Vibration sensor

Abstract

A vibration sensor (1) comprises a light projecting unit (10) that includes a laser light source (20) and a light projecting optical system (30) that projects laser light onto a target (90), a light receiving unit (40) that includes an imaging sensor (50) and a light receiving optical system (60) that condenses, on the imaging sensor (50), reflected and scattered light of the laser light emitted at the target, and an image processing device (70) that calculates an amount of movement, between frames, of a speckle pattern generated in the reflected and scattered light received by the imaging sensor (50), and measures vibration of the target (90) on the basis of the amount of movement, wherein: the light projecting optical system (30) includes an imaging lens, and focuses on a virtual plane that is on the object side and is closer than the target, between the target (90) and the light receiving optical system; and the light receiving optical system is configured such that the absolute value (|ψ|) of an angle (ψ) formed by a light beam (96d) incident on the outermost side of a light receiving surface of the imaging sensor (50) and an optical axis (41) of the light receiving unit is smaller than the cone half angle (θNA) of the light beam flux on the object side, determined by the numerical aperture (NA) of the imaging lens.

Description

Vibration Sensor

[0001] The present disclosure relates to a vibration sensor that irradiates an object with laser light and measures vibrations of the object using a speckle pattern that occurs in the reflected and scattered light.

[0002] When a coherent laser beam is irradiated onto the rough surface of an object, a speckle pattern, which is a pattern of bright and dark spots, appears in the reflected and scattered light. If the object vibrates at this time, the observed speckle pattern will displace in accordance with the vibration of the object. Patent Document 1 discloses a technology for measuring the vibration of an object by irradiating the rough surface of the object with laser beam and capturing the displacement of the generated speckle pattern with a two-dimensional camera.

[0003] Furthermore, Non-Patent Document 1 proposes an apparatus for measuring acoustic vibrations of an object by imaging a speckle pattern generated by irradiation with laser light using a line scan camera.

[0004] U.S. Patent No. 8,638,991

[0005] S. Bianchi et al., “Long-range detection of acoustic vibrations by speckle tracking,” Applied Optics, Vol. 58, No. 28, pp. 7805-7809, (2019).

[0006] However, the above-mentioned conventional technology uses a measurement system optimized for small vibrations, and therefore has the problem that it cannot measure vibrations accurately when the surface of the object is significantly tilted due to large vibrations of the object.

[0007] An object of the present disclosure is to provide a vibration sensor that can optimize the accuracy and measurement range according to the magnitude of vibration of an object.

[0008] The vibration sensor disclosed herein comprises a light-projecting unit having a laser light source and a light-projecting optical system that projects the laser light emitted from the laser light source as a spot onto an object; a light-receiving unit having an imaging sensor and a light-receiving optical system that focuses the reflected and scattered light of the laser light irradiated onto the object onto the imaging sensor; and an image processing device that calculates the amount of movement between frames of a speckle pattern generated in the reflected and scattered light received by the imaging sensor and measures the vibration of the object based on the amount of movement, wherein the light-receiving optical system includes an imaging lens and is focused on a virtual plane between the object and the light-receiving optical system on the object side, which is the side where the object exists, that is closer to the light-receiving optical system than the object, and the light-receiving optical system is configured so that the absolute value of the angle that a first ray included in the ray bundle incident on the outermost part of the light-receiving surface of the imaging sensor makes with the optical axis of the light-receiving unit is smaller than the cone half angle of the ray bundle on the object side, which is determined by the numerical aperture of the imaging lens.

[0009] According to the vibration sensor of the present disclosure, the accuracy and measurement range can be optimized according to the magnitude of the vibration of the object.

[0010] 1A is a schematic perspective view showing the configuration and main light rays of a vibration sensor according to a first embodiment, and FIG. 1B is a front view showing a linear spot formed on an object by laser light. FIG. 1A is a schematic plan view showing the configuration and main light rays of a light projecting unit of the vibration sensor according to the first embodiment, and FIG. 1B is a schematic plan view showing the configuration and main light rays of a light projecting unit of the vibration sensor according to the first embodiment. FIG. 1A is a schematic side view showing the configuration and main light rays of a light receiving unit of the vibration sensor according to the first embodiment, and FIG. 1B is a schematic plan view showing the configuration and main light rays of a light receiving unit of the vibration sensor according to the first embodiment. FIG. 1A to FIG. 1C are diagrams showing design examples when the light receiving unit includes a wide-angle lens. FIG. 1A to FIG. 1C are diagrams showing design examples when the light receiving unit includes a telecentric lens. FIG. 1A to FIG. 1D are diagrams showing design examples when the light receiving unit includes a hypercentric lens. FIG. 1C are diagrams showing examples of speckle patterns on an area sensor when the light receiving unit includes a wide-angle lens. 9A to 9D are diagrams illustrating a design example in which the light receiving unit includes a lens that is slightly out of a strict telecentric state. (A) and (B) are schematic plan views illustrating vibration of an object, and (C) and (D) are diagrams illustrating movement of a speckle pattern caused by vibration of the object shown in FIGS. 9A and 9B. (C) and (D) are diagrams illustrating an example of a one-dimensional speckle pattern waveform that moves due to vibration. (A) and (B) are diagrams illustrating an example process for calculating the vibration amount of a speckle pattern from waveform matching. (A) and (B) are diagrams illustrating an example process for calculating the vibration amount of a speckle pattern from waveform matching. (A) and (B) are diagrams illustrating the configuration of the light receiving unit and main light rays (optical paths) when zoomed in on the vibration sensor according to the first embodiment. (A) is a diagram illustrating an example of the hardware configuration of the vibration sensor according to the first embodiment. (A) is a schematic perspective view illustrating the configuration and main light rays of a vibration sensor according to the second embodiment, and (B) is a front view illustrating a circular spot formed on an object by laser light. 10A, 10B, and 10C are a perspective view, a plan view, and a side view showing the configuration of a light receiving unit and main light rays of a vibration sensor according to a second embodiment.1A, 1B, and 1C are perspective views, plan views, and side views showing the configuration of a light receiving unit and main light rays of a vibration sensor according to a second embodiment. 1A, 1B, and 1C are perspective views, plan views, and side views showing the configuration of a light receiving unit and main light rays of a vibration sensor according to a third embodiment. 1A, 1B, and 1C are perspective views, plan views, and side views showing the configuration of a light receiving unit and main light rays of a vibration sensor according to a third embodiment. 1A is a schematic perspective view showing the configuration and main light rays of a vibration sensor according to a fourth embodiment, and 1B is a front view showing a linear spot formed on an object by laser light. 1B is a schematic plan view showing the configuration and main light rays of a vibration sensor according to the fourth embodiment. 1A is a schematic side view showing the configuration and main light rays of a light projecting unit of a vibration sensor according to the fourth embodiment, and 1B is a schematic plan view showing the configuration and main light rays of a light projecting unit of a vibration sensor according to the fourth embodiment. (A) is a schematic side view showing the configuration of the light receiving unit and main light rays of the vibration sensor according to embodiment 4, and (B) is a schematic plan view showing the configuration of the light receiving unit and main light rays of the vibration sensor according to embodiment 4. (A) to (C) are diagrams showing the overlap of the light receiving surface of the line sensor and the image of the speckle pattern (image of a line-shaped spot). (A) to (D) are schematic plan views showing the image shift when the distance changes in the vibration sensor according to embodiment 3.

[0011] Vibration sensors according to embodiments will be described below with reference to the drawings. The following embodiments are merely examples, and the embodiments can be appropriately combined and modified. In addition, the same reference numerals are used in each drawing to designate similar components.

[0012] <<1>> Embodiment 1 <<1-1>> Configuration and Operation> FIG. 1(A) is a schematic perspective view showing the configuration and main light beams of a vibration sensor 1 according to embodiment 1. FIG. 1(B) is a front view showing a spot 91 formed by a laser beam irradiated onto an object 90, which is the target of vibration sensing. The vibration sensor 1 is a device that irradiates the object 90 (rough surface) with laser beam and measures the vibration of the object 90 using a speckle pattern generated in the reflected and scattered light. The vibration sensor 1 includes a light-projecting unit 10 that irradiates the object 90 with laser beam, a light-receiving unit 40 that receives the reflected and scattered light generated by the object 90 irradiated with the laser beam, and an image processing device 70 that serves as an information processing device that detects vibrations based on a detection signal output from the light-receiving unit 40. Typically, the light-projecting unit 10 and the light-receiving unit 40 are housed within a light-projecting and light-receiving head 5 (e.g., within a single housing).

[0013] The figure shows the coordinate axes of an X'YZ' Cartesian coordinate system as a first coordinate system used to explain the light-projecting unit 10. The figure also shows the coordinate axes of an XYZ Cartesian coordinate system as a second coordinate system used to explain the light-receiving unit 40, the target object 90, and the observation surface 92. The central ray of the laser light emitted from the light-projecting unit 10 is parallel to the Z' axis, and the central ray of the light received by the light-receiving unit 40 is parallel to the Z axis. The Y axis is a coordinate axis normal to a plane including the Z' axis and the Z axis. The X' axis is a coordinate axis perpendicular to both the Y axis and the Z' axis. The X axis is a coordinate axis perpendicular to both the Y axis and the Z axis.

[0014] The light-projecting unit 10 has a laser light source 20 and a light-projecting optical system 30 that projects laser light emitted from the laser light source 20 onto the object 90 as a circular spot 91. The light-receiving unit 40 has an area sensor 50 (also called a "two-dimensional area sensor" or "area camera") as an imaging sensor, and a light-receiving optical system 60 that focuses the reflected and scattered light of the laser light irradiated onto the object 90 onto the area sensor 50 (i.e., onto the light-receiving surface of the area sensor 50). The image processing device 70 calculates the amount of movement (i.e., shift amount) between frames of a speckle pattern generated in the reflected and scattered light received by the area sensor 50, and estimates (i.e., calculates) the vibration of the object 90 based on this amount of movement.

[0015] The light-projecting unit 10 and the light-receiving unit 40 are arranged so that a first optical axis 11, which is the optical axis of the light-projecting unit 10, and a second optical axis 41, which is the optical axis of the light-receiving unit 40, intersect on the target object 90. The light-projecting unit 10 and the light-receiving unit 40 are arranged side by side in the same direction as the first direction (X direction). Here, the optical axis of the light-projecting unit 10 may be the axis of the laser light emitted from the light-projecting unit 10. Furthermore, the optical axis of the light-receiving unit 40 may be the axis of reflected and scattered light that can be received by the line sensor 50.

