Note: Descriptions are shown in the official language in which they were submitted.
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1
DEVICE AND METHOD FOR MACHINING yVORKPIECES
The invention relates to an apparatus for processing workpieces by relative
displacement of a plurality of simultaneously operating functional elements in
relation to
the workpieces which are being worked on, with a device to hold the functional
elements.
Such apparatuses are known in the field of tailored blanks or in the
production of tubes.
for internal high-pressure forming; and they are also known in other fields.
"Tailored blanks" (Platinen) are metal sheets produced by welding different
sheet-metal
pieces together. The individual sheet-metal pieces are laid side by side and
welded
together, e.g. by roller seam welding with.the adjacent sheets overlapping, or
by laser
welding with the sheets butted together.
It is also possible to form tubular parts from different sheet-metal pieces by
closing the
tube by subsequent welding and by then welding several such tubular pieces
together to
produce a tube made up of different sheet-metal pieces.
Tailored blanks or tubes ofithis type have applications e.g. in the motor-
vehicle industry.
Tailored blanks for some years; tubes are making their debut. Tailored blanks
are deep-
drawn and formed e.g. into beams for body framework, with defined dissimilar
mechanical properties of the beam produced derived from the dissimilar
materials or
thicknesses of the individual sheet-metal pieces. Tubes are likewise formed
into parts
for body framework, by internal high-pressure fom~ing (IHU); with the
advantage that
complicated shapes no longer have to be builf up frpm individual parts, and
costly.
tolerance problems upon assembly disappear.
It is evident from the foregoing that very exacting requirements have to be
imposed on
the weld seams, since these are already highly stressed by the forming
process. It is
also evident that no structure-weakening weld flaws possibly leading to
defects in the
finished product that could have serious consequences can be allowed to occur.
EP 0770445 indicates a method and an apparatus for assuring and monitoring the
quality of the welding process in the fabrication of inter aiia tailored
blanks. (Reference
is hereby expressly made to the total disclosure of EP 0770445). The said
document
discloses an apparatus for the fabrication of tailored blanks wherein the
individual
sheet-metal pieces are fixed on a carriage with the welding edges butted
together and
are led through and under a stationary welding station in a single straight
pass. This
relative displacement between the carriage (with its straight absolute motion
through the
apparatus) and the stationary welding station results in a linear processing
path on the
workpieces.
In principle, individual sheets of any size can be welded together to produce
tailored
blanks of any desired size. Nowadays, finished tailored blanks can attain
dimensions of
several metres. For instance, the side-panel of the Cheep Cherokee is a
tailored blank.
Lengths of weld seam in the range of a few metres are possible in certain
applications.
On the other hand, the effective laser focus has a diameter of 0.2 mm and has
to be
kept on the processing path with a precision commensurate with this diameter,
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otherwise weld defects will ensue. Although the mechanics of the apparatus do
allow
very precise guidance of the carriage through and under the welding station,
tolerances
are unavoidable. Moreover, further dimensional changes may arise in operation
e.g. due
to heating of the laser beam path. Therefore in accordance with EP 0770445 a
corrective adjustment is used for the line of the laser beam, the necessary
measurements or correction data being obtained by image processing (corrective
adjustment of a laser beam is known per se and is effected e.g. by alterations
to the tilt
of the mirror in the laser's optical system). According to EP 0770445, the
correction data
are obtained by detecting the actual position of the edges before the welding
point by
image processing, and are used to control the laser's optical system.
Deviations from
the required edge-position of down to a few tenths of a millimetre can be
compensated
in this way. The weld seam produced then runs along the straight processing
path
required with a maximum deviation of those few tenths of a millimetre.
But this compensation will work only if the laser beam guide system produces
the
effective laser focus at the required spot, which is not always the case,
owing to e.g.
heating of the beam guide as previously mentioned.
Therefore, another functional element after the welding point detects the
actual position
of the weld seam, again by image processing. If the weld seam is not at the
spot to
which the laser focus has been corrected, there is an unpermitted tolerance in
the beam
guide. Thus a further correction signal for the laser optical system can be
obtained. The
result is a control maintaining the correct position of the beam on the
straight processing
path, thus assuring high weld quality.
