WO2019188661A1

WO2019188661A1 - Ultrasonic distance measurement device and ultrasonic distance measurement method

Info

Publication number: WO2019188661A1
Application number: PCT/JP2019/011701
Authority: WO
Inventors: 米澤　良
Original assignee: 株式会社ブイ・テクノロジー
Priority date: 2018-03-29
Filing date: 2019-03-20
Publication date: 2019-10-03
Also published as: TWI783123B; CN111788456B; JP7040766B2; JP2019174381A; TW201942591A; CN111788456A

Abstract

The present invention is capable of highly accurate distance measurement. The present invention transmits ultrasound on the basis of a transmission signal in which the frequency becomes zero after a square wave having a fixed period and a first number of cycles from approximately 10 to 15, and receives ultrasound reflected by an object. The present invention measures the distance between a sensor and the object on the basis of the correlation between an ultrasound reception waveform received by the sensor and a template that is either a first waveform in which a second number of cycles less than the first number of cycles from the start of a base waveform that is a reception waveform under prescribed conditions are extracted or a second waveform resulting from multiplying the amplitude of the first waveform by a prescribed factor.

Description

Ultrasonic distance measuring device and ultrasonic distance measuring method

The present invention relates to an ultrasonic distance measuring device and an ultrasonic distance measuring method.

In Patent Document 1, an ultrasonic wave is transmitted from an ultrasonic sensor to an object, an ultrasonic wave reflected by the object is received again by the ultrasonic sensor, a delay time or a phase is measured from the received signal, and the delay An ultrasonic rangefinder is disclosed in which a moving average process or a weighted moving average process is performed on a measurement value of time or phase, and a distance between an ultrasonic sensor and an object is obtained based on the result.

JP 2005-291857 A

When the distance is obtained based on the result of performing the moving average process or the weighted moving average process on the received signal as in the invention described in Patent Document 1, generally, the distance is accurate to about ± 0.1 mm. Is said to be measurable. However, for example, when an inspection is performed by imaging the surface of a semiconductor substrate, an accuracy of about ± 0.1 mm is not sufficient, and it is required to measure the distance with higher accuracy.

The present invention has been made in view of such circumstances, and an object thereof is to provide an ultrasonic distance measuring device and an ultrasonic distance measuring method capable of measuring a distance with high accuracy.

In order to solve the above-described problem, an ultrasonic distance measuring device according to the present invention includes, for example, a sensor that transmits ultrasonic waves toward an object and receives ultrasonic waves reflected by the object; A signal processing unit that measures a distance between the sensor and the object based on a correlation between a received waveform of the ultrasonic wave received by the sensor and a template, the sensor having a constant cycle, and a cycle After a rectangular wave having a first cycle number of about 10 to 15 cycles, an ultrasonic wave is transmitted using a transmission signal having a frequency of 0, and the signal processing unit is the received waveform under a predetermined condition A template that holds, as the template, a first waveform obtained by extracting a basic waveform from the rising edge by a second cycle number less than the first cycle number, or a second waveform obtained by multiplying the amplitude of the first waveform by a predetermined amount. Characterized in that it has a holding portion.

According to the ultrasonic distance measuring device according to the present invention, after a rectangular wave having a constant cycle and a first cycle number of about 10 to 15 cycles, the frequency is increased based on a transmission signal having a frequency of 0. A sound wave is transmitted and an ultrasonic wave reflected by the object is received. Then, the first waveform obtained by extracting the reception waveform of the ultrasonic wave received by the sensor and the basic waveform (reception waveform under a predetermined condition) by the second cycle number (second cycle number <first cycle number) from the rising edge, or The distance between the sensor and the object is measured based on the correlation with the template that is the second waveform obtained by multiplying the amplitude of the first waveform by a predetermined value. In this way, a part of the received waveform under a predetermined condition is held in advance as a template, and the distance is measured with high accuracy by comparing the actual received waveform obtained by reflection from the measurement object with the template. be able to. In addition, after the rectangular wave having the first cycle number of about 10 to 15 cycles, the frequency is set to 0, so that the resonance of the sensor is stopped and the ultrasonic wave is transmitted and received by the same sensor, Distances can be measured to objects that are separated by a short distance (eg, 40 mm).

Here, the signal processing unit obtains a correlation value by subtracting the received waveform and the template and adding the absolute value of the difference, and when the correlation value is the smallest, the received waveform and the template are The rising time of the received waveform may be determined as coincident, and the distance between the sensor and the object may be measured based on the time. Thereby, the rising timing of the received waveform can be accurately known, and the distance can be measured with high accuracy.

Here, the signal processing unit may include a template adjustment unit that adjusts the amplitude of the template. Thereby, even if the amplitude of the received waveform changes due to conditions such as the distance to the object O, the correlation between the received waveform and the template can be obtained correctly.

Here, the template adjustment unit may adjust the amplitude of the template so that the peak value of the template matches the peak value of the received waveform. Thereby, even if the peak value of the received waveform, that is, the amplitude changes, the correlation between the received waveform and the template can be obtained correctly.

Here, the sensor may perform sampling at a frequency approximately 20 times the frequency of the first waveform. Thus, the distance with high accuracy (for example, when the frequency of the ultrasonic wave transmitted and received by the sensor is 300 kHz and the sampling frequency is 6 MHz, the resolution is 30 μm which is half of the ultrasonic wavelength 1/20 (one way)). Can be measured.

Here, a wavelength measurement object provided at a predetermined distance from the sensor is provided, and the signal processing unit transmits the ultrasonic wave from the sensor, and then transmits the transmitted ultrasonic wave to the wavelength measurement The wavelength of the ultrasonic wave transmitted from the sensor is obtained based on the time until it is reflected by the object to be received and received by the sensor and the predetermined distance, and the sensor is obtained based on the obtained wavelength. And the distance between the object and the object. The wavelength of the ultrasonic wave changes minutely when the temperature changes, but by obtaining the wavelength of the ultrasonic wave transmitted from the sensor and obtaining the distance based on the obtained wavelength, the distance can be accurately determined regardless of the temperature change. Can be measured.

