JPH01100489A - Ultrasonic range finder - Google Patents

Abstract

PURPOSE:To enable stable and accurate measurement of a distance regardless of changes in the level of a received wave, by controlling a gain of an amplifying means by a reference signal with the size thereof proportional to amplitude of the received signal. CONSTITUTION:An ultrasonic wave signal is transmitted to an object to be measured from an ultrasonic wave transmitter 4. The reflected ultrasonic wave signal from the object being measured is received with ultrasonic wave receivers 5 and 6. The ultrasonic wave receiver 6 receives the ultrasonic wave signal earlier by a specified time than the ultrasonic wave receiver 5. An output of the ultrasonic wave receiver 6 is applied to a variable gain amplification circuit 7 as control signal through a receiving amplification circuit 8 and a peak holding circuit 9. An output of the ultrasonic wave receiver 5 is applied to voltage comparators 10 and 11 through the variable gain amplification circuit 7. Outputs of the voltage comparators 10 and 11 trigger monostable multivibrators 12 and 13 to reset a flip-flop 15 by the outputs thereof through an AND gate 14. Counts of a counter 17 present a distance.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an ultrasonic distance measuring device that uses ultrasonic waves to measure the distance to an object to be measured.

[Conventional technology] Conventionally, the distance to the object to be measured has been measured by measuring the time from when ultrasonic waves are transmitted toward the object to be measured until the ultrasonic waves are reflected by the object and returned. Ultrasonic distance measuring devices are known. In such an ultrasonic distance measuring device, an ultrasonic receiver converts ultrasonic waves transmitted from an ultrasonic transmitter and reflected from an object to be measured into a voltage signal, and this voltage signal is converted to a predetermined voltage signal by an amplifier. After the amplification to the level of The zero-crossing point immediately after crossing (the voltage signal is O
It was assumed that the ultrasonic wave had arrived at the point at which the ultrasonic wave reached V.

However, ultrasonic waves propagating in a medium are composed of components of the medium.
The amount of attenuation varies depending on the temperature of the medium, impurities in the medium, etc., and reflection, refraction, etc. occur on the propagation path due to temperature distribution and other non-uniformity of the medium, so it is difficult to receive it with an ultrasonic receiver. The level of the transmitted ultrasound waves varies significantly. In particular, when the medium is gas, it is more affected than when it is a liquid.

FIG. 4 is a diagram illustrating a situation in which the ultrasonic level changes. In Fig. 4, A is an ultrasonic signal transmitted from an ultrasonic transmitter (hereinafter referred to as a transmitted wave), B is an ultrasonic signal received by an ultrasonic receiver (hereinafter referred to as a received wave), and C is an ultrasonic signal received by an ultrasonic receiver (hereinafter referred to as a received wave). This is a zero-cross pulse that is output when the received wave crosses the first zero-cross point after crossing the trigger level Vth. Note that the received wave B is shown with the time axis expanded. Fourth
As shown in the figure, the zero cross pulse corresponding to the received wave B1 is C, but the zero cross pulse corresponding to the received wave B2 is C2, and the propagation time is from t2 to t3.
It is measured as if it fluctuated.

[Problem that the invention seeks to solve]

By the way, in order to capture the received wave stably, a conventional method has been used in which AGC (automatic gain control) is applied to the received wave amplification circuit to keep the level of the received wave constant and then compared with the trigger level.

However, the AGC applied to the amplification circuit of the received wave (or the voltage signal corresponding to the received wave) is determined by the level of the received wave before the AGC is applied. Therefore, even if AGC is applied to the received wave amplification circuit, it does not predict the level of the received wave that will be received in the future, so it is effective when the fluctuation of the received wave level is slow, but it is effective when the fluctuation of the received wave level is slow. In the case of severe fluctuations (fast fluctuations in the received wave level), not only would there be no effect, but there was a risk that it would even have the opposite effect. (Since there is at least the time interval between transmitting the transmitting waves toward the object to be measured, the level of the received waves may fluctuate during this time.) Therefore, fluctuations in the temperature of the ultrasonic propagation medium, etc. If this occurs, the received wave level will fluctuate, resulting in large errors in measurement values.

The present invention has been made to solve such problems, and an object of the present invention is to provide an ultrasonic distance nj determination device that can measure distance stably and with high measurement accuracy even when the received wave level fluctuates. It is something.

