A difference frequency acoustic field time grating linear displacement sensing system

Abstract

The present invention discloses a difference-frequency acoustic field-type time-grating linear displacement sensing system, comprising a laser light source, a movable ruler, a fixed ruler, a photoelectric receiver, and a signal control system; the movable ruler has a movable ruler acousto-optic crystal, and the fixed ruler has a fixed ruler acousto-optic crystal. The laser light source, movable ruler, fixed ruler, and photoelectric receiver are arranged from top to bottom, and the movable ruler can move left and right relative to the fixed ruler. The signal control system comprises a signal generation and loading module and a signal processing module. The signal generation and loading module generates a DC excitation signal I0 to drive the laser light source, generates a reference signal with a frequency of |f1-f2| and inputs it into the signal processing module, generates an ultrasonic drive signal I related to frequency f1, and an ultrasonic drive signal II related to frequency f2, and loads them to the movable ruler acousto-optic crystal and the fixed ruler acousto-optic crystal respectively through ultrasonic transducers. The use of the present invention can improve anti-interference performance while reducing dependence on manufacturing processes.

Description

Technical Field

[0001] The invention belongs to the field of precision measurement, and in particular relates to a difference frequency acoustic field type time grating linear displacement sensing system. Background Art

[0002] Currently, there are two main types of ultra-precision, large-scale displacement measurement: laser interferometer and grating interferometer. Due to the different ways of generating the measurement base, these two measurement methods have their own advantages and disadvantages in practical applications. In summary, they are as follows: (1) The laser interferometer, which uses the wavelength of light as the measurement base, has the advantages of no scratching of the base, high precision, and large range. However, due to the lack of physical protection of the measurement base, it has high environmental requirements and is difficult to integrate. (2) The grating interferometer, which uses the grating pitch as the measurement base, has the advantages of high precision, strong anti-interference, and easy integration. However, due to the mechanical scratching of the grating pitch, it has high processing requirements, resulting in high manufacturing difficulty and high cost. Summary of the Invention

[0003] The purpose of the present invention is to provide a difference frequency acoustic field type time grating linear displacement sensing system to improve anti-interference performance while reducing dependence on manufacturing technology.

[0004] The difference-frequency acoustic field-type time-grating linear displacement sensing system described in the present invention comprises a laser light source, a movable ruler, a fixed ruler, a photoelectric receiver, and a signal control system. The movable ruler comprises a movable ruler acousto-optic crystal, and the fixed ruler comprises a fixed ruler acousto-optic crystal. The movable ruler acousto-optic crystal is made of the same material as the fixed ruler acousto-optic crystal. The movable ruler is longer than the fixed ruler. The laser light source is positioned above the movable ruler, the fixed ruler is positioned parallel to the movable ruler, and the photoelectric receiver is positioned below the fixed ruler. The laser light source, fixed ruler, and photoelectric receiver are fixedly mounted, and the movable ruler can move left and right relative to the fixed ruler.

[0005] The signal control system includes a signal generation and loading module and a signal processing module. The signal generation and loading module is connected to the laser light source and the signal processing module. The signal generation and loading module is connected to the movable scale and the fixed scale through the ultrasonic transducer. The photoelectric receiver is connected to the signal processing module. The signal generation and loading module generates a DC excitation signal I0 to drive the laser light source to emit a light signal with constant light intensity, generates a reference signal with a frequency of |f1-f2| and inputs it into the signal processing module, generates an ultrasonic driving signal I related to the frequency f1 and loads it to the movable scale acousto-optic crystal through the ultrasonic transducer, and generates an ultrasonic driving signal II related to the frequency f2 and loads it to the fixed scale acousto-optic crystal through the ultrasonic transducer.

[0006] When the movable ruler moves relative to the fixed ruler, the optical signal passes through the movable ruler acousto-optic crystal and the fixed ruler acousto-optic crystal from top to bottom, reaching the photoelectric receiver. The photoelectric receiver converts the received optical signal into an electrical signal and inputs it into the signal processing module. The signal processing module processes the electrical signal (i.e., the electrical signal converted by the photoelectric receiver) with the reference signal to obtain the linear displacement value of the movable ruler relative to the fixed ruler. Where 0 < |f1-f2| < min(f1,f2), min() represents the smaller value, and min(f1,f2) represents the smaller value of f1 or f2.

[0007] Preferably, there are two types of ultrasonic driving signals I and II.

