Shape measuring device

Abstract

To provide a shape measuring device permitting high-speed noncontact shape measurement with a simple configuration.SOLUTION: A shape measuring device includes: a light source portion for emitting linearly polarized light along a predetermined direction; a transmission type birefringence element that has a slow axis at 45 degrees to a predetermined direction and imparts retardation at a different level to linearly polarized light according to a position through which the linearly polarized light is transmitted; a 1 / 4 wavelength plate for converting light emitted from the transmission type birefringence element to linearly polarized light in a different direction according to a level of imparted retardation; a polarization image sensor that has multiple pixel polarizers having different transmission axis directions, and generates an image in which values of the respective pixels correspond to a relationship between the directions of the transmission axes of the pixel polarizers and the level of retardation imparted by the transmission type birefringence elements; and a calculation portion for calculating a shape of an object on the basis of an image.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a shape measuring device. [Background technology]

[0002] Techniques for measuring the three-dimensional shape of an object are known. In particular, in the field of product inspection, non-contact shape measurement techniques that do not affect product quality are used. Non-contact shape measurement techniques are useful in that they can measure the shape of a product in parallel with laser processing when the product is being processed. A known non-contact shape measurement technique with an excellent measurement range in the height direction of an object is the pattern projection method, which generates images of the object when multiple light beams with different shading patterns are projected onto the object, and then calculates the shape of the object based on the generated images.

[0003] Non-Patent Document 1 describes a method for simultaneously generating images of an object when four types of light with different shading patterns are projected onto it using a reflective spatial light modulator and a polarization image sensor. According to the method in Non-Patent Document 1, multiple images are generated without switching the projected light, which speeds up measurement. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] Yuuki Maeda, et al. (2020) Single shot 3D profilometry by polarization pattern projection. Applied Optics, vol. 59, No. 6, 1654-1659. Summary of the Invention [Problem to be solved by the invention]

[0005] The method of Non-Patent Document 1 uses a reflective spatial light modulator, which results in a large optical system and makes it difficult to introduce into existing processing equipment.

[0006] The present invention has been made to solve the above-mentioned problems, and has an object to provide a shape measuring device that has a simple configuration and is capable of high-speed non-contact shape measurement. [Means for solving the problem]

[0007] A shape measuring device according to an embodiment of the present invention comprises: a light source unit that emits linearly polarized light along a predetermined direction; a transmissive birefringent element that has a slow axis that forms a 45-degree angle with the predetermined direction and transmits the linearly polarized light emitted from the light source unit, and imparts retardation of different magnitudes to the linearly polarized light depending on the position through which the linearly polarized light passes; a quarter-wave plate that has a slow axis that is parallel or perpendicular to the predetermined direction and converts the light emitted from the transmissive birefringent element into light having a linear polarization pattern that includes linearly polarized light in multiple directions that differ depending on the magnitude of the retardation imparted; a polarization image sensor that has a plurality of pixels and pixel polarizers arranged corresponding to each pixel and with different transmission axis directions, receives light emitted from the quarter-wave plate and reflected by an object, and generates an image in which the value of each pixel corresponds to the light that has passed through the pixel polarizer; and a calculation unit that generates a predetermined number of pattern images that show the intensity distribution of light reflected by the object based on the values ​​of pixels included in the image that have pixel polarizers with transmission axes in the same direction, and calculates the shape of the object based on the predetermined number of pattern images.

[0008] Furthermore, it is preferable that the predetermined number of pattern images correspond to the intensity distribution of linearly polarized light that corresponds to the direction of the transmission axis of the pixel polarizer, among the linearly polarized light included in the linearly polarized light pattern.

[0009] Furthermore, it is preferable that the pixel polarizers of the polarization image sensor are arranged such that, for each pixel group including a predetermined number of mutually adjacent pixels, the directions of the transmission axes corresponding to each pixel included in that pixel group are spaced at equal angular intervals.

[0010] Furthermore, it is preferable that the transmission type birefringent element imparts retardation of a magnitude that changes linearly with the position through which linearly polarized light emitted from the light source is transmitted.

[0011] Preferably, the shape measuring device further comprises a non-polarizing beam splitter that guides the light emitted from the quarter-wave plate to the object and guides the light reflected by the object to the polarization image sensor.

