CN103322923A - Optical heterodyne interference method for removing non-linear error based on square wave mean value method - Google Patents
Optical heterodyne interference method for removing non-linear error based on square wave mean value method Download PDFInfo
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Abstract
The invention belongs to the field of optical heterodyne interference, and discloses an optical heterodyne interference method for removing a non-linear error based on a square wave mean value method. The method comprises the steps that at least three paths of signals are obtained from an optical path where non-linear error interference elements exist, phase angles, on signal frequency elements to be removed, of the periodic non-linear error interference elements of the at least three paths of signals are made to be different in a corresponding circumference angle range or in a corresponding circumference angle range after integral multiples of circumference angles are removed, meanwhile, signals are filtered through a filter in an analog electrical signal channel, a phase difference between each path of measuring signals and a reference signal is computed by the adoption of the square wave mean value method, and then analog-digital conversion, displacement calculation, weighting and iterative processing are conducted so as to remove or restrain the interference elements conveniently. The optical heterodyne interference method for removing the non-linear error based on the square wave mean value method can remove specific harmonic elements of the non-linear error or the interference, the regulation process is very easy, system performance is improved, and cost is reduced.
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 based on square wave mean value and phaselocked loop filter method elimination nonlinearity erron of exempting from accurate adjustment.
Background technology
The laser heterodyne interference system can be used for measuring the physical quantitys such as displacement, length, is one of best nano measurement method.This system is converted to tested displacement in the frequency or phase place variation of heterodyne signal, again with this measure of the change out, because the frequency ratio optical frequency of heterodyne signal is much lower, photosignal is easily processed, can be through electronic fine-grained and reach higher Measurement Resolution, resolution can reach micromicron (pm) or better.
But ubiquity non-linear (nonlinearity) problem in the laser heterodyne interferometry 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 different light beam of frequency can not well separate.These periodic nonlinearity erron problems are the obstacles of this art development always.
Constantly invent for many years the method for some improvement both at home and abroad, but also have some restrictions or problems more, for example Badami and Pattersom use ratemeter and frequency spectrograph are directly measured the nonlinearity erron composition and are compensated in mobile system; TaeBong Eom and TaeYoungChoi etc. come the compensating non-linear error to the method for carrying out ellipse fitting behind the phase signal integration.These methods can be when the auxiliary interferometer that does not have other exists the compensating non-linear error, but system complex, and need a large amount of fluctuation signal cycle and relative a large amount of computing, the real-time of impact measurement.In being the Chinese invention patent of CN101660924, publication number announced a kind of new method, 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 is regulated usually relatively difficulty.
Summary of the invention
The system complex, the operand that have the existence of laser heterodyne interference system now are large, real-time is poor, the coarse technical matters of result in order to solve, the invention provides a kind of laser heterodyne interferometry method of eliminating nonlinearity erron based on the square wave averaging method, can eliminate the particular harmonic composition of nonlinearity erron or interference, and remove the needed precision optics regulating device of nonlinearity erron and the minute adjustment process eliminated from, make this adjustment become very easy, significantly improve simultaneously system performance, reduce cost.
The AC signal that the photodetector output terminal of laser heterodyne interference systematic survey light arm obtains is take the poor electric signal as frequency of alien frequencies optical frequency, and its additional phase differential and measured position moves into accurate proportionate relationship.But wherein comprising so-called nonlinearity erron, mainly be distributed on the first harmonic (also can be called fundamental frequency according to Fourier series character generally speaking, be a kind of spatial frequency) of Fourier spectrum.Method of the present invention can be eliminated the fundamental component of nonlinearity erron; In fact method of the present invention all is effectively to a certain frequency arbitrarily, and need not optical system is done special minute adjustment.