Here, in the reception waveform, the signal processing unit determines that the reception waveform and the template are at a point where the reception waveform and the center line coincide with each other in the vicinity of the time point when the correlation between the reception waveform and the template is highest. The distance between the sensor and the object may be measured as coincident. Thereby, the distance can be measured with higher accuracy.

Here, the apparatus further includes a reflection plate, the sensor transmits ultrasonic waves obliquely toward the object, and the reflection plate transmits an ultrasonic path between the sensor and the reflection plate, and the reflection plate. The ultrasonic wave transmitted from the sensor and reflected by the object is reflected so that the ultrasonic path between the sensor and the sensor matches, and the signal processing unit includes the sensor, the reflector, The distance between the sensor and the object may be obtained based on the distance between the sensor and the incident angle of the ultrasonic wave transmitted from the sensor to the object. Thereby, the measurement accuracy of the distance between the sensor and the object can be further increased.

Here, the apparatus further includes a housing, the sensor includes a frame, the frame is provided with a metal weight, and an elastic member is provided between the frame and the housing. The elastic member may sandwich the frame. Thereby, the vibration of the sensor can be easily settled, and reception can be performed immediately after transmission.

In order to solve the above-described problem, the ultrasonic distance measuring method according to the present invention has a frequency of 0 after a rectangular wave having a constant cycle and a first cycle number of about 10 to 15 cycles. An ultrasonic wave is transmitted from the sensor using the transmission signal to be received, the ultrasonic wave reflected by the object is received by the sensor, the received waveform of the ultrasonic wave received by the sensor, a template held in advance, An ultrasonic distance measurement method for obtaining a distance based on a correlation between the ultrasonic wave, the ultrasonic wave transmitted from the sensor using the transmission signal under a predetermined condition, and the ultrasonic wave reflected by the object by the sensor. The first waveform extracted by the second number of cycles less than the first number of cycles from the rising of the reflected waveform of the received waveform of the ultrasonic wave received by the sensor, or the vibration of the first waveform The is characterized in that the predetermined multiple the template a second waveform. Thereby, the distance can be measured with high accuracy. Further, it is possible to measure the distance to an object separated by a short distance (for example, 40 mm) while performing transmission and reception of ultrasonic waves with the same sensor.

According to the present invention, the distance can be measured with high accuracy.

1 is a block diagram showing a schematic configuration of an ultrasonic distance measuring device 1 according to a first embodiment. 1 is a diagram illustrating an example of a circuit configuration of an ultrasonic sensor 10. FIG. It is a figure which shows typically the process of the received signal in the ultrasonic distance measuring device. It is an example of a basic waveform. This is an example of a template Ta having 9 cycles. It is an example of template Tb whose number of cycles is 4. The figure which shows an example of the correlation value which is a difference between the received waveform when the distance to the object O is 125 mm and the template T1a based on the template Ta with 9 cycles and adds the absolute value of the difference. It is. FIG. 8 is an enlarged view of the horizontal axis in the vicinity of the circle in FIG. 7 as a result shown in FIG. The figure which shows an example of the correlation value which is a result of adding the absolute value of the difference by subtracting the received waveform when the distance to the object O is 125 mm and the template T1b based on the template Tb having a cycle number of 4 It is. FIG. 10 is an enlarged view of the horizontal axis in the vicinity of the circle in FIG. 9 as a result shown in FIG. 9. It is a figure which shows the relationship between the received waveform and the template T1b based on the template Tb, and the rising part of the received waveform is enlarged and displayed. It is a figure which shows an example of the correlation value of a received waveform and template T1 when changing the magnification input from the template adjustment input part 22b, (A) is the magnification input from the template adjustment input part 22b from 1. It is an example of a correlation value when it is small, (B) is an example of a correlation value when the magnification input from the template adjustment input unit 22b is 1, and (C) is a magnification input from the template adjustment input unit 22b. It is an example of a correlation value when is larger than 1. It is a figure which shows an example of the autofocus apparatus 5 to which the ultrasonic distance measuring device 1 concerning this invention is applied. It is a figure which shows typically the relationship between the change of the distance h, and the change of the distance L, (A) shows the case where (theta) is 45 degree | times, (B) shows the case where (theta) is 0 degree | times. It is a figure which shows typically an example of the attachment structure of the ultrasonic sensor 10. It is a block diagram which shows schematic structure of the ultrasonic distance measuring device 2 which concerns on 2nd Embodiment. It is the figure which expanded and displayed the rising part of the received waveform in the horizontal direction. FIG. 18 is an enlarged view of the vicinity of a cross point β ′ of the received waveform shown in FIG. 17.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The present invention measures the distance from an object using ultrasonic waves. An ultrasonic wave is an elastic vibration wave (sound wave) having a high frequency that cannot be heard by the human ear, generally, a frequency exceeding 20 kHz, and higher than the audible range. Sounds that are not intended to be heard in are also included in the ultrasound.

<First Embodiment>
FIG. 1 is a block diagram showing a schematic configuration of an ultrasonic distance measuring apparatus 1 according to the first embodiment. The ultrasonic distance measuring device 1 mainly includes an ultrasonic sensor 10, an ultrasonic sensor driving unit 15, a signal processing unit 20, and an output unit 30.

The ultrasonic sensor 10 is electrically connected to a power source and vibrates when an electric signal is given to generate ultrasonic waves. The ultrasonic sensor 10 includes a sensor (transducer) 103 (see FIG. 2), transmits an ultrasonic wave toward the object O based on a transmission signal (detailed later), and is reflected by the object O. Receive ultrasound. In this embodiment, an ultrasonic wave having a frequency of 300 kHz is used. This frequency of ultrasonic waves is characterized by high directivity. However, the frequency of the ultrasonic wave used by the ultrasonic distance measuring device 1 is not limited to this.

