CN111788456A

CN111788456A - Ultrasonic distance measuring device and ultrasonic distance measuring method

Info

Publication number: CN111788456A
Application number: CN201980015779.5A
Authority: CN
Inventors: 米泽良
Original assignee: V Technology Co Ltd
Current assignee: V Technology Co Ltd
Priority date: 2018-03-29
Filing date: 2019-03-20
Publication date: 2020-10-16
Anticipated expiration: 2039-03-20
Also published as: TWI783123B; WO2019188661A1; CN111788456B; JP7040766B2; JP2019174381A; TW201942591A

Abstract

The ultrasonic distance measuring device and the ultrasonic distance measuring method can measure the distance with high precision. The ultrasonic waves are transmitted by using a transmission signal with a fixed period, a frequency of 0 after a1 st cycle number of rectangular waves with a cycle number of about 10-15 cycles, and the ultrasonic waves reflected by the object are received. Then, the distance between the sensor and the object is measured based on the correlation between the received waveform of the ultrasonic wave received by the sensor and a template in which a1 st waveform, which is a number of 2 nd cycles smaller than the 1 st cycle, is extracted from the rising edge as a basic waveform of the received waveform under a predetermined condition, or a 2 nd waveform, which is a waveform in which the amplitude of the 1 st waveform is a predetermined multiple.

Description

Ultrasonic distance measuring device and ultrasonic distance measuring method

Technical Field

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

Background

Patent document 1 discloses an ultrasonic distance meter that transmits an ultrasonic wave from an ultrasonic sensor toward an object, receives the ultrasonic wave reflected by the object again by the ultrasonic sensor, measures a delay time or a phase from the received signal, performs moving average processing or weighted moving average processing on the measured value of the delay time or the phase, and obtains the distance between the ultrasonic sensor and the object based on the result.

Prior art documents

Patent document

Patent document 1: japanese patent laid-open publication No. 2005-291857

Disclosure of Invention

Problems to be solved by the invention

As in the invention described in patent document 1, when the distance is determined based on the result of the moving average processing or the weighted moving average processing performed on the received signal, it is considered that the distance can be measured with an accuracy of about ± 0.1 mm. However, for example, when the surface of a semiconductor substrate is imaged and inspected, the accuracy of about ± 0.1mm is not sufficient, and the distance is required to be measured with higher accuracy.

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

Means for solving the problems

In order to solve the above problem, an ultrasonic distance measuring device according to the present invention includes, for example: a sensor that transmits ultrasonic waves to an object and receives ultrasonic waves reflected by the object; and a signal processing unit configured to measure 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, wherein the sensor transmits the ultrasonic wave using a transmission signal having a fixed cycle and a frequency of 0 after a1 st cycle number of rectangular waves, which is a cycle number of about 10 to 15 cycles, and the signal processing unit includes a template holding unit configured to extract a1 st waveform, which is a number of 2 nd cycles less than the 1 st cycle number, from a rising edge as a basic waveform of the received waveform under a predetermined condition, or a 2 nd waveform, which is a waveform having an amplitude of the 1 st waveform at a predetermined multiple, as the template.

According to the ultrasonic distance measuring device of the present invention, ultrasonic waves are transmitted based on a transmission signal having a frequency of 0 after a rectangular wave having a fixed period and a1 st cycle number of cycles of about 10 to 15 cycles, and the ultrasonic waves reflected by an object are received. Then, the distance between the sensor and the object is measured based on the correlation between the reception waveform of the ultrasonic wave received by the sensor and the 1 st waveform, which is a 2 nd cycle number (2 nd cycle number < 1 st cycle number) extracted from the rising edge of the basic waveform (reception waveform under a predetermined condition), or the template of the 2 nd waveform in which the amplitude of the 1 st waveform is a predetermined multiple. In this way, by previously holding a part of the received waveform under a predetermined condition as a template and comparing the actual received waveform reflected by the object to be measured with the template, the distance can be measured with high accuracy. Further, by setting the frequency to 0 after the 1 st cycle number of rectangular waves, which is about 10 to 15 cycles, the resonance of the sensor can be stopped, ultrasonic waves can be transmitted and received by the same sensor, and the distance to an object separated by a short distance (for example, 40mm) can be measured.

Here, the signal processing unit may calculate a correlation value by subtracting the received waveform from the template and adding absolute values of the differences, and may measure the distance between the sensor and the object based on a timing when the received waveform matches the template to calculate a rising edge of the received waveform when the correlation value is minimum. This makes it possible to accurately know the timing of the rising edge of the received waveform, and to measure the distance with high accuracy.

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

Here, the template adjustment unit may adjust the amplitude of the template so that the peak value of the template coincides with the peak value of the received waveform. Thus, even if the peak value, that is, the amplitude of the received waveform changes, the correlation between the received waveform and the template can be accurately obtained.

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

Here, the ultrasonic sensor may further include a wavelength measurement object provided at a predetermined distance from the sensor, and the signal processing unit may determine the wavelength of the ultrasonic wave transmitted from the sensor based on the 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, and determine the distance between the sensor and the object based on the determined wavelength. The wavelength of the ultrasonic wave slightly changes 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 measured with high accuracy regardless of the temperature change.

Here, the signal processing unit may be configured to measure the distance between the sensor and the object by matching the received waveform with the template at a point in the received waveform, which is provided near a time point at which the correlation between the received waveform and the template is highest and at which the received waveform matches a center line. This enables the distance to be measured with higher accuracy.

