CN113280729A - Pretreatment device and method for demodulating dual-frequency laser interferometry signal - Google Patents
Pretreatment device and method for demodulating dual-frequency laser interferometry signal Download PDFInfo
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- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B9/00—Measuring instruments characterised by the use of optical techniques
- G01B9/02—Interferometers
- G01B9/02001—Interferometers characterised by controlling or generating intrinsic radiation properties
- G01B9/02002—Interferometers characterised by controlling or generating intrinsic radiation properties using two or more frequencies
- G01B9/02003—Interferometers characterised by controlling or generating intrinsic radiation properties using two or more frequencies using beat frequencies
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B9/00—Measuring instruments characterised by the use of optical techniques
- G01B9/02—Interferometers
- G01B9/02001—Interferometers characterised by controlling or generating intrinsic radiation properties
- G01B9/02007—Two or more frequencies or sources used for interferometric measurement
Abstract
The invention provides a pretreatment device and a pretreatment method for demodulating a dual-frequency laser interferometry signal. The device comprises a photoelectric conversion module 1, a high-pass filter 2, a signal compensation module 3, a DDS signal generation module 4, analog multiplier modules 5 and 6, low-pass filter modules 7 and 8, signal compensation modules 9 and 10, analog-to-digital conversion modules 11 and 12 and an FPGA module 13. The method is characterized in that a high-pass filter, a multiplier circuit, a low-pass filter circuit and the like designed by hardware are used for designing an analog operation circuit to replace a front-end digital signal processing part which consumes extremely high resources in an FPGA demodulation algorithm to finish the pre-processing of the demodulation of the dual-frequency laser interference measurement signal. The invention can be used for the high-speed phase subdivision operation of the double-frequency laser interferometry, and can effectively reduce the requirement on the operation performance of the system, improve the operation speed, reduce the operation delay and reduce the cost of the system.
Description
(I) technical field
The invention relates to a preprocessing device and a preprocessing method for demodulating a dual-frequency laser interference measurement signal, which can be used for preprocessing the interference measurement signal demodulation in the dual-frequency laser interference measurement, are applied to the high-speed phase subdivision operation of the dual-frequency laser interference measurement, and can effectively reduce the requirement on the operation performance of a system, improve the operation speed and reduce the cost of the system by using hardware to replace a resource-consuming digital signal processing process.
(II) background of the invention
In the fields of precision measurement, nano-scale processing and the like, the application of laser interference measurement is very wide. With the development of the technology in these fields, the requirements for the resolution and the measurement speed of the signal measurement of the dual-frequency laser interferometer are continuously increased.
The demodulation method for the dual-frequency laser interferometry signal is mainly divided into software demodulation, hardware demodulation and software and hardware combined demodulation in the aspect of component devices.
The demodulation mode of part of hardware is to carry out high-frequency multiplication on the original double-frequency laser interferometry signal and then carry out phase counting on the frequency-multiplied signal. The frequency multiplication is difficult to achieve very high due to the hardware performance, and the ultrahigh frequency signal after frequency multiplication is seriously influenced.
The mode of partial software and hardware combined demodulation is that one path of original reference signal sent by a laser is subjected to 90-degree phase shift and mixed with the other path of signal, and then AD reading mixed signals are used for processing. However, the phase shift process of the signal causes phase delay and time delay, so that the time of the phase-shifted reference signal is not synchronous with that of the current measurement signal, and the error of the laser cannot be completely cancelled.
The mode of part of software demodulation is that original measurement signals and reference signals are completely read in by using AD, then the FPGA is used for digital signal processing, and operations including FFT operation, low-pass filtering, signal generation, signal multiplication and the like are carried out in the FPGA, so that the accuracy of measurement and calculation is ensured, the consistency of time is ensured, but higher requirements are provided for the hardware performance of the FPGA and the performance of the AD.
The invention provides a pretreatment device and a pretreatment method for demodulating a dual-frequency laser interference measurement signal, which can be used for pretreatment of demodulating the interference measurement signal in the dual-frequency laser interference measurement and are applied to the operation of high-speed phase subdivision of the dual-frequency laser interference measurement. The pretreatment device and the method for demodulating the dual-frequency laser interference measurement signal are improved based on the operation steps of a biorthogonal demodulation algorithm, and the process that part of signals are suitable for being processed by using a hardware circuit is separated, so that the digital signal processing process by using an FPGA (field programmable gate array) is replaced by using a suitable hardware architecture design, the requirement on the operation performance of a system can be effectively reduced, the operation speed is increased, and the cost of the system is reduced.
