Apparatus and method for determining a distance measure on wound-up materials
Description
The present invention relates to an apparatus and a method for determining an overlap
length of wound-up materials, and particularly to how the overlaps, which may occur at the
end of winding up a material strip on a carrier body, can be determined reliably and with
high precision.
Apparatuses and/or methods in which the overlap length of materials wound and/or applied
onto a carrier in layers is to be determined are required in many applications.
For example, when laminating glass fiber mats or carbon fiber mats, the mats are applied
in layers, wherein the layers must not abut each other bluntly, but rather should have a
specified overlap for achieving maximum stability. This means that the new mat following
a mat already applied is to cover the applied mat by a predetermined length at its contact
area.
Similar problems may also arise when winding up band- or strip-shaped material on a
carrier or a drum or a base body. In some such cases of application, such as winding up a
cable and/or a winding of a coil or the like, it may also be necessary to determine the
overlap of the end of the wound cable with the underlying sheets, so as to obtain a coil
with a particularly homogenous magnetic field, for example, in which the overlap of the
last winding is approximately zero. This may be particularly relevant in coils with few
individual windings.
A broad field of application, for example, also is the manufacturing process of car tires,
wherein individual strip- or band-shaped rubber sheets are wound onto a base body, for
example, or to the casing already put up. For example, the base body may be a drum of
cylindrical geometry or another rotation-symmetrical body consisting of individual straight
segments, the circumference of which has a circular and/or cylindrical envelope. What is to
be achieved as a final product here is a tire having a thickness as constant as possible
perpendicular to its circumference, the wall thickness of which is thus as uniform as
possible so as to avoid height run-out in the finished product, for example. Typically, the
most diverse materials are combined with each other here so that, in some manufacturing
methods, band- and/or strip-shaped rubber strips of predetermined lengths are wound onto
a rotating carrier, wherein the end of the strip-shaped wound material may overlap with the
beginning of the same material strip. This overlap may be intended, but its overlap length,
i.e. generally speaking that region in which the beginning and the end of the same material
strip usually overlap, must satisfy exactly predefined geometric boundary conditions.
On the one hand, the length in the tangential direction, i.e. along the expansive dimension
or winding direction of the material strip, may here be regarded as the overlap length.
Alternatively, also the offset that may develop due to the fact that the material strip is not
superimposed identically at the beginning and at the end transversely to its winding
direction (in the width direction), i.e. in the axial direction parallel to the axis of the
rotating body, may also be regarded as the overlap length.
Generally speaking, it is often required to determine geometrical properties of the wound
material and/or the surface of the wound material. Among other things, negative overlap
lengths, i.e. gaps in the surface developing when the wound material is too short, may also
be of interest here. An offset of a wound material between the beginning and the end of the
winding also often has to be controlled. Generally, it is often required to determine a
distance measure between certain characteristic points of a wound-up material strip, as
well as the distance measure between the beginning (starting edge) and the end (end edge)
of the material strip, for example.
In other words, for example, various material sheets are wound successively onto a tire
construction drum in the production of vehicle tires, for example. Here, faulty overlap
lengths of the various materials may develop, which may significantly affect the
mechanical properties, and hence the stability, of the tire. Detection of such faulty
conditions, particularly of open splice (the gap or overlap between the beginning and the
end), and correction and/or segregation of such wound material is hence desirable. An
open splice is to be understood as the condition in which the material strip does not overlap
at all with the beginning of the material strip at its end, so that an area not covered by
wound material is obtained.
One difficulty in the measurement of the overlap length of overlapping materials is that
only the material end edge is still visible on the outside after the winding operation,
because the starting edge of the material itself is covered in the end and/or overlap area.
This results in the fact that it is not possible to perform exact measurement of the overlap
length merely due to the measurement of the overlap area itself.
Previously, for checking the overlap length during the industrial fabrication, for example
human examiners, who performed a subjective assessment of the overlap length after the
finished winding, were often employed. On the other hand, it has been attempted to
employ measurement methods and/or sensors working point by point, which generate a
binary output signal, i.e. in which the sensor itself immediately detects the presence of an
edge.
For example, this may be achieved by way of optical sensors, which react to the brightness
change caused by reflected light on a sensor. If a new sheet is applied and/or a sheet
overlaps, the point at which irradiated light is reflected approaches the stationary sensor so
that it detects an altogether increased radiation intensity. When a certain limit value is
exceeded, the detector then indicates the presence of an edge. Apart from the fact that such
a sensor works either point by point or that it is only possible to determine a few
measurement points this way in materials having a certain width, these binarily working
methods cannot be employed without extended control logic, among other things, in the
control of a frequently occurring scenario, the measurement of the overlap length of so-
called "blunt splices", i.e. of wound materials with a target overlap length of 0. In the
normal case of the desired seamless transition, such a sensor cannot detect an edge, so that
the following evaluation logic obtains an invalid input signal.
Even if the logic could interpret such a missing input signal correctly, applications in
which the wound material does not have any abrupt starting or end edge, e.g. because it is
chamfered, could not be controlled satisfactorily with such sensors. In some applications,
such an edge-detecting sensor is used to first detect the starting edge of the material strip to
be wound up during a winding process, wherein the associated angular position of the
drum is detected by means of an angular measurement means at the same time. After
winding up the material and/or during winding up, the end edge of the material strip is
detected after (approximately) a single drum revolution, and the associated angular
position of the drum is detected at the same time. From the difference of the two absolute
angular positions of the drum and the mandatorily previously known drum radius, the
length of the material strip is determined, and then the resulting overlap length of the
material is calculated if the drum circumference is known.
In some application scenarios partially already discussed briefly above, such a method
and/or such an apparatus implementing such a method cannot lead to any positive result. If
the material and/or the material beginning does not start abruptly with a perpendicular
edge, for example, but is cut flat (i.e. starts with a cutting angle in the tangential direction
of <45°, for example), unequivocal determination of a position value of the starting edge
cannot be performed. Frequently used angular drums and/or base bodies, which are
structured such that individual axially parallel segments alternate with interposed open
gaps, per se have a multiplicity of successive edge structures, so that the application of the
above-described method is not possible here. This is the case even in a continuous, i.e. for
example round surface of the winding drum if material strips already wound previously
have an overlap, and hence lead to an end edge.
