Optical measuring apparatus and method

Abstract

The present invention relates to the field of optical measuring devices, and more particularly to displacement sensors and three-dimensional sensors for measuring the position and / or shape or thickness of an object to be measured. Measuring light is projected onto the object to be measured after being filtered by a Fabry-Perot filter, so that at each point on the measuring surface, the filtered measuring light has a locally unique wavelength or combination of wavelengths in at least one direction within the measuring surface. Measuring light reflected from the surface of the object to be measured is also filtered by a Fabry-Perot filter so that measuring light reflected from anywhere other than the intersection of the object and the measuring surface is removed.

Description

Technical Field

[0001] The present invention relates to the field of optical measurement devices, and more particularly to displacement sensors and 3D sensors for measuring the position and / or shape or thickness of a measurement object.

Background Art

[0002] In many displacement and 3D profile sensors known in the art, light is projected onto a measurement object, and the light reflected from the surface of the measurement object is measured to determine the shape of the object. In many such devices, the angle of incidence of light on the image sensor is offset from zero. Image sensors such as CCDs and APSs are not designed to operate at such angles, resulting in degraded performance. In devices based on triangulation, it is possible to reduce the angle of incidence by increasing the triangulation angle, but this strategy is limited by the physical constraints of the system. For example, increasing the triangulation angle to 90 degrees is impossible because the sensor would occupy the same space as the measurement object. Furthermore, increasing the triangulation angle also has an undesirable side effect of increasing the occlusion of the reflected light due to changes in the height of the measurement object. The greater the triangulation angle, the smaller the height change that causes occlusion. Additionally, the magnification that results in image enlargement causes further rotation of the intermediate image plane, and when the image sensor is placed on the intermediate image plane, it further increases the angle of incidence of light, effectively making the use of such magnification, which could be useful for improving the accuracy of the sensor, practically impossible.

Summary of the Invention

[0003] A first aspect of the present invention relates to a sensor for measuring the displacement of a surface of a measurement object relative to the sensor. The sensor includes the following: · A light source configured to emit measurement light; · At least one Fabry - Perot filter; A first optical system configured to focus the measurement light onto the measurement plane and to focus the measurement light reflected from the measurement plane to infinity; • Light sensor; • A second optical system for focusing the reflected measurement light onto the light sensor.

[0004] The measurement light emitted from the light source and incident on the measurement surface, as well as the reflected measurement light from the measurement surface, are filtered by at least one Fabry-Perot filter, so that at least a portion of the measurement light reflected from outside the measurement surface is removed from the reflected measurement light incident on the photosensor.

[0005] The illumination axis extends from the light source to the measurement surface, and the measurement axis extends from the measurement surface to the light sensor. The coaxial portions of the illumination axis and the measurement axis can be coaxial adjacent to the measurement surface.

[0006] At least one Fabry-Perot filter may be positioned on the coaxial portion and tilted relative to the coaxial portion.

[0007] At least one Fabry-Perot filter may include two Fabry-Perot filters, of which the first Fabry-Perot filter may be positioned outside the coaxial portion of the illumination axis, and the second Fabry-Perot filter may be positioned outside the coaxial portion of the measurement axis. The angle of the first Fabry-Perot filter with respect to the illumination axis may be equal to the angle of the second Fabry-Perot filter with respect to the measurement axis.

[0008] The measuring surface may be located within the focal plane of the first optical system.

[0009] The light sensor may be located within the focal plane of the second optical system.

[0010] The sensor may further include a beam splitter or split aperture between the light source and at least one Fabry-Perot filter, so that at least a portion of the measurement light reflected from the measurement surface is transmitted to or reflected back to the photosensor.

[0011] The first optical system may include a first optical subset, a diffraction grating, and a second optical subset. The diffraction grating may be positioned at the focal plane of the first optical subset, and the focal point of the measurement light diffracted from the diffraction grating may be focused on the measurement plane by the second optical subset.

[0012] The measuring surface and diffraction grating may be inclined with respect to the lens surface of the second optical subset according to the Scheimpflug principle.

[0013] The reflected light from the measurement surface may be focused onto the diffraction grating by a second optical subset.

[0014] The diffraction grating may be a first diffraction grating, and the first optical system may further include a specular reflector, a second diffraction grating, and a third optical subset. Measurement light from a light source may be incident on the first side of the measurement surface, and reflected measurement light received from the second side of the measurement surface by the second optical subset may be focused onto the second diffraction grating by the second optical subset. The second diffraction grating may be positioned at the focal plane of the third optical subset, and the third optical subset may focus the measurement light diffracted from the second diffraction grating to infinity. The specular reflector may be configured to reflect reflected measurement light received from the second side of the measurement surface onto the second diffraction grating, or to reflect measurement light diffracted from the first diffraction grating onto the second optical subset.

[0015] The diffraction grating may be a first diffraction grating, and the first optical system may further include a second diffraction grating, a beam splitter and combiner, a first reflecting surface and a second reflecting surface, and a third optical subset. Measurement light from a light source may be incident on the beam splitter and combiner, and some of the measurement light may be transmitted by the beam splitter and combiner, and some of the measurement light may be reflected by the beam splitter and combiner. The measurement light transmitted by the beam splitter and combiner may be focused on the first diffraction grating by the first optical subset, and the measurement light diffracted by the first diffraction grating may be reflected from the first reflecting surface and incident on the second optical subset, and focused on the measurement surface. The second diffraction grating may be positioned at the focal plane of the third optical subset, and the measurement light reflected by the beam splitter and combiner may be focused on the second diffraction grating by the third optical subset, and the measurement light diffracted by the second diffraction grating may be reflected from the second reflecting surface and incident on the second optical subset, and focused on the measurement surface.

