TECHNICAL FIELD AND PRIOR ART
[0001] The invention relates to an auxiliary nozzle for supporting a weft thread in a weaving
machine, which auxiliary nozzle comprises a hollow needle, wherein the hollow needle
comprises a tip and an outflow opening for an air jet, wherein the outflow opening is provided in
a side wall adjoining the tip and is arranged to direct the air jet to a weft insertion channel when
the auxiliary nozzle is mounted on the weaving machine. The invention also relates to a method
for manufacturing an auxiliary nozzle and to a weaving machine provided with at least one
auxiliary nozzle.
[0002] Auxiliary nozzles, also referred to as relay nozzles, are intended to support a weft thread
during insertion of the weft thread into the shed of a weaving machine. To this end a plurality of
auxiliary nozzles is arranged distributed across the width of the weft insertion channel of the
reed of the weaving machine.
[0003] Auxiliary nozzles are disclosed for example in US 3,978,896, wherein the outflow
opening is composed of a plurality of elementary apertures arranged close to each other.
[0004] CH 656 905 A5 discloses an auxiliary nozzle, wherein a plurality of tubular elements
connected to each other at their outer surfaces, are arranged in the outflow opening for forming
small channels. The tubular elements have a circular or a hexagonal cross-section.
[0005] Providing a plurality of small elementary apertures either drilled into the side wall or by
fitting tubular elements in an outflow opening having a larger dimension is advantageous for
directing the air flow to blow on a weft thread for supporting the weft thread during the insertion.
However, the mass flow rate generally is substantially decreased compared to nozzles having
one single large outflow opening.
SUMMARY OF THE INVENTION
[0006] It is an object of the invention to provide an auxiliary nozzle having a plurality of
elementary apertures, which auxiliary nozzle allows for an increased mass flow rate. It is further
an object of the invention to provide a method for manufacturing such an auxiliary nozzle.
[0007] This object is solved by the auxiliary nozzle with the features of claim 1, the weaving
machine with the features of claim 8, and the method with the features of claim 9.
[0008] According to a first aspect, an auxiliary nozzle for supporting a weft thread in a weaving
machine is provided, which auxiliary nozzle comprises a hollow needle, wherein the hollow
needle comprises a tip, an outflow opening for an air jet and a side wall, wherein the outflow
opening is provided in the side wall of the hollow needle adjoining the tip and is arranged to
direct the air jet to a weft insertion channel when the auxiliary nozzle is mounted on the weaving
machine, and wherein the outflow opening is composed of a plurality of elementary apertures
having straight lateral surfaces, which elementary apertures are formed in the side wall of the
hollow needle by laser cutting and are arranged close to each other in a tessellation pattern for
maximizing the total flow-through section of the outflow opening.
[0009] Adjacent elementary apertures are separated by partitions. The straight lateral surfaces
allow for an arrangement of the elementary apertures close to one another and allow to
minimize the surface area occupied by the partitions between the elementary apertures. By
minimizing the surface area occupied by the partitions between the elementary apertures, the
total flow-through section of the outflow opening is increased for a determined enveloping
circumference of the outflow opening. Forming such elementary apertures is possible by
applying a laser cutting technology. For example, the laser cutting is done by melting, blowing
and/or burning. For example, use can be made of a low power laser with compressed air as
amplifier or use can be made of a high power laser.
[0010] The tessellation pattern in one embodiment is composed of square or triangular
elementary apertures. In other embodiments, elementary apertures having different crosssectional
shapes are combined for forming a tessellation pattern for the outflow opening. The
shape of the cross-section of the elementary apertures is chosen suitably by the person skilled
in the art. Preferably, the size and shape of each elementary aperture is chosen in order to
allow dust to pass through the elementary aperture and to avoid clogging of the elementary
apertures.
[001 1] According to a preferred embodiment, the tessellation pattern is a hexagonal tessellation
pattern, wherein the elementary apertures have an at least substantially hexagonal crosssection.
In order to allow for a tessellation pattern minimizing the surface area of the partitions
between the elementary apertures, the cross-sections fulfill the so-called Conway criterion, this
means the hexagonal cross-section has at least one pair of opposite lateral surfaces that are
parallel and congruent. Preferably, all elementary apertures have an at least substantially
hexagonal cross-section. In some embodiments, elementary apertures arranged at a boundary
of the outflow opening have a different shape. In one embodiment, elementary apertures having
a regular hexagonal cross-section with six equal lateral surfaces, six equal angles and six equal
corners are provided.
