therefore lead to measurement errors. Furthermore, modification
of the component position due to clamping devices is not taken into
account.
[0005] US 2005/02 47 681 A1 describes a welding head, which
comprises a housing through which a beam path for a laser beam is
formed. The housing comprises focusing optics, two light section
devices which generate two lines of light extending parallel, two
CMOS cameras and a processing unit, which is used to observe a
joint gap and a weld seam and to monitor a position of the welding
head relative to the weld seam.
[0006] WO 2008/028 580 A1 describes a method and a device for
optical assessment of the weld quality in welding. During the laser
welding, the welding region is imaged coaxially to the laser beam
through the laser optics, both a triangulation line and a gray or
color image of the solidified weld seam, as well as the process
light of the welding process, being recorded. Optimal quality
assessment of the welding process and the weld seam can be carried
out from these three image elements.
[0007] DE 10 2006 004 919 A1 describes a laser beam welding head.
This laser beam welding head for welding metal parts comprises at
least one beam path for a welding beam and means for optically
recording the position of the weld seam at a first measurement
position, the means for optically recording the position of the
weld seam allowing arrangement of the first measurement position
running in front of the welding position of the welding beam in the
welding direction, and generating a correction signal for
correcting the welding position of the welding beam at least as a
function of a lateral deviation of the weld seam from a setpoint
position, and a corresponding use of the laser beam welding
head.
[0008] EP 2 062 674 A1 describes a method of preparing for and
carrying out a laser welding process. This method of preparing for
a laser welding process on a workpiece comprises the steps:
recording the position of a joint site on the workpiece with the
aid of a sensor device in a first measurement region running in
front of a laser beam position, recording the position of the joint
site with the sensor device in a second measurement region at the
laser beam position and/or in a third measurement region running
behind the laser beam position, recording the laser beam position
in the second measurement region with the sensor device, and
comparing the positions of the joint site in the respective
measurement regions and the laser beam position in order to adapt
the position, alignment and/or coordinate system of the sensor
device and/or of a laser processing head relative to the
workpiece.
[0009] DE 10 2007 030 395 A1 describes a method and a device for
laser beam welding of a workpiece. This method is provided for
preferably continuous laser beam welding of a workpiece, in
particular a tube, along a welding direction along the workpiece,
at least one marking offset with respect to a joint gap in the
workpiece being detected on the workpiece in front of a welding
site in the welding direction. The at least one marking is also
detected behind the welding site in the welding direction, and an
optimal welding position of the laser beam transversely to the
welding direction is determined from the position transversely to
the welding direction of the marking detected in front of and
behind the welding site.
[0010] EP 0 770 445 A2 describes a method for controlling and
positioning a beam for processing workpieces. In a method for
controlling and positioning a beam for processing workpieces, a
first sensor in front of the beam or a specification determines the
path to be tracked by the beam. A second sensor behind the beam
monitors the activity of the beam. The specification or the
recording results of the first sensor relating to a setpoint
position of the beam are compared with recording results of the
second sensor relating to an actual position of the beam, while
taking into account the speed-dependent relative beam/workpiece
displacement. In the event of a difference of the actual position
from the setpoint position, the beam is corrected to a base
position.
[0011] It is an object of the invention to provide a welding head
and a method for joining a workpiece, by which quality monitoring
of a joint seam can be carried out easily during an ongoing joining
process.
[0012] This object is achieved by the welding head as claimed in
claim 1 and by the method for joining a workpiece as claimed in
claim 15. Advantageous configurations and refinements of the
invention are presented in the dependent claims.