[0016] Reflectance measurement light from a first side of the measurement surface may be reflected onto a first diffraction grating by a first reflective surface and focused onto the first diffraction grating by a second optical subset. Reflectance measurement light from a second side of the measurement surface may be reflected onto a second diffraction grating by a second reflective surface and focused onto the second diffraction grating by a second optical subset. Reflectance measurement light diffracted by the first diffraction grating may be focused to infinity by a first optical subset, and reflection measurement light diffracted by the second diffraction grating may be focused to infinity by a third optical subset. Reflectance measurement light diffracted by the first diffraction grating and reflection measurement light diffracted by the second diffraction grating may be combined by a beam splitter and a combiner, and the combined reflection measurement light may be incident on at least one Fabry-Perot filter.

[0017] When the sensor is in use, the distance from the light sensor to the surface of the object being measured is determined by measuring one or more local intensity maximum locations of light received by the light sensor.

[0018] The second aspect of the present invention relates to a method. The method includes placing a measurement object at a first position relative to the sensor such that the surface of the measurement object intersects the measurement surface, and measuring the intensity of the light received by the optical sensor.

[0019] The method may further include repositioning the measurement object from the first position to a second position relative to the sensor, where the change in the position of the measurement object is defined by a first displacement vector, and may include measuring the intensity of the light received by the optical sensor.

[0020] The method may further include determining the displacement of one or more points of a first set on the surface of the measurement object by identifying the position of the peak intensity of the light measured by the optical sensor when the measurement object is at the first position.

[0021] The method may further include determining the displacement of one or more points of a second set on the surface of the measurement object by identifying the position of the peak intensity of the light measured by the optical sensor when the measurement object is at the second position.

[0022] The method may further include generating a three-dimensional model of the measurement object by combining the displacement of one or more points of the first set, the displacement of one or more points of the second set, and the first displacement vector.

[0023] The method may further include determining the thickness of the transparent layer of the measurement object by calculating the distance between two or more different peak intensities of light on the optical sensor.

[0024] The third aspect of the present invention relates to using the above sensor to measure the displacement of the surface of a measurement object relative to the sensor, measure the profile of the measurement object, measure the three-dimensional shape of the measurement object, and / or measure the thickness of the transparent layer of the measurement object.

Brief Description of the Drawings

[0025] [Figure 1] It is a schematic diagram of a first optical sensor using a beam splitter. [Figure 2] It is a schematic diagram of a first optical sensor using a split aperture. [Figure 3] It is a schematic diagram of a second optical sensor using a beam splitter. [Figure 4] It is a schematic diagram of a second optical sensor using a split aperture. [Figure 5] It is a schematic diagram of a third optical sensor. [Figure 6] is a schematic diagram of a fourth optical sensor.

Embodiments for Carrying Out the Invention

[0026] The present invention relates to an apparatus, a system, and a method for measuring the displacement of an object relative to a sensor. Such displacement measurement can be used to determine the position, shape, and / or thickness of the object to be measured or its layer. In the sensor of the present invention, the measurement light is filtered using a Fabry - Perot filter before being projected onto the object to be measured, such that at each point of the measurement plane that intersects the object to be measured, the measurement light has a locally unique wavelength or combination of wavelengths in the direction of distance measurement. The measurement light reflected from the surface of the object to be measured is filtered again by the Fabry - Perot filter in order to remove or attenuate the measurement light that has not been reflected from the measurement plane. In this context, "removing" or "attenuating" does not mean complete removal of the measurement light reflected from outside the measurement plane, but simply means that the intensity of this light is reduced. As will be described below, a high - finesse Fabry - Perot filter can more effectively remove the measurement light that has not been reflected from the measurement plane, leading to more accurate measurements, but the present invention can also function with one or more relatively low - finesse Fabry - Perot filters.

[0027] The basic operation of the sensor and the method for measuring the displacement of an object relative to the sensor are described in relation to claim 1, but the basic principle of using the Fabry-Perot filter as described above is common to all embodiments of the present invention.

[0028] The sensor 100 in Figure 1 includes a light source 101 configured to emit polychromatic measurement light. The emitted measurement light may have a relatively narrow bandwidth or emit light over a broad spectrum, but the spectrum must be sufficiently broad and passable at a range of angles so that the light can pass through the first Fabry-Perot filter 104, as described later. The term “measurement light” is used throughout this description, but it should be understood that the device is not limited to electromagnetic radiation in the visible wavelength range and may include, or substitute for, infrared, ultraviolet, or other wavelengths depending on the specific application. The measurement light emitted from the light source 101 is incident on the first Fabry-Perot filter 104. The light source 101 is preferably a diffuse surface light source, emitting light at various angles from each point on its surface. In this way, the measurement light is incident on the first Fabry-Perot filter 104 at various angles. The light source 101 may be a single light source or multiple light sources. The light source 101 may emit light across its entire surface or may include a series of parallel light-emitting lines.

