CN103322923B - The optical heterodyne interference method of nonlinearity erron is eliminated based on square wave mean value - Google Patents
The optical heterodyne interference method of nonlinearity erron is eliminated based on square wave mean value Download PDFInfo
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Abstract
The optical heterodyne interference method eliminating nonlinearity erron based on square wave mean value belongs to laser heterodyne interferometry field, the method is in the light path that there is nonlinearity erron interference component, reach out at least 3 road signals and periodicity nonlinearity erron interference component respective in making wherein at least 3 tunnels, phasing degree on the signal frequency composition that will be eliminated is within the scope of a corresponding angle of circumference or get rid of in a corresponding circle week angular region after integral multiple angle of circumference different, and in analog electrical signal passage, adopt wave filter to carry out filtering to signal, and adopt square wave mean value to obtain phase differential between each road measuring-signal and reference signal, then analog to digital conversion is carried out, displacement calculates, weighted sum overlap-add procedure, to eliminate or to suppress these interference components.The present invention can eliminate the particular harmonic composition of nonlinearity erron or interference, and its adjustment process is very easy to, and improves system performance, reduces cost.
Description
Technical field
The invention belongs to laser heterodyne interferometry (HeterodyneInterferometry) fields of measurement, be specifically related to a kind of laser heterodyne interferometry measuring method eliminating nonlinearity erron based on square wave mean value and phaselocked loop filter method exempting from accurate adjustment.
Background technology
Laser heterodyne interference system can be used for measuring the physical quantity such as displacement, length, is one of best nano measurement method.This system is in the frequency or phase place change tested displacement being converted to heterodyne signal, again by this measure of the change out, because the frequency of heterodyne signal is more much lower than optical frequency, photosignal easily processes, can through electronic fine-grained and reach higher Measurement Resolution, resolution can reach micromicron (pm) or better.
But ubiquity non-linear (nonlinearity) problem in optical heterodyne interference method, these factors can be the main source of error of displacement measurement, make its precision generally only have nanoscale to tens nanometer, its reason is that the light beam that frequency is different can not well be separated.These periodic nonlinearity erron problems are the obstacles of this art always.
Constantly invent some methods improved both at home and abroad for many years, but also there are some restriction or problems more, such as Badami and Pattersom uses ratemeter and frequency spectrograph directly measure nonlinearity erron composition in a mobile system and compensate; TaeBongEom and TaeYoungChoi etc. carry out compensating non-linear error to the method for carrying out ellipse fitting after phase signal integration.These methods can when there is no other auxiliary interferometer compensating non-linear error, but system complex, and need a large amount of fluctuation signal cycles and relative a large amount of computing, the real-time that impact is measured.Be disclose a kind of new method in the Chinese invention patent of CN101660924 at publication number, the method can address this problem effectively, if but wish to obtain very accurate result, also need point-device optics to regulate, this precise optical regulates usually more difficult.
Summary of the invention
In order to the system complex, the operand that solve the existence of existing laser heterodyne interference system are large, the coarse technical matters of poor real, result, the invention provides a kind of optical heterodyne interference method eliminating nonlinearity erron based on square wave mean value, the particular harmonic composition of nonlinearity erron or interference can be eliminated, and remove from and eliminate precision optics regulating device required for nonlinearity erron and minute adjustment process, this adjustment is made to become very easy, significantly improve system performance simultaneously, reduce costs.
The electric signal that the AC signal that the photodetector output terminal of laser heterodyne interference systematic survey light arm obtains is is frequency with alien frequencies optical frequency difference, its additional phase differential and measured position move into accurate proportionate relationship.But wherein contain so-called nonlinearity erron, be mainly distributed on the first harmonic (generally also can be called fundamental frequency according to Fourier series character, be a kind of spatial frequency) of Fourier spectrum.Method of the present invention can eliminate the fundamental component of nonlinearity erron; In fact method of the present invention is all effective to arbitrary a certain frequency, and without the need to doing special minute adjustment to optical system.
