JPH056549Y2 - - Google Patents

Description

[Detailed description of the invention] <Industrial application field> This invention emits an ultrasonic pulse to a measurement surface, receives the reflected wave, and measures the distance to the measurement surface from the round trip time of the ultrasonic pulse. The present invention relates to an ultrasonic distance measuring device, and particularly to an ultrasonic distance measuring device with improved transmission and reception efficiency of its transducer.

<Conventional technology> A conventional ultrasonic ranging device emits ultrasonic pulses from a transducer to a measurement surface using a drive voltage from a drive circuit, and receives reflected pulses from the measurement surface via the transducer. A circuit receives the waves and measures the distance to the measurement surface from the round trip time of these pulses.

In this case, an inductance is connected in parallel to the transducer and the output impedance seen from the drive circuit is equivalently used as a resistance component to prevent reactive power from being sent out from the drive circuit to improve efficiency.

<Problems to be solved by the invention> However, in such an ultrasonic distance measuring device, air is the medium, and for example, in the case of 40KHz ultrasonic waves, the size of the ultrasonic pulse is inversely proportional to the 1.6 to 2 power of the measured distance. The magnitude of the reflected pulse also varies greatly depending on the state of the reflecting surface. For example, when bubbles occur on the water surface, the reflectance drops to about 1/10, so the wave height of the transmitted ultrasonic pulse is increased to ensure the reception voltage.

However, with so-called two-wire level meters, which receive current through two wires and use the power from this current to cover all of the power for the level conversion circuit, the usable power is limited, so the peak value of the ultrasonic pulse is increased. There are limits to what you can do.

<Means for solving the problem> Therefore, it is necessary to improve the efficiency of transmitting the wave from the drive circuit to the transducer.

In order to increase the transmitted ultrasonic pulse without increasing the drive voltage, it is necessary to match the impedance between the drive circuit and the transducer. 7th
The figure shows the circuit configuration.

In the case of FIG. 7A, the drive voltage of the drive circuit 10
V _s is applied to a transducer 11 represented by a parallel circuit of a resistor R ₁ and a capacitor C via a switch SW ₁ and an inductance 12 .

With such a configuration, the capacitor C portion of the transducer 11 is canceled out by the inductance 12, leaving only a pure resistance, and this value is made equal to the output impedance of the drive circuit 10 that supplies the drive voltage V _S to create an impedance matrix. Take Ching. By removing the capacitor C portion of the transducer 11 in this way, reactive power can be removed, so the power burden on the drive circuit can be reduced.

For example, transducer 1 with C=1.1nF and R ₁ =50KΩ
1, the natural vibration frequency is 40KHz, the inductance 12 resonates at L = 14mH, and the equivalent impedance is R ₀ = l/CR ₁
=255Ω, the input impedance of the transducer 11 becomes equivalently small, and power supply to the transducer 11 becomes easy.

On the other hand, in the case of FIG. 7B, the inductance 13 is connected in parallel to the transducer 11, and a driving voltage is supplied thereto via the switch _SW1 .

In this case, if you calculate the equivalent impedance at resonance in the same way as in A, it will be 50KΩ, indicating a high equivalent impedance.

Therefore, it can be seen that when driving the transducer 11 from the drive circuit 10, the circuit configuration shown in FIG. 7A is better.

FIG. 8 shows an equivalent circuit for receiving a reception signal from a transducer.

8A shows an equivalent circuit at the time of reception corresponding to FIG. 7A, and FIG. 8B shows an equivalent circuit at the time of reception corresponding to FIG. 7B.

_The voltage Vr' in FIG _.
It is attenuated to 1/(R ₁ +1/ω ₀ C ₀ ). For example, C ₀
= 1.1nF, R ₁ = 50KΩ, ω = 2πf = 2 x 40KHz, Vr = 0.07Vr', which attenuates to less than 1/10.

On the other hand, if configured as shown in Figure 8B, Vr=
Vr′, which improves reception efficiency.

Taking these points into consideration, the present invention includes a transducer that sends ultrasonic pulses to a measurement surface and receives the reflected pulses reflected from the destination measurement surface, and a drive that supplies a driving voltage to the transducer. circuit, a receiving circuit that is connected in parallel to the previous transducer and receives a received signal corresponding to the reflected pulse of the previous transducer received by this transducer, and between the previous driving circuit and the previous transducer. An inductance connected in series via the first switch, a second switch inserted in parallel to the series circuit of the previous inductance and the previous transducer, and the ultrasonic pulse being transmitted from the previous transducer. The first step is
The device is equipped with a switch driving circuit that turns on a second switch that is turned on, and then turns on a second switch that turns off the first switch when receiving a received signal.

