Speed measuring device and speed measurement method

Abstract

To provide a speed measuring device with which it is possible to grasp whether or not it is properly located with respect to a measurement object.SOLUTION: Provided is a speed measuring device comprising: a first lighting optical system 31A for irradiating a measurement object 10 with first light at a first incidence angle θ1; a second lighting optical system 31B for irradiating the measurement object 10 with second light at a second incidence angle θ2 whose absolute value is the same as the first incidence angle and the sign of which is opposite; a light receiving optical system 40 for receiving reflected light from the measurement object being irradiated with the first or the second light; a light detector array 50 for receiving reflected light having passed through the light receiving optical system 40; a deviation measurement unit 301 for measuring a deviation α of the optical axis of the light receiving optical system 40 from the normal of the measurement object 10, on the basis of the difference between the intensity of reflected light when the first light is radiated and the intensity of reflected light when the second light is radiated; and a speed measurement unit 302 for measuring the speed of the measurement object on the basis of the reflected light received by the light detector array 50.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a speed measurement device and a speed measurement method. [Background technology]

[0002] A method for measuring the moving speed of a measurement object without contact has been proposed. Non-Patent Document 1 describes a method for projecting an irregular pattern of a measurement object onto a spatial filter, extracting a specific periodic signal from a signal obtained by photoelectric conversion, and determining the speed of the measurement object. Patent Document 1 describes a displacement measuring device that extracts and compares a common portion of interest between reference image data and measurement image data of the measurement object, and calculates the amount of displacement of the measurement object by determining the amount of deviation between the reference image and the measurement image. The method described in Patent Document 1 is also called a pattern matching method. Patent Document 2 discloses a method for detecting the distance to an object and the tilt angle. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2001-241919 A [Patent Document 2] Japanese Patent Application Publication No. 11-257917 [Non-patent literature]

[0004] [Non-Patent Document 1] Yoshihisa Aizu, Toshimitsu Asakura, Spatial Filtering Velocimetry: Fundamentals and Applications (Springer Series in Optical Sciences, 116), 2006 Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present invention is to provide a speed measurement device and a speed measurement method that can determine whether or not the device is properly positioned with respect to an object to be measured. [Means for solving the problem]

[0006] A speed measuring device according to an embodiment of the present invention comprises a first illumination optical system for irradiating a measurement object with a first light at a first angle of incidence, a second illumination optical system for irradiating a measurement object with a second light at a second angle of incidence having the same absolute value as the first angle of incidence but opposite sign, a light receiving optical system for receiving reflected light from a measurement object irradiated with the first light or the second light, a photodetector array for receiving reflected light that has passed through the light receiving optical system, a deviation measuring unit for measuring a deviation of an optical axis of the light receiving optical system from a normal to the measurement object based on a difference between the intensity of the reflected light received by the photodetector array when the first light is irradiated and the intensity of the reflected light received by the photodetector array when the second light is irradiated, and a speed measuring unit for measuring the speed of the measurement object based on the reflected light received by the photodetector array.

[0007] In the above speed measurement device, the intensity of the first light and the intensity of the second light may be the same.

[0008] In the above-mentioned speed measurement device, when there is no deviation of the optical axis of the receiving optical system from the normal to the object to be measured, the first illumination optical system, the second illumination optical system and the receiving optical system may be arranged so that the difference between the intensity of the reflected light received by the photodetector array when the first light is irradiated and the intensity of the reflected light received by the photodetector array when the second light is irradiated is zero.

[0009] The above speed measuring device may further include an output device that outputs a deviation of the optical axis of the light receiving optical system from a normal to the object to be measured.

[0010] In the above speed measuring device, the speed measuring section may measure the speed of the object to be measured based on the frequency of a signal obtained by spatially filtering the reflected light received by the photodetector array.

[0011] In the above-mentioned speed measuring device, the speed measuring unit may compare a first light distribution due to reflected light imaged by the photodetector array at a first time with a second light distribution due to reflected light imaged by the photodetector array at a second time, calculate an amount of movement of the object to be measured between the first time and the second time, and measure the speed of the object to be measured based on the amount of movement.

