Target identifying apparatus

Abstract

To provide an object identification device advantageous to the improvement of identification performance, miniaturization and cost reduction.SOLUTION: A plurality of light emitting elements configured to emit light having different center wavelengths in a predetermined direction, at least one light receiving element configured to generate a signal corresponding to intensity of light received from the predetermined direction, and a control unit configured to control a light emission timing of the plurality of light emitting elements and to extract a signal component having a wavelength corresponding to each of the plurality of light emitting elements from the signal, wherein an object existing in the predetermined direction is identified on the basis of a reflectance obtained from the signal component, the control unit includes a pulse modulation unit configured to execute ON / OFF of each of the plurality of light emitting elements simultaneously in parallel in a predetermined modulation pattern in synchronization with a predetermined frequency, and the modulation pattern is defined by an orthogonal matrix having an array of the plurality of light emitting elements as a row and an ON / OFF timing of each of the plurality of light emitting elements as a column.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an object identification device. [Background technology]

[0002] As a method for detecting and identifying an obstacle, a method for identifying an object based on the reflectance of a specific wavelength or a specific wavelength range of visible light to short-wave infrared light is known.

[0003] For example, as an example of using measurement results at two wavelengths, the Normalized Difference Human Index (NDHI) is an index that determines the presence or absence of human skin based on the normalized difference in reflectance at two wavelengths in the shortwave infrared range, and other examples include the Normalized Difference Vegetation Index (NDVI) and the Normalized Difference Water Index (NDWI).

[0004] Patent Documents 1 and 2 disclose object identification devices that irradiate an object with a plurality of types of light with different center wavelengths and identify the object based on the amount of reflected light (energy) from each of the light sources. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-217149 [Patent Document 2] Japanese Patent Application Laid-Open No. 2013-117454 DISCLOSURE OF THE INVENTION [Problem to be solved by the invention]

[0006] When using such an object identification device as an obstacle detection means for a moving object, for example, a personal mobility device such as an electric wheelchair, there are many types of obstacles on the road, such as plants and buildings in addition to people and vehicles, so it is preferable to be able to obtain measurement data at many wavelengths in order to identify them.

[0007] In particular, Patent Document 1 identifies objects based on logical operations on multiple normalized difference indices. In this case, simultaneous measurement of reflectance at N wavelengths (N≧3) is required. Patent Document 2 modulates the brightness values ​​of two LEDs at two wavelengths using two orthogonal and exclusive signals, such as a sine function and a cosine function. However, to achieve simultaneous measurement at three or more wavelengths, it is necessary to modulate light sources at more wavelengths using mutually orthogonal functions, and obtain detection signals corresponding to the response signals of each modulated signal in the light-receiving mechanism. This requires the use of bandpass filters according to the number of wavelengths. Furthermore, since multiple LEDs are exclusively illuminated, the light-emission time (duty ratio) per wavelength decreases as the number of wavelengths increases, which can lead to a decrease in the S / N ratio due to insufficient light intensity and a decrease in accuracy due to motion blur of the object caused by long-term light emission. Furthermore, if Patent Document 1 were to be implemented using separate observation systems for each wavelength, the same number of light-receiving elements would be required as the number of wavelengths (LEDs) used, which is disadvantageous for miniaturizing and reducing costs.

[0008] Furthermore, when using only background light without LED light, stable measurements cannot be performed in low-light environments such as indoors or at twilight. Even if the illumination is sufficient, the sunlight spectrum reaching the ground surface changes depending on the time of day and weather, making it necessary to correct the amount of incident light for each wavelength, which complicates the measurement system and processing method.

