JP7840219B2 - Measuring device - Google Patents

Description

This invention relates to a measuring device.

Patent Document 1 describes a distance measuring device that measures the distance to a reflecting object based on the time of flight of light from the time pulse light is emitted until the reflected light is received.

Japanese Patent Publication No. 2021-152536

To reduce the influence of noise from background light such as sunlight, a bandpass filter may be provided in the light-receiving optical system. However, if the wavelength of light emitted from the light-emitting part changes with temperature, it is necessary to extend the passband of the bandpass filter. As a result, the noise mixed into the light-receiving data of the photodetector may increase, potentially reducing measurement accuracy.

The present invention aims to suppress the effects of noise.

One embodiment of the present invention for achieving the above objective is a measuring device comprising: a light-emitting unit that irradiates light with a wavelength corresponding to the temperature within a predetermined wavelength band; a filter that allows light in the predetermined wavelength band to pass through and also allows reflected light from the light-emitting unit to pass through; a light-receiving sensor having a plurality of light-receiving elements; and a dispersion element disposed between the filter and the light-receiving sensor, which disperses the light that has passed through the filter among two or more of the light-receiving elements.

Furthermore, the problems disclosed in this application and their solutions are clearly indicated in the section on embodiments for carrying out the invention and in the drawings.

According to this invention, the effects of noise can be suppressed.

Figure 1 is an explanatory diagram of the overall configuration of the measuring device 1. Figure 2 is a schematic diagram of the measuring device 1. Figure 3 is a timing chart illustrating an example of a measurement method. Figure 4A is an explanatory diagram of the light-receiving unit 20 of this embodiment. Figure 4B is an explanatory diagram of the light-receiving unit 20 of a reference example. Figure 5 is a correspondence table used in the first measurement method. Figures 6A to 6C are explanatory diagrams of the first measurement method. Figure 7A shows the table used in the second measurement method. Figure 7B is an explanatory diagram of the second measurement method. Figure 8 is an explanatory diagram illustrating the correspondence between the light-emitting element 121 and the light-receiving element 222. Figure 9 is an explanatory diagram illustrating another correspondence between the light-emitting element 121 and the light-receiving element 222.

The embodiments for carrying out the present invention will be described below with reference to the drawings. In the following description, identical or similar components may be denoted by common reference numerals, and redundant explanations may be omitted.

<Overall Structure>
Figure 1 is an explanatory diagram of the overall configuration of the measuring device 1. Figure 2 is a schematic explanatory diagram of the measuring device 1.

In the following explanation, the directions are defined as shown in Figure 2. The Z direction is the direction along the optical axis of the light-receiving optical system 24. The object 90 to be measured by the measuring device 1 is located away from the measuring device 1 in the Z direction. The X and Y directions are perpendicular to the Z direction. The multiple light-emitting elements 121 constituting the light-emitting section 12 are arranged two-dimensionally along the X and Y directions. The multiple pixels 221 of the light-receiving sensor 22 are also arranged two-dimensionally along the X and Y directions.

The measuring device 1 is a device for measuring the distance to an object 90. The measuring device 1 functions as a so-called LiDAR (Light Detection and Ranging, Laser Imaging Detection and Ranging) device. The measuring device 1 emits measurement light, detects the reflected light reflected from the surface of the object 90, and measures the time from the emission of the measurement light to the reception of the reflected light, thereby measuring the distance to the object 90 using the TOF (Time of Flight) method. The measuring device 1 comprises an irradiation unit 10, a light receiving unit 20, and a control unit 30. Furthermore, the measuring device 1 in this embodiment includes a temperature sensor 41.

The irradiation unit 10 is an irradiation device that irradiates measurement light toward the object 90. The irradiation unit 10 irradiates measurement light toward the measurement area 50 (see Figure 2) at a predetermined field of view. The irradiation unit 10 has a light-emitting unit 12 and a light-projection optical system 14. The light-emitting unit 12 is a member (light source) that emits light. For example, the light-emitting unit 12 is composed of a surface-emitting laser (VCSEL) array chip. The light-emitting unit 12 has a plurality of light-emitting elements 121 (e.g., surface-emitting lasers; VCSELs), and the plurality of light-emitting elements 121 are arranged two-dimensionally along the X and Y directions. The light-projection optical system 14 is an optical system that irradiates the measurement area 50 with light emitted from the light-emitting unit 12. The light-emitting unit 12 can make each of the light-emitting elements 121 emit light individually. Each of the light-emitting elements 121 of the light-emitting unit 12 is associated with a predetermined area of the measurement area 50 via the light-projection optical system 14. Light emitted from a light-emitting element 121 is transmitted via the light-projection optical system 14 to the corresponding area of the measurement area 50. However, the irradiation unit 10 may be configured to emit light from the entire light-emitting surface of the light-emitting unit 12, illuminating the entire measurement area 50 simultaneously. The wavelength of the light emitted by the light-emitting element 121 changes depending on the temperature. This will be discussed later.

