JP5591818B2 - Inspection apparatus and inspection method - Google Patents

Description

  The present invention relates to a preform which is a preform of an optical fiber in which holes are formed, that is, a preform inspection apparatus and a method for inspection in which a through hole is formed.

  In recent years, a photonic crystal fiber (PCF) has attracted attention as an optical fiber suitable for long-distance transmission. A photonic crystal fiber is an optical fiber in which the refractive index of the cladding is reduced by holes, and it is known that optical characteristics that cannot be obtained by conventional optical fibers in which the refractive index of the cladding is reduced by impurities are obtained. It has been.

  As described in Patent Documents 1 to 4, the photonic crystal fiber includes (1) a preform manufacturing process for manufacturing a columnar base material made of silica glass (hereinafter referred to as “preform”), (2 It is manufactured through a through-hole forming step for forming a through-hole serving as a base material for holes in the preform, and (3) a drawing step for drawing the preform with the through-hole formed therein.

  In the photonic crystal fiber, the position of the holes greatly affects the optical characteristics. Therefore, in order to manufacture an optical fiber having desired optical characteristics, it is important to form a through hole at a predetermined appropriate position in the preform.

  In the through hole forming step, through holes extending in a direction perpendicular to these end surfaces from one end surface of the preform to the other end surface are formed by drilling. For this reason, if the machining accuracy of the machine tool that forms the through hole is low, the drilling position gradually shifts as the drilling progresses even if drilling starts from an appropriate position on one end surface, and the other end surface penetrates. Large positional displacement of the holes may occur, or the through holes may be connected on the way. For this reason, after forming a through-hole, it is necessary to test | inspect whether the through-hole is formed in the appropriate position.

  Conventionally, the inspection of whether or not the through-hole is formed at an appropriate position is generally performed by a method of observing the preform from the end surface direction using an optical microscope.

Japanese Patent Publication “JP 2002-145634” (published on May 22, 2002) Japanese Patent Publication “JP 2002-249335” (published on September 6, 2002) Japanese Patent Publication “JP 2002-293562 A” (published on October 9, 2002) Japanese Published Patent Publication "Japanese Patent Laid-Open No. 2006-160528" (Released on June 22, 2006)

  However, the conventional inspection method using an optical microscope has a problem that only the formation position of holes near the end face of the preform can be inspected. That is, there has been a problem that the formation position of the through hole cannot be inspected in the middle of both end faces (arbitrary cross section between both end faces). An intermediate through-hole formation position is also estimated from a hole formation position on one end face and a hole formation position on the other end face. The position where the hole is formed cannot be specified with high accuracy. For this reason, when the through hole formation position on the end face is greatly deviated from the proper position, it is necessary to examine which part can be used for manufacturing an optical fiber by cutting the preform. This increases the manufacturing cost.

  The present invention has been made in view of the above problems, and its purpose is to determine whether or not the through hole is formed at an appropriate position in the middle of both end faces of the preform without destroying the preform. The object is to realize an inspection apparatus and inspection method that can be confirmed well.

  In order to solve the above problems, an inspection apparatus according to the present invention is an inspection apparatus that inspects a cylindrical preform having a through-hole, and is generated by allowing light to enter from a side surface of the preform. Detection means for successively detecting the intensity distribution of the forward scattered light of the preform, and rotating the preform around the center axis of the preform or moving the detection means so as to go around the preform Rotating / moving means for calculating, and calculating means for calculating a time series of feature values having values corresponding to the arrangement of the through holes from the intensity distribution of the forward scattered light detected sequentially. It is said.

  Moreover, in order to solve the said subject, the test | inspection method which concerns on this invention is a test | inspection method which test | inspects the cylindrical preform in which the through-hole was formed, Comprising: By making a light ray enter from the side surface of the said preform A detection step of sequentially detecting the intensity distribution of the forward scattered light of the preform generated by the detection means, and the preform is rotated with the central axis of the preform as a rotation axis, or the preform is circulated. A rotation / movement step for moving the detection means, a calculation step for calculating a time series of feature amounts having values corresponding to the arrangement of the through holes from the intensity distribution of the forward scattered light detected sequentially, and the features And a determination step of determining whether or not the through hole is formed at a predetermined position based on a time series of quantities.

  The time series of feature values calculated from the intensity distribution of the forward scattered light detected sequentially while rotating the preform around the central axis or moving the detection means to circulate around the preform is the through hole. It shows different behavior depending on whether it is formed at an appropriate position. For this reason, referring to the time series of the feature amounts, it can be accurately confirmed whether or not the through hole is formed at a predetermined position without destroying the preform.

  According to the present invention, it can be accurately confirmed whether or not the through hole is formed at a predetermined position without destroying the preform.

It is a schematic structure figure showing the schematic structure of the inspection device concerning the embodiment of the present invention. The upper stage is a graph showing the intensity distribution of forward scattered light obtained when a parallel light beam is irradiated to a preform having no through-holes, and the lower stage is a cross-sectional view of such a preform. The upper row is a graph showing the intensity distribution of forward scattered light obtained when parallel rays are irradiated to a preform having through holes formed at appropriate positions, and the lower row is a cross-sectional view of such a preform. It is. The upper graph is a graph showing the intensity distribution of forward scattered light obtained when a parallel beam is irradiated to a preform in which one through-hole is displaced, and the lower graph is a cross section of such a preform. FIG. The upper graph is a graph showing the intensity distribution of forward scattered light obtained when a parallel beam is irradiated to a preform in which two through holes are displaced, and the lower graph is a cross section of such a preform. FIG. It is sectional drawing of the ideal preform in which all the through-holes were formed in the appropriate position. It is a graph which shows the time series of the dark part width | variety in the intensity distribution of the forward scattered light obtained by rotating the preform shown in the lower stage of FIG. 5 is a graph showing a time series of dark part widths in the intensity distribution of forward scattered light obtained by rotating the preform shown in the lower part of FIG. 4. It is a graph which shows the time series of the dark part width | variety in the intensity distribution of the forward scattered light obtained by rotating the preform shown in the lower stage of FIG. The upper graph is a graph showing the intensity distribution of forward scattered light obtained when a parallel beam is irradiated to a preform in which all the through holes are uniformly displaced, and the lower graph is a graph showing such a profile. It is sectional drawing of reform. The upper graph is a graph showing the intensity distribution of forward scattered light obtained when parallel rays are irradiated to a preform in which all through holes are formed at appropriate positions, and the lower graph is a graph of such a preform. It is sectional drawing. The upper graph is a graph showing the intensity distribution of forward scattered light obtained when a parallel beam is irradiated to a preform in which all the through holes are uniformly displaced, and the lower graph is a graph showing such a profile. It is sectional drawing of reform. The upper graph is a graph showing the intensity distribution of forward scattered light obtained when parallel rays are irradiated to a preform in which all through holes are formed at appropriate positions, and the lower graph is a graph of such a preform. It is sectional drawing. The upper graph is a graph showing the intensity distribution of forward scattered light obtained when a parallel beam is irradiated to a preform in which all the through holes are uniformly displaced, and the lower graph is a graph showing such a profile. It is sectional drawing of reform. The upper graph is a graph showing the intensity distribution of forward scattered light obtained when parallel rays are irradiated to a preform in which all through-holes are shifted by 3 mm from the preform central axis. It is sectional drawing of such a preform. 12 is a graph showing a time series of an integral value difference | S2-S1 | obtained by rotating the preform shown in the lower part of FIG. It is a graph which shows the time series of integral value difference | S2-S1 | obtained by rotating the preform shown in the lower stage of FIG. It is a graph which shows the time series of the bright part width | variety | W2-W1 | obtained by rotating the preform shown in the lower stage of FIG. It is a graph which shows the time series of the bright part width | variety | W2-W1 | obtained by rotating the preform shown in the lower stage of FIG.

