CN110186551B - Amplitude measurement device and method for square wave transform based on self-mixing interference - Google Patents

Abstract

The invention discloses a square wave transform amplitude measurement device based on self-mixing interference, comprising a light source unit, a signal processing unit and a data processing unit. The signal processing unit introduces a hysteresis comparator to process signals to output a required square wave signal, and data processing The unit searches for a flip point for the output square wave signal to calculate the vibration amplitude of the object according to the number of fringes in the same oblique direction between adjacent flip points. The invention also discloses a square wave transform amplitude measurement method based on self-mixing interference. The invention adopts a hysteresis comparator circuit with adjustable upper and lower limits to perform square wave transformation on the obtained laser self-mixing signal, thereby effectively reducing the influence of external noise on measurement stability and accuracy. The self-mixing interference principle has no specific requirements on the coherence of the laser light source, and the laser selection has a large degree of freedom. At the same time, the amplification of the signal is controllable, and the measurable minimum amplitude value can reach the nanometer level, which is easy to realize wide-range real-time measurement.

Description

Amplitude measurement device and method for square wave transform based on self-mixing interference

technical field

The invention relates to the technical field of optical nanometer measurement, in particular to a square wave transformation amplitude measurement device and method based on self-mixing interference.

Background technique

Nano-vibration measurement has become more and more important in many applications such as high-precision engineering technology, precision machining, aerospace and so on. At present, researchers have proposed some meaningful amplitude measurement methods for weakly vibrating objects. Among them, the measurement method based on optical technology has the advantages of non-contact high precision and has received much attention.

Commonly used optical vibration measurement methods include geometric optics and optical interferometry. However, most of the reported geometric optics methods require complex and precise optical adjustment systems; in the field of laser interferometry, self-mixing interferometry methods have been extensively studied and applied due to their simple optical structure and easy alignment. In the self-mixing interferometric vibration method, there are frequency domain analysis measurement method and time domain fringe counting method.

The frequency domain measurement method is sensitive to external noise, and has high requirements for the signal-to-noise ratio of the signal. When the noise becomes larger, the spectrum will be unstable, the useful frequency components are easily covered by the noise spectrum, and the measurement results become inaccurate. The traditional fringe counting method is divided into manual counting and automatic counting. The manual counting method is very time-consuming when the vibration amplitude of the measured object is large, while the traditional automatic counting method is easy to count the noise voltage fluctuation at the threshold value as an effective fringe, resulting in relatively high frequency. Large counting error. At the same time, the accuracy of the fringe counting method is usually only λ/2, so it is not suitable for real-time simple and stable measurement and applications requiring nanometer-level high-precision resolution.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a square wave transform amplitude measurement device and method based on self-mixing interference, which have simple and compact structure, simple and efficient method, stable and accurate measurement results, high resolution and wide application range.

To achieve the above object, the present invention adopts the following technical solutions:

A square wave transform amplitude measurement device based on self-mixing interference, including:

a light source unit, which is used to monitor the vibrating object to be measured, to generate a self-mixing laser intensity signal and convert it into a corresponding current signal;

a signal processing unit, which includes a signal pre-processing module and a signal post-processing module; the signal pre-processing module converts the current signal into a voltage signal and amplifies it; the signal post-processing module includes a hysteresis comparator, and the hysteresis comparator The hysteresis comparator uses a variable resistor as a feedback resistor to achieve variable upper and lower threshold voltages. The hysteresis comparator is used to realize signal processing, so that the square wave in the output square wave signal has the largest number and the glitch level in a unit time. least;

a data processing unit, which searches for a flip point for the output square wave signal, so as to calculate the vibration amplitude of the object according to the number of fringes in the same oblique direction between adjacent flip points;

The light source unit includes a semiconductor laser, a laser drive circuit and a photodetector; the signal preprocessing module includes a transconductance operational amplifier circuit, a DC blocking circuit and a proportional operational amplifier circuit; the data processing unit includes an ADC sampling circuit and a DSP real-time a processing module; the laser driving circuit and the photodetector are respectively connected with the semiconductor laser, the photodetector, the transconductance operational amplifier circuit, the DC blocking circuit, the proportional operational amplifier circuit, the hysteresis comparator, the ADC sampling circuit and the The DSP real-time processing modules are connected in sequence, and the ADC sampling circuit samples the square wave signal output by the hysteresis comparator, inputs the obtained sampled signal into the DSP real-time processing module, and finds through the program that the level width is significantly larger than The method of adjacent stripes is used to obtain the flip point, and then the number of stripes in the same inclined direction between flip points is calculated, so as to calculate the amplitude of the vibration of the object according to A=λ*N/4, where A is the amplitude of the object, and λ is the laser. wavelength, N is the number of fringes in the same oblique direction between two adjacent flip points;

