Measuring apparatus and method

Abstract

To provide a measuring device and method capable of detecting the positional deviation in a straight axis direction only by two components of an interferometer and a mirror by using the interference phenomenon of a laser beam.SOLUTION: A measuring device includes: a branching optical system for branching the laser light into measurement light of a first polarization component and the reference light of a second polarization component perpendicular to the first polarization component; a retroreflector which is installed so as to be movable along a linear axis of a measurement object and reflects the measurement light in a direction parallel to and opposite to an incident direction when the measurement light is incident; a synthesizing optical system for emitting the measurement light reflected by the retroreflector in a state where the optical axis of the measurement light is inclined with respect to the optical axis of reference light; and an imaging element for imaging a striped pattern obtained by the interference of the measurement light and the reference light emitted from the synthesizing optical system.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a measuring device and method, and particularly to a measuring device and method for measuring straightness by utilizing the interference phenomenon of laser light.

Background Art

[0002] As methods for measuring straightness using laser light, the following (1) to (3) can be cited. (1) Method using laser interference (2) Method for detecting the movement of a laser beam in the straight axis direction (3) Method for estimating the displacement amount in the straight axis direction by accumulating the change in the inclination of the object to be measured

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] When using the laser interference of (1), since electromagnetic waves have the property that their traveling direction is always perpendicular to the equiphase surface, it is impossible in principle to detect the displacement amount in the straightness direction only by the interference phenomenon with only two components of an interferometer and a mirror. For this reason, a configuration as shown in FIG. 6 can be considered.

[0005] As shown in FIG. 6, when the single-polarized laser light (laser incident light) emitted from the laser oscillator enters the polarization film 100A of the polarization beam splitter 100, it is separated into transmitted light (measurement light) and reflected light (reference light). Here, the optical axis of the polarization film 100A has an inclination of 45° with respect to the polarization direction of the laser light.

[0006] The measurement light that has passed through the polarizing film 100A passes through the quarter-wave plate 102, then through the optical path P1 and enters the polarizing prism 104, where it is given a tilt of approximately 1.3°. The light reflected from the reflecting prism 106 while maintaining this tilt passes through the optical path P1 and again passes through the quarter-wave plate 102. At this time, the polarization direction of the light changes by 90°, so it is reflected by the polarizing film 100A, and the reflected light is incident on the corner cube prism 108.

[0007] Light emitted from the corner cube prism 108 is reflected again by the polarizing film 100A, passes through optical path P2, and travels back and forth in the same way as in optical path P1.

[0008] By arranging the optical path in this way, the effects of pitching and yawing of the polarizing prism 104, which are one of the error components in straightness and perpendicularity measurements, can be reduced.

[0009] Furthermore, the reference light reflected by the first polarizing film 100A first travels back and forth along optical path P3 in the same manner as described for the measurement light's optical path L1, and then travels back and forth along optical path P4 in the same manner as optical path P2.

[0010] The measurement light and the reference light are incident on the same optical path in an interference system, with their polarization directions being orthogonal. The interference signal is then photoelectrically converted, and the optical path difference between the measurement light and the reference light is counted.

[0011] In this way, the measurement system is configured with two parallel measurement beams and two reference beams spread out at approximately 2.6°. ru.

[0012] In this measurement system, when the polarizing prism 104 or the reflective prism 106 (generally the polarizing prism 104) moves in a direction that is spread by 2.6°, an optical path difference is generated, allowing for the measurement of straightness and perpendicularity.

[0013] In the configuration shown in Figure 6, as the distance of the linear axis increases, the size of the reflecting prism 106 increases proportionally, making it difficult to maintain measurement accuracy, and the reflecting prism 106 also becomes considerably more expensive.

[0014] In the method of detecting the movement of the laser beam in the straightness direction described in (2), if a corner cube prism is used as a reflective mirror, the position of the laser beam returning to the interferometer is proportional to the amount of movement of the corner cube prism in the straightness direction. There is also a method of detecting this amount of laser beam movement with an image sensor (for example, Patent Document 1), but the ratio of the maximum amount of laser beam movement in the straightness direction that can be captured to its detection resolution is determined by the number of pixels of the image sensor.