[0012] Preferably, the elementary apertures have a modified regular hexagonal cross-section
with six equal lateral surfaces, six equal angles and six equal rounded corners. Using
elementary apertures having such a modified regular hexagonal cross-section with six equal
lateral surfaces, six equal angles and six equal rounded corners, allows to provide a hexagonal
tiling and, hence, a division of the outflow opening into regions of equal flow-through section,
wherein the total flow-through section of all elementary apertures together is maximized with an
enveloping circumference of the outflow opening as small as possible. The modified regular
hexagonal cross-section having rounded corners instead of sharp corners is advantageous for
avoiding turbulent airflows through the elementary apertures.
[0013] The elementary apertures are formed in the side wall of the hollow needle. In one
embodiment, a flow-through section of the elementary apertures is constant over the thickness
of the side wall. In preferred embodiments, the flow-through section of each of the elementary
apertures increases from an inner side of the needle to an outer side of the needle. This
embodiment is particular suitable for forming such an outflow opening using laser cutting.
[0014] The enveloping shape of the outflow opening composed of a plurality of elementary
apertures is chosen suitably by the person skilled in the art to direct the air flow of the auxiliary
nozzles towards the weft thread and to support the weft thread during its insertion into the shed.
[0015] In one embodiment, the elementary apertures are arranged in several stacked rows in
the longitudinal direction of the hollow needle, wherein each row comprising at least one
elementary aperture and wherein in a row closest to the tip of the hollow needle the at least one
elementary aperture is oriented with one of its lateral surfaces facing towards the tip of the
hollow needle. Preferably, this row closest to the tip comprises only one single elementary
aperture. This arrangement is advantageous for providing an outflow opening ejecting an air jet
having a sufficient width and a sufficient strength while keeping a height of the enveloping
shape of the outflow opening small.
[0016] In one embodiment, the enveloping shape of the outflow opening composed of a plurality
of elementary apertures at least approximates the shape of a regular hexagon. This
arrangement allows ejecting an air jet, which is similar to an air jet ejected by an outflow
opening having one single elliptical opening.
[0017] According to another embodiment, the elementary apertures are provided to abut lateral
surface to lateral surface in a plurality of lines, preferably three lines or four lines, arranged at an
angle between about 30° and about 60° with respect to the longitudinal axis of the hollow
needle so that all elementary apertures cross a lower warp plane earlier than when arranged in
mirror symmetry to the longitudinal axis. With such an arrangement, all elementary apertures
and, hence, the total flow-through section of the outflow opening enters earlier into the shed,
thereby blowing on the inserted weft thread by means of this auxiliary nozzle is started earlier
than by means of an auxiliary nozzle moved along an identical path, but having the elementary
apertures arranged in mirror symmetry to the longitudinal axis.
[0018] According to a second aspect a weaving machine is provided, which weaving machine
has at least one auxiliary nozzle as described above. Preferably, the weaving machine is
provided with a plurality of auxiliary nozzles arranged distributed across the width of the weft
insertion channel of the reed of the weaving machine.
[0019] According to a third aspect, a method for manufacturing an auxiliary nozzle for
supporting a weft thread in a weaving machine is provided, which auxiliary nozzle comprises a
hollow needle, wherein the hollow needle comprises a tip and an outflow opening for an air jet,
and wherein the outflow opening is provided in a side wall of the hollow needle adjoining the tip
and is arranged to direct the air jet to a weft insertion channel when the auxiliary nozzle is
mounted on the weaving machine, the method comprises the step of laser cutting using a laser
cutting device of a plurality of elementary apertures having straight lateral surfaces in a
tessellation pattern into the side wall of the hollow needle for forming an outflow opening
composed of a plurality of elementary apertures arranged close to each other. By applying a
laser cutting technology, elementary apertures having straight lateral surfaces instead of circular
cross-sections can be provided. Laser cutting such a tessellation pattern into the side wall,
allows to minimize the size of the partitions between the elementary apertures and to provide an
auxiliary nozzle having a maximized total flow-through section for a determined enveloping
circumference of the outflow opening.
