Calibration method of image measuring device

The present invention includes a preparatory step of providing a calibration work piece having a flat reflecting surface as a work piece, and arranging the reflecting surface to be parallel to a standard optical axis and orthogonal or parallel to pixel array directions of an image capture element; a rotation step of rotating a prism centered on the standard optical axis; a brightness detection step of detecting the brightness of an image captured by the image capture element at each of a plurality of rotation positions of the prism; and a positioning step of aligning the prism at a rotation position where the brightness detected by the brightness detection step is greatest.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority under 35 U.S.C. § 119 of Japanese Application No. 2017-201946, filed on Oct. 18, 2017, the disclosure of which is expressly incorporated by reference herein in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a calibration method of an image measuring device.

2. Description of Related Art

Conventionally, an optical interference measuring device is known which accurately measures the surface shape of a work piece using brightness information in an interference pattern generated by optical interference. For example, the optical interference measuring device disclosed in Japanese Patent Laid-open Publication No. 2012-093166 includes an optical interference optical system which splits light from a light source into measurement light and reference light, and combines the measurement light that is reflected off a work piece and the reference light that is reflected off a reflecting plane. While changing the optical path length of the reference light or measurement light, the optical interference measuring device uses an image capture element such as a CCD camera to capture an interference image showing a two-dimensional distribution of interference optical intensity. Then, based on the captured image information, the surface shape of the work piece can be accurately measured by detecting the focal depth where the intensity of optical interference reached a peak at each measurement position within the image capture field of view.

In recent years, techniques have been developed for making accurate observations of an interior wall of a cylindrical work piece, such as an engine cylinder, using optical interference measuring devices (for example, Japanese Application No. 2016-034436). The optical interference measuring device used in such a technique includes a probe capable of being inserted inside the cylindrical work piece and an optical interference optical system configured by the probe. The optical interference optical system includes a prism that splits light advancing along a standard optical axis that is substantially coaxial with the axis of the probe into measurement light, which advances in a direction orthogonal to the standard optical axis, and reference light, which advances along the standard optical axis; and combines the measurement light reflected off a work piece and the reference light reflected off a reference plane.

In such an optical interference measuring device, it is essential that the prism be positioned appropriately. For example, in order to measure a region that is broader than the surface of the work piece, the probe is displaced relative to the work piece in a vertical or transverse direction of the measurement region to change measurement regions, and after performing measurement for each measurement region, images of adjacent measurement regions are spliced together. At this point, in order to splice together interference images, a displacement axis of the probe on the image and the vertical or transverse direction of the image are preferably parallel to each other.

However, when a rotation position of the prism centered on the standard optical axis is offset from the position the prism is meant to occupy, this causes the measurement light to be bent by the prism, and the image may be captured in a form slightly rotated from the intended image. In such a case, the displacement axis of the probe on the image is oblique relative to the vertical and transverse directions of the image, and therefore offset occurs at peripheral regions of each image in the images of adjacent measurement regions. Accordingly, splicing together the images of adjacent measurement regions may become difficult.

Also, a similar problem is shared by measuring devices which bend measurement light, and is not limited to optical interference measuring devices. Specifically, in an image measuring device that includes an optical axis converter (represented by the prism described above, or the like), there is a similar problem caused by the positioning of the optical axis converter being offset due to the measurement light reflected off the work piece being bent in a direction lying along the standard optical axis which intersects the measurement optical axis of the measurement light.

SUMMARY OF THE INVENTION

The present invention provides a calibration method of an image measuring device for appropriately positioning an optical axis converter that bends measurement light.

A calibration method of an image measuring device according to the present invention is a calibration method of an image measuring device that includes an optical axis converter bending measurement light reflected off a work piece in a direction lying along a standard optical axis that intersects with a measurement optical axis of the measurement light, and an image capture element receiving the measurement light bent by the optical axis converter. The calibration method includes a preparatory step of providing a calibration work piece having a flat reflecting surface as the work piece, and arranging the reflecting surface to be parallel to the standard optical axis and orthogonal or parallel to pixel array directions of the image capture element; a rotation step of rotating the optical axis converter centered on the standard optical axis; a brightness detection step of detecting the brightness of an image captured by the image capture element at each of a plurality of rotation positions of the optical axis converter; and a positioning step of aligning the optical axis converter at a rotation position where the brightness detected by the brightness detection step is greatest.

