TWI805001B - Method for calculating time-of-flight - Google Patents

Abstract

A method for calculating time-of-flight includes: emitting an acoustic wave by a transmitting sensor; receiving the acoustic wave and converting the received acoustic wave into a received signal by a receiving sensor; performing fast Fourier transform on the received signal to obtain a main frequency range of the received signal; filtering the received signal to obtain a main signal by a bandpass filter according to the main frequency range; inputting the main signal into a Schmitt-trigger to generate a triggered signal; obtaining a received time point of the acoustic wave according to the triggered signal; and calculating time-of-flight of the acoustic wave according to the received time point and an emitted time point that the transmitting sensor emits the acoustic wave.

Description

Calculation method of flight time

The present invention relates to a calculation method of flight time, and in particular to a calculation method of flight time after sound waves pass through a heat source.

The transmission speed of the sound wave is related to the type of medium, the state of the medium and the influence of the external environment. When the sound wave passes through a heat source, the intensity and waveform of the sound wave signal will change. In other words, when the sound wave signal passes through the heat source, it will cause waveform variation and affect the magnitude of the peak value in the sound wave signal, thus resulting in an error in calculating the time of flight of the sound wave based on the common peak-to-peak value. In addition, as confirmed by measurement and simulation, the above-mentioned variation of the waveform cannot be corrected theoretically.

The object of the present invention is to propose a calculation method of flight time, which includes: transmitting sound waves by the transmitting sensor; receiving the sound waves by the receiving sensor and converting the sound waves into receiving end signals; performing fast Fourier transform on the receiving end signals to obtain the main frequency of the receiving end signals range; the band-pass filter filters the signal at the receiving end according to the main frequency range to obtain the main signal; the main signal Input the Schmitt trigger to generate a trigger signal; obtain the receiving time point of the sound wave according to the trigger signal;

In some embodiments, the time-of-flight of the sound wave is the difference between the receiving time point and the emitting time point, and the sound velocity of the sound wave is the ratio of the distance between the transmitting sensor and the receiving sensor to the time-of-flight.

In some embodiments, the receiving time point of the sound wave is the time point corresponding to the first peak value of the trigger signal.

In some embodiments, the calculation method of the time-of-flight further includes: filtering the main signal by a band-rejection filter according to the main frequency range to obtain a noise signal; multiplying the strength of the noise signal by a proportional constant to obtain a high threshold ; The high threshold is used as the high trigger level of the Schmitt trigger; and the negative value of the high threshold is used as the low trigger level of the Schmitt trigger.

In some embodiments, the strength of the noise signal is the root mean square value of the noise signal.

In some embodiments, the above-mentioned calculation method of the time-of-flight further includes: before obtaining the receiving time point of the sound wave, performing a continuity judgment on the trigger signal.

In some embodiments, the above-mentioned trigger signal is composed of multiple square waves, and the above-mentioned continuity judgment includes: judging whether the width of each square wave is greater than the width threshold; filtered out from the signal.

In some embodiments, the above-mentioned calculation method of the time-of-flight further includes: before obtaining the receiving time point of the sound wave, judging the length of the trigger signal.

In some embodiments, the above-mentioned trigger signal is composed of multiple square waves The above-mentioned length judgment includes: judging whether the total duration of each square wave set is less than a duration threshold; and filtering out the square wave set whose judging result is yes from the trigger signal.

In some embodiments, the continuity determination is performed on the trigger signal before the length determination is performed on the trigger signal.

In order to make the above-mentioned features and advantages of the present invention more comprehensible, the following specific embodiments are described in detail together with the accompanying drawings.

120: launch sensor

140: Receive sensor

160: control unit

aw: sound wave

BPF: Band Pass Filter

BSF: band rejection filter

c1: control signal

c2: Receiver signal

CST: trigger signal

D: distance

d1~d5: wave width

f1: main signal

f2: noise signal

FFT: Fast Fourier Transform

FR: main frequency range

HL: high trigger level

LL: Low trigger level

RMS: root mean square value

S1~S7: steps

SCM: Schmitt Trigger

ST: trigger signal

T2: Receiving time point

w1~w5: square wave

x1~x3: square wave set

A better understanding of aspects of the present invention can be obtained from the following detailed description in conjunction with the accompanying drawings. It is to be noted that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or decreased for clarity of discussion.