Disclosure of the invention
Aiming at the processing process of the demodulation of the double-frequency laser interference measurement signal, the invention aims to provide an improved pretreatment device and method for the demodulation of the double-frequency laser interference measurement signal, which can effectively reduce the requirement of the operation performance of a system, improve the operation speed, reduce the operation delay and reduce the cost of the system.
The invention provides a pretreatment device for demodulating a dual-frequency laser interference measurement signal, which consists of a photoelectric conversion module 1, a high-pass filter 2, a signal compensation module 3, a DDS signal generation module 4, analog multiplier modules 5 and 6, low- pass filter modules 7 and 8, signal compensation modules 9 and 10, analog-to- digital conversion modules 11 and 12 and an FPGA module 13.
The device comprises a photoelectric conversion module 1, a signal processing module and a signal processing module, wherein the photoelectric conversion module is used for converting an input dual-frequency laser interference measurement optical signal into an electric signal;
the high-pass filter 2 in the device is connected with the photoelectric conversion module 1 and used for filtering direct current and low frequency in signals;
in the device, a signal compensation module 3 is connected with the high-pass filter 2 and compensates signals to an input range suitable for an analog multiplier;
the FPGA module 13 in the device is connected with the DDS signal generation module 2 and is used for controlling the DDS signal generation module to output two paths of orthogonal fixed frequency signals: one path of sine signal and one path of cosine signal;
low- pass filters 7 and 8 in the device are respectively connected with the analog multipliers 5 and 6 to filter high-frequency components after signal multiplication;
analog-to- digital conversion modules 11 and 12 in the device are respectively connected with the signal compensation modules 9 and 10 and used for collecting pre-processed dual-frequency laser interferometry electric signals;
the hardware structure of the apparatus will be further explained below.
The hardware of the photoelectric conversion module 1 adopted in the pre-processing device for demodulating the dual-frequency laser interference measurement signal comprises circuits such as an APD (avalanche photo diode), an APD (avalanche photo diode) driver and a trans-impedance amplifier, and is used for converting the received dual-frequency laser interference measurement optical signal into an electric signal.
The high-pass filter 2 adopted in the pre-processing device for demodulating the dual-frequency laser interference measurement signal is a high-pass passive filter design with the cut-off frequency far lower than the low frequency band of the signal, and is only used for filtering direct current and low-frequency noise.
The signal compensation module 3 adopted in the pre-processing device for demodulating the dual-frequency laser interference measurement signal is used for conditioning the signal to a voltage range suitable for the operation of the analog multiplier, and dividing the signal into two paths to be input into the two analog multipliers.
The DDS signal generating module 4 is used in the pre-processing device for demodulating the dual-frequency laser interference measuring signal, and a DDS signal generating chip of the DDS signal generating module receives a control signal of the FPGA, and sends out two paths of orthogonal signals with certain frequency according to the setting of the FPGA for carrying out multiplication mixing in the pre-processing of demodulating the dual-frequency laser interference measuring signal. One path of signal is fsinOne path of signal is fcosAnd the two signals are multiplied by two paths of measuring signals which are respectively branched by the signal compensation module 3. Whose signal frequency is set to the beat of the frequency variation produced by the double-frequency laser interferometryThe center frequency of the frequency signal is the beat frequency of the reference signal which is emitted by the laser and does not pass through the measuring optical path, and the beat frequency of the signal of the measuring optical path when the measured object is static.
The analog multipliers 5 and 6 used in the pre-processing device for demodulating the dual-frequency laser interference measurement signal have the circuit structure that an analog multiplier chip is used, for example, AD834 forms an analog multiplication circuit, and the bandwidth of the chip is larger than the high-frequency band generated by frequency spectrum shifting after signal multiplication. And outputting a mixing signal obtained by multiplying the double-frequency laser interference measurement signal by the signal generated by the DDS signal generation module 4 after the matching of the output circuit.
The low- pass filters 7 and 8 adopted in the pre-processing device for demodulating the dual-frequency laser interference measurement signal adopt a passive low-pass filter design to filter out a high-frequency signal generated after signal multiplication and frequency mixing, only a low-frequency signal is reserved, and the cut-off frequency is set as the frequency of two paths of orthogonal signals generated by the DDS signal generation module 4, namely the beat frequency of a reference signal which is emitted by a laser and does not pass through a measurement optical path and the beat frequency of a signal of the measurement optical path when an object to be measured is static.