In the laser heterodyne interference system, exist on the signal light path of nonlinearity erron interference component, reach out at least 3 road signals (passage), obtain these signals by carrying the method that at least 3 interference light photodetection parts are set on the light arm that is detected signal, and make and have wherein that the phase angle of contained nonlinearity erron first harmonic (or other frequency content) is different in the circumference of a correspondence separately in 3 the tunnel at least, so just obtained sufficient information, enable pass later face the processing such as weighted sum stack and eliminate fundamental frequency (or any one frequency) composition in the nonlinearity erron.The phase angle of realizing first harmonic (or other frequency content) different method in the circumference of a correspondence is a lot, for example can change the phase angle of corresponding first harmonic by adjusting light path, by the error measurement method of disclosed first harmonic in the prior art, can be easy to obtain amplitude and the starting phase angle of first harmonic.Generally speaking, the phase angle of the several signals error of different light paths is usually unequal, if the situation that has phase angle to equate can be known by the method for measurement phase angle in the prior art, and pass through to adjust light path so that they are unequal.Furtherly, our optical system of setting up at random generally speaking, do not have in any 2 the tunnel nonlinearity erron phasing degree identical in a corresponding circumference, if but finish after the adjusting of optical system, there is the phase angle of 2 tunnel nonlinearity erron first harmonic (or other frequency content that will be eliminated) to be more or less the same then can to affect the amplitude of the useful signal after the weighted stacking in 3 the tunnel, thereby affect the signal to noise ratio (S/N ratio) of output signal, at this moment we can roughly adjust the phase angle of the frequency content that will be eliminated in wherein the 1-2 road with respect to the difference of (frequency content that will be eliminated of nonlinearity erron) signal phase angle corresponding in other passages, and it is increased to fully till (namely enough) to some extent.The method that a lot of detection nonlinearity erron first harmonics (or other frequency content that will be eliminated) phase place and amplitude are arranged now is such 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., photoelectron laser, 2005, etc.The method of adjusting phase angle can realize by the optical path difference of regulating between two light that participate in interfering.
Based on the periodicity of hamonic function, certainly can several integral multiple angles of circumference eliminatings that comprise in the above-mentioned phase differential be disregarded as usually (following no longer do similar prompting).
Adopt and carry out in the following method subsequent treatment: at first hypothesis only has the situation of 3 road signals, 3 road signals is carried out the phase bit comparison with reference signal respectively, until solve 3 displacements.At this moment the phase place of the nonlinearity erron in each passage is different.
By following proof as can be known, have non-vanishing weighting coefficient array can so that after the stack amplitude of the fundamental frequency of nonlinearity erron or other frequency contents be zero, and keep useful signal.
In above-mentioned 3 displacements that solve, the displacement measurement on i road can be expressed as:
Wherein, first χ of equal sign right-hand member is real physical displacement, and second is the primary components of nonlinearity erron, certainly with first harmonic content of the present invention is described here and is without loss of generality; A is coefficient, expresses the nonlinearity erron amplitude, is an a small amount of generally speaking, but does not make approximate processing in the derivation afterwards.
Be the initial phase angle of nonlinearity erron, λ is optical wavelength.Here the wave number in the nonlinearity erron item
Expression be the first harmonic composition, and by the situation of measuring prism individual reflection.For the situation of second harmonic, this can become
With 3 weighted stacking as a result, be normalized into:
One group of new ki just for pro forma clean and tidy, can be regarded as new weighting coefficient.Our purpose be find one group of ki so that: X=x.
We can obtain following system of linear equations by above-mentioned condition:
k
1+k
2+k
3=b
Wherein, b ≠ 0
The factor arrays of variable ki is 3 rank square formations of full rank, about the system of equations of ki untrivialo solution is arranged.That is, can make
To sum up, verified after such weighted stacking, the first harmonic composition of nonlinearity erron is eliminated.
If
In have any 2 to differ 180 °, can make problem become simple and favourable, this situation generally needs accurate optics adjusting just can obtain, and only need non-linear component to differ 180 ° the 2 road signals enough nonlinearity erron composition of elimination characteristic frequency just, in this that patent of invention of in background technology, having mentioned than being illustrated in more detail.