[0015] As a method for estimating the displacement in the straight-ahead direction by accumulating the change in the tilt of the object being measured in (3), one possible method is to estimate the displacement in the straight-ahead direction by accumulating the tilt of a moving body that moves along the object being measured (for example, Patent Document 2). However, errors will occur if the movement in the straight-ahead direction occurs with a period smaller than the size of the moving body, and if the sampling is insufficient.

[0016] This invention has been made in view of these circumstances, and aims to provide a measuring device and method that can detect positional deviations in the straight axis direction using only two components, an interferometer and a mirror, by utilizing the interference phenomenon of laser light. [Means for solving the problem]

[0017] To solve the above problems, a measuring device according to a first aspect of the present invention comprises: a branching optical system that branches laser light into a measurement light with a first polarization component and a reference light with a second polarization component perpendicular to the first polarization component; a retroreflector that is installed so as to be movable along the linear axis of the object to be measured and reflects the measurement light in a direction parallel to and opposite to the direction of incidence when the measurement light is incident on it; a combining optical system that emits the measurement light reflected by the retroreflector with its optical axis tilted with respect to the optical axis of the reference light; and an image sensor that images a striped pattern obtained by the interference of the measurement light and the reference light emitted from the combining optical system.

[0018] A measuring device according to a second aspect of the present invention, in the second aspect, includes a calculation unit that calculates the straightness of an object to be measured from the amount of movement of the striped pattern accompanying the movement of a retroreflector.

[0019] In the measuring apparatus according to the third aspect of the present invention, in the first aspect, the combining optical system includes a first combining optical system that emits the measurement light reflected by the retroreflector with the optical axis of the measurement light inclined with respect to the optical axis of the reference light, and a second combining optical system that emits the measurement light reflected by the retroreflector with the optical axis of the measurement light inclined on the opposite side to the first combining optical system with respect to the optical axis of the reference light. The imaging device includes a first imaging device that images the fringe pattern obtained by the interference of the measurement light and the reference light emitted from the first combining optical system, and a second imaging device that images the fringe pattern obtained by the interference of the measurement light and the reference light emitted from the second combining optical system.

[0020] In the measuring apparatus according to the fourth aspect of the present invention, in the third aspect, it includes an arithmetic unit that calculates the displacement amount in the direction along the linear axis and the straight axis of the measurement object from the amount of movement of the fringe pattern accompanying the movement along the linear axis and the straight axis of the retroreflector.

[0021] The measuring method according to the fifth aspect of the present invention includes a step of branching a laser beam into measurement light of a first polarization component and reference light of a second polarization component perpendicular to the first polarization component, a step of reflecting the measurement light in a direction parallel and opposite to the incident direction when the measurement light is incident by a retroreflector installed movably along the linear axis of the measurement object, a step of emitting the measurement light reflected by the retroreflector with the optical axis of the measurement light inclined with respect to the optical axis of the reference light, and a step of imaging the fringe pattern obtained by the interference of the measurement light and the reference light.

Advantages of the Invention

[0022] According to the present invention, by utilizing the interference phenomenon between the measurement light and the interference light that are inclined to each other, it becomes possible to detect the displacement in the straight-axis direction with only two components, an interferometer and a mirror.

Brief Description of the Drawings

[0023] [Figure 1] FIG. 1 is a diagram showing a straightness measuring apparatus according to the first embodiment of the present invention. [Figure 2] Figure 2 is a diagram showing an enlarged view of the measurement light and the reference light in part II of FIG. 1. [Figure 3] Figure 3 is a diagram showing a straightness measuring apparatus according to a second embodiment of the present invention. [Figure 4] Figure 4 is a diagram showing an enlarged view of the measurement light and the reference light in part IV of FIG. 3. [Figure 5] Figure 5 is a diagram showing an enlarged view of the measurement light and the reference light in part V of FIG. 3. [Figure 6] Figure 6 is a diagram showing a measurement principle by a conventional straightness measuring apparatus.

