Patent Application
20180019521
The present invention relates to a corner reflector which functions as a decoy by reflecting radio waves from a tracking radar apparatus, a missile radar seeker, and the like and a method for fabricating the same.
The corner reflector is described in Patent Document 1, for example. The corner reflector of Patent Document 1 has the configuration of
For example, as illustrated in
The corner reflector is released from a flying body, a vessel, the ground, and the like, and then developed to the shape of
With the configuration described above, when radio waves enter the corner reflector developed in the air from a tracking radar apparatus or a missile radar seeker, for example, the corner reflector can reflect the radio waves in the entered directions as illustrated in
PTL 1: International Publication WO 2013/008513
The annular balloons 23a, 23b, and 23c can be fabricated according to the following procedure.
As illustrated in
Thereafter, as illustrated in
Next, the cylindrical balloon 29 is bent into an annular shape, and then annular direction end portions 29a are joined to each other (with an adhesive, for example). Thus, the cylindrical balloon 29 is transformed into the annular balloon 23a, 23b, or 23c annularly extending around a virtual central axis C0 as illustrated in
Next, long side direction end portions 25b of the constraint fabric 25 are joined to each other by sewing, for example. Thus, the annular balloon 23a, 23b, or 23c around which the constraint fabric 25 is wound is fabricated.
The annular balloons 23a, 23b, and 23c thus fabricated are assembled to each other so as to be orthogonal to each other, and then the radio wave reflective films 21 are attached to the annular balloons 23a, 23b, and 23c to fabricate a corner reflector. Thereafter, gas is removed from the inside of the annular balloons 23a, 23b, and 23c to keep the annular balloons deflated until the use of the corner reflector.
In the state where the cylindrical balloon 29 is annularly bent so that the long side direction end portions 25b of the constraint fabric 25 are joined to each other, the annular direction length of an outer peripheral side portion (portion on the side opposite to the virtual central axis C0 side described above) of the annular balloon is longer than the annular direction length of an inner peripheral side portion (portion on the virtual central axis C0 side described above) of the annular balloon.
Meanwhile, an inner peripheral side fabric portion and an outer peripheral side fabric portion of the constraint fabric 25 support the same surface pressure from the annular balloon, so that the inner peripheral side fabric portion and the outer peripheral side fabric portion try to elongate by the same amount in the annular direction. However, the annular direction length of the inner peripheral side fabric portion of the constraint fabric 25 is smaller than the annular direction length of the outer peripheral side fabric portion. Therefore, the elongation in the annular direction of the inner peripheral side fabric portion is restricted, and thus the inner peripheral side fabric portion cannot freely extend in the annular direction.
For such a reason, the elongated amount in the annular direction varies in the inner peripheral side portion of the constraint fabric 25, so that the shape of the constraint fabric 25 is not an exact annular (circular) shape, which results in the fact that the constraint fabric 25 is deformed in a direction different from the annular direction, at a part in the annular direction.
Under the influence, the annular shape accuracy of the annular balloons also decreases.
Therefore, in the constraint fabric 25, tuck processing (pinching and sewing a part of the constraint fabric 25 to make a tuck) for the inner peripheral side portion can be performed at equal intervals in the annular direction. Thus, the shape accuracy reduction of the annular balloon can be reduced.
However, the tuck processing requires time and effort and is complicated, and therefore the cost increases for making tucks so as to obtain a balloon of an annular ring shape with high accuracy.
In view of it, it is an object of the present invention to provide a corner reflector including an annular balloon of which expansion amount is restricted by a constraint fabric, with the shape accuracy of the annular balloon being high even when tuck processing or another processing is not performed on the constraint fabric, and to provide a method for fabricating the same.
