Displacement sensing device and method

Abstract

A displacement sensing device includes a wave transmitter that transmits a modulated wave having a plurality of frequencies to an object, a wave receiver that receives a reflected wave from the object and generates a reception signal indicating a reception result, and a control section that controls transmission of the modulated wave by the wave transmitter and acquires the reception signal from the wave receiver. The control section outputs a first transmission signal to the wave transmitter to cause transmission of the modulated wave in a first measurement period, acquires a first reception signal in response thereto, extracts first phase information indicating a phase specified in correlation between the first transmission signal and the reception signal, outputs a second transmission signal to the wave transmitter in a second measurement period following the first measurement period, acquires a second reception signal in response thereto, extracts second phase information indicating a phase in correlation between the second transmission signal and the reception signal, and senses displacement of the object in the first measurement period and the second measurement period based on a difference between the first phase information and the second phase information.

Description

Technical Field

[0001] This invention relates to a displacement sensing device and method for sensing minute displacements of an object based on the transmission and reception of broadband ultrasonic waves, etc. Background Technology

[0002] Non-Patent Document 1 discloses a method for percutaneously measuring minute displacements caused by minute vibrations of the heart wall in ultrasound diagnosis. In the method of Non-Patent Document 1, high-frequency ultrasound signals are transmitted at least twice via an ultrasound transducer on the chest surface, and the received signals reflected by the heart wall are received. In this method using a phase difference tracking method, the phase difference of the complex signals obtained by orthogonally demodulating each of the two received signals is calculated, and the change in the delay time of the received signal is inferred from the phase change of the received signal. Thus, the method of Non-Patent Document 1 aims to sense minute displacements at the body surface in contact with the ultrasound transducer.

[0003] Prior art literature

[0004] Non-patent literature

[0005] Non-patent literature 1: H.Kanai, M.Sato, Y.Koiwa and N.Chubachi, "Transcutaneous measurement and spectrum analysis of heart wall vibrations", in IEEETransactions On Ultrasonics, Ferroelectrics, and Frequency Control, vol.43, no.5, pp.791-810, Sept.1996, doi: 10.1109 / 58.535480. Summary of the Invention

[0006] The problem the invention aims to solve

[0007] The purpose of this invention is to provide a displacement sensing device and method capable of accurately sensing minute displacements of an object.

[0008] Technical solutions for solving the problem

[0009] The displacement sensing device of the present invention includes a wave transmitter, a wave receiver, and a control unit. The wave transmitter transmits modulated waves of multiple frequencies to an object. The wave receiver receives reflected waves from the object and generates a received signal representing the reception result. The control unit controls the transmission of the modulated waves by the wave transmitter and acquires the received signal from the wave receiver. During a first measurement period, the control unit outputs a first transmission signal to the wave transmitter to transmit the modulated waves and acquires a corresponding first received signal. Based on the first transmission signal and the first received signal, the control unit extracts first phase information representing the phase defined in the correlation between the first transmission signal and the first received signal. During a second measurement period following the first measurement period, the control unit outputs a second transmission signal to the wave transmitter to transmit the modulated waves and acquires a corresponding second received signal. Based on the second transmission signal and the second received signal, the control unit extracts second phase information representing the phase defined in the correlation between the second transmission signal and the second received signal. The control unit senses the displacement of the object during the first measurement period and the second measurement period based on the difference between the first phase information and the second phase information.

[0010] The present invention can also be implemented by methods, computer programs, and combinations thereof.

[0011] Invention Effects

[0012] The displacement sensing device and method according to the present invention can accurately sense minute displacements of an object. Attached Figure Description

[0013] Figure 1 This is a diagram illustrating the outline of the displacement sensing device in Embodiment 1.

[0014] Figure 2 This is a block diagram showing the structure of the displacement sensing device.

[0015] Figure 3 This is a block diagram showing the functional structure of the control unit in a displacement sensing device.

[0016] Figure 4 It is a graph used to illustrate the analytical signal in a displacement sensing device.

[0017] Figure 5 This is an example Figure 4 The graph shows the envelope and phase curve of the analytic signal.

[0018] Figure 6 This is a flowchart illustrating the operation of a displacement sensing device.

[0019] Figure 7 This diagram illustrates the transmission and reception of signals in a displacement sensing device.

[0020] Figure 8 This is a diagram used to illustrate the operation of a displacement sensing device.

[0021] Figure 9 This is a flowchart illustrating the phase extraction process of the analytical signal in a displacement sensing device.

[0022] Figure 10 This is a diagram used to illustrate the phase extraction process of analytical signals.

[0023] Figure 11 This is a flowchart illustrating the inter-frame displacement calculation process in a displacement sensing device.

[0024] Figure 12 This is a diagram used to illustrate the inter-frame displacement calculation process.

[0025] Figure 13 This is a diagram used to illustrate heart rate measurement using a displacement sensing device.

[0026] Figure 14 This is a graph showing the relationship between the measurement frame rate and positioning accuracy in a displacement sensing device.

[0027] Figure 15 This is a graph showing the relationship between the SNR of the received signal and the positioning accuracy in a displacement sensing device. Detailed Implementation

[0028] Hereinafter, embodiments of the displacement sensing device of the present invention will be described with reference to the accompanying drawings.

[0029] (Implementation Method 1)

[0030] In Embodiment 1, an example of a displacement sensing device using a thermoelectric generator will be described, wherein the thermoelectric generator is a thermally excited sound wave generating device.

[0031] 1. Structure

[0032] 1-1. Overview

[0033] use Figure 1 An overview of the displacement sensing device according to Embodiment 1 will be described.

[0034] Figure 1 This is a diagram illustrating the outline of the displacement sensing device 1 of this embodiment. The displacement sensing device 1 of this embodiment is a device that senses information such as the distance to an object 3 by transmitting and receiving sound waves using a thermoelectric generator.

[0035] The displacement sensing device 1 can be used, for example, in medical applications to measure a patient's heart rate or respiration. In this case, the object 3 being sensed includes, for example, the patient's body surface. Furthermore, the displacement sensing device 1 is not limited to medical applications and can be applied to a wide variety of uses. For example, in automotive applications, the object sensed by the displacement sensing device 1 can be the driver or passenger of a car. Moreover, the object 3 being sensed is not limited to living organisms such as humans, but can also be objects. The displacement sensing device 1 can also be used in industrial applications, such as for product inspection of containers, to measure minute changes in distance from a portion of the container surface to which a label is adhered.

[0036] In the displacement sensing device 1, in sensing information such as minute distances, a linear frequency modulated pulse wave with a frequency varying over time is sent to the object 3, and the reflected wave, i.e., the echo, is received by the object 3 reflecting the linear frequency modulated pulse wave. In the displacement sensing device 1, by using a thermoelectric generator, it is possible to generate a sound wave with broadband frequency characteristics, such as a linear frequency modulated pulse wave.