Embodiments for Carrying Out the Invention

[0024] Hereinafter, embodiments of the measuring apparatus and method according to the present invention will be described with reference to the accompanying drawings.

[0025] [First Embodiment] Figure 1 is a diagram showing a straightness measuring apparatus according to a first embodiment of the present invention.

[0026] As shown in FIG. 1, the straightness measuring apparatus 10 according to the present embodiment includes a laser light source 12, an interferometer 14, and a corner cube prism 16. In the following description, a three-dimensional orthogonal coordinate system is used in which a direction parallel to the optical axis direction of the laser light L0 is defined as the X direction, and a direction parallel to the vertical direction is defined as the Y direction.

[0027] The corner cube prism 16 is an example of a retroreflector (retroreflecting mirror) that reflects incident light parallel and in the opposite direction to the incident direction. Specifically, the corner cube prism 16 is formed by combining three plane plates having the property of reflecting laser light at right angles to each other to form a part of a cube. The image of the reflected light retroreflected by such a corner cube prism 16 is an inverted image of the incident light image. In FIG. 1, the reflecting surfaces of the corner cube prism 16 are shown simplified as two surfaces.

[0028] The corner cube prism 16 is attached to the object to be measured for straightness and is installed to be movable along the linear axis direction (in the direction of the white arrow in the diagram).

[0029] Here, the linear axis refers to the axis parallel to the geometrically correct straight line of the linear shape being measured. The true straight axis refers to the axis perpendicular to the two parallel planes when the magnitude of deviation of a linear shape from a geometrically correct straight line is defined by the distance between those two parallel planes. Straightness refers to the magnitude of deviation from a geometrically correct straight line in the true straight axis direction when a moving object is moved along the linear axis direction in a machine tool with a moving mechanism that moves a moving object.

[0030] In this embodiment, an example is described in which the straightness is measured by installing an interferometer 14 on the fixed part and a corner cube prism 16 (reflecting mirror) on the moving part. It is also possible to measure the straightness by attaching the Nacube prism 16 (reflecting mirror) and the interferometer 14 to the moving object.

[0031] The laser light source 12 includes, for example, a He-Ne laser tube and emits laser light L0 in the +X direction having a polarization component perpendicular to the plane of the paper in Figure 1. In the following explanation, polarization perpendicular to the plane of the paper is called "vertical polarization," and polarization horizontal to the plane of the paper is called "horizontal polarization." In the figure, vertically polarized laser light may be shown with an arrowhead, and horizontally polarized laser light may be shown with a double arrow.

[0032] The quarter-wave plate 18 is an optical element containing a birefringent material, which creates a 90° phase difference between two mutually orthogonal polarization components. The quarter-wave plate 18 is positioned with its anisotropic axis tilted at 45° with respect to the plane of the paper. Therefore, the longitudinally polarized laser light L0 that passes through the quarter-wave plate 18 becomes circularly polarized laser light, that is, laser light that is a combination of longitudinally and transversely polarized light.

[0033] The Polarizing Beam Splitter (PBS) 20 is an optical element designed to transmit one polarization component of incident light, which is a mixture of two mutually orthogonal polarization components, while reflecting the other polarization component by a dielectric multilayer coating. Of the laser light L0 converted to circular polarization, the transversely polarized component (first polarization component) of the laser light L1 passes through the polarizing beam splitter 20 and travels in a straight line, while the longitudinally polarized component (second polarization component) of the laser light L2 is reflected (bent) by the dielectric multilayer coating of the beam splitter at a 90° angle to the optical axis. Subsequently, the longitudinally polarized laser light L2 passes through a half-wave plate 21 whose anisotropy is tilted at 45° with respect to the plane of the paper, and becomes the transversely polarized laser light L2. Hereafter, the transversely polarized laser light L2 that has passed through the half-wave plate 21 will be called the "reference light".

