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"Method and device to discriminate two ends of an article from each other"
DESCRIPTION
Technical Field
The present invention relates to improvements to methods and to
devices for handling articles having a longitudinal extension and two ends
that
differ from each other, for example and in particular tubular knitted articles
such as stockings or socks.
More specifically, the present invention relates to a new method and a
new device to detect, i.e. distinguish or discriminate from each other two
ends
of the same article that differ in shape from each other, such as, in
particular
although not exclusively, a sock or stocking or other tubular knitted article.
State of the Art
In the manufacture of stockings and socks it is the trend to increasingly
use automation of production processes, starting from knitting of the article
up
to sewing of the toe.
In this trend towards automation, one of the most critical aspects is
represented by the difficulty in automatically detecting which of the two ends
of a tubular article, such as a sock delivered from a circular knitting
machine
with the toe open and placed randomly in a container, is the band end and
which is the toe, to allow subsequent automated handling of the article in the
sewing machines.
Frequently, these operations are performed by hand: an operator picks
up the individual semi-finished articles from a container, such as a basket,
in
which the semi-finished articles coming from knitting machines are placed
randomly with the toe end still open, i.e. not yet sewn or linked. The
operator
then inserts the semi-finished article onto a conveying tube oriented in the
correct direction, i.e. in the position required by the machinery downstream,
which will automatically perform sewing or linking of the toe.
Attempts have been made to solve the problem of automating detection,
i.e. discrimination, of the elastic band end and toe of semi-finished knitted
articles. For example, US-A-5,040,475 describes a complex machine -that
picks up individual tubular articles from a container in which these are
placed
randomly. By making the article follow a specific processing path, detection
means first detect the orientation of the tubular article along the feed path,
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identifying whether the article is oriented with the toe or with the elastic
band
end facing forward along said path. After this has been detected, the tubular
article is disposed in an intermediate station, from which it is delivered in
one
direction or in the opposite direction as a function of the orientation with
which
it entered said station.
JP-A-7468502 and JP-A-1272801 describe other apparatus for handling
tubular articles such as stockings or socks in order to orient them
appropriately.
US-A-6719577 describes a device that longitudinally orients individual
tubular articles coming from a container, in which they are placed randomly.
EP-A-1221502 describes a device in which the individual socks or other
tubular articles are picked up from a container in which they are placed
randomly and are then oriented so that one of the ends thereof is always the
leading end by means of a particular pneumatic path and using detection
systems capable of distinguishing the elastic band end from the toe of the
article through different stretch characteristics of the fabric.
US-A-5769286 describes a spreading device for longitudinally spreading
socks or other tubular knitted articles.
EP-A-178143 describes a further system to detect the orientation of a
tubular textile article by distinguishing the elastic band end from the toe.
US-A-5511501 describes a complex machine that picks up individual
tubular articles from a container, in which they are placed randomly and
separates them placing each individual tubular article in a respective
container
of smaller dimensions. Subsequently, each article is picked up from the
respective container of smaller dimensions and inserted in a specific
pneumatic path inside which the tubular article is oriented so that it is
delivered from the pneumatic path always with the same orientation.
US-A-5884822 describes a further device and a method to pick up
individual tubular articles from a container.
US-A-5992712 describes yet another device to pick up individual tubular
knitted articles and orient them appropriately.
Similar problems of orientation of tubular articles can be found in the
feed of stockings or socks to setting machines. For example, in producing
feminine stockings, there is the problem of inserting each single stocking,
with
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the toe already sewed, onto a setting board and for this purpose the
individual
stockings must be picked up from a container in which they are placed
randomly to insert them over the board.
The methods and devices currently known to automatically distinguish
from one another a first end and a second end of an article, such as a tubular
knitted article, are not particularly reliable and are costly.
Objects and summary of the invention
An object of an embodiment of the present invention is to provide a
method and a device that allow detection, i.e. automatic distinguishing from
each other of the two ends of an article, which has ends that differ in shape
from each other. According to a particular aspect, the object of the invention
is
to provide a method and a device which allow the toe or the elastic band end
of a sock or stocking to be distinguished and detected.
Although in the present description reference is frequently made to the
need to detect the toe of the sock still to be sewn, it must be understood
that
the teachings of the present invention can also be applied when the
orientation of an already sewn article shall be detected, for example to
perform thereon further operations required in the production and/or
packaging cycle, such as orienting the article correctly before it is placed
on
setting boards, feeding the packaging machine or the like.
