JP2009180712A - Inner diameter measuring device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inner diameter measuring device for measuring the inner diameter also of an object to be measured having a small inner diameter, in inner diameter dimension measurement of the cylindrical object to be measured using white interference. <P>SOLUTION: This inner diameter measuring device 1 includes a surface reflecting element 3 for reflecting a first light flux divided from incident light from a white light source 2 on the object to be measured and causing the first optical path difference corresponding to the inner diameter of the object 10 between the first light flux and the second light flux divided from the incident light, an interferometer 4 for dividing the light flux coming from the spherical surface reflecting element 3 into a third light flux and a fourth light flux going to a moving mirror 44, and causing the second optical path difference between the third light flux and the fourth light flux, a detector 5 for receiving the third and fourth light fluxes, and a controller 6 for determining the inner diameter of the object by measuring the position of the moving mirror 44 corresponding to the maximum value of the interference signal occurring when the first optical path difference is substantially equal to the second optical path difference and by calculating the second optical path difference. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an inner diameter measuring apparatus that measures the inner diameter of a cylindrical object to be measured, and more particularly, to an inner diameter measuring apparatus that uses white interference.

  Conventionally, a method using the principle of white interference has been proposed as a method for accurately measuring a cylindrical part in a non-contact manner. For example, an interferometer for measuring the inner diameter of a cylinder using white interference is known (see Non-Patent Document 1). In the interferometer described in Non-Patent Document 1, light emitted from a white light source is converted into parallel light by a collimator and divided into two light beams by a half mirror arranged in a cylinder. Then, these light beams are reflected by the inner surface of the cylinder or the plane mirror, and then, for example, an optical path difference corresponding to twice the inner diameter of the cylinder is generated, and are combined again by the half mirror and emitted from the cylinder. Then, the light beam emitted from the inside of the cylinder is divided again into two light beams by an interferometer provided separately, and an optical path difference substantially equal to the optical path difference generated in the cylinder is generated, thereby generating white interference fringes. Since the white interference fringe has the maximum amplitude when the optical path difference generated in the cylinder is equal to the optical path difference generated on the interferometer side, measure the optical path difference between the two light beams generated on the interferometer side. Thus, the inner diameter of the cylinder can be accurately measured.

Ueki, Oiwa, "Interferometer for measuring inner diameter of cylinder", Report of Metrology Institute, January 1988, Vol. 37, No. 1, p.53-57

  By the way, due to the recent progress in microfabrication technology, parts having an extremely small inner diameter, and in some cases having an inner diameter of only 1 mm or less have been used for various products. For such parts, there is a demand for measuring the inner diameter with high accuracy in order to confirm processing accuracy. In order to meet such a demand, if it is going to measure the internal diameter of a cylindrical part using said interferometer, it will be necessary to use a half mirror smaller than the internal diameter. Furthermore, in order to fix the position of the half mirror inside the cylinder of the component, it is necessary to arrange the holding member of the half mirror inside the cylinder. However, since there is a limit to downsizing the half mirror and its holding member, if the inner diameter becomes too small, it becomes difficult to dispose the half mirror and its holding member inside the cylinder. For this reason, it has been difficult to accurately measure the inner diameter of a component having such a small inner diameter.

  In view of the above problems, an object of the present invention is to provide an inner diameter measuring apparatus capable of measuring an inner diameter of a measured object having a small inner diameter in measuring the inner diameter of a cylindrical measured object using white interference. There is.

  According to one embodiment of the present invention, an inner diameter measuring device for measuring an inner diameter dimension of a cylindrical object to be measured is provided. Such an inner diameter measuring apparatus reflects a first light beam divided from incident light emitted from a white light source and the white light source by an object to be measured, and measures between the second light beam divided from the incident light. An interferometer having a surface reflecting element that generates a first optical path difference corresponding to the inner diameter of an object, a fixed mirror that is fixed in position, and a movable mirror that is movable along the optical path, The emitted first and second light beams are branched into a third light beam directed toward the fixed mirror and a fourth light beam directed toward the movable mirror, respectively, and the second light beam is between the third light beam and the fourth light beam. An interferometer that generates the optical path difference, and the third and fourth light fluxes are received, an interference signal that is generated when the first optical path difference and the second optical path difference are substantially equal is detected, and the interference signal is detected. The position of the moving mirror corresponding to the maximum value of the detected interference signal and the detector that outputs the signal corresponding to Constant, and by calculating the second optical path difference from that position, and a controller for determining the inner diameter of the object.

  Further, according to the present invention, the surface reflecting element is a sphere, and the surface reflecting element reflects a part of incident light on the surface of the surface reflecting element so as to enter the inner surface of the object to be measured substantially perpendicularly. To form a first light flux and reflect another part of the incident light on the vertex of the white light source side of the surface reflection element or the surface of the installation base on which the surface reflection element is installed. Preferably formed.

  Further, according to the present invention, the surface reflecting element has a shape in which a cross-sectional shape in a plane including the axis of the object to be measured is a trapezoid, and the surface reflecting element is configured to allow a part of incident light to be side surfaces of the surface reflecting element. The first light beam is formed by being incident substantially perpendicularly on the inner surface of the object to be measured, and the other part of the incident light is installed on the top surface of the surface reflecting element or the surface reflecting element. It is preferable to form the second light flux by reflecting on the surface of the installation table.

  According to the present invention, it is preferable to further include a light beam splitting element that splits the light emitted from the white light source into a first light beam and a second light beam.

