JP7805866B2 - Speed measurement device and speed measurement method - Google Patents

Description

The present invention relates to a speed measurement device and a speed measurement method.

A method for measuring the movement speed of an object without contact has been proposed. Patent Document 1 describes a method in which two spatial filters are placed at positions with different optical path lengths from the object, the reflected light from the object is imaged on both spatial filters, and the movement speed of the object is calculated using both frequencies of the two signals filtered by the two spatial filters.

Japanese Patent Application Publication No. 53-138381

Conventional non-contact speed measurement devices are unable to accurately measure the speed of an object when the distance between the object and the speed measurement device fluctuates because the position where the image of reflected light from the object is formed shifts from the spatial filter. Therefore, one of the objects of the present invention is to provide a speed measurement device and speed measurement method that can accurately measure the speed of an object even when the distance between the object and the speed measurement device fluctuates.

A speed measuring device according to one aspect of the present invention includes a splitter that splits reflected light from a moving object to be measured into first light and second light; an object-side telecentric lens or a double-telecentric lens that receives the reflected light; a comparison unit that compares the amplitude of a first signal obtained by spatially filtering the first light at a first distance from the splitter with the amplitude of a second signal obtained by spatially filtering the second light at a second distance from the splitter; and a movement speed calculation unit that calculates the movement speed of the object to be measured based on the first signal or the second signal, whichever has the larger amplitude.

The above-mentioned velocity measurement device may further include a first spatial filter for spatially filtering the first light at a first distance from the splitter, and a second spatial filter for spatially filtering the second light at a second distance from the splitter.

In the above-mentioned speed measurement device, each of the first spatial filter and the second spatial filter may include photodetectors arranged in a striped pattern at a predetermined pitch.

In the above-mentioned speed measurement device, each of the first spatial filter and the second spatial filter may include a grating having light-shielding portions arranged in stripes at a predetermined pitch, and a photodetector that receives light that has passed through the grating.

The above-mentioned speed measurement device may further include a first imaging element that captures an image of a first light at a first distance from the splitter, a second imaging element that captures an image of a second light at a second distance from the splitter, and an image processing unit that spatially filters the images captured by each of the first and second imaging elements.

In the above-mentioned velocity measuring device, an object-side telecentric lens or a double-telecentric lens may be arranged before the splitter in the direction of travel of the reflected light.

In the above-mentioned velocity measuring device, an object-side telecentric lens or a double-telecentric lens may be arranged after the splitter in the direction of travel of the reflected light.

The above-mentioned speed measurement device may further include a light source that irradiates light onto the object to be measured.

A velocity measurement method according to one aspect of the present invention includes splitting reflected light from a moving object into first and second light using a splitter; receiving the reflected light using an object-side telecentric lens or a double-telecentric lens; comparing the amplitude of a first signal obtained by spatially filtering the first light at a first distance from the splitter with the amplitude of a second signal obtained by spatially filtering the second light at a second distance from the splitter; and calculating the moving velocity of the object based on the first or second signal, whichever has the larger amplitude.

In the above-described velocity measurement method, the first signal obtained by spatially filtering the first light and the second signal obtained by spatially filtering the second light may each be obtained by a photodetector arranged in a striped pattern at a predetermined pitch.

In the above-described velocity measurement method, the first signal obtained by spatially filtering the first light and the second signal obtained by spatially filtering the second light may each be obtained by a grating having light-shielding portions arranged in a striped pattern at a predetermined pitch, and a photodetector that receives light that has passed through the grating.

The above-mentioned velocity measurement method may further include capturing an image of the first light at a first distance from the splitter, capturing an image of the second light at a second distance from the splitter, and spatially filtering the images captured by the first and second image capture elements.

In the above velocity measurement method, an object-side telecentric lens or a double-telecentric lens may be positioned before the splitter in the direction of travel of the reflected light.

In the above velocity measurement method, an object-side telecentric lens or a double-telecentric lens may be arranged after the splitter in the direction of travel of the reflected light.

The above velocity measurement method may further include irradiating the object to be measured with light.

The present invention provides a speed measurement device and a speed measurement method that can accurately measure the speed of an object even if the distance between the object and the speed measurement device varies.