We have solved the nonlinearity erron problem in the laser heterodyne interference in 3 dimensional linear spaces of electronics to this.
For having the above situation of 3 road signals (passage), but we are the different signal of advance reservation 3 road phase angles at least, again with all the other several signals and reservation 3 the tunnel in the stack of any one road signal, and with its change on certain frequency of nonlinearity erron phase angle difference each non-vanishing 3 the tunnel.So just dissolve the problem that has solved above becoming, i.e. the situation of 3 passages, and be proven.Certainly also can not adopt recited abovely at first to be simplified to 3 tunnel processing procedure, but in weighted overlap-add procedure, together finish.
Can obtain correct weighting coefficient array by following method in practice and eliminate error percentage: (1) incites somebody to action 2 route stacks wherein, because in 2 dimension spaces of this nonlinear certain harmonic components, this two paths of signals is one group of substrate of Special composition, so can generate any one vector by adjusting the stack coefficient, we allow the vector and the 3rd signal (vector) that generate just in time be opposite directions on nonlinear certain harmonic components, then with the signal and the 3rd signal (vector) linear superposition that generate, adjust weighting coefficient and just can make nonlinear certain harmonic components be kept to fully mutually zero, and useful signal can still be retained.(2) weighting coefficient that can electricity consumption accent method repeats alternate sweep at least 2 tunnel is measured nonlinearity erron value in the output after the stack simultaneously, it is constantly reduced, until be zero.(3) adopt the most basic method, after measuring phase angle described in every road and amplitude, directly calculated by analytic method, also can adopt the thinking in (1) here, but be not to decompose to adjust, but calculate step by step, no longer carefully separate here.That is to say, can cancel each other by weighted stacking having found the first harmonic error, thereby remove after the above-mentioned principle of error percentage, the related content of record can be selected the weighted stacking mode that is fit to according to the present invention, just can realize the elimination of first harmonic error.The method of above-mentioned multiple acquisition weighting coefficient only is for the ease of enumerating of understanding, and is not the fully restriction to technical scheme.
In order to remove corresponding optics accurate adjustment from, eliminate or the inhibition nonlinearity erron, and be conducive to keep useful signal and select rational parameter, as preferred version, make the difference between the phase angle on the signal frequency composition that will be eliminated of 3 periodicity nonlinearity errons at least 3 road signals 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 with 60 ° of lower limits as this angle, this is beneficial to the signal to noise ratio (S/N ratio) after processing, can not make the useful signal of output be lower than the amplitude of single channel after the weighted stacking, simultaneously as long as attempt blindly device 3 to 5 times on the random fixing light path that can affect phase differential between 3 tunnel, roughly just once chance meet this condition, thereby realize mechanically " adjustment-free ", and saved corresponding adjuster, so that adjusting 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 of mentioning, thereby stop to adjust.Also can nonlinear certain harmonic components be transferred nothing by the similar aforementioned actual method (1) (2) of eliminating error percentage, and then the amplitude of inspection useful signal, if excessively low, just " 60 degree condition " or similar standard are not satisfied in explanation.It is complete whether check is adjusted, and having eliminated error can be by relatively waiting method to judge such as adopting more accurate surveying instrument to carry out the result.
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 that optics is regulated can descend 2-3 more than the order of magnitude.And the precision that whole system shows on the nonlinearity erron characteristic frequency also can be significantly improved.
Clearly, whether advantage and meaning that the ultimate principle of the method and itself exist and adopt the integrated optics mode, comprise the optical fiber mode, or bulk wave mode etc. is irrelevant.The method all is effectively for the periodic error in all laser heterodyne interferometry systems, as long as we can access the different signal of at least 3 road its interference component phase places.