[0012] In addition, the shape measuring device further has an objective lens facing the object, and an imaging lens arranged between the quarter-wave plate and the objective lens to form an image of the birefringent layer of the transmissive birefringent element on a predetermined imaging plane, and it is preferable that the transmissive birefringent element is arranged so that the imaging plane is a plane different from the focal plane of the objective lens.

[0013] It is also preferable that the shape measuring device further has a processing optical system that includes a transmissive birefringent element and a quarter-wave plate, is coaxial with an optical system that guides light emitted from the light source unit to the polarization image sensor, and guides processing light for processing the object to the object. [Effects of the Invention]

[0014] The shape measuring device according to the present invention has a simple configuration and enables high-speed non-contact shape measurement. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a schematic diagram for explaining the configuration of a shape measuring device 1. FIG. [Figure 2] FIG. 2 is a schematic exploded perspective view of a transmissive birefringent element 33. [Figure 3] 3 is a schematic diagram for explaining the polarization state of light transmitted through a transmissive birefringent element 33 and a quarter-wave plate 34. FIG. [Figure 4] 3 is a schematic diagram for explaining the polarization state of light transmitted through a quarter-wave plate 34. FIG. [Figure 5] FIG. 2 is a schematic diagram for explaining the configuration of a polarization image sensor 4. [Figure 6] (A) is a schematic diagram of the shape measuring device 1 when the transmissive birefringent element 33 and the object T are in an imaging relationship, and (B) is a schematic diagram of the shape measuring device 1 when the transmissive birefringent element 33 and the object T are not in an imaging relationship. DETAILED DESCRIPTION OF THE INVENTION

[0016] Various embodiments of the present invention will be described below with reference to the drawings. Please note that the technical scope of the present invention is not limited to these embodiments, but extends to the inventions set forth in the claims and their equivalents.

[0017] 1 is a schematic diagram illustrating the configuration of a shape measuring device 1 according to an embodiment of the present invention. The shape measuring device 1 performs laser processing on an object T and measures the shape of the object T in parallel with the laser processing. The shape measuring device 1 has a measurement light source 2, a measurement optical system 3, a polarization image sensor 4, a calculation device 5, a processing light source 6, and a processing optical system 7. The calculation device 5 is an example of a calculation unit.

[0018] The measurement light source 2 is a light emitting element such as an InGaN-based LED (Light Emitting Diode) or an Nd-YAG (Yttrium Aluminum Garnet) laser. The measurement light source 2 irradiates the object T with measurement light for measuring the shape of the object T.

[0019] The measurement optical system 3 guides light emitted from the measurement light source 2 to the object T and guides light reflected by the object T to a polarization image sensor 4. The measurement optical system 3 has a collimator lens 31, a polarizer 32, a transmissive birefringent element 33, a quarter-wave plate 34, a non-polarizing beam splitter 35, a convex lens 36, a dichroic mirror 37, and an objective lens 38. In the following description, the x, y, and z directions are defined so that the measurement surface of the object T is parallel to a plane including the x and y directions and perpendicular to the z direction.

[0020] The collimator lens 31 converts the light emitted from the measurement light source 2 into substantially parallel light and emits it toward the polarizer 32 .

[0021] The polarizer 32 has a transmission axis aligned with a predetermined direction, and transmits only the polarized light component having a polarization plane aligned with the direction of the transmission axis, among the light emitted from the measurement light source 2 and transmitted through the collimating lens 31. That is, the polarizer 32 converts the light emitted from the measurement light source 2 into linearly polarized light aligned with the predetermined direction and outputs the light. Hereinafter, the predetermined direction is defined as a direction that forms an angle of 45 degrees with the y direction and the z direction in a plane including the y direction and the z direction (i.e., a direction midway between the y direction and the z direction). The measurement light source 2, the collimating lens 31, and the polarizer 32 are an example of a light source unit that emits linearly polarized light aligned with the predetermined direction.

[0022] The transmissive birefringent element 33 and the quarter-wave plate 34 function as a spatial light modulator that transmits the light emitted from the polarizer 32 and converts the transmitted light into linearly polarized light of different directions depending on the transmission position. The configurations and functions of the transmissive birefringent element 33 and the quarter-wave plate 34 will be described later with reference to Figures 2 to 4.