[ FIG. 1 ] is a flowchart of a calculation method of flight time according to an embodiment of the present invention.

[ FIG. 2 ] is a schematic diagram of a framework for calculating flight time according to an embodiment of the present invention.

[ FIG. 3 ] is a schematic diagram of the amplitude spectrum after performing fast Fourier transform on the signal at the receiving end according to an embodiment of the present invention.

[ FIG. 4 ] is a schematic diagram of filtering a receiving end signal with a bandpass filter to obtain a main signal according to an embodiment of the present invention.

[ FIG. 5 ] is a schematic diagram of inputting a main signal into a Schmitt trigger to generate a trigger signal to obtain a receiving time point according to an embodiment of the present invention.

[Fig. 6] is the calculation method of flight time according to an embodiment of the present invention Step-by-step detailed flow chart.

[ FIG. 7 ] is a schematic diagram of filtering a main signal with a band rejection filter to obtain a noise signal according to an embodiment of the present invention.

[ Fig. 8 ] is an explanatory diagram of continuity judgment according to an embodiment of the present invention.

[ Fig. 9 ] is an explanatory diagram illustrating length judgment according to an embodiment of the present invention.

Embodiments of the invention are discussed in detail below. It should be appreciated, however, that the embodiments provide many applicable concepts that can be implemented in a wide variety of specific contexts. The discussed and disclosed embodiments are for illustration only, and are not intended to limit the scope of the present invention. The terms “first”, “second”, etc. used herein do not specifically refer to a sequence or sequence, but are only used to distinguish elements or operations described with the same technical terms.

The present invention proposes a calculation method of flight time, using the first changing point of the sound wave signal to optimize the judgment of the arrival time of the sound wave signal, because the first turning point of the sound wave signal is least affected by the interference generated by the heat source , it is possible to calculate the flight time of the sound wave (that is, the time difference from the sound wave to the receiving end). In addition to being closer to the time difference between the theoretical transmitting end and the receiving end, the first turning point of the sound wave signal also meets the conditions of a stable reference point. Therefore, the present invention proposes By identifying the first turning point of the sound wave signal, the arrival time point of the received signal after the sound wave passes through the heat source can be judged more accurately.

Accordingly, the present invention proposes a time-of-flight calculation method based on the Schmitt Trigger Method (Schmitt Trigger Method), which converts the sound wave signal into a trigger signal, so as to accurately identify the time point of the first turning point of the sound wave signal , so that the flight time of the sound wave can be accurately calculated without being affected by the heat source.

FIG. 1 is a flowchart of a calculation method of flight time according to an embodiment of the present invention. FIG. 2 is a schematic diagram of an architecture for calculating flight time according to an embodiment of the present invention. Please refer to Figure 1 and Figure 2 together.

The calculation method of flight time in the embodiment of the present invention includes steps S1-S7. In step S1 , an acoustic wave aw is emitted by the emission sensor 120 . In the embodiment of the present invention, the transmitting sensor 120 may be, for example, an ultrasonic transmitter, an ultrasonic transmitter, or a sound projector. In an embodiment of the present invention, the emission sensor 120 uses electric energy and a ceramic transducer to convert energy into sound waves for emission.

The emission sensor 120 is electrically coupled to the control unit 160 (such as a control circuit), and the control unit 160 is used to send a control signal c1 to trigger the emission sensor 120 to emit the sound wave aw, so the emission time point T1 of the emission sensor 120 emitting the sound wave aw can be regarded as The time point at which the control unit 160 sends the control signal c1 to the emission sensor 120 , in other words, the emission time point T1 is one of known parameters of the control unit 160 .

In step S2, the receiving sensor 140 receives the acoustic wave aw and converts the acoustic wave aw into a signal c2 at the receiving end. In the embodiment of the present invention, the receiving sensor 140 may be, for example, an ultrasonic receiver, an ultrasonic receiver, or a sound receiver. In an embodiment of the present invention, the receiving sensor 140 is, for example, used The piezoelectric material converts the sound wave aw into an electrical signal (receiver signal c2).

The receiving sensor 140 is electrically coupled to the control unit 160 (such as a control circuit), and the control unit 160 is used for receiving the receiving end signal c2 and performing subsequent processing.