The light-receiving unit 20 receives reflected light from the object 90. The light-receiving unit 20 receives reflected light from the measurement area 50 (see Figure 2). The light-receiving unit 20 has a light-receiving sensor 22 and a light-receiving optical system 24. The light-receiving sensor 22 has a plurality of pixels 221 arranged in two dimensions. For example, in the case of a VGA light-receiving sensor 22, 480 x 640 pixels 221 are arranged in two dimensions. Each pixel 221 has a light-receiving element 222, which outputs a signal (received light data) according to the amount of light received. The light-receiving optical system 24 is an optical system that causes the light-receiving unit 20 to receive reflected light from the measurement area 50. The light-receiving optical system 24 forms an image of the measurement area 50 on the light-receiving surface of the light-receiving sensor 22. Each pixel 221 of the light-receiving sensor 22 is associated with a predetermined area of the measurement area 50 via the light-receiving optical system 24. A certain pixel 221 of the light-receiving sensor 22 receives light (reflected light and background light) from the corresponding area of the measurement area 50 via the light-receiving optical system 24. Furthermore, each pixel 221 of the light-receiving sensor 22 is associated with a predetermined light-emitting element 121 of the light-emitting unit 12. Light emitted from a certain light-emitting element 121 is received by the corresponding pixel 221 via the light-emitting optical system 14 and the light-receiving optical system 24. The light-receiving sensor 22 and the light-receiving optical system 24 will be described later.

The control unit 30 controls the measuring device 1. The control unit 30 controls the irradiation unit 10 and controls the light emitted from it. Furthermore, the control unit 30 measures the distance to the object 90 using the Time of Flight (TOF) method based on the output result of the light receiving unit 20. The control unit 30 includes a calculation unit and a memory device (not shown). The calculation unit is, for example, a CPU, GPU, or other arithmetic processing unit. Part of the calculation unit may be composed of analog arithmetic circuits. The memory device consists of a main memory and an auxiliary memory device, and stores programs and data. The calculation unit executes the programs stored in the memory device, thereby executing various processes for measuring the distance to the object 90. Figure 1 shows the functional blocks of the various processes.

The control unit 30 includes a setting unit 32, a timing control unit 34, and a distance measuring unit 36. The setting unit 32 performs various settings. The timing control unit 34 controls the processing timing of each unit. For example, the timing control unit 34 controls the timing of light emission from the light-emitting unit 12. The distance measuring unit 36 measures the distance to the object 90. The distance measuring unit 36 includes a signal processing unit 362, a time detection unit 364, and a distance calculation unit 366. The signal processing unit 362 processes the output signal (received light data) of the light-receiving sensor 22. The time detection unit 364 detects the time of flight of light (the time from when light is irradiated until the reflected light arrives). The distance calculation unit 366 calculates the distance to the object 90.

Figure 3 is a timing chart illustrating an example of a measurement method.

The control unit 30 (timing control unit 34) causes the light-emitting unit 12 of the irradiation unit 10 to emit pulsed light at a predetermined period. The upper part of Figure 3 shows the timing (emission timing) when the light-emitting unit 12 emits pulsed light. The light emitted from the light-emitting unit 12 is irradiated onto the measurement area 50 via the light-projection optical system 14. The light reflected from the surface of the object 90 within the measurement area 50 is received by the light-receiving sensor 22 via the light-receiving optical system 24. The pixel 221 of the light-receiving sensor 22 receives pulsed reflected light. The center of Figure 3 shows the timing (arrival timing) when the pulsed reflected light arrives. The lower part of Figure 3 shows the pixel data S of a certain pixel 221 of the light-receiving sensor 22 (the light-receiving data of the light-receiving element 222 of a certain pixel 221). The pixel data S of the light-receiving sensor 22 is data indicating the amount of light received by the pixel 221.

The control unit 30 (timing control unit 34) may either emit light from all the light-emitting elements 121 of the light-emitting unit 12 to illuminate the entire measurement area 50 at once, or it may emit light from only some of the light-emitting elements 121 of the light-emitting unit 12 (for example, one light-emitting element 121) to illuminate only a predetermined area of the measurement area 50. When light is emitted from only some of the light-emitting elements 121 of the light-emitting unit 12 (for example, one light-emitting element 121), the control unit 30 (signal processing unit 362) will acquire pixel data S of the pixel 221 corresponding to the emitted light-emitting element 121. The pixel data S acquired by the control unit 30 will be described later.

The distance measuring unit 36 (signal processing unit 362) of the control unit 30 detects the arrival timing of the reflected light based on the pixel data S of each pixel 221. For example, the signal processing unit 362 detects the arrival timing of the reflected light based on the peak timing of the pixel data of each pixel 221.
The distance measuring unit 36 (time detection unit 364) detects the time Tf from when light is emitted until the reflected light arrives, based on the timing of light emission and the timing of light arrival. Time Tf corresponds to the time it takes for light to travel back and forth between the measuring device 1 and the object 90. Then, the distance measuring unit 36 (distance calculation unit 366) calculates the distance L to the object 90 based on time Tf. Note that when Tf is the time from when light is emitted until the reflected light arrives, and C is the speed of light, the distance L is L = C × Tf / 2. The control unit 30 generates a distance image by calculating the distance to the object 90 for each pixel 221 based on the time Tf detected for each pixel 221 of the light receiving unit 20.

<About the light-receiving unit 20>
Figure 4B is an explanatory diagram of the light-receiving unit 20 in a reference example.

