WO2023163279A1 - Distance measurement method and device using ultrasonic waves - Google Patents

Abstract

Disclosed are a distance measurement method and device using ultrasonic waves, whereby degradation in distance resolution can be overcome. The distance measurement device using ultrasonic waves comprises a setting module, an acquisition module, a calculation module, a first distance computation module, an error check module, and a second distance computation module. The setting module sets each of a PWM clock of an ultrasonic wave sensor, a reference frequency at which the transmission and reception sensitivity, among the frequency characteristics of the ultrasonic wave sensor, are best, and the transmission frequency range of the ultrasonic wave sensor. The acquisition module acquires a reference approximate distance on the basis of a time of flight (ToF) acquired using transmitted ultrasonic waves of the reference frequency reflected by a reflecting object. The calculation module calculates an initial frequency and adjacent frequencies calculated from the reference approximate distance. The first distance computation module sequentially transmits ultrasonic waves of the calculated initial frequency and ultrasonic waves of each of the calculated adjacent frequencies and computes a plurality of distances on the basis of the measured ToFs of each of the ultrasonic waves. The second distance computation module computes precise distances on the basis of the ToFs.

Description

Distance measuring method and device using ultrasonic waves

The present invention relates to a distance measuring method and device using ultrasonic waves, and more particularly, to a distance measuring method and device using ultrasonic waves capable of overcoming a decrease in distance resolution while maintaining a long-distance sensing capability even when a low frequency is used. .

Ultrasound is a sound wave of a frequency higher than the audible sound that can be heard by the human ear in the range of 20 Hz to 20 kHz among sound waves, and refers to a sound wave of a frequency that cannot be directly heard by the human ear. It is possible, has a small effect on light reflection, is easy to process, and has the advantage of not having to design a complicated filter, so it is often used for distance measurement or for detecting the presence or absence of an object in front.

In particular, the distance measurement using ultrasonic waves is to measure the distance by calculating the transmission speed of sound waves from the time interval between the ultrasonic transmission time and the ultrasonic reception time after transmitting the ultrasonic wave and receiving the signal returned after hitting the reflective object.

When ultrasonic waves are emitted and reflected from objects, attenuation occurs. The ultrasonic signal reflected from a distant object is attenuated more than that reflected from a nearby object, so the size of the received signal becomes smaller.

The higher the frequency of sound waves in the air, the higher the resolution for the minute distance and space to the reflective object to be detected. There is a characteristic that

On the other hand, at low frequencies, the resolution for distance and space is reduced, but it is easy to detect the distance between the measuring device and the reflective object because the attenuation in the atmosphere is small.

From the point of view of system implementation, the higher the frequency, the larger the ultrasonic signal propagated in the air decreases in log-scale as the distance increases. A relatively low ultrasonic frequency must be used, but distance accuracy cannot be secured due to reduced distance resolution due to the low frequency.

Considering the physical characteristics of ultrasound, the resolution of the distance that increases as the frequency increases is linearly improved with a relationship of 1/2 of the ultrasound wavelength (λ), whereas the signal attenuation due to the increase of frequency is logarithmic. Because of the increase in scale, it is commercially desirable to improve the distance resolution while using a low frequency for the realization of a long-distance ultrasonic distance measurement system.

Even if a relatively low frequency is used, it must be possible to overcome the degradation of distance resolution by other methods while maintaining long-distance sensing capability.

[Prior art literature]

[Patent Literature]

(Patent Document 0001) Korean Patent Publication No. 2007-0066136 (2007. 06. 27.) (Distance measuring method and device using ultrasonic waves)

(Patent Document 0002) Korean Patent Publication No. 2019-0123686 (2019. 11. 01.) (zero-cross detection circuit and sensor device)

Accordingly, the technical problem of the present invention is to focus on this point, and an object of the present invention is to provide a distance measurement method using ultrasonic waves capable of overcoming a decrease in distance resolution while maintaining a long-distance sensing ability even when a low frequency is used.

Another object of the present invention is to provide a distance measuring device using ultrasonic waves that performs the distance measuring method using ultrasonic waves.

According to an embodiment to realize the above object of the present invention, a distance measuring method using ultrasonic waves for measuring a distance between an ultrasonic sensor and a reflective object using ultrasonic waves transmitted from an ultrasonic sensor having an ultrasonic transmitter and an ultrasonic receiver has Setting each of the PWM clock of the ultrasonic sensor, a reference frequency that is a frequency value having the best transmission and reception sensitivity among frequency characteristics of the ultrasonic sensor, and a transmission frequency range of the ultrasonic sensor; Obtaining a standard approximate distance based on a time of flight (ToF) obtained by using ultrasonic waves of the reference frequency transmitted and reflected by a reflective object; calculating an initial frequency and adjacent frequencies from the reference approximation distance; Calculating a plurality of distances based on ToF of each of the ultrasonic waves measured by sequentially transmitting the ultrasonic wave of the initial frequency and the ultrasonic wave of each of the adjacent frequencies: and calculating a precise distance based on the ToFs do.

In one embodiment, the value of the sound speed used in the step of acquiring the reference approximate distance based on the time of flight (ToF) may be used after real-time compensation of temperature or real-time compensation of humidity.

In one embodiment, the step of calculating the initial frequency and the adjacent frequencies from the reference approximate distance, setting a frequency closest to the reference frequency within the outgoing frequency range among the frequencies constituting the condition of the standing wave as the initial frequency step; and calculating and obtaining at least one adjacent frequency having a different phase based on the initial frequency.

In one embodiment, the offset phase calculation value for each adjacent frequency is

(Here, fside is the number of adjacent frequencies).

In one embodiment, when four adjacent frequencies are used, each of the adjacent frequencies may have phases of ±10% and ±20% based on the initial frequency.

In one embodiment, when eight adjacent frequencies are used, each of the adjacent frequencies may have a phase of ±5.56%, ±11.11%, ±16.67%, and ±22.22% based on the initial frequency.

In one embodiment, the distance measurement method using ultrasonic waves may include checking whether the calculation of the distances corresponds to an error condition; feeding back to the step of acquiring the standard approximate distance if it is checked that the error condition is the case; and if it is checked that the error condition is not the case, calculating a precision distance based on the ToFs.

In one embodiment, the error condition may be ToF out of measurement range.

In one embodiment, the error condition may include a case in which the difference between ToF0 and ToF4 is out of the expected time difference due to the difference between f0 and f4.

In one embodiment, calculating the precise distance based on the ToFs may include determining a signal arriving first as the precise distance.

In an embodiment, calculating the precision distance based on the ToFs may include determining a value with the smallest ToF as the precision distance.

In an embodiment, calculating the precision distance based on the ToFs may include determining an average of the ToFs as the precision distance.

