JP4151154B2 - Ultrasonic sensor transmission circuit - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a transmission circuit of an ultrasonic sensor.
[0002]
[Prior art]
Conventionally, an ultrasonic wave is transmitted from an ultrasonic transducer, a reflected wave from an object is received by the ultrasonic transducer, and based on the time difference between the transmitted ultrasonic wave and the received reflected wave. Ultrasonic sensors that detect the distance from an ultrasonic transducer to an object are known.
[0003]
Some ultrasonic sensors of this type have a configuration as shown in FIG. 6, for example. This ultrasonic sensor is received by an ultrasonic transducer 1 that transmits and receives ultrasonic waves, a transmission circuit 2 ′ that transmits ultrasonic waves by driving the ultrasonic transducer 1, and the ultrasonic transducer 1. And a receiving circuit 3 for generating a received signal (described later) based on the ultrasonic wave.
[0004]
The transmission circuit 2 'intermittently outputs a pulsed high-frequency signal (hereinafter referred to as a high-frequency pulse signal) having a predetermined time width at a predetermined frequency (usually about 40 KHz), so that an ultrasonic wave is output from the ultrasonic transducer 1. Send a pulse wave. That is, a synchronization pulse for setting the timing for outputting the high frequency pulse signal is generated by the periodic oscillation circuit 2a, and is intermittently output at the timing of the synchronization pulse by the transmission gate circuit 2b for setting the time width of the high frequency pulse signal. The high-frequency pulse signal is generated, and the high-frequency pulse signal is amplified by the amplification circuit 2c to a level at which the ultrasonic transducer 1 can be driven, whereby the ultrasonic transducer 1 is driven.
[0005]
The ultrasonic transducer 1 transmits an ultrasonic pulse wave by oscillating based on the above-described high-frequency pulse signal, receives an ultrasonic wave including a reflected wave from an object, and transmits the received ultrasonic wave. A signal obtained by converting the sound pressure change into the voltage change is output to the wave receiving circuit 3.
[0006]
In the wave receiving circuit 3, the signal output from the ultrasonic transducer 1 is amplified by the amplifier 3a and then input to the detection circuit 3b. In order to obtain a voltage signal proportional to the sound pressure level of the ultrasonic wave received by the ultrasonic transducer 1, the detection circuit 3b extracts an envelope of the output voltage of the amplifier 3a, and this voltage is supplied to the waveform shaping circuit 3c. Output. The waveform shaping circuit 3c compares a preset reference voltage with the output voltage of the detection circuit 3b, and uses as a received signal a binary signal whose H level is a period in which the output voltage of the detection circuit 3b exceeds the reference voltage. Output to the control unit 20.
[0007]
With the above-described configuration, the output signal of the amplifier 3a has a waveform as shown in FIG. 7A, for example, and the drive time T1 during which the ultrasonic transducer 1 is driven outputs a signal due to the wraparound of the high-frequency pulse signal. . Further, even after an ultrasonic wave is transmitted from the ultrasonic transducer 1, a signal due to reverberation vibration is output for a duration T2. During the time excluding the driving time T1 and the duration T2, the reflected wave from the object can be received, and the reflected waveform B1 is obtained when the reflected wave from the object is received.
[0008]
By detecting the waveform of the output signal from the amplifier 3a and shaping the waveform, as shown in FIG. 7B, the incident signal F based on the drive waveform and the reverberation waveform and the reflected signal B based on the reflected waveform B1 are obtained. The received wave signal is input to the control unit 20.
[0009]
The control unit 20 is configured to include a microcomputer, and controls the entire ultrasonic sensor and determines the distance from the ultrasonic transducer 1 to the object based on the time difference between the synchronization pulse and the reflected signal B described above. The distance is obtained and displayed on the display unit 21.
[0010]
By the way, as the ratio (S / N ratio) between the signal level corresponding to the reflected wave from the object and the noise level caused by other acoustic noise or electrical noise is larger, the detectable spatial region can be set wider. it can. In order to widen the detectable spatial region on the short distance side, it is required to reduce the duration T2 of the reverberation vibration. That is, if the duration T2 of the reverberation vibration becomes longer, it becomes impossible to detect an object located in the immediate vicinity of the ultrasonic transducer 1 due to the influence of the reverberation vibration. Therefore, as shown in FIG. 8A, it is conceivable to connect a coil L1 ′, which is a variable coil, in parallel with the ultrasonic transducer 1. By adjusting the inductance of the coil L1 ′, the resonance frequency of the parallel resonance circuit formed by the interelectrode capacitance of the ultrasonic transducer 1 and the coil L1 ′ can be matched with the frequency of the reverberation vibration. When this condition is set, the reverberation vibration duration T2 can be shortened, and as a result, an object located in the immediate vicinity of the ultrasonic transducer 1 can be detected.
