Vibration sensor

Abstract

A vibration sensor (1) comprises: a light projection unit (10) having a laser light source (20) and a light projection optical system (30) that projects a spot (91) of laser light onto an object (90); a light reception unit (40) having an imaging sensor (50) and a light reception optical system (60) that condenses, on the imaging sensor (50), reflected and scattered light of the laser light with which the object is irradiated; and an image processing device (70) that measures vibration of the object (90) on the basis of the amount of inter-frame movement of a speckle pattern generated in the reflected and scattered light received by the imaging sensor (50). A first optical axis (11), which is the optical axis of the light projection unit (10), and a second optical axis (41), which is the optical axis of the light reception unit (40), intersect on the object (90). The light projection optical system (30) includes a spot-changing mechanism that changes the size of a spot (91) on the object (90). The image processing device (70) causes the spot-changing mechanism to change the size of the spot (91) on the object (90) on the basis of the measured vibration.

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 vibration 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 a spot of laser light emitted from the laser light source 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 a first optical axis that is the optical axis of the light-projecting unit and a second optical axis that is the optical axis of the light-receiving unit intersect on the object, the light-projecting optical system includes a spot changing mechanism that changes the size of the spot on the object, and the image processing device causes the spot changing mechanism to change the size of the spot on the object based on the measured vibration.

[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] 4A is a schematic perspective view showing the configuration and main light rays of a vibration sensor according to a first embodiment, and FIG. 4B is a front view showing a spot formed on an object by laser light. (A) 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. 4B 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. (A) 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. 4B 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. (A) and (B) are schematic plan views showing vibration of an object, and (C) and (D) are diagrams showing movement of a speckle pattern generated by vibration of the object shown in FIGS. 4A and 4B. (A) and (B) are diagrams showing an example of a one-dimensional speckle pattern waveform that moves due to vibration. (A) and (B) are diagrams showing an example of a process for calculating the vibration amount of a speckle pattern from waveform matching. 1A and 1B are diagrams showing an example of a process for calculating the vibration amount of a speckle pattern from waveform matching; 1C are diagrams showing an example of a speckle pattern (spot size 1.4 [mm]); 1D are diagrams showing an example of a speckle pattern change; 1E are diagrams showing an example of the sum of absolute differences; 1F are diagrams showing an example of superposition of speckle pattern waveforms between successive frames; 1G are diagrams showing examples of speckle patterns and cross-sectional profiles with different spot sizes; 1H are diagrams showing examples of R with different spot sizes; ＳＡＤ1 is a diagram illustrating an example of a hardware configuration of a vibration sensor according to a first embodiment; FIG. 2 is a diagram illustrating an example of a hardware configuration of a vibration sensor according to a second embodiment; FIG. 3 is a diagram illustrating an example of a hardware configuration of a vibration sensor according to a first embodiment; FIG. 4 is a diagram illustrating an example of a hardware configuration of a vibration sensor according to a second embodiment; FIG. 5 is a diagram illustrating an example of a hardware configuration of a vibration sensor according to a first embodiment; FIG. 6 is a diagram illustrating an example of a hardware configuration of a vibration sensor according to a first embodiment; FIG. 7 is a diagram illustrating an example of a hardware configuration of a vibration sensor according to a second embodiment; FIG. 8 is a diagram illustrating an example of a hardware configuration of a vibration sensor according to a first embodiment; FIG. 9 is a diagram illustrating an example of a hardware configuration of a vibration sensor according to a second embodiment; 1A is a schematic side view showing the configuration of a light receiving unit and main light rays of a vibration sensor according to a third embodiment, and FIG. 1B is a schematic plan view showing the configuration of a light receiving unit and main light rays of a vibration sensor according to a third embodiment. (A) to (C) are diagrams showing the overlap of a light receiving surface of a line sensor and an image of a speckle pattern (image of a line-shaped spot). (A) is a schematic side view showing a first configuration example of a light projecting unit of a vibration sensor according to a third embodiment and main light rays, and (B) to (D) are schematic plan views showing the first configuration example of a light projecting unit and main light rays. (A) is a schematic side view showing a second configuration example of a light projecting unit of a vibration sensor according to a third embodiment and main light rays, and (B) to (D) are schematic plan views showing the second configuration example of a light projecting unit and main light rays. (A) to (D) are schematic plan views showing image shifts when the distance changes in the vibration sensor according to the third embodiment. (A) to (D) are diagrams showing image shifts when the distance changes in the vibration sensor according to the third embodiment.