The signal compensation modules 9 and 10 adopted in the pre-processing device for demodulating the dual-frequency laser interference measurement signal are used for compensating the signal to an intensity range suitable for analog-to-digital conversion acquisition so as to exert the maximum performance of AD sampling.
The analog-to- digital conversion modules 11 and 12 adopted in the pre-processing device for demodulating the dual-frequency laser interferometry signal can be composed of a dual-channel AD or two single-channel ADs and are used for collecting the pre-processed dual-frequency laser interferometry signal.
The invention provides a pretreatment method for demodulating a dual-frequency laser interferometry signal, which comprises the following steps:
(1) inputting the double-frequency laser interference measurement optical signal into a photoelectric conversion module of the device, and converting a same-frequency electrical signal of the double-frequency laser interference measurement optical signal;
(2) filtering out direct current and low-frequency interference signals of the electric signals by using a high-pass filter of the device;
(3) a DDS signal generation module of the device generates two paths of orthogonal signals with fixed frequency;
(4) the electric signals converted by the device are respectively multiplied by two paths of orthogonal signals with fixed frequency generated by a signal generating module;
(5) the device filters the high-frequency component of the multiplied signal through a low-pass filter to finish the pre-processing of the signal;
(6) the device collects the pre-processed signals through an analog-to-digital conversion module and carries out subsequent calculation;
through signal preprocessing, the frequency of the signal to be sampled by the AD is halved, and the FPGA does not need to perform complex digital signal processing operation. This means that the speed of the signal demodulation process is increased while substantially maintaining the accuracy of the software demodulation. In addition, on the hardware architecture, not only the sampling rate required by the AD and the frequency and speed requirements of subsequent circuit design are reduced by half, but also the hardware performance requirements of the FPGA are greatly reduced. For most AD chips in the market, the rising of the sampling rate can lead to the exponential rise of the chip price, the price of one high-sampling-rate AD chip is far higher than that of two single-channel chips with half of the sampling rate or two-channel chips with half of the sampling rate, and the hardware cost can be greatly reduced due to the reduction of the performance requirement of FPGA hardware.
(IV) description of the drawings
Fig. 1 is a schematic diagram of a hardware configuration of a preprocessing device for demodulating a dual-frequency laser interferometry signal.
Fig. 2 is an algorithm schematic of dual frequency laser interferometry signal demodulation.
FIG. 3 is a block diagram of an embodiment of a pre-processing apparatus and method using dual-frequency laser interferometry signal demodulation.
(V) detailed description of the preferred embodiments
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention. It should be understood that the described embodiments are only some of the applicable embodiments of the present invention, and are not intended to limit the scope of the present invention. Variations and modifications of the embodiments may be made without departing from the spirit and scope of the invention.
The invention is described in detail, and the principle of the laser interferometer signal demodulation algorithm is described first.
Referring to fig. 2, fig. 2 is a schematic diagram of an algorithm for demodulating a dual-frequency laser interferometry signal.
Taking single-channel measurement as an example, the dual-frequency laser interferometer will receive two paths of measurement optical signals respectively:
one path is a reference signal fr，fr＝Rsin(2πfrt), R is the reference signal amplitude;
one path is a measurement signal fm，
M is the amplitude of the measurement signal and,
for the initial phase of the signal,. DELTA.f is fmRelative to f due to Doppler shiftrThe frequency difference is the information to be demodulated.
The DDS signal generates two paths of orthogonal sine signals, and because the reference signal can generate frequency jitter taking fundamental frequency as the center, the frequency of the orthogonal signal is the fundamental frequency of the reference signal, namely:
fsin＝sin(2πf2t)，fcos＝cos(2πf2t), the two signals are orthogonal.
The reference signal and the measurement signal are respectively multiplied by two paths of orthogonal signals generated by the DDS:
with f2The low-pass filter cuts off the frequency, filters the high-frequency component, and obtains four paths of phase difference signals:
thus, four paths of phase signals required by the FPGA for phase calculation are obtained.
Referring to fig. 3, fig. 3 is a structural diagram of a preprocessing apparatus and method for demodulating a dual-frequency laser interferometry signal according to an embodiment of the present invention, which is a single-channel dual-frequency laser interferometry structure.
The embodiment comprises two photoelectric conversion modules 301, two high-pass filters 302, two signal compensation modules 303, a DDS signal generation module 304, four analog multiplier modules 305, 306, 307 and 308, a four low-pass filter module 309, a four signal compensation module 310, a four analog-to-digital conversion module 311 and an FPGA operation module 312.