  Embodiments of the present invention will be described below with reference to the drawings. It should be noted that the term “optical fiber” in each embodiment described below refers to an optical fiber in which one or more holes extending in the central axis direction are formed unless otherwise specified. Further, when “preform” is described in the present embodiment, unless otherwise specified, a preform that is a base material of an optical fiber in which one or more holes are formed, that is, one or more penetrations. It refers to a preform in which holes are formed.

<First Embodiment>
A first embodiment of the present invention (hereinafter referred to as “this embodiment”) will be described with reference to FIGS. The inspection apparatus according to the present embodiment is an inspection apparatus suitable for detecting a positional shift that has occurred in some of the through holes formed in the preform.

[Inspection equipment]
The inspection apparatus according to the present embodiment will be described with reference to FIG. FIG. 1 is a schematic configuration diagram illustrating a schematic configuration of an inspection apparatus 100 according to the present embodiment.

  The inspection apparatus 100 is an apparatus for inspecting whether or not the through hole 11 is formed at a predetermined appropriate position in each cross section of the preform 10, and as shown in FIG. A detector (detection means) 102, a rotation mechanism (rotation / movement means) 103, a parallel movement mechanism (parallel movement means) 104, a calculation unit 105 (calculation means), a determination unit 106, and a position detection unit 107.

  The light source 101 is a means for irradiating the preform 10 with parallel rays from the side surface, and is, for example, an LED (Light Emitting Diode). The parallel rays irradiated to the preform 10 are repeatedly refracted and reflected at the boundary separating the inside and outside of the preform 10 and the boundary separating the inside and outside of the through hole 11, and forward on the opposite side of the preform 10 from the light source 101 side. This produces scattered light. The forward scattered light generated in this way is hereinafter simply referred to as “forward scattered light of the preform 10”.

  The detector 102 is means for sequentially detecting the intensity distribution of the forward scattered light of the preform 10. More specifically, in a plane opposite to the light source 101 side of the preform 10 and orthogonal to the parallel rays irradiated from the light source 101, the plane is orthogonal to the orthogonal projection of the central axis of the preform 10. This is means for sequentially detecting the intensity distribution on the straight line. Such a detector 102 can be realized, for example, by arranging a CCD (Charge Coupled Device) line sensor along this straight line.

  The rotation mechanism 103 is a means for rotating the preform 10 gripped by the grip portion 103a about the center axis (of the preform 10) as a rotation axis. By rotating the preform 10 using the rotation mechanism 103, it becomes possible to sequentially detect the forward scattered light of the preform 10 in each direction. Instead of adopting a configuration in which the preform 10 is rotated using the rotation mechanism 103 as in the present embodiment, a configuration in which the light source 101 and the detector 102 are moved so as to go around the preform 10 is the same. It becomes possible.

  The translation mechanism 104 is a means for translating the light source 101 and the detector 102 held by the holding unit 104 a in the central axis direction of the preform 10. While the preform 10 is rotated about the central axis using the rotation mechanism 103, the light source 101 and the detector 102 are translated using the parallel movement mechanism 104, whereby forward scattered light of the preform 10 in each direction. Can be detected for each cross section. Instead of adopting a configuration in which the light source 101 and the detector 102 are translated in the central axis direction of the preform 10 using the translation mechanism 104 as in the present embodiment, the preform 10 is moved in the central axis direction. The same can be achieved even if the configuration is adopted.

  The intensity distribution of the forward scattered light of the preform 10 has a dark portion corresponding to the “shadow” of the through hole 11 as described later. The computing unit 105 is means for sequentially calculating the width of the dark part (hereinafter abbreviated as “dark part width”) from the intensity distribution of the forward scattered light sequentially detected by the detector 102. The determination unit 106 is a unit for determining whether or not the through hole 11 is formed at a predetermined appropriate position based on the time series of the dark part width sequentially calculated by the calculation unit 105. Note that a method for determining whether or not the through hole 11 is formed at a predetermined appropriate position based on the time series of the dark part width will be described later with reference to another drawing.

  The position detection unit 107 is a means for detecting the positions of the light source 101 and the detector 102. The determination unit 106 outputs or records a determination result indicating whether or not the through-hole 11 is properly arranged in association with the positions of the light source 101 and the detector 102 detected by the position detection unit 107. Therefore, by referring to the information output or recorded by the determination unit 106, it is possible to know in which cross section of the preform 10 the arrangement of the through holes 11 is disturbed.

[Intensity distribution of forward scattered light]
Next, the intensity distribution of the forward scattered light of the preform will be described in detail with reference to FIGS. 2 to 5 and FIGS.

  The upper part of FIG. 2 is a graph showing the intensity distribution of the forward scattered light obtained when the parallel light beam 20 is irradiated to the preform 10 ′ in which no through-hole is formed, and the lower part of FIG. 2 is a cross-sectional view of a preform 10 ′.