In the "blunt splice" case of application and with obliquely cut material, recognition of the
material end edge, and hence measurement of the material overlap, is thus not possible
either, since the starting and end edges virtually join seamlessly in the error-free case, and
hence there is no detectable edge. When cut obliquely, a slight overlap, which leads to only
a minimal, but possibly already disturbing height difference, cannot be detected if the
height difference lies below the threshold value limit of the edge-sensitive method.
Basically, in these conventional methods, the end edges often cannot be determined and/or
unambiguously associated because of structures due to material overlap from the material
preparation, from the underlying sheets, and because of other spurious effects, such as
wrinkling, material structuring, drum structuring, etc. The detection of material properties
in the axial direction is not possible either in these methods.
Hence, there is the need to provide an apparatus and/or a method allowing for more
reliable measurement of wound-up materials strips with respect to geometrical features,
such as distance measures.
According to some embodiments of the present invention, this is made possible during the
winding of a material strip that is wound onto a body in a tangential direction by creating a
height profile of the surface of the material strip, covering both the beginning and the end
of the wound material strip in the tangential direction.
In the height profile, the position of the beginning and/or a position value for the beginning
of the material strip is then determined, so that a distance measure between the beginning
and the end of the material strip may then be determined precisely using this position and
the height profile covering the end.
It is to be pointed out that, in the following discussion, mainly an overlap of the wound
material strip is determined as the distance measure. This is done for reasons of simple
illustration. Nevertheless, any distance measure on the surface of the wound material strip
is, of course, to be understood by the term "distance measure", for example the distance of
the beginning and the end of the material strip if there is no overlap, i.e. if a gap in the
surface develops between the beginning and the end of the material strip. In general, the
distance measure and/or the value associated therewith may become positive, negative or
also zero, in arbitrary units or in SI units. If a distance measure of zero is determined, this
means a perfectly blunt splice, i.e. material wound together seamlessly. In many fields of
application, this represents the ideal. Of course, the term "distance measure" is not to be
limited exclusively to distances in a tangential direction, but rather arbitrary distance
measures in any orientation may also be determined and serve for quality control. For
example, an offset of the material strip in the axial direction, i.e. in the direction
perpendicular to the tangential direction, can be detected with some embodiments of the
inventive method and/or inventive apparatus.
Through the use of a height profile created in the tangential direction, it is possible to be
sensitive not only to abrupt edges, but to any form of the beginning of the wound material
strip, such as the flat incline of cut material. By creating a height profile, it is also made
possible to detect arbitrary (edge) shapes at the end of the material, and particularly also
positively detect the presence of a blunt splice. This is the case if no elevation or
depression shows in the height profile near the position of the beginning of the material
strip following a complete winding, i.e. the surface of the wound material strip does not
have any depression or superelevation.
Of course, in applications in which there is an overlap, the position of the end of the
material strip and/or an end edge of the material strip in the height profile may also be
determined with utmost accuracy.
In other words, the height profile determined distinguishes itself by having at least two, but
in some embodiments a multiplicity of height values in the tangential direction, which are
each associated with measurement positions (position values) and/or measurement
locations or pixels in a tangential direction. In the simplest case, a one-dimensional height
profile thus may be visualized by plotting the height measurement values versus the
measurement positions depicted on the X-axis of a coordinate system. Of course,
evaluation of the height profile is also possible without such visualization.
In some embodiments, a two-dimensional height profile is created, which may
conceptionally be understood as a plurality of one-dimensional height profiles extending
across the entire width (in a width direction) of the material strip to be measured, i.e. are
adjacent to each other in the axial direction (width direction). For example, this may be
achieved with a height sensor working line by line, which generates a plurality of
measurement points across the entire width.
In some embodiments, the height profile is created by contactless measurement. For
example, this has the advantage of quick and wearless measurement. In some
embodiments, a light sectioning measurement method is used for this, and spatially
resolved ultrasound distance methods or pulse echo methods can be used in other
embodiments. In other embodiments, tactile methods can be used, wherein a plurality of
adjacently arranged measurement sensors are arranged on the surface of the material strip,
for example, so as to record a height profile. In the methods, in general, a change in the
height of the wound-up material is detected, be it due to a variation of the distance of the
surface of the material strip to the detector observed or directly by scanning or the like. In
alternative embodiments, pressurized air sensors determining a change in distance to a
surface via a change in air pressure of a stream between material strips and the sensor may
also be employed.
In some embodiments, for reasons of computational savings, a height profile is created
only in the areas of the beginning and/or the end, with no height profile being created in
the area lying therebetween. The approximate position of the beginning and/or of the end
may, for example, be given to the measurement system by way of external trigger signals.
For example, the beginning of feeding the material strip onto the drum may be used to
commence a measurement operation including the beginning of the material strip, wherein
the knowledge of the rotation speed of the drum may again be used to predict the end
and/or the end time instant once the winding operation has started, in order to trigger the
creation of a height profile in the end region, which includes the end of the material strip in
any case.
Detecting the beginning or a starting edge as well as detecting and/or determining an end
or an end edge may here take place in the most diverse ways, since all relevant information
is present and may be evaluated due to the creation of the height profile. Here, it would be
a simple and not computationally intensive method to define a threshold value indicating
the presence of an edge if it is exceeded. For example, if a height difference exceeding the
threshold value is determined between two neighboring measurement positions, an edge
can be indicated and/or detected.
In alternative methods sensitive to more complicated starting forms of the material strip, a
parametrization and/or a function describing the edge or a start course may be fitted to the
height profile to infer the exact position from optimum parameters determined during the
fitting. For example, a staircase function with a smeared edge can be fitted to the height
profile, wherein the position of half the incline of the staircase function could be associated
with the position of the edge. This has the advantage that the height values in the
immediate surroundings of the position of the start or the end also contribute to the
determination of this position, and the accuracy of the position determination is increased
significantly thereby. Generally speaking, by at first creating a height profile, which
contains an object region of interest, such as the starting or end region, more information
may be used for finding the beginning or the end of the material strip than this is the case
in the previously employed methods. Accordingly, both the beginning and the end can be
found with greater accuracy and/or at all in the first place.
In further embodiments of the present invention, the two-dimensional height profile of the
surface of the material strip is recorded during a winding process, for example with the aid
of a light sectioning measurement method. In other words, this means that a two-
dimensional height profile having several measurement tracks is created, with each
measurement track containing a one-dimensional height profile along the tangential
direction. The measurement tracks generated are thus arranged in parallel and next to each
other in a direction running perpendicularly to the tangential direction. This means that the
entire width of the material strip to be wound up is detected simultaneously with a plurality
of measurement tracks, so that the information on the course of the beginning of the
material strip may be acquired across the entire width thereof in the reconstruction.