[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 causes the spot changing mechanism 35 to change the size of the spot 91 on the object 90 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. 3A is a schematic side view (i.e., a view of the light receiving unit 40 in the X direction) showing the configuration and main light rays of the light receiving unit 40 of the vibration sensor 1 according to the first embodiment. FIG. 3B is a schematic plan view (i.e., a view of the light receiving unit 40 in the -Y direction) showing the configuration and main light rays of the light receiving unit 40 of the vibration sensor 1. In the first embodiment, the light receiving unit 40 includes an area sensor 50 as an image sensor and an imaging lens 61. The imaging lens 61 constitutes the light receiving optical system 60 and is an object-side telecentric optical system or a hyper-trick optical system. FIGS. 3A and 3B show an example in which the imaging lens 61 is a hyper-trick optical system. An object-side telecentric optical system is an optical system in which the group of chief rays from each image height directed from the lens to the object is parallel to the optical axis (i.e., the second optical axis 41). Specifically, it is an optical system in which the group of chief rays from each image height traveling from the lens to the object is parallel to such an extent that they do not intersect with the optical axis within the range of the distance from the vibration sensor 1 to the object 90. The hyperchromatic optical system is a special optical system in which the group of chief rays from each image height traveling from the lens to the object converges toward the optical axis (i.e., the second optical axis 41).

[0020] 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 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 the first optical axis 11 and the second optical axis 41 intersect even if the distance to the target 90 changes.

[0021] The surface of object 90 is rough, and the light reflected and scattered by object 90 from circular spot 91 irradiated by light projector 10 generates a speckle pattern throughout the entire space. An image of the speckle pattern generated in the space is acquired by light receiver 40 (i.e., the image is formed on the light-receiving surface of area sensor 50 of light receiver 40). The position where the speckle pattern image is acquired is speckle pattern observation surface 92.

[0022] The plane conjugate with the light-receiving surface of area sensor 50 is not object 90 but a plane at a distance Ls in front of imaging lens 61, and this plane is called speckle pattern observation plane 92. The distance between speckle pattern observation plane 92 and object 90 is L. In other words, light-receiving unit 40 does not acquire an image of circular spot 91 on object 90, but rather acquires an image of circular spot 91 that is defocused by a large distance L. Image information acquired by area sensor 50 is sent to image processing device 70, where the vibration amount of the speckle pattern is calculated using an algorithm described below.

[0023] 4A and 4B 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 the first embodiment, the main light rays, and the displacement (e.g., vibration) of the object 90. FIGS. 4A and 4B show the displacement caused by the vibration of the object 90. FIGS. 4C and 4D are diagrams showing the movement on the observation plane 92 of the speckle pattern caused by the vibration of the object 90 shown in FIGS. 4A and 4B, respectively.

[0024] As shown in Figures 4A and 4B, the speckle pattern observed on the observation surface 92 is a random granular pattern, as shown in Figures 4C and 4D, for example. When the object 90 faces the light receiving unit 40 as shown in Figure 4A, the speckle pattern observed on the observation surface 92 of the speckle pattern is shown in Figure 4C. The imaging lens 61 causes the area sensor 50 to acquire the two-dimensional image of Figure 4C. 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 angular vibration modes include vibrations in all directions within the XY plane, the direction of vibration is considered to be constant.

[0025] For simplicity, a case in which the object 90 vibrates around the Y axis will be described. FIG. 4B 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. 4A, but the speckle pattern image acquired by the area sensor 50 is shifted by δX in the X direction from the image in FIG. 4C, as shown in FIG. 4D. In FIGS. 4C and 4D, 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.

[0026] Fig. 5 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. 5 are one-dimensional waveforms corresponding to the profiles on the cross-sectional line 96 in Figs. 4(C) and (D), and are one-dimensional cross-sectional waveforms of the output image of the area sensor 50. As shown in Fig. 5, due to the tilt angle α (angle change) of the object 90, wave(a) shifts in the X direction by a shift amount δX, as shown in wave(b). 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.

[0027] <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. 5 , 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.

[0028] 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 (1): 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 number x is calculated. ＳＡＤ The 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 (2). ＳＡＤ The x that minimizes (x) is defined as the shift amount δX.

[0029]

[0030] 6A and 6B, and 7A and 7B are diagrams showing an example of a process for calculating the vibration amount of a speckle pattern from waveform matching. In FIG. 6A, the horizontal axis represents x and the vertical axis represents R. ＳＡＤ6(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. 6(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. 6(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 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 (3).

[0031]

[0032] FIG. 7A shows an example of the amount of movement X(n) from the initial position in the nth frame. In the case of vibration, data should be distributed above and below the line where the vertical axis is zero. However, 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 amount of movement of the speckle pattern image and the gradual movement of the irradiation position of the spot 91 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 we are interested in.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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 (3) is proportional to the vibration amount of the object 90.