  As shown in the lower part of FIG. 2, the parallel light beam 20 incident on the preform 10 ′ is refracted when entering the preform 10 ′ from the air and when entering the air from the preform 10 ′. The other side of the reform 10 'is reached. As a result, the intensity distribution of the forward scattered light of the preform 10 'becomes a smooth intensity distribution having one peak at the center as shown in the upper part of FIG.

  The upper part of FIG. 3 is a graph showing the intensity distribution of the forward scattered light obtained when the parallel light beam 20 is applied to the preform 10 in which the through-holes 11 are formed at appropriate positions, and the lower part of FIG. FIG. 2 is a cross-sectional view of such a preform 10.

  As shown in the lower part of FIG. 3, among the parallel rays 20 incident on the preform 10, rays whose optical axis is far from the central axis of the preform 10 are projected from the air as in the case where the through hole 11 is not formed. When entering the reform 10 and when entering the air from the preform 10, the light is refracted and reaches the opposite side of the preform 10. On the other hand, as shown in the lower part of FIG. 3, among the parallel light rays 20 incident on the preform 10, a light beam whose optical axis is close to the central axis of the preform 10 is refracted when entering the preform 10 from the air, Furthermore, refraction and reflection are repeated at the boundary with the through-hole 11, and the loss is made almost without being scattered forward. As a result, the intensity distribution of the forward scattered light of the preform 10 is an intensity distribution having two peaks and a dark part sandwiched between these two peaks, as shown in the upper part of FIG. In the present specification, the “dark width” refers to the distance between these two peaks.

It should be noted that when the preform 10 is rotated at a constant rotation speed as shown in the lower part of FIG. 3, the dark portion width periodically changes. As shown in the lower part of FIG. 3, when the through-hole 11 is arranged on the apex of a regular hexagon centering on the central axis of the preform 10, it passes through the central axis of the preform 10 and is perpendicular to the parallel light beam 20. When the two through-holes 11 are simultaneously arranged on the straight line, the dark part width takes the maximum value L ₀ and the two through-holes 11 are simultaneously formed on the straight line passing through the central axis of the preform 10 and parallel to the parallel light beam 20. When placed, the dark space width takes the minimum value. If the time series of the dark part width obtained when the preform 10 is rotated as shown in the lower part of FIG. 3 is plotted, a sine waveform is obtained as shown in FIG.

  It should be noted that such a periodic change in the dark portion width that occurs when the preform 10 is rotated at a constant rotational speed is such that the through-hole 11 is disposed on the vertex of a regular polygon having an even number of vertices. It is a common case. Further, even when the through hole is arranged on the vertex of a regular polygon having an odd number of vertices, the dark portion width remains unchanged at a specific maximum value and minimum value.

  The upper part of FIG. 4 is a graph showing the intensity distribution of the forward scattered light obtained when the parallel light beam 20 is irradiated to the preform 10 in which one through hole 11a is displaced. The lower part of FIG. These are sectional views of such a preform 10. The point where the intensity distribution of the forward scattered light has two peaks and a dark part sandwiched between these two peaks is the case where the through hole 11 is formed at an appropriate position as shown in the upper part of FIG. It is the same.

The lower preform 10 in FIG. 4 is different from the lower preform 10 in FIG. 3 in that one through hole 11a is formed to be shifted outward. Therefore, passing through the central axis of the preform 10, the dark area width when the through-hole 11a that misaligned perpendicular straight line into parallel beams 20 are arranged to take the maximum value L ₁ (L _1> L ₀ ). When the time series of the dark part width obtained when the preform 10 is rotated as shown in the lower part of FIG. 4 is plotted, the waveform is broken as shown in FIG.

  In addition, when the through hole 11 a is formed so as to be displaced inward, the through hole 11 a causing the positional displacement is arranged on a straight line that passes through the central axis of the preform 10 and is perpendicular to the parallel light beam 20. The dark part width at the time does not reach the maximum value.

  The upper part of FIG. 5 is a graph showing the intensity distribution of forward scattered light obtained when the preform 10 in which the two through-holes 11a and 11b are displaced is irradiated with a parallel light beam. The lower part is a cross-sectional view of such a preform 10. As shown in the upper part of FIG. 5, the through hole 11 is formed at an appropriate position in that the intensity distribution of the forward scattered light has two peaks and an intensity distribution having a dark part sandwiched between these two peaks. It is the same as if

The lower preform 10 in FIG. 5 differs from the lower preform 10 in FIG. 3 and the lower preform 10 in FIG. 4 in that two through-holes 11 a and 11 b that are opposed to each other via the central axis are formed to be shifted outward. . Therefore, passing through the central axis of the preform 10, the vertical straight line into parallel beams 20, dark portion width when the two through holes 11a · b are misaligned is disposed a maximum value L _{2 (L 2> L 1> L} 0). When the time series of the dark part width obtained when the preform 10 is rotated as shown in the lower part of FIG. 5 is plotted, the waveform is broken as shown in FIG.

  Even when the through holes 11a and 11b are formed to be displaced inwardly, the through holes 11a and 11b that are misaligned are on a straight line that passes through the central axis of the preform 10 and is perpendicular to the parallel light beam 20. The dark portion width when placed in the position does not reach the maximum value.

[Judgment method based on whether or not the through-hole is formed at an appropriate position based on the dark width]
Next, a method for the determination unit 106 (see FIG. 1) to determine whether or not the through hole is formed at a predetermined appropriate position based on the time series of the dark part width will be described with reference to FIG. To do. FIG. 6 is a cross-sectional view of an ideal preform 10 in which all through holes 11 are formed at appropriate positions.

As described above, when the through hole 11 formed in the ideal preform 10 shown in FIG. 6 deviates from an appropriate position to the outside, the dark portion width obtained when the preform 10 is rotated once. The maximum value L of the series becomes larger than the maximum value L ₀ of the time series of the dark part width obtained when the ideal preform 10 is rotated once.

