JP4297026B2 - Object detection method and object detection apparatus - Google Patents

Description

  The present invention relates to an object detection method for detecting an object in a detection region using the coarse / fine wave by transmitting a coarse / fine wave to a target detection region, and an object detection apparatus for detecting an object using the object detection method. Is.

  Conventionally, as a technique for detecting an object, a transmitter for intermittently transmitting a dense wave and a receiver for receiving a dense wave are provided adjacent to each other in a target detection region. It is known that when a transmitted dense wave is reflected by an object existing in the detection region and returns to the wave receiver, it is determined that the object exists in the detection region.

  As shown in FIG. 22, an object detection apparatus for detecting an object by this technique includes a receiver 6 by arranging a plurality of receiving elements 9 for converting a dense wave into a received signal which is an electric signal. There is something configured. In the object detection apparatus shown in FIG. 22, among the plurality of piezoelectric elements arranged on the plane, the piezoelectric element in the broken frame in the figure selected by the transmission switching circuit 29 is used as the transmitter 4 to receive the wave. The piezoelectric elements selected by the switching circuit 30 are used as the wave receiving elements 9. The transmitter 4 is driven by a drive circuit 5 connected to a transmission switching circuit 29. Each received signal of each receiving element 9 is amplified by the amplifier 10, converted into a digital signal by the AD converter 11, and input to the computing unit 13 (see, for example, Patent Document 1).

  Here, in order to determine the presence or absence of an object based on the intensity of the received signal, a certain threshold is set for the intensity of the received signal. If the intensity of the received signal is greater than the threshold, the object If the intensity of the received signal is smaller than the threshold value, it is determined that no object exists.

In the arithmetic unit 13, the time required from when the dense / dense wave is transmitted until it is received corresponds to the distance to the object, and the time difference of each received signal at each receiving element 9 is determined as the direction of the object. By responding to (that is, the direction in which the receiver 6 receives the dense wave), it is possible to identify the region occupied by the object (that is, the size and shape of the object) in the detection region. For example, when the object is relatively large, the intensity of the received signal is larger than the threshold over a relatively wide range in the detection area, and when the object is relatively small, the intensity of the received signal is within the detection area. It becomes larger than the threshold value over a relatively narrow range.
Japanese Unexamined Patent Publication No. 2000-28589 (6th page, FIG. 1)

  By the way, the peak value of the intensity of the received signal differs depending on the reflection coefficient of the dense wave in the object, and becomes smaller as the object has a smaller reflection coefficient. On the other hand, in the object detection device described above, the threshold value for the intensity of the received signal is set to be constant regardless of the reflection coefficient of the object. Depending on the difference, the range in which the intensity of the received signal increases with respect to a certain threshold in the detection region is different, and may be detected as an object of a different size or an object of a different shape.

  The present invention has been made in view of the above-described reason, and changes a threshold for the intensity of a received signal for determining the presence or absence of an object based on the intensity of the received signal according to the reflection coefficient of the object. An object detection method capable of accurately identifying the size and shape of an object even for objects having different reflection coefficients, and an object detection device for detecting an object using the object detection method. To do.

  According to the first aspect of the present invention, there are a plurality of wave receiving elements for intermittently transmitting the coarse / fine wave from the wave transmitter to the target detection region and converting the coarse / fine wave into a received signal which is an electric signal. By the received wave receiver, the rough wave from the wave transmitter reflected by the object existing in the detection region is received, and the time required for receiving the wave after the rough wave is transmitted is received. A method for detecting an object in a detection region by identifying a distance to an object and an orientation of the object corresponding to a time difference between each received signal of each receiving element, and transmitted from a transmitter The reflection coefficient of the object is obtained using the transmitted sound pressure, which is the sound pressure of the dense wave, and the received sound pressure, which is the sound pressure of the dense wave received by the receiver, and the presence or absence of the object is determined as the intensity of the received signal. The threshold for the intensity of the received signal for discrimination by As smaller than the strength of the received signals to respond, and sets smaller object the reflection coefficient is small.

  According to this method, the threshold value for the intensity of the received signal is not made constant, but the threshold value is made smaller for an object having a smaller reflection coefficient. Therefore, if the object has the same size and the same shape, Even if the reflection coefficient is different, the range in which the intensity of the received signal is larger than the threshold value in the detection area can be the same regardless of the difference in the reflection coefficient. It can be detected as an object. In short, the size and shape of an object can be accurately identified even for objects having different reflection coefficients.

  According to a second aspect of the present invention, in the first aspect of the present invention, a divergence loss, which is a loss caused by the divergence of the coarse / fine wave in a period from when the coarse / fine wave is transmitted to the reception, and acoustic energy of the coarse / fine wave And the reflection coefficient is calculated by dividing the received sound pressure by the product of the transmitted sound pressure, the divergence loss, and the absorption loss. Features.

  When the distance to the object changes, the relationship between the transmitted sound pressure and the received sound pressure may vary depending on the divergence loss and the absorption loss. According to the method of claim 2, the divergence loss and the absorption loss are taken into account. Since the reflection coefficient is obtained, the reflection coefficient can be obtained accurately regardless of the distance to the object.

  According to a third aspect of the present invention, in the first or second aspect of the present invention, a plurality of the receiving elements are respectively arranged in a plurality of directions.

  According to this method, the direction of the object corresponding to each time difference of each receiving element can be identified in a plurality of directions.

  According to a fourth aspect of the present invention, in any one of the first to third aspects of the present invention, the threshold value is decreased as the direction in which the receiver receives low density waves is lower.