[0037] The displacement sensing device 1 of this embodiment repeatedly transmits and receives sound waves as described above, thereby sensing changes in the distance between itself and the object 3, that is, the displacement of the object 3. The details of the structure of the displacement sensing device 1 will be described below.

[0038] 1-2. Device Structure

[0039] use Figure 1 as well as Figure 2 The structure of the displacement sensing device 1 in this embodiment will be described. Figure 2 This is a block diagram showing the structure of the displacement sensing device 1.

[0040] For example, such as Figure 2 As shown, the displacement sensing device 1 of this embodiment includes a wave transmitter 10, a wave receiver 11, a control unit 13, and a storage unit 14. For example, as Figure 1 As shown, the wave transmitter 10 and the wave receiver 11 are arranged close to each other on the side of the displacement sensing device 1 opposite to the object 3. The wave transmitter 10 and the wave receiver 11 are communicatively connected to the control unit 13, for example, via various signal lines.

[0041] The wave transmitter 10 of this embodiment is configured to include a thermoelectric generator as a sound source. The wave transmitter 10 generates, for example, ultrasonic waves with frequencies of 20 kHz or higher. The wave transmitter 10 can generate linear frequency modulated pulse waves with frequencies modulated over a wide bandwidth, for example, from 20 kHz to 100 kHz, using the thermoelectric generator. The wave transmitter 10 of this embodiment generates, for example, a linear frequency modulated pulse wave based on a linear frequency chirp whose frequency changes linearly with time. Furthermore, by using a thermoelectric generator, the wave transmitter 10 can be configured to be small and lightweight.

[0042] The wave transmitter 10 may also include a drive circuit for driving a thermally induced sound generator. For example, the wave transmitter 10 generates sound waves by driving the thermally induced sound generator through the drive circuit based on a transmission signal input from the control unit 13. The drive circuit of the wave transmitter 10 can also set the frequency band of the generated sound wave, the length, intensity, signal length, and directivity of the linear frequency modulated pulse indicating the period of frequency change. Not necessarily limited to ultrasound, the wave transmitter 10 can generate sound waves of various frequency bands. The wave transmitter 10 can also be various omnidirectional sound sources without particular directivity, or it can be a variable or fixed directional sound source.

[0043] In the wave emitter 10, as a thermoelectric generator that heats air to produce sound waves, it includes, for example, a heating element, a heat insulation layer, a substrate, and electrodes. The heating element and the heat insulation layer are stacked on the substrate. The heating element is made of a resistive element and heats up by current flowing through the electrodes from a drive circuit. The heating element is configured to form a sound-emitting surface in contact with air, causing the air around the sound-emitting surface to expand or contract according to temperature changes. As a result, air pressure, i.e., sound waves, are generated near the sound-emitting surface. The heat insulation layer is provided between the heating element and the substrate to suppress heat conduction from the heating element to the side opposite to the sound-emitting surface. The substrate dissipates heat conducted from the heating element.

[0044] The wave receiver 11 is, for example, a microphone such as a MEMS (Micro Electro Mechanical System) microphone. The wave receiver 11 receives the echo from the object 3 and generates a received signal representing the reception result. The distance between the wave receiver 11 and the wave transmitter 10 can be preset, for example, taking into account the distance from the displacement sensing device 1 to the object 3 during the intended sensing. The wave receiver 11 is not limited to a MEMS microphone; for example, it can also be constructed from other microphones having frequency characteristics capable of receiving broadband ultrasonic waves transmitted from the wave transmitter 10. For example, a condenser microphone can also be used for the wave receiver 11. The wave receiver 11 can be omnidirectional or can appropriately have various directional characteristics.

[0045] The control unit 13 controls the overall operation of the displacement sensing device 1. The control unit 13, for example, is a microcomputer that works in conjunction with software to achieve given functions. The control unit 13 reads data and programs stored in the storage unit 14 and performs various calculations to achieve various functions. For example, the control unit 13 generates a transmission signal for causing the wave transmitter 10 to generate a linear frequency modulated pulse wave and outputs it to the wave transmitter 10. The control unit 13, for example, stores the generated transmission signal in the storage unit 14. Details about the control unit 13 will be described later.

[0046] Alternatively, the control unit 13 can be a dedicated electronic circuit, a reconfigurable electronic circuit, or other hardware circuit designed to perform a given function. The control unit 13 can also be composed of various semiconductor integrated circuits such as CPUs, MPUs, DSPs, FPGAs, and ASICs. Furthermore, the control unit 13 can be configured to include both analog-to-digital (A / D) converters and digital-to-analog (D / A) converters, and can apply A / D or D / A conversions to various signals.

[0047] The storage unit 14 is a storage medium that stores the programs and data required to implement the functions of the control unit 13, and is, for example, composed of flash memory. For example, the storage unit 14 stores the transmission signals generated by the control unit 13.

[0048] 1-3. Regarding the Control Department

[0049] use Figure 3 Details of the control unit 13 in the displacement sensing device 1 of this embodiment will be described.

[0050] Figure 3 This is a block diagram showing the functional structure of the control unit 13. For example... Figure 3 As shown, the control unit 13, for example, includes, as a functional unit, FFT units 131a and 131b, cross-spectral calculation unit 132, Hilbert transform unit 133, IFFT units 134a and 134b, and analytical processing unit 135. Each functional unit 131 to 135 respectively implements the functions of Fast Fourier Transform (FFT), cross-spectral calculation, Hilbert transform, inverse Fast Fourier Transform (IFFT), and analytical processing described later.

[0051] The control unit 13 receives a transmission signal Sd from the storage unit 14 and a reception signal Sr from the wave receiver 11, thereby performing signal processing based on each of the functional units 131 to 135. Each of the functional units 131 to 135 can operate periodically, for example, at a given measurement frame rate (e.g., 30 frames / second) as described later.

[0052] To generate an analytical signal based on the transmitted signal Sd and the received signal Sr of each frame, a series of processes are performed based on the FFT unit 131 to the IFFT unit 134 in each of the functional units 131 to 135. The analytical signal is a complex signal composed of the cross-correlation function of the transmitted signal Sd and the received signal Sr, and is used for displacement sensing in the displacement sensing device 1. The cross-correlation function represents the correlation between the two signals Sd and Sr in the time domain.

[0053] The FFT unit 131a performs a Fast Fourier Transform on the transmitted signal Sd input to the control unit 13, and outputs the transformation result from the time domain to the frequency domain to the cross-spectral calculation unit 132. The FFT unit 131b performs a Fast Fourier Transform on the received signal Sr input to the control unit 13 in the same manner as the transmitted signal Sd, and outputs the transformation result to the cross-spectral calculation unit 132.

[0054] The cross-spectrum calculation unit 132 calculates the cross-spectrum based on the Fourier transform results of each signal Sd and Sr by the FFT unit 131, and outputs it to the Hilbert transform unit 133 and the IFFT unit 134b. The cross-spectrum corresponds to the Fourier transform of the cross-correlation function of the transmitted signal Sd and the received signal Sr. By applying the inverse Fourier transform to the cross-spectrum, the cross-correlation function is obtained.