According to another embodiment of the present invention, an inner diameter measuring device for measuring an inner diameter dimension of a cylindrical object to be measured is provided. The inner diameter measuring apparatus is an interferometer having a white light source, a reference mirror whose position is fixed, and a movable mirror that can move along the optical path. The inner diameter measuring device transmits light emitted from the white light source toward the reference mirror. An interferometer that branches into a first light beam and a second light beam that travels toward the moving mirror to produce a first optical path difference between the first light beam and the second light beam, and a first light emitted from the interferometer The third light beam divided from the first light beam and the second light beam is reflected by the object to be measured, and the inner diameter of the object to be measured is between the first light beam and the fourth light beam divided from the second light beam. A surface reflection element that causes a corresponding second optical path difference, and a third light flux and a fourth light flux are received, and an interference signal that is generated when the first optical path difference and the second optical path difference are substantially equal is detected. The detector that outputs a signal corresponding to the interference signal and the position of the movable mirror corresponding to the maximum value of the detected interference signal It was measured by calculating the first optical path difference from that position, having a controller for determining the inner diameter of the object.
In each of the above embodiments, the white light source is not limited to a light source that emits light in a broad band in the visible light range, but a light source that emits light in a certain wavelength band with a predetermined wavelength as a center wavelength.

  ADVANTAGE OF THE INVENTION According to this invention, it became possible to provide the internal diameter measuring apparatus which can measure an internal diameter also about the to-be-measured object which has a small internal diameter in the internal-diameter dimension measurement of the cylindrical to-be-measured object using white interference.

Hereinafter, embodiments in which the present invention is applied to an inner diameter measuring device that measures the inner diameter of a cylindrical object to be measured, such as a ring gauge and a cylinder, will be described with reference to the drawings.
An inner diameter measuring apparatus to which the present invention is applied causes light from a white light source to be incident on a spherical surface reflecting element disposed substantially at the center of an object to be measured. The surface reflecting element vertically reflects a part of the incident light at the apex, and another part of the incident light at a position different from the apex of the sphere surface in a direction substantially perpendicular to the inner surface of the object to be measured. By reflecting, the light from the white light source is split into two light beams having an optical path difference determined according to the inner diameter of the object to be measured. Then, the inner diameter measuring device causes each light beam to enter a separately prepared interferometer. In the interferometer, white interference fringes are generated by splitting the light beam into two optical paths that cause an optical path difference substantially equal to the optical path difference to cause interference. Then, the inner diameter of the object to be measured is obtained by detecting the maximum signal value of the white interference fringe with a detector and measuring the optical path difference between the two optical paths of the interferometer.

  FIG. 1 is a diagram showing a schematic configuration of an inner diameter measuring apparatus 1 to which the present invention is applied. The inner diameter measuring device 1 includes a white light source 2, a surface reflecting element 3 that generates two light fluxes having an optical path difference determined according to the inner diameter of the object to be measured, and an optical path that is approximately the same as the optical path difference generated by the surface reflecting element 3. An interferometer 4 that generates a white interference fringe by causing a difference, a detector 5 that detects the interference fringe generated by the interferometer 4, and controls each part, and from the detected interference fringes, the inner diameter of the object to be measured It has the controller 6 which calculates | requires. Further, the inner diameter measuring device 1 includes an optical fiber 7 that transmits light from the white light source 2 to the surface reflecting element 3, an optical fiber 8 that transmits the light beam emitted from the surface reflecting element 3 to the interferometer 4, and the direction of the light beam. It has a beam splitter 9 for entering the optical fiber 8 instead.

  The white light source 2 is a light source that has a short coherence length and can emit light having a broad wavelength. As the white light source 2, for example, an LED, an SLD (super luminescent diode), an SOA (Semiconductor Optical Amplifier) light source, an ASE (Amplified Spontaneous Emission) light source, or the like can be used. The center wavelength of the light emitted from the white light source 2 can be set to 750 nm, 1300 nm, 1550 nm, and the like, for example. In the present embodiment, an infrared LED having a center wavelength of 1550 nm is used as the white light source 2.

  FIG. 2 shows a schematic layout of the DUT 10 and the surface reflection element 3. The DUT 10 is placed on the XYZ stage 14. Further, the installation table 16 is installed through a hole provided in a substantially central portion of the XYZ stage 14. And the surface reflective element 3 is installed on the installation stand 16 so that it may be located inside the cylinder of the DUT 10. The surface reflecting element 3 generates two light beams B1 and B2 having an optical path difference determined according to the inner diameter of the DUT 10. The light emitted from the white light source 2 is guided to the surface reflecting element 3 through the first optical fiber 7, the collimator lens 11, the beam splitter 9 and the wedge prism 12. The collimator lens 11 makes incident light parallel light. The wedge prism 12 adjusts the position of the parallel light incident through the collimator lens 11 and emits it. Then, the light emitted from the wedge prism 12 is incident on the surface reflecting element 3 disposed at the approximate center of the inner diameter of the DUT 10.

  The surface reflecting element 3 is formed of a sphere, and reflects light incident through the wedge prism 12 on the surface thereof. A part of the light is vertically reflected at the apex of the surface reflecting element 3 to become a light beam B <b> 2 directed to the beam splitter 9. Further, another part of the light emitted from the wedge prism 12 is reflected at another position on the surface of the surface reflecting element 3 and travels toward the inner surface S <b> 1 of the DUT 10. Of the light, the light perpendicularly incident on the inner surface S1 of the object to be measured 10 is reflected by the inner surface S1 and then reflected again by the surface of the surface reflecting element 3 and travels toward the beam splitter 9. B1.