[0023] The light emitted from the quarter-wave plate 34 is reflected by the non-polarizing beam splitter 35 and travels in the z direction, which is the direction of the object T.

[0024] The light emitted from non-polarizing beam splitter 35 passes through convex lens 36, dichroic mirror 37, and objective lens 38, and is reflected by the measurement surface of object T. The light reflected by the measurement surface of object T passes again through objective lens 38, dichroic mirror 37, and convex lens 36, and is incident on non-polarizing beam splitter 35. The light that has passed through non-polarizing beam splitter 35 is incident on polarization image sensor 4.

[0025] The polarization image sensor 4 generates an image in which the value of each pixel corresponds to the incident light. The calculation device 5 is an information processing device such as a PC (Personal Computer) communicatively connected to the polarization image sensor 4. The calculation device 5 includes a storage unit such as a semiconductor memory and a processing circuit such as a CPU (Central Processing Unit), and the processing circuit executes programs stored in the storage unit. The processing circuit of the calculation device 5 generates a predetermined number of pattern images according to the images generated by the polarization image sensor 4 and calculates the shape of the object T based on the generated pattern images. The relationship between the images generated by the polarization image sensor 4, the pattern images generated by the calculation device 5, and the shape of the object T will be described later using FIG. 5.

[0026] The processing light source 6 is a light emitting element that irradiates processing light for laser processing, such as a femtosecond laser, a CW fiber laser, or a CO2 laser. The processing light is light in a wavelength band different from that of the measurement light emitted from the measurement light source 2.

[0027] The processing optical system 7 has a collimating lens 71 as well as a dichroic mirror 37 and an objective lens 38 that are shared with the measurement optical system 3 .

[0028] The collimator lens 71 converts the processing light emitted from the processing light source 6 into approximately parallel light and emits it toward the dichroic mirror 37. The processing light emitted from the collimator lens 71 is reflected by the dichroic mirror 37 in the z direction, which is the direction of the object T. In other words, the dichroic mirror 37 transmits the measurement light and reflects the processing light. The processing light reflected by the dichroic mirror 37 passes through the objective lens 38 and reaches the object T.

[0029] The processing light source 6 and the collimator lens 71 are arranged so that the optical axis of the processing optical system 7 coincides with the optical axis of the measurement optical system 3 after the dichroic mirror 37. In other words, the processing optical system 7 is coaxial with the measurement optical system 3. This enables the shape measuring device 1 to measure the shape at the processed position in real time.

[0030] The object T is positioned so that its measurement surface is flush with the focal plane of the objective lens 38 and so that an image of a point on the measurement surface is formed on the imaging plane of the polarization image sensor 4. That is, there is an imaging relationship between the measurement surface of the object T and the imaging plane of the polarization image sensor 4. Furthermore, the transmissive birefringent element 33 is positioned so that an image of a point on its birefringent layer is formed on the measurement surface of the object T (i.e., the focal plane of the objective lens 38). That is, there is an imaging relationship between the birefringent layer of the transmissive birefringent element 33 and the measurement surface of the object T.

[0031] 2 is an exploded perspective view of the transmissive birefringent element 33. The transmissive birefringent element 33 has a first transparent substrate 331, a second transparent substrate 332, a first electrode 333, a second electrode 334, a first alignment film 335, a second alignment film 336, a sealing member 337, and a liquid crystal layer 338. The liquid crystal layer 338 is an example of a birefringent layer.

[0032] The first transparent substrate 331 and the second transparent substrate 332 are light-transmitting flat plates, such as glass plates, and are disposed opposite each other.

[0033] The first electrode 333 and the second electrode 334 are light-transmitting conductive films, such as an ITO (Indium Tin Oxide) film. The first electrode 333 is a solid electrode disposed on the surface of the first transparent substrate 331 facing the second transparent substrate 332. The first electrode 333 is connected to a power supply (not shown) via transparent wiring (not shown) so that its potential is V.