[0034] The transversely polarized laser light L1, which has passed through the polarizing beam splitter 20 and traveled in a straight line, exits the interferometer 14, is reflected by the corner cube prism 16 installed on the object to be measured, and returns to the interferometer 14. Hereafter, the transversely polarized laser light L1 that has returned to the interferometer 14 will be referred to as the "measurement light".

[0035] The unpolarized beam splitter (hereinafter referred to as the beam splitter) 22 is an optical element manufactured to transmit 50% of the incident light and reflect 50%. The measurement light L1 transmitted through the beam splitter 22 and the reference light L2 reflected by the beam splitter 22 are combined by the beam splitter 22. Hereafter, the combined light of the measurement light L1 transmitted through the beam splitter 22 and the reference light L2 reflected by the beam splitter 22 will be called "composite light". Since the polarization directions of the measurement light L1 and the reference light L2 are the same, the waveforms of each laser beam are added together at the stage when they are transmitted through the beam splitter 22.

[0036] Note that the quarter-wave plate 18, the polarizing beam splitter 20, and the half-wave plate 21 are examples of optical systems for branching. Also, the beam splitter 22 is an example of an optical system for combining beams.

[0037] Here, the beam splitter 22 is rotatable in the direction of the double arrows in the figure. The beam splitter 22 is positioned with its reflective surface tilted at an angle θ greater than 45° with respect to the incident direction of the reference light L2, and the angle θ between the optical axis of the measurement light L1 transmitted through the beam splitter 22 and the optical axis of the reference light L2 reflected by the beam splitter 22 is θ ≠ 0°, meaning they are non-parallel.

[0038] The combined light L3, synthesized via the beam splitter 22, is magnified by lenses 24 and 26 and incident on the image sensor 28. The number and arrangement of lenses for magnifying the combined light L3 are not limited to those exemplified in Figure 1.

[0039] The image sensor 28 is an optical element for imaging the combined light L3 and outputs an electrical signal (voltage) corresponding to the intensity of the combined light L3. The image sensor 28 includes, for example, a photodiode, a CCD (Charge Coupled Device), or a CMOS (Complementary Metal Oxide Semiconductor).

[0040] The detection result of the composite light L3 by the image sensor 28 is output to the calculation unit 30. The calculation unit 30 includes a processor such as a CPU (Central Processing Unit) and performs calculations on the straightness of the object to be measured.

[0041] In this embodiment, the measurement light L1 reflected by the beam splitter 22 and the reference light L2 (the component directed towards the X mark in the figure) transmitted through the beam splitter 22 are not used.

[0042] Although the measurement light L1 and the reference light L2 were combined via the beam splitter 22, the present invention is not limited to this. The measurement light L1 and the reference light L2 may be guided towards the image sensor 28 side at an angle θ relative to each other using any light guiding means (for example, one or more mirrors) to prevent any unused components from occurring.

[0043] Furthermore, the beam splitter 22 may be made movable in the Z direction so that the overlap between the measurement light L1 and the reference light L2 is optimized. Alternatively, a separate optical element may be provided to adjust the overlap between the measurement light L1 and the reference light L2.

[0044] Figure 2 is an enlarged view of the measurement light L1 and reference light L2 in part II of Figure 1. Note that the slope between the measurement light L1 and reference light L2 is exaggerated in Figure 2.

[0045] As shown in Figure 2, in this embodiment, the optical axes of the measurement light L1 and the reference light L2 are non-parallel. Therefore, a pattern of light and dark stripes is generated depending on the wavelength of the laser light (measurement light L1 and reference light L2) and the inclination angle θ between the measurement light L1 and the reference light L2 (hereinafter referred to as the interference angle). This stripe pattern moves in proportion to the displacement of the object being measured in the direction of the perpendicular axis. Therefore, the amount of displacement in the direction of the perpendicular axis can be determined from the amount of movement of the stripe pattern.

[0046] When the optical axes of the measurement light L1 and the reference light L2 are perfectly parallel, the interference light produced by the interference of the measurement light L1 and the reference light L2 changes in brightness across its entire beam diameter in accordance with the change in distance to the object being measured.