The ultrasonic wave transmitted from the ultrasonic sensor 10 is reflected by the object O and reaches the ultrasonic sensor 10 (see the two-dot chain line in FIG. 1). That is, the ultrasonic waves reciprocate between the ultrasonic sensor 10 and the object O (double pass). The ultrasonic sensor 10 converts the ultrasonic wave received by the sensor 103 into an electric signal.

The ultrasonic sensor driving unit 15 mainly includes a high frequency driving circuit 16 and a high frequency generation logic unit 17. The high frequency drive circuit 16 includes a D / A converter 101a (see FIG. 2). The high-frequency generation logic unit 17 drives the high-frequency drive circuit 16 so as to apply a DC (frequency 0) signal after vibrating the D / A converter for about 10 to 15 cycles with a rectangular wave having a frequency of 300 kHz. The ultrasonic sensor driving unit 15 includes a switch 18 and switches whether the ultrasonic sensor 10 is connected to the ultrasonic sensor driving unit 15 (drive) or connected to the signal processing unit 20 (reception). .

FIG. 2 is a diagram illustrating an example of a circuit configuration of the ultrasonic sensor 10 and the ultrasonic sensor driving unit 15. The ultrasonic sensor 10 is a multi-channel sensor having a large number of sensors 103 (103a to 103h). The ultrasonic sensor driving unit 15 mainly includes a high frequency driving circuit 101, semiconductor relays 102 and 105, and a receiving circuit 104. Here, photo MOS relays are used for the semiconductor relays 102 and 105.

The high frequency drive circuit 101 includes a D / A converter 101a, a transformer 101b, and an amplifier 101c, and generates a transmission signal. The high frequency drive circuit 101 vibrates the D / A converter 101a with a rectangular wave having a frequency of 300 kHz for about 10 to 15 cycles, and then stops the vibration by applying a DC (frequency 0) signal. That is, the transmission signal has a constant period, and after a rectangular wave having a first cycle number of about 10 to 15 cycles (for example, in the present embodiment, the first cycle number is 15 cycles), This signal has a frequency of zero.

When the disable terminal of the amplifier 101c is set to enable, the transmission signal from the D / A converter 101a is input to the semiconductor relay 102 via the transformer 101b. The semiconductor relay 102 switches so that a large number of sensors 103 are sequentially driven and received. In FIG. 2, the sensor 103 has eight channels and includes eight sensors 103a to 103h, but the number of sensors 103 (number of channels) is not limited to this.

The semiconductor relay 102 sequentially drives and receives the sensor 103 approximately every 1 msec. For example, when a 20-channel sensor is sequentially driven and received approximately every 1 msec, distance measurement is performed in each channel of the sensor approximately every 20 msec.

When the sensor 103 is driven, an ultrasonic wave based on the transmission signal is transmitted from the sensor 103. In this embodiment, since the transmission signal includes 15 cycles of the rectangular wave, the sensor 103 outputs 15 cycles of ultrasonic waves having a frequency of 300 kHz. The transmission signal is a rectangular wave, but the ultrasonic wave output from the sensor 103 does not increase instantaneously and does not become a rectangular wave. The waveform of the ultrasonic wave actually output from the sensor 103 has a shape like a sine wave, and has a small amplitude close to 0 at first, and the amplitude gradually increases with time.

After outputting a rectangular wave having a frequency of 300 kHz for 15 cycles (for 15 clocks), a signal having a frequency of 0 is output for a certain time (for example, 10 clocks), thereby stopping the vibration of the vibrating sensor 103. Accordingly, the ultrasonic wave can be received by the sensor 103 immediately after the ultrasonic wave is transmitted from the sensor 103.

When a signal having a frequency of 0 is output, the amplifier 101c is disabled, a current is passed through the photoelectric element of the semiconductor relay 105 to turn on the semiconductor relay 105, and the sensor 103 is switched from the transmitting side to the receiving side (switch 18 (FIG. 1)).

When the sensor 103 is switched to the receiving side by the semiconductor relay 105, the ultrasonic wave received by the sensor 103 is output to the receiving circuit 104, and an electric signal is generated by the receiving circuit 104.

The receiving circuit 104 has a band-pass filter 104a that allows only a predetermined range of frequencies (including 300 kHz in this case) to pass. The signal that has passed through the bandpass filter 104a passes through the A / D converter 104b and is output to the signal processing unit 20 (see FIG. 1) as a received signal.

While the sensor 103 is being driven, the semiconductor relay 105 is turned off so that a large transmission signal does not enter the receiving circuit 104. Further, a limiter 104c is provided before and after the band pass filter 104a. This is to prevent the sensor 103 from resonating at 300 kHz when the semiconductor relay 105 is turned on, and to prevent a large signal from entering the amplifier or the A / D converter 104b. As the limiter 104c, a Schottky barrier diode having a forward voltage as small as about 0.3V is used.

Returning to the explanation of FIG. The signal processing unit 20 receives the reception signal output from the ultrasonic sensor 10. The signal processing unit 20 mainly includes a template holding unit 21, a template adjustment unit 22, a correlation calculation unit 23, a distance calculation unit 24, and a temperature correction unit 25.

The template holding unit 21 holds a template. The template adjustment unit 22 adjusts the amplitude of the template held by the template holding unit 21. The correlation calculation unit 23 obtains a correlation between the received signal and the template held by the template holding unit 21 or the template whose amplitude is adjusted by the template adjustment unit 22.

FIG. 3 is a diagram schematically illustrating received signal processing in the ultrasonic distance measuring apparatus 1. The ultrasonic wave received by the sensor 103 is converted into a reception signal by the reception circuit 104 and input to the correlation calculation unit 23. The reception circuit 104 outputs a 6 MHz clock signal and continuously generates a reception signal. 6 MHz is 20 times the frequency of ultrasonic waves 300 kHz received by the sensor 103. That is, the reception circuit 104 acquires a reception signal 20 times during one period of the received ultrasonic wave (20 times oversampling). In the reception circuit 104, a plurality of reception signals obtained continuously are connected to generate a reception waveform.