[0034] The second electrode 334 is disposed on the surface of the second transparent substrate 332 facing the first transparent substrate 331. The second electrode 334 has a plurality (N pieces) of partial electrodes 334-1 to 334-N having the same rectangular shape. In the example shown in FIG. 2, the second electrode 334 has 18 partial electrodes, but the number of partial electrodes is not limited to 18. In the example shown in FIG. 2, the extension direction of the partial electrodes 334-1 to 334-N is the z direction. The partial electrodes 334-1 to 334-N are spaced apart from each other and disposed at equal intervals in this order on the surface of the second transparent substrate 332 facing the first transparent substrate 331. Adjacent partial electrodes are connected to each other via electrical resistors (not shown) having the same resistance value. The partial electrodes 334-1 and 334-N are connected to a power supply (not shown) via transparent wiring (not shown) so that their potentials become V1 and V2, respectively. As a result, a voltage is applied to the liquid crystal layer 338, the voltage varying linearly in the y direction in the range from voltage |V-V1| to voltage |V-V2|.

[0035] The first alignment film 335 and the second alignment film 336 are light-transmitting thin films made of, for example, polyimide. The first alignment film 335 and the second alignment film 336 are arranged so as to cover the first electrode 333 and the second electrode 334, respectively. A large number of grooves are formed on the surface of the first alignment film 335 facing the second alignment film 336, and on the surface of the second alignment film 336 facing the first alignment film 335. The extension direction of the grooves is a direction that forms an angle of 45 degrees with a predetermined direction. In the example shown in FIG. 2, the extension direction of the grooves is the y direction, which is perpendicular to the extension direction of the partial electrodes 334-1 to 334-N.

[0036] The sealing member 337 connects the first transparent substrate 331 and the second transparent substrate 332 so as to seal the liquid crystal layer 338 between the first alignment film 335 and the second alignment film 336. The sealing member 337 is, for example, a resin or metal adhesive.

[0037] The liquid crystal constituting the liquid crystal layer 338 is a homogeneously aligned nematic liquid crystal, such as a cyanobiphenyl-based liquid crystal. The liquid crystal molecules contained in the liquid crystal layer 338 are aligned by the grooves formed in the first alignment film 335 and the second alignment film 336 so that the molecular long axes are aligned in the direction of the grooves. This results in the transmissive birefringent element 33 having a slow axis that forms a 45-degree angle with the predetermined direction. In the example shown in FIG. 2, the transmissive birefringent element 33 has a slow axis in the y direction. The thickness of the liquid crystal layer 338 is set according to the magnitude of the retardation imparted to transmitted light. As will be described later, the thickness of the liquid crystal layer 338 is set, for example, to 10 μm so that the retardation imparted to light passing through the liquid crystal layer 338 when the liquid crystal molecules are aligned in the y direction is 720 degrees or more.

[0038] Fig. 3 is a schematic diagram for explaining the polarization state of light emitted from the transmissive birefringent element 33 and the quarter-wave plate 34. Note that while Fig. 3 schematically shows the polarizer 32, the transmissive birefringent element 33, and the quarter-wave plate 34 viewed from the z direction, the arrows indicating the polarization state in Fig. 3 indicate the polarization state viewed from the x direction, which is the traveling direction of the light. Furthermore, the first alignment film 335, the second alignment film 336, and the sealing member 337 of the transmissive birefringent element 33 are omitted from Fig. 3.

[0039] As described above, the partial electrodes 334-1 to 334-N of the transmissive birefringent element 33 have different potentials that change linearly in the y direction within a predetermined range, and apply a voltage to the liquid crystal layer 338 whose magnitude changes linearly in the y direction.

[0040] When a voltage is applied to the liquid crystal layer 338, polarization occurs in the liquid crystal molecules, and the liquid crystal molecules align in the x direction, which is the direction of the electric field. The stronger the electric field, the easier it is for alignment due to polarization to occur, so the long axis direction of the liquid crystal molecules is closest to the y direction at the position of partial electrode 334-1, to which a small voltage is applied, and closest to the x direction at partial electrode 334-N, to which a large voltage is applied.

[0041] When the liquid crystal molecules are aligned in the y direction, birefringence causes a phase difference between the y-direction polarized component and the z-direction polarized component of light passing through the liquid crystal layer 338. That is, retardation is imparted to the light passing through the liquid crystal layer 338. On the other hand, when the liquid crystal molecules are aligned in the x direction, no retardation is imparted to the light passing through the liquid crystal layer 338. The magnitude of the retardation imparted to the light passing through the liquid crystal layer 338 decreases as the long axis direction of the liquid crystal molecules approaches the x direction from the y direction. Because the long axis direction of the liquid crystal molecules changes depending on the magnitude of the voltage applied to the liquid crystal layer 338, the liquid crystal layer 338 imparts to the light passing through the liquid crystal layer 338 a retardation whose magnitude changes linearly with the position where the light passes through the liquid crystal layer 338.