In fact the laser heterodyne interference signal is typical weak signal, particularly more requires signal pure in the exquisite system of this elimination nonlinearity erron, and the wave filter in the analog electrical signal is a very important link in the machine system.The useful signal of considering this system is single some frequency composition, when testee exists speed and acceleration, will have the rate of change of frequency displacement and frequency.The wave filter of simple inductance and capacitance type is longer for the response time of input signal phase place, has limited 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 accurately measure the immediate movement of object in the motion, even the immediate movement of object in the acceleration, can promote the complete machine index.Can carry out the phase-detection between each road signal and the reference signal after the phase-locked filtering.Consider the symmetry requirement of at least 3 tunnel measuring-signal, the filtering part in each measuring-signal passage should be identical generally speaking.
In system, also must obtain the measuring-signal on each road and the phase differential of reference signal.We ask each drive test amount signal respectively and the phase differential in angle of circumference between the reference signal with following square wave qualitative modeling.By the particular phases of measuring-signal and reference signal a road (such as reference signal) wherein (as rising, position, angle during zero passage, can generate according to this transition along) trigger certain memory section (such as trigger) and be output as high level, the particular phases of the signal on another road (such as measuring-signal) then reverts to low level with it 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 in the following method dutycycle, the high-low level of described trigger output is stable, by low-pass filter dutycycle is transformed into stably output voltage, it is the mean value of square wave, linear with the dutycycle of described square wave, this simple circuit can access point-device result.When above-mentioned low level was got earth potential, the above-mentioned stably output voltage that is transformed into by dutycycle was proportional to two phase differential between the signal, and when phase angle reaches maximal value, namely output voltage also reaches maximal value, i.e. high level voltage during 2 π radian.The method can obtain very fast processing speed and good precision by very simple high speed circuit.Corresponding circuit can be called the square wave average circuit of checking phase angle difference.Whole system to this can without any numerical portion participate in signal and process, more without the pressure of operand, and stronger antijamming capability is arranged, such as anti-particle radiation ability.Entering numerical portion by analog to digital conversion after this carries out displacement calculating, weighted sum stack etc. and relatively simply processes.
To sum up, adopt the phase differential of obtaining in the following method between each drive test amount signal and the reference signal, namely trigger respectively and recover the output level state of certain memory section in each road by the particular phases of the measuring-signal on each road and reference signal, the high-low level that to export square wave (or the square wave after the negate) is stable, dutycycle is transformed into the output voltage that accurate linear relationship is arranged with phase differential stably by low-pass filter, then carries 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.
Carry out for above-mentioned square wave can adding 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 frequencies (such as 1 frequency multiplication and 2,3 frequencys multiplication, i.e. f
r, 2f
r, 3f
rDeng), like this to the leeway that design pressure will diminish even output is certain of low-pass filter, the inversion frequency of low-pass filter can approach or surpass signal frequency, in order to faster processing time and raising precision.
After phaselocked loop filtering and the processing of square wave mean value and before being weighted stack, we can obtain fully each road information, comprise phase relation between each road signal and phase relation of interference component etc., this category information is useful in some cases, such as being conducive to determine weighting coefficient array etc.
Based on foregoing, the invention provides a kind of first harmonic or other frequency content that can eliminate or reduce the periodicity nonlinearity erron, improve measuring accuracy, the laser heterodyne interferometry method that the corresponding precision optics that omits is adjusted, namely eliminate the laser heterodyne interferometry method of nonlinearity erron based on the square wave averaging method, the method is: on the light path that exists the nonlinearity erron interference component, obtain at least 3 drive test amount signals and 1 tunnel reference signal by light splitting, and make at least 3 drive test amount signals wherein periodically nonlinearity erron is different in the angle of circumference scope of the phasing degree on the frequency content that will be eliminated a correspondence separately; At least 3 drive test amount signals and 1 tunnel reference signal are separately converted to corresponding at least 3 drive test amount analog electrical signals and 1 tunnel with reference to analog electrical signal; The first filtering is carried out respectively on each road of described at least 3 drive test amount analog electrical signals, 1 the tunnel carry out the second filtering with reference to analog electrical signal after, input respectively square wave average module, utilize the duty cycle square wave mean value method to record each road and 1 tunnel of at least 3 drive test amount analog electrical signals with reference to the phase differential between the analog electrical signal; After the phase differential analog to digital conversion, be converted into again displacement, obtain at least 3 tunnel displacement measurement, contain nonlinearity erron in each road displacement measurement this moment; At least 3 tunnel displacement measurement that obtain are carried out the real number ranking operation, carry out again additive operation and can obtain final measurement; Described the first filtering comprises the 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; 1 tunnel particular phases with reference to analog electrical signal triggers memory section, the output second electrical level; The first level is not identical with second electrical level; Measure the dutycycle of the square wave of above-mentioned two level composition, be described phase differential.