In substance, in an embodiment of the invention there is provided a
method for distinguishing from each other, i.e. for discriminating one from
the
other a first end and a second end of an elongated article, comprising the
steps of: generating a curve that approximates the profile of one of said
ends;
and processing said curve to detect whether it approximates the profile of
said
first or of said second end.
In substance, according to this aspect of the invention, there is provided
the generation by points of a curve that approximates the real profile of one
of
the two ends of the article, i.e. the one that is presented to the reading
sensors. On the basis of the conformation of this approximation curve the
device is able to detect whether this end is the first or the second of two
ends
characterized by profiles which are substantially different from each other,
such as typically the toe and the elastic band end of a sock.
According to an aspect of an embodiment of the invention, the points of
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the approximation curve are each characterized by two coordinates in a
reference system, which can advantageously be a Cartesian reference
system, although it would also be possible to use other reference systems,
preferably two-dimensional, as the article will normally have a flat
conformation.
In practice, in a possible embodiment, the method provides for moving
with respect to each other an article and an array of photocells, for example
aiigned along a straight line, to gradually intercept the beams of the
photocells
with the end of the article. On the basis of the relative positions taken by
the
article and the photocells and of the electrical signals generated by gradual
interception of the optical beams of the photocells, a plurality of points are
determined lying on a profile that approximates the profile of the end of the
article. As the profiles of the two ends differ from each other, the trends of
the
profiles reconstructed by point approximation will also differ from each
other.
By processing the curves that approximate these profiles the two ends can be
discriminated from each other.
According to a possible embodiment, the method provides the steps of:
arranging a plurality of photocells according to a predetermined arrangement;
moving said arrangement of photocells and said article with respect to each
other along a direction of relative movement, so that one end of said article
intercepts the beams of said photocells during the relative movement;
determining the coordinates of a plurality of points belonging to the profile
of
said end of the article that intercepts said beams, on the basis of: the
relative
positions taken by said article with respect to said photocells during the
reciprocal movement, and of the arrangement of the photocells.
Preferably, in an embodiment of the invention, each time a photocell is
intercepted by said article during said relative movement, the relative
position
between article and said photocells is detected, the position of the
intercepted
photocell and the reciprocal position between photocells and article along
said
direction of relative movement defining the coordinates of a point belonging
to
said profile.
The curve that approximates the profile of the end of the article that
intercepts the photocells can be generated by interpolating the points
belonging to the profile of said end, for example with a linear interpolation.
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More complex processing would also be possible to obtain high degree
interpolating polynomials of, although this is not absolutely necessary. An
approximation through segments of straight line that join together the various
points identified on the profile of the end of the article is usually
sufficiently
accurate. Therefore, in the present description and in the appended claims,
curve is intended in general also as a broken line, obtained for example from
the sequence of the portions of straight lines that join the points identified
on
the profile of the end of the article.
In a possible embodiment of the method according to the invention, the
curve that approximates the profile of the end of the article read by the
photocells is processed to determine the trend of the slope thereof, the first
end and the second end of said article being detected and distinguished as a
function of this trend of the slope. This can, for example, be performed 'by
calculating the derivative of the curve obtained through the points identified
on
the end profile. The derivative can also be calculated by points, and
therefore
be constituted by a broken line that approximates, even roughly, the trend of
the derivative.
In a particularly simple embodiment, although sufficiently accurate in
many cases, the maximum and minimum values of the derivative are
determined and the difference is calculated. The two ends of the article are
detected, i.e. discriminated from each other, on the basis of a comparison'
between the maximum and minimum value of the derivative and a threshold
value. This is possible thanks to the fact that, for example in the case of
socks, the toe has a trend with a highly variable curvature, and therefore
with
a derivative that takes values differing greatly from one another along the
extension of the profile representing the end, while the greater part of the
band end is instead normally more or less rectilinear, and therefore its
derivative has a flat trend.
According to another aspect, the invention relates to a device to
distinguish from each other, i.e. to discriminate from one another a first end
and a second end of an article, comprising an arrangement of sensors to
identify a plurality of points belonging to the profile of an end of said
article,
and a control and processing unit which, as a function of the coordinates of
said points, detects whether they belong to said first end or to said second
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end.
In practice, the control and processing unit can be programmed so as
to generate a curve that approximates the profile of said end as a function of
said points identified by said sensors.