In the two-dimensional height profile thus created, basically any arbitrary surface structure
may be found and/or determined. The created height profile thus allows for a multiplicity
of measures for quality control.
Here, the detection accuracy may even be increased in various ways, for example by at
first determining separately, in one dimension, a position of the beginning and the end of
the material strip or each of the measurement tracks. By way of correlation between the
various measurement tracks, enhanced detection security of the material edge course
sought and/or the course of the beginning and of the end of the material strip can be
achieved. One example of this would be smoothing the edge course by weighting the
position and/or the position value found of the beginning or of the end with the position
values of neighboring measurement tracks for the currently considered pixels and/or for the
currently considered measurement track. Alternatively, simple consistency tests may also
take place, in which it is checked as to whether the position value found in the neighboring
measurement track lies within a sensible interval around the position value of the currently
considered measurement track. Furthermore, by creating a two-dimensional height profile,
it becomes possible to detect the course of the beginning or the end across the entire axial
width of the material strip. Hence, overlap lengths can be determined in a spatially
resolved manner, i.e. the overlap lengths partially varying strongly across the width of the
material strip can be measured accurately.
Furthermore, when creating a two-dimensional height profile, it is possible to determine
further measurement values in an axial or a width direction, such as the overall width of
the material strip, the material offset or acentricity. Furthermore, it is also possible to
determine the orientation of the splice angle, i.e. the orientation of the splice edge with
respect to the tangential or axial direction. Particularly in tire production, this is often
desirable because material strips which are cut pointedly, i.e. have an angle that may be up
to 80° or even greater with respect to the tangential direction, may be put on here. Even in
the case of a splice covering the entire circumference, the splice can be detected reliably in
its entire length when creating a two-dimensional height profile.
Furthermore, it is possible to recognize also other types of errors in the recorded height
profile. Examples of this may be folded-over material corners, wrinkles, an open splice at
the material edge and other irregularities.
Furthermore, by recording the height profile, it is not absolutely necessary to provide
control of the winding device originating from the apparatus for creating the height profile,
or, conversely, control of the apparatus for creating the height profile by the winding
device. This is due to the fact that a direct relation between the winding progress, i.e. the
absolute angular position of a winding drum for example, and the condition of the data
capturing detector or sensor creating the height profile does not have to exist at any time.
So as to allow for conversion of the initially dimensionless position values of the height
profiles into length values, at first it is only necessary for the individual height values in
the height profile to be captured in known portions - in a tangential direction. This may, for
example, be achieved by the winding means working at a constant rotational frequency,
while height values for the height profile are generated at constant time intervals
completely independently of the winding means. At a constant rotational speed of the
winding apparatus, the clocking of the individual capturing steps for creating a height
value can be determined freely. Then, the length scale in the height profile can be created
by way of a single geometrical factor, so that, without a direct connection between the
winding apparatus and a control device for determining the overlap length, it is possible to
determine the overlap length in absolute length units from the height profile with high
precision.
In summary, some embodiments of the present invention allow for secure detection of
starting and end edges or the beginning and the end of wound material strips, also in the
case of obliquely cut material edges and blunt splices. Creating a height profile here also
serves to avoid faulty measurement. In 2-dimensional height profiles, properties are also
determined in a non-tangential direction (e.g. material width, offset, measurement of the
splice angle and/or axial direction), and the detection of other winding faults (fold-over of
material corners, wrinkling, faulty preparation splices, etc.) is made possible. Some of the
embodiments of the present invention will be described in greater detail in the following
with reference to the accompanying figures, in which:
Fig. 1 shows an embodiment of a system for winding a material strip onto a body;
Fig. 2 shows an embodiment of a sensor device for creating a height profile;
Fig. 3 shows examples of a height profile determined by means of the sensor device
of Fig. 2;
Fig. 4a shows an example with a negative distance measure;
Fig. 4b shows a further example of a height profile;
Fig. 5 shows an alternative example of rotation means for winding a material strip;
and
Fig. 6 shows an embodiment of a method of determining a distance measure.
Fig. 1 shows an embodiment of a system allowing for winding a material strip onto a body,
wherein the system includes a control device for determining the overlap length of the
material strip wound onto the body.
Fig. 1 shows an example of a rotation means 2, which is suited for winding a material strip
4 onto a body in a tangential direction 6. In the simple example shown in Fig. 1, the
rotation means 2 consists of a cylindrical drum pivoted rotatably about a central axis 8, on
the surface of which the material strip 4 is being wound. The body, onto which the material
strip 4 is being wound, is thus formed by the rotation means 2 itself. In alternative
embodiments, however, the body may, of course, be formed separately from the device
causing the rotation.
The system further comprises a control device 10 for determining an overlap length of the
material strip 4 wound onto the body in the tangential direction 6. The control device 10
comprises a sensor device 12 suited to create a height profile of the surface of the material
strip covering a beginning 20 and an end 22 of the wound material strip 5 in the tangential
direction 6. In the example shown in Fig. 1, the sensor device 12 is implemented as a light
sectioning measurement means, which records a measurement light line 26 projected onto
the surface of the material strip 4 by means of a laser or another light source 24 and creates
a height profile of the surface of the material strip 4 therefrom, as will be explained in
greater detail in the subsequent figures. Briefly anticipating this explanation, the height
profile consists of a plurality of known measurement positions in a tangential direction and
height values respectively associated therewith.
Known measurement positions in the sense of the previous paragraph, for example, may be
equidistant measurement positions, i.e. a series of measurement positions having a
previously known, constant distance in a tangential direction. In other embodiments, the
measurement positions may indeed be known, but are not necessarily equidistant. Thus, for
example, the distance of neighboring measurement positions in the areas of particular
interest, in which an overlap and/or the beginning and the end of the material strip are
expected, may be chosen to be particularly small, in order to achieve high spatial resolution
at these locations. In the areas lying therebetween, in some embodiments of the present
invention, the spatial resolution is reduced in a tangential direction by increasing the
distance between neighboring measurement positions. This allows for observing the entire
surface at a reduced computational effort, in order to discover more severe faults, for
example, while employing the highest spatial resolution only in the areas of the distance
measure to be determined.
The control device 10 further includes evaluating means 30 to analyze the height profile
and determine a position value of the beginning of the material strip in the height profile.