[0016] The projection optical system 30 includes a collimator lens 31 as a lens through which the laser light passes, and a spot changing mechanism 35 that changes the size of the spot 91 on the object 90. The spot changing mechanism 35 includes a distance adjustment mechanism that can adjust the distance Lc between the light emitting point of the laser light source 20 and the collimator lens 31. In addition, in the first embodiment, the image processing device 70 changes the size of the spot 91 on the object 90 using the spot changing mechanism 35 based on the measured vibration.

[0017] Fig. 2(A) is a schematic plan view (i.e., a view of the light-projecting unit 10 viewed in the -Y direction) showing the configuration and main light rays of the light-projecting unit 10 of the vibration sensor 1 according to embodiment 1. Fig. 2(B) is a schematic plan view (i.e., a view of the light-projecting unit 10 viewed in the -Y direction) showing the configuration and main light rays of the light-projecting unit 10 of the vibration sensor 1.

[0018] The light projection unit 10 includes a laser light source 20, a collimator lens 31, and a spot changing mechanism 35 that can adjust the distance Lc between the light emission point of the laser light source 20 and the collimator lens 31. Fig. 2A shows a case where the distance Lc is small, in which case the diameter W of the circular spot 91 on the object 90 is large. Fig. 2B shows a case where the distance Lc is large, in which case the diameter W of the circular spot 91 on the object 90 is small. In other words, as the collimator lens 31 approaches the light emission point of the laser light source 20, the diameter W of the circular spot 91 on the object 90 increases, and as the collimator lens 31 becomes farther from the light emission point of the laser light source 20, the diameter W of the circular spot 91 on the object 90 decreases.

[0019] Fig. 3(A) is a schematic side view (i.e., a view of the light receiving unit 40 when viewed in the X direction) showing the configuration and main light rays of the light receiving unit 40 of the vibration sensor 1 according to embodiment 1. Fig. 3(B) is a schematic plan view (i.e., a view of the light receiving unit 40 when viewed in the -Y direction) showing the configuration and main light rays of the light receiving unit 40 of the vibration sensor 1.

[0020] In the first embodiment, the light receiving unit 40 includes an area sensor 50 as an imaging sensor and a light receiving optical system 60. The light receiving optical system 60 is composed of an imaging lens 61 and an aperture 69, and is an object-side telecentric optical system or a hyper-tric optical system. FIG. 1 shows a configuration in which the aperture 69 is located between the area sensor 50 and one imaging lens 61, which is the simplest configuration for realizing an object-side telecentric optical system. However, in actual lens designs, an object-side telecentric optical system is realized using multiple lens combinations and apertures. FIGS. 3A and 3B show an example in which the light receiving optical system 60 is a hyper-tric optical system. An object-side telecentric optical system is an optical system in which chief rays 96a to 96d from each image height directed from the lens to the object are parallel to the optical axis (i.e., the second optical axis 41). Specifically, it is an optical system in which chief rays 96a to 96d (shown in FIGS. 5A to 5C, which will be described later) from each image height directed from the lens to the object are parallel to the extent that they do not intersect with the optical axis within the range of the distance from the light-receiving optical system 60 to the object 90. A hypertropic optical system is a special optical system in which chief rays 96a to 96d (FIGS. 5A to 5C) from each image height directed from the lens to the object converge toward the optical axis (i.e., the second optical axis 41). Specifically, it is an optical system in which chief rays 96a to 96d (FIGS. 5A to 5C) from each image height directed from the lens to the object converge toward the optical axis within the range of the distance from the light-receiving optical system 60 to the object 90.

[0021] In the first embodiment, the object side refers to the side on which the object 90 exists as viewed from the light receiving optical system 60. The light receiving optical system 60 forms a focus on a virtual plane that is closer to the light receiving optical system 60 than the object 90 between the object 90 and the light receiving optical system 60 on the object side. In other words, the light receiving optical system 60 is configured so that an object-side focal plane that forms an image on the area sensor 50 exists at a position that is closer to the light receiving optical system 60 than the object 90 between the object 90 and the light receiving optical system 60 on the object side. The light receiving optical system 60 is preferably a lens (optical system) that is telecentric on the object side or a lens (optical system) that is nearly telecentric on the object side. In other words, the light receiving unit 40 is configured such that the absolute value |ψ| of the angle ψ that a light ray incident on the outermost part of the light receiving surface of the area sensor 50 makes with the second optical axis 41, which is the optical axis of the light receiving unit 40, is smaller than the cone half angle θ of the light ray bundle on the object side, which is determined by the numerical aperture NA of the light receiving optical system 60. ＮＡ It is configured to be smaller.

[0022] The first optical axis 11, which is the optical axis of the light-projecting unit 10, and the second optical axis 41 of the light-receiving unit 40 intersect on the target 90. The vibration sensor 1 has a mechanism for adjusting the direction of the first optical axis 11 of the light-projecting unit 10 (i.e., the direction of the central ray of the laser light emitted from the light-projecting unit 10) or the direction of the second optical axis 41 of the light-receiving unit 40 so that they intersect even if the distance to the target 90 changes.

[0023] The surface of the object 90 is rough, and the light reflected and scattered by the object 90 from the circular spot 91 irradiated by the light projecting unit 10 generates a speckle pattern throughout the entire space. An image of the speckle pattern generated in this space is acquired by the light receiving unit 40 (i.e., the image is formed on the light receiving surface of the area sensor 50 of the light receiving unit 40). The position where the image of the speckle pattern is acquired is an observation plane 92 of the speckle pattern. Note that the observation plane 92 is an example of a virtual plane where the light receiving optical system 60 focuses at a position closer to the light receiving optical system 60 than the object 90 between the object 90 and the light receiving optical system 60 on the object side.

[0024] The plane conjugate with the light-receiving surface of the area sensor 50 is not the object 90 but a virtual plane at a distance L in front of the light-receiving optical system 60, and this virtual plane is called a speckle pattern observation plane 92. The distance between the speckle pattern observation plane 92 and the object 90 is L. In other words, the light-receiving unit 40 does not acquire an image of the circular spot 91 on the object 90, but rather acquires an image of the circular spot 91 that is defocused by a large distance L. The image information acquired by the area sensor 50 is sent to the image processing device 70, where the vibration amount of the speckle pattern is calculated using an algorithm described later.

[0025] <Reason why an object-side telecentric optical system or an optical system close to it is desirable> The light-receiving optical system 60 of the light-receiving unit 40 is desirably an object-side telecentric optical system. However, when the distance L is relatively short, for example, 0.5 m or less, the light-receiving optical system 60 of the light-receiving unit 40 may be a hyper-telecentric optical system. The reason for this will be explained using design examples of the light-receiving unit 40 in Figures 4(A) to 4(C), Figures 5(A) to 5(C), and Figures 6(A) to 6(D).

[0026] In Figures 4(A) to (C), Figures 5(A) to (C), and Figures 6(A) to (D), image points P0, P1, P2, and P3 for the ray tracing simulation are placed on the area sensor 50, and rays are traced from there in the direction opposite to the direction in which the rays actually travel. Figures 4(A), 5(A), and 6(A) show ray bundles 95a to 95d from the area sensor 50 to a plane 94 on the object 90. Figures 4(B), 5(B), and 6(B) show only chief rays 96a to 96d extracted from the ray bundles 95a to 95d in Figures 4(A), 5(A), and 6(A). Figures 4(C), 5(C), and 6(C) are enlarged views of the sections from the area sensor 50 to the speckle pattern observation surface 92 in Figures 4(A), 5(A), and 6(A).

[0027] In the illustrated example, the focal length f of the imaging lens 61 is 6.5 mm, and the X coordinate values ​​of image points P0 to P3 are 0 mm, 1 mm, 2 mm, and 4 mm, respectively. The light-receiving surface of the area sensor 50 is assumed to be 8 mm x 8 mm in size. Image point P3 is the outermost image point (farthest from the optical axis). The aperture diameter of the diaphragm 69 is 1.6 mm. The diaphragm 69 plays an important role in determining the numerical aperture NA of the ray bundle that can be captured on the object side. Furthermore, by changing the distance between the imaging lens 61 and the diaphragm 69, the degree of divergence of the principal ray on the object side can be changed, allowing the construction of an object-side telecentric optical system or a hypercentric optical system. Of the ray bundles 95a to 95d emitted from each image point P0 to P3, the principal rays that pass through the center of the diaphragm are designated 96a to 96d. The width (diameter W) of the circular spot 91 irradiated onto the object 90 from the light projecting unit 10 is set to 6 mm.

[0028] 4A to 4C show an example in which the light receiving optical system 60 of the light receiving unit 40 is a wide-angle lens. The position of the aperture 69 is the same as the position of the imaging lens 61. In this case, the respective bundles of rays 95a to 95d emanating from the image points P0, P1, P2, and P3 are focused on the observation plane 92 of the speckle pattern. Chief rays 96b to 96d, excluding the chief ray 96a traveling on the second optical axis 41, are incident on the observation plane 92 of the speckle pattern at an angle and each travel in a downward rightward direction (positive direction) as represented by the angle ψ in FIG. 4C. Since the observation plane 92 of the speckle pattern is a virtual surface in space and does not have a screen for transmitting and diffusing light, the respective chief rays 96a to 96d are largely spread out on the plane 94 of the object 90, as shown in FIG. 4B. As shown in FIG. 4A, each of the light beams 95a-95d also spreads around the chief rays 96a-96d after passing through the speckle pattern observation plane 92. Here, when actually measuring a speckle pattern, a diffused light source emitted from the circular spot 91 is read. In FIG. 4A, the light beams 95b-95d do not overlap with the circular spot 91, so the light beams emitted from the circular spot 91 reach only the area inside the image point P1 on the area sensor 50. In other words, as shown in FIGS. 4A to 4C, when a wide-angle lens is used as the light-receiving optical system 60, the outline of the speckle pattern reaching the area sensor 50 becomes extremely small, as shown in FIG. 7. In vibration sensing, a sufficiently large number of pixels is required to measure the movement of the speckle pattern. Therefore, the light-receiving unit 40 shown in FIGS. 4A to 4C is not suitable for vibration sensing.