[0037] In the above explanation, calculations were performed on a one-dimensional waveform at the cross-sectional line 96 in FIGS. 4C and 4D, 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 (4) can be used: ＳＡＤ Find the (x, y) that gives the minimum value of δX = √(x ２ +y ２ ) can be used.

[0038]

[0039] The above processing is performed by the image processing device 70 shown in FIG.

[0040] <<1-2>> Description of the Problem: When sensing vibration from the image movement of a speckle pattern, there is a problem in that the range of vibration angles that can be measured is narrow. Specific data will be used for explanation. In FIG. 1 , a semiconductor laser (wavelength 670 [nm]) is used as the laser light source 20, and a beam with a diameter of 1.4 [mm] is irradiated onto an object 90 having a rough surface as a circular spot 91. In reality, due to a distribution in the radiation angle from the light-emitting point of the semiconductor laser, the circular spot 91 is not a perfect circle but an oval shape, with a width of approximately 1.4 [mm] in the X direction and 0.7 [mm] in the Y direction. Here, such a spot 91 is also referred to as a circular spot 91.

[0041] FIG. 8 shows an example of an image of a speckle pattern generated on an observation surface 92 of a speckle pattern located at a distance L = 500 mm from the object 90, acquired by the area sensor 50. The imaging lens 61 has a magnification of 2x, and the pixel size of the area sensor 50 is 4.5 μm. The area sensor 50 can capture a large range of 1600 × 1200 pixels, but to measure the movement of the speckle pattern, it is sufficient to crop the image to an appropriate pixel size and perform processing only within that range. FIG. 8 shows an image cropped to 800 × 600 pixels. The actual dimensions of FIG. 8 are 3.6 mm × 2.7 mm because the pixel size is 4.5 μm, and because the lens magnification is 2x, the size of the speckle pattern on the observation surface 92 is 1.8 mm × 1.35 mm. A large number of granular patterns, each of which is not identical in shape but is roughly the same size, are randomly arranged, and this is called a speckle pattern. The size s of this speckle pattern ０ It is known that s is expressed by the following equation (5) using wavelength λ, distance L, and spot size W. ０ λ·L / W (5) When formula (5) is calculated in the above case, the size s of the speckle pattern０ is approximately 0.24 mm.

[0042] 9A shows a plot of the intensity waveform of the cross-sectional line 94 in FIG. 8. The size of the pattern in the X direction is approximately 90 [pixel], so the dimension of the speckle pattern on the observation surface 92 is s ａ This is converted to 0.2 mm. ０ and ａ It can be seen that the values ​​are roughly close to each other. When the object 90 vibrates, the speckle pattern waveform measured in the frame next to that of FIG. 9A is that shown in FIG. 9B. In order to find the amount of movement of the speckle pattern waveform between these two frames, R defined by Equation (1) is used. ＳＡＤ The calculation results are shown in Figure 10. The pixel movement amount was calculated in the range of x = -130 [pixel] to +130 [pixel]. ＳＡＤ The pixel shift amount that gives the minimum value of δX is estimated to be the actual shift amount δX of the speckle pattern due to vibration. １ However, a significant minimum value is also seen at the position of x = 5 [pixel], and the actual pixel movement amount is δX ２ If noise in the measurement is superimposed on the signal, the X that gives the minimum value is δX １ rather than δX ２ It is easy to imagine that it could change to

[0043] In order to analyze the state of these two pixel movement amounts in detail, the waveform of FIG. 9(B) is compared with the waveform of FIG. 9(A) by δX １ = -87 [pixel] and δX ２ 11(A) and (B) show graphs that are overlaid after shifting by sa = 5 [pixels]. It can be seen that both of the graphs in Fig. 11(A) and (B) roughly match. As such, the waveform of the speckle pattern has repeated peaks and valleys at a period of 90 [pixels], which corresponds to sa ~ 0.2 [mm], so R ＳＡＤ The minimum value appears at roughly 90 [pixel] intervals. ＳＡＤIn an algorithm in which the x that gives the minimum value of is the actual δX, there is a possibility that a large error will occur between these minimum values.

[0044] That is, the conventional technique disclosed in Patent Document 1 has a problem in that the measurable range is limited. The measurable range is the range in which the shift amount δX of the speckle pattern is larger than the size s of the speckle pattern. ０ This is a range not exceeding half of the value of −0.5·s, and is expressed by the following formula (6). ０ <δX<0.5 s ０ (6)

[0045] On the other hand, when the vibration is small and the shift amount δX of the speckle pattern generated by the vibration is smaller than the size s of the speckle pattern, ０ For example, if the maximum value of δX during vibration is 0.1 s ０ If the value is smaller than R, the measurement accuracy will be deteriorated. ＳＡＤ In the algorithm for finding the minimum value of ＳＡＤ Since the amount of change in becomes small, errors due to noise are included, and R ＳＡＤ The error in the value of δX, which is the value of X that gives the minimum value of σ, also becomes large.