According to a preferred embodiment of the invention, the sensors
comprise an arrangement of photocells, and there are also provided handling
members to move with respect to each other, along a direction of relative
movement, said article and said arrangement of photocells, with a system to
detect the reciprocal position between said article and said photocells. The
control and processing unit can be programmed to determine the plurality of
points associating the positions of the photocells that are intercepted by
said
article, during the relative movement between the article and the photocells,
with the position taken each time by the article with respect to the
photocells
along said direction of relative movement.
The arrangement of photocells can be of various types. Preferably, they
will be disposed according to a linear string of photocells. This string of
photocells is preferably disposed according to an alignment orthogonal to said
direction of relative movement. In this way, a series of points in a system of
Cartesian coordinates is obtained simply by translating the article and the
array of photocells with respect to each other.
Advantageously, the control and processing unit can be programmed
so that each time a photocell is intercepted by said article during said
relative
movement, the relative position between article and photocells is detected,
the
position of the intercepted photocell and the reciprocal position between
article
and photocells along said direction of relative movement, forming the
coordinates of a point belonging to said profile.
Further advantageous features and embodiments of the method and of
the device according to the invention are indicated in the appended claims
and will be described in greater detail hereunder with reference to non-
limiting
possible embodiments of the invention.
Brief description of the drawings
The invention will be better understood by following the description and
accompanying drawing, which shows practical non-limiting embodiments of
the invention. In the drawing:
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Figure 1 shows a diagram of the device in a front view;
Figure 2 shows a section according to II-II in Figure 1;
Figures 3A-3D schematically show a sequence of movement of an
article like a stocking or sock, which is positioned with the toe facing the
optical reading system;
Figure 4 shows a diagram of the profile of the toe of the article and the
derivative thereof;
Figures 5A-5B schematically show a sequence of movement of an
article which is positioned with the band end facing the optical reading
system;
Figure 6 shows a diagram of the profile of the band end and the
derivative thereof;
Figure 7 schematically shows a different method of processing to
discriminate the first and the second end of an article from each other, on
the
basis of the trend of a curve that approximates the profile of the end of the
article viewed by the sensors of the device;
Figures 8 and 9 show a further embodiment of the method according to
the present invention; and
Figures 10A and 10B show a modified embodiment of the invention.
Detailed description of a preferred embodiment of the invention
Figures 1 and 2 very schematically show the device according to the
invention. The numeral I indicates a supporting surface of an article M, which
in the example illustrated is a sock with a toe P to be sewn and an elastic
band end B.
.Above the supporting surface 1, which can be constituted by a
conveyor or the like, there is disposed a movable element 3, such as a
presser provided with a lifting and lowering movement fv and a translational
movement according to the double arrow fo. The presser 3 is moved
according to the double arrow fv by a piston-cylinder actuator 5, in turn
carried
by a slide 7 sliding in a guide (not shown). The movement according to fo of
the slide 7 along the guide is controlled by a belt 9 driven around two
pulleys
11, 13 the second of which is motorized by means of a motor 15. The numeral
17 indicates an encoder or other angular transducer that allows detection of
the movement of the motor 15 and consequently of the slide 7 according to
the double arrow fo. Instead of an encoder associated with the motor 15, any
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other means could be used to detect the movements of the slide 7 or even of
the presser 3 directly. This detection means (the encoder 17 in the example)
is connected to a programmable control unit, indicated with 19, interfaced,
for
example, with a monitor 20 or other user interface. The control unit 19 can be
provided with a keypad and other peripherals and units typical of a
programmable control device usable to control the device.
The numeral 21 indicates a system of photocells comprising a linear
array of photoemitters and a linear array of photoreceivers, the two arrays
being parallel to and opposite each other. In the drawing the numeral 23
indicates a first of said arrays, for example the array of photoemitters,
while
the numeral 25 indicates the opposite array, for example the array of
photoreceivers. As will be apparent from the description below of two
operating cycles, the arrangement is such that the article M is 'made to
translate with one or other of the ends thereof facing towards the detecting
or
reading device 21, to intercept with said end the beams of the photocells to
detect whether the end that intercepts the photocells is the band end B or the
toe P.
As in general the two ends P, B of the article M have profiles which differ
from each other, by feeding the article M gradually with the end thereof under
the linear array of photocells of the reading system 21 it is possible to read
and detect the form of the profile of said end, using the following data: the
position in space of the photocells; the signal of each photocell; the
position of
the presser 3 along the direction of movement fo and consequently the
position of the article along the direction of feed according to the arrow F.
