JP2019100715A - Ultrasonic sensor - Google Patents

Abstract

To provide an ultrasonic sensor for distance measurement with which the distance measurement responsiveness of an ultrasonic sensor is speeded up and which is designed in a compact size.SOLUTION: Provided is an ultrasonic sensor for measuring the distance to a measurement object using an ultrasonic wave, comprising: a frequency signal generation unit for generating a plurality of frequency signals; distance measurement means for generating ultrasonic waves of multiple frequencies on the basis of the plurality of frequency signals, as well as receiving a plurality of reflected waves from the measurement object that correspond to the ultrasonic waves of multiple frequencies and generating a plurality of received signals; and selection means for selecting from the plurality of received signals. Before the reflected wave based on an ultrasonic wave transmitted with a first frequency becomes multiple reflection and is unable to be received due to the attenuation of the multiple reflection, transmission and reception are carried out using an ultrasonic wave of a second frequency different from the first frequency.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an ultrasonic sensor that measures the distance to an object to be measured using ultrasonic waves.

  A method of measuring a distance by acquiring a propagation time TOF (Time-OF-Flight) of an ultrasonic wave in the air (in the air) has become widespread. Ultrasonic distance measurement has a feature that the distance measurement ability is substantially independent of the material of the object. Therefore, it is possible to cope with a wide range of materials such as transparent materials such as glass, metals and insulators. Further, since the sound wave has a spread, it is also possible to measure the distance without leaking the object. Since the distance range of general ultrasonic distance measurement is several tens cm to several m, detection of an obstacle viewed from front and rear bumpers of a car is widely known.

  By the way, ultrasonic waves in the air have strong distance attenuation, and a large generated sound pressure is required to measure the distance range. Therefore, it is common to use an ultrasonic sensor having vibration characteristics of a resonant system. In that case, if the base component of the noise signal present in the surroundings overlaps the sensitivity band of the sensor, there is a possibility that the signal may be erroneously amplified.

  In order to avoid that, Patent Document 1 discloses a method of selecting the center frequency of the sound wave with a band pass filter and identifying the pseudo sound wave and the self sound wave.

  When a plurality of sensors are arranged to measure the surrounding area, it is effective to set ultrasonic waves to be transmitted / received for each sensor in different frequency bands in order to prevent mutual interference of the ultrasonic waves. However, in this case, if the ranging task is sequentially processed for each sensor, the waiting time for the other sensors is increased, and the responsiveness of ranging as a whole is reduced.

  In order to avoid this, Patent Document 2 discloses a method of parallelizing the distance measurement task for each sensor by interrupting the distance measurement task of each sensor to improve the response of distance measurement.

JP-A-4-175682 JP 2003-130952

  Research and development aiming at the application to a robot hand has been started by making use of such excellent characteristics of ultrasonic distance measurement. The target distance when the ultrasonic sensor is mounted on the fingertip of the robot hand is extremely close to several mm to several 10 mm, which is extremely higher than general ultrasonic distance measurement. When ultrasonic distance measurement is performed at a distance of several millimeters, the transmitted ultrasonic waves are not sufficiently attenuated and become multiple reflections, and distance measurement can not be started while waiting for the attenuation, and the responsiveness is degraded. In addition, although the intensity of multiple reflection decreases when the distance becomes several mm or more, the waiting time from transmission to reception of the sound wave becomes long. Generally speaking, in order to improve distance measurement accuracy, taking into account that multiple measurements are averaged, the total waiting time in one measurement takes only the total number of measurements, and the response of distance measurement Sex is reduced. Therefore, there is a problem that the distance measurement by the current ultrasonic sensor is insufficient in response to the high speed operation (msec order) required by the robot hand.

  Only by providing a band pass filter for identifying the frequency of the sound wave described in Patent Document 1, it is possible to identify the frequency to be received, but it is not possible to transmit transmission sound waves having different frequencies.

  In addition, if different frequencies are associated with each ultrasonic sensor and distance measurement is performed as described in Patent Document 2, it becomes possible to identify sound waves, and the responsiveness deterioration due to waiting for elimination of multiple reflections is improved. However, since a plurality of sensors corresponding to each frequency are provided, it becomes difficult to satisfy the constraints of the mounting area. In addition, using a plurality of sensors corresponding to each frequency makes it difficult to measure the same target point at a short distance. An object of the present invention is to speed up the distance measurement response of an ultrasonic sensor and to provide a compact ultrasonic sensor for distance measurement.

An ultrasonic sensor provided by the present invention is an ultrasonic sensor that measures the distance to an object to be measured using ultrasonic waves,
A frequency signal generator for generating a plurality of frequency signals;
While generating ultrasonic waves of a plurality of frequencies based on the plurality of frequency signals, a distance for receiving a plurality of reflected waves from the object to be measured corresponding to the plurality of ultrasonic waves and generating a plurality of reception signals Measuring means,
And sorting means for sorting the plurality of received signals,
Transmitted using an ultrasonic wave of a second frequency different from the first frequency before reflected waves based on the ultrasonic wave transmitted at the first frequency become multiple reflections and the multiple reflections are attenuated and can not be received. And receiving.

  According to the present invention, it is possible to speed up the distance measurement response of the ultrasonic sensor and to provide a small-sized ultrasonic sensor for distance measurement.

It is a schematic diagram explaining the basic composition of the ultrasonic sensor of this invention. It is a schematic diagram explaining the ultrasonic sensor of this invention. It is a schematic diagram explaining the ultrasonic sensor of this invention. It is a schematic diagram explaining the example of ranging by the ultrasonic sensor of this invention. It is a schematic diagram explaining the example of ranging by the ultrasonic sensor of this invention. It is a schematic diagram explaining another example of ranging by the ultrasonic sensor of the present invention. It is a schematic diagram explaining another example of ranging by the ultrasonic sensor of the present invention. It is a schematic diagram explaining 1st embodiment. It is a schematic diagram explaining the time transition of the sequential ranging based on this invention. It is a schematic diagram explaining the time transition of the interruption ranging based on this invention. It is a schematic diagram explaining the functional block diagram in 1st embodiment. It is a schematic diagram explaining the operation | movement sequence in 1st embodiment. It is a schematic diagram explaining the data acquisition flow in 1st embodiment. It is a schematic diagram explaining the cross-sectional structure about an example of the distance measurement means in 1st embodiment. It is a schematic diagram explaining the cross-sectional structure about an example of the distance measurement means in 1st embodiment. It is a schematic diagram explaining the upper surface arrangement | positioning of the distance measurement means in 1st embodiment. It is a schematic diagram explaining the robot hand system in 1st embodiment. It is a schematic diagram explaining the cross-sectional structure of the distance measurement means in 2nd embodiment. It is a schematic diagram explaining the functional block diagram in 2nd embodiment. It is a schematic graph explaining the ranging error for every frequency which concerns on this invention. It is a schematic diagram explaining the data acquisition flow in 3rd embodiment.