[0012] A speed measurement method according to an embodiment of the present invention includes preparing a speed measurement device including a first illumination optical system for irradiating a first light onto a measurement object at a first angle of incidence, a second illumination optical system for irradiating a second light onto the measurement object at a second angle of incidence having the same absolute value as the first angle of incidence but opposite sign, a light receiving optical system for receiving reflected light from the measurement object irradiated with the first light or the second light, and a photodetector array for receiving the reflected light that has passed through the light receiving optical system, measuring a deviation of the optical axis of the light receiving optical system from a normal to the measurement object based on the difference between the intensity of the reflected light received by the photodetector array when the first light is irradiated and the intensity of the reflected light received by the photodetector array when the second light is irradiated, and measuring the speed of the measurement object based on the reflected light received by the photodetector array.

[0013] In the above speed measurement method, when there is no deviation of the optical axis of the light receiving optical system from the normal to the object to be measured, the first illumination optical system, the second illumination optical system, and the light receiving optical system may be arranged so that the difference between the intensity of the reflected light received by the photodetector array when the first light is irradiated and the intensity of the reflected light received by the photodetector array when the second light is irradiated is zero.

[0014] The above velocity measuring method may further include outputting a deviation of an optical axis of the light receiving optical system from a normal to the object to be measured.

[0015] The above-mentioned velocity measuring method may further include correcting the direction of the optical axis of the light receiving optical system so that there is no deviation of the optical axis of the light receiving optical system from the normal to the object to be measured.

[0016] In the above velocity measuring method, the velocity of the object may be measured based on the frequency of a signal obtained by spatially filtering the reflected light received by the photodetector array.

[0017] In the above speed measurement method, a first light distribution due to reflected light imaged by a photodetector array at a first time and a second light distribution due to reflected light imaged by a photodetector array at a second time may be compared to calculate the amount of movement of the object to be measured between the first time and the second time, and the speed of the object to be measured may be measured based on the amount of movement. Effect of the Invention

[0018] According to the present invention, it is possible to provide a speed measurement device and a speed measurement method that can determine whether or not a speed measurement device is properly positioned with respect to an object to be measured. [Brief description of the drawings]

[0019] [Figure 1] FIG. 1 is a schematic side view showing a speed measuring device according to an embodiment. [Diagram 2] FIG. 2 is a schematic graph showing the relationship between the deviation of the optical axis of the light receiving optical system according to the embodiment from the normal to the measurement object and the intensity of the reflected light from the measurement object. [Diagram 3] FIG. 3 is a schematic graph showing the relationship between the deviation of the optical axis of the light receiving optical system of the embodiment from the normal to the object to be measured and the difference in intensity between the reflected light of the first light and the reflected light of the second light. [Figure 4] FIG. 4 is a schematic diagram of a circuit included in the speed measuring device according to the embodiment. [Diagram 5] FIG. 5 is an example of a timing chart of the speed measuring device according to the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. However, the drawings are schematic. Therefore, specific dimensions and the like should be judged in light of the following description. In addition, the drawings naturally include parts in which the dimensional relationships and ratios differ from one another.

[0021] As shown in FIG. 1, the speed measuring device of the embodiment includes a first illumination optical system 31A for irradiating a first light onto a measurement object 10 at a first incident angle θ1, a second illumination optical system 31B for irradiating a second light onto the measurement object 10 at a second incident angle θ2 (=-θ1) whose absolute value is the same as that of the first incident angle but whose sign is opposite, a light receiving optical system 40 for receiving reflected light from the measurement object irradiated with the first light or the second light, and a photodetector array 50 for receiving reflected light that has passed through the light receiving optical system 40.

[0022] The speed measuring device according to the embodiment further includes a displacement measuring unit 301 that measures a displacement α of the optical axis of the light receiving optical system 40 from the normal to the measurement object 10 based on the difference between the intensity of the reflected light received by the photodetector array 50 when the first light is irradiated and the intensity of the reflected light received by the photodetector array 50 when the second light is irradiated, and a speed measuring unit 302 that measures the speed of the measurement object based on the reflected light received by the photodetector array 50. The displacement measuring unit 301 and the speed measuring unit 302 are included in, for example, a central processing unit (CPU) 300.