In the present invention, first the preparatory step is performed, in which the calibration work piece having the flat reflecting surface is arranged as the work piece. At this point, preparations for subsequent steps are carried out by arranging the reflecting surface of the calibration work piece to be parallel to the standard optical axis and orthogonal or parallel to the pixel array directions of the image capture element.

Next, the rotation step of rotating the optical axis converter centered on the standard optical axis and the brightness detection step of detecting the brightness of the image at each of the plurality of rotation positions of the optical axis converter are performed. At this point, the rotation step and the brightness detection step may detect the brightness of the image each time the optical axis converter is rotated by a predetermined angle, or may continuously detect the brightness of the image while the optical axis converter is rotated within a predetermined angle range. Also, although the overall rotation angle of the optical axis converter from the rotation step is not particularly limited, when the optical axis converter is aligned to some extent beforehand, the overall rotation angle is preferably no more than 90°.

In the brightness detection step, the detected brightness of the image varies in accordance with the rotation position of the optical axis converter. For example, when the measurement optical axis is orthogonal to the reflecting surface of the calibration work piece, the amount of light incident on the image capture element is the greatest and the brightness of the image is the greatest. Meanwhile, when the measurement optical axis is oblique to the reflecting surface of the calibration work piece, the amount of light incident on the image capture element is reduced and the brightness of the image drops. In the brightness detection step, the brightness of the image may also be detected by a worker verifying an image displayed on a display (described below), or the brightness of the image (for example, the brightness of a predetermined coordinate region or the average brightness of the entire image) may be detected with a controller that controls operations of the image measuring device acting as a brightness detector (described below).

Next, the positioning step is performed, in which the optical axis converter is aligned at the rotation position where the brightness detected by the brightness detection step is greatest. Accordingly, the optical axis converter is positioned such that the measurement optical axis is orthogonal to the reflecting surface of the calibration work piece. In other words, the optical axis converter is positioned such that the measurement optical axis is orthogonal or parallel to the pixel array directions of the image capture element. The “brightness” of the image means a degree of brilliance of the image, and detecting the greatest level of brightness means detecting a state where the image is most brilliant.

According to the method described above, the optical axis converter is positioned appropriately in the image measuring device. Accordingly, when the probe that includes the optical axis converter is displaced relative to the work piece in a vertical or transverse direction of a measurement region in order to change measurement regions, for example, a displacement axis of the image captured by the image capture element is parallel to the vertical or transverse direction of the image. Therefore, offset at the peripheral regions of each image can be constrained, and the images of adjacent measurement regions can be readily spliced together.

In the calibration method of the image measuring device according to the present invention, preferably, the image measuring device further includes a brightness detector detecting the brightness of the image, and in the brightness detection step, the brightness detector detects the brightness of the image. According to this method, the brightness of the image can be detected as a numerical value, and therefore the optical axis converter can be aligned more accurately.

In the calibration method of the image measuring device according to the present invention, preferably, the image measuring device further includes a display displaying brightness information, and in the brightness detection step, the brightness information is displayed on the display for each of the plurality of rotation positions of the optical axis converter. According to this method, a worker can readily comprehend the rotation position with the greatest brightness. The brightness information should be at least one of the image captured by the image capture element and a value for the brightness (brightness value) detected by the brightness detector.

The present invention can provide a calibration method of an image measuring device for appropriately positioning an optical axis converter that bends measurement light.

DETAILED DESCRIPTION OF THE INVENTION

Hereafter, an embodiment of the present invention is described with reference to the drawings.

Configuration of Optical Interference Measuring Device

As illustrated inFIGS. 1 and 2, an optical interference measuring device1includes a table10, a stage20, a support column31, a Z axis displacement mechanism32, a probe support mechanism41, a probe42, a controller70, and a display80. The optical interference measuring device1is one example of an image measuring device according to the present invention, and is a device capable of measuring the surface shape of a work piece in fine detail based on an interference image. In addition, the probe42is configured to include a prism65, which is an example of an optical axis converter according to the present invention, and an image capture element52which receives measurement light that is bent by the prism65(seeFIG. 2).

The optical interference measuring device1according to the present embodiment is appropriate for measuring an interior wall of a cylindrical work piece by inserting a tip portion of the probe42into the cylindrical work piece. An example of the cylindrical work piece may be an engine cylinder, for example. However, rather than a work piece, a calibration work piece90is shown inFIGS. 1 and 2in order to describe a calibration method for the optical interference measuring device1hereafter.