Therefore, for example, a value slightly larger than the time series maximum value L ₀ of the dark part width obtained when the ideal preform 10 is rotated once is stored in advance in the memory included in the determination unit 106 as the threshold Th. In addition, the determination unit 106 extracts (1) the time series maximum value L of the dark part width calculated by the calculation unit 105, (2) compares the extracted maximum value L with the threshold Th, and (3) When the extracted maximum value L is larger than the threshold value Th, it is possible to detect that the through-hole 11 has shifted outward from an appropriate position by determining that the “through-hole 11 has shifted outward”. The inspection apparatus 100 can be realized. The time series maximum value L ₀ of the dark part width obtained when the ideal preform 10 is rotated once may be determined by actual measurement or opposed to the ideal preform 10 via the central axis. the distance between the centers of the two through holes D, diameter of the through-holes (diameter) as d, may be calculated by the equation L _{0 =} D + d.

Further, when any one of the through holes 11 is displaced inward from an appropriate position, a maximum value that does not reach the maximum value L ₀ appears in the time series of the dark part width obtained when the preform 10 is rotated once. Therefore, for example, a value slightly smaller than the time series maximum value L ₀ of the dark part width obtained when the ideal preform 10 is rotated once is stored in the memory included in the determination unit 106 in advance as the threshold Th. In addition, the determination unit 106 (1) extracts all the maximum values included in the time series of the dark portion width calculated by the calculation unit 105, and (2) compares each of the extracted maximum values with the threshold Th. (3) If it is determined that “the through hole 11 is displaced inward” when a maximum value smaller than the threshold Th is present, the through hole 11 may be displaced inward from an appropriate position. A detectable inspection apparatus 100 can be realized.

  Here, the determination method for determining that the through-hole 11 is not formed at a predetermined position when the time series of the dark part width has a maximum value exceeding a predetermined threshold has been described. Is not limited to this.

  For example, if all the through holes 11 are at appropriate positions, the time series of the dark portion width shows a sine waveform as shown in FIG. On the other hand, if the through hole 11 is deviated from an appropriate position, the waveform is broken as shown in FIGS. Therefore, the time-series frequency spectrum (with one sharp peak) of the dark part width obtained when the ideal preform 10 is rotated once is stored in advance in the memory provided in the determination unit 106. By comparing with the frequency spectrum calculated by the calculation unit 105, it can be appropriately determined whether or not the through hole is formed at an appropriate position.

[Summary]
As described above, the inspection apparatus according to the present embodiment is an inspection apparatus that inspects a cylindrical preform having a through-hole formed therein, and the above-described profile generated by making a light beam incident from the side surface of the preform. Detection means for sequentially detecting the intensity distribution of the forward scattered light of the reform, and rotation for rotating the preform around the center axis of the preform or moving the detection means so as to go around the preform / Moving means, and calculating means for calculating a time series of the dark width from the intensity distribution of the forward scattered light detected sequentially.

  Further, the inspection method according to the present embodiment is an inspection method for inspecting a cylindrical preform in which a through-hole is formed, and the front of the preform generated by allowing light to enter from a side surface of the preform. A detection step of sequentially detecting the intensity distribution of scattered light by a detection means, and a rotation for rotating the preform around the center axis of the preform or moving the detection means to go around the preform. / The moving step, the calculation step of calculating the time series of the dark part width from the intensity distribution of the forward scattered light sequentially detected, and the through hole is formed at a predetermined position based on the time series of the dark part width And a determination step of determining whether or not it has been performed.

  According to said structure or method, the dark part according to the formation position of a through-hole arises in intensity distribution of the said forward scattered light. Moreover, since the preform is rotated with the central axis as the rotation axis, or the detection means is moved so as to go around the preform, the time series of the dark part width in the intensity distribution of the forward scattered light is: It behaves differently depending on whether or not the through hole is formed at an appropriate position. For this reason, referring to the time series of the dark portion width in the intensity distribution of the forward scattered light calculated by the above configuration, whether the through hole is formed at a predetermined position or not is determined as follows. There is an effect that it can be confirmed with high accuracy without destruction.

  In the inspection apparatus according to the present embodiment, it is preferable that the inspection apparatus further includes translation means for translating the preform or the detection means in the central axis direction of the preform.

  According to the above configuration, it is possible to accurately check whether or not the through hole is formed at a predetermined position for each cross section of the preform without destroying the preform. Play.

  The inspection apparatus according to this embodiment compares the time series maximum value or maximum value of the dark part width with a predetermined threshold value to determine whether the through hole is formed at a predetermined position. It is preferable to further comprise determination means for determining.

  The through holes formed in the preform are usually arranged at equal intervals on a circumference centered on the central axis of the preform in order to give the optical fiber axial symmetry.

  In this case, when any of the through holes is shifted from the circumference to the outside, the maximum value of the time series of the dark part width obtained when the preform is rotated once, all the through holes are on the circumference. It becomes larger than the time series maximum value of the dark part width obtained when the formed preform is rotated once. Further, when any of the through holes is displaced inward from the circumference, all the through holes are formed on the circumference in a time series of dark portion widths obtained when the preform is rotated once. A maximum value that does not reach the maximum value of the time series of the dark width obtained when the preform is rotated once appears. Accordingly, if the time series maximum value of the dark part width obtained when the preform having the through hole formed on the circumference is rotated once is set as a threshold value, the time series maximum value of the dark part width is determined. Can be accurately determined whether or not the through hole is formed at a predetermined position. Further, when any of the through holes is shifted inward from the circumference, the through hole is formed at a predetermined position by comparing each time series maximum value of the dark portion with this threshold value. It can be accurately determined whether or not there is.

  The inspection apparatus according to the present embodiment determines whether or not the through hole is formed at a predetermined position by comparing the time-series frequency spectrum of the dark part width with a predetermined frequency spectrum. It is preferable to further comprise determination means.

  The through holes formed in the preform are usually arranged at equal intervals on a circumference centered on the central axis of the preform in order to give the optical fiber axial symmetry. In this case, the time series of the dark part width shows a sine waveform, and when the position shift occurs in the through hole, the time series of the dark part width becomes a sine waveform collapsed. Therefore, by comparing the time-series frequency spectrum of the dark part width with the spectrum of the dark part width obtained when the preform having the through holes arranged at equal intervals on the circumference is rotated once, the through hole becomes circular. There is an effect that it can be accurately determined whether or not they are arranged at equal intervals on the circumference.