  The ultrasonic sensor of the present invention is a sensor that measures the distance to an object to be measured using ultrasonic waves. The sensor of the present invention has a frequency signal generator that generates a plurality of frequency signals. Then, ultrasonic waves of a plurality of frequencies are generated based on a plurality of frequency signals, and a plurality of reflected waves from the object to be measured corresponding to the ultrasonic waves of the plurality of frequencies are received to generate a plurality of reception signals. It has distance measuring means. And a sorting means for sorting the plurality of received signals. Furthermore, before the reflected wave based on the ultrasonic wave transmitted at the first frequency becomes multiple reflection and the multiple reflection is attenuated and can not be received, the ultrasonic wave of the second frequency different from the first frequency is It is characterized in that it can be used for transmission and reception.

  In the ultrasonic sensor of the present invention, distance measurement can be performed by transmitting and receiving ultrasonic waves of a plurality of frequencies using a single distance measuring means constituting the ultrasonic sensor.

  The present invention includes a mode in which a plurality of thin film membranes having non-resonant vibration characteristics in a transmission sound wave band are combined to constitute a sound wave source of one distance measuring means. And the form which performs transmission / reception which modulated the frequency of the sound wave by one distance measurement means is included.

  The short distance measurement includes a mode in which the sound wave of the next task whose frequency is modulated is transmitted after receiving the sound wave in a situation where multiple reflections occur in the transmission sound wave, that is, the distance measurement is sequentially performed. Moreover, in the distance measurement, in a situation where multiple reflections occur in the transmission sound wave, it includes a mode of transmitting the sound wave of the next task whose frequency is modulated before receiving the sound wave, that is, performing interrupt distance measurement.

  Hereinafter, embodiments of the present invention will be described using the drawings. However, the present invention is not limited to these embodiments, and various modifications and changes are possible within the scope of the present invention.

First Embodiment
FIG. 1 is a schematic view for explaining the basic configuration of the ultrasonic sensor of the present invention. In FIG. 1, reference numeral 105 denotes an object to be measured, the ultrasonic wave 104 is transmitted from the distance measuring means 101 to the object to be measured 105, and the distance measuring means 101 receives the reflected wave reflected by the object 105 to be measured. Thereby, the distance between the measuring object 105 and the distance measuring means 101 is measured. A frequency signal generation unit 123 generates a plurality of frequency signals, and generates a waveform corresponding to a predetermined frequency signal. The distance measuring means 101 generates ultrasonic waves of a plurality of frequencies based on the frequency signals generated by the frequency signal generator. The sorting means 117 is a means for receiving a reflected wave of a frequency corresponding to the transmission frequency. A control unit 118 performs control including generation of a predetermined frequency signal by the frequency signal generation unit 123 and selection of reflected waves of a predetermined frequency by the selection unit 117. Although the basic configuration of the ultrasonic sensor of the present invention is shown in FIG. 1, the details will be described later with reference to FIG. In the following, the ultrasonic sensor of the present invention will be described first, including the functions and the like.

  FIG. 2A is a schematic view illustrating the ultrasonic sensor of the present invention. In FIG. 2A, the distance measuring means 101 is disposed in the finger portion 102 of the robot hand. After the distance measurement means 101 receives the distance measurement start signal 103, the transmission sound wave (ultrasound) 104 is generated, the reception sound wave (ultrasound) 106 reflected by the object 105 is received, and the processing signal is calculated. Is output. With regard to the distance signal 107, for example, a voltage raw signal measured by a mechanical / electrical transducer constituting the distance measuring means or calculation information is outputted if the processing function can be integrated. If the mounting space of the sensor unit of the transducer is limited, the sensor unit and the processing unit may be separated.

  FIG. 2B is a schematic view for explaining transmission and reception waveforms of the ultrasonic sensor of the present invention, and shows time transition of transmission sound waves and reception sound waves. At a certain time, the distance measurement means 101 generates a transmission sound wave 104, and the distance measurement means 101 receives the reception sound wave 106 reflected by the object. When the transducers constituting the distance measuring means 101 receive the sound pressure, the received sound pressure is converted into an electric signal and processed. In air, sound wave attenuation is strong, the reception sound pressure is 1 / several times to 1 / several of the transmission sound pressure, and the scale of the transmission sound pressure and the reception sound pressure is a relative ratio. A time 108 from the transmission time to the reception time is defined as TOF (Time-OF-Flight, sound wave propagation time), and the distance is calculated by sound velocity (m / sec) × TOF (sec) / 2. Here, TOF is calculated based on the peaks of the transmission and reception waveforms, but depending on the system, the rise time of the sound wave may be used. Further, in the electric signal obtained by converting the received sound wave, the time when the signal level reaches a predetermined threshold may be used. The transmission sound wave may be a single wave or a plurality of waves, and a rectangular wave or a sine wave may be used as the waveform shape. Hereinafter, in the diagram for explaining the transmission and reception timing of the sound wave, the shape of the sound wave is omitted, and only the transmission and reception timings are described.

  The distance measuring means 101 is composed of a transducer having a function of generating an ultrasonic wave and transmitting the ultrasonic wave to the measurement object 105. The transmission sound wave 104 irradiated to the object is reflected on the surface of the object 105 due to the difference in acoustic impedance at the interface of the object 105. A part of the ultrasonic wave reflected by the object 105 is returned to the distance measuring means to become the received sound wave 106. Generally, the acoustic impedance difference between air and an object is very large, and the reflectance at the interface of the object 105 is nearly 100%.

  Further, since it is desired to measure the shortest distance from the ultrasonic wave transmission surface of the distance measurement means 101 with respect to the measurement object 105, it is preferable that the directivity of the sound wave is sharp in the front. In order to impart such directivity of sound waves, a frequency of several hundred KHz to about 500 KHz or more is required. By thus increasing the frequency, it is possible to prevent the dissipation of energy due to the sound diffusion and to prevent the reduction of the signal strength. Moreover, since the distance resolution is approximately proportional to the frequency, it is preferable to use as high frequency as possible. Furthermore, if the sensor is mounted in a narrow portion such as a robot hand, the size of the sound source is several mm or less due to the limitation of the mounting space. Generally, the smaller the sound source size, the lower the directivity of the sound wave, so it is necessary to use a higher frequency sound wave to compensate for it.

  On the other hand, when high frequency sound waves are used, distance attenuation due to frequency becomes strong. Considering the merits of enhancing the sound wave directivity by raising the frequency and the demerit of the distance attenuation, the frequency band for measuring at close distance is from several hundred kHz on the low frequency side to about 2 to 4 MHz on the high frequency side. is there. The extent to which the high frequency ultrasonic waves can be used is determined by the balance with the signal strength and S / N including the system configuration.

  The distance measuring means 101 has a function of receiving the received sound wave 106 and measuring a period (time interval) from the time of transmission to the time of reception. Since the time interval t occurs from transmission to reception corresponding to the propagation path length of the ultrasonic wave, the distance to the object can be measured by measuring this time interval t. The distance measuring means has a function of calculating the distance to the object based on the time interval t and outputting a distance measurement signal.