[Means for solving the problem] The ultrasonic path fi#J determination device according to the present invention detects the first received wave for measuring the distance to the object by a predetermined time, a reference signal output means for outputting a reference signal having a magnitude proportional to the amplitude of a second received wave having substantially the same waveform as the first received wave; and an amplifier whose gain is controlled by the reference signal to amplify the first received wave. and a comparing means for outputting a received signal when the first received wave amplified by the amplifying means becomes larger than a preset second reference signal.

[Function] In the present invention, the reference signal output means outputs a reference signal having a magnitude proportional to the amplitude of the second received wave, and the amplification means is gain-controlled by the first reference signal, so that the first received wave and the comparison means outputs a transfer signal when the first received wave becomes larger than the second reference signal.

[Embodiment] FIG. 1 is a circuit block diagram of an ultrasonic distance measuring device according to an embodiment of the present invention. In FIG. 1, 1 is a clock pulse generation circuit that outputs a clock pulse CP of a predetermined frequency, and 2 is a clock pulse generation circuit that appropriately divides the clock pulse CP of the clock pulse generation circuit 1 to generate a timing pulse T necessary for the operation of this device. A timing circuit 3 outputs a transmission signal B according to a transmission command signal A output from the timing circuit 2. A transmission circuit 4 converts the transmission signal B into an ultrasonic signal and measures the converted ultrasonic signal. The ultrasonic transmitters 5 and 6 that transmit waves toward the object are ultrasonic receivers that receive ultrasonic signals reflected by the object to be measured and convert them into electrical signals. The ultrasonic transmitter 4 and the ultrasonic receiver 5 are arranged close to the object to be measured at an equal distance h1, and the ultrasonic receiver 6 is arranged close to the object to be measured at an equal distance h1. It is placed in close proximity at a distance h2 from .

Further, 7 is a variable gain amplifier circuit that outputs a voltage signal C corresponding to the received wave received by the ultrasonic receiver 5, and 8 is a voltage signal C corresponding to the received wave received by the ultrasonic receiver 6. 9 is a peak hold circuit that detects and holds the maximum value D of the voltage signal; 10 is a peak hold circuit that outputs the voltage signal C with reference voltage V;
11 compares the voltage signal C with the reference voltage VR which is normally set to Ov, and outputs a comparison signal of high level "1" when the voltage signal C is larger than the reference voltage V. , a voltage comparator that outputs a comparison signal of high level "1" when the voltage signal C crosses the reference voltage VR, and 12 outputs a comparison signal of high level "1" when the voltage signal C crosses the reference voltage VR; 13 is a monostable multi-by-break that outputs a pulse signal F with a width corresponding to approximately one cycle of the voltage, and 13 is a high level "1" from the voltage comparator 11.
14 is a monostable multivibrator that outputs a zero-cross pulse of a predetermined pulse width when a comparison signal of
15 is an AND gate that outputs a zero-cross pulse G when both outputs of 3 are "1", and a transmission command signal A is input to the set terminal S and a zero-cross pulse G is input to the reset terminal R of the AND gate 15, and a high level "1" or a flip-flop that outputs a signal H at a low level rOJ; 1B is an AND gate that outputs a clock pulse CP when the output signal H of the flip-flop 15 is between a high level "1";
A counter 17 counts the number of clock pulses CP corresponding to the time when the output signal H of the flip-flop 15 is at a high level "1".

The operation of the ultrasonic distance measuring device configured as described above is explained in the second section.
This will be explained based on the timing chart shown in the figure. Second
In the figure, waveforms indicated by symbols A to H indicate output waveforms in the main parts of the circuit diagram shown in FIG.

When the transmitting circuit 3 receives the transmitting command signal A from the timing circuit 2 (see FIG. 2(a)), it outputs the transmitting signal B (see FIG. 2(b)). Furthermore, the peak hold circuit 9 is reset by the output of the transmission command signal A. Furthermore, since the flip-flop 15 is set by the output of the transmission command signal A and outputs a signal H of high level "1", the counter 17 counts the number of clock pulses CP output by the clock pulse generation circuit 1. start.

When the ultrasonic wave transmitter 4 receives the transmission signal B, it converts the transmission signal B into an ultrasonic signal and transmits it as a transmission wave toward the a-1 constant target object. The ultrasonic receivers 5 and 6 each receive an ultrasonic signal reflected by the object to be measured and convert it into a voltage signal. The reception amplification circuit 8 amplifies the voltage signal output from the ultrasonic receiver 6 and outputs a voltage signal corresponding to the received wave to the peak hold circuit 9 (see FIG. 2).
d)).