<Second Embodiment>
A second embodiment of the present invention (hereinafter referred to as “this embodiment”) will be described with reference to FIGS. 10 to 14 and FIGS. 16 to 19. The inspection apparatus according to the present embodiment is an inspection apparatus suitable for detecting a uniform positional deviation generated in all through holes formed in the preform.

  FIG. 10 shows a mode of misregistration to be detected in the present embodiment. The lower part of FIG. 10 is a cross-sectional view of the preform 10 in which all the through holes 11 ′ are uniformly displaced, and the upper part of FIG. 10 shows the parallel light beam 20 with respect to such a preform 10. It is a graph which shows intensity distribution of the forward scattered light obtained when it irradiates. As shown in the upper part of FIG. 10, the point that the intensity distribution of the forward scattered light has two peaks and a dark part sandwiched between these two peaks is the same as described above.

When all the through-holes 11 ′ formed in the preform 10 are uniformly displaced, that is, all the through-holes 11 ′ formed in the preform 10 are on the vertices of an eccentric regular hexagon. The maximum dark portion width L obtained when the preform 10 is rotated once is the maximum dark portion width obtained when the ideal preform 10 (see FIG. 6) is rotated once. It will match the value _{L 0.} Therefore, the inspection apparatus 100 according to the first embodiment may not be able to detect a uniform positional deviation that has occurred in all the through holes 11 ′ formed in the preform 10.

  Therefore, in this embodiment, instead of referring to the dark portion width L of the forward scattered light, (1) the integrated value S1 obtained by integrating the intensity of the forward scattered light on the first bright portion, and the forward scattering By referring to the absolute value of the difference from the integrated value S2 obtained by integrating the light intensity on the second bright part (hereinafter abbreviated as “integrated value difference”) ΔS = | S2−S1 | (2) The width of the first bright portion of forward scattered light (hereinafter sometimes abbreviated as “first bright portion width”) W1 and the width of the second bright portion of forward scattered light (hereinafter referred to as “first”). 2 may be abbreviated as “bright portion width”) (referred to as “bright portion width difference”) ΔW = | W2−W1 | A uniform positional deviation generated in all the through-holes 11 'is detected.

  Here, as shown in FIG. 10, the bright portion of the forward scattered light refers to a region where the intensity of the forward scattered light spreads outside the two peaks and becomes greater than a predetermined intensity Io (explanation). For the sake of convenience, the bright part spreading to the left of the dark part is referred to as “first bright part” and the bright part spreading to the right of the dark part is referred to as “second bright part”). The lower limit intensity Io that defines the left end of the first bright part and the right end of the second bright part can be set to an arbitrary value of 0 or more.

  The configuration of the inspection apparatus according to the present embodiment is the same as the configuration of the inspection apparatus 100 according to the first embodiment shown in FIG. However, when the inspection is performed with reference to the integral value difference ΔS = | S1-S2 |, the calculation unit 105 calculates the integral value difference ΔS = | S1-S2 from the intensity distribution of the forward scattered light sequentially detected by the detector 102. | Is sequentially calculated, and the determination unit 106 determines whether or not the through hole 11 is formed at an appropriate position based on the time series of the integral value difference ΔS sequentially calculated by the calculation unit 105. The On the other hand, when the inspection is performed with reference to the bright part width difference ΔW = W2−W1, the calculation unit 105 sequentially calculates the bright part width difference ΔW from the intensity distribution of the forward scattered light sequentially detected by the detector 102, A configuration is employed in which the determination unit 106 determines whether or not the through hole 11 is formed at an appropriate position based on the time series of the bright part width difference ΔW sequentially calculated by the calculation unit 105.

[Determination method based on integrated value difference ΔS as to whether or not the through hole is formed at an appropriate position]
Next, a method for determining whether or not the through hole is formed at an appropriate position based on the integral value difference ΔS will be described with reference to FIGS. 11 to 12 and FIGS. 16 to 17. .

  First, the intensity distribution of the forward scattered light obtained when the parallel light beam 20 is applied to the preform 10 in which the through holes 11 are formed at appropriate positions will be described with reference to FIG. The lower part of FIG. 11 is a cross-sectional view of such a preform 10, and the upper part of FIG. 11 shows the intensity distribution of forward scattered light obtained when such a preform 10 is irradiated with parallel rays 20. It is a graph to show.

  In the upper part of FIG. 11, the area on the graph having an area corresponding to the integrated value S1 obtained by integrating the intensity of the forward scattered light on the first bright portion, and the intensity of the forward scattered light are the second A region on the graph having an area corresponding to the integral value S2 obtained by integrating on the bright part is clearly indicated by hatching.

  As shown in the lower part of FIG. 11, when all the through holes 11 are formed at appropriate positions, the intensity of the forward scattered light is integrated on the first bright part as shown in the upper part of FIG. The obtained integrated value S1 and the integrated value S2 obtained by integrating the intensity of the forward scattered light on the second bright portion are substantially equal. Even if the preform 10 is rotated, the intensity distribution of the forward scattered light in these two bright portions changes substantially symmetrically with respect to the central axis of the preform 10, so that the integral value S1 and the integral value S2 are substantially equal. Keep on.

  FIG. 16 shows a time series of the integral value difference ΔS = | S2−S1 | calculated by the calculation unit 105 when the preform 10 in which all the through holes 11 are formed at appropriate positions is an inspection target. . It can be seen from FIG. 16 that the maximum value of the integral value difference ΔS = | S2−S1 | calculated by the calculation unit 105 does not exceed the threshold value ΔSo set as appropriate.

  Next, the intensity distribution of the forward scattered light obtained when the preform 10 in which all the through holes 11 ′ are uniformly displaced is irradiated with the parallel light beam 20 will be described with reference to FIG. 12. To do. The lower part of FIG. 12 is a cross-sectional view of such a preform 10, and the upper part of FIG. 12 shows the intensity distribution of forward scattered light obtained when such a reformer 10 is irradiated with parallel rays 20. It is a graph.

  Also in the upper part of FIG. 12, the region on the graph having an area corresponding to the integrated value S1 obtained by integrating the intensity of the forward scattered light on the first bright portion, and the intensity of the forward scattered light are the second A region on the graph having an area corresponding to the integral value S2 obtained by integrating on the bright part is clearly indicated by hatching.

