Speed measurement device and speed measurement method

Abstract

A velocity measurement device is provided with: a bilateral telecentric lens (4) that receives reflected light from a moving object to be measured (10); a spatial filter (50) disposed at an angle to an image plane formed by the reflected light passing through the two-side telecentric lens (4); and a movement speed calculation unit (302) that calculates the movement speed of the object to be measured on the basis of the frequency of a signal obtained by spatially filtering the reflected light by the spatial filter (50).

Description

Technical Field

[0001] The invention relates to a speed measuring device and a speed measuring method. Background Art

[0002] A method for measuring the moving speed of an object in a non-contact manner is proposed. Patent document 1 states that: two spatial filters are arranged at positions where the optical path lengths from the object are different from each other, the reflected light from the object is imaged on both sides of the two spatial filters, and the moving speed of the object is calculated using the frequencies of both signals obtained by filtering through the two spatial filters.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 53-138381 Summary of the invention

[0006] Problems to be solved by the invention

[0007] In conventional non-contact speed measuring devices, when the distance between an object and the speed measuring device changes, the position of the image formed by the reflected light from the object deviates from the spatial filter, so that the speed of the object cannot be accurately measured. Therefore, one of the objects of the present invention is to provide a speed measuring device and a speed measuring method that can accurately measure the speed of an object even if the distance between the object and the speed measuring device changes.

[0008] Solutions for solving problems

[0009] A speed measuring device according to one embodiment of the present invention comprises: two side telecentric lenses for receiving reflected light from a moving measuring object; a spatial filter for being tilted relative to an image plane formed by the reflected light passing through the two side telecentric lenses; and a moving speed calculating unit for calculating the moving speed of the measuring object based on the frequency of a signal obtained by spatially filtering the reflected light through the spatial filter.

[0010] In the above-mentioned velocity measurement device, the spatial filter may include photodetectors arranged in a stripe shape at a predetermined pitch.

[0011] In the velocity measurement device described above, the spatial filter may include a grating having light shielding portions arranged in stripes at a predetermined pitch, and the velocity measurement device may further include a photodetector for receiving light having passed through the grating.

[0012] Alternatively, in the above-mentioned velocity measuring device, the spatial filter includes a grating having a light shielding portion arranged in a stripe shape at a predetermined pitch, and the above-mentioned velocity measuring device further includes: a first photodetector for receiving light passing through the grating; and a second photodetector for receiving light reflected by the grating.

[0013] The velocity measurement device may further include a differential amplifier configured to amplify a differential signal between a signal from the first photodetector and a signal from the second photodetector.

[0014] In the above-mentioned speed measurement device, the moving speed calculation unit may calculate the moving speed of the measurement object based on the frequency of the amplified difference signal.

[0015] The velocity measurement device may further include a prism, wherein the prism is disposed between the telecentric lenses on both sides and the spatial filter.

[0016] The velocity measurement device may further include a light source for irradiating light to the object to be measured.

[0017] A speed measurement method of one embodiment of the present invention includes: receiving reflected light from a moving measurement object through telecentric lenses on both sides; spatially filtering the reflected light through a spatial filter, wherein the spatial filter is tilted relative to an image plane formed by the reflected light passing through the telecentric lenses on both sides; and a moving speed calculation unit that calculates the moving speed of the measurement object based on the frequency of a signal obtained by spatially filtering the reflected light.

[0018] In the above-mentioned velocity measurement method, the spatial filter may include photodetectors arranged in a stripe shape at a predetermined pitch.

[0019] In the velocity measurement method described above, the spatial filter may include a grating having light shielding portions arranged in stripes at a predetermined pitch, and the velocity measurement method may further include generating a signal by photoelectrically converting light that has passed through the grating.

[0020] Alternatively, in the above-mentioned speed measurement method, the spatial filter has a grating, the grating has a shading portion arranged in a stripe shape at a prescribed interval, and the above-mentioned speed measurement method also includes: performing photoelectric conversion on light passing through the grating to generate a first signal; and performing photoelectric conversion on light reflected by the grating to generate a second signal.

[0021] Alternatively, the speed measurement method further includes amplifying a differential signal between the first signal and the second signal.

[0022] In the above-described velocity measurement method, the moving velocity of the measurement object may be calculated based on the frequency of the amplified differential signal.

[0023] Alternatively, the velocity measurement method further includes receiving reflected light through a prism disposed between the telecentric lenses on both sides and the spatial filter.

[0024] The velocity measurement method may further include irradiating the measurement object with light.

[0025] Effects of the Invention

[0026] According to the present invention, it is possible to provide a speed measuring device and a speed measuring method which can accurately measure the speed of an object even if the distance between the object and the speed measuring device varies. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 (A) is a schematic plan view showing a velocity measuring device according to an embodiment. Figure 1 (B) is a schematic side view showing the speed measuring device according to the embodiment.