[0009] The present invention has been made in consideration of the above-described circumstances, and its purpose is to provide an object identification device that can separate and detect multiple wavelength components emitted simultaneously using a single light-receiving element, and that is advantageous in terms of handling multiple wavelengths, improving identification performance, miniaturization, and cost reduction. [Means for solving the problem]

[0010] In order to solve the above problems, the present invention provides: a plurality of light emitting elements that emit light beams having different center wavelengths in predetermined directions; at least one light receiving element that generates a signal according to the intensity of light received from the predetermined direction; a control unit that controls light emission timings of the plurality of light-emitting elements and extracts signal components of wavelengths corresponding to the plurality of light-emitting elements from the signal; An object identification device configured to identify an object present in the predetermined direction based on a reflectance calculated from the signal component, The control unit is provided with a pulse modulation unit that simultaneously and in parallel turns on / off each of the plurality of light-emitting elements in synchronization with a predetermined frequency in a predetermined modulation pattern, and the modulation pattern is defined by an orthogonal matrix with the arrangement of the plurality of light-emitting elements as rows and the on / off times of each element as columns. [Effects of the Invention]

[0011] As described above, the object identification device of the present invention synchronizes multiple light-emitting elements and causes them to emit light simultaneously and in parallel using a modulation pattern defined by an orthogonal matrix, thereby making it possible to separate and detect each wavelength component from time-series data received simultaneously by a single light-receiving element using the modulation pattern, and since the elements are emitted non-exclusively, the light-emitting time (duty ratio) of each light-emitting element can be ensured, which is advantageous for handling multiple wavelengths, improving identification performance, miniaturization, and cost reduction. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a block diagram illustrating an object identification device according to an embodiment of the present invention. [Figure 2] 4 is a time chart showing a modulation pattern of a light emitting element in the embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In Figure 1, the object identification device 1 according to an embodiment of the present invention comprises a light-emitting unit 20 including a plurality of light-emitting elements 21 oriented in a predetermined direction and their drive, a light-receiving unit 30 including one light-receiving element 31 oriented in the same direction, and a control unit 10 that controls the light-emitting timing of each light-emitting element 21 and performs arithmetic processing of the signal generated by the light-receiving element 31.

[0014] The light-emitting unit 20 is composed of N light-emitting elements 21 (LEDs) that emit light with different center wavelengths, and the output and irradiation width of each LED are made equal, so that the amount of energy irradiated in a predetermined direction is constant for each wavelength. In a preferred embodiment, the light-emitting unit 20 is composed of N=7 light-emitting elements 21 (LED1 to LED7), but the number of light-emitting elements 21 is not limited to this.

[0015] The control unit 10 is implemented as a one-chip CPU and includes an oscillator circuit 11 that generates an internal operating clock (clock pulse, pulse width Δt) for the CPU, and a pulse modulator 12 that generates a modulation signal that turns on / off the light-emitting elements 21 (LED1 to LED7) in synchronization with the operating clock. The modulation signal is given in the form of a modulation pattern defined by an n x n orthogonal matrix, with the arrangement of the light-emitting elements 21 (LED1 to LED7) as rows and the on / off times as columns. This modulation pattern is stored in a register in the CPU.

[0016] The light receiving unit 30 is configured as an analog front end (AFE) including a light receiving element 31 made of a photodiode (PD) or phototransistor that generates an electrical signal according to the intensity of received light, a high-pass filter 32, and a buffer amplifier 33. From the electrical signal generated by the light receiving element 31, DC components due to background light are removed by the high-pass filter 32, and the analog signal containing only modulated components due to reflected light of light emitted from the light emitting element 21 is converted into a digital signal by the A / D converter 14 of the control unit 10. This digital signal is represented by n-step time series data (signal data series) X(x1 to x2) corresponding to one cycle (one sequence) of illumination of the light emitting element 21 (LED1 to LED7). n ) is included.

[0017] On the other hand, the pulse modulation section 12 of the control unit 10 generates a reference signal Y k (Y k1 ~Y kn ) is generated. k (Y k1 ~Y kn ) is subjected to a phase shift 13 to align the phase with the reflected light as necessary, and is then processed by a processing unit 15 to generate a signal data series X (x1 to x n ) and modulated components W (w1 to w n ) is calculated.

[0018] Furthermore, the discrimination unit 16 of the control unit 10 discriminates each modulation component W (w1 to w n ) based on the reflectance of each wavelength calculated from the normalized index, and an object present in a predetermined direction is identified based on the calculated normalized index and a predetermined identification condition.