Here, the ultrasonic sensor may further include a reflecting plate that reflects the ultrasonic wave transmitted from the sensor and reflected by the object so that a path of the ultrasonic wave between the sensor and the reflecting plate matches a path of the ultrasonic wave between the reflecting plate and the sensor, and the signal processing unit may determine the distance between the sensor and the object based on the distance between the sensor and the reflecting plate and an incident angle of the ultrasonic wave transmitted from the sensor to the object. This can further improve the accuracy of measuring the distance between the sensor and the object.

The sensor may further include a housing, wherein the sensor includes a frame, a metal weight is provided on the frame, and an elastic member is provided between the frame and the housing, and the frame is sandwiched between the elastic member and the housing. This makes it easy to converge the vibration of the sensor, and enables the sensor to receive the vibration immediately after transmission.

In order to solve the above-mentioned problems, an ultrasonic distance measuring method according to the present invention is an ultrasonic distance measuring method for transmitting ultrasonic waves from a sensor with a fixed period and a frequency of 0 after a rectangular wave with a number of 1 cycle of about 10 to 15 cycles, receiving ultrasonic waves reflected by an object by the sensor, and determining a distance based on a correlation between a received waveform of the ultrasonic waves received by the sensor and a template held in advance, the method including transmitting the ultrasonic waves from the sensor using the transmission signal under a predetermined condition, receiving the ultrasonic waves reflected by the object by the sensor, extracting a1 st waveform corresponding to a number of 2 cycles smaller than the 1 st cycle from a rising edge of a reflected waveform in the received waveform of the ultrasonic waves received by the sensor, or the 2 nd waveform with the amplitude of the 1 st waveform being a predetermined multiple is used as the template. This enables the distance to be measured with high accuracy. Further, the same sensor can be used for transmission and reception of ultrasonic waves, and the distance to an object separated by a short distance (for example, 40mm) can be measured.

Effects of the invention

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

Drawings

Fig. 1 is a block diagram showing a schematic configuration of an ultrasonic distance measuring apparatus 1 according to embodiment 1.

Fig. 2 is a diagram showing an example of the circuit configuration of the ultrasonic sensor 10.

Fig. 3 is a diagram schematically showing processing of a received signal in the ultrasonic distance measuring apparatus 1.

Fig. 4 shows an example of a basic waveform.

Fig. 5 shows an example of the template Ta having cycle number 9.

Fig. 6 shows an example of the template Tb with the cycle number of 4.

Fig. 7 is a diagram showing an example of a correlation value which is a result of adding absolute values of differences between a reception waveform obtained when the distance to the object O is 125mm and the template T1a based on the template Ta with the cycle number of 9.

Fig. 8 is a diagram of the horizontal axis in the vicinity of the circle in fig. 7, which enlarges the result shown in fig. 7.

Fig. 9 is a diagram showing an example of a correlation value which is a result of adding absolute values of differences between a reception waveform obtained when the distance to the object O is 125mm and the template T1b based on the template Tb with the cycle number of 4.

Fig. 10 is a diagram of the horizontal axis in the vicinity of the circle in fig. 9, which enlarges the result shown in fig. 9.

Fig. 11 is a diagram showing a relationship between the reception waveform and the template T1b based on the template Tb, and the rising edge portion of the reception waveform is displayed in an enlarged manner.

Fig. 12 is a diagram showing an example of a correlation value between a received waveform and a template T1 when the magnification input from the template adjustment input unit 22B is changed, (a) is an example of a correlation value when the magnification input from the template adjustment input unit 22B is smaller than 1, (B) is an example of a correlation value when the magnification input from the template adjustment input unit 22B is 1, and (C) is an example of a correlation value when the magnification input from the template adjustment input unit 22B is larger than 1.

Fig. 13 is a diagram showing an example of the autofocus device 5 to which the ultrasonic distance measuring device 1 according to the present invention is applied.

Fig. 14 schematically shows the relationship between the change in the distance h and the change in the distance L, where (a) shows the case where θ is 45 degrees, and (B) shows the case where θ is 0 degrees.

Fig. 15 is a diagram schematically showing an example of the mounting structure of the ultrasonic sensor 10.

Fig. 16 is a block diagram showing a schematic configuration of the ultrasonic distance measuring device 2 according to embodiment 2.

Fig. 17 is a diagram showing a rising edge portion of the reception waveform in an enlarged manner in the lateral direction.

Fig. 18 is an enlarged view of the vicinity of the intersection β' of the reception waveform shown in fig. 17.

Detailed Description

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The present invention measures the distance to an object using ultrasonic waves. Ultrasonic waves are high-frequency waves that cannot be heard in the human ear, and are generally elastic vibration waves (sound waves) having a frequency exceeding 20kHz and above the audible range, but ultrasonic waves also include sound that is not heard by the human ear even if the sound waves are heard at 20kHz or below.