  As shown in the lower part of FIG. 12, the center of gravity of six through-holes 11 ′ passing through the central axis of the preform 10 and perpendicular to the parallel rays 20 (a regular hexagon in which the through-holes 11 ′ are arranged at each vertex) The difference ΔS = | S2−S1 | between the two integral values shown in the upper part of FIG. 12 takes a maximum value.

  FIG. 17 shows a time series of the integral value difference ΔS = | S2−S1 | calculated by the calculation unit 105 when the preform 10 in which all the through holes 11 ′ are uniformly displaced is set as the inspection target. Shown in It can be seen from FIG. 17 that each local maximum value of the integral value difference ΔS = | S2−S1 | calculated by the calculation unit 105 exceeds the threshold value ΔSo described above.

  Therefore, the determination unit 106 determines whether or not the through hole is formed at an appropriate position by comparing each local maximum value of the integral value difference ΔS = | S2−S1 | calculated by the calculation unit 105 with the threshold value ΔSo. Can be determined. Specifically, when each maximum value of the integral value difference ΔS = | S2−S1 | calculated by the calculation unit 105 does not exceed the threshold value So, it is determined that the through hole is formed at an appropriate position. When any of the integral value differences ΔS = | S2−S1 | calculated by the calculation unit 105 exceeds the threshold value So, the through-hole is not formed at an appropriate position (causes a positional shift). Can be determined.

[Determination method based on the bright part width difference ΔW, whether or not the through hole is formed at an appropriate position]
Next, a method by which the determination unit 106 determines whether or not the through hole is formed at an appropriate position based on the bright portion width difference ΔW will be described with reference to FIGS. 13 to 14 and FIGS. 18 to 19. To do.

  First, the intensity distribution of the forward scattered light obtained when the preform 10 having the through holes 11 formed at appropriate positions is irradiated with the parallel light beam 20 will be described with reference to FIG. The lower part of FIG. 13 is a sectional view of such a preform 10, and the upper part of FIG. 13 shows the intensity distribution of forward scattered light obtained when such a preform 10 is irradiated with parallel rays 20. It is a graph to show. In the upper part of FIG. 13, the first bright part width W1 and the second bright part width W2 of the forward scattered light are clearly shown by the lengths of the arrows.

  As shown in the lower part of FIG. 13, when all the through holes 11 are formed at appropriate positions, as shown in the upper part of FIG. 13, the first bright part width W1 and the second bright part of the forward scattered light are obtained. The part width W2 is substantially equal. Even if the preform 10 is rotated, the intensity distribution of the forward scattered light in these two bright portions changes substantially symmetrically with respect to the central axis of the preform 10, so that the first bright portion width W1 and the second bright portion are changed. The part width W2 is kept substantially equal.

  FIG. 18 shows a time series of the bright part width difference ΔW = | W1−W2 | calculated by the calculation unit 105 when the preform 10 in which all the through holes 11 are formed at appropriate positions is an inspection target. Show. It can be seen from FIG. 18 that the maximum value of the bright part width difference ΔW = | W1−W2 | calculated by the calculation unit 105 does not exceed the threshold ΔWo set as appropriate.

  Next, the intensity distribution of the forward scattered light obtained when the parallel light beam 20 is applied to the preform 10 in which all the through-holes 11 ′ are uniformly displaced will be described with reference to FIG. To do. The lower part of FIG. 14 is a cross-sectional view of such a preform 10, and the upper part of FIG. 14 shows the intensity distribution of forward scattered light obtained when such a reformer 10 is irradiated with parallel rays 20. It is a graph.

  As shown in the lower part of FIG. 14, the center of gravity of six through-holes 11 ′ on a straight line that passes through the central axis of the preform 10 and is perpendicular to the parallel rays 20 (a regular hexagon in which the through-holes 11 ′ are arranged at each vertex) 14), the difference ΔW = | W1−W2 | between the bright part width W1 and the bright part width W2 shown in the upper part of FIG. 14 takes a local maximum value.

  A time series of the bright part width difference ΔW = | W1−W2 | calculated by the calculation unit 105 when the preform 10 in which all the through holes 11 ′ are uniformly displaced is set as the inspection target. 19 shows. It can be seen from FIG. 19 that each local maximum value of the bright part width difference ΔW = | W1−W2 | calculated by the calculation unit 105 exceeds the threshold value ΔWo.

  Therefore, the determination unit 106 compares each maximum value of the bright portion width difference ΔW = | W1−W2 | calculated by the calculation unit 105 with a predetermined threshold value ΔWo, so that the through hole is formed at an appropriate position. It can be determined whether or not. Specifically, when each maximum value of the bright part width difference ΔW = | W1−W2 | calculated by the calculation unit 105 does not exceed the threshold value Wo, it is determined that the through hole is formed at an appropriate position. When any of the maximum values of the bright part width difference ΔW = | W1−W2 | calculated by the calculation unit 105 exceeds the threshold value ΔWo, the through hole is not formed at an appropriate position (position shift) It is sufficient to determine that the

<Additional notes>
The present invention is not limited to the above-described embodiment, and various modifications are possible within the scope of the claims, and the technique of the present invention also relates to an embodiment obtained by appropriately combining the disclosed technical means. Included in the scope.

  In the embodiment described above, as feature quantities used for detecting the displacement of the through hole, (1) the dark part width of the forward scattered light and (2) the intensity of the forward scattered light are integrated on the two bright parts. (3) The absolute value of the difference between the two bright part widths of the forward scattered light is exemplified, but the feature quantity that can be used to detect the positional deviation of the through hole is It is not limited to. That is, any feature amount can be used as long as it is a feature amount that can be calculated from the intensity distribution of the forward scattered light and has a value corresponding to the arrangement of the through holes formed in the preform. It can be used to detect the positional deviation of

  The embodiment of the present invention will be described in more detail with reference to the following examples. Of course, the present invention is not limited to the following examples, and various modes are possible for details.

[Example 1]
The effectiveness of the inspection apparatus 100 according to the first embodiment of the present invention was confirmed as follows.

  First, a preform A having a cross section as shown in the lower part of FIG. Specifically, for a preform having an outer diameter of 90 mmφ, six through-holes having a diameter of 4 mmφ were formed by a drill method at a position 20 mm from the center of the preform. In addition, a preform B having a cross section as shown in the lower part of FIG. 4 in the entire longitudinal direction and a preform C having a cross section as shown in the lower part of FIG. Created by the method. However, when forming the preform B, the position where one through hole (through hole 11a in FIG. 4) is formed is shifted outward by 4 mm, and when forming the preform C, two through holes (through holes in FIG. 5) are formed. The positions of the holes 11a and the through holes 11b) were shifted outward by 4 mm respectively.