  The surface reflecting element 3 is made of, for example, metal, optical glass, or optical plastic. A reflective film corresponding to the wavelength of light emitted from the white light source 2 may be formed on the surface of the surface reflective element 3. Further, the surface reflecting element 3 is fixed to the installation table 16 with an adhesive or the like. Alternatively, when the radius of the surface reflecting element 3 is measured in advance, a recess may be provided on the surface of the installation table 16, and the surface reflecting element 3 may be installed in the recess.

  The XYZ stage 14 is movable in two directions orthogonal to each other within an axial direction of the device under test 10 (that is, a vertical direction in FIGS. 2 and 3) and a cylindrical cross section orthogonal to the axis direction of the device under test 10. It is driven by the stage controller 15. The stage controller 15 is electrically connected to the controller 6 and controlled by the controller 6. Then, the stage controller 15 drives the XYZ stage 14 based on the control signal from the controller 6 and adjusts the positional relationship between the surface reflecting element 3 and the device under test 10.

  With reference to FIG. 3, the optical path difference generated between the light beams B1 and B2 will be described. In this embodiment, the light emitted from the wedge prism 12 is parallel light and is incident on the surface reflecting element 3 from above substantially parallel to the inner surface S <b> 1 of the DUT 10. Further, the surface reflecting element 3 is arranged so that the center O of the surface reflecting element 3 is positioned on the central axis of the inner diameter of the DUT 10. At this time, a part of the incident light beam B2 is vertically reflected at the vertex a on the wedge prism side of the surface reflecting element 3 and is emitted in the direction opposite to the incident direction. On the other hand, another part of the incident light beam B1 is incident on the surface b from the upper side of the surface reflecting element 3 at an angle of 45 °. Therefore, the light beam B <b> 1 is reflected by the surface reflecting element 3 along the horizontal direction, that is, the direction perpendicular to the inner surface S <b> 1 of the DUT 10. Then, the light beam B1 is vertically reflected by the inner surface S1 of the object to be measured, and then reflected again by the point b on the surface of the surface reflecting element 3, and is emitted upward. In addition, the light reflected by the other part of the surface reflective element 3 whose height from the surface of the installation base 16 is equal to the point b is the same as the light reflected by the point b. The light is emitted upward through the vertical reflection at S1 and the reflection at the surface reflection element 3 again. Therefore, the light beam B1 becomes a ring-shaped light beam.

Here, the radius of the surface reflecting element 3 is r. At this time, the normal bO with respect to the surface of the surface reflecting element 3 at the point b on the surface of the surface reflecting element 3 where the light beam B1 is reflected is a line aO passing through the vertex a and the center O of the surface reflecting element 3 (that is, the object to be covered). The angle formed with the axis of the inner diameter of the measured object 10 is 45 °. Therefore, the height difference Δh between the vertex a and the point b is r (1-1 / √2). On the other hand, the distance between the point b and the line aO is r / √2. Therefore, when the inner diameter of the DUT 10 is D, the distance Δd from the point b to the inner surface S1 of the DUT 10 is D / 2−r / √2. Therefore, the optical path difference Δl between the light beams B1 and B2 can be obtained by the following equation.
Δl = 2 (Δh + Δd) = (2-2√2) r + D (1)

  From the equation (1), in order to measure the inner diameter D of the DUT 10, it is necessary to know the radius r of the surface reflecting element 3 accurately. Here, the radius r of the surface reflecting element 3 can be measured in advance using various known methods. Alternatively, as shown in FIG. 3, the optical path difference between the light beam B3 vertically reflected by the upper surface of the installation table 16 on which the surface reflecting element 3 is installed and the light beam B2 is measured by using an interferometer 4 and obtained. Further, ¼ of the optical path difference can be set as the radius r of the surface reflecting element 3. Note that it is preferable to remove the DUT 10 from the XYZ stage 14 when measuring the optical path difference between the light beams B2 and B3. This is because the possibility of erroneous measurement can be reduced by limiting the light fluxes that generate the interference fringes observable by the interferometer 4 to the light fluxes B2 and B3.

  Furthermore, a case where the surface reflecting element 3 is arranged eccentrically with respect to the object to be measured 10 (that is, a case where the center O of the surface reflecting element 3 does not exist on the axis of the object to be measured 10) is assumed. In this case, the distance from the point on the surface of the surface reflecting element 3 having the same height as the point b to the inner surface S1 of the DUT 10 varies depending on the position of the point on the surface. Further, the light reflected by the surface reflecting element 3 in a direction not parallel to the eccentric direction is obliquely incident on the inner surface S1 in a plane orthogonal to the axis of the object to be measured 10 and is vertically reflected by the inner surface S1. The optical path is longer than. Therefore, the optical path length of the light beam B1 differs depending on the reflection position on the surface reflecting element 3, and the optical path difference from the light beam B2 also differs depending on the reflection position.

In such a case, the amplitude of the white interference fringe observed by the detector 5 decreases as the amount of eccentricity of the surface reflecting element 3 increases, and the range in which the interference fringe can be observed becomes wider. Therefore, the position where the surface reflecting element 3 is not eccentric with respect to the inner diameter of the DUT 10 is determined by the following procedure.
First, the measurement of interference fringes is repeated while shifting the positional relationship between the surface reflecting element 3 and the device under test 10 in a specific direction within a cylindrical cross section orthogonal to the axial direction of the device under test 10. And the position of the surface reflective element 3 when the measured value of the amplitude of the obtained interference fringe becomes the maximum is determined. Thereafter, the position where the amplitude of the interference fringes is maximized is obtained while moving the surface reflecting element 3 in the same direction in the direction orthogonal to the specific direction. Finally, when the amplitude of the interference fringes becomes the largest, it is determined that the surface reflecting element 3 is arranged without eccentricity with respect to the inner diameter of the DUT 10.