[0013] The invention provides a welding head for joining a
workpiece, which comprises a welding device which is adapted to
weld a joint site of the workpiece to be processed inside a working
region, a light section device which is attached to the welding
device, can be rigidly connected to the housing and has at least
one light source for generating at least one line of light inside
the working region on the workpiece, which crosses a site to be
joined and a site joined after processing by the welding device at
a predetermined distance, at least one camera for observing the
working region of the workpiece to be processed, which images the
line of light in or at the site to be joined and the line of light
in or at the joined site at regular time intervals, in order to
generate reference data relating to the geometry of the site to be
joined and measurement data relating to the geometry of the joined
site with a joint seam, and a processing unit for receiving the
reference data and measurement data from the at least one camera
and for comparing the reference data and measurement data
respectively at the same workpiece site before and after processing
by the laser beam, so that the geometry of the joint seam can be
determined independently of the geometry of the site to be
joined.
[0014] A welding head for joining by means of welding or soldering
is thus provided, in which the monitoring of the weld or solder
seam is carried out by recording the geometry of the seam to be
joined by means of a line of light running in front and comparing
these recorded data with the data recorded by means of a line of
light running behind, which images the joined seam. In this case, a
processing unit is provided in the welding head, which compares the
recorded geometrical data before the joining process and after the
joining process so that the data at the same respective workpiece
site can be compared with one another. According to the invention,
this may be done by determining the joining displacement traveled
on the basis of integrating a known joining speed, which
corresponds to the speed of the welding head or the speed of the at
least one camera which is rigidly connected to the welding head,
the joining displacement traveled being compared with the known
predetermined distance between the line of light running in front
and the line of light running behind, so that a time difference
between the reference data and the measurement data can be
calculated. From the comparison of the reference data, the geometry
of the joint seam can therefore be determined independently of
irregularities in the workpiece to be joined in the region of the
seam to be joined, and quality monitoring can be carried out in an
ongoing joining process.
[0015] In one configuration according to the invention, it is
particularly advantageous for the welding device to be a metal
shielding gas welding head.
[0016] In this case, it is particularly expedient for the at least
one camera to be attached to an outer side of the welding device.
In the case of metal shielding gas welding, it may be expedient to
attach two cameras to the outer side of the welding device, since
the line of light running in front and the line of light running
behind cannot be recorded by means of one camera owing to
obstruction by the device. In this case, the recorded images of the
two cameras are correlated with one another so that corresponding
reference data and measurement data can be generated, as is the
case when recording by means of one camera.
[0017] In another advantageous configuration, it is expedient for
the welding head according to the invention to be a welding head or
laser welding head, the welding device comprising a housing,
through which a beam path for a laser beam is formed and which has
focusing optics for focusing the laser beam onto the joint site of
the workpiece to be processed inside the working region. In this
case, the light section device having at least one light source for
generating at least one line of light inside the working region on
the workpiece, which crosses a site to be joined and a site joined
after processing by the laser beam at a predetermined distance, is
attached to the housing.
[0018] For operation of the processing unit, to determine a
corrected geometry of the joint seam from the reference data and
the measurement data, it is advantageous for the processing unit to
comprise a buffer memory for temporarily storing the received
reference data, a comparator for comparing the measurement data at
a respective first instant with the reference data at a respective
second instant, the respective first and second instants
respectively having a predetermined time difference, and an
integrator for determining the respective predetermined time
difference by means of integration of the joining speed with
respect to time and comparing the calculated joining displacement
with the predetermined distance between the lines of light.
[0019] Although in principle it is conceivable for the light
section device to be suitable for projecting an annular line of
light onto the workpiece, according to a particularly simple
configuration of the invention the light section device comprises a
first light fan device having a first light source for generating a
straight line of light, which crosses the site to be joined, and a
second light fan device having a second light source for generating
a straight line of light on the workpiece, which crosses the joined
site.
[0020] For particularly simple evaluation of the reference data and
the measurement data and for simple determination of the
predetermined distance between the site to be joined and the joined
site at the line of light crossing point, it is expedient for the
straight lines of light of the first and second light fan devices,
which are generated on the workpiece, to run parallel to one
another.