The reception waveform generated by the reception circuit 104 is input to the shift register 231 of the correlation calculation unit 23. Thereby, the correlation calculation part 23 acquires the received waveform by ultrasonic reception of a fixed period. 3, the shift register 231 has 80 D flip-flops 231-1, 231-2, 231-3,... 231-80. 80 means 20 times oversampling (detailed later) × 4 cycles, which matches the number of templates T recorded in the template holding unit 21 (detailed later). When the A / D converter 104b digitizes an analog signal with a resolution of 16 bits, each of the D flip-flops 231-1 to 231-80 includes 16 D flip-flops.

One D flip-flop 231-1 to 231-80 holds an ultrasonic reception result (reception level) for one clock. Here, the reception level is a value obtained by A / D converting the reception signal for one clock. When the next reception level is input from the A / D converter 104b of the reception circuit 104 to the shift register 231, the reception level held in the shift register 231 is forwarded to the right (for example, held in the D flip-flop 231-1). The received reception level is sent to the D flip-flop 231-2), and the new reception level input from the reception circuit 104 is held in the shift register 231. Thus, the shift register 231 holds the reception level having the same length as the template T.

The template holding unit 21 holds the template T. The template T consists of template level information for 80 clocks. The template level information is a value of each clock when A / D conversion is performed for 80 rising portions of a standard received waveform (basic waveform). The template level information is read from the template holding unit 21 to the correlation calculating unit 23 and held in the shift register 232. Similarly to the shift register 231, the shift register 232 has 80 D flip-flops 232-1 to 232-80, and the shift register 232 holds template level information for 80 clocks. When each of the D flip-flops 231-1 to 231-80 includes 16 D flip-flops, each of the D flip-flops 232-1 to 232-80 also includes 16 D flip-flops.

Here, the template T will be described. The template is obtained by extracting a basic waveform, which is a received waveform under a predetermined condition, from the rising edge by several cycles (however, less than the number of transmitted ultrasonic cycles). The basic waveform includes a waveform including sensor reverberation immediately after transmission (for example, a waveform when the distance to the object O is about 40 mm), and a waveform with a small value and a low S / N ratio (for example, the object O). 4), and a clean waveform as shown in FIG.

FIG. 4 is an example of a basic waveform. Here, the basic waveform is acquired assuming that the distance to the object O is 75 mm under the predetermined condition. The horizontal axis in FIG. 4 is the number of clocks (that is, time). The basic waveform is divided into a region A having a high peak value and a region B having a low peak value thereafter. Region A is a period in which ultrasonic waves transmitted mainly by 15 cycles of rectangular waves are received. The resonance frequency of the region A is 300 kHz (same as the frequency of the transmitted ultrasonic wave), and the period of the basic waveform in the region A is substantially the same as the period of the rectangular wave of the transmission signal. In the region A, the amplitude reaches a peak in about nine cycles from the rising edge. On the other hand, the resonance frequency of the region B depends on the sensor 103 and is slightly different from 300 kHz. That is, the period of the basic waveform in region B is slightly different from the period of the rectangular wave of the transmission signal.

The received waveform varies depending on conditions such as the distance to the object O, the variation of the sensor 103, the cable length from the sensor 103, and the like. However, only the amplitude (width in the height direction) of the received waveform changes as a whole with respect to the basic waveform, and the characteristics of the waveform do not change due to a change in conditions due to a change in distance to the object O or the like. For example, when the distance to the object O becomes longer than 75 mm, the received waveform shifts to the rear side of the position of the basic waveform shown in FIG. 4, and the amplitude is generally smaller than that of the basic waveform shown in FIG. However, region A and region B have a resonance frequency of 300 kHz, but region B does not have a resonance frequency of 300 kHz (varies depending on conditions), and region A has an amplitude of about 9 cycles from the rise. Reaching the peak does not change.

Therefore, in the present invention, the rising portion of the basic waveform (a part of the region A) is held in advance as a template, and the actual received waveform is compared with the template, so that the rising portion of the actual received waveform, that is, the object O Find the distance to exactly.

5 and 6 show examples of the template T in which the rising portion of the received waveform shown in FIG. 4 is extracted. FIG. 5 is an example of a template Ta with a cycle number of 9, and FIG. 6 is an example of a template Tb with a cycle number of 4. Nine cycles is the number of cycles until the received waveform rises and reaches the peak value, and 4 cycles is about half the number of cycles until the received waveform rises and reaches the peak value. However, the number of cycles extracted as a template from the rising edge of the received waveform acquired in advance may be smaller than the number of cycles included in the transmission signal (here, 15 cycles), and is not limited to 4 cycles or 9 cycles.

Note that the template holding unit 21 holds one template T, which may be the template Ta or the template Tb, but does not hold both the templates Ta and Tb.

Returning to the explanation of FIG. The template adjustment unit 22 multiplies the amplitude of the template T by a predetermined amount, and mainly includes a peak hold circuit 22a and a template adjustment input unit 22b used by the user to adjust the magnification of the template T.

The peak hold circuit 22a holds the peak value of the received waveform held in the last D flip-flop 231-80. The template adjustment input unit 22b can change the magnification in 10 stages from “0” to “9”, and when the template adjustment input unit 22b is set to “5” (“5” is an example). The magnification is configured to be 1.

The template adjustment unit 22 holds the peak hold circuit 22a when no change in magnification is input from the template adjustment input unit 22b (here, the template adjustment input unit 22b is set to “5”). The peak value is output to the correlation calculation unit 23. That is, the template adjustment unit 22 adjusts the amplitude of the template T (the value of the template level information) so that the peak value when the template T is obtained matches the peak value of the received signal.

Further, when a change in magnification is input from the template adjustment input unit 22b, the template adjustment unit 22 multiplies the peak value held by the peak hold circuit 22a by the magnification input by the template adjustment input unit 22b. It outputs to the correlation calculation part 23.

The correlation calculation unit 23 obtains a correlation between the received waveform and the template T (or template T1). Here, the received level held in each D flip-flop 231-1 to 231-80 of the shift register 231 and the template level information held in each D flip-flop 232-1 to 232-80 of the shift register 232 are used as templates. Correlation with the level information of the template T1 multiplied by the magnification input from the adjustment unit 22 is obtained. The template T1 is obtained by multiplying the amplitude of the template T by a predetermined value. When the predetermined multiple is 1, the template T and the template T1 are the same.