[0020] In one embodiment a plurality of elementary apertures are cut using the laser cutting
device in a hexagonal tessellation pattern into the side wall, wherein the elementary apertures
have an at least substantially hexagonal cross-section. As described above, in preferred
embodiments elementary apertures having congruent hexagonal cross-sections with at least
one pair of opposite lateral surfaces, that are parallel and congruent, are provided.
[0021] More particular, in preferred embodiments, a plurality of elementary apertures is cut
using the laser cutting device into the side wall, which elementary apertures each have a
modified regular hexagonal cross-section with six equal lateral surfaces, six equal angles and
six equal rounded corners.
[0022] In preferred embodiments, the elementary apertures are cut using a laser cutting device
into the side wall from an outer side of the hollow needle, so that a flow-through section of each
of the elementary apertures decreases from an outer side of the hollow needle to an inner side
of the hollow needle. In other words, elementary apertures are provided that diverge from an
inner side of the hollow needle to an outer side of the hollow needle allowing an air flow through
the elementary aperture to expand. This is favorable for obtaining air flows having a high
velocity.
[0023] The arrangement of the elementary apertures in the tessellation pattern is chosen
suitably by the person skilled in the art. In one embodiment, the elementary apertures are cut
into the side wall using the laser cutting device so that the tessellation pattern comprises
several stacked rows, wherein each row comprises at least one elementary aperture and
wherein in a row closest to the tip of the hollow needle the at least one elementary aperture is
oriented with one of its lateral surfaces facing towards the tip of the hollow needle. Preferably
only one single elementary aperture is provided in the row closest to the tip of the hollow
needle. The enveloping shape of the outflow opening follows the side wall of the hollow needle.
[0024] In alternative or in addition, the elementary apertures are cut into the side wall using the
laser cutting device so that the shape of the outflow opening composed of a plurality of
elementary apertures at least approximates the shape of a regular hexagon.
[0025] In another embodiment, the elementary apertures are cut into the side wall using the
laser cutting device to abut lateral surface to lateral surface in a plurality of lines, preferably
three lines or four lines, arranged at an angle between about 30° and about 60° with respect to
the longitudinal axis of the hollow needle so that all elementary apertures cross a lower warp
plane earlier than when arranged in mirror symmetry to the longitudinal axis.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] Further characteristics and advantages of the invention will emerge from the following
description of the embodiments schematically illustrated in the drawings. Throughout the
drawings, the same elements will be denoted by the same reference numerals.
[0027] Figure 1 shows in a schematic view a part of a weaving machine with a plurality of
auxiliary nozzles, in particular a part of an air jet weaving machine.
[0028] Figure 2 shows an auxiliary nozzle mounted on a holder to be provided on a sley of the
air jet weaving machine of Figure 1.
[0029] Figure 3 is a front view of a hollow needle of the auxiliary nozzle of Figure 2.
[0030] Figure 4 is a cross-sectional view along plane IV-IV of Figure 3.
[0031] Figure 5 is a cross-sectional view along plane V-V of Figure 3.
[0032] Figure 6 is a top view of the hollow needle of Figure 3.
[0033] Figure 7 is a cross-sectional view along plane VII-VII of Figure 3.
[0034] Figure 8 is a detail at the height of one of the elementary apertures of Figure 3.
[0035] Figure 9 is a front view of a hollow needle according to an alternative embodiment.
[0036] Figure 10 is a cross-sectional view along plane X-X of Figure 9.
[0037] Figure 11 is a front view of a hollow needle similar to Figure 9.
[0038] Figure 12 is a cross-sectional view along plane XII-XII of Figure 11.
[0039] Figure 13 is a schematic illustration of a method for manufacturing the auxiliary nozzle of
Figure 2.
DETAILED DESCRIPTION OF EMBODIMENTS
[0040] The weaving machine shown in Figure 1 comprises a reed 3 consisting of a plurality of
dents, each having a cross-section suitable to form a U-shaped weft insertion channel 4, also
referred to as guiding channel. Along this weft insertion channel 4, weft threads 1, 2 are inserted
into a shed formed between an upper plane of warp threads and a lower plane of warp threads
(not shown the figures). The weft threads 1 or 2 are each blown into the weft insertion channel 4
by a main nozzle 5, 6. The further transportation of the weft threads 1 or 2 through the weft
insertion channel 4 is supported by air jets 7 which are blown into the weft insertion channel 4
by the auxiliary nozzles 8. A holder 9 is assigned to each auxiliary nozzle 8 for mounting the
auxiliary nozzle 8 to a sley 10. The auxiliary nozzles 8 are evenly or at a variable distance
arranged distributed across the width of the weft insertion channel 4 of the reed 3. The reed 3
and the main nozzles 5, 6 are also mounted to the sley 10.