In order to realize the other object of the present invention described above, according to an embodiment, a distance measuring device using ultrasonic waves for measuring a distance between an ultrasonic sensor and a reflective object by using ultrasonic waves transmitted from an ultrasonic sensor having an ultrasonic transmitter and an ultrasonic receiver. A setting module for setting each of the PWM clock of the ultrasonic sensor, a reference frequency that is a frequency value having the best transmission and reception sensitivity among frequency characteristics of the ultrasonic sensor, and a transmission frequency range of the ultrasonic sensor; an acquisition module for acquiring a reference approximate distance based on a Time Of Flight (ToF) obtained by using ultrasonic waves of the reference frequency transmitted and reflected by a reflective object; a calculation module for calculating an initial frequency and adjacent frequencies from the reference approximation distance; a first distance calculation module for calculating a plurality of distances based on ToF of each of the ultrasonic waves measured by sequentially transmitting the calculated initial frequency ultrasonic waves and ultrasonic waves of adjacent frequencies; and a second distance calculation module that calculates a precise distance based on the ToFs.

In one embodiment, the calculation module sets, as an initial frequency, a frequency closest to the reference frequency within the outgoing frequency range among frequencies constituting a condition of a standing wave as an initial frequency, and at least one neighboring frequency having a different phase based on the initial frequency. frequencies can be obtained.

In one embodiment, the offset phase calculation value for each adjacent frequency is

(Here, fside is the number of adjacent frequencies).

In one embodiment, when four adjacent frequencies are used, each of the adjacent frequencies may have phases of ±10% and ±20% based on the initial frequency.

In one embodiment, when eight adjacent frequencies are used, each of the adjacent frequencies may have a phase of ±5.56%, ±11.11%, ±16.67%, and ±22.22% based on the initial frequency.

In one embodiment, the acquisition module may include a zero-cross detector for determining an echo time by detecting a voltage higher than a reference voltage by a specific offset voltage and a voltage lower by a specific offset voltage based on the reference voltage. .

In one embodiment, the zero-cross detector may include: a first resistor having one end connected to a power supply voltage and the other end to which a reference voltage is applied; a second resistor having one end connected to the reference voltage and the other end to which a ground voltage is applied; A positive terminal to which an ultrasonic reception signal is applied, a negative terminal connected to the first resistor to which a first voltage as high as a specific offset voltage based on the reference voltage is applied, and a size between the ultrasonic reception signal and the first voltage a first voltage comparator having an output terminal outputting a first output voltage according to comparison; And a positive terminal connected to the second resistor to which a second voltage lower than a specific offset voltage based on the reference voltage is applied, a negative terminal to which the ultrasonic reception signal is applied, and the ultrasonic reception signal and the second voltage It may include a second voltage comparator having an output terminal for outputting a second output voltage according to the comparison of the size of the liver.

In one embodiment, the distance measuring device using ultrasonic waves further includes an error check module that checks whether the calculation of distances by the first distance calculation module corresponds to an error condition, and the second distance calculation The module may calculate a precision distance based on the ToFs if the error condition is checked by the error check module.

According to the distance measurement method and device using such ultrasonic waves, two zero-cross detectors having a 180° symmetrical structure for the upper and lower voltages of the reference voltage are applied in a ToF detection method for the received signal, and between the ultrasonic transmitter and the reflective target By selectively using the outgoing frequency that satisfies the standing wave condition at the distance L, the wave energy incident on the reflective object and the reflected wave energy are overlapped with each other to control constructive interference or resonance to occur, thereby improving reception sensitivity. can make it In addition, unlike the generally known distance resolution (±1/2 of the period of the ultrasonic frequency) by the frequency of the ultrasonic wave, the present invention provides the phase between the received signal generated in the process of transmitting and receiving different frequencies of f0 to f4 for the same distance. By using two zero-cross detectors that react due to the difference, the resolution can be improved to ±1/20 of the period.

1 is a block diagram illustrating a distance measuring device using ultrasonic waves according to an embodiment of the present invention.

2 is a graph for explaining a standing wave condition and a sound pressure level according to a distance.

3 is a graph for explaining the distance measurement principle of the pulse-echo method.

4A is a circuit diagram for explaining a general zero-cross detector, and FIG. 4B is a graph for explaining a waveform by a conventional zero-cross detector that compares only a voltage above or below a reference voltage.

5A is a circuit diagram for explaining a zero-cross detector according to the present invention, and FIG. 5B is a graph for explaining a waveform by an improved zero-cross detector that simultaneously compares upper and lower levels of a reference voltage.

6 is a graph for explaining frequency characteristics of an ultrasonic sensor of 40 kHz.

7 is a diagram showing the code of the Python program for obtaining the fundamental frequency according to the distance.

FIG. 8 is a diagram showing a result of 25% phase angle difference frequency calculation at a distance of 0.5 m by the code of the Python program of FIG. 7 .

9 is a graph for explaining a received waveform for each frequency and a detection result by a zero-cross detector.

10A is a flowchart illustrating a method for measuring a distance using ultrasonic waves according to an embodiment of the present invention.

FIG. 10B is a flowchart for explaining step S400 of FIG. 10A.

Hereinafter, with reference to the accompanying drawings, the present invention will be described in more detail. Since the present invention may have various changes and various forms, specific embodiments are illustrated in the drawings and described in detail in the text. However, it should be understood that this is not intended to limit the present invention to the specific disclosed form, and includes all modifications, equivalents, and substitutes included in the spirit and scope of the present invention.

Terms such as first and second may be used to describe various components, but the components should not be limited by the terms. These terms are only used for the purpose of distinguishing one component from another. For example, a first element may be termed a second element, and similarly, a second element may be termed a first element, without departing from the scope of the present invention. Singular expressions include plural expressions unless the context clearly dictates otherwise.

In this application, terms such as "comprise" or "have" are intended to designate that there is a feature, number, step, operation, component, part, or combination thereof described in the specification, but one or more other features It should be understood that it does not preclude the possibility of the presence or addition of numbers, steps, operations, components, parts, or combinations thereof.

In addition, unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs. Terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with the meaning in the context of the related art, and unless explicitly defined in the present application, they should not be interpreted in an ideal or excessively formal meaning. don't

1 is a block diagram illustrating a distance measuring device using ultrasonic waves according to an embodiment of the present invention. In particular, a distance measuring device using ultrasonic waves in the case of using four adjacent frequencies is shown.

Referring to FIG. 1, a distance measuring device 100 using ultrasonic waves according to an embodiment of the present invention includes an ultrasonic transmitter 110 that transmits ultrasonic waves to a reflective object and an ultrasonic receiver that receives ultrasonic waves reflected by the reflective object. 120, and a sensor driving unit 130 that calculates a distance to a reflection target through operation control of each of the ultrasonic transmitter 110 and the ultrasonic receiver 120.

The ultrasonic transmitter 110 transmits an ultrasonic signal to a reflective object under the control of the sensor driver 130 .