< embodiment 1 >

Fig. 1 is a block diagram showing a schematic configuration of an ultrasonic distance measuring apparatus 1 according to embodiment 1. 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 supply, and generates ultrasonic waves by being vibrated by an applied electric signal. The ultrasonic sensor 10 includes a Transducer 103 (see fig. 2), transmits an ultrasonic wave to the object O based on a transmission signal (described later), and receives an ultrasonic wave reflected by the object O. In the present embodiment, ultrasonic waves having a frequency of 300kHz are used. Ultrasonic waves of this frequency are characterized by high directivity. However, the frequency of the ultrasonic wave used in the ultrasonic distance measuring apparatus 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 wave reciprocates (double path) between the ultrasonic sensor 10 and the object O. The ultrasonic sensor 10 converts the ultrasonic waves received by the sensor 103 into electrical signals.

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 17 oscillates the D/a converter by 10 to 15 cycles with a rectangular wave having a frequency of 300kHz, and then drives the high frequency drive circuit 16 so that a DC (frequency of 0) signal is applied. The ultrasonic sensor driving unit 15 has a switch 18, and switches between connection (driving) of the ultrasonic sensor 10 to the ultrasonic sensor driving unit 15 and connection (reception) of the ultrasonic sensor to the signal processing unit 20.

Fig. 2 is a diagram showing an example of the circuit configuration of the ultrasonic sensor 10 and the ultrasonic sensor driving unit 15. The ultrasonic sensor 10 is a multichannel sensor having a plurality of sensors 103(103a to 103 h). 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, a photo MOS relay is 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 by 10 to 15 cycles with a rectangular wave having a frequency of 300kHz, and then applies a DC (frequency of 0) signal to stop the vibration. That is, the transmission signal is a signal having a frequency of 0 after a rectangular wave having a fixed period and a1 st cycle number (for example, in the embodiment, the 1 st cycle number is 15 cycles) of about 10 to 15 cycles.

When the disable terminal of the amplifier 101c is set to the enable side, the transmission signal from the D/a converter 101a is input to the semiconductor relay 102 via the transformer 101 b. The semiconductor relay 102 is switched to sequentially drive and receive the plurality of sensors 103. In fig. 2, the sensors 103 are 8 channels and have 8 sensors 103a to 103h, but the number of sensors 103 (the number of channels) is not limited thereto.

The semiconductor relay 102 sequentially drives and receives the sensors 103 every approximately 1 msec. For example, when sensors of 20 channels are sequentially driven and received at intervals of approximately 1msec, distance measurement is performed by each channel of the sensor at intervals of approximately 20 msec.

When the sensor 103 is driven, an ultrasonic wave based on the transmission signal is transmitted from the sensor 103. In the present embodiment, since a rectangular wave of 15 cycles is included in the transmission signal, an ultrasonic wave 15 cycle having a frequency of 300kHz is output from the sensor 103. The transmission signal is a rectangular wave, but the ultrasonic wave output from the sensor 103 does not increase at a moment, instead of a rectangular wave. Actually, the waveform of the ultrasonic wave output from the sensor 103 is a sine wave shape, and has a small amplitude close to 0 at first, and the amplitude gradually increases with the passage of time.

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

After outputting the signal having the frequency of 0, the amplifier 101c is disabled, and a current is passed through the photoelectric element of the semiconductor relay 105 to turn on the semiconductor relay 105, thereby switching the sensor 103 from the transmission side to the reception side (corresponding to switching of the switch 18 (see 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 in the receiving circuit 104.

The receiving circuit 104 has a band-pass filter 104a that passes only a predetermined range of frequencies (here, 300kHz is included). The signal having passed through the band pass filter 104a is passed through an a/D converter 104b and is output to the signal processing unit 20 (see fig. 1) as a reception signal.

During driving of the sensor 103, the semiconductor relay 105 is turned off so that a large transmission signal does not enter the receiving circuit 104. In addition, limiters 104c are provided before and after the band pass filter 104 a. This is because when the semiconductor relay 105 is turned on, the sensor 103 resonates at 300kHz, and a large signal generated thereby does not enter the amplifier, the a/D converter 104 b. The limiter 104c uses a schottky barrier diode having a forward voltage as small as about 0.3V.

The description returns to fig. 1. The reception signal output from the ultrasonic sensor 10 is input to the signal processing unit 20. 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 portion 21 holds a template. The template adjusting section 22 adjusts the amplitude of the template held by the template holding section 21. The correlation calculation unit 23 obtains the correlation between the received signal and the template held by the template holding unit 21 or the template whose amplitude has been adjusted by the template adjustment unit 22.

Fig. 3 is a diagram schematically showing processing of a received signal 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 receiving circuit 104 outputs a clock signal of 6MHz to continuously generate a reception signal. 6MHz is 20 times the 300kHz frequency of the ultrasound received by the transducer 103. That is, the reception circuit 104 acquires 20 times (20 times oversampling) of the reception signal between 1 cycle of the received ultrasonic wave. The receiving circuit 104 connects a plurality of received signals obtained in succession to generate a received 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 unit 23 acquires a reception waveform of the ultrasonic wave reception for a certain period. In addition, in FIG. 3, the shift register 231 has 80D flip-flops 231-1, 231-2, 231-3 … 231-80. The 80 templates are 20 times oversampling (described later) by 4 cycles, and correspond to the number of templates T recorded in the template holding unit 21 (described later). In addition, in the case where the A/D converter 104b digitizes the analog signal at a resolution of 16 bits, the D flip-flops 231-1 to 231-80 each include 16D flip-flops.