The light-receiving optical system 24 includes a condensing lens 241 and a bandpass filter BPF. The condensing lens 241 is an optical element that forms an image of the measurement area 50 on the light-receiving surface of the light-receiving sensor 22. The bandpass filter BPF is a filter that allows light of a specific wavelength to pass through and cuts out light of other wavelengths. In the following description, the wavelength range of light that passes through the bandpass filter BPF may be referred to as the "passband," and the wavelength range of light that is cut off by the bandpass filter BPF may be referred to as the "cutoff band." Since the bandpass filter BPF needs to transmit reflected light, it must be able to transmit at least the wavelength of light emitted from the light-emitting unit 12. In other words, the passband of the bandpass filter BPF must include at least the wavelength of light emitted from the light-emitting unit 12. By including a bandpass filter BPF in the light-receiving optical system 24, light in the cutoff band of background light such as sunlight can be cut, thereby suppressing the influence of noise caused by background light.

On the other hand, the wavelength λ of the light emitted from the light-emitting unit 12 changes with temperature. For example, as the temperature of the light-emitting unit 12 rises, the wavelength λ of the light emitted from the light-emitting unit 12 increases. Here, as an example, let's assume that the wavelength λ of the light emitted from the light-emitting unit 12 changes within the range of 875 to 935 nm depending on the temperature. Furthermore, let's assume that the temperature of the light-emitting unit 12 changes within the range of T1 to T3, where the wavelength λ1 at temperature T1 is 875 nm, the wavelength λ2 at temperature T2 is 905 nm, and the wavelength λ3 at temperature T3 is 935 nm. The light-emitting unit 12 will emit light with a wavelength λ corresponding to the temperature within the wavelength band of λ1 (= 875 nm) to λ3 (= 935 nm).

The bandpass filter (BPF) needs to transmit the wavelength of light emitted from the light-emitting unit 12. Therefore, if the wavelength of the light emitted from the light-emitting unit 12 changes within a predetermined wavelength range (λ1 (=875 nm) to λ3 (=935 nm)) depending on the temperature, the bandpass filter (BPF) needs to transmit light within that wavelength range (λ1 to λ3). In other words, the passband of the bandpass filter (BPF) needs to be extended to include the entire wavelength range (λ1 to λ3) of the light emitted from the light-emitting unit 12. However, as a result of extending the passband of the bandpass filter (BPF), the amount of background light passing through the bandpass filter (light within the passband in the background light) increases. Therefore, in the configuration shown in the example, the noise in the pixel data S (data indicating the amount of light received by pixel 221) increases.

Figure 4A is an explanatory diagram of the light-receiving unit 20 of this embodiment.

The light-receiving optical system 24 in this embodiment includes a bandpass filter BPF and a dispersion element 25. Although the light-receiving optical system 24 in the figure includes a condensing lens 241, as will be described later, the light-receiving optical system 24 does not necessarily have to include a condensing lens 241. In this embodiment as well, the passband of the bandpass filter BPF is set to include the entire wavelength range of the light emitted from the light-emitting unit 12 (the range from λ1 (=875 nm) to λ3 (=935 nm)).

The dispersion element 25 is an optical element that disperses light. The dispersion element 25 is positioned between the bandpass filter BPF and the light receiving sensor 22. Light that has passed through the bandpass filter BPF is incident on the dispersion element 25, and the light dispersed by the dispersion element 25 is incident on the light receiving element 222 of the light receiving sensor 22. In this embodiment, the dispersion element 25 is set to disperse the light that has passed through the bandpass filter BPF (light in the passband of the bandpass filter BPF) across multiple light receiving elements 222. In other words, the dispersion element 25 spectrally separates the light that has passed through the bandpass filter BPF into multiple light receiving elements 222. Here, it is assumed that three light receiving elements 222 are associated with a certain light-emitting element 121, and these three light receiving elements 222 may be referred to as the first light receiving element 222A, the second light receiving element 222B, and the third light receiving element 222C, respectively. Furthermore, the light received by the first light-receiving element 222A may be indicated as S1, the light received by the second light-receiving element 222B as S2, and the light received by the third light-receiving element 222C as S3. The dispersion element 25 distributes the light from a predetermined area of the measurement area 50 corresponding to the light-emitting element 121 (an area on the measurement area 50 to which light emitted from the light-emitting element 121 is irradiated) across the three light-receiving elements 222 (first light-receiving element 222A, second light-receiving element 222B, and third light-receiving element 222C) associated with the light-emitting element 121, which is light in the passband of the bandpass filter BPF.
Furthermore, the range over which the dispersion element 25 disperses the light in the passband of the bandpass filter BPF is not limited to the range spanning three photodetectors 222, but may span two or more photodetectors 222.

The dispersion element 25 can be composed of a prism, diffraction grating, metamaterial, etc. A metamaterial is an optical element in which microstructures smaller than the wavelength of light are arranged on a substrate (e.g., a glass substrate). The dispersion element 25 may be composed of a metamaterial with microstructures arranged in three dimensions, or of a metamaterial (metasurface) with microstructures arranged in two dimensions.

Metamaterials can be used to construct optical elements (metalens) with light-gathering capabilities. Therefore, when the dispersion element 25 in this embodiment is constructed from a metamaterial, it is possible to incorporate a light-gathering function into the dispersion element 25, which focuses light that has passed through the bandpass filter BPF onto the light-receiving sensor 22. This allows for miniaturization of the light-receiving optical system 24. Note that if the dispersion element 25, constructed from a metamaterial, has a light-gathering function, the light-receiving optical system 24 does not necessarily need to include the light-gathering lens 241 shown in the figure. On the other hand, if the light-receiving optical system 24 includes the light-gathering lens 241, there is no need to incorporate a light-gathering function into the dispersion element 25. This reduces design constraints on the dispersion element 25, making it easier to construct the dispersion element 25 from a metamaterial.