  Next, the time series of the dark part width regarding the preform A was obtained using the inspection apparatus 100. The time-series acquisition of the dark part width is performed by rotating the preform A attached to the rotation mechanism 103 (with the central axis of the preform A as a rotation axis) and the light source 101 and the detector 102 attached to the parallel movement mechanism 104. Was detected by detecting the intensity distribution of the forward scattered light with the detector 102 while translating along the central axis of the preform A. At this time, LEDs and a CCD line sensor were used as the light source 101 and the detector 102. Further, the rotation speed of the preform was set to 100 rpm, the moving speed of the LED and the CCD line sensor was set to 10 mm / min, and the sampling period in the CCD line sensor was set to 500 milliseconds.

As a time series of dark portion widths related to the preform A, a time series having a sine wave shape shown in FIG. 7 was obtained. In this example, the threshold value Th used for the inspection of the preforms B to C was set using this time series. Specifically, the maximum value of the dark space width in this time series is set to L ₀ , and the threshold value Th is set to a value slightly larger than L ₀ , specifically, L ₀ +0.5 mm. If the through-hole can be accurately formed at a position 20 mm from the central axis at the time of forming the preform A, the maximum value Lo of the dark part width may be set to 40 mm without being obtained by actual measurement.

  Next, the preforms B to C were inspected using the inspection apparatus 100 according to the first embodiment. As in the case of the actual measurement of the dark part width, the inspection is performed by rotating the preforms B to C attached to the rotating mechanism 103 (with the center axis of the preform as the rotating axis) and detecting the light source 101 attached to the parallel moving mechanism 104 and the detection. The vessel 102 was moved in parallel along the central axis of the preforms B to C. At this time, an LED and a CCD line sensor were used as the light source 101 and the detector 102, as in the actual measurement of the dark part width. Similarly to the actual measurement of the dark part width, the rotation speed of the preform was set to 100 rpm, the moving speed of the LED and the CCD line sensor was set to 10 mm / min, and the sampling period in the CCD line sensor was set to 500 milliseconds.

  The time series of the dark portion width calculated by the calculation unit 105 when the preform B is an inspection target has a waveform as shown in FIG. All the local maximum values in this time series exceeded the previously set threshold value Th. This is because one through hole is formed so as to be shifted outward as shown in FIG. 4, so that the maximum value of the dark part width is larger than when all the through holes are formed at appropriate positions. is there. As a result, the determination unit 106 outputs a determination that “a through-hole is formed at a position shifted outward from an appropriate position” over the entire longitudinal direction.

  The time series of the dark portion width calculated by the calculation unit 105 when the preform C is an inspection target has a waveform as shown in FIG. All the local maximum values in this time series exceeded the previously set threshold value Th. This is because the two through holes are formed so as to be shifted outward as shown in FIG. 5, so that the maximum value of the dark portion width is larger than when all the through holes are formed at appropriate positions. is there. As a result, the determination unit 106 outputs a determination that “a through-hole is formed at a position shifted outward from an appropriate position” over the entire longitudinal direction.

  As described above, it was confirmed that the positional deviation generated in a part of the through holes formed in the preform can be effectively detected by using the inspection apparatus 100 according to the first embodiment.

[Example 2]
The effectiveness of the inspection apparatus 100 according to the second embodiment of the present invention was confirmed as follows.

  First, a preform having a cross section as shown in the lower part of FIG. Specifically, for a preform having an outer diameter of 90 mmφ, six through-holes having a diameter of 4 mmφ were formed by a drill method at a position 20 mm from the center of the preform (this preform was formed by using the preform used in Example 1). Since it is the same preform as the reform A, it is also called the preform A in this embodiment). In addition, a preform D having a cross section as shown in the lower part of FIG. However, when forming the preform D, as shown in the lower part of FIG. 15, the formation positions of all the through holes were shifted by 3 mm in the same direction.

  Next, the effectiveness of the determination method based on the integral value difference ΔS was confirmed as follows. Note that, as described above, the integral value difference ΔS is the integral value S1 obtained by integrating the intensity of the forward scattered light on the first bright part and the intensity of the forward scattered light on the second bright part. The difference | S2−S1 | from the integrated value S2 obtained in this way. The first bright part and the second bright part refer to a region where the intensity of forward scattered light spreading on both sides of the dark part is larger than a predetermined intensity Io. In the present embodiment, the first bright part and the second bright part are defined with Io = 0.

  First, the time series of the integral value difference ΔS related to the preform A was obtained using the inspection apparatus 100. The integral value difference ΔS is obtained by rotating the preform A attached to the rotating mechanism 103 and moving the light source 101 and the detector 102 attached to the parallel moving mechanism 104 along the central axis of the preform A. However, the detection was performed by detecting the intensity distribution of the forward scattered light with the detector 102. At this time, LEDs and a CCD line sensor were used as the light source 101 and the detector 102. Further, the rotation speed of the preform was set to 100 rpm, the moving speed of the LED and the CCD line sensor was set to 10 mm / min, and the sampling period in the CCD line sensor was set to 500 milliseconds.

A time series shown in FIG. 16 was obtained as a time series of the integral value difference ΔS regarding the preform A. In this embodiment, the threshold value ΔSo used for the inspection of the preform D is set using this time series. Specifically, the maximum value of the integrated value difference in this time series is set to ΔS _max , and the threshold value ΔS _o is set to a value larger than ΔS _max , specifically, three times ΔS _max (see the graph shown in FIG. 16). The vertical axis is the logarithm of the area).

  Next, the preform D was inspected using the inspection apparatus 100. In the inspection, the preform D attached to the rotation mechanism 103 was rotated (with the central axis of the preform D as the rotation axis) and attached to the parallel movement mechanism 104, as in the actual measurement of the integral value difference ΔS related to the preform A. The light source 101 and the detector 102 were moved while being translated along the central axis of the preform D. At this time, the rotation speed of the preform is set to 100 rpm, the moving speed of the LED and the CCD line sensor is set to 10 mm / min, and the sampling period in the CCD line sensor is set to 500 milliseconds, as in the actual measurement of the integral value difference ΔS related to the preform A. Set each.