[0021] In order to be able to determine the distance between the
welding device, in particular the focusing optics, and the
workpiece easily by means of triangulation, it is expedient for the
first and second light fan devices to be arranged with respect to
one another so that the light fan of the first light source and the
light fan of the second light source respectively strike the
workpiece to be processed obliquely with respect to the optical
axis of the laser beam.
[0022] For producing a small distance between the parallel lines of
light in the case of light fan devices mounted rigidly on the
welding head, it is particularly expedient for the light fans of
the first light source and of the second light source to be
arranged with respect to one another so that they converge with one
another starting from the respective light sources.
[0023] For the function of processing the reference data and the
measurement data, a constant distance between the lines of light is
indispensable. It is therefore particularly expedient for the
welding head furthermore to have a control unit which regulates the
distance between the welding device, in particular the focusing
optics, and the workpiece to a constant value by determining the
distance between the mutually parallel lines of light of the first
and second light fan devices.
[0024] In a particularly expedient configuration of the welding
head, the at least one camera is a CMOS camera.
[0025] For a particularly compact configuration of the welding
head, it is expedient for the welding head furthermore to have a
beam splitter by which an observation beam path of the at least one
camera, in the form of a single camera, can be coupled coaxially
into the laser beam path. The use of merely one camera is preferred
owing to the lower costs and owing to the simpler calculation of
the reference data and the measurement data.
[0026] Owing to the high intensity and the small beam broadening of
laser light, it is advantageous for the first and second light
sources to be lasers, in particular semiconductor lasers.
[0027] In order to eliminate interfering radiation, such as occurs
for example during operation of the welding head, it is expedient
for an optical bandpass filter, which is tuned to the wavelengths
of the first and second light sources, to be arranged in front of
the at least one camera.
[0028] The invention furthermore provides a method for joining a
workpiece by means of the welding head according to the invention,
in particular by a laser beam, which comprises the following steps:
generating at least one line of light inside a working region of a
workpiece, which crosses a site to be joined and a site joined
after processing by the welding device at a predetermined distance,
imaging the lines of light in or at the site to be joined and in or
at the joined site at regular time intervals by means of at least
one camera, in order to generate reference data relating to the
geometry of the site to be joined and measurement data relating to
the geometry of the joined sites, and processing the reference data
and measurement data generated by the at least one camera by means
of a processing unit, the processing comprising the comparison of
the reference data and measurement data respectively at one and the
same workpiece site before and after processing by the laser beam,
in order to determine the geometry of the joint seam independently
of the geometry of the site to be joined.
[0029] Expediently, the processing step furthermore comprises the
temporary storage of the received reference data; comparison of the
measurement data at a respective first instant with the reference
data at a respective second instant, the respective first and
second instants respectively having a predetermined time
difference; and determining the respective predetermined time
difference by means of integration of the joining speed with
respect to time and comparison of the calculated joining
displacement with the predetermined distance between the lines of
light.
[0030] In order to ensure a constant distance between the lines of
light on the workpiece in the region of the site to be joined and
of the joined site, it is furthermore advantageous for the method
to comprise the step of regulating the distance between the welding
device, in particular the focusing optics, and the workpiece by
means of triangulation.
[0031] The invention will be explained in more detail with the aid
of the drawing, in which:
[0032] FIG. 1 shows a highly simplified schematic view of a welding
head according to an exemplary embodiment of the invention,
[0033] FIG. 2A shows a highly simplified perspective detail view of
the workpiece during a joining process at a first instant,
[0034] FIG. 2B shows a highly simplified perspective detail view of
the workpiece during the joining process at a second instant,
and
[0035] FIG. 3 shows a block diagram of a processing unit of the
welding head according to the invention.
[0036] In the various figures of the drawing, components which
correspond to one another are provided with the same
references.