[0008] The first ultrasonic driving signal I is a modulated signal obtained by the signal generation and loading module by modulating the ultrasonic excitation signal U' using the sinusoidal modulation signal U1. The ultrasonic driving signal I is expressed as: A1sin(f1t)[A0sin(f0t)+U n The first ultrasonic driving signal II is a modulated signal obtained by the signal generation and loading module using the sinusoidal modulation signal U2 to modulate the ultrasonic excitation signal U′. The ultrasonic driving signal II is expressed as: A2sin(f2t)[A0sin(f0t)+U m ] Among them, the ultrasonic excitation signal U', the sinusoidal modulation signal U1, and the sinusoidal modulation signal U2 are all generated by the signal generation and loading module, U1 = A1sin(f1t), U2 = A2sin(f2t), U' = A0sin(f0t)+U m ,f1<f0,f2<f0,U m Represents the DC voltage component in the ultrasonic excitation signal U′. The voltage amplitude of the ultrasonic excitation signal U′ is A0 and the voltage frequency is f0. The voltage amplitude of the sinusoidal modulation signal U1 is A1 and the voltage frequency is f1. The voltage amplitude of the sinusoidal modulation signal U2 is A2 and the voltage frequency is f2.

[0009] The second ultrasonic driving signal I is the ultrasonic excitation signal U′1 generated by the signal generation and loading module; the second ultrasonic driving signal II is the ultrasonic excitation signal U′2 generated by the signal generation and loading module. Wherein, U′1=A1sin(f1t)+U m1 , U′2=A2sin(f2t)+U m2 , U m1 It represents the DC voltage component in the ultrasonic excitation signal U′1. The voltage amplitude of the ultrasonic excitation signal U′1 is A1, the voltage frequency is f1, and U m2 It represents the DC voltage component in the ultrasonic excitation signal U′2. The voltage amplitude of the ultrasonic excitation signal U′2 is A2 and the voltage frequency is f2.

[0010] Preferably, the photoelectric receiver receives two types of optical signals.

[0011] The first optical signal received by the photoelectric receiver is the -1 order fixed-scale diffraction light emitted by the fixed-scale acousto-optic crystal. The -1 order fixed-scale diffraction light is generated by the light signal with constant light intensity output by the laser light source and incident on the moving-scale acousto-optic crystal. The +1 order moving-scale diffraction light is diffracted by the moving-scale acousto-optic crystal and incident on the fixed-scale acousto-optic crystal, and then diffracted by the fixed-scale acousto-optic crystal.

[0012] The second optical signal received by the photoelectric receiver is the +1-order fixed-scale diffraction light emitted by the fixed-scale acousto-optic crystal. The +1-order fixed-scale diffraction light is generated by the light signal with constant light intensity output by the laser light source and incident on the moving-scale acousto-optic crystal. The -1-order moving-scale diffraction light is diffracted by the moving-scale acousto-optic crystal and incident on the fixed-scale acousto-optic crystal, and then diffracted by the fixed-scale acousto-optic crystal.

[0013] Preferably, the signal processing module processes the electrical signal and the reference signal to obtain the linear displacement value of the movable ruler relative to the fixed length by performing bandpass filtering on the electrical signal to obtain an electrical traveling wave signal, then performing zero-crossing comparison on the electrical traveling wave signal to obtain a square wave signal having a frequency of |f1-f2| corresponding to the electrical signal. This square wave signal is then compared with the reference signal, with the phase difference represented by the number of interpolated high-frequency clock pulses, and then converted to obtain the linear displacement value of the movable ruler relative to the fixed length; wherein the reference signal is a square wave signal.

[0014] Preferably, the frequencies f1 and f2 satisfy the following relationship: |f1-f2|≤0.1min(f1, f2). The smaller the value of |f1-f2|, the higher the resolution of the displacement measurement. |f1-f2|≤0.1min(f1, f2) is a reasonable limit for improving measurement resolution.

[0015] The present invention uses ultrasonic traveling waves (corresponding to ultrasonic drive signals I and II) propagating within an acousto-optic crystal as the measurement carrier. The physical principles of acousto-optic diffraction and acousto-optic communication are employed to detect the ultrasonic traveling wave signal, thereby achieving displacement measurement based on ultrasonic length. Drawing on the principle of controlling diffracted light intensity through ultrasonic power modulation in acousto-optic communication, combined with the spatial motion of the ultrasonic traveling wave (corresponding to the movement of a moving ruler), the diffracted light intensity shifts back and forth in time as the moving ruler moves to different positions, thereby synthesizing a new ultrasonic traveling wave signal that can be directly detected using the diffracted light intensity signal.