[0055] The Hilbert transform unit 133 performs the Hilbert transform on the cross spectrum calculated by the cross spectrum calculation unit 132, and outputs the transformation result, which shifts each frequency component of the cross spectrum by π / 2, to the IFFT unit 134a.

[0056] The IFFT unit 134a performs an inverse fast Fourier transform on the cross spectrum with Hilbert transform applied, and outputs the transform result from the frequency domain to the time domain to the analysis processing unit 135. The IFFT unit 134b performs an inverse fast Fourier transform on the cross spectrum processed by the cross spectrum operation unit 132, and outputs the transform result to the analysis processing unit 135.

[0057] Through the above calculations, a signal I representing the cross-correlation function between the transmit and receive signals Sd and Sr is output as the transformation result based on the IFFT unit 134b, and a signal Q that is orthogonal to signal I is output as the transformation result based on the IFFT unit 134a.

[0058] The analytical processing unit 135 generates analytical signals having signals I and Q as real and imaginary parts, respectively, and performs processing related to the analytical signals. The analytical signals generated based on the transmitted signal Sd and the received signal Sd represent analytical functions in the complex domain. Hereinafter, the aforementioned signals I and Q will be referred to as the in-phase component I and quadrature component Q of the analytical signal, respectively.

[0059] The various functions of the control unit 13, as described above, can be implemented, for example, by a program stored in the storage unit 14, or by implementing some or all of the various functions through hardware circuitry. Alternatively, instead of performing a cross-spectrum calculation followed by an inverse Fourier transform, the control unit 13 can directly calculate the cross-correlation function based on the transmitted and received signals Sd and Sr using a multiply-accumulate operation. For example, the control unit 13 could also include an FPGA or similar circuitry for performing multiply-accumulate operations. Furthermore, the generation of the analytic signal in the control unit 13 is not limited to the Hilbert transform; for example, it can be implemented using a quadrature detection function.

[0060] 2. Actions

[0061] The operation of the displacement sensing device 1 configured as described above will be explained below.

[0062] 2-1. Summary of the action

[0063] use Figure 1 , Figure 4 as well as Figure 5 A summary of the operation of sensing the displacement of object 3 in the displacement sensing device 1 of this embodiment will be described.

[0064] In the displacement sensing device 1 of this embodiment, for example, as Figure 1 As shown, the action of sending a linear frequency modulated pulse wave once from the wave transmitter 10 to the object 3 and receiving the echo of the linear frequency modulated pulse wave through the wave receiver 11 is defined as a measurement action of one frame, and the measurement actions of each frame are executed sequentially. In the displacement sensing device 1, the control unit 13 generates an analytical signal for each measurement frame in order to analyze the correlation between the transmitted signal and the received signal.

[0065] Figure 4 This is a graph illustrating the analytical signal z(t) in displacement sensing device 1. Figure 4 The example illustrates a one-frame analytic signal z(t). The analytic signal z(t) contains the in-phase component I(t) representing the cross-correlation function of the transmitted and received signals as its real part, and the corresponding quadrature component Q(t) as its imaginary part, thus being complexized and having a complex range.

[0066] The displacement sensing device 1, for example, calculates the envelope E(t) = |z(t)| of the analytic signal z(t) and detects the peak time t0. The peak time t0 is the timing when the amplitude |z(t)| of the analytic signal z(t) in one frame becomes the largest, which can be considered as the timing corresponding to the reflection by the object 3 during the transmission and reception of the linear frequency modulated pulse wave in that frame.

[0067] Previously, a method for measuring displacement based solely on the analysis of the envelope E(t) of the analytic signal z(t) was proposed. In this method, the peak time of the envelope E(t) is detected for each frame, and the peak times of two consecutive frames are compared to determine the displacement. However, with this method, it is conceivable that the resolution used to detect the peak time from the envelope E(t) becomes the limit for displacement measurement, or that the method is affected by noise in the envelope E(t), making it difficult to accurately sense minute displacements.

[0068] Therefore, in the analytical signal z(t) in which the cross-correlation function is complexified, the displacement sensing device 1 of this embodiment analyzes the phase ∠z(t), which is information not included in the envelope E(t). Figure 5 (a) illustrates Figure 4 The envelope E(t) of the analytic signal z(t). Figure 5 (b) illustrates Figure 4 The phase curve θ(t) of the analytic signal z(t).

[0069] The phase curve θ(t) shows the correspondence between the phase ∠z(t) and time t as defined in the domain of the complex number in the analytic signal z(t). Figure 5 The phase curve θ(t) illustrated in (b) is in relation to Figure 5 The vibrational linkage in the envelope E(t) of (a) has a jagged curve shape with a steep gradient. The gradient of the phase curve θ(t) is defined by the frequency (i.e., the instantaneous frequency) of the analytic signal z(t) at each time t.

[0070] In the phase curve θ(t) of the analyzed signal z(t) for each frame, the phase ∠z(t0) at the peak time t0 of that frame is theoretically zero, and can be considered to have an offset value corresponding to various noises in the installation. Furthermore, in the phase curve θ(t), the linearity can theoretically be considered to be relatively high near the peak time t0 of the envelope E(t).

[0071] The displacement sensing device 1 of this embodiment calculates the phase difference between two consecutive frames, using the peak time t0 of one frame as a reference, and determines the displacement of the object 3 by performing a conversion based on the phase difference. Thus, even within a range smaller than the resolution described above, the displacement of the object 3 can be sensed with high precision. For example, in such a conversion based on the phase difference, a small displacement can be calculated based on the steepness of the gradient of the phase curve θ(t).

[0072] 2-2. Details of the movement

[0073] use Figures 3 to 12The operation details of the displacement sensing device 1 in the embodiment will be explained.

[0074] Figure 6 This is a flowchart illustrating the operation of displacement sensing device 1. Figure 7 This is a diagram illustrating the transmitted signal Sd and the received signal Sr in the displacement sensing device 1. Figure 8 This is a diagram used to illustrate the operation of the displacement sensing device 1. Figure 6 The processes shown in the flowchart are repeatedly executed by the control unit 13 of the displacement sensing device 1, for example, at a given cycle of every two frames.

[0075] Figure 7 (a) illustrates a transmission signal Sd that causes the wave transmitter 10 to generate a linear frequency modulated pulse wave. Figure 7 (b) illustrates the response to Figure 7 The received signal Sr of the wave receiver 11 of (a). Figure 8 (a) illustrates the envelopes E1 and E2 of the analytic signals z(t) in the first and second frames. Figure 8 (b) illustrates the phase curves θ1 and θ2 of the analytic signal z(t) in frames 1 and 2. Figure 8 In the first frame, the envelope E1 and phase curve θ1 illustrate five points near the peak time t0 of the sampling points of the analytic signal z(t). The sampling points represent times t in the analytic signal z(t) generated as a discrete signal. i signal value z(t) i ).