Also exist in the signal light path of nonlinearity erron interference component in laser heterodyne interference system, reach out at least 3 road signals (passage), by by carry be detected signal light arm at least 3 interference light photodetecting part are set method obtain these signals, and to make wherein to have at least in 3 tunnels the phase angle of nonlinearity erron first harmonic (or other frequency content) contained separately different in a corresponding circumference, so just obtain sufficient information, the process such as weighted sum superposition in face after enable pass and fundamental frequency (or any one frequency) composition that eliminates in nonlinearity erron.The method different in a corresponding circumference of the phase angle realizing first harmonic (or other frequency content) is a lot, the phase angle of corresponding first harmonic such as can be changed by adjustment light path, by the error measurement method of disclosed first harmonic in prior art, the amplitude and the starting phase angle that obtain first harmonic can be easy to.Generally, the phase angle of the several signals error of different light paths is usually unequal, if the situation having phase angle equal, can be known by the method measuring phase angle in prior art, and makes them unequal by adjustment light path.Furtherly, generally our optical system of setting up at random, do not have nonlinearity erron phasing degree in any 2 tunnels identical in a corresponding circumference, if but after completing the adjustment of optical system, the phase angle of the nonlinearity erron first harmonic on 2 tunnels (or other frequency content that will be eliminated) is had to be more or less the same in 3 tunnels, the amplitude of the useful signal after affecting weighted stacking, thus the signal to noise ratio (S/N ratio) of impact output signal, at this moment we roughly can adjust the difference of phase angle relative to (frequency content that will be eliminated of nonlinearity erron) signal phase angle corresponding in other passages of the frequency content that will be eliminated in 1-2 road wherein, it is made to increase to some extent fully till (namely enough).There are now a lot of detection nonlinearity erron first harmonic (or other frequency content that will be eliminated) phase places and the method for amplitude, as " measuring method of laser heterodyne interference nonlinearity erron " " Beijing University of Technology's journal " the 6th phase in 2010 of Chen Hongfang etc.; " the novel measuring method of a kind of laser heterodyne interference nonlinearity erron " of Zhong Zhi etc., optoelectronic laser, 2005, etc.The method of adjustment phase angle can realize by regulating the optical path difference between two light participating in interference.
Based on the periodicity of hamonic function, certainly as usually, several integral multiple angles of circumference comprised can be got rid of disregard (no longer doing similar prompting below) in above-mentioned phase differential.
Adopt and carry out subsequent treatment in the following method: first hypothesis only has the situation of 3 road signals, 3 road signals is carried out phase compare with reference signal respectively, until solve 3 displacements.The phase place of the nonlinearity erron at this moment in each passage is different.
Known by proof below, have non-vanishing weighting coefficient array can make superposition after the fundamental frequency of nonlinearity erron or the amplitude of other frequency contents be zero, and retain useful signal.
In above-mentioned 3 displacements solved, the displacement measurement on the i-th tunnel can be expressed as:
Wherein, equal sign right-hand member Section 1 χ is real physical displacement, and Section 2 is the primary components of nonlinearity erron, certainly illustrates that content of the present invention also without loss of generality with first harmonic here; A is coefficient, and expressing nonlinearity erron amplitude, is generally an a small amount of, but does not make approximate processing in derivation afterwards.
be the initial phase angle of nonlinearity erron, λ is optical wavelength.Here the wave number in nonlinearity erron item
what represent is first harmonic composition, and by the situation of measuring prism individual reflection.For the situation of second harmonic, this can become
By 3 result weighted stacking, be normalized into:
One group of new ki, just in order to neatly pro forma, can be regarded as new weighting coefficient.Our object finds one group of ki to make: X=x.
By above-mentioned condition, we can obtain system of linear equations below:
k
1+k
2+k
3=b
Wherein, b ≠ 0
The factor arrays of variable ki is 3 rank square formations of full rank, and the system of equations about ki has untrivialo solution.That is, can make
To sum up, demonstrated after such weighted stacking, the first harmonic composition of nonlinearity erron is eliminated.