[0046] In the speckle pattern, the individual pattern shapes and intensity distributions are not identical, but the size s ０ Many patterns of similar size appear in the image. Therefore, if a movement amount greater than half the size of each individual pattern occurs, a large error occurs, which limits the range of vibration that can be measured. Conversely, there is also the issue that measurement errors become large when the vibration is small.

[0047] <<1-3>> Advantages of the First Embodiment In the vibration sensor 1 according to the first embodiment, the light projecting unit 10 is provided with a spot changing mechanism 35 for adjusting the distance Lc between the light emitting point of the laser light source 20 and the collimator lens 31. Utilizing this, the size of the spot 91 of the laser light irradiated on the object 90 can be easily changed. The experimental data is shown in FIGS. 12(A) to 12(F). FIGS. 12(A), 12(B), and 12(C) are speckle pattern images when the spot sizes on the object 90 are 1.4 mm, 0.5 mm, and 3.6 mm, respectively. The cross-sectional profiles on the cross-sectional line 95 in FIGS. 12(A), 12(B), and 12(C) are shown in FIGS. 12(D), 12(E), and 12(F). s according to equation (5) ０ The spot sizes are as follows:

[0048] When the spot size is 1.4 mm, s ０ ~0.24 [mm] When the spot size is 0.5 [mm], s ０ ~0.67 [mm] When the spot size is 3.6 [mm], s ０ ~0.09 [mm]

[0049] In this way, the size of the speckle pattern observed by the light receiving unit 40 can be freely changed simply by adjusting the spot changing mechanism 35 provided in the light projecting unit 10. As a result, in the case of large vibrations, the spot size can be reduced in advance to expand the measurement range. Conversely, in the case of small vibrations, the spot size can be increased in advance to narrow the measurement range and increase the sensitivity.

[0050] For example, in the case of each spot size shown in FIGS. 12(A), (B), and (C), the obtained R ＳＡＤExamples of (x) are shown in Figures 13(A), (B), and (C). In Figure 13(A), it can be seen that the shift amount (movement amount) δX can be measured in the range of -45 [pixel] to +45 [pixel]. In Figure 13(B), it can be seen that there is only one minimum value within the range of ±100 [pixel], and the measurement range is wide, but the slope of the peak of the minimum value is gentle, so the accuracy of determining x that gives the peak is poor. In Figure 13(C), there are many minimum values, and the interval between X that gives the minimum value is approximately 34 [pixel]. Although the range that can be accurately measured is about ±17 [pixel], it can be seen that the slope of the peak is sharp, and δX can be determined accurately in the case of small vibrations.

[0051] If the magnitude of vibration can be predicted before starting vibration measurement, the spot changing mechanism 35 can be adjusted to obtain an appropriate speckle pattern size before starting measurement. However, when performing vibration measurement on an unknown object 90, it is difficult to predict the magnitude of vibration in advance. The amplitude of the vibration angle varies greatly depending on the measurement point because the vibration mode changes depending on the shape and holding structure of the object 90. Therefore, with a method of capturing angle changes of the object, such as in this embodiment, it is difficult to predict the displacement of the speckle pattern in advance.

[0052] In the above example, the theoretical value s of the speckle pattern size ０ The experimental value was roughly the same as that of the speckle pattern. ０ often deviates significantly from the theoretical value expressed by Equation (5) because there is a large variation in the degree of roughness of the object 90. This makes it even more difficult to irradiate the spot 91 to generate an appropriate speckle pattern before measurement.

[0053] In the vibration sensor 1 according to the first embodiment, the image processing device 70 is provided with a function of first irradiating the target object 90 with a medium-sized circular spot 91 that generates the speckle pattern shown in Fig. 11(A), acquiring several frames of images, and determining whether the size of the speckle pattern is appropriate for the magnitude of the vibration. One of the methods for this determination is as follows.

[0054] <<1-4>> Method for Determining Whether the Vibration Magnitude is Appropriate In the vibration sensor 1 according to the first embodiment, the image processing device 70 determines whether the magnitude of the vibration is appropriate based on the first frame or the first plurality of frames n. ｃｈｅｃｋ After acquiring the image of the speckle pattern, the area sensor 50 has a function of estimating the size of the speckle pattern. There are several methods for estimating the size of the speckle pattern, but for example, the simplest method is to apply a high frequency removal filter to the waveform (or image in the case of two dimensions) and then count the number of maximum or minimum values. From this, the size s of the speckle pattern on the area sensor 50 can be calculated. ａ ' [pixel] can be estimated. From this calculation, it is found that the range in which the shift amount δX of the speckle pattern can be correctly measured under these measurement conditions is expressed by the following equation (7), which is similar to equation (6). Note that when the image processing device 70 measures the first multiple frames n ｃｈｅｃｋ When acquiring an image, it is sufficient to acquire a predetermined number of frames of images.