In the embodiment shown in Fig. 1, the evaluating means 30 further comprises evaluation
or determining means (not illustrated) for determining the overlap length using the position
value of the beginning as well as the height profile covering the end of the material strip
when the material strip 4 is completely wound onto the body.
In the case shown in Fig. 1, the evaluating means and the evaluation or determining means
are thus combined in one housing, wherein the two may, for example, be implemented in
software or in dedicated computer hardware, in order to determine the overlap length of the
material strip, as described in the following figures, for example.
In the case shown in Fig. 1, the sensor device 12 is further coupled to the rotation means 2
to allow for synchronization. This coupling is optional, however, since direct coupling of
the rotations means 2 and the sensor device 12 is not necessary due to recording the height
profile, as long as both are operated in a stationary manner.
Furthermore, it is assumed in Fig. 1 that the light sectioning projection and/or the
projection of the measurement line 26 is generated by a laser 24 irradiating onto the
rotation means 32 in a radial direction. In alternative embodiments it is, of course, also
possible to vary the direction from which the measurement light projection is generated, in
order to increase the height resolution of the light sectioning measurement means, for
example.
Figs. 2 to 5 illustrate, on the basis of the system shown schematically in Fig. 1, how
embodiments of devices for determining an overlap length may be implemented to
recognize, with high precision, the overlap length of a material strip 4 wound onto the
body 2 in the tangential direction 4. Here, for reasons of generality, a light sectioning
measurement method allowing for creating a two-dimensional height profile of the surface
of the material strip 4 is illustrated. In this connection, it is to be mentioned that the
inventive advantages are also obtained in a one-dimensional implementation, so that in the
discussion of the height profiles, without limitation of generality, only one-dimensional
height profiles are discussed, in order to be able to clearly illustrate the concept underlying
the invention, without impeding the basic understanding through additional technical
complipations.
Figs. 2, 4a, 4b and 5 show further embodiments. In the figures, a two-dimensional
sectional view is shown of the apparatus shown in a perspective view in Fig. 1. The section
of the apparatus shown in Fig. 1 may be at an arbitrary position along the width direction
40 parallel to the rotation axis 8 of the rotation means 2, i.e. perpendicular to the tangential
direction 6.
Fig. 2 here shows, from top to bottom in this two-dimensional sectional view, three
different stages of the winding process and the individual captures respectively associated
therewith, which are assembled into a height profile passing in a tangential direction. Here,
the concept of the light sectioning measurement, by means of which the height profile is
created in this specific embodiment, will again be explained briefly.
The positions in the one-dimensional height profiles associated with the individual
positions I, II and III of the various partial images of Fig. 2 are also indicated in the height
profiles schematically illustrated in Fig. 3. Without limitation of generality, it is assumed
here that the laser 24 projects onto the cylindrical drum 2 in a radial direction. This
projection, particularly the light point or the light line generating a reflection of the laser
light on the surface of the drum 2 and/or the material strip 4 is recorded by means of the
sensor device 12, i.e. with a light sectioning camera. The light sectioning camera 12 here
records a two-dimensional image, which is characterized by the fact that the observed light
line is imaged at a certain position on the two-dimensional sensor (for example CCD or
CMOS). Here, the relative alignment between the sensor and the light projection is
typically chosen such that a direction (the X-axis) corresponds to the width direction 40,
whereas the Y-axis on the sensor corresponds to a provisional height value 42. In the
illustration shown in the upper partial image of Fig. 2, it is simplistically assumed that the
drum 2 is perfectly planar, i.e. the image in the sensor device 12 is a straight line 44. The
middle partial image shows a configuration in which the starting edge or the beginning of
the material strip 4 has been wound up to position 2. Due to the given geometry, in the case
of an otherwise perfectly planar surface, the projection of the light measurement strip on
the two-dimensional sensor will now yield a line 46, which corresponds to a greater
(provisional) height value.
For illustrating the principle, the imaging location 44 of the two-dimensional sensor
associated with the above configuration again is illustrated in dashed lines in the middle
illustration of Fig. 2.
The upper illustration of Fig. 3 shows the illustration corresponding to the middle
illustration of Fig. 2 of a one-dimensional height profile, which here is to be assumed to
correspond to the third pixel of the two-dimensional sensor, i.e. to x values between two
and three.
In other words, the illustration of the height profile shown at the top of Fig. 3 corresponds
to the multiplicity of height values measured at the equidistant positions when producing
the light sectioning capture. These position values are plotted on the X-axis of the height
profile 60 in arbitrary units. The height values plotted on the Y-axis may here, for example,
directly correspond to the (provisional) height values or pixel values determined on the 2-
dimensional sensor in the height direction 42. In other embodiments, it is also possible that
a conversion depending on the geometry of the arrangement in Fig. 2 of the height values
h' observed on the sensor into radial height changes has already been performed before the
height profile is created. Whether this is the case, will be neglected for the further
discussion, since all embodiments may be implemented on the basis of both alternatives.
As can be taken from the above illustration of Fig. 3, the height value at position 1,
corresponding to the 2-dimensional illustration of the measured line 44, is small, while
rising to an again approximately constant level up to position 2, wherein the increase
happens abruptly, as shown in Fig. 3, in the case of a sharp edge of the material strip 4
illustrated in Fig. 2, so that altogether the height profile shown at the top of Fig. 3 is
obtained.
A position value of the beginning of the material strip 4 can now be determined directly
from this height course with high precision, for example by using a threshold value
criterion or fitting a suitable function and/or parametrization. The position value may here
at first be determined in arbitrary, dimensionless units, wherein conversion into a length
value in SI units on the basis of a geometrical factor may, for example, take place prior to
creating the height profile or only after determining the overlap length. For example, if
working at a constant image capture frequency at a constant rotational speed of the rotation
means 2, this geometrical factor results from the number of captures per revolution and the
radius of the rotation device, corrected by the change of the radius caused by material
strips already wound onto the rotation device or body, if applicable.
A further example of how the position of an edge or an edge course can be determined is to
determine and evaluate the gradient of the height profile. If the magnitude of the gradient
exceeds a maximum or threshold value, it can be inferred therefrom that a jump in height is
present, for example an edge. (The sign of the gradient may, for example, be used to
determine the type of the edge.) In alternative embodiments, a window may further be set
for the magnitude of the gradient, wherein, as a criterion for the presence of an edge or a
beginning or an end a window, a window within which the magnitude of the gradient is to
lie is determined. Thereby, it is made possible to separate other artifacts from the
beginning and/or the end of a material strip. For example, certain materials may protrude
steeply from the circumference of the wound material, so that the derivative at this location
lies far above the threshold for a "normal" edge. By setting a window, such artifacts can be
taken into account by then no longer leading to the detection of an edge. Additionally, in
some embodiments, the orientation of the gradient vector can be used to further increase
the accuracy of the edge detection.