[0029] In this context, the term “Fabry-Perot filter” preferably refers to an etalon with a fixed distance between reflectors, but other types of Fabry-Perot filters, such as tunable interference filters and interferometers with variable distances between reflectors, can also be used. The wavelength of light transmitted by a Fabry-Perot filter is defined by the distance l between reflectors, the refractive index n of the materials between the reflectors, and the angle θ of incidence of the light to the Fabry-Perot filter. The transmission peak occurs when the optical path length 2nl cosθ of the light reflected between the reflectors is an integer multiple of the wavelength λ of the incident light. Therefore, when the refractive index n and the distance l between reflectors are fixed, the wavelength of light transmitted by the Fabry-Perot interferometer depends on the angle of incidence θ. Thus, when measurement light is incident on the first Fabry-Perot filter 104, some of the light incident at various wavelengths and at different angles to the first Fabry-Perot filter 104 is not completely removed by the first Fabry-Perot filter 104.

[0030] Since the angle of incidence of the incident light onto the Fabry-Perot filter and the angle of exit of the filtered light are essentially the same, all parallel light filtered by the first Fabry-Perot filter 104 has the same wavelength or combination of wavelengths.

[0031] As shown in Figure 1, the normal vector of the first Fabry-Perot filter 104 is offset by an angle of 131 from the illumination axis 121 extending from the light source 101 to the measurement surface 152.

[0032] The filtered light is focused on the measuring surface 152 through the first optical system 105. In the embodiment of Figure 1, the first optical system 105 is a lens, but the first optical system may be a composite optical system such as a lens assembly, as shown in Figure 3, for example. In all cases, the function of the first optical system is the same: to focus the light filtered by the first Fabry-Perot filter onto the measuring surface. Since all parallel light is focused on the focal plane of the first optical system, i.e., the same point on the measuring surface 152, and all parallel light has the same wavelength or combination of wavelengths due to filtering by the Fabry-Perot filter, all measurement light focused on a given point on the measuring surface 152 has the same wavelength or combination of wavelengths.

[0033] The measurement light, filtered by the first Fabry-Perot filter 104 and focused by the first optical system 105, is reflected from the surface of the object to be measured 151. The intensity of the reflected light is maximum at the point where the surface of the object to be measured 151 intersects with the measurement surface 152, i.e., where the measurement light is focused on the surface of the object to be measured 151. The measurement light is usually scattered, or diffusely reflected, from the surface of the object to be measured 151. Some of this reflected measurement light is reflected again in the direction of the first optical system 105. As a result, the measurement light reflected from the measurement surface 152 is focused to infinity by the first optical system 105. In other words, all the measurement light reflected from a given point on the measurement surface 152 propagates in parallel after passing through the first lens 105.

[0034] The reflected measurement light, focused to infinity by the first optical system 105, enters the Fabry-Perot filter 104 again from the opposite direction and on the opposite side from the unfiltered measurement light emitted from the light source 101. The Fabry-Perot filter 104 filters out the measurement light reflected from points other than the measurement surface 152. Since all light focused on a predetermined point on the measurement surface 152 has the same wavelength or combination of wavelengths, the light rays reflected from the measurement surface 152 and propagating parallel to the Fabry-Perot filter 104 from the first optical system 105 have the same wavelength or combination of wavelengths. Furthermore, the angle at which the measurement light reflected from the measurement surface propagates is equal to the angle at which light of the same wavelength propagated after the initial filtering by the Fabry-Perot filter 104. Therefore, light reflected from the measuring surface 152 and incident on the Fabry-Perot filter 104 may pass through the second Fabry-Perot filter, but light reflected from other parts of the object being measured 151 that do not intersect with the measuring surface 152 does not propagate at an angle suitable for passing through the Fabry-Perot filter 104 and is removed by the Fabry-Perot filter 104.

[0035] This configuration is particularly effective when the wavelength or combination of wavelengths of light focused at each point on the measuring surface is locally unique in at least one direction within the measuring surface. In other words, the wavelength or combination of wavelengths of light focused at each point on the measuring surface is unique among points existing along at least one axis within the measuring surface. Preferably, this axis is parallel to the z-axis shown in the drawing. To put it another way, at each point with the same y-coordinate within the measuring surface, light of a different wavelength or combination of wavelengths is focused.

[0036] The performance of the optical sensor 100 for measuring the height of the object 152, i.e., its position on the z-axis at each y-coordinate, is improved when the wavelength or combination of wavelengths of light focused at each point on the measuring surface 152 is unique among points with the same y-coordinate. Therefore, it is desirable that the angle 131 of the Fabry-Perot filter 104 be set such that the wavelength or combination of wavelengths of light focused at each point on the measuring surface is unique among points with the same y-coordinate, with respect to the illumination axis 131 and the entire angular range used. The Fabry-Perot filter 104 is preferably tilted by rotating it about an axis parallel to the measuring surface and perpendicular to the illumination axis 121 with respect to the illumination axis 121. In the drawing of Figure 1, this is the Y-axis. The offset angle 131 is measured in the ZX plane as shown in Figure 1.

[0037] The angle of incidence of light to the first Fabry-Perot filter 102, i.e., the angle of incidence, may be restricted to only positive or negative angles to prevent light of the same wavelength or combination of wavelengths from being transmitted at two different angles of incidence.

[0038] Since the illumination axis 121 and the measurement axis 122 are coaxial in the region between the Fabry-Perot filter 104 and the measurement surface 152, in the embodiment of Figure 1, a beam splitter 103 is used to deflect the reflected measurement light from the coaxial region 123 toward the photosensor 107. Therefore, the reflected filter measurement light that has passed through the Fabry-Perot filter 104 enters the beam splitter 103 and is reflected toward the photosensor 107. The sensor lens 106 focuses the reflected measurement light received from the Fabry-Perot filter 104 onto the sensor surface, i.e., the focal plane of the sensor lens 106. Again, because the angle of incidence of the reflectance measurement light onto the Fabry-Perot filter 104 and the angle of exit of the reflectance measurement light after passing through the Fabry-Perot filter 104 are the same, the ray of the reflectance measurement light from a single point on the measurement surface 152 has the same wavelength or combination of wavelengths, propagates parallel to the direction of the sensor lens 106, and is focused on the same point on the sensor surface.