The ultrasonic receiving unit 120 receives ultrasonic waves reflected by a reflective object and provides the received ultrasonic waves to the sensor driving unit 130 . In this embodiment, the ultrasonic transmitter 110 and the ultrasonic receiver 120 define ultrasonic sensors.

The sensor driver 130 includes a setting module 310, an acquisition module 320, a calculation module 330, a first distance calculation module 340, an error check module 350, and a second distance calculation module 360. And, the operation of the ultrasonic transmission unit 110 is controlled so that the frequency of the ultrasonic waves transmitted to the reflective object is changed, and the distance to the reflective object is calculated based on the ultrasonic waves received through the ultrasonic receiver 120. In this embodiment, the sensor driver 130 includes a setting module 310, an acquisition module 320, a calculation module 330, a first distance calculation module 340, an error check module 350, and a second distance calculation module. Although it has been described that it is composed of 360, it is logically divided for convenience of description, but not hardware-wise.

The setting module 310 sets each of the PWM clock of the ultrasonic sensor, a reference frequency that is a frequency value having the best transmission and reception sensitivity among frequency characteristics of the ultrasonic sensor, and a transmission frequency range of the ultrasonic sensor.

The acquisition module 320 calculates the Time Of Flight (ToF) of the ultrasonic wave using the ultrasonic reception signal received after the ultrasonic transmission signal transmitted in response to the reference frequency is reflected by the reflective object, and the calculated ToF A reference approximation distance (d _ref ) is obtained based on . Here, the reference approximation distance (d _ref ) may be calculated using Equation (1) below.

[Formula 1]

here,

is the velocity of ultrasonic waves in the air (m/s), and ToF is the ultrasonic round-trip measurement time.

The calculation module 330 calculates the initial frequency f0 and adjacent frequencies f1, f2, f3, and f4 from the reference approximate distance d _ref . Specifically, the calculation module 330 sets a frequency closest to the reference frequency within the transmission frequency range among frequencies of the ultrasonic reception signal constituting a condition of a standing wave as the initial frequency f0, and Adjacent frequencies f1, f2, f3, and f4 having phases of ±10% and ±20%, respectively, based on the frequency f0 are acquired. Here, the standing wave means that the wave is confined in a limited space and vibrates in place. A standing wave is a concept in contrast to a progressive wave, which is a wave traveling in an arbitrary direction in space, and means a wave in which nodes of vibration are fixed. It is also called a stationary wave or a standing wave.

The first distance calculation module 340 sequentially transmits ultrasonic waves of the calculated initial frequency f0 and ultrasonic waves of adjacent frequencies f1, f2, f3, and f4 to measure the measured time of flight (Time Of Flight, ToF) calculates a plurality of distances.

The error check module 350 checks whether the calculation of the distances by the first distance calculation module 340 is an error condition. That is, the error check module 350 determines an error condition when ToF is out of the measurement range or when the difference between ToF0 and ToF4 is out of the expected time difference due to the difference between f0 and f4. Here, ToF0 is calculated according to ultrasonic transmission and reception of the initial frequency f0, ToF1 is calculated according to ultrasonic transmission and reception of the first adjacent frequency f1, and ToF2 is calculated according to ultrasonic transmission of the second adjacent frequency f2. and reception, ToF3 is calculated according to ultrasonic transmission and reception of the third adjacent frequency f3, and ToF4 is calculated according to ultrasonic transmission and reception of the fourth adjacent frequency f4.

The second distance calculation module 360 calculates a precision distance from the ToFs when it is checked that the error condition is not an error condition by the error check module 350. For example, precise distance can be calculated using ToF corresponding to the first arriving signal. Alternatively, the ToF can be calculated as a precision distance using the smallest value. Alternatively, it can be calculated as a precision distance using the average of ToFs.

The higher the frequency of sound waves in the air, the higher the resolution of the minute distance and space to the target object to be detected. there is On the other hand, low frequencies reduce the resolution of distance and space, but because the attenuation in the air is small, it is easy to detect long distances between the measuring device and the target. The sound pressure level according to the distance is shown in Equation 2.

[Formula 2]

Here, p ₀ is the reference sound pressure (20 uPa), and p _rms is the RMS value of the sound pressure.

2 is a graph for explaining a standing wave condition and a sound pressure level according to a distance.

Referring to FIG. 2 , the sound pressure level gradually decreases as the distance from the sound wave source increases. At gradually decreasing sound pressure levels, standing waves appear in the form of apex. That is, the standing wave is actually implemented as (1/2), 1, 1+(1/2), etc. of the wavelength (λ) along the X-axis.

Looking at these characteristics from the system implementation point of view, the higher the frequency, the larger the ultrasonic signal propagated in the air decreases in a log-scale as the distance increases. Therefore, in order to detect the distance to an object from a long distance in a non-contact manner, a relatively low ultrasonic frequency must be used. However, due to the low frequency, the distance resolution is degraded and thus the accuracy of the distance cannot be secured. Thus, a contradictory relationship exists between frequency and resolution.

Considering the physical characteristics of ultrasound, the resolution of the distance that increases as the frequency increases is linearly improved with a relationship of 1/2 of the ultrasound wavelength (λ), whereas the signal attenuation due to the increase of frequency is logarithmic. -Since it increases with the scale, it is important to improve the distance resolution while using a low frequency for the realization of a long-distance ultrasonic distance measurement system.

Therefore, distance measurement using ultrasonic waves should be able to overcome a decrease in distance resolution while maintaining long-distance sensing capability even when a relatively low frequency is used.

Accordingly, in the present invention, as an embodiment, a distance resolution similar to that of an ultrasonic signal of 200 kHz to 400 kHz is implemented using 40 kHz ultrasonic waves, while maintaining the characteristic of 40 kHz measurement distance or zero-cross by a hardware method to improve the distance measurement capability. improve the detector. Zero-crossing refers to a state in which voltage is not applied to a specific terminal, that is, a state of zero. A circuit that finds such a point and transmits a signal is called a zero-crossing detector, zero-crossing detector, or zero-crossing. By counting the point where it becomes zero, it is possible to count the frequency and also to control AC alternating current based on this.

A general zero-cross detector uses one voltage comparator that detects a voltage higher or lower than a specific offset voltage based on a reference voltage, but the zero-cross detector according to the present invention uses a voltage comparator that is higher or lower than a specific offset voltage based on a reference voltage. It uses two voltage comparators, each detecting the voltage. Here, the specific offset voltage is 0V in the case of an ideal zero-cross detector, but in practice, a specific voltage is set according to the noise environment of the transmission/reception system. In this embodiment, the offset voltage was set to 15 mV to 30 mV.

Subsequently, in order to further improve the fine resolution, further improvement is performed in a software method for transmitting and receiving ultrasonic waves. That is, the detection distance is improved and the resolution of the detection distance is improved by using a resonant frequency selection (A) of the overlapping phenomenon using a standing wave and a similar frequency set having a different phase from the resonant frequency.