FIG. 1 is a schematic diagram showing a speed measurement device according to an embodiment. FIG. 2 is a schematic diagram showing a photodetector according to the embodiment. FIG. 3 is a schematic graph showing the change over time in signal intensity according to the embodiment. FIG. 4 is a schematic graph showing a frequency spectrum of a signal according to the embodiment. FIG. 5 is a schematic diagram showing a speed measuring device according to an embodiment. FIG. 6 is a schematic diagram showing a photodetector according to an embodiment. FIG. 7 is a schematic graph showing the time variation of the intensities of two signals according to the embodiment. FIG. 8 is a schematic graph showing the change over time of the difference between the two intensities of the signals according to the embodiment. FIG. 9 is a schematic diagram showing a speed measuring device according to an embodiment. FIG. 10 is a schematic diagram showing a speed measuring device according to an embodiment.

Embodiments of the present invention will be described below with reference to the drawings. In the following description of the drawings, identical or similar parts are represented by identical or similar reference numerals. However, the drawings are schematic. Therefore, specific dimensions, etc. should be determined in reference to the following description. Naturally, there are also parts in which the dimensional relationships and ratios differ between the drawings.

As shown in FIG. 1, the speed measurement device according to this embodiment includes a splitter 20 that splits reflected light from a moving measurement object 10 into first light and second light, an object-side telecentric lens or a double-telecentric lens 4 that receives the reflected light, a comparison unit 301 that compares the amplitude of a first signal obtained by spatially filtering the first light at a first distance L from the splitter 20 with the amplitude of a second signal obtained by spatially filtering the second light at a second distance L+D from the splitter 20, and a movement speed calculation unit 302 that calculates the movement speed of the measurement object 10 based on the first signal or the second signal, whichever has the larger amplitude. The comparison unit 301 and the movement speed calculation unit 302 are included in, for example, a central processing unit (CPU) 300.

The object to be measured 10 moves in parallel. The object to be measured 10 moves relative to the speed measurement device. For example, the speed measurement device may be placed stationary and the object to be measured 10 may move, or the object to be measured 10 may be placed stationary and the speed measurement device may move. When the speed measurement device is placed stationary and the object to be measured 10 moves, examples of the object to be measured 10 include, but are not limited to, films and nonwoven fabrics. When the object to be measured 10 is placed stationary and the speed measurement device moves, examples of the object to be measured 10 include, but are not limited to, a road surface.

The speed measuring device according to the embodiment may further include a light source 30 that irradiates the object 10 to be measured. The light source 30 may be, but is not limited to, a laser or a light-emitting diode (LED). The light intensity is constant, for example. The speed measuring device according to the embodiment may further include an irradiation lens 31 that collimates the light emitted by the light source 30. When the light source 30 irradiates light, reflected light is generated from the object 10 to be measured. However, if reflected light is generated from the object 10 to be measured due to sunlight or ambient lighting, even if the light source 30 does not irradiate light, the light source 30 may not be necessary.

The bilateral telecentric lens 4 includes a first lens 40 that focuses reflected light and a second lens 41 that converts the focused reflected light into parallel light. The chief ray on the object side of the first lens 40 is parallel. This allows the imaging magnification to remain constant even if the distance between the first lens 40 and the measurement object 10 changes. The first lens 40 is positioned so that its optical axis is approximately perpendicular to the measurement object 10. The second lens 41 is positioned so that its optical axis is approximately perpendicular to the measurement object 10. For example, the optical axis of the first lens 40 and the optical axis of the second lens 41 coincide. An aperture 61 may be positioned between the first lens 40 and the second lens 41. The first lens 40, the second lens 41, and the aperture 61 may be positioned within the lens barrel 71. The bilateral telecentric lens 4 is positioned, for example, between the measurement object 10 and the splitter 20. Note that an object-side telecentric lens may be used instead of the double-telecentric lens 4.

The splitter 20 splits the reflected light into a first light and a second light. Each of the first light and the second light is, in effect, reflected light from the measurement object 10. The speed measurement device according to the embodiment may further include a first spatial filter 50 for spatially filtering the first light at a first distance L from the splitter 20, and a second spatial filter 51 for spatially filtering the second light at a second distance L+D from the splitter 20. The first distance L and the second distance L+D are different. The starting points of the first and second distances are, for example, the intersection of the optical axis of the double-telecentric lens 4 and the splitter 20.

Because the first distance L and the second distance L + D are different, when an image of the measurement object 10 is formed on the first spatial filter 50, the image of the measurement object 10 is blurred on the second spatial filter 51. Also, when an image of the measurement object 10 is formed on the second spatial filter 51, the image of the measurement object 10 is blurred on the first spatial filter 50.