[0029] 5A to 5C show an example in which the light-receiving optical system 60 of the light-receiving unit 40 is an object-side telecentric optical system. When the distance between the imaging lens 61 and the aperture stop 69 is equal to the focal length f of the imaging lens 61 (=6.5 mm), the light-receiving optical system 60 becomes an object-side telecentric optical system. This state is shown in FIG. 5C, in which simulated ray bundles 95a to 95d emanating from image points P0 to P3 are all converted by the imaging lens 61 into directions parallel to the optical axis (second optical axis 41 in the Z direction), and are focused on the speckle pattern observation surface 92. The chief rays 96a to 96d that pass through the speckle pattern observation surface 92 propagate parallel to the optical axis, as shown in FIG. 5B. Therefore, even if the distance L between the plane 94 on the object 90 and the observation plane 92 of the speckle pattern is large, the width in the X direction of the group of chief rays (i.e., the group of chief rays 96a to 96d) does not change. Therefore, as shown in FIG. 5A , even if the distance L is large, the amount of overlap deviation of the light beams 95a to 95d on the plane 94 does not change, and all of the light beams 95a to 95d overlap with the circular spot 91. This indicates that, considering the actual direction of travel of the light beams, scattered light emitted from the circular spot 91 can reach all points on the area sensor 50. In this case, unlike FIG. 7 , the speckle pattern appears across the entire light-receiving surface of the area sensor 50. Therefore, when the light-receiving optical system 60 of the light-receiving unit 40 is an object-side telecentric optical system, an image with a sufficiently large number of pixels can be obtained to measure the amount of movement of the speckle pattern, which is suitable for vibration sensing. In other words, the light-receiving optical system 60, which is an object-side telecentric optical system, is focused on a speckle pattern observation surface 92 located between the object 90 and the light-receiving optical system 60 on the object side, which is the side on which the object 90 exists, and which is closer to the light-receiving optical system 60 than the object 90. This is an example of a light-receiving optical system that is configured so that the absolute value of the angle formed by the light ray (first light ray) included in the light ray bundle 95d incident on the outermost side of the light-receiving surface of the area sensor 50 and the optical axis of the light-receiving unit 40 is smaller than the cone half angle of the light ray bundle on the object side 92, which is determined by the numerical aperture of the light-receiving optical system 60.

[0030] 6A to 6D show an example in which the light-receiving optical system 60 of the light-receiving unit 40 is a hypertric optical system on the object side. When the distance between the imaging lens 61 and the aperture 69 is greater than the focal length f of the imaging lens 61 (=6.5 mm), the light-receiving unit 40 becomes a hypertric optical system. This state is shown in FIG. 6C, in which simulated ray bundles 95a to 95d emanating from image points P0 to P3 are redirected by the imaging lens 61 so that their chief rays 96a to 96d are directed toward the optical axis, and are focused on the speckle pattern observation plane 92. A system in which the inclination of the chief rays 96a to 96d toward the optical axis is called a hypertric optical system. As shown in FIG. 6B, chief rays 96a to 96d that pass through speckle pattern observation surface 92 intersect at point Q, which is located between speckle pattern observation surface 92 and object 90 and is closer to speckle pattern observation surface 92 than to object 90, and then diverge from each other. Therefore, in the case shown in FIG. 6A, ray bundles 95a to 95d completely overlap at point Q, with a slight deviation in overlap at plane 94. However, in the case of FIG. 6A, all ray bundles 95a to 95d include a circular spot 91 on plane 94. Therefore, even in this case, unlike in FIG. 7, the speckle pattern appears across the entire light-receiving surface of area sensor 50. In other words, an image with a sufficiently large number of pixels can be obtained to measure the amount of movement of the speckle pattern, making it suitable for vibration sensing. In other words, the light-receiving optical system 60, which is a hyperoptic optical system on the object side, is focused on a speckle pattern observation surface 92 that is located closer to the light-receiving optical system 60 than the object 90 is between the object 90 and the light-receiving optical system 60 on the object side, which is the side on which the object 90 exists, and this is an example of a light-receiving optical system that is configured so that the absolute value of the angle that a light ray (first light ray) included in the light ray bundle 95d incident on the outermost side of the light-receiving surface of the area sensor 50 makes with the optical axis of the light-receiving unit 40 is smaller than the cone half angle of the light ray bundle on the object side 92, which is determined by the numerical aperture of the light-receiving optical system 60.

[0031] As is clear from the above explanation, in the case of a hypertric optical system, when the distance L to the object 90 is short, the overlap of the light beams 95a to 95d is large and a speckle pattern appears over the entire surface. On the other hand, when the distance L is very large compared to the degree of inclination of the chief rays 96a to 96d, the overlap of the light beams 95a to 95d becomes small and the outer shape of the speckle pattern may become smaller than the size of the area sensor 50. Therefore, a hypertric optical system is an optical system that is effective for an object 90 that is close to the object 90.

[0032] 8A to 8D illustrate cases in which the light-receiving optical system 60 of the light-receiving unit 40 is not completely telecentric toward the object side, but the group of chief rays immediately after passing through the imaging lens 61 diverges outward (away from) the second optical axis 41 at a small angle. This state occurs when the distance between the imaging lens 61 and the aperture 69 is slightly smaller than the focal length f of the imaging lens 61, which is 6.5 mm. This state is shown in FIG. 8C, in which the bundles of rays 95a to 95d emanating from the image points P0 to P3 are converted by the imaging lens 61 so that their chief rays 96a to 96d diverge at a small angle from the optical axis, and are focused on the speckle pattern observation surface 92. The group of chief rays passing through the speckle pattern observation surface 92 gradually diverges, as shown in FIG. 8B. In this case, as shown in Fig. 8A, the overlapping of the light beams 95a to 95d does not change significantly even when the distance L increases. Therefore, in the case of Fig. 8A, all of the light beams 95a to 95d include a circular spot 91 on the plane 94. In other words, even in this case, unlike Fig. 7, a speckle pattern appears over the entire light-receiving surface of the area sensor 50. In other words, an image having a sufficiently large number of pixels with a width large enough to measure the amount of movement of the speckle pattern can be obtained, which is suitable for vibration sensing.

[0033] 8, it will be clarified how much deviation from the strict telecentric state can result in obtaining an image on the entire surface of the area sensor 50. The cone half angle of the light beams 95a to 95d on the object side of the light receiving optical system 60 is defined as θ ＮＡ(shown in FIGS. 8B and 8C). Since the observation surface 92 of the speckle pattern is in air (refractive index n=1), the numerical aperture NA of the light receiving optical system 60 is defined by the following equation (1): NA=sin θ ＮＡ (1)

[0034] Of the light beam 95d emanating from image point P3, the lowermost light beam shown in FIG. 8C is designated as light beam 97. In other words, light beam 97 is the outermost light beam of light beam 95d in the direction from image point P3 toward image point P0 (-X direction). After passing through observation plane 92 of the speckle pattern, light beam 97 becomes the innermost light beam of light beam 95d as shown in FIG. 8D. In other words, after passing through observation plane 92 of the speckle pattern, light beam 97 becomes the light beam of light beam 95d that exists furthest in the +X direction in the direction from image point P0 toward image point P3 (+X direction). The condition for the reflected and scattered light of circular spot 91 to reach point P3 is that light beam 97 is located above the lower end of circular spot 91 on plane 94. A necessary condition for this is that the light ray 97 must be at least angled upward, and this is expressed by the following equation (2) using the angle ψ that the chief ray 96d makes with the optical axis: ＮＡ >ψ (2) In other words, the light-receiving optical system 60 that is not completely telecentric on the object side focuses the speckle pattern observation plane 92 at a position closer to the light-receiving optical system 60 than the object 90 is between the object 90 and the light-receiving optical system 60 on the object side, which is the side on which the object 90 exists, and is an example of a light-receiving optical system that is configured so that the absolute value of the angle that a light ray (first light ray) included in the light ray bundle 95d incident on the outermost side of the light-receiving surface of the area sensor 50 makes with the optical axis of the light-receiving unit 40 is smaller than the cone half angle of the light ray bundle on the object side 92, which is determined by the numerical aperture of the light-receiving optical system 60.

[0035] Here, ψ is the half angle of the angle of view of the light receiving unit 40. When formula (2) is satisfied, if L is sufficiently large, the circular spot 91 falls within the range of the light beam 95d. At this time, the reflected and scattered light from the circular spot 91 also reaches point P3, and a speckle pattern is superimposed over the entire light receiving surface of the area sensor 50.

[0036] The same explanation as in the cases of FIGS. 8A to 8D can also be applied to the hypertric optical system described in FIGS. 6A to 6D. In the case of a hypertric optical system, the angle ψ that the chief ray 96d makes with the optical axis is defined as a negative value. As in the explanation given in FIG. 8D, FIG. 6D shows a ray diagram extracting only the optical path of the ray bundle 95d emanating from point P3. As in the explanation given in FIG. 8D, the cone half angle θ of the ray bundle 95d on the object side can be calculated. ＮＡ Whereas, θ ＮＡ >|ψ| (3) is satisfied, if L is sufficiently large, the circular spot 91 falls within the range of the ray bundle 95d. At this time, the reflected and scattered light from the circular spot 91 also reaches the point P3, and a speckle pattern is generated over the entire light-receiving surface of the area sensor 50.

[0037] To summarize the configuration of the optical system of the light receiving unit 40, in order to generate a speckle pattern over the entire light receiving surface of the area sensor 50, it is desirable to satisfy the following condition (A1) or (A2): (A1) The light receiving unit 40 is an object-side telecentric optical system. (A2) The light receiving unit 40 is an optical system that is slightly deviated from an object-side telecentric optical system (i.e., an optical system that is close to an object-side telecentric optical system). Note that an object-side hypercentric optical system is a light receiving optical system that satisfies condition (A2).

[0038] Here, the meaning of "slightly shifted" is that the angle ψ between the chief ray 96d from the outermost image point, which is the image point farthest from the optical axis, and the optical axis (second optical axis 41) is smaller than the cone half angle θ ＮＡ This means that ψ is smaller than ψ≡0°, and is expressed by equation (3). Note that in the case of an object-side telecentric optical system, all of the chief rays 96a to 96d are parallel to the optical axis (second optical axis 41), that is, ψ=0°, and therefore equation (3) always holds.

[0039] <Shift of Speckle Pattern Image> Figures 9(A) and (B) are schematic plan views (i.e., views of the light receiving unit 40 viewed in the -Y direction) showing the configuration of the light receiving unit 40 of the vibration sensor 1 according to embodiment 1, the main light rays, and the displacement (e.g., vibration) of the object 90. Figures 9(A) and (B) show the displacement due to vibration of the object 90. Figures 9(C) and (D) are diagrams showing the movement on the observation plane 92 of the speckle pattern generated by the vibration of the object 90 shown in Figures 9(A) and (B), respectively.