Furthermore, it is possible to construct an optical element with a polarizing filter function using metamaterials. Therefore, when the dispersion element 25 of this embodiment is constructed from a metamaterial, it is possible to equip the dispersion element 25 with the function of allowing light vibrating in a predetermined direction to pass through while absorbing light vibrating in a direction intersecting the predetermined direction (polarizing filter function). For example, if the light emitted by the light-emitting unit 12 vibrates in a predetermined direction, the dispersion element 25, constructed from a metamaterial, can suppress the effects of noise by allowing light vibrating in the predetermined direction to pass through while absorbing light vibrating in a direction intersecting the predetermined direction. Also, for example, by having a polarizing filter function where the polarization axis is vertical and the absorption axis is horizontal, it is possible to allow reflected light directly from the object 90 to pass through while absorbing reflected light reflected from the road surface (light vibrating horizontally). In this way, by having a polarizing filter function in the dispersion element 25, the effects of noise from unwanted light can be suppressed.

The dispersion element 25 may be composed of a prism or a diffraction grating. However, if the dispersion element 25 is composed of a prism, the angle of light deflection is small, so in order to disperse light across multiple photodetectors 222, the distance between the dispersion element 25 and the photodetector 22 must be set to be long. Also, if the dispersion element 25 is composed of a diffraction grating, if the number of grooves in the diffraction grating is small, similar to a prism, the distance between the dispersion element 25 and the photodetector 22 must be set to be long. Furthermore, even if the dispersion element 25 is composed of a diffraction grating with a large number of grooves, the intensity of the light received by the photodetector 222 decreases due to light loss corresponding to the diffraction efficiency. In contrast, if the dispersion element 25 is composed of a metamaterial, the distance between the dispersion element 25 and the photodetector 22 can be set to be short, and the decrease in the intensity of the light received by the photodetector 222 can also be suppressed. For example, if the dispersion element 25 is constructed from a prism, the distance between the dispersion element 25 and the light-receiving sensor 22 needs to be set to approximately several tens of millimeters. However, if the dispersion element 25 is constructed from a metamaterial, the distance between the dispersion element 25 and the light-receiving sensor 22 can be set to approximately 10 μm.

For example, when the temperature is T1, the light-emitting unit 12 emits light with wavelength λ1 (= 875 nm), and the reflected light of wavelength λ1 is spectrally separated by the dispersion element 25 and received by the first photodetector 222A. When the temperature is T2, the light-emitting unit 12 emits light with wavelength λ2 (= 905 nm), and the reflected light of wavelength λ2 is spectrally separated by the dispersion element 25 and received by the second photodetector 222B. When the temperature is T3, the light-emitting unit 12 emits light with wavelength λ3 (= 935 nm), and the reflected light of wavelength λ3 is spectrally separated by the dispersion element 25 and received by the third photodetector 222C. In this way, the dispersion element 25 spectrally separates the reflected light (light of the wavelength emitted by the light-emitting unit 12) to the photodetectors 222 in directions corresponding to the wavelength.

Of the background light, background light with wavelengths in the range of λ1 to λ3 passes through the bandpass filter (BPF). In this embodiment, the background light that has passed through the bandpass filter (BPF) is incident on the dispersion element 25 and dispersed across the three photodetectors 222. Therefore, in the configuration shown in this embodiment, the influence of noise contained in the pixel data S (data indicating the amount of light received by pixel 221; light received data from the photodetector 222 that received reflected light) can be reduced to approximately 1/3 compared to the reference example. In the configuration shown in this embodiment, the signal-to-noise ratio (S/N ratio) is improved by approximately 3 times compared to the reference example.

As shown in Figure 1, the measuring device 1 is equipped with a temperature sensor 41. The temperature sensor 41 measures the temperature of the measuring device 1 (particularly the temperature of the light-emitting section 12). The temperature sensor 41 outputs temperature data indicating the measurement result to the control unit 30. The control unit 30 measures the distance based on the light-receiving data of the light-receiving element 222 corresponding to the temperature data of the temperature sensor 41. This point will be explained below.

<First measurement method>
Figure 5 is a correspondence table used in the first measurement method.
The signal processing unit 362 of the control unit 30 has the correspondence table shown in Figure 5 pre-stored. The correspondence table associates temperature T with the received light data that should be used as pixel data S.

When the temperature is between T1 and T12, the light-emitting unit 12 emits light with a wavelength of 875 to 895 nm, and the dispersion element 25 spectrally separates this wavelength range of light toward the first photodetector 222A. When the temperature is between T12 and T23, the light-emitting unit 12 emits light with a wavelength of 895 to 915 nm, and the dispersion element 25 spectrally separates this wavelength range of light toward the second photodetector 222B. When the temperature is between T23 and T3, the light-emitting unit 12 emits light with a wavelength of 915 to 935 nm, and the dispersion element 25 spectrally separates this wavelength range of light toward the third photodetector 222C.