With reference to FIGS. 4A and 4B, another measurement method of the inner diameter D of the device under test 10 when the surface reflecting element 3 is eccentric with respect to the device under test 10 will be described. FIG. 4A is a schematic side sectional view showing the positional relationship between the part to be measured 10 and the surface reflecting element 3, and FIG. 4B is a shutter element 31 that restricts the light beam incident on the surface reflecting element 3. FIG.
As shown in FIG. 4A, in this measurement method, a portion of the light beam B1 that is reflected at one point (for example, point b) on the surface of the surface reflecting element 3 and a vertex a of the surface reflecting element 3 are perpendicular to each other. A shutter element 31 having a slit-like opening 32 through which only the reflected light beam B 2 can be transmitted is disposed between the wedge prism 12 and the surface reflecting element 3. The length of the opening 32 in the longitudinal direction is substantially equal to the radius r of the surface reflecting element 3, for example. Furthermore, the shutter element 31 is configured to be movable along the longitudinal direction of the opening 32. In this case, as shown in FIGS. 4A and 4B, the light beam B1 is generated only when the longitudinal direction of the slit-like opening 32 and the eccentric direction of the surface reflecting element 3 with respect to the object to be measured 10 are substantially parallel. It can pass through the opening. Therefore, first, with the shutter element 31 disposed, the optical path difference Δl ₁ between the light beam B1 (for example, the light beam reflected at the point b) and B2 is measured based on the observed white interference fringes. Thereafter, the reflection position on the surface reflecting element 3 is set to an axially symmetric position (for example, in FIG. The shutter element 31 is moved in parallel along the longitudinal direction of the slit so as to be point c). Then, the optical path difference Δl ₂ between the light beams B1 and B2 is measured again. Then, the average value of the measured optical path differences Δl ₁ and Δl ₂ can be set as the optical path difference Δl when the surface reflecting element 3 is not decentered.

  The light beams B 1 and B 2 reflected by the surface reflecting element 3 and emitted in the direction opposite to the incident direction pass through the wedge prism 12 again, are reflected by the beam splitter 9, and enter the optical fiber 8. The light beams B 1 and B 2 enter the interferometer 4 through the optical fiber 8.

  FIG. 5 shows a schematic configuration diagram of the interferometer 4. The light beams B1 and B2 emitted from the optical fiber 8 pass through the collimator lens 41 of the interferometer 4 and become parallel light. Then, the light enters the beam splitter 42. The light beams B1 and B2 are reflected by the beam splitter 42 and branched into light beams B11 and B21 that travel toward the first optical path, and light beams B12 and B22 that pass through the beam splitter 42 and travel toward the second optical path. The light beam B11 represents the light beam B1 emitted from the surface reflection element 3 toward the first optical path of the interferometer 4, and the light beam B21 represents the interferometer among the light beam B2 emitted from the surface reflection element 3. 4 represents a light beam traveling toward the first optical path 4. Similarly, the light beam B12 represents the light beam B1 emitted from the surface reflection element 3 toward the second optical path of the interferometer 4, and the light beam B22 represents the interference light beam B2 emitted from the surface reflection element 3. This represents the light flux toward the second optical path in total.

  A reference mirror 43 whose position is fixed is installed in the first optical path. The light beams B <b> 11 and B <b> 21 going to the first optical path are reflected by the reference mirror 43 and return to the beam splitter 42, and part of the light passes through the beam splitter 42 and goes to the detector 5. On the other hand, a movable mirror 44 that is movable along the optical path is provided in the second optical path. Then, the light beams B12 and B22 traveling toward the second optical path are reflected by the moving mirror 44 and returned to the beam splitter 42. A part of the light beams B12 and B22 are reflected by the beam splitter 42 and travel to the detector 5 together with B11 and B21.

  The movable mirror 44 is attached to the support member 45. The movable mirror 44 and the support member 45 are installed on a piezo fine movement stage 46 that can finely adjust the position of the movable mirror 44 although the movement range is narrow. The movable mirror 44 and the support member 45 are installed on a coarse movement stage 47 that, together with the piezo fine movement stage 46, has a relatively large movement range and roughly determines the position of the movement mirror 44. The piezo fine movement stage 46 and the coarse movement stage 47 are electrically connected to the piezo controller 51 and the stage controller 52, respectively. Then, the piezo fine movement stage 46 and the coarse movement stage 47 move the movable mirror 44 along the second optical path based on control signals from the piezo controller 51 and the stage controller 52.

A corner cube 48 is attached to the back surface of the support member 45. Further, an interferometer 49 for measuring the position of the movable mirror 44 is installed behind the support member 45 (that is, on the opposite side of the beam splitter 42 with the support member 45 as the center). The position measurement interferometer 49 is irradiated to the corner cube 48, reflected by the corner cube 48 and returned to the position measurement interferometer 49, and interference observed between the reference light and the reference light. The amount of movement of the movable mirror 44 can be measured by counting the number of moving stripes.
If the interference signal is continuously measured during the movement while moving the movable mirror 44, the piezo fine movement stage 46 and the piezo controller 51 may be omitted.

The detector 5 outputs the detected light quantity as an electrical signal. As the detector 5, for example, a semiconductor detection element such as a photodiode, CCD, or C-MOS can be used. In this embodiment, a detector in which CCD elements are arranged in a two-dimensional array is used as the detector 5.
The detector 5 is electrically connected to the controller 6 and transmits an electrical signal corresponding to the detected light amount to the controller 6.