Above-mentioned particular phases comprises: the phase place when rising or descending zero angle.
The step of the above-mentioned duty cycle square wave of above-mentioned measurement comprises: first and second level equalization with described memory section output, by low-pass filtering dutycycle is transformed into stably output voltage, and above-mentioned voltage is the mean value of square wave, and is linear with duty cycle square wave.
Above-mentioned square wave is carried out can add in the low-pass filter of filtering comprise and reference signal with trapper frequently or the trapper of its several times frequency.
The phase differential of at least 3 periodicity nonlinearity errons in the above-mentioned at least 3 drive test amount signals is not less than 60 °.
Above-mentioned step by light splitting acquisition at least 3 drive test amount signals and 1 tunnel reference signal comprises: the A road light signal of output obtains respectively A1, A2 by at least 4 light-dividing devices successively ... An road light signal, wherein n 〉=4; The B road light signal that has frequency difference with the A road light signal of exporting obtains B1 road light signal by light-dividing device, and all the other light signals of B road obtain B2 by light-dividing device after reflecting by reflection unit successively ... Bn road light signal, wherein n 〉=4; A1 road light signal and B1 road light signal are interfered formation reference signal, A2 ... An road light signal and B2 ... the corresponding interference forms n-1 drive test amount signal to Bn road light signal respectively.
Because the principle of work of phase detector in the phaselocked loop may be subject to the interference of input signal noise and other frequency contents, causes the phase detector output noise.Therefore, added the narrow band filter that is made of the inductance of one-level or two-stage or more multistage serial or parallel connection and resonant circuit that electric capacity forms before phase detector, it is useful that simulating signal is carried out filtering.The effect of this wave filter is important, and it can not be remedied by any wave filter after the phaselocked loop.
Adding resistance or equivalent resistance adjustment quality factor are carried out filtering in resonant tank, in order to make quality factor adjustable and stable.In the wave filter loop that the inductance capacitance resonant tank of the in parallel of a relative high quality factor (Q value) or series connection consists of, add resistance and (contain adjustable resistance, potentiometer, or method of equal value), so that quality factor are mainly determined by lumped parameters such as resistors, rather than be distributed the parameter decision, obtain desirable, stable Q value.The Q value has a lot of physical significances, such as the too high highest movement speed that also can affect under the accuracy requirement of Q value here.
Each basic resonant tank in the wave filter that consists of for the inductance capacitance resonant tank of above-mentioned single-stage, two-stage or more multistage in parallel or series connection, and between the output terminal of its prime, and adopt the weak coupling method to have certain quality factor and make it stable to guarantee this resonant tank between the input end of rear class, the method of these weak couplings realizes by one of following method at least, 1) capacitive coupling, 2) inductive coupling, 3) resistively couple, 4) the winding mode is transformer coupled.