  Depending on the directivity of the receiver, the sensitivity may differ depending on the direction. However, according to the method of claim 4, the threshold is made smaller in the direction of lower sensitivity in consideration of the directivity of the receiver. The size and shape of the object can be accurately identified regardless of the orientation of the object.

  According to a fifth aspect of the present invention, in any one of the first to fourth aspects of the invention, the threshold value is reduced in the direction in which the intensity of the coarse wave transmitted from the transmitter is smaller. .

  The intensity of the coarse wave may vary depending on the direction depending on the directivity of the transmitter. According to the method of claim 5, the threshold value becomes smaller in the direction where the intensity of the coarse wave is smaller in consideration of the directivity of the transmitter. Therefore, the size and shape of the object can be accurately identified regardless of the orientation of the object.

  According to the invention of claim 6, in the invention of any one of claims 1 to 5, the divergence loss which is a loss due to the divergence of the dense wave during the period from when the coarse wave is transmitted to when it is received. An absorption loss that is a loss due to the acoustic energy of the dense wave being absorbed in the medium, a transmission intensity that is the intensity of the dense wave transmitted from the transmitter according to the direction, and according to the direction. And the reflection coefficient is the product of the transmission sound pressure, the divergence loss, the absorption loss, the transmission intensity, and the reception sensitivity. The calculation is performed by dividing the received sound pressure.

  When the distance to the object changes, the relationship between the transmitted sound pressure and the received sound pressure may differ depending on the divergence loss and the absorption loss. According to the method of claim 6, the divergence loss and the absorption loss are taken into account. Since the reflection coefficient is obtained, the reflection coefficient can be obtained accurately regardless of the distance to the object. In addition, since the transmission intensity and the reception sensitivity are also taken into consideration, the reflection coefficient can be obtained accurately regardless of the orientation of the object.

  The invention of claim 7 is the invention according to any one of claims 1 to 6, wherein the detection area is divided into a plurality of sections of equal distance from the transmitter and the receiver with a predetermined width. The threshold value is set every time.

  According to this method, since a threshold is set for each section, if a section is determined from the distance to the object and the direction of the object, the threshold corresponding to this section can be set. The sheath shape can be accurately identified.

  The invention of claim 8 is the invention according to any one of claims 1 to 7, wherein the detection area is divided into a plurality of sections equidistant from the transmitter and the receiver with a predetermined width. The reflection coefficient is obtained every time, and the position where the reflectance is maximum in each section is set as the existence position of the object, and the threshold value is set so as to be smaller by a specified ratio than the intensity of the received signal at the existence position. It is characterized by setting.

  According to this method, since the reflection coefficient is obtained for each section, even when a plurality of objects having different reflection coefficients exist in the detection region, the reflection coefficient of each object can be obtained. In addition, each threshold is set to a threshold that is smaller by a specified percentage than the intensity of the received signal corresponding to the dense wave reflected by the object in each section, so that the size and shape of each object can be accurately identified. Can do.

  The invention according to claim 9 is the image output unit according to any one of claims 1 to 8, wherein an image having a plurality of pixels respectively associated with each direction in the detection area and having a pixel value as a distance is provided. A region in which the intensity of the received signal exceeds the threshold value is displayed in time series on the image output unit.

  According to this method, since the objects in the detection area are displayed in time series, the movement of the objects can be seen.

  A tenth aspect of the invention is characterized in that, in any of the first to ninth aspects of the invention, the transmitter does not have a resonance frequency in the frequency of the coarse / fine wave to be transmitted.

  According to this method, the reverberation component in the close-packed wave transmitted from the transmitter is relatively small, and each received signal of each receiving element is prevented from spreading in the time axis direction due to the reverberation component. The detection unit can accurately identify the distance to the object and the direction of the object.

  The invention of claim 11 is the invention according to any one of claims 1 to 10, wherein the receiver does not have a resonance frequency in the frequency of the dense wave transmitted from the transmitter. To do.

  According to this method, the reverberation component in the received signal output from the receiver is relatively small, and each received signal of each receiving element is prevented from spreading in the time axis direction due to the reverberant component. It is possible to accurately identify the distance to the object and the direction of the object 2 in the detection unit.

  The invention according to claim 12 includes a transmitter that intermittently transmits a coarse / fine wave to a target detection region, and a plurality of wave receiving elements that respectively convert the coarse / fine wave into a reception signal that is an electric signal. A receiver for receiving the dense wave from the transmitter reflected by the object existing in the detection region, and the object corresponding to the time required from the time when the dense wave is transmitted until the wave is received And a detection unit that detects the object in the detection region by identifying the distance to and the azimuth of the object corresponding to the time difference between the reception signals of each reception element, the detection unit from the transmitter The reflection coefficient of the object is obtained using the transmitted sound pressure, which is the sound pressure of the transmitted dense wave, and the received sound pressure, which is the sound pressure of the dense wave received by the receiver, and the presence or absence of the object is received. The threshold for the intensity of the received signal for discrimination by the intensity of the wave signal is set to the dense wave reflected by the object. As smaller than the strength of the received signals to respond, characterized in that it is set smaller as the object the reflection coefficient is small.

  According to this configuration, the threshold with respect to the intensity of the received signal is not made constant, but the threshold is decreased as the reflection coefficient is smaller, so if the object has the same size and the same shape, Even if the reflection coefficient is different, the range in which the intensity of the received signal is larger than the threshold value in the detection area can be the same regardless of the difference in the reflection coefficient. It can be detected as an object. In short, the size and shape of an object can be accurately identified even for objects having different reflection coefficients.

  A thirteenth aspect of the invention is characterized in that, in the twelfth aspect of the invention, the image output section includes a plurality of pixels respectively associated with the respective directions in the detection region and outputs an image having a distance as a pixel value. And

  According to this configuration, the size and shape of the object in the detection area can be notified to the outside by the image output unit.