[0055] -0.5 s ａ ´<δX<0.5・s ａ ´ (7) Then, multiple frames n ｃｈｅｃｋ δX is calculated in the frame n=1, 2, ..., n, and it is checked whether δX is within the range of the formula (7). ｃｈｅｃｋ Calculated up to (n ｃｈｅｃｋ -1) Among the δXs, the one with the largest absolute value is δX ｍａｘ The subsequent measurement process changes depending on the following three cases:

[0056] |δX ｍａｘ |≧0.5 s ａIn the case of ', the vibration amount exceeds the amount that can be measured appropriately. In order to enlarge the speckle pattern and increase the measurement range, the spot size W is reduced by adjusting the spot changing mechanism 35.

[0057] 0.1 s ａ ´<|δX ｍａｘ |<0.5 s ａ In the case of ´, the size of the speckle pattern is appropriate for the vibration amount, and the spot size does not change. (3) |δX ｍａｘ |≦0.1 s ａ in the case of

[0058] The vibration amount is too small compared to the speckle pattern. To reduce the speckle pattern and increase sensitivity, the spot size W is increased by adjusting the spot changing mechanism 35.

[0059] The above-described method of determining whether the vibration magnitude is appropriate is repeated until the speckle pattern size is appropriate for the vibration amount. The spot changing mechanism 35 may be adjusted manually, or an electrically operated stage or the like may be attached so that the spacing can be automatically adjusted by feeding back the results of the above-described determination method in the image processing device 70.

[0060] 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.

[0061] 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).

[0062] 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.

[0063] 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.

[0064] 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.

[0065] <<2>> Second Embodiment Fig. 15(A) is a schematic perspective view showing the configuration and main light beams of a vibration sensor 2 according to the second embodiment. Fig. 15(B) is a front view showing a spot 91 formed by a laser beam irradiated onto an object 90 to be vibration-sensed. The vibration sensor 2 detects vibration of the object 90 by irradiating the object 90 (rough surface) with laser beam and observing the reflected and scattered light. The vibration sensor 2 includes a light-projecting unit 10 that irradiates the object 90 with laser beam, a light-receiving unit 40a that receives the reflected and scattered light generated by the object 90 irradiated with the laser beam, and an image processing device 70 as an information processing device that detects vibration based on a detection signal output from the light-receiving unit 40a. Typically, the light-projecting unit 10 and the light-receiving unit 40a are housed within the light-projecting and light-receiving head 5 (e.g., within a single housing).

[0066] The light-projecting unit 10 of the vibration sensor 2 according to the second embodiment is the same as the light-projecting unit 10 of the vibration sensor 1 according to the first embodiment. The light-receiving unit 40a of the vibration sensor 2 according to the second embodiment is provided with a cylindrical lens 62 for collecting light that has a concave surface in the Y direction (i.e., a surface that has a curvature in the Y direction) in front of (upstream of) the imaging lens 61a that constitutes the light-receiving optical system 60. Furthermore, the image sensor of the vibration sensor 2 is not an area sensor 50 but a line sensor (also referred to as a "line camera") 50a. The light-receiving unit 40a is located in the same XZ plane (i.e., the X'Z' plane) as the light-projecting unit 10, and the line sensor 50a extends in the X direction.

[0067] Fig. 16(A) is a schematic side view (i.e., a view of the light receiving unit 40a when viewed in the X direction) showing the configuration and main light rays of the light receiving unit 40a of the vibration sensor 2 according to embodiment 2. Fig. 16(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 40a of the vibration sensor 2 according to embodiment 2. As described above, in embodiment 2, the light receiving unit 40a has a line sensor 50a as an imaging sensor, an imaging lens 61a, and a cylindrical lens 62.

[0068] In the cross section in the YZ plane, the focus is on a circular spot 91 on the object 90 due to the action of the cylindrical lens 62. The focal length of the cylindrical lens 62, which is a concave lens, 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, in the YZ plane, the surface of the object 90 and the surface of the area sensor 50 are conjugate. When the distance L is finite but sufficiently large, L ｃｙｌ is f ｃｙｌ When measuring vibration, adjust the distance L to L ｃｙｌis 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.

[0069] The one-dimensional waveform of the speckle pattern acquired by the line sensor 50a is similar to the waveform in Fig. 5 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.