In the embodiment of the device, two paths of photoelectric conversion modules 301 respectively receive the reference light signal frAnd measuring the optical signal fmMeasuring the input dual-frequency laser interference optical signalConverted into a common-frequency electrical signal.
Two high-pass filters 302 in the device are connected with the photoelectric conversion module 301 to filter out direct current and low-frequency noise in signals.
Two-way signal compensation module 303 in the device is connected with the high-pass filter 302, and compensates the signal to the input range adapted by the analog multiplier.
In the device, the FPGA module 312 controls the DDS signal generating module 304 to output two orthogonal fixed-frequency signals: sinusoidal signal fsinAnd cosine signal fcos(ii) a Sinusoidal signal fsinConnected to the analog multipliers 305, 307, the cosine signal fcosAnalog multipliers 306, 308 are connected.
In the device, a four-path analog multiplier module receives an electric signal converted by photoelectricity and a signal generated by a DDS signal generating module, and completes multiplication of the signals:
Four paths of same low-pass filters 309 in the device are respectively connected with the analog multipliers 305, 306, 307 and 308, high-frequency components obtained after multiplication of signals are filtered, phase signals required by subsequent operation are obtained, and preprocessing of the signals is completed.
Four identical signal compensation modules 310 in the device are respectively connected with the low-pass filters 309 and used for compensating signals to an intensity range suitable for analog-to-digital conversion acquisition.
The analog-to-digital conversion module 311 in the device is respectively connected with the signal compensation module 310 and is used for collecting the pre-processed dual-frequency laser interferometry electric signals.
The modules of the examples are further illustrated below:
the photoelectric conversion module 301 used in the pre-processing device for demodulating the dual-frequency laser interference measurement signal comprises circuits such as an APD (avalanche photo diode), an APD driver, a trans-impedance amplifier and the like, and is used for converting the received dual-frequency laser interference measurement optical signal into an electric signal.
The high-pass filter 302 adopted in the pre-processing device for demodulating the dual-frequency laser interference measurement signal is designed as a high-pass passive filter with the cut-off frequency far lower than the low frequency band of the signal, and is only used for filtering direct current and low-frequency noise.
The signal compensation module 303 adopted in the embodiment of the pre-processing device for demodulating the dual-frequency laser interferometry signal is used for conditioning the signal to a voltage range suitable for the operation of the analog multiplier, and dividing the signal into two paths to be input into the four analog multipliers 305, 306, 307 and 308 respectively.
The DDS signal generating module 304 used in the pre-processing device for demodulating the dual-frequency laser interference measuring signal, the DDS signal generating chip of which receives the control signal of the FPGA, and sends out two paths of orthogonal signals with certain frequency according to the setting of the FPGA for carrying out multiplication mixing in the pre-processing of demodulating the dual-frequency laser interference measuring signal. One path of signal is fsinOne path of signal is fcosThe signals are respectively input into analog multipliers 305, 306, 307 and 308, and are respectively multiplied by the measurement signals branched by the two-path signal compensation module 303. The signal frequency of the orthogonal signal is set as the central frequency of a beat frequency signal with frequency change generated by the double-frequency laser interferometry, namely the beat frequency fundamental frequency of a reference signal which is emitted by the laser and does not pass through the measuring optical path and the beat frequency fundamental frequency of the signal of the measuring optical path when the measured object is static.
The analog multipliers 305, 306, 307 and 308 adopted in the pre-processing device for demodulating the dual-frequency laser interference measurement signal have the circuits that analog multiplier chips are used, for example, AD834 form an analog multiplication circuit, the bandwidth of the chips is larger than a high-frequency band generated by frequency spectrum shifting after signal multiplication, for example, the bandwidth of AD834 can reach 800M. And outputs a mixing signal obtained by multiplying the dual-frequency laser interference measurement signal by the signal generated by the DDS signal generation module 304 after being adapted by an output circuit.
Four groups of low-pass filters 309 adopted in the pre-processing device for demodulating the dual-frequency laser interference measurement signal adopt a passive low-pass filter design, filter out high-frequency signals generated after signal multiplication and frequency mixing, only keep low-frequency signals, and the cut-off frequency of the low-pass filters is set as the frequency of two paths of orthogonal signals generated by the DDS signal generation module 304, namely the fundamental frequency of the beat frequency of the reference signal which is emitted by the laser and does not pass through the measurement optical path and the fundamental frequency of the beat frequency of the signal of the measurement optical path when the measured object is static.