Another technical scheme of the present invention is: a kind of laser heterodyne interferometry device of above-mentioned laser heterodyne interferometry method that adopts comprises: the first light-dividing device obtains A1, A2 with the light signal light splitting of A road ... An road light signal, wherein n 〉=4; The second light-dividing device, the B road light signal light splitting that will have with the A road light signal of output frequency difference obtains B1 road light signal and remaining light signal thereof, and described all the other light signals are obtained B2 by the second light-dividing device light splitting after the reflection unit reflection ... Bn road light signal, wherein n 〉=4; Interfere to form device, so that A1 road light signal and B1 road light signal are interfered the reference signal that forms, A2 ... An road light signal and B2 ... the corresponding interference forms n--1 drive test amount signal to Bn road light signal respectively; Signal detecting device is converted to respectively 1 road reference electrical signal, n--1 drive test amount electric signal with above-mentioned 1 tunnel reference signal, n--1 drive test amount signal; The first filtration module carries out respectively the first filtering to n--1 drive test amount analog electrical signal; The second filtration module carries out the second filtering to 1 the tunnel with reference to analog electrical signal; Square wave average module utilizes the duty cycle square wave mean value method to record each road and 1 tunnel of at least 3 drive test amount analog electrical signals with reference to the phase differential between the analog electrical signal; Analog to digital conversion and displacement computing module after the phase differential analog to digital conversion of n--1 road, are converted into the displacement of n--1 road again, calculate n--1 road displacement measurement; The weighted stacking module is carried out real number ranking operation and additive operation with the n--1 road displacement measurement that obtains.
The present invention has omitted explanation and the statement of some prior aries, row as omitted wiring board distribution filtering electric capacity to sampling thheorem, power-supply system, be the set discussion details such as amplifier, general foundation of system-gain and block diagram etc.
The invention has the beneficial effects as follows: the present invention is on common laser heterodyne interference system-based, creatively optical path is divided into multichannel, carry out respectively the process such as adjustment, signal processing, weighted stacking of electronics, length with the electronics minute adjustment, light filling is learned the short of minute adjustment, the optics accurate adjustment that has omitted complicated or other non-electronic adjustment, the substitute is the adjustment and the signal processing method that adopt electronics and eliminate nonlinearity erron, reduced the complexity that optics is adjusted, reduce cost, improved efficient.Simultaneously, effectively eliminate or reduced significantly the periodicity interference component such as nonlinearity erron and then improve measuring accuracy or reduce interference, simultaneously the phase locked loop filter of particular design etc. make that the whole system measuring accuracy improves, antijamming capability is strong, stable, be conducive to large-scale production, production cost is low.
Description of drawings
Fig. 1 the present invention is based on the opticator schematic diagram that the square wave mean value method is eliminated the laser heterodyne interferometry method of nonlinearity erron.
Fig. 2 is the phase locked loop filter circuit diagram among the present invention.
Fig. 3 the present invention is based on the laser heterodyne interferometry ratio juris schematic diagram that the square wave mean value method is eliminated nonlinearity erron.
Embodiment
Below in conjunction with accompanying drawing the present invention is described in further details.
Realization the present invention is based on the phase-detection, phaselocked loop filtering of square wave mean value and in 3 dimensional linear spaces the system of the laser heterodyne interferometry method of the elimination nonlinearity erron of weighted stacking can be divided into opticator and electronics signal processing afterwards.Wherein the principle of opticator as shown in Figure 1, the present invention has increased the part in the dotted line frame among the figure on the basis of an original opticator.At first set forth the opticator principle of work of original difference interference measuring system: send laser by laser instrument 101, incide acousto-optical device 103 through first's catoptron 102, shone second portion catoptron 114 behind the shift frequency, transmitted light is reflected by measuring prism 115, incide third part catoptron 111, reflecting part and another bundle light are interfered through the first polaroid 131.The light (it provides reference ray for each road interference portion of back) that is reflected by first's catoptron 102 is through the first catoptron 125, again through after the 4th partially reflecting mirror 124, the 5th partially reflecting mirror 123, the 6th partially reflecting mirror 122, the second catoptron 121, together incide the first polaroid 131 with the reflected light of third part catoptron 111, the interference light of its outgoing partly converts the difference frequency of two light to electric signal by the first photodetector 141.This electric signal has wherein included the displacement information that obtains as measuring-signal above measuring prism 115, also contain the nonlinearity erron composition.