The controller 6 is configured by a so-called PC, and is configured in accordance with a communication unit such as RS232C and Ethernet (registered trademark), and a storage unit including an electrically rewritable nonvolatile memory, a magnetic disk, an optical disk, and a reading device thereof. A communication unit including software such as an electronic circuit and a device driver.
Further, the controller 6 is a functional module realized by a CPU, ROM, RAM and its peripheral circuits (not shown) and a computer program executed on the CPU, based on the detected light quantity and the position of the movable mirror 44. It has a control unit that obtains the inner diameter D of the object to be measured 10 and controls devices connected to the controller 6 such as a position measurement interferometer 49, a piezo controller 51, a stage controller 52, and a detector 5.

Hereinafter, an operation for measuring the inner diameter of the DUT 10 by the inner diameter measuring apparatus 1 will be described.
Since the light from the white light source 2 has a short coherence length, interference fringes are generated only when the optical path differences are substantially equal. Here, it is assumed that the distance from the beam splitter 42 to the reference mirror 43 in the first optical path of the interferometer 4 is L1, and the distance from the beam splitter 42 to the moving mirror 44 in the second optical path is L2. An optical path difference ΔL = 2 (L2−L1) occurs between the third light flux and the fourth light flux (where L2> L1). At this time, if the optical path difference ΔL is equal to the optical path difference Δl generated between the light beams B1 and B2, the interferometer 4 out of the light beam B1 reflected by the inner surface S1 of the object to be measured 10 by the surface reflecting element 3. The optical path difference between the light beam B11 passing through the first optical path and the light beam B2 vertically reflected by the apex a of the surface reflecting element 3 is 0 in the interferometer 4 with the light beam B22 passing through the second optical path. Become. Therefore, the maximum interference signal can be observed. Then, as the difference between the optical path difference ΔL generated in the interferometer 4 and the optical path difference Δl generated between the light beams B1 and B2 increases, the magnitude of the interference signal rapidly decreases. Further, the optical path difference Δl generated between the light beams B1 and B2 is determined based on the radius r of the surface reflecting element 3 and the inner diameter D of the part to be measured 10 as shown in the above equation (1). Is done. Therefore, the radius r of the surface reflecting element 3 is measured in advance or after measuring the optical path difference ΔL. Then, the inner diameter D of the DUT 10 can be obtained by substituting the measured value of the optical path difference ΔL for Δl in the equation (1) and substituting the measured value for the radius r.

  When the moving mirror 44 is moved closer to the beam splitter 42, the optical path difference ΔL = 2 (L1−L2) generated between the third light flux and the fourth light flux is the second interference in the light flux B1. Even when the optical path difference between the light beam B12 passing through the second optical path in the total 4 and the light beam B21 passing through the first optical path in the second interferometer 4 among the light beams B2 is 0, interference fringes are generated. Can be observed (where L1> L2). Therefore, the difference between the position of the moving mirror 44 at which the interference signal generated between the light beams B11 and B22 is maximized and the position of the moving mirror 44 at which the interference signal generated between the light beams B12 and B21 is maximized. The value divided by 2 can be used as the above ΔL.

FIG. 6 shows an operation flowchart of the inner diameter measuring apparatus 1 when measuring the inner diameter D of the DUT 10. First, as advance preparation, the radius r of the surface reflecting element 3 is measured and stored in the storage unit of the controller 6. Note that the value of the radius r can be measured by using a known measurement method as described above or by measuring the optical path difference between the light beams B2 and B3.
When the measurement is started, first, as an initialization procedure, the reference position of the movable mirror 44, that is, the position of the movable mirror 44 at which the optical path difference between the first optical path and the second optical path of the interferometer 4 becomes 0 is determined ( Step S101). Therefore, the position where the interference fringes are detected by the interferometer 4 is obtained without installing the DUT 10 in the inner diameter measuring device 1. At this time, since there is no light beam reflected from the inner surface of the DUT 10, all the light beams emitted from the surface reflecting element 3 are B2. In order to avoid generation of interference fringes between the light beam B3 and the light beam B2 vertically reflected on the surface of the installation table 16, a diaphragm is provided between the optical fiber 7 and the surface reflection element 3, and only the surface reflection element 3 is provided. Light may be irradiated. In the interferometer 4, when the difference between the distance L1 from the beam splitter 42 to the reference mirror 43 in the first optical path and the distance L2 from the beam splitter 42 to the movable mirror 44 in the second optical path is zero, the interference signal is Maximum. Therefore, the controller 6 moves the movable mirror 44, observes the light amount detected by the detector 5 at a plurality of measurement points, and finds the position where the detected light amount is maximum, that is, the interference signal is maximum. The controller 6 receives the position of the movable mirror 44 when the interference signal reaches the maximum value from the position measurement interferometer 49 and stores it in the storage unit of the controller 6 as a position P1 where L1 = L2. .

  Next, the device under test 10 is placed on the XYZ stage 14 so that the surface reflecting element 3 is positioned inside the cylinder of the device under test 10. At this time, as described above, the white interference fringes are observed only at a position where the optical path difference Δl generated between the light beams B1 and B2 is substantially equal to ΔL = 2 (L2−L1). Therefore, the controller 6 drives the coarse movement stage 47 through the stage controller 52 and moves the moving mirror 44 of the interferometer 4 backward until white interference fringes are observed. Then, similarly to the above, the controller 6 moves the movable mirror 44 to check increase / decrease in the amount of light detected by the detector 5 at a plurality of measurement points, and the maximum value of the output signal value, that is, the maximum value of the interference signal. Is obtained (step S102). The position P2 of the movable mirror 44 when the output signal becomes maximum is received from the position measurement interferometer 49 (step S103). Then, the controller 6 reads the position P1 of the movable mirror 44 when L1 = L2 from the storage unit, calculates the value P2-P1, and obtains the optical path difference ΔL = 2 (L2-L1) (step S104). When the optical path difference generated in the interferometer 4 is obtained, the controller 6 reads the value of the radius r of the surface reflecting element 3 from the storage unit (step S105). Then, the inner diameter D of the device under test 10 is obtained from the optical path difference ΔL obtained for the device under test 10 and the value of the radius r according to the equation (1) (step S106).

