JP2018105703A - Object detection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an object detection device with which it is possible to improve object detection performance and suppress unnecessary detection of an object.SOLUTION: An ultrasonic sensor 30 transmits an ultrasonic wave from a vibrator and generates a received-wave signal along with vibration of the vibrator. An object detection device 20 detects an object present around a vehicle 10 as a mobile entity on the basis of a reflected wave that is received by the ultrasonic sensor 30. The object detection device 20 comprises an object detection unit for detecting an object on the basis of a direct wave that is a reflected wave received by a transmitted-wave sensor and an indirect wave that is a reflected wave received by a received-wave sensor, a beat detection unit 28 for detecting the beat state of reverberation after the ultrasonic wave is transmitted from the vibrator, and a time setting unit for variably setting an acquisition start time at which the received-wave sensor starts acquiring the received-wave signal as a signal based on the indirect wave on the basis of the result of detection of the beat state by the beat detection unit 28.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an object detection apparatus that detects an object using an ultrasonic sensor.

  Conventionally, an ultrasonic sensor is mounted on a moving body to detect objects existing around the moving body, and various controls for improving the traveling safety of the moving body based on the detection result, for example, to the driver For example, a notification is made or a braking device is operated.

  In general, object detection by an ultrasonic sensor is performed by detecting the received wave received by the transmission / reception unit as an envelope and determining that there is an object around the moving object when the detection threshold is exceeded (for example, Patent Document 1). reference). Japanese Patent Application Laid-Open No. H10-228561 discloses detecting whether the icing abnormality, disconnection abnormality, or normal state is based on the reverberation time after the ultrasonic transmission is stopped and the result of frequency analysis. This makes it possible to distinguish between freezing and disconnection and to perform more precise abnormality determination when abnormality occurs.

Japanese Patent Laid-Open No. 2001-221849

  In an ultrasonic sensor, when a foreign substance such as water is attached to a transmission / reception unit that transmits a survey wave and receives a reflected wave, the directivity characteristic of the transmission / reception unit changes, so that an exploration wave is generated in an adjacent sensor. It may be easy to receive directly. In this case, there is a concern of causing unnecessary detection. In order to avoid such unnecessary detection, a mask time is generally provided as a period during which object detection based on the reflected wave of the exploration wave transmitted from an ultrasonic sensor different from the adjacent sensor is not performed. However, when the mask time is set to be long, there arises a problem that the detection performance for an object existing at a short distance is deteriorated.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an object detection apparatus capable of achieving both improvement in object detection performance and suppression of unnecessary detection of an object.

  The present invention employs the following means in order to solve the above problems.

  The present invention uses a plurality of ultrasonic sensors (30) that transmit ultrasonic waves from a vibrator and generate a reception signal along with the vibration of the vibrator, and based on the reflected waves received by the ultrasonic sensors, The present invention relates to an object detection device (20) that detects an object existing around (10). The present invention provides a sensor that transmits the ultrasonic wave and receives the reflected wave among a plurality of the ultrasonic sensors, and a sensor that receives the reflected wave of the ultrasonic wave transmitted by the wave transmitting sensor. An object detection unit configured to detect the object based on a direct wave that is a reflected wave received by the transmission sensor and an indirect wave that is a reflected wave received by the wave receiving sensor; Based on the detection result of the beat state by the beat detection unit by the beat detection unit that detects the state of reverberation after the ultrasonic wave is transmitted, the reception sensor converts the reception signal into the indirect wave. And a time setting unit that variably sets an acquisition start time for starting acquisition as a signal based thereon.

  When foreign matter is attached to the transmission / reception part of the transmission sensor, if there is a difference in the reverberation vibration characteristics from the normal state where no foreign matter is attached, and the reverberation waveform deviates from the normal state, Therefore, it can be estimated that the deposit is present in the transmission / reception unit. In view of this point, in the above-described configuration, a reverberation beat state is detected, and based on the detected beat state, the reception start time when the reception sensor starts acquiring the reception signal as a signal based on an indirect wave is variable. The configuration is set. If foreign matter adheres to the transmission / reception unit, the directivity of the transmission / reception unit may change due to the foreign matter. In this regard, according to the above configuration, the object detection can be started in the wave receiving sensor in accordance with the directivity of the wave transmitting / receiving unit of the wave transmitting sensor. Thereby, the detection performance with respect to the object which exists in a short distance can be aimed at, suppressing the unnecessary detection of the object by the exploration wave of a transmission sensor being directly received by the receiving part.

The figure which shows schematic structure of the vehicle object detection system of 1st Embodiment. The schematic diagram showing an exploration wave, a direct wave, and an indirect wave. The figure explaining the object detection by an ultrasonic sensor. The figure explaining the state which does not generate the beat by reverberation. The figure showing the 2nd mask time when no beat has occurred. The flowchart which shows the process sequence of the beat detection process of 1st Embodiment. The flowchart which shows the process sequence of the setting process of 2nd mask time. The flowchart which shows the process sequence of the object detection process based on an indirect wave. The figure which shows schematic structure of the object detection system of the vehicle of 2nd Embodiment. The time chart which shows the specific aspect of the reverberation beat detection method. The flowchart which shows the process sequence of the beat detection process of 2nd Embodiment. The time chart explaining the beat detection method based on a reverberation frequency. The time chart explaining the beat detection method based on a reverberation frequency. The schematic block diagram of the object detection system of the vehicle of 3rd Embodiment. The flowchart which shows the process sequence of the beat detection process of 3rd Embodiment.