[0016] The laser light source outputs continuous laser light in a continuous excitation mode, which is irradiated through the moving scale acousto-optic crystal and the fixed scale acousto-optic crystal in turn. The fixed scale is installed parallel to the moving scale. When the moving scale moves relative to the fixed scale, the ultrasonic traveling wave undergoes periodic changes in the moving scale acousto-optic crystal and the fixed scale acousto-optic crystal respectively. Through the acousto-optic effect, a diffraction light intensity signal reflecting the movement of the moving scale and the ultrasonic traveling wave motion of the moving scale can be obtained. After photoelectric conversion and bandpass filtering, an electrical traveling wave signal is obtained. The electrical traveling wave signal shows a temporal sequence change with the change of spatial position, thereby realizing the measurement of spatial displacement by time.

[0017] This invention uses traveling waves within a physical body as a motion reference system to convert spatial measurements into temporal measurements. Guided by the concept of time-grating measurement, this invention uses traveling waves within a physical body as a measurement carrier, integrating the advantages of multiple sensing measurement methods.

[0018] The present invention has the following advantages:

[0019] (1) The traveling wave wavelength in the physical object (moving-scale acousto-optic crystal, fixed-scale acousto-optic crystal) is used as the measurement reference. The physical ruler protects the measurement reference from interference from the external environment, improves the anti-interference ability, and reduces the dependence of traditional physical sensors on the manufacturing process of equidistant grating lines. At the same time, the stability and accuracy of the traveling wave wavelength are combined to improve the measurement accuracy.

[0020] (2) A measurement model is established with the traveling wave in the object as the motion reference system, and the displacement of the object to be measured is converted into a time measurement. The measurement resolution is improved by taking advantage of the high resolution characteristics of the clock frequency.

[0021] (3) The light signal with constant light intensity is diffracted by the moving-scale acousto-optic crystal driven by ultrasonic driving signal I and the fixed-scale acousto-optic crystal driven by ultrasonic driving signal II to obtain the acousto-optic diffraction light intensity signal. After photoelectric conversion and bandpass filtering, the difference frequency (i.e., the frequency of |f1-f2|) electric traveling wave signal is obtained. Since the values of frequency f1 and frequency f2 are relatively close, the number of pulses of high-frequency clock interpolation is increased, and the resolution of displacement measurement is greatly improved.

[0022] (4) The excitation light source is driven by a DC excitation signal I0 and emits a light signal with constant light intensity. The generation of the light signal is relatively simple and easy. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a structural principle diagram of the difference frequency acoustic field type time grating linear displacement sensing system in Example 1.

[0024] Figure 2 This is a block diagram of the measurement principle of the difference frequency acoustic field time grating linear displacement sensing system in Example 1.

[0025] Figure 3This is a structural principle diagram of the difference frequency acoustic field time grating linear displacement sensing system in Example 2.

[0026] Figure 4 This is a block diagram of the measurement principle of the difference frequency acoustic field time grating linear displacement sensing system in Example 2.

[0027] Figure 5 This is a graph showing the relationship between ultrasonic power and (acousto-optic) diffraction efficiency. DETAILED DESCRIPTION

[0028] Example 1: Figure 1 、 Figure 2 As shown, the difference-frequency acoustic field-type time-grating linear displacement sensing system in this embodiment includes a laser light source 1, a movable scale 2, a fixed scale 3, a photoelectric receiver 4, and a signal control system 5. The laser light source 1 is a He-Ne laser with a wavelength of 633 nm, and the photoelectric receiver 4 is an avalanche photodetector.

[0029] The movable ruler 2 has a movable ruler acousto-optic crystal 21, and the fixed ruler 3 has a fixed ruler acousto-optic crystal 31. The movable ruler acousto-optic crystal 21 is made of the same material as the fixed ruler 31. The movable ruler 2 is longer than the fixed ruler 3. The laser light source 1 is located above the movable ruler 2, with a 5mm gap between them. The fixed ruler 3 is located below the movable ruler 2, parallel to the fixed ruler 3, with a 5mm gap. The photoelectric receiver 4 is located below the fixed ruler 3. The laser light source 1, fixed ruler 3, and photoelectric receiver 4 are fixedly mounted, and the movable ruler 2 can move left and right relative to the fixed ruler 3.

[0030] The signal control system 5 includes a signal generation and loading module 51 and a signal processing module 52. The signal generation and loading module 51 integrates a signal generator and two multipliers. The signal generation and loading module 51 is connected to the laser light source 1 and the signal processing module 52. The signal generation and loading module 51 is connected to the movable scale 2 and the fixed scale 3 via an ultrasonic transducer (not shown). The photoelectric receiver 4 is connected to the signal processing module 52.