Figures 6A to 6C are explanatory diagrams of the first measurement method.
The signal processing unit 362 refers to a correspondence table based on the temperature data acquired from the temperature sensor 41 and determines the received light data to be used as pixel data S. For example, if the temperature data from the temperature sensor 41 is in the range of T1 to T12 (here, T1 or more and T12 or less), as shown in Figure 6A, the signal processing unit 362 acquires the received light data S1 of the first light-receiving element 222A from among the three light-receiving elements 222 (first light-receiving element 222A, second light-receiving element 222B, and third light-receiving element 222C) corresponding to the light-emitting element 121, based on the correspondence table. Similarly, if the temperature data from the temperature sensor 41 is in the range of T12 to T23, the control unit 30 acquires the received light data S2 of the second light-receiving element 222B based on the correspondence table, as shown in Figure 6B. Furthermore, if the temperature data from the temperature sensor 41 is in the range of T23 to T3, the control unit 30 acquires the received light data S3 of the third light-receiving element 222C based on the correspondence table, as shown in Figure 6C. The signal processing unit 362 acquires pixel data S of the pixel 221 corresponding to the light-emitting element 121 by acquiring light-receiving data from the light-receiving element 222 selected according to the temperature.

The distance measuring unit 36 (signal processing unit 362) of the control unit 30 detects the arrival timing of reflected light based on the light reception data (pixel data S of pixel 221; see Figure 3) acquired from the light receiving element 222 selected according to the temperature. Then, the distance measuring unit 36 (time detection unit 364) detects the time Tf from when the light is emitted until the reflected light arrives, based on the light emission timing and the light arrival timing. Furthermore, the distance measuring unit 36 (distance calculation unit 366) calculates the distance L to the object 90 based on the time Tf.

Incidentally, in the case of the measuring device 1 employing the first measurement method, when the temperature data of the temperature sensor 41 is changed under conditions where the first light-receiving elements 222A to the third light-receiving elements 222C output predetermined light-receiving data (reference conditions), the control unit 30 outputs different distances. This point will be explained below.
First, the light-emitting unit 12 is set to a predetermined temperature (reference temperature), a predetermined distance (reference distance) is set between the measuring device 1 and the object 90, and the first to third light-receiving elements 222A to 322C output predetermined light-receiving data S1 to S3. This condition is defined as the reference condition. The reference temperature and reference distance can be set arbitrarily. For example, when the reference temperature is T2, the light-emitting unit 12 emits light with a wavelength of λ2 (= 875 nm), the dispersion element 25 spectrally separates the reflected light of wavelength λ2 toward the second light-receiving element 222B, and disperses the light with wavelengths λ1 to λ3 that passes through the bandpass filter BPF across the three light-receiving elements 222 according to their wavelengths. The three light-receiving elements 222 then output light-receiving data S1 to S3 according to this reference condition. Furthermore, since the temperature T2 is in the range of T12 to T23, the control unit 30 acquires the light reception data S2 from the second light receiving element 222B as pixel data S, as shown in Figure 6B, and outputs the distance calculated based on the pixel data S.
Next, under the above-described reference conditions, the temperature data from the temperature sensor 41 is changed. Here, only the temperature data acquired by the control unit 30 is changed (in other words, only dummy temperature data is input to the control unit 30), the wavelength of the light emitted by the light-emitting unit 12 is the same as under the reference conditions, and the received light data output by the light-receiving elements 222 is also the same as under the reference conditions. For example, when the reference temperature is T2, when the temperature data from the temperature sensor 41 is changed to T1, the light-emitting unit 12 emits light with a wavelength of λ2 (= 875 nm), and the three light-receiving elements 222 each output the same received light data S1 to S3 as under the reference conditions. When the temperature data from the temperature sensor 41 is changed under the reference conditions, the received light data acquired by the control unit 30 changes, and therefore the control unit 30 outputs different distances. For example, when the temperature data of the temperature sensor 41 is changed from T2 to T1 under reference conditions, even though the temperature of the light-emitting unit 12 and the distance between the measuring device 1 and the object 90 are maintained, and the received data S1 to S3 output by the first light-receiving element 222A to the third light-receiving element 222C are under the same conditions, the control unit 30 changes the distance it outputs from the distance corresponding to the received data S2 of the second light-receiving element 222B to the distance corresponding to the received data S1 of the first light-receiving element 222A. Thus, in the case of the measuring device 1 employing the first measurement method, when the temperature data of the temperature sensor 41 changes under conditions in which the light-receiving element 222 outputs predetermined received data (reference conditions), the control unit 30 outputs a different distance. In other words, by changing the temperature data of the temperature sensor 41 under conditions in which the light-receiving element 222 outputs predetermined received data (reference conditions), it is possible to verify that the distance is measured based on the received data of the light-receiving element 222 corresponding to the temperature data of the temperature sensor 41.

<Second measurement method>
The angle at which the dispersion element 25 emits light toward the photodetector 222 gradually changes according to the wavelength. As a result, the dispersion element 25 spectrally separates the reflected light toward the boundary between the two photodetectors 222 (for example, the first photodetector 222A and the second photodetector 222B), and the two photodetectors 222 may receive the reflected light. In such a case, it is more advantageous to measure the distance based on the received light data of the two photodetectors 222 that receive the reflected light, rather than measuring the distance based on the received light data of one of the three photodetectors 222, as in the first measurement method. In the second measurement method, it is possible to measure the distance based on the received light data of two or more photodetectors 222 depending on the temperature data.

Figure 7A shows the table used in the second measurement method. Figure 7B is an explanatory diagram of the second measurement method.