In embodiments with one-dimensional height profiles, a derivative of the height profile can
be performed in a tangential direction, so that when the derivative of the height profile
exceeds a maximum value at a certain location, it may be inferred therefrom that there is a
height jump, i.e. an edge.
This geometrical factor hence could also be referred to as a tangential measurement
resolution.
If, differing from the embodiment shown in Fig. 2, a light sectioning measurement means
or light source 24 not projecting in a radial direction onto the surface of the material strip 4
were used, the tangential shift due to the non-radial irradiation of the laser can be taken
into account for increasing the measurement accuracy. This results from the fact that the
diameter of the wound material increases from sheet to sheet. For example, if a height
value H1(P1) associated with the position value is assumed for the pixel P1 and/or the
position value P1 associated with the starting edge, and a height value H2(P2) for the pixel
P2 associated with the end edge or the end, i.e. the height difference is ?H = H1 (P1) - H2
(P2), simple geometrical considerations lead to a correction value of K = ?H x TAN (a).
The bottom illustration of Fig. 2 exemplarily shows a situation as it arises after completely
winding up a material strip 4, wherein the lower illustration in Fig. 3 shows the height
profile corresponding to the complete winding. As can be taken from Fig. 3, at the end of
the measurement, i.e. after a height profile covering the end of the wound materials strip
was created, the height profile is again at a level lower than the maximum level observed,
which is due to the observed overlap area. This means that the height profile has the
overlap and/or the jump marking the beginning of the overlap at the position 66, at which
the material strip overlaps with itself, wherein the height profile again drops to the level
before the beginning of the overlap after the end of the winding operation and/or with the
end of the material strip, because the laser light now is only scattered by the surface of the
material strip wound once. The overlap and/or the overlap length may thus be determined
as the distance measure 68 with high precision. Here, both the measure in the height profile
and on the surface of the material is understood as the distance measure.
In the lower illustration of Fig. 2, this fact is outlined by the height value reached prior to
the end of the capture as a maximum being illustrated in dashed lines in the 2-dimensional
sensor capture of the lower illustration.
As can be taken from the description in Figs. 1 to 3, in some embodiments of the invention
a system for generating measurement data allowing for the creation of a height profile
during the winding operation is thus employed. The measurement system works with an
internally (free-running) or externally triggered measurement camera, wherein the
individual measurements take place in equidistant or known step sizes on the material
and/or on the drum casing area or the surface of the wound material strip. Here, the sensor
and/or the measurement system may be operated at a constant measurement frequency, i.e.
without an external trigger impulse, or the measurement may be triggered externally, for
example by a small wheel running along on the circumference of the rotation means and/or
the drum 2 so that the recorded data have a known tangential measurement distance to the
material to be examined. Alternatively, a rotation indicator built in the drum 2, which
triggers the individual captures, may be used. In alternative embodiments, a geometrical
measurement system measuring line by line, such as a laser light sectioning measurement
system, is used, which not only allows for one-dimensional display and/or the one-
dimensional creation of a height profile, but permits complete 2D detection of the winding
drum and of the material during the winding operation. This measurement system may also
work with an internally (free-running) or externally triggered measurement camera, so that
it is ensured that the line-by-line measurements are equidistant and/or correspond to known
locations, i.e. correspond to known step sizes on the material and/or on the drum casing
area.
The secure detection of the material edge and/or the end of the material strip is based on
the fact that the complete information is present in the form of a height profile, and that a
special evaluation algorithm capable of detecting an edge and/or a material step or the
beginning and end may be used. This evaluation algorithmics does not work point by point
on the basis of a single measurement point, but is applied to composite "height data", i.e. to
height profiles, which may be created in one or in two dimensions. Hence, the evaluation is
performed asynchronously after the data capture.
In some embodiments, the evaluation of the height profile may be commenced already
with the beginning of the winding operation, and/or as soon as the height profile covering
the beginning of the material strip has been created. The complete evaluation, however,
takes place only after completion of the entire winding operation and/or when the end of
the material strip is included in the height profile.
Ideally, an end edge cannot be detected in a butt-wound material strip and/or material strip
overlapping with chamfered edges, since it is exactly the aim of this kind of winding of the
material strip to prevent the occurrence of such an edge. In contrast to conventional, point-
wise and/or threshold-value-comparison-based measurement methods, in some
embodiments of the invention, here a positive acknowledgement of the winding process
can be performed in that it is observed that a homogenous and smooth surface exists in the
area in which the end of the material strip is expected. This may be verified because the
complete height information and/or a complete height profile of the material strip is
available.
Hence, the detection accuracy and/or the precision of the control of the winding progress
can be increased significantly as opposed to such methods directed at the detection of an
edge and drawing the conclusion that the winding has taken place seamlessly only in case
of the non-detection thereof. Since the detection of an edge, which such systems are
focused on, requires exceeding a threshold value, these systems are clearly less sensitive in
seamlessly wound or obliquely overlapping starting and end areas. This means that small
jumps in height, which may occur in the case of imperfect winding, remain undiscovered
in the conventional systems.
In other words, for some examples of the automatic recognition of the end of the material
strip and/or the material end edge described here, use is made of the finding that the
material end edge sought can only be localized for a certain tolerable range near the
starting edge plus one exact drum revolution, so that it may be logically distinguished
between the material end edge sought or the end of the material and other artifact
structures (as far as these occur). When using a 2-dimensional geometrical measurement
method, further improvement in the edge detection security can be achieved by additional
correlation of the measurement points of various neighboring measurement tracks, as
already described in the previous paragraphs.
In summary, the algorithm used for the evaluation of the measurement data can be
summarized briefly as follows. At first, a position value and/or a pixel coordinate for the
beginning or the starting edge P1(n) is determined in the height profile. Here, for reducing
the computational sensitivity, the search for this edge may be limited to an area within
which the beginning of the material strip must lie due to the geometrical framework
conditions.
In some embodiments, the expected pixel position and/or the expected position value of the
end and/or the end edge may then be extrapolated from the position value P1(n) by the
addition of a complete revolution to a position value P1'(n).