[0040] As shown in Figures 9A and 9B, the speckle pattern observed on the observation surface 92 is a random granular pattern, as shown in Figures 9C and 9D, for example. When the object 90 faces the light receiving unit 40 as shown in Figure 9A, the speckle pattern observed on the observation surface 92 of the speckle pattern is shown in Figure 9C. The light receiving optical system 60 causes the area sensor 50 to acquire the two-dimensional image of Figure 9C. When the object 90 vibrates, it may not only vibrate in the Z direction at the laser irradiation position, but also may vibrate angularly in the angular direction. While possible modes of angular vibration include vibration in any direction within the XY plane, the direction of vibration is considered to be constant.

[0041] For simplicity, a case where the object 90 vibrates around the Y axis will be described. FIG. 9B shows the optical path of the light receiving system when the object 90 is tilted around the Y axis by a tilt angle α. The optical path is almost the same as in FIG. 9A, but the speckle pattern image acquired by the area sensor 50 is shifted by δX in the X direction from the image in FIG. 9C, as shown in FIG. 9D. In FIGS. 9C and 9D, due to the vibration of the object 90, the image acquired by the area sensor 50 is displaced (vibrated) only in the X direction. When the object 90 is tilted by the tilt angle α, the shift amount δX of the speckle pattern on the observation surface 92 is expressed as the product of the distance L and α (i.e., δX = L × α), as disclosed in Patent Document 1.

[0042] 10 is a diagram showing an example of a one-dimensional speckle pattern waveform that moves due to vibration. Wave(a) and wave(b) in FIG. 10 are one-dimensional waveforms corresponding to the profiles on the cross-sectional line 96 in FIGS. 9C and 9D, and are one-dimensional cross-sectional waveforms of the output image of the area sensor 50. As shown in FIG. 5, wave(a) shifts in the X direction by a shift amount δX as shown in wave(b) due to the tilt angle α (angle change) of the object 90. When used as a vibration sensor, the amount of movement in the X direction of the signal waveform acquired by the area sensor 50 is calculated for each frame, and the amount of movement is integrated to obtain a vibration waveform corresponding to the angle change due to vibration.

[0043] <Algorithm for Extracting Displacement Amount from Successive Speckle Pattern Images> To calculate the amount of movement of a signal waveform, for example, waveform matching processing is used. As shown in FIG. 10 , ideally, a waveform is obtained that is shifted by a shift amount δX in the X direction while maintaining its waveform shape. Several methods are known for calculating the shift amount δX from these two waveforms. For example, the sum of absolute values ​​of differences for each pixel (SAD) or the sum of squared differences (SSD) of differences for each pixel can be calculated as the similarity, and the shift amount δX can be calculated from the calculated similarity. The pixel pitch is, for example, a value within a range of approximately 5 μm to 2 μm, but is not limited thereto. Here, a case where similarity is calculated using SAD will be described as an example.

[0044] If the luminance value of wave(a) at pixel number i=1, 2, 3, . . . is fa(i), and the luminance value of wave(b) is fb(i), the similarity R ＳＡＤ (x) is calculated using the following formula (4): ＳＡＤ (x) is pixel number i ｍｉｎ From i ｍａｘ The similarity between the luminance value fa(i) in the pixel range up to and including the luminance value fb(i+x) at a position obtained by shifting the luminance value fb(i) by the unknown quantity x is calculated. ＳＡＤThe smaller the value of (x), the more similar the brightness value fb(i+x) and the brightness value fa(i) are. ＳＡＤ (x) is calculated, and the similarity R is calculated as shown in the following formula (5). ＳＡＤ The x that minimizes (x) is defined as the shift amount δX.

[0045]

[0046] 11A and 11B, and 12A and 12B are diagrams showing an example of a process for calculating the vibration amount of a speckle pattern from waveform matching. In FIG. 11A, the horizontal axis represents x and the vertical axis represents R. ＳＡＤ 11(A) is a graph showing the shift amount δX. The x that gives the minimum value (most similar) of this graph is the shift amount δX, and in the case of FIG. 11(A), δX = 5 [pixel]. By this method, the shift amount δX, which is the amount of movement between consecutive image frames, can be calculated. This is performed between all consecutive frames. An example of calculating the shift amount δX for the first 50 frames is shown in FIG. 11(B). The shift amount δX is the amount of movement of the image between adjacent frames, and to calculate the amount of movement from the start of measurement, it is necessary to take the sum of the shift amounts δX for the frames up to that point. When the image frames are in order, n = 0, 1, 2, ..., the shift amount, which is the amount of movement from the (n-1)th frame to the nth frame, is δX. ｎ Then, the movement amount X(n) from the initial position in the nth frame is obtained by integrating the movement amount between frames, as shown in the following equation (6).

[0047]

[0048] FIG. 7A shows an example of the displacement X(n) from the initial position in the nth frame. In the case of vibration, data should be distributed above and below the zero line on the vertical axis, but actual data contains a low-frequency offset, as shown here. The offset is thought to be due to factors such as the accumulation of errors when calculating the displacement of the speckle pattern image and the gradual movement of the irradiation position of the linear spot 91a on the object 90. To subtract this offset, for example, a process of removing low-frequency components using a high-pass filter or the like can be performed. FIG. 7B shows the data in FIG. 7A after passing through a high-pass filter, and this is the vibration signal to be determined.

[0049] It should be noted that the brightness distribution (speckle pattern waveform) of the actually observed speckle pattern gradually changes as the tilt angle α of the object 90 increases. ＳＡＤ The inter-frame shift amount δX obtained by calculating the minimum value of (x) will contain a large error if the tilt angle α is large.

[0050] For example, if the object 90 has a vibration frequency v ｏｂｊ = 1 [kHz], amplitude angle ±α １ If the amplitude angle is α １ However, when the shift amount δX, which is the amount of movement of the speckle pattern calculated by δX = L × α, is large enough to be observed (for example, δX = several pixels), the sampling frequency of the sensor is ν ｓｅｎｓｏｒ = 2 kHz, the shape of the speckle pattern waveform does not change significantly, so the shift amount δX can be obtained correctly and the vibration of the sine wave can be reproduced.

[0051] On the other hand, the amplitude angle α １ is large, and ν ｏｂｊ If the speckle pattern waveform changes significantly within a vibration period of ν = 1 [kHz], ｓｅｎｓｏｒ= 2 [kHz], matching of speckle pattern waveforms between frames is not achieved well, and the error in the shift amount δX becomes large. In such a case, by acquiring speckle pattern waveforms at a higher frame rate, it is possible to suppress deformation of the waveform between frames. For example, when ν ｓｅｎｓｏｒ = 10 [kHz], the shift amount δX is calculated before the deformation of the speckle pattern waveform becomes large, so that the error in the shift amount δX can be suppressed and a sine wave of 1 [kHz] can be correctly reproduced.

[0052] Vibration frequency ν of the object 90 ｏｂｊ , the sampling frequency of the area sensor 50 is ｓｅｎｓｏｒ If is sufficiently large (high speed), the waveform obtained by equation (6) is proportional to the vibration amount of the object 90.

[0053] In the above explanation, calculations were performed on a one-dimensional waveform at the cross-sectional line 96 in Figures 9C and 9D, but it can be easily extended to a discussion on estimating the amount of movement of a two-dimensional image. ＳＡＤ For R, the following formula (7) can be used: ＳＡＤ Find the (x, y) that gives the minimum value of δX = √(x ２ +y ２ ) can be used.

[0054]

[0055] The above processing is performed by the image processing device 70 shown in FIG.

[0056] <<1-2>> Description of the Problems: In the vibration sensor described in Patent Document 1, the light receiving unit is neither an object-side telecentric optical system nor an object-side hypercentric optical system, nor an optical system close to an object-side telecentric optical system. Therefore, the outer shape of the speckle pattern acquired by the area sensor 50 is small relative to the area sensor 50, as illustrated in FIG. 7 . Therefore, even when attempting to calculate the movement amount of the speckle pattern based on Equation (4), there is a problem that the number of pixels is insufficient, resulting in poor image matching accuracy. Furthermore, when the shift amount δX between consecutive frames is large, δX exceeds the outer size of the speckle pattern, making image pattern matching impossible. In other words, with the conventional method, the outer size of the speckle pattern that can be acquired is not sufficiently large, making it impossible to perform vibration measurement with sufficiently high accuracy and a sufficiently wide measurement range.

[0057] <<1-3>> Advantages of the First Embodiment As described above, the light receiving unit 40 of the vibration sensor in the first embodiment is an object-side telecentric optical system, an object-side hypercentric optical system, or an optical system slightly shifted from an object-side telecentric optical system (an optical system close to an object-side telecentric optical system), and can generate a speckle pattern image over the entire light receiving surface of the area sensor 50. Therefore, it is possible to obtain an image with a width sufficiently large relative to the shift amount δX of the speckle pattern. This can improve the accuracy of the vibration sensor 1 and expand the vibration measurement range.

[0058] For ease of understanding, the above description has been made on the assumption that the speckle pattern overlaps the entire light-receiving surface of area sensor 50. However, as long as an image having a width sufficiently large relative to the shift amount δX of the speckle pattern can be obtained, there is no problem even if the outer shape of the speckle pattern is slightly smaller than area sensor 50. In this case, half the value of the required image width can be considered by substituting the coordinate values ​​of image point P3 shown in Fig. 6 or 8, and the allowable range of the absolute value |ψ| of the angle ψ, which is half the angle of view, becomes smaller by the amount of shift amount δX.

[0059] <When Zoom Function is Provided> In the first embodiment, when the light receiving optical system 60 has a zoom function, it is possible to improve the measurement accuracy and expand the vibration measurement range in accordance with the magnitude of the vibration of the target object 90. Figures 13A and 13B show optical path diagrams in which three image points are placed on the area sensor 50 and light rays are traced from there in the direction opposite to the normal direction in order to show the range in which the light receiving unit 40 can capture an image of a speckle pattern.

[0060] 13A shows the case where the reduction magnification of the light receiving unit 40 is M=1. In this case, the light receiving unit 40 can transfer the speckle pattern generated within the range of the field of view width X2a on the speckle pattern observation surface 92 onto the area sensor 50 at a reduction magnification of 1.

[0061] 13B shows the case where the reduction magnification of the light receiving unit 40 is M=1 / 2. In this case, the field of view width X2b on the observation surface 92 of the speckle pattern imaged by the area sensor 50 is twice the field of view width X2a.

[0062] It is known that the displacement δXs of the speckle pattern on the speckle pattern observation plane 92 is expressed as δXs = L·α. Here, α represents the difference in tilt of the object 90 between successive frames. When the tilt angle α becomes large and δXs between successive frames exceeds the field of view width X2 on the speckle pattern observation plane 92, no matching patterns exist between the images of the successive frames, making image matching impossible. To actually perform image matching, approximately half of the images must match. In other words, the following condition must be met: X2 > 0.5·δXs (8). However, because the number of pixels in the area sensor 50 does not change even when the field of view width is widened, the number of samples for the same speckle pattern range is halved, resulting in a deterioration in the accuracy of image matching.