[0037] FIG. 1 shows a highly simplified view of a welding head 10,
in particular a laser welding head, according to an exemplary
embodiment of the invention, in the way it is used with laser
processing machines or systems. A working laser beam 12 coming from
the laser processing machine is directed through a housing 14 of
the welding head 10 onto a workpiece 16 and focused by means of
focusing optics 18 onto the workpiece 16, as indicated by the
optical axis L. The working laser beam 12 may be broadened, in the
case of supply to the welding head 10 by means of a light guide
fiber, owing to the extraction of the laser beam from the light
guide fiber by collimator optics.
[0038] Instead of a laser welding head, a metal shielding gas
welding head may also be used as the welding device, in which case
two cameras (not shown) are used in order to observe the workpiece.
In what follows, however, the invention will be explained with
reference to the use of one camera.
[0039] In the housing 14 of the welding head 10, a beam splitter 20
is arranged in the passage region of the working laser beam 12 so
that an observation beam path (indicated by its optical axis) of a
camera 24 is coupled coaxially into the beam path of the working
laser beam 12. In the observation beam path 22, imaging optics 26
and an optical bandpass filter 28 are arranged in front of the
camera 24. In the exemplary embodiment of the invention as shown in
FIG. 1, the observation beam path 22 of the camera 24 is directed
by means of the beam splitter 20 onto a working region of the
workpiece 16. It is, however, also possible to fit the camera 24
with observation optics on an outer side of the housing 14 of the
welding head 10, in which case, however, it is necessary to ensure
that the image of the working region of the workpiece 16 as
recorded by the camera 24 moves synchronously with a movement of
the welding head 10 with the housing 14 and in particular with the
focusing optics 18.
[0040] Arranged on an outer side of the housing 14 is a light
section device 30 which comprises a first light fan device 32 and a
second light fan device 34. The first light fan device 32 is
mounted by means of a support 36 on a side of the housing 14 which
lies at the front during movement of the welding head 10 in its
movement direction (indicated by the arrow A).
[0041] The first light fan device 32 comprises a first light source
38, by which a light fan 40 is projected in the direction of the
workpiece 16, in order to generate a line of light 42 (shown in
FIG. 2A) on its surface inside the working region of the welding
head 10.
[0042] The second light fan device 34 is mounted by means of a
support 44 on a side of the housing 14 of the welding head 10 which
lies on a rear side of the housing 14 during movement of the
welding head 10 in the movement direction A. The second light fan
device 34 comprises a second light source 46, by which a light fan
48 is projected in the direction of the workpiece 16, in order to
generate a line of light 50 on its surface inside the working
region of the welding head 10.
[0043] As first and second light sources 38, 46 of the first and
second light fan devices 32, 34, respectively, a laser light source
is suitable owing to the high intensity and a small intrinsic beam
broadening, in which case it may be a semiconductor laser diode.
For this, for example, AlGaInP laser diodes having multiple quantum
well structures may be used, which have an emission maximum in a
wavelength range of between 635 nm and 670 nm. For example, a laser
diode having an emission wavelength of 658 nm and an emission power
of 66 mW may be used. In this case, for reduction of the
interfering radiation recorded by the camera, the transmission
wavelength of the optical bandpass filter 28 may be tuned to the
wavelength of the first and second light sources 38, 46.
[0044] The welding head 10 furthermore comprises a processing unit
52 connected to the camera 24 and a control unit 54, likewise
connected to the camera 24, the functions of which will be
described in more detail below.
[0045] Although the light section device 30 is not restricted to
comprising two light fan devices 32 and 34, but may also be in the
form of a single device which, for example, projects a conical
light fan around the focal point of the laser beam 12 onto the
workpiece 16 in order to generate a circular or elliptical line of
light, according to the invention it is advantageous for the first
light fan device 32 and the second light fan device 34 respectively
to generate light fans 40 and 48 which lie in an emission plane, so
that straight lines of light 42 and 50 are respectively projected
onto the surface of the workpiece 16.
[0046] The function of the welding head 10 according to the
invention will now be explained below with the aid of FIGS. 2A and
2B.
