JP2016075577A - Shape measurement device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a shape measurement device that can measure a three-dimensional shape of an inner face of a cylindrical measurement object in high speed and with high accuracy.SOLUTION: Light emitted from a white color light source 12 is split into measurement light and reference light by a beam splitter 16 via a collimator 14. The measurement light is enlarged by a telecentric optical system 18, is paralleled, and is deflected at a right angle as maintaining parallelism by a conical prism 20. An inner face of a workpiece W serving as a cylindrical measurement object is irradiated over an entire peripheral direction with the measurement light. A reference mirror 22 movable in an optical axis direction is irradiated with the reference light. The measurement light reflected upon the inner face of the workpiece W and the reference light reflected upon the reference mirror 22 are synthesized by the beam splitter 16, and the interference light in this case is detected by an optical detector 24. On the basis of optical intensity of the interference light to be detected by each light reception element of the optical detector 24, a three-dimensional shape of the inner face of the workpiece W is measured.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a shape measuring apparatus, and more particularly to a shape measuring apparatus that measures a three-dimensional shape of an inner surface of a cylindrical measuring object (cylindrical measuring object) using a white interference method.

  Conventionally, a measurement method using a white interference method (low coherence interference method) is known as a method for accurately measuring a dimension of a measurement object in a non-contact manner (see, for example, Patent Document 1). In this method, the light emitted from the white light source is divided into measurement light directed to the measurement object and reference light directed to the reference mirror, and the measurement light reflected on the measurement surface of the measurement object and the reference surface of the reference mirror The reference light reflected in step 1 is interfered with, and the intensity of the interference light is detected. At that time, when the optical path length of the measurement light and the optical path length of the reference light are equal, the amplitude of the white interference fringes is maximized. Therefore, this method moves the reference mirror, measures the position of the reference mirror when the amplitude of the white interference fringes becomes maximum, and examines the optical path length of the reference light, thereby measuring the dimensions of the measurement object (surface height). Can be measured.

JP 2010-43954 A

  By the way, when the three-dimensional shape of the inner surface of a cylindrical measurement object (hereinafter referred to as a cylindrical measurement object) is to be measured by the measurement method using the white interference method described above, the axial direction of the cylindrical measurement object is the center. Since it is necessary to scan the measurement light in the circumferential direction, there is a problem that measurement takes time and high-precision measurement is difficult due to variations in the scanning speed and irradiation position of the measurement light.

  In Patent Document 1, no consideration is given to the above-described problem when measuring a cylindrical measurement object, and no solution is shown.

  This invention is made | formed in view of such a situation, and it aims at providing the shape measuring apparatus which can measure the three-dimensional shape of the inner surface of a cylindrical measurement object at high speed and with high precision.

  In order to achieve the above object, a shape measuring apparatus according to the present invention is a shape measuring apparatus for measuring a three-dimensional shape of an inner surface of a cylindrical measurement object, and includes a white light source and light generated from the white light source as measurement light. Splitting means for splitting into reference light, optical path length changing means for relatively changing the optical path length of the measurement light and the reference light, and an optical deflection element for deflecting the measurement light toward the entire circumferential direction of the inner surface of the cylindrical measurement object And a plurality of light receiving elements, based on the detection result by the light detecting means, the light detecting means for detecting the interference light between the measurement light reflected on the inner surface of the cylindrical measurement object and the reference light by the plurality of light receiving elements, Computing means for calculating the three-dimensional shape of the inner surface of the cylindrical measurement object.

  An aspect of the shape measuring apparatus according to the present invention includes a reference optical path length changing unit that includes a reference mirror that reflects the reference light, and changes the optical path length of the reference light by moving the reference mirror in the optical axis direction of the reference light. A reference mirror position detecting means for detecting the position of the reference mirror in the optical axis direction, and the light detecting means detects the position of the reference mirror when the intensity of the interference light is maximum for each light receiving element. It is preferable to calculate the three-dimensional shape of the inner surface of the cylindrical measurement object irradiated with the measurement light.

