JP2012220434A - Object detecting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an object detecting device capable of detecting reflection waves buried in reverberation vibrations even when the reverberation vibrations of an ultrasonic transducer are small and detecting an object existing within a short distance.SOLUTION: An object detecting device comprises: an ultrasonic transducer 1 that sends ultrasonic waves to an object A1 and receives reflection waves reflected on the object A1; a drive part 2 and a control part 3 that drive the ultrasonic transducer 1 at a first frequency f1 and then drive the ultrasonic transducer 1 at a second frequency f2 that is different from the first frequency f1; an envelope detection part 7 for detecting a beat signal based on the difference between the first frequency f1 and the second frequency f2; and a signal processing part 8 for detecting the object A1 based on an output of the envelope detection part 7.

Description

  The present invention relates to an object detection apparatus that detects the presence of an object and obtains a distance to the object.

  2. Description of the Related Art Conventionally, an ultrasonic sensor that detects the presence of an object and calculates a distance to the object by detecting a reflected wave from the object of an ultrasonic signal is known. The ultrasonic sensor outputs the ultrasonic signal from the transducer and receives the reflected wave from the object by the transducer to detect the presence of the object, or the time from the sending time of the ultrasonic signal to the receiving time of the reflected wave The distance from the object to the object is detected. Many of such ultrasonic sensors transmit an ultrasonic signal and receive a reflected wave with a single transducer.

  Here, when the oscillation output is applied to the transducer and the ultrasonic signal is transmitted, the output of the transducer due to the reverberation appears even after the oscillation output stops. For this reason, when detecting the reflected wave from the object, there is a problem that the object cannot be detected if the distance to the object is short and the reflected wave is buried in the reverberation vibration. Even in the case where the transmission of the ultrasonic signal and the reception of the reflected wave are performed by different transducers, the transmitted ultrasonic signal wraps around the receiving transducer, and thus has substantially the same problem.

  A solution to the above problem is disclosed in Patent Document 1. In this conventional example, in an ultrasonic sensor that transmits an ultrasonic signal and receives a reflected wave from an object of the ultrasonic signal by a transducer, a pulse oscillation output having a frequency f0 different from the resonance frequency fr of the transducer is applied to the transducer. An oscillation circuit to be added is provided. This conventional example includes a filter that is connected to the reception output of the transducer and passes the frequency of | fr−f0 |, and a processing circuit that processes the filter output.

  Therefore, in this conventional example, even if the reflected wave of the frequency f0 overlaps the reverberation vibration of the resonance frequency fr, an output indicating the presence of the reflected wave appears at the frequency of | fr−f0 | It is possible to extract the presence of a reflected wave buried in the reverberation vibration.

JP-A-10-268035

  However, in the above conventional example, the reflected wave buried in the reverberation vibration is detected based on the frequency difference component between the reverberation vibration having the resonance frequency fr of the transducer (ultrasonic transducer) and the reflected wave having the frequency f0. . For this reason, when a sufficiently large reverberation vibration is generated, a reflected wave buried in the reverberation vibration can be detected, but when the reverberation vibration is small, the frequency difference component can be detected. However, there is a problem that it is difficult to detect the reflected wave buried in the reverberation vibration.

  The present invention has been made in view of the above points, and detects an object existing in a short distance by detecting a reflected wave buried in the reverberation vibration even when the reverberation vibration of the ultrasonic vibrator is small. It is an object of the present invention to provide an object detection device capable of performing the above.

  The object detection device of the present invention includes one or more ultrasonic transducers, and transmits and receives an ultrasonic wave, and after driving the wave transmitting and receiving unit at a first frequency, A drive control unit that drives the transmission / reception unit at a second frequency different from the first frequency, and an envelope detection unit that detects a beat signal based on a difference between the first frequency and the second frequency; And a signal processing unit for detecting the object based on the output of the envelope detection unit.

  In this object detection apparatus, it is preferable that the transmission / reception unit has one ultrasonic transducer and transmits and receives ultrasonic waves using the ultrasonic transducer.