[0011]
[Problems to be solved by the invention]
On the other hand, in order to expand the space area that can be detected on the far side, the ultrasonic sensor described above needs to efficiently transmit and receive ultrasonic waves. In other words, it is conceivable to increase the energy of transmission and increase the sensitivity of reception. However, such a configuration generally results in a significant increase in the number of parts, which causes an increase in size and price.
[0012]
The present invention has been made in view of the above-mentioned reasons, and an object of the present invention is to increase the energy of ultrasonic wave transmission without significantly increasing the number of parts, thereby improving the S / N ratio. It is to provide a sensor transmission circuit.
[0015]
[Means for Solving the Problems]
According to the first aspect of the present invention, an ultrasonic transducer is driven by a high-frequency signal to transmit an ultrasonic wave, a reflected wave from an object is received, and a relationship between the transmitted ultrasonic wave and the received reflected wave is received. Is used in an ultrasonic sensor for detecting the object, a coil connected in parallel with the ultrasonic transducer and provided with an intermediate terminal, and a coil between one end of the coil and the intermediate terminal and a DC power source. And a switching circuit for generating the high-frequency signal by switching, and a core inserted in and out of the winding so as to make the inductance between the intermediate terminal and the one end of the coil variable. Is provided . According to this configuration, since the DC voltage from the DC power source is intermittently applied by the switching circuit and applied to one winding between the one end of the coil and the intermediate terminal, the switching circuit switches to the one winding. Since the amplitude of the voltage applied to both ends of the ultrasonic vibrator can be made larger than the voltage of the DC power supply using the generated electromotive force, the energy of ultrasonic wave transmission from the ultrasonic vibrator is increased. And the S / N ratio can be improved. Further, since the other winding between the other end of the coil and the intermediate terminal is connected in series with the ultrasonic transducer, a series resonance circuit is formed by the inter-electrode capacitance of the ultrasonic transducer and the other winding. By configuring the series resonance circuit to flow a resonance current, the voltage across the ultrasonic transducer can be further increased, and the efficiency of ultrasonic wave transmission from the ultrasonic transducer can be increased. In addition, by using the coil provided with the intermediate terminal, it is not necessary to separately provide the two coils, and the transmission circuit can be reduced in size and cost. Furthermore, the inductance between the one end of the coil and the intermediate terminal can be changed by inserting and removing the core, and the resonance frequency of the parallel resonance circuit constituted by the interelectrode capacitance of the ultrasonic transducer and the coil Since the resonance frequency can be set so as to reduce the amplitude of the reverberation vibration of the ultrasonic vibrator, the duration of the reverberation vibration can be shortened.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0018]
( Reference Example 1 )
As shown in FIG. 1A, the transmission circuit 2 of the present reference example includes a coil L1 connected in parallel with an ultrasonic transducer 1 serving as a transducer circuit, a power supply circuit 10 that is a DC power supply, and a coil L1. And a switching circuit 4 for generating a high-frequency pulse signal by switching the DC power supplied from the power supply circuit 10, and this high-frequency pulse signal is applied to a parallel circuit of the ultrasonic transducer 1 and the coil L1. By applying this, ultrasonic waves are intermittently transmitted from the ultrasonic transducer 1.
[0019]
The switching circuit 4 includes a switching element Q1 made of a transistor and an oscillation circuit 5 that generates a signal for switching the switching element Q1. The configuration of the wave receiving circuit 3 is the same as that of the conventional example.
[0020]
With the configuration described above, the high-frequency pulse signal from the switching circuit 4 is given to the parallel circuit of the ultrasonic transducer 1 and the coil L1. This high-frequency pulse signal is obtained by intermittently supplying a DC voltage from the power supply circuit 10.