  In one aspect of the shape measuring apparatus according to the present invention, it is preferable that the light deflection element is formed of a conical prism.

  In the aspect of the shape measuring apparatus according to the present invention, it is preferable that a telecentric optical system for expanding and collimating the measuring light is provided between the dividing unit and the light deflection element.

  Moreover, it is preferable that the one aspect | mode of the shape measuring apparatus which concerns on this invention is further provided with the measurement area change means which changes the measurement area where measurement light is irradiated to the inner surface of a cylindrical measurement object to the axial direction of a cylindrical measurement object.

  According to the present invention, the measurement light can be simultaneously irradiated over the entire inner surface of the cylindrical measurement object, so that the three-dimensional shape of the inner surface of the cylindrical measurement object can be measured at high speed and with high accuracy.

Schematic configuration diagram showing a shape measuring apparatus according to an embodiment of the present invention The figure which showed the structure of the measurement light emission part vicinity of the shape measuring apparatus shown in FIG. Schematic configuration diagram of light receiving surface of photodetector Explanatory drawing showing the correspondence between the measurement area on the inner surface of the workpiece and the interference image acquired by the photodetector The figure which shows the example of the interference signal output from a photodetector The flowchart figure which showed the shape measuring method using the shape measuring apparatus of this embodiment

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

  FIG. 1 is a schematic configuration diagram showing a shape measuring apparatus according to an embodiment of the present invention. As shown in FIG. 1, the shape measuring apparatus 10 according to this embodiment uses a white interference method to obtain a three-dimensional shape of an inner surface (measurement surface) of a cylindrical measurement object having an inner diameter of several tens of millimeters at high speed and with high accuracy. A device that measures (with accuracy on the order of micrometers), a white light source 12, a collimator 14, a beam splitter 16, a telecentric optical system 18, a conical prism 20, a reference mirror 22, a photodetector 24, A stage 26 and a controller 28 are provided.

  The stage 26 has a placement surface on which a workpiece W that is a cylindrical measurement object is placed. The stage 26 is configured to be movable in the x, y, and z directions by the stage driving means 30. The stage 26 is an example of a measurement area changing unit.

  The white light source 12 is a light source that has a short coherence length and can emit light having a broad wavelength. As the white light source 12, a xenon lamp, a laser light source, an LED (Light Emitting Diode), or the like that outputs light in the visible light region (wavelength 400 to 800 nm) is used. Further, the output of light emitted from the white light source 12 is preferably about 100 W. The spectral width of the light emitted from the white light source 12 is preferably 50 nm or more. The spectral intensity distribution of the light emitted from the white light source 12 is preferably approximated to a Gaussian function type with a certain wavelength as the center.

  Light (white light) generated from the white light source 12 is collimated (collimated) by the collimator 14 via a light guide (optical fiber) 32, and is divided into measurement light and reference light by the beam splitter 16. The measurement light is applied to the inner surface of the workpiece W via the telecentric optical system 18 and the conical prism 20. On the other hand, the reference light is applied to the reference surface of the reference mirror 22. The measurement light and the reference light reflected by the inner surface of the workpiece W and the reference surface of the reference mirror 22 are combined by the beam splitter 16, and the interference light at that time is detected by the photodetector 24.

  FIG. 2 is a diagram illustrating a configuration in the vicinity of the measurement light emitting unit of the shape measuring apparatus 10. The telecentric optical system 18 is provided to increase the image plane resolution of the measurement light and suppress aberrations such as image plane distortion. The telecentric optical system 18 is designed as a bi-telecentric optical system, and expands and collimates the measurement light emitted from the beam splitter 16 (see FIG. 1) as shown in FIG. The image plane resolution of the measurement light expanded and collimated by the telecentric optical system 18 is 4.0 μm or more in consideration of measuring the three-dimensional shape of the inner surface of the workpiece W, which is a cylindrical measurement object, with high accuracy. It is preferable.