Figures 3A-3D and 4 show detection of a toe P of the article M. These
figures show four relative positions of the toe P with respect to the array of
photocells 21, indicated in these diagrams with X1-X8. In the examples eight
emitter-receiver pairs are shown, but it must be understood that a different
number of photocells can also be used. The number is dictated by
requirements of cost i and sufficient detection accuracy. In the position in
Figure 3A none of the photocells is intercepted by the toe P of the article.
In
Figure 3B the photocell X4 is intercepted, while in the position in Figure 3C
the
position photocells X3-X6 are intercepted. In Figure 3D the position
photocells
X2-X7 are intercepted.
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The positions of the photocells X1-X8 represent a corresponding number
of values on the axis of the abscissas of a Cartesian diagram reproduced in
Figure 4, while the positions of the article M, determined by the encoder 17
associated with the motor 15, represent the ordinates. By reproducing on a
diagram X,Y (Figure 4) in the abscissas the coordinates corresponding to the
photocells that for each discrete value of Y (position of the article) are
intercepted, a'set of points P1-P6 is obtained which, interpolated,
approximately provide the profile PF of the end of the article. More
specifically,
the point P4 is defined by the coordinate on the axis of the abscissas (x)
defined by the position of the photocell X4 (the first which is intercepted)
(Figure 3B) and by the coordinate YO. It is not necessary to know the absolute
value of the coordinate Y0 on the axis of the ordinates, as what matters is
the
position of the coordinates on said axis of the subsequent points of the
profile.
As the article M advances, the position photocells X3, X5 are intercepted at
the value of the ordinate Yl, followed by the photocell X6 (Figure 3C) at the
ordinate Y2 and finally the photocell X7 at the ordinate Y3 (Figure 3D). In
this
way the points of the profile PF are obtained. The value of the ordinate Y0
can
be taken as the zero value and the subsequent ordinates are determined on
the basis of the relative movement performed by the presser 3 and therefore
by the article M.
The same occurs in the case in which the end that is read by the array of
photocells is the band end. This case is represented schematically in Figures
5A and 5B, and Figure 6 shows the curve PF which is obtained by
appropriately interpolating the points identified by the coordinates X,Y thus
determined. The points on the diagram are again indicated with P1-P6.
It can be seen that the diagrams PF in Figures 4 and 6 have a highly
different shape in the two cases. In particular, it can be seen that the
interpolating curve in Figure 4 has a much more variable slope with respect to
the curve in Figure 6. Having generated the interpolating curve, with any
suitable criterion, the derivative can be calculated. The trend of the
derivative
(again reproduced for the two cases in the diagrams in Figures 4 and 6 and
indicated with D) represents the variation of the slope of the curve and is
therefore indicative of the greater or lesser curvature of the profile PF
detected
by the photocells.
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The derivative can be used, for example through a simple criterion of
comparison with a threshold value, to detect i.e to distinguish the toe from
the
band end. In fact, it is for example possible simply to determine the maximum
and minimum values of the derivative and calculate the difference. The
difference in value can be compared with an experimentally determined
threshold. If the difference in value exceeds the threshold value, this is
indicative of a curved profile and consequently identifies a toe, while if the
difference in value does not exceed the threshold, this is indicative of a
flat
profile and consequently identifies a band end.
Experimentally, it is easy to identify a threshold value according to which
the difference between maximum and minimum value of the derivative is
significantly below and above this threshold for band end B and toe P profiles
of the article, respectiveiy.
Figure 7 schematically shows a different embodiment of the invention. In
substance, in this case the device remains substantially as described with
reference to Figures 1 and 2. The methods with which the points P1-Pn
belonging to the profile of the end of the article that is read by the
sensors, for
example constituted by the photocells 23, 25, also remain substantially the
same. Conversely, the methods with which the data representing the points
belonging to the approximation curve are processed change.
Figure 7A represents a Cartesian reference system, the abscissas and
ordinates of which are represented respectively with X and Y. P1-P5 indicate
points belonging to the profile of the end of the article M. In this example
five
points are shown, but it must be understood that the number of points can
vary (in this as in the previous embodiment) on the basis of the conformation
of the system and of the shape of the article.