In step S3 , the control unit 160 performs Fast Fourier Transform (FFT) on the receiving signal c2 received from the receiving sensor 140 to obtain the main frequency range FR of the receiving signal c2 .

FIG. 3 is a schematic diagram of the amplitude spectrum (amplitude spectrum) after performing fast Fourier transform FFT on the receiving end signal c2 according to an embodiment of the present invention. The horizontal axis of the amplitude spectrum in FIG. 3 is frequency, and the unit is Hertz (Hz). The vertical axis of the amplitude spectrum of 3 is the normalized amplitude (normalized amplitude), so it is unitless, and the amplitudes corresponding to different frequencies are different with 0 to 1. For example, the results shown in FIG. 3 show that the main frequency range FR with the strongest amplitude is about 1300-1400 Hz, but the above numerical values are only examples, and the present invention is not limited thereto.

In step S4, the control unit 160 uses a bandpass filter (BPF) to filter the receiving signal c2 according to the main frequency range FR to obtain the main signal f1. FIG. 4 is a schematic diagram of filtering the signal c2 at the receiving end to obtain the main signal f1 by using a band-pass filter BPF according to an embodiment of the present invention. Specifically, in step S4, the band-pass filter BPF is used to filter out the undesired noise part in the signal c2 at the receiving end.

In step S5 , the control unit 160 inputs the main signal f1 into a Schmitt Trigger SCM (Schmitt Trigger) to generate a trigger signal ST. In step S6, the control unit 160 obtains the receiving time point T2 of the sound wave aw according to the trigger signal ST.

In the embodiment of the present invention, the time point T2 of receiving the sound wave aw is the time point corresponding to the first peak value of the trigger signal ST. FIG. 5 is a schematic diagram of inputting the main signal f1 into the Schmitt trigger SCM to generate the trigger signal ST to obtain the receiving time point T2 according to an embodiment of the present invention.

In step S7 , the control unit 160 calculates the time-of-flight TOF of the acoustic wave aw according to the receiving time point T2 and the emission time point T1 of the acoustic wave aw emitted by the transmitting sensor 120 .

In an embodiment of the present invention, the time-of-flight TOF of the acoustic wave aw is the difference between the receiving time point T2 and the transmitting time point T1, that is, TOF=T2-T1. In an embodiment of the present invention, the sound velocity vs of the sound wave aw is the ratio of the distance D between the transmitting sensor 120 and the receiving sensor 140 to the time-of-flight TOF, ie vs=D/TOF.

The details of step S3 to step S5 will be further described below according to FIG. 6 . FIG. 6 is a detailed flow chart of steps S3 to S5 of the calculation method of flight time according to an embodiment of the present invention.

As shown in Figure 6, the fast Fourier transform FFT is performed on the receiving signal c2 to obtain the main frequency range FR of the receiving signal c2, and the receiving end signal c2 is processed by the bandpass filter BPF according to the main frequency range FR of the receiving end signal c2 Filter to obtain the main signal f1.

The time-of-flight calculation method of the embodiment of the present invention further includes: filtering the main signal f1 by a bandstop filter BSF (bandstop filter) according to the main frequency range FR of the receiving signal c2 to obtain the noise signal f2. FIG. 7 is a schematic diagram of filtering the main signal f1 with a band rejection filter BSF to obtain a noise signal f2 according to an embodiment of the present invention. Specifically, the present invention obtains the noise level of the main signal f1 through the band rejection filter BSF.

Please refer to Fig. 6 again, the calculation method of the time of flight of the embodiment of the present invention further includes: multiplying the strength of the noise signal f2 by the proportional constant K to obtain a high threshold; using the high threshold as the Schmitt trigger SCM the high trigger level HL; and the negative value of the high threshold as the low trigger level LL of the Schmitt trigger SCM. In an embodiment of the present invention, the strength of the noise signal f2 is the RMS (Root Mean Square) of the noise signal f2. In other words, HL=RMS(f2)×(+K); LL=RMS(f2)×(−K). In the embodiment of the present invention, the proportional constant is a positive value selected by the user according to the actual situation, such as a positive integer or a positive number with a decimal point. FIG. 7 also shows a schematic diagram of the main signal f1, the noise signal f2, the high trigger level HL, and the low trigger level LL.