The time series of the dark part width calculated by the arithmetic unit 105 when the preform D is an inspection target has the waveform shown in FIG. All local maximum values in this time series exceeded the previously set threshold value ΔS _o . As a result, the determination unit 106 outputs a determination that “the through hole is displaced” over the entire length direction.

  Next, the effectiveness of the determination method based on the bright part width difference ΔW was confirmed as follows. The bright part width difference ΔW indicates the difference | W2−W1 | between the width W1 of the first bright part of the forward scattered light and the width W2 of the second bright part of the forward scattered light, as described above. . The first bright part and the second bright part refer to a region where the intensity of forward scattered light spreading on both sides of the dark part is larger than a predetermined intensity Io. In the present embodiment, the first bright part and the second bright part are defined with Io = 0.

  First, the time series of the bright part width difference ΔW related to the preform A was obtained using the inspection apparatus 100. The bright part width difference ΔW is acquired by rotating the preform A attached to the rotating mechanism 103 and moving the light source 101 and the detector 102 attached to the parallel moving mechanism 104 along the central axis of the preform A. The intensity distribution of the forward scattered light was detected by the detector 102. At this time, LEDs and a CCD line sensor were used as the light source 101 and the detector 102. Further, the rotation speed of the preform was set to 100 rpm, the moving speed of the LED and the CCD line sensor was set to 10 mm / min, and the sampling period in the CCD line sensor was set to 500 milliseconds.

The time series shown in FIG. 18 was obtained as the time series of the bright part width difference ΔW related to the preform A. In this embodiment, the threshold ΔWo used for the inspection of the preform D is set using this time series. Specifically, the maximum value of the bright part width difference in this time series is set to ΔW _max , and the threshold value ΔW _o is set to a value larger than ΔW _max , specifically, three times ΔW _max .

  Next, the preform D was inspected using the inspection apparatus 100. As in the case of the actual measurement of the bright part width difference ΔW related to the preform A, the inspection is attached to the parallel movement mechanism 104 while rotating the preform D attached to the rotation mechanism 103 (with the central axis of the preform D as the rotation axis). The light source 101 and the detector 102 were moved while being translated along the center axis of the preform D. At this time, as in the actual measurement of the bright part width difference ΔW related to the preform A, the rotation speed of the preform is set to 100 rpm, the moving speed of the LED and the CCD line sensor is set to 10 mm / min, and the sampling period in the CCD line sensor is set to 500 milliseconds. Respectively.

The time series of the bright part width difference ΔW calculated by the calculation unit 105 when the preform D is an inspection target has a waveform as shown in FIG. All local maximum values in this time series exceeded the previously set threshold value ΔW _o . As a result, the determination unit 106 outputs a determination that “the through hole is displaced” over the entire length direction.

  In this way, it was confirmed that uniform positional deviation generated in all the through holes formed in the preform can be effectively detected by using the inspection apparatus 100 according to the second embodiment. .

  The inspection method according to the present invention can be suitably used for inspection of a preform that is a base material of an optical fiber in which holes are formed, such as a photonic crystal fiber.

DESCRIPTION OF SYMBOLS 10 Preform 10 'Preform 11 Through-hole 20 Parallel light beam 101 Light source 102 Detector (detection means)
103 Rotating mechanism (rotating / moving means)
104 Translation mechanism (parallel translation means)
105 Calculation unit (calculation means)
106 determination unit 107 position detection unit

Claims (7)

A circular columnar preform, there is provided an inspection apparatus for inspecting a preform having a through hole formed from one end face leading to the other end surface,
Detection means for sequentially detecting the intensity distribution of the forward scattered light of the preform produced by the incidence of light from the side surface of the preform;
Rotating / moving means for rotating the preform around the center axis of the preform or moving the detecting means to go around the preform;
From the intensity distribution of the forward scattered light detected sequentially, a calculation means for calculating a time series of feature values having a value according to the arrangement of the through holes ,
Determination means for determining whether or not the through hole is formed at a predetermined position by comparing the time-series maximum value or local maximum value of the feature amount with a predetermined threshold value. An inspection device characterized by that. The feature amount is a dark width of the forward scattered light.
The inspection apparatus according to claim 1.   The feature amount includes the two regions where the intensity of the forward scattered light, which spreads outside the two peaks of the forward scattered light, becomes larger than a predetermined intensity, and the intensity of the forward scattered light as these areas. The inspection apparatus according to claim 1, wherein the inspection apparatus is an absolute value of a difference between integral values obtained by integration on two bright portions.   The feature amount is defined as two regions where the intensity of the forward scattered light is larger than a predetermined intensity and spreads outside the two peaks of the forward scattered light. The inspection apparatus according to claim 1, wherein the inspection apparatus is an absolute value of the difference. A cylindrical preform, an inspection device for inspecting a preform in which a through hole extending from one end surface to the other end surface is formed,
Detection means for sequentially detecting the intensity distribution of the forward scattered light of the preform produced by the incidence of light from the side surface of the preform;
Rotating / moving means for rotating the preform around the center axis of the preform or moving the detecting means to go around the preform;
A calculation means for calculating a time series of the dark part width of the forward scattered light having a value corresponding to the arrangement of the through holes from the intensity distribution of the forward scattered light sequentially detected;
Determination means for determining whether or not the through-hole is formed at a predetermined position by comparing the time-series frequency spectrum of the dark width with a predetermined frequency spectrum ; inspection device you wherein a. The inspection apparatus according to any one of claims 1 to 5 , further comprising translation means for translating the preform or the detection means in a direction of a central axis of the preform. A circular columnar preform, there is provided an inspection method for inspecting a preform having a through hole formed from one end face leading to the other end surface,
A detection step of sequentially detecting the intensity distribution of the forward scattered light of the preform generated by the incidence of light from the side surface of the preform by a detection unit;
Rotating / moving step of rotating the preform around the center axis of the preform or moving the detection means so as to go around the preform;
From the intensity distribution of the forward scattered light detected sequentially, a calculation step of calculating a time series of feature values having values according to the arrangement of the through holes,
A determination step of determining whether or not the through hole is formed at a predetermined position by comparing the time-series maximum value or maximum value of the feature amount with a predetermined threshold value . An inspection method characterized by that.

Images