[0070] In the second embodiment, as in the first embodiment, there is a problem that the range in which vibration can be measured is limited by the size of the speckle pattern in the X direction. The solution to this problem is the same as in the first embodiment. The spot changing mechanism 35, which adjusts the distance Lc between the light emitting point of the laser light source 20 and the collimator lens 31, is adjusted, and feedback is performed to change the spot size so that the size of the speckle pattern matches the magnitude of the vibration of the target object 90.

[0071] Generally, the line sensor 50a has fewer pixels than the area sensor 50, and products with a high frame rate are readily available. Therefore, the vibration sensor 2 according to the second embodiment has the advantage of being able to measure vibrations at a higher speed than that according to the first embodiment. The frame rate of the line sensor 50a is, for example, 3 kHz, but is not limited to this.

[0072] In the above description, the line sensor 50a extends in the X direction. However, this configuration has the following advantages. When the distance L to the object 90 changes (becoming L≠L0) from a state in which the first optical axis 11 in the Z' direction and the second optical axis 41 in the Z direction intersect on the object 90 (L = L0), the circular spot 91 illuminated by the light-projecting unit 10 and the second optical axis 41 of the light-receiving unit 40a are shifted in the X direction. The line sensor 50a extends within a plane including the first optical axis 11 in the Z' direction of 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 focal position is slightly shifted in the X direction, light can reach the line sensor 50a, and the speckle pattern image can be captured on the light-receiving surface of the line sensor 50a. Therefore, even if the position of the object 90 moves back and forth, vibration measurement can be performed without readjustment.

[0073] Except for the above, the second embodiment is the same as the first embodiment.

[0074] <3> Third Embodiment <3-1> Configuration and Operation FIG. 17(A) is a schematic perspective view showing the configuration and main light beams of a vibration sensor 3 according to the third embodiment. FIG. 17(B) is a front view showing a linear spot 91a formed by laser light irradiated onto an object 90, which is the target of vibration sensing. FIG. 18 is a schematic plan view (i.e., a view of the light-projecting unit 10a and the light-receiving unit 40a in the -Y direction) showing the configuration and main light beams of the vibration sensor 3 according to the third embodiment. The vibration sensor 3 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 3 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).

[0075] 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.

[0076] 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.

[0077] 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 10a may be the axis of the laser light emitted from the light-projecting unit 10a. Furthermore, the optical axis of the light-receiving unit 40a may be the axis of reflected and scattered light that can be received by the line sensor 50a.

[0078] 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.

[0079] In this embodiment, the light projecting unit 10a and the light receiving unit 40a are arranged side by side in the X direction (or X' direction). In addition, it is desirable that the light projecting optical system 30 includes a spot changing mechanism 35 that changes the size of the linear spot 91a in the X direction.

[0080] In this embodiment, the projection optical system 30 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 30 includes the concave cylindrical lens 32 as an asymmetric optical system. The X-direction beam width conversion element 34 is an optical system (e.g., a lens or a group of lenses) that can change the X-direction width (length Bx) of the laser light emitted from the laser light source 20.

[0081] 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.

[0082] 19A 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 3 according to the embodiment. Fig. 19B 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 3.

[0083] 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 3 to the object 90 changes.

[0084] 19A and 19B show a beam emitted from a single point of the laser light source 20. In FIGS. 19A and 19B, 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 from the vibration sensor 3 within a range of several tens of centimeters to approximately 10 meters.

[0085] 19A and 19B, 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 +f３３ = 25 [mm], the light emitted from the cylindrical lens 33 moves in the X direction as 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. As will be described later, the beam width can also be changed by changing the distance between the cylindrical lenses 32 and 33.

[0086] 19A and 19B, since the light is focused at a finite position in the Y direction, 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 is emitted is considered to be slightly different from the above value. 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.

[0087] FIG. 20A 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 3 according to the third embodiment. FIG. 20B 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 3. In this embodiment, the light receiving unit 40a includes a line sensor 50a, an imaging lens 61, and a cylindrical lens 62. The imaging lens 61a and the cylindrical lens 62 constitute a light receiving optical system 60a. The imaging lens 61a is an object-side telecentric or hyper-tric optical system. FIGS. 20A and 20B 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 the chief rays from each image height directed from the lens to the object are parallel to the optical axis. A hyperchromatic optical system is a special optical system in which a group of chief rays from each image height traveling from the lens to the object converges toward the optical axis.

[0088] 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 20A and 20B, 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 20A and 20B depict light rays that are reflected and scattered on the object 90 and reach points P1, P2, and P3. As shown in Figure 20B, in the X direction, the imaging lens 61 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.

[0089] By inserting a focusing cylindrical lens 62 that has 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 farther away. The focal length of the focusing cylindrical lens 62 is f62, and the distance between the focusing cylindrical lens 62 and the observation surface 92 is L62. For example, let f62 = -50 mm. In this case, if L62 = |f62| = 50 mm, the focus will be at infinity in the Y direction. If L62 is made slightly larger than 50 mm, the focus can be adjusted to a point closer than infinity.