[0023] The surface of the measurement object 10 may have fine irregularities. The surface of the measurement object 10 may have a pattern. The measurement object 10 moves parallel to the surface to be measured. The measurement object 10 moves relative to the speed measuring device. For example, the speed measuring device may be placed stationary and the measurement object 10 may move, or the measurement object 10 may be placed stationary and the speed measuring device may move. When the speed measuring device is placed stationary and the measurement object 10 moves, examples of the measurement object 10 include, but are not limited to, a film and a nonwoven fabric. When the measurement object 10 is placed stationary and the speed measuring device moves, examples of the measurement object 10 include, but are not limited to, a road surface.

[0024] The first illumination optical system 31A may include a first light source 30A that irradiates the measurement object 10 with a first light. The second illumination optical system 31B may include a second light source 30B that irradiates the measurement object 10 with a second light. The intensity of the first light emitted by the first light source 30A and the intensity of the second light emitted by the second light source 30B are, for example, the same. The intensity of the first light and the intensity of the second light are, for example, constant. As the first light source 30A and the second light source 30B, a laser and a light-emitting diode (LED) can be used, but are not particularly limited. The first light source 30A and the second light source 30B may be a point light source or a surface light source.

[0025] The first illumination optical system 31A may include, for example, a first lens 32A that converts the first light emitted by the first light source 30A into a parallel light. The optical axis of the first illumination optical system 31A intersects the measurement object 10 obliquely. The second illumination optical system 31B may include, for example, a second lens 32B that converts the second light emitted by the second light source 30B into a parallel light. The optical axis of the second illumination optical system 31B intersects the measurement object 10 obliquely. The intensity of the first light when it reaches the measurement object 10 and the intensity of the second light when it reaches the measurement object 10 are, for example, the same.

[0026] The light receiving optical system 40 may include, for example, a lens 41 that collects the reflected light from the measurement object 10, and a lens 42 that converts the reflected light collected by the lens 41 into a parallel light. The optical axis of the first illumination optical system 31A and the optical axis of the light receiving optical system 40 are non-parallel and intersect at one point. The optical axis of the second illumination optical system 31B and the optical axis of the light receiving optical system 40 are non-parallel and intersect at one point. The optical axis of the light receiving optical system 40 preferably intersects with the measurement object 10 at a right angle and is parallel to the normal to the surface of the measurement object 10.

[0027] When the direction of the optical axis of the light receiving optical system 40 deviates from the direction of the normal to the surface of the measurement object 10, the magnification of the image of the measurement object 10 on the photodetector array 50 may change depending on the position. When the magnification of the image changes depending on the position, it may be difficult to accurately measure the speed of the measurement object 10. Furthermore, when the direction of the optical axis of the light receiving optical system 40 deviates from the direction of the normal to the surface of the measurement object 10, the depth of field of the light receiving optical system 40 may change depending on the position of the measurement object 10. When a part of the measurement object 10 is out of the depth of field, the frequency signal output from the photodetector array 50 used in the spatial filter method described later decreases, the S / N ratio decreases, and the speed measurement error may increase.

[0028] The photodetector array 50 includes, for example, a plurality of photodetectors arranged in a stripe pattern. Each of the plurality of photodetectors may be a pixel. Each of the plurality of photodetectors may be a photoelectric conversion element such as a photodiode. The plurality of photodetectors arranged in a stripe pattern may form a spatial filter.