  When the distance measuring means 101 is used for a robot hand, it is preferable that the specification be such that it can measure a distance of about 1 mm to several tens of mm. As means for transmitting and receiving ultrasonic waves of the distance measuring means 101, any means capable of transmitting and receiving ultrasonic waves can be used. For example, a capacitance type transducer using a thin membrane by MEMS (Micro Electro Mechanical Systems) can be employed. A specific device is a CMUT (Capasitive Micro-machined Ultrasound Transducer). And in order to perform transmission and reception with a plurality of ultrasonic waves with one type of transducer, it is preferable that the response characteristic of the membrane in the transmission band is non-resonant. This is because if resonance occurs at a specific frequency in the transmission band, the transmission and reception sensitivity at other frequencies will be significantly degraded. In addition, when the resonance frequency of the sound wave transmission band is close to the resonance frequency of the membrane, a reverberation sound excited immediately after the generated sound wave accompanies an increase in the measured wave number more than in actuality, and the measurement response decreases. is there.

  In order to make the membrane characteristics non-resonant in the sound wave band to be transmitted, it is preferable that the resonance frequency of the membrane be at least 2 to 3 times, preferably 5 to 10 times higher than the transmission frequency.

  The time interval t of transmission and reception of ultrasonic waves can be measured and signal output can be easily realized by combining a microcomputer or an analog circuit and a logic circuit.

  FIG. 3 is a schematic view illustrating sequential distance measurement using the ultrasonic sensor of the present invention. The waveform shape used to transmit and receive the sound wave is omitted, and the time to transmit the sound wave and the time to receive it are illustrated. Further, as for the received sound wave, the state of the sound pressure decreasing as the received sound wave becomes higher is schematically shown.

  Here, distance measurement at a close distance of approximately several mm or less (approximately 5 mm to 10 mm or less) is assumed. The time to acquire the primary received sound wave here is 30 to 60 μsec.

  201 is the time transition of the ultrasonic wave at the frequency F1, 202 is the time when the sound wave is transmitted at the frequency F1, and 203 is the time when the sound wave at the frequency F1 is received. The time difference between both times corresponds to TOF. The multiple waves are not sufficiently attenuated at a short distance of about several mm, and the multiple waves of the received sound waves are observed because they reciprocate between the ultrasonic sensor surface and the object. The time difference between the transmission sound wave and the primary reception sound wave is a first-order TOF, and the time difference between the transmission sound wave and the second-order reception sound wave is a second-order TOF. When a first-order TOF is used, the distance = (sound velocity × first-order TOF) / 2. Further, for example, in the case of using a second-order TOF, the distance = (sound velocity × second-order TOF) / 4. Furthermore, since the time interval between the second-order TOF and the first-order TOF is equal to the first-order TOF, the distance may be equal to (sound velocity × (second-order TOF−1th-order TOF)) / 2. In addition to the first-order TOF, distance measurement may be performed using a higher-order TOF. In order to enhance the response of distance measurement, it is preferable to complete the distance measurement with the lowest possible TOF.

  At a short distance of several mm or less, after the transmission and reception of the sound wave at the frequency F1 is completed, the frequency of the transmission sound wave is sequentially modulated to F2, and the next length measurement is started. 204 is a time transition of the ultrasonic wave at the frequency F2, 205 is the time when the sound wave is transmitted at the frequency F2, and 206 is the time when the sound wave at the frequency F2 is received. Although multiple waves with frequency F1 are generated, by modulating the frequency to F2, interference due to multiple waves with frequency F1 can be eliminated. As for the timing of modulating the frequency, after transmission and reception of the frequency F1 is completed (time 203), while the multiple wave of the frequency F1 is reverberating, the frequency is modulated to F2 and sound wave transmission is sequentially started .

  When performing transmission and reception using one distance measurement means, it is also necessary not to match the timing of transmission and reception, and to perform the next transmission with the frequency modulated after confirming the completion of reception, In reality, the waiting time 211 is considered.

  The next measurement using frequency F1 transmits a sound wave at time 207 when the multiple wave of frequency F1 is attenuated to a noise level, acquires a first-order received sound wave at time 208, and generates a first-order TOF. calculate. In the next measurement using frequency F2, the sound wave is transmitted at time 209 when the multiple wave of frequency F2 is attenuated to the noise level, the first-order received sound wave is acquired at time 210, and the first-order TOF is obtained. calculate. Although it depends on the transmission sound pressure and the frequency, it is preferable to keep the time until the multiple wave by the self-sound wave is attenuated to about several tens of μsec to 100 μsec. The sound pressure and frequency are adjusted so that the generation order of multiple waves is reduced within the range allowed by the S / N on the system side. If the generation order of the multiple waves is small, the return time to the state in which transmission and reception on the same frequency are possible becomes short again, and the cost increase and complexity associated with the number of frequency modulations are reduced. Further, although the case where two frequencies are used has been described in the figure, it is possible to use a plurality of frequencies within the range permitted by the system.

  FIG. 4 is a schematic view for explaining sequential distance measurement using the ultrasonic sensor of the present invention. It shows the time transition of the length measurement mode described in FIG. Reference numeral 301 denotes a transmission / reception task on the frequency F1, 302 denotes a transmission mode, and 303 denotes a reception mode. Reference numeral 304 denotes a transmission / reception task on the frequency F2, 305 denotes a transmission mode, 306 denotes a reception mode, 307 denotes a frequency modulation switching time, and 308 denotes a waiting time.

  When the distance measurement of the ultrasonic wave by the frequency F1 is completed, transmission of the ultrasonic wave modulated to the frequency F2 is sequentially started in a situation where multiple waves of the frequency F1 are generated, and the reflected sound wave of the frequency F2 is received Measure the distance with. When the distance measurement of the frequency F1 is completed, the end flag of the F1 distance measurement is obtained, and the next distance measurement in which the frequency is modulated to F2 is started. Although two frequency modulations are illustrated in FIG. 4, the number of modulations may be more than one. The processing of the distance measurement value can be performed in the background of the ultrasonic sensor operation, and the display is omitted.

  As shown in FIG. 4, a waiting time 308 is provided between the transmission mode and the reception mode. This is because it is necessary to sufficiently reduce the influence of electrical noise mixed in with the transmission. In general, the switching time 307 of the mode is several microseconds or less, the waiting time 308 is several microseconds or more, and the waiting time 308 is longer. In order to increase the limit of proximity distance measurement, it is important to shorten these times, and it is preferable to complete transmission and reception of ultrasonic waves without generating an excessive sound pressure. FIG. 5 is a schematic view for explaining another distance measurement (interruptive) using the ultrasonic sensor of the present invention. It is a method of interrupting ranging which starts transmission of the sound wave of the frequency F2 after transmission of the sound wave of the frequency F1 before reception is completed. The ranging (sequential) already described in FIG. 2 is a method of ranging in which transmission and reception of the sound wave of the frequency F2 are performed after transmission and reception of the sound wave of the frequency F1 are completed, which are largely different. FIG. 4 shows the time transition of the sound pressure for the transmission sound wave and the reception sound wave. The sound wave shape used for transmission and reception is omitted, and only the timing of transmitting and receiving the sound wave is illustrated.