If
in have any 2 difference 180 °, problem can be made to become simple and favourable, this situation generally needs accurate optics adjustment just can obtain, and the 2 road signals only needing non-linear component to differ 180 ° just enough eliminate the nonlinearity erron composition of characteristic frequency, than being illustrated in more detail in this that patent of invention mentioned in the introduction.
To this, we have solved the nonlinearity erron problem in laser heterodyne interference in 3 dimensional linear spaces of electronics.
For the situation with more than 3 road signals (passage), we at least can retain the different signal of 3 road phase angles in advance, again by any road Signal averaging in 3 tunnels of all the other several signals and reservation, and changed into each 3 non-vanishing tunnels of phase angle difference in certain frequency of nonlinearity erron.So just dissolve the problem solved above becoming, i.e. the situation of 3 passages, and be proven.Certainly also can not adopt the processing procedure being first simplified to 3 tunnels recited above, but together complete in weighted overlap-add procedure.
Obtain correct weighting coefficient array by following method in practice and eliminate error percentage: (1) is by linear for 2 wherein superposition, because in 2 dimension spaces of this certain harmonic components nonlinear, one group of substrate of this two paths of signals Special composition, so any one vector can be generated by adjustment superposition coefficient, we allow the vector generated be just in time that direction is contrary with the 3rd signal (vector) on certain harmonic components nonlinear, then by the signal of generation and the 3rd signal (vector) linear superposition, adjustment weighting coefficient just can make certain harmonic components nonlinear be kept to zero completely mutually, and useful signal can still be retained.(2) electricity consumption tune method can repeat the weighting coefficient on alternate sweep at least 2 tunnel, measure nonlinearity erron value in the output after superposition simultaneously, make it constantly reduce, until be zero.(3) adopt the most basic method, after phase angle described in the every road of measurement and amplitude, directly calculated by analytic method, also can adopt the thinking in (1) here, but be not decompose adjustment, but decoupled method, no longer carefully separate here.That is, finding that first harmonic error can be cancelled each other by weighted stacking, thus after removing the above-mentioned principle of error percentage, the weighted stacking mode be applicable to can be selected according to the related content of the present invention's record, just can realize the elimination of first harmonic error.The method of above-mentioned multiple acquisition weighting coefficient is only used to be convenient to enumerating of understanding, is not the restriction completely to technical scheme.
In order to remove corresponding optics accurate adjustment from, eliminate or suppress nonlinearity erron, and be conducive to retaining useful signal and selecting rational parameter, preferably, the difference between the phase angle on the signal frequency composition that will be eliminated of 3 at least 3 road signals periodicity nonlinearity errons is made to be not less than 60 degree.This is because we always can, easily by regulating or arranging, make the declinate between any two-phase not too little in practice.Theoretical and experiment all illustrates, a rational numerical value using 60 ° of lower limits as this angle, this is beneficial to the signal to noise ratio (S/N ratio) after process, the amplitude of useful signal lower than single channel of output can not be made after weighted stacking, as long as attempt blindly fixingly affecting device in the light path of phase differential between 3 tunnels 3 to 5 times at random simultaneously, roughly just once chance meets this condition, thus " adjustment-free " that realize mechanically, and eliminate corresponding adjuster, make adjustment or the work that arranges become simple and easy.Can judge whether to meet this condition according to the method for the starting phase angle of the aforementioned measurement first harmonic error mentioned, thus stop adjustment.Also can be eliminated by similar aforementioned reality method (1) (2) of error percentage, certain harmonic components nonlinear be adjusted nothing, and then checks the amplitude of useful signal, if too low, just illustrate and do not have to meet " 60 degree of conditions " or similar standard.It is complete whether inspection adjusts, and having eliminated error can judge by such as adopting more accurate surveying instrument to carry out the methods such as results contrast.
This " minute adjustment " by electronics replaces the release precision optical machinery of " minute adjustment " of optics to regulate or exempts from the method for optics accurate adjustment, and cost is significantly reduced, and the accuracy requirement regulated optics can decline more than 2-3 the order of magnitude.And the precision that whole system shows on nonlinearity erron characteristic frequency is also significantly improved.