The data processing unit can also calculate the vibration frequency of the object according to F=2*fs/(X2-X1) according to the sampling sequence number and sampling rate of the flip point, where F is the vibration frequency of the object, and X1 is the vibration frequency of the previous flip point. Sampling sequence number, X2 is the sampling sequence number of the next flip point, fs is the sampling rate, and the final calculation result is displayed and output through the display screen. Further, the data processing unit also calculates the vibration information of the vibrating object to be measured according to the sampling sequence number of the flip point.

Further, the proportional op amp circuit uses a varistor as the negative feedback resistor to achieve variable amplification; or, the proportional operational amplifier circuit uses a fixed resistor as the negative feedback resistor to achieve a fixed amplification.

Further, the hysteresis comparator adopts a variable resistor as a feedback resistor to realize variable upper and lower threshold voltages.

The invention also discloses a square wave transform amplitude measurement method based on self-mixing interference, comprising the following steps:

S1. Signal generation and output: The emitted light of the semiconductor laser hits the surface of the vibrating object to be measured, and part of the light returns to the laser cavity to generate a self-mixing laser intensity signal; the photodetector detects the self-mixing laser intensity signal and converts it into corresponding The current signal output;

S2. Signal processing: convert the current signal into a voltage signal and amplify the signal; input the amplified voltage signal into the hysteresis comparator, and adjust the upper and lower threshold voltages of the hysteresis comparator within the signal amplitude range, so that the output square The square wave in the wave signal has the largest number and the least burr per unit time;

S3, data processing:

S31, perform AD sampling on the square wave signal output by S2, and calculate the width of each level for the sampled signal;

S32. Find the flip point according to the width of the level: if the ratio of a certain level to the two levels of the same polarity before and after exceeds the set threshold, the level is the flip point;

S33. Calculate the vibration amplitude of the object: A=λ*N/4, where A is the amplitude of the object, λ is the wavelength of the laser, and N is the number of fringes in the same inclined direction between two adjacent flip points;

S34. Calculate the vibration frequency of the object: F=2*fs/(X2-X1), where F is the vibration frequency of the object, X1 is the sampling number of the previous flip point, X2 is the sampling number of the next flip point, and fs is the sampling number Rate.

Further, in S31, the point at which the high and low levels jump are detected, the time coordinates of each edge of the square wave are obtained, the time width of each level is obtained by calculating the difference between the time coordinates of adjacent edges, and the level width is obtained. .

Further, in S32, the set threshold value≥2.

Further, in S33, if the sum of incomplete stripes in the same oblique direction between two adjacent flip points is less than half a stripe, it is processed as 0.5 stripes, and if the sum of more than 0.5 stripes and less than one stripe is processed as one stripe.

After adopting the above-mentioned technical scheme, the present invention has the following advantages compared with the background technology:

1. The present invention does not need the reference arm of the traditional laser interferometer, and its single optical path has easy collimation and reduces the sensitivity of the system to external noise. The self-mixing interference principle has no specific requirements on the coherence of the laser light source, and the laser selection has a large degree of freedom.

2. Since the self-mixing signal is processed by the hysteresis comparator, the high and low square waves with different widths are output. The square wave level width corresponding to the square wave signal at the flip point is significantly larger than the square wave level width at the non-flip point, making The requirement for the signal-to-noise ratio of the obtained self-mixing waveform is reduced, and the impact of the burr on the self-mixing signal on the measurement results can be ignored, so it is not necessary to use a low-pass filter circuit, and it is not necessary to use a high-precision, ultra-low noise integrated operational amplifier circuit to form The edge low-pass filter reduces the cost; and when the self-mixing signal stripe shape is not good or there is an envelope, the measurement accuracy is still good.

3. The overall design of the measurement system is easy to integrate, the measurement method is simple and reliable, and the resolution reaches λ/8, which is suitable for industrial application.

Description of drawings

Figure 1 is a schematic diagram of the laser self-mixing interference technology.

FIG. 2 is a schematic structural diagram of the amplitude measuring device of the present invention.

FIG. 3 is a schematic flowchart of the amplitude measurement method of the present invention.

FIG. 4 is a schematic diagram of a square wave obtained by the present invention.

FIG. 5 is a schematic diagram of a measurement result of the present invention.

Detailed ways

In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, but not to limit the present invention.