  Here, it is assumed that the distance range is approximately several mm or more (approximately 5 mm to 10 mm or more). Here, the time for acquiring the primary received sound wave is 30 to 60 μsec. As the distance to an object increases, the time (TOF) from transmission to reception of a sound wave increases. That is, for the ultrasonic sensor, the ratio of the waiting time from transmission to reception increases. The ranging method described in FIG. 5 is to improve the responsiveness of ranging by utilizing the standby time for ranging.

  401 is a time transition of the ultrasonic wave at the frequency F1, 402 is the time when the sound wave is transmitted at the frequency F1, and 403 is the time when the sound wave at the frequency F1 is received. The difference between the two times corresponds to the first order TOF. The multiple waves are not completely attenuated even at a distance of several mm or more, and a high-order multiple wave as shown in FIG. 5 is observed because the object travels back and forth between the ultrasonic wave transmitting surface of the distance measuring means. However, the number of occurrences of multiple waves is smaller than distance measurement at a distance of several mm or less.

  In this embodiment, before the reception of the sound wave at the frequency F1 is completed, the frequency of the transmission sound wave is modulated to F2 and the length measurement is started. 404 is a time transition of the ultrasonic wave at the frequency F2, 405 is the time of transmitting the sound wave, and 406 is the time of receiving the primary received sound wave. The next task of length measurement using frequency F1 is to transmit the sound wave at time 407 when the multiple wave is attenuated to the noise level, acquire the first-order received sound wave at time 408, and calculate the first-order TOF . The next task of length measurement using frequency F2 is to transmit the sound wave at time 409 when the multiple wave is attenuated to the noise level, acquire the first-order received sound wave at time 410, and calculate the first-order TOF Do. Although it depends on the transmission sound pressure and the frequency, it is preferable to keep the time until the multiple wave by the self-sound wave is attenuated to about several tens of μsec to 100 μsec. The sound pressure and frequency are adjusted so that the generation order of multiple waves is reduced within the range allowed by the S / N on the system side. Although two frequency modulations are shown in FIG. 5, the number of modulations may be more than one.

  As for the timing of modulating the frequency, after transmitting the sound wave of frequency F1 (time 402), while the multiple wave of frequency F1 is reverberating, the frequency is modulated to F2 and the sound wave transmission is interruptedly started. . When transmitting and receiving with one ultrasonic sensor, it is not possible to match the timing of transmission and reception. After waiting for the reduction of the electrical noise mixed in after transmitting the sound wave of the frequency F1, a slight waiting time 411 is considered to transmit the sound wave at the frequency F2.

  FIG. 6 is a schematic view for explaining the distance measurement corresponding to FIG. 5 using the ultrasonic sensor of the present invention, and shows the time transition of the length measurement mode described in FIG. Reference numeral 501 denotes a transmission / reception task on the frequency F1, 502 denotes a transmission mode of the frequency F1, and 503 denotes a reception mode of the frequency F1. Reference numeral 504 denotes a transmission / reception task on frequency F2, 505 denotes a transmission mode of frequency F2, 506 denotes a reception mode of frequency F2, 507 denotes a switching time of frequency modulation, and 508 denotes a waiting time.

  The interruption distance measurement in this embodiment means that the transmission of the ultrasonic wave at the frequency F2 is promptly started as an interruption before the transmission and reception of the ultrasonic wave at the frequency F1 is completed, and the distance measurement is performed by the sound wave of the frequency F2. It is something to do. First, when the transmission of the frequency F1 is completed, the sound wave transmission end flag of the F1 is obtained, and the next distance measurement in which the frequency is modulated to F2 is started within several microseconds. Although two frequency modulations are shown in FIG. 6, there may be more than one. The processing of the distance measurement value can be performed in the background, and the display is omitted. When the distance to the object is long, the waiting time 508 until the sound wave returns is inevitably long. Conventionally, the standby time has not been utilized, but in the present invention, it is possible to use it as a ranging task by modulating the frequency. As a result, the response of distance measurement can be made faster.

  In order to perform distance measurement in an interruptive manner in an ultrasonic sensor using one distance measuring means, it is desirable to grasp an approximate distance range in advance and set the number of modulations (described in detail later). As understood from FIG. 6, when there are too many modulations with respect to the distance, interference may occur between the reception timing at a certain frequency and the transmission timing of another frequency. However, by shortening the transmission time of the sound wave, such as setting the transmission sound wave to one wave with high frequency, it is possible to avoid the time when distance measurement can not be performed as much as possible (error processing).

  FIG. 7 is a schematic view showing a relationship between an actual distance to a measurement object and TOF (Time-Of-Flight, sound wave propagation time) obtained by distance measurement. TOF is sound wave propagation time, and it is calculated by TOF = (2 * distance) / sound velocity, and the relationship between the distance and TOF corresponds to the straight line 601. The closer the distance, the shorter the TOF, and the farther the distance, the longer the TOF. The absolute value of the velocity of sound C is important to improve the distance accuracy. The sound velocity C is calculated as a function of air temperature from the ideal sound velocity C0 (343.62 m / s) at a temperature of 293.15 K and a humidity of 0% dry air. Since the speed of sound is sensitive to air temperature, it is necessary to obtain temperature information in the vicinity. It is convenient to install a temperature sensor near the measurement space and acquire the temperature through an external system.

  When the distance to the object is short, a high-order multiple wave is generated between the sensor and the object, and the next measurement can not be performed until the multiple wave is attenuated. The time 602 until the multiple wave attenuates is shown. In the short distance symmetrical distance measurement system of the present invention, a time 602 of about 100 μsec is sufficient, which is about 17 mm in terms of distance.

  With respect to standby constraints at short distances, it is possible to escape from these constraints by performing sequential ranging with the frequency modulation (see FIGS. 3 and 4). Also, in the vicinity of the time range 602 and in the distance range beyond that, the waiting time due to reception waiting can be utilized for distance measurement by performing the above-mentioned interruptive distance measurement (see FIGS. 5 and 6). .

  The response of distance measurement is improved by performing sequential distance measurement and interruptive distance measurement according to the present invention with reference to FIG. Since the distance measurement is finally averaged to obtain the final distance measurement value (described later), the larger the number of times of distance measurement per time, the faster the distance measurement response.

  FIG. 8A is a schematic view showing time transition of a ranging sequence in the conventional ranging and the sequential ranging of the present invention. As described with reference to FIG. 7, when the distance is short, multiple waves due to the self-sounds are reflected. In the conventional distance measurement, it is necessary to perform next distance measurement after waiting for a time 602 during which the multiple stray waves attenuate (time 701 until the start of the next distance measurement in the prior art). However, by performing sequential ranging while modulating the frequency of the present invention, it is possible to perform next ranging without almost waiting (a time 702 until the start of next ranging in sequential ranging). In consideration of securing the sound pressure necessary for the distance measurement, the time 602 for which the multiple wave attenuates is about 100 μsec. Since the constraint time 602 is substantially fixed, the distance measurement efficiency of the sequential distance measurement becomes higher as the distance is shorter.