The principle of improving the sensing distance is as follows.

Constructive interference caused by the superposition of the phase relationship between the outgoing signal incident on the reflective object in a standing wave and the reflected signal reflected on the reflective object, similar to a resonance phenomenon, determines and uses the ultrasonic main frequency (wave length) It is a principle that a large signal is incident and it is possible to measure a longer distance than the conventional method.

The above method serves to increase the size of the first echo signal (the starting point of one cycle).

Although it may be difficult to use this signal as a ToF detection signal in actual application circuits (i.e., because of its low SNR and common feature of being mixed with noise and detected), if an ideal zero-cross detector is designed in the ultrasonic receiver of an ultrasonic sensor, It can contribute to sensitivity improvement.

The resolution improvement of the detection distance is similar to the frequency of the above detection distance improvement, but when several frequencies with a slight difference in phase incident on the reflective object are calculated and transmitted, the reflected signal also has a phase difference little by little. Even though they have such a phase difference, ToF is the same even if the frequency is different (i.e. same distance, same speed of sound), so ToFs with different incident phases are read by a voltage comparator (i.e. zero cross detector). Since multiple phases are incident on the detector, if the shortest ToF time is obtained among the ToFs measured for each frequency, time resolution much more precise than the resolution by the wavelength of the frequency can be obtained.

In general, distance measurement using ultrasonic waves uses a ToF measurement method using a pulse-echo.

3 is a graph for explaining the distance measurement principle of the pulse-echo method.

Referring to FIG. 3 , the pulse-echo distance measurement is a measurement method in which a distance to a reflective object is calculated by measuring a signal (Echo) returned after the ultrasonic wave is transmitted and reflected by the reflective object.

For precise distance measurement, since it has a resolution corresponding to a distance of 1/2 of the ultrasonic wavelength (λ), it is advantageous to use a high frequency to improve the distance resolution. However, the higher the frequency, the greater the attenuation in the air, which limits the measurable distance.

The ultrasonic receiver of the ultrasonic sensor for receiving ultrasonic waves includes a zero-cross detector for determining an echo time signal.

4A is a circuit diagram for explaining a general zero-cross detector, and FIG. 4B is a graph for explaining a waveform by a conventional zero-cross detector that compares only a voltage above or below a reference voltage.

Referring to FIGS. 4A and 4B, a general zero-cross detector includes a first resistor R11, a second resistor R12, and a first voltage comparator OP11, and a constant upper amplitude of a received waveform to measure ToF. detect

The first resistor R11 has one end connected to the power supply voltage VCC and the other end to which the reference voltage VCOM is applied. The second resistor R12 has one end connected to the reference voltage VCOM and the other end to which the ground voltage is applied. The first voltage comparator OP11 includes a positive terminal to which the ultrasonic reception signal VIN is applied, a negative terminal connected to the first resistor R11 and applied with a first voltage VP higher than the reference voltage VCOM, and an output terminal outputting a first output voltage VOUTP according to a magnitude comparison between the ultrasonic reception signal VIN and the first voltage VP.

The first voltage comparator OP11 outputs a high-level first output voltage VOUTP at an amplitude higher than the first voltage VP in the waveform of the ultrasonic reception signal VIN and is lower than or equal to the first voltage VP. A low level first output voltage VOUTP is output in amplitude.

A typical zero-cross detector measures ToF by detecting a certain upper amplitude or a certain lower amplitude of a received waveform. However, according to a general zero-cross detector, a measurement error of λ/2 exists.

5A is a circuit diagram for explaining a zero-cross detector according to the present invention, and FIG. 5B is a graph for explaining a waveform by an improved zero-cross detector that simultaneously compares upper and lower levels of a reference voltage.

5A and 5B, the zero cross detector according to the present invention includes a first resistor R21, a second resistor R22, a first voltage comparator OP21 and a second voltage comparator OP22, To measure ToF, each of the constant upper amplitude and constant lower amplitude of the received waveform is detected. The zero-cross detector illustrated in FIG. 5A may be included in the acquisition module 320 illustrated in FIG. 1 .

The first resistor R21 has one end connected to the power supply voltage VCC and the other end to which the reference voltage VCOM is applied. The second resistor R22 has one end connected to the reference voltage VCOM and the other end to which the ground voltage is applied.

The first voltage comparator OP21 includes a positive terminal to which the ultrasonic reception signal VIN is applied, a negative terminal connected to a first resistor to which a first voltage VP higher than the reference voltage VCOM is applied, and the ultrasonic wave It has an output terminal for outputting a first output voltage VOUTP according to a magnitude comparison between the received signal VIN and the first voltage VP. In this embodiment, the first resistor R21 to which the negative terminal of the first voltage comparator OP21 is connected may be a variable resistor.

The second voltage comparator OP22 is connected to the second resistor R22 and has a positive polarity terminal to which a second voltage VN lower than the reference voltage VCOM is applied, and a unit to which the ultrasonic reception signal VIN is applied. It has a polarity terminal and an output terminal for outputting a second output voltage VOUTN according to a magnitude comparison between the ultrasonic reception signal VIN and the second voltage VN. In this embodiment, the second resistor R22 to which the positive terminal of the second voltage comparator OP22 is connected may be a variable resistor.

The first resistor R21 and the first voltage comparator OP21 may define the positive detection part of the zero-cross detector, and the second resistor R22 and the second voltage comparator OP22 define the negative detection part of the zero-cross detector. can do. The positive detector detects a phase transition of the received waveform from negative to positive, and the negative detector detects a phase transition of the received waveform from positive to negative.

The zero-cross detector according to the present invention measures ToF by detecting each of the constant upper amplitude and the constant lower amplitude of the received waveform. According to the zero-cross detector according to the present invention, a measurement error of λ/4 exists. Therefore, there is an advantage in that the measurement error by the zero-cross detector according to the present invention can be reduced to 1/2 compared to the measurement error by the general zero-cross detector.

As described above, the zero-cross detector for determining the echo time signal in the ultrasonic receiver of the ultrasonic sensor uses only one comparison voltage above or below the reference voltage and uses only one comparison voltage as a result to determine the echo time. By improving the design so that the echo time can be determined by comparing both the upper and lower voltages of the reference voltage, the minimum distance resolution according to the frequency determined by the length of the ultrasonic wave can be improved by about twice.

A voltage slightly higher than the reference voltage (VCOM) in the receiving system for the time of flight (ToF) of the ultrasonic wave that starts from the ultrasonic transmitter of the ultrasonic sensor and is reflected by the reflective object and arrives at the ultrasonic receiver of the ultrasonic sensor again. to decide That is, it is generally determined as a value slightly higher than the level of reception noise generated in the system according to the characteristics of the system and the application environment.

In this specification, the value was determined between about 15 mV and 30 mV. A system that outputs “1” if a signal higher than the set comparison voltage is detected, otherwise “0” is the operating principle of a zero-cross detector in a general pulse-echo system.