  In the present invention, the threshold value for the intensity of the received signal is not made constant, but the threshold value is made smaller for an object having a smaller reflection coefficient. Even if they are different, the range in which the intensity of the received signal is greater than the threshold value within the detection area can be made the same regardless of the difference in the reflection coefficient, and as an object of the same size and shape Can be detected. In short, even an object having a different reflection coefficient has an advantage that the size and shape of the object can be accurately identified.

(Embodiment 1)
In the present embodiment, a configuration for identifying a distance to an object and an orientation of the object in an object detection device that detects an object existing in a target detection region will be described.

  As shown in FIG. 1, the object detection apparatus of the present embodiment includes a wave transmission means 1 that intermittently transmits a dense wave to a target detection area (in the air) and an object 2 that exists in the detection area. Receiving means 3 for receiving the reflected dense wave. The wave transmitting means 1 includes a wave transmitter 4 that converts a wave signal, which is an electrical signal, into a coarse / fine wave, and a drive circuit 5 that drives the wave transmitter 4 so that the coarse / fine wave is intermittently transmitted. The wave receiving means 3 receives the received signal from the receiver 6 that receives the received signal from the receiver 6 and receives the received signal from the receiver 6. And a detection unit 7 that determines the presence or absence of the object 2 based on the intensity. The transmitter 4 and the receiver 6 are disposed adjacent to each other and constitute a sensor unit.

  Here, the drive circuit 5 and the detection unit 7 are connected to each other, and the detection unit 7 can obtain the time required from when the dense / dense wave is transmitted until it is received. The time required for transmission / reception of the dense wave corresponds to the distance to the object 2. In addition, as shown in FIG. 2, a total of 10 receivers 6 are arranged on the element array substrate 8 at five equal intervals in the vertical direction (vertical direction) and five in the horizontal direction (horizontal direction). Each receiving element 9 converts the coarse / fine wave into a received signal by each receiving element 9, so that the detection unit 7 can detect the object 2 due to the time difference between the received signals of each receiving element 9. The direction can be identified. For example, as shown in FIG. 3, when receiving a close-packed wave from a direction inclined by an angle θ with respect to a direction orthogonal to the element array substrate 8 of the receiver 6, The time difference Δt between the received signals of (d) is expressed by the following equation. Here, the sound speed is c.

Δt = (d · sin θ) / c
As shown in FIG. 4, the detection unit 7 includes an amplifier 10 that amplifies the received signal from each receiving element 5, an AD converter 11 that A / D converts the received signal amplified by the amplifier 10, and A frame memory 12 that stores the received signal converted into a digital signal by the AD converter 11, and a calculator 13 that identifies the distance to the object 2 and the orientation of the object 2 using the received signal stored in the frame memory 12. Have A series of processing of amplifying the received signal, A / D converting it, and storing it in the frame memory 12 is performed for each receiving element 9. Here, the amplification factor of the amplifier 10 is set to 40 dB to 60 dB, and the S / N ratio is about 60 dB. A 16-bit AD converter 11 is used, and the sampling frequency is 1 MHz. The frame memory 12 has a storage area divided for each receiving element 9 so that the amplitude of the received signal can be stored for each sampling period (here, 1 μs) of the AD converter 11.

  The computing unit 13 of this embodiment delays the received signal from each receiving element 9 by a delay time in order to identify the direction (that is, the direction of the object 2) at which the receiver 6 has received the density wave. Delay means 14 (see FIG. 5) to be added, and addition means 15 (see FIG. 5) for adding the delayed received signal. Here, the computing unit 13 reads out each received wave element 9 from the frame memory 12 in a state where the received wave signal is delayed, thereby receiving the received signal of the coarse / fine wave received from the direction corresponding to the combination of the delay times. Can be taken out as an output of the adding means 15.

  In the following, an outline of processing for identifying the distance to the object 2 and the orientation of the object 2 will be described on the assumption that there are two objects 2 and 2 ′ in the detection area as shown in FIG. 5. However, here, it is assumed that the orientation on one plane is identified, and a case where five receiving elements 9 are arranged on the plane will be described. 6B and 6D show combinations of delay times with the horizontal length of the rectangle as the magnitude of the delay time. In FIGS. 6C and 6E, the horizontal axis Represents a received signal for each of the receiving elements 9 in FIG. FIG. 6 (f) and FIG. 6 (g) show the received signal after addition with the horizontal axis as the time axis.

  The close-packed waves transmitted from the transmitter 4 are reflected by the objects 2 and 2 ′, so that the receiving elements 9 are oriented in the directions of the objects 2 and 2 ′ as shown in FIG. Receives dense waves with a corresponding time difference. By delaying the received signal from each receiving element 9 by the delay time of the combination shown in FIG. 6B, all the dense waves reflected by the object 2 as shown in FIG. The timings of the received signals can be matched. On the other hand, by delaying the received signal from each receiving element 9 by the delay time of the combination shown in FIG. 6D, it is possible to cope with the dense wave reflected by the object 2 ′ as shown in FIG. 6E. The timings of all received signals can be matched. Here, the combination of delay times in FIG. 6B corresponds to the orientation of the object 2, and the combination of delay times in FIG. 6D corresponds to the orientation of the object 2 ′.

  Further, as shown in FIG. 7A, the time t1 required for transmission / reception of the dense wave in the azimuth of the object 2 is converted into the distance to the object 2, and as shown in FIG. The time t2 required for transmission / reception of the dense wave in the 2 ′ direction is converted into the distance to the object 2 ′. In this way, by identifying the distance to the object 2 and the orientation of the object 2, it is possible to identify the area occupied by the object 2 in the detection area (that is, the size and shape of the object 2).