  FIG. 8B is a schematic view showing the time transition of the distance measurement sequence with respect to the conventional distance measurement and another distance measurement (interruptive) of the present invention. When the distance measurement distance becomes long, in the conventional distance measurement, the time from when the ultrasonic sensor transmits the sound wave to when the sound wave is received (the time until the next distance measurement start in the conventional case 703) becomes long. That is, the standby time becomes long, and the next distance measurement can not be started promptly. On the other hand, by performing the interruption distance measurement according to the present invention, it is possible to perform the next distance measurement almost without waiting (time 704 until the next distance measurement start in the interruption distance measurement). In the case of the interruption distance measurement, the distance measurement efficiency becomes higher as the distance is longer (in addition, it is necessary to modulate the frequency).

  In the present invention, the successive distance measurement has higher distance measurement efficiency as the distance is shorter, and the interrupting distance becomes higher as the distance distance is longer. Therefore, it is preferable to properly select two ranging methods according to the distance range. That is, it is possible to regard sequential ranging as the first measurement mode and interruptive ranging as the second measurement mode, and switch between these measurement modes for measurement. For example, 10 μsec is assumed as the sound wave transmission time (the net time used for sound wave transmission is several μsec). Then, in the case of the interrupting distance measurement, it is assumed that an interval from transmission of the sound wave transmission to transmission of the next sound wave is secured for 10 μsec. In that case, the boundary distance at which the superiority of each distance measuring method is a trade-off is about 5 to 7 mm. Therefore, in the case of measuring only a short distance of about several mm, it is only necessary to perform sequential distance measurement. When distance measurement is performed from several millimeters (5 mm) to several tens of millimeters, it is preferable to perform distance measurement by switching between two types of distance measurement modes, sequential distance measurement and interruptive distance measurement.

  FIG. 9 is a schematic view illustrating a functional block diagram of the ultrasonic sensor of the present invention. In FIG. 9, 805 is a measurement object to be measured, 804 is an ultrasonic wave propagating in the air, and 801 is a distance measurement means MUT (Micro-machined Ultrasound Transducer). In the present embodiment, a CMUT (Capasitive Micro-machined Ultrasound Transducer) is used as the MUT. In the CMUT, the transmission / reception operation is performed in a state where DC-BIAS 814 is applied to the counter electrode of the signal electrode. In order to prevent high frequency noise from being superimposed on the DC-BIAS 814 in the frequency band to be transmitted / received, it is preferable to dispose an LPF with strong damping force in the vicinity of the MUT.

  First, the signal block of the received sound wave will be described. The protection circuit 1 (815) is for preventing the high voltage signal for generating the transmission sound wave to the MUT 815 from being mixed into the reception circuit side. The protection circuit 1 (815) can use, for example, a commercially available protection IC for ultrasonic waves. Because the received signal strength (current signal) is small in the CMUT, it is general to perform current-voltage conversion (impedance conversion) in the preamplifier 806 first. The preamplifier 816 of the CMUT often uses a current input circuit (transimpedance circuit) to prioritize broadband characteristics, but a voltage input circuit may be used if S / N and band characteristics are acceptable.

  At the subsequent stage of the preamplifier 816, a BPF (band pass filter) 817 configured of an analog circuit for selecting a frequency is disposed. In order to use the BPF 817 corresponding to the desired frequency, the controller 818 instructs a selection signal of the BPF 817. The BPF 817 is selected to receive the frequency of the sound wave corresponding to the frequency of the transmission sound wave. Next, the signal is amplified 100 times or more by the LNA (low noise amplifier) 819, separated from the noise signal intensity stored in advance by the comparator 820, and the control device 818 counts the time required for transmitting and receiving the ultrasonic waves. Is recorded in The arrangement in the block of the BPF 817 may be after the LNA 819. The control unit 822 of the external system instructs the start of distance measurement of the ultrasonic sensor, acquires a distance measurement value, and the like. In order to receive the sound wave corresponding to the frequency of the transmission sound wave, the control device 818 outputs a signal for selecting the BPF 817 of the corresponding frequency.

  Next, a signal block of sound wave transmission will be described. The waveform generation unit 823 has a function of generating a plurality of modulated frequency signals. The waveform generation function and the signal amplification function may be independent for each frequency, or one amplification AMP may be connected to the subsequent stage of the waveform generation unit that generates a plurality of frequencies. The waveform of the transmission sound wave is configured such that a specific one frequency component is a main component, and the number of pulses is approximately 1 to 10. Although one pulse number is ideal, in view of the influence of environmental noise, it may be configured with a plurality of pulse numbers. In order to transmit a sound wave of frequency F 1, the drive pulse generated by the waveform generation unit 823 is applied to the MUT 801. The drive voltage of the CMUT is set so that the total voltage of the DC-BIAS 814 and the drive pulse does not exceed the pull-in voltage. The pull-in voltage is a state in which the membrane of the CMUT is in contact between the upper and lower electrodes, and once it is in contact, the membrane material is charged and drifts in characteristics, so it should be avoided. The voltage actually used is about ± several tens of volts, and it may be supplied from the system side.

  The protection circuit 2 (824) is disposed between the waveform generation unit 823 and the MUT 801. The protection circuit 2 has a function of passing a high voltage drive signal for generating a transmission sound wave but not passing a weak reception signal when the sound wave is received. In general, it is possible to configure a diode clip circuit. The output end of the waveform generation unit 823 is generally low impedance, and it is necessary to prevent the reception signal from entering the output end. Generally, in the transmission / reception circuit of an ultrasonic sensor, a signal path for generating an acoustic wave in the MUT 801 and a protection circuit for making a signal path for receiving an acoustic wave in the MUT 801 independent in the system are required.

  The controller 818 is described in one block, but can be configured, for example, by using a commercially available microcomputer IC having a time counter and a flag function, and PLD (programmable logic device) for processing / control. Although it is possible to use a single chip PLD, it is preferable to use a low cost PLD in combination with a commercially available IC in order to achieve high speed / low cost. Although the processing / control in the present invention is not complicated, it is assumed that it is not easy to configure only with a commercial IC, and the use of PLD facilitates the functional confirmation. In mass production, one-chip integration by ASIC is also useful. FIG. 10 is a schematic view showing an operation sequence using the ultrasonic sensor of the present invention. Description will be made by using the functional blocks shown in FIG. After the control device 818 receives a timing signal to start length measurement from the control unit 8222 of the external system, length measurement starts (S1). First, environmental noise is measured (S2) using the MUT 801, and the reference signal level is stored. Environmental noise measurement may be performed during processing waiting time.