[0031] The signal generator in the signal generation and loading module 51 generates a DC excitation signal I0, an ultrasonic excitation signal U′, a sinusoidal modulation signal U1, and a sinusoidal modulation signal U2. A multiplier in the signal generation and loading module 51 modulates the ultrasonic excitation signal U′ by adding the sinusoidal modulation signal U1 to obtain an ultrasonic drive signal I. The ultrasonic drive signal I is expressed as: A1sin(f1t)[A0sin(f0t)+U m ](i.e., U1*U′). Another multiplier in the signal generation and loading module 51 is used to load the ultrasonic excitation signal U′ with the sinusoidal modulation signal U2 for modulation to obtain the ultrasonic driving signal II. The ultrasonic driving signal II is expressed as: A2sin(f2t)[A0 sin(f0t)+U m] (i.e. U2*U′). Among them, U1=A1sin(f1t), U2=A2sin(f2t), U′=A0sin(f0t)+U m , f2<f1<f0, U m represents the DC voltage component in the ultrasonic excitation signal U'. The voltage amplitude of the ultrasonic excitation signal U' is A0, and the voltage frequency is f0. The voltage amplitude of the sinusoidal modulation signal U1 is A1, and the voltage frequency is f1. The voltage amplitude of the sinusoidal modulation signal U2 is A2, and the voltage frequency is f2. In this embodiment, f0 = 80 MHz, A1 = 5 V, f1 = 10.1 MHz, A2 = 5 V, and f2 = 10 MHz. The difference frequency |f1 - f2| = 10.1 - 10 = 0.1 MHz = 0.01 min (f1, f2) = 0.01 * 10. The output power of the ultrasonic drive signal I does not exceed 5 W, and the output power of the ultrasonic drive signal II does not exceed 5 W.

[0032] The signal generator in the signal generation and loading module 51 generates a reference signal with a frequency of f1-f2 (ie, 0.1 MHz) and a phase of 0, and inputs the reference signal to the signal processing module 52. The reference signal is a square wave signal.

[0033] The signal generation and loading module 51 uses the DC excitation signal I0 to drive the laser light source 1 to emit a light signal with constant light intensity. The signal generation and loading module 51 loads the ultrasonic drive signal I to the movable-scale acousto-optic crystal 21 through the ultrasonic transducer, and loads the ultrasonic drive signal II to the fixed-scale acousto-optic crystal 31 through the ultrasonic transducer.

[0034] When the movable scale 2 moves relative to the fixed scale 3, the laser light source 1 emits a light signal with constant light intensity which passes through the movable scale acousto-optic crystal 21. By adjusting the angle of the incident light, the intensity of the 0th order light is minimized to obtain the +1st order movable scale diffraction light 22 after diffraction. Then, the +1st order movable scale diffraction light 22 after diffraction is used as the incident light to pass through the fixed scale acousto-optic crystal 31. By adjusting the angle of the incident light, the -1st order fixed scale diffraction light 32 which passes through the fixed scale acousto-optic crystal 31 is obtained. Finally, the -1st order fixed scale diffraction light 32 is received by the photoelectric receiver 4.

[0035] The photoelectric receiver 4 converts the received -1st-order fixed-length diffracted light 32 into an electrical signal and inputs it into the signal processing module 52. The signal processing module 52 performs bandpass filtering on the electrical signal to obtain an electrical traveling wave signal with a frequency of 0.1 MHz. This traveling wave signal is then subjected to zero-crossing comparison to obtain a corresponding square wave signal with a frequency of 0.1 MHz. This square wave signal with a frequency of 0.1 MHz and a phase of 0 is compared with a reference signal with a frequency of 0.1 MHz and a phase of 0. The phase difference is represented by the number of interpolated high-frequency clock pulses. This phase difference is then converted to obtain the linear displacement of the movable scale 2 relative to the fixed scale 3.

[0036] In addition, in this embodiment, the optical signal received and converted into an electrical signal by the photoelectric receiver 4 can also be the +1-order fixed-length diffracted light 33. The specific propagation process is as follows: the laser light source 1 emits an optical signal with constant light intensity, which passes through the dynamic-length acousto-optic crystal 21. By adjusting the angle of the incident light, the diffracted -1-order dynamic-length diffracted light 23 is obtained. Then, the diffracted -1-order dynamic-length diffracted light 23 is used as the incident light, which passes through the fixed-length acousto-optic crystal 31. By adjusting the angle of the incident light, the +1-order fixed-length diffracted light 33 that has passed through the fixed-length acousto-optic crystal 31 is obtained. Finally, the photoelectric receiver 4 receives the +1-order fixed-length diffracted light 33, converts it into an electrical signal, and inputs it into the signal processing module 52 for processing.