Then, analysis of the position value in the surrounding of the extrapolated position value
P1'(n) is performed to determine the end and/or, if present, an end edge P2(n) and/or an end
value associated therewith.
The tangential distance T(n) may be determined from these two position values either
directly in metric units or in units of position values. In the one case, the difference T(n) of
the position values is to be determined directly, in the case of metric units this difference
may also be multiplied by the tangential measurement resolution A.
Unless the laser light projection is in a radial direction, the overlap length may still be
corrected by the correction value K(n), which is due to the tangential shift of the
determined edge positions.
Fig. 4a shows a case of application in which a negative distance measure 68 is determined,
since the material strip does not overlap itself at its end, but a gap remains between the
starting edge and the end edge and/or between the beginning and the end of the material
strip. As can be seen in the height profile illustrated in Fig. 4a, in this case the height level
in the height profile again falls back to the initial value in the area associated with the
distance measure 68, because there is no additionally wound material here. By way of the
above-described evaluation of the complete information in the height profile, it is easily
possible to determine a distance measure also in the case of a gap. Whether this is
distinguished from the case of the overlap by positive or negative signs is convention. Both
alternatives are possible.
Furthermore, Fig. 4a shows that the laser does not necessarily have to irradiate radially
onto the surface of the material. Rather, in some embodiments, it may be advantageous for
laser and/or measurement light projections not to be generated in a radial direction, in
order to enhance the height resolution. For the same reason, it is also possible to arrange
the camera, by means of which the light projection is observed, in arbitrary angles relative
to the radial direction. Furthermore, in some embodiments, the light measurement strip
may not run axially, i.e. parallel to the width direction, on the surface of the wound
material strip, as indicated in the previous figures. Rather, an arbitrary angle of this light
measurement strip with respect to the width and/or axial direction is possible. Thereby, in
some embodiments, the height resolution may be enhanced further in the evaluation
because, even in the case of an edge wound in parallel to the width direction, the projection
of the light measurement beam on a 2-dimensional sensor is imaged in different pixel lines
for respectively neighboring measurement tracks due to the "tilted" light measurement
beam. Thereby, in some embodiments, additional interpolation between the pixel positions
on the sensor may be used so as to even enhance the height resolution if the laser beam is
tilted.
Figs. 4b and 5 show two further measurement scenarios, wherein the edge course can be
determined reliably only through the employment of the inventive method and/or through
the use of an inventive apparatus, since there are boundary conditions complicating the
geometry. In the example shown in Fig. 4b, the example of a material strip 4 the front and
maybe also the rear edge of which is chamfered is illustrated, as already partially discussed
in the preceding paragraphs. In the case shown in Fig. 4b, the beginning of the winding-up
of a material strip 4 with a chamfered edge is illustrated in the upper image, wherein the
lower illustration shows the one-dimensional height profile corresponding thereto. As can
be taken from the illustration, the relative change in height and/or the relative change of the
height values in the height profile is comparably small in the starting area 70, in which the
material strip is chamfered, so that the edge detection, which aims at the change of
neighboring height measurement points and/or jumps in height, will have difficulties with
determining the exact position of the edge here.
By way of the evaluation of the height profile, it becomes possible to use the complete
information of the analysis as a basis for defining such a criterion adapted to the
application. For example, when fitting a parametrization to the height profile, the
beginning may be defined as the actual beginning of the strip, or also as half the increase in
the height profile, if this is more appropriate for the purposes to be achieved.
Fig. 5 shows a configuration that frequently occurs in practice, in which a material strip
from elastic material, such as rubber, is wound onto a surface that is not perfectly
cylindrical. Rather, eight linear segments 80a to 80d (wherein this number may vary
arbitrarily), the distance d of which to a rotation center may be varied to change the
diameter of the body onto which the material strip is being wound are used in Fig. 5. Here,
upon completed winding, the cylindrical geometry is produced by the self-elasticity of the
material used.
In such an application scenario, the use of conventional methods, which aim at detecting
only an edge, is impossible. This is due to the fact that the body used for winding itself
already has a plurality of edges, for example between the segments 80a and 80b, which
would each be found by the edge-based methods. Due to the multiplicity of such edges, no
sensible statement on the wound material itself is possible any more. Even when the edges
have already been covered by a sheet of wound material, sensible evaluation is not possible
with these conventional methods, because edges in the wound material strip, which could
again erroneously lead to interpreting this edge as an end edge of the material strip, are
each caused in the wound material strip by the section-wise linear segments at the segment
boundaries. If the height profile is known, individual contributions may be distinguished
reliably, however.
In summary, a system for winding a material strip onto a body in a tangential direction thus
may be characterized as follows, for example:
* Example of an instrumental prerequisite of the entire system:
- Supply means
- Winding drum
- Sensor for line-wise measurement of the radial height change of the drum (3D
geometrical measurement system)
- The sensor is triggered internally (free-running at constant measurement
frequency) or externally (e.g. with a distance indicator on the drum), so that the
captured data have a known tangential measurement distance on the material to
be examined. (An external triggering impulse of the capture may, for example,
be generated by a little wheel running along on the drum surface. Alternatively,
a rotation indicator directly connected to the winding drum may be used. The
tangential measurement resolution may, for example, be calibrated by means of
suitable apparatuses and methods prior to the actual measurement.)
* Start of the winding operation and start of the line-wise recording of the 3D height
data of a measurement sensor.
* Transmission of the measurement data to an evaluation unit either in portions or
completely following the capture, and assembling the measurement data to an overall
representation.
* Detection of the pixel coordinates of the starting edge Pl(n) in all measurement
tracks n in the overall representation or in the partial representations by 1- or 2-
dimensional edge detection algorithms on the evaluating unit, possibly also using a-
priori information on the expected pixel position of the starting edge and its angular
orientation with respect to the axial direction.
* Extrapolation of the pixel coordinates Pl(n) of the starting edge to the pixel position
of the starting edge after one revolution of the drum Pl'(n);
* Detection of the pixel coordinates of the end edge P2(n) in the direct surrounding of
the pixel positions P1'(n);
* Determination of the difference values D(n) of the coordinates P1'(n) and P2(n);
* Determination of the tangential distances T(n) in metric units, corresponding to the
difference values D(n), by multiplication of the difference values D(n) by the
tangential measurement resolution A;
* If applicable, correction K(n) of T(n) due to tangential shift of the determined edge
positions in case of a non-zero angle between surface normal and angle of incidence
of the laser (only for laser light sectioning).