Clearly, whether the ultimate principle of the method and the advantage itself existed and meaning, and adopt integrated optics mode, comprises optical fiber solutions, or bulk wave mode etc. is irrelevant.The method is all effective for the periodic error in all laser heterodyne interferometry systems, as long as we can obtain the different signal of its interference component phase place of at least 3 roads.
In fact laser heterodyne interference signal is typical weak signal, in the exquisite system of this elimination nonlinearity erron, particularly more require that signal is pure, and the wave filter in analog electrical signal is a very important link in machine system.Consider that the useful signal of this system is single some composition frequently, when testee exists speed and acceleration, the rate of change of frequency displacement and frequency will be there is.The wave filter of simple inductance and capacitance type is longer for the response time of input signal phase place, limits the movement velocity of object being measured under the requirement of precision.Phase locked loop filter then can address this problem preferably, it has very low phase noise and extraordinary transient phase error and static phase error index, be conducive to the immediate movement of accurately measuring object in motion, the even immediate movement of object in acceleration, can promote complete machine index.The phase-detection between each road signal and reference signal can be carried out after phase-locked filtering.Consider the symmetry requirement of the measuring-signal at least 3 tunnels, the filtering part generally in each measuring-signal passage should be identical.
Also must obtain the measuring-signal on each road and the phase differential of reference signal in systems in which.We use the phase differential angle of circumference in of square wave qualitative modeling Qiu Ge road measuring-signal respectively and between reference signal below.By the particular phases on measuring-signal and a reference signal road (as reference signal) wherein (as risen, Angle Position during zero passage, transition edge can be generated according to this) output that triggers certain memory section (as trigger) is high level, the particular phases of the signal (as measuring-signal) on another road is then reverted to low level similarly, at this moment the phase differential between trigger output duty cycle and two signals is linear, measure its dutycycle and can obtain phase differential, can adopt and measure dutycycle in the following method, the low and high level that described trigger exports is stablized, by low-pass filter, dutycycle is transformed into stable output voltage, it is the mean value of square wave, linear with the dutycycle of described square wave, this simple circuit can obtain point-device result.When above-mentioned low level gets earth potential, the above-mentioned stable output voltage be transformed into by dutycycle is proportional to the phase differential between two signals, and when phase angle reaches maximal value, namely during 2 π radian, output voltage also reaches maximal value, i.e. high level voltage.The method can by very simple high speed circuit acquisition processing speed quickly and good precision.Corresponding circuit can be called the square wave average circuit of inspection phase angle difference.Whole system to this can without any numerical portion participate in signal transacting, more without the pressure of operand, and have stronger antijamming capability, such as anti-particle radiation ability.Enter numerical portion by analog to digital conversion after this to carry out displacement calculating, weighted sum superposition etc. and relatively simply process.
To sum up, adopt the phase differential obtained in the following method between each road measuring-signal and reference signal, the measuring-signal on Ji Youge road and the particular phases of reference signal trigger respectively and recover the output level state of certain memory section in each road, the low and high level that will export square wave (or the square wave after negate) is stablized, dutycycle to be transformed into stably by low-pass filter and phase differential has the output voltage of accurate linear relationship, then to carry out analog to digital conversion, displacement calculating, weighted sum overlap-add procedure etc.;
Above-mentioned high level voltage can be follow-up part such as analog to digital converter, provides witness mark (benchmark) voltage, in order to improve measuring accuracy.
Above-mentioned square wave is carried out can add in the low-pass filter of filtering and comprise with reference signal with (frequency is f frequently
r) trapper and the trapper of front several integer multiple frequency (as 1 frequency multiplication and 2,3 frequencys multiplication, i.e. f
r, 2f
r, 3f
rdeng), will to diminish the leeway that even output is certain to the design pressure of low-pass filter like this, the inversion frequency of low-pass filter can close to or exceed signal frequency, in order to faster processing time with improve precision.
After phaselocked loop filtering and the process of square wave mean value and before being weighted superposition, we can obtain sufficient each road information, comprise the phase relation etc. of phase relation between the signal of each road and interference component, this category information is useful in some cases, is such as conducive to determining weighting coefficient array etc.