[0090] The focus in the Y direction is adjusted on the object 90 using a spot position adjustment mechanism 64 that adjusts the position of the cylindrical lens 62 in the Y 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.

[0091] 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 60, 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 60 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, again resulting in a large amount of light leaking outside the line sensor 50.

[0092] 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 60 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 60 is used to focus the light on the object 90 in the Y direction, thereby achieving highly efficient light propagation.

[0093] However, if the focal position of the light receiving optical system 60a 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.

[0094] 21A to 21C 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, an image 93 of the linear spot 91a of the object 90 on the light-receiving 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. 21A to 21C 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 X-direction length Bx of the linear spot 91a. FIG. 21A shows a state in which the light receiving surface of the line sensor 50a and the image 93 of the linear spot 91a are overlapped, and in this state, the vibration sensor 1 of this embodiment can operate normally.

[0095] However, as shown in Figure 21 (B), 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, 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.

[0096] 21C, 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 sufficient number of pixels cannot be observed by 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.

[0097] An example of the spot position adjustment mechanisms 63, 64 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 61 can be shifted in the Y direction. In other words, the state of FIG. 21B can be adjusted to the state of FIG. 21A. 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 mechanisms 63, 64 can adjust the image 93 of the linear spot 91a so that it can be received by the line sensor 50a.

[0098] 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. 21C can be adjusted to the state shown in FIG. 21A.

[0099] 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 61.

[0100] Similarly, the method for adjusting the rotation of the spot 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 for adjusting the rotation of the line sensor 50a around the Z axis relative to the imaging lens 61 may be provided.

[0101] 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. 21(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 be 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 third embodiment, the spot changing mechanism 35 is not used, and the beam width adjusting mechanism 36 provided in the X-direction beam width conversion element 34 can be used. The beam width adjusting mechanism provided in the X-direction beam width conversion element 34 is an example of a spot changing mechanism.

[0102] <3-2> Specific Examples of X-Direction Beam Width Conversion Element Fig. 22(A) is a schematic side view showing a first configuration example and main light rays of the light projecting unit 10a of the vibration sensor 3 according to embodiment 3. Figs. 22(B) to 22(D) are schematic plan views showing the first configuration example and main light rays of the light projecting unit 10a. As shown in Figs. 22(A) to 22(D), the first configuration example of the X-direction beam width conversion element 34 is composed of a cylindrical lens 32 which is a concave lens and a cylindrical lens 33 which is a convex lens. The X-direction beam width conversion element 34 has a curvature in the X' direction, and the focal length 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 and the cylindrical lens 33 is f = 50 [mm]. ３３ +f ３２ = 25 [mm], the light emitted from the cylindrical lens 33 moves in the X direction as ３３ | / f ３２ = 2 times expanded collimated beam. Focal length f ３３ and f ３２22A to 22D, 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 above value.

[0103] 22B is a light path diagram viewed from the Y-axis direction when the gap between the two lenses is Le1 = 16 mm. The width of the light beam in the X'-axis direction is expanded to approximately twice the width when it exits cylindrical lens 33 compared to when it enters cylindrical lens 32, and it is collimated in the X'-axis direction and propagates to object 90. The spot width in the X'-axis direction on object 90 is Bx1.

[0104] 22C is a light path diagram viewed from the Y-axis direction when the gap between the two lenses is Le2 = 26 mm. The light emitted from the cylindrical lens 33 propagates to the object 90 while converging in the X'-axis direction. The spot width Bx2 in the X'-axis direction on the object 90 is smaller than Bx1.

[0105] 22(D) is a light path diagram viewed from the Y-axis direction when the gap between the two lenses is Le2 = 6 [mm]. The light emitted from the cylindrical lens 33 propagates to the object 90 while diverging in the X'-axis direction. The spot width Bx3 in the X'-axis direction on the object 90 is larger than Bx1.

[0106] Fig. 23(A) is a schematic side view showing a second configuration example and main light rays of the light projecting unit 10a of the vibration sensor 3 according to embodiment 3. Figs. 23(B) to 23(D) are schematic plan views showing the second configuration example and main light rays of the light projecting unit 10a. As shown in Figs. 23(A) to 23(D), the second configuration example of the X-direction beam width conversion element 34 is composed of a cylindrical lens 32a which is a convex lens and a cylindrical lens 33 which is a convex lens. The lens has a curvature in the X' direction, and the focal length f ３２ａ =12.5 [mm], f ３３When the light emitted from the collimator lens 31 is completely collimated, the distance between the cylindrical lens 32a and the cylindrical lens 33 is f = 25 [mm]. ３３ +f ３２ａ = 37.5 [mm], the light emitted from the cylindrical lens 33 has a rotational angle of f ３３ / f ３２ａ = 2 times expanded collimated beam. Focal length f ３３ and f ３２ａ 23A to 23D, the light is focused at a finite position in the Y direction, and therefore the light beam emitted from the collimator lens 31 is not collimated light but is weakly converged light, so the lens spacing at which the collimated light is emitted is slightly different from the above value.