* Calculation of the overlap length values in a tangential direction U(n) + K(n).
* Calculation of the overlap length perpendicular to the material edge by projection of
the overlap length in the edge direction with the aid of cos(a); a is the angle between
the axial direction and the material edge.
An embodiment, underlying the instrumental realization, of a method of determining an
overlap length of a material strip wound onto a body in a tangential direction may be
characterized as follows, as also illustrated on the basis of Fig. 6.
In a profile step 100, at first a height profile of a surface of the material strip, which covers
the beginning and the end of the wound material strip in the tangential direction, is created.
In a detection step 102, a position value of the beginning of the material strip is determined
in the height profile.
In an evaluating step 104, the overlap length of the material strip is determined on the basis
of the determined position value of the beginning and the height profile covering the end of
the material strip.
Although a few possibilities of edge detection have been discussed on the basis of the
previous embodiments, of course it is possible to apply further criteria within the height
profile, in order to detect an edge and/or the beginning of a material strip. For example, the
surroundings of all captured measurement points can be examined and evaluated with
respect to a change in the slope. For example, edges would then be determined by the fact
that this change in slope has a relative maximum value.
In 2-dimensional height profiles, the correlation between axially (i.e. in the width
direction) neighboring edge detection results may be provided in a sensor capturing in a
line-wise manner. Thereby, potentially faulty values, i.e. erroneously detected edge
position values, may be blocked out logically (for example loose threads). Furthermore, the
group of points of the detected edge position values may be combined into a common
curve which may be smoothed as a whole by means of further evaluating operations. The
smoothing reduces the remaining noise, i.e. potential measurement inaccuracies, among
other things. Furthermore, although not expressly shown in the previously described
embodiments, a special light sectioning measurement camera can be used, which performs
pre-evaluation of the two-dimensional image of the sensor element matrix so as to output,
per measurement track (column of the detector), only that pixel value and/or height value
corresponding to the position of the light measurement strip in the sensor element matrix,
for example.
In some further embodiments, the result values of the overlap lengths may also be
combined to an overall curve, which may be supplied to further logical or quality checks,
for example for evaluating tolerance overshoots within a certain evaluation interval.
When using materials and/or material strips having no "perpendicular", but chamfered
cutting edges in the splice area, the position and/or the position value corresponding to the
"upper" transition between an oblique cutting area and a "flat" strip surface can be
determined by means of the evaluating algorithmics. Such materials are often wound in a
"blunt splice", i.e. with a splice overlap of zero length.
For such a case of intentional blunt splice, ideally no material end edge can be detected,
since the material joins practically seamlessly. In some embodiments, the material end
edge may hence be searched for within a certain tolerance window around the expected
position, and in case of failed edge detection and/or in case of a steady, smooth surface
area and/or height profile in this region, it may be inferred therefrom that the blunt splice
has been wound as desired. When employing a sensor with a multiplicity of measurement
tracks across the axial width, the material strip can be sensed across the entire axial width.
In this case, not only the measurement of the overlap length, but also, e.g., the detection of
the lateral edges of the material strip is possible, which may be used for determining the
material width, the axial offset of the material, folded-over material edges, partially open
splice and splice angles relative to the axial direction.
In further embodiments, on the basis of the 2-dimensional height profile, the distance
measure and/or the overlap can be determined alone with the knowledge of the part of the
height profile covering the beginning and the end of the wound material strip, for example
by fitting a suitable parametrization of a 2-dimensional height profile to this area. From the
parameters determined by fitting, the distance measure of the overlap can be determined,
without directly observing the placement of the material strip (the production of a
beginning and/or a starting edge) in the height profile. Only the part of the next sheet
covering the beginning is detected in the height profile, wherein the underlying beginning
and/or its position value can be determined with suitable parametrization.
Given a suitable choice of the geometry, a spatial resolution in a tangential direction better
than 0.5 mm, according to further embodiments even better than 0.25 mm, can be
generated by embodiments of the inventive method and/or when using embodiments of
inventive apparatuses. Depending on the number of measurement tracks, i.e. depending on
the sensor and/or light sectioning sensor used or tactile measurement methods, the
resolution in the width direction can be adapted variably to the requirements by using
either another imaging scale, sensors with higher resolution and/or a greater number of
tactile sensors. Thus, for example, spatial resolutions better than 0.5 mm or even better
than 0.25 mm can be achieved with some embodiments of the invention.
Likewise, by way of the suitable choice of the sensor and/or the geometry of the light
sectioning measurement method, a height resolution better than 0.5 mm or even better than
0.1 mm can be achieved when the thickness of the material strips to be examined varies
between 1 mm and 10 mm. Generally speaking, a height resolution at least 5 or 10 times
greater than the thickness of a material examined can be achieved.
Depending on the conditions, embodiments of the inventive method of determining an
overlap length of a material strip wound onto a body in a tangential direction may
implemented in hardware or in software. The implementation may be on a digital storage
medium, particularly a disk or CD with electronically readable control signals capable of
cooperating with a programmable computer system so that an embodiment of the method
of determining an overlap length of a material strip wound onto a body in a tangential
direction is executed. In general, the invention thus also consists in a computer program
product having program code stored on a machine-readable carrier for performing the
method, when the computer program product is executed on a computer. In other words,
the invention may thus also be realized as a computer program having program code for
performing the method, when the computer program is executed on a computer.

WE CLAIM
1. Method of determining a distance measure between a beginning and an end of a
material strip (4) wound onto a body in a tangential direction (6) by a winding
operation, comprising:
creating a height profile (60) of a surface of the material strip (4), which covers the
beginning (20) and the end (22) of the wound material strip (4) in the tangential
direction (6);
determining a position value (P1(n)) of the beginning (20) of the material strip (4) in
the created height profile (60); and
determining the distance measured by using the position value of the beginning (20)
and the height profile (60) covering the end (22) of the material strip (4),
wherein the height profile (60) is created during the winding operation, wherein
height information associated with respective position values is determined and
stored for a plurality of position values known or being equidistant in a tangential
direction, and
wherein the step of determining comprises extrapolating the position value (P1(n)) of
the beginning (20) of the material strip (4) to an extrapolated position value (P1'(n))
by adding a complete revolution of the body to the position value (P1(n)), performing
an analysis of the position values only in a range surrounding the extrapolated
position value (P1'(n)) in order to find a position value (P2(n)) of the end (22) of the
material strip (4), so that the end (22) of the material strip is logically distinguished
from artifacts occurring outside of the range surrounding the extrapolated position
value (P1'(n)), and determining, as the distance measure, a tangential distance (T(n))
between the position value (P1(n)) of the beginning (20) of the material strip (4) and
the position value (P2(n)) of the end (22) of the material strip (4).