  Instead of measuring the reference position P1 of the movable mirror 44 in step S101, as described above, the movable mirror 44 is moved closer to the beam splitter 42 than the reference mirror 43, and interference occurs between the light beams B12 and B21. The position P3 of the movable mirror 44 that maximizes the signal may be obtained. Then, the value of (P2−P3) / 2 is calculated, and the value may be ΔL.

  As described above, the inner diameter measuring apparatus 1 to which the present invention is applied has an optical path difference corresponding to the inner diameter of the device under test 10 by disposing the surface reflecting element 3 inside the cylinder of the device under test 10. Two light fluxes are generated, and white interference fringes corresponding to the optical path difference can be generated. Further, since the surface reflection element having a high sphericity can be manufactured using a known manufacturing technique even when the diameter is 1 mm or less, the inner diameter measuring apparatus 1 has an inner diameter of the object to be measured 10. Even if it is small, the inner diameter can be accurately measured. Further, the surface reflecting element 3 reflects the incident light at the surface when splitting the incident light into the first light flux and the second light flux, and does not use the light that has entered the inside. Does not occur. Therefore, the inner diameter measuring device 1 can accurately measure the inner diameter of the DUT 10.

  In addition, this invention is not limited to said embodiment. For example, in the above embodiment, a condensing lens may be disposed between the wedge prism 12 and the surface reflecting element 3 so that convergent light is incident on the surface reflecting element 3. For example, the case where the condensing lens is configured so that the incident light on the surface reflecting element 3 is focused on the surface of the installation table 16 will be described. In this case, a line connecting the center O and the vertex a of the surface reflecting element 3 and a point c on the surface of the surface reflecting element 3 through which a normal line forming an angle of 60 degrees at the center O passes, with respect to the line aO. When a light beam having an angle of 30 degrees is incident, the light is reflected by the surface reflecting element 3 and becomes light parallel to the cylindrical cross section of the object to be measured 10 (that is, the light beam B1).

With reference to FIG. 7, the optical path difference Δl ′ between the light beam B1 in this case and the light beam B2 reflected by the apex a of the surface reflecting element 3 will be described. First, let L be the optical path length from the equiphase surface 70 of the convergent light to the focal point f of the surface of the installation table 16 when the surface reflecting element 3 is not installed. In this case, with respect to the light beam B1, the distance from the line aO passing through the center O of the surface reflecting element 3 to the point c is r√3 / 2. Therefore, the distance Δd ′ from the point c to the inner surface S1 of the DUT 10 is D / 2−r√3 / 2. The distance from the point c to the focal point f is √3r. Therefore, the optical path length l ₁ of the light beam B1 from the equiphase surface 70 until it reaches the equiphase surface 70 again via the point c and the inner surface S1 is:
l ₁ = 2L−2 × √3r + 2Δd ′ = 2L + D−3√3r (2)
It becomes. On the other hand, the optical path length l ₂ of the light beam B2 from the equiphase surface 70 until it reaches the equiphase surface again after being reflected from the equiphase surface 70 is 2r from the vertex a to the focal point f.
l ₂ = 2L−2 × 2r = 2L−4r (3)
It becomes. Accordingly, the optical path difference Δl ′ between the light beams B1 and B2 is as follows from the equations (2) and (3).
Δl ′ = l ₁ −l ₂ = D + (4−3√3) r (4)

By adjusting the position where the incident light on the surface reflecting element 3 is focused, the light reflected at other positions on the surface reflecting element 3 can be changed to the light beam B1.
Further, the inner diameter D of the object to be measured can be measured by using a light beam vertically reflected on the surface of the installation table 16 instead of a light beam vertically reflected at the apex of the surface reflecting element 3 as the light beam B2. In this case, the optical path difference Δl ″ between the light beams B1 and B2 is, for example, when the incident light to the surface reflecting element 3 is parallel light, from the equation (1), Δl ″ = Δl−2 · 2r = D− (2 + 2√ 2) r.

  Further, a mask element configured to pass only the light beam B1 and the light beam B2 may be disposed between the wedge prism 12 and the surface reflecting element 3. By arranging the mask elements in this way, it is possible to prevent light that is not related to the generation of white interference fringes from propagating to the interferometer 4, thereby improving the S / N ratio of the interference fringes detected by the detector 5. be able to. Such a mask element is formed by making only the part through which the light beam B1 or the light beam B2 pass transparent or hollow, and configuring the other part with an opaque member or providing an opaque film on the surface of the other part. it can.

Furthermore, before entering the surface reflecting element 3, the light beam perpendicularly incident on the apex “a” of the surface reflecting element 3 and the light beam incident on another position of the surface reflecting element 3 may be divided. An example of such a configuration is shown in FIGS. In FIGS. 8A and 8B, only the components necessary for explaining the positional relationship between the DUT 10 and the surface reflecting element 3 and the light beams incident thereon are shown for ease of understanding. Yes.
As shown in FIG. 8A, the light from the white light source is split into light beams B1 and B2 by the half mirror 81. The light beam B1 is further reflected by the mirror 82 and travels toward the surface reflecting element 3. The light beam B1 is reflected by the surface reflecting element 3, then reflected by the inner surface S1 of the object to be measured 10, reflected again by the surface reflecting element 3, and travels in the direction opposite to the original incident direction. On the other hand, after being reflected by the half mirror 81, the light beam B2 is vertically reflected by the vertex a of the surface reflecting element 3, and proceeds in the direction opposite to the original incident direction. In this case, the optical path difference between the light beams B1 and B2 includes the radius r of the surface reflecting element 3, the distance between the half mirror 81 and the mirror 82, the incident angle at which the light beam B1 enters the surface reflecting element 3, and the object to be measured. It can be determined based on the inner diameter D of ten.