[0039] The light sensor 107, for example, an image sensor, is positioned on the sensor surface, with its effective surface aligned with the sensor surface, and the reflected filter measurement light is focused on the effective surface of the light sensor. By measuring the intensity of light received at each point (e.g., each pixel) of the image sensor, the shape of the object to be measured 151 at the point where it intersects with the measurement surface 152 can be determined. In particular, the measurement light reflected from the intersection of the surface of the object to be measured 151 and the measurement surface 152 generates a local maximum intensity on the surface of the photosensor 107. The location of the local maximum intensity on the photosensor 107 can be used to determine the distance from the photosensor 107 to each point on the surface of the object to be measured 151 (i.e., the intersection of the measurement surface 152 and the object to be measured 151) where the focused measurement light was reflected. This is because each point (e.g., a pixel) of the photosensor 107 corresponds to a single point on the measurement surface 152, and the position of the measurement surface 152 relative to the photosensor 107 is known. The position of the measurement surface 152 relative to the photosensor 107 is determined by the optical properties of the optical element placed between the measurement surface 152 and the photosensor 107. For example, in sensor 100, the position of the measuring surface 152 relative to sensor 107 is determined by the focal length of the first optical system 105, the angle of the lens surface of the first optical system 105 with respect to the coaxial portion 123 of the illumination axis and the measuring axis, the angle of the coaxial portion 123 of the illumination axis and the measuring axis with respect to the surface of the beam splitter 103, the focal length of the sensor lens 106, and the angle of the lens surface of the sensor lens 106 with respect to the measuring axis 122. This list is not exhaustive.

[0040] An image sensor may be divided physically or logically into multiple regions, such as individual pixels or groups of pixels, each of which is sensitive to only a single wavelength or combination of wavelengths, or a narrow range of wavelengths or combinations of wavelengths.

[0041] The sensor 100 may include a light source lens 102 that receives light from a light source 101. In this case, the light source 101 can be positioned outside the focal plane of the light source lens 102 so that the measurement light is incident on each point of the Fabry-Perot filter 104 at multiple angles, preventing potential small inhomogeneities, such as gaps between different individual light source elements, from creating non-illuminated points on the measurement surface. This makes it possible to use smaller or less diffusive light sources, for example, by positioning the light source outside the focal plane of an additional lens. If the light source is small, the angular range from the light source to the focusing lens needs to be increased in order to obtain the same angle and power distribution in the first Fabry-Perot filter 102.

[0042] The bandwidth of the light source 101 may be limited based on the offset (tilt) angle 131 of the Fabry-Perot filter 104 and the incident angle range of the Fabry-Perot filter 104 in order to ensure local uniqueness of the wavelength or combination of wavelengths that are in focus on the measurement surface and / or sensor surface.

[0043] Limiting the bandwidth of the light source can be achieved, for example, by using a suitable narrowband light source such as an LED, or by additionally filtering the light emitted from the broadband light source 101 before it is incident on the measurement surface 152.

[0044] Alternatively, if a broadband light source is used, the measurement light can be filtered to an appropriate wavelength range at any point between the light source 101 and the sensor 107, ensuring local uniqueness of the wavelength or combination of wavelengths that focus on the sensor surface.

[0045] In the sensor 100 of Figure 1, the Fabry-Perot filter 104 is positioned on the coaxial portion 123 of the illumination axis 121 and the measurement axis 122. This allows the same Fabry-Perot filter to be used to filter both the measurement light from the light source 101 and the reflected measurement light from the measurement surface 152, ensuring that the tilt angle of the Fabry-Perot filter is the same for measurement light from both directions. However, the single Fabry-Perot filter 104 may be replaced by two separate Fabry-Perot filters positioned on the non-coaxial portions of the illumination axis 121 and the measurement axis 122. That is, the first Fabry-Perot filter is positioned on the illumination axis 121 outside the coaxial portion 123, and the second Fabry-Perot filter is positioned on the measurement axis 122 outside the coaxial portion 123. In this case, the tilt angle of the first Fabry-Perot filter with respect to the illumination axis 121 is equal to the tilt angle of the second Fabry-Perot filter with respect to the measurement axis 122.

[0046] If the two Fabry-Perot filters described above are present, the tilt angle of each Fabry-Perot filter can be adjusted so that the measurement light reflected from the measurement surface 152 is filtered by the first filter before passing through the second Fabry-Perot filter. The tilt angles of one or both can be adjusted to maximize the transmittance of light passing through the second Fabry-Perot filter positioned between the measurement surface and the light sensor 107. Alternatively, if a Fabry-Perot interferometer or interference filter with adjustable distance between reflectors is used, this can be used instead of, or in addition to, adjusting the relative angle of the Fabry-Perot filters to ensure accurate operation of the device. The use of a fixed etalon is preferable, as this usually only requires angle adjustment once during the manufacturing process. As an example, angle adjustment of one or both Fabry-Perot filters can be achieved by screws that adjust the angle of the Fabry-Perot filters.