Based on foregoing, the invention provides a kind of first harmonic or other frequency content that can eliminate or reduce periodically nonlinearity erron, improve measuring accuracy, the optical heterodyne interference method of the corresponding precision optics that omits adjustment, namely the optical heterodyne interference method of nonlinearity erron is eliminated based on square wave mean value, the method is: in the light path that there is nonlinearity erron interference component, at least 3 road measuring-signals and 1 tunnel reference signal is obtained by light splitting, and make the phasing degree of the respective periodicity nonlinearity erron of wherein at least 3 road measuring-signals in the frequency content that will be eliminated different within the scope of a corresponding angle of circumference, at least 3 road measuring-signals and 1 tunnel reference signal are separately converted to corresponding at least 3 drive test amount analog electrical signals and 1 tunnel reference analog electrical signal, the first filtering is carried out respectively in each road of described at least 3 drive test amount analog electrical signals, after the second filtering is carried out with reference to analog electrical signal in 1 tunnel, input square wave average module respectively, utilize duty cycle square wave mean value method to record each roads of at least 3 drive test amount analog electrical signals and 1 tunnel with reference to the phase differential between analog electrical signal, after phase differential analog to digital conversion, then be converted into displacement, obtain at least 3 tunnel displacement measurement, now contain nonlinearity erron in the displacement measurement of each road, the at least 3 tunnel displacement measurement obtained are carried out real number ranking operation, then carries out additive operation and can obtain final measurement, described first filtering comprises employing phase locked loop filter.
Above-mentioned duty cycle square wave mean value method comprises: the particular phases on each road of at least 3 drive test amount analog electrical signals triggers memory section, exports the first level; Memory section is triggered with reference to the particular phases of analog electrical signal in 1 tunnel, exports second electrical level; First level and second electrical level are not identical; Measure the dutycycle of the square wave of above-mentioned two level composition, be described phase differential.
Above-mentioned particular phases comprises: rise or declined zero angle time phase place.
The step of the above-mentioned duty cycle square wave of above-mentioned measurement comprises: first and second level equalization exported by described memory section, is transformed into stable output voltage by low-pass filtering by dutycycle, and above-mentioned voltage is the mean value of square wave, linear with duty cycle square wave.
Carry out above-mentioned square wave can adding in the low-pass filter of filtering and comprise and the trapper of reference signal with frequency or the trapper of its several times frequency.
The phase differential of at least 3 periodicity nonlinearity errons in above-mentioned at least 3 road measuring-signals is not less than 60 °.
The step obtaining at least 3 road measuring-signals and 1 tunnel reference signal above by light splitting comprises: the A road light signal of output obtains A1, A2 respectively by least 4 light-dividing devices successively ... An road light signal, wherein n >=4; The B road light signal with the A road light signal exported with frequency difference obtains B1 road light signal by light-dividing device, obtains B2 successively after all the other light signals of B road are reflected by reflection unit by light-dividing device ... Bn road light signal, wherein n >=4; A1 road light signal and B1 road light signal interfere formation reference signal, A2 ... An road light signal and B2 ... the corresponding interference forms n-1 road measuring-signal to Bn road light signal respectively.
Due to the principle of work of phase detector in phaselocked loop, the interference of input signal noise and other frequency contents may be subject to, cause phase detector output noise.Therefore, before phase detector, add the narrow band filter that the resonant circuit that is made up of the inductance of the serial or parallel connection of one or two or more multi-level and electric capacity is formed, it is useful for carrying out filtering to simulating signal.The effect of this wave filter is important, it can not make up by any wave filter after phaselocked loop.
Resistance is added or equivalent resistance adjustment quality factor carry out filtering, to make quality factor adjustable and stable in resonant tank.Resistance is added (containing adjustable resistance in the filter circuits that the parallel connection of a relative high quality factor (Q value) or the inductance capacitance resonant tank of series connection are formed, potentiometer, or the method for equivalence), quality factor are mainly determined by lumped parameters such as resistors, instead of be distributed parameter decision, obtain desired, stable Q value.Q value has a lot of physical significances, as the here too high highest movement speed that also can affect under accuracy requirement of Q value.