[0029] For example, when the surface of the measurement object 10 is a perfect diffusing surface and the reflected light from the measurement object 10 follows a Lambertian distribution, the intensity of the reflected light is given by a cosine function of the angle of incidence of the light irradiated on the measurement object 10. Even if the surface of the measurement object 10 is not a perfect diffusing surface, the intensity of the reflected light can be approximated to a cosine function. With respect to the angle α formed by the normal to the measurement object 10 and the optical axis of the light receiving optical system 40, the distribution of the intensity I1 of the reflected light of the first light received by the photodetector array 50 and the distribution of the intensity I2 of the reflected light of the second light received by the photodetector array 50 are symmetrical across the angle α of 0°, as shown in FIG.

[0030] Therefore, the difference I1-I2 between the intensity I1 of the reflected light of the first light and the intensity I2 of the reflected light of the second light is 0 when the angle α is 0°, as shown in Fig. 3, and the absolute value of I1-I2 increases as the absolute value of the angle α increases. Therefore, I1-I2 being 0 indicates that the optical axis of the light-receiving optical system 40 is parallel to the normal to the measurement object 10. The magnitude of the absolute value of I1-I2 indicates the magnitude of the deviation α of the optical axis of the light-receiving optical system 40 from the normal to the measurement object 10.

[0031] The displacement measurement unit 301 shown in FIG. 1 turns on the first light source 30A without turning on the second light source 30B. In this case, the photodetector array 50 outputs a signal of the intensity I1 of the reflected light of the first light. Also, the displacement measurement unit 301 turns on the second light source 30B without turning on the first light source 30A. In this case, the photodetector array 50 outputs a signal of the intensity I2 of the reflected light of the second light. The displacement measurement unit 301 calculates the difference I between the intensity I1 of the reflected light of the first light and the intensity I2 of the reflected light of the second light. D Receive (=I1-I2).

[0032] The deviation measurement unit 301 may calculate the difference I between the intensity I1 of the reflected light of the first light and the intensity I2 of the reflected light of the second light, as shown in the following formula (1): D and the deviation α of the optical axis of the light receiving optical system 40 from the normal to the object 10 to be measured is stored. α = f(I D ) (1) The deviation measurement unit 301 may, for example, determine the relationship shown in formula (1) and the difference I between the intensity I1 of the reflected light of the first light and the intensity I2 of the reflected light of the second light. D Based on this measurement, a measurement value of the deviation α of the optical axis of the light receiving optical system 40 from the normal to the measurement object 10 is calculated.

[0033] The deviation measuring unit 301 outputs, for example, a deviation α of the optical axis of the light receiving optical system 40 from the normal to the measurement object 10 to the output device 402. For example, a display device can be used as the output device 402. Based on the deviation output to the output device 402, the direction of the optical axis of the light receiving optical system 40 with respect to the measurement object 10 is corrected so as to eliminate the deviation, thereby making it possible to accurately measure the speed of the measurement object 10.

[0034] The speed measurement device according to the embodiment may include a displacement measurement circuit 500 shown in Fig. 4 between the photodetector array 50 and the displacement measurement unit 301. The displacement measurement circuit 500 includes an amplifier 501 that receives a signal of the reflected light intensity I1 of the first light or a signal of the reflected light intensity I2 of the second light from the photodetector array 50. The amplifier 501 includes a first sample-and-hold circuit 502 to which the signal of the reflected light intensity I1 of the first light is input via a switch SW1; A second sample and hold circuit 503 is connected to which a signal of the reflected light intensity I2 of the second light is input.

[0035] The output of the first sample & hold circuit 502 is connected to an operational amplifier 504 via a switch SW2. The output of the second sample & hold circuit 503 is connected to the operational amplifier 504 via a switch SW3. The output of the operational amplifier 504 is connected to an amplifier 506 via a switch SW4.

[0036] The operation of the deviation measurement circuit 500 will be described with reference to the timing chart shown in Fig. 5. The deviation measurement unit 301 turns on the first light source 30A without turning on the second light source 30B. Furthermore, the deviation measurement unit 301 connects the switch SW1 to the first sample & hold circuit 502, connects the switch SW2, connects the switch SW3, and disconnects the switch SW4. As a result, a signal of the reflected light intensity I1 of the first light is input to the first sample & hold circuit 502, and the signal of the reflected light intensity I1 of the first light is accumulated and held in the capacitor 521.