[0076] exist Figure 6 In the flowchart, firstly, the control unit 13 of the displacement sensing device 1 outputs a transmission signal Sd to the wave transmitter 10, controlling the wave transmitter 10 to transmit a linear frequency modulated pulse wave (S1) based on the transmission signal Sd. Figure 7 The transmitted signal Sd of (a) is a linear frequency modulated (LFM) pulse wave whose frequency varies with time via the LFM pulse length Tc, transmitted from the wave transmitter 10. The LFM pulse length Tc is set to a period shorter than the inter-frame time interval.

[0077] The displacement sensing device 1 in this embodiment uses a linear frequency modulated pulse signal based on pulse interval modulation as the transmitted signal Sd. (Similar to...) Figure 7 As illustrated in (a), pulse interval modulation causes the interval between consecutive pulses to vary over time. In this embodiment, in the wave transmitter 10, which is composed of a thermoelectric generator, the power consumption caused by the drive circuit is large during the period when each pulse is in the on state. By pulse interval modulation, the power consumption in the wave transmitter 10 can be suppressed.

[0078] exist Figure 7 In example (a), the transmitted signal Sd is a downlink linear frequency modulated pulse signal with a frequency that decreases over time, but it could also be an uplink linear frequency modulated pulse signal with a frequency that increases over time. Based on such a linear frequency modulated pulse wave, for example, compared to using ultrasound based on a single high frequency as in Non-Patent Document 1, attenuation during propagation in air can be suppressed, enabling displacement sensing with good accuracy.

[0079] Return to Figure 6 After transmitting a linear frequency modulated pulse wave (S1), the control unit 13 acquires a received signal Sr (S2) from the wave receiver 11, representing the reception result of the first frame. The reception result of the first frame represents the echo in response to the linear frequency modulated pulse wave transmitted in step S1. Figure 7 In (b), from Figure 7 Starting from the rising edge of the continuous pulse of (a), a received signal Sr is received that is delayed accordingly with respect to the time difference from the transmission of the linear frequency modulated pulse wave to the reception of the echo (i.e., the propagation period of the linear frequency modulated pulse wave).

[0080] Next, the control unit 13 calculates the cross-correlation function between signals Sd and Sr based on the transmitted signal Sd and the received signal Sr of the first frame, thereby generating an analytical signal z(t), and performs processing to extract phase information from the analytical signal z(t) (S3). In this phase extraction processing of the analytical signal (S3), the control unit 13, for example, uses the transmitted signal Sd held in the storage unit 14 and the received signal Sr acquired in step S2 as... Figure 3 The functional units 131 to 135 generate and process the analytical signal z(t).

[0081] The cross-correlation function c(τ) between signals Sd and Sr can be expressed by the following formula.

[0082] [Mathematical Expression 1]

[0083]

[0084] Here, T is the period of one frame, and τ is the delay time. The cross-correlation function c(τ) represents the correlation between two signals Sd and Sr with a delay time τ.

[0085] Control unit 13, for example, as Figure 3The control unit 13 functions as the FFT unit 131, cross-spectrum operation unit 132, and IFFT unit 134b, performing inverse Fourier transform operations on the cross-spectrum data between signals Sd and Sr, thereby outputting the in-phase component I(t) representing the cross-correlation function c(τ). Furthermore, the control unit 13 functions as the FFT unit 131, cross-spectrum operation unit 132, Hilbert transform unit 133, and IFFT unit 134a, performing inverse Fourier transform operations on the Hilbert transform of the cross-spectrum data, thereby outputting the orthogonal component Q(t) representing the Hilbert transform of the cross-correlation function c(τ). Thus, the analytic signal z(t) = I(t) + jQ(t) (where j is the imaginary unit) can be obtained from each component I(t) and Q(t).

[0086] In the phase extraction process (S3) of the analytic signal, the control unit 13 detects the peak time t0 from the envelope E(t) of the analytic signal z(t) and extracts the phase information of the phase ∠z(t0) containing the peak time t0 from the phase ∠z(t). Figure 8 (a) and (b) correspond to Figure 5 Images (a) and (b) magnify the area around the peak time t0. Figure 8 In example (a), the peak time t0 was detected in the envelope E1 of the first frame. From Figure 8 The phase ∠z(t) on the phase curve θ1 of the first frame shown in (b) is used to extract phase information based on the peak time t0. The details of the phase extraction processing (S3) of the analytical signal will be described later.

[0087] Next, similar to steps S1 and S2, the control unit 13 performs the second transmission and reception of the linear frequency modulated pulse wave and receives the received signal Sr corresponding to the transmitted signal Sd of the second frame (S4, S5).

[0088] The control unit 13 uses the phase information of the first frame and the phase information of the analytical signal z(t) generated based on the transmit and receive signals Sd and Sr of the second frame to perform a differential calculation of the displacement Δx of the object 3 based on the phase information between the two frames (S6). In this inter-frame displacement calculation process (S6), the control unit 13 serves as, for example, as... Figure 3 The functional units 131 to 135 shown generate the analytical signal z(t) of the second frame and extract the phase information of the second frame.

[0089] In the inter-frame displacement calculation process (S6), the control unit 13, for example, serves as... Figure 3 The analysis and processing unit 135 performs its function by calculating the difference in phase information of each frame. First, the control unit 13... Figure 8The phase ∠z(t) on the phase curve θ2 of the second frame shown in (b) is extracted, for example, based on the peak time t0 of the first frame. Next, the control unit 13 calculates the inter-frame phase difference Δφ at the peak time t0 based on the difference in phase information between each frame. The control unit 13 calculates the inter-frame displacement Δx through this conversion based on the peak phase difference Δφ.

[0090] The inter-frame displacement Δx can be expressed as shown in equation (1).

[0091] [Mathematical Expression 2]

[0092]

[0093] Here, c is the speed of sound, π is pi, and fc is the center frequency of the analytic signal z(t). In the inter-frame displacement calculation process (S6) of this embodiment, fc is determined based on the analytic signal z(t) of the first frame and is calculated as the gradient of the phase ∠z(t0) at the peak time t0 (i.e., the instantaneous frequency). The details of the inter-frame displacement calculation process (S6) will be described later.

[0094] Based on the above processing, the displacement sensing device 1 extracts the phase information (S3) of the analytical signal z(t) obtained through the first transmission and reception of the linear frequency modulated pulse wave (S1, S2), and calculates the displacement Δx (S6) based on the peak phase difference Δφ between the analytical signal z(t) obtained through the second transmission and reception (S4, S5). This reduces sensing errors caused by factors such as attenuation of the received signal Sr in the air and noise superposition, enabling accurate sensing of minute displacements of the object 3 even without contact with it. Furthermore, with this displacement sensing device 1, sensing can be performed without contact with the object 3, thus easily sensing minute displacements.