  Hereinafter, embodiments will be described with reference to the drawings. In the following embodiments, parts that are the same or equivalent to each other are denoted by the same reference numerals in the drawings, and the description of the same reference numerals is used.

(First embodiment)
The object detection system of this embodiment is mounted on a vehicle as a moving body. The object detection system shown in FIG. 1 detects an object (for example, another vehicle or a road structure) existing around the vehicle 10 using the distance measurement result of the ultrasonic sensor 30 mounted on the vehicle 10. .

  The ultrasonic sensor 30 is a sensor that detects the presence / absence of an object around the vehicle and the distance to the object by transmitting the ultrasonic wave as the exploration wave and receiving the reflected wave reflected by the surrounding object. is there. The ultrasonic sensor 30 is communicably connected to a driving support ECU 40 that performs driving support control (for example, collision avoidance control) of the vehicle 10, and outputs object detection information based on a command from the driving support ECU 40. . The object detection information includes information regarding the position, distance, and direction of an object existing around the vehicle 10.

  A plurality of ultrasonic sensors 30 are mounted on the vehicle 10. In the present embodiment, for example, four sensors are attached to the front and rear bumpers of the vehicle 10 at predetermined intervals in the vehicle width direction. In FIG. 1, for convenience, three sensors 30 a to 30 c are illustrated as the plurality of ultrasonic sensors 30. Since all of the plurality of ultrasonic sensors have the same configuration, FIG. 1 shows a specific configuration only for the sensor 30a.

  The ultrasonic sensor 30 includes a transmission / reception unit 21 and a detection ECU 20 as an object detection device. The transmission / reception unit 21 includes a vibrator, and one vibrator is configured to use both transmission and reception. The wave transmitting / receiving unit 21 is disposed, for example, on the front surface of the bumper. Note that the number and attachment positions of the ultrasonic sensors 30 are arbitrary, and may be attached to the side of the vehicle 10, for example.

  The detection ECU 20 includes a wave transmission unit 22, a wave reception unit 23, and a control unit 24, and implements a wave transmission / reception function. Based on a transmission command from the control unit 24, the transmission unit 22 generates a pulse signal by pulse-modulating a sine wave having a predetermined frequency in the ultrasonic region and outputs the pulse signal to the transmission / reception unit 21. The vibrator is vibrated at a predetermined transmission cycle. Thereby, an ultrasonic wave is output as an exploration wave. The wave receiving unit 23 converts the vibration of the vibrator into an electric signal based on a reception command from the control unit 24 and outputs the electric signal to the waveform processing unit 25 as a wave receiving signal.

  Based on a command from the driving support ECU 40, the control unit 24 outputs a wave transmission / reception command signal to the wave transmission unit 22 and the wave receiving unit 23, and the object detection information recognized based on the reflected wave is output to the driving support ECU 40. Output to. The detection ECU 20 further includes a waveform processing unit 25, an amplitude measurement unit 26, and a frequency measurement unit 27, and inputs various information for object detection to the control unit 24 as an object detection unit.

  As the waveform processing, the waveform processing unit 25 performs filter processing and amplification processing on the received signal, and detects the envelope with the envelope detection circuit. The amplitude measuring unit 26 measures the amplitude value of the received wave (including reverberation and reflected wave). In the present embodiment, an upper limit value of the amplitude value is determined, and when the amplitude value is larger than the upper limit value, the amplitude value is fixed at the upper limit value Amax. The frequency measuring unit 27 measures the frequency of the received wave. For example, a point at which the voltage changes from a positive value to a negative value is defined as a zero cross point, and the reciprocal of the time between the zero cross points is defined as a frequency. The control unit 24 detects an object around the vehicle based on the comparison result between the amplitude of the received wave (including reverberation and reflected wave) input from the amplitude measurement unit 26 and the amplitude threshold value.

  The driving support ECU 40 is configured mainly with a microcomputer including a CPU, various memories, and the like, and performs driving support control of the vehicle 10 based on object detection information acquired from the ultrasonic sensor 30. As driving support control, a warning sound is given to the driver of the vehicle 10 so that the vehicle 10 does not touch the object, or various controls such as braking control and steering control for avoiding contact with the object are performed. Or do. The vehicle 10 is provided with an outside air temperature sensor 41 that detects the outside air temperature.

  Each ultrasonic sensor 30 receives the reflected wave of the exploration wave transmitted by itself as a direct wave, and acquires the reflected wave time, which is the time from transmission to reception, as distance information. Moreover, the reflected wave of the exploration wave transmitted by the other ultrasonic sensor 30 is received as an indirect wave, and the reflected wave time is acquired as distance information. The detection ECU 20 calculates the relative position (coordinates) of the object with respect to the vehicle 10 using the distance information acquired by the direct wave and the distance information acquired by the indirect wave. Hereinafter, the ultrasonic sensor 30 that has transmitted the exploration wave is referred to as a “transmitting sensor”, and the ultrasonic sensor 30 that has received the indirect wave is referred to as a “received sensor”. Each of the ultrasonic sensors 30 and the driving support ECU 40 are connected by a signal line (not shown) by, for example, a daisy chain method or a star connection method, and can communicate with each other.