One D flip-flop 231-1 to 231-80 holds the ultrasonic wave reception result (reception level) corresponding to 1 clock. Here, the reception level is a value obtained by a/D converting a reception signal corresponding to 1 clock. When the next reception level is input to the shift register 231 from the a/D converter 104b of the reception circuit 104, the reception levels held in the shift register 231 are sequentially transmitted to the right (for example, the reception level held in the D flip-flop 231-1 is transmitted to the D flip-flop 231-2), and a new reception level input from the reception circuit 104 is held in the shift register 231. Thus, the shift register 231 maintains the reception level of the same length as the template T.

The template holding unit 21 holds a template T. The template T is composed of a corresponding amount of template level information of 80 clocks. The template level information is a value of each clock when a/D conversion is performed for a corresponding amount of 80 clocks in the rising edge portion of the standard reception waveform (basic waveform). The template level information is read from the template holding section 21 to the correlation calculation section 23 and held in the shift register 232. The shift register 232 has 80D flip-flops 232-1 to 232-80 similarly to the shift register 231, and template level information corresponding to 80 clocks is held in the shift register 232. In addition, when the D flip-flops 231-1 to 231-80 respectively include 16D flip-flops, the D flip-flops 232-1 to 232-80 also respectively include 16D flip-flops.

Here, the template T will be explained. The template is a template in which a basic waveform as a reception waveform under a predetermined condition is extracted from a rising edge by a number of cycles (however, the number of cycles of the transmitted ultrasonic wave is equal to or less). The basic waveform is not a waveform into which the sensor reverberation immediately after transmission enters (for example, a waveform when the distance to the object O is about 40mm), but a waveform having a small value and a low S/N ratio (for example, a waveform when the distance to the object O is about 120 mm), but a clear waveform as shown in fig. 4.

Fig. 4 shows an example of a basic waveform. Here, the basic waveform is obtained under the predetermined condition that the distance to the object O is 75 mm. The horizontal axis of fig. 4 is the number of clocks (i.e., time). The basic waveform is divided into an area a where the peak is high and an area B where the peak is low thereafter. The region a is mainly a period during which ultrasonic waves transmitted by a 15-cycle rectangular wave are received. The resonance frequency of the region a is 300kHz (the same frequency as the ultrasonic wave to be transmitted), 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 peaks at about 9 cycles from the rising edge. In contrast, 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 the region B is slightly different from the period of the rectangular wave of the transmission signal.

The reception waveform changes depending on conditions such as the distance to the object O, the deviation of the sensor 103, and the cable length from the sensor 103. However, the received waveform changes only in amplitude (width in the height direction) as a whole with respect to the basic waveform, and the characteristics of the waveform do not change due to a change in conditions such as a change in distance to the object O. For example, if the distance to the object O is longer than 75mm, the received waveform is shifted rearward from the position of the basic waveform shown in fig. 4, and the amplitude is smaller than the entire basic waveform shown in fig. 4. However, since the region A, B is present, the region a has a resonance frequency of 300kHz, but the region B does not have a resonance frequency of 300kHz (variation occurs depending on conditions), and the region a does not change when the amplitude reaches a peak from the rising edge to the 9-cycle side.

Therefore, in the present invention, the rising edge portion of the basic waveform (a part of the region a) is held as a template in advance, and the actual received waveform is compared with the template, whereby the distance to the object O, which is the rising edge portion of the actual received waveform, is accurately obtained.

Fig. 5 and 6 show examples of templates T from which the rising edge portions of the reception waveforms shown in fig. 4 are extracted. Fig. 5 shows an example of the template Ta having 9 cycles, and fig. 6 shows an example of the template Tb having 4 cycles. The 9-cycle is the number of cycles from when the received waveform rises completely to when it reaches the peak, and the 4-cycle is the number of cycles that is about half the number of cycles from when the received waveform rises completely to when it reaches the peak. However, the number of cycles extracted from the rising edge of the received waveform obtained in advance as a template is not limited to 4 cycles and 9 cycles, as long as the number of cycles is smaller than the number of cycles included in the transmission signal (here, 15 cycles).

The number of the templates T held by the template holding unit 21 is 1, and may be Ta or Tb, but both of Ta and Tb are not held.

The explanation returns to fig. 3. The template adjustment unit 22 is mainly provided with a peak hold circuit 22a and a template adjustment input unit 22b for adjusting the magnification of the template T, for setting the amplitude of the template T to a predetermined multiple.

The peak hold circuit 22a holds the peak value of the received waveform held by the last D flip-flop 231-80. The template adjustment input unit 22b is configured to be capable of changing the magnification at 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 1 time.

When there is no input for changing the magnification from the template adjustment input unit 22b (here, the template adjustment input unit 22b is set to "5"), the template adjustment unit 22 outputs the peak value held by the peak hold circuit 22a 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 at the time of arrival at the template T matches the peak value of the received signal.

When the magnification is changed from the template adjustment input unit 22b, the template adjustment unit 22 multiplies the magnification input from the template adjustment input unit 22b by the peak value held by the peak hold circuit 22a and outputs the multiplication result to the correlation calculation unit 23.

The correlation calculation unit 23 obtains the correlation between the received waveform and the template T (or the template T1). Here, the correlation between the reception level held by each of the D flip-flops 231-1 to 231-80 of the shift register 231 and the level information of the template T1 obtained by multiplying the template level information held by each of the D flip-flops 232-1 to 232-80 of the shift register 232 by the magnification input from the template adjustment unit 22 is obtained. The template T1 is obtained by setting the amplitude of the template T to a predetermined multiple, and when the predetermined multiple is 1, the template T matches the template T1.