[0047] The reflectivity of the reflective surface within the Fabry-Perot filter determines the width of the transmission peak of the Fabry-Perot filter in the frequency (or wavelength) domain. A Fabry-Perot filter with a narrow transmission peak, i.e., a high Q-factor, is said to have high finesse. The use of a high-finesse Fabry-Perot filter improves the accuracy of the sensor of this invention. This is because the filtering of the measurement light reflected from outside the measurement surface by the Fabry-Perot filter is improved, resulting in a narrower intensity peak on the photosensor.

[0048] However, in embodiments using two separate Fabry-Perot filters, the narrower the transmission peak of the Fabry-Perot filter, the more precise the filter alignment required to ensure the desired overlap of transmission peaks. Therefore, the ability to precisely adjust the angle of the Fabry-Perot filter, as described above, enables the use of high-finesse Fabry-Perot filters.

[0049] The sensor 100 in Figure 1 uses a beam splitter 103 to guide the reflected measurement light toward the photosensor 107, but any configuration or arrangement may be used that allows the unfiltered measurement light from the light source to reach a Fabry-Perot filter and the reflected measurement light to be deflected toward the photosensor. For example, in Figure 2, a split aperture 201 is used instead of the beam splitter 103 in Figure 1. Figure 2 shows a second optical sensor 200, which operates in essentially the same manner as described above with respect to the displacement sensor 100 in Figure 1. Equivalent components of both devices are indicated by similar reference numbers, for example, 101 and 201 indicate light sources as described above. The hatched area shown in Figure 2 indicates the space through which the reflected measurement light propagates from the measurement surface 252 to the photosensor 207, in contrast to the unhatched area through which the light propagates from the light source 201 to the measurement surface 252.

[0050] Furthermore, in both embodiments shown in Figures 1 and 2, the arrangement of the illumination axis 121 and the measurement axis 122 can be swapped so that unfiltered measurement light is reflected from the beam splitter 103 or the split aperture 203, and reflected measurement light is propagated directly to the sensor lenses 106, 206 and the photosensors 107, 207.

[0051] Figure 3 shows yet another sensor 300, which corresponds to sensor 100 in Figure 1, with the first optical system 105 of sensor 100 replaced by the first optical system 305 of sensor 300. Equivalent components of both devices are indicated by similar reference numbers, for example, 101 and 301 indicate light sources as described above. The first optical system 305 of sensor 300 is a composite optical system including a diffraction grating 308, a first optical subset 309, and a second optical subset 310. The diffraction grating 308 is positioned at the focal plane of the first optical subset 309, and the measurement light diffracted from the diffraction grating 308 is focused on the measurement surface 352 by the second optical subset 310. The measurement surface 352 and the diffraction grating 308 are inclined with respect to the lens surface of the second optical subset 310 according to the Scheimpflug principle. The use of the diffraction grating in this configuration makes it possible to change the angle of the measurement axis of the measurement surface 352 with respect to the coaxial portion 323.

[0052] The first optical subset 309 may be a single lens as shown in Figure 3, or it may be a composite optical system. One of the functions of the first optical subset 309 is to focus the measurement light filtered by the Fabry-Perot filter 304 onto the surface of the diffraction grating 308. Since all parallel rays emitted from the Fabry-Perot filter 304 have the same wavelength or combination of wavelengths, all measurement light focused on each point on the surface of the diffraction grating 308 by the first optical subset 309 has the same wavelength or combination of wavelengths.

[0053] θ - the diffraction angle of light from a diffraction grating mThese are the grooves or slit pitch d of the diffraction grating (also called groove or slit spacing), the wavelength λ of the incident light, and the angle of incidence θ. i According to this, the diffraction grating equation d(sinθ) i -sinθ m The mode is determined according to ) = ±mλ, where m is the mode number and m∈N={0,1,2,3…}. The angle of incidence θ i and diffraction angle θ m This is defined in the opposite direction to the plane parallel to the grooves or slits of the diffraction grating, and to the plane extending perpendicular to the planar surface of the diffraction grating (also called the normal of the diffraction grating).

[0054] The filtered measurement light is diffracted from the surface of the diffraction grating 308 toward the second optical subset 310. The second optical subset 310 focuses the light diffracted from the surface of the diffraction grating 308 onto the measurement surface 352. In other words, in an optical system consisting of the diffraction grating 308, the second optical subset 310, and the measurement surface 352, the diffraction grating 308 is located on the object plane, the lens plane is defined by the second optical subset 310, and the measurement surface 352 is located on the image plane defined by the Scheimpflug principle.

[0055] The measurement light reflected from the surface of the object to be measured 352 is received by the second optical subset 310 and focused onto the surface of the diffraction grating 308. The reflected measurement light diffracted by the diffraction grating 308 is then received by the first optical subset 309, which focuses the reflected measurement light, now focused on the surface of the diffraction grating 308, to infinity.

[0056] Since the diffraction angle of light from the diffraction grating 308 is not necessarily the same as the incident angle, the angle of the measurement surface 352 can be changed with respect to the coaxial portion 323 of the illumination axis by selecting an appropriate diffraction grating and wavelength range of the measurement light. When the sensor of the present invention is used to measure the three-dimensional shape of an object to be measured, the object is passed through the measurement surface in a direction parallel to the X axis shown in the drawings, and its surface is sampled at multiple X positions. In sensors 100 and 200 in Figures 1 and 2, the measurement surface is perpendicular to the coaxial portion 123 of the illumination axis, so in order for the object to be measured to intersect the measurement surfaces 152 and 252 at different Z positions, the coaxial portion 123 of the illumination axis and the measurement axis must be tilted with respect to the Z axis. This means that large changes in the height of the object to be measured will cast shadows on parts of the surface of the object, and those parts will not be measured. In contrast, with the sensor 300 in Figure 3, the coaxial portions 323 of the illumination axis and measurement axis can be arranged parallel to the Z-axis, so that features with a high aspect ratio (i.e., surface features of the object being measured that have large changes in height) do not cast shadows.