[0063] When actually measuring vibration, it is difficult to predict in advance the amount of vibration that will appear. Therefore, a practical method is to first measure the vibration and then use the results as feedback to change the zoom magnification.

[0064] For example, initially, the zoom reduction ratio M is set to a minimum value, such as M = 0.2. If the result of the first measurement shows that the displacement amount δXs of the speckle pattern is small, the reduction ratio is increased slightly, for example, to M = 0.3. If δXs is still small, the reduction ratio is increased further. In this way, the reduction ratio M is changed in accordance with the magnitude of δXs until an appropriate field of view width X2 is obtained.

[0065] <<1-4>> Effects According to the vibration sensor 1 of the first embodiment, vibration is measured and the results are fed back to change the zoom magnification (by operating the spot change mechanism 35). This makes it possible to reduce the zoom magnification to expand the measurement range when the vibration is large, and to increase the zoom magnification to improve accuracy when the vibration is small.

[0066] The vibration sensor 1 can reconstruct sound from vibrations when the object 90 is a vibration source that emits sound or an object that vibrates due to sound waves. In this case, the vibration sensor 1 is a sound reconstruction device and is called a laser microphone. The audible range used in everyday conversation is approximately 4 kHz. The minimum frame rate required for the line sensor 50a based on the sampling theorem is twice that, or 8 kHz. However, as already explained, a faster frame rate is required to accurately capture vibration waveforms even when the vibration amplitude is large. Therefore, it is desirable for the line sensor 50a to have a frame rate of 20 kHz to 40 kHz. Since the exposure time of the line sensor 50a cannot be longer than the frame period, an increase in the frame rate shortens the exposure time (i.e., the image becomes darker). According to the first embodiment, the light receiving efficiency is improved, allowing the frame rate to be increased, and the sensor can also be used as a laser microphone to reconstruct sounds that require a high frame rate. Furthermore, since the laser microphone can remotely measure only the vibrations at the point on the object where the laser is irradiated, without passing through air compression waves, it can obtain the necessary sound information even in a noisy environment.

[0067] Furthermore, even when the reduction magnification M is set to the minimum, if the displacement amount δXs of the speckle pattern exceeds the measurement range, it becomes necessary to take other measures, such as (B1) shortening the distance L to the object 90, or (B2) increasing the frame rate for acquiring images to reduce the change in the tilt angle α between successive frames.

[0068] 14 is a diagram showing an example of the hardware configuration of an image processing device 70 of the vibration sensor 1. The image processing device 70 has a processor 101, a memory 102, a storage device 103, and an interface 104. The image processing device 70 may be a computer. The processor 101 is a CPU (Central Processing Unit) or the like. The memory 102 is a volatile semiconductor memory such as a RAM (Random Access Memory). The storage device 103 is a non-volatile storage device such as a hard disk drive (HDD) or a solid state drive (SSD). A detection signal from an area sensor 50 serving as an imaging sensor is input to the interface 104.

[0069] Each function of the image processing device 70 may be realized by a processing circuit. The processing circuit may be dedicated hardware, or may be a processor 101 that executes a program stored in a memory 102. The processor 101 may be any of a processing device, an arithmetic unit, a microprocessor, a microcomputer, and a DSP (Digital Signal Processor).

[0070] Where the processing circuitry is dedicated hardware, the processing circuitry may be, for example, a single circuit, a multiple circuit, a programmed processor, a parallel programmed processor, an ASIC (Application Specific Integrated Circuit), an FPGA (Field-Programmable Gate Array), or any combination thereof.

[0071] When the processing circuit is the processor 101, the program is realized by software, firmware, or a combination of software and firmware. The software and firmware are written as programs and stored in the memory 102. The processor 101 can realize the functions of the image processing device 70 shown in FIG. 1 by reading and executing the programs stored in the memory 102.

[0072] <<2>> Second Embodiment Fig. 15(A) is a schematic perspective view showing the configuration and main light rays of a vibration sensor 2 according to the second embodiment. Fig. 15(B) is a front view showing a circular spot 91 formed on an object 90 by laser light. The light-projecting unit 10 of the vibration sensor 2 is the same as that shown in Fig. 2. The light-receiving unit 40a is provided with a cylindrical lens 62 for collecting light, which has a concave surface in the Y direction, in front of (upstream of) the imaging lens 61. The imaging sensor is not an area sensor 50, but a line sensor 50a extending in the X direction.

[0073] 16A, 16B, and 16C are perspective views, plan views (i.e., views of the light receiving unit 40a in the -Y direction), and side views (i.e., views of the light receiving unit 40a in the X direction) showing the configuration and main light rays of the light receiving unit 40a of the vibration sensor 2 according to the second embodiment. FIGS. 17A, 17B, and 17C are perspective views, plan views (i.e., views of the light receiving unit 40a in the -Y direction), and side views (i.e., views of the light receiving unit 40a in the X direction) showing the configuration and main light rays of the light receiving unit 40a of the vibration sensor 2 according to the second embodiment. The imaging lens 61a is an axially symmetric lens, and, as in the case of FIG. 3, forms an object-side hyperchromatic optical system in combination with the aperture 69. The imaging lens 61a, the aperture 69, and the cylindrical lens 62 together constitute the light receiving optical system 60. The light receiving optical system 60 and the line sensor 50a together constitute the light receiving unit 40a. The imaging lens 61a has a zoom function, and the transfer magnification M from the object plane to the image plane can be changed, for example, from M = 1 to M = 0.5. Figures 16A to 16C show the optical path when M = 1, and Figures 17A to 17C show the optical path when M = 0.5.

[0074] In a cross section in the XZ plane, the focusing cylindrical lens 62 does not have a light focusing effect, and therefore, as in the case of FIG. 3B , the focus is on the speckle pattern observation plane 92. That is, in the X direction, the plane conjugate with the plane of the line sensor 50a is not the object 90 but the speckle pattern observation plane 92, which is located at a distance Ls in front of the imaging lens 61a. The distance between the speckle pattern observation plane 92 and the object 90 is L. In the X direction, the light receiving unit 40a does not acquire an image of the circular spot 91 on the object 90, but rather acquires an image of the circular spot 91 that is defocused by a distance L. The one-dimensional image information acquired by the line sensor 50a is sent to the image processing device 70, which calculates the vibration amount of the speckle pattern.

[0075] In the cross section in the YZ plane, the light is focused onto a circular spot 91 on the object 90 by the action of the condensing cylindrical lens 62. The focal length of the concave cylindrical lens 62 is defined as -f ｃｙｌ and the distance from the cylindrical lens 62 to the observation surface 92 of the speckle pattern is L ｃｙｌ When the distance L is infinite, L ｃｙｌ = | f ｃｙｌ |, then the surface of the object 90 and the surface of the line sensor 50a are conjugate in the YZ plane. When the distance L is finite but sufficiently large, L ｃｙｌ is | f ｃｙｌ When measuring vibration, the position of the cylindrical lens 62 in the Z direction is adjusted by using the position adjustment mechanism 36 to adjust the position of the cylindrical lens 62 in the Z direction according to the distance L. ｃｙｌ is adjusted so that the focus in the Y direction is on the object 90. By inserting the cylindrical lens 62 having a curvature in the Y direction in this way, there is an advantage that the light can be more efficiently guided to the line sensor 50a in the Y direction, and the amount of received light can be increased.

[0076] The one-dimensional waveform of the speckle pattern acquired by the line sensor 50a is similar to the waveform in Fig. 10 in the first embodiment. Therefore, the same algorithm as that in the first embodiment can be used to detect changes in the speckle pattern waveform that shifts in the X direction. The vibration sensor 2 according to the second embodiment differs from the vibration sensor 1 according to the first embodiment in that it can detect only the vibration component in the X direction among the vibration angle components of the object 90.

[0077] As in the second embodiment, even in the case of a light receiving unit 40a using a line sensor 50a, by using a zoom function that changes the transfer magnification from the speckle pattern observation surface 92 to the line sensor 50a, it is possible to improve the measurement accuracy and expand the vibration measurement range in accordance with the magnitude of vibration of the object 90. As described in the first embodiment, the zoom magnification can be changed appropriately each time during the measurement process in accordance with the magnitude of vibration. In this case, the difference from the first embodiment is that it is only necessary to change the transfer magnification in the X direction while keeping the focus on the circular spot 91 on the object 90 in the Y direction. Below, a specific example will be described in which only the transfer magnification in the X direction is changed while keeping the focus in the Y direction.

[0078] The combination of the axially symmetric imaging lens 61a and aperture 69 allows the transfer magnification to be changed while maintaining the object-side hyper-contrast condition. Comparing Figures 16B and 17B, the field width X2 on the speckle pattern observation surface 92 doubles when M is changed from 1x to 0.5x (X2b = 2·X2a). Therefore, in the X direction, in which the shift amount of the speckle pattern waveform is measured, the observation width of the speckle pattern waveform doubles, and the measurable amplitude doubles. In the Y direction, the position adjustment mechanism 36 is fine-tuned so that the focus is always on the object 90 even when the zoom magnification of the imaging lens 61a is changed. This ensures maximum light-gathering effect in the Y direction as well.

[0079] As explained in the first embodiment, by first measuring vibration and then feeding back the results to change the zoom magnification, when the vibration is large, the zoom magnification can be reduced to expand the measurement range, and when the vibration is small, the zoom magnification can be increased to improve accuracy.

[0080] Furthermore, even if the zoom magnification is changed, the light-collecting ability is maintained in the Y direction, so there is also the effect that the amount of light is not lost.

[0081] Furthermore, compared to the first embodiment, the line sensor 50a has a smaller number of pixels than the area sensor 50, and products with a high frame rate are readily available. Therefore, the second embodiment has the advantage of being able to measure vibrations at higher speeds than the first embodiment. The frame rate of the line sensor 50a is, for example, 3 kHz, but is not limited to this.

[0082] In the above description, the line sensor 50a extends in the X direction, but this has the following advantage. When the distance L to the object 90 changes (to L≠L0) from a state in which the first optical axis 11 and the second optical axis 41 intersect on the object 90 (L=L0), the circular spot 91 irradiated by the light-projecting unit 10 and the second optical axis 41 of the light-receiving unit 40a are misaligned in the X direction. The line sensor 50a extends within a plane defined by the first optical axis 11 of the laser from the light-projecting unit 10 and the second optical axis 41 of the light-receiving unit 40a. The light-receiving unit 40a is an optical system that is focused on the object 90 in the Y direction but is significantly out of focus from the object 90 in the X direction. Therefore, even if the position is slightly misaligned in the X direction, light can reach the line sensor 50a, and the speckle pattern can be captured by the line sensor 50a.