  By the way, the computing unit 13 discriminates the presence / absence of the object 2 in the azimuth corresponding to the combination of the delay times based on the intensity of the received signal after addition (see FIG. 6 (f) and FIG. 6 (g)). (Not shown), the discrimination means compares the intensity of the received signal after addition with a threshold value, and if the received signal intensity is greater than the threshold value, it is determined that the object 2 exists in the direction. To do. In the present embodiment, the threshold value for the intensity of the received signal is not set to a constant value in the discriminating means, but the threshold value is changed according to the reflection coefficient of the dense wave in the object 2. There are features.

  More specifically, the object 2 having a smaller reflection coefficient is less likely to receive a dense wave, and the peak value of the intensity of the received signal is smaller. Therefore, the threshold value is reflected by the object 2 regardless of the magnitude of the reflection coefficient. The object 2 having a smaller reflection coefficient is set to be smaller so as to be smaller than the intensity of the received signal corresponding to the rough dense wave. According to this configuration, if the object 2 has the same size and the same shape, even if the reflection coefficients are different, the intensity of the received signal corresponding to the dense wave reflected by the object is lower than the threshold value. The larger range (that is, the region occupied by the object 2 in the detection region) can be made similar, and can be detected as the object 2 having the same size and shape.

For example, if the object detection device detects an object 2 existing within 1 m (within a reciprocation distance of 2 m), the rough wave will reciprocate a maximum distance of 1 m in the air. Due to the divergence loss due to divergence, the absorption loss due to the acoustic energy of the dense wave being absorbed in the air, and the reflection loss when the dense wave is reflected by the object 2 (depending on the reflection coefficient), Attenuates about 45 dB. That is, the relationship between the transmitted sound pressure V _s that is the sound pressure of the dense wave transmitted from the transmitter 4 and the received sound pressure V _r that is the sound pressure of the dense wave received by the receiver 6 is Using the divergence loss {1 / (4πR ² )} and absorption loss exp (−αR) in the air depending on the round-trip distance R to the object 2 and the reflection coefficient K _r , the following expression is used. it can. However, α in the absorption loss is an absorption coefficient.

V _r = V _s · 1 / (4πR ² ) · exp (−αR) · K _r
In this embodiment, the reflection coefficient of the object 2 is obtained from the above equation using the transmitted sound pressure, the received sound pressure, the divergence loss, and the absorption loss. The threshold value is set to be smaller for the object 2 having a smaller reflection coefficient.

  Further, in this embodiment, by adopting the transmitter 4 and the receiver 6 that do not have a resonance frequency in the frequency of the transmitted / received coarse / fine wave, the coarse / fine wave transmitted from the transmitter 4 is used. Both the reverberation component in the signal and the reverberation component in the received signal output from the receiver 6 are made relatively small, and the received signal of each receiving element 9 is prevented from spreading in the time axis direction due to the reverberation component. In addition, the detection unit 7 can accurately identify the distance to the object 2 and the orientation of the object 2.

  As a specific configuration, the transmitter 4 employs a thermal excitation type as shown in FIG. The wave transmitter 4 includes a substrate 16 made of single crystal silicon (c-Si) or the like, a thermal insulating layer 17 made of nanocrystalline silicon (nc-PS) or the like provided on the substrate 16, and the wave transmitter 4. And a metal thin film 18 such as tungsten (W) formed on the heat insulating layer 17 as a sound source. In FIG. 8, a pair of current-carrying electrodes 19 made of aluminum (Al) or the like are provided on the left and right ends of the metal thin film 18. The horizontal dimension of the conductive electrode 19 is 5 mm. The metal thin film 18 generates heat when energized through the energizing electrode 19, and the heat insulating layer 17 prevents heat from the metal thin film 18 from escaping to the substrate 16 side.

  Here, when the drive circuit 5 applies an AC voltage between the energizing electrodes 19 to cause a drive current as a transmission signal to flow, the medium (air) that contacts the metal thin film 18 is changed by the temperature change of the metal thin film 18. It expands and contracts to generate a dense wave having the same frequency as the drive current. As described above, the transmitter 4 according to the present embodiment generates a dense wave due to a temperature change of the metal thin film 18, and does not vibrate mechanically and does not have a resonance frequency. When this occurs, no reverberation component due to resonance is generated. Further, in the transmitter 4 of the present embodiment, the portion serving as a sound source is planar, and transmits a dense wave in a direction orthogonal to the plane. The part which becomes the sound source is formed in a square shape.

  The drive circuit 5 drives the wave transmitter 4 by flowing a Gaussian wave-shaped drive current as shown in FIG. 9 through the metal thin film 18 of the wave transmitter 4. Since the frequency component of the drive current in the form of a Gaussian wave has a Gaussian distribution, it is possible to generate a dense wave having a specific frequency band by driving the transmitter 4 with such a drive current. Here, the frequency band of the coarse / fine wave is set to an ultrasonic region of 50 kHz to 70 kHz. Further, the drive current output from the drive circuit 5 is a single pulse current, and a single coarse / fine wave is transmitted from the transmitter 4, and side lobes are generated in the coarse / fine wave transmitted by the transmitter 4. To prevent it. As shown in FIG. 10, the drive circuit 5 includes a capacitor C1 connected to a power source DC via a switch SW. The capacitor C1 is connected via a series circuit of a switching element Q1, an inductor L1, and a resistor R1. It has a configuration connected to the transmitter 4. Here, when the switch SW is on, the capacitor C1 is charged, and the switching element Q1 is turned on, so that a drive current flows through the transmitter 4. The waveform of the drive current varies depending on the values of the inductor L1 and the resistor R1. A protective resistor R2 is provided between the output terminals of the drive circuit 5 in parallel with the transmitter 4 to prevent a short circuit of the transmitter 4 as a load.