[0041] Figure 2 shows an embodiment of an auxiliary nozzle 8 and an associated holder 9. The
holder 9 is to be mounted on the sley 10 (shown in Figure 1) .
[0042] The auxiliary nozzle 8 comprises a hollow needle 11 with a tip 12, an outflow opening 13
for an air jet 7 (shown in Figure 1) and a side wall 14, which outflow opening 13 is provided in
the side wall 14 adjoining the tip 12. The outflow opening 13 is composed of a plurality of
elementary apertures 15 arranged close to each other in the side wall 14.
[0043] The auxiliary nozzle 8 further comprises a connecting socket 16 for a connection to a
supply of compressed air (not shown).
[0044] The hollow needle 11 of Figure 2 is shown in more detail in Figures 3 to 7, in a front
view, two cross-sectional views, a top view and another cross-sectional view, respectively.
Figure 8 is a detail at the height of one of the elementary apertures 15 of Figure 3.
[0045] As can best be seen in Figure 3, the outflow opening 13 is composed of a plurality of
elementary apertures 15 having straight lateral surfaces 17, which elementary apertures 15 are
arranged in a tessellation pattern. More particular, in the embodiment shown in Figures 3 to 7,
the tessellation pattern is a hexagonal tessellation pattern. As can best be seen in Figure 8, the
elementary apertures 15 each have a modified regular hexagonal cross-section with six equal
lateral surfaces 17, six equal angles a and six equal rounded corners 18. The rounded corners
18 are favorable for directing the air jet 7 (shown in Figure 1) and avoiding turbulences that may
develop in the transition area of sharp corners.
[0046] Due to the substantially hexagonal cross-section, the elementary apertures 15 can be
arranged close to each other and the surface occupied by the partitions 19 (indicated amongst
others in Figure 8) between the elementary apertures 15 can be minimized. As a result thereof,
the total flow-through section of the outflow opening 13 is increased without increasing the
enveloping circumference of the outflow opening 13.
[0047] As can best be seen in Figure 4, in the embodiment shown, the region of the side wall
14 at which the elementary apertures 15 forming the outflow opening 13 are provided, is
inclined with respect to the longitudinal axis 24 of the hollow needle 11 allowing for an improved
directing of the air jet 7 (shown Figure 1) for supporting a weft thread 1, 2.
[0048] The hollow needle 11 shown in Figures 3 to 8 has an oval cross-sectional shape (shown
in Figure 5) in order to be able to provide a wider side wall 14 without increasing the total
volume of the hollow needle 11.
[0049] As will be explained in more detail below, the elementary apertures 15 forming the
outflow opening 13 are cut into the side wall 14 adjacent to the tip 12 of the hollow needle 11
using a laser cutting technology.
[0050] As can best be seen in Figure 7, a flow-through section of each of the elementary
apertures 15 decreases from an outer side 25 of the hollow needle 11 to an inner side 26 of the
hollow needle 11. In other words, the flow-through sections of the elementary apertures 15
diverge towards the outer side 25 so that compressed air flowing through the elementary
apertures 15 will expand before finally being ejected. This expansion is advantageous for
obtaining air jets 7 (shown in figure 1) having a high velocity.
[0051] In the embodiment shown in Figures 3 to 8, the elementary apertures 15 are arranged in
a tessellation pattern having several, namely seven, stacked rows in the direction of the
longitudinal axis 24 of the hollow needle 11, wherein in a row of the tessellation pattern, which is
located closest to the tip 12 of the hollow needle 11 only one single elementary aperture 15 is
arranged. This elementary aperture 15 as well as all other elementary apertures 15 is oriented
with one of its lateral surfaces 17 facing towards the tip 12 of the hollow needle 11.
[0052] As can best be seen in Figure 3, the elementary apertures 15 are arranged so that an
enveloping shape of the outflow opening 13 approximates the shape of a regular hexagon.