  FIG. 2 schematically shows a case where the exploration wave V transmitted from the transmission sensor is reflected by the object P and received as a reflected wave by the transmission sensor and the reception sensor. In FIG. 2, of the two adjacent ultrasonic sensors 30a and 30b, the sensor 30a is a transmission sensor that transmits the exploration wave V and receives the reflected wave as a direct wave W, and the sensor 30b is the sensor 30a. It is a receiving sensor which receives the reflected wave of the exploration wave transmitted from as the indirect wave X. According to the distance information acquired by the sensor 30a and the distance information acquired by the sensor 30b, the coordinates (x, y) of the object P can be calculated using the principle of triangulation.

  The object detection by the ultrasonic sensor 30 will be described with reference to FIG. In FIG. 3, (a) shows the transmission sensor and (b) shows the reception sensor. In FIG. 3A, the horizontal axis is time, and the vertical axis is the amplitude value A. FIG. 3A shows a waveform obtained by envelope detection.

  First, the wave transmission sensor will be described. The transmission unit 22 outputs a pulse signal to the transmission / reception unit 21 from time t10 to time t11 in response to a control command from the control unit 24. As a result, the transducer of the wave transmitting / receiving unit 21 vibrates, and an ultrasonic wave having a predetermined frequency is transmitted from the wave transmitting / receiving unit 21 (time t10 to t11). In the period after the transmission end time t11 (t11 to t12), the reverberation of the transmission wave occurs. Reverberation occurs when mechanical inertial vibration of the vibrator continues after the vibration for transmission is stopped.

  When the ultrasonic wave transmitted from the time t10 to the time t11 is reflected by an object existing around the vehicle and received by the wave transmitting / receiving unit 21, the time corresponding to the distance from the object (in FIG. 3A) The amplitude value A increases at time t13). The control unit 24 compares the amplitude value A of the reflected wave with the amplitude threshold Ath at this time, and determines that there is an object when the amplitude value A is larger than the amplitude threshold Ath. The shorter the distance between the vehicle 10 and the object, the earlier the reflected wave is received.

  In the transmission sensor, in the period t11 to t12 during which reverberation continues, there is a possibility that the reverberation is erroneously recognized as a reflected wave and the detection of an object is erroneous. Therefore, the control unit 24 of the wave transmission sensor prohibits reading of the reflected wave until a predetermined mask time (hereinafter referred to as “first mask time TmA”) elapses from the end of the ultrasonic transmission command. Then, when the first mask time TmA has elapsed, reading of the reflected wave is started, and object detection based on the amplitude value of the reflected wave is performed. The first mask time TmA is set so as to correspond to a period starting from time t11 when the ultrasonic transmission command ends and ending at time t12 when reverberation ends. With regard to the determination of the end of reverberation, in this embodiment, the end of reverberation is determined when a predetermined time Ty has elapsed after the amplitude value A has become smaller than the amplitude threshold Ath after the end of transmission of ultrasonic waves.

  In addition, although the amplitude threshold value used for the end determination of reverberation and the amplitude threshold value used for object detection are the same value, they may be different values. Reference symbol Tc is an ultrasonic transmission cycle, and ultrasonic waves are transmitted from the transmission / reception unit 21 of the same or different ultrasonic sensor 30 at every transmission cycle Tc (for example, at intervals of several hundred milliseconds). About 1st mask time TmA, it is good also as a period from the start of the transmission command of an ultrasonic sensor to the end of reverberation.

  Next, object detection by the wave receiving sensor will be described. In the wave receiving sensor, as shown in FIG. 2, the exploration wave transmitted from the wave transmitting sensor is not received as a reflected wave on the object P, but the ultrasonic wave Y is directly received by the wave receiving sensor from the wave transmitting sensor. "Skip" may occur. In such a case, there is a possibility that the wave receiving sensor detects the presence of an object based on reception of the ultrasonic wave Y due to a lateral jump even though no object actually exists at that position.

  Therefore, as shown in FIG. 3B, the control unit 24 of the wave receiving sensor outputs a predetermined mask time (hereinafter referred to as “second mask” after a command to start transmitting the exploration wave is output to the wave transmitting sensor. During the period until “time TmB”), reception of the reflected wave is prohibited, and after the second mask time TmB has elapsed, reading of the received wave as the reflected wave is started. Then, object detection is performed by the read reflected wave. The second mask time TmB is determined based on the distance (pitch) between the sensors and the sound speed.

  In the reverberation part of the transmission sensor, a “beat” may occur due to a plurality of waves having different frequencies interfering with each other to generate a synthesized wave. That is, as shown in FIG. 3A, the amplitude value A of the reverberation may fluctuate in the reverberation continuation period after the end of transmission at time t11. In this system, a circuit configuration such as a coil and a capacitor in the ultrasonic sensor 30 is designed so that a beat is generated by reverberation when the ultrasonic sensor 30 is normal. Therefore, if the ultrasonic sensor 30 can detect an object normally, the reverberation waveform is a waveform that has increased or decreased as shown in FIG.