[0047] In contrast, in this embodiment, the optical axes of the measurement light L1 and the reference light L2 are tilted by an interference angle θ, and the combined light L3 of the measurement light L1 and the reference light L2 is captured by the image sensor 28, and the displacement amount in the straight axis direction (the amount of movement of the object to be measured in the straight axis direction) is calculated from the pattern of light and dark stripes.

[0048] As described above, in the combined light L3 generated by tilting the optical axes of the measurement light L1 and the reference light L2, no change in brightness across the entire combined light L3 occurs in accordance with the distance to the object being measured. Instead, a striped pattern appears corresponding to the interference angle θ. This striped pattern moves in the direction of the straight axis as the object being measured moves in that direction. The repetition of this striped pattern is determined by the wavelengths of the measurement light L1 and the reference light L2 and the interference angle θ.

[0049] Therefore, if the wavelengths of the measurement light L1 and the reference light L2, and the interference angle θ are known, the amount of movement in the straight axis direction can be calculated from the amount of movement of the fringe pattern accompanying the movement of the corner cube prism 16.

[0050] Furthermore, as mentioned above, the brightness and darkness across the entire composite light L3, depending on the distance to the object being measured, Since no change occurs, the area received by the image sensor 28 does not need to cover the entire combined light L3. It is sufficient that at least one period of the striped pattern obtained by tilting the measurement light L1 and the reference light L2 is included in the light-receiving range of the image sensor 28.

[0051] In this embodiment, unlike the case where the optical axes of the measurement light L1 and the reference light L2 are perfectly parallel, the interference phenomenon between the measurement light L1 and the reference light L2 repeats in a periodic manner, so in principle, the measurable measurement range is infinite. However, since the range exceeding the spot diameter of the measurement light L1 and the reference light L2 cannot be measured, the spot diameter becomes the limit of the measurement range.

[0052] Furthermore, the resolution of the measurement of the displacement in the straight axis direction is determined by the ratio to the light-receiving range of the image sensor 28, and is therefore not affected by the limitations of the light-receiving range of the image sensor 28. For example, if the light-receiving range of the image sensor 28 is equivalent to one period of the stripe pattern, the resolution is determined by the ratio to that one period.

[0053] [Second Embodiment] Figure 3 shows a straightness measuring device according to a second embodiment of the present invention.

[0054] The movement of the striped pattern obtained from the synthesized light L3 described above occurs not only due to displacement in the straight axis direction but also due to displacement in the linear axis direction. In this embodiment, two optical systems (the first synthesis optical system OS1 and the second synthesis optical system OS2) are provided such that the interference angles of the measurement light L1 with respect to the reference light L2 are ±θ, respectively, so that only the displacement in the straight axis direction can be calculated. Furthermore, the displacement in the linear axis direction can also be calculated using the two optical systems (OS1 and OS2).

[0055] As shown in Figure 3, the straightness measuring device 50 according to this embodiment includes a laser light source 52, an interferometer 54, and a corner cube prism 56. In the following description, a three-dimensional Cartesian coordinate system is used in which the direction parallel to the optical axis of the laser beam L0 is defined as the X direction, and the direction parallel to the perpendicular direction is defined as the Y direction.

[0056] The corner cube prism 56 is an example of a retroreflector that reflects incident light parallel to and in the opposite direction to the direction of incidence (retroreflection). In Figure 3, the reflective surfaces of the corner cube prism 56 are simplified to two surfaces.

[0057] The corner cube prism 56 is attached to the object to be measured for straightness and is installed to be movable along the linear axis direction and the straight axis direction (direction of the white arrow in the figure).

[0058] In this embodiment, an example is described in which the straightness is measured by installing the interferometer 54 on the fixed part and the corner cube prism 56 (reflecting mirror) on the moving part. However, it is also possible to measure the straightness by installing the corner cube prism 56 (reflecting mirror) on the fixed part and the interferometer 54 on the moving part.