  Next, sequential distance measurement (S3) is performed to grasp an approximate initial position Li. Here, there are two purposes for grasping the initial position. (1) In order to select a distance measurement mode (sequential distance measurement, interruptive distance measurement) according to the distance, (2) in an interrupting distance measurement, a reception mode at a certain frequency, This is to control so that temporal overlap of transmission modes at different frequencies does not occur. In sequential ranging, since transmission and reception are completed on one frequency and then transmission and reception are started on another frequency, interference problems such as interruptive ranging do not occur.

  As described with reference to FIG. 8, if the distance is a few mm or less, the response of sequential distance measurement is high, and if the distance is several mm or more, the interruptive distance measuring response is high. It is preferable to select the most suitable ranging method according to the distance range (S5). Further, as described with reference to FIG. 6, in the case of interruptive ranging, when the number of modulations of the frequency increases, the temporal overlap of the reception mode at one frequency and the transmission mode at another frequency becomes May occur. The simultaneous operation of the transmitting operation and the receiving operation can not be performed in one ultrasonic sensor, so it is necessary to prevent them from overlapping in time. If the initial position can be roughly grasped, this overlap can be eliminated by controlling the number of modulations. Since the interference time is short if the transmission sound wave is one high frequency wave, etc., it is possible to process some TOF signals by error exclusion. However, in the case of transmitting a plurality of pulses of the transmission sound wave, it may be desirable to take measures in advance because the interference time becomes long.

  Then, the distance threshold Lt (the distance 704 in FIG. 8B) set in advance is compared with the initial position Li, and if Li <Lt, sequential ranging (S7), if Li な ら ば Lt, interruptive ranging (S8) To start. In both of the distance measurement, the distance measurement is performed a plurality of times while modulating the frequency, and the distance is calculated using the average value (S9). Whether to continue the distance measurement (S10) is determined by the length measurement start flag of the control unit 812 of the external system. When continuing the ranging, since the approximate distance range is already known, the initial sequential ranging is not performed. When continuous distance measurement is to be performed, the number of sound wave modulations is referred to and set from table data from approximate distance range information. FIG. 11 is a schematic view showing a data acquisition flow using the ultrasonic sensor of the present invention. Data group 1001 corresponds to the first ranging data (time count) when ranging while modulating the frequency to F1, F2,... Fn by sequential ranging or interrupting ranging. . A data group 1002 corresponds to the k-th distance data (time count) acquired by performing distance measurement using the same frequency in a state where multiple reflections are sufficiently attenuated. Although the total number of data is selected from about 16 to 128, if it is acceptable to reduce the response, it may be accumulated further. Since noise is reduced by √ (number of data), S / N is improved by √ (number of data). In order to improve S / N, it is preferable to increase the number of data. The distance information of each frequency is stored in the storage unit 811. The data 1003 corresponds to the final distance measurement information obtained by averaging the distance information. It is convenient to output the distance measurement information as a distance by dividing it by the speed of sound at the front stage of outputting the time count.

  12A and 12B are schematic views for explaining the cross-sectional configuration of the distance measuring means of the ultrasonic sensor of the present invention. In the present embodiment, a CMUT is used as the distance measuring means. The CMUT constitutes means for transmitting and receiving sound waves by utilizing the change in electrostatic attraction and the change in capacitance between the electrode 1102 disposed on the membrane 1101 and the electrode 1103 disposed on the opposite substrate. The basic configuration of the device is described in, for example, JP-A-2017-85257, JP-A-2016-101417, and JP-A-2014-17566. The CMUT can be appropriately designed based on the contents described.

  In order to achieve non-resonance in the transmission band, several tens of μm thick membranes with several tens of μm to several hundreds of μm in diameter are integrated, making one ultrasonic wave in several mm area. The form which comprises a sensor can be adopted. For example, the membrane 1101 of the CMUT is mainly configured using a SiN material, and the cell diameter can be 40 μm, and the gap between the upper and lower electrodes can be about 200 nm. The resonance frequency of the membrane 1101 is about 13 MHz when the total thickness with the electrode is about 2 μm and Vb (bias voltage) is about -50 V applied. When a drive waveform of 4 MHz was applied to such a structure, it was confirmed that non-resonance characteristics were maintained. Here, the resonance frequency of the membrane 1101 is approximately 4 to 26 times in the transmission band (500 KHz to 3 MHz).

  In order to perform distance measurement using the ultrasonic sensor of the present invention, it is useful that the vibration characteristic of the membrane 1101 becomes non-resonant in the transmission sound wave band since one distance measuring means is provided. Therefore, it is useful that the resonance frequency of the membrane 1101 be at least several times, preferably 5-10 times higher than the transmission frequency. From the relationship between the membrane structure and the resonant frequency, in order to increase the resonant frequency, it is desirable to make the membrane thickness smaller and the cell diameter smaller.

  In FIGS. 12A and 12B, the first electrode 1102 is disposed on the membrane 1101, and the second electrode 1103 is disposed on the substrate facing the membrane 1101. A ground electrode is disposed below the second electrode 1103 (not shown). The membrane 1101 is supported by a partition 1104 disposed on a substrate. A structure including a pair of electrodes shown here constitutes a cell 1105.

  A predetermined potential difference Vb is applied from the wiring 1106 between the first electrode 1102 and the second electrode 1103, and the membrane 1101 is bent toward the substrate side, and tension is applied toward the substrate side. Be done. By applying a potential difference of alternating current from the wiring 1107 between the first electrode 1102 and the second electrode 1103, the membrane 1101 is vibrated to transmit ultrasonic waves. On the other hand, when the ultrasonic wave returned from the object reaches the membrane 1101, the membrane 1101 vibrates, and the capacitance between the first electrode 1102 and the second electrode 1103 changes. Since a predetermined potential difference Vb is always applied between the first electrode 1102 and the second electrode 1103, the reception timing and the magnitude of the received ultrasonic waves are detected by detecting the minute current generated along with the capacitance change. Can be measured. The combination of an electrode for applying an AC potential difference and an electrode for applying Vb may be either the first electrode 1102 or the second electrode 1103 or the second electrode 1103 or the first electrode 1101. It is selected in consideration of process constraints of device fabrication, signal S / N, responsiveness, and the like.

  As shown in FIG. 12A, no member is disposed on the membrane 1101 of the distance measuring means, and the structure is in direct contact with the air. The CMUT constituting the distance measuring means of the ultrasonic sensor of the present invention is not limited to this, and as shown in FIG. 12B, the elastic body 1108 may be disposed on the membrane 1101 of the distance measuring means. It is relatively easy to place the elastic body 1108 on one side of the substrate relatively easily, and the surface of the membrane 1101 is protected, so that breakage of the membrane 1101 when it comes in contact with an object can be prevented. Good. As the elastic body 1108 used here, it is preferable to use a material which is excellent in ultrasonic wave permeability and which hardly affects the mechanical properties of the membrane 1101 (a material smaller than the longitudinal elastic modulus of the material of the membrane is more suitable). desirable. The material can be selected from silicone rubber, EPDM (ethylene propylene rubber), PDMS (dimethylpolysiloxane), urethane rubber and the like.