Besides the quality assurance afforded by the three functions of (i) first
sensor for image
processing, (ii) laser optical system and (iii) second sensor for image
processing, further
functions may be critical for the welding process, such as for example a
material feed
for the welding point (in the form of welding wire or metal powder) known in
itself in
welding technology. Further or other functions may be adopted as the need
arises, such
as for example when cutting rather than welding is taking place, as cutting
may likewise
involve precise guiding of the cutting element (such as a laser, water jet,
etc.). Further
functions may also arise when workpieces other than tailored blanks are worked
with.
In addition to the trend which has been described towards ultra-high
requirements in
respect of weld quality, increasing use of tailored blanks is also resulting
in a growing
demand not just for straight welded joints but also for the ability to produce
non-linear
welded joints - and this for increasingly large production runs. Currently,
the stringent
requirements that have to be imposed on the welding process are achievable for
linear
weld seams, but not for seams that are curved or crooked.
It is true that it is known to mount tailored blanks requiring non-linear
joints on a carriage
and to propel the carriage through the apparatus in the longitudinal direction
as the
welding station travels to and fro on a transverse bridge; with suitable
control of the two
motions of carriage and welding station (each in a straight line), processing
paths of any
desired curvature can be traversed. Such apparatuses work with a single
functional
element - the focusing head for a laser beam. Hence they fail to realize a
welding
process of high quality, since other functions, e.g. as disclosed in EP
0770445, are
absent.
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Hence the problem of the present invention is to provide an apparatus which
enables
several functional elements to be used simultaneously on a curved processing
path of
an apparatus for processing workpieces.
The problem is solved by the characterizing features of Claim 1 and/or the
method
according to Claim 20.
By modifying the position of functional elements, it is possible on the one
hand, for
elements acting in succession one after the other to be individually kept in
their standard
position {e.g. vertically over the workpiece surface) on curved sections of
the processing
path at all times, independently of the absolute motions in the apparatus; but
on the
other hand, for individual elements also to be deflected from their standard
position and
thus for radii of curvature to be executed which could not be executed in the
standard
position because of the dimensions of the elements themselves or, owing to the
high
accelerations involved, could only be executed at high cost.
For the purposes of the invention it does not matter how the relative motion
between the
workpieces and the functional elements is produced, whether by functional
elements
that are fixed in position in combination with a carriage for the workpieces
that can be
moved in all directions, or vice versa; or by a hybrid solution such as
transverse motion
of functional elements with respect to the longitudinal motion of the
carriage.
The invention will now be described in detail with reference to the figures,
in which:
Figures 1 a to 1 c show schematically three functional elements, in each case
on a
curved processing path with position modified accordingly.
Figures 2a to 2c show three functional elements on the processing paths
corresponding
to Figures 1a to 1c, shown with regard to the mutual change in position.
Figure 3 shows a cross-section through one embodiment of a device for
positioning the
functional elements.
Figure 4a is a view from above of a further embodiment.
Figure 4b shows a cross-section through the embodiment of Figure 4a.
Figure 5a is a view of a further embodiment.
Figure 5b shows a section through part of the embodiment of Figure 5a.
Figure 5c is a side view of the embodiment of Figure 5a.
Figure 6 shows schematically the suspension of an orientatable functional
element.
Figure 1 a shows two workpieces 10 and 11 which have been butted together for
processing (in this case, welding). The juxtaposed edges of the workpieces
form a
processing path 4. Three functional units 1, 2 and 3 are arranged in a device
13 for
holding the functional units, and are located above the processing path.4 in
the
operative position to weld the workpieces 10 and 11 e.g. in the manner
proposed in EP
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0770445. This is performed by a laser beam whose position is controlled with
the aid of
two sensors for image processing. An energy beam of a different type, such as
an
electron beam for example, could also be used. The functional unit 1 (a head
with a
laser optical system) is located between a precursor functional unit 2 and a
follower
functional unit 3 (both sensors for image processing).