[0019] A normalized index, for example, a normalized difference human skin index NDHI, is expressed by the following equation. NDHI=(R1070-R1550) / (R1070+R1550) Here, R1070 and R1550 are the reflectances at wavelengths of 1070 nm and 1550 nm in the short-wave infrared region, and if NDHI>0.5, it is determined that human skin is present.

[0020] The normalized difference vegetation index (NDVI) and normalized difference moisture index (NDWI) are expressed by the following equations: NDVI=(Rnir1-Rred) / (Rnir1+Rred), NDWI=(Rgreen-Rnir2) / (Rgreen+Rnir2) Here, Rnir1 and Rnir2 are the reflectances of a specific or fixed range of wavelengths in the near infrared (λ=720 to 1200 nm), Rred is the reflectance of a specific or fixed range of wavelengths in red (λ=620 to 690 nm), and Rgreen is the reflectance of a specific or fixed range of wavelengths in green (λ=420 to 500 nm).

[0021] Next, the modulation pattern of the light emitting element 21 will be specifically described. It has already been mentioned that the modulation pattern of the light-emitting element 21 is defined by an n×n orthogonal matrix. If n=N+1, where N is the number of light-emitting elements 21 (number of wavelengths) and a DC component corresponding to the background light (Amb), then the n×n orthogonal matrix is ​​an n-th order Hadamard matrix H n and the Hadamard matrix H n is the value of each row vector (Y k ) is a Walsh function sequence, and any two rows form an orthogonal function system (orthogonal vector) that is orthogonal to each other.

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[0022] For example, when the light emitting section 20 is configured with N=7 light emitting elements 21 (LED1 to LED7), an eighth-order Hadamard matrix H8 can be used for the modulation pattern as shown in the following equation 2.

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[0023] In this case, the first row is the background light (Amb), the second to seventh rows correspond to the arrangement of the light-emitting elements 21 (LED1 to LED7), the matrix element "1" corresponds to lighting (LED on) and "-1" corresponds to lighting (LED off), and the on / off times t1 to t8 of one cycle (one sequence) correspond to the columns. The modulation pattern of the light-emitting elements 21 (LED1 to LED7) is shown in Table 1 below, and is as shown in the time chart of Figure 2. [Table 1]

[0024] When the light-emitting elements 21 (LED1 to LED7) are made to emit light in accordance with the above modulation pattern (H8), the signal data series X (x1 to x8) corresponding to the received light intensity obtained by the light-receiving element 31 is as shown in the columns of Table 2 below. Note that here, the reflectance of LED1 is set to 1.0, the amount of energy received by the light-receiving element 31 when this LED1 is on is set to the reference (1.0), and the amount of energy received by the light-receiving element 31 from background light is set to 100. [Table 2]

[0025] The modulation components W (w0 to w7) corresponding to each wavelength of the light-emitting elements 21 (LED1 to LED7) by the above modulation pattern (H8) are obtained by linearly transforming the signal data series X (x1 to x8) with the matrix (H8), i.e., by multiplying by the matrix (H8), as shown in the following equation 3. Note that W0 represents the amount of energy of the DC component, and is the sum of the DC components of the background light and the light from each LED.

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[0026] An orthogonal matrix is ​​a square matrix whose inverse is equal to its transpose, and when multiplied by its own transpose, it becomes an identity matrix. Therefore, when an orthogonal matrix that defines a modulation pattern is multiplied by its transpose (inverse), it becomes an identity matrix. Furthermore, a Hadamard matrix is ​​defined as a square matrix whose elements are either "1" or "-1" and whose rows are orthogonal to each other, and is an orthogonal matrix that is equal to its own transpose.