In this embodiment, the curve on which the points P1-P5 lie is sloping
with respect to the coordinates X-Y. This means that the article has reached
the photocells 23, 25 in an inclined and not in a straight position. This
embodiment includes a preliminary step to process the data detected to
correct this error. In substance, the curve on which the points P1-P5 lie is
reproduced in a system of reference X'-Y' rotated by an angle a, the straight
line X' of the abscissas of which is more or less orthogonal to the axis of
the
article, consequently passing through the end points P1, P5 of the curve.
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Indicating with (a) and (b) the differences between the abscissa and the
ordinate of the point P5 and the abscissa and the ordinate of the point P1,
therefore
a = arctan(b/a)
the equations that transform the coordinates of the points P1-P5 from the
system X-Y to the system X'-Y' are:
X' = Xcos(-a) - Ysin(-a)
Y'= Xsin(-a) + Ycos(-a)
Figure 7B represents the curve obtained by interpolation of the points
P1-P5 in the reference system X'-Y, where the coordinates have been placed
in horizontal and vertical position respectively. It is understood that this
preliminary operation to correct the slope of the approximation curve of the
profile of the end of the article (and consequently the interpolation curve of
the
points belonging to the profile) can be performed as a preliminary step also
in
the embodiment described with reference to Figures 3 to 6.
Once the curve has been reproduced in the reference system X'-Y, the
difference between the maximum value and the minimum value of the
ordinates of the points P1-P5, indicated in Figure 7B with DY, can be
determined. As the two ends of the article M (toe P and band end B) are
characterized by profiles that differ by degree of curvature, the value AY' of
the difference of ordinates will differ significantly for the two ends. Figure
7B
reproduces with a broken line the curve approximating the band end B of the
article and AC indicates a comparison value determined experimentally on the
basis of analysis of the shape of the ends of an adequate number of articles.
The device can be programmed so that all the ends of articles in which
AY'>AC are classified as "toes" and all the ends of articles in which AY'<AC
are classified as "band ends".
Figures 8A and 8B describe an improved procedure or method to
discriminate between toe and band end, which prevents discrimination errors
due, for example, to interception of the photocells by the side of the article
rather than by the end profile (band end or toe) if the article is positioned
with
a particularly high inclination with respect to the direction of movement.
In Figures 8A and 8B, B indicates the band end of the article M, FO, F1...
FN indicate the photocells in number equal to N+1 and X, Y or X, Y' indicate
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the Cartesian reference axes with respect to which the coordinates of the
points belonging to the profile of the end (toe or band end) of the article M
that
intercepts the photocells are identified (the system X,Y is constituted by
axes
parallel respectively to the alignment of the photocells and to the relative
movement between photocells and article, while the system X'Y' is the one
rotated by an angle corresponding to the angle of inclination, with respect to
the axis X, of the line joining the first and the last point of the profile
considered for discrimination, according to the criterion of rotation
described
with reference to the previous embodiment).
Figures 8A and 8B represent an article M (such as a sock) from the
side of the band end while it passes in front of the photocells slightly
inclined
with respect to the direction of relative motion, represented by the arrow F.
The amount of movement (H), i.e. the relative movement of the article with
respect to the photocells, is established in advance and the article moves
forward by said amount irrespective of the number of photocells effectively
intercepted at the end of this movement. The amount H is preferably just
sufficient to allow the profile of the band end B of an inclined article
(angle 0 in
the figure) to pass, to prevent a high number of photocells from intercepting
the side of the article in the event of an inclined article. The amount (H) is
determined experimentally on the basis of the type of article.
As can be easily understood by observing Figure 8A, in order not to
distort the analysis, not all the points of the profile that have been
intercepted
by the photocells must be considered, but it is advisable to discard the two
end points, as the point that intercepts the photocell marked with F8 would
cause a distorted signal.
To discard both the first and the last point of the profile an algorithm
described below can be used. To understand the following, it must be
mentioned that before starting a detection operation the variables involved in
the calculations are put equal to zero and ordered from 0 to N (with N+1 equal
to the number of photocells) in the sense that the first photocell is assigned
the input 0 of a PLC or other programmable control unit and the corresponding
captured ordinate is Y0; the second photocell is assigned the input 1 and the
ordinate Y1 and so forth up to the last with input N and ordinate YN.
Moreover, the second point of the profile intercepted by the photocells is
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indicated with n1 and the second last point with n2 respectively.