[0053] Figures 9 to 12 show two alternative embodiments of hollow needles 11 for an auxiliary
nozzle 8 of Figure 1 having an outflow opening 13 composed of a plurality of elementary
apertures 15 with a modified regular hexagonal cross-section, which elementary apertures 15
are arranged close to each other in the side wall 14 of the hollow needle 11. In the
embodiments of Figures 9 to 12, the elementary apertures 15 are provided in a hexagonal
tessellation pattern to abut lateral surface to lateral surface in a plurality of lines 20, namely four
lines 20 in Figures 9 and 10 and three lines 20 in Figures 11 and 12.
[0054] The lines 20 are arranged at an angle between about 30° and about 60° with respect to
the longitudinal axis 24 of the hollow needle 11. Due to this arrangement, all elementary
apertures 15 in use cross a lower warp plane 2 1, indicated by lines in Figures 9 and 11, earlier
than when arranged in mirror symmetry to the longitudinal axis 24.
[0055] Figure 13 schematically shows a method for manufacturing a hollow needle 11 having
an outflow opening 13 composed of a plurality of elementary apertures 15 using a laser cutting
device 22. With the laser cutting device 22 a plurality of elementary apertures 15 each having
an at least substantially hexagonal cross-section is cut into the side wall 14, wherein the
elementary apertures 15 are arranged in a hexagonal tessellation pattern with small partitions
19 between the elementary apertures 15, as shown in any one of the Figure 3, the Figure 9 or
the Figure 11.
[0056] The laser cutting device 22 is arranged to direct a laser beam 23 towards the hollow
needle 11 for cutting the elementary apertures 15 into the hollow needle 11 as schematically
shown in Figure 13.
[0057] As shown in Figure 13, the laser beam 23 is directed towards the outer side 25 of the
hollow needle 11. As a result thereof, the elementary apertures 15 cut into the side wall 14 have
larger dimensions at the outer side 25 of the hollow needle 11 than at the inner side 26 of the
hollow needle 11, in other words the elementary apertures 15 converge from the outer side 25
of the hollow needle 11 to the inner side 26 of the hollow needle 11.
[0058] When cutting the elementary apertures 15 into the hollow needle 11 using the laser
cutting device 22, the partitions 19 will form a surface at the height of the lateral surfaces of the
elementary apertures 15 which is sufficient rough for increasing contact properties of the air flow
along the lateral surfaces 17, which is sufficient rough for improving a directing of the air flow
towards the outer side, and which is sufficient smooth for limiting a noticeable braking of the air
flow at the surface of the lateral surfaces 17.
[0059] The auxiliary nozzle and the method according to the invention are not limited to the
embodiments described by way of example and shown in the drawings. Variants and
combinations of the described and shown embodiments that fall under the claims are also
possible.

CLAIMS
1. An auxiliary nozzle for supporting a weft thread ( 1 , 2) in a weaving machine, which
auxiliary nozzle (8) comprises a hollow needle ( 1 1) , wherein the hollow needle ( 1 1)
comprises a tip (12), an outflow opening (13) for an air jet (7) and a side wall (14), wherein
the outflow opening (13) is provided in the side wall (14) adjoining the tip (12) and is
arranged to direct the air jet (7) to a weft insertion channel (4) when the auxiliary nozzle
(8) is mounted on the weaving machine, and wherein the outflow opening (13) is
composed of a plurality of elementary apertures (15) formed in the side wall (14),
characterized in that
the outflow opening (13) is composed of a plurality of elementary apertures (15) having
straight lateral surfaces (17), wherein the elementary apertures (15) are formed by laser
cutting and are arranged in a tessellation pattern for maximizing the total flow-through
section of the outflow opening (13).
2. The auxiliary nozzle according to claim 1, characterized in that the tessellation pattern is a
hexagonal tessellation pattern, wherein the elementary apertures (15) have an at least
substantially hexagonal cross-section. .
3. The auxiliary nozzle according to claim 2, characterized in that the elementary apertures
(15) have a modified regular hexagonal cross-section with six equal lateral surfaces (17),
six equal angles (a) and six equal rounded corners (18).
4. The auxiliary nozzle according to claim 1, 2 or 3, characterized in that a cross-section of
each of the elementary apertures (15) increases from an inner side (26) of the hollow
needle ( 1 1) to an outer side (25) of the hollow needle ( 1 1) .