The light that the light that is reflected by second portion catoptron 114 and the 4th partially reflecting mirror 124 reflect converges, incide the second polaroid 134, the interference light of its outgoing partly converts the difference frequency of two light to electric signal by the second photodetector 144, and this electric signal is exactly reference signal.
Above-mentioned laser instrument 101, first's catoptron 102 and acousto-optical device 103 have consisted of the double-frequency laser generator that frequency has elementary errors, also can be replaced by other scheme.
The present invention has increased the part in the dotted line frame among Fig. 1, and it mainly comprises two new measurement light arm/light paths and corresponding circuit part.With original the first smooth arm that is consisted of by the third part catoptron 111 among the figure, the first polaroid 131, the first photodetector 141 etc., have three light arms, or be called three optical paths, and obtaining thus measuring-signal output 1, measuring-signal output 2 and measuring-signal output 3, these two new measurement light arms are identical with the first smooth arm structurally.Add reference signal, altogether four road signals output, this four road signal has just consisted of the output of opticator, is transferred to the electronics signal processing of back, as described in Figure 3.
In the electronics signal processing, its signal passes through respectively phase locked loop filter shown in Figure 2 (filtering part for first passage to the four-way is respectively 211 among Fig. 3,221,231,241); Reduce the low-pass filter (first to fourth passage is distinguished in the drawings correspondence 212,222,232,242) of high frequency interference composition; Through the square wave average circuit part of check phase differential (for first to third channel be 213 among the figure, 223,233) obtain phase differential; Three drive test amount data are sent to respectively analog to digital conversion and displacement calculating section (for first to third channel respectively in the drawings corresponding 214,224,234), finish corresponding analog to digital conversion, displacement calculating and cycle count, obtain the measurement result on each road; Certainly the nonlinearity erron that contains equally destruction system accuracy separately among the result.Again three tunnel measurement result is delivered to respectively weighted stacking arithmetic section 301 and carry out the real number ranking operation, 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 (11)
1. eliminate the laser heterodyne interferometry method of nonlinearity erron based on the square wave averaging method, it is characterized in that: the method comprises:
On the light path that exists the nonlinearity erron interference component, obtain at least 3 drive test amount signals and 1 tunnel reference signal by light splitting, and make at least 3 drive test amount signals wherein periodically nonlinearity erron is different in the angle of circumference scope of the phasing degree on the frequency content that will be eliminated a correspondence separately.
At least 3 drive test amount signals and 1 tunnel reference signal are separately converted to corresponding at least 3 drive test amount analog electrical signals and 1 tunnel with reference to analog electrical signal;
The first filtering is carried out respectively on each road of described at least 3 drive test amount analog electrical signals, 1 the tunnel carry out the second filtering with reference to analog electrical signal after, input respectively square wave average module, utilize the duty cycle square wave mean value method to record each road and 1 tunnel of at least 3 drive test amount analog electrical signals with reference to the phase differential between the analog electrical signal.
After the phase differential analog to digital conversion, be converted into again displacement, obtain at least 3 tunnel displacement measurement, contain nonlinearity erron in each road displacement measurement this moment;
At least 3 tunnel displacement measurement that obtain are carried out the real number ranking operation, carry out again additive operation and can obtain final measurement.
Described the first filtering comprises the employing phase locked loop filter.
2. the laser heterodyne interferometry method of eliminating nonlinearity erron based on the square wave averaging method as claimed in claim 1, 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; 1 tunnel particular phases with reference to analog electrical signal triggers memory section, the output second electrical level; The first level is not identical with second electrical level; Measure the dutycycle of the square wave of above-mentioned two level composition, be described phase differential.
3. the laser heterodyne interferometry method of eliminating nonlinearity erron based on the square wave averaging method as claimed in claim 1 or 2, it is characterized in that: described particular phases comprises: the phase place when rising or descending zero angle.