  Here, if foreign matter such as water or dirt adheres to the transmission / reception unit 21 of the ultrasonic sensor 30, the directivity of the transmission / reception unit 21 spreads, and the exploration wave directly enters the adjacent sensor from the transmission sensor. Jumping easily occurs. In order to reduce such unnecessary detection due to the change in directivity, it is conceivable to design the reception sensor with a longer mask time (second mask time TmB). However, if the second mask time TmB is increased, the period during which object detection based on the reflected wave is prohibited after the exploration wave transmission command is extended, and the detection accuracy for an object existing at a short distance of the vehicle 10 is reduced. Is concerned.

  When foreign matter adheres to the transmission / reception unit 21 of the ultrasonic sensor 30, a difference appears in the reverberation vibration characteristics. When the reverberation waveform deviates from the normal state, the foreign matter adheres to the transmission / reception unit 21. Can be estimated. In the present embodiment, paying attention to the change in the reverberation beat state, if the reverberation beat state is different from the normal state, it is considered that the foreign substance has adhered to the transmission / reception unit 21, and the second is the mask time of the reception sensor. The mask time TmB is set longer than normal. As a result, the reception sensor delays the acquisition start time when the reception signal is started to be acquired as a signal based on the reflected wave.

  Specifically, as shown in FIG. 1, the detection ECU 20 of each ultrasonic sensor 30 includes a beat detection unit 28 that detects a reverberation beat state when the sensor ECU 20 is a transmission sensor. The control unit 24 of the receiving sensor acquires the detection result of the reverberation beat state from the transmission sensor, and sets the second mask time TmB based on the acquired reverberation beat state.

  Regarding the method for detecting the reverberation beat state, the slope of the amplitude value A in the period in which the reverberation amplitude value A tends to decrease differs depending on whether or not the reverberation beat occurs. Specifically, when a beat occurs due to reverberation, as shown in FIG. 3, a period in which the amplitude value A of the reverberation monotonously decreases toward zero (hereinafter referred to as “amplitude falling period Td”). ) Is relatively steep. On the other hand, when no beat occurs due to reverberation, as shown in FIG. 4, the slope of the amplitude value A in the amplitude fall period Td is gentler than that when the beat occurs. . Focusing on this point, the beat detector 28 detects the presence or absence of a reverberation beat based on the slope of the amplitude value A during the amplitude fall period Td.

  Specifically, in the wave transmission sensor, the beat detector 28 includes an inclination calculator 28a and a beat determiner 28b as shown in FIG. The slope calculation unit 28a is configured to perform an amplitude falling period in a period during which reverberation of the exploration wave transmitted by itself is continued, more specifically, in a period before the amplitude value A falls below the amplitude threshold Ath after the exploration wave is transmitted. The absolute value of the slope of the amplitude value A at Td (hereinafter referred to as “falling slope α”) is calculated. Note that the falling slope α corresponds to the “amplitude slope”.

  The beat determination unit 28b compares the falling inclination α calculated by the inclination calculation unit 28a with the beat determination value αth. When the falling slope α is equal to or less than the beat determination value αth, that is, when the decrease in the amplitude value A when the reverberation attenuates is slow, it is determined that no reverberation has occurred. On the other hand, when the falling slope α is larger than the beat determination value αth, that is, when the decrease of the amplitude value A when the reverberation attenuates is steep, it is determined that the reverberation has occurred. The beat detection unit 28 outputs the detection result of the reverberation beat state to the control unit 24 as beat information.

  In addition, when the reverberation has occurred, as shown in FIG. 3, the amplitude value A fluctuates in the period during which reverberation continues, so that the amplitude value of the reverberation within one reverberation period. A period in which A tends to decrease appears multiple times. The beat detector 28 calculates the slope of the amplitude value A every time the amplitude value A decreases and rewrites it each time, thereby recognizing the slope of the amplitude value A at the last amplitude fall Ap and The beat is determined as the inclination α.

  The control unit 24 of the receiving sensor acquires reverberation beat information from the control unit 24 of the transmission sensor via the signal line, and variably sets the second mask time TmB according to the acquired beat information. The ultrasonic sensor 30 of the present embodiment is designed so that a beat is generated by reverberation when no foreign matter is attached to the transmission / reception unit 21, and the control unit 24 is configured so that the reverberation beat state is normal. In the state, that is, in the state where the beat is generated due to reverberation, the reference value Tm1 is set as the second mask time TmB. In addition, when no reverberation occurs in the reverberation and the reverberation state of the reverberation is different from the normal state, a correction value Tm2 (Tm1 <Tm2) that is longer than the reference value Tm1 is set as the second mask time TmB. Set. The control unit 24 of the wave receiving sensor performs object detection based on the reflected wave using the set second mask time TmB. In the present embodiment, the control unit 24 functions as a “time setting unit”.