  In this object detection apparatus, the wave transmitting / receiving unit includes at least two ultrasonic transducers, and the at least one ultrasonic transducer is a transmitter that transmits ultrasonic waves, and at least one of the ultrasonic transducers. It is preferable that the acoustic transducer is a receiver that receives ultrasonic waves, and the drive control unit drives the transmitter.

  In this object detection apparatus, the first frequency is a frequency different from the resonance frequency of the transmission / reception unit, and the second frequency is the same as or close to the resonance frequency of the transmission / reception unit. Preferably there is.

  In the object detection device, the drive control unit includes a transformer that boosts a drive voltage applied to the wave transmitting / receiving unit, and a resistor connected in series to a primary side winding of the transformer, When driving the transmission / reception unit at a frequency, do not use the resistor, and when driving the transmission / reception unit at the second frequency, connect the resistance to the primary winding of the transformer. Is preferred.

  In this object detection apparatus, the drive control unit has a short distance mode for detecting the object existing at a short distance and a long distance mode for detecting the object existing at a long distance. Driving the transmitting / receiving unit at the second frequency after driving the transmitting / receiving unit at the second frequency, and driving the transmitting / receiving unit at the second frequency in the long-distance mode. It is preferable to stop driving of the transmission / reception unit.

  In this object detection apparatus, it is preferable that the drive control unit drives the wave transmitting / receiving unit in the short distance mode with a higher drive voltage than in the long distance mode.

  The present invention has an effect that even when the reverberation vibration of the ultrasonic vibrator is small, a reflected wave buried in the reverberation vibration can be detected and an object existing at a short distance can be detected.

It is a figure which shows embodiment of the object detection apparatus which concerns on this invention, (a) is a block diagram, (b) is a wave form diagram. It is a figure which shows the drive part of an object detection apparatus same as the above, (a) is a circuit schematic diagram, (b) is a circuit schematic diagram which shows another structure, (c) is a circuit which shows the specific structure of (b). FIG. It is a block diagram which shows the other structure of an object detection apparatus same as the above.

  Hereinafter, embodiments of an object detection device according to the present invention will be described with reference to the drawings. In the present embodiment, as shown in FIG. 1A, an ultrasonic transducer 1 (transmission / reception unit) that transmits an ultrasonic wave to an object A1 and receives a reflected wave reflected by the object A1, and an ultrasonic wave A driving unit 2 that applies a driving voltage to the vibrator 1 and a control unit 3 that controls the driving unit 2 are provided. The present embodiment also includes a first oscillator 4 that outputs an oscillation signal having a first frequency f1, and a second oscillator 5 that outputs an oscillation signal having a second frequency f2 different from the first frequency f1. And an amplifying unit 6 that amplifies and outputs a signal received by the ultrasonic transducer 1. Further, in the present embodiment, an envelope detection unit 7 that detects an envelope of the output signal of the amplification unit 6, a signal processing unit 8 that detects the object A1 based on the output signal of the envelope detection unit 7, and an object A1 And a distance measuring unit 9 for calculating the distance up to. The “drive control unit” in the claims includes the drive unit 2 and the control unit 3.

  This embodiment is mounted on a vehicle (not shown), for example, to detect an obstacle (object A1) around the vehicle and determine the distance to the obstacle. When the present embodiment is mounted on a vehicle, the ultrasonic transducer 1 is embedded in a vehicle bumper, and other members are disposed in the vehicle interior.

  The ultrasonic transducer 1 vibrates when a pulsed drive voltage is applied from the drive unit 2 and transmits ultrasonic waves having the frequency of the drive voltage to the external space. The ultrasonic transducer 1 receives a reflected wave from the object A1 existing in the external space and vibrates, thereby outputting a received signal based on the frequency of the reflected wave and giving it to the amplifier 6.

  The drive unit 2 amplifies an oscillation signal given from any of the oscillators 4 and 5 via the control unit 3 and applies a drive voltage to the ultrasonic transducer 1. Here, an example of a circuit configuration of the drive unit 2 will be described with reference to the drawings. As shown in FIG. 2A, the drive unit 2 of the present embodiment includes a constant voltage source VR1, a switching element Q1 composed of a PNP transistor, a transformer 20, and a parallel circuit of a resistor R1 and a switch SW1. . A constant voltage source VR1 is connected to one end of the primary winding 20A of the transformer 20 via a switching element Q1, and a resistor R1 is connected in series to the other end. Further, the ultrasonic transducer 1 is connected in parallel to the secondary winding 20B of the transformer 20. The turn ratio between the number of turns of the primary side winding 20A and the number of turns of the secondary side winding 20B is 1 to n (n> 1).