In order to achieve the above-described object, according to the present invention, there is provided a corner reflector reflecting a radio wave, the corner reflector comprising:
three annular balloons each of which has flexibility and airtightness, and, when gas is supplied to an inside thereof, expands in an annular shape extending in an annular direction around a virtual central axis due to gas pressure; and
radio wave reflective films each of which includes an outer peripheral edge portion attached to the annular balloon so as to be developed to a plane due to the expansion of the annular balloon,
wherein the three annular balloons are provided so as to be orthogonal to each other in the expansion,
the corner reflector further comprises a constraint fabric wound around each of the annular balloons in a winding direction orthogonal to the annular direction,
the constraint fabric supports surface pressure from the annular balloon in an expansion state where the annular balloon annularly expand, to thereby restrict expansion of the annular balloon,
the constraint fabric includes an inner peripheral side fabric portion which is located on a side of the virtual central axis of the annular balloon and which extends in the annular direction in the expansion state, and an outer peripheral side fabric portion which is located on a side opposite to the virtual central axis and which extends in the annular direction in the expansion state, and
concerning an elongation degree representing an elongation characteristic of the constraint fabric, the elongation degree of the outer peripheral side fabric portion in the annular direction is higher than the elongation degree of the inner peripheral side fabric portion in the annular direction.
The corner reflector of the present invention may be configured as follows.
The constraint fabric is formed by warp fiber threads and weft fiber threads which are woven with each other, and in the expansion state, the warp fiber threads each extend in the annular direction and the weft fiber thread each extend in a direction crossing the annular direction, and
concerning an elongation degree representing an elongation characteristic of each of the warp fiber threads, the elongation degree of each of the warp fiber thread forming the outer peripheral side fabric portion is higher than the elongation degree of each of the warp fiber thread forming the inner peripheral side fabric portion.
Thus, a fiber thread having a relatively high elongation degree is used as the warp fiber thread forming the outer peripheral side fabric portion, and a fiber thread having a relatively low elongation degree is used as the warp fiber thread forming the inner peripheral side fabric portion. Thereby, it is possible to form the constraint fabric having a high elongation degree in the outer peripheral side fabric portion and a low elongation degree in the inner peripheral side fabric portion.
As another option, the constraint fabric is formed by warp fiber threads and weft fiber threads which are woven with each other, and in the expansion state, the warp fiber threads each extend in the annular direction and the weft fiber thread each extend in a direction crossing the annular direction, and
a weaving density of the warp fiber threads forming the outer peripheral side fabric portion is lower than a weaving density of the warp fiber threads forming the inner peripheral side fabric portion.
Thus, the weaving density of the warp fiber threads forming the outer peripheral side fabric portion is lower than the weaving density of the warp fibers thread forming the inner peripheral side fabric portion. Thereby, it is possible to form the constraint fabric having a high elongation degree in the outer peripheral side fabric portion and a low elongation degree in the inner peripheral side fabric portion.
The weft fiber threads include a first fiber thread and a second fiber thread,
concerning an elongation degree representing an elongation characteristic of each of the weft fiber threads, the elongation degree of the second fiber thread is lower than the elongation degree of the first fiber thread,
strength of the second fiber thread is higher than strength of the first fiber thread, and
in the expansion state, the second fiber threads are arranged in the annular direction such that a density of the second fiber threads is less than a density of the first fiber threads.
Thus, provided as the weft fiber threads are the first fiber threads which are densely arranged in the annular direction and have relatively low strength and relatively high elongation degree, and the second fiber threads which are sparsely arranged in the annular direction and have relatively high strength and relatively low elongation degree are provided.
Accordingly, the force with which the first fiber threads restrict the expansion of the annular balloon can be reinforced by the second fiber threads with higher strength and a lower elongation degree. Although the second fiber thread is expensive, the cost can be suppressed, and the force of restricting the expansion of the annular balloon can be reinforced by arranging the second fiber threads such that a density of the second fiber threads is less than a density of the first fiber threads.
In order to achieve the above-described object, according to the present invention, there is provided a method for fabricating a corner reflector reflecting a radio wave comprising the steps of:
(A) preparing a balloon which has expanded in a cylindrical shape by supply of gas to an inside thereof, and a constraint fabric,
(B) winding the constraint fabric wound around the cylindrical balloon,
(C) joining axial direction end portions of the cylindrical balloon around which the constraint fabric is wound, to each other to transform the balloon into an annular balloon extending in an annular direction around a virtual central axis; and
(D) joining end portions of the constraint fabric in the annular direction of the annular balloon, fabricating the annular balloons of which number is three, by the steps (A), (B), (C), and (D),
the method comprising the steps of:
(E) assembling the three annular balloons to each other so that planes including annular shapes of the three annular balloons are orthogonal to each other,
(F) attaching a radio wave reflective film to an inner side of each of the annular balloons to form a corner reflector, and
(G) removing the gas from the inside of the annular balloons to deflate the annular balloons,
wherein the constraint fabric supports surface pressure from the annular balloon in an expansion state where the annular balloon extends in the annular direction around the virtual central axis and annularly expand, to thereby restrict expansion of the annular balloon,
the constraint fabric includes an inner peripheral side fabric portion which is located on a side of the virtual central axis of the annular balloon and which extends in the annular direction in the expansion state, and an outer peripheral side fabric portion which is located on a side opposite to the virtual central axis and which extends in the annular direction in the expansion state, and
concerning an elongation degree representing an elongation characteristic of the constraint fabric, the elongation degree of the outer peripheral side fabric portion in the annular direction is higher than the elongation degree of the inner peripheral side fabric portion in the annular direction.