In the present embodiment, the received waveform is differentiated from the template T1, the correlation value which is the result of adding the absolute values of the differences is obtained, and the received waveform is assumed to match the template T1 at the time point 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 by using a value obtained by squaring the difference between the received waveform and the template T1.

Fig. 7 is a diagram showing an example of a correlation value which is a result of adding absolute values of differences between a reception waveform obtained when the distance to the object O is 125mm and the template T1a based on the template Ta with the cycle number of 9. The horizontal axis of fig. 7 represents time, and the vertical axis represents correlation values. It can be seen that the received waveform coincides with or most closely coincides with the template T1a at the position where the correlation value is the smallest (see the circle in fig. 7).

Fig. 8 is an enlarged view of the result shown in fig. 7, taken along the horizontal axis near the circle in fig. 7. The dots in fig. 8 indicate the timing when oversampling is performed 20 times in the receiving circuit 104. The points with small correlation values (see the circle in fig. 8) are arranged in 3 rows, and the correlation value is smallest at the center point α among the points. From this, it is understood that the received waveform matches the template T1a at the timing of the point α.

Fig. 9 is a diagram showing an example of a correlation value which is a result of adding absolute values of differences between a reception waveform obtained when the distance to the object O is 125mm and the template T1b based on the template Tb with the cycle number of 4. The horizontal axis of fig. 9 represents time, and the vertical axis represents correlation values. It can be seen that the received waveform coincides with or most closely coincides with the template T1b at the position where the correlation value is the smallest (see the circle in fig. 9).

Fig. 10 is an enlarged view of the result shown in fig. 9, taken along the horizontal axis near the circle in fig. 9. The dots in fig. 10 indicate the timings at which oversampling is performed 20 times in the receiving circuit 104. It is known that the timing correlation value at the point β is minimum, and the received waveform coincides with the template T1 b.

In this way, the correlation calculation unit 23 calculates when the received signal most agrees with the template T1. In the example shown in fig. 9, the timing at the point α indicates the end of the 9 th cycle of the received waveform, and in the example shown in fig. 10, the timing at the point β indicates the end of the 4 th cycle of the received waveform.

The description returns to fig. 1. 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 a relationship between the reception waveform and the template T1b based on the template Tb, and the rising edge portion of the reception waveform is displayed in an enlarged manner.

At the timing of the point β, the received waveform coincides with the last (4 th cycle) of the template T1 b. The timing of the rising edge of the received waveform is accurately known by superimposing the received waveform on the template T1b so that the last of the template T1b is located at the point β and setting the point γ at which the contour line of the template T1b (see the dotted line in fig. 1) intersects as the rising edge of the received waveform. The distance calculation unit 24 starts reception of the ultrasonic wave at the rising edge (point γ) of the reception waveform thus obtained, and calculates the distance between the ultrasonic sensor 10 and the object O by dividing the time of the rising edge by the oversampling number (20 in this case) and integrating the half wavelength (two paths) of the transmitted ultrasonic wave (300 kHz in this case), that is, 0.57mm (═ 1.13mm/2), as shown in expression (1).

[ numerical formula 1]

Timing of round trip distance ═ point gamma/20X 0.57mm (1)

However, due to variations in measurement conditions such as the distance between the ultrasonic sensor 10 and the object O, the received waveform may not be well matched with the template T1. As the reason why the received waveform does not match the template T1 well, for example, there is a case where the vibration at the time of excitation, in which the resonance frequency of the sensor 103 is greatly deviated from 300kHz, the cable length to the sensor 103 is long and the series resistance is large, and the distance to the object O is close to 40mm, interferes with the reflected wave. In this case, the magnification is input via the template adjustment input unit 22b shown in fig. 3, and the template T1 is tuned.

Fig. 12 is a diagram showing an example of a correlation value between a received waveform and the template T1 when the magnification input from the template adjustment input unit 22B is changed, (a) is an example of a correlation value when the magnification input from the template adjustment input unit 22B is smaller than 1 (here, the template adjustment input unit 22B is set to "1"), (B) is an example of a correlation value when the magnification input from the template adjustment input unit 22B is 1 (here, the template adjustment input unit 22B is set to "5"), (C) is an example of a correlation value when the magnification input from the template adjustment input unit 22B is larger than 1 (here, the template adjustment input unit 22B is set to "9").

In the case shown in fig. 12 (a) and (C), two points are present in parallel at the point of low value in the waveform of the correlation value, and the waveform of the correlation value becomes a so-called "double bottom". In contrast, in the case shown in fig. 12 (B), only a point where one value is low exists in the waveform of the correlation value, and the waveform of the correlation value is formed as a so-called "single base".

In this way, the waveform of the correlation value changes by changing the magnification by which the amplitude of the template T is multiplied. Therefore, when the waveform of the correlation value becomes a so-called "double base", the magnification inputted through the template adjustment input unit 22b is changed to change the waveform of the correlation value into a so-called "single base". This makes it possible to obtain a timing at which the correlation value is the smallest, that is, the received waveform and the template T1 sufficiently match or most closely match.