[0107] 23B is a light path diagram viewed from the Y-axis direction when the gap between the two lenses is Le1 = 31.4 mm. The width of the light beam in the X'-axis direction is expanded to approximately twice the width when it is emitted from cylindrical lens 33 compared to when it is incident on cylindrical lens 32a, and it is collimated in the X'-axis direction and propagates to object 90. The spot width in the X'-axis direction on object 90 is Bx1.

[0108] 23C is a light path diagram viewed from the Y-axis direction when the gap between the two lenses is Le2 = 37 mm. The light emitted from the cylindrical lens 33 propagates to the object 90 while converging in the X'-axis direction. The spot width Bx2 in the X'-axis direction on the object 90 is smaller than Bx1.

[0109] 23(D) is a light path diagram viewed from the Y-axis direction when the gap between the two lenses is Le2 = 28 [mm]. The light emitted from the cylindrical lens 33 propagates to the object 90 while diverging in the X'-axis direction. The spot width Bx3 in the X'-axis direction on the object 90 is larger than Bx1.

[0110] In both the first and second configuration examples of the X-direction beam width conversion element 34, the cylindrical lens has no curvature in the Y direction, so even if the position of the cylindrical lens 32, 32a or the cylindrical lens 33 is changed, the size of the spot in the Y direction on the object 90 does not change. In the X direction, a line-shaped spot 91a having an arbitrary spot width Bx can be generated on the object 90. This allows the typical size s of the waveform of the speckle pattern to be determined. ａ ´ can be changed arbitrarily.

[0111] <<3-3>> Effects As described above, by using the vibration sensor 3 according to the third 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 a one-dimensional waveform of the speckle pattern and detect vibrations.

[0112] 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).

[0113] 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.

[0114] 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.

[0115] 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.

[0116] 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 91a 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.

[0117] Fig. 24 is a schematic plan view showing image displacement when the distance changes in the vibration sensor 1 according to the embodiment. Fig. 25(A) to (D) are schematic plan views showing image displacement when the distance changes in the vibration sensor 3 according to the embodiment 3.

[0118] As shown in Figure 24, 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).

[0119] 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. 25(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. 25(B).

[0120] 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 25(C), and there is no problem with the function of the vibration sensor 1. However, if the distance L in Figure 25(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 shifted as shown in Figure 25(D). In the case of Figure 25(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 21(A) to (C).

[0121] 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.

[0122] Other than the above, the third embodiment is the same as the first or second embodiment.

[0123] 1 to 3 vibration sensor, 5 light emitting / receiving head, 10, 10a light emitting unit, 11 first optical axis, 20 laser light source, 30, 30a light emitting optical system, 31 collimating lens, 32 cylindrical lens, 33 cylindrical lens, 34 X-direction beam width conversion element, 35 spot adjustment mechanism, 40, 40a 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, 70 image processing device, 90 object, 91 spot, 91a line 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 a spot of laser light emitted from the laser light source 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 vibration of the object based on the amount of movement; wherein a first optical axis that is the optical axis of the light-projecting unit and a second optical axis that is the optical axis of the light-receiving unit intersect on the object; the light-projecting optical system includes a spot changing mechanism that changes the size of the spot on the object; and the image processing device causes the spot changing mechanism to change the size of the spot on the object based on the measured vibration.

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

3. 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, the image of the object formed by the light receiving optical system is not focused on the light receiving surface of the line sensor in the first direction, and the image of the object formed by the light receiving optical system is focused on the light receiving surface of the line sensor in the second direction.

4. The vibration sensor according to claim 3, wherein the light-emitting portion and the light-receiving portion are arranged side by side in the first direction.

5. A vibration sensor as described in claim 3 or 4, characterized in that the projection optical system projects a linear spot as the spot on the object, the 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.

6. The vibration sensor according to claim 5, wherein the light projection optical system includes a pair of cylindrical lenses that form the linear spot.

7. A vibration sensor as described in claim 5 or 6, characterized in that the third direction of the linear spot and the first direction in which the line sensor extends are parallel to a plane containing the first optical axis and the second optical axis.

8. The vibration sensor according to any one of claims 1 to 7, characterized in that the image processing device reconstructs sound based on the vibration of the object.

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