  The second mask time TmB when a foreign substance adheres to the transmission / reception unit 21 will be described with reference to FIG. When it is detected that a foreign object adheres to the transmission / reception unit 21 of the transmission sensor and that no reverberation has occurred in the reverberation of the transmission sensor (FIG. 5A), the control unit 24 of the reception sensor As shown in FIG. 5B, the period from the time t20 when the command to start transmitting the exploration wave to the wave transmission sensor is output until the correction value Tm2 elapses is set as the second mask time TmB. Thereby, the acquisition start time of the reflected wave is set to a time later than when the reverberation beat state is normal, and the object detection is performed after the correction value Tm2 has elapsed from time t20.

  Next, processing executed by the object detection apparatus of the present embodiment will be described using the flowcharts of FIGS.

  FIG. 6 shows the procedure of the reverberation beat detection process. The processing of FIG. 6 is executed at predetermined intervals by the detection ECU 20 of the transmission sensor after a transmission command for transmitting an ultrasonic wave is output from the transmission / reception unit 21 of the transmission sensor.

  In FIG. 6, in step S <b> 101, the reverberation unit 23 receives reverberation. In step S102, the falling slope α of the amplitude value A is calculated in a period before the amplitude value A of the received reverberation falls below the amplitude threshold value Ath.

  In step S103, it is determined whether or not the falling slope α is larger than the beat determination value αth. When the falling slope α is larger than the beat determination value αth, the process proceeds to step S104, where it is determined that a beat is generated due to reverberation, and the determination result is stored as beat information. On the other hand, if the falling slope α is equal to or smaller than the beat determination value αth, the process proceeds to step S105, where it is determined that no beat is generated due to reverberation, and the determination result is stored as beat information. Thereafter, this process is terminated.

  Next, a description will be given of a process procedure of a mask setting process (FIG. 7) for setting the second mask time TmB and an object detection process (FIG. 8) using a reflected wave (indirect wave). The processing of FIGS. 7 and 8 is executed at predetermined intervals by the detection ECU 20 of the wave receiving sensor after a transmission command for transmitting an ultrasonic wave is output from the wave transmitting / receiving unit 21 of the wave transmitting sensor.

  In FIG. 7, in step S <b> 201, reverberation beat information is acquired from the detection ECU 20 of the transmission sensor. In a succeeding step S202, it is determined whether or not the reverberation has occurred based on the acquired beat information. If the beat occurs due to reverberation, the process proceeds to step S203, and the reference value Tm1 is set as the second mask time TmB.

  On the other hand, if no beat is generated due to reverberation, the process proceeds to step S204, and it is determined based on the outside air temperature information detected by the outside air temperature sensor 41 whether or not the outside air temperature has changed more than a predetermined temperature. (Temperature change determination unit). Here, a positive determination is made if there is no rapid temperature change in which the outside air temperature is equal to or higher than the predetermined temperature within a predetermined short time (for example, several minutes to several tens of minutes). A situation in which a rapid temperature change occurs may occur when the vehicle 10 enters a space that is blocked from the outside, such as a garage, a tunnel, or an indoor parking lot.

  If the outside air temperature has not changed by a predetermined temperature or more, an affirmative determination is made in step S204, the process proceeds to step S205, and a correction value Tm2 is set as the second mask time TmB. On the other hand, if the outside air temperature has changed by a predetermined temperature or more, the process proceeds to step S203, and the reference value Tm1 is set as the second mask time TmB. In the situation where the outside air temperature has changed drastically, the cause of the disappearance of the reverberation is not due to the adhesion of foreign matter to the wave transmitting / receiving unit 21 but to the temperature characteristics of the circuit in the ultrasonic sensor 30. Because. Thereafter, this process is terminated.

  Next, the object detection process by the wave receiving sensor of FIG. 8 will be described. In FIG. 8, in step S301, the second mask time TmB set in FIG. 7 is acquired, and it is determined whether or not the second mask time TmB has elapsed since the search wave transmission command was output to the transmission sensor. judge. Until the second mask time TmB elapses, the reflected wave is not read, and this routine is ended once. On the other hand, if the second mask time TmB has elapsed, an affirmative determination is made in step S301, the process proceeds to step S302, and the received wave is read as a reflected wave. In the subsequent step S303, the amplitude value of the reflected wave (indirect wave) is compared with the amplitude threshold value Bth. Note that the amplitude threshold value Bth used for object detection by indirect waves may be the same value as or different from the amplitude threshold value Ath used for object detection by direct waves.

  If the amplitude value of the reflected wave is equal to or smaller than the amplitude threshold Bth, the process proceeds to step S304, and it is determined that there is no object. On the other hand, if the amplitude value of the reflected wave is larger than the amplitude threshold value Bth, the process proceeds to step S305, where it is determined that there is an object. Then, this process ends.

  According to the embodiment described in detail above, the following excellent effects can be obtained.

  Based on the reverberation state of the reverberation of the exploration wave transmitted by the transmission sensor, the reception sensor based on the reflected wave causes the reception signal to be based on the reflected wave by variably setting the second mask time TmB, which is the mask time of the reception sensor. Since the acquisition start time for starting acquisition as a signal is variably set, object detection based on indirect waves can be performed using a mask time corresponding to the presence or absence of deposits in the wave transmission / reception unit 21 of the wave transmission sensor. . As a result, it is possible to achieve both improvement in detection performance of short-distance objects and suppression of unnecessary detection of objects.