[0047] In a joining process carried out by the welding head 10,
which may be a welding or soldering process, the welding head 10,
as shown by the arrow A indicated in FIG. 1 and FIG. 2, is moved
with a speed v(t) over a workpiece 16 to be joined (which may
consist of two metal sheets or similar elements to be connected
together), the focused laser beam 12 striking a respective joint
site 56 and, owing to the welding process, generating a joint seam
58 which connects together the workpiece parts shown in FIG.
2A.
[0048] The line of light 42 of the first light fan device 32 is
projected onto the workpiece 16 so that it runs in front of the
focal point of the laser beam 12, i.e. the respective joint site
56, so that geometrical data of the site to be joined can be
recorded by means of the camera 24 which acquires the entire
working region including the line of light 42, the joint site 56
and the line of light 50, in order to record reference data
relating to the site 60 to be joined.
[0049] In a similar way, the line of light 50 generated by the
second light fan device 34 on the workpiece 16 runs behind the
focal point 56 of the laser beam 12 and crosses an already joined
site 62, so that measurement data can be recorded by the camera 42
relating to the geometry of the weld seam 58.
[0050] As shown in FIG. 1 and FIG. 2A, the first light fan device
32 and the second light fan device 34 are arranged with respect to
one another so that they generate light fans which respectively
strike the workpiece 16 to be processed obliquely with respect to
the optical axis of the laser beam 12, so that, during an up and
down movement of the housing 14 along the optical axis L (see arrow
B), the respective projected lines of light 42 and 50 on the
workpiece 16 move to and fro relative to the working laser beam 12
striking the workpiece 16. In the case shown in FIG. 1 and FIG. 2A,
the line of light 42 generated by the first light fan device 32 and
the line of light 50 generated by the second light fan device (in
the case of a plane surface of the workpiece 16) extend mutually
parallel to one another, the light fans of the first and second
light fan devices 32, 34 converging with one another. A distance d
between the lines of light 42 and 50 therefore increases when the
welding head 10 is moved downward and the distance d between the
lines of light 42, 50 decreases when the welding head 10 is moved
upward.
[0051] Since, for an optimal joining process, the focus of the
working laser beam 12 should always extend at a predetermined
height along the sites to be joined, the distance d between the
lines of light recorded by the camera 24 is evaluated by the
control unit 54 (FIG. 1) and, by controlling an actuator (not
shown) for an upward or downward movement of the housing 14 (see
arrow B), is regulated to a predetermined distance d which in turn
corresponds to an optimal focal position of the working laser beam
12 on the joint site 56.
[0052] Thus, a constant predetermined distance d between the line
of light 42 of the first light fan device 32 and the line of light
50 of the second light fan device 34 can be maintained by the
control unit 54 during the joining process.
[0053] The method according to the invention for quality monitoring
of the joint seam 58 will now be explained below with the aid of
FIGS. 2A, 2B and 3.
[0054] FIG. 2A shows the lines 42 and 50 projected onto the
workpiece 16 at an instant t.sub.1. On the basis of the line shape,
the lines of light 42 and 50 respectively at the site 60 to be
joined and the joined site 62, which are imaged by the camera 24 at
regular time intervals, provide information about the geometry or
the height profile of the respective sites 60 to be joined or the
respective joined sites 62 at corresponding discrete instants
throughout the joining process. The object of the monitoring method
according to the invention is in this case to determine geometrical
data of the joined site 62 independently of the geometry of the
site 60 to be joined, so that only lines of light which are located
at the same workpiece site (before and after the joining process)
are respectively compared with one another for matching or
balancing.
[0055] This object is achieved according to the invention in that,
as shown in FIG. 2A, the line of light 42 is first recorded by the
camera at an instant t.sub.1 and these data are stored as reference
data. At an instant t.sub.2 (FIG. 2B), at which the line of light
50 running behind the laser processing beam 12 has moved forward by
the predetermined distance d because of the joining speed v(t), the
line of light 50 is recorded and the geometrical data of the seam
now joined are stored as measurement data. The reference data for
the instant t.sub.1 are then compared with the measurement data for
the instant t.sub.2, which relate to the same workpiece site.
