CN1038781C - High-precision large aperture phase-shifting digital planar interferometer - Google Patents

Abstract

The present invention discloses a high-precision large aperture phase-shifting digital plane interferometer which is mainly composed of a vertical Fizeau interferometer, an expanding device, a phase shifter, a driving source, a controlling source, an image collecting system, a microcomputer, etc. The present invention has the advantages that an efficiency detection aperture of the instrument is phi245 mm, the degree of accuracy is lambada/50 (peak-valley values), the optical quality of a system is lambada/20, an expanded aperture can reach phi500 mm, and the degree of accuracy is lambada/20. The instrument can automatically correct non-linear displacement errors of the phase shifter and also uses a liquid level with a damping plate as a reference plane for systemic errors of a correcting instrument; therefore, the present invention enhances the detection precision of the instrument, and is especially suitable for the detection of large caliber optical plane glass.

Description

High-precision large aperture phase-shifting digital planar interferometer

The present invention relates to a kind of plane interference gauging instrument, particularly a kind of high-precision large aperture phase-shifting digital planar interferometer.

At present, adopt movable phase interfere art principle to carry out the instrument that the plane is detected, Mark type interferometer as U.S. Zygo company, mainly adopted a horizontal Feisuo type interferometer in its system, utilize two piezoelectric crystals level under drive source drives to promote the reference planes displacement, system controlled by computer photodetector and data collecting card are sampled and data-storing to the interferogram light intensity of displacement simultaneously, utilize the General Principle of movable phase interfere art at last, restore tested phase place.This apparatus measures aperture is under 4 inches (Φ 102mm) situations, and accuracy of measurement is λ/50 (peak one valleies), and the supplementary lens device can be surveyed sphere face shape.By utilizing burnt expanding system far away, make the test aperture expand to 12 inches (Φ 300mm), corresponding measuring accuracy drops to λ/10.The main deficiency that Mark type interferometer exists is: 1. detection aperture is little, have only 4 inches (Ω 102mm), also can only reach 12 inches (Φ 300mm) after the expansion, and order is because its expansion is to adopt afocal system, the precision of this kind instrument can only reach λ/10, can not satisfy high precision, large aperture measurement requirement; 2. the absolute bearing calibration of the systematic error of this instrument is to utilize three inspections mutually, and this method is subjected to the restriction of three mutual checking device precision and the precision of method own, makes the initial calibration of instrument just have error, finally has influence on the raising of Instrument measuring precision; Product export is to be with three flat boards and three mutual checking devices in addition, so the user can't self-correcting; 3. piezoelectricity product body the Controlling Source of not exercising with producing compensation of nonlinearity voltage, therefore the nonlinearity erron that displacement brings to piezoelectric crystal can't be eliminated, again because instrument uses the movable phase interfere art to restore the corrugated, relatively more responsive to the displacement error of piezoelectric crystal, so that the precision of instrument is subjected to very big influence; 4. cost an arm and a leg because China does not still have such large aperture plane surveying instrument at present, as by import then every want 170,000 dollars, as be with burnt beam-expanding system far away to make the aperture expand to 12 inches (Φ 300mm) prices will to reach 250,000 dollars.

The objective of the invention is to provide a kind of absolute reference that under general working environment, can adopt liquid level as the systematic error that rectifies an instrument at above-mentioned the deficiencies in the prior art; Can and can make detection aperture bigger and expand to the high-precision large aperture phase-shifting digital planar interferometer of Φ 500mm from the nonlinear displacement error of normal moveout correction phase shifter.