The signal compensation module 310 adopted in the pre-processing device for demodulating the dual-frequency laser interference measurement signal is used for compensating the signal to an intensity range suitable for analog-to-digital conversion acquisition so as to exert the maximum performance of AD sampling.
The analog-to-digital conversion module 311 used in the pre-processing device for demodulating the dual-frequency laser interferometry signal can be composed of a dual-channel AD or two single-channel ADs and is used for collecting the pre-processed dual-frequency laser interferometry electrical signal.
The application embodiment of the preprocessing method for demodulating the dual-frequency laser interferometry signal comprises the following steps of taking the beat frequency fundamental frequency as frFor example, a 20MHz laser and a measuring optical path with a frequency difference of 18MHz, the frequency band of the measuring signal is 20MHz ± 18MHz, i.e. fm＝2MHz～38MHz：
(1) Measuring optical signal f by dual-frequency laser interferometryrWith reference optical signal fmInputting the signal into a photoelectric conversion module of the device, and converting a common-frequency electrical signal of the dual-frequency laser interference measurement optical signal;
(2) the high-pass filter of the device embodiment is used for filtering the direct current quantity and the low-frequency interference signals of the electric signals, and the cut-off frequency of the high-pass filter can be set to be 500 KHz;
(3) the DDS signal generation module of the device embodiment generates two paths of orthogonal signals f with fixed frequencysin、fcosFrequency of f2＝20MHz；
(4) The electrical signals converted by the embodiment of the device are respectively multiplied by two paths of fixed-frequency orthogonal signals generated by a signal generation module, so that the following steps in the algorithm pretreatment are realized: f. ofr·fsin、fr·fcos、fm·fsin、fm·fcos；
(5) The device embodiment filters out high-frequency components of the multiplied signal through a low-pass filter: frequency fr+f2、fm+f2Preserving the low frequency component of the signal: frequency fr-f2、fm-f2Finishing the pre-processing of the signals, and acquiring sinA, cosA, sinB and cosB in the pre-processing of the algorithm;
(6) the embodiment of the device collects the preprocessed signals compensated by the signal compensation module through the analog-to-digital conversion module, and carries out subsequent phase demodulation calculation;
through signal preprocessing, the signal acquisition bandwidth required to be designed is reduced from 40MHz to 20MHz, namely the frequency of a signal required to be sampled by AD is reduced by half, the sampling rate requirement of AD is reduced by half, and the FPGA does not need to perform complex digital signal processing operation such as signal filtering and the like. This means that the speed of the signal demodulation process is increased while substantially maintaining the accuracy of the software demodulation.
On the hardware architecture, not only the sampling rate required by the AD and the frequency and speed requirements of subsequent circuit design are reduced by half, but also the hardware performance requirements of the FPGA are greatly reduced. For most AD chips in the market, the rising of the sampling rate can lead to the exponential rise of the chip price, the price of a high-sampling-rate AD chip is far higher than that of a single-channel chip with half of the sampling rate or that of a double-channel chip with half of the sampling rate, and the hardware cost can be greatly reduced due to the reduction of the performance requirement of FPGA hardware.
The described embodiments are merely illustrative of the principles and utilities of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or change the above-mentioned embodiments without departing from the spirit and scope of the present invention. Accordingly, it is intended that all equivalent modifications or changes which can be made by those skilled in the art without departing from the spirit and technical spirit of the present invention be covered by the claims of the present invention.
Claims (10)
1. A pretreatment device for demodulating a dual-frequency laser interference measurement signal is characterized in that: the digital signal synthesizer consists of a photoelectric conversion module 1, a high-pass filter 2, a signal compensation module 3, a DDS signal generation module 4, analog multiplier modules 5 and 6, low-pass filter modules 7 and 8, signal compensation modules 9 and 10, analog-to-digital conversion modules 11 and 12 and an FPGA module 13.