The table10is the base of the optical interference measuring device1. The stage20is provided on the table10and includes a placement surface21that is parallel to a horizontal direction (XY plane direction), an X axis displacement mechanism22, and a Y axis displacement mechanism23. The work piece is placed on the placement surface21. The placement surface21is capable of displacement in X and Y axis directions using the X axis displacement mechanism22and the Y axis displacement mechanism23.

The support column31is provided rising along a Z axis direction from a top surface of the table10, and supports a slider33via the Z axis displacement mechanism32. The slider33is capable of displacement in the Z axis direction using the Z axis displacement mechanism32. In addition, the slider33supports the probe42via a probe support mechanism41.

The probe support mechanism41includes a rotation driver411and a linear driver412. The rotation driver411is provided to the slider33via a connecting member not shown in the drawings, and can rotate the probe42on a θ axis, as the axis of rotation, that is parallel to the Z direction. The linear driver412is provided to the rotation driver411and can displace the probe42along a W axis that is one direction parallel to the XY plane.

The probe42has a shape that extends along the Z axis and is mounted to the linear driver412such that a measurement optical axis Am described hereafter is parallel to the W axis. In addition, the probe42may include, for example, a light source that is a white light source (not shown in the drawings), an image capturer50, and an interference object lens60.

The image capturer50includes a case51that is attached to the linear driver412and the image capture element52that is installed inside the case51. The image capture element52may be configured by an image sensor such as a CCD (Charge Coupled Device) or CMOS (Complementary Metal Oxide Semiconductor), for example. A light-receiving surface521of the image capture element52is arranged so as to be orthogonal to the Z axis, and faces an optical path of the interference object lens60via an aperture (not shown in the drawings) formed in the bottom of the case51. In addition, a plurality of pixels configuring the image capture element52are arrayed along mutually orthogonal ix and iy directions, on a plane orthogonal to the Z axis (seeFIG. 3). The image capture element52is installed such that the ix and iy directions (pixel array directions) are either orthogonal or parallel to the W axis of the linear driver412.

The interference object lens60is configured to include a first case61, a second case62, a third case63, a guiding optical system64, the prism65, and a reference flat66.

The first case61includes, in an upper portion thereof, a connector611that rotatably connects to the image capturer50. This allows the interference object lens60to rotate relative to the image capturer50as necessary, for calibration for example. In addition, the guiding optical system64is installed inside the first case61and an aperture (not shown in the drawings) for the optical path is formed in the top and bottom of the first case61. The second case62is connected below the first case61, and the prism65is installed inside the second case62. An aperture (not shown in the drawings) for the optical path is formed in the top and bottom of the second case62, and a measurement aperture621that faces the front surface side of the prism65(measurement light emission side, described below) is formed in the side of the second case62. The third case63is connected below the second case62, and the reference flat66is installed inside the third case63. An aperture (not shown in the drawings) for the optical path is formed in the top of the third case63.

The guiding optical system64is configured by optical members such as a plurality of lenses, and expands the diameter of the optical path of a light beam fired from the light source and calibrates the light beam to be parallel light oriented toward the prism65along a standard optical axis As that is parallel to the Z axis. In addition, the guiding optical system64guides combined light (described below) emitted from the prism65toward the light-receiving surface521of the image capture element52. The center axis line of the first case61is substantially coaxial with the standard optical axis As of the guiding optical system64. Also, the lenses of the guiding optical system64depicted inFIG. 2are schematic renderings.

The prism65may configure a half mirror tilted 45° relative to the standard optical axis As, for example. The prism65reflects light from the guiding optical system64to serve as measurement light, while the remainder passes through to serve as reference light. In other words, the prism65splits the light from the guiding optical system64into measurement light and reference light. In the present embodiment, a side of the prism65that configures a reflecting surface650has a side651that is parallel to the XY plane and orthogonal to the measurement optical axis Am (seeFIG. 3A). The reference flat66may be a disk-like mirror, for example, and includes a reference plane661. The reference plane661reflects the reference light divided by the prism65.