  Specifically, when the reverberation beat state detected by the beat detection unit 28 is different from the normal state in which there is no deposit on the wave transmission / reception unit 21 of the transmission sensor, acquisition of the reflected wave is started in the wave reception sensor. The second mask time TmB is changed so that the timing becomes later. According to this configuration, when there is no deposit on the transmission / reception unit 21, the second mask time TmB is set to be short, so that an object existing at a short distance of the vehicle 10 can be detected with high accuracy. In addition, when there is a deposit on the transmission / reception unit 21, the second mask time TmB is set to a long time, so that the exploration wave from the transmission sensor directly enters the transmission / reception unit 21 of the reception sensor. Unnecessary object detection can be suppressed.

  The second mask time TmB is variably set based on the detection result of the reverberation beat state on condition that the outside air temperature does not change by a predetermined temperature or more. Under circumstances where the outside air temperature has changed by a predetermined temperature or more, the cause of the change in the reverberation state of the reverberation may be due to the temperature characteristics of the circuit in the ultrasonic sensor 30 rather than the adhesion of foreign matter to the transmission / reception unit 21. That is, when the state of reverberation changes in a state in which the outside air temperature has not changed more than a predetermined value, there is a high probability that foreign matter has adhered to the transmission / reception unit 21. By considering this point and adopting the above-described configuration, it is possible to increase the accuracy of determining the presence / absence of deposits on the wave transmitting / receiving unit 21.

  Focusing on the fact that the falling slope α of the amplitude of the reverberant wave differs depending on the reverberating state of the reverberation, the reverberating state of reverberation is detected based on the falling slope α. According to this configuration, it is only necessary to calculate at least the slope of the amplitude value A in the period of the last amplitude fall Ap, so that it is possible to detect a reverberating beat state with a small processing load.

(Second Embodiment)
Next, the second embodiment will be described focusing on the differences from the first embodiment. In the first embodiment, the reverberation beat state is detected based on the falling slope α which is the absolute value of the slope of the falling portion of the reverberant waveform. On the other hand, in the present embodiment, the reverberation state of the reverberation is detected by detecting the frequency at which the amplitude value A of the reverberation increases or decreases with a predetermined change or more.

  FIG. 9 is a schematic configuration diagram of the object detection system of the present embodiment. FIG. 9 shows a different part from FIG. In FIG. 9, the beat detection unit 28 includes a fluctuation detection unit 28c and a beat determination unit 28d. The fluctuation detection unit 28c is configured to increase or decrease the reverberation amplitude value A by a fluctuation amount equal to or greater than a predetermined value in a period before the amplitude value A falls below the amplitude threshold Ath after transmitting the ultrasonic wave (hereinafter, “the number of beats δ ”)). For example, as shown in FIG. 10, in the period after the end time t31 of the exploration wave transmission command, the number of appearances of the minimum point P where the amplitude value A is less than the fluctuation threshold Dth is counted, and the number of appearances is set as the number of beats δ. To do. The fluctuation threshold value Dth is set to a value smaller than the upper limit value Amax and larger than the amplitude threshold value Ath.

  The beat determination unit 28d compares the number of beats δ detected by the fluctuation detection unit 28c with the beat determination value δth. If the number of beats δ is equal to or less than the beat determination value δth, no beat is generated due to reverberation. judge. On the other hand, when the number of beats δ is larger than the beat determination value δth, it is determined that a beat is generated due to reverberation.

  A processing procedure of reverberation beat detection processing in the present embodiment will be described with reference to the flowchart of FIG. This process is executed at predetermined intervals by the detection ECU 20 of the transmission sensor after a transmission command for transmitting an ultrasonic wave is output from the transmission / reception unit 21.

  In FIG. 11, in step S <b> 401, reverberation is received by the wave receiver 23. In step S402, the number of beats δ is calculated based on the reverberation amplitude value A in a period before the received reverberation amplitude value A falls below the amplitude threshold Ath.

  In step S403, it is determined whether or not the number of beats δ is greater than the beat determination value δth. If the number of beats δ is greater than the beat determination value δth, the process proceeds to step S404, where it is determined that a beat has occurred due to reverberation, and the determination result is stored as beat information. On the other hand, when the number of beats δ is equal to or smaller than the beat determination value δth, the process proceeds to step S405, where it is determined that no beat is generated due to reverberation, and the determination result is stored as beat information. The beat information stored in the process of FIG. 11 is used in the mask time setting process of FIG. 7, and the object detection is performed by the object detection process of FIG.

  According to the second embodiment described in detail above, focusing on the fact that the frequency at which the amplitude of the reverberation wave increases or decreases varies depending on the state of the reverberation, the reverberation of the reverberation is based on the number of beats δ representing the frequency. It was set as the structure which detects a state. According to this configuration, it is possible to directly detect the reverberation beat and to detect the beat state with higher accuracy. As a result, it is possible to set a suitable second mask time TmB from the viewpoint of coexistence of suppression of unnecessary object detection and improvement of object detection performance.