  Hereinafter, the operation of the drive unit 2 will be described. An oscillation signal is input from one of the oscillators 4 and 5 to the base terminal of the switching element Q1 via the control unit 3. Therefore, the switching element Q1 is switched on / off alternately based on the frequency of the oscillation signal. Thereby, the voltage of the constant voltage source VR1 is intermittently applied to the primary side winding 20A. That is, a pulse voltage having the same cycle as the oscillation signal is applied to the primary winding 20A. In the transformer 20, an induced voltage (for example, 30V) obtained by boosting a pulsed voltage applied to the primary side winding 20A is induced in the secondary side winding 20B. The induced voltage is applied as a drive voltage to the ultrasonic transducer 1.

  Here, when transmitting an ultrasonic wave from the ultrasonic transducer 1 to detect the object A1, the output of the ultrasonic wave increases if the drive voltage applied to the ultrasonic transducer 1 is large. In this case, it is desirable that the impedance on the primary side of the transformer 20 as viewed from the ultrasonic transducer 1 is small. On the other hand, when receiving a reflected wave from the object A1, the reception sensitivity increases if the received signal at the ultrasonic transducer 1 is large. In this case, it is desirable that the impedance on the primary side of the transformer 20 as viewed from the ultrasonic transducer 1 is large.

  Therefore, in the present embodiment, a parallel circuit of the resistor R1 and the switch SW1 is connected to the primary winding 20A. The switch SW1 is turned on / off by a control signal supplied from the control unit 3, and is turned on when transmitting an ultrasonic wave having the first frequency f1, and is ultrasonically vibrated at the second frequency f2. When the child 1 is driven, it is switched off. In the present embodiment, the period for driving the ultrasonic transducer 1 at the second frequency f2 is a period for receiving the reflected wave from the object A1.

  Therefore, when transmitting ultrasonic waves from the ultrasonic transducer 1, the switch SW1 is turned on so that the resistor R1 is not connected to the primary winding 20A. The primary side impedance can be reduced. Further, when receiving the reflected wave from the object A1, the resistor R1 is connected to the primary winding 20A when the switch SW1 is turned off, so that the transformer 20 viewed from the ultrasonic transducer 1 is seen. The impedance on the primary side can be increased.

  Note that, when receiving the reflected wave from the object A1, the ultrasonic transducer 1 is driven at the second frequency f2, but the drive voltage can be kept low by increasing the impedance as described above. it can. Therefore, when receiving the reflected wave from the object A1, the frequency component of the first frequency f1 included in the oscillation signal of the second frequency f2 driving the ultrasonic transducer 1 can be reduced. The floor noise in the state where there is no input to the ultrasonic transducer 1 can be suppressed.

  The control unit 3 includes, for example, a microcomputer, a path for supplying an oscillation signal having a first frequency f1 oscillated from the first oscillator 4 to the drive unit 2, and a second frequency oscillated from the second oscillator 5. Switching control for the path for supplying the oscillation signal of f2 to the drive unit 2 is performed. Further, the control unit 3 outputs a control signal for switching on / off of the switch SW1 to the drive unit 2 as described above. Further, when the control unit 3 switches to the path for supplying the oscillation signal of the first frequency f1 oscillated from the first oscillator 4 to the drive unit 2, the ultrasonic transducer 1 transmits the ultrasonic wave at the timing. This is given to the distance measuring unit 9 as wave transmission timing.