Before describing the embodiments, the basic principles of the present invention are first explained. The invention is designed based on the principle of self-mixing interference of laser. When the measured object is displaced, the reflected light carrying the optical path change signal of the outer cavity will affect the inner cavity and disturb the laser power, that is, the displacement information of the measured object. It is reflected in the fluctuation of optical power.

Example 1

Referring to FIG. 2 , the present invention discloses a square wave transform amplitude measurement device based on self-mixing interference, which includes a light source unit, a signal processing unit and a data processing unit.

The light source unit is used to monitor the vibrating object to be measured to generate a self-mixing laser intensity signal and convert it into a corresponding current signal; the signal processing unit processes the signal output by the light source unit to obtain the required method. wave signal; the data processing unit analyzes and calculates the square wave signal to obtain the amplitude and frequency of the vibrating object to be measured.

In this embodiment, the light source unit includes a semiconductor laser, a photodetector and a laser driving circuit respectively connected to the semiconductor laser. The photodetector is packaged in a semiconductor laser, and the laser light of the semiconductor laser is collected by the focusing lens of the laser and then hits the surface of the vibrating object to be measured, and the part of the laser irradiated on the surface is returned to the laser cavity, and the cavity is connected with the cavity. The laser light inside interferes to generate a self-mixing laser intensity signal, and the photodetector converts the self-mixing laser intensity signal into a corresponding current signal.

Among them, the surface of the vibrating object to be measured is required to have a certain reflectivity, and the part of the laser irradiated on it can be returned to the laser cavity. If the surface can be pasted with a mirror, the surface of the object to be measured is not required.

Of course, an external independent photodetector can also be used to detect the output light intensity of the laser through a beam splitter. The light source 1 can also use other lasers with required collimation, which is not specifically limited in the present invention.

In this embodiment, the signal processing unit includes a signal preprocessing module and a signal postprocessing module.

The signal preprocessing module sequentially includes a transconductance operational amplifier circuit, a DC blocking circuit and a proportional operational amplifier circuit. The transconductance operational amplifier circuit converts the current signal into a voltage signal; the DC blocking circuit filters out DC components in the signal through a DC blocking capacitor; and the proportional operational amplifier circuit amplifies the weak signal. In this embodiment, the proportional op amp circuit can use a varistor as a negative feedback resistor to achieve variable amplification; a fixed resistor can also be used as a negative feedback resistor to achieve a fixed amplification; the same-direction proportional op amp can be used, or Use an inverse proportional op amp. The present invention is not specifically limited.

The signal post-processing module includes a hysteresis comparator, which processes the signal output by the proportional operational amplifier circuit to output a square wave signal. Wherein, the hysteresis comparator can deal with self-mixing signals of different amplitudes in the future by adjusting the upper and lower threshold voltages, so that the number of square waves output per unit time is the largest and the level burr is the least.

The data processing unit includes an ADC sampling circuit and a DSP real-time processing module. The ADC sampling circuit samples the square wave signal output by the hysteresis comparator, inputs the obtained sampling signal into the DSP real-time processing module, and searches for a method in which the level width is significantly larger than the adjacent stripes through the program. Obtain the flip point, and then calculate the number of stripes in the same inclined direction between flip points), so as to calculate the amplitude of the vibration of the object according to A=λ*N/4, where A is the amplitude of the object, λ is the wavelength of the laser, and N is the two-phase The number of stripes in the same oblique direction between adjacent flip points.

At the same time, the data processing unit can also calculate the vibration frequency of the object according to F=2*fs/(X2-X1) according to the sampling sequence number and sampling rate of the flip point, where F is the vibration frequency of the object, and X1 is the previous flip The sampling number of the point, X2 is the sampling number of the next flip point, and fs is the sampling rate.

The final calculation result is displayed on the display and output.

Example 2

Referring to FIG. 3 , the present invention also provides a method for measuring amplitude of square wave transform based on self-mixing interference, which includes three core steps.

S1. Signal generation and output: The emitted light of the semiconductor laser hits the surface of the vibrating object to be measured, and part of the light returns to the laser cavity to generate a self-mixing laser intensity signal; the photodetector detects the self-mixing laser intensity signal and converts it into corresponding current signal output.

S2. Signal processing: convert the current signal into a voltage signal and amplify the signal; input the amplified voltage signal into the hysteresis comparator, and adjust the upper and lower threshold voltages of the hysteresis comparator within the signal amplitude range, so that the output square The square wave in the wave signal has the largest number and the least glitches per unit time.

In this embodiment, the conversion of the current signal into the voltage signal is realized by the transconductance operational amplifier circuit; the signal amplification is realized by the proportional operational amplifier circuit.