  Further, as shown in FIG. 8B, another half mirror 83 is installed on the white light source side of the half mirror 81, and is at the same height as the position where the light beam B1 is reflected, and the surface is reflected. A light beam B3 whose angle formed with respect to the surface of the element 3 is the same as that of the light beam B1 may be generated. In this case, even if the surface reflection element 3 is installed eccentrically in the direction parallel to the light from the white light source with respect to the inner diameter of the object to be measured 10, the optical path difference between the light beams B1 and B2 and the light beams B3 and B2 By separately measuring the optical path difference between them, the inner diameter D of the DUT 10 can be measured.

  In the present invention, the surface reflecting element disposed inside the cylinder of the object to be measured is not limited to a sphere. FIG. 9 shows a schematic side sectional view of a surface reflecting element 90 that can be used in place of the surface reflecting element 3 in the inner diameter measuring apparatus of the present invention. In FIG. 9, only the components necessary for explaining the positional relationship between the DUT 10 and the surface reflecting element 90 and the light beams incident thereon are shown for easy understanding. As shown in FIG. 9, the surface reflecting element 90 has a shape in which the vicinity of the apex of the triangular prism is cut out by a plane parallel to the bottom surface. That is, the surface reflecting element 90 is formed so that the cross-sectional shape in the cross section along the axial direction of the object to be measured is a trapezoid. The side surfaces 91 and 92 formed symmetrically with respect to the top surface 93 are formed so as to form an angle of 90 ° in the cross section, that is, to form an angle of 45 degrees with the bottom surface. The surface reflecting element 90 has a bottom surface facing the installation table 16, a top surface 93 positioned on the side where light from the white light source is incident, and side surfaces 91 and 92 with respect to the axis of the DUT 10. They are arranged so as to be inclined at 45 °.

  In this case, the light from the white light source is converted into parallel light and is incident on the apex and side surfaces 91 and 92 of the surface reflecting element along the axis of the DUT 10. At this time, the light beam B2 that is vertically reflected by the top surface 93 and the light beams B1 and B1 that are reflected by the side surfaces 91 and 92, are vertically reflected by the inner surface S1 or S2 of the object to be measured 10, and then are reflected again by the side surfaces. 'And get. The inner diameter of the DUT 10 can be measured by measuring the optical path difference between the light beams B1 and B2 and the optical path difference between the light beams B1 ′ and B2 with an interferometer. The optical path difference between the light beams B1 and B2 in this case will be described below.

As shown in FIG. 9, a point a is defined as a point where the side surfaces 91 and 92 are virtually extended. In addition, the distance from the point a to the inner surface S1 of the DUT 10 is defined as d ₁ . Further, the length of the bottom surface of the surface reflecting element 90 is x, and the height from the top surface 93 to the bottom surface is h. The length x of the bottom surface is measured in advance using a known length measuring method. At this time, since the side surfaces 91 and 92 form an angle of 45 ° with respect to the axis of the DUT 10, the distance from the point a to the top surface 93 is (x / 2−h). Therefore, the optical path difference between the light beam B1 and the light beam B2 is 2 (d ₁ − (x / 2−h)). Similarly, the optical path difference between the light beam B1 ′ and the light beam B2 is 2 (d ₂ − (x / 2−h)) when the distance d ₂ from the point a to the inner surface S2 of the object to be measured 10 is obtained. Accordingly, the inner diameter D of the object to be measured 10, after measuring according to the procedure given d _1, d ₂ to the above FIG. 6, respectively, is determined by summing the d ₁ and d _2. Note that the shutter element 31 described above may be used to separately measure the optical path difference between the light beams B1 and B2 and the optical path difference between the light beams B1 ′ and B2.
Further, the height h of the surface reflecting element 90 is determined by the optical path difference between the light beam B3 reflected by the surface of the installation table 16 and the light beam B2 reflected by the top surface 93 of the surface reflecting element 90 according to the above procedure. It is calculated | required by measuring with the measuring apparatus 1. FIG. Alternatively, the height h may be measured in advance using another method. Furthermore, the inner diameter D of the object to be measured can be measured using the light beam B3 vertically reflected by the surface of the installation table 16 instead of the light beam B2. In this case, the optical path differences between the light beams B1, B1 ′ and B3 are 2d ₁ −x and 2d ₂ −x, respectively.

  In addition, as a surface reflection element, instead of using the above-described triangular prism cut out, a conical or polygonal pyramid may be cut out with a plane parallel to the bottom. Even in this case, in the cross section including the axis of the object to be measured, each side surface at a position facing each other across the top surface is formed so as to form an angle of 45 ° with the bottom surface. The surface reflecting element has a bottom surface facing the installation table 16, a top surface located on the side where light from the white light source is incident, and each side surface inclined by 45 ° with respect to the axis of the object to be measured 10. To be arranged. Then, by making the light from the white light source incident on the top surface, the light beam is vertically reflected on the top surface, reflected on the side surface of the surface reflecting element, and vertically reflected on the inner surface of the object to be measured 10, and then again. A light beam reflected on the side surface is obtained. Then, the inner diameter of the DUT 10 can be measured by measuring the optical path difference between the two light beams with an interferometer.