The peak hold circuit 9 holds the peak value of the voltage signal. (See Figure 2(e)).

On the other hand, the variable gain amplification circuit 7 amplifies the voltage signal output from the ultrasonic receiver 5 and outputs a voltage signal C having a magnitude corresponding to the received wave to the voltage comparators 10 and 11 (Fig. 2(c) )
, (d)). This variable gain amplifier circuit 7 is provided with feedforward AGC so that the amplification gain decreases in inverse proportion to the increase in the voltage signal E.

The voltage comparator 10 compares the voltage signal corresponding to the ultrasonic signal reaching the ultrasonic receiver 6 for a predetermined time (h2/sonic speed C).
A voltage signal V with the voltage signal C corresponding to the ultrasonic signal that has arrived at the ultrasonic receiver 5 with a delay of
, and when ef voltage signal C becomes larger than voltage i signal V, re
f' Outputs a high level "1" comparison signal. When the voltage comparator 10 outputs a comparison signal of high level "1", the monostable multi-by-break 12 outputs a pulse signal F with a width corresponding to approximately one period of the voltage signal (see Fig. 2 (f)
')reference).

By the way, the voltage signal C output by the reception amplifier circuit 8 is always shorter than the voltage signal C output by the reception amplifier circuit 7 (h2/
It will arrive at the speed of sound C) faster.

Furthermore, since the ultrasonic transmitter 4 and the ultrasonic receivers 5 and 6 are installed close to each other, it can be assumed that the propagation paths of the ultrasonic waves to the ultrasonic receivers 5 and 6 are almost the same. Therefore, the received signals C and D fluctuate in almost the same way due to temperature irregularities in the medium and other disturbances.

Furthermore, since the amplification gain of the variable gain amplifier circuit 7 is subjected to feedforward AGC in which the amplification gain decreases in inverse proportion to the increase in the voltage signal E, it is possible to output a constant voltage signal C. Become.

Therefore, no matter how the ultrasonic signal received by the ultrasonic receiver 5 fluctuates, the voltage comparator 10 will go high at the point ref' when the voltage signal C of a constant magnitude exceeds the reference voltage V. A comparison signal of level "1" is output. In other words, the voltage comparator 10 gradually increases the voltage signal C from 0, and for example, at the third peak of the voltage signal C, the reference voltage V is reached.
If it exceeds ef, a comparison signal of high level ef "1" will be output.

On the other hand, the voltage comparator 11 indicates that the received wave corresponding to the voltage signal C has been received at the time when the voltage signal C crosses the reference voltage ■R (in this embodiment, the time when the voltage signal C crosses from a positive value to a negative value). A comparison signal of high level "1" is output. When the voltage comparator 11 outputs the high level rlJ comparison signal, the monostable multivibrator 13 outputs a zero-cross pulse with a pulse width equivalent to approximately 1/2 cycle or less of the voltage signal C (see Fig. 2 (g)). )reference).

The AND gate 14 takes the AND of the outputs of the monostable multivibrators 12 and 13, and generates a zero-cross pulse G corresponding to the zero-cross point immediately after a specific peak of the voltage signal C (for example, the third peak of the voltage signal C). Output.

The flip-flop 15 set by the output of the transmission command signal A is reset by the zero-cross pulse G of the AND gate 14. Note that the voltage comparator 11 outputs a pulse signal every time the voltage signal C crosses the zero-crossing point, but as long as the voltage signal C does not exceed the voltage signal V, the voltage comparator 10 outputs a pulse signal when the voltage signal C crosses the zero cross point. Since no comparison signal is output, the flip-flop 15 is not reset.

The counter 7 stops counting the number of clock pulses CP by resetting the flip-flop 15. Therefore, the counter 17 counts the number of clock pulses CP for the sum of the time opening t1 corresponding to the propagation time of the ultrasonic wave and the trigger delay time t2 (the second
(See figure (h)). Since the trigger delay time 12 can be kept constant, if the sound speed C is known, the distance to the object to be measured can be calculated from the count value of the counter 17.