  The conical prism 20 has a flat surface 20a on one side (incident side) and a conical surface 20b on the other side (exit side), and is made of a material that easily transmits light such as quartz or BK7. . The conical prism 20 is an example of a light deflection element. In this conical prism 20, the angle (vertical angle) of the conical portion is set by the wavelength of the incident measurement light and the refractive index of the material, and the central axis of the conical prism 20 is arranged on the optical axis L of the measurement light. .

  As a result, the measurement light expanded and collimated by the telecentric optical system 18 is deflected at a right angle while maintaining parallelism by the conical prism 20, and is emitted toward the entire circumferential direction around the central axis of the conical prism 20. Is done. In other words, the inner surface (measurement surface) of the workpiece W is simultaneously irradiated with measurement light over the entire circumferential direction, and is irradiated perpendicularly to the inner surface of the workpiece W. Then, the measurement light reflected by the inner surface of the workpiece W is returned to the beam splitter 16 via the conical prism 20 and the telecentric optical system 18.

  Returning to FIG. 1, the reference mirror 22 is an example of a reference optical path length changing unit that relatively changes the optical path lengths of the measurement light and the reference light, and can be moved in the optical axis direction of the reference light by the reference mirror driving unit 34. It is configured. As the reference mirror driving unit 34, for example, a voice coil, a piezoelectric element, an ultrasonic motor, or the like is used.

  The position of the reference mirror 22 (the position of the reference light in the optical axis direction) is detected by the encoder 36. The encoder 36 is an example of a reference mirror position detection unit. The position information of the reference mirror 22 detected by the encoder 36 is output to the controller 28.

  The photodetector 24 is an example of a light detection unit, and is configured by arranging a large number of light receiving elements (pixels) 38 in a matrix as shown in FIG. Each light receiving element 38 accumulates electric charge according to the intensity of the received light. The photodetector 24 converts the signal charge accumulated in each light receiving element 38 into a signal voltage and outputs it as an electric signal (interference signal). As the photodetector 24 having such a function, for example, a solid-state imaging device such as a CCD image sensor (Charge Coupled Device Image Sensor) or a CMOS image sensor (Complementary Metal Oxide Semiconductor Image Sensor) is preferably used. It is preferable to use a photodetector 24 having a high resolution (preferably 5 million pixels or more) in order to enable high-resolution measurement.

  The measurement light reflected by the inner surface of the workpiece W and the reference light reflected by the reference mirror 22 are combined into one by the beam splitter 16 and optically interfered, and are incident on each light receiving element 38 of the photodetector 24.

  The intensity of the interference light detected by each light receiving element 38 of the photodetector 24 changes as the reference mirror 22 moves. That is, since the intensity of the interference light changes due to the optical path length difference between the measurement light and the reference light, when the reference mirror 22 is moved to change the optical path length of the reference light, the optical path length difference between the measurement light and the reference light is changed. The intensity of interference light changes. At this time, the intensity amplitude of the interference light is maximized when the optical path length difference between the measurement light and the interference light is zero.

  The photodetector 24 samples at a predetermined time interval, converts the detected light quantity at each sampling time into an electric signal (interference signal), and outputs it to the controller 28.

  Here, the correspondence relationship between the measurement area on the inner surface of the workpiece W (the area irradiated with the measurement light on the inner surface of the workpiece W) and the interference image acquired by the photodetector 24 will be described with reference to FIG.

  As shown in FIG. 4A, the measurement light expanded and collimated by the telecentric optical system 18 is deflected at a right angle while maintaining parallelism by the conical prism 20, and the optical axis L of the measurement light (conical prism). The light is emitted toward the entire circumferential direction centering on 20 central axes). As a result, the measurement light emitted from the conical prism 20 is irradiated perpendicularly to the inner surface (measurement surface) of the workpiece W and simultaneously irradiated in a strip shape over the entire circumferential direction of the inner surface of the workpiece W. Then, the interference light between the measurement light reflected from the inner surface of the workpiece W and the reference light is detected by the photodetector 24.