The memory unit (not shown) of the control unit 30 has the weight table shown in Figure 7 pre-stored. The weight table associates temperature T with weight coefficients. The weight coefficients correspond to the weight data associated with the temperature data from the temperature sensor 41. The weight coefficients include a first weight coefficient W1, a second weight coefficient W2, and a third weight coefficient W3. The first weight coefficient W1 is the weight coefficient for the light-receiving data S1 of the first light-receiving element 222A. The second weight coefficient W2 is the weight coefficient for the light-receiving data S2 of the second light-receiving element 222B. The third weight coefficient W3 is the weight coefficient for the light-receiving data S3 of the third light-receiving element 222C.

The signal processing unit 362 obtains weight coefficients (weight data) corresponding to the temperature data acquired from the temperature sensor 41 from a weight table stored in the memory unit. That is, the signal processing unit 362 refers to the weight table based on the temperature data acquired from the temperature sensor 41 and obtains weight coefficients (first weight coefficient W1, second weight coefficient W2, and third weight coefficient W3) corresponding to the temperature data. Then, the signal processing unit 362 acquires the light-receiving data S1 to S3 of the three light-receiving elements 222 (first light-receiving element 222A, second light-receiving element 222B, and third light-receiving element 222C) corresponding to the light-emitting element 121 that emits light, and calculates the pixel data S by weighting the light-receiving data S1 to S3 of each light-receiving element 222 according to the weight coefficients. Specifically, the signal processing unit 362 calculates the pixel data S based on the following formula.
S=S1×W1+S2×W2+S3×W3

For example, when the temperature T1 (when reflected light with wavelength λ1 (= 875 nm) is spectrally separated by the dispersion element 25 to the first photodetector 222A), the weighting coefficients are set to W1=1, W2=0, and W3=0, respectively. Similarly, when the temperature T2 (when reflected light with wavelength λ2 (= 905 nm) is spectrally separated by the dispersion element 25 to the second photodetector 222B), the weighting coefficients are set to W1=0, W2=1, and W3=0, respectively. Furthermore, when the temperature T3 (when reflected light with wavelength λ3 (= 935 nm) is spectrally separated by the dispersion element 25 to the third photodetector 222C), the weighting coefficients are set to W1=0, W2=0, and W3=1, respectively. When the temperature T is between T1 and T2, W1 and W2 are set such that the closer the temperature T is to T1 than T2, the larger W1 becomes than W2 (W3 is set to zero). This allows for accurate distance measurement even when the dispersion element 25 is spectrally separating reflected light at the boundary between the first photodetector 222A and the second photodetector 222B. Furthermore, when the temperature T is between T2 and T3, W2 and W3 are set such that W2 becomes larger than W3 as the temperature T approaches T2 (W1 is set to zero). This allows for accurate distance measurement even when the dispersion element 25 is spectrally separating reflected light at the boundary between the second photodetector 222B and the third photodetector 222C.

Furthermore, the distance measuring unit 36 (signal processing unit 362) of the control unit 30 detects the arrival timing of the reflected light based on the calculated pixel data S (see Figure 3). The distance measuring unit 36 (time detection unit 364) then detects the time Tf from the time of light emission until the reflected light arrives, based on the light emission timing and the light arrival timing. The distance measuring unit 36 (distance calculation unit 366) then calculates the distance L to the object 90 based on the time Tf.

Incidentally, even in the case of the measuring device 1 employing the second measurement method, if the temperature data of the temperature sensor 41 changes under conditions where the light-receiving element 222 outputs predetermined light-receiving data (reference conditions), the control unit 30 will output a different distance. In other words, by changing the temperature data of the temperature sensor 41 under conditions where the light-receiving element 222 outputs predetermined light-receiving data (reference conditions), it is possible to verify that the distance is measured based on the light-receiving data of the light-receiving element 222 corresponding to the temperature data of the temperature sensor 41. Furthermore, in the case of the measuring device 1 employing the second measurement method, if the temperature data of the temperature sensor 41 is gradually changed, the distance output by the control unit 30 will gradually change.

<Regarding irradiation methods>
Figure 8 is an explanatory diagram illustrating the correspondence between the light-emitting element 121 and the light-receiving element 222. Figure 8 also illustrates the correspondence between the pixel 221 and the light-receiving element 222.

As already explained, the light-emitting unit 12 is equipped with a plurality of light-emitting elements 121. The figure shows two adjacent light-emitting elements 121 (#1, #2) of the plurality of light-emitting elements 121 of the light-emitting unit 12. The figure also shows regions (#1, #2) on the measurement area 50 corresponding to the two light-emitting elements 121 (#1, #2). The figure also shows two pixels 221 (#1, #2) of the light-receiving sensor 22 that correspond to the two light-emitting elements 121 (#1, #2) and the two regions (#1, #2) on the measurement area 50. The two pixels 221 (#1, #2) correspond to the two light-emitting elements 121 (#1, #2) of the light-emitting unit 12. Light emitted from light-emitting element 121 #1 irradiates region #1 on the measurement area 50, and light from region #1 (reflected light and background light) is received by pixel 221 #1. Furthermore, the light emitted from the light-emitting element 121#2 illuminates region #2 on the measurement area 50, and the light from region #2 (reflected light and background light) is received by the pixel 221#2.