[0056] According to the invention, this is achieved by the
processing unit 52 (FIG. 1), the block diagram of which is shown in
FIG. 3.
[0057] The processing unit 52 receives at an instant t.sub.1 image
data of the lines of light 42, 50 from the camera 24, from which
reference data DataR(t) relating to the site 60 to be joined are
determined by means of the line of light 42 and measurement data
DataM(t) relating to the geometry of the joined site 62 are
determined by means of the line of light 50, i.e. the corresponding
light sections.
[0058] In order to permit comparison of the reference data DataR(t)
relating to the site 60 to be joined with corresponding measurement
data DataM(t) at the same workpiece site, the reference data
DataR(t) are first loaded into a buffer memory 64 in which the
reference data DataR(t) can be temporarily stored over a particular
period of time. The processing unit 52 furthermore comprises an
integrator 66, which receives from the welding head 10 the current
joining speed v(t) (which may also be constant) and which
determines the associated joining displacement that has been
traveled by integrating the joining speed v(t) with respect to
time. By comparing the joining displacement traveled with the
predetermined distance d, the integrator 66 can thus determine the
time difference .DELTA.t by which the reference data DataR(t) and
the current measurement data DataM(t) are mutually shifted in time,
so that a comparison of the temporally offset reference data
DataR(t-.DELTA.t) and the current measurement data DataM(t)
corresponds to a comparison of measurement data and reference data
at the same workpiece site.
[0059] This instant is illustrated in FIG. 2B. After the time
.DELTA.t has elapsed, because of the joining speed v(t) the line of
light 50 has traveled forward by the predetermined distance d in
the movement direction of the welding head 10, so that now at the
instant t.sub.2 it is at a site of the workpiece 16 where the line
of light 42 was at the instant t.sub.1 (FIG. 2A). By integrating
the joining speed v(t) with respect to time and comparing the
displacement traveled with the predetermined distance d,
measurement data and reference data can therefore be determined at
the same workpiece site.
[0060] Furthermore, in addition, by recording the position and
orientation of the welding head 10 relative to the workpiece 16
(for example by determining the path data of a robot arm which
carries the welding head 10), it is possible to correct errors
which result from the projection of the lines of light 42, 50 onto
the workpiece 16 starting from a welding head 10, the beam axis L
of which is not perpendicular to the workpiece surface.
[0061] As shown in FIG. 3, geometrical data DataC(t) of the joint
seam 58 at corresponding instants (which may be discrete) are
determined from the comparison of the reference data
DataR(t-.DELTA.t) and the measurement data DataM(t), which are
independent of the geometry of the site 60 to be joined, in a
comparator 68.
[0062] Thus, by integrating sensors running in front and behind in
or on the welding head 10, reference data relating to the geometry
of the parts before the welding and measurement data relating to
the geometry after the welding can be acquired simultaneously, so
the matching of the geometrical data can be carried out during the
welding process. Online monitoring of the weld seam being produced
is therefore possible during the welding process.
[0063] The method according to the invention and the welding head
according to the invention therefore have the advantage that a
reference run for recording reference data is obviated, so that a
higher measurement accuracy is achieved and effects on the weld
seam analysis due to component tolerances, a clamping device which
is used or deformation by the joining, can be minimized or even
eliminated owing to the recording of reference data directly before
the joining process. Furthermore, the inspection sensors can be set
up simply.
[0064] Thus, even during the process of joining a workpiece having
component variations, in the event of path inaccuracies of the
sensor guiding system or in the event of deformations during the
joining process or modifications due to the clamping device, simple
quality monitoring of weld and solder seams of all kinds can thus
be carried out in the ongoing joining process.
* * * * *