[0042] The magnitude of the retardation imparted to light passing through the liquid crystal layer 338 varies depending on the angle that the long axis direction of the liquid crystal molecules makes with the x-direction. For example, the voltage applied to the liquid crystal layer 338 at the position of the partial electrode 334-N is set so that the retardation of the light passing through that position is 0 degrees. Also, the voltage applied to the liquid crystal layer 338 at the position of the partial electrode 334-1 is set so that the retardation of the light passing through that position is 720 degrees (i.e., two wavelengths).

[0043] The linearly polarized light P1 emitted from the polarizer 32 passes through the transmissive birefringent element 33. The linearly polarized light P1 is given a retardation of 0 to 720 degrees, which varies depending on the position at which it passes through the transmissive birefringent element 33, and is converted into elliptically polarized light P2 having an ellipticity corresponding to the magnitude of the retardation given. Note that the term "elliptically polarized light" here includes circularly polarized light and linearly polarized light. Because the slow axis of the transmissive birefringent element 33 forms an angle of 45 degrees with respect to the polarization direction of the linearly polarized light P1, the direction of the major axis of the elliptically polarized light P2 emitted from the transmissive birefringent element 33 is parallel or perpendicular to the polarization direction of the linearly polarized light P1.

[0044] In the above description, the transmissive birefringent element 33 imparts a retardation of 0 to 720 degrees depending on the position through which light passes, but this is not limited to this example. The transmissive birefringent element 33 may impart a retardation in any range having a width of at least 360 degrees. For example, the transmissive birefringent element 33 may impart a retardation of 180 to 540 degrees depending on the position through which light passes.

[0045] The quarter-wave plate 34 has a slow axis parallel or perpendicular to the predetermined direction. The slow axis of the quarter-wave plate 34 is parallel or perpendicular to the major axis of the elliptically polarized light P2 emitted from the transmissive birefringent element 33. Therefore, the elliptically polarized light P2 is converted into linearly polarized light P3 with a different direction depending on the ellipticity of the elliptically polarized light P2. That is, the quarter-wave plate 34 converts the elliptically polarized light P2 emitted from the transmissive birefringent element 33 into linearly polarized light with a different direction depending on the magnitude of the retardation imparted by the transmissive birefringent element 33. In the example shown in FIG. 3, the retardation imparted by the transmissive birefringent element 33 ranges from 0 degrees to 720 degrees. Therefore, the linearly polarized light P3 emitted from the quarter-wave plate 34 includes linearly polarized light with a direction that forms any angle between 0 degrees and 360 degrees with respect to the predetermined direction.

[0046] Fig. 4 is a schematic diagram illustrating the polarization state of light transmitted through the quarter-wave plate 34. Fig. 4 is a schematic diagram of the linearly polarized light P3 of Fig. 3 as viewed from the x direction. As shown in Fig. 4, the direction of the linearly polarized light P3, i.e., the angle that the linearly polarized light P3 makes with a predetermined direction, changes linearly with the position in the y direction. Furthermore, the direction of the linearly polarized light P3, i.e., the angle that the linearly polarized light P3 makes with a predetermined direction, does not change with the position in the z direction.

[0047] FIG. 5 is a schematic diagram illustrating the configuration of the polarization image sensor 4. The polarization image sensor 4 has multiple image sensors 41 arranged on an imaging surface that is in an imaging relationship with the measurement surface of the object T, pixel polarizers 42 arranged in front of each pixel, and an image generation circuit 43 that generates an image based on the output from the image sensors 41. The multiple image sensors 41 correspond to multiple pixels, respectively. The image sensors 41 output, as the value of each pixel, a value that corresponds to the intensity of light that has passed through the corresponding pixel polarizers 42. The pixel polarizers 42 are arranged for each pixel group, each group including a predetermined number of adjacent pixels, so that the directions of the transmission axes corresponding to the pixels included in that pixel group are equiangularly spaced.