  On the other hand, each receiving element 9 of the receiver 6 employs a capacitance type microphone having no resonance frequency. As shown in FIG. 11, the wave receiving element 9 includes a substrate 21 made of single crystal silicon or the like and formed with a wave receiving hole 20 in a part thereof, and a substrate 21 so as to cover one opening of the wave receiving hole 20. A thin-film wave receiving body 22 that is continuously formed integrally and provided with a movable electrode (not shown), a fixed electrode holding portion 24 that faces the wave receiving body 22 through a gap 23, and a fixed electrode holding portion 24. The fixed electrode 25 and the substrate 21 and the wave receiver 22 form a diaphragm structure. The wave receiving hole 20 is formed in a shape that becomes narrower toward the wave receiving body 22 side. With this configuration, when the wave receiving body 22 receives a close-packed wave, the wave receiving body 22 vibrates, and the distance between the wave receiving body 22 and the fixed electrode 25 changes. As a result, the capacitance between the movable electrode and the fixed electrode 25 changes. When a voltage is applied between the movable electrode and the fixed electrode 25, a voltage that changes depending on the change in capacitance can be extracted as a received signal. The structure of the wave receiving element 9 is not limited to the diaphragm structure described above, and may be a cantilever structure in which the wave receiving body 22 is made continuous with the substrate 21 at one side of the wave receiving hole 20.

  In the wave receiving means 3 of this embodiment in which ten wave receiving elements 9 are arranged on one plane, the inclination is 0 degree with respect to the direction orthogonal to the plane on which the wave receiving elements 9 are arranged. When the intensity is 0 dB, the directivity is relatively sharp, such that the intensity is -3 dB when the inclination is 5 degrees. In addition, since the receiver 4 does not resonate even when receiving the dense wave, the wave receiving elements 9 can be arranged at relatively narrow intervals equal to or less than the wavelength of the dense wave.

  In the present embodiment, the computing unit 13 of the detection unit 7 makes the received signal valid in accordance with the timing at which the transmitter 4 transmits the dense wave (hereinafter referred to as “received period”). It has a function as a timing control unit for determining For example, if the object detection device detects an object existing within 1 m (within a reciprocation distance of 2 m), the time required for the dense wave to reciprocate a distance of 1 m in the air is about 6 ms. The unit sets a 6 ms reception period immediately after the transmitter 4 transmits the dense wave. By having the function as the timing control unit in this way, the received signal can be made effective only during the period in which the receiver 6 receives the coarse / fine wave transmitted from the transmitter 4. It is possible to prevent the detection unit 6 from malfunctioning by receiving a received signal due to noise, multiple reflection, or the like. However, the AD converter 11 may be provided with a function as a timing control unit so that the AD converter 11 converts the received signal into a digital signal only during the reception period. Here, the reception period is 6 ms as described above. When the number of receiving elements 9 is 10 as in this embodiment, a frame memory 12 of (6 ms) × (1 MHz) × (16 bits) × (10) = (120 kbytes) is required. .

  When the divergence loss and the absorption loss can be ignored for the reason that the distance to the object 2 is relatively small, for example, the reflection coefficient may be obtained from the transmitted sound pressure and the received sound pressure. In addition, when a dense wave is used to detect the object 2 as in this embodiment, there is an advantage that even an object 2 that is not visually recognized, such as a so-called colorless and transparent object 2, can be detected.

(Embodiment 2)
The object detection apparatus according to the present embodiment is capable of displaying the object 2 existing in the target detection area as a three-dimensional image. This object detection apparatus has the same basic configuration as that described in the first embodiment, and uses the fact that the object detection apparatus can identify the distance to the object 2 and the orientation of the object 2 as described in the first embodiment. The three-dimensional position where the object 2 exists in the detection area is identified.

  In the present embodiment, on the front side of the sensor unit (transmitter 4 and receiver 6), the sensor unit is the apex, the plane is inclined at an angle of 45 degrees to the left, and the angle is 45 degrees to the right. An area surrounded by an inclined plane, a plane inclined upward at an angle of 45 degrees, and a plane inclined downward at an angle of 45 degrees, and a range within 5 m from the sensor unit is defined as a detection area. In the following, the left and right angles are expressed with respect to the front direction of the sensor unit as a negative angle, the right direction as a positive angle, and the right and left direction angles. The angle in the vertical direction is represented by a negative angle and an upward inclination as a positive angle. Here, the detection area is divided into a plurality of small areas, and the presence or absence of the object 2 is detected in each of the small areas, thereby imaging the object 2 in the detection area.

In the propagation direction of the dense wave transmitted from the transmitter 4 (hereinafter referred to as “depth direction”), the detection area is divided into a plurality of sections with a predetermined width a as shown in FIG. Here, the sections are separated by a spherical surface centered on the sensor unit, so that each section forms a space equidistant from the sensor unit. That is, the plurality of objects 2 that are equidistant from the sensor unit are all present in the same section. In this embodiment, a section from a position away from the sensor unit by a predetermined distance is set. The width a (dimension in the depth direction) of each section is determined based on the wavelength of the dense wave, and in the present embodiment, it is 10 times the wavelength of the dense wave. Here, the wavelength of the dense wave is 6.8 mm, and the width a of each section is 68 mm.