[0057] Figure 3 shows the diffraction grating 308 as a reflective diffraction grating, but a transmission diffraction grating may also be used.

[0058] Figure 4 shows an alternative sensor 400 in which the beam splitter 303 of sensor 300 is replaced by a split aperture 403. Equivalent components of both devices are indicated by similar reference numbers, for example, 301 and 401 indicate light sources as described above. The split aperture 403 in Figure 4 functions in a similar manner to that described above with respect to the split aperture 203 in Figure 2.

[0059] Figure 5 shows another sensor 500, with separate Fabry-Perot filters on the illumination axis and measurement axis, respectively, as described above with respect to Figure 1. Equivalent components of both sensors 100 and 500 are indicated by similar reference numbers, for example, 101 and 501, which represent light sources as described above.

[0060] Unlike the single lens shown in Figure 1, the first optical system 505 of sensor 500 is a composite optical system, similar to sensors 300 and 400. The illumination modes of sensor 500 function in essentially the same way as sensors 300 and 400. The first optical subset 509 may be a single lens, as shown in Figure 5, or it may be a composite optical system. The function of the first optical subset 509 is to focus the measurement light filtered by the Fabry-Perot filter 504 onto the surface of the diffraction grating 508. Since all parallel rays emitted from the Fabry-Perot filter 504 have the same wavelength or combination of wavelengths, all measurement light focused on each point on the surface of the diffraction grating 508 by the first optical subset 509 has the same wavelength or combination of wavelengths. The filtered measurement light is diffracted from the surface of the diffraction grating 508 toward the second optical subset 510. The second optical subset 510 focuses the light diffracted from the surface of the diffraction grating 508 onto the measurement surface 552. In other words, in an optical system consisting of a diffraction grating 508, a second optical subset 510, and a measuring surface 552, the diffraction grating 508 is located on the object plane, the lens plane is defined by the second optical subset 510, and the measuring surface 552 is located on the image plane defined by the Scheimpflug principle.

[0061] The measurement light reflected from the measurement surface 552 is received by the second optical subset 510 and focused on the surface of the second diffraction grating 511 via the specular reflector 514. The specular reflector 514 functions as a split aperture, allowing the measurement light in illumination mode to enter the second optical subset 510 while deflecting the reflected measurement light emitting from the second optical subset 510 toward the second diffraction grating 511. The reflected measurement light diffracted by the second diffraction grating 511 is received by the third optical subset 512, focusing the reflected measurement light, which is focused on the surface of the second diffraction grating 511, toward infinity.

[0062] In an alternative configuration, the specular reflector 514 may be positioned such that light diffracted from the first diffraction grating 508 is reflected by the specular reflector 514 and incident on the second optical subset 510.

[0063] The reflected measurement light emitted from the third optical subset 512 enters the second Fabry-Perot filter 516. The second Fabry-Perot filter 516 is positioned such that its tilt angle with respect to the measurement axis extending from the second diffraction grating 511 to the photosensor 507 is the same as the tilt angle of the first Fabry-Perot filter 504 with respect to the illumination axis extending from the light source 501 to the first diffraction grating 508. In this way, the second Fabry-Perot filter 516 removes or attenuates measurement light reflected from points other than the measurement surface 552.

[0064] As shown in Figure 5, the measuring surface 552 may be aligned with the surface of the first diffraction grating 508, that is, the measuring surface 552 and the surface of the diffraction grating 508 are parallel. Furthermore, the measuring surface 552 is aligned with the Z-axis. This configuration largely prevents shadows of the measurement light caused by high-aspect-ratio features on the surface of the object being measured 551, but it is not essential.

[0065] The additional sensor 600 shown in Figure 6 corresponds to sensors 100, 200, 300, and 400 shown in Figures 1 to 4, and is common in that it has a single Fabry-Perot filter 604 positioned in the coaxial portion of the illumination axis and measurement axis. However, as with sensors 100, 200, 300, and 400, the single Fabry-Perot filter 604 may be replaced by a separate Fabry-Perot filter positioned outside the coaxial region on the illumination axis and measurement axis. As with the other figures described above, equivalent components of sensor 600 are indicated by similar reference numbers as shown in the other figures, for example, 101, 201, 301, 401, 501, and 601 indicate light sources as described above.

[0066] In sensor 600, the first optical system 605 includes a first optical subset 609, a first diffraction grating 608, a second optical subset 610, a second diffraction grating 611, and a third optical subset 612. The first optical system 605 also includes a beam splitter and combiner 613, a first reflecting surface 614, and a second reflecting surface 615. The first and second reflecting surfaces 614 and 615 are specular reflectors and may be part of a single component having multiple reflecting surfaces as shown in Figure 6, or they may be separate reflectors.

[0067] The measurement light from the light source 601, filtered by the Fabry-Perot filter 604, is incident on the beam splitter and combiner 613. A portion of the measurement light is transmitted by the beam splitter and combiner 613 along a first optical path toward the first optical subset 609, and a portion of the measurement light is reflected by the beam splitter and combiner along a second optical path toward the third optical subset 612.