[0021]
Thus, when the switching element Q1 is on, the output voltage V of the power supply circuit 10 is applied to both ends of the ultrasonic transducer 1, and the current i flows into the coil L1. Thereafter, when the switching element Q1 is turned off, an electromotive force is generated in a direction in which the current i continues to flow through the coil L1, and thereby a negative voltage −Va having a polarity opposite to the output voltage V is applied to the ultrasonic vibrator 1. Is done. The magnitude of the negative voltage −Va is determined by the current i flowing through the coil L1 and the inductance of the coil L1 when the switching element Q1 is on. As a result, the voltage applied to the ultrasonic transducer 1 has a waveform that oscillates between the output voltage V and the negative voltage −Va as shown in FIG. 1B, and the absolute value is larger than the output voltage V. A voltage will be applied.
[0022]
As described above, in this reference example , since the DC voltage from the power supply circuit 10 is intermittently applied by the switching circuit 4 and applied to the parallel circuit of the ultrasonic transducer 1 and the coil L1, the applied voltage to the ultrasonic transducer 1 is applied. Can be made larger than the output voltage V of the power supply circuit 10, the energy of the ultrasonic wave transmitted from the ultrasonic vibrator 1 can be made larger than that of the conventional configuration, and the ultrasonic vibrator 1. Therefore, the S / N ratio of the ultrasonic sensor can be improved.
[0023]
Further, a variable coil is used as the coil L1, and if the inductance of the coil L1 is adjusted, the resonance frequency of the parallel resonance circuit formed by the interelectrode capacitance of the ultrasonic vibrator 1 and the coil L1 is set to the ultrasonic vibrator. The reverberation vibration duration time T2 shown in FIG. 1B can be minimized.
[0024]
( Reference Example 2 )
In this reference example , as shown in FIG. 2A, the coil L2 is connected in series with the ultrasonic transducer 1, and the coil L1 is connected in parallel with the series circuit of the ultrasonic transducer 1 and the coil L2. Other configurations are the same as those in Reference Example 1 .
[0025]
In this reference example , a series resonance circuit is configured by the interelectrode capacitance of the ultrasonic transducer 1 and the coil L2, and the voltage across the ultrasonic transducer 1 is shown in FIG. Thus, the amplitude can be made larger than that of the waveform of Reference Example 1 shown in FIG. Further, when the resonance frequency of the series resonance circuit and the switching frequency of the switching element Q1 are matched, the amplitude of the voltage across the ultrasonic transducer 1 is maximized.
[0026]
As described above, in this reference example , the voltage across the ultrasonic transducer 1 can be made larger than that in the reference example 1 by connecting the coil L1 in parallel to the series circuit of the ultrasonic transducer 1 and the coil L2. It is possible to increase the efficiency of ultrasonic wave transmission from the ultrasonic transducer 1.
[0027]
( Reference Example 3 )
In the present reference example, as shown in FIG. 3, a coil L3a provided with an intermediate terminal TM is connected in parallel with the ultrasonic transducer 1, and the emitter of the switching element Q1 is connected to the intermediate terminal TM. When one coil between the grounded one end of the coil L3a and the intermediate terminal TM is a coil L1a and the other coil is a coil L2a, a high frequency pulse signal generated by the switching circuit 4 is provided at both ends of the coil L1a. And the coil L2a is connected in series with the ultrasonic transducer 1. Other configurations are the same as those in Reference Example 1 .
[0028]
With this configuration, a coil L1a, so L2a is the same as the connection status between the coils L1, L2 described in the reference example described above, in the same manner as the reference example described above, the voltage applied to the ultrasonic vibrator 1 Can be increased to efficiently transmit ultrasonic waves from the ultrasonic transducer 1 and improve the S / N ratio of the ultrasonic sensor.
[0029]
In addition, by using the coil L3a provided with the intermediate terminal TM, it is not necessary to provide the coils L1a and L2a as separate coils, and the transmission circuit 2 can be reduced in size and cost.
[0030]
( Embodiment 1 )
In the present embodiment, as shown in FIG. 4, a coil L3b provided with an intermediate terminal TM is connected in parallel to the ultrasonic transducer 1 and the emitter of the switching element Q1 is connected to the intermediate terminal TM as in Reference Example 3. It is. However, the ground side coil L1b is a variable coil.
[0031]
As shown in FIG. 5 (a), the coil L3b has a configuration in which a core 6 having a flange 6a at one end is inserted in and out of the coil L3b. Therefore, as shown in FIG. 5B, when the core 6 is pulled up in the direction indicated by the arrow A in the figure, a gap W is generated between the lower end of the core 6 and the lower end of the coil L1b, and the inductance of the coil L1b. Changes. That is, the coil L1b becomes a variable coil (see FIG. 5C) whose inductance changes when the core 6 is inserted and removed. Other configurations are the same as those in Reference Example 1 .