[0028] Figure 2 Schematic diagram showing a photodetector according to an embodiment.

[0029] Figure 3 It is a schematic graph showing the temporal change of the intensity of the signal according to the embodiment.

[0030] Figure 4 : is a schematic graph showing the frequency spectrum of a signal according to an embodiment.

[0031] Figure 5 It is a schematic side view showing the speed measuring device according to the embodiment.

[0032] Figure 6 Schematic diagram showing a photodetector according to an embodiment.

[0033] Figure 7 : is a schematic graph showing the time variation of the intensity of two signals according to an embodiment.

[0034] Figure 8 1 is a schematic graph showing the temporal variation of a signal representing the difference in intensity between two signals according to an embodiment.

[0035] Fig. 9 It is a schematic side view showing the speed measuring device according to the embodiment.

[0036] Fig.10 It is a schematic side view showing the speed measuring device according to the embodiment. DETAILED DESCRIPTION

[0037] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the following description of the accompanying drawings, identical or similar parts are indicated by identical or similar reference numerals. However, the accompanying drawings are schematic. Therefore, specific dimensions and the like should be determined by comparing them with the following description. In addition, the accompanying drawings also include parts with different dimensional relationships or ratios.

[0038] like Figure 1 As shown, the speed measuring device of the embodiment includes: a telecentric lens 4 on both sides, which receives reflected light from a moving measuring object 10; a spatial filter 50, which is arranged obliquely with respect to an image plane formed by the reflected light passing through the telecentric lens 4 on both sides; and a moving speed calculation unit 302, which calculates the moving speed of the measuring object based on the frequency of a signal obtained by spatially filtering the reflected light through the spatial filter 50. The moving speed calculation unit 302 is included in, for example, a central processing unit (CPU) 300.

[0039] The object 10 to be measured moves in parallel. The object 10 to be measured moves relative to the speed measuring device. For example, the speed measuring device may be stationary and the object 10 to be measured may be moved, or the object 10 to be measured may be stationary and the speed measuring device may be moved. When the speed measuring device is stationary and the object 10 to be measured moves, examples of the object 10 to be measured include films and nonwoven fabrics, but are not particularly limited. When the object 10 to be measured is stationary and the speed measuring device is moved, examples of the object 10 to be measured include road surfaces, but are not particularly limited.

[0040] Alternatively, the speed measuring device of the embodiment further includes a light source 30 for irradiating light to the measuring object 10. As the light source 30, a laser and a light-emitting diode (LED) can be used, but it is not particularly limited. The intensity of the light is, for example, constant. Alternatively, the speed measuring device of the embodiment further includes an irradiation lens 31 for forming the light emitted by the light source 30 into parallel light. The light source 30 irradiates light, thereby generating reflected light from the measuring object 10. However, in the case where reflected light is generated from the measuring object 10 by sunlight or surrounding illumination light even if the light source 30 does not irradiate light, the light source 30 may not be present.

[0041] The double-sided telecentric lens 4 may further include a first lens 40 for focusing reflected light from the measuring object 10. The first lens 40 is, for example, arranged in such a manner that the optical axis is substantially perpendicular to the measuring object 10. The principal rays on the object side of the first lens 40 are parallel. Thus, even if the distance between the first lens 40 and the measuring object 10 changes, the imaging magnification is constant. In addition, the double-sided telecentric lens 4 may include a second lens 41 for forming the reflected light focused by the first lens 40 into parallel light. For example, the second lens 41 is arranged in such a manner that the optical axis is substantially perpendicular to the measuring object 10. The principal rays on the image side of the second lens 41 are parallel. Thus, even if the distance between the second lens 41 and the spatial filter 50 changes, the imaging magnification is constant. For example, the optical axis of the first lens 40 coincides with the optical axis of the second lens 41. An aperture 61 may also be arranged between the first lens 40 and the second lens 41. The first lens 40, the second lens 41, and the aperture 61 may also be arranged in the lens barrel 71. The bilateral telecentric lenses 4 are disposed, for example, between the measurement target 10 and the spatial filter 50 .

[0042] The spatial filter 50 is tilted relative to the optical axis of the telecentric lenses 4 on both sides, for example. The spatial filter 50 is tilted relative to the image plane formed by the reflected light that has passed through the telecentric lenses 4 on both sides, so that the image of the measurement object 10 is formed clearly in a part of the area on the spatial filter 50, and the image of the measurement object 10 is formed blurred in other areas on the spatial filter 50. Figure 2 As shown in FIG. 1 , the spatial filter 50 may also include light detectors 52 arranged in stripes at a predetermined pitch P. Figure 1 The photodetector 52 of the spatial filter 50 shown converts the spatially filtered light into an electrical signal. The signal is amplified by an amplifier and sent to the moving speed calculation unit 302. Figure 3 As shown, the signal includes an AC component having a frequency proportional to the speed of the measurement object 10 and the pitch P of the spatial filter 50 .