[0037] The theoretical analysis of the 0.1 MHz electric traveling wave signal obtained by two diffraction and conversion in Example 1 is as follows:

[0038] The ultrasonic power signal is obtained by applying the ultrasonic field converted by the ultrasonic transducer to the acousto-optic crystal, which makes the laser beam passing through the acousto-optic crystal diffract under the action of sound and light, and the intensity of the diffracted light is determined by the power of the ultrasonic driving signal. s and (acousto-optic) diffraction efficiency η s The relationship curve is as follows Figure 5 As shown, when the ultrasonic power P s In the linear region (i.e. P a <P s <P b ), the diffraction efficiency varies linearly with the ultrasonic power. During ultrasonic drive signal operation, to ensure diffraction efficiency, the ultrasonic drive signal power is typically set at the rated power, meaning that the ultrasonic power converted by the ultrasonic transducer is a constant value. When the ultrasonic excitation signal is loaded with a modulation signal, modulating its output power into the linear region, the ultrasonic power varies with the applied sinusoidal AC voltage.

[0039] The signal processing module 52 performs bandpass filtering on the -1 order fixed-length diffracted light 32 received by the photoelectric receiver 4 to remove high-frequency and DC components, and obtains an electric traveling wave signal reflecting the movement of the movable scale 2 relative to the fixed scale 3: Among them, H1 and P1 are constant values obtained based on the parameters of the moving scale, and H2 and P2 are constant values obtained based on the parameters of the fixed scale. represents the phase of the diffracted light intensity passing through the moving-rule acousto-optic crystal, It represents the phase of the diffracted light intensity passing through the fixed-length acousto-optic crystal.

[0040] Fixed length, is a fixed value. Due to the movement of the moving ruler and the movement of the ultrasonic traveling wave of the moving ruler, the diffraction light intensity signal of the moving ruler when the moving ruler moves to different positions corresponds to different values in time, that is, It will change with the movement of the ruler. The change in is used to reflect the change in the linear displacement of the movable scale 2 relative to the fixed scale 3.

[0041] After zero comparison, the above electric traveling wave signal is compared with the reference signal with a frequency of f1-f2 and a phase of 0, and the displacement of the movable scale 2 relative to the fixed scale 3 is obtained by conversion:

[0042]

[0043] Among them, x i represents the i-th displacement value, λ1 is the wavelength of the ultrasonic traveling wave in the moving ruler acousto-optic crystal 21, V is the velocity of ultrasonic traveling waves in the moving-scale acousto-optic crystal 21 (a known constant), is the phase difference of the electrical traveling wave signal relative to the reference signal, because It is a fixed value, so during the measurement process, the initial value x0 is set to 0, and then the displacement value of the measured object relative to the initial position (that is, the linear displacement value x of the moving ruler relative to the fixed ruler) can be calculated according to the above formula. i ) to achieve measurement.

[0044] In Example 1, the ultrasonic excitation signal is modulated by two sinusoidal modulation signals of known and similar frequencies to obtain a difference frequency electric traveling wave signal. At the same time, the wavelength of the difference frequency electric traveling wave signal depends on the sinusoidal modulation signal. This has the advantage of increasing the number of pulses for clock interpolation by using the difference frequency signal while keeping the spatially varying wavelength unchanged, which can proportionally improve the resolution of displacement measurement. For example, in this embodiment, a sinusoidal modulation signal U1 with a frequency of f1 is used for modulation, and the corresponding wavelength is After the diffraction light of the fixed-length acousto-optic crystal is modulated, and then subjected to photoelectric conversion and band-pass filtering, an electric traveling wave signal with a frequency of f1-f2 can be obtained, so it can be proportional (the ratio is ) increases the number of clock pulses within the wavelength λ1, and thus the resolution of the displacement measurement is increased proportionally.

[0045] Example 2: Figure 3 、 Figure 4 As shown, most of the structures of the difference frequency acoustic field type time grating linear displacement sensor system in this embodiment are the same as those in embodiment 1, except that: the two multipliers are not integrated in the signal generation and loading module 51, the ultrasonic driving signal I is the ultrasonic excitation signal U′1 generated by the signal generator in the signal generation and loading module 51, and the ultrasonic driving signal II is the ultrasonic excitation signal U′2 generated by the signal generator in the signal generation and loading module 51. Wherein, U′1=A1sin(f1t)+U m1 , U′2=A2sin(f2t)+Um2 , U m1 It represents the DC voltage component in the ultrasonic excitation signal U′1. The voltage amplitude of the ultrasonic excitation signal U′1 is A1, the voltage frequency is f1, and U m2 The voltage amplitude of the ultrasonic excitation signal U'2 is A2, and the voltage frequency is f2. In this embodiment, A1 = 5V, f1 = 81MHz, A2 = 5V, f2 = 80MHz, and the difference frequency |f1-f2| = 1MHz.