The measurement light divided by the prism65travels toward the work piece (or the calibration work piece90) along the measurement optical axis Am that is orthogonal to the standard optical axis As and, after the measurement light has been reflected off the surface of the work piece, the measurement light returns to the prism65along the measurement optical axis Am. Meanwhile, the reference light divided by the prism65travels toward the reference flat66along a reference optical axis Ar that is coaxial with the standard optical axis As and, after the reference light has been reflected off the reference plane661of the reference flat66, the reference light returns to the prism65along the reference optical axis Ar.

The prism65combines the reference light reflected by the reference plane661with the measurement light reflected by the work piece and guides the combined light to the guiding optical system64. Interference between the reference light and the measurement light is produced in the combined light. The combined light passes through the guiding optical system64and strikes the light-receiving surface521of the image capture element52. The image capture element52is capable of capturing an image of an interference pattern in the incident combined light.

The controller70controls operations of the optical interference measuring device1by executing a program stored in an internal memory. Specifically, the controller70can control driving of the X axis displacement mechanism22, the Y axis displacement mechanism23, the Z axis displacement mechanism32, and the probe support mechanism41. In addition, the controller70can display an image82captured by the image capture element52on the display80, and can parse a three-dimensional shape of the work piece surface based on the image82. The controller70can act as a brightness detector71. The brightness detector71detects the brightness of the image82captured by the image capture element52. In this example, the brightness of the image82detected by the brightness detector71may, for example, be the brightness of a predetermined coordinate region of the image82, or may be the average brightness of the image82overall. The “brightness” of the image82means a degree of brilliance of the image82, and the brightness detector71can detect the brightness of the image82using a known technique.

The display80displays, as brightness information, the image82captured by the image capture element52and a value for the brightness (hereafter referred to as the brightness value)83detected by the brightness detector71. In the present embodiment, the display80displays the image82within a display screen81, and also provides an overlay display of the brightness value83on the displayed image82(seeFIG. 3B, for example). In the present embodiment, the controller70and the display80are integrally configured as a PC (Personal Computer).

In the optical interference measuring device1configured as described above, the relative positioning of the probe42with respect to the work piece is determined by the X axis displacement mechanism22, the Y axis displacement mechanism23, the Z axis displacement mechanism32, and the rotation driver411. In addition, the W axis direction of the linear driver412on the XY plane is determined by determining the rotation position of the probe42relative to the θ axis using the rotation driver411. In this example, the W axis direction is preferably a direction orthogonal to a measured surface of the work piece. Also, the linear driver412displaces the probe42in the W axis direction, thereby bringing the probe42closer to or farther from the work piece. While the probe42is displacing in this way, the image capture element52captures an image of a predetermined region of the work piece, thereby enabling the controller70to acquire an interference image in which the optical path length of the measurement light has been altered.

Calibration Method of Optical Interference Measuring Device

Calibration of the optical interference measuring device1is described with reference toFIGS. 3A to 7.FIGS. 3A to 5Billustrate a state where the calibration work piece90is provided instead of the work piece. Normally, the probe42is arranged as illustrated inFIG. 3A. Specifically, the image capture element52is provided such that the ix and iy directions (pixel array directions) are either orthogonal or parallel to the W axis, and the prism65is provided such that the measurement optical axis Am is parallel to the W axis. In other words, the measurement optical axis Am is parallel to the W axis, and is parallel to one of the pixel array directions (the ix direction inFIG. 3A) of the image capture element52.

In this example, a case is considered where the probe42is displaced relative to the work piece and the measurement region of the work piece is modified. At this point, the probe42is displaced in the Z axis direction or in a circumferential direction within the XY plane, and the image82captured by the image capture element52transitions in accordance with the displacement direction of the probe42. When the probe42is positioned appropriately, as illustrated inFIG. 3A, displacement axes pX and pY of the probe42in the image82are parallel to a transverse direction or vertical direction of the image82, as illustrated inFIG. 3B. Accordingly, the images82of adjacent measurement regions on the work piece can be readily spliced together.

If, as illustrated inFIGS. 4A and 5A, the prism65is offset from the appropriate positioning, the measurement optical axis Am of the prism65is positioned obliquely to the W axis and the pixel array directions (ix direction and iy direction) of the image capture element52. In such a case, the image82captured by the image capture element52is in a state slightly rotated from an original state, which is due to measurement light Lm being bent by the prism65(seeFIGS. 4B and 5B). At this point, the displacement axes pX and pY of the probe42in the image82are oblique relative to the vertical and transverse directions of the image82. Accordingly, offset is produced at peripheral regions of each image82, and therefore splicing together the images82of adjacent measurement regions may become difficult.

