JP5256141B2 - Method and apparatus for non-contact measurement of dielectric shape - Google Patents

Description

The present invention relates to a noncontact measurement method及BiSo location dielectric shape, in particular, used in fine shape measurement of the inner diameter or the like of the micro holes of a diameter of several tens μm approximately open the transparent body such as glass (dielectric) suitable for, for non-contact measuring method及BiSo location dielectric shape.

  Regarding the measurement of a fine shape such as the inner diameter of a minute hole, the applicant proposed in Patent Document 1 a method for manufacturing a three-dimensional measurement stylus having a tip sphere diameter of several tens of μm, and a contact sensor equipped with this stylus. Document 2 proposes a technique for measuring the surface shape by detecting a change in the vibration state due to contact while minutely vibrating the stylus in the axial direction by a piezoelectric element. By making it possible to manufacture an ultrafine stylus as proposed in Patent Document 1, it is possible to measure the inner diameter of a very small hole, which has been considered difficult until now.

  However, in the techniques described in Patent Documents 1 and 2, the measurement error is caused by the shape error of the microsphere at the tip of the stylus which is difficult to process. Further, because of the contact type, deformation of the workpiece due to the measuring force or deformation of the stylus shaft causes a measurement error. Furthermore, since it is necessary to detect a change in the vibration state due to contact by minutely vibrating the stylus with a piezoelectric element, the measurement system is complicated and expensive.

  On the other hand, when light enters from a medium having a large refractive index into a medium having a small refractive index, if the incident angle is equal to or larger than a certain angle, the incident light does not pass through the boundary surface and is totally reflected. This phenomenon is called total reflection. However, strictly speaking, as shown in FIG. 2 (A), after penetrating from the interface by a few times the wavelength of light into a medium having a low refractive index (air in the figure), a substance having a high refractive index (in the figure, Returning to the core 12). This penetrating light is called evanescent light (near-field light).

  When a medium having a large refractive index (dielectric workpiece 16 in the figure) is brought closer to the evanescent light as shown in FIG. 2B, a part of the light is transmitted to the closer medium side (total reflection is reduced). Collapses).

  Patent Documents 3 and 4 are techniques using such evanescent light.

  The optical fiber coupler described in Patent Document 3 uses the collapse of total reflection of light by thinning the clad portions of two optical fibers and bringing the cores close to each other, and evanescent light travels between the cores. In this way, light is branched and coupled (clad polishing type optical coupler). It can also be said to be an optical fiber type beam splitter, and branching can be adjusted by the distance between cores.

  On the other hand, in the scanning near-field microscope (SNOM) described in Patent Document 4, a fine optical fiber whose tip is sharply sharpened by stretching or processing using the tunneling effect of light, not the collapse of total reflection of light. By utilizing the fact that the evanescent field generated in the small aperture at the tip of the optical fiber changes due to the proximity of the sample when a probe with a metal coating around the sample surface is brought close to the sample surface, the axis of the optical fiber is The proximity of the sample to the direction tip is detected.

  Patent Document 5 describes that a reflection surface for reflecting light of a specific wavelength is provided inside the core of the optical fiber.

JP 2003-114118 A Japanese Patent No. 4009152 Japanese Patent Publication No. 7-7136 Japanese Patent Laid-Open No. 2003-207437 Japanese Patent Laid-Open No. 10-213719

  However, conventionally, no probe has been proposed that uses the collapse of total reflection of evanescent light on the side surface of the core of the optical fiber.

  The present invention has been made to solve the above-mentioned conventional problems, and makes contactless measurement of fine shapes such as inner diameters of minute holes by utilizing the collapse of total reflection of evanescent light on the core side surface of the optical fiber. It is an object of the present invention to make it possible to improve the accuracy of the system and to simplify the system and to reduce the price based on the simple detection principle of detecting a change in the amount of light.

  In an optical fiber, light is confined in a core and transmitted while being totally reflected at the boundary between an inner core having a high refractive index and an outer cladding having a low refractive index. Here, as shown in FIG. 1, the clad 14 from the middle of the optical fiber 10 is removed by, for example, chemical etching to make only the core 12 (core diameter, for example, from 6 μm to several hundred μm in diameter, removal length of several mm). ~ About several cm). At this time, the exposed core side surface 12B becomes a sensing surface.

  At this time, the total reflection condition should continue to be satisfied between the core having a high refractive index and the surrounding air having a low refractive index. Accordingly, when the dielectric to be measured is not close, the evanescent light returns to the core 12 and propagates through the core while maintaining total reflection as shown in FIG.

  On the other hand, when a dielectric (for example, transparent body) workpiece having a refractive index larger than that of air approaches the core side surface (sensing surface) 12B and approaches a distance (several μm) of the optical wavelength, as shown in FIG. Thus, total reflection is lost, and a part of the evanescent light does not return to the core 12 but is transmitted to the adjacent dielectric work 16 side.