The description returns to fig. 1. The temperature correction unit 25 corrects a wavelength change of the ultrasonic wave due to a temperature change. The wavelength of the ultrasonic wave changes slightly when the temperature changes. In order to obtain the distance with high accuracy, the wavelength of the ultrasonic wave actually transmitted and received by the ultrasonic sensor 10 is obtained in the temperature correction unit 25, and the distance is obtained using the wavelength obtained by the temperature correction unit 25 in the distance calculation unit 24.

For example, the temperature correction unit 25 may have a thermometer for measuring the temperature, or may determine 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, one of the plurality of sensors 103 (see fig. 2) is used to transmit ultrasonic waves, and the same sensor 103 is used to receive ultrasonic waves reflected by the object for wavelength measurement set apart from the sensor 103 by a predetermined distance (referred to as distance D). The correlation calculation unit 23 and the distance calculation unit 24 measure the time t from the transmission of the ultrasonic wave from the sensor 103 to the reflection of the ultrasonic wave by the wavelength measurement target portion and the reception of the ultrasonic wave by the sensor 103, and the temperature correction unit 25 can obtain the wavelength of the ultrasonic wave transmitted from the ultrasonic sensor 10 based on the time t and the distance D. 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 general display device that is already known, and displays the output distance.

The configuration of the ultrasonic distance measuring apparatus 1 shown in fig. 1 has been described mainly in describing the features of the present embodiment, and for example, the configuration of a general information processing apparatus is not excluded. The functional configurations shown in fig. 1 are classified to facilitate understanding of the configuration of the ultrasonic distance measuring apparatus 1, and the method and name of classifying the components are not limited to the embodiment shown in fig. 1. The configuration of the ultrasonic distance measuring apparatus 1 may be classified into more components according to the processing contents, or may be configured such that processing of a plurality of components is executed by one component.

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 one embodiment of an ultrasonic distance measuring device.

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

The reflecting plate 51 is provided at a position where the path of the ultrasonic wave from the ultrasonic sensor 10 to the reflecting plate 51 coincides with the path of the ultrasonic wave from the reflecting plate 51 to the ultrasonic sensor 10 (see the arrow in fig. 13).

The signal processing unit 20 obtains the distance h between the ultrasonic sensor 10 and the object O based on the distance between the ultrasonic sensor 10 and the reflecting plate 51 and the incident angle θ of the ultrasonic wave transmitted from the ultrasonic sensor 10 to the object O.

The output unit 30 outputs the measured distance h to the imaging device 52. The photographing device 52 performs focus processing based on the distance h. Since the focus adjustment process is well known, the description is omitted.

In the autofocus apparatus 5, since the ultrasonic wave is transmitted obliquely toward the object O and the ultrasonic wave travels back and forth (double path) between the ultrasonic sensor 10 and the reflecting plate 51, the change in the distance h when the distance L between the ultrasonic sensor 10 and the reflecting plate 51 changes is L/2 × cos θ, and the change in the distance h is significantly smaller than the change in the distance L. For example, when θ is 45 degrees, the change Δ h of the distance h when the distance L is changed by Δ L is Δ h ═ Δ L/2 × 1/√ 2, and Δ L is approximately 2.8 times Δ h (Δ L × √ 2 × Δ h). Therefore, the distance h is measured with higher accuracy than the distance L.

Fig. 14 schematically shows the relationship between the change in the distance h and the change in the distance L, where (a) shows the case where θ is 45 degrees, and (B) shows the case where θ is 0 degrees. The surfaces O1, O2, and O3 are surfaces of the object O, 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, the position of the surface O2 indicates a case where the distance between the ultrasonic sensor 10 and the object O is a distance h + Δ h, and the position of the surface O3 indicates a case where the distance between the ultrasonic sensor 10 and the object O is a distance h + Δ 2 h. In fig. 14, the path of the ultrasonic wave is indicated by a two-dot chain line.

In fig. 14 (a), the distances to the surfaces O1, O2, O3 are calculated from the distances of the ultrasonic sensor 10 from the reflection plate 53. When the distance h varies by Δ h, the distance from the ultrasonic sensor 10 to the reflection plate 53 varies by 2 × √ 2 × Δ h. In contrast, in fig. 14 (B), when the distance h from the ultrasonic sensor 10 is changed by Δ h in order to directly measure the distances to the surfaces O1, O2, and O3, the path of the ultrasonic wave is changed by 2 (amount corresponding to the round trip) × Δ h. Therefore, in the case shown in fig. 14 (a), the distance can be obtained as much as v 2 times finer than the case shown in fig. 14 (B).

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

Further, according to the present embodiment, since the template adjustment unit 22 for adjusting the amplitude of the template T is provided, even if the amplitude of the received waveform changes due to a change in the measurement condition such as the distance to the object O, the correlation between the received waveform and the template T can be accurately obtained. Therefore, the distance to the object O can be measured with high accuracy regardless of the change 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 300kHz, and the sampling frequency of the reception signal is 6MHz (1 cycle of the ultrasonic wave of 300kHz is sampled 20 times), so that the distance can be measured with high accuracy of 30 μm as obtained by the following expression (2). Here, 0.6mm is an approximate value of 0.57mm of half of 1.13mm (because of dual path) of the wavelength λ of 300kHz ultrasonic waves.