In view of this, in the present embodiment, when mounting the interference object lens60on the image capturer50or when calibrating the optical interference measuring device1, for example, the optical interference measuring device1is calibrated as described below.

First, the calibration work piece90is arranged on the placement surface21of the stage20(preparatory step S1). The calibration work piece90includes a flat reflecting surface91. Using chrome deposition or the like, a predetermined pattern84is formed on the reflecting surface91as a test chart. AlthoughFIGS. 3B, 4B, and 5Billustrate a rectangular pattern84in order to simplify the description, the pattern of the test chart is not limited to this. In the preparatory step S1, by positioning the reflecting surface91of the calibration work piece90so as to be parallel to the standard optical axis As, an amount of light received by the image capture element52is ensured. In addition, by positioning the reflecting surface91of the calibration work piece90so as to be orthogonal to the W axis, the reflecting surface91is arranged orthogonal or parallel to the pixel array directions (ix direction and iy direction) of the image capture element52. At this point, the brightness of the image82at the current rotation position of the interference object lens60may be detected.

Next, the interference object lens60is rotated by a very small angle, centered on the standard optical axis As (rotation step S2; seeFIG. 6A). In this example, the very small angle by which the prism65is rotated is not particularly limited, but is preferably from several degrees to several tens of degrees. For example, the very small angle may be rotated by a manual operation by a worker, or the connector611of the interference object lens60may be configured so as to rotate very slightly at a predetermined pitch.

Next, the brightness of the image82at the current rotation position of the interference object lens60is detected (brightness detection step S3; seeFIG. 6B). Specifically, the brightness detector71may detect the brightness of the image82and record the detected brightness in a memory of the controller70or the like. In addition, the brightness detector71displays on the display80the brightness value83, which indicates the detected brightness, and thereby the worker may verify the brightness value83displayed on the display80.

In the brightness detection step S3, the detected brightness of the image82varies in accordance with the angle of rotation of the prism65from the appropriate position (seeFIG. 6C). For example, when the direction in which the prism65emits the measurement light Lm (that is, the measurement optical axis Am of the prism65) is orthogonal to the reflecting surface91of the calibration work piece90, the amount of light incident on the image capture element52is the greatest and the brightness of the image82is the greatest. Meanwhile, when the measurement optical axis Am of the prism65is oblique to the reflecting surface91of the calibration work piece90, the amount of light incident on the image capture element52is reduced and the brightness of the image82drops.

Next, a determination is made as to whether the highest brightness value constituting a peak (a brightness peak) was detected (peak detection step S4). In this step, the brightness detector71may detect the brightness peak based on the recorded brightness values and display the detected brightness peak on the display80. In addition, the worker may judge the brightness peak based on the brightness value83displayed on the display80.

The procedure from the rotation step S2through the peak detection step S4described above is repeated until a brightness peak is detected. Accordingly, the brightness of the image82is detected at each of a plurality of rotation positions of the prism65. Although the overall rotation angle of the prism65from the rotation step S2is not particularly limited, when the prism65is aligned to some extent beforehand, the overall rotation angle is preferably no more than 90°. When a brightness peak is detected in the peak detection step S4, the worker calibrates the rotation position of the prism65while referencing the brightness value83displayed on the display80, such that the brightness value83shows the brightness peak. Accordingly, the prism65is aligned at the rotation position where the brightness peak is detected (peak position) (positioning step S5).

With the positioning step S5, the prism65is positioned such that the measurement optical axis Am is orthogonal to the reflecting surface91of the calibration work piece90. Accordingly, the prism65is positioned such that the measurement optical axis Am is parallel to the W axis; in other words, such that the measurement optical axis Am is orthogonal or parallel to the pixel array directions (ix direction and iy direction) of the image capture element52.

Effect of the Embodiment

The following advantages can be achieved according to the above-described embodiment. According to the present embodiment, in the optical interference measuring device1, the rotation position of the prism65around the standard optical axis As is arranged appropriately. In the optical interference measuring device1calibrated according to the present embodiment, the displacement axes pX and pY of the probe42in the image82can be made parallel to the transverse and vertical directions of the image82. Therefore, the images82of adjacent measurement regions on the work piece can be readily spliced together.