  At that time, the photodetector 24 receives a circular interference image corresponding to the measurement area on the inner surface of the workpiece W, as shown in FIG. For example, measurement points A and B shown in FIG. 4A correspond to points a and b in the interference image shown in FIG. 4B, respectively. That is, each light receiving element 38 of the photodetector 24 has a one-to-one correspondence with each measurement point in the measurement area irradiated with the measurement light on the inner surface of the workpiece W, and interference of the measurement light reflected at each measurement point. Light enters the corresponding light receiving element 38. Therefore, by detecting the intensity of the interference light by each light receiving element 38 of the photodetector 24, it becomes possible to measure the dimensions of each measurement point set on the inner surface of the workpiece W corresponding to each light receiving element 38. .

  Since the central portion of the interference image shown in FIG. 4B on the inner surface of the work W has a lower resolution than the other portions, the non-measurement area where the three-dimensional shape of the inner surface of the work W is not measured is used. Is desirable.

  Returning to FIG. 1, the controller 28 functions as a calculation unit that calculates the three-dimensional shape of the inner surface of the workpiece W, and also functions as a control unit that controls the overall operation of the shape measuring apparatus 10. The controller 28 is configured by a so-called PC (Personal Computer) and executes a predetermined program to realize functions as a calculation unit and a control unit.

  The controller 28 performs drive control of each part such as movement control of the stage 26, movement control of the reference mirror 22, and light emission control of the white light source 12.

  Further, the controller 28 calculates the three-dimensional shape of the workpiece W. That is, the controller 28 outputs an interference signal (intensity of interference light) of each light receiving element 38 output from the photodetector 24, position information of the reference mirror 22 output from the encoder 36, and a stage position detection unit (not shown). The position information of the stage 26 to be obtained is acquired, and the three-dimensional shape of the inner surface (measurement surface) of the workpiece W is calculated based on the information.

  Here, a method for calculating the three-dimensional shape of the inner surface of the workpiece W will be described.

  Since the light emitted from the white light source 12 has a short coherence length, interference fringes (white interference fringes) are detected only when the difference in optical path length between the measurement light and the reference light is zero or in the vicinity thereof. The interference fringes have a maximum contrast when the optical path length of the measurement light and the optical path length of the reference light coincide with each other, that is, when the difference between the optical path lengths is zero. The contrast of the interference fringes is expressed as the intensity of the interference light detected by the photodetector 24. As shown in FIG. 5, the position of the reference mirror 22, that is, the optical path length difference between the measurement light and the reference light is used. Change.

  Therefore, in the dimension measurement using the white light interferometry, the position of the reference mirror 22 when the intensity of the interference light is maximized is obtained for the standard product (master) having a known dimension. Next, for the workpiece W, the position of the reference mirror 22 when the intensity of the interference light is maximized is obtained. Then, an optical path length difference corresponding to the obtained difference in the position of the reference mirror 22 is obtained, and this optical path length difference is added to the dimensions of the reference product to obtain the dimensions of the workpiece W.

  In the shape measuring apparatus 10 of the present embodiment, the light intensity of the interference light is detected by each light receiving element (pixel) 38 constituting the photodetector 24. Therefore, for each light receiving element 38, the position of the reference mirror 22 when the intensity of the interference light is maximized for the standard product and the position of the reference mirror 22 when the intensity of the interference light is maximized for the workpiece W are obtained. . Then, the optical path length difference is obtained for each light receiving element 38, and the obtained optical path length difference is added to the dimensions of the reference product to obtain the dimensions for each light receiving element 38. The dimensions required for each light receiving element 38 indicate the dimensions of the corresponding measurement points, and the three-dimensional shape of the measurement area is acquired by acquiring the dimensions of all the measurement points.