In the configuration shown in Figure 8, one pixel 221 of the light-receiving sensor 22 contains multiple (three in this case) light-receiving elements 222. Here, the dispersive element 25 of the light-receiving optical system 24 spectrally separates the light (reflected light and background light) arriving from region #1 on the measurement area 50 across multiple light-receiving elements 222 belonging to pixel 221#1 (here, the first light-receiving element 222A to the third light-receiving element 222C). Similarly, the dispersive element 25 of the light-receiving optical system 24 spectrally separates the light (reflected light and background light) arriving from region #2 on the measurement area 50 across multiple light-receiving elements 222 belonging to pixel 221#2.

In Figure 8, the multiple light-receiving elements 222 associated with light-emitting element 121#1 (multiple light-receiving elements 222 belonging to pixel 221#1) and the multiple light-receiving elements 222 associated with light-emitting element 121#2 (multiple light-receiving elements 222 belonging to pixel 221#2) are separate and do not overlap. Thus, when the multiple light-receiving elements 222 associated with one of the two light-emitting elements 121 are different from those associated with the other light-emitting element 121, the control unit 30 (timing control unit 34) can simultaneously emit light from both light-emitting elements 121. In the case shown in Figure 8, the control unit 30 (timing control unit 34) may emit light from all light-emitting elements 121 of the light-emitting unit 12 to illuminate the entire measurement area 50 at once, or it may emit light from some of the light-emitting elements 121 of the light-emitting unit 12 (for example, one light-emitting element 121) to illuminate only a predetermined area of the measurement area 50.

Figure 9 is an explanatory diagram illustrating another correspondence between the light-emitting element 121 and the light-receiving element 222. Figure 9 is also an explanatory diagram illustrating another correspondence between the pixel 221 and the light-receiving element 222.

In the configuration shown in Figure 9, one pixel 221 of the light-receiving sensor 22 is composed of one light-receiving element 222. Here, the dispersion element 25 of the light-receiving optical system 24 spectrally separates the light (reflected light and background light) arriving from region #1 on the measurement area 50 across three light-receiving elements 222, each composed of three pixels 221. In addition, the dispersion element 25 of the light-receiving optical system 24 spectrally separates the light (reflected light and background light) arriving from region #2 on the measurement area 50 across three light-receiving elements 222, each composed of three pixels 221.
In Figure 9, the multiple light-receiving elements 222 associated with light-emitting element 121#1 and the multiple light-receiving elements 222 associated with light-emitting element 121#2 partially overlap. When the multiple light-receiving elements 222 associated with each of the two light-emitting elements 121 partially overlap in this way, the control unit 30 (timing control unit 34) does not emit light from the two light-emitting elements 121 simultaneously. In this case, the control unit 30 emits light from some of the light-emitting elements 121 of the light-emitting unit 12 (for example, one light-emitting element 121) to irradiate only a predetermined area of the measurement area 50 with light. When light is to be emitted simultaneously from two or more light-emitting elements 121, the control unit 30 (timing control unit 34) irradiates light from multiple light-emitting elements 121 whose corresponding multiple light-receiving elements 222 do not overlap.

Furthermore, as shown in Figure 4A, it is desirable to place a condensing lens 241 in front of the dispersion element 25 (on the side of the measurement area 50) and use the condensing lens 241 to focus light (reflected light and background light) arriving from different regions (#1, #2) on the measurement area 50 to different positions on the dispersion element 25. This makes it easier to configure the light-receiving optical system 24 so that the multiple light-receiving elements 222 belonging to pixel 221#1 and the multiple light-receiving elements 222 belonging to pixel 221#2 do not overlap, as shown in Figure 8.

===Summary===
The measuring device 1 of this embodiment includes a light-emitting unit 12, a bandpass filter BPF (corresponding to a filter), a light-receiving sensor 22, and a dispersion element 25. The light-emitting unit 12 irradiates light with a wavelength corresponding to the temperature within a predetermined wavelength band range. The bandpass filter BPF allows light in the predetermined wavelength band to pass through and also allows reflected light from the light-emitting unit 12 to pass through. The light-receiving sensor 22 has a plurality of light-receiving elements 222. The dispersion element 25 is placed between the bandpass filter BPF and the light-receiving sensor 22 and disperses the light that has passed through the bandpass filter BPF to two or more light-receiving elements 222. With this configuration, light with a wavelength corresponding to the temperature is irradiated from the light-emitting unit 12, and after passing through the bandpass filter BPF, the light is spectrally separated by the dispersion element 25 to specific light-receiving elements 222 according to the wavelength. On the other hand, the background light that has passed through the bandpass filter BPF is dispersed by the dispersion element 25 across two or more light-receiving elements 222. Therefore, the background light received by the light-receiving element 222, which receives reflected light, can be reduced, and the influence of noise contained in the received data output from the light-receiving element 222 can be suppressed.

Furthermore, the measuring device 1 of this embodiment further includes a temperature sensor 41 and a control unit 30. The control unit 30 measures the distance based on the light-receiving data of the light-receiving element 222 corresponding to the temperature data of the temperature sensor 41. This allows for distance measurement based on light-receiving data with reduced noise interference, thereby improving measurement accuracy.

Furthermore, the measuring device 1 of this embodiment further comprises a temperature sensor 41 and a control unit 30. When the temperature data of the temperature sensor 41 changes under conditions where the light-receiving element 222 outputs predetermined light-receiving data (reference conditions), the control unit 30 outputs a different distance. In other words, by changing the temperature data of the temperature sensor 41 under conditions where the light-receiving element 222 outputs predetermined light-receiving data (reference conditions), it is possible to verify that distance is measured based on the light-receiving data of the light-receiving element 222 corresponding to the temperature data of the temperature sensor 41.