  Accordingly, as in the first example of the probe shown in FIG. 1, for example, the front end surface 12A of the optical fiber core 12 is polished and mirror-coated, and the light incident from the top of FIG. By doing so, the proximity of the dielectric to the core side surface 12B, which is the sensing surface, can be detected in a non-contact manner from the degree of attenuation of the amount of light in the fiber detected by the change in the amount of reflected light. The method of reflecting the light propagating in the optical fiber is not limited to this, and a reflection surface that reflects light of a specific wavelength is provided inside the core of the optical fiber as described in Patent Document 5. Alternatively, a separate reflecting surface may be provided outside the core end surface.

The present invention has been made based on such a principle, and includes only a core whose side surface is a sensing surface, and the end surface of the core, or the core between the sensing surface and the core end surface, or Using a non-contact measurement probe including an optical fiber having a reflection surface on at least one of the outer sides of the core end surface, and caused by the proximity of a dielectric workpiece to the sensing surface of the non-contact measurement probe , A dielectric shape characterized by detecting an attenuation of light incident on an optical fiber and reflected and returned by the reflecting surface, and generating a workpiece proximity detection signal when the attenuation of the light exceeds a threshold value The above-mentioned problem is solved by the non-contact measurement method .

  The present invention also includes only a core whose side surface is a sensing surface, and is at least one of the end surface of the core, the inside of the core between the sensing surface and the core end surface, or the outside of the core end surface. A non-contact measurement probe having an optical fiber having a reflecting surface, a light source for entering light into the optical fiber of the probe, and light reflected by the reflecting surface of the probe and returned to the optical fiber A light-attenuating element that detects the attenuation of light detected by the light-receiving element, and a light-attenuation detecting circuit that detects the attenuation of light detected by the light-receiving element. There is provided a dielectric-shaped non-contact measuring device including a workpiece proximity detection signal generation circuit that generates a workpiece proximity detection signal when a threshold value is exceeded.

  According to the present invention, (1) since the measurement can be performed in a non-contact manner, high accuracy can be achieved. That is, there is no shape error or the like of the stylus tip sphere of Patent Documents 1 and 2. Moreover, since it is a non-contact type, there is no measurement error due to deformation of the workpiece due to measurement force or deformation of the stylus shaft, and even a soft workpiece can be measured with high accuracy. Further, since there are no active elements in the probe, there is no drift due to heat generation.

  Also, (2) the probe structure is simple, and the signal processing is simple by simply sending light into the optical fiber and detecting the light quantity attenuation of the return light, so that the system can be reduced in price and simplified.

  In addition, (3) since the sensing portion composed of the bare core of the optical fiber is thin, the inner diameter of the minute hole can be measured.

1A is a plan view and FIG. 1B is a longitudinal sectional view showing a configuration of a first example of a probe according to the present invention. Sectional view showing the principle of the present invention The block diagram which shows the structure of 1st Embodiment of the measuring apparatus which concerns on this invention. The perspective view which shows the state which attached 1st Embodiment to the three-dimensional coordinate measuring machine. The top view for demonstrating the effect | action of this invention The front view which shows the principal part structure of 2nd Embodiment of the measuring apparatus which concerns on this invention. The front view which shows the principal part structure of 3rd Embodiment of the measuring apparatus which concerns on this invention. Sectional drawing which shows the structure of the 2nd example of the probe which concerns on this invention

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  As shown in FIG. 3, the first embodiment of the measuring apparatus according to the present invention is a light which is mirror-coated by removing the clad at the tip and leaving only the core, and polishing the tip of the core (bottom edge in the figure). A probe 20 of the first example including the fiber 10 (see FIG. 1), a light source (for example, a laser diode LD) 22 that makes light incident on the optical fiber 10 of the probe 20, and a light emitting circuit 24 that drives the light source 22. For example, an optical fiber coupler 30 having a configuration as described in Patent Document 3 for taking out light reflected by the core tip surface of the probe 20 and returning from the optical fiber 10, and light is transmitted by the optical fiber coupler 30. A light receiving element 34 for receiving the light extracted into the fiber 32, a light amount attenuation detecting circuit 36 for detecting the attenuation of the light detected by the light receiving element 34, and the light amount attenuation detecting circuit 36. , And a workpiece proximity detection signal generating circuit 38 for generating a workpiece proximity detection signal when the attenuation of the light generated by the dielectric adjacent the workpiece 16 to the core side is a sensing surface is equal to or greater than a threshold value.

  The probe 20 is moved with high accuracy in a narrow range in the (inner diameter) measurement direction of the workpiece 16 by the fine movement mechanism 40.