[0048] 5, pixel group G includes four (2x2) adjacent pixels. Pixel polarizers 421, 422, 423, and 424 are arranged to correspond to the four pixels included in one pixel group G, respectively. The directions of the transmission axes of the pixel polarizers 421 to 424 are oriented at angles of 0 degrees, 45 degrees, 90 degrees, and 135 degrees with respect to the y direction, with the angle from the y direction toward the x direction being a positive angle. That is, the pixel polarizers 421 to 424 are arranged so that the directions of their transmission axes are spaced apart by 45 degrees.

[0049] The value of each pixel output by the image sensor 41 corresponds to the relationship between the direction of the transmission axis of the pixel polarizers 421-424 and the direction of the linearly polarized light incident on the pixel polarizers 421-424. As shown in FIG. 4, the light transmitted through the quarter-wave plate 34 contains linearly polarized light with different directions depending on the magnitude of the retardation imparted by the transmissive birefringent element 33. Similarly, the light reflected by the measurement surface of the object T and incident on the polarization image sensor 4 has a linear polarization pattern containing linearly polarized light that varies linearly with position in the y direction. Therefore, the value of each pixel in the polarization image sensor 4 corresponds to the amount of polarization component of the linearly polarized light contained in the linear polarization pattern that can be transmitted along the direction of the transmission axis of the pixel polarizers 421-424.

[0050] The image generation circuit 43 acquires the pixel values ​​output by the image sensor 41 and generates image data.

[0051] The calculation device 5 acquires the image generated by the polarization image sensor 4. The calculation device 5 extracts pixel values ​​corresponding to pixel polarizers 42 having transmission axes in the same direction, and generates a predetermined number of pattern images that indicate the intensity distribution of light reflected by the object T. The calculation device 5 calculates the shape of the object T based on the generated pattern images.

[0052] For example, the calculation device 5 calculates the shape of the object T using a known phase shift method described in Non-Patent Document 1. That is, the intensity distributions I0(x,y), I45(x,y), I90(x,y), and I135(x,y) of light transmitted through pixel polarizers 421, 422, 423, and 424, which correspond to the four pattern images, are respectively expressed by the following equations.

number

number

[0053] Furthermore, the contrast of a sinusoidal image on an ideal plane is expressed by a Bessel function of the first kind using the height z (i.e., the position in the z direction) of the measurement surface of the object T. Since the Bessel function of the first kind is approximated by a Gaussian function, the contrast H of the sinusoidal image is expressed by the following equation:

number

number

[0054] The calculation device 5 outputs the calculated shape of the object T by transmitting it to another device.

[0055] As mentioned above, the contrast H of a sinusoidal image is expressed by a Bessel function of the first kind. Therefore, the range of z that can be calculated using the above equation, i.e., the measurement range, is limited by the first zero M of the Bessel function of the first kind and is expressed by the following equation:

number

[0056] As described above, the shape measurement device 1 includes the measurement light source 2, collimating lens 31, polarizer 32, transmissive birefringent element 33, quarter-wave plate 34, polarization image sensor 4, and calculation device 5. The measurement light source 2, collimating lens 31, and polarizer 32 emit linearly polarized light along a predetermined direction. The transmissive birefringent element 33 has a slow axis at a 45-degree angle with respect to the predetermined direction. The transmissive birefringent element 33 transmits the linearly polarized light emitted from the polarizer 32 and imparts a retardation of a different magnitude to the linearly polarized light depending on the position through which the linearly polarized light passes. The quarter-wave plate 34 has a slow axis parallel or perpendicular to the predetermined direction and converts the light emitted from the transmissive birefringent element 33 into linearly polarized light of a different direction depending on the magnitude of the retardation imparted. The polarization image sensor 4 receives light reflected by the object T and generates an image in which the value of each pixel corresponds to the relationship between the direction of the transmission axis of the pixel polarizer 42 and the magnitude of the retardation imparted by the transmissive birefringent element 33. The calculation device 5 generates a predetermined number of pattern images that indicate the intensity distribution of the light reflected by the object T, and calculates the shape of the object based on the generated pattern images. This enables the shape measurement device 1 to perform high-speed non-contact shape measurement with a simple configuration.