It is evident from the figure that the functional units have modified their
position in
relation to a straight processing path:
ZO The relative position of the three functional units 1, 2 and 3 alters
continually in
accordance with the changing curvature of the processing path 12. If only two
functional
units are operative, they still after their position in relation to the
workpieces 10, 11
(and/or to the device 13 as the case may be) even though the distance between
them
remains constant.
Figure 1 b shows a circular processing path 4. It can be seen from the figure
that with
the functional units 1, 2 and 3 arranged over the processing path the smallest
possible
distance between two functional units (here functional units 2 and 3)
determines the
minimum radius of curvature. Were the circle formed by the processing path 12
smaller
20 than the distance between the units 2 and 3, one of the units could no
longer be kept on
the processing path 12.
Figure 1 c shows a processing path 4 through a rounded right-angled comer with
a very
small radius of curvature. If the precursor functional unit 2 deviates
sideways from the
processing path 4 and stays on the track 5 drawn as a broken line, a simpler
movement
cycle results. First of all, large accelerations of the unit 2 are prevented,
which is in
keeping with the need to keep the rate of deposition as uniform as possible,
and hence
to keep the rate of travel of the functional unit 1 in relation to the
processing path 4 as
uniform as possible; then, there is a larger radius of curvature of the track
to be followed
30 by the individual functional units, which can be a decisive factor in the
case of a
processing path 4 with a complex course. The track curve 5 in the figure
presupposes
that the position of the functional unit 2 can be modified so that it is able
to operate on
the processing path 4, and thus stay in the operative position, even when
laterally offset,
as indicated by the arrow 6. This contrasts with the arrangement of Figure 1 a
where the
functional units 1 to 3 are shown in an arrangement directly over the
processing path 4.
Figure 2a shows the processing path 4 of two workpieces 10 and 11 and the
functional
units 1, 2 and 3, the device 13 being omitted so as not to clutter the
drawing. A
reference point 14 marked with a cross does however denote the position of the
device
40 13 in relation to the workpieces. In this instance this point coincides
with the position of
the precursor functional unit 1. As indicated in Figure 2a, the position of
the functional
units 2 and 3 is defined from the reference point 14: firstly by the shorter
vector 7
(distance between units 1 and 2), secondly by the longer vector 8 {distance
between
units 1 and 3).
Figure 2b shows the arrangement of Figure 2a, with the position of the
functional unit 3
in relation to the functional unit 1 (and the reference point 14) defined by
the position of
the functional unit 2. The sum of the vectors 7 and 9 gives the mutual
position of the
functional units 1 and 3.
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Figure 2c again shows the arrangement of Figure 2a, with the functional unit 1
(and the
reference point 14) lying between the functional units 2 and 3 whose position
is thus
defined by the vectors 7 and 9 (distance between units 2 and 3).
Although all variants in Figures 2a to 2c are feasible depending on the
purpose for
which the apparatus is used, the artanaement of Figure 2c is especially
appropriate. If
the reference point 14 (which preferably, though not necessarily, coincides
with one of
the functional units 1 to 3) is the basis for computation by the control unit
of the
respective position of the functional units 1 to 3, or for the mechanical
traversing of the
track curve 4 by holders arranged movably in the vectors 6 to 9, rounding
errors,
tolerances etc. are inevitable. The effects of angular errors grow larger as
the distance
between the reference point 14 and the respective functional unit 1, 2 or 3
increases; for
this reason, the arrangement of Figure 2c with the short vectors shown is
preferable to
the arrangement of Figure 2a. The arrangement of Figure 2c is also preferable
to that of
Figure 2b, as in the latter the errors between the reference point 14 and the
functional
unit 3 are cumulative.
Figure 3 shows a cross-section through an embodiment of the device 13
according to
the invention with the functional units 1, 2 and 3. The figure also shows
schematically a
processing path 4l4'. The reference point 14 defines the position of the
device 13 in
relation to the workpieces 10 and 11, enabling the overriding control of the
apparatus to
assure the as part of the predetermined relative displacement by modifying the
direction
and/or rate of displacement between the workpieces 10, 11 and the device 13.