In the present embodiment, the received waveform and the template T1 are differentiated, and a correlation value that is a result of adding the absolute values of the differences is obtained, and it is assumed that the received waveform and the template T1 match when the correlation value is the smallest. . However, instead of adding the absolute value of the difference between the received waveform and the template T1, the correlation value may be obtained using a value obtained by squaring the difference between the received waveform and the template T1.

FIG. 7 shows a correlation value obtained by subtracting the received waveform when the distance to the object O is 125 mm and the template T1a based on the template Ta having 9 cycles and adding the absolute value of the difference. It is a figure which shows an example. In FIG. 7, the horizontal axis represents time, and the vertical axis represents the correlation value. It can be seen that the received waveform matches the template T1a at the position where the correlation value is the smallest (see the circle in FIG. 7) or is closest to the match.

FIG. 8 is an enlarged view of the horizontal axis in the vicinity of the circle in FIG. 7 of the result shown in FIG. The points in FIG. 8 indicate the timing at which the reception circuit 104 oversamples 20 times. Three points with small correlation values (see circles in FIG. 8) are arranged, and the correlation value is the smallest at the central point α among them. As a result, it can be seen that the received waveform matches the template T1a at the timing of the point α.

FIG. 9 shows a correlation value that is a result of adding the absolute value of the difference between the received waveform when the distance to the object O is 125 mm and the template T1b based on the template Tb having a cycle number of 4. It is a figure which shows an example. In FIG. 9, the horizontal axis represents time, and the vertical axis represents the correlation value. It can be seen that the received waveform matches the template T1b at the position where the correlation value is the smallest (see the circle in FIG. 9) or is closest to the match.

FIG. 10 is an enlarged view of the horizontal axis in the vicinity of the circle in FIG. 9 of the result shown in FIG. The points in FIG. 10 indicate the timing at which the reception circuit 104 oversamples 20 times. It can be seen that the correlation value is the smallest at the timing of point β, and the received waveform matches the template T1b.

Thus, the correlation calculation unit 23 calculates when the received signal and the template T1 are the best match. In the example shown in FIG. 9, the ninth cycle of the received waveform is finished at the timing of the point α, and in the example shown in FIG. 10, the fourth cycle of the received waveform is finished at the timing of the point β.

Returning to the explanation of FIG. The distance calculation unit 24 calculates the distance between the ultrasonic sensor 10 and the object O based on the result calculated by the correlation calculation unit 23. FIG. 11 is a diagram showing the relationship between the received waveform and the template T1b based on the template Tb. The rising portion of the received waveform is enlarged and displayed.

At the timing of point β, the received waveform matches the end of template T1b (fourth cycle). The received waveform and the template T1b are overlapped so that the end of the template T1b is positioned at the point β, and the point γ where the outline of the template T1b (see the dotted line in FIG. 1) intersects is set as the rising edge of the received waveform. The timing of rising is accurately known. The distance calculation unit 24 assumes that the reception of the ultrasonic wave is started at the rising edge (point γ) of the received waveform thus obtained, and represents the rising time as the number of oversampling (here, as shown in Expression (1)). Then, dividing by 20) and integrating 0.57 mm (= 1.13 mm / 2) which is half of the wavelength of the transmitted ultrasonic wave (300 kHz in this case) (because it is a double path), the ultrasonic sensor 10 and The distance from the object O is calculated.

[Equation 1]
Reciprocal distance = timing of point γ / 20 × 0.57 mm (1)

However, the received waveform and the template T1 may not match well due to variations in measurement conditions such as the distance between the ultrasonic sensor 10 and the object O. The reason why the received waveform and the template T1 do not match well is, for example, that the resonance frequency of the sensor 103 is greatly deviated from 300 kHz, that the cable length to the sensor 103 is long and the series resistance is large, and the distance to the object O. May be close to 40 mm, and vibration during excitation may interfere with the reflected wave. In such a case, the template T1 is tuned by inputting the magnification via the template adjustment input unit 22b shown in FIG.

FIG. 12 is a diagram illustrating an example of the correlation value between the received waveform and the template T1 when the magnification input from the template adjustment input unit 22b is changed. FIG. 12A is input from the template adjustment input unit 22b. This is an example of a correlation value when the magnification is smaller than 1 (here, the setting of the template adjustment input unit 22b is “1”), and (B) is when the magnification input from the template adjustment input unit 22b is 1 (here Is an example of a correlation value in which the setting of the template adjustment input unit 22b is “5”), and (C) is a case where the magnification input from the template adjustment input unit 22b is greater than 1 (here, the template adjustment input unit 22b). Is an example of a correlation value of “9”).

In the cases shown in FIGS. 12A and 12C, two low-value points are present side by side in the correlation value waveform, and the waveform of the correlation value is a so-called “double bottom”. On the other hand, in the case shown in FIG. 12B, there is only one point having a low value in the waveform of the correlation value, and the waveform of the correlation value is a so-called “single bottom”.

The waveform of the correlation value changes by changing the magnification applied to the amplitude of the template T in this way. Accordingly, when the waveform of the correlation value is a so-called “double bottom”, the magnification input via the template adjustment input unit 22b is changed to make the waveform of the correlation value a so-called “single bottom”. Thereby, when the correlation value is the smallest, that is, the timing when the received waveform and the template T1 are in good agreement or closest to each other can be obtained.

Returning to the explanation of FIG. The temperature correction unit 25 corrects the wavelength change of the ultrasonic wave due to the temperature change. The wavelength of the ultrasonic wave changes minutely as the temperature changes. In order to obtain the distance with high accuracy, the temperature correction unit 25 obtains the wavelength of the ultrasonic wave actually transmitted / received by the ultrasonic sensor 10, and the distance calculation unit 24 obtains the distance using the wavelength obtained by the temperature correction unit 25. Ask.