[0083] However, the extension direction of the line sensor 50a does not have to be the X direction, as long as the extension direction of the line sensor 50a coincides with the direction in which the cylindrical lens 62 having a concave surface has no curvature, vibration measurement is possible.

[0084] Except for the above, the second embodiment is the same as the first embodiment.

[0085] 18(A), (B), and (C) are a perspective view, a plan view (i.e., a view of the light receiving unit 40b in the -Y direction), and a side view (i.e., a view of the light receiving unit 40b in the X direction) showing the configuration and main light rays of the light receiving unit 40a of a vibration sensor 3 according to embodiment 3. FIGS. 19(A), (B), and (C) are a perspective view, a plan view (i.e., a view of the light receiving unit 40b in the -Y direction), and a side view (i.e., a view of the light receiving unit 40b in the X direction) showing the configuration and main light rays of the light receiving unit 40b of a vibration sensor 3 according to embodiment 3. The vibration sensor 3 for vibration sensing in embodiment 3 is configured by replacing the light receiving unit 40a in FIG. 15 of embodiment 2 with the light receiving unit 40b in FIGS. 18(A) to 18(C) and 19(A) to 19(C). As in the second embodiment, the light projecting unit 10 is the same as that shown in FIG. 2, and projects a circular spot 91 onto the object 90 .

[0086] As shown in FIG. 18A, the light receiving unit 40b includes a cylindrical lens 62a with a convex surface in the X direction in front of an axially symmetric imaging lens 61. In other words, in the third embodiment, the imaging lens 61 and the cylindrical lens 62a constitute a light receiving optical system 60. A line sensor 50a is installed as the imaging sensor, rather than an area sensor 50. The light rays shown in FIGS. 18A to 18C and 19A to 19C are virtual light rays propagating in the reverse direction from the line sensor 50a. In other words, these figures show light rays that can reach the line sensor 50a. The axially symmetric imaging lens 61 is the wide-angle lens shown in FIG. 4 (first embodiment), and the imaging lens 61 alone is not a telecentric optical system on the object side. Furthermore, the imaging lens 61 in the third embodiment includes a zoom mechanism. For example, the focal length can be changed by a factor of two, from f = 20 mm to f = 40 mm. This wide-angle imaging lens 61 alone is not telecentric on the object side, and therefore, as explained in the first embodiment using FIG. 7, it is not possible to obtain a speckle pattern image (one-dimensional waveform) with a sufficiently large outer width on the line sensor 50a.

[0087] However, if the cylindrical lens 62a is placed at an appropriate position in front of the imaging lens 61, an object-side telecentric optical system can be created in the X direction. In FIGS. 18A to 18C and 19A to 19C, the cylindrical lens 62a has a focal length f ６２ In this case, the distance from the principal point of the imaging lens 61 to the principal point of the cylindrical lens 62a is Ls=100 [mm] and the focal length in the X direction is f ６２ If the angle .theta. is equal to the angle .theta., the optical system will be telecentric on the object side in the X direction.

[0088] The third embodiment differs from the second embodiment in the method of optical alignment. In the Y direction, the light receiving unit 40b must be focused on the object 90. Because the cylindrical lens 62a does not have a refractive effect in the Y direction, the focus adjustment mechanism of the imaging lens 61 can be used (for example, by turning a focus adjustment ring) to focus on a circular spot 91 on the object 90. Then, the position adjustment mechanism 36, which moves the position of the cylindrical lens 62a in the optical axis direction (i.e., the Z direction), can be used to adjust the distance Ls so that the lens is telecentric in the X direction. Since the focus is set at a distant distance L in the Y direction, the focus is set at a position close to the cylindrical lens 62a in the X direction, which becomes the observation plane 92 of the speckle pattern.

[0089] 18A to 18C show the case where the focal length of the imaging lens 61 is f=20 mm, and FIGS. 19A to 19C show the case where f=40 mm. The field width X2b of FIG. 19B on the observation surface 92 of the speckle pattern is twice as wide as the field width X2a of FIG. 18B. Therefore, as in the description of the second embodiment, in the X direction in which the shift amount of the speckle pattern waveform is measured, the width for observing the speckle pattern waveform is doubled, and the measurable amplitude is doubled. In the Y direction, the focus of the imaging lens 61 is finely adjusted so that the focus is always on the object 90 even when the zoom magnification of the imaging lens 61 is changed. This ensures that the maximum light-gathering effect is always achieved in the Y direction as well.

[0090] As explained in the first embodiment, by first measuring vibration and then feeding back the results to change the zoom magnification, when the vibration is large, the zoom magnification can be reduced to expand the measurement range, and when the vibration is small, the zoom magnification can be increased to improve accuracy.

[0091] Furthermore, while lenses with a zoom function in a telecentric optical system are generally large, the imaging lens 61 with a zoom function as in the third embodiment is small and inexpensive, making it possible to obtain a vibration sensor 3 that is smaller than the light receiving unit 40 of the first embodiment.

[0092] Furthermore, compared to the first embodiment, the line sensor 50a has a smaller number of pixels than the area sensor 50, and products with a high frame rate are readily available. Therefore, the third embodiment has the advantage of being able to measure vibrations at higher speeds than the first embodiment.

[0093] In the above description, the line sensor 50a extends in the X direction, but this has the following advantage. When the distance L to the object 90 changes (to L≠L0) from a state in which the first optical axis 11 and the second optical axis 41 intersect on the object 90 (L=L0), the circular spot 91 irradiated by the light-projecting unit 10 and the second optical axis 41 of the light-receiving unit 40b are shifted in the X direction. The line sensor 50a extends within a plane defined by the first optical axis 11 of the laser from the light-projecting unit 10 and the second optical axis 41 of the light-receiving unit 40b. The light-receiving unit 40b is an optical system that is focused on the object 90 in the Y direction but is significantly out of focus from the object 90 in the X direction. Therefore, even if the position is slightly shifted in the X direction, light can reach the line sensor 50a, and the speckle pattern can be captured by the line sensor 50a.

[0094] However, the extension direction of the line sensor 50a does not have to be the X direction, as long as the extension direction of the line sensor 50a coincides with the direction of curvature of the cylindrical lens 62a having a convex surface, vibration measurement is possible.

[0095] Other than the above, the third embodiment is the same as the first or second embodiment.

[0096] {4} Fourth Embodiment {4-1} Configuration and Operation FIG. 20(A) is a schematic perspective view showing the configuration and main light beams of a vibration sensor 4 according to the fourth embodiment. FIG. 20(B) is a front view showing a linear spot 91a formed by laser light irradiated onto an object 90 that is the target of vibration sensing. FIG. 21 is a schematic plan view (i.e., a view of the light-projecting unit 10a and the light-receiving unit 40a as viewed in the -Y direction) showing the configuration and main light beams of the vibration sensor 4 according to the fourth embodiment. The vibration sensor 4 detects vibration of the object 90 by irradiating the object 90 (rough surface) with laser light and observing the reflected and scattered light. The vibration sensor 4 includes a light-projecting unit 10a that irradiates the object 90 with laser light, a light-receiving unit 40a that receives the reflected and scattered light generated by the object 90 irradiated with the laser light, and an image processing device 70 as an information processing device that detects vibrations based on a detection signal output from the light-receiving unit 40a. Normally, the light projecting unit 10a and the light receiving unit 40a are housed in the light projecting / receiving head 5 (for example, in a single housing).

[0097] The figure shows the coordinate axes of an X'YZ' Cartesian coordinate system as a first coordinate system used to explain the light-projecting unit 10a. The figure also shows the coordinate axes of an XYZ Cartesian coordinate system as a second coordinate system used to explain the light-receiving unit 40a, the target object 90, and the observation surface 92. The central ray of the laser light emitted from the light-projecting unit 10a is parallel to the Z' axis, and the central ray of the light received by the light-receiving unit 40a is parallel to the Z axis. The Y axis is a coordinate axis normal to a plane including the Z' axis and the Z axis. The X' axis is a coordinate axis perpendicular to both the Y axis and the Z' axis. The X axis is a coordinate axis perpendicular to both the Y axis and the Z axis.

[0098] The light-projecting unit 10a has a laser light source 20 and a light-projecting optical system 30a that projects laser light emitted from the laser light source 20 as a line spot 91a onto the object 90. The light-receiving unit 40a has a line sensor 50a and a light-receiving optical system 60a that focuses the reflected and scattered light of the laser light irradiated onto the object 90 onto the line sensor 50a (i.e., onto the light-receiving surface of the line sensor 50a). The image processing device 70 calculates the amount of movement between frames of a speckle pattern generated in the reflected and scattered light received by the line sensor 50a, and estimates (i.e., calculates) the vibration of the object 90 based on this amount of movement.

[0099] The light-projecting unit 10a and the light-receiving unit 40a are arranged so that a first optical axis 11, which is the optical axis of the light-projecting unit 10a, and a second optical axis 41, which is the optical axis of the light-receiving unit 40a, intersect on the target object 90. The light-projecting unit 10a and the light-receiving unit 40a are arranged so that a first direction (X direction) in which the line sensor 50a extends (i.e., the light-receiving surface of the line sensor 50a extends) is the same as the direction in which the linear spot 91a extends. Here, the optical axis of the light-projecting unit 10 may be the axis of the laser light emitted from the light-projecting unit 10. Furthermore, the optical axis of the light-receiving unit 40 may be the axis of reflected and scattered light that can be received by the line sensor 50.

[0100] The light receiving optical system 60a is asymmetric with respect to the X direction, which is a first direction, and the Y direction, which is a second direction perpendicular to the X direction (i.e., axially asymmetric with respect to the X and Y axes). In the X direction, which is the longitudinal direction of the line sensor 50a (i.e., the longitudinal direction of the light receiving surface of the line sensor 50a), the image of the object 90 (i.e., the image 93 of the linear spot 91a) formed by the light receiving optical system 60a is not focused on the light receiving surface of the line sensor 50a. In the Y direction, which is the lateral direction of the line sensor 50a (i.e., the lateral direction of the light receiving surface of the line sensor 50a), the image of the object 90 (i.e., the image 93 of the linear spot 91a) formed by the light receiving optical system 60a is focused on the light receiving surface of the line sensor 50a.