The functional unit 1 is configured as a sensor for image processing, and
detects e.g.
the position of the edges of the juxtaposed workpieces 10, 11 in a defined
section, now
about to be processed, of the path 4. The functional unit 2 is configured as a
focusing
head for an energy beam, e.g. the beam of a jag laser, and functions as a
welding unit
to weld the workpieces 10, 11 together. The functional unit 3 in turn is
configured as a
sensor for image processing, and detects the position and/or quality of the
weld seam.
EP 0770445 shows a possible way in which these functional units can work
together.
A baseptate 12 forms the base for the an-angement of the functional units 1, 2
and 3 in
the device 13, and is preferably arranged displaceably on a bridge 15 (see
Figure 4a).
This sets up the arrangement previously described in the apparatus configured
in
acxordance with the invention in which workpieces 10, 11 fixed to a carriage
advanced
longitudinally and so pass under a device 13 held displaceably in the
transverse
direction on the bridge 15. However, the invention is not limited to such an
arrangement
and can be used wherever any kind of relative displacement is created between
the
4 0 workpieces 10, 11 and the device 13.
A holder 16 whose orientation can be varied is arranged on the base 12. It is
configured
as a body of revolution and has an axis of symmetry 16'. It is mounted
rotatably on the
base 12 by the schematically indicated ball bearing 17. It has a central
opening 18 with
an insert 18 enabling the functional element 1, which is fixed in position
with respect to
the base 12, to retain its orientation independently of any rotation of the
holder 16. The
axis of symmetry 16' of the holder 16 coincides with the operative line 1' of
the functional
element 1; the position of the operative line 1' on the processing path
constitutes the
reference point 14. The position of the base 13 in relation to the workpieces
10, 11 is
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thus defined, as is the position of the functional element 1 in relation to
the workplaces
10, 11.
A motor 20 attached to the base 12 acts via a belt drive 21 on a belt pulley
22 fixedly
arranged on the holder 16 so that the holder 16 can be turned in relation to
the base 12,
thus altering the position of the functional element 2 mounted in the holder
16.
Also arranged on the holder 16 is a ring structure 25 which in turn serves as
holder for
the functional element 3. The ring structure 25 and holder 16 are connected to
each
other by a schematically shown ball bearing 26, with the result that the ring
25 can be
rotated in relation to the holder 15 (and also, of course, in relation to the
base 14). The
drive for the ring 25 is provided by a pinion 27 acting on internal toothing
28 on the inner
circumference of the ring 25. The pinion 27 is mounted on a shaft 24 which
extends
through an opening 29 in the holder 16. Shown schematically is a drive 30
mounted on
the holder 16 for the shaft 24, by means of which the relative position of the
ring 25 in
relation to the holder 16 can be altered:
The mounting of the ring 25 on the holder 16 and, in turn, the mounting of the
latter on
the base 12 are in effect a cascade arrangement, the ring 25 being mounted on
the
base 12 indirectly through the holder 16.
The processing path 4 and the reference point 14 are indicated in the lower
part of the
figure. The configuration of the functional units on the processing path 4
corresponds to
that of Figure 2a. However, the configuration of Figure 2c can be created
simply by
rotating the holder 12; in the figure, this would give the arrangement running
on the
processing path 4' drawn as a broken line.
The functional element 1 for its part can be mounted rotatably about its own
axis on the
base 12, for example where for image processing purposes the same defined
orientation in relation to the viewed section of the processing path 4 must be
maintained
at all times. This also applies to the mounting of the functional element 2 on
the holder
16, which may be fixed or rotatable. A fixed arrangement is possible if a
round laser
focus is used for welding the workplaces 10, 11; for an oval focus, a
constant, defined
orientation of the focus relative to the section of processing path is
necessary, hence
the functional element 2 will need to be rotatable as indicated by the an-ow
31. The
corresponding drive has been omitted to avoid unduly encumbering the drawing.
What
has just been stated in relation to the mounting of the functional elements
also applies
to the functional element 3; here again, the corresponding drive (or fixed
mounting as
the case may be) has been omitted from the figure for the sake of simplicity.
The mounting and rotational drive of the functional elements can be of
conventional
design and construction and will therefore not be described in detail here.