[ numerical formula 2]

0.6mm/20＝0.03mm(＝30μm) (2)

Further, according to the present embodiment, since the ultrasonic wave is transmitted and received by the ultrasonic sensor 10 and the ultrasonic wave is measured in a double path (reciprocating measurement) of reciprocating between the ultrasonic sensor 10 and the object O, the distance to the object O can be measured with high accuracy by eliminating the influence of the wind speed in the path of the ultrasonic wave.

The D/A converter is vibrated by 10 to 15 cycles of a signal of DC (frequency 0) from the left to the right by a rectangular wave having a frequency of 300kHz, and the sensor 103 is braked to stop the shaking of the sensor 103. This enables the sensor 103 to receive the ultrasonic wave immediately after the ultrasonic wave is transmitted from the sensor 103. Therefore, it is possible to perform transmission and reception of ultrasonic waves with the same sensor 103, and perform measurement of a short distance (for example, 40 mm).

In the present embodiment, the received signal is acquired at 20 times the frequency 300kHz of the received ultrasonic wave, but the received signal may be acquired (oversampled) at a frequency of about 10 times or more of the received ultrasonic wave. 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 small, and the peak of the received waveform hardly changes. Therefore, in such a case, the template adjustment unit 22 is not required, and the template holding unit 21 may create the template T using the reception waveform at the time of focusing and hold the template T.

In the present embodiment, the oscillation of the sensor 103 is stopped by adding a DC (frequency of 0) signal after the rectangular wave of about 10 to 15 cycles, but the vibration of the ultrasonic sensor 10 can be further suppressed by examining the mounting of the ultrasonic sensor 10 having the sensor 103 therein. Fig. 15 is a diagram schematically showing an example of the mounting structure of the ultrasonic sensor 10.

The ultrasonic sensor 10 has a housing 10 a. An elastic member 111 (e.g., an O-ring) is provided between the housing 113 and the housing 10a, and the ultrasonic sensor 10 is provided inside the housing 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 abuts against a side surface 10c adjacent to the surface 10b on which the vibration surface of the sensor 103 is provided.

When the sensor 103 transmits ultrasonic waves, the sensor 103 vibrates back and forth due to a reaction when air is vibrated, and the vibration of the ultrasonic sensor 10 is hard to converge. In order to converge the vibration of the ultrasonic sensor 10, a metal weight is provided in the housing 10 a. Here, as the weight, a sheet-like member made of lead, that is, a lead plate 112 is used, and the lead plate 112 coated with the adhesive is wound around the side surface 10 c. As the adhesive, an adhesive having elasticity (for example, a modified silicone resin adhesive such as an acrylic modified silicone resin) is used. This enables efficient conversion of the vibration energy into heat, and enables the transmission/reception to be switched earlier. Therefore, after the ultrasonic wave is transmitted from the sensor 103, the ultrasonic wave can be received by the sensor 103 immediately, that is, measurement at a short distance (for example, 40mm) can be performed.

< embodiment 2 >

In embodiment 1 of the present invention, the received waveform and the template T1 are matched or most closely matched when the correlation value is the smallest, and the distance to the object O is determined.

Embodiment 2 of the present invention is a method of determining the distance to the object O by matching or closest matching the received waveform with the template T1 at a point where the received waveform matches the center line, that is, at a so-called intersection point. The ultrasonic distance measuring device 2 according to embodiment 2 will be described below. The same components as those of the ultrasonic distance measuring device 1 according to embodiment 1 are denoted by the same reference numerals, and description thereof is omitted.

Fig. 16 is a block diagram showing a schematic configuration of the ultrasonic distance measuring device 2 according to embodiment 2. 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 obtains an intersection 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 intersection point. Fig. 17 is a diagram showing a rising edge portion of the reception waveform in a laterally enlarged manner.

The point β in fig. 17 is the point at which the correlation value is minimum in fig. 9 and 10. The point β 1 is a measurement point at the timing subsequent to the point β. The intersection point β' is located between the point β and the point β 1, and is an intersection point in the vicinity of the point β (time point at which the correlation value is smallest). In embodiment 2, it is assumed that the received waveform coincides with the end of the template T1 at the intersection point β' where the received waveform coincides with the center line.

Fig. 18 is an enlarged view of the vicinity of the intersection β' of the reception waveform shown in fig. 17. Assuming that the distance in the height direction between the point β and the intersection β 'is a, the distance in the height direction between the point β' and the point β 1 is b, the distance in the lateral direction between the point β and the intersection β 'is a1, and the distance in the lateral direction between the point β' and the point β 1 is b1, a: b-a 1: b1 and the distance a1 are calculated by the following equation (3). Here, 30 μm is 1/20 (oversampling number) of half the wavelength of the ultrasonic wave of 300kHz (because of the double path), and corresponds to half the wavelength of the ultrasonic wave of 6 MHz.

[ numerical formula 3]

1/6MHz＝30μm×a/(a+b) (3)

The distance calculator 24 receives the waveform at the timing at the intersection β' and the last of the template T1, and receives the waveform rise at the position where the contour line of the template T1 intersects. Then, the distance calculation unit 24 starts reception of the ultrasonic wave at the position where the reception waveform thus obtained rises, and calculates the distance between the ultrasonic sensor 10 and the object O as shown in expression (4).

[ numerical formula 4]

Round-trip distance (timing of point β/20+ distance a1) × 1.13mm (4)

According to the present embodiment, the distance is obtained based on the intersection, and therefore the distance can be measured with higher accuracy.