As shown in FIG. 2, each of the first spatial filter 50 and the second spatial filter 51 may include photodetectors 52 arranged in a striped pattern at a predetermined pitch P. The pitch P of the first spatial filter 50 and the pitch P of the second spatial filter 51 are the same. The photodetector constituting the first spatial filter 50 shown in FIG. 1 converts the spatially filtered first light into a first signal, which is an electrical signal. The photodetector constituting the second spatial filter 51 converts the spatially filtered second light into a second signal, which is an electrical signal. Each of the first signal and the second signal is amplified by an amplifier and sent to the comparison unit 301.

As shown in FIG. 3, each of the first signal and the second signal contains an AC component having a frequency proportional to the velocity of the measurement object 10 and the pitch P of each of the first spatial filter 50 and the second spatial filter 51. Here, if a clear image of the measurement object 10 is formed on the first spatial filter 50 and a blurred image of the measurement object 10 is formed on the second spatial filter 51, the amplitude of the first signal will be relatively large as shown in FIG. 3A, and the amplitude of the second signal will be relatively small as shown in FIG. 3B. If a clear image of the measurement object 10 is formed on the second spatial filter 51 and a blurred image of the measurement object 10 is formed on the first spatial filter 50, the amplitude of the first signal will be relatively small as shown in FIG. 3B, and the amplitude of the second signal will be relatively large as shown in FIG. 3A.

When the first signal and the second signal are accumulated for a predetermined time and subjected to fast Fourier transform (FFT) processing, a frequency spectrum (amplitude spectrum) such as that shown in Figure 4 is obtained. In the frequency spectrum, the positive frequencies that give amplitude peaks, excluding those near zero, are the frequencies of the signals. Here, if a clear image of the measurement object 10 is formed on the first spatial filter 50 and a blurred image of the measurement object 10 is formed on the second spatial filter 51, the amplitude of the peaks in the frequency spectrum of the first signal will be relatively large, as shown in Figure 4A, and the amplitude of the peaks in the frequency spectrum of the second signal will be relatively small, as shown in Figure 4B. If a clear image of the measurement object 10 is formed on the second spatial filter 51 and a blurred image of the measurement object 10 is formed on the first spatial filter 50, the amplitude of the peaks in the frequency spectrum of the first signal will be relatively small, as shown in Figure 4B, and the amplitude of the peaks in the frequency spectrum of the second signal will be relatively large, as shown in Figure 4A. A frequency spectrum that gives peaks with large amplitudes has a higher S/N ratio than a frequency spectrum that gives peaks with small amplitudes, and is therefore more reliable when identifying the frequency of a signal. Note that the spectrum may also be a power spectrum.

Therefore, the comparison unit 301 shown in FIG. 1 compares the amplitude of the first signal with the amplitude of the second signal and selects the signal with the larger amplitude. Alternatively, the comparison unit 301 may compare the frequency spectrum of the first signal with the frequency spectrum of the second signal and select the signal with the larger peak amplitude. Furthermore, since the narrower the half-width of a peak in a frequency spectrum, the larger the peak amplitude, the comparison unit 301 may compare the frequency spectrum of the first signal with the frequency spectrum of the second signal and select the signal with the smaller half-width of the peak. At least one of the comparison unit 301 and the movement speed calculation unit 302 calculates the frequency F of the selected signal. Furthermore, the movement speed calculation unit 302 calculates the movement speed V of the measurement object 10, for example, using the following equation (1).
V = FP / M (1)
Here, P is the pitch of the first spatial filter 50 and the second spatial filter 51. M is the magnification of the double telecentric lens 4. Note that the moving speed V may be calculated using the period of the signal instead of the frequency F of the signal.

When the second lens 41 is present, the magnification M in equation (1) is the same whether the first signal or the second signal is used. However, when the second lens 41 is not present, the magnification of the first lens 40 differs between the position of the first spatial filter 50 and the position of the second spatial filter 51. Therefore, when the second lens 41 is not present and the first signal is used, the magnification at the position of the first spatial filter 50 is used, and when the second lens 41 is not present and the second signal is used, the magnification at the position of the second spatial filter 51 is used.