2. Method according to claim 1 or 2, wherein no height profile (60) is created in an
intermediate area lying between the beginning (20) and the end (22) of the material
strip (4) in a tangential direction.
3. Method according to claim 1, wherein a position value of a starting or end edge is
determined in the height profile (60) if the absolute value of a difference of the
height values of two position values adjacent in a tangential direction in the height
profile (60) exceeds a predetermined maximum value.
4. Method according to claim 1, wherein determining a position value of a starting or
end edge includes forming a derivative of the height profile.
5. Method according to claim 1, wherein a position value for a starting or end edge is
determined if the value of the derivative of the height profile satisfies a threshold
value criterion or lies within a predetermined interval.
6. Method according to one of claims 1 or 3, wherein when determining the position
values of the starting or the end edge, a parameterization describing an edge course is
fitted to the height profile (60).
7. Method according to one of the preceding claims, wherein when determining the
distance measure, a length value is generated from the position values of the
beginning (20) and of the end (22), taking a geometrical correction value into
account.
8. Method according to claim 7, wherein when determining the distance measure, a
difference of the position values of the beginning (20) and of the end (22) is
combined with the correction value.
9. Method according to one of the preceding claims, wherein the height profile (60) is
created by means of a contactless or tactile measurement method.
10. Method according to claim 9, wherein the measurement method is a light sectioning
measurement method.
11. Method according to one of the preceding claims, wherein a two-dimensional height
profile (60) comprising height values for a plurality of measurement tracks is created,
wherein the plurality of measurement tracks are arranged adjacently with respect to
each other in a width direction passing perpendicularly to the tangential direction (6).
12. Method according to claim 11, wherein for determining a height value associated
with a measurement track at a predetermined position value, additional height
information, associated with the predetermined tangential position value, of a
measurement track adjacent in the width direction is taken into account.
13. Method according to claims 11 or 12, wherein, for determining the position value of
the beginning (20) or of the end (22), a parameterization describing a line or area is
fitted to the two-dimensional height profile (60).
14. Method according to one of claims 11 or 12, wherein determining the position value
of the beginning (20) and/or the end (22) comprises:
determining a provisional position value of the beginning (20) and/or the end (22) for
each of the measurement tracks of the 2-dimensional height profile (60); and
determining the position value of the beginning (20) and/or the end (22) by
combination of the provisional position value with the provisional position value of
at least one of the measurement tracks immediately adjacent in the width direction.
15. Apparatus for determining a distance measure between a beginning and an end of a
material strip (4) wound onto a body in a tangential direction (6) by a winding
operation, comprising:
a sensor device formed to create a height profile (60) of a surface of the material strip
(4), which covers the beginning (20) and the end (22) of the wound material strip (4)
in a tangential direction;
evaluating means formed to analyze the height profile (60) so as to determine a
position value (P1(n)) of the beginning (20) of the material strip (4) in the height
profile (60); and
determining means formed to determine the distance measure using the position
value of the beginning (20) and the height profile (60) covering the end (22) of the
material strip (4);
wherein the height profile (60) is created during the winding operation, wherein
height information associated with respective position values is determined and
stored for a plurality of position values known or being equidistant in a tangential
direction, and
wherein the determining means is configured to extrapolate the position value (P1(n)
of the beginning (20) of the material strip (4) to an extrapolated position value (P1'(n))
by adding a complete revolution of the body to the position value (P1(n)), to perform
an analysis of the position values only in a range surrounding the extrapolated
position value (P1'(n)) in order to find a position value (Pi(n)) of the end (22) of the
material strip (4), so that the end (22) of the material strip is logically distinguished
from artifacts occurring outside of the range surrounding the extrapolated position
value (P1'(n)), and to determine, as the distance measure, a tangential distance (T(n))
between the position value (P1(n)) of the beginning (20) of the material strip (4) and
the position value (P2(n)) of the end (22) of the material strip (4).
16. Computer program with a program code for performing the method according to one
of claims 1 to 18, when the program is executed on a computer.
17. System for winding a material strip (4) onto a body in a tangential direction (6) by a
winding operation, comprising:
rotation means (2) coupled to the body and formed to set the body to rotation in a
tangential direction (6) and wind up the material strip (4); and
a control device (10) for determining a distance measure between a beginning and an
end of the material strip (4) wound onto the body in the tangential direction (6),
comprising:
a sensor device formed to create a height profile (60) of a surface of the material strip
(4), which covers the beginning (20) and the end (22) of the wound material strip (4)
in a tangential direction (6);
evaluating means formed to analyze the height profile (60) so as to determine a
position value (P1(n)) of the beginning (20) of the material strip (4) in the height
profile (60); and
determining means formed to determine the distance measure using the position
value of the beginning (20) and the height profile (60) covering the end (22) of the
material strip (4),
wherein the height profile (60) is created during the winding operation, wherein
height information associated with respective position values is determined and
stored for a plurality of position values known or being equidistant in a tangential
direction, and
wherein the determining means is configured to extrapolate the position value (P1(n))
of the beginning (20) of the material strip (4) to an extrapolated position value (P1(n))
by adding a complete revolution of the body to the position value (P1(n)), to perform
an analysis of the position values only in a range surrounding the extrapolated
position value (P1'(n)) in order to find a position value (P2(n)) of the end (22) of the
material strip (4), so that the end (22) of the material strip is logically distinguished
from artifacts occurring outside of the range surrounding the extrapolated position
value (P1'(n)), and to determine, as the distance measure, a tangential distance (T(n))
between the position value (P1(n)) of the beginning (20) of the material strip (4) and
the position value (P2(n)) of the end (22) of the material strip (4).

A distance measure between a beginning and an end of a material strip (4) wound onto a
body in a tangential direction (6) can be determined by creating a height profile (60) of a
surface of the material strip (4), which covers the beginning (20) and the end of the wound
material strip (4) in the tangential direction (6). If a position value of the beginning (20) of
the material strip (4) is determined in the created height profile (60), the distance measure
can be determined using this position value and the height profile (60) covering the end of
the material strip (4).