[0095] Regarding displacement sensing, a known method involves calculating the distance to object 3 based on the change in the peak time of the analytical signal z(t) twice, and then calculating the difference between the two distances as the displacement Δx. However, if this method of calculating distance based on peak times is used, then in sensing minute displacements, the change in the peak time, for example… Figure 8 When the time interval (i.e., sampling rate) of the sampling points of the analytical signal z(t) shown in (a) is small, it is difficult to sense displacement. In contrast, the displacement sensing device 1 according to this embodiment can, even in such cases, convert the displacement amount Δx into the peak phase difference Δφ obtained by transmitting and receiving the linear frequency modulated pulse wave, thereby sensing small displacements with good accuracy.

[0096] Furthermore, in the conventional methods for calculating distances described above, changes in the propagation period of sound waves due to airflow or other factors can lead to a decrease in calculation accuracy. In contrast, in the displacement sensing device 1 of this embodiment, the displacement amount Δx over short periods, such as between frames, is calculated directly without relying on distance calculation. Therefore, from the viewpoint of suppressing the influence of airflow or other factors on the propagation period, displacement sensing can be performed with good accuracy.

[0097] In the inter-frame displacement calculation process (S6) described above, an example was given where only phase information was used for the analytical signal z(t) of the second frame. Alternatively, the displacement sensing device 1 could also detect the peak time in the analytical signal z(t) of the second frame, and use it together with the peak time t0 of the first frame to calculate the displacement Δx, and could also use it for the phase extraction process of the analytical signal in the next execution cycle (S3). Furthermore, in the inter-frame displacement calculation process (S6), the peak phase difference could also be calculated based on the peak time of the second frame. The displacement sensing device 1 could, for example, detect the peak time in the analytical signal z(t) of the second frame instead of the first frame.

[0098] In addition, regarding the above Figure 6 The processing was illustrated with an example executed every two frames, but it can also be executed at a different cycle. For example, Figure 6 The processing can also be performed on a frame-by-frame basis. Alternatively, the transmit and receive signals Sd and Sr from the second linear frequency modulated pulse wave (S4, S5) can be pre-stored, and the phase extraction processing of the analytical signal can begin in the next execution cycle based on the stored signals Sd and Sr (S3).

[0099] 2-2-1. Phase Extraction Processing of Analytic Signals

[0100] use Figure 9 as well as Figure 10 right Figure 6 The details of the phase extraction processing of the analytical signal in step S3 will be explained.

[0101] Figure 9 This is a flowchart illustrating the phase extraction process (S3) of the analytical signal in the displacement sensing device 1 of this embodiment. Figure 10 This is a diagram used to illustrate the phase extraction process (S3) of the analytical signal. Figure 10 (a) and (b) show the amplitude |z(t)| and phase ∠z(t) of the analytic signal z(t) in the time range near the peak time t0, respectively.

[0102] Figure 9 The process shown in the flowchart is, for example, to maintain Figure 6The state of the first frame's transmission signal Sd and reception signal Sr in steps S1 and S2 begins.

[0103] First, the control unit 13 of the displacement sensing device 1 detects the peak time t0 (S11) in the amplitude |z(t)| of the analytic signal z(t) obtained based on the transmitted signal Sd and the received signal Sr. The control unit 13 is, for example, as... Figure 3 The FFT units 131 to 134 shown calculate the in-phase component I and the quadrature component Q based on the transmitted signal Sd and the received signal Sr. The control unit 13 is, for example, as... Figure 3 The analytical processing unit 135 calculates the envelope E(t) = |z(t)| based on the square root of the sum of the squares of the in-phase component I and the quadrature component Q. The control unit 13 detects the moment when the amplitude |z(t)| becomes the maximum based on the envelope E(t) as the peak moment t0 = argmax|z(t)|.

[0104] Next, the control unit 13 determines a given number (e.g., 5 points) of sampling points of the analytic signal z(t) near the peak time t0, and extracts the phase ∠z(t) of each sampling point as phase information (S12). Figure 10 In example (a), with the peak time t0 as the center, the two sampling times t before and after are... -2 t -1 Five points of the analytic signal at t1 and t2 were determined as sampling points. Figure 10 In (b), as in Figure 10 The phase ∠z(t) of each sampling point determined in (a) is used to extract the sampling time t. -2 The phase φ of the analytic signal z(t) at ~t2 -2 φ -1 φ0, φ1 and φ2.

[0105] Time t i The phase φ of the analytic signal i =∠z(t i It can be obtained through time t i In-phase component I(t) i ) and orthogonal components Q(t) i It can be expressed as follows.

[0106] ∠z(t i )=arctan(Q(t i ) / I(t i ))

[0107] For example, the control unit 13 maintains the sampling time t near the peak time t0 in the storage unit 14. -2 ~t2 and the phase φ of the extracted sampling points -2 ~φ2.

[0108] Control unit 13, for example, calculates the phase φ for the extracted sampling points using the least squares method. -2 The slope of the regression line ~φ2 (i.e., the regression coefficient) is taken as the instantaneous frequency f corresponding to the center frequency of the analytic signal z(t). c (S13). In Figure 10 In example (b), the instantaneous frequency fc is calculated with respect to the phase φ. -2 The slope of the regression line L1 ~ φ2.

[0109] Control unit 13, for example, stores the calculated instantaneous frequency fc in storage unit 14 and ends the phase extraction process of the analyzed signal (S3). Then, it jumps to... Figure 6 Step S4.

[0110] Based on the phase extraction processing of the analytical signal described above (S3), after detecting the peak time t0 of the amplitude |z(t)| of the analytical signal z(t) (S11), the phase φ of the sampling points near the peak time t0 is extracted. -2 ~φ2(S12). Then, based on the regression line L1 of the phase of each extracted sampling point, the instantaneous frequency fc of the analytic signal z(t) is calculated (S13). Thus, in the analytic signal z(t), the phase φ of multiple sampling points is obtained. -2 ~φ2, thus enabling accurate calculation of instantaneous frequency fc and inter-frame displacement calculation (S6).

[0111] In the phase extraction process (S3) of the analytic signal described above, an example was given of determining five sampling points near the peak and using them for phase ∠z(t). The sampling points near the peak are not limited to five points; for example, three points can also be used: the peak time t0 and one sampling time before and after the peak time t0.

[0112] 2-2-2. Inter-frame displacement calculation and processing

[0113] use Figure 11 as well as Figure 12 right Figure 6 The details of the inter-frame displacement calculation process in step S6 will be explained.

[0114] Figure 11 This is a flowchart illustrating the inter-frame displacement calculation process (S6) in the displacement sensing device 1 of this embodiment. Figure 12 This is a diagram used to illustrate the inter-frame displacement calculation process (S6). Figure 12 The phase curves θ1 and θ2 of each analytical signal z(t) in the first and second frames are shown.

[0115] Figure 11The flowcharts show the various processes, for example, to maintain in Figure 6 The phase φ of the analytic signal z(t) of the first frame obtained in steps S3 to S5 -2 ~φ2 and sampling time t near the peak -2 The states of the transmit and receive signals Sd and Sr in frame ~t2 and the second frame begin.