While the embodiments of the present invention have been described in detail with reference to the drawings, the specific configuration is not limited to the embodiments, and design changes and the like are included without departing from the scope of the present invention.

In the present invention, the term "substantially" is a concept including not only the case where they are strictly identical but also errors and variations to the extent that they do not lose their identity. For example, the rough agreement is not limited to the strict agreement. For example, when only the vertical and the uniform are expressed, not only the vertical and the uniform in strict sense but also the substantially vertical and the uniform are included. In the present invention, "near" indicates, for example, a concept that, when a is near, a is close to a, and a may or may not be included.

Description of the symbols

1. 2: ultrasonic distance measuring device

5: automatic focusing device

10: ultrasonic sensor

10 a: frame body

10 b: noodle

10 c: side surface

20. 20A: signal processing unit

21: template holding part

22: template adjusting part

22 a: peak holding circuit

22 b: template adjustment input part

23: correlation calculation unit

24. 24A: distance calculating part

25: temperature correction unit

30: output unit

51: reflecting plate

52: image capturing apparatus

101: high frequency drive circuit

10 la: D/A converter

101 b: transformer device

101 c: amplifier with a high-frequency amplifier

102. 105: semiconductor relay

103: sensor with a sensor element

104: receiving circuit

104 a: band-pass filter

104 b: A/D converter

111: elastic member

112: lead plate

113: shell body

231. 232: shift register

231-1 to 231-80, 232-1 to 232-80: and D, a trigger.

Claims

1. An ultrasonic distance measuring apparatus is characterized by comprising:

a sensor that transmits ultrasonic waves to an object and receives ultrasonic waves reflected by the object; and

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 transmits ultrasonic waves by using a transmission signal having a fixed period, a frequency of 0 after a1 st cycle of rectangular waves having a cycle number of about 10 to 15 cycles,

the signal processing unit includes a template holding unit that extracts a1 st waveform, which is a base waveform of the received waveform under a predetermined condition and is smaller than the 1 st cycle by a 2 nd cycle from a rising edge, or a 2 nd waveform, which is a waveform having an amplitude of the 1 st waveform multiplied by a predetermined factor, and holds the 1 st waveform as the template.

2. The ultrasonic distance measuring device according to claim 1,

the signal processing unit calculates a correlation value by subtracting the received waveform from the template and adding the absolute value of the difference, and measures the distance between the sensor and the object based on the time when the received waveform matches the template and the rising edge of the received waveform is calculated when the correlation value is minimum.

3. The ultrasonic distance measuring device according to claim 1 or 2,

the signal processing unit includes a template adjustment unit for adjusting the amplitude of the template.

4. The ultrasonic distance measuring device according to claim 3,

the template adjustment unit adjusts the amplitude of the template so that the peak value of the template coincides with the peak value of the received waveform.

5. The ultrasonic distance measuring device according to any one of claims 1 to 4,

the sensor samples at a frequency that is approximately 20 times the frequency of the 1 st waveform.

6. The ultrasonic distance measuring device according to any one of claims 1 to 5,

includes an object for measuring a wavelength, which is provided at a predetermined distance from the sensor,

the signal processing unit obtains the wavelength of the ultrasonic wave transmitted from the sensor based on the time from when the ultrasonic wave transmitted from the sensor is reflected by the object for wavelength measurement and received by the sensor and the predetermined distance, and obtains the distance between the sensor and the object based on the obtained wavelength.

7. The ultrasonic distance measuring device according to any one of claims 1 to 6,

the signal processing unit may be configured to measure a distance between the sensor and the object at a point in the received waveform where the received waveform coincides with the template at a center line in the vicinity of a time point at which the correlation between the received waveform and the template is highest.

8. The ultrasonic distance measuring device according to any one of claims 1 to 7,

the utility model is also provided with a reflecting plate,

the sensor transmits ultrasonic waves obliquely toward the object,

the reflecting plate reflects the ultrasonic wave transmitted from the sensor and reflected by the object so that a path of the ultrasonic wave from between the sensor and the reflecting plate and a path of the ultrasonic wave from between the reflecting plate and the sensor coincide,

the signal processing unit obtains the distance between the sensor and the object based on the distance between the sensor and the reflector and the incident angle of the ultrasonic wave transmitted from the sensor to the object.

9. The ultrasonic distance measuring device according to any one of claims 1 to 8,

the utility model is also provided with a shell body,

the sensor is provided with a frame body,

the frame body is provided with a metal counterweight,

an elastic member is provided between the frame and the housing, and the frame is sandwiched by the elastic member.

10. An ultrasonic distance measuring method for transmitting ultrasonic waves from a sensor using a transmission signal having a frequency of 0 after a rectangular wave having a fixed cycle number of 1 st cycle number, i.e., a cycle number of about 10 to 15 cycles, receiving the ultrasonic waves reflected by an object by the sensor, and determining a distance based on a correlation between a received waveform of the ultrasonic waves received by the sensor and a template held in advance,

under a predetermined condition, the ultrasonic wave is transmitted from the sensor using the transmission signal, the ultrasonic wave reflected by the object is received by the sensor, and a1 st waveform extracted by a number of 2 nd cycles smaller than the 1 st cycle from a rising edge of a reflection waveform in a reception waveform of the ultrasonic wave received by the sensor or a 2 nd waveform having an amplitude of the 1 st waveform multiplied by a predetermined number is set as the template.