For example, the temperature correction unit 25 may include a thermometer that measures the temperature, and obtain the wavelength of the ultrasonic wave at the temperature measured by the thermometer based on information indicating the relationship between the temperature and the wavelength.

For example, the temperature correction unit 25 may calculate the wavelength of the ultrasonic wave actually transmitted from the ultrasonic sensor 10. In this case, an ultrasonic wave is transmitted using one of a plurality of sensors 103 (see FIG. 2), and is a wavelength measurement target provided at a predetermined distance (referred to as distance D) from the sensor 103. The ultrasonic wave reflected by the object is received using the same sensor 103. The correlation calculation unit 23 and the distance calculation unit 24 measure a time t from when the ultrasonic wave is transmitted from the sensor 103, reflected by the wavelength measurement target unit and received by the sensor 103, and the temperature correction unit 25 Based on t and the distance D, the wavelength of the ultrasonic wave transmitted from the ultrasonic sensor 10 can be obtained. The correlation calculation unit 23 and the distance calculation unit 24 can measure the distance more accurately by obtaining the distance to the object O based on the wavelength calculated by the temperature correction unit 25.

The output unit 30 outputs the distance obtained by the distance calculation unit 24 to an external device such as a display device. The display device is a known general display device, and displays the output distance.

Note that the configuration of the ultrasonic distance measuring device 1 shown in FIG. 1 has described the main configuration in describing the features of the present embodiment, and does not exclude, for example, the configuration of a general information processing device. . Further, the functional configuration shown in FIG. 1 is classified for easy understanding of the configuration of the ultrasonic distance measuring device 1, and the classification method and names of the constituent elements are not limited to the form shown in FIG. The configuration of the ultrasonic distance measuring device 1 may be classified into more components according to the processing content, or one component may execute processing of a plurality of components.

FIG. 13 is a diagram showing an example of the autofocus device 5 including the ultrasonic distance measuring device 1 according to the present invention. The autofocus device 5 is a form of an ultrasonic distance measuring device.

The autofocus device 5 mainly includes an ultrasonic distance measuring device 1 (ultrasonic sensor 10, signal processing unit 20 (not shown in FIG. 13) and output unit 30 (not shown in FIG. 13)), a reflecting plate 51, An imaging device 52. The ultrasonic sensor 10 transmits ultrasonic waves obliquely toward the object O, receives the ultrasonic waves reflected by the reflecting plate 51 and reflected by the object O.

In the reflection plate 51, the ultrasonic path between the ultrasonic sensor 10 and the reflection plate 51 coincides with the ultrasonic path between the reflection plate 51 and the ultrasonic sensor 10 (see the arrow in FIG. 13). Provided in position.

Based on the distance between the ultrasonic sensor 10 and the reflection plate 51 and the incident angle θ of the ultrasonic wave transmitted from the ultrasonic sensor 10 to the object O, the signal processing unit 20 is connected to the ultrasonic sensor 10 and the object O. The distance h is obtained.

The output unit 30 outputs the measured distance h to the imaging device 52. The imaging device 52 performs a focusing process based on the distance h. Since the focusing process is known, the description thereof is omitted.

In the autofocus device 5, ultrasonic waves are transmitted obliquely toward the object O, and the ultrasonic waves reciprocate between the ultrasonic sensor 10 and the reflection plate 51 (double path), and therefore the ultrasonic sensor 10 and the reflection plate 51. The change in the distance h when the distance L is changed to L / 2 × cos θ, and the change in the distance h is significantly smaller than the change in the distance L. For example, if θ is 45 degrees, the change Δh in the distance h when the distance L changes by ΔL is Δh = ΔL / 2 × 1 / √2, and ΔL is approximately 2.8 times Δh (ΔL = 2 × √2 × Δh). Therefore, the measurement accuracy of the distance h is higher than the measurement accuracy of the distance L.

FIG. 14 is a diagram schematically showing the relationship between the change in the distance h and the change in the distance L. (A) shows the case where θ is 45 degrees, and (B) shows the case where θ is 0 degrees. . Surfaces O1, O2, and O3 are surfaces of the object O, and the position of the surface O1 indicates a case where the distance between the ultrasonic sensor 10 and the object O is a distance h, and the position of the surface O2 is an ultrasonic wave. The case where the distance between the sensor 10 and the object O is a distance h + Δh is shown, and the position of the surface O3 shows the case where the distance between the ultrasonic sensor 10 and the object O is a distance h + Δ2h. In FIG. 14, the ultrasonic path is indicated by a two-dot chain line.

14A, the distances to the surfaces O1, O2, and O3 are calculated from the distances between the ultrasonic sensor 10 and the reflection plate 53. When the distance h changes by Δh, the distance from the ultrasonic sensor 10 to the reflecting plate 53 changes by 2 × √2 × Δh. On the other hand, in FIG. 14B, since the distances to the surfaces O1, O2, and O3 are directly measured, if the distance h from the ultrasonic sensor 10 is changed by Δh, the ultrasonic path is 2 (reciprocal). It changes by ΔΔh. Therefore, in the case shown in FIG. 14A, the distance can be obtained more finely by √2 times than in the case shown in FIG.

According to the present embodiment, a part of an actual reception waveform under a predetermined condition is held in advance as a template T, and the reception waveform based on the ultrasonic wave reflected by the object O, the template T (template T1), Since the distance is obtained based on the correlation, the distance can be measured with high accuracy.

In addition, according to the present embodiment, since the template adjustment unit 22 that adjusts the amplitude of the template T is provided, even if the amplitude of the received waveform changes due to a change in measurement conditions such as the distance to the object O, the received waveform And the template T can be correctly obtained. Therefore, the distance to the object O can be accurately measured regardless of changes in the measurement conditions.