  The envelope detector 7 detects the envelope of the beat signal having the frequency | f 1 −f 2 | from the output signal from the amplifier 6. Here, the output signal from the amplifying unit 6 includes a transmission signal having the first frequency f1, a transmission signal having the second frequency f2, and reverberation vibration having the resonance frequency fr of the ultrasonic transducer 1. The output signal from the amplifying unit 6 includes a beat signal having a frequency | fr−f2 | and a beat signal having a frequency | f1−f2 |. Accordingly, paying attention to the fact that the frequency | f1-f2 | is separated from the frequency of other signals, the envelope detector 7 has a band-pass filter or a low-pass filter that allows only the beat signal having the frequency | f1-f2 | (Not shown) is provided.

  The signal processing unit 8 further includes an envelope detection circuit (not shown) that further detects an envelope of the output signal of the envelope detection unit 7, and a comparator (not shown) that compares the output value of the envelope detection circuit with a predetermined threshold value. Z)). The signal processing unit 8 obtains a rectangular wave pulse by performing envelope detection on the output signal of the envelope detection unit 7. Then, the signal processing unit 8 compares the output value of the rectangular wave pulse with a predetermined threshold value to detect the rising timing of the rectangular wave pulse and outputs a high level signal to the distance measuring unit 9. That is, the signal processing unit 8 detects that the object A1 exists in the external space by detecting the rising timing of the rectangular wave pulse. Further, the signal processing unit 8 detects the reception timing of the reflected wave from the object A 1 by detecting the rising timing of the rectangular wave pulse, and gives the detection result to the distance measuring unit 9.

  In the signal processing unit 8 described above, the output signal of the envelope detection unit 7 is detected by the envelope detection circuit, but instead of the envelope detection circuit, the peak value of the output signal of the envelope detection unit 7 is obtained. A peak hold circuit for holding may be used. Even in this case, the reception timing of the reflected wave from the object A1 can be detected in the same manner as described above.

  The distance measuring unit 9 obtains the ultrasonic wave propagation time T1 from the transmission timing given from the control unit 3 and the wave receiving timing given from the signal processing unit 8, and the distance to the object A1 based on the propagation time T1. Is calculated. This calculation result is given to a device such as a buzzer. When given to the buzzer, it is conceivable that an alarm sound is generated when the distance to the object A1 becomes a predetermined threshold value or less. A configuration in which the calculation result is displayed on the display and the driver is notified of the distance to the object A1 is also conceivable.

  Hereinafter, the operation of the present embodiment will be described with reference to FIG. In the following description, it is assumed that the first frequency f1 is 62 kHz, the second frequency f2 is 57 kHz, and the resonance frequency fr of the ultrasonic transducer 1 is 72 kHz.

  First, the control unit 3 switches to a path for supplying the oscillation signal having the first frequency f <b> 1 output from the first oscillator 4 to the drive unit 2. The drive unit 2 amplifies the oscillation signal and applies a pulsed drive voltage having the first frequency f <b> 1 to the ultrasonic transducer 1. Accordingly, the ultrasonic transducer 1 transmits the ultrasonic wave having the first frequency f1 toward the external space for a certain period.

  After the elapse of a certain period, the control unit 3 switches to a path for supplying an oscillation signal having the second frequency f2 output from the second oscillator 5 to the drive unit 2. The drive unit 2 amplifies the oscillation signal and applies a pulsed drive voltage having the second frequency f2 to the ultrasonic transducer 1. As a result, the ultrasonic transducer 1 stops driving at the first frequency f1, and transmits the ultrasonic wave of the second frequency f2 toward the external space for a certain period.

  Here, since the ultrasonic transducer 1 has a high Q value, even if the driving at the first frequency f1 is stopped, the vibration cannot be stopped immediately, and the vibration is gradually attenuated. This is the reverberation vibration of the ultrasonic vibrator 1, and the frequency at the time of the reverberation vibration is the natural frequency of the ultrasonic vibrator 1, that is, the resonance frequency fr.

  When the object A1 exists in the external space, the ultrasonic wave having the first frequency f1 transmitted from the ultrasonic vibration 1 is reflected by the object A1, and the reflected wave is received by the ultrasonic vibrator 1. At this time, since the ultrasonic transducer 1 is driven at the second frequency f2, the ultrasonic transducer 1 is distorted by the reflected wave at the first frequency f1 and the transmitted wave at the second frequency f2. The beat signal generated by this beat is expressed by the following equation.