  Note that the reference product is measured before the workpiece W is measured. Information obtained by the measurement is stored in a storage device (not shown) in the controller 28.

  Next, a shape measuring method using the shape measuring apparatus 10 of the present embodiment will be described with reference to FIG. FIG. 6 is a flowchart showing a shape measuring method using the shape measuring apparatus 10 of the present embodiment.

  First, as a reference product measurement step performed before measuring the three-dimensional shape of the inner surface of the workpiece W, a reference product with a known dimension (surface position of the inner surface) (reference measurement object serving as a reference for a cylindrical measurement object) is used. Measure the inner surface (reference surface).

  In the reference product measurement process, first, the reference product is set on the stage 26 (step S10). At this time, the controller 28 moves the stage 26 in the x, y, and z directions according to the operation of the operator, so that the central axis of the reference product and the optical axis L of the measurement light (the central axis of the conical prism 20) are obtained. In addition to aligning in the x and y directions (horizontal direction) so as to match, the reference product is aligned in the z direction (height direction). Thereby, the relative position between the apparatus main body 10A of the shape measuring apparatus 10 and the reference product is adjusted, and the position of the measurement area irradiated with the measurement light on the inner surface of the reference product is adjusted.

  Next, when the start of measurement is instructed by the operator, the controller 28 turns on the white light source 12 (step S12). As a result, the light generated from the white light source 12 is split into measurement light and reference light by the beam splitter 16 via the light guide 32. The measurement light is expanded and collimated by the telecentric optical system 18, further deflected at right angles while maintaining parallelism by the conical prism 20, and emitted toward the entire circumferential direction around the central axis of the conical prism 20. . Thereby, the measurement light is irradiated simultaneously and perpendicularly to the inner surface over the entire circumferential direction on the inner surface (measurement surface) of the reference product. Then, the measurement light reflected by the inner surface of the reference product is returned to the beam splitter 16 via the conical prism 20 and the telecentric optical system 18. On the other hand, the reference light is reflected by the reference surface of the reference mirror 22 and returned to the beam splitter 16. Then, the measurement light and the reference light reflected by the inner surface (measurement surface) of the standard product and the reference surface of the reference mirror 22 are combined by the beam splitter 16, and the interference light at that time is detected by the photodetector 24.

  Next, the controller 28 starts scanning the reference mirror 22 (step S14). That is, the controller 28 drives the reference mirror driving unit 34 to move the reference mirror 22 in the optical axis direction of the reference light. As a result, the optical path length of the reference light changes, and the optical path length difference between the reference light and the measurement light changes.

  Next, the controller 28 acquires the position information of the reference mirror from the encoder 36, and acquires the interference signal of each light receiving element 38 from the photodetector 24 (step S16). Then, the controller 28 detects the position P0 of the reference mirror when the intensity of the interference light is maximized for each light receiving element 38 of the photodetector 24 (step S18).

  The controller 28 stores information on the position P0 of the reference mirror 22 obtained for each light receiving element 38 in a storage device (not shown) in the controller 28 as reference position information.

  Thereafter, the controller 28 ends the scanning of the reference mirror 22 and turns off the white light source 12.

  After the reference product measurement process is completed as described above, a work measurement process for measuring the inner surface (measurement surface) of the work W is performed.

  The workpiece measurement process is performed in the same manner as the reference product measurement process. Although the description in the reference product measurement process is duplicated, the work measurement process will be described. First, the work W is set on the stage 26 (step S20). At this time, the controller 28 moves the stage 26 in the x, y, and z directions according to the operation of the operator, whereby the central axis of the workpiece W and the optical axis L of the measurement light (the central axis of the conical prism 20) are obtained. The alignment in the x and y directions (horizontal direction) is performed so as to match, and the alignment of the workpiece W in the z direction (height direction) is performed. Accordingly, the relative position between the apparatus main body 10A of the shape measuring apparatus 10 and the workpiece W is adjusted, and the position of the measurement area irradiated with the measurement light on the inner surface of the workpiece W is adjusted. The measurement area on the inner surface of the workpiece W and the measurement area on the inner surface of the reference object are set to be the same area.