[0043] When the signal is accumulated for a specified time and subjected to fast Fourier transform (FFT), the following is obtained: Figure 4 The frequency spectrum (amplitude spectrum) shown in FIG. In the frequency spectrum, except for the vicinity of zero, the positive frequency that gives the peak value of the amplitude is the frequency of the signal. It should be noted that the frequency spectrum can also be a power spectrum.

[0044] The moving speed calculation unit 302 calculates the frequency F of the signal. The moving speed calculation unit 302 calculates the moving speed V of the measurement target object 10 using, for example, the following equation (1).

[0045] V=FP / M(1)

[0046] Here, P is the pitch of the spatial filter 50. M is the magnification of the telecentric lenses 4. It should be noted that in the calculation of the moving speed V, the period of the signal may be used instead of the frequency F of the signal.

[0047] When the distance between the speed measuring device and the object to be measured is constant, if the object to be measured is imaged on a spatial filter arranged parallel to the image plane, the moving speed of the object to be measured can be stably measured. However, due to the shaking of either the speed measuring device or the object to be measured, it may happen that the distance between the speed measuring device and the object to be measured cannot be kept constant. When the spatial filter is arranged parallel to the image plane, when the distance between the speed measuring device and the object to be measured changes and the image of the object to be measured on the spatial filter is blurred, the moving speed of the object to be measured may not be calculated. In contrast, in the speed measuring device of the embodiment, the spatial filter 50 is tilted relative to the image plane formed by the reflected light passing through the telecentric lenses 4 on both sides. Therefore, when the distance between the speed measuring device and the object to be measured 10 changes by shortening or lengthening, the position where the image of the object to be measured 10 is clearly imaged on the spatial filter 50 continuously moves, but the image blur of the object to be measured 10 in the entire area on the spatial filter 50 can be suppressed. Therefore, in the velocity measurement device of the embodiment, even if the distance between the velocity measurement device and the measurement object 10 varies, the moving velocity of the measurement object 10 can be stably measured.

[0048] like Figure 5 As shown, the velocity measuring device of the embodiment may also include a prism 60 disposed between the telecentric lenses 4 on both sides and the spatial filter 50. The prism 60 has a thickness that changes continuously in the traveling direction of the reflected light. The prism 60 is, for example, a wedge-shaped prism, but is not particularly limited. The prism 60 has, for example, a constant thickness in the moving direction of the measuring object 10. When the reflected light passes through the prism 60 having a thickness that changes continuously in the traveling direction of the reflected light, the image plane formed by the reflected light is inclined relative to the optical axis of the telecentric lenses 4 on both sides. In this case, the spatial filter 50 may be disposed perpendicularly to the optical axis of the telecentric lenses 4 on both sides, or the spatial filter 50 may be disposed obliquely relative to the optical axis of the telecentric lenses 4 on both sides. Since the image plane formed by the reflected light is inclined relative to the optical axis of the telecentric lenses 4 on both sides by the prism 60, the image of the measuring object 10 is formed clearly in a part of the area of ​​the spatial filter 50, and the image of the measuring object 10 is formed blurred in other areas of the spatial filter 50.

[0049] like Figure 6 As shown, Figure 1 and Figure 5The spatial filter 50 shown may also include: first photodetectors 53 arranged in stripes at a predetermined pitch P; and second photodetectors 54 arranged in stripes at a predetermined pitch P. The second photodetectors 54 are arranged in the gaps between the first photodetectors 53, and the stripe portions of the first photodetectors 53 and the stripe portions of the second photodetectors 54 are arranged alternately.

[0050] The first photodetector 53 and the second photodetector 54 are connected to a differential amplifier 303. Figure 7 As shown, the phase of the signal photoelectrically converted by the first light detector 53 is inverted relative to the phase of the signal photoelectrically converted by the second light detector 54. The differential amplifier 303 obtains the difference between the signal photoelectrically converted by the first light detector 53 and the signal photoelectrically converted by the second light detector 54. Figure 8 The differential signal shown in FIG. 1 is a differential signal in which the offset component is removed. The differential amplifier 303 amplifies the differential signal and sends the amplified differential signal to the moving speed calculation unit 302. The moving speed calculation unit 302 calculates the frequency F of the signal based on the differential signal. By removing the offset component, the amplification factor of the signal can be increased.