[0037] Next, the deviation measurement unit 301 turns off the first light source 30A, connects the switch SW1 to the second sample & hold circuit 503, and connects the switch SW3 to ground via a resistor, causing the signal held in the capacitor 531 of the second sample & hold circuit 503 to disappear.

[0038] The deviation measurement unit 301 turns on the second light source 30B without turning on the first light source 30A. Furthermore, the deviation measurement unit 301 connects the switch SW3. As a result, a signal of the reflected light intensity I2 of the second light is input to the second sample & hold circuit 503, and the signal of the reflected light intensity I2 of the second light is accumulated and held in the capacitor 531.

[0039] Next, the deviation measurement unit 301 connects the switch SW4. As a result, a differential signal SD between the signal of the reflected light intensity I1 of the first light and the signal of the reflected light intensity I2 of the second light is output from the operational amplifier 504 to the amplifier 506, and the differential signal SD amplified by the amplifier 506 is output to the deviation measurement unit 301. In addition, the differential signal SD is accumulated in the capacitor 505. Next, the deviation measurement unit 301 disconnects the switch SW4. As a result, the differential signal SD is held in the capacitor 505.

[0040] Next, the deviation measurement unit 301 turns off the second light source 30B, connects the switch SW1 to the first sample & hold circuit 502, and connects the switch SW2 to ground via a resistor. This causes the signal held in the capacitor 521 to disappear. When the deviation measurement unit 301 needs to acquire the difference signal SD again, it causes the deviation measurement circuit 500 to repeat the above operation.

[0041] When the speed measurement unit 302 shown in FIG. 1 measures the speed, only the first light source 30A may be turned on, only the second light source 30B may be turned on, or both the first light source 30A and the second light source 30B may be turned on.

[0042] The speed measurement unit 302 may measure the speed of the measurement object 10 by a spatial filter method. The speed measurement unit 302 receives a differential signal between, for example, a signal SO output from an odd-numbered photodetector and a signal SE output from an even-numbered photodetector among the multiple photodetectors arranged in a striped pattern in the photodetector array 50.

[0043] The frequency of the signal SO output from the odd-numbered photodetector is proportional to the speed of the measurement object 10 and the pitch of the odd-numbered photodetector. The frequency of the signal SE output from the even-numbered photodetector is the same as the frequency of the signal SO output from the odd-numbered photodetector, and the phase of the signal SE output from the even-numbered photodetector is the opposite phase to the phase of the signal SO output from the odd-numbered photodetector.

[0044] In the differential signal between the signal SO output from the odd-numbered photodetector and the signal SE output from the even-numbered photodetector, the bias components contained in the signal SO output from the odd-numbered photodetector and the bias components contained in the signal SE output from the even-numbered photodetector are removed. Also, the amplitude of the differential signal is twice the amplitude of the signal SO output from the odd-numbered photodetector and twice the amplitude of the signal SE output from the even-numbered photodetector.

[0045] The speed measurement unit 302, for example, accumulates the difference signal for a predetermined time, and performs fast Fourier transform (FFT) processing on the accumulated difference signal to calculate a frequency spectrum (amplitude spectrum). In the frequency spectrum, a positive frequency that gives an amplitude peak excluding the vicinity of zero is the frequency F of the difference signal. The spectrum may be a power spectrum.

[0046] The speed measurement unit 302 calculates the speed V1 of the measurement object 10 using, for example, the following equation (2). V1=FP / M (2) Here, P is the pitch of the odd-numbered photodetectors and the pitch of the even-numbered photodetectors, and M is the magnification of the light receiving optical system 40. Note that the speed V1 may be calculated using the period of the signal instead of the frequency F of the signal.

[0047] The speed measurement unit 302 may measure the speed of the measurement target 10 by a pattern matching method. An example of the pattern matching method is the phase-only correlation method described in Japanese Patent Application Laid-Open No. 2000-221139. The speed measurement unit 302 acquires, for example, a distribution of light intensity due to reflected light detected by the photodetector array 50.