[0046] The signal generator in the signal generation and loading module 51 generates a reference signal with a frequency of f1-f2 (ie, 1 MHz) and a phase of 0, and inputs the reference signal to the signal processing module 52. The reference signal is a square wave signal.

[0047] The signal generation and loading module 51 uses the DC excitation signal I0 to drive the laser light source 1 to emit a light signal with constant light intensity. The signal generation and loading module 51 loads the ultrasonic drive signal I to the movable-scale acousto-optic crystal 21 through the ultrasonic transducer, and loads the ultrasonic drive signal II to the fixed-scale acousto-optic crystal 31 through the ultrasonic transducer.

[0048] When the movable scale 2 moves relative to the fixed scale 3, the laser light source 1 emits a light signal with constant light intensity which passes through the movable scale acousto-optic crystal 21. By adjusting the angle of the incident light, the intensity of the 0th order light is minimized to obtain the +1st order movable scale diffraction light 22 after diffraction. Then, the +1st order movable scale diffraction light 22 after diffraction is used as the incident light to pass through the fixed scale acousto-optic crystal 31. By adjusting the angle of the incident light, the -1st order fixed scale diffraction light 32 which passes through the fixed scale acousto-optic crystal 31 is obtained. Finally, the -1st order fixed scale diffraction light 32 is received by the photoelectric receiver 4.

[0049] The photoelectric receiver 4 converts the received -1st-order fixed-length diffracted light 32 into an electrical signal and inputs it into the signal processing module 52. The signal processing module 52 performs bandpass filtering on the electrical signal to obtain an electrical traveling wave signal with a frequency of 1 MHz. This traveling wave signal is then subjected to a zero-crossing comparison to obtain a corresponding square wave signal with a frequency of 1 MHz. This square wave signal with a frequency of 1 MHz and a phase of 0 is compared with a reference signal with a frequency of 1 MHz. The phase difference is represented by the number of interpolated high-frequency clock pulses. This phase difference is then converted to obtain the linear displacement of the movable scale 2 relative to the fixed scale 3.

[0050] In addition, in this embodiment, the optical signal received and converted into an electrical signal by the photoelectric receiver 4 can also be the +1-order fixed-length diffracted light 33. The specific propagation process is as follows: the laser light source 1 emits an optical signal with constant light intensity, which passes through the dynamic-length acousto-optic crystal 21. By adjusting the angle of the incident light, the diffracted -1-order dynamic-length diffracted light 23 is obtained. Then, the diffracted -1-order dynamic-length diffracted light 23 is used as the incident light, which passes through the fixed-length acousto-optic crystal 31. By adjusting the angle of the incident light, the +1-order fixed-length diffracted light 33 that has passed through the fixed-length acousto-optic crystal 31 is obtained. Finally, the photoelectric receiver 4 receives the +1-order fixed-length diffracted light 33, converts it into an electrical signal, and inputs it into the signal processing module 52 for processing.

[0051] The theoretical analysis of the 1 MHz electric traveling wave signal obtained by two diffraction and conversion in Example 2 is as follows:

[0052] The ultrasonic power signal is obtained by applying the ultrasonic field converted by the ultrasonic transducer to the acousto-optic crystal, which makes the laser beam passing through the acousto-optic crystal diffract under the action of sound and light, and the intensity of the diffracted light is determined by the power of the ultrasonic driving signal. s and (acousto-optic) diffraction efficiency η s The relationship curve is as follows Figure 5 As shown, when the ultrasonic power is in the linear region (i.e. P a <P s <P b ), the diffraction efficiency will change linearly with the ultrasonic power. In this embodiment, the ultrasonic powers of the ultrasonic drive signal I and the ultrasonic drive signal II are in a linear region that is proportional to the diffraction efficiency.

[0053] The signal processing module 52 performs bandpass filtering on the -1 order fixed-length diffracted light 32 received by the photoelectric receiver 4 to remove high-frequency and DC components, and obtains an electric traveling wave signal reflecting the movement of the movable scale 2 relative to the fixed scale 3: Among them, P1 is a constant value obtained based on the parameters of the moving scale, and P2 is a constant value obtained based on the parameters of the fixed scale. represents the phase of the diffracted light intensity passing through the moving-rule acousto-optic crystal, It represents the phase of the diffracted light intensity passing through the fixed-length acousto-optic crystal.