[0057] That is, the shape measurement device 1 uses a transmissive birefringent element 33 that imparts different amounts of retardation depending on the position, and a polarization image sensor 4. This eliminates the need to sequentially project light with different shade patterns, as in conventional pattern projection methods, enabling high-speed non-contact shape measurement. Furthermore, when a reflective spatial light modulator is used as in Non-Patent Document 1, a beam splitter is required to guide the measurement light to the spatial light modulator. In contrast, because the shape measurement device 1 uses a transmissive birefringent element 33, there is no need to incorporate an additional beam splitter into the optical system, simplifying the configuration.

[0058] The shape measuring device 1 also has a processing optical system 7 that is coaxial with the measurement optical system 3 and that guides processing light for processing the object T to the object. This allows the shape measuring device 1 to measure the shape of the object T in parallel with processing the object T.

[0059] In the above description, the shape measuring device 1 has the processing light source 6 and the processing optical system 7, but is not limited to this example, and the shape measuring device 1 does not have to have the processing light source 6 and the processing optical system 7. In this case, although the shape measuring device 1 cannot measure the shape of the object T in parallel with processing of the object T, it enables high-speed non-contact shape measurement.

[0060] In the above description, the birefringent layer of the transmissive birefringent element 33, the measurement surface of the object T, and the imaging surface of the polarization image sensor 4 are in an imaging relationship, but this is not limited to an example. The birefringent layer of the transmissive birefringent element 33 and the measurement surface of the object T do not have to be in an imaging relationship. In other words, the transmissive birefringent element 33 may be arranged so that the image of its birefringent layer is formed on a plane other than the measurement surface of the object T or the focal plane of the objective lens 38.

[0061] 6(A) is a schematic diagram of the form measuring apparatus 1 when the birefringent layer of the transmissive birefringent element 33 and the measurement surface of the object T are in an imaging relationship, and FIG. 6(B) is a schematic diagram of the form measuring apparatus 1 when the birefringent layer of the transmissive birefringent element 33 and the measurement surface of the object T are not in an imaging relationship. Note that in both FIGS. 6(A) and 6(B), the imaging relationship between the measurement surface of the object T and the imaging surface of the polarization image sensor 4 is maintained. In other words, the measurement surface of the object T is located on the focal plane of the objective lens 38.

[0062] In Figure 6(A), the dashed lines indicate the optical path until an image of a point on the birefringent layer of the transmissive birefringent element 33 is formed, and the optical path until an image of a point on the measurement surface of the object T is formed. In Figure 6(A), the image formation surface of the birefringent layer of the transmissive birefringent element 33 and the focal plane of the objective lens 38 coincide with each other, so the two optical paths coincide. In this case, the contrast H measured by the polarization image sensor 4 is maximum when the measurement surface of the object T is on the focal plane of the objective lens 38.

[0063] The contrast H is maximized at the position of the measurement surface of the object T, thereby widening the measurement range in the z direction. On the other hand, at the position where the contrast H is maximized, the amount of change in contrast relative to changes in the z direction of the measurement surface of the object T is small, which may reduce the measurement accuracy for minute irregularities on the measurement surface. Also, it may not be possible to determine from the contrast value alone whether the change in the z direction of the measurement surface of the object T is a positive or negative change with respect to the focal plane.

[0064] In FIG. 6(B), the solid lines indicate the optical paths until an image of a point on the birefringent layer of the transmissive birefringent element 33 is formed, and the dashed lines indicate the optical paths until an image of a point on the focal plane of the objective lens 38 is formed. In FIG. 6(B), the transmissive birefringent element 33 is positioned at a distance L1 farther from the measurement light source 2 than when the birefringent layer of the transmissive birefringent element 33 and the measurement surface of the object T are in an imaging relationship. Therefore, the point on the birefringent layer of the transmissive birefringent element 33 is imaged on a plane farther from the measurement light source 2 than the focal plane of the objective lens 38 (i.e., the measurement surface of the object T). In this case, the polarization image sensor 4 is not the plane on which the point on the birefringent layer of the transmissive birefringent element 33 is imaged, so the contrast H measured by the polarization image sensor 4 is not maximized when the measurement surface of the object T is on the focal plane of the objective lens 38.