According to the present invention described above, since the elongation degree of the outer peripheral side fabric portion is higher than the elongation degree of the inner peripheral side fabric portion in the constraint fabric, an annular balloon with high shape accuracy is obtained. The details are as follows.
When the annular balloon expands, a difference occurs between the annular direction length on the inner peripheral side of the annular balloon and the annular direction length on the outer peripheral side of the annular balloon.
With regard to this, according to the present invention, the elongation degree of the outer peripheral side fabric portion is higher than the elongation degree of the inner peripheral side fabric portion in the constraint fabric, and therefore the outer peripheral side fabric portion easily elongates but the inner peripheral side fabric portion has difficulty in elongating. More specifically, the inner peripheral side fabric portion is more resistant to elongate in the annular direction than the outer peripheral side fabric portion before expansion of the annular balloons. Thus, in the expansion state of the annular balloon, a variation in the elongated amount of the annular direction is suppressed or eliminated in the inner peripheral side fabric portion.
Accordingly, the constraint fabric can be prevented from being deformed in a direction different from the annular direction, at a part in the annular direction, or such deformation can be eliminated.
Therefore, even when the tuck processing is not performed on the inner peripheral side fabric portion of the constraint fabric, an annular balloon with high shape accuracy is obtained.
A preferable embodiment of the present invention is described with respect to the drawings. Portions common in respective drawings are designated by the same reference numerals and a duplicated description thereof is omitted.
The annular balloons 3a, 3b, and 3c have flexibility and airtightness, and, when gas is supplied to the inside thereof, each expand in an annular shapes extending in the annular direction around a virtual central axis due to the gas pressure as illustrated in
Outer peripheral edge portions 5a of the radio wave reflective films 5 are attached to the annular balloons 3a, 3b, and 3c so that the radio wave reflective films 5 are developed to the plane by the expansion of the annular balloons 3a, 3b, and 3c. Each of the radio wave reflective films 5 attached to each of the annular balloons 3a, 3b, and 3c is developed on a virtual plane containing the annular shape of the corresponding annular balloon by the expansion of each of the annular balloons 3a, 3b, and 3c. In the present embodiment, when three outer surfaces of the radio wave reflective films 5 orthogonal to each other as illustrated in
The outer surface of the radio wave reflective film 5 is formed of a conductive material reflecting radio waves. As a preferable example, the radio wave reflective film 5 is fabric formed of conductive fibers. Here, the conductive fibers may be nylon fibers coated with a metal film (copper, silver, or the like), for example.
The constraint fabric 7 is formed of fibers (for example, nylon, polyester, and the like) through which radio waves penetrate.
The constraint fabrics 7 are attached to the annular balloons 3a, 3b, and 3c and restrict the expansion amount of the annular balloons 3a, 3b, and 3c. More specifically, the constraint fabrics 7 each extend in a winding direction
(
In this application, the annular direction means a direction in which the annular balloons 3a, 3b, and 3c annularly extend around a virtual central axis C in the state where the annular balloons 3a, 3b, and 3c expand.
In the expansion state of the annular balloons, the constraint fabrics 7 each extend in the annular direction over the entire annular direction of the corresponding annular balloon 3a, 3b, or 3c.