Furthermore, the measuring device 1 of this embodiment includes a storage unit that stores weighting coefficients (corresponding to weight data) associated with the temperature data of the temperature sensor 41 (see Figure 7A). The control unit 30 then retrieves the weighting coefficients (weight data) corresponding to the temperature data of the temperature sensor 41 from the storage unit, and calculates the received light data S by applying weights according to the weighting coefficients to the received light data of two or more light-receiving elements 222. The distance is then measured based on this received light data S. This allows for accurate distance measurement even when the dispersion element 25 is spectrally separating reflected light at the boundary of the light-receiving elements 222.

Furthermore, the dispersion element 25 in this embodiment is made of metamaterial. This allows the distance between the dispersion element 25 and the light receiving sensor 22 to be set shorter, thereby enabling miniaturization of the measuring device 1.
When the dispersion element 25 is made of a metamaterial, it is desirable that the dispersion element 25 has a light-gathering function (a function that focuses the light that has passed through the filter onto the light-receiving sensor 22). This makes it possible to miniaturize the light-receiving optical system 24. Furthermore, when the dispersion element 25 is made of a metamaterial, it is desirable that the dispersion element 25 has a polarizing filter function (a function that allows light vibrating in a predetermined direction to pass through while absorbing light vibrating in a direction intersecting the predetermined direction). This makes it possible to suppress the influence of noise caused by unwanted light.
The dispersion element 25 may be composed of a prism or a diffraction grating. This allows the dispersion element 25 to be constructed at a low cost.

Furthermore, the measuring device 1 of this embodiment includes a focusing lens 241 positioned between the bandpass filter BPF and the dispersion element 25. This eliminates the need for the dispersion element 25 to also have a focusing function, thereby reducing design constraints on the dispersion element 25.

Although embodiments of the present invention have been described in detail above, the present invention is not limited to the above embodiments and includes various modifications. Furthermore, the above embodiments are described in detail to clearly explain the present invention and are not necessarily limited to those comprising all the described components. Also, some components of the above embodiments can be added, deleted, or replaced with other components.

1 measurement device, 10 irradiation section,
12 Light-emitting section, 121 Light-emitting element, 14 Optical system for light projection,
20 Light receiving unit, 22 Light receiving sensor, 221 Pixel,
222 Photodetector, 222A-C First to Third Photodetectors,
24 Optical system for light reception, 241 Focusing lens,
BPF bandpass filter, 25 dispersion elements,
30 Control unit, 32 Setting unit,
34 Timing control unit, 36 Distance measuring unit,
362 Signal processing unit, 364 Time detection unit, 366 Distance calculation unit,
41. Temperature sensor,
50 measurement area, 90 target object

Claims (7)

A light-emitting unit that emits light with a wavelength corresponding to the temperature within a predetermined wavelength band,
A filter that allows light in the predetermined wavelength band to pass through and allows reflected light from the light-emitting unit to pass through,
A light-receiving sensor having multiple light-receiving elements,
A dispersion element is placed between the filter and the light receiving sensor and disperses the light that has passed through the filter to two or more light receiving elements,
A temperature sensor and
A control unit that measures distance based on light-receiving data from the light-receiving element corresponding to the temperature data of the temperature sensor,
A storage unit that stores weight data associated with the temperature data of the temperature sensor,
Equipped with ,
The control unit,
The weight data corresponding to the temperature data of the temperature sensor is obtained from the storage unit.
The distance is measured by assigning weights to the light-receiving data of each of the two or more light-receiving elements according to the weight data.
Measuring device. A light-emitting unit that emits light with a wavelength corresponding to the temperature within a predetermined wavelength band,
A filter that allows light in the predetermined wavelength band to pass through and allows reflected light from the light-emitting unit to pass through,
A light-receiving sensor having multiple light-receiving elements,
A dispersion element is placed between the filter and the light receiving sensor and disperses the light that has passed through the filter to two or more light receiving elements,
A temperature sensor and
When the light-receiving element outputs predetermined light-receiving data, if the temperature data of the temperature sensor changes, the control unit outputs a different distance.
A storage unit that stores weight data associated with the temperature data of the temperature sensor,
Equipped with ,
The control unit,
The weight data corresponding to the temperature data of the temperature sensor is obtained from the storage unit.
The distance is measured by assigning weights to the light-receiving data of each of the two or more light-receiving elements according to the weight data.
Measuring device. A measuring device according to claim 1 or 2 ,
The aforementioned dispersion element is made of metamaterial, and the measuring device is a measuring device. The measuring device according to claim 3 ,
The aforementioned dispersion element is a measuring device having the function of focusing the light that has passed through the filter onto the light receiving sensor. The measuring device according to claim 3 ,
The aforementioned dispersion element is a measuring device having the function of allowing light vibrating in a predetermined direction to pass through while absorbing light vibrating in a direction intersecting the predetermined direction. A measuring device according to claim 1 or 2 ,
The measuring device is configured such that the dispersion element is composed of a prism or a diffraction grating. A measuring device according to claim 1 or 2 ,
A measuring device comprising a focusing lens positioned between the filter and the dispersion element, which focuses the light that has passed through the filter onto the dispersion element.