[0054] Fixed length, is a fixed value. Due to the movement of the moving ruler and the movement of the ultrasonic traveling wave of the moving ruler, the diffraction light intensity signal of the moving ruler when the moving ruler moves to different positions corresponds to different values in time, that is, It will change with the movement of the ruler. The change in is used to reflect the change in the displacement of the movable scale 2 relative to the fixed scale 3.

[0055] After zero comparison, the above electric traveling wave signal is compared with the reference signal with a frequency of f1-f2 and a phase of 0, and the displacement of the movable scale 2 relative to the fixed scale 3 is obtained by conversion:

[0056]

[0057] Among them, x i represents the i-th displacement value, λ1 is the wavelength of the ultrasonic traveling wave in the moving ruler acousto-optic crystal 21, V is the velocity of ultrasonic traveling waves in the moving-scale acousto-optic crystal 21 (a known constant), is the phase difference of the electrical traveling wave signal relative to the reference signal, because It is a fixed value, so during the measurement process, the initial value x0 is set to 0, and then the displacement value of the measured object relative to the initial position (that is, the displacement value x of the moving ruler relative to the fixed ruler) can be calculated according to the above formula. i ) to achieve measurement.

[0058] In Example 2, two ultrasonic excitation signals with similar frequencies are used as the measurement reference to obtain a difference frequency electric traveling wave signal. At the same time, the spatial period of the electric traveling wave signal is the wavelength of the ultrasonic excitation signal. The advantage of this is that the difference frequency signal is used to increase the number of pulses in the clock interpolation. At the same time, the spatially varying wavelength remains unchanged, which can proportionally improve the resolution of the displacement measurement. For example, in this embodiment, the ultrasonic excitation signal U′1 with a frequency of f1 is used to drive the moving ruler acousto-optic crystal. The corresponding wavelength is After the diffraction light of the fixed-length acousto-optic crystal is modulated, and then subjected to photoelectric conversion and band-pass filtering, an electric traveling wave signal with a frequency of f1-f2 can be obtained, so it can be proportional (the ratio is ) increases the number of clock pulses within the wavelength λ1, and thus the resolution of the displacement measurement is increased proportionally.

Claims

1. A difference frequency acoustic field time grating linear displacement sensing system, comprising a laser light source (1), a movable ruler (2), a fixed ruler (3), a photoelectric receiver (4) and a signal control system (5), characterized in that: The movable ruler (2) has a movable ruler acousto-optic crystal (21), and the fixed ruler (3) has a fixed ruler acousto-optic crystal (31). The material of the movable ruler acousto-optic crystal is the same as that of the fixed ruler acousto-optic crystal. The length of the movable ruler (2) is greater than the length of the fixed ruler (3). The laser light source (1) is located above the movable ruler (2), the fixed ruler (3) is located below the movable ruler (2) and is placed in parallel, the photoelectric receiver (4) is located below the fixed ruler (3), the laser light source (1), the fixed ruler (3), and the photoelectric receiver (4) are fixedly installed, and the movable ruler (2) can move left and right relative to the fixed ruler (3); The signal control system (5) includes a signal generating and loading module (51) and a signal processing module (52). The signal generating and loading module (51) is connected to the laser light source (1) and the signal processing module (52). The signal generating and loading module (51) is connected to the movable scale (2) and the fixed scale (3) through an ultrasonic transducer. The photoelectric receiver (4) is connected to the signal processing module (52). The signal generating and loading module (51) generates a DC excitation signal I0 to drive the laser light source (1) to emit a light signal with a constant light intensity, generates a reference signal with a frequency of |f1-f2| and inputs it into the signal processing module (52), generates an ultrasonic driving signal I related to the frequency f1 and loads it to the movable scale acousto-optic crystal (21) through the ultrasonic transducer, and generates an ultrasonic driving signal II related to the frequency f2 and loads it to the fixed scale acousto-optic crystal (31) through the ultrasonic transducer. When the movable ruler moves relative to the fixed ruler, the optical signal passes through the movable ruler acousto-optic crystal and the fixed ruler acousto-optic crystal from top to bottom and reaches the photoelectric receiver (4). The photoelectric receiver (4) converts the received optical signal into an electrical signal and inputs it into the signal processing module (52). The signal processing module (52) processes the electrical signal and the reference signal to obtain the linear displacement value of the movable ruler (2); wherein 0<|f1-f2|<min(f1,f2), min( ) represents the smaller operation.