<Example> Hereinafter, an example of the present invention will be described based on the drawings. FIG. 1 is a block diagram showing the principle of the present invention. Note that parts having the same functions as those shown in FIGS. 7 and 8 are given the same symbols, and their explanations will be omitted as appropriate.

The drive voltage V _S of the drive circuit 10 is determined by the switch SW ₁ ,
It is applied to a series circuit composed of an inductance 12 and a transducer 11. Further, an inductance 12 is connected in series between the drive circuit 10 and the transducer 11 via a switch SW ₁ , and a switch SW ₂ is connected in parallel to the series circuit of the inductance 12 and the transducer 11. .

Further, a series circuit including a resistor R ₂ and diodes D ₁ and D ₂ connected in opposite directions is connected to both ends of the transducer 11 . Both ends of the diodes D ₁ and D ₂ are connected to the input end of the receiving circuit 14 . Switch SW ₁ and SW ₂ are each switch drive circuit 1
It is opened and closed by 5.

The operation of the above configuration will be explained using FIG. 2.

When sending out the drive voltage V _S from the drive circuit 10, the switch SW _S is turned on (FIG. 2A) and the switch SW _S is turned OFF (FIG. 2 B) to supply the drive voltage V _S to the transducer 11.

At this time, since the driving voltage V _S is large, these are short-circuited by diodes D ₁ and D ₂ and the receiving circuit 1
The drive voltage V _S is not input to 4.

On the other hand, the transducer 11 transmits an ultrasonic pulse and the reflected pulse reflected from the measurement surface is received by the transducer 11. At this time, the switch SW ₁ is turned off by the switch drive circuit 15 (Fig. 2 A), and the switch
SW ₂ is turned on (Figure 2 B). In this case, since the voltage received by the transducer 11 is a small value, the diodes D ₁ and D ₂ are not short-circuited and the voltage is received by the receiving circuit 14 .

The above points will be explained in comparison with the case of driving with a conventional driving circuit shown in FIG. 7B.

First, when C ₀ = 1.1 nF, L = 14 mH, R ₁ = 50 KΩ, and V _S = 500 V, the power supplied to the transducer 11 in the configuration shown in Fig. 7B is P = 500 ² /
50KΩ=5W, but according to the configuration shown in Figure 1,
Since the impedance is 255Ω, the voltage to obtain power of P = 5W is 5W = V ² /255Ω, or V = 35V.
becomes. That is, with this configuration, the drive voltage V _S
can be reduced to 1/14.

On the other hand, after transmission is complete, switch SW ₁ is off and SW ₂ is off.
turns on, transducer 11 and inductance 1
1 are connected in parallel, resulting in the state shown in FIG. 7B. The voltage generated in the transducer 11 is input to the receiving circuit 14 via a resistor R ₂ and diodes D ₁ and D ₂ .
Since this received voltage is generally lower than the forward voltage of the diode (approximately 0.6 V), the voltage detected by the transducer 11 is supplied to the receiving circuit 14 as is.

FIG. 3 is a block diagram showing another embodiment of the present invention. Both the series circuit of switches SW ₃ and SW ₄ and the series circuit of switches SW ₅ and SW ₆ are connected to the power supply E.
A series circuit of an inductance L and a transducer 11 is connected between a connection point A between switches SW ₃ and SW ₄ and a connection point B between switches SW ₅ and SW ₆ .

A parallel circuit in which diodes D ₁ and D ₂ are connected in parallel with opposite polarities and a series circuit in which a resistor R ₂ is connected in series connects the connection point between the inductance L and the transducer 11 and the switches SW ₄ and SW ₅ . connected between points.

The voltage across the diodes D ₁ and D ₂ is the receiving circuit 1.
4 is entered.

Further, the switches SW ₃ to _{SW 6} are opened and closed by control signals S ₃ to _{S 6} from the switch drive circuit 16.

The operation of the embodiment shown in FIG. 3 constructed as above will be explained using the waveform diagram shown in FIG. 4.

When sending out the driving voltage, switch SW ₃ and SW ₅ , switch SW ₄ and
SW ₆ alternately turns on and off in the same phase. Switches SW ₃ and SW ₅ , Switches SW ₄ and SW ₆ on/off
The off period is equal to or close to the resonant frequency of the transducer 11, and is driven by drive signals S ₃ , S ₅ , S ₄ , and S ₆ from the switch drive circuit 16 .

Therefore, +E and -E voltages are applied alternately between A and B, equivalently creating an alternating current rectangular wave voltage of ±E.
V _AB is generated (FIG. 4(e)), and as a result, a voltage twice the power supply voltage E is applied to the transducer 11.