[0059] The laser light source 52 includes, for example, a He-Ne laser tube and emits laser light L0 in the +X direction having a polarization component perpendicular to the plane of the paper in Figure 3.

[0060] The quarter-wave plate 58 is positioned with its anisotropic axis tilted at 45° with respect to the plane of the paper. Therefore, the longitudinally polarized laser light L0 that passes through the quarter-wave plate 58 becomes circularly polarized laser light, that is, laser light that is a combination of longitudinally and transversely polarized light.

[0061] The polarizing beam splitter 60 is an optical element fabricated to transmit one of the polarization components of incident light, which is a mixture of two mutually orthogonal polarization components, and reflect the other polarization component by a dielectric multilayer coating. Of the laser light L0 converted to circular polarization, the transversely polarized laser light L1 passes through the polarizing beam splitter 20 and travels in a straight line, while the longitudinally polarized laser light L2 The beam is reflected (bent) by the dielectric multilayer coating of the beam splitter at a 90° angle to the optical axis.

[0062] The vertically polarized laser light L2 passes through a half-wave plate 61, whose anisotropy is tilted at 45° with respect to the plane of the paper, and becomes the transversely polarized laser light L2, which then enters the beam splitter 84. The beam splitter 84 is an optical element manufactured to transmit 50% of the incident light and reflect 50%. Beam splitters 64, 66, and 76 in the figure are also optical elements similar to beam splitter 84.

[0063] The transversely polarized laser light L2 is split by the beam splitter 84 into a first reference light L2a, which is the component reflected by the beam splitter 84, and a second reference light L2b, which is the component transmitted through the beam splitter 84. The first reference light L2a is sequentially reflected by the mirror (total reflection mirror) 86 and the beam splitter 66 and heads towards the image sensor 72. On the other hand, the second reference light L2b is reflected by the beam splitter 76 and heads towards the image sensor 72.

[0064] The transversely polarized laser beam L1, which has passed through the polarizing beam splitter 60 and traveled in a straight line, exits the interferometer 54, is reflected by the corner cube prism 56 installed on the object being measured, and returns to the interferometer 54. The transversely polarized laser beam L1 that has returned to the interferometer 54 is reflected by the mirror (total internal reflection mirror) 62 and incident on the beam splitter 64.

[0065] The laser beam L1 is split into a first measurement beam L1a, which is the component reflected by the beam splitter 64, and a second measurement beam L1b, which is the component transmitted through the beam splitter 64.

[0066] The first measurement light L1a is reflected by the beam splitter 64 and then incident on the beam splitter 66. The component of the first measurement light L1a that has passed through the beam splitter 66 is combined with the component of the first reference light L2a that has been reflected by the beam splitter 66, and is amplified by lenses 68 and 70 before being incident on the image sensor 72.

[0067] Meanwhile, the second measurement light L1b is reflected by the mirror (total internal reflection mirror) 74 and then incident on the beam splitter 76. The component of the second measurement light L1b that passes through the beam splitter 76 is combined with the component of the second reference light L2b that is reflected by the beam splitter 76, and these are amplified by lenses 78 and 80 before being incident on the image sensor 82.

[0068] The first combined light L3a is obtained by combining the component of the first measurement light L1a that was transmitted through the beam splitter 66 and the component of the first reference light L2a that was reflected by the beam splitter 66. Similarly, the second combined light L3b is obtained by combining the component of the second measurement light L1b that was transmitted through the beam splitter 76 and the component of the second reference light L2b that was reflected by the beam splitter 76.

[0069] The first synthesis optical system OS1 includes a beam splitter 66, lenses 68 and 70 in the path of the first synthesized light L3a. On the other hand, the second synthesis optical system OS2 includes a beam splitter 76, lenses 78 and 80 in the path of the second synthesized light L3b.