2. The difference frequency acoustic field time-grating linear displacement sensing system according to claim 1, characterized in that: The ultrasonic driving signal I is a modulated signal obtained by the signal generation and loading module (51) modulating the ultrasonic excitation signal U' using the sinusoidal modulation signal U1; The ultrasonic driving signal II is a modulated signal obtained by the signal generation and loading module (51) modulating the ultrasonic excitation signal U' using the sinusoidal modulation signal U2; Among them, the ultrasonic excitation signal U', the sinusoidal modulation signal U1, and the sinusoidal modulation signal U2 are all generated by the signal generation and loading module (51), U1=A1sin(f1t), U2=A2sin(f2t), U'=A0sin(f0t)+ U m ,f1<f0,f2<f0,U m Represents the DC voltage component in the ultrasonic excitation signal U'. The voltage amplitude of the ultrasonic excitation signal U' is A0 and the voltage frequency is f0. The voltage amplitude of the sinusoidal modulation signal U1 is A1 and the voltage frequency is f1. The voltage amplitude of the sinusoidal modulation signal U2 is A2 and the voltage frequency is f2.

3. The difference frequency acoustic field time-grating linear displacement sensing system according to claim 2, characterized in that: The ultrasonic driving signal I is: A1sin(f1t)[ A0sin(f0t)+ U m ]; The ultrasonic driving signal II is: A2sin(f2t)[ A0sin(f0t)+ U m ].

4. The difference frequency acoustic field time-grating linear displacement sensing system according to claim 1, characterized in that: The ultrasonic driving signal I is an ultrasonic excitation signal U'1 generated by the signal generating and loading module (51); The ultrasonic driving signal II is an ultrasonic excitation signal U'2 generated by the signal generating and loading module (51); Among them, U'1=A1sin(f1t)+U m1 ,U'2=A2sin(f2t)+U m2 , U m1 The DC voltage component of the ultrasonic excitation signal U'1 is represented by the voltage amplitude of the ultrasonic excitation signal U'1, the voltage frequency is f1, and U m2 It represents the DC voltage component in the ultrasonic excitation signal U'2. The voltage amplitude of the ultrasonic excitation signal U'2 is A2 and the voltage frequency is f2.

5. The difference frequency acoustic field time grating linear displacement sensing system according to any one of claims 1 to 4, characterized in that: The optical signal received by the photoelectric receiver (4) is the -1st order fixed-length diffraction light (32) emitted by the fixed-length acousto-optic crystal (31). The -1st order fixed-length diffraction light is generated by the optical signal with constant light intensity output by the laser light source (1) and incident on the movable-length acousto-optic crystal (21). The +1st order moving-length diffraction light (22) is diffracted by the movable-length acousto-optic crystal and incident on the fixed-length acousto-optic crystal (31). The +1st order moving-length diffraction light (22) is then diffracted by the movable-length acousto-optic crystal and generated.

6. The difference frequency acoustic field time-grating linear displacement sensing system according to any one of claims 1 to 4, characterized in that: The optical signal received by the photoelectric receiver (4) is the +1-order fixed-length diffraction light (33) emitted by the fixed-length acousto-optic crystal (31). The +1-order fixed-length diffraction light is generated by the optical signal with constant light intensity output by the laser light source (1) and incident on the movable-length acousto-optic crystal (21). The +1-order fixed-length diffraction light is diffracted by the movable-length acousto-optic crystal to generate the -1-order movable-length diffraction light (23) which is incident on the fixed-length acousto-optic crystal (31) and then diffracted by the fixed-length acousto-optic crystal.

7. The difference frequency acoustic field time-grating linear displacement sensing system according to any one of claims 1 to 4, characterized in that: The signal processing module (52) processes the electrical signal and the reference signal to obtain the linear displacement value of the movable ruler (2) in the following manner: The signal processing module (52) performs bandpass filtering on the electrical signal to obtain an electrical traveling wave signal, and then performs zero-crossing comparison on the electrical traveling wave signal to obtain a square wave signal with a frequency of |f1-f2| corresponding to the electrical signal; The square wave signal is compared with the reference signal, and the phase difference is represented by the number of interpolated high-frequency clock pulses, and then converted to obtain the linear displacement value of the moving ruler (2); wherein the reference signal is a square wave signal.

8. The difference frequency acoustic field time-grating linear displacement sensing system according to any one of claims 1 to 4, characterized in that: The frequencies f1 and f2 satisfy: |f1-f2|≤0.1min(f1,f2).

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