The pinion 27 co-operating with internal toothing 28 can of course also be
arranged on
an outer circumference 32 of the ring 25.
Figure 4a shows a device 13 for mounting functional elements 1, 2 and 3,
arranged on a
bridge 15. This means that the device 18 is held slidably in the transverse
direction with
respect to the longitudinal feed of the workplaces 10 and 11 indicated by the
double-
headed arrow 35. A diso-shaped holder 40 is mounted rotatably on the baseplate
12 of
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_ 7 _
the device 13. A motor 42 mounted on the base 12 imparts the required rotation
via a
belt drive 41. At the centre of the holder 40 in turn, and likewise rotatable
about its own
axis, the functional element 1 is mounted and is thus located in a defined and
spatially
frxed position in relation to the base 12.
Rotation of the functional element 1 is by means of a shaft 43 driven by a
motor 44. The
motor 44 is mounted on the base 12, but the corresponding arrangement has been
omitted from the drawing in the interest of clarity.
The functional element 2 is also mounted on the holder 40, but not centrally,
and so
changes its position in relation to the base 12 as the holder 40 rotates. A
secondary
holder 45 follows the rotation of the holder 40 and carries a drive 46 which
in turn, by a
schematically shown belt drive 47, causes the element 2 to rotate about its
own axis.
A further holder 50, which mounts the functional element 3, is arranged on the
mounting
of the functional element 2. A schematically indicated drive 51 acts via a
pinion 52 on a
toothed quadrant 53 to rotate the functional element 3 about its own axis. A
glass fibre
cable 39 for a jag laser arranged in the element 2 is merely suggested
schematically.
The holder 40 is configured as a body of revolution or ring; its axis of
symmetry 48
coincides with the operative line 49 of the functional unit 1; axis of
symmetry 48 and
operative line 49 pass through the workpieces at the location of the reference
point 14.
The device 13 illustrated in Figure 4a has the configuration of Figure 2b.
Figure 4b shows part of the arrangement of Figure 4a in cross-section.
The holder 40 is mounted on the base 12 via a schematically shown ball bearing
55.
The functional unit 1 is mounted by a bearing element 56 at the centre of the
holder 40
so that it does not itself participate in the tatter's rotation but is only
altered in its position
in relation to the base 12 by the drive 44. The sweeping holder 50 is mounted
in the
holder 40 and undergoes a change in position when the latter rotates. This
change in
position is also imparted to the functional element 2. The functional element
2 can be
rotated about its own axis by the drive 46, 47 shown in Figure 4a. The
functional
element 3 is mounted on the sweeping holder 50. The drive 52, 53, shown in
Figure 4a,
for rotating the functional element 3 has been omitted to clarify the figure.
Figure 5a shows a further embodiment of a device 13 for mounting the
functional
elements 1, 2 and 3. This shows a view from above of the device 13 and the
workpieces
10, 11 and processing path 4 underneath. The contour of the base 12 is
schematically
suggested by the broken outline, as is that of the bridge 15. In the figure, a
ring-shaped
holder 60 conceals similarly configured holders 61 and 62 arranged beneath it.
Thus
the holders 60, 61 and 62 are located over the base 12, vertically one above
the other,
and their axes of symmetry coincide and are perpendicular to the base 12. The
holder
60 is mounted on the base via guide rollers 63, 63' and 63" (see Figure 5b).
The holders
61 and 62 are mounted via guide rollers 64, 64' and 64" in the same way as the
holder
60 is mounted, and as shown in Figure 5b. The rings 60, 61 and 62 are thus
arranged
rotatably about their axis of symmetry on the base 12.
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Belt drives 66, 67 and 68 each act upon one of the holders 60, 61 and 62.
Pinions 69,
70 and 71 of the drives 66, 67 and 68 act on external toothing 72, 73 and 74
on the
corresponding ring 60, 61 and 62. The diameter of the pinion 69, 70, 71 is
preferably
made small in proportion to the diameter of the rings 60, 69 and 62. With this
gear
reduction, the rotation of the rings can be very precisely controlled, which
can be crucial
for proper operation of the functional elements.