[0048] The speed measurement unit 302 stores the distribution of light intensity due to reflected light detected by the photodetector array 50 at a first time as a first light distribution. The first light distribution is expressed as f1(x), for example. Here, x is the number or position of a plurality of photodetectors included in the photodetector array 50. The first light distribution may be an image. The photodetector array 50 also stores the distribution of light intensity due to reflected light detected by the photodetector array 50 at a second time after the first time as a second light distribution. The second light distribution is expressed as f2(x), for example. The second light distribution may be an image.

[0049] The speed measurement unit 302 compares a common part common to the first light distribution and the second light distribution, and calculates the amount of movement of the common part from the first light distribution to the second light distribution. The common part may be a feature part. For example, the speed measurement unit 302 performs a discrete Fourier transform process on the first light distribution f1(x) to calculate first Fourier transform data F1(u). Here, u is a spatial frequency. The speed measurement unit 302 also performs a discrete Fourier transform process on the second light distribution f2(x) to calculate second Fourier transform data F2(u). Furthermore, the speed measurement unit 302 combines the first Fourier transform data F1(u) and the second Fourier transform data F2(u) to calculate third Fourier transform data F3(u), as shown in the following formula (3). F3(u)=F1 * (u)·F2(u) (3) * represents the complex conjugate.

[0050] The speed measurement unit 302 performs phase limitation processing on the third Fourier transform data F3(u) to calculate fourth Fourier transform data F4(u) given by the following equation (4). F4(u)=F3(u) / |F3(u)| (4) As a result, the amplitude of the third Fourier transform data F3(u) is set to 1 at all frequencies, and the fourth Fourier transform data F4(u) representing only the phase is obtained.

[0051] The speed measurement unit 302 performs an inverse Fourier transform on the fourth Fourier transform data F4(u) to calculate the inverse Fourier transform data f4(x). The position x of the peak in the inverse Fourier transform data f4(x) corresponds to the amount of movement of the common part from the first light distribution f1(x) to the second light distribution f2(x), and the amount of movement of the common part corresponds to the amount of movement of the measurement object 10 between the first time and the second time. The speed measurement unit 302 divides the amount of movement of the measurement object 10 between the first time and the second time by the elapsed time from the first time to the second time to calculate the speed of the measurement object 10.

[0052] Although the present invention has been described above by way of the embodiment, the description and drawings forming a part of this disclosure should not be understood as limiting the present invention. Various alternative embodiments, examples and operation techniques should be apparent to those skilled in the art from this disclosure. For example, when the speed measurement unit 302 measures the speed of the measurement object 10 by the spatial filter method, the speed measurement unit 302 calculates the frequency of the differential signal between the signal SO output from the odd-numbered photodetector and the signal SE output from the even-numbered photodetector, and calculates the speed V1 of the measurement object 10 based on the frequency of the differential signal.

[0053] Alternatively, instead of calculating the differential signal, the frequency of the signal may be calculated based only on the signal SO output from the odd-numbered photodetector, and the velocity V1 of the object 10 to be measured may be calculated based on the frequency of the signal. Alternatively, the frequency of the signal may be calculated based only on the signal SE output from the even-numbered photodetector, and the velocity V1 of the object 10 to be measured may be calculated based on the frequency of the signal. However, using the differential signal provides higher measurement accuracy because the bias component is removed.

[0054] Alternatively, the diffuse reflected light may reach the photodetector array 50, and the regular reflected light may not reach it. For example, a polarizing plate may be arranged in each of the first illumination optical system 31A, the second illumination optical system 31B, and the light receiving optical system 40. Here, the polarizing plates are arranged so that the polarization axis of the polarizing plate arranged in the first illumination optical system 31A and the second illumination optical system 31B is perpendicular to the polarization axis of the polarizing plate arranged in the light receiving optical system 40. As a result, the regular reflected light, which is linearly polarized light, cannot pass through the polarizing plate arranged in the light receiving optical system 40, and the diffuse reflected light, which is unpolarized light, passes through the polarizing plate arranged in the light receiving optical system 40 and reaches the photodetector array 50. In this way, it should be understood that the present invention includes various embodiments and the like that are not described here. [Explanation of symbols]