  Further, the angular resolution in the left-right direction is set to 5 degrees, and the angular resolution in the vertical direction is also set to 5 degrees. Here, since the angular resolution is set to 5 degrees and the sampling period of the AD converter 11 corresponding to the resolution of the time difference Δt of the received signal in the receiving element 9 is 1 μs, the above-described formula Δt = ( Based on (d · sin θ) / c, the wave receiving elements 9 are arranged at an interval of 3.9 mm, which is smaller than the wavelength of the dense wave (that is, 6.8 mm). Here, the speed of sound c is 340 m / s. Thereby, each section is divided into 19 parts in the left-right direction and 19 parts in the up-down direction. Further, as shown in FIG. 13, a two-dimensional map of 361 pixels, each having 19 pixels in the horizontal direction and the vertical direction, is associated with each section. Assuming that one pixel in this two-dimensional map is a small area b (see FIG. 12), the presence or absence of the object 2 is detected in each small area b.

By the way, the intensity of the dense wave transmitted from the transmitter 4 (hereinafter referred to as “transmitted intensity”) differs depending on the direction, and the dense wave is a pulse sine wave as shown in FIG. Furthermore, if the wavelength of the dense wave is λ and the length of one side of the portion that becomes the sound source of the transmitter 4 is 2a, the transmission intensity D _s (θ) is orthogonal to the element array substrate 8 of the receiver 6. It is expressed by either of the following two formulas depending on the inclination θ with respect to the direction to be performed.

When θ is 0 ≦ θ ≦ sin ⁻¹ (λ / 4a),
D _s (θ) = {sin (π · 2a / λ · sin θ)} / (π · 2a / λ · sin θ)
When θ is sin ⁻¹ (λ / 4a) ≦ θ ≦ π / 2,
D _s (θ) = 1 / (π · 2a / λ · sin θ)
Here, as shown in FIG. 15, in the distribution of the transmission intensity in the detection region, the transmission intensity decreases as the distance from the front direction of the sensor unit increases.

On the other hand, the sensitivity at which the receiver 6 receives the dense and dense waves (hereinafter referred to as “received sensitivity”) also differs depending on the orientation. As in the present embodiment, the sensitivity is 5 in each of the vertical and horizontal directions. In the receiver 6 in which each receiving element 9 is arranged, a region having a high received sensitivity D _r (θ) is generated in a cross shape extending vertically and horizontally with the front direction of the sensor unit as the center. FIG. 16 shows a simulation result of the distribution of received wave sensitivity in the detection region.

As described above, the transmission intensity and the reception sensitivity are not uniform in the detection region, and are different depending on the inclination θ with respect to the direction orthogonal to the element array substrate 8 of the receiver 6. Considering the inclination θ with respect to the direction orthogonal to the substrate 8, the relationship between the transmitted sound pressure V _s and the received sound pressure V _r is a divergence loss {1 / (4πR ² )}, an absorption loss exp (−αR), Using the transmission intensity D _s (θ), the received wave sensitivity D _r (θ), and the reflection coefficient K _r , the following expression is used.

V _r = V _s · 1 / (4πR ² ) · exp (−αR) · D _s (θ) · D _r (θ) · K _r
Therefore, the discriminating means of the present embodiment obtains the reflection coefficient of the object 2 from the above equation using the transmitted sound pressure, received sound pressure, divergence loss, absorption loss, transmitted intensity, and received sensitivity. The threshold value is set to be smaller for the object 2 having a smaller reflection coefficient.

  Even when an object 2 having the same reflection coefficient is detected, the peak value of the intensity of the received signal is smaller as the object 2 is farther from the sensor unit. Therefore, in this embodiment, the threshold value is smaller as the interval is farther from the sensor unit. As described above, a threshold is set for each section. Furthermore, since the intensity of the received signal is smaller as the object 2 is present in the azimuth where the transmission intensity is smaller, in this embodiment, the threshold value is smaller as the azimuth is lower. In addition, since the intensity of the received signal is smaller as the object 2 exists in the azimuth having lower reception sensitivity, the threshold value is decreased as the azimuth has lower reception sensitivity.

  In short, in this embodiment, when detecting the presence or absence of the object 2 in each of the small areas, the threshold value is set based not only on the reflection coefficient of the object 2 but also on the three-dimensional position of the small area. Thus, the size and shape of the object 2 existing at different positions can be accurately identified.

  In the following, as an example of the operation of the present embodiment, the object detection device has a distribution of received signal intensity (hereinafter referred to as “reference intensity”) when the reflectance is 100% in all regions in the section. A corresponding data table is provided for each section in advance, and an operation when a threshold value is set using this data table is shown. The reference intensity in each section takes into account the distance from the sensor section to each section, and the distribution of the transmission intensity and the reception sensitivity in each section, and decreases as the distance from the front direction of the sensor section increases. . Here, a description will be given with reference to FIG. 17 showing the intensity distribution of the received signal in the horizontal direction of a certain section. In FIG. 17, the horizontal axis indicates the angle in the left-right direction, and the vertical axis indicates the intensity of the received signal.

  First, a position (hereinafter referred to as “existing position”) where the reflectance of the object 2 is maximum is obtained from the intensity A of the received signal corresponding to the dense wave reflected by the object 2 in the detection region. Since the reference intensity C is the intensity of the received signal when the reflectance is 100%, the difference between the intensity A of the received signal and the reference intensity C reflects the reflectance, and this difference is minimized. The reflectance is maximum at the position. Accordingly, in FIG. 17, the position where the difference Y between the received signal intensity A and the reference intensity C is the minimum is the existence position X.