[0070] Image sensors 72 and 82 are optical elements (first and second image sensors) for imaging the first combined light L3a and the second combined light L3b, respectively, and output electrical signals (voltages) corresponding to the intensity of the first combined light L3a and the second combined light L3b. Image sensors 72 and 82 are, for example, photodiodes, CCDs (Charge Coupled Devices), or CMOS (Complementary Metal). It contains an oxide semiconductor.

[0071] The detection results of the first combined light L3a and the second combined light L3b by the image sensors 72 and 82 are calculated. The output is sent to unit 88. The calculation unit 88 includes a processor such as a CPU (Central Processing Unit) and performs calculations such as the straightness of the object to be measured.

[0072] The beam splitter 64 is rotatable in the direction of the double arrows in the figure. By adjusting the angle of the beam splitter 64 with respect to the optical axis direction (incident direction) of the laser beam L1, the tilt angle (interference angle) θ of the first measurement beam L1a with respect to the first reference beam L2a can be adjusted.

[0073] Furthermore, the mirror 74 is rotatable in the direction of the double arrows in the figure. By adjusting the angle of the mirror 74 with respect to the optical axis direction (incident direction) of the laser beam L1, the tilt angle (interference angle) θ of the second measurement beam L1b with respect to the second reference beam L2b can be adjusted.

[0074] In this embodiment, the first measurement light L1a reflected by the beam splitter 66 and the first reference light L2a (the component directed towards the X mark in the figure) transmitted through the beam splitter 66 are not used. Also, the second measurement light L1b reflected by the beam splitter 76 and the second reference light L2b (the component directed towards the X mark in the figure) transmitted through the beam splitter 76 are not used.

[0075] In this embodiment, the first measurement light L1a and the first reference light L2a are combined via a beam splitter 66, and the second measurement light L1b and the second reference light L2b are combined via a beam splitter 76. However, the present invention is not limited thereto. Any light guiding means (for example, one or more mirrors) may be used to prevent any unused components from occurring.

[0076] The beam splitter 64 or 66 may be moved in the Z direction to optimize the overlap between the first measurement light L1a and the first reference light L2a. The mirror 74 or beam splitter 76 may also be moved in the Z direction to optimize the overlap between the second measurement light L1b and the second reference light L2b. In addition, separate optical elements may be provided to adjust the overlap between the first measurement light L1a and the first reference light L2a, and between the second measurement light L1b and the second reference light L2b.

[0077] Figures 4 and 5 are enlarged views of the measurement light and reference light in sections IV and V of Figure 3, respectively. Note that the slope between the measurement light and the reference light is exaggerated in both figures.

[0078] As shown in Figure 4, the inclination angle (interference angle) of the first measurement light L1a with respect to the first reference light L2a is +θ. In contrast, as shown in Figure 5, the inclination of the second measurement light L1b with respect to the second reference light L2b is in the opposite direction to that in Figure 4 (opposite side around the Y axis on the ZX plane), and the inclination angle (interference angle) is -θ.

[0079] In the parallel optical systems described above, the striped pattern moves in the same direction for displacements in the straight axis direction, but moves in opposite directions for displacements in the linear axis direction. Therefore, by calculating the amount of striped pattern movement in each of the two optical systems (OS1 and OS2) and taking the average (arithmetic mean), the effect of displacement in the linear axis direction is canceled out, and only the displacement in the straight axis direction can be extracted.

[0080] Furthermore, by determining the difference in the amount of movement of the stripe pattern in the two optical systems described above (OS1 and OS2), the effect of displacement in the straight axis direction is canceled out, and only the displacement in the straight axis direction can be extracted.