[0116] First, the control unit 13 calculates, for example, the sampling times t near the peak time t0 of the first frame from the analytic signal z(t) obtained based on the transmit and receive signals Sd and Sr of the second frame. -2 The phase at ~t2 is used as the phase information for the second frame (S21). The control unit 13 generates the analyzed signal z(t) for the second frame in the same manner as generating the analyzed signal z(t) for the first frame in the phase extraction process of the analyzed signal (S3). Figure 12 In the example, in the generated analytic signal z(t) of the second frame, the sampling time t of the phase ∠z(t) on the phase curve θ2 is calculated. -2 Phase ψ of ~t2 -2 ψ -1 ψ0, ψ1 and ψ2.

[0117] Next, the control unit 13 calculates the sampling time t. -2 The inter-frame phase difference (S22) at ~t2. Figure 12 In, according to each sampling time t -2 ~t2 calculates the phase φ of the first frame -2 ~φ2 and the phase ψ of the second frame -2 The difference between ~ψ2 is taken as the phase difference Δφ. -2 , Δφ -1 , Δφ0, Δφ1 and Δφ2.

[0118] Control unit 13 calculates each sampling time t -2 Phase difference Δφ between the first and second frames under ~t2 -2 The average of ~Δφ2 is taken as the peak phase difference Δφ between frames (S23).

[0119] The control unit 13 calculates the inter-frame displacement Δx (S24) based on the peak phase difference Δφ, for example using the instantaneous frequency fc of the first frame, through the conversion shown in the above equation (1).

[0120] Based on the above inter-frame displacement calculation process (S6), and based on the sampling time t near the peak of the first frame... -2 Phase difference Δφ between ~t2 and the second frame -2~Δφ2, calculate the peak phase difference Δφ (S21~S23), and calculate the inter-frame displacement Δx based on the peak phase difference Δφ (S24). Therefore, the phase difference Δφ from multiple sampling points can be used. -2 The peak phase difference Δφ is calculated using ~Δφ2, and displacement is accurately sensed based on the peak phase difference Δφ.

[0121] In the inter-frame displacement calculation process (S6) described above, it was explained that the sampling time t was used... -2 Phase difference Δφ ~t2 -2 The average of ~Δφ2 is used as an example of the peak phase difference Δφ. The peak phase difference Δφ is not limited to the above example; for example, the inter-frame phase difference Δφ0 at the peak time t0 of the first frame can also be used. Furthermore, for example, the peak time of the analyzed signal z(t) of the second frame can also be detected through the same process as step S11 of the phase extraction process (S3) of the analyzed signal, and the peak phase difference Δφ can be calculated based on the average of the phase differences near the peak time of the second frame. The peak phase difference Δφ can also be calculated based on... Figure 10 The regression line L1 of the first frame illustrated in (b) is calculated, along with a function representing the regression line that can be operated on in the same way as the regression line L1 for the phase ∠z(t) of the second frame.

[0122] In step S24 above, an example of calculating the displacement Δx using the instantaneous frequency fc of the first frame was described. Step S24 is not limited to the instantaneous frequency fc of the first frame. For example, the instantaneous frequency can be calculated based on the phase ∠z(t) of the analyzed signal z(t) of the second frame using the same processing as steps S11 to S13 of the phase extraction processing (S3) of the analyzed signal, and then used to calculate the displacement Δx. Alternatively, the displacement Δx can be calculated by averaging the instantaneous frequency fc of the first frame and the instantaneous frequency of the second frame.

[0123] 3. Summary

[0124] As described above, the displacement sensing device 1 of this embodiment includes a wave transmitter 10, a wave receiver 11, and a control unit 13. The wave transmitter 10 transmits a linear frequency modulated pulse wave to the object 3, as an example of a modulated wave having multiple frequencies. The wave receiver 11 receives the reflected wave (i.e., echo) from the object 3 and generates a received signal Sr representing the reception result. The control unit 13 controls the transmission of the linear frequency modulated pulse wave by the wave transmitter 10 and acquires the received signal Sr from the wave receiver. In the first frame, as an example of a first measurement period, the control unit 13 outputs a first transmission signal Sd to the wave transmitter 10, causing the transmission of the linear frequency modulated pulse wave (S1), and acquires a corresponding first received signal Sr (S2). Based on the first transmission signal Sd and the first received signal Sr, the control unit 13 extracts first phase information (S3) representing the phase defined in the correlation between the first transmission signal Sd and the first received signal Sr. In the second frame, which is an example of a second measurement period following the first measurement period, the control unit 13 outputs a second transmission signal Sd to the wave transmitter 10, causing the transmission of a linear frequency modulated pulse wave (S4), and acquires a corresponding second reception signal Sr (S5). Based on the second transmission signal Sd and the second reception signal Sr, the control unit 13 extracts second phase information representing the phase defined in the correlation between the second transmission signal Sd and the second reception signal Sr (S6). Based on the difference between the first phase information and the second phase information, the control unit 13 senses the displacement of the object between the first frame and the second frame, which is an example of both the first and second measurement periods (S6).

[0125] Based on the displacement sensing device 1 described above, the displacement of the object 3 during the first measurement period and the second measurement period is sensed based on the difference between the first phase information and the second phase information. Therefore, for example, it is possible to sense the displacement of the object 3 during the first measurement period and the second measurement period based on the difference between the first phase information and the second phase information. Figure 5 The steepness of the phase gradient shown in (b) accurately senses minute displacements.

[0126] In this embodiment, the control unit 13 generates a first analyzed signal z(t) based on the first transmitted signal Sd and the first received signal Sr, which includes the amplitude |z(t)| and the phase ∠z(t) defined in the correlation between the first transmitted signal Sd and the first received signal Sr. As an example of first phase information, the control unit 13 extracts the phase φ of the first frame from the first analyzed signal z(t). -2 ~φ2(S3, S11~S12). Based on the second transmitted signal Sd and the second received signal Sr, the control unit 13 generates a second analytical signal z(t) containing the amplitude |z(t)| and phase ∠z(t) defined in the correlation between the second transmitted signal Sd and the second received signal Sr, and extracts the phase ψ of the second frame from the second analytical signal z(t) as an example of the second phase information. -2~ψ2(S6, S21). Therefore, it is possible to analyze the phase ∠z(t) separately from the amplitude |z(t)| in the analytic signal z(t), thereby extracting the phase information.

[0127] In this embodiment, as an example where at least one of the amplitudes of the first analytical signal and the second analytical signal reaches its maximum, the control unit 13 detects the peak time t0 (S3, S11) when the amplitude |z(t)| of the analytical signal z(t) of the first frame reaches its maximum, and calculates the peak phase difference Δφ (S6, S21 to S24) as an example of the difference between the first phase information and the second phase information, based on the detected timing. Thus, the peak phase difference Δφ can be calculated based on the timing corresponding to the reflection by the object 3 during the transmission and reception of the linear frequency modulated pulse wave in that frame.