Please refer to Figure 6 again, the main signal f1 is input to the Schmitt trigger SCM, and the Schmitt trigger SCM performs potential triggering on the main signal f1 according to the high trigger level HL and the low trigger level LL: when the main signal f1 When the signal strength is higher than the high trigger level HL, the Schmitt trigger SCM will output a high level trigger signal ST; when the signal strength of the main signal f1 is lower than the low trigger level LL, the Schmitt trigger SCM will output Outputting a low-level trigger signal ST. FIG. 5 shows a schematic diagram of the main signal f1 and the trigger signal ST.

Since the Schmitt trigger SCM will trigger all the parts of the main signal f1 that meet the conditions of the high trigger level HL and the low trigger level LL, if the main signal f1 still contains large noise, or the echo signal , then the receiving time point T2 cannot be selected correctly. In order to make the result of the calculation method of the flight time meet expectations, the present invention further proposes that after the Schmidt trigger SCM is executed and before the receiving time point T2 of the acoustic wave aw is obtained, , it is also necessary to perform continuity judgment and length judgment, so as to obtain a better and more accurate receiving time point T2.

In an embodiment of the present invention, the calculation method of the flight time further includes: before obtaining the receiving time point T2 of the sound wave aw, performing a continuity judgment on the trigger signal ST generated by the Schmitt trigger SCM. In an embodiment of the present invention, the trigger signal ST is composed of multiple square waves. The above-mentioned continuity judgment includes: judging whether the width of each square wave is greater than the width threshold; waves are filtered out from the trigger signal ST. Specifically, the width of each square wave of the trigger signal ST should be similar or even the same, so the square waves with too long width should be filtered out.

FIG. 8 is an explanatory schematic diagram of continuity judgment according to an embodiment of the present invention. The thick frame in FIG. 8 is a part of the trigger signal and is used to represent the correct trigger signal CST. Those outside the thick frame in FIG. news section. As shown in Figure 8, the wave width d1 of square wave w1, the wave width d2 of square wave w2, the wave width d3 of square wave w3, the wave width d4 of square wave w4, and the wave width d5 of square wave w5 are judged to be greater than wave width Wide threshold (for example, 1000 seconds, this example is only an example, the present invention is not limited thereto), therefore, square wave w1, square wave w2, square wave w3, square wave w4, square wave w5 are filtered from the trigger signal ST remove.

In an embodiment of the present invention, the calculation method of the time-of-flight further includes: before obtaining the receiving time point T2 of the sound wave aw, judging the length of the trigger signal ST generated by the Schmitt trigger SCM. In an embodiment of the present invention, the trigger signal ST is composed of a plurality of square wave sets, and the above-mentioned length judgment includes: judging whether the total duration of each square wave set is less than the duration threshold; The square wave set of is filtered from the trigger signal. Specifically, since the main signal f1 has a known specific wavelength and each periodic wave should be closely adjacent and close to each other, the trigger signals ST after executing the Schmitt trigger SCM should be close to each other and this close The total duration of the waveform should be long enough, and this length judgment is to filter out the places where the distance between the trigger signals ST is too short.

Fig. 9 is a schematic diagram illustrating the length judgment according to an embodiment of the present invention. The left diagram of Fig. 9 is a schematic diagram of the main signal f1 and the trigger signal ST before execution of the length judgment, and the right diagram of Fig. 9 is the main signal after execution of the length judgment Schematic diagram of f1 and trigger signal ST. As shown in Figure 9, the trigger signal ST is composed of a square wave set x1, a square wave set x2, and a square wave set x3 (it should be noted that only a part of the square wave set x3 is shown in Figure 9), and after judgment, the square wave set The total duration of the wave set x1 and the total duration of the square wave set x2 are less than the duration threshold (for example, 10000 seconds, this example is only for illustration, and the present invention is not limited thereto), therefore, the square wave set x1, square wave The wave set x2 is filtered out from the trigger signal ST, and the square wave set x3 is the expected correct trigger signal.

In the embodiment of the present invention, the continuity judgment is performed on the trigger signal ST before the length judgment is performed. In other words, in the embodiment of the present invention, after executing the Schmitt trigger SCM, the continuity judgment is first performed, and then Then execute the length judgment, and finally obtain the receiving time point T2 of the sound wave aw accurately by the trigger signal ST after the execution of the length judgment and the continuity judgment.