In the measurement apparatus of the above embodiment, the interferometer may be a Fizeau interferometer. Furthermore, the device under test is not limited to a cylindrical one. The measuring apparatus of the above embodiment can be applied as it is when measuring the distance between two opposing surfaces of an object to be measured.
Furthermore, the white light source arranged on the surface reflecting element side and the detector arranged on the interferometer side may be interchanged. In this case, two light beams having an optical path difference corresponding to the measurement target dimension of the object to be measured are generated in advance on the interferometer side, and these light beams are sent to the surface reflecting element side through the optical fiber. In the surface reflecting element, the received two light beams are further divided into a light beam reflected on the inner surface of the object to be measured and two light beams reflected on the apex or top surface of the surface reflecting element. The white interference fringes are observed by detecting them with a detector. In this case as well, the inner diameter of the object to be measured can be obtained by measuring the optical path difference generated on the interferometer side.
As described above, various modifications can be made within the scope of the present invention according to the embodiment to be implemented.

It is a schematic block diagram of the internal diameter measuring apparatus to which this invention is applied. It is a schematic arrangement | positioning figure which shows the positional relationship of a to-be-measured object and a surface reflective element. It is a figure which shows the optical path difference of the two light beams divided | segmented by the surface reflective element. (A) is a figure which shows the structure for measuring the internal diameter of a to-be-measured object when a surface reflective element is eccentric with respect to a to-be-measured object, (b) is the plane of the shutter used by the structure. FIG. It is a schematic block diagram of the interferometer which comprises an internal diameter measuring apparatus. It is an operation | movement flowchart of an internal diameter measuring apparatus. It is a figure which shows the optical path difference of the two light beams divided | segmented by the surface reflection element when convergent light injects into a surface reflection element. (A) And (b) is a schematic side view of embodiment which produces | generates the several light beam which has an optical path difference according to the internal diameter of a to-be-measured object, respectively using a light beam splitting means. It is a schematic side sectional drawing of other embodiment of a surface reflective element.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Inner diameter measuring apparatus 10 Object to be measured 2 White light source 3 Surface reflection element 4 Interferometer 5 Detector 6 Controller 7, 8 Optical fiber 9 Beam splitter 11 Collimator lens 12 Wedge prism 13 Condensing lens 14 XYZ stage 15 Stage controller 16 Installation stand 31 Shutter 32 Aperture 44 Moving mirror 45 Support member 46 Piezo fine movement stage 47 Coarse movement stage 48 Corner cube 49 Position measurement interferometer 51 Piezo controller 52 Stage controller 81, 83 Half mirror 82 Mirror 90 Surface reflection element

Claims (5)

An inner diameter measuring device for measuring an inner diameter dimension of a cylindrical object to be measured,
A white light source,
The first light beam divided from the incident light emitted from the white light source is reflected by the object to be measured, and corresponds to the inner diameter of the object to be measured between the second light beam divided from the incident light. A surface reflective element that produces a first optical path difference;
An interferometer having a fixed mirror whose position is fixed and a movable mirror movable along an optical path, wherein the first and second light beams emitted from the surface reflecting element are directed to the fixed mirror, respectively. An interferometer for branching into a third light flux and a fourth light flux toward the movable mirror to produce a second optical path difference between the third light flux and the fourth light flux;
The third light beam and the fourth light beam are received, an interference signal generated when the first optical path difference and the second optical path difference are substantially equal is detected, and a signal corresponding to the interference signal is output. A detector to
A controller that determines the inner diameter of the object to be measured by measuring the position of the movable mirror corresponding to the maximum value of the interference signal and calculating the second optical path difference from the position;
An inner diameter measuring device comprising:   The surface reflecting element is a sphere, and the surface reflecting element reflects a part of the incident light on the surface of the surface reflecting element so as to be incident substantially perpendicularly on the inner surface of the object to be measured. And the other part of the incident light is reflected on the top of the surface light reflecting element on the white light source side or on the surface of the installation base on which the surface reflecting element is installed. The inner diameter measuring apparatus according to claim 1, wherein the inner diameter measuring apparatus forms a light beam.   The surface reflecting element has a shape in which a cross-sectional shape in a plane including the axis of the object to be measured is a trapezoid, and the surface reflecting element reflects a part of the incident light on a side surface of the surface reflecting element. The first light beam is formed by being incident substantially perpendicularly on the inner surface of the object to be measured, and the top surface of the surface reflecting element or the surface reflecting element is installed as another part of the incident light. The inner diameter measuring apparatus according to claim 1, wherein the second light flux is formed by reflection on a surface of the installation table.   The inner diameter measuring device according to any one of claims 1 to 3, further comprising a light beam splitting element that splits light emitted from the white light source into the first light beam and the second light beam. An inner diameter measuring device for measuring an inner diameter dimension of a cylindrical object to be measured,
A white light source,
An interferometer having a reference mirror having a fixed position and a movable mirror movable along an optical path, wherein the light emitted from the white light source is directed to the first light flux toward the reference mirror, and the movement An interferometer that branches into a second light beam directed to the mirror to produce a first optical path difference between the first light beam and the second light beam;
A third beam split from the first beam and the second beam emitted from the interferometer is reflected by the object to be measured, and a fourth beam split from the first beam and the second beam. A surface reflection element that generates a second optical path difference corresponding to the inner diameter of the object to be measured,
The third light beam and the fourth light beam are received, an interference signal generated when the first optical path difference and the second optical path difference are substantially equal is detected, and a signal corresponding to the interference signal is output. A detector to
A controller that determines the inner diameter of the object to be measured by measuring the position of the movable mirror corresponding to the maximum value of the interference signal and calculating the first optical path difference from the position;
An inner diameter measuring device comprising:

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