For each basic resonant tank in the wave filter that the parallel connection of above-mentioned single-stage, two-stage or more level or the inductance capacitance resonant tank of series connection are formed, and between the output terminal of its prime, and between the input end of rear class, adopt weak coupling method have certain quality factor to ensure this resonant tank and make it stablize, the method of these weak couplings is at least realized by one of following method, 1) capacitive coupling, 2) inductive coupling, 3) resistively couple, 4) winding method is transformer coupled.
Another technical scheme of the present invention is: a kind of laser heterodyne interferometry device of above-mentioned optical heterodyne interference method that adopts comprises: the first light-dividing device, obtains A1, A2 by the light signal light splitting of A road ... An road light signal, wherein n >=4; Second light-dividing device, obtains B1 road light signal and remaining light signal thereof by the B road light signal light splitting that the A road light signal with output has frequency difference, and all the other light signals described are obtained B2 by the second light-dividing device light splitting after reflection unit reflection ... Bn road light signal, wherein n >=4; Interfere forming apparatus, make A1 road light signal and B1 road light signal interfere the reference signal formed, A2 ... An road light signal and B2 ... the corresponding interference forms n--1 road measuring-signal to Bn road light signal respectively; Signal detecting device, is converted to 1 road reference electrical signal, n--1 drive test amount electric signal respectively by above-mentioned 1 tunnel reference signal, n--1 road measuring-signal; First filtration module, carries out the first filtering respectively to n--1 drive test amount analog electrical signal; Second filtration module, carries out the second filtering to 1 tunnel with reference to analog electrical signal; Square wave average module, utilizes duty cycle square wave mean value method to record each roads of at least 3 drive test amount analog electrical signals and 1 tunnel with reference to the phase differential between analog electrical signal; Analog to digital conversion and displacement computing module, after the phase differential analog to digital conversion of n--1 road, then be converted into the displacement of n--1 road, calculates n--1 road displacement measurement; Weighted stacking module, carries out real number ranking operation and additive operation by the n--1 road displacement measurement obtained.
Present invention omits explanation and the statement of some prior aries, row as omit to the details such as the wiring board distribution filtering electric capacity of sampling thheorem, power-supply system, the amplifier set by system-gain, the discussion of general foundation and block diagram etc.
The invention has the beneficial effects as follows: the present invention is in common laser heterodyne interference system-based, creatively optical path is divided into multichannel, carry out the process such as adjustment, signal transacting, weighted stacking of electronics respectively, with the length of electronics minute adjustment, light filling minute adjustment short, omitted complicated optics accurate adjustment or other non-electronic adjustment, the substitute is the adjustment and signal processing method elimination nonlinearity erron that adopt electronics, reduce the complexity of pH effect, reduce cost, improve efficiency.Simultaneously, effectively eliminate or reduce significantly the periodic interference components such as nonlinearity erron and then improve measuring accuracy or reduce interference, simultaneously the phase locked loop filter etc. of particular design make that whole system measuring accuracy improves, antijamming capability is strong, stable, be conducive to large-scale production, production cost is low.
Accompanying drawing explanation
Fig. 1 the present invention is based on the opticator schematic diagram that square wave mean value method eliminates the optical heterodyne interference method of nonlinearity erron.
Fig. 2 is the phase locked loop filter circuit diagram in the present invention.
Fig. 3 the present invention is based on the principle schematic that square wave mean value method eliminates the optical heterodyne interference method of nonlinearity erron.
Embodiment
Below in conjunction with accompanying drawing, the present invention is described in further details.