[0128] In this embodiment, the control unit 13 measures the displacement Δx (S6, S24) representing the displacement of the object 3 based on the peak phase difference Δφ, which is an example of the difference between the first phase information and the second phase information, and the instantaneous frequency fc, which is an example of the gradient of the phase ∠z(t) at the peak time t0 (an example of the reference timing). Therefore, the instantaneous frequency fc can be converted into the displacement Δx based on the peak phase difference Δφ.

[0129] In this embodiment, as an example of at least one of the envelopes of the first and second analytical signals, the control unit 13 calculates the envelope E(t) of the analytical signal z(t) of the first frame, and based on the calculated envelope E(t), detects the peak time t0 (S11), which is an example of the timing when the amplitude |z(t)| becomes the largest. Thus, the peak time t0 can be detected with good accuracy in the envelope E(t) obtained from the in-phase component I and the quadrature component Q.

[0130] In this embodiment, the control unit 13 performs calculations based on the first transmitted signal Sd and the first received signal Sr, making the cross-correlation function of the first transmitted signal Sd and the first received signal Sr complex, and generates a first analytic signal z(t) (S3). The control unit 13 also performs calculations based on the second transmitted signal Sd and the second received signal Sr, making the cross-correlation function of the second transmitted signal Sd and the second received signal Sr complex, and generates a second analytic signal z(t) (S6). Thus, the phase ∠z(t) defined in the complex range of the complex analytic signal z(t) can be calculated based on the cross-correlation function representing the correlation between the transmitted signal Sd and the received signal Sr in the time domain.

[0131] In this embodiment, each transmitted signal Sd causes the wave transmitter 10 to transmit a modulated wave (S1, S4) via a linear frequency linearly modulated pulse. Thus, for example, displacement can be sensed with good accuracy using information obtained according to different frequencies.

[0132] In this embodiment, the wave transmitter 10 includes a thermally induced sound generator that transmits a linear frequency modulated pulse wave, which is an example of a sound wave having multiple frequencies, as a modulated wave. Thus, the wave transmitter 10 is capable, for example, of transmitting a linear frequency modulated pulse wave based on a broadband ultrasonic wave in the range of 20 kHz to 100 kHz.

[0133] The displacement sensing method in this embodiment is executed by a control unit 13, which controls a wave transmitter 10 that transmits linear frequency modulated pulse waves (an example of a modulated wave) having multiple frequencies to an object 3, and acquires a received signal representing the reception result from a wave receiver 11 that receives reflected waves from the object 3. In the first frame, an example of a first measurement period, the control unit 13 outputs a first transmission signal Sd to the wave transmitter 10, causing the transmission of a linear frequency modulated pulse wave (S1), and acquires a corresponding first received signal Sr (S2). Based on the first transmission signal Sd and the first received signal Sr, the control unit 13 extracts first phase information (S3) representing the phase defined in the correlation between the first transmission signal Sd and the first received signal Sr. In the second frame, an example of a second measurement period following the first measurement period, the control unit 13 outputs a second transmission signal Sd to the wave transmitter 10, causing the transmission of a linear frequency modulated pulse wave (S4), and acquires a corresponding second received signal Sr (S5). Based on the second transmitted signal Sd and the second received signal Sr, the control unit 13 extracts second phase information representing the phase defined in the correlation between the second transmitted signal Sd and the second received signal Sr (S6). The control unit 13 senses the displacement of the object during the first measurement period and the second measurement period based on the peak phase difference Δφ, which is an example of the difference between the first phase information and the second phase information (S6).

[0134] In this embodiment, a program can be provided for the control unit 13 to execute a displacement sensing method as described above. Based on the displacement sensing method and program described above, minute displacements of the object 3 can be sensed with high accuracy.

[0135] (Example)

[0136] use Figures 13-15 Examples related to Implementation Method 1 described above will be described.

[0137] Figure 13 This is a diagram illustrating heart rate measurement performed using the displacement sensing device 1 of this embodiment. Figure 13(a) shows a structural example of a heart rate measurement system using displacement sensing device 1. Figure 13 (b) shows the result of Figure 13 The measurement results obtained from the heart rate measurement system of (a). Figure 14 as well as Figure 15 The simulation results for the operation of displacement sensing device 1 are shown.

[0138] Figure 13 The heart rate measurement system 2 illustrated in (a) senses minute displacements on the body surface of a subject 30, for example, wearing clothing, caused by the heartbeat, via a displacement sensing device 1, thereby measuring the heart rate of the subject 30 in a non-contact manner. Figure 13 In the heart rate measurement system 2 of (a), the heart rate of the subject 30 is measured by the displacement sensing device 1 and the reference electrocardiograph 4 at the same time.

[0139] Figure 13 (b) shows the inter-frame displacement R1 sensed by displacement sensing device 1 and the heart rate waveform R0 measured by electrocardiograph 4. Figure 13 In (b), the horizontal axis represents time (in seconds), the left vertical axis represents displacement (in millimeters), and the right vertical axis represents the voltage of the heart rate waveform (in volts). Figure 13 In (b), a displacement R1 that changes over time in sync with the heart rate waveform R0 is sensed. In this way, it can be confirmed that the displacement sensing device 1 according to this embodiment can accurately sense minute displacements such as body movements caused by heartbeats.

[0140] In order to... Figure 13 In the heart rate measurement shown, the preferred measurement conditions were determined, and the operation of the displacement sensing device 1 was simulated as follows.

[0141] (1) On the relationship between frame rate and positioning accuracy

[0142] Figure 14 Simulation results are shown regarding the relationship between the measurement frame rate and the positioning (displacement sensing) accuracy in displacement sensing device 1. Figure 14 In the middle, it will be like Figure 7 The linear frequency modulated pulse length Tc of the transmitted signal Sd shown in (a) is set to 10 milliseconds, and the frequency band is set to 80 kHz to 20 kHz, thereby numerically simulating the change in positioning accuracy associated with the change in the measurement frame rate. In this embodiment, positioning accuracy represents the deviation of the measured value when a given number of measurements are performed without changing the measurement conditions, and 3σ (3 times the standard deviation of the measured value) is used.

[0143] For example, in heart rate measurement where a positioning accuracy of 20 μm (i.e., 0.02 mm) is desired, Figure 14 As shown in the diagram, it is clear that a measurement frame rate of 30 frames per second (fps) or higher is sufficient. Furthermore, at this measurement frame rate, the duration of one frame is approximately 33 milliseconds. Therefore, if the distance from the displacement sensing device 1 to the object 3 being sensed is 50 cm, the maximum linear frequency modulated (LFM) pulse length, considering the sound wave propagation period (approximately 3 ms), is 30 ms. The maximum LFM pulse length represents the upper limit of the LFM pulse length Tc that can be used for the transmitted signal Sd in one frame.

[0144] (2) The relationship between the received signal SNR and positioning accuracy

[0145] Figure 15 Simulation results are shown regarding the relationship between the SNR and positioning accuracy of the received signal in displacement sensing device 1. Figure 15 In this study, the linear frequency modulated pulse length Tc of the transmitted signal Sd was set to 30 milliseconds, and the frequency band was set to 100kHz to 20kHz. Numerical simulation was then performed to study the changes in positioning accuracy associated with changes in the SNR of the received signal.