This being stated, the detection algorithm is developed in the following
steps:
Assignment of the variables
1) at the start of the procedure all the variables Yj and all the pointers j
and z
are reset, where j is the pointer or counter relative to the photocells (from
0
to N) and z is a flag required for correct execution of the algorithm, and
which can take two alternative values: 0 or 1;
2) after resetting the values of the variables the relative motion between
photocells and article M is started. It is necessary to take into account that
the distance between the article and the photocells is not known in
advance and therefore the movement continues until the profile of the
article intercepts the first photocell;
3) at the first signal (interception of the first photocell by the article)
the
position Yj is captured (as according to the aforesaid j=0). This value is
considered as the "zero" value of the relative movement, in the sense that
the final value of the movement is set at this point. As H is the maximum
travel between the instant in which interception starts and stopping of the
relative movement between article and photocell, consequently
4) the position at which the motor that feeds the article stops is determined
equal to the sum Yj + H
5) during the movement from Y0 to YO+H the interception positions of the
profile (ordinates Yi) are captured and memorized. I.e.: during the relative
movement equal to the travel H the values of the relative movement
corresponding to each single interception signal of a photocell are
collected;
6) the motion is stopped at the position Y+H.
Definition of the polygonal that approximates the profile:
The polygonal is determined considering the coordinate points Yj excluding
the first and the last point intercepted. With reference to Figure 8A, the end
points of the polygonal which must be considered are the points n1 and n2
(second and second last). The procedure to discard the point preceding n1
and the point subsequent to n2 is as follows:
7) reading of the ordinate Yj indicated by the pointer j
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ifYj= Oandz=0,skiptostep8
ifYj> 0andz= 0, skiptostep 9
if Yj = 0 and z= 1, skip to step 9
if Yj > O and z= 1, skip to step 8
8)j=j+1 andreturntostep7
9) if z= 0, n1 = j+ 1, z= z+ 1, skip to step 8
ifz= 1,n2=j- 1,skiptostepl0
At the end of this iteration the points n1 and n2 have been identified and
consequently the polygonal that approximates the profile intercepted by the
photocells is given by the totality of the points n1, n2 and intermediate
points.
In the subsequent step analysis of the polygornal is performed. The
coordinates in the system X, Y of the points n 1 and n2 respectively are
indicated with Xnl, Yn1, and with Xn2, Yn2.
10) A = arctan ((Yn2-Yn 1)/((Xn2-Xn 1))
11) rotation of the coordinates (the equations already described with
reference
to the preceding example are applied)
12) search for the minimum and maximum values of the ordinates Y
13) comparison with the value set to assign the type of profile: if the
difference
between maximum and minimum value of the ordinates Y' is greater than the
predetermined value, the profile intercepted belongs to a toe, otherwise it
belongs to a band end.
It is understood from the algorithm described and from Figure 8 that by
discarding the first and the last point identified by passage of the profile
of the
article in front of the photocells, the end identified is prevented, for
example in
the case in Figure 8, from being interpreted as a toe, while it is actually a
band
end. Due to the inclination between axis of the article and direction of
motion,
this error could derive from interception of the point n3 belonging to the
side of
the article by the photocell F8.
In the embodiment previously described it was assumed that the article
M will be positioned with a toe P always substantially flattened frontally,
i.e.
with an arched profile as shown in the figures. However, this is not always
the
case and in particular according to how the article is handled and flattened,
it
can be positioned lying on one side, so that the toe P does not have the
arched profile, shown for example in Figure 2, but a stepped profile, as shown
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in Figure 9, with an approximately rectilinear area.
This could cause difficulty in interpretation, i.e. a risk of incorrect
detection, as both the toe and the band end would in this case have
rectilinear
profile portions, although of different lengths, if the amount H of reciprocal
movement between article M and photocells is below the length L. On the
other hand, in the case of inclined articles (angle P Figure 8), to prevent an
excessive number of photocells from being intercepted by the sides of the
article rather than by the end profile, the amount H must be limited.
To avoid an error in discriminating between toe and band end in the case
in which the toe is positioned as shown in Figure 9, rather than using the
criterion of discrimination described above, based on the difference between
maximum and minimum height with respect to the system of reference X', Y',
of the points of the profile, a toe is discriminated from a band end by
counting
the number of photocells that have intercepted the profile, as in the toe
these
are undoubtedly fewer than those involved in a band end. According to an
improved embodiment of the method of the present invention, therefore, after
performing the movement of a degree H between article and photocells, in the
first place the total number of photocells intercepted by the profile of the
article
is determined. If this is below a given minimum number, then the end that has
passed before the photocells is a toe. If the number of photocells intercepted
is higher than said given minimum, then the discrimination procedure
described is performed on the basis of the difference of coordinates.