[0027] Therefore, the signal data series X (x1 to x8) including the wavelength components of the light emitting elements 21 (LED1 to LED7) modulated by the modulation pattern (H8) defined by the Hadamard matrix is ​​converted into a reference signal Y corresponding to the original modulation pattern (H8), which is also a transpose matrix. k By multiplying by the above, the amount of received light energy W (w0 to w7) can be obtained as a diagonal matrix obtained by multiplying each wavelength component by a unit matrix.

[0028] The amount of light energy received W (w0 to w7) for each modulation pattern obtained is shown in the 9th row of Table 3 below, and the breakdown of each modulation component is shown in the 1st to 8th rows. [Table 3]

[0029] As described above, the component amount of each modulation pattern, excluding the Y0 component, is four times the set reflectance of the LED light modulated by each pattern. This corresponds to each of the light-emitting elements 21 (LED1 to LED7) being turned on four times per cycle (one sequence), as shown in FIG. 2 and Table 1. In other words, in this embodiment, the light-emitting time (duty ratio) of each light-emitting element is four times longer than when the same number of light-emitting elements are each turned on exclusively once per cycle.

[0030] Although the contribution of each LED light occurs to the Y0 component corresponding to the background light (Amb), the Y0 component is irrelevant to object identification, and this does not pose a problem.

[0031] By the above calculations, it is possible to separate the components of each light-emitting element 21 (LED1 to LED7) from the time series data X (x1 to x8) of the total amount of energy received by one light-receiving element 31, and further it is possible to separate it from the background light (Amb), which is a DC component.

[0032] (Other embodiments) In the above embodiment, an eighth-order Hadamard matrix (H8) is used for the modulation pattern, and the light-emitting unit 20 is configured with N=7 light-emitting elements 21 (LED1 to LED7), but the number of light-emitting elements 21 is not limited to this.

[0033] For example, if the modulation pattern uses the fourth-order Hadamard matrix (H4) shown in the following equation 4, the light-emitting unit 20 is configured with N=3 light-emitting elements 21 (LED1 to LED3), and the first row corresponds to background light (Amb), signal processing similar to that of the previously described embodiment can be performed.

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[0034] Conversely, by using a higher-order Hadamard matrix in the modulation pattern, the number of light-emitting elements 21 (LEDs) can be further increased. For example, if the modulation pattern uses a 16th-order Hadamard matrix (H 16 ), the light emitting unit 20 can be configured with N=15 light emitting elements 21 (LED1 to LED15), the background light (Amb) can be assigned to the first row, and similar signal processing can be performed. Here, H8 is an 8th-order Hadamard matrix.

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[0035] The number of light-emitting elements 21 (LEDs) can also be increased by providing two or more light-receiving elements 31 (light-receiving units 30) with different wavelength ranges. For example, by providing two units each including a pulse modulation unit 12, a light-emitting unit 20, a light-receiving unit 30, and a calculation processing unit 15, with one being a first unit corresponding to the visible light range and the other being a second unit corresponding to the short-wave infrared range, it becomes possible to support 14 types of wavelengths when an eighth-order Hadamard matrix (H8) is used for each modulation pattern, and six types of wavelengths when a fourth-order Hadamard matrix (H4) is used.

[0036] In each of the above embodiments, the modulation pattern includes each row vector (Y k ) is defined by a sequence of Walsh functions, this has the following advantages. (i) The elements of each row are represented by only "1" and "-1", which is advantageous for associating with the on / off state of light-emitting elements (LEDs). (ii) The light emitting time (duty ratio) of each light emitting element can be increased. (iii) The calculation of each modulation component can be easily performed.

[0037] Although the Walsh function sequence has the above advantages, the orthogonal functions used in the modulation pattern are not limited to this, and other orthogonal functions can be used in combination with light emitting elements (LEDs).

[0038] Furthermore, in each of the above embodiments, an LED is used as the light-emitting element, but instead of an LED, an LD may be used as the light-emitting element, or the light-emitting unit may be configured by a combination of a strobe discharge tube and a narrow-band optical filter, or a combination of a halogen lamp, a narrow-band optical filter, and a liquid crystal shutter.