However, such a zero-cross detector generates a measurement time error such as delta-h1 when a signal having a phase difference of up to 180° from the waveform to be compared is received. The maximum value of this ToF error is 1/2 of the period (wavelength, λ) of the ultrasonic frequency. This also means the limit of the resolution of the distance according to the ultrasonic frequency, which is meant in this specification.

As described above, according to the present invention, in order to overcome the resolution limit, voltage comparators are placed at the top and bottom of the reference voltage (VCOM) at the same time, and the upper and lower sensors are designed to operate for zero-cross detection at the same time did

The detection period of the existing ToF can be reduced from delta-p1 to delta-p2 or delta-n2 by performing zero-cross detection based on the first output signal of the two comparators on the time axis from the received ultrasonic signal. .

As a result of the circuit improvement, the resolution of the sensing distance was obtained from 1/2 of the existing value of the period (wavelength, λ) to at least 1/4 or less. This means that it is possible to implement a level of distance resolution that can be expected with a frequency higher than or equal to.

On the other hand, ultrasonic waves have the property of propagating through a medium and do not have mass, but have energy. Ultrasonic pulses are transmitted like longitudinal waves in the medium in which the direction of motion of the particles in the medium and the direction of motion of the ultrasonic waves are the same.

A longitudinal wave is a wave in which the movement (displacement) of a medium appears in the same direction as the direction of movement of the wave in which energy is transmitted. The medium is compressed or relaxed along the axis of motion of the wave, and it is expressed as a mill and a cow, respectively, and a wave is formed between mills and mills or between cows and cows. Representatively, there are p-waves among sound waves and seismic waves.

A transverse wave means a wave in which the movement (displacement) of a medium appears in a direction perpendicular to the transmission direction of the wave through which energy is transmitted.

Longitudinal and transverse waves both have characteristics of simple vibration, and the wave equation for time is expressed as Equation 3 below in the form of a sine wave of the same shape.

[Formula 3]

where A is the amplitude,

is the angular velocity,

is the phase

In Equation 3, when a wave with a sine wave propagates and hits a reflective object while propagating, it causes destructive interference according to the principle of superposition between the incident wave and the reflected wave according to the boundary condition (phase angle) when it hits the boundary surface. Alternatively, a form of constructive interference appears, and the case of vibration with the maximum constructive interference is called a standing wave condition.

The total time at which the transmitted ultrasonic signal reaches the ultrasonic receiver of the ultrasonic sensor after being reflected by the reflective object, and the reached sine wave signal ideally reaches the point where the phase is 0°, that is, the zero-cross point (ToF, round-trip) time), the distance information is extracted using the known speed of sound. In addition to the center frequency of 40 kHz, the ultrasonic sensor used at this time has a characteristic in that a sound pressure sensitivity of a level that can be used as an ultrasonic sensor is formed in a section of about ±5 kHz to the left and right of the center frequency.

6 is a graph for explaining frequency characteristics of an ultrasonic sensor of 40 kHz.

Referring to FIG. 6, a 40 kHz ultrasonic sensor has a sound pressure level of 120 dB in a frequency band of 40 kHz. In addition, the sound pressure level is 80 dB in the frequency band of 30 kHz, and the sound pressure level is 98 dB in the frequency band of 35 kHz. In addition, the sound pressure level is 104 dB in the frequency band of 45 kHz, and the sound pressure level is 90 dB in the frequency band of 50 kHz.

[Formula 4]

here,

is the speed of ultrasonic waves in the air (m/s), d is the distance from the reflective object (m), and ToF is the ultrasonic round-trip measurement time.

Usually, ultrasound waves propagate at the speed of sound. The speed of sound traveling through air at 15 degrees Celsius is approximately 340 m/s. The speed of sound has nothing to do with the frequency of ultrasonic waves or atmospheric pressure, but only depends on the temperature of the air. The speed of sound changes with temperature because the density of air changes with temperature. Therefore, the lower the density or the higher the temperature, the easier the medium is to move, so the speed of sound increases. When air contains water vapor, the speed of sound changes, but the effect is smaller than that of temperature, so it is neglected.

The speed of sound in any medium other than air (including liquids and solids) also depends on temperature. In general, the speed of sound in a liquid is greater than the speed of sound in a gas, and the speed of sound in a solid is greater than the speed of sound in a liquid. When the humidity in the air is 0%, the formula for the propagation speed of sound is as shown in Equation (5) below.

[Formula 5]

here,

is the speed of sound (m/s) and T is the temperature in degrees Celsius (°C).

Depending on the application, for precise measurement, compensation for temperature and compensation for humidity are selectively applied to calculate and apply the sound velocity of the environment to be measured in real time.

In the present invention, (i) two zero-cross detectors having a 180° symmetrical structure for the upper and lower voltages of the reference voltage are applied in the ToF detection method for the ultrasonic reception signal, and (ii) the distance between the ultrasonic transmitter and the reflective object In (L), by selectively using a transmission frequency that satisfies the standing wave condition, the wave energy incident on the reflective object and the reflected wave energy are overlapped with each other and controlled to generate constructive interference or resonance, thereby increasing reception sensitivity. can improve.

[Equation 6]

Here, λ is the wavelength of the ultrasonic wave, L is the distance between the reflective object and the ultrasonic sensor, and n is an integer.

At this time, since the distance (L) is calculated based on the ToF value obtained by first measuring at a frequency of 40 kHz, it is the distance including the error within the resolution of 40 kHz, and various frequencies that satisfy the standing wave condition calculated with the distance (L) value. Among them, f0 selected as the closest frequency to 40 kHz also becomes a frequency that includes an error.

In order to improve the resolution of distance measurement, the standing wave frequency (f0) obtained by defining the distance (L) value as the reference distance (L_ref) and calculating the reference distance (L_ref) as a reference value as a method for minimizing such an error stochastically Compared to , the difference in phase when the ultrasonic signal transmitted from the transmitter reaches the position of the reference distance (L_ref) is ±10% (±36°) and ±20% (±72°) for the period, respectively, and f0 and The closest frequencies f1 to f4 are determined respectively.

Among the ToF obtained by sequentially transmitting and receiving 5 frequencies in a frequency range in which the phase angle of the ultrasonic wave reaching the reflective object is ±20% of the expected standing wave frequency, a range of frequencies with ideal standing wave conditions are stochastically included. Among them, the smallest ToF value was extracted and used as the most accurate distance information.

In addition, at the time of reception, five different phase angles pass through the zero-cross point based on the ultrasonic receiver of the ultrasonic sensor, so the resolution of ToF measurement due to the phase angle is secured to further improve the distance resolution. can also be used.

In this embodiment, the phase difference between the adjacent frequencies f1 to f4 is set in units of 10%, but the above-described phase difference may be set larger than 10%.