The constraint fabrics 7 each include an inner peripheral side fabric portion 7a surrounded by a dashed line X of
In the present embodiment, the constraint fabrics 7 each include an intermediate fabric portion 7c (surrounded by a dashed line Z of
In
As illustrated in
Although
According to the present embodiment, an elongation degree of each warp fiber thread 11 (hereinafter referred to as warp fiber thread 11b) forming the outer peripheral side fabric portion 7b is higher than an elongation degree of each warp fiber thread 11 (hereinafter referred to as warp fiber thread 11a) forming the inner peripheral side fabric portion 7a. Here, the elongation degree represents the elongation characteristic of one warp fiber thread (for example, each warp fiber thread 11a or 11b) as a constituent element of the constraint fabric 7, and is defined as follows. More specifically, the elongation degree of the warp fiber thread 11 is defined as the numerical value representing an elongated amount of a fixed unit length of one warp fiber thread 11 when certain tensile force acts on the warp fiber thread 11 from the state where no external force acts on the warp fiber thread 11. As the elongation degree of the warp fiber thread 11 is higher, the elongated amount of the warp fiber thread 11 due to fixed tensile force also becomes larger.
Therefore, the annular-direction elongated amount of the unit length of each warp fiber thread 11b due to tensile force acting on each warp fiber thread 11b in the annular direction from the state where no external force acts on each warp fiber thread 11b forming the outer peripheral side fabric portion 7b is larger than the annular-direction elongated amount of the same unit length of each warp fiber thread 11a due to the same tensile force acting on each warp fiber thread 11a in the annular direction from the state where no external force acts on each warp fiber thread 11a forming the inner peripheral side fabric portion 7a.
In an example, first fiber threads 13a and second fiber threads 13b are provided as the weft fiber threads 13. The first fiber threads 13a are densely arranged in the long side direction (annular direction in the expansion state). The second fiber threads 13b are sparsely arranged in the long side direction (annular direction in the expansion state). More specifically, the second fiber threads 13b are arranged more sparsely than the first fiber threads 13a, in the long side direction (annular direction in the expansion state). In
An elongation degree of the second fiber thread 13b is lower than an elongation degree of the first fiber thread 13a. Here, the elongation degree represents the elongation characteristic of one weft fiber thread 13 (first fiber thread 13a or second fiber thread 13b) as a constituent element of the constraint fabric 7, and is defined as follows. The elongation degree of the weft fiber thread 13 is defined as the numerical value representing an elongated amount of a fixed unit length of one weft fiber thread 13 when certain tensile force acts on the weft fiber thread 13 from the state where no external force acts on the weft fiber thread 13. As the elongation degree of the weft fiber thread 13 is higher, the elongated amount of the weft fiber thread 13 due to the fixed tensile force becomes also larger.
Therefore, the elongated amount of a unit length of the second fiber thread 13b due to tensile force acting on the second fiber thread 13b from the state where no external force acts on the second fiber thread 13b is smaller than the elongated amount of the same unit length of the first fiber thread 13a due to the same tensile force acting on the first fiber thread 13a from the state where no external force acts on the first fiber thread 13a.
The strength of the second fiber thread 13b is higher than the strength (i.e., tensile strength) of the first fiber thread 13a.
Specific examples of materials of each fiber thread forming the constraint fabric 7 are described. In an example, each warp fiber thread 11b forming the outer peripheral side fabric portion 7b and each warp fiber thread 11 (hereinafter referred to as warp fiber thread 11c) forming the intermediate fabric portion 7c are formed of nylon, each warp fiber thread 11a forming the inner peripheral side fabric portion 7a is formed of polyester, the first fiber thread 13a is formed of nylon, and the second fiber thread 13b is formed of liquid crystalline polyester or aramid fibers (for example, Kevlar (®)).
Assuming that the elongation degree of each warp fiber thread 11a forming the inner peripheral side fabric portion 7a is A, and the elongation degree of each warp fiber thread 11b forming the outer peripheral side fabric portion 7b is B, the ratio of A to B is 5% to 30% in an example, 5% to 20% in another example, and 5% to 15% in a still another example.
However, according to the present invention, the ratio of A to B is not limited to these examples, as described below. According to the present invention, since the inner peripheral side fabric portion 7a exhibits less elongation in the annular direction than the outer peripheral side fabric portion 7b before and after expansion of the annular balloons 3a, 3b, and 3c, a variation in the elongated amount in the annular direction is suppressed or eliminated in the inner peripheral side fabric portion 7a in the expansion state of the annular balloons 3a, 3b, and 3c. The ratio of A to B may be set so as to obtain such an operational effect.