4. the laser heterodyne interferometry method of eliminating nonlinearity erron based on the square wave averaging method as claimed in claim 2, it is characterized in that: the step of the above-mentioned duty cycle square wave of described measurement comprises: with first and second level equalization of described memory section output, by low-pass filtering dutycycle is transformed into stably output voltage, above-mentioned voltage is the mean value of square wave, and is linear with duty cycle square wave.
5. the laser heterodyne interferometry method of eliminating nonlinearity erron based on the square wave averaging method as claimed in claim 4 is characterized in that: above-mentioned square wave is carried out can add in the low-pass filter of filtering comprise and reference signal with trapper frequently or the trapper of its several times frequency.
6. the laser heterodyne interferometry method of eliminating nonlinearity erron based on the square wave averaging method as claimed in claim 1 is characterized in that: adopt the weak coupling mode to be coupled between described resonant tank and its prime output terminal and the rear class input end.
7. the laser heterodyne interferometry method of eliminating nonlinearity erron based on the square wave averaging method as claimed in claim 1 is characterized in that: add resistance or equivalent resistance adjustment quality factor in the described resonant tank, so that quality factor are adjustable and stable.
8. the laser heterodyne interferometry method of eliminating nonlinearity erron based on the square wave averaging method as claimed in claim 6, it is characterized in that: described weak coupling method is capacitive couplings or inductive coupling method or resistively couple method or the transformer coupled method of winding type.
9. the laser heterodyne interferometry method of eliminating nonlinearity erron based on the square wave averaging method as claimed in claim 1 is characterized in that: in the described at least 3 drive test amount signals at least 3 periodically the phase differential of nonlinearity errons be not less than 60 °.
10. the laser heterodyne interferometry method of eliminating nonlinearity erron based on the square wave averaging method as claimed in claim 1, it is characterized in that: the step that obtains at least 3 drive test amount signals and 1 tunnel reference signal by light splitting comprises: the A road light signal of output obtains respectively A1, A2 by at least 4 light-dividing devices successively ... An road light signal, wherein n 〉=4; The B road light signal that has frequency difference with the A road light signal of exporting obtains B1 road light signal by light-dividing device, and all the other light signals of B road obtain B2 by light-dividing device after reflecting by reflection unit successively ... Bn road light signal, wherein n 〉=4; A1 road light signal and B1 road light signal are interfered formation reference signal, A2 ... An road light signal and B2 ... the corresponding interference forms n-1 drive test amount signal to Bn road light signal respectively.
11. the laser heterodyne interferometry device of an employing such as the described laser heterodyne interferometry method of claim 1-10 is characterized in that: comprising:
The first light-dividing device obtains A1, A2 with the light signal light splitting of A road ... An road light signal, wherein n 〉=4;
The second light-dividing device, the B road light signal light splitting that will have with the A road light signal of output frequency difference obtains B1 road light signal and remaining light signal thereof, and described all the other light signals are obtained B2 by the second light-dividing device light splitting after the reflection unit reflection ... Bn road light signal, wherein n 〉=4;
Interfere to form device, so that A1 road light signal and B1 road light signal are interfered the reference signal that forms, A2 ... An road light signal and B2 ... the corresponding interference forms n-1 drive test amount signal to Bn road light signal respectively;
Signal detecting device is converted to respectively 1 road reference electrical signal, n-1 drive test amount electric signal with above-mentioned 1 tunnel reference signal, n-1 drive test amount signal;
The first filtration module carries out respectively the first filtering to n-1 drive test amount analog electrical signal;
The second filtration module carries out the second filtering to 1 the tunnel with reference to analog electrical signal;
Square wave average module utilizes the duty cycle square wave mean value method to record each road and 1 tunnel of at least 3 drive test amount analog electrical signals with reference to the phase differential between the analog electrical signal;
Analog to digital conversion and displacement computing module after the phase differential analog to digital conversion of n-1 road, are converted into the displacement of n-1 road again, calculate n-1 road displacement measurement;
The weighted stacking module is carried out real number ranking operation and additive operation with the n-1 road displacement measurement that obtains.
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