(Third embodiment)
Next, the third embodiment will be described focusing on the differences from the first embodiment. In the first embodiment, the reverberation beat state is detected based on the falling slope α. In the present embodiment, the beat state is detected based on the reverberation frequency.

  The beat detection process based on the reverberation frequency will be described with reference to FIGS. FIG. 12 illustrates a case where a beat is generated due to reverberation in the transmission sensor, and FIG. 13 illustrates a case where no beat is generated due to reverberation. 12 and 13, the upper part represents the transition of the amplitude value A of the synthesized wave, and the lower part represents the transition of the amplitude value A of each of the low frequency component and the high frequency component.

  Reverberation of reverberation occurs when a plurality of waves having different frequencies interfere to generate a composite wave. When the beat is generated by reverberation, as shown in FIG. 12, the amplitude values A of the low frequency component and the high frequency component change substantially the same over time. The frequency is measured. On the other hand, when the reverberation is shifted to the low frequency side and the frequency of the vibration of the low frequency component is measured by the frequency measuring unit 27, the reverberation does not occur as shown in FIG. Focusing on this point, in this embodiment, the beat state is detected based on the reverberation frequency.

  FIG. 14 is a schematic configuration diagram of the object detection system of the present embodiment. FIG. 14 shows a different part from FIG. The beat detection unit 28 inputs a reverberation frequency (hereinafter, referred to as “reverberation measurement frequency fa”) measured after the exploration wave transmission command ends, from the frequency measurement unit 27, and based on the input reverberation measurement frequency fa, It is determined whether or not there is a beat in the reverberation. In the present embodiment, frequency information indicating the relationship between the reverberation frequency at the reference temperature (for example, normal temperature) and the driving frequency is stored in the storage unit in advance, and the reverberation state of the reverberation is detected using the frequency information. To do. In the present embodiment, the ultrasonic sensor 30 is designed so that a beat is generated by reverberation at a reference temperature, and the amplitude component of the amplitude component is used as the reverberation frequency in a normal state where no foreign matter is attached to the transmission / reception unit 21. A large high-frequency component frequency (a frequency higher than the drive frequency) is measured. The reference temperature is an environmental temperature during normal vehicle travel, and may be set according to, for example, a shipping region.

  Specifically, the beat detector 28 determines whether or not the relationship between the reverberation measurement frequency fa and the drive frequency is the same as the relationship between the reverberation frequency and the drive frequency at the reference temperature. If the relationship between the two is the same as that at the reference temperature, it is determined that the beat is generated in the reverberation part. On the other hand, if the relationship between the two is different from that at the reference temperature, it is determined that no reverberation occurs in the reverberation portion.

  Next, the mask time setting process of this embodiment will be described with reference to the flowchart of FIG. This process is executed at predetermined intervals by the detection ECU 20 of the transmission sensor after a transmission command for transmitting an ultrasonic wave is output from the transmission / reception unit 21.

  In FIG. 15, in step S <b> 501, reverberation is received by the wave receiver 23. In step S502, the reverberation measurement frequency fa is acquired, and in step S503, it is determined whether or not the relationship between the reverberation measurement frequency fa and the drive frequency is the same as that at the reference temperature. When the relationship between the reverberation measurement frequency fa and the drive frequency is the same as that at the reference temperature, the process proceeds to step S504, where it is determined that a beat is generated due to the reverberation, and the determination result is stored in the storage unit as beat information. On the other hand, if the relationship between the reverberation measurement frequency fa and the drive frequency is not the same as that at the reference temperature, the process proceeds to step S505, where it is determined that no reverberation has occurred due to reverberation, and the determination result is stored in the storage unit as beat information. Remember. The beat information stored in the process of FIG. 15 is used in the mask time setting process of FIG. 7, and the object detection is performed by the object detection process of FIG.

  According to the third embodiment described in detail above, attention is paid to the point that the appearance of the reverberation frequency differs depending on the reverberation state of the reverberation, and the reverberation state of the reverberation is detected based on the reverberation frequency. According to this configuration, it is possible to detect a reverberating beat state relatively easily using the reverberant frequency. Further, by setting the second mask time TmB variably using the detection result, it is possible to achieve both suppression of unnecessary detection of an object and improvement in detection performance of a short-range object.

(Other embodiments)
The present invention is not limited to the above embodiment, and may be implemented as follows, for example.

  In the above-described embodiment, the case where the ultrasonic sensor 30 is applied to a system that is designed to generate a beating due to reverberation has been described. You may apply to the system provided with a sound wave sensor. In this case, the second mask time TmB is changed to a longer time when the state where no beat is generated due to reverberation changes to the state where the beat occurs.

  In the above-described embodiment, the presence or absence of reverberation is detected by the beat detection unit 28. However, the second mask time TmB may be variably set based on the detection result. . Specifically, in the configuration for detecting the reverberating beat state based on the falling slope α, the reflected wave is increased by increasing the second mask time TmB as the deviation from the normal falling slope α increases. The acquisition start time of is set to a late time. Alternatively, in the configuration in which the second mask time TmB is set according to the number of beats, the acquisition start time of the reflected wave is increased by increasing the second mask time TmB as the amount of deviation from the normal number of beats increases. Set to a later time.