  Next, the beat signal represented by the above equation received by the ultrasonic transducer 1 is detected by the envelope detector 7. Here, the envelope detection unit 7 performs envelope detection and ignores the high frequency component, thereby obtaining an output signal represented by the following equation.

  Therefore, the envelope detector 7 can detect a beat signal having a frequency | f1-f2 | (= 5 kHz). The output signal of the envelope detector 7 is input to the signal processor 8. Then, the signal processing unit 8 detects the presence of the object A1 in the external space by processing the output signal as described above, and determines the reception timing of the reflected wave from the object A1 by the distance measurement unit 9. To give. The distance measuring unit 9 obtains the ultrasonic wave propagation time T1 from the transmission timing given from the control unit 3 and the wave receiving timing given from the signal processing unit 8, and the distance to the object A1 based on the propagation time T1. Is calculated.

  Note that during the period in which the ultrasonic transducer 1 is driven at the second frequency f2, a beat signal is generated by the reverberation vibration of the ultrasonic transducer 1 and the transmitted wave of the second frequency f2. This envelope signal becomes a frequency component of frequency | fr−f2 | (= 15 kHz) when envelope detection is performed in the envelope detection unit 7 as described above. Therefore, by providing the envelope detector 7 with a low-pass filter having a cutoff frequency of 5 to 15 kHz, the beat signal can be cut off, so that only the beat signal having the frequency | f1-f2 | can be detected.

  Further, by driving the ultrasonic transducer 1 at the second frequency f2, ultrasonic waves having the second frequency f2 are transmitted from the ultrasonic transducer 1 to the external space. This transmission wave is reflected by the object A1 and received by the ultrasonic vibrator 1 as a reflected wave of the second frequency f2, but since the ultrasonic vibrator 1 is driven at the second frequency f2, the beat signal Does not occur and is not detected by the envelope detection unit 7. Furthermore, since the reflected wave of the second frequency f2 is received after the reflected wave of the first frequency f1 is received by the ultrasonic transducer 1, the object A1 is detected and the distance to the object A1 is calculated. Does not affect.

  As described above, in this embodiment, after transmitting the ultrasonic wave of the first frequency f1, the ultrasonic transducer 1 is driven at the second frequency f2, and the reflected wave of the first frequency f1 and the second frequency f1 A reflected wave from the object A1 is detected by detecting a beat signal generated by the transmission wave having the frequency f2. Accordingly, since the reflected wave from the object A1 can be detected regardless of the presence or absence of the reverberation vibration of the ultrasonic vibrator 1, even when the reverberation vibration of the ultrasonic vibrator 1 is small, the reflection buried in the reverberation vibration. A wave can be detected and an object A1 existing at a short distance can be detected.

  In the present embodiment, the second frequency f2 is set to a frequency different from the first frequency f1 and the resonance frequency fr of the ultrasonic transducer 1, but the second frequency f2 of the ultrasonic transducer 1 is set. The frequency may be set to the same frequency as the resonance frequency fr or a frequency close thereto. In this case, the beat signal due to the reverberation vibration of the ultrasonic vibrator 1 and the transmission wave of the second frequency f2 is unlikely to occur during the period in which the ultrasonic vibrator 1 is driven at the second frequency f2. It becomes easy to detect a beat signal due to the reflected wave having the frequency f1 and the transmitted wave having the second frequency f2.

  However, in practice, after the ultrasonic transducer 1 is driven at the first frequency f1, the frequency of the reverberation vibration of the ultrasonic transducer 1 changes transiently from the first frequency f1 to the resonance frequency fr. The reverberation vibration includes frequency components other than the resonance frequency fr. Accordingly, since the reverberation vibration of the ultrasonic vibrator 1 includes a small amount of the frequency component of the first frequency f1, a beat signal is generated by the reverberation vibration of the ultrasonic vibrator 1 and the transmission wave of the second frequency f2. obtain. Of course, since the beat signal is small, it does not affect the detection of the beat signal by the reflected wave of the first frequency f1 and the transmission wave of the second frequency f2.