[0081] Therefore, according to this embodiment, the amount of movement in both the linear axis direction and the straight axis direction can be obtained simultaneously. [Explanation of symbols]

[0082] 10, 50…Straightness measuring device, 12, 52…Laser light source, 14, 54…Interferometer, 16, 56…Corner cube prism, 30, 88…Calculation unit

Claims

1. A branching optical system that branches a laser beam into a measurement light of a first polarization component and a reference light of a second polarization component perpendicular to the first polarization component, A retroreflector is installed so as to be movable along the linear axis of the object to be measured, and when measurement light is incident on it, the retroreflector reflects the measurement light in a direction parallel to and opposite to the direction of incidence, A combining optical system in which the optical axis of the measurement light reflected by the retroreflector is emitted in a state inclined with respect to the optical axis of the reference light, An image sensor for capturing a striped pattern obtained by the interference of the measurement light and the reference light emitted from the aforementioned synthesis optical system, Equipped with, A measuring device comprising a calculation unit that calculates the straightness of the object to be measured from the amount of movement of the striped pattern accompanying the movement of the retroreflector.

2. A branching optical system that branches a laser beam into a measurement light of a first polarization component and a reference light of a second polarization component perpendicular to the first polarization component, A retroreflector is installed so as to be movable along the linear axis of the object to be measured, and when measurement light is incident on it, the retroreflector reflects the measurement light in a direction parallel to and opposite to the direction of incidence, A combining optical system in which the optical axis of the measurement light reflected by the retroreflector is emitted in a state inclined with respect to the optical axis of the reference light, An image sensor for capturing a striped pattern obtained by the interference of the measurement light and the reference light emitted from the aforementioned synthesis optical system, Equipped with, The aforementioned synthesis optical system is A first combining optical system in which the optical axis of the measurement light reflected by the retroreflector is emitted at an angle with respect to the optical axis of the reference light, The system includes a second combining optical system in which the optical axis of the measurement light reflected by the retroreflector is emitted at an angle opposite to the optical axis of the reference light, on the opposite side from the first combining optical system, The aforementioned imaging sensor is A first image sensor for imaging the stripe pattern obtained by the interference of the measurement light and the reference light emitted from the first synthesis optical system, A measuring device comprising: a second image sensor for imaging a stripe pattern obtained by the interference of the measurement light and the reference light emitted from the second synthesis optical system.

3. The measuring device according to claim 2, further comprising a calculation unit that calculates the amount of displacement of the object to be measured in the direction along the linear axis and the straight axis from the amount of movement of the striped pattern accompanying the movement of the retroreflector along the linear axis and the straight axis.

4. The steps include splitting the laser light into a measurement light with a first polarization component and a reference light with a second polarization component perpendicular to the first polarization component, A retroreflector, which is installed to be movable along the linear axis of the object to be measured, reflects the measurement light in a direction parallel to and opposite to the direction of incidence when the measurement light is incident on it. The steps include: the optical axis of the measurement light reflected by the retroreflector is emitted in a state inclined with respect to the optical axis of the reference light; The steps include: capturing an image of a striped pattern obtained by the interference of the measurement light and the reference light; The steps include: calculating the straightness of the object to be measured from the amount of movement of the striped pattern accompanying the movement of the retroreflector; A measurement method comprising the following features.

5. A step of splitting a laser beam into a measurement light of a first polarization component and a reference light of a second polarization component perpendicular to the first polarization component, A retroreflector, which is installed to be movable along the linear axis of the object to be measured, reflects the measurement light in a direction parallel to and opposite to the direction of incidence when the measurement light is incident on it. An emission step in which the optical axis of the measurement light reflected by the retroreflector is emitted in a state inclined with respect to the optical axis of the reference light, An imaging step of capturing an image of a striped pattern obtained by the interference of the measurement light and the reference light, Equipped with, The aforementioned ejection step is, The steps include: the optical axis of the measurement light reflected by the retroreflector being tilted with respect to the optical axis of the reference light, and the light being emitted from the first combining optical system; The process includes the step of the optical axis of the measurement light reflected by the retroreflector being tilted in the opposite direction to the first combining optical system with respect to the optical axis of the reference light, and being emitted from the second combining optical system, The aforementioned imaging step is, The steps include capturing the stripe pattern obtained by the interference of the measurement light and the reference light emitted from the first synthesis optical system using a first image sensor, A measurement method comprising: a second step of imaging a stripe pattern obtained by the interference of the measurement light and the reference light emitted from the second synthesis optical system using a second image sensor.

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