[0039] (Main components and effects) As described above, the object identification device according to the present invention is configured to modulate a multi-wavelength (Nch) light-emitting element (LED) in accordance with each basis function of an orthogonal function sequence, thereby separating and extracting each wavelength component from time-series data simultaneously received by a single light-receiving element, thereby: Regardless of the number of wavelengths of the light-emitting element (LED), the signal level of each wavelength can be extracted with a single light-receiving element, allowing the device to be made smaller than when a light-receiving element is provided for each wavelength, making it suitable for use as an obstacle detection means for personal mobility devices with limited installation space.

[0040] Furthermore, compared to the case where light is received exclusively by a single light receiving element in a time-division manner, this method is advantageous for multi-wavelength applications, and it allows for a longer light emission time (duty ratio) per wavelength, which is advantageous for improving the S / N ratio and reducing the effects of motion blur.

[0041] Furthermore, because it is an active sensor system that uses LED light, background light can be removed when extracting the signal level of each wavelength, making it usable day or night and in any weather.

[0042] In particular, the object identification device of the present invention is configured to simultaneously turn on / off each of multiple light-emitting elements (LEDs) in a modulation pattern defined by an orthogonal matrix with the rows representing the arrangement of the light-emitting elements and the columns representing their on / off times.This allows the signal components corresponding to each wavelength to be extracted by a calculation process in which the signal data series generated by one light-receiving element is multiplied by the inverse matrix (transpose matrix) of the orthogonal matrix used for modulation, and in addition to the above advantages, this has the advantage of being able to perform signal processing in a short period of time and with fewer steps.

[0043] Furthermore, by assigning a virtual DC component assuming background light to the first row of the orthogonal matrix that defines the modulation pattern, all elements in the first column of the orthogonal matrix have values, resulting in a pattern in which all light-emitting elements emit light simultaneously, which is advantageous in terms of ensuring the duty ratio.In addition, compared to when light is emitted exclusively, the range of application of orthogonal matrices is expanded, and there is the advantage that a Hadamard matrix, which has many advantages in various respects, can be applied as an orthogonal matrix.

[0044] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications and variations are possible within the scope of the present invention based on the technical concept of the present invention. [Explanation of symbols]

[0045] 10. Object Identification Device 11 Oscillator Circuit 12 Pulse modulation section 13 Phase Shift 14 A / D converter 15 Processing unit 16 Identification unit 20 Light-emitting part 21 LED (light emitting element) 22 LED driver 30 Light receiving part 31 Photodetector 32 Bypass Filter 33 Buffer amplifier

Claims

1. a plurality of light emitting elements that emit light beams having different center wavelengths in predetermined directions; at least one light receiving element that generates a signal according to the intensity of light received from the predetermined direction; a control unit that controls light emission timings of the plurality of light-emitting elements and extracts signal components of wavelengths corresponding to the plurality of light-emitting elements from the signal; An object identification device configured to identify an object present in the predetermined direction based on a reflectance calculated from the signal component, The control unit is provided with a pulse modulation unit that simultaneously and in parallel turns on / off each of the plurality of light-emitting elements in synchronization with a predetermined frequency in a predetermined modulation pattern, and the modulation pattern is defined by an orthogonal matrix in which the arrangement of the plurality of light-emitting elements is the rows and the on / off times of each element are the columns.

2. 2. The object identification device according to claim 1, wherein the control unit further comprises a calculation processing unit that calculates signal components corresponding to each of the plurality of light-emitting elements by multiplying a signal data series generated by the light-receiving elements in synchronization with the predetermined frequency by an inverse matrix of the orthogonal matrix.

3. 3. The object identification device according to claim 2, wherein the modulation pattern has a DC component assigned to the first row of the orthogonal matrix.

4. 4. The object identification device of claim 3, wherein the orthogonal matrix defining the modulation pattern is a Hadamard matrix.

5. The object identification device according to any one of claims 1 to 4, wherein the control unit further includes an identification unit that identifies an object present in the predetermined direction based on a normalized index calculated based on the reflectance of each of the plurality of wavelengths and predetermined identification conditions.

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