  Further, it is desirable to make the thickness of the elastic body 1108 on the membrane 1101 of the distance measuring means as thin as possible. As a result, since attenuation of the ultrasonic wave in the elastic body can be minimized at the time of transmission and reception of the ultrasonic wave, a large transmission and reception signal can be obtained, and more accurate distance measurement can be performed. FIG. 13 is a schematic view for explaining the top surface arrangement of the distance measuring means in the ultrasonic sensor of the present invention. A transducer as an actual distance measuring means integrates a plurality of cells 1105 each having a diameter of several tens of μm to several hundreds of μm to form one element 1201 of several mm in size. The upper surface electrode, the lower electrode, and the ground potential arranged in each membrane are wired such that one element has a common potential. The arrangement of the cells 1105 may be various arrangements such as a staggered arrangement even in a lattice arrangement. The shape of the cell 1105 viewed from the top is circular, and the shape of the vibrating part is circular, but may be square, rectangle, polygon or the like.

  For example, when the cell diameter of 40 μm described in FIG. 12 is finely arranged in about 4000 cells, the size becomes about 3 mm in diameter. Since the reception sensitivity of the CMUT is proportional to the area, the larger the transmission sensitivity, the easier it is to increase the transmission / reception sensitivity. The sensor size is determined almost from the space of the mounting space. FIG. 14 is a schematic view for explaining a robot hand system equipped with the ultrasonic sensor of the present invention. The distance measuring means 101 of the present invention is disposed at the tip of the finger portion 102 of the robot hand. The finger portion 102 is supported by the finger driving means 1301 from the fixed portion. The finger drive means 1301 has a drive mechanism such as a motor inside, and has a mechanism movable in the directions of arrows A and B based on a drive signal 1302 from the outside. The output signal 1303 from the distance measuring unit 101 is input to the finger position calculating unit 1304, and the finger position calculating unit 1304 receives the input signal of the position coordinate of the place where the distance measuring unit 101 of each finger portion is disposed. The original position is calculated and output as finger portion position information. The finger control unit 1305 generates a finger drive signal for instructing the drive of the finger 102 based on the finger position information. For example, if the distance to the object 105 is long, processing is performed to bring the finger portion 102 closer, and if the distance is short, the position of the finger portion 102 is adjusted so as to grasp slowly so as not to damage the object.

  Although FIG. 14 illustrates the configuration in which the two finger portions and the drive unit provided with the finger portion are one, the present invention is not limited to this configuration. The finger portion 102 can be configured to have more than two, and various configurations can be adopted, such as a configuration having a plurality of driving means included in the finger portion and having an articulated finger. By using the ultrasonic sensor according to the present embodiment, it is possible to feed back distance measurement information while performing distance measurement at intervals of several msec at the shortest distance in the close distance. In particular, in proximity operation in a robot, high-speed (several msec or more) and high-precision (several 10 μm or more) operations are required, but it is possible to provide an ultrasonic sensor that substantially meets the required specifications.

Second Embodiment
The present embodiment is characterized in that a transducer composed of a piezoelectric film (thin film) is used as a sound wave source. The other items are in accordance with the first embodiment.

  FIG. 15 is a schematic view illustrating the cross-sectional structure of a transducer (PMUT; Piezoelectric Micromachined Ultrasonic Transducers) composed of a piezoelectric film (thin film). It is characteristic that a distance measuring means is constituted by using a thin membrane 1403 in which a piezoelectric thin film 1402 is disposed on a thin substrate 1401. The membrane constituting the distance measuring means can be appropriately used as long as it can obtain necessary mechanical properties such as silicon nitride film, silicon, metal and the like. The substrate may be suitably selected from silicon, glass, metal, glass epoxy and the like as long as necessary mechanical properties, adhesion to the membrane, and insulation can be obtained. As the electrode, a metal material can be widely adopted, but as an example, it is possible to adopt Pt based if it is subjected to a firing process, and Al based if it can separate the firing process. The piezoelectric film has a large capacitance, and the electrical resistance of the Pt-based electrode is larger than that of the Al-based electrode. It is preferable to minimize the loss of high frequency characteristics due to a large CR delay. In the case of driving a several mm size transducer (PMUT) with several MHz, it should be noted that the effect of CR delay can not be ignored.

  The membrane 1403 constituting the distance measuring means transmits ultrasonic waves by vibrating the membrane 1403 by applying a drive voltage of the piezoelectric thin film 1402. In order to displace the membrane 1403 of the piezoelectric thin film in both directions normal to the surface, for example, the wire 1404 is connected to the ground potential, and a BIAS voltage is superimposed on the wire 1405 to apply a pulse waveform in the ± direction. The reverse usage may be applied to the wiring 1404 and the wiring 1405.

  In a thin film, the electric field strength is necessarily high, so that the polarization is substantially reversed when a reverse electric field is applied. Therefore, it is general to apply a pulse waveform of both poles in a state where the reference potential is offset by the BIAS voltage (one-side electric field direction). Of course, driving (negative pressure or positive pressure only) may be performed to apply a pulse waveform of one pole on the basis of 0 V. With ultrasonic waves propagating in the air, transmission and reception of both positive pressure sound waves and negative pressure sound waves, only positive pressure sound waves, and only negative pressure sound waves are possible.

  On the other hand, the reflected ultrasonic wave reaches the transducer and vibrates the membrane 1403 to generate an electric charge in the piezoelectric thin film 1402. Reception is performed by converting the generated charge into a voltage using a conversion circuit such as a resistance voltage conversion circuit or a charge amplifier circuit through the wiring 1405.

  Also in the PMUT, as in the CMUT, a plurality of cells of approximately 50 to 100 μm or less can be finely arranged to constitute a sensor of several mm or so. The reason for using a small cell is to secure non-resonance characteristics in the transmission sound wave band. For example, it is possible to obtain frequency characteristics similar to the CMUT of the first embodiment with the following configuration. That is, the cell size is 50 μm square, the diaphragm is SiN (film thickness 2.5 μm) and SiO 2 (film thickness 0.5 μm), the lower electrode is Ti / Pt, PZT (film thickness 2 μm), upper electrode Pt, protective film SiO 2 By setting (0.3 μm), a resonance frequency of 10 to 13 MHz can be obtained. The 2130 cells can be finely arranged to have a size of about 3 mm. FIG. 16 is a schematic view for explaining functional blocks of the ultrasonic sensor in the present embodiment. The voltage application method according to the difference in the device configuration of CMUT and PMUT is different, but the other configuration is basically the same. 805 is an object to be measured, and 804 is an ultrasonic wave propagating in the air. In this embodiment, PMUTs (Piezoelectric Micromachined Ultrasonic Transducers) are used as the distance measurement means 801. Also in the PMUT, DC-BIAS is applied to the signal electrode side in order to perform transmission and reception using positive pressure and negative pressure as in the CMUT. Needless to say, DC-BIAS is not necessary in the case of transmission and reception operations of only negative pressure or only positive pressure. The merit of PMUT over CMUT is that the configuration is simple and the voltage can be lowered. In addition, it is preferable to make DC-BIAS unnecessary.