  Next, when the start of measurement is instructed by the operator, the controller 28 turns on the white light source 12 (step S22). As a result, the light generated from the white light source 12 is split into measurement light and reference light by the beam splitter 16 via the light guide 32. The measurement light is expanded and collimated by the telecentric optical system 18, further deflected at right angles while maintaining parallelism by the conical prism 20, and emitted toward the entire circumferential direction around the central axis of the conical prism 20. . Thereby, the measurement light is irradiated simultaneously and perpendicularly to the inner surface over the entire circumferential direction on the inner surface (measurement surface) of the workpiece W. Then, the measurement light reflected by the inner surface of the workpiece W is returned to the beam splitter 16 via the conical prism 20 and the telecentric optical system 18. On the other hand, the reference light is reflected by the reference surface of the reference mirror 22 and returned to the beam splitter 16. Then, the measurement light and the reference light reflected by the inner surface (measurement surface) of the workpiece W and the reference surface of the reference mirror 22 are combined by the beam splitter 16, and the interference light at that time is detected by the photodetector 24.

  Next, the controller 28 starts scanning the reference mirror 22 (step S24). That is, the controller 28 drives the reference mirror driving unit 34 to move the reference mirror 22 in the optical axis direction of the reference light. As a result, the optical path length of the reference light changes, and the optical path length difference between the reference light and the measurement light changes.

  Next, the controller 28 acquires the position information of the reference mirror from the encoder 36 and also acquires the interference signal of each light receiving element 38 from the photodetector 24 (step S26). Then, the controller 28 detects the position P1 of the reference mirror when the intensity of the interference light is maximized for each light receiving element 38 of the photodetector 24 (step S28).

  The controller 28 stores information on the position P1 of the reference mirror 22 obtained for each light receiving element 38 in a storage device (not shown) in the controller 28 as detected position information.

  Thereafter, the controller 28 ends the scanning of the reference mirror 22 and turns off the white light source 12.

  Next, the controller 28 calculates the optical path length difference ΔP (= P1−P0) corresponding to the difference between the detection position P1 and the reference position P0 for each light receiving element 38 (step S30).

  Next, the controller 28 adds the optical path length difference ΔP calculated in step S30 to the surface position of the inner surface of the reference object, and determines the dimension of the workpiece W (surface position of the inner surface) for each light receiving element 38 (step S32). . Since the dimensions required for each light receiving element 38 indicate the dimensions of the corresponding measurement points, the dimensions of each measurement point in the measurement area can be obtained by obtaining the dimensions of all the measurement points. Are obtained.

  Thus, according to the present embodiment, the conical prism 20 can simultaneously irradiate the inner surface of the workpiece W, which is a cylindrical measurement object, with the measurement light over the entire circumferential direction. Thereby, it becomes unnecessary to scan the measurement light in the circumferential direction of the inner surface of the workpiece W, and it is possible to prevent the influence of variations in the scanning speed and irradiation position of the measurement light. Therefore, the three-dimensional shape of the inner surface of the cylindrical measurement object can be measured at high speed and with high accuracy.

  Further, according to the present embodiment, the telecentric optical system 18 that expands and collimates the measurement light is provided in front of the conical prism 20, so that the image plane resolution of the measurement light can be increased, and more accurate measurement can be performed. Can be done.