[0101] In the fourth embodiment, the light projecting unit 10a and the light receiving unit 40a are arranged side by side in the X direction (or the X' direction). In addition, the light projecting optical system 30a preferably includes a spot changing mechanism 35 that changes the size of the linear spot 91a in the X direction.

[0102] In the fourth embodiment, the projection optical system 30a includes an X-direction beam width conversion element 34, which is a set of two cylindrical lenses 32, 33 that form the linear spot 91a. The projection optical system 30a includes the concave cylindrical lens 32 as an axisymmetric optical system. The X-direction beam width conversion element 34 is an optical system (for example, a lens or a lens group) that can change the X-direction width (length Bx) of the laser light emitted from the laser light source 20.

[0103] The light projecting unit 10a also has a collimating lens 31. A spot changing mechanism 35 that changes the size of the linear spot 91a in the Y direction is a mechanism for adjusting (for example, by manual operation) the distance Lc between the light emitting point of the laser light source 20 and the collimating lens 31.

[0104] Fig. 22(A) is a schematic side view (i.e., a view of the light-projecting unit 10a viewed in the X' direction) showing the configuration and main light rays of the light-projecting unit 10a of the vibration sensor 4 according to embodiment 4. Fig. 22(B) is a schematic plan view (i.e., a view of the light-projecting unit 10a viewed in the -Y direction) showing the configuration and main light rays of the light-projecting unit 10a of the vibration sensor 4.

[0105] The first optical axis 11 of the light-projecting unit 10a and the second optical axis 41 of the light-receiving unit 40a intersect on the object 90. It is desirable to provide a mechanism for adjusting the direction of the first optical axis 11 of the light-projecting unit 10a or the direction of the second optical axis 41 of the light-receiving unit 40a so that the first optical axis 11 of the light-projecting unit 10a and the second optical axis 41 of the light-receiving unit 40a intersect even if the distance from the vibration sensor 4 to the object 90 changes.

[0106] 22A and 22B show a beam emitted from a single point of the laser light source 20. In FIGS. 22A and 22B, the laser light source 20 is, for example, a semiconductor laser. The beam (laser light) emitted from the semiconductor laser has a divergence. The beam is converted into a roughly parallel beam by a collimating lens 31. The parallel beam is converted into a beam diverging in the X' direction by an X-direction beam width conversion element 34, which serves as a beam width conversion unit installed downstream of the collimating lens 31, and is irradiated onto a distant object 90 as a linear spot 91a extending in the X direction. Here, the collimating lens 31 is finely adjusted back and forth in the optical axis direction (i.e., the Z' direction) using a spot changing mechanism 35, thereby adjusting the Y-direction width of the linear spot 91a on the object 90 to be minimized. In other words, the laser light is focused in the Y direction on the object 90, which is located a finite distance from the laser light source 20. Here, it is assumed that the object 90 is located at a distance ranging from several tens of centimeters to approximately 10 meters from the vibration sensor 4 .

[0107] 22A and 22B, an example of the configuration of the X-direction beam width conversion element 34 includes a cylindrical lens 32 which is a concave lens and a cylindrical lens 33 which is a convex lens. The cylindrical lenses 32 and 33 have a curvature in the X' direction, and the focal length of each lens is f ３２ , f ３３ For example, f ３２ =-25 [mm], f ３３ When the light emitted from the collimator lens 31 is completely collimated, the distance between the cylindrical lens 32, which is a concave lens, and the cylindrical lens 33, which is a convex lens, is f = 50 [mm]. ３２ +f ３３ = 25 [mm], the light emitted from the cylindrical lens 33 has a rotational angle of f ３２ / | f ３３ | = 2 times expanded collimated beam. Focal length f ３３ and f ３２ By changing the value of , the width of the light beam can be converted into a collimated beam of any width.

[0108] 22A and 22B, the light is focused at a finite position in the Y direction, so the light beam emitted from the collimator lens 31 is not a collimated light beam but a weakly convergent light beam, and the lens spacing at which the collimated light beam is emitted is slightly different from the value described above. In this way, the X-direction beam width conversion element 34 can make the beam width in the X' direction (i.e., length Bx) on the object 90 different from the length in the Y direction (i.e., make it axially asymmetric). In this way, the laser light irradiated on the object 90 is focused in the Y direction to form a linear spot 91a having a length Bx in the X direction.

[0109] FIG. 23(A) is a schematic side view (i.e., a view of the light receiving unit 40a in the X direction) showing the configuration and main light rays of the light receiving unit 40a of the vibration sensor 4 according to the fourth embodiment. FIG. 23(B) is a schematic plan view (i.e., a view of the light receiving unit 40a in the -Y direction) showing the configuration and main light rays of the light receiving unit 40a of the vibration sensor 4. In the fourth embodiment, the light receiving unit 40a includes a line sensor 50a, an imaging lens 61a, and a cylindrical lens 62. The imaging lens 61a, the aperture 69, and the cylindrical lens 62 constitute a light receiving optical system 60a. The imaging lens 61a is an object-side telecentric optical system or a hyper-telecentric optical system. FIGS. 23(A) and 23(B) show an example in which the imaging lens 61a is an object-side telecentric optical system. An object-side telecentric optical system is an optical system in which chief rays 96a to 96d from each image height directed from the lens to the object are parallel to the second optical axis 41. A hypercentric optical system is a special optical system in which chief rays 96a to 96d from each image height directed from the lens to the object converge toward the second optical axis 41.

[0110] The surface of the object 90 is rough, and the reflected and scattered light from the linear spot 91a generates a speckle pattern throughout the entire space. In Figures 23A and 23B, the points at both ends of the light-receiving surface of the line sensor 50a in the X direction are designated P1 and P3, and the central point is designated P2. Figures 23A and 23B depict light rays that are reflected and scattered on the object 90 and reach points P1, P2, and P3. As shown in Figure 23B, in the X direction, the imaging lens 61a of the light-receiving unit 40a focuses the speckle pattern on an observation surface 92. That is, in the X direction, the speckle pattern that appears on the observation surface 92 is transferred to the light-receiving surface of the line sensor 50a.

[0111] By inserting a condensing cylindrical lens 62 having a concave curvature only in the Y direction, the focal position on the object side in the Y direction can be moved from the observation surface 92 to the target object 90 located far away. The focal length of the cylindrical lens 62 is f ６２ and the distance between the cylindrical lens 62 and the observation surface 92 is L ６２ For example, specifically, f ６２ = -50 mm. In this case, L ６２ = | f ６２ If |=50 mm, the focus will be at infinity in the Y direction. ６２ If you make it a little larger than 50 mm, you can focus on a point closer than infinity.

[0112] The focus in the Y direction is adjusted on the object 90 by using a spot position adjustment mechanism 64 that adjusts the position of the cylindrical lens 62 in the Z direction according to the distance to the object 90. In other words, the line sensor 50a and the object 90 are at conjugate positions in the Y direction. Therefore, light reflected and scattered from the object 90 is efficiently propagated in the Y direction to the line sensor 50a.

[0113] As described above, by irradiating the object 90 with a linear spot 91a having a narrow width in the Y direction and focusing on the object 90 in the Y direction by the axially asymmetric light-receiving optical system 60a, an image 93 of the linear spot 91a having a narrow width in the Y direction is irradiated onto the line sensor 50. This allows the reflected and scattered light from the object 90 to be efficiently transmitted to the line sensor 50, making it possible to function as a vibration sensor even with a weak power laser light. If the spot irradiated onto the object 90 is circular and wide in the Y direction, only a wide beam can be focused onto the line sensor 50 in the Y direction, resulting in a large amount of light leaking outside the line sensor 50. Furthermore, if the light-receiving optical system 60a is not focused on the object 90 in the Y direction, a blurred image in the Y direction will be projected onto the line sensor 50, resulting in a large amount of light leaking outside the line sensor 50.

[0114] On the other hand, as will be described in detail later, in order to observe speckles in the X direction, it is necessary to irradiate a linear spot 91a that is wide in the X direction, and the focal position in the X direction of the light-receiving optical system 60a must also be significantly deviated from the object 90. For this reason, in this embodiment, in the optical system for observing a speckle pattern in the X direction, a linear spot 91a that is narrow in the Y direction is irradiated, and the axially asymmetric light-receiving optical system 60a is used to focus the light on the object 90 in the Y direction, thereby achieving highly efficient light propagation.

[0115] However, if the focal position in the Y direction on the object 90 deviates from the position of the linear spot 91a, no light will be propagated to the line sensor 50a, so it is necessary to fine-tune the line sensor 50a or the cylindrical lens 62 in the Y direction so that the linear spot 91a is imaged on the line sensor 50a in the Y direction.

[0116] 24A to 24C are diagrams showing the overlap of the light-receiving surface of the line sensor 50a and the speckle pattern. In the Y direction, the light-receiving surface of the line sensor 50a and the surface of the object 90 are conjugate. Therefore, the image 93 of the linear spot 91a of the object 90 on the surface of the line sensor 50a has a narrow width in the Y direction. In other words, the reflected and scattered light is focused on the light-receiving surface of the line sensor 50a in the Y direction. FIGS. 24A to 24C show examples of the image 93 of the linear spot 91a projected onto the surface of the line sensor 50a. As shown, the image 93 of the linear spot 91a has a narrow width in the Y direction and is elongated in the X direction. The image 93 of the linear spot 91a has a brightness distribution in the X direction according to the length Bx of the linear spot 91a in the X direction. FIG. 24A shows a state in which the light receiving surface of the line sensor 50a and the image 93 of the linear spot 91a overlap, and in this state, the vibration sensor 4 of the fourth embodiment can operate normally.

[0117] However, as shown in Figure 24 (B), if the Y-direction position of the image 93 of the linear spot 91a is deviated from the position of the second optical axis 41 of the light-receiving unit 40a, the light-receiving surface of the line sensor 50a and the image 93 of the linear spot 91a do not overlap, and the speckle pattern cannot be observed by the line sensor 50a.

[0118] 24C, if the extension direction of the image 93 of the linear spot 91a is inclined with respect to the extension direction of the light receiving surface of the line sensor 50a, a speckle pattern waveform with a sufficiently large number of pixels cannot be observed with the line sensor 50a. For this reason, it is desirable to provide spot position adjustment mechanisms 63 and 64 and a spot rotation adjustment mechanism 65.