It has been confirmed by actual measurement that for the sound waves that have not passed through the heat source and the sound waves that have passed through the heat source, the traditional sound velocity calculation method (Max peak method) and the application method disclosed in the present invention are respectively used for the receiving end signal received by the receiving end. The calculation method of the time-of-flight of the Mitte trigger SCM is used to judge the speed of sound, and the results show that, whether it is a sound wave that has not passed through a heat source or a sound wave that passes through a heat source, the results of the calculation method for the time-of-flight disclosed by the present invention are all better than the traditional calculation method for the speed of sound. The result is more stable, and for the sound wave passing through the heat source, the maximum value of the signal at the receiving end will change due to passing through the heat source, which will lead to a large error in the calculated sound velocity, and even appear slower than the sound velocity not passing through the heat source Relatively speaking, the calculation method of flight time disclosed by the present invention not only does not have the extreme value of great error, but also the overall distribution of data under the same environmental conditions is more stable than the traditional calculation method of speed of sound.

To sum up the above, the present invention proposes a calculation method of time of flight, applying the Schmidt trigger method, which can avoid the impact of changes in the intensity and waveform of the sound wave signal when the sound wave passes through the heat source. Therefore, even when the sound wave passes through the heat source, The time-of-flight of sound waves can still be accurately calculated.

The features of several embodiments are outlined above, so those skilled in the art can better understand aspects of the present invention. Those skilled in the art will appreciate that they can readily use the present invention as a basis to design or modify other processes and structures to achieve the same goals and/or achieve the same goals as the embodiments described herein. to the same advantage. Those skilled in the art should also understand that these equivalent constructions do not depart from the spirit and scope of the present invention, and that they can make various changes, substitutions and alterations without departing from the spirit and scope of the present invention.

S1~S7 : Steps

Claims (10)

A calculation method for flight time, comprising: emitting sound waves from a transmitting sensor; receiving the sound wave by a receiving sensor and converting the sound wave into a receiving end signal; performing a fast Fourier transform on the receiving signal to obtain a dominant frequency range of the receiving signal; filtering the signal at the receiving end by a band-pass filter according to the main frequency range to obtain a main signal; inputting the main signal into a Schmitt trigger to generate a trigger signal; obtaining a receiving time point of the sound wave according to the trigger signal; and A time-of-flight of the sound wave is calculated according to the receiving time point and an emission time point when the emitting sensor emits the sound wave. The method for calculating the time-of-flight of claim 1, wherein the time-of-flight of the sound wave is a difference between the receiving time point and the transmitting time point, wherein the sound velocity of the sound wave is the distance between the transmitting sensor and the receiving sensor A ratio of a distance to the flight time. The method for calculating flight time according to claim 1, wherein the receiving time point of the sound wave is a time point corresponding to a first peak value of the trigger signal. The calculation method of flight time as stated in claim 1 further includes: filtering the main signal by a band rejection filter according to the main frequency range to obtain a noise signal; multiplying a strength of the noise signal by a proportional constant to obtain a high threshold; using the high threshold as a high trigger level of the Schmitt trigger; and A negative value of the high threshold is used as a low trigger level of the Schmitt trigger. The calculation method of flight time as described in Claim 4, wherein the intensity of the noise signal is the root mean value of the noise signal. The calculation method of flight time as stated in claim 1 further includes: Before obtaining the receiving time point of the sound wave, a continuity judgment is performed on the trigger signal. The calculation method of flight time as described in Claim 6, wherein the trigger signal is composed of a plurality of square waves, wherein the continuity judgment includes: judging whether a wave width of each of the square waves is greater than a wave width threshold; and The square wave whose judgment result is yes is filtered out from the trigger signal. The calculation method of flight time as stated in claim 6 further includes: Before obtaining the receiving time point of the sound wave, a length judgment is performed on the trigger signal. The method for calculating flight time as described in Claim 8, wherein the trigger signal is composed of a plurality of square wave sets, and the length judgment includes: judging whether a total duration of each of the square wave sets is less than a duration threshold; and The square wave set whose judgment result is yes is filtered out from the trigger signal. The method for calculating flight time as described in Claim 8, wherein the continuity judgment is performed on the trigger signal before the length judgment is performed on the trigger signal.

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