  Next, based on the reflection coefficient of the object 2 at the existence position X, a threshold value B in the section is set. In the present embodiment, the threshold value B for each direction is obtained by multiplying the reference intensity C for each direction by a positive number of 1 or less associated with the reflection coefficient at the existence position X. As a result, the threshold value B decreases as the distance from the front direction (0 degree) of the sensor portion becomes the same as the reference strength C. The number associated with the reflection coefficient is determined so that the threshold value B is smaller than the intensity A of the received signal at the existing position X by a prescribed ratio. In the present embodiment, the existing position X The threshold value B is determined to be 90% of the intensity A of the received signal.

  The presence or absence of the object 2 is determined by whether or not the received signal intensity A is greater than the threshold value B. In FIG. 17, the object 2 exists over a region Z where the received signal intensity A exceeds the threshold value B. Then it is determined. Here, the size of the area Z occupied by the object 2 corresponds to the size of the object 2.

  Further, the intensity of the received signal to be invalidated so that the non-existent object 2 is not erroneously detected when the receiver 6 receives noise other than the coarse wave reflected by the object 2. Is set to the minimum threshold value D. This is invalid for a received signal whose intensity is smaller than the minimum threshold value D. As with the threshold value B, the minimum threshold value D decreases as the distance from the front direction (0 degree) of the sensor unit increases.

  Here, for the purpose of explanation, the intensity distribution of the received signal is shown only in the left-right direction, but in reality, it corresponds to the dense wave reflected by the object 2 on the two-dimensional map spreading in the left-right direction and the up-down direction. The intensity of the received signal is distributed. On the two-dimensional map, the shape of the region occupied by the object 2 corresponds to the shape of the object 2 viewed from the sensor unit side.

  By the way, the object detection device of the present embodiment includes an image output unit (not shown) that outputs an image having a plurality of pixels respectively associated with each small region in the detection region. The image output unit displays only a small area where the intensity of the received signal exceeds the threshold value. In the section where the distance from the sensor unit is 1 m, the person 26 standing at a position where the angle in the left-right direction is 0 degrees, and in the section where the distance from the sensor unit is 1.3 m, the angle in the left-right direction is 40 degrees, FIG. 18 shows an image generated when a ball 27 existing at a position where the angle is −20 degrees is detected. FIG. 18A is a front view of the detection area viewed from the sensor unit side, and FIG. 18B is an image of the detection area as a perspective view obliquely viewed. The reflection coefficient of the person 26 at this time is about 11%, and the threshold value is set based on this reflection coefficient. On the other hand, the reflection coefficient of the ball 27 is about 5%, and a threshold value different from that of the person 26 is set. In this way, the size and shape can be detected relatively accurately even for objects having different reflection coefficients.

  In the above-described example, the detection area is divided into a plurality of sections with a constant width (68 mm). However, in addition to the detection of the object 2 in a state where the detection area is divided into the sections, the detection area is detected by the sensor. The object 2 may be detected even in a state where it is shifted by 34 mm with respect to the section in the front direction of the part and divided by a width of 68 mm, so that a dense wave is generated across the two sections in the former divided state. Even when it is reflected, it is possible to accurately detect the latter divided state.

  Note that the receiver 6 only needs to have a plurality of receiving elements 9 arranged in a plurality of directions on the element arrangement substrate 8, and the arrangement of the receiving elements 9 on the element arrangement substrate 8 is as described above. It is not limited to what you did. The number of the wave receiving elements 9 is not limited to ten. For example, as shown in FIG. 19, on a circular arc surrounding one wave receiving element 9 arranged at the center of the element arrangement substrate 8 or the like. Six receiving elements 9 may be arranged at intervals. When the receiver 6 adopting the arrangement shown in FIG. 19 is used, as shown in FIG. 20 which is a simulation result of the distribution of received sensitivity in the detection region, a circular shape centered on the front direction of the sensor unit. The receiving sensitivity of the area spread over is increased. Other configurations and functions are the same as those of the first embodiment.

(Embodiment 3)
In the present embodiment, in the object detection device of the second embodiment, a dense wave is transmitted from the transmitter 4 at a constant time interval, and an image displayed on the image output unit is updated in accordance with this time interval. An example is shown. Here, the distance to the object 2 is displayed in association with the pixel value.

  In this configuration, the object 2 existing in the detection area can be displayed in time series. An example in which a person 28 moving in the detection area is detected is shown in FIG.

  The person 28 who was present in the vicinity of the sensor unit in FIG. 21A displayed first is positioned farther from the sensor unit than in the state of FIG. 21A in FIG. 21B displayed next. In FIG. 21 (c) displayed next, it is present at a position further away from the sensor unit. That is, it can be seen that the person 28 has moved away from the sensor unit.

  In addition, since the image output unit displays only the region where the intensity of the received signal exceeds the threshold value in the detection region, only the object 2 existing in the detection region can be displayed with the background omitted. . As for the display method of the object, the shape of the object 2 may be displayed in an identifiable form by using a well-known image processing technique, or the object 2 may be tracked and displayed. Furthermore, the direction in which the object 2 has moved may be automatically determined by plotting the position of the object 2 having the same reflection coefficient in time series. Other configurations and functions are the same as those of the second embodiment.

  In addition, the numerical value shown by each embodiment mentioned above is an example, Comprising: It is not limited to this.