When the distance between the speed measurement device and the object to be measured is constant, forming an image of the object to be measured on a single spatial filter allows for stable measurement of the object's moving speed. However, there may be cases where the distance between the speed measurement device and the object to be measured cannot be maintained constant due to shaking of either the speed measurement device or the object to be measured. If only one spatial filter is used, the image of the object to be measured on the single spatial filter may become blurred, making it impossible to calculate the object's moving speed. In contrast, the speed measurement device of the embodiment includes first and second spatial filters 50, 51 with different optical path lengths from the object to be measured 10. To calculate the moving speed, the device selects the signal with the larger amplitude from the first and second spatially filtered signals and calculates the moving speed of the object to be measured. Therefore, even if the distance between the speed measurement device and the object to be measured 10 fluctuates, shortening or lengthening, the device can accurately calculate the moving speed of the object to be measured 10. Note that the speed measurement device according to the embodiment may be equipped with three or more spatial filters, and may select the signal with the largest amplitude from the three or more spatially filtered signals to calculate the moving speed of the object to be measured.

In Figure 1, an example is shown in which a telecentric lens is placed before the splitter 20 in the direction of travel of the reflected light, but a telecentric lens may also be placed after the splitter 20. For example, as shown in Figure 5, the speed measurement device according to the embodiment may include a double-sided telecentric lens 4A that receives the first light and a double-sided telecentric lens 4B that receives the second light. The double-sided telecentric lens 4A and the double-sided telecentric lens 4B are positioned so that the intersection of their optical axes is located at the splitter 20.

The double-telecentric lens 4A includes a first lens 40A that focuses the first light and a second lens 41A that converts the first light focused by the first lens 40A into parallel light. For example, the optical axis of the first lens 40A and the optical axis of the second lens 41A coincide. An aperture 61A may be disposed between the first lens 40A and the second lens 41A. The first lens 40A, the second lens 41A, and the aperture 61A may be disposed within a lens barrel 71A.

The double-telecentric lens 4B includes a first lens 40B that focuses the second light and a second lens 41B that converts the second light focused by the first lens 40B into parallel light. For example, the optical axis of the first lens 40B and the optical axis of the second lens 41B coincide. A diaphragm 61B may be disposed between the first lens 40B and the second lens 41B. The first lens 40B, the second lens 41B, and the diaphragm 61B may be disposed within a lens barrel 71B.

In addition, an object-side telecentric lens may be used instead of the double-telecentric lenses 4A and 4B.

Even if a telecentric lens is placed after the splitter 20 in the direction of travel of the reflected light, the comparison unit 301 and movement speed calculation unit 302 are the same as above.

As shown in FIG. 6, each of the first spatial filter 50 and second spatial filter 51 shown in FIG. 1 and FIG. 5 may include a first photodetector 53 arranged in a striped pattern at a predetermined pitch P, and a second photodetector 54 arranged in a striped pattern at a predetermined pitch P. The second photodetector 54 is arranged in the gaps between the first photodetectors 53, and the striped portions of the first photodetector 53 and the striped portions of the second photodetector 54 are arranged alternately.

A differential amplifier 303 is connected to the first photodetector 53 and the second photodetector 54. As shown in FIG. 7, the phase of the signal photoelectrically converted by the first photodetector 53 is inverted relative to the phase of the signal photoelectrically converted by the second photodetector 54. The differential amplifier 303 obtains a differential signal, shown in FIG. 8, between the signal photoelectrically converted by the first photodetector 53 and the signal photoelectrically converted by the second photodetector 54. The bias component is removed from the differential signal. The differential amplifier of the first spatial filter 50 amplifies the differential signal and sends the amplified differential signal to the comparison unit 301 as a first signal. The differential amplifier of the second spatial filter 51 amplifies the differential signal and sends the amplified differential signal to the comparison unit 301 as a second signal. By removing the bias component, it is possible to increase the signal amplification factor.

As shown in FIG. 9 , the first spatial filter 50 may include a grating 150 having light-shielding portions arranged in a striped pattern at a predetermined pitch P, a lens 151 that focuses light that has passed through the grating 150, and a photodetector 152 that receives light that has passed through the grating 150 and focused by the lens 151. The photodetector 152 sends a first signal to the comparison unit 301. The second spatial filter 51 may also include a grating 250 having light-shielding portions arranged in a striped pattern at a predetermined pitch P, a lens 251 that focuses light that has passed through the grating 250, and a photodetector 252 that receives light that has passed through the grating 250 and focused by the lens 251. The photodetector 252 sends a second signal to the comparison unit 301. In this case, the photodetectors 152 and 252 do not need to be striped.