It is desirable that the weft fiber thread 13 has a low elongation degree and high strength. This is because the weft fiber threads 13 constrain the annular balloons 3a, 3b, and 3c in the expansion state. Therefore, the weft fiber thread 13 is preferably formed of liquid crystalline polyester or aramid fibers, for example. However, when all the weft fiber threads 13 are formed of liquid crystalline polyester fibers or aramid fibers, the constraint fabric 7 becomes hard, heavy, and expensive. In consideration of this matter, it is preferable to densely dispose the first fiber threads 13a formed of nylon which is inexpensive and lightweight but has high elongation degree and low strength and sparsely dispose the second fiber threads 13b formed of liquid crystalline polyester or aramid fibers. Thus, the annular balloons 3a, 3b, and 3c in the expansion state can be constrained with the inexpensive and lightweight constraint fabric 7. However, the present invention is not limited to such a configuration and all the weft fiber threads 13 may be formed of the liquid crystalline polyester fibers or aramid fibers or may be formed of other materials.
Next, a method for fabricating the corner reflector 10 according to an embodiment of the present invention is described.
At the step S1, as illustrated in
At the step S1, gas is supplied to the inside of the balloon 4 from a gas supply hole provided in the balloon 4 to expand the balloon 4, and then the gas supply hole is closed with appropriate means so that the expansion state of the balloon 4 is maintained.
At the step S2, the constraint fabric 7 is wound around the cylindrical balloon 4 as illustrated in
At the step S3, the cylindrical balloon 4 is bent to be formed into an annular shape as illustrated in
At the step S4, the end portions 7e in the longitudinal direction (annular direction in the state of
By the steps S1 to S4 described above, one annular balloon 3a, 3b, or 3c around which the constraint fabric 7 is wound is fabricated. Other two annular balloons around which the constraint fabric 7 is wound are also fabricated by the steps S1 to S4 described above. Thus, each of the three annular balloons 3a, 3b, and 3c around which the constraint fabric 7 is wound is fabricated by the steps S1 to S4.
At the step S5, the three annular balloons 3a, 3b, and 3c around which the constraint fabric 7 is wound are assembled to each other as illustrated in
However, according to the present invention, it is sufficient that the three annular balloons 3a, 3b, and 3c are assembled to each other in the state where the planes including the annular shapes of the three annular balloons 3a, 3b, and 3c are orthogonal to each other. In order to maintain the state where the three annular balloons 3a, 3b, and 3c are assembled to each other as described above, at each portion (each portion surrounded by a dashed line N of
At the step S6, the radio wave reflective film 5 is attached to the inner side of each of the annular balloon 3a, 3b, and 3c as illustrated in
For example, the step S6 may be performed as follows. The twelve radio wave reflective films 5 of a fan shape having the central angle of 90° are prepared.
As illustrated in
As illustrated in
At the step S7, gas is removed from the inside of the annular balloons 3a, 3b, and 3c to deflate the annular balloons 3a, 3b, and 3c. In addition, a gas supply device (not illustrated) supplying gas into the annular balloons 3a and 3b and 3c is attached to the corner reflector 10.
The corner reflector 10 is launched from a vessel (ship), the ground, or the like, for example, into the air in the state where the annular balloons are deflated, and then gas is supplied into the annular balloons 3a and 3b and 3c by the gas supply device attached to the corner reflector 10 so that the corner reflector is developed as illustrated in
Due to the development of the corner reflector 10 in the air, for example, a missile radar seeker sets the corner reflector 10 as a tracking target by a reflected radio wave from the corner reflector 10. Thus, the corner reflector 10 can be used as a decoy for a missile.
According to the embodiment of the present invention described above, the annular balloons 3a, 3b, and 3c with high shape accuracy are obtained since the elongation degree of the outer peripheral side fabric portion 7b is higher than the elongation degree of the inner peripheral side fabric portion 7a in the constraint fabric 7. The details are as follows.
When the annular balloons 3a, 3b, and 3c expand, a difference occurs between the annular direction length on the inner peripheral side of the annular balloons 3a, 3b, and 3c and the annular direction length on the outer peripheral side of the annular balloons.