  The second mask time TmB may be variably set according to the outside air temperature or the temperature information of the sensor individual. Specifically, the second mask time TmB is set shorter as the temperature is higher.

  In the third embodiment, frequency information indicating the relationship between the reverberation frequency and the drive frequency at the reference temperature is determined in advance, and whether or not the relationship between the reverberation measurement frequency fa and the drive frequency is the same as that at the reference temperature. While the reverberation beat state is detected by the determination, the beat state detection method based on the reverberation frequency is not limited to this. For example, it may be configured to determine whether or not the level of the reverberation frequency with respect to the drive frequency has changed within a period during which reverberation occurs, and to detect the reverberating beat state based on the determination result. Specifically, when the reverberation measurement frequency fa transitions from a frequency higher than the drive frequency to a lower frequency within a period in which reverberation occurs, or the reverberation measurement frequency fa transitions from a frequency lower than the drive frequency to a higher frequency. In such a case, it is determined that no beat is generated due to reverberation. Further, when the reverberation measurement frequency fa continues to be higher than the drive frequency within a period in which reverberation is occurring, it is determined that a beat has occurred due to reverberation.

  -It is good also as a structure which detects a reverberation beat state combining several detection methods. For example, a configuration for detecting a reverberation beat state based on the falling slope α and the number of beats δ, a configuration for detecting a reverberation beat state based on the falling slope α and the reverberation frequency, and the like can be given. According to the configuration in which a plurality of detection methods are combined, the beat state of reverberation can be detected with higher accuracy.

  In the first embodiment, the period in which the amplitude value A monotonously decreases, that is, the falling slope α at the amplitude falling Ap is recognized, and the beat determination is performed based on this. However, the amplitude value A monotonously decreases. With respect to the increase / decrease fluctuation of the amplitude value A that occurred before the period to be performed, a decrease amount per unit time of the amplitude may be calculated, and a beat determination may be performed based on this.

  In the above embodiment, the case where the detection ECU 20 of the ultrasonic sensor 30 functions as an object detection device has been described. However, the ECU on the vehicle 30 side may function as the object detection device.

  In the above-described embodiment, the object detection device mounted on the vehicle has been described as an example. However, the object detection device may be mounted on a moving body such as a railway vehicle, a ship, an aircraft, or a robot.

  -Each said component is conceptual and is not limited to the said embodiment. For example, the functions of one component may be realized by being distributed to a plurality of components, or the functions of a plurality of components may be realized by one component.

  DESCRIPTION OF SYMBOLS 10 ... Vehicle (moving body), 20 ... Detection ECU (object detection apparatus), 21 ... Transmission / reception part, 28 ... Beat detection part, 30 ... Ultrasonic sensor, 40 ... Driving assistance ECU.

Claims (6)

A plurality of ultrasonic sensors (30) that transmit ultrasonic waves from the vibrator and generate a reception signal along with the vibration of the vibrator, and based on the reflected waves received by the ultrasonic sensor, the moving body (10) An object detection device (20) for detecting an object existing around,
Among the plurality of ultrasonic sensors, a sensor that transmits the ultrasonic wave and receives the reflected wave is a transmission sensor, and a sensor that receives the reflected wave of the ultrasonic wave transmitted by the transmission sensor is a receiving sensor.
An object detection unit that detects the object based on a direct wave that is a reflected wave received by the transmission sensor and an indirect wave that is a reflected wave received by the reception sensor;
A beat detection unit for detecting a beat state of reverberation after the ultrasonic wave is transmitted from the vibrator;
Based on the detection result of the beat state by the beat detection unit, a timing setting unit that variably sets an acquisition start time at which the reception sensor starts acquiring the received signal as a signal based on the indirect wave;
An object detection device comprising:   The timing setting unit sets the acquisition start timing to a timing later than when the beat state is normal when the beat state detected by the beat detection unit is different from the normal time. The object detection apparatus described. A temperature change determination unit for determining that the outside air temperature has not changed more than a predetermined temperature;
The timing setting unit is configured to obtain the acquisition start time based on a detection result of the beat state by the beat detection unit when it is determined by the temperature change determination unit that the outside air temperature has not changed more than the predetermined temperature. The object detection device according to claim 1, wherein the variable is set to be variable. A slope calculator that calculates an amplitude slope as a decrease amount per unit time of the amplitude in a period in which the amplitude of the reverberation tends to decrease;
The object detection device according to any one of claims 1 to 3, wherein the beat detection unit detects the beat state based on the amplitude inclination calculated by the inclination calculation unit. A fluctuation detector that detects the frequency of fluctuation of the amplitude of the reverberation with a change amount greater than or equal to a predetermined amount,
The object detection device according to any one of claims 1 to 4, wherein the beat detection unit detects the beat state based on the frequency detected by the fluctuation detection unit. A frequency measurement unit for measuring the frequency of the reverberation;
The object detection device according to any one of claims 1 to 5, wherein the beat detection unit detects the beat state based on a frequency measured by the frequency measurement unit.

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