[0119] An example of the spot position adjustment mechanism 63 is a moving stage for finely adjusting the cylindrical lens 62 in the Y direction. If the position of the light ray incident from the center of the cylindrical lens 62 is shifted in the Y direction, the beam emission direction is deflected. Therefore, by finely adjusting the cylindrical lens 62 in the Y direction, the position of the beam focused by the imaging lens 61a can be shifted in the Y direction. In other words, the state of FIG. 24B can be adjusted to the state of FIG. 24A. Therefore, even if the Y direction position of the image 93 of the linear spot 91a is deviated from the optical axis position of the light receiving unit 40a in the initial state, the spot position adjustment mechanism 63 can be adjusted so that the image 93 of the linear spot 91a can be received by the line sensor 50a.

[0120] An example of the spot rotation adjustment mechanism 65 is a rotation stage for finely adjusting the cylindrical lens 62 around the Z axis. When the cylindrical lens 62 is rotated around the Z axis, the image 93 of the linear spot 91a rotates within the XY plane. By rotating the rotation stage of the spot rotation adjustment mechanism 65 while observing the output waveform from the line sensor 50a so that an output is obtained from all pixels, the state shown in FIG. 24C can be adjusted to the state shown in FIG. 24A.

[0121] The method for adjusting the position of the image 93 of the linear spot 91a is not limited to the above example. For example, by adjusting the tilt of the entire light receiving unit 40a around the X axis, the image 93 of the linear spot 91a can be moved in the Y direction on the light receiving surface of the line sensor 50a. Alternatively, a stage may be provided that shifts the line sensor 50a in the Y direction relative to the imaging lens 61a.

[0122] Similarly, the method of spot rotation adjustment is not limited to the above example. For example, a mechanism for rotating the entire light receiving unit 40a around the Z axis may be provided. Alternatively, a rotation stage may be provided for adjusting the rotation of the line sensor 50a around the Z axis relative to the imaging lens 61a.

[0123] After proper alignment is performed and the light-receiving pixels of the line sensor 50a are superimposed on the image 93 of the linear spot 91a as shown in Fig. 24(A), vibration sensing is started. As in the first and second embodiments, the typical magnitude s of the waveform of the speckle pattern is ａ ' is the shift amount δX between consecutive frames during vibration, and 0.1 s ａ ´<|δX ｍａｘ |<0.5 s ａ It is desirable that the speckle pattern is in the range of '. In order to adjust the speckle pattern, in the first and second embodiments, the spot changing mechanism 35 is used to adjust the position of the collimator lens 31 in the Z-axis direction, and the size of the circular spot 91 is adjusted. However, in the fourth embodiment, the spot changing mechanism 35 is not used, and the beam width adjusting mechanism 38 provided in the X-direction beam width converting element 34 can be used. The beam width adjusting mechanism 38 provided in the X-direction beam width converting element 34 is an example of a spot changing mechanism.

[0124] <<4-2>> Effects As described above, by using the vibration sensor 4 according to the fourth embodiment, the linear spot 91a of the laser light emitted from the light-projecting unit 10a is focused in the Y direction on the object 90, and the light-receiving unit 40a is used to focus the reflected and scattered light of the linear spot 91a on the object 90 only in the Y direction and receive it with the line sensor 50a, thereby making it possible to receive light more efficiently than with conventional techniques. Therefore, even when a laser light with a low power is used, it is possible to quickly acquire the one-dimensional waveform of the speckle pattern and detect vibrations.

[0125] Furthermore, when the extension direction of the line sensor 50a is aligned with the X direction in which the light-projecting unit 10a and the light-receiving unit 40a are aligned, even if the distance L shown in FIG. 24 changes, the image 93 of the linear spot 91a of the speckle pattern is unlikely to deviate from the light-receiving surface of the line sensor 50a, as shown in FIGS. 25(A) and 25(B).

[0126] Furthermore, since the size of the line-shaped spot 91a of the light-projecting unit 10a on the object 90 can be changed only in the extension direction, the size of the speckle pattern waveform received by the line sensor 50a can be changed. Therefore, the size of the speckle pattern can be optimized according to the magnitude of the vibration, thereby improving the accuracy of vibration detection.

[0127] Furthermore, when the structure for converting the laser light from light projecting unit 10a into a line beam is configured with a pair of cylindrical lenses 32, 33, the size of the speckle pattern can be changed without changing the width of the line beam in the focusing direction. Since the size of the speckle pattern can be changed without changing the width of the line beam in the focusing direction, there is little loss of light intensity.

[0128] Furthermore, since the non-axisymmetric optical system of the light receiving unit 40a includes a cylindrical concave lens, the size of the speckle pattern can be changed without changing the width of the line-shaped beam in the focusing direction.

[0129] In the above description, the extension direction of the image 93 of the linear spot 91a (i.e., the third direction in which the linear spot extends) and the extension direction of the line sensor 50a are both the X direction, but the extension directions do not necessarily have to be the X direction as long as both extension directions are facing the same direction. However, when the extension direction is the X direction, there are the following advantages.

[0130] Fig. 25 is a schematic plan view showing image displacement when the distance changes in the vibration sensor 4 according to embodiment 4. Fig. 26(A) to (D) are schematic plan views showing image displacement when the distance changes in the vibration sensor 4 according to embodiment 4.

[0131] As shown in Figure 25, assume that the distance L to the object 90 changes (becomes L≠L0) from a state where the first optical axis 11 and the second optical axis 41 intersect on the object 90 (a state where L = L0).

[0132] Both the image 93 of the linear spot 91a and the light receiving surface of the line sensor 50a extend in the X direction, and when L = L0, the image 93 of the linear spot 91a and the light receiving surface of the line sensor 50a overlap as shown in Fig. 26(A). Even if the distance L is slightly shifted so that L ≠ L0, the image 93 of the linear spot 91a is long in the X direction, and therefore the overlap between the image 93 of the linear spot 91a and the light receiving surface of the line sensor 50a remains as shown in Fig. 26(B).

[0133] When the image 93 of the linear spot 91a and the light receiving surface of the line sensor 50a are inclined with respect to the X direction and L = L0, the image 93 of the linear spot 91a and the light receiving surface of the line sensor 50a can be properly superimposed as shown in Figure 26(C), and there is no problem with the function of the vibration sensor 1. However, if the distance L in Figure 26(C) is slightly shifted so that L ≠ L0, the overlap between the image 93 of the linear spot 91a and the light receiving surface of the line sensor 50a is misaligned as shown in Figure 26(D). In the case of Figure 26(D), the light receiving surface of the line sensor 50a and the image 93 of the linear spot 91a do not overlap, so the line sensor 50a cannot observe the image 93 of the linear spot 91a. Therefore, it is necessary to make another adjustment to superimpose the two, as shown in Figures 24(A) to 24(C).

[0134] As described above, it is desirable that the extension direction of the image 93 of the linear spot 91a and the extension direction of the light receiving surface of the line sensor 50a are both the X direction.

[0135] Except for the above, the fourth embodiment is the same as any of the first to third embodiments.

[0136] 1 to 4 vibration sensor, 5 light emitting / receiving head, 10, 10a light emitting unit, 11 first optical axis, 20 laser light source, 30 light emitting optical system, 31 collimating lens, 32 cylindrical lens, 33 cylindrical lens, 34 X-direction beam width conversion element, 35 spot adjustment mechanism, 36 position adjustment mechanism, 38 beam width adjustment mechanism, 40, 40a, 40b light receiving unit, 41 second optical axis, 50 area sensor (image sensor), 50a line sensor (image sensor), 60, 60a light receiving optical system, 61, 61a imaging lens, 62 cylindrical lens, 63, 64 spot position adjustment mechanism, 65 spot rotation adjustment mechanism, 69 aperture, 70 image processing device, 90 object, 91 spot, 91a Line-shaped spot, 92 observation surface, 93 spot image, X first direction, Y second direction, α tilt angle, δX shift amount (movement amount).

Claims

1. A vibration sensor comprising: a light-projecting unit having a laser light source and a light-projecting optical system that projects the laser light emitted from the laser light source as a spot onto an object; a light-receiving unit having an image sensor and a light-receiving optical system that focuses the reflected and scattered light of the laser light irradiated on the object onto the image sensor; and an image processing device that calculates the amount of movement between frames of a speckle pattern generated in the reflected and scattered light received by the image sensor and measures the vibration of the object based on the amount of movement, wherein the light-receiving optical system includes an imaging lens and is focused on a virtual plane that is closer to the light-receiving optical system than the object on the object side, between the object and the light-receiving optical system, on the object side where the object exists; and the light-receiving optical system is configured so that the absolute value of the angle that a first light ray included in the light beam incident on the outermost part of the light-receiving surface of the image sensor makes with the optical axis of the light-receiving unit is smaller than the cone half angle of the light beam on the object side, which is determined by the numerical aperture of the imaging lens.

2. The vibration sensor according to claim 1, wherein the imaging sensor is an area sensor.

3. A vibration sensor according to claim 1 or 2, characterized in that the light projection optical system includes a spot changing mechanism for changing the size of the spot on the object.

4. The vibration sensor according to claim 3, wherein said image processing device causes said spot changing mechanism to change the size of said spot on said object based on said measured vibration.

5. The vibration sensor described in claim 1, characterized in that the imaging sensor is a line sensor extending in a first direction, the light receiving optical system is an optical system that is axially asymmetric with respect to the first direction and a second direction perpendicular to the first direction, and in the first direction, the image of the object formed by the light receiving optical system is focused in front of the light receiving surface of the line sensor, and in the second direction, the image of the object formed by the light receiving optical system is focused on the light receiving surface of the line sensor.

6. The vibration sensor described in claim 5, characterized in that the light receiving optical system includes an imaging lens that is composed of an axially symmetric telecentric lens, and in addition to the imaging lens, includes a cylindrical lens that has a concave surface in the second direction.

7. A vibration sensor according to claim 5 or 6, wherein said light receiving optical system includes a first zoom mechanism that gives said imaging lens a zoom function.

8. The vibration sensor described in claim 5, characterized in that the light receiving optical system includes an imaging lens that is composed of a lens that is axially symmetric with respect to the first direction and the second direction, and that in addition to the imaging lens, includes a cylindrical lens that has a convex surface in the first direction.

9. A vibration sensor as described in any one of claims 5 to 8, characterized in that the projection optical system includes a spot changing mechanism that changes the size of the spot on the object, the projection optical system projects a linear spot as the spot on the object, a third direction in which the linear spot extends is the same as the first direction, and the spot changing mechanism changes the size of the linear spot in the third direction.

10. The vibration sensor according to claim 9, wherein the light projection optical system includes a pair of cylindrical lenses that form the linear spot.

11. The vibration sensor according to any one of claims 1 to 10, wherein the image processing device reconstructs sound based on the vibration of the object.

Images