According to Equation 4, the condition of the standing wave corresponds to the case where the phase of the ultrasonic waves reaching the reflective object is 0° or 180°.

In order to interpret these conditions as a formula, the frequency at which the 40 kHz ultrasonic sensor can sufficiently transmit and receive sound pressure is defined within ±5 kHz from the center frequency of 40 kHz with a python program, and the measurement range of the measurement system was limited to 0.5 m to 2.0 m, and the frequency band was calculated.

7 is a diagram showing the code of a Python program for obtaining a fundamental frequency according to a distance. FIG. 8 is a diagram showing a result of 25% phase angle difference frequency calculation at a distance of 0.5 m by the code of the Python program of FIG. 7 .

7 and 8, after measuring a rough distance (L_ref) using the center frequency (fc) of the ultrasonic sensor, an initial frequency (f0) having a standing wave condition most similar to the center frequency for the approximate measured distance and the results of the python program for obtaining values of neighboring frequencies f1, f2, f3, and f4, which are adjacent to the initial frequency f0 and have different phases reaching the ultrasonic receiver of the ultrasonic sensor. In this embodiment, a set of pulse-echo frequencies was obtained using the program language Python.

As described above, the present invention proposes a distance measurement device using ultrasonic waves that is designed to measure respiration-related signals in a non-contact manner using ultrasonic waves and analyzes ultrasonic transmission and an ultrasonic receiving part of an ultrasonic sensor. In particular, by utilizing the relationship between the frequency of the ultrasonic wave used to detect the distance and the roughly measured distance, the center frequency satisfying the standing wave condition is predicted in the measurement space, and several frequency sets around the center frequency are generated, The resolution of the distance to be measured is improved by using the phase difference of several sets of frequencies with the same ToF while increasing the strength of the received signal and ensuring the best sound pressure by the ultrasonic sensor.

9 is a graph for explaining a received waveform for each frequency and a detection result by a zero-cross detector.

Referring to FIG. 9 , an initial frequency f0 and first to fourth adjacent frequencies f1 , f2 , f3 , and f4 sequentially transmitted are reflected by a reflective object and received. That is, the third adjacent frequency f3 precedes, and the first adjacent frequency f1, the initial frequency f0, the second adjacent frequency f2, and the fourth adjacent frequency f4 are sequentially received.

The positive detection unit of the zero-cross detector outputs a high-level detection signal at a time when the phase of each of the initial frequency f0 and the first to fourth adjacent frequencies f1, f2, f3, and f4 transitions from negative to positive, , outputs a low-level detection signal at the time of transition from positive to negative.

Specifically, the positive detection unit of the zero-cross detector outputs a high-level detection signal at a time when the phase of the third adjacent frequency f3 transitions from negative to positive, and the phase of the first adjacent frequency f1 changes from negative to positive. A high-level detection signal is output at the time of positive transition, and a high-level detection signal is output at the time of transition of the phase of the initial frequency f0 from negative to positive. In addition, the positive detection unit of the zero-cross detector outputs a high-level detection signal at a time when the phase of the second adjacent frequency f2 transitions from negative to positive, and the phase of the fourth adjacent frequency f4 changes from negative to positive. At the transition time, a high-level detection signal is output.

On the other hand, the negative detection unit of the zero-cross detector generates a low-level detection signal at a time when the phase of each of the initial frequency f0 and the first to fourth adjacent frequencies f1, f2, f3, and f4 transitions from negative to positive. output, and outputs a high-level detection signal at the time of transition from positive to negative.

Specifically, the negative detection unit of the zero-cross detector outputs a low-level detection signal at a time when the phase of the third adjacent frequency f3 transitions from negative to positive, and the phase of the first adjacent frequency f1 changes from negative to positive. A high-level detection signal is output at the time of positive transition, and a low-level detection signal is output at the time of transition of the phase of the initial frequency f0 from negative to positive. In addition, the negative detection unit of the zero-cross detector outputs a low-level detection signal at a time when the phase of the second adjacent frequency f2 transitions from negative to positive, and the phase of the fourth adjacent frequency f4 changes from negative to positive. At the transition time, a low-level detection signal is output.

Based on the distance (L), the initial frequency (f0) selected as the frequency closest to 40 kHz, the center frequency of the receiving sensor, while satisfying the standing wave condition calculated by the estimated distance, and the initial frequency (f0) based on arrival at the target First to fourth adjacent frequencies f1, f2, f3, and f4 are set by selecting a frequency most adjacent to the initial frequency f0 among frequencies having a difference of ±10% and ±20% of the wavelength of .

Then, by repeating the operation of sequentially transmitting and receiving the initial frequency f0 and the first to fourth adjacent frequencies f1, f2, f3, and f4, respectively, the positive detection unit and the negative detection unit of the zero-cross detector respectively receive Calculate precision distance based on ToFs.

Specifically, since two ToFs are measured according to transmission and reception of each of the initial frequency f0 and the first to fourth adjacent frequencies f1, f2, f3, and f4, a total of ten ToFs are measured.

As an example, the above precision distance may be calculated based on the smallest ToF among 10 ToFs.

As another example, the precise distance may be calculated based on an average value or a median value of 10 ToFs. Here, the median value is the average of the remaining values after removing the largest and smallest values.

As another example, among the 5 ToFs received from the positive detection unit of the zero-cross detector and the 5 ToFs received from the negative detection unit of the zero-cross detector, 5 valid ToFs are determined, and among the determined ToFs, the smallest value or average value, Based on the median value, the above precision distance can be calculated.

10A is a flowchart illustrating a method for measuring a distance using ultrasonic waves according to an embodiment of the present invention.

Referring to FIG. 10A, a PWM clock of an ultrasonic sensor, a reference frequency that is a frequency value having the best transmission and reception sensitivity among frequency characteristics of the ultrasonic sensor, and an transmission frequency range of the ultrasonic sensor are respectively set (step S100). Here, the reference frequency means a frequency value having the best transmission and reception sensitivity among frequency characteristics of the ultrasonic sensor.

Next, based on the PWM clock, reference frequency, and transmission frequency range set in step S100, an ultrasonic signal is transmitted to the reflective object and the ultrasonic signal reflected by the reflective object is received (step S200).

Subsequently, a standard approximate distance is obtained based on a time of flight (ToF) obtained using the ultrasonic waves of the reference frequency transmitted and reflected by the reflective object (step S300). Specifically, when measuring the total time (ToF, round-trip time) at the point at which the received ultrasonic signal, that is, the signal of the sine wave, reaches the point where the phase is ideally 0 degrees, that is, the zero-cross point, the distance information is obtained using the known speed of sound. will extract

Subsequently, an initial frequency f0 and adjacent frequencies f1, f2, f3, and f4 are calculated from the reference approximate distance (step S400).

FIG. 10B is a flowchart for explaining step S400 of FIG. 10A.