  The probe 20 and the fine movement mechanism 40 are mounted on a head 44 of a three-dimensional coordinate measuring device 42 as shown in FIG. 4, for example, and can move along the entire shape of the workpiece 16.

  Hereinafter, the operation will be described by taking an example of measuring the inner diameter of a minute hole (about several tens of micrometers in diameter) opened in a transparent dielectric such as glass.

  As shown in FIG. 5, the tip of the optical fiber 10 is placed in the hole 16A of the workpiece 16, moved by a fine movement mechanism 40 movable in the diameter direction of the hole, and positions at both ends in the hole diameter direction where return light becomes an attenuation threshold. x1 and x2 are measured.

  Then, the inner diameter D of the hole can be measured by the following equation.

D = X + 2r + 2d (1)
Here, X is the distance (x2-x1) between the both end positions x1, x2, r is the radius of the core 12 of the optical fiber 10, and d is the distance between the dielectric and the core side surface 12B at the attenuation threshold. is there.

  The optical fiber includes a glass optical fiber and a plastic optical fiber, but the present invention can be applied to any optical fiber. Since glass has material deterioration characteristics due to moisture (hydroxyl) in the air, it is desirable to coat the optical fiber with a protective film. At this time, the coating thickness of the core side surface 12B, which is the sensing surface, can be set to submicron or less to ensure sensing sensitivity.

  Moreover, as a mode of light propagating through the optical fiber, either single mode or multi mode can be used.

  The method of exposing the core is not limited to chemical etching, and the method of extracting return light is not limited to the method using the optical fiber coupler 30.

  In the above embodiment, the present invention is applied to the measurement of the inner diameter of the hole. However, the application target of the present invention is not limited to this, and as shown in FIG. 4, for example, the head of the three-dimensional coordinate measuring machine 42 By moving the probe 20 along the outside of the workpiece 16 by 44, it is possible to measure a fine shape other than the hole, such as the outer shape.

  Furthermore, depending on the shape of the workpiece 16, as in the second embodiment shown in FIG. 6, the lower end of the core 12 is gripped by the gripping mechanism 46 and pulled from below so that the core side surface (sensing surface) 12B does not bend. Can do. In this case, the grip mechanism 46 may be mirror coated.

  Further, as in the third embodiment shown in FIG. 7, the core 12 can be bent into a U shape so that the position of the upper surface, not the side surface of the workpiece 16, can be detected.

  In addition, the probe is not limited to the first example shown in FIG. 1, and has a specific wavelength inside the core of the optical fiber as described in Patent Document 5 as in the second example shown in FIG. 8. You may use the thing provided with the reflective surface which reflects light. In the figure, reference numeral 50 denotes a fiber collimator (refractive index distribution type fiber chip lens), and 52 denotes a fiber diffraction grating (glass fiber chip with a black diffraction grating). In the case of FIG. 6, a reflecting surface may be provided on the gripping mechanism 46 side instead of the optical fiber side.

DESCRIPTION OF SYMBOLS 10 ... Optical fiber 12 ... Core 12A ... Core front end surface (mirror coat surface)
12B ... Core side (sensing side)
14 ... Cladding 16 ... Dielectric work 16A ... Hole 20 ... Probe 22 ... Light source (LD)
DESCRIPTION OF SYMBOLS 24 ... Light emission circuit 30 ... Optical fiber coupler 34 ... Light receiving element 36 ... Light quantity attenuation detection circuit 38 ... Work proximity detection signal generation circuit 40 ... Fine movement mechanism 42 ... Three-dimensional coordinate measuring machine 44 ... Head

Claims (2)

It has only a core whose side surface is a sensing surface, and has a reflecting surface on at least one of the end surface of the core, the inside of the core between the sensing surface and the core end surface, or the outside of the core end surface. Using a non-contact measurement probe with an optical fiber ,
Attenuation of light incident on the optical fiber, reflected by the reflecting surface and returned by the proximity of the dielectric work to the sensing surface of the non-contact measurement probe is detected, and the attenuation of the light is a threshold value. A non-contact measuring method for a dielectric shape , wherein a workpiece proximity detection signal is generated when the above is reached . It has only a core whose side surface is a sensing surface, and has a reflecting surface on at least one of the end surface of the core, the inside of the core between the sensing surface and the core end surface, or the outside of the core end surface. A non-contact measuring probe with an optical fiber;
A light source for entering light into the optical fiber of the probe;
A light receiving element that receives light reflected by the reflecting surface of the probe and returning from the optical fiber;
A light amount attenuation detection circuit for detecting attenuation of light detected by the light receiving element;
A workpiece proximity detection signal generation circuit that generates a workpiece proximity detection signal when the attenuation of light generated by the proximity of the dielectric workpiece to the sensing surface exceeds a threshold detected by the light amount attenuation detection circuit;
A non-contact measuring apparatus having a dielectric shape, comprising:

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