[0051] Fig. 9 The spatial filter 50 shown may also include a grating having a light shielding portion arranged in a stripe shape at a predetermined pitch P. The grating is arranged at an angle relative to an image plane formed by the reflected light from the measurement object 10. The grating is arranged at an angle relative to the optical axis of the telecentric lenses 4 on both sides, for example. The speed measuring device may also include: a lens 151 that focuses light that has passed through the spatial filter 50 as a grating; and a photodetector 152 that receives light that has passed through the grating and is focused by the lens 151. The photodetector 152 sends a signal to the moving speed calculation unit 302. In this case, the photodetector 152 may not be in a stripe shape.

[0052] like Fig.10 As shown, the spatial filter 50 may also include a grating having a light shielding portion arranged in a stripe shape at a predetermined pitch P. The grating is arranged at an angle relative to an image plane formed by the reflected light from the measurement object 10. The grating is arranged at an angle relative to the optical axis of the telecentric lenses 4 on both sides, for example. The velocity measuring device may also include: a first lens 153 for focusing light that has passed through the spatial filter 50 as a grating; a first photodetector 154 for receiving light that has passed through the grating and has been focused by the first lens 153; a second lens 155 for focusing light reflected by the grating; and a second photodetector 156 for receiving light that has passed through the grating and has been focused by the second lens 155. The first photodetector 154 and the second photodetector 156 may not be in a stripe shape.

[0053] The first photodetector 154 and the second photodetector 156 are connected to a differential amplifier 303. The differential amplifier 303 obtains a differential signal between a signal photoelectrically converted by the first photodetector 154 and a signal photoelectrically converted by the second photodetector 156. The differential amplifier 303 amplifies the differential signal and sends the amplified differential signal to the moving speed calculation unit 302. The moving speed calculation unit 302 calculates the frequency F of the signal based on the differential signal.

[0054] As described above, the present invention is described through the embodiments, but the description and drawings forming part of the present disclosure should not be understood as limiting the present invention. For those skilled in the art, various alternative embodiments, examples and application techniques should be obvious based on the present disclosure. For example, the spatial filter can also have: a grating; and a planar light detector that is in close contact with or close to the grating. It should be understood that the present invention includes various embodiments not described herein, etc.

[0055] Description of Reference Numerals

[0056] 4: Telecentric lenses on both sides; 10: Measurement object; 30: Light source; 31: Illumination lens; 40: First lens; 41: Second lens; 50: Spatial filter; 52: Photodetector; 53: Photodetector; 54: Photodetector; 60: Prism; 71: Lens barrel; 151: Lens; 152: Photodetector; 153: Lens; 154: Photodetector; 155: Lens; 156: Photodetector; 302: Moving speed calculation unit; 303: Differential amplifier.

Claims

1. A speed measuring device, comprising: Telecentric lenses on both sides receive reflected light from the moving measurement object; a spatial filter arranged to be tilted with respect to an image plane formed by the reflected light having passed through the telecentric lenses on both sides; and The moving speed calculation unit calculates the moving speed of the measurement object based on the frequency of a signal obtained by spatially filtering the reflected light with the spatial filter.

2. The speed measuring device according to claim 1, wherein: The spatial filter includes photodetectors arranged in a stripe shape at a predetermined pitch.

3. The speed measuring device according to claim 1, wherein: The spatial filter includes a grating having light shielding portions arranged in stripes at a predetermined pitch. The velocity measurement device further includes a photodetector that receives the light that has passed through the grating.

4. The speed measuring device according to claim 1, wherein: The spatial filter includes a grating having light shielding portions arranged in stripes at a predetermined pitch. The velocity measurement device further includes: a first photodetector that receives light that has passed through the grating; and a second photodetector that receives light reflected by the grating.

5. The speed measuring device according to claim 4, further comprising: The differential amplifier amplifies a differential signal between a signal from the first photodetector and a signal from the second photodetector.

6. The speed measuring device according to claim 5, wherein: The moving speed calculation unit calculates the moving speed of the measurement object based on the frequency of the amplified difference signal.

7. The speed measuring device according to claim 1, further comprising: The prism is arranged between the telecentric lenses on both sides and the spatial filter.

8. The speed measuring device according to claim 1, further comprising: The light source irradiates light to the measurement object.

9. A method for measuring speed, comprising: The reflected light from the moving measuring object is received through the object side telecentric lens or the telecentric lenses on both sides; spatially filtering the reflected light by a spatial filter, the spatial filter being arranged obliquely with respect to an image plane formed by the reflected light having passed through the bilateral telecentric lenses; and A moving speed calculation unit calculates a moving speed of the measurement object based on a frequency of a signal obtained by spatially filtering the reflected light.

10. The velocity measurement method according to claim 9, wherein: The spatial filter includes a grating having light shielding portions arranged in stripes at a predetermined pitch. The speed determination method further comprises: Performing photoelectric conversion on the light that has passed through the grating to generate a first signal; and The light reflected by the grating is photoelectrically converted to generate a second signal.

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