Realize the present invention is based on the phase-detection of square wave mean value, phaselocked loop filtering and in 3 dimensional linear spaces the system of the optical heterodyne interference method of the elimination nonlinearity erron of weighted stacking can be divided into opticator and electrical signal processing section afterwards.Wherein the principle of opticator as shown in Figure 1, and the present invention, on the basis of an original opticator, adds the part in dotted line frame in figure.First the opticator principle of work of original heterodyne interferometry system is set forth: send laser by laser instrument 101, acousto-optical device 103 is incided through Part I catoptron 102, Part II catoptron 114 is shone after shift frequency, transmitted light is reflected by measuring prism 115, incide Part III catoptron 111, reflecting part and another Ray Of Light are interfered through the first polaroid 131.The light that reflected by Part I catoptron 102 (it provide reference ray for each road interference portion below) is through the first catoptron 125, again after Part IV catoptron 124, Part V catoptron 123, Part VI catoptron 122, second catoptron 121, together incide the first polaroid 131 with the reflected light of Part III catoptron 111, the interference light of its outgoing converts the difference frequency part of two light to electric signal by the first photodetector 141.This electric signal, as measuring-signal, has wherein included the displacement information obtained above measuring prism 115, also containing nonlinearity erron composition.
The light that the light reflected by Part II catoptron 114 and Part IV catoptron 124 reflect converges, incide the second polaroid 134, the interference light of its outgoing converts the difference frequency part of two light to electric signal by the second photodetector 144, and this electric signal is exactly reference signal.
Above-mentioned laser instrument 101, Part I catoptron 102 and acousto-optical device 103 constitute the double-frequency laser generator that frequency has elementary errors, also can be replaced by other scheme.
Invention increases the part in dotted line frame in Fig. 1, it mainly comprises two new measurement light arm/light paths and corresponding circuit part.Together with original the first smooth arm be made up of Part III catoptron 111, first polaroid 131, first photodetector 141 etc. in figure, have three light arms, or be called three optical paths, and obtain that measuring-signal exports 1 thus, measuring-signal export 2 and measuring-signal export 3, structurally smooth arm is identical to these two new measurement light arms with first.Add reference signal, four road signals export altogether, and this four roads signal just constitutes the output of opticator, is transferred to electrical signal processing section below, as described in Figure 3.
In electrical signal processing section, its signal is respectively through the phase locked loop filter (be respectively in Fig. 3 211,221,231,241 for first passage to the filtering part of four-way) shown in Fig. 2; Reduce the low-pass filter (to first to fourth passage difference correspondence 212,222,232,242 in the drawings) of high frequency interference composition; Through check phase differential square wave average circuit part (for the first to third channel be 213 in figure, 223,233) obtain phase differential; Three tunnel measurement data are sent to analog to digital conversion and displacement calculating section (for the first to third channel difference correspondence 214,224,234 in the drawings) respectively, complete corresponding analog to digital conversion, displacement calculating and cycle count, obtain the measurement result on each road; The same nonlinearity erron containing respective destruction system accuracy in certain result.The measurement result on Zai Jiang tri-tunnel is delivered to weighted stacking arithmetic section 301 respectively and is carried out real number ranking operation, and then do additive operation and just can draw last measurement result, the fundamental frequency of its nonlinearity erron has been eliminated or has significantly suppressed.
Claims (8)
1. eliminate the optical heterodyne interference method of nonlinearity erron based on square wave mean value, it is characterized in that: the method comprises:
In the light path that there is nonlinearity erron interference component, obtain at least 3 road measuring-signals and 1 tunnel reference signal by light splitting, and make the phasing degree of the respective periodicity nonlinearity erron of wherein at least 3 road measuring-signals in the frequency content that will be eliminated different within the scope of a corresponding angle of circumference;
At least 3 road measuring-signals and 1 tunnel reference signal are separately converted to corresponding at least 3 drive test amount analog electrical signals and 1 tunnel reference analog electrical signal;
The first filtering is carried out respectively in each road of described at least 3 drive test amount analog electrical signals, after the second filtering is carried out with reference to analog electrical signal in 1 tunnel, input square wave average module respectively, utilize duty cycle square wave mean value method to record each roads of at least 3 drive test amount analog electrical signals and 1 tunnel with reference to the phase differential between analog electrical signal;
After phase differential analog to digital conversion, then be converted into displacement, obtain at least 3 tunnel displacement measurement, now contain nonlinearity erron in the displacement measurement of each road;
At least 3 tunnel displacement measurement obtained are carried out real number ranking operation, then carries out additive operation and can obtain final measurement;
Described first filtering comprises employing phase locked loop filter.