With regard to this, according to the present embodiment, the elongation degree of the outer peripheral side fabric portion 7b is higher than the elongation degree of the inner peripheral side fabric portion 7a in the constraint fabric 7, and therefore the outer peripheral side fabric portion 7b easily elongates, but the inner peripheral side fabric portion 7a has difficulty in elongating. More specifically, the inner peripheral side fabric portion 7a is more resistant to elongate in the annular direction than the outer peripheral side fabric portion 7b before expansion of the annular balloons 3a, 3b, and 3c. Thus, the constraint fabric 7 can be prevented from being deformed in a direction different from the annular direction or such deformation can be eliminated.
Therefore, even when tuck processing is not performed to the inner peripheral side portion 7a of the constraint fabric 7, the annular balloons 3a, 3b, and 3c with high shape accuracy can be obtained.
The present invention is not limited to the embodiment described above, and can be variously modified without deviating from the scope of the present invention. For example, according to the present invention, any one of the following modification examples 1 to 4 may be adopted or two or more of the modification examples 1 to 4 may be adopted in combination. In this case, the contents which are not described below are the same as the above-described contents.
According to the present invention, it is sufficient that the elongation degree of the outer peripheral side fabric portion 7b in the annular direction is higher than the elongation degree of the inner peripheral side fabric portion 7a in the annular direction in the constraint fabric 7.
According to Modification Example 1, in an example, the constraint fabric 7 may be formed by sewing a fabric composed of the outer peripheral side fabric portion 7b and the intermediate fabric portion 7c to the inner peripheral side fabric portion 7a.
The elongation degree of each warp fiber thread llc forming the intermediate fabric portion 7c in the range Z in
In the above description, the elongation degree of each warp fiber thread 11b forming the outer peripheral side fabric portion 7b is set to be higher than the elongation degree of each warp fiber thread 11a forming the inner peripheral side fabric portion 7a so that the elongation degree of the outer peripheral side fabric portion 7b in the annular direction is made higher than the elongation degree of the inner peripheral side fabric portion 7a in the annular direction (in this case, the weaving density of the warp fiber threads 11b and the weaving density of the warp fiber threads 11a may be the same.) .
In contrast to this, according to Modification Example 3, the elongation degree of the outer peripheral side fabric portion 7b in the annular direction may be set to be higher than the elongation degree of the inner peripheral side fabric portion 7a in the annular direction by setting the weaving density of the warp fiber threads 11b forming the outer peripheral side fabric portion 7b to be lower than weaving density of the warp fiber threads 11a forming the inner peripheral side fabric portion 7a in the state of
In the expansion state, the elongation degree in the annular direction of the intermediate fabric portion 7c may gradually decrease as shifting toward the virtual central axis C side. Similarly, in the expansion state, the elongation degree in the annular direction of the outer peripheral side fabric portion 7b may gradually decreases as shifting toward the virtual central axis C side. Furthermore, in the expansion state, the elongation degree in the annular direction of the inner peripheral side fabric portion 7a may gradually decrease as shifting toward the virtual central axis C side. In such a case, the elongation degree in the annular direction of a portion on the side closest to the virtual central axis C in the intermediate fabric portion 7c may be equal to or higher than the elongation degree in the annular direction of a portion on the side farthest from the virtual central axis C in the inner peripheral side fabric portion 7a. The elongation degree in the annular direction of a portion on the side farthest from the virtual central axis C in the intermediate fabric portion 7c may be equal to or lower than the elongation degree in the annular direction of a portion on the side closest to the virtual central axis C in the outer peripheral side fabric portion 7b.
3
a, 3b, 3c Annular balloon, 4 Balloon, 4a Axial direction end portion of balloon, 5 Radio wave reflective film, 5a Outer peripheral edge portion, 5b Outer edge portion, 6 Joining thread, 7 Constraint fabric, 7a Inner peripheral side fabric portion, 7b Outer peripheral side fabric portion, 7c Intermediate fabric portion, 7d Short side direction end portion, 7e Long side direction end portion, 9 Sewing thread, 10 Corner reflector, 11, 11a, 11b, 11c Warp fiber thread, 13 Weft fiber thread, 13a First fiber thread, 13b Second fiber thread, C Virtual central axis
| Number | Date | Country | Kind |
|---|---|---|---|
| 2015/032549 | Feb 2015 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2016/054608 | 2/17/2016 | WO | 00 |