  By the way, in the drive unit 2, the primary-side impedance of the transformer 20 viewed from the ultrasonic transducer 1 is small when transmitting ultrasonic waves from the ultrasonic transducer 1 as described above, and is reflected from the object A1. It only needs to be large when receiving waves. Accordingly, as shown in FIG. 2B, the high impedance driving unit 21 that is driven when transmitting the ultrasonic wave of the second frequency f2 and the driving when transmitting the ultrasonic wave of the first frequency f1 are driven. The low impedance drive part 22 to be connected may be connected to the primary winding 20B.

  For example, as shown in FIG. 2C, the high impedance drive unit 21 includes a series circuit of a constant voltage source VR1, a switching element Q2 composed of a PNP transistor, and a resistor R2 at one end of the primary winding 20A. Connected and configured. For example, as shown in FIG. 2C, the low impedance drive unit 22 is configured by connecting a series circuit of a constant voltage source VR1 and a switching element Q3 made of a PNP transistor to one end of the primary winding 20A. Is done.

  Therefore, when transmitting the ultrasonic wave of the first frequency f1, the control unit 3 gives a control signal to the switching element Q3 to switch it on. In this case, since the resistor R2 is not connected in series with the primary winding 20A, the impedance on the primary side of the transformer 20 viewed from the ultrasonic transducer 1 can be reduced. Moreover, when transmitting the ultrasonic wave of the 2nd frequency f2, the control part 3 gives a control signal to the switching element Q2, and switches it on. In this case, since the resistor R2 is connected in series to the primary side winding 20A, the impedance on the primary side of the transformer 20 as viewed from the ultrasonic transducer 1 can be increased.

  By the way, this embodiment is configured in consideration of the case where the reflected wave is buried in the reverberation vibration of the ultrasonic vibrator 1, that is, the case where the distance to the object A1 is short. On the other hand, when the reflected wave is not buried in the reverberation vibration of the ultrasonic transducer 1, that is, when the distance to the object A1 is long, the frequency of the ultrasonic wave transmitted from the ultrasonic transducer 1 is the highest sensitivity of the transmitted and received waves. It is preferable that the resonance frequency fr of the ultrasonic transducer 1 is high or a frequency close thereto.

  Therefore, the control unit 3 may be controlled to switch between a short distance mode for detecting the object A1 existing at a short distance and a long distance mode for detecting the object A1 existing at a long distance. For example, as shown in FIG. 3, a configuration in which a switch SW2 is provided in parallel with the envelope detector 7 and a mode switching signal is given to the switch SW2 and the controller 3 from an external control device (not shown) is conceivable. . Hereinafter, the operation in the configuration will be described.

  When the mode switching signal instructs switching to the short distance mode, the switch SW2 is turned off by the mode switching signal. In the control unit 3, the ultrasonic transducer 1 is driven at the second frequency f2 after the ultrasonic transducer 1 is driven at the first frequency f1 as in the above embodiment. Therefore, in the short distance mode, as in the above embodiment, even when the reverberation vibration of the ultrasonic vibrator 1 is small, the reflected wave buried in the reverberation vibration is detected, and the object A1 existing at a short distance is detected. can do.

  On the other hand, when the mode switching signal instructs switching to the long distance mode, the switch SW2 is turned on by the mode switching signal. Thereby, the output signal of the amplifying unit 6 is given to the signal processing unit 8 without going through the envelope detection unit 7. Then, the controller 3 stops driving the ultrasonic transducer 1 after driving the ultrasonic transducer 1 at the second frequency f2. Therefore, in the long distance mode, ultrasonic waves are simply transmitted / received at the second frequency f2 and envelope detection is not performed, so there is no need to detect a beat signal. Therefore, by setting the second frequency f2 to the resonance frequency fr of the ultrasonic transducer 1 or a frequency close thereto, the sensitivity of the transmission / reception wave of the ultrasonic transducer 1 can be maximized, and the object A1 The measurement distance can be extended.

  In the above configuration, the mode switching signal is given from the external control device, but the mode switching signal may be given by the control unit 3 itself and the mode switching signal may be given from the control unit 3 to the switch SW2. In this configuration, for example, the control unit 3 first detects the object A1 and measures the distance to the object A1 in the long-distance mode, and when the distance to the object A1 obtained by the distance measuring unit 9 falls below a predetermined threshold, the short distance Control to switch to the mode is possible.