2. the optical heterodyne interference method of nonlinearity erron is eliminated as claimed in claim 1 based on square wave mean value, it is characterized in that: described duty cycle square wave mean value method comprises: the particular phases on each road of at least 3 drive test amount analog electrical signals triggers memory section, exports the first level; Memory section is triggered with reference to the particular phases of analog electrical signal in 1 tunnel, exports second electrical level; First level and second electrical level are not identical; Measure the dutycycle of the square wave of above-mentioned two level composition, be described phase differential.
3. eliminate as claimed in claim 2 the optical heterodyne interference method of nonlinearity erron based on square wave mean value, it is characterized in that: described particular phases comprises: rise or declined zero angle time phase place.
4. the optical heterodyne interference method of nonlinearity erron is eliminated as claimed in claim 2 based on square wave mean value, it is characterized in that: the step of the above-mentioned duty cycle square wave of described measurement comprises: first and second level equalization that described memory section is exported, by low-pass filtering, dutycycle is transformed into stable output voltage, above-mentioned voltage is the mean value of square wave, linear with duty cycle square wave.
5. eliminate as claimed in claim 4 the optical heterodyne interference method of nonlinearity erron based on square wave mean value, it is characterized in that: carry out above-mentioned square wave can adding in the low-pass filter of filtering comprise and reference signal with the trapper of trapper frequently or its several times frequency.
6. eliminate the optical heterodyne interference method of nonlinearity erron as claimed in claim 1 based on square wave mean value, it is characterized in that: the phase differential of at least 3 periodicity nonlinearity errons in described at least 3 road measuring-signals is not less than 60 °.
7. the optical heterodyne interference method of nonlinearity erron is eliminated as claimed in claim 1 based on square wave mean value, it is characterized in that: the step being obtained at least 3 road measuring-signals and 1 tunnel reference signal by light splitting is comprised: the A road light signal of output obtains A1, A2 respectively by least 4 light-dividing devices successively ... An road light signal, wherein n >=4; The B road light signal with the A road light signal exported with frequency difference obtains B1 road light signal by light-dividing device, obtains B2 successively after all the other light signals of B road are reflected by reflection unit by light-dividing device ... Bn road light signal, wherein n >=4; A1 road light signal and B1 road light signal interfere formation reference signal, A2 ... An road light signal and B2 ... the corresponding interference forms n-1 road measuring-signal to Bn road light signal respectively.
8. adopt a laser heterodyne interferometry device for the optical heterodyne interference method as described in any one of claim 1-7, it is characterized in that: comprising:
First light-dividing device, obtains A1, A2 by the light signal light splitting of A road ... An road light signal, wherein n >=4;
Second light-dividing device, obtains B1 road light signal and remaining light signal thereof by the B road light signal light splitting that the A road light signal with output has frequency difference, and all the other light signals described are obtained B2 by the second light-dividing device light splitting after reflection unit reflection ... Bn road light signal, wherein n >=4;
Interfere forming apparatus, make A1 road light signal and B1 road light signal interfere the reference signal formed, A2 ... An road light signal and B2 ... the corresponding interference forms n-1 road measuring-signal to Bn road light signal respectively;
Signal detecting device, is converted to 1 road reference electrical signal, n-1 drive test amount electric signal respectively by above-mentioned 1 tunnel reference signal, n-1 road measuring-signal;
First filtration module, carries out the first filtering respectively to n-1 drive test amount analog electrical signal;
Second filtration module, carries out the second filtering to 1 tunnel with reference to analog electrical signal;
Square wave average module, utilizes duty cycle square wave mean value method to record each roads of at least 3 drive test amount analog electrical signals and 1 tunnel with reference to the phase differential between analog electrical signal;
Analog to digital conversion and displacement computing module, after the phase differential analog to digital conversion of n-1 road, then be converted into the displacement of n-1 road, calculates n-1 road displacement measurement;
Weighted stacking module, carries out real number ranking operation and additive operation by the n-1 road displacement measurement obtained.
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