Further, according to the present embodiment, the frequency of the ultrasonic wave transmitted and received from the ultrasonic sensor 10 is set to 300 kHz, and the sampling frequency of the received signal is set to 6 MHz (one cycle of 300 kHz ultrasonic wave is sampled 20 times). The distance can be measured with a high accuracy of 30 μm as determined by the following mathematical formula (2). Here, 0.6 mm is an approximate value of 0.57 mm, which is half of the wavelength λ = 1.13 mm of the ultrasonic wave of 300 kHz (because of the double pass).

[Equation 2]
0.6 mm / 20 = 0.03 mm (= 30 μm) (2)

Further, according to the present embodiment, the ultrasonic sensor 10 transmits and receives ultrasonic waves, and performs double-pass measurement (reciprocal measurement) in which the ultrasonic waves reciprocate between the ultrasonic sensor 10 and the object O. The influence of the wind speed in the ultrasonic path can be eliminated, and the distance to the object O can be accurately measured.

By applying a DC (frequency 0) signal after oscillating the D / A converter for about 10 to 15 cycles with a rectangular wave with a frequency of 300 kHz, the sensor 103 is braked to stop the shaking of the sensor 103. it can. As a result, it is possible to receive the ultrasonic wave at the sensor 103 immediately after transmitting the ultrasonic wave from the sensor 103. Therefore, it is possible to measure a short distance (for example, 40 mm) while performing transmission and reception of ultrasonic waves with the same sensor 103.

In the present embodiment, the received signal is acquired at 20 times the frequency of the received ultrasonic wave of 300 kHz. However, if the received signal is acquired (oversampling) at a frequency of about 10 times or higher than the received ultrasonic wave. Good. However, the oversampling number is preferably an integer multiple.

In the present embodiment, the signal processing unit 20 includes the template adjustment unit 22, but the template adjustment unit 22 is not essential. For example, when the ultrasonic distance measuring device 1 is applied to the autofocus device 5, the amount of change in the distance between the ultrasonic sensor 10 and the object O is very small, and the peak value of the received waveform hardly changes. Therefore, in such a case, the template adjustment unit 22 is unnecessary, and the template holding unit 21 may create the template T using the received waveform at the time of focusing and hold it.

Further, in this embodiment, the shaking of the sensor 103 is stopped by applying a DC (frequency 0) signal after a rectangular wave of about 10 to 15 cycles, but an ultrasonic sensor having the sensor 103 inside By devising the attachment of 10, it is possible to further suppress the vibration of the ultrasonic sensor 10. FIG. 15 is a diagram schematically illustrating an example of the attachment structure of the ultrasonic sensor 10.

The ultrasonic sensor 10 has a frame 10a. An elastic member 111 (for example, an O-ring) is provided between the casing 113 and the frame body 10a, and the ultrasonic sensor 10 is provided inside the casing 113 by the elastic member 111 being elastically deformed. In other words, the ultrasonic sensor 10 is held by the elastic member 111. The elastic member 111 contacts the side surface 10c adjacent to the surface 10b on which the vibration surface of the sensor 103 is provided.

When the sensor 103 transmits an ultrasonic wave, the sensor 103 shakes back and forth due to a reaction when the air is vibrated, and the vibration of the ultrasonic sensor 10 is difficult to be settled. A metal weight is provided on the frame body 10a so that the vibration of the ultrasonic sensor 10 is easily settled. Here, as a weight, a lead sheet 112 which is a sheet-like member formed of lead is used, and the lead sheet 112 coated with an adhesive is wound around the side surface 10c. As the adhesive, an adhesive having elasticity (for example, a modified silicone resin-based adhesive such as an acrylic modified silicone resin) is used. Thereby, vibration energy can be efficiently converted into heat, and switching between transmission and reception is accelerated. Therefore, it is possible to receive an ultrasonic wave immediately after transmitting an ultrasonic wave from the sensor 103, that is, to measure a short distance (for example, 40 mm).

<Second Embodiment>
In the first embodiment of the present invention, when the correlation value is the smallest, the received waveform and the template T1 coincide with each other, or the distance to the object O is determined as being closest to each other. The method for obtaining the distance is not limited to this.

In the second embodiment of the present invention, the distance to the object O is assumed that the received waveform and the template T1 coincide with each other at the point where the received waveform coincides with the center line, that is, the so-called cross point, or the closest match. This is the desired form. Hereinafter, the ultrasonic distance measuring device 2 according to the second embodiment will be described. In addition, about the part same as the ultrasonic distance measuring device 1 concerning 1st Embodiment, the same code | symbol is attached | subjected and description is abbreviate | omitted.

FIG. 16 is a block diagram showing a schematic configuration of the ultrasonic distance measuring apparatus 2 according to the second embodiment. The ultrasonic distance measuring device 1 mainly includes an ultrasonic sensor 10, a signal processing unit 20A, and an output unit 30.

The signal processing unit 20A mainly includes a template holding unit 21, a template adjustment unit 22, a correlation calculation unit 23, a distance calculation unit 24A, and a temperature correction unit 25.

The distance calculation unit 24A calculates a cross point based on the result calculated by the correlation calculation unit 23, and calculates the distance between the ultrasonic sensor 10 and the object O based on the cross point. FIG. 17 is a diagram in which the rising portion of the received waveform is displayed in an enlarged manner in the horizontal direction.

The point β in FIG. 17 is the point with the smallest correlation value in FIGS. Point β1 is a measurement point at the timing next to point β. The cross point β ′ is located between the point β and the point β1, and is a cross point in the vicinity of the point β (at the time when the correlation value is the smallest). In the second embodiment, it is assumed that the received waveform coincides with the end of the template T1 at the cross point β ′ where the received waveform coincides with the center line.

FIG. 18 is an enlarged view of the vicinity of the cross point β ′ of the received waveform shown in FIG. The distance in the height direction between the point β and the cross point β ′ is a, the distance in the height direction between the point β ′ and the point β1 is b, and the lateral distance between the point β and the cross point β ′ is a1. Assuming that the horizontal distance between the point β ′ and the point β1 is b1, a: b = a1: b1, and the distance a1 is calculated using the following equation (3). Here, 30 μm is 1/20 (the number of oversampling) of half of the wavelength of 300 kHz ultrasonic waves (because of the double path), and corresponds to half of the wavelength of ultrasonic waves of 6 MHz.