[0068] The measurement light transmitted along the first optical path by the beam splitter and combiner 613 is focused on the first diffraction grating 608 by the first optical subset 609. The measurement light diffracted by the first diffraction grating 608 is reflected from the first reflecting surface 614, incident on the second optical subset 610, and focused on the measurement surface 652. The first diffraction grating 608, the first reflecting surface 614, the second optical subset 610, and the measurement surface 652 are arranged according to the Scheimpflug principle, with the first diffraction grating 608 located on the object plane, the lens plane defined by the second optical subset 610, and the measurement surface 652 located on the image plane.

[0069] The measurement light reflected along the second optical path by the beam splitter and combiner 613 is focused on the second diffraction grating 611 by the third optical subset 612. The measurement light diffracted by the second diffraction grating 611 is reflected from the second reflective surface 615, incident on the second optical subset 610, and focused on the measurement surface 652. The second diffraction grating 611, the second reflective surface 615, the second optical subset 610, and the measurement surface 652 are arranged according to the Scheimpflug principle, with the second diffraction grating 611 located on the object plane, the lens plane defined by the second optical subset 610, and the measurement surface 652 located on the image plane.

[0070] When measurement light is reflected from the measurement surface, a portion of it is reflected towards the second optical subset 610. Reflected measurement light emitted from the second optical subset 610 and reflected from the first reflective surface 614 is focused by the second optical subset 610 onto the surface of the first diffraction grating 608. Reflected measurement light emitted from the second optical subset 610 and reflected from the second reflective surface 615 is focused by the second optical subset onto the surface of the second diffraction grating 611.

[0071] The reflected measurement light focused on the first diffraction grating 608 is diffracted by the first diffraction grating 608 and incident on the first optical subset 609, focusing the measurement light reflected from the measurement surface to infinity. Similarly, the reflected measurement light focused on the second diffraction grating 611 is diffracted by the second diffraction grating 611 and incident on the third optical subset 612, focusing the measurement light reflected from the measurement surface to infinity.

[0072] The measurement light reflected from the measurement surface and focused by the first optical subset 609 and the third optical subset 612 is combined by the beam splitter and combiner 613 and propagates toward the Fabry-Perot filter 604. The reflected measurement light incident on the Fabry-Perot filter 604 is filtered by the Fabry-Perot filter, and only the measurement light reflected from the measurement surface 652 is transmitted.

[0073] The other components of the sensor 600 function in a similar manner, as described above with respect to Figures 1 to 4.

[0074] Since the measurement light is split and recombined after being reflected from the measurement surface 652, it is important that the first and second optical paths have the same optical path length.

[0075] Any of the displacement sensors described above can be used as three-dimensional sensors to measure the three-dimensional shape of an object. A three-dimensional model of the object can be constructed by imaging the measurement light projected onto the object at multiple locations on the object. In practice, displacement measurements are performed repeatedly or continuously as the object passes through the measurement surface. This is achieved, for example, on a conveyor belt by moving the sensor relative to a stationary object or by moving the object relative to the sensor. Each measurement can be considered as measuring the profile of a cross-sectional slice of the object, and the three-dimensional shape of the object can be reconstructed by combining these profile measurements with the known displacement between each measurement.

[0076] These sensors can also be used for multilayer measurements, such as measuring the thickness of transparent films. The reflection of measurement light from the surface of each layer of a transparent film generates identifiable intensity peaks, and if the refractive index of the layer is known, the thickness can be calculated based on the distance between two consecutive peaks on the light sensor.

[0077] Furthermore, if the optical sensor is an image sensor such as a CCD or APS, or a CMOS sensor, it can simultaneously acquire a normal two-dimensional image of the surface of the object being measured while measuring displacement as described above.

Claims

1. The sensor is a sensor for measuring the displacement of the surface of the object being measured relative to the sensor, and includes the following: Light sources configured to emit measurement light (101, 201, 301, 401, 501, 601); At least one Fabry-Perot filter (104, 204, 304, 404, 504, 512, 604, 612; A first optical system (105, 205, 305, 405, 505, 605) configured to focus the measurement light onto the measurement surface and to focus the measurement light reflected from the measurement surface to infinity; Light sensors (107, 207, 307, 407, 507, 607); and Second optical system (106, 206, 306, 406, 506, 606) for focusing the reflected measurement light onto the light sensor; Here, the measurement light emitted from the light source and incident on the measurement surface, as well as the measurement light reflected from the measurement surface, are filtered by at least one Fabry-Perot filter, so that at least a portion of the measurement light reflected from outside the measurement surface is removed from the reflected measurement light incident on the photosensor.

2. A sensor according to any of the above claims, wherein the illumination axis (121, 221, 321, 421, 521, 621) extends from the light source to the measuring surface, the measuring axis (122, 222, 322, 422, 522, 622) extends from the measuring surface to the light sensor, and the coaxial portions of the illumination axis and the coaxial portions of the measuring axis (123, 223, 323, 423, 523, 623) are coaxial adjacent to the measuring surface.

3. A sensor according to any of the above claims, wherein at least one Fabry-Perot filter (104, 204, 304, 404) is positioned on a coaxial portion and inclined with respect to the coaxial portion.

4. The sensor according to claim 2, wherein at least one Fabry-Perot filter (504, 512, 604, 612) comprises two Fabry-Perot filters, the first Fabry-Perot filter (504, 604) is positioned outside the coaxial portion of the illumination axis, the second Fabry-Perot filter (512, 612) is positioned outside the coaxial portion of the measurement axis, and the angle of the first Fabry-Perot filter with respect to the illumination axis is equal to the angle of the second Fabry-Perot filter with respect to the measurement axis.