The ring 60 has a segment 75 which supports the functional unit 2. The ring 61
has a
segment 76 for mounting the functional unit 2, and the ring 62 has a segment
77 for
mounting the functional unit 3. The operative line of the functional unit 1
passes through
the processing path 4 at the reference point 14, which has been omitted to
alleviate the
figure.
From the configuration shown in Figure 5a it can be seen that the functional
elements 1,
2 and 3 are arranged in the region inside the rings 60, 61 and 62, which means
that the
distances between them are unaffected by the design of the rings 60, 61 and 62
(apart
from their diameter, which can easily be increased if need be). The ring
structure also
means that guide rollers and drives for the rotation of the rings can be
arranged in the
outer region with the result that the whole of the inner space is available
for the
functional elements.
Consequently the structure shown is universally usable for simple and complex
processing paths, and for a single functional unit or a larger number of
functional units.
The minimum distance between the functional units is not governed by the
holder
structure but solely by the construction of the elements themselves.
Data exchange and power supply to the functional units can be effected via
cable or slip
rings. Slip rings may be arranged e.g. on an outer circumference, and have the
advantage that the rings can be rotated as desired without having to take
cable twisting
into account. Wireless data-transmission is of purse also feasible.
The configuration of the device 13 shown in Figure 5a corresponds to the
arrangement
of Figure 2c.
Figure 5b shows a cross-section through the ring 60, the guide rollers 63, 63'
(shown
opposite one another in the figure) and the base 12. The guide rollers run on
the outer
circumference of the holder 60, thus supporting it radially; at the.same time,
axial
support is given through the bevelled flanks by the matched contact faces of
the rollers
63, 63', with a form-fitting connection. The other rings 61 and 62 are omitted
to simplify
the figure, as are the drives 66, 67 and 68. Also shown schematically are the
functional
unit 2 with its operative line 2', and the axis of symmetry 75 of the ring 60.
The
workpieces 10, 11 also appear. The guide rollers 63 are freely rotatably
arranged on the
schematically shown guide roller holders 64, 64'. These holders 64, 64' are
mounted in
turn on the base 12. With this configuration, any number of rings can be
mounted one
above the other on the base 14 by means of the same mounting 64, by an-anging
a
number of guide rollers 63, 64 or 65.
Alternatively, the guide rollers may have toothing co-operating with the
extemai toothing
of the rings 60 to 63, with the advantage that separate drives 66 to 68 are no
longer
necessa ry.
CA 02426226 2003-04-22
9
:=figure 5c is a side view of the arrangement shown in Figures 5a and 5b.
Parts are
referred to by the same numbers as before. Bridge 15 and base 12 are omitted,
to
relieve the drawing.
Further embodiments can be configured as follows:
- e.g. arrangement as Figure 3 with ring 25 omitted so that only two
functional elements
can be used. The element 2 is arranged as in Figure 3 without modification,
whereas the
element 1 is not placed centrally in the holder 16, but offset, like the
element 2. When a
change in position occurs, the relative situation of the elements 1, 2 is not
altered, but
their position is. Thus, again, any desired processing path can be traversed
as relative
movement occurs between the workpieces 10, 11 and the device 13.
- e.g. arrangement as Figure 4a, a number of holders 50 being provided, with
these
holders linked at a common point and preferably having a common sweep axis.
- e.g. arrangement as Figure 4a, with the element 1 arranged on its shaft 43
with
provision for vertical adjustment and/or for tilting. Figure 6 shows
schematically the
element 1 In the configuration of Figure 4a, albeit not directly connected to
the shaft 43
but arranged on an auxiliary holder 70 so as to be tiltable at a tilting point
73 (see
double-headed arrow 75). Tilting drive is provided by a motor 71 via a pushrod
72. In
addition to the shaft 43, a threaded spindle 43' is provided which runs ~in a
mating part
43" of the auxiliary holder 70 and whose rotation causes a vertical shift of
the auxiliary
holder 70 as indicated by the double-headed arrow 74. Rotation of the
auxiliary holder
70 can be effected, as before, by the motor 44, here indicated in broken
lines.