  Although there are slight differences between CMUT and PMUT used as distance measuring means of the ultrasonic sensor, the difference between the two will be mainly described here.

  As for the signal block of the received sound wave, since the received signal strength (voltage signal) of the PMUT is not as small as that of the CMUT, the preamplifier 806 shown in FIG. 9 may not be used. Of course, a current input circuit (transimpedance circuit) may be used in order to prioritize broadband characteristics, and a voltage input circuit may be used if S / N and band characteristics are acceptable. For the signal block of sound wave transmission, the drive waveform of PMUT is set to be in the direction of one pole with respect to the GND potential. The drive voltage to be actually used has a pulse waveform of several tens volts. The voltage may be supplied from the system side.

  In the present embodiment using a PMUT as an ultrasonic wave generation source, as in the first embodiment, it is possible to perform distance measurement for several msec at the fastest in the close distance. Furthermore, with respect to the CMUT of the first embodiment, it is possible to reduce the number of parts without a preamplifier and without a BIAS power supply, and to lower the drive voltage.

Third Embodiment
The present embodiment is characterized in that a correction for improving distance measurement accuracy is performed using a CMUT as a sound wave source. The other components are in accordance with the first embodiment.

  FIG. 17 is a graph showing the relative difference in distance measurement value for each frequency when distance measurement is performed while modulating the frequency using a CMUT as a sound wave generation source. The distance measurement value at the frequency of 500 KHz of the transmitted sound wave is Ref. It will be a value. As the frequency becomes higher, the distance measurement value is Ref. There was a tendency to be relatively long with respect to the value. This is a combination of the mechanical phase characteristics of the device and the phase characteristics of the transmitting circuit and the receiving circuit. As shown in FIG. 17, since the phase characteristic does not depend on the measurement distance, it is easy to correct this deviation.

  When actually using the sensor, the absolute distance is measured at the main frequency in advance and calibration work is performed. The correction factor for each major frequency is acquired, and the measured value obtained by the measurement is corrected. Since actual pre-correction data is recorded in the storage device 821 in FIG. 9, a sequence for performing correction processing in the control device 818 or the control unit 822 of the external system is required. The correction coefficient may be prepared as table data if the frequency to be modulated is small, or if the frequency to be modulated is large, the correction curve is derived from the fitting, and if the distance accuracy allows, correction is made at an arbitrary frequency You may go.

  FIG. 18 is a schematic view showing a data acquisition flow using the ultrasonic sensor of the present invention. A data group 1001 corresponds to first distance data (time count) measured while modulating the frequency with F1, F2,... Fn by sequential distance measurement or interrupt distance measurement. A data group 1002 corresponds to the k-th distance data (time count) acquired by performing ranging using the same frequency in a state where multiple reflections are attenuated. The number of data is selected from about 16 to about 128. If it is acceptable to reduce the responsiveness, it may be integrated further. In order to improve the S / N, it is preferable to increase the number of data. A data group 1701 corresponds to data obtained by averaging distance information for each frequency. A data group 1702 corresponds to data obtained by correcting phase shift for distance information for each frequency. Data 1703 corresponds to data obtained by averaging the data group 1702 and becomes final distance measurement information. It is convenient to output the distance measurement information as a distance by dividing it by the speed of sound at the front stage of outputting the time count. Since the distance measurement information is obtained after correcting the phase error for each frequency, the distance accuracy is improved. The ultrasonic sensor of the present invention was configured using CMUT as a distance measurement means (ultrasonic wave generation source). As in the first embodiment, it is possible to perform distance measurement for several milliseconds at the fastest in the close distance. Furthermore, it is possible to improve the accuracy of the absolute distance by correcting the distance error for each frequency.

101 Distance Measurement Means 104 Ultrasonic Wave 105 Measurement Object 117 Sorting Means 118 Control Means 123 Frequency Signal Generator

Claims (15)

An ultrasonic sensor that measures the distance to an object to be measured using ultrasonic waves,
A frequency signal generator for generating a plurality of frequency signals;
While generating ultrasonic waves of a plurality of frequencies based on the plurality of frequency signals, a distance for receiving a plurality of reflected waves from the object to be measured corresponding to the plurality of ultrasonic waves and generating a plurality of reception signals Measuring means,
And sorting means for sorting the plurality of received signals,
Transmitted using an ultrasonic wave of a second frequency different from the first frequency before reflected waves based on the ultrasonic wave transmitted at the first frequency become multiple reflections and the multiple reflections are attenuated and can not be received. And an ultrasonic sensor characterized by performing reception.   The distance measuring means sequentially performs transmission and reception using an ultrasonic wave of the second frequency after receiving a reflected wave based on the first frequency. Ultrasonic sensor described in.   The distance measuring means transmits ultrasonic waves of the second frequency before transmitting reflected waves of the first frequency after transmitting the ultrasonic waves of the first frequency. The ultrasonic sensor according to claim 1, characterized in that:   The ultrasonic sensor according to any one of claims 1 to 3, wherein one distance measuring means is provided.   The ultrasonic sensor according to any one of claims 1 to 4, wherein the distance measuring means comprises a transducer.   The ultrasonic sensor according to claim 5, wherein the transducer is configured using a piezoelectric film.   The ultrasonic sensor according to claim 5, wherein the transducer is a capacitive transducer using a membrane.   The ultrasonic sensor according to any one of claims 1 to 7, wherein the sorting means is configured using a band pass filter.   The ultrasound non-sensor according to claim 8, wherein a band-pass filter different from the ultrasound-based reception of the first frequency is used for the ultrasound-based reception of the second frequency.   After receiving a reflected wave based on the first frequency, a first measurement mode in which transmission and reception using an ultrasonic wave of the second frequency are sequentially performed, and transmitting an ultrasonic wave of the first frequency After that, before the reflected wave based on the first frequency is received, measurement can be performed by switching between the second measurement mode for transmitting the ultrasonic wave of the second frequency and the second measurement mode. The ultrasonic sensor according to any one of 1 to 9.   The ultrasonic sensor according to claim 10, wherein the switching of the measurement mode is performed in accordance with a set threshold value and a distance to the measurement object.   In the case where the distance to the measurement object is smaller than the threshold, the measurement in the first measurement mode is performed, and when the distance from the measurement object is larger than the threshold, the measurement in the second measurement mode is performed. The ultrasonic sensor according to claim 11, characterized in that:   The ultrasonic sensor according to claim 12, wherein the threshold is in the range of 5 mm to 10 mm.   The ultrasonic sensor according to any one of claims 1 to 13, further comprising means for storing a correction coefficient that corrects the measured value based on the reference distance.   The ultrasonic sensor according to any one of the preceding claims, wherein the frequency is in the range of 500 KHz to 4 MHz.

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