On the other hand, when receiving reflected pulses, switch
SW ₄ and SW ₅ are turned on, and switches SW ₃ and SW ₆ are turned off. Therefore, the inductance 12 and the transducer 11 are connected in parallel, resulting in the state shown in FIG. 8B, and the receiving efficiency is improved. For this reason, the power source E
does not require high voltage, so switch SW ₃ ~
SW ₆ can be configured with an analog switch, simplifying the drive circuit.

FIG. 5 is a block diagram showing still another embodiment of the present invention in which a transistor is used as the switch element. FIG. 6 is a waveform diagram showing waveforms at various parts of the embodiment shown in FIG.

Monostable multi (one-shot multivibrator) 17 has a start pulse S _T at regular intervals.
(Fig. 6 A) is applied, and in synchronization with the rising edge of the pulse, a constant width pulse is sent from the output terminal Q of the monostable multi 17.
P ₁ (FIG. 6b) is applied to the reset terminal R of the oscillator 18. By applying pulse P ₁ ,
The oscillator 18 starts oscillation after its reset is released, and while the pulse P ₁ is at a high level H, it emits a pulse P ₂ (FIG. 6C) with a duty cycle of 50%. This pulse P ₂ is set equal to the resonant frequency of the transducer 11. Pulse P ₂ is inverted by inverter 19 to produce pulse P ₃ shown in FIG. 6D.

The NAND gate 20 receives the pulse P ₁ and the pulse P ₂ , NANDs them, and outputs the result as a pulse P ₄ (FIG. 6(e)). In addition, the NAND gate 21 receives pulse P ₁ and pulse P ₃ and outputs their NAND
is taken and output as a pulse P ₅ (FIG. 6).
As can be seen from FIG. 6, the pulses P ₄ and P ₅ have opposite phases in the transmission period and have the same phase in the reception period.

Pulse P ₄ drives transistors 22 and 23 corresponding to switches SW ₃ and SW ₄ in FIG.
_P5 drives transistors 34 and 25 corresponding to switches _SW5 and _SW6 in FIG.

Therefore, in the transmission section, the transistor 22
, 25, and transistors 23 and 24 are turned on/off in the same phase. Pulse in reception section
P ₄ and P ₅ are both at high level H and have the same phase, transistors 23 and 25 are turned on and transistors 22 and 24 are turned off, resulting in the same operation as in FIG. 3. In addition, switches SW ₃ to SW ₆ are FET,
A switch element such as a thyristor may also be used. Also,
In Figure 5, the Q output of the monostable multi 17 is the oscillator 1.
8, but the reset terminal R is always in the release state H and the pulse P ₂ is always output.
It may also be configured to transmit.

<Effects of the invention> As described above in detail with the embodiments, according to the invention, the inductances for impedance matching of the transducer can be connected in series and parallel when transmitting/receiving ultrasonic waves. To do this, when sending/
Efficiency during reception can be maximized. Also,
By improving the efficiency of transmission and reception, the voltage on the drive circuit side can be reduced, and as a result, the configuration of the drive circuit can be simplified.

[Brief explanation of drawings]

Figure 1 is a block diagram showing the principle of the present invention, Figure 2
The figure is a waveform diagram showing the waveforms of each part of Fig. 1, Fig. 3 is a block diagram showing another embodiment of the present invention, Fig. 4 is a waveform diagram showing the waveforms of each part of Fig. 3, and Fig. 5 is a waveform diagram showing the waveforms of each part of Fig. 3. A block diagram showing still another embodiment of the present invention in which a transistor is used as a switch element; FIG. 6 is a waveform diagram showing waveforms of various parts of the embodiment shown in FIG. 5;
FIG. 7 is an equivalent circuit diagram explaining problems on the conventional transmitting side, and FIG. 8 is an equivalent circuit diagram explaining problems on the conventional receiving side. 10... Drive circuit, 11... Transmitter/receiver, 14...
...Reception circuit, 15, 16...Switch drive circuit,
17... Monostable multi, 18... Oscillator, 22~
25...transistor.

Claims (1)

[Scope of utility model registration request] a transducer that sends out ultrasonic pulses to a measurement surface and receives reflected pulses reflected from the measurement surface; a drive circuit that supplies a driving voltage to the transducer; and a drive circuit that is connected in parallel to the transducer. a receiving circuit that receives a reception signal corresponding to the reflected pulse received by the transducer; an inductance connected in series between the drive circuit and the transducer via a first switch; A second switch is inserted in parallel in a series circuit of a transducer, and when transmitting an ultrasonic pulse from the transducer, the first switch is turned on and the second switch is turned off to receive the received signal. An ultrasonic ranging device characterized by comprising a switch drive circuit that turns off the first switch and turns on the second switch when necessary.