Referring to FIG. 10B , a frequency closest to the reference frequency within the transmission frequency range among the frequencies forming the standing wave condition is set as the initial frequency f0 (step S410).

Subsequently, adjacent frequencies f1, f2, f3, and f4 having phases of ±10% and ±20% based on the initial frequency f0 are acquired (step S420). Here, the first adjacent frequency f1 has a phase component of +10% compared to the phase component of the initial frequency f0, and the second adjacent frequency f2 has a phase component of -10% compared to the phase component of the initial frequency f0. has a phase component of In addition, the third adjacent frequency f3 has a phase component of +20% compared to the phase component of the initial frequency f0, and the fourth adjacent frequency f4 has a phase component of -20% compared to the phase component of the initial frequency f0. has a topological component. For example, if the phase of the initial frequency f0 is 360°, the phase of the first adjacent frequency f1 is approximately 396° (=360°+36°), and the phase of the second adjacent frequency f2 is approximately 324° (=360°-36°), the phase of the third adjacent frequency f3 is approximately 432° (=360°+72°), and the phase of the second adjacent frequency f2 is approximately 288° (= 360°-72°).

Referring to FIG. 10A again, the ultrasonic waves of the initial frequency f0 calculated in step S400 and the ultrasonic waves of the adjacent frequencies f1, f2, f3, and f4 are sequentially transmitted and the time-of-flight (ToF) of each of the ultrasonic waves measured ), a plurality of distances are calculated based on (step S500). Specifically, the initial distance is calculated based on the initial time-of-flight (ToF0) measured by transmitting ultrasonic waves of the initial frequency (f0). Subsequently, a first distance is calculated based on a first time-of-flight (ToF1) measured by transmitting an ultrasonic wave having a first adjacent frequency (f1). Subsequently, a second distance is calculated based on a second time-of-flight (ToF2) measured by transmitting ultrasonic waves of a second adjacent frequency (f2). Next, a third distance is calculated based on a third time-of-flight (ToF3) measured by transmitting ultrasonic waves of a third adjacent frequency (f3). Subsequently, a fourth distance is calculated based on a fourth time-of-flight (ToF4) measured by transmitting ultrasonic waves of a fourth adjacent frequency (f4).

Next, it is checked whether the calculation of the distances calculated in step S500 corresponds to an error condition (step S600). For example, when ToF is out of the measurement range or when the difference between ToF0 and ToF4 is out of the expected time difference due to the difference between f0 and f4, it is determined that it corresponds to an error condition. Here, ToF0 is calculated according to ultrasonic transmission and reception of the initial frequency f0, ToF1 is calculated according to ultrasonic transmission and reception of the first adjacent frequency f1, and ToF2 is calculated according to ultrasonic transmission of the second adjacent frequency f2. and reception, ToF3 is calculated according to ultrasonic transmission and reception of the third adjacent frequency f3, and ToF4 is calculated according to ultrasonic transmission and reception of the fourth adjacent frequency f4.

If it is checked that it is not an error condition in step S500, a precise distance is calculated based on the ToFs (step S700). For example, precise distance can be calculated using ToF corresponding to the first arriving signal. Alternatively, the ToF can be calculated as a precision distance using the smallest value. Alternatively, it can be calculated as a precision distance using the average of ToFs.

In general, when detecting a distance with ultrasound, if the frequency is low, the attenuation in the air is small, so it is detected far away, but the resolution of the distance is low because the wavelength of the frequency is long. On the other hand, if the frequency is high, the wavelength is short, so the resolution of the distance increases, but the attenuation in the air (or passing through a medium) is large, making it difficult to detect a long distance.

In order to solve this problem, the distance measurement using ultrasonic waves according to the present invention uses a low frequency and sequentially transmits several frequencies whose frequencies are slightly changed to slightly change the phase when arriving at a standing wave condition and a reflective object, Receive to obtain high distance resolution. Accordingly, it is possible to dramatically improve distance resolution when detecting a distance using ultrasonic waves.

In addition, unlike the generally known distance resolution (±1/2 of the period of the ultrasonic frequency) by the frequency of the ultrasonic wave, the present invention provides the phase between the received signal generated in the process of transmitting and receiving different frequencies of f0 to f4 for the same distance. By using two zero-cross detectors that react due to the difference, the resolution can be improved to ±1/20 of the period.

When the initial frequency (f0) is 1 (fini = 1), the adjacent frequencies are 4 (fside = 4), and the voltage comparator is 2 (Ncom = 2), the distance resolution of the distance measurement according to the frequency of the present invention is It is expressed by the following Equation (7).

[Formula 7]

On the other hand, the distance resolution of distance measurement according to the conventional frequency is

is expressed as

As a result, when there are 4 adjacent frequencies (fside = 4) and 2 voltage comparators (Ncom = 2), the distance resolution of the distance measurement according to the frequency of the present invention is

Calculated as described above, it is possible to improve the distance resolution by 10 times at the same frequency compared to the prior art.

If, in order to further improve the distance resolution, if fside = 8, that is, if 8 adjacent frequencies are used, the intervals of f1 to f8 are the values at ±10% and ±20% of the existing fside = 4. are assigned smaller ±5.55%, ±11.11%, ±16.67% and ±22.22%. In this case, the distance resolution of the distance measurement over frequency is

Calculated as described above, it is possible to improve the distance resolution by 18 times at the same frequency compared to the prior art.

The offset value of the frequency phase difference by the number of adjacent frequencies (fside) is implemented as Equation (8) below.

[Formula 8]

Offset phase calculation values for each adjacent frequency when the number of adjacent frequencies (fside) is 4 and the number of voltage comparators is 2, and offset phase for each adjacent frequency when the number of adjacent frequencies (fside) is 8 and the number of voltage comparators is 2 The calculated values are summarized in Table 1 below.

[Table 1]

As described above, according to the present invention, in order to improve the previously known ultrasonic distance measurement method, the distance resolution is improved by comparing both the upper limit and the lower limit of the zero-cross point of the received signal in terms of hardware.

In addition, in terms of the ToF detection method, the reception sensitivity due to constructive interference or resonance is improved by using a frequency set of f0 to f4 close to the standing wave condition for the roughly determined distance to the reflective object, and each frequency for the same distance We proposed a pulse-echo method that improves the distance resolution by measuring the received signal whose phase is dispersed by the zero-cross detection circuit.

Although the above has been described with reference to examples, those skilled in the art can variously modify and change the present invention without departing from the spirit and scope of the present invention described in the claims below. You will understand.

The method and apparatus for measuring distance using ultrasound according to the present invention can detect respiration at a remote location, so that non-contact biosignals can be smoothly acquired for improving medical services and providing convenience in treatment. In addition, the distance measuring method and apparatus using ultrasonic waves according to the present invention can be applied to an ultrasonic flowmeter such as a water level sensor, a distance measuring device for measuring precise distance, a non-destructive inspection device, a ToF camera, etc., and thus has industrial applicability.