  When the object A1 is detected in the short distance mode, the frequency of the ultrasonic wave transmitted from the ultrasonic transducer 1 is the first frequency f1 and not the resonance frequency fr. For this reason, the output of the ultrasonic wave transmitted in the short distance mode is smaller than that in the case of transmitting at the resonance frequency fr. In the short distance mode, the object is to detect the object A1 existing at a short distance. Therefore, the output of the ultrasonic wave transmitted from the ultrasonic transducer 1 does not need to be increased so much, but the object A1 is detected more reliably. In order to achieve this, it is desirable that the output of the ultrasonic wave to be transmitted is large.

  Therefore, in order to increase the output of the ultrasonic wave transmitted in the short distance mode, for example, by increasing the amplification factor of the drive unit 2, the ultrasonic transducer 1 is driven with a higher drive voltage than in the long distance mode. You may comprise. For example, as shown by a broken line in FIG. 3, a configuration is conceivable in which a mode switching signal is given to the drive unit 2 to increase the amplification factor of the drive unit 2 when switched to the short distance mode. Since the configuration for changing the amplification factor of the drive unit 2 is well known in the art, a detailed description thereof is omitted here.

  In the present embodiment, a description has been given of a case in which the transmission / reception unit is configured by one ultrasonic transducer 1 that transmits and receives ultrasonic waves. However, the transmission / reception unit includes two or more ultrasonic transducers 1. You may comprise. For example, at least one or more transmitters that transmit ultrasonic waves and at least one receiver that receives ultrasonic waves are provided, and the transmitter is driven by the drive unit 2 and the control unit 3. May be. Even with this configuration, the same effects as in the present embodiment can be achieved.

1 Ultrasonic transducer (transmission / reception unit)
2 Drive unit (drive control unit)
3 Control unit (drive control unit)
7 Envelope detector 8 Signal processor A1 Object

Claims (7)

  A transmission / reception unit having one or more ultrasonic transducers for transmitting and receiving ultrasonic waves, and a first frequency different from the first frequency after driving the transmission / reception unit at a first frequency; A drive control unit that drives the transmission / reception unit at a frequency of 2, an envelope detection unit that detects a beat signal based on a difference between the first frequency and the second frequency, and an output of the envelope detection unit And a signal processing unit for detecting the object based on the object detection device.   The object detection apparatus according to claim 1, wherein the transmission / reception unit includes one ultrasonic transducer, and transmits and receives ultrasonic waves using the ultrasonic transducer.   The wave transmitting / receiving unit includes at least two ultrasonic transducers, at least one of the ultrasonic transducers is a transmitter that transmits ultrasonic waves, and at least one of the ultrasonic transducers is an ultrasonic wave. The object detection apparatus according to claim 1, wherein the drive control unit drives the wave transmitter.   The first frequency is a frequency different from a resonance frequency of the transmission / reception unit, and the second frequency is the same as or close to the resonance frequency of the transmission / reception unit. The object detection apparatus of any one of Claim 1 thru | or 3.   The drive control unit includes a transformer that boosts a drive voltage applied to the transmission / reception unit, and a resistor connected in series to a primary side winding of the transformer, and the transmission / reception unit at the first frequency The resistor is not used when driving the transformer, and the resistor is connected to a primary side winding of the transformer when driving the transmitting / receiving unit at the second frequency. The object detection device according to any one of 1 to 4.   The drive control unit has a short distance mode for detecting the object existing at a short distance and a long distance mode for detecting the object existing at a long distance. In the short distance mode, the transmission / reception unit is Driving the transmitting / receiving unit at the second frequency after driving at the first frequency, and driving the transmitting / receiving unit after driving the transmitting / receiving unit at the second frequency in the long distance mode. The object detection device according to claim 1, wherein the object detection device is stopped.   The object detection apparatus according to claim 6, wherein the drive control unit drives the transmission / reception unit with a higher driving voltage in the short-distance mode than in the long-distance mode.

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