5. The auxiliary nozzle according to any one of claims 1 to 4, characterized in that the
elementary apertures (15) are arranged in several stacked rows in the longitudinal
direction (I) of the hollow needle ( 1 1) , wherein each row comprises at least one
elementary aperture (15) and wherein in a row closest to the tip (12) of the hollow needle
( 1 1) the at least one elementary aperture (15) is oriented with one of its lateral surfaces
(17) facing towards the tip (12) of the hollow needle ( 1 1).
6. The auxiliary nozzle according to any one of claims 1 to 5, characterized in that the shape
of the outflow opening (13) composed of a plurality of elementary apertures (15) at least
approximates the shape of a regular hexagon.
7. The auxiliary nozzle according to any one of claims 1 to 5, characterized in that the
elementary apertures (15) are provided to abut lateral surface (17) to lateral surface (17)
in a plurality of lines (20) arranged at an angle between about 30° and about 60° with
respect to the longitudinal axis (24) of the hollow needle ( 1 1) so that all elementary
apertures (15) cross a lower warp plane (21 ) earlier than when arranged in mirror
symmetry to the longitudinal axis (24).
8. A weaving machine, characterized in that the weaving machine is provided with at least
one auxiliary nozzle (8) according to any one of claims 1 to 7.
9. A method for manufacturing an auxiliary nozzle (8) for supporting a weft thread ( 1 , 2) in a
weaving machine, which auxiliary nozzle (8) comprises a hollow needle ( 1 1), wherein the
hollow needle ( 1 1) comprises a tip (12), an outflow opening (13) for an air jet (7) and a
side wall (14), and wherein the outflow opening (13) is provided in the side wall (14)
adjoining the tip (12) and is arranged to direct the air jet (7) to a weft insertion channel (4)
when the auxiliary nozzle (8) is mounted on the weaving machine,
characterized in that
the method comprises the step of cutting using a laser cutting device (22) of a plurality of
elementary apertures (15) having straight lateral surfaces (17) in a tessellation pattern into
the side wall (14) of the hollow needle ( 1 1) for forming an outflow opening (13) composed
of a plurality of elementary apertures (15) arranged close to each other.
10. The method according to claim 9, characterized in that the method comprises the step of
laser cutting a plurality of elementary apertures (15) in a hexagonal tessellation pattern
into the side wall (14), wherein the elementary apertures (15) have an at least
substantially hexagonal cross-section.
11. The method according to claim 10, characterized in that the method comprises the step of
laser cutting a plurality of elementary apertures (15) into the side wall (14), which
elementary apertures (15) have modified regular hexagonal cross-sections with six equal
lateral surfaces (17), six equal angles (a) and six equal rounded corners (18) .
12. The method according to claim 9, 10 or 11, characterized in that the elementary apertures
(15) are cut using the laser cutting device (22) into the side wall (14) of the hollow needle
( 1 1) , so that a cross-section of each of the elementary apertures (15) increases from an
inner side (26) of the hollow needle ( 1 1) to an outer side (25) of the hollow needle ( 1 1) .
13. The method according to any one of claims 9 to 12, characterized in that the elementary
apertures (15) are cut into the side wall (14) using the laser cutting device (22) so that the
tessellation pattern comprises several stacked rows in the longitudinal direction (I) of the
hollow needle ( 1 1) , wherein each row comprises at least one elementary aperture (15)
and wherein in a row closest to the tip (12) of the hollow needle ( 1 1) the at least one
elementary aperture (15) is oriented with one of its lateral surfaces (17) facing towards the
tip (12) of the hollow needle ( 1 1).
14. The method according to any one of claims 9 to 13, characterized in that the elementary
apertures (15) are cut into the side wall (14) using the laser cutting device (22) so that the
shape of the outflow opening (13) composed of the plurality of elementary apertures (15)
at least approximates the shape of a regular hexagon.
15. The method according to any one of claims 9 to 13, characterized in that the elementary
apertures (15) are cut into the side wall (14) using the laser cutting device (22) to abut
lateral surface (17) to lateral surface (17) in a plurality of lines (20) arranged at an angle
between about 30° and about 60° with respect to the longitudinal axis (24) of the hollow
needle ( 1 1) so that all elementary apertures (15) cross a lower warp plane (21) earlier
than when arranged in mirror symmetry to the longitudinal axis (24).