When the upper and lower threshold voltages of the hysteresis comparator are adjusted too large, the square wave corresponding to the stripes will not flip. Therefore, the upper and lower threshold voltages of the hysteresis comparator need to be adjusted within the signal amplitude range. The number of stripes is the largest, but if the upper and lower threshold voltages are adjusted too small, the burrs will increase. Therefore, here, the upper and lower threshold voltages of the hysteresis comparator should be adjusted within the signal amplitude range, so that the number of square waves output is the largest (that is, the stripes between the flip points are not lost) and the glitch level is the least (the glitch level It refers to a level signal with a very small level width, usually less than one-sixth of the stripe width. When the upper and lower threshold voltages are adjusted to be close to 0V, the noise fluctuations on the signal around 0V break through the upper and lower threshold voltages.). As shown in FIG. 4 , it is a schematic diagram of generating a square wave by processing the upper and lower threshold voltages of the hysteretic comparator.

S3, data processing:

S31, perform AD sampling on the square wave signal output by S3, and calculate the width of each level for the sampled signal;

S32. Find the flip point: according to the width of the square wave level corresponding to the flip strip is significantly larger (usually more than 2 times, this embodiment is set to 2) the width of the first two square wave levels and the width of the last two square wave levels Flat width, determine the flip point;

S33. Calculate the vibration amplitude of the object: A=λ*N/4, where A is the amplitude of the object, λ is the wavelength of the laser, and N is the number of fringes in the same inclined direction between two adjacent flip points;

S34. Calculate the vibration frequency of the object: F=2*fs/(X2-X1), where F is the vibration frequency of the object, X1 is the sampling number of the previous flip point, X2 is the sampling number of the next flip point, and fs is the sampling number Rate.

In S31, the level width is obtained by the following method: detecting the point where the high and low level jumps, obtaining the time coordinates of each edge of the square wave, and obtaining the time width of each level by calculating the difference between the time coordinates of the adjacent edges, that is, Obtain the level width.

In this embodiment, in S33, the minimum unit of N is set to 0.5. Specifically, it is calculated in the following way: if the addition of incomplete stripes in the same oblique direction between two adjacent flip points is less than half a stripe, it will be treated as 0.5 stripes, and if it is greater than 0.5 stripes and less than one stripe, it will be treated as one stripe. In this way, the resolution of the measurement can reach λ/8.

Please refer to Figure 5, which is an example of applying this method to measure. In the figure, the upper part is the amplified voltage signal, and the lower part is the square wave signal output after processing. In this example, the flip points are all located at the top, that is, the gray ellipse area. Among them, the laser wavelength λ is equal to 650nm (the measurement resolution is 81.25nm), N is calculated as 2.5, and the calculation result of the formula in S43 is substituted into A=406.3nm. The actual vibration amplitude is estimated to be 422.5nm by directly reading the number of self-mixing fringes. , the error is 3.8%. In the experiment, the vibration frequency calculated by DSP is 211Hz, the actual vibration frequency is 200Hz obtained by the signal generator, and the error is 5.5%, which can meet the requirements of industrial measurement accuracy.

Those skilled in the art can clearly understand that, for the convenience and conciseness of the description, only the division of the above-mentioned functional units and modules is used for illustration. The above-mentioned function distribution is accomplished by different functional units and modules, that is, the internal structure of the device is divided into different functional units or modules, so as to accomplish all or part of the functions described above. Each functional unit and module in the embodiment may be integrated in one processing unit, or each unit may exist physically alone, or two or more units may be integrated in one unit, and the above-mentioned integrated units may adopt hardware. It can also be realized in the form of software functional units. In addition, the specific names of the functional units and modules are only for the convenience of distinguishing from each other, and are not used to limit the protection scope of the present application.

In the foregoing embodiments, the description of each embodiment has its own emphasis. For parts that are not described or described in detail in a certain embodiment, reference may be made to the relevant descriptions of other embodiments.