  Further, according to the present embodiment, the stage 26 as the measurement area changing means is moved in the Z direction, and the relative position between the apparatus main body 10A of the shape measuring apparatus 10 and the work W, that is, the inner surface of the work W is set. By changing the position of the measurement area in the z direction, the three-dimensional shape of the inner surface of the workpiece W can be measured over a wide range in the z direction. As a mode for changing the relative position between the apparatus main body 10A of the shape measuring apparatus 10 and the work W, the apparatus main body 10A of the shape measuring apparatus 10 is moved in the z direction in addition to the mode in which the stage 26 is moved in the z direction. Alternatively, it is possible to adopt a mode in which both the apparatus main body 10A of the shape measuring apparatus 10 and the stage 26 are moved in the z direction.

  In the present embodiment, the conical prism 20 is used as the light deflecting element. However, the conical prism 20 has the same function as that of the conical prism 20, that is, on the inner surface of the workpiece W while maintaining the parallelism of the measurement light. There is no particular limitation as long as it can simultaneously irradiate measurement light over the entire circumferential direction.

  Moreover, in this embodiment, although the aspect which changes the optical path length difference of measurement light and reference light by changing the optical path length of reference light was shown, not only this but the aspect which changes the optical path length of measurement light, A mode in which both the measurement light and the reference light are changed can be employed.

  In this embodiment, the beam splitter is used as the dividing unit and the optical interference unit. However, the present invention is not limited to this, and an optical coupler or the like can also be used.

  In addition, although the shape measuring apparatus 10 in this embodiment is mainly used in an industrial field, it is not restricted to this, For example, the application to a medical field etc. is also possible.

  The embodiments of the present invention have been described above. However, the present invention is not limited to the above examples, and various improvements and modifications may be made without departing from the scope of the present invention. .

  DESCRIPTION OF SYMBOLS 10 ... Shape measuring apparatus, 10A ... Apparatus main body, 12 ... White light source, 14 ... Collimator, 16 ... Beam splitter, 18 ... Telecentric optical system, 20 ... Conical prism, 22 ... Reference mirror, 24 ... Photo detector, 26 ... Stage 28 ... Controller, 30 ... Stage drive means, 32 ... Light guide, 34 ... Reference mirror drive means, 36 ... Encoder, 38 ... Light receiving element, W ... Workpiece

Claims (5)

A shape measuring device for measuring the three-dimensional shape of the inner surface of a cylindrical measuring object,
A white light source,
Splitting means for splitting light generated from the white light source into measurement light and reference light;
Optical path length changing means for relatively changing the optical path length of the measurement light and the reference light;
An optical deflection element that deflects the measurement light toward the entire circumferential direction of the inner surface of the cylindrical measurement object;
A light detecting means having a plurality of light receiving elements and detecting interference light between the measurement light reflected by the inner surface of the cylindrical measurement object and the reference light by the plurality of light receiving elements;
An arithmetic means for calculating a three-dimensional shape of the inner surface of the cylindrical measurement object based on a detection result by the light detection means;
A shape measuring apparatus comprising: A reference optical path length changing unit that includes a reference mirror that reflects the reference light, and changes the optical path length of the reference light by moving the reference mirror in the optical axis direction of the reference light;
Reference mirror position detection means for detecting the position of the reference mirror in the optical axis direction,
The light detecting means detects the position of the reference mirror when the intensity of the interference light is maximized for each light receiving element, so that the three-dimensional shape of the inner surface of the cylindrical measurement object irradiated with the measurement light is detected. The shape measuring apparatus according to claim 1, wherein the shape is calculated.   The shape measuring apparatus according to claim 1, wherein the light deflection element is configured by a conical prism.   The shape measuring apparatus according to claim 1, wherein a telecentric optical system that expands and collimates the measurement light is provided between the dividing unit and the light deflection element.   The shape measuring apparatus according to claim 1, further comprising a measurement area changing unit that changes a measurement area in which the measurement light is irradiated on an inner surface of the cylindrical measurement object in an axial direction of the cylindrical measurement object. .