[0032]
In the present embodiment, similarly to the reference example 3 , by using the coil L3b provided with the intermediate terminal TM, the transmission circuit 2 can be reduced in size and cost. Moreover, if the inductance of the coil L1b is adjusted by moving the core 6 in and out, the resonance frequency of the parallel resonance circuit formed by the interelectrode capacitance of the ultrasonic vibrator 1 and the coil L3b is set to the reverberation vibration of the ultrasonic vibrator 1. The frequency of reverberation vibration can be minimized.
[0035]
【The invention's effect】
According to the first aspect of the present invention, an ultrasonic transducer is driven by a high-frequency signal to transmit an ultrasonic wave, a reflected wave from an object is received, and a relationship between the transmitted ultrasonic wave and the received reflected wave is received. Is used in an ultrasonic sensor for detecting the object, a coil connected in parallel with the ultrasonic transducer and provided with an intermediate terminal, and a coil between one end of the coil and the intermediate terminal and a DC power source. And a switching circuit for generating the high-frequency signal by switching, and a core inserted in and out of the winding so as to make the inductance between the intermediate terminal and the one end of the coil variable. are those provided in, because applied to one of the windings between the one end and the middle terminal of the coil by intermittently by the switching circuit a DC voltage from the DC power supply, switch the switching circuit Since the amplitude of the voltage applied to both ends of the ultrasonic transducer can be made larger than the voltage of the DC power source using the electromotive force generated in the one winding by the winding, the ultrasonic wave from the ultrasonic transducer Thus, there is an effect that the energy of transmission can be increased and the S / N ratio can be improved. Further, since the other winding between the other end of the coil and the intermediate terminal is connected in series with the ultrasonic transducer, a series resonance circuit is formed by the inter-electrode capacitance of the ultrasonic transducer and the other winding. By configuring the series resonance circuit to flow a resonance current, the voltage across the ultrasonic transducer can be further increased, and the efficiency of transmitting ultrasonic waves from the ultrasonic transducer can be increased. is there. In addition, by using a coil provided with an intermediate terminal, there is an advantage that it is not necessary to provide two coils separately, and the transmission circuit can be reduced in size and cost.
[0036]
Furthermore, the inductance between the one end of the coil and the intermediate terminal can be changed by inserting and removing the core, and the resonance frequency of the parallel resonance circuit constituted by the interelectrode capacitance of the ultrasonic transducer and the coil Since the resonance frequency can be set so as to reduce the amplitude of the reverberation vibration of the ultrasonic vibrator, the duration of the reverberation vibration can be shortened.
[Brief description of the drawings]
FIG. 1A is a block diagram of Reference Example 1 of the present invention, and FIG. 1B is a waveform diagram of voltages at both ends of an ultrasonic transducer in the same as above.
2A is a block diagram of Reference Example 2 of the present invention, and FIG. 2B is a waveform diagram of voltages at both ends of an ultrasonic transducer in the same as above.
FIG. 3 is a block diagram of Reference Example 3 of the present invention.
FIG. 4 is a block diagram of Embodiment 1 of the present invention.
5A and 5B show coils used in the above, wherein FIG. 5A is a front view when the core is inserted to the end, FIG. 5B is a front view when the core is pulled up, and FIG. 5C is a circuit diagram. is there.
FIG. 6 is a block diagram of a conventional example.
FIG. 7 is an operation waveform diagram of the receiving circuit of the above.
8A is a principal block diagram of the above, and FIG. 8B is an output waveform diagram of the transmission circuit of the same.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Ultrasonic transducer 2 Transmission circuit 4 Switching circuit 6 Core 10 Power supply circuit L1, L1a, L1b Coil L2, L2a, L2b Coil L3a, L3b Coil TM Intermediate terminal

Claims (1)

An ultrasonic transducer is driven by a high-frequency signal to transmit an ultrasonic wave, receive a reflected wave from the object, and detect the object based on the relationship between the transmitted ultrasonic wave and the received reflected wave. A high-frequency signal used for a sound wave sensor, inserted between a coil connected in parallel with the ultrasonic transducer and provided with an intermediate terminal, a winding between one end of the coil and the intermediate terminal, and a DC power supply, and switched by switching. And a switching circuit for generating a coil, wherein the coil is provided with a core inserted in and out of the winding so that an inductance between the intermediate terminal of the coil and the one end is variable. transmitting circuitry for the ultrasonic sensor.

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