The above description is only a preferred embodiment of the present invention, but the protection scope of the present invention is not limited to this. Substitutions should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims (7)

1. a square wave transform amplitude measurement device based on self-mixing interference, is characterized in that, comprises: a light source unit, which is used to monitor the vibrating object to be measured, to generate a self-mixing laser intensity signal and convert it into a corresponding current signal; a signal processing unit, which includes a signal pre-processing module and a signal post-processing module; the signal pre-processing module converts the current signal into a voltage signal and amplifies it; the signal post-processing module includes a hysteresis comparator, and the hysteresis comparator The hysteresis comparator uses a variable resistor as a feedback resistor to achieve variable upper and lower threshold voltages. The hysteresis comparator is used to realize signal processing, so that the square wave in the output square wave signal has the largest number and the glitch level in a unit time. least; a data processing unit, which searches for a flip point for the output square wave signal, so as to calculate the vibration amplitude of the object according to the number of fringes in the same oblique direction between adjacent flip points; The light source unit includes a semiconductor laser, a laser drive circuit and a photodetector; the signal preprocessing module includes a transconductance operational amplifier circuit, a DC blocking circuit and a proportional operational amplifier circuit; the data processing unit includes an ADC sampling circuit and a DSP real-time a processing module; the laser driving circuit and the photodetector are respectively connected with the semiconductor laser, the photodetector, the transconductance operational amplifier circuit, the DC blocking circuit, the proportional operational amplifier circuit, the hysteresis comparator, the ADC sampling circuit and the The DSP real-time processing modules are connected in sequence, and the ADC sampling circuit samples the square wave signal output by the hysteresis comparator, inputs the obtained sampled signal into the DSP real-time processing module, and finds through the program that the level width is significantly larger than The method of adjacent stripes is used to obtain the flip point, and then the number of stripes in the same inclined direction between flip points is calculated, so as to calculate the amplitude of the vibration of the object according to A=λ*N/4, where A is the amplitude of the object, and λ is the laser. wavelength, N is the number of fringes in the same oblique direction between two adjacent flip points; The data processing unit can also calculate the vibration frequency of the object according to F=2*fs/(X ₂ -X ₁ ) according to the sampling sequence number and sampling rate of the flip point, where F is the vibration frequency of the object, and X ₁ is the previous one. The sampling number of the flip point, X ₂ is the sampling number of the next flip point, fs is the sampling rate, and the final calculation result is displayed and output through the display screen. 2 . The self-mixing interference-based square wave transform amplitude measurement device according to claim 1 , wherein the data processing unit further calculates the vibration information of the vibrating object to be measured according to the sampling sequence number of the inversion point. 3 . 3. The square wave transform amplitude measurement device based on self-mixing interference as claimed in claim 1, characterized in that: the proportional op amp circuit adopts a varistor as a negative feedback resistor to realize variable magnification; The discharge circuit uses a fixed resistor as a negative feedback resistor to achieve a fixed magnification. 4. The square wave transform amplitude measurement method based on self-mixing interference, is characterized in that, comprises the following steps: S1. Signal generation and output: The emitted light of the semiconductor laser hits the surface of the vibrating object to be measured, and part of the light returns to the laser cavity to generate a self-mixing laser intensity signal; the photodetector detects the self-mixing laser intensity signal and converts it into corresponding The current signal output; S2. Signal processing: convert the current signal into a voltage signal and amplify the signal; input the amplified voltage signal into a hysteresis comparator, which uses a variable resistor as a feedback resistor to achieve its upper and lower threshold voltages Variable, adjust the upper and lower threshold voltages of the hysteresis comparator within the signal amplitude range, so that the square wave in the output square wave signal has the largest number and the least burr per unit time; S3, data processing: S31, perform AD sampling on the square wave signal output by S2, and calculate the width of each level for the sampled signal; S32. Find the flip point according to the width of the level: if the ratio of a certain level to the two levels of the same polarity before and after exceeds the set threshold, the level is the flip point; S33. Calculate the vibration amplitude of the object: A=λ*N/4, where A is the amplitude of the object, λ is the wavelength of the laser, and N is the number of fringes in the same inclined direction between two adjacent flip points; S34. Calculate the vibration frequency of the object: F=2*fs/(X ₂ -X ₁ ), where F is the vibration frequency of the object, X ₁ is the sampling number of the previous flip point, and X ₂ is the sampling number of the next flip point , fs is the sampling rate. 5. The method for measuring the amplitude of square wave transformation based on self-mixing interference as claimed in claim 4, characterized in that: in S31, the point at which the high and low levels jump are detected, and the time coordinates of each edge of the square wave are obtained by The time width of each level is obtained by taking the difference of the time coordinates of adjacent edges, and the level width is obtained. 6 . The method for measuring amplitude of square wave transform based on self-mixing interference according to claim 4 , wherein: in S32 , the set threshold value is greater than or equal to 2. 7 . 7. The square wave transform amplitude measurement method based on self-mixing interference as claimed in claim 4, characterized in that: in S33, the addition of incomplete fringes in the same oblique direction between two adjacent flip points is less than half of the fringes. Treated as 0.5 stripes, more than 0.5 stripes and less than 1 stripe as 1 stripe.

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