In conclusion, the more efficient system comprises both the criterion of
rotation of the coordinates of the profile and therefore of comparison between
Ymax and the set vaiue, and the one that takes account of the number of
photocells that intercept the profile.
In the above described embodiments, only one end of the article is
caused to interact with the photocells or other sensors, in order to recognize
whether said end is the first end or the second end of the article. Once said
end is recognized as being the first end (for example the toe), the other end
is
assumed to be the second end (for example the band end). This way of
performing the method is not however the only possible alternative. Indeed,
e.g. in order to achieve a higher degree of accuracy and reproducibility of
the
method, or else in order to reduce the risk of misinterpretation of the
detected
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data, in an improved embodiment of the method according to the invention
both ends of one and the same article are subject to detection by means of
the same or of two different sensor arrangements.
In one possible embodiment, described here below with reference to
Figs. IOA and 10B, the device includes a single linear array of photocells 21.
In an embodiment, said photocells include photoemitters 23 and
photoreceivers 25 arranged on two sides of an intermediate position where
the article of manufacture M is caused to pass, as described above. However,
in a different embodiment (which can be applied in the above disclosed
embodiments as well) the photocells can include photoemitters arranged on
the same side of e.g. a reflective surface or conveyor on which the article M
is
placed.
Two handling members 5A and 5B are arranged, one on each side of the
photocells arrangement 21. In an embodiment the members 5A, 5B are
movable in a vertical direction according to double arrow fv and are
suspended from a supporting structure schematically shown at 8. In an
embodiment the two handling members 5A, 5B include respective endless
belts 6A, 6B, entrained around rollers (three for each handling member in the
example shown). At least one of each three-roller cluster is motorized while
the others can be idle. The motorized roller causes the respective belt 6A, 6B
to move according to double arrow fo.
An article of manufacture M having a first end (e.g. a toe end P) and a
second end (e.g. a band end B) is moved under the handling members 5A,
5B. As in the previous examples the orientation of the article M is random,
i.e.
it is not known beforehand which is the toe end and which is the band end. In
the example shown the band end B is on the left-hand side of the figure and
the toe P is on the right-hand side.
Once the article M is placed underneath one or the other of the two
members 5A, 5B, the members are lowered (arrow fv), such that at least one
of said handling members touch the article M and presses it against the
supporting surface 1, for example a conveyor moving orthogonally to the
figure. One or both belts 6A, 6B are put in motion in the same direction, for
example such as to push the article towards the left-hand side. During this
motion one of the ends of the article pass between the surface I and the
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emitters 23, i.e. intercepts the emitter-receiver pairs 23, 25. In the example
shown, in the position shown in Fig. 10A the band end B has just intercepted
the photocells. Once this happened, the device is able to determine, on the
basis of one of the above disclosed modes, whether the end which just
passed between the photoemitters 23 and photoreceivers 25 is the first or
second end. The motion of the belts 6A, 6B can be reversed or continued
(depending on the starting position of the article) such that also the second
end passes through the photocells 21. The device determines whether the
second end is a band end or a toe end, adopting one of the above disclosed
methods.
If the two readings are consistent (i.e. if the first reading determines that
the end first detected is e.g. the band end, as in the example shown, and the
second is the toe end) then the orientation of the article M is properly
determined. If, however, the readings are inconsistent (e.g. if both ends are
read as being toe ends or both as being band ends), then the control unit
considers the reading as aborted and discards the article. The article can in
such case e.g. be resent to the basket or other container from which it is
picked up again for a subsequent detection process.
Errors (double-toe detection or double-band end detection) can be
caused e.g. if the article is not properly spread on the surface 1.
If both ends are read the system reduces the chance of errors to a really
negligible value, even if a somewhat less reliable algorithm is used to
discriminate between toe and band end portions respectively. Thus a reliable
system can be implemented using a substantially simple algorithm.
It is understood that the drawing only shows an example provided purely
as a practical embodiment of the invention, which can vary in forms and
arrangements without however departing from the scope of the concept
underlying the invention. Any reference numerals in the appended claims are
provided to facilitate reading of the claims with reference to the description
and to the drawing, and do not limit the scope of protection represented by
the
claims.