[0065] Since the position of the measurement surface of the object T is different from the position z0 where the contrast H is maximum, the amount of change in contrast H with respect to the change in the z direction of the measurement surface of the object T increases, improving the measurement accuracy for minute irregularities on the measurement surface. Preferably, the position of the measurement surface of the object is disposed at a position where the amount of change in contrast H with respect to the change in the z direction of the measurement surface of the object T is maximum. This further improves the measurement accuracy for minute irregularities on the measurement surface. As described above, the contrast H is approximated by a Gaussian function, so the position z1 in the z direction of the surface where the amount of change in contrast H is maximum is roughly expressed by the following equation.

number

[0066] In this case, within a predetermined range including z1, the amount of change in contrast H relative to the change in the z direction of the measurement surface of the object T is approximately linear. Since the amount of change in contrast H relative to the change in the z direction of the measurement surface is approximately linear, the measurement accuracy of the shape of the object T is further improved. The range of z in which the amount of change in contrast H is approximately linear is expressed by, for example, the following equation.

number

[0067] Furthermore, the arrangement position L1 of the transmissive birefringent element 33 for determining z1 as in the above formula is determined by the following formula.

number

[0068] It should be understood by those skilled in the art that various changes, substitutions, and alterations can be made to the present invention without departing from the scope of the present invention. For example, the above-described embodiments and modifications may be implemented in appropriate combination within the scope of the present invention. [Explanation of symbols]

[0069] 1 Shape measuring device 2 Measurement light source 3 Measurement optical system 32 Polarizer 33 Transmissive birefringent element 34 1 / 4 wave plate 35 Non-polarizing beam splitter 4 Polarization image sensor 5. Calculation device 6 Processing light source 7 Processing optical system

Claims

1. a light source unit that emits linearly polarized light along a predetermined direction; a transmission type birefringent element having a slow axis that forms an angle of 45 degrees with respect to the predetermined direction, which transmits the linearly polarized light emitted from the light source unit and imparts a retardation of a different magnitude to the linearly polarized light depending on a position through which the linearly polarized light has passed; a quarter-wave plate having a slow axis parallel or orthogonal to the predetermined direction, and converting the light emitted from the transmissive birefringent element into light having a linear polarization pattern including linearly polarized light in a plurality of directions that differ according to the magnitude of the retardation imparted; a polarization image sensor having a plurality of pixels and pixel polarizers arranged corresponding to the respective pixels and having different transmission axis directions, the polarization image sensor receiving light emitted from the quarter-wave plate and reflected by an object, and generating an image in which the value of each pixel corresponds to the light transmitted through the pixel polarizer; a calculation unit that generates a predetermined number of pattern images that indicate an intensity distribution of light reflected by the object based on values ​​of pixels that are included in the image and that have pixel polarizers with transmission axes in the same direction, and calculates a shape of the object based on the predetermined number of pattern images; and the transmissive birefringent element is arranged so that an image of the birefringent layer of the transmissive birefringent element is formed on a plane different from a measurement plane of the object; A shape measuring device characterized by:

2. the predetermined number of pattern images correspond to an intensity distribution of linearly polarized light, among the linearly polarized light included in the linearly polarized light pattern, that corresponds to the direction of the transmission axis of the pixel polarizer; The shape measuring device according to claim 1 .

3. the pixel polarizers of the polarization image sensor are arranged for each pixel group including a predetermined number of mutually adjacent pixels such that directions of transmission axes corresponding to the pixels included in the pixel group are spaced at equal angular intervals; The shape measuring device according to claim 1 .

4. the transmissive birefringent element imparts retardation of a magnitude that changes linearly with respect to the position through which the linearly polarized light emitted from the light source unit is transmitted; The shape measuring device according to claim 1 .

5. The optical system further includes a non-polarizing beam splitter that guides the light emitted from the quarter-wave plate to the object and guides the light reflected by the object to the polarization image sensor. The shape measuring device according to claim 1 .

6. an objective lens facing the object; an imaging lens disposed between the quarter-wave plate and the objective lens, and configured to form an image of the birefringent layer on a predetermined imaging plane; The shape measuring device according to claim 1 .

7. a processing optical system including the transmissive birefringent element and the quarter-wave plate, coaxial with an optical system that guides light emitted from the light source unit to the polarization image sensor, and that guides processing light for processing the object to the object; The shape measuring device according to claim 1 .

Images