As shown in FIG. 10 , the speed measurement device according to the embodiment may include a first image sensor 255 that captures the first light at a first distance L from the splitter 20, a second image sensor 256 that captures the second light at a second distance L+D from the splitter 20, and an image processing unit 304 that spatially filters the images captured by the first and second image sensors. The image processing unit 304 performs processing on the image captured by the first image sensor 255 that corresponds to spatial filtering of the first light at the first distance L from the splitter 20, and generates a first signal. The image processing unit 304 also performs processing on the image captured by the second image sensor 256 that corresponds to spatial filtering of the second light at the second distance L+D from the splitter 20, and generates a second signal.

While the present invention has been described above using embodiments, the descriptions and drawings that form part of this disclosure should not be understood as limiting the present invention. Various alternative embodiments, examples, and operating techniques will become apparent to those skilled in the art from this disclosure. For example, the spatial filter may include a grating and a surface-shaped photodetector that is in close contact with or adjacent to the grating. It should be understood that the present invention encompasses various embodiments not described herein.

4...double telecentric lens, 4A...double telecentric lens, 4B...double telecentric lens, 10...measurement object, 20...splitter, 30...light source, 31...illumination lens, 40...first lens, 40A...first lens, 40B...first lens, 41...second lens, 41A...second lens, 41B...second lens, 50...spatial filter, 51...spatial filter, 52...photodetector, 53...photodetector, 54...photodetector, 71...lens barrel, 71A...lens barrel, 71B...lens barrel, 150...grating, 151...lens, 152...photodetector, 250...grating, 251...lens, 252...photodetector, 255...image sensor, 256...image sensor, 301...comparison unit, 302...movement speed calculation unit, 303...differential amplifier, 304...image processing unit

Claims (9)

a splitter that splits reflected light from the moving measurement object into a first light and a second light;
an object-side telecentric lens or a double-side telecentric lens that receives the reflected light;
a comparison unit that compares the amplitude of a first signal obtained by spatially filtering the first light at a first distance from the splitter with the amplitude of a second signal obtained by spatially filtering the second light at a second distance from the splitter that is different from the first distance;
a movement speed calculation unit that calculates a movement speed of the object to be measured based on the signal having the larger amplitude of the first signal or the second signal;
A speed measurement device comprising:
the measurement object moves relatively in parallel with the object-side telecentric lens or the bilateral telecentric lens, and the calculated movement speed of the measurement object is a speed of movement relatively in parallel with the object-side telecentric lens or the bilateral telecentric lens;
Speed measuring device . a first spatial filter for spatially filtering the first light at the first distance from the splitter;
a second spatial filter for spatially filtering the second light at the second distance from the splitter;
The velocity measurement device of claim 1 further comprising: The velocity measurement device of claim 2, wherein each of the first spatial filter and the second spatial filter comprises a photodetector arranged in a striped pattern at a predetermined pitch. The velocity measurement device of claim 2, wherein each of the first spatial filter and the second spatial filter comprises a grating having light-shielding portions arranged in stripes at a predetermined pitch, and a photodetector that receives light that has passed through the grating. a first image capture element configured to capture an image of the first light at the first distance from the splitter;
a second image sensor configured to capture an image of the second light at the second distance from the splitter;
an image processing unit that spatially filters images captured by the first and second image capturing elements;
The velocity measurement device of claim 1 further comprising: The velocity measuring device of claim 1, wherein the object-side telecentric lens or the double-telecentric lens is disposed before the splitter in the direction of travel of the reflected light. The velocity measuring device of claim 1, wherein the object-side telecentric lens or the double-telecentric lens is disposed after the splitter in the direction of travel of the reflected light. The speed measurement device of claim 1, further comprising a light source that irradiates the object to be measured with light. Splitting the reflected light from the moving measurement object into a first light and a second light by a splitter;
receiving the reflected light with an object-side telecentric lens or a double-telecentric lens;
comparing an amplitude of a first signal obtained by spatially filtering the first light at a first distance from the splitter with an amplitude of a second signal obtained by spatially filtering the second light at a second distance from the splitter that is different from the first distance;
calculating a moving speed of the object to be measured based on the signal having the larger amplitude between the first signal and the second signal;
A velocity measurement method comprising:
the measurement object moves relatively in parallel with the object-side telecentric lens or the bilateral telecentric lens, and the calculated movement speed of the measurement object is a speed of movement relatively in parallel with the object-side telecentric lens or the bilateral telecentric lens;
How to measure speed .