It is a block diagram which shows the structure of Embodiment 1 of this invention. It is the schematic which shows a receiver same as the above. It is explanatory drawing for demonstrating the direction in which a receiver same as the above receives a dense wave. It is a block diagram which shows the structure of a wave receiving means same as the above. It is operation | movement explanatory drawing which shows operation | movement of a wave receiving means same as the above. It is explanatory drawing for demonstrating operation | movement of a wave receiving means same as the above. (A) shows the received signal corresponding to the object 2, and (b) is an explanatory view showing the received signal corresponding to the object 2 '. The structure of a wave transmitter same as the above is shown, (a) is a front view, (b) is a sectional view. It is a graph which shows the waveform of a drive current same as the above. It is a circuit diagram which shows a drive circuit same as the above. It is sectional drawing which shows the structure of a receiving element same as the above. It is explanatory drawing which shows the detection area | region of Embodiment 2 of this invention. It is explanatory drawing which shows the two-dimensional map assumed to each area same as the above. It is a graph which shows the same density wave as above. It is a graph which shows distribution of the transmission intensity same as the above. It is a graph which shows distribution of a receiving sensitivity same as the above. It is explanatory drawing which shows intensity distribution of a received signal same as the above. It is explanatory drawing which shows the image displayed on an image output part same as the above. It is explanatory drawing which shows other arrangement | positioning of a receiving element same as the above. It is a graph which shows distribution of a receiving sensitivity same as the above. It is operation | movement explanatory drawing which shows operation | movement of Embodiment 3 of this invention. It is a block diagram which shows the structure of a prior art example.

Explanation of symbols

2 Object 4 Transmitter 6 Receiver 7 Detector 9 Receiving element

Claims (13)

  Detection is performed by a receiver having a plurality of receiving elements that intermittently transmit a coarse / fine wave from a transmitter to a target detection area and convert the coarse / fine wave into a received signal that is an electrical signal. Receive the dense wave from the transmitter reflected by the object existing in the region, and the distance to the object corresponding to the time required from the time when the dense wave is transmitted to the received wave and each reception A method for detecting an object in a detection region by identifying an orientation of the object corresponding to a time difference between reception signals of wave elements, and a sound pressure of a dense wave transmitted from a transmitter. Received wave for determining the reflection coefficient of the object using the transmitted sound pressure and the received sound pressure which is the sound pressure of the dense wave received by the receiver, and for determining the presence or absence of the object based on the intensity of the received signal The threshold for the signal strength is set to the received signal strength corresponding to the dense wave reflected by the object. As smaller and object detection method and setting smaller object the reflection coefficient is small.   In the period from when the dense wave is transmitted to when it is received, the divergence loss, which is the loss due to the divergence of the dense wave, and the absorption loss, which is the loss due to the acoustic energy of the dense wave being absorbed in the medium The object detection method according to claim 1, wherein the reflection coefficient is calculated by dividing the received sound pressure by a product of the transmitted sound pressure, divergence loss, and absorption loss.   The object detection method according to claim 1, wherein a plurality of the receiving elements are arranged in a plurality of directions.   The object detection method according to any one of claims 1 to 3, wherein the threshold value is decreased as the direction in which the receiver receives low density waves is lower.   5. The object detection method according to claim 1, wherein the threshold value is decreased in the direction in which the intensity of the dense wave transmitted from the transmitter is smaller.   In the period from when the dense wave is transmitted to when it is received, the divergence loss, which is the loss due to the divergence of the dense wave, and the absorption loss, which is the loss due to the acoustic energy of the dense wave being absorbed in the medium And the transmission intensity which is the intensity of the dense wave transmitted from the transmitter according to the azimuth and the reception sensitivity which is the sensitivity with which the receiver according to the direction receives the dense wave. 2. The reflection coefficient is calculated by dividing the received sound pressure by a product of the transmitted sound pressure, divergence loss, absorption loss, transmitted intensity, and received sensitivity. 6. The object detection method according to any one of 5 above.   7. The detection area is divided into a plurality of sections equidistant from the transmitter and the receiver with a predetermined width, and the threshold value is set for each section. The object detection method according to any one of the above.   The detection area is divided into a plurality of sections that are equidistant from the transmitter and the receiver with a predetermined width, the reflection coefficient is obtained for each section, and the position where the reflectance is maximum in each section is determined as the object. 8. The threshold value is set so that the threshold value is smaller by a prescribed ratio than the intensity of the received signal at the presence position. Object detection method.   An image having a plurality of pixels respectively associated with each direction in the detection region and having a distance as a pixel value is output to the image output unit, and an area in which the intensity of the received signal exceeds the threshold value is output to the image output unit 9. The object detection method according to claim 1, wherein the object detection method is displayed in time series.   10. The object detection method according to claim 1, wherein the transmitter does not have a resonance frequency in a frequency of the dense wave transmitted. 10.   11. The object detection method according to claim 1, wherein the receiver does not have a resonance frequency in a frequency of the dense wave transmitted from the transmitter. 11.   There are a transmitter that intermittently transmits a dense wave in a target detection region, and a plurality of receiving elements that convert the dense wave into a received signal that is an electric signal, and exists in the detection region. A receiver that receives the dense wave from the transmitter reflected by the object, a distance to the object corresponding to the time required from the time when the dense wave is transmitted to the received wave, and each received wave A detection unit for detecting the object in the detection region by identifying the direction of the object corresponding to the time difference of each received signal of the element, the detection unit of the dense wave transmitted from the transmitter The reflection coefficient of the object is obtained by using the transmitted sound pressure that is the sound pressure and the received sound pressure that is the sound pressure of the close-packed wave received by the receiver, and the presence or absence of the object is determined based on the intensity of the received signal. A threshold for the intensity of the received signal for the intensity of the received signal corresponding to the dense wave reflected by the object Ri so as to reduce, object detection apparatus characterized by being set smaller as the object the reflection coefficient is small.   The object detection apparatus according to claim 12, further comprising an image output unit that outputs a picture having a plurality of pixels associated with each direction in the detection area and having a distance as a pixel value.