In this embodiment, the peak hold circuit 9 peak-holds the voltage signal output from the reception amplifier circuit 8 as it is, that is, at the carrier stage; however, the voltage signal output from the reception amplifier circuit 8 is detected. A similar effect can be obtained by inputting the signal to the peak hold circuit 9 later. - Next, FIG. 3 shows an ultrasonic distance n1 according to an embodiment of the present invention.
FIG. 3 is a circuit block diagram of another embodiment of the device. Note that in FIG. 3, parts that perform the same functions as those in FIG. 1 are designated by the same reference numerals, and a description thereof will be omitted. In the above embodiment, two ultrasonic receivers were provided, and the amplification gain of the voltage signal corresponding to the received wave received later was controlled based on the received wave received first, but in this example Only one ultrasonic receiver 5 is provided, a peak hold circuit 9 holds a voltage signal corresponding to the received wave, and a delay circuit 18 obtains a voltage signal C delayed by a predetermined time. The other operations of this embodiment are exactly the same as the embodiment shown in FIG. 1, and a count value corresponding to the distance to the object to be measured can be obtained. In this example, a delay element that operates stably is used, the delay time t is set to a known value, the delay time t is kept constant as described above, and the propagation time t1 is calculated.
do.

Note that although an analog delay element is normally used as the delay circuit 18, a sampling type delay element such as a COD may also be used depending on the measurement conditions. For example, if you want to reduce the measurement error to 1!111 or less when measuring in the air, it is sufficient to operate the sampling clock at 1.7 MHz or higher.

In this way, this embodiment uses the ultrasonic receiver 5 as a received signal.
Because only the output of It has the effect of being reduced.

[Effects of the Invention] As explained above, the present invention allows the reference signal output means to output a reference signal having a magnitude proportional to the amplitude of the second received wave, and the amplification means whose gain is controlled by the reference signal to output the first reference signal.
After amplifying the received wave of the first received wave and keeping the relative relationship between the first received wave and the reference signal constant, the comparing means
Since the received signal is output when the received wave becomes larger than the preset second reference signal, it is possible to stably and accurately measure the distance to the object without being affected by fluctuations in the received wave level. It is possible to obtain an ultrasonic distance measuring device that can measure .

[Brief explanation of the drawing]

FIG. 1 is a circuit block diagram of an ultrasonic distance measuring device according to the present invention, FIG. 2 is a waveform diagram showing waveforms of each part of the above block diagram, and FIG. 3 is an ultrasonic distance measuring device according to another embodiment of the present invention. FIG. 4, a circuit diagram of the measuring device, is an explanatory diagram of a situation in which the level of ultrasonic waves fluctuates. 1... Clock pulse generation circuit, 2... Timing circuit, 3... Transmission circuit, 4... Ultrasonic transmitter, 5.
6... Ultrasonic receiver, 7... Variable gain amplifier circuit, 8
...Reception amplifier circuit, 9...Peak hold circuit, 1
0.11... Voltage comparator, 12. ia... Monostable multivibrator, 14.16... AND gate, 15... Flip-flop, 17... Counter, 18... Delay circuit.

Claims (5)

[Claims] (1) Calculate the distance to the object to be measured based on the propagation time of the ultrasonic wave from when the transmitting wave is sent toward the object to when the received wave reflected by the object is received. In the ultrasonic distance measuring device to be measured, a second reception wave having substantially the same waveform as the first reception wave is received a predetermined time earlier than the detection of the first reception wave for measuring the distance to the object to be measured. a reference signal output means for outputting a first reference signal having a magnitude corresponding to the amplitude of the wave; an amplification means whose gain is controlled by the first reference signal and amplifies the first received wave; and the amplification means. 1. An ultrasonic distance measuring device comprising: comparison means for outputting a received signal when the first received wave amplified by the second reference signal becomes larger than a preset second reference signal. (2) The reference signal output means is located at a position close to a first ultrasonic receiver that receives the first received wave and closer to the object to be measured than the first ultrasonic receiver. established in
Claim 1, comprising: a second ultrasonic receiver that receives the second received wave; and a peak hold circuit that detects and holds the maximum value of the second received wave. The ultrasonic distance measuring device described. (3) The reference signal output means includes a delay circuit that delays the first received wave for a predetermined time, detects and holds a maximum value of the first received wave, and detects and holds the maximum value of the first received wave. The ultrasonic distance measuring device according to claim 1, comprising a peak hold circuit that outputs a peak hold circuit. (4) The ultrasonic distance measurement according to claim 1, 2 or 3, wherein the amplification means performs gain control to change the amplification gain so as to be inversely proportional to the reference signal. Device. (5) The comparison means outputs the received signal when the first received wave crosses a zero cross point after the first received wave becomes larger than the reference signal. The ultrasonic distance measuring device according to any one of Items 1, 2, 3, and 4.