High-precision large aperture phase-shifting digital planar interferometer of the present invention, it mainly comprises Feisuo type interferometer, laser instrument, phase shifter and drive source, image capturing system, microcomputer and utility appliance, phase shifter is arranged in the bottom of Feisuo type interferometer reference planes mirror, and drive by drive source and to hold the displacement together of reference planes mirror, image capturing system is by ccd video camera, image pick-up card and monitor are formed, the emergent pupil face conjugation of the target surface of ccd video camera and interferometer wherein, the ccd video camera output terminal is connected with image pick-up card, image pick-up card is inserted in the microcomputer main frame board slot, be subjected to system controlled by computer, image pick-up card also joins with monitor, it is characterized in that phase shifter is also by a Controlling Source control, the input end of Controlling Source and microcomputer join and by system controlled by computer, output terminal and drive source join, and synchronous triggering mouth and image pick-up card join; The Feisuo interferometer is a vertical structure, and the reference plane of the systematic error that rectifies an instrument is a liquid level, is placed with damping sheet in the liquid level; Below the reference planes mirror in interferometer, a multifunctional workstation is arranged, it is by the self-equilibrating brace table, rotating disc, lead-screw drive mechanism and level(l)ing mechanism are formed, in order to overcome the distortion that vertical arrow that the tested flat board of big aperture mirror causes by deadweight causes face shape, adopt nine point-supported self-equilibrating brace tables, the self-equilibrating brace table is made up of platen and three set squares, a nail all is housed on three angles of set square, there is the pin of a flexible connection in set square bottom center, platen is drilled with a registration hole along three circumference mean lines, set square lays respectively on three circumference mean lines of platen, and by pin and pilot hole and platen flexible connection, rotating disc is positioned at self-equilibrating brace table below and is attached thereto and connects, level(l)ing mechanism is made up of base plate and microspindle, lead-screw drive mechanism is fixed on the base plate in the level(l)ing mechanism, and be positioned at rotating disc below.The present invention be with light, mechanical, electrical, combine, the union hardware and software is in one, adopt vertical Feisuo interferometer structure, make the detection aperture of instrument reach Φ 250mm, the effective aperture is Φ 245mm, the present invention also restores the new method of full aperture face shape according to the overlapping interference detection in sub-aperture, utilize a multifunctional working table apparatus to realize that the apparatus measures aperture is expanded to the detection below the large aperture of Φ 500mm by Φ 245mm.In addition, systematic error of the present invention is proofreaied and correct and is adopted liquid level, particularly adding shockproof damping sheet in liquid level matches with the instrument shock isolation system, thereby make liquid level in the general work environment, become possibility as the absolute reference of interfering instrument corrective system error, guaranteed the high precision of apparatus measures, for guaranteeing the accuracy of detection of instrument, the present invention has also taked following measure, on phase shifter (PZT), adopted a voltage signal Controlling Source that can produce nonlinear compensation, make the nonlinear displacement error of PZT obtain proofreading and correct, on the algorithm of movable phase interfere art, adopted again the insensitive new algorithm of the displacement error of phase shifter---the overlapping method of average simultaneously, make the phase retrieval precision be guaranteed, improved the measuring accuracy of instrument.Phase-shifting digital planar interferometer of the present invention, before dispatching from the factory or the user think when needing, at first utilize liquid level as absolute reference, obtain the modified value of the systematic error of instrument by the movable phase interfere art, this group modified value is stored in the microcomputer, in the big plane actual detected afterwards, all deduct this group at every turn and revise data, just can eliminate the constant systematic error of instrument itself.The practical work process of instrument is divided two parts, the one, the initial adjustment of instrument, another part is a testing process, the trimming process of instrument is such: earlier tested plane or liquid dish are placed on the multifunctional workstation, instrument is carried out initial adjustment, by the collimated light beam of collimator objective outgoing in the lower surface reflection of reference planes mirror and tested plane upper surface or liquid level beam reflected after system transmissions, imaging is on a cross-graduation plate, by the CDD gamma camera it is imaged on the target surface again, adjusts two relevant light beam imaging points by monitor; Two picture points are overlapped in the central authorities of cross-graduation plate, this promptly is the initial adjustment of instrument, then with one in the system movably catoptron be passed to and measure the light path position from adjusting light path by handwheel, at this moment, in monitor, just see by reference planes and tested plane or liquid level two surperficial formed interference fringes, three horizontal adjustment microspindles by the accurate adjustment multifunctional workstation make interference fringe the simplest, and interferometer light path is just adjusted and finished this moment.The test process of plane or liquid level is such: at first by microcomputer Controlling Source is carried out initial parameter setting (parameter is proofreaied and correct the parameter that the back is obtained by phase shifter (PZT)), send instruction then and give Controlling Source and image pick-up card simultaneously; Controlling Source is pressed sequential and the voltage signal pattern controlling and driving power drives phase shifter (PZT) that microcomputer is provided with, PZT promotes the displacement of reference planes mirror and produces phase-shifted, ccd video camera carries out several to interference field, the array sampling, deposit in the picture frame module by the image collection card digitizing then, the displacement of this process sampling and phase shifter is carried out synchronously by system controlled by computer, sampling finishes the back and calculates the face shape of tested plane or liquid level according to the algorithm of movable phase interfere art by microcomputer, what adopt here is a kind of to the insensitive new algorithm of phase shifter displacement error---the overlapping method of average, tabulate the at last optical path difference data on the tested plane of printout, image, provide the two-dimentional equal-value map of tested surface shape intuitively, 3 D stereo and one dimension mean level of the sea surface form deviation curve.Said process is finished by computer operation.

More than being the present invention to the testing process less than the optical plate glass of Φ 250mm, for the detection of the large aperture optical plate glass that surpasses Φ 250mm, is the new principle of restoring full aperture face shape according to the overlapping interference detection in sub-aperture.Tested plane is placed on the multifunctional workstation, and make by the center of master plate and overlap with the worktable rotation center to guarantee that the maximum support state is promptly because the vertical arrow distortion that the deadweight of the optical plate glass of macropore causes is minimum, then according to the size on tested plane, provide the one dimension displacement parameter of multifunctional workstation automatically and corresponding to the angle parameter in each sub-aperture by microcomputer.The one dimension displacement parameter is the side-play amount of worktable rotation center and interferometer aperture center, and angle parameter is meant when measuring each sub-aperture plane shape, the pairing rotation angle value of measured lens.The measuring method in single sub-aperture is with above-mentioned consistent.After all tested sub-aperture plane shape tests are finished, utilize the overlapping interference detection in sub-aperture to restore the mathematical model of full aperture face shape new principle, microcomputor program will be eliminated relative tilt and the displacement to axial between each sub-aperture automatically, recover unified shape of measured piece, and the output net result.

The present invention compared with prior art its significant advantage is: 1. this instrument adopts