In addition, in the present embodiment, the controller70carries out operations as the brightness detector71, which detects the brightness of the image82. With the brightness detector71, the brightness of the image82is detected as a numerical value, and therefore the rotation position of the prism65around the standard optical axis As can be arranged more accurately. Also, in the present embodiment, the brightness value83indicating the brightness of the image82is displayed on the display80. Therefore, the worker can calibrate the rotation position of the prism65by referencing the brightness value83displayed on the display80.

Modification

The present invention is not limited to the above-described embodiment, and includes modifications within a scope capable of achieving the advantages of the present invention.

In the embodiment described above, the image82is displayed on the display80, but display of the image82may be omitted. In other words, the brightness value83may be the only brightness information displayed on the display80.

In the embodiment described above, the controller70carries out operations as the brightness detector71. However, the present invention is not limited to this, and the image82may be the only brightness information displayed on the display80without the controller70carrying out operations as the brightness detector71. For example, in the brightness detection step S3, the peak detection step S4, and the positioning step S5, the worker may also detect the brightness of the image82by simply looking at the image82displayed on the display screen81, and may judge the brightness peak and carry out alignment of the prism65based on the viewed detection information. In other words, as noted above, the “brightness” of the image means the degree of brilliance of the image, and therefore the image82displayed on the display screen81may be used as the brightness information. Specifically, the worker comprehends the degree of brilliance of the image82displayed on the display screen81, and the worker may judge whether the image82becomes brighter or darker each time the prism65rotates very slightly. In addition, the prism65may be aligned at the rotation position where the image82is brightest.

InFIGS. 3B, 4B, and 5Bwhich were referenced in the embodiment described above, in order to provide an illustration where the image82is readily understood, the entire image82is displayed on the display screen81. However, it is also possible to display only a partial region of the image82. In cases where the worker visually detects the brightness of the image82displayed on the display screen81, the worker may also detect the brightness of the partial region of the image82.

In the embodiment described above, the process of performing the rotation step S2of rotating the prism65very slightly and then performing the brightness detection step S3is repeated, but the present invention is not limited to this. For example, the brightness of the image82may be continuously detected while rotating the prism65within a predetermined angle range.

In the rotation step S2of the embodiment described above, the interference object lens60is rotated relative to the image capturer50. However, the present invention is not limited to this. For example, in the interference object lens60, the second case62which houses the prism65may be rotated relative to the first case61.

The optical interference measuring device1according to the embodiment described above includes the display80. However, at the point in time where the calibration method of the present invention is carried out, the optical interference measuring device1need not include the display80. For example, the brightness of the image82captured by the image capture element52may be detected using a brightness detector or the like.

In addition, the optical interference measuring device1according to the embodiment described above includes the prism65as a light splitting and combining element in order to achieve an interferometer, but the present invention is not limited to this. In other words, the light splitting and combining element in the optical interference measuring device1can be any element that achieves a splitting optical system that splits light from a light source into measurement light and reference light, and a combining optical system that causes the measurement light reflected off a work piece to interfere with the reference light reflected off a reference plane. In addition, the splitting optical system and the combining optical system may be configured as separate systems.

Furthermore, the calibration method of the optical interference measuring device1is described in the embodiment described above, but the present invention is not limited to this. In other words, the calibration method of the present invention can be broadly applied to image measuring devices that include an optical axis converter that bends measurement light reflected off a work piece in a direction lying along a standard optical axis that intersects with a measurement optical axis. For example, the optical axis converter of the present invention is not limited to the light splitting and combining element, and may be configured by a simple mirror or the like.

In addition, in the embodiment described above, the prism65(as the optical axis converter) configures both the emission optical system emitting the measurement light toward the work piece and the incident optical system where the measurement light reflected off the work piece is incident. However, the present invention is not limited to this. In other words, the optical axis converter of the present invention should configure at least an incident optical system where the measurement light reflected off the work piece is incident, and the emission optical system emitting the measurement light at the work piece may be configured by an optical system separate from the optical axis converter. Furthermore, the measurement optical axis (direction in which the measurement light reflected off the work piece advances) and the standard optical axis (direction in which the measurement light advances after being bent by the optical axis converter) are not limited to being orthogonal to each other, and may also be configured to at least intersect with each other.

The present invention can be used as a calibration method of an image measuring device for appropriately positioning an optical axis converter that bends measurement light.