The device comprises a photoelectric conversion module 1, a signal processing module and a signal processing module, wherein the photoelectric conversion module is used for converting an input dual-frequency laser interference measurement optical signal into an electric signal;
the high-pass filter 2 in the device is connected with the photoelectric conversion module 1 and used for filtering direct current and low-frequency noise in signals;
in the device, a signal compensation module 3 is connected with the high-pass filter 2 and compensates signals to an input range suitable for an analog multiplier;
the FPGA module 13 in the device is connected with the DDS signal generation module 2 and is used for controlling the DDS signal generation module to output two paths of orthogonal fixed frequency signals: one path of sine signal and one path of cosine signal;
analog multipliers 5 and 6 in the device are connected with the signal compensation module 3 and are respectively connected with a sine signal and a cosine signal generated by the DDS signal generation module to realize signal multiplication;
low-pass filters 7 and 8 in the device are respectively connected with the analog multipliers 5 and 6 to filter high-frequency components after signal multiplication;
signal compensation modules 9 and 10 in the device are respectively connected with the low-pass filters 7 and 8 and are used for compensating signals to an intensity range suitable for analog-to-digital conversion acquisition;
analog-to-digital conversion modules 11 and 12 in the device are respectively connected with the signal compensation modules 9 and 10 and used for collecting pre-processed dual-frequency laser interferometry electric signals.
2. The photoelectric conversion module 1 used in the pre-processing device for demodulating the dual-band laser interferometry signal according to claim 1, comprising: the device comprises circuits such as an APD, an APD driver and a trans-impedance amplifier, and is used for converting received double-frequency laser interferometry optical signals into electric signals.
3. The high-pass filter 2 used in the pre-processing device for demodulating the dual-band laser interferometry signal according to claim 1, wherein: and the passive filter is used for filtering the direct current quantity and the low-frequency noise.
4. The signal compensation module 3 used in the pre-processing device for demodulating the dual-band laser interferometry signal according to claim 1, wherein: the signal is conditioned to a voltage range suitable for the operation of the analog multiplier, and is divided into two paths to be input into the two analog multipliers.
5. The DDS signal generating module 4 used in the pre-processing device for demodulating dual-frequency laser interferometry signal as claimed in claim 1, wherein: two paths of orthogonal signals with certain frequency are sent out according to the setting of the FPGA and are used for multiplication frequency mixing in the demodulation pretreatment of the double-frequency laser interference measurement signals. One path of signal is fsinOne path of signal is fcosAnd the two signals are multiplied by two paths of measuring signals which are respectively branched by the signal compensation module 3. The signal frequency is set as the central frequency of the beat frequency signal of the frequency change generated by the double-frequency laser interferometry, namely the beat frequency of the reference signal which is emitted by the laser and does not pass through the measuring optical path and the signal beat frequency of the measuring optical path when the measured object is static.
6. The analog multipliers 5 and 6 used in the pre-processing device for demodulating the dual-band laser interferometry signal according to claim 1, wherein: an analog multiplier chip is used for forming an analog multiplication circuit, the bandwidth of the chip is larger than the high-frequency band generated by frequency spectrum shifting after signal multiplication, and a mixing signal obtained by multiplying the double-frequency laser interference measurement signal and the signal generated by the DDS signal generation module 4 is output after the output circuit is adaptive.
7. The low-pass filters 7 and 8 used in the pre-processing device for demodulating the dual-band laser interferometry signal according to claim 1, wherein: and filtering out a high-frequency signal generated after signal multiplication and mixing, only keeping a low-frequency signal, and setting the cut-off frequency of the high-frequency signal as the frequency of two paths of orthogonal signals generated by the DDS signal generation module 4, namely the beat frequency of a reference signal which is emitted by a laser and does not pass through a measuring optical path and the beat frequency of a signal of the measuring optical path when an object to be measured is static.
8. The signal compensation modules 9 and 10 used in the pre-processing device for demodulating the dual-band laser interferometry signal according to claim 1, wherein: for compensating the signal to an intensity range suitable for analog-to-digital conversion acquisition.
9. The analog-to-digital conversion module 11, 12 used in the pre-processing device for demodulating the dual-band laser interferometry signal according to claim 1, wherein: the device consists of a double-channel AD or two single-channel AD and is used for collecting pre-processed double-frequency laser interferometry electrical signals.
10. A pretreatment method for demodulating a dual-frequency laser interferometry signal is characterized by comprising the following steps:
(1) inputting the double-frequency laser interference measurement optical signal into a photoelectric conversion module of the device, and converting a same-frequency electrical signal of the double-frequency laser interference measurement optical signal;
(2) filtering out direct current and low-frequency interference signals of the electric signals by using a high-pass filter of the device;
(3) a DDS signal generation module of the device generates two paths of orthogonal signals with fixed frequency;
(4) the electric signals converted by the device are respectively multiplied by two paths of orthogonal signals with fixed frequency generated by a signal generating module;
(5) the device filters the high-frequency component of the multiplied signal through a low-pass filter to finish the pre-processing of the signal;
(6) the device collects the pre-processed signals through the analog-to-digital conversion module and carries out subsequent calculation.
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