5. The sensor according to any of the above claims, wherein the measuring surface (152, 252, 352, 452, 552, 652) is located within the focal plane of the first optical system (105, 205, 305, 405, 505, 605).

6. The sensor according to any of the above claims, wherein the light sensor (107, 207, 307, 407, 507, 607) is located in the focal plane of the second optical system (106, 206, 306, 406, 506, 606).

7. A sensor according to any of the preceding claims, further comprising a beam splitter (103, 303, 603) or a split aperture (203, 403) between a light source and at least one Fabry-Perot filter, wherein at least a portion of the measurement light reflected from the measurement surface is transmitted to or reflected toward the photosensor.

8. A sensor according to any of the above claims, wherein the first optical system (305, 405, 505, 605) includes a first optical subset (309, 409, 509, 609), a diffraction grating (308, 408, 508, 608), and a second optical subset (310, 410, 510, 610), the diffraction grating being positioned at the focal plane of the first optical subset, and the measurement light diffracted from the diffraction grating being focused on the measurement plane by the second optical subset.

9. The sensor according to claim 8, wherein the measuring surfaces (352, 452, 552, 652) and diffraction gratings (308, 408, 508, 608) are inclined with respect to the lens surfaces of the second optical subset (310, 410, 510, 610) according to the Scheimpflug principle.

10. The sensor according to claim 8 or 9, wherein the reflected light from the measuring surface (352, 452) is focused on the diffraction grating by a second optical subset (310, 410).

11. A sensor according to claim 8 or 9, wherein the diffraction grating is a first diffraction grating (508), and the first optical system (505) further includes a specular reflector (514), a second diffraction grating (511), and a third optical subset (512), and is configured as follows: The measurement light from the light source (501) is incident on the first side of the measurement surface (552); the reflected measurement light received from the second side of the measurement surface by the second optical subset is focused on the second diffraction grating; The second diffraction grating is positioned at the focal plane of the third optical subset, which focuses the measurement light diffracted from the second diffraction grating to infinity; The specular reflector is configured to reflect the reflected measurement light received from the second side of the measurement surface to the second diffraction grating, or to reflect the measurement light diffracted from the first diffraction grating to the second optical subset.

12. A sensor according to claim 8 or 9, wherein the diffraction grating is a first diffraction grating (608), and the first optical system (605) further includes a second diffraction grating (611), a beam splitter and combiner (613), a first reflecting surface (614) and a second reflecting surface (615), and a third optical subset (612), and is configured as follows: Measurement light from the light source (601) is incident on the beam splitter / combiner, a portion of the measurement light is transmitted by the beam splitter / combiner, and a portion of the measurement light is reflected by the beam splitter / combiner; The measurement light transmitted by the beam splitter / combiner is focused onto the first diffraction grating by the first optical subset; The measurement light diffracted by the first diffraction grating is reflected from the first reflecting surface, incident on the second optical subset (610), and focused on the measurement surface (652); The second diffraction grating is positioned at the focal plane of the third optical subset, and the measurement light reflected by the beam splitter / combiner is focused onto the second diffraction grating by the third optical subset; The measurement light diffracted by the second diffraction grating is reflected from the second reflective surface, incident on the second optical subset, and focused on the measurement surface.

13. The sensor according to claim 12, having the following configuration: reflected light from the first side of the measuring surface (652) is reflected by the first reflecting surface (614) to the first diffraction grating (608) and focused on the first diffraction grating by the second optical subset (610); Reflected light from the second side of the measurement surface is reflected by the second reflective surface (615) to the second diffraction grating (611), and focused on the second diffraction grating by the second optical subset; The reflected light diffracted by the first diffraction grating is focused to infinity by the first optical subset (609); The reflected light diffracted by the second diffraction grating is focused to infinity by the third optical subset (612); The reflectance measurement light diffracted by the first diffraction grating and the reflectance measurement light diffracted by the second diffraction grating are combined by a beam splitter / combiner (613), and the combined reflectance measurement light is incident on at least one Fabry-Perot filter (604).

14. A sensor according to any of the above claims, wherein during use, the distance from the optical sensor to the surface of the object to be measured is determined by measuring one or more local maximum intensity locations of light received by the optical sensor.

15. A method comprising: positioning an object to be measured at a first position relative to the sensor described in any of the claims such that the surface of the object to be measured intersects the measuring surface; and measuring the intensity of light received by the light sensor.

16. A method according to claim 15, further comprising: repositioning an object to be measured from a first position to a second position relative to a sensor, wherein the change in the position of the object to be measured is defined by a first displacement vector; and measuring the intensity of light received by a light sensor.

17. A method according to claim 15 or 16, further comprising: determining the displacement of one or more points of a first set on the surface of an object by identifying the locations of one or more intensity peaks of light measured by a photosensor when the object is in a first position.

18. A method according to claim 17, further comprising: determining the displacement of one or more points in a second set on the surface of an object by identifying the location of one or more intensity peaks of light measured by a light sensor when the object is in a second position.

19. A method according to claim 18, further comprising: generating a three-dimensional model of an object to be measured by combining the displacements of one or more points in a first set with the displacements of one or more points in a second set and a first displacement vector.

20. A method according to claim 16, further comprising: determining the thickness of the transparent layer of an object to be measured by calculating the distance between at least two different intensity peaks on a light sensor.

21. The use of the sensor according to any one of claims 1 to 14, which is used for measuring the displacement of the surface of an object relative to the sensor, measuring the profile of an object, measuring the three-dimensional shape of an object, and / or measuring the thickness of the transparent layer of an object.

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