<Description of codes>

100: distance measuring device 110: ultrasonic transmitter

120: ultrasonic receiving unit 130: sensor driving unit

310: setting module 320: acquisition module

330: calculation module 340: first distance calculation module

350: error check module 360: second distance calculation module

Claims (20)

1. In a distance measurement method using ultrasonic waves for measuring a distance between an ultrasonic sensor and a reflective object using ultrasonic waves transmitted from an ultrasonic sensor having an ultrasonic transmitter and an ultrasonic receiver,

   Setting each of a PWM clock of the ultrasonic sensor, a reference frequency that is a frequency value having the best transmission and reception sensitivity among frequency characteristics of the ultrasonic sensor, and a transmission frequency range of the ultrasonic sensor;

   Obtaining a standard approximate distance based on a time of flight (ToF) obtained by using ultrasonic waves of the reference frequency transmitted and reflected by a reflective object;

   calculating an initial frequency and adjacent frequencies from the reference approximation distance;

   Calculating a plurality of distances based on ToF of each of the ultrasonic waves measured by sequentially transmitting the ultrasonic wave of the initial frequency and the ultrasonic wave of each of the adjacent frequencies: and

   A distance measurement method using ultrasonic waves, comprising calculating a precise distance based on the ToFs.
2. The method of claim 1, wherein the value of the sound speed used in the step of acquiring the standard approximate distance based on the time of flight (ToF) is used after real-time compensation of temperature or real-time compensation of humidity. Distance measurement method using ultrasound.
3. The method of claim 1, wherein calculating the initial frequency and the adjacent frequencies from the reference approximate distance comprises:

   setting a frequency closest to the reference frequency within the transmission frequency range among frequencies constituting a condition of a standing wave as an initial frequency; and

   and calculating and obtaining at least one adjacent frequency having a different phase based on the initial frequency.
4. The method of claim 3, wherein the offset phase calculation value for each adjacent frequency is

   

   (Here, fside is the number of adjacent frequencies) Distance measuring method using ultrasound, characterized in that calculated by.
5. The method of claim 3, wherein when four adjacent frequencies are used, each of the adjacent frequencies has a phase of ±10% and ±20% based on the initial frequency.
6. The method of claim 3, wherein when eight adjacent frequencies are used, each of the adjacent frequencies has a phase of ±5.56%, ±11.11%, ±16.67%, and ±22.22% based on the initial frequency. A method for measuring distance using ultrasonic waves.
7. According to claim 1,

   checking whether the calculation of the distances corresponds to an error condition;

   feeding back to the step of acquiring the standard approximate distance if it is checked that the error condition is the case; and

   If it is checked that the error condition is not the case, calculating a precise distance based on the ToFs.
8. The method of claim 7, wherein the error condition is ToF out of a measurement range.
9. The method of claim 7, wherein the error condition includes a case in which the difference between ToF0 and ToF4 is out of a time difference expected from a difference between f0 and f4.
10. The method of claim 1, wherein calculating the precise distance based on the ToFs comprises determining a signal arriving first as the precise distance.
11. The method of claim 1, wherein calculating the precision distance based on the ToFs comprises determining a value with the smallest ToF as the precision distance.
12. The method of claim 1, wherein calculating the precision distance based on the ToFs comprises determining an average of the ToFs as the precision distance.
13. In a distance measuring device using ultrasonic waves for measuring a distance between an ultrasonic sensor and a reflective object using ultrasonic waves transmitted from an ultrasonic sensor having an ultrasonic transmitter and an ultrasonic receiver,

    a setting module configured to set each of a PWM clock of the ultrasonic sensor, a reference frequency that is a frequency value having the highest transmission and reception sensitivity among frequency characteristics of the ultrasonic sensor, and a transmission frequency range of the ultrasonic sensor;

    an acquisition module for acquiring a reference approximate distance based on a Time Of Flight (ToF) obtained by using ultrasonic waves of the reference frequency transmitted and reflected by a reflective object;

    a calculation module for calculating an initial frequency and adjacent frequencies from the reference approximation distance;

    a first distance calculation module for calculating a plurality of distances based on ToF of each of the ultrasonic waves measured by sequentially transmitting the calculated initial frequency ultrasonic waves and ultrasonic waves of adjacent frequencies; and

    A distance measuring device using ultrasound characterized in that it comprises a second distance calculation module that calculates a precise distance based on the ToFs.
14. The method of claim 13, wherein the calculation module,

    Among the frequencies constituting the condition of the standing wave, a frequency closest to the reference frequency within the transmission frequency range is set as an initial frequency;

    A distance measuring device using ultrasonic waves, characterized in that for obtaining one or more adjacent frequencies having different phases based on the initial frequency.
15. 15. The method of claim 14, wherein the offset phase calculation value for each adjacent frequency is

    

    (Here, fside is the number of adjacent frequencies) Distance measuring device using ultrasound, characterized in that calculated by.
16. 15. The distance measuring device using ultrasonic waves according to claim 14, wherein when four adjacent frequencies are used, each of the adjacent frequencies has a phase of ±10% and ±20% based on the initial frequency.
17. The method of claim 14, wherein when eight adjacent frequencies are used, each of the adjacent frequencies has a phase of ±5.56%, ±11.11%, ±16.67%, and ±22.22% based on the initial frequency. A distance measuring device using ultrasonic waves.
18. The method of claim 14, wherein the acquisition module,

    A distance measuring device using ultrasonic waves, characterized in that it comprises a zero-cross detector for determining the echo time by detecting a voltage as high as a specific offset voltage based on the reference voltage and a voltage as low as a specific offset voltage based on the reference voltage.
19. The method of claim 18, wherein the zero cross detector,

    a first resistor having one end connected to the power supply voltage and the other end to which a reference voltage is applied;

    a second resistor having one end connected to the reference voltage and the other end to which a ground voltage is applied;

    A positive terminal to which an ultrasonic reception signal is applied, a negative terminal connected to the first resistor to which a first voltage as high as a specific offset voltage based on the reference voltage is applied, and a size between the ultrasonic reception signal and the first voltage a first voltage comparator having an output terminal outputting a first output voltage according to comparison; and

    Between a positive terminal connected to the second resistor and applied with a second voltage lower than a specific offset voltage based on the reference voltage, a negative terminal to which the ultrasonic reception signal is applied, and the ultrasonic reception signal and the second voltage A distance measuring device using ultrasonic waves, characterized in that it comprises a second voltage comparator having an output terminal for outputting a second output voltage according to size comparison.
20. 14. The method of claim 13, further comprising an error check module that checks whether the calculation of the distances by the first distance calculation module corresponds to an error condition,

    The distance measuring device using ultrasonic waves, characterized in that the second distance calculation module calculates a precise distance based on the ToFs when it is checked that the error condition is not an error condition by the error check module.

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