[Equation 3]
1/6 MHz = 30 μm × a / (a + b) (3)

The distance calculating unit 24 assumes that the received waveform rises at a position where the end of the received waveform and the template T1 coincide with each other at the timing of the cross point β ′ and the outline of the template T1 intersects. Then, the distance calculation unit 24 assumes that the reception of the ultrasonic wave is started at the position where the reception waveform obtained in this way rises, and calculates the distance between the ultrasonic sensor 10 and the object O as shown in Equation (4). calculate.

[Equation 4]
Round trip distance = (Timing of point β / 20 + distance a1) × 1.13 mm (4)

According to the present embodiment, since the distance is obtained based on the cross point, the distance can be measured with higher accuracy.

The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and design changes and the like within a scope not departing from the gist of the present invention are included. .

In the present invention, “substantially” is a concept that includes not only exactly the same but also errors and deformations that do not lose the identity. For example, “substantially coincidence” is not limited to the case of exact coincidence. Further, for example, in the case where the expression is simply vertical, coincidence, etc., not only strictly vertical, coincidence, but also the case of substantially vertical, substantially coincidence, etc. is included. Further, in the present invention, the “neighborhood” is a concept indicating that when it is in the vicinity of A, for example, it is near A and may or may not include A.

1, 2: Ultrasonic distance measuring device 5: Autofocus device 10: Ultrasonic sensor 10a: Frame 10b: Surface 10c:

Side surface

20, 20A: Signal processing unit 21: Template holding unit 22: Template adjustment unit 22a: Peak hold Circuit 22b: Template adjustment input unit 23:

Correlation calculation unit

24, 24A: Distance calculation unit 25: Temperature correction unit 30: Output unit 51: Reflecting plate 52: Imaging device 101: High frequency drive circuit 101a: D / A converter 101b: Transformer 101c: amplifier 102, 105: semiconductor relay 103: sensor 104: receiving circuit 104a: band-pass filter 104b: A / D converter 111: elastic member 112: lead sheet 113: housings 231, 232: shift registers 231-1 to 231 80,232-1 ~ 232-80: D flip-flop

Claims

A sensor for transmitting an ultrasonic wave toward an object and receiving an ultrasonic wave reflected by the object;
A signal processing unit for measuring a distance between the sensor and the object based on a correlation between a received waveform of the ultrasonic wave received by the sensor and a template;
With
The sensor transmits an ultrasonic wave using a transmission signal having a frequency of 0 after a rectangular wave having a constant period and a first cycle number of about 10 to 15 cycles,
The signal processing unit is a first waveform obtained by extracting the basic waveform, which is the received waveform under a predetermined condition, by a second number of cycles less than the first number of cycles from the rising edge, or a predetermined multiple of the amplitude of the first waveform. An ultrasonic distance measuring device comprising a template holding unit for holding a second waveform as the template.
The signal processing unit calculates the correlation value by subtracting the received waveform from the template and adding the absolute value of the difference, and the received waveform and the template match when the correlation value is the smallest. The ultrasonic distance measuring apparatus according to claim 1, wherein a rising time of the received waveform is obtained and a distance between the sensor and the object is measured based on the time.
The ultrasonic distance measuring device according to claim 1, wherein the signal processing unit includes a template adjustment unit that adjusts an amplitude of the template.
The ultrasonic distance measuring device according to claim 3, wherein the template adjustment unit adjusts the amplitude of the template so that a peak value of the template matches a peak value of the received waveform.
The ultrasonic distance measuring device according to any one of claims 1 to 4, wherein the sensor performs sampling at a frequency that is approximately 20 times the frequency of the first waveform.
A wavelength measuring object provided at a predetermined distance from the sensor;
The signal processing unit includes a time from when the ultrasonic wave is transmitted from the sensor to when the transmitted ultrasonic wave is reflected by the wavelength measurement object and received by the sensor, and the predetermined distance. The wavelength of the ultrasonic wave transmitted from the sensor is obtained based on the above, and the distance between the sensor and the object is obtained based on the obtained wavelength. The ultrasonic distance measuring device according to item.
In the received waveform, the signal processing unit assumes that the received waveform and the template coincide with each other at a point where the received waveform and the center line coincide with each other in the vicinity of the time when the correlation between the received waveform and the template is highest. The ultrasonic distance measuring device according to any one of claims 1 to 6, wherein a distance between the sensor and the object is measured.
Further comprising a reflector,
The sensor transmits ultrasonic waves obliquely toward the object,
The reflector is transmitted from the sensor so that an ultrasonic path between the sensor and the reflector coincides with an ultrasonic path between the reflector and the sensor, and the object Reflects the ultrasonic waves reflected by
The signal processing unit obtains a distance between the sensor and the object based on a distance between the sensor and the reflector and an incident angle of an ultrasonic wave transmitted from the sensor to the object. The ultrasonic distance measuring device according to any one of claims 1 to 7.
A housing,
The sensor has a frame,
The frame body is provided with a metal weight,
The ultrasonic distance according to any one of claims 1 to 8, wherein an elastic member is provided between the frame and the housing, and the elastic member sandwiches the frame. measuring device.
After a rectangular wave having a constant period and a first cycle number of about 10 to 15 cycles, an ultrasonic wave is transmitted from the sensor using a transmission signal having a frequency of 0,
The ultrasonic wave reflected by the object is received by the sensor,
An ultrasonic distance measuring method for obtaining a distance based on a correlation between a received waveform of an ultrasonic wave received by the sensor and a template held in advance,
Under a predetermined condition, an ultrasonic wave is transmitted from the sensor using the transmission signal, an ultrasonic wave reflected by the object is received by the sensor, and an ultrasonic wave received waveform of the ultrasonic wave is received by the sensor. The first waveform extracted from the rising edge of the reflected waveform by the number of second cycles smaller than the first cycle number, or the second waveform obtained by multiplying the amplitude of the first waveform by a predetermined number is used as the template. Distance measurement method.