[0146] For example, in heart rate measurement where a positioning accuracy of around 20 μm is desired, Figure 15 As shown in the diagram, it is clear that an SNR of 0 dB or higher is sufficient. The SNR of the received signal can be set, for example, by the drive voltage of the drive circuit of the wave transmitter 10, depending on the measurement environment.

[0147] (Other implementation methods)

[0148] As described above, Embodiment 1 has been presented as an example of the present invention. However, the present invention is not limited thereto and can be applied to other embodiments. Hereinafter, other embodiments will be illustrated.

[0149] In Embodiment 1, an example of a wave emitter 10 being composed of a thermoelectric generator was described. The wave emitter 10 is not limited to a thermoelectric generator; for example, it may be composed of a ribbon tweeter or the like. Furthermore, the wave emitter 10 may also be an ultrasonic transducer using a piezoelectric vibrator or the like.

[0150] In Embodiment 1, an example of the wave transmitter 10 generating a linear frequency modulated pulse wave based on a linear frequency modulated pulse of linear frequency (LFM). In this embodiment, the wave transmitter 10 may also generate, for example, a LFM pulse wave based on a linear period chirp with a period that varies linearly with time. Furthermore, the wave transmitter 10 may also generate a broadband modulated wave using a spreading code such as an M-series code or a Gold code.

[0151] In Embodiment 1, an example was described where a linear frequency modulated pulse signal based on pulse interval modulation was used as the transmission signal Sd in the displacement sensing device 1. In this embodiment, the displacement sensing device 1 is not limited to generating the transmission signal Sd by pulse interval modulation; for example, the transmission signal Sd may also be generated by pulse width modulation, which changes the time width of each pulse in a continuous pulse over time.

[0152] In Embodiment 1, an example of sound waves being generated by the wave transmitter 10 was described. In the displacement sensing device 1 of this embodiment, it is not necessarily limited to sound waves; for example, a wave transmitter 10 that generates electromagnetic waves may also be used. Even in this case, the phase difference of the analytical signal can be analyzed by using a signal obtained by transmitting and receiving a broadband electromagnetic wave whose frequency varies with time, thereby achieving accurate sensing of minute displacements of an object.

[0153] In Embodiment 1, an example was described where the displacement sensing device 1 includes one wave transmitter 10 and one wave receiver 11. In this embodiment, the displacement sensing device 1 may also include multiple wave transmitters and wave receivers, or both.

[0154] In the other embodiments described above, descriptions of matters common to embodiment 1 have been omitted, and only the differences have been explained. Each embodiment is illustrative, and it is self-evident that partial substitutions or combinations of the structures shown in different embodiments are possible.

[0155] Industrial availability

[0156] This invention can be applied to displacement sensing devices, methods, and procedures, and in particular, to the sensing of minute displacements of objects.

[0157] Explanation of reference numerals in the attached figures

[0158] 1: Displacement sensing device;

[0159] 10: Wave transmitter;

[0160] 11: Wave receiver;

[0161] 13: Control Department.

Claims

1. A displacement sensing device, comprising: A wave transmitter that sends modulated waves with multiple frequencies to an object; A wave receiver that receives reflected waves from the object and generates a received signal representing the reception result; and The control unit controls the transmission of the modulated wave by the wave transmitter and acquires the received signal from the wave receiver. During the first measurement period, the control unit outputs a first transmission signal to the wave transmitter to transmit the modulated wave, and acquires a corresponding first reception signal. The control unit extracts first phase information, representing a phase defined in the correlation between the first transmitted signal and the first received signal, based on the first transmitted signal and the first received signal. During the second measurement period following the first measurement period, the control unit outputs a second transmission signal to the wave transmitter to transmit the modulated wave, and acquires a corresponding second reception signal. The control unit extracts second phase information, representing the phase specified in the correlation between the second transmitted signal and the second received signal, based on the second transmitted signal and the second received signal. The control unit senses the displacement of the object during the first measurement period and the second measurement period based on the difference between the first phase information and the second phase information.

2. The displacement sensing device according to claim 1, wherein, The control unit generates a first analytical signal based on the first transmitted signal and the first received signal, which includes the amplitude and phase specified in the correlation between the first transmitted signal and the first received signal, and extracts the first phase information from the first analytical signal. The control unit generates a second analytical signal based on the second transmitted signal and the second received signal, which includes the amplitude and phase specified in the correlation between the second transmitted signal and the second received signal, and extracts the second phase information from the second analytical signal.

3. The displacement sensing device according to claim 2, wherein, The control unit detects when at least one of the amplitudes of the first analytical signal and the second analytical signal reaches its maximum. The control unit calculates the difference between the first phase information and the second phase information based on the detected timing.

4. The displacement sensing device according to claim 3, wherein, The control unit measures the displacement amount representing the displacement of the object based on the difference between the first phase information and the second phase information and the gradient of the phase under the timing of the reference.

5. The displacement sensing device according to any one of claims 2 to 4, wherein, The control unit performs calculations on at least one of the envelopes of the first analytical signal and the second analytical signal, and detects the timing when the amplitude reaches its maximum based on the calculated envelope.

6. The displacement sensing device according to any one of claims 2 to 4, wherein, The control unit performs calculations based on the first transmitted signal and the first received signal, making the cross-correlation function of the first transmitted signal and the first received signal complex, and generates the first analytical signal. The control unit performs calculations based on the second transmitted signal and the second received signal to make the cross-correlation function of the second transmitted signal and the second received signal complex, and generates the second analytical signal.

7. The displacement sensing device according to any one of claims 1 to 4, wherein, The wave transmitter includes a thermally induced sound generator that transmits sound waves having multiple frequencies as the modulated wave.

8. The displacement sensing device according to any one of claims 1 to 4, wherein, The first and second transmission signals cause the wave transmitter to transmit the modulated wave via a linear frequency modulated pulse.

9. A displacement sensing method, wherein, The control unit controls a wave transmitter that sends modulated waves with multiple frequencies to an object, and obtains a received signal indicating the reception result from a wave receiver that receives reflected waves from the object. During the first measurement period, the control unit outputs a first transmission signal to the wave transmitter to transmit the modulated wave, and acquires a corresponding first reception signal. The control unit extracts first phase information, representing a phase defined in the correlation between the first transmitted signal and the first received signal, based on the first transmitted signal and the first received signal. During the second measurement period following the first measurement period, the control unit outputs a second transmission signal to the wave transmitter to transmit the modulated wave, and acquires a corresponding second reception signal. The control unit extracts second phase information, representing the phase specified in the correlation between the second transmitted signal and the second received signal, based on the second transmitted signal and the second received signal. The control unit senses the displacement of the object during the first measurement period and the second measurement period based on the difference between the first phase information and the second phase information.

10. A program product comprising a program for causing the control unit of claim 9 to perform the displacement sensing method of claim 9.

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