[0055] 10....measurement object, 30A...first light source, 30B...second light source, 31A...first illumination optical system, 31B...second illumination optical system, 32A...lens, 32B...lens, 40...light receiving optical system, 41...lens, 42...lens, 50...photodetector array, 301...displacement measuring section, 302...speed measuring section, 402...output device, 500...displacement measuring circuit, 501...amplifier, 502...sample & hold circuit, 503...sample & hold circuit, 504...operational amplifier, 505...capacitor, 506...amplifier, 521...capacitor, 531...capacitor

Claims

1. a first illumination optical system for irradiating a first light onto a measurement object at a first angle of incidence; a second illumination optical system for irradiating the measurement object with a second light at a second angle of incidence having the same absolute value as the first angle of incidence but an opposite sign; a light receiving optical system that receives reflected light from the measurement object irradiated with the first light or the second light; a photodetector array that receives the reflected light that has passed through the light receiving optical system; a deviation measuring unit that measures a deviation of an optical axis of the light receiving optical system from a normal line of the measurement object based on a difference between an intensity of the reflected light received by the photodetector array when the first light is irradiated and an intensity of the reflected light received by the photodetector array when the second light is irradiated; a speed measurement unit that measures the speed of the measurement object based on the reflected light received by the photodetector array; A speed measuring device comprising:

2. 2. The speed measurement device according to claim 1, wherein the first illumination optical system, the second illumination optical system, and the receiving optical system are arranged so that, when there is no deviation of the optical axis of the receiving optical system from the normal line of the object to be measured, the difference between the intensity of the reflected light received by the photodetector array when the first light is irradiated and the intensity of the reflected light received by the photodetector array when the second light is irradiated is zero.

3. The velocity measuring device according to claim 1 , further comprising an output device that outputs a deviation of an optical axis of the light receiving optical system from a normal line of the object to be measured.

4. 2. The speed measuring device according to claim 1, wherein the speed measuring unit measures the speed of the object based on a frequency of a signal obtained by spatially filtering the reflected light received by the photodetector array.

5. 2. The speed measuring device according to claim 1, wherein the speed measuring unit compares a first light distribution due to the reflected light imaged by the photodetector array at a first time with a second light distribution due to the reflected light imaged by the photodetector array at a second time to calculate a movement amount of the object to be measured between the first time and the second time, and measures the speed of the object to be measured based on the movement amount.

6. providing a speed measuring device including a first illumination optical system for irradiating a measurement object with a first light at a first angle of incidence, a second illumination optical system for irradiating the measurement object with a second light at a second angle of incidence having the same absolute value as the first angle of incidence but an opposite sign, a light receiving optical system for receiving reflected light from the measurement object irradiated with the first light or the second light, and a photodetector array for receiving the reflected light that has passed through the light receiving optical system; measuring a deviation of an optical axis of the light receiving optical system from a normal line of the measurement object based on a difference between an intensity of the reflected light received by the photodetector array when the first light is irradiated and an intensity of the reflected light received by the photodetector array when the second light is irradiated; Measuring the velocity of the measurement object based on the reflected light received by the photodetector array; A method for measuring speed, comprising:

7. 7. The speed measurement method according to claim 6, wherein the first illumination optical system, the second illumination optical system, and the light receiving optical system are arranged so that, when there is no deviation of the optical axis of the light receiving optical system from the normal line of the object to be measured, a difference between the intensity of the reflected light received by the light detector array when the first light is irradiated and the intensity of the reflected light received by the light detector array when the second light is irradiated is zero.

8. The velocity measuring method according to claim 6 , further comprising outputting a deviation of an optical axis of the light receiving optical system from a normal to the object to be measured.

9. The velocity measuring method according to claim 6 , further comprising correcting a direction of the optical axis of the light receiving optical system so that there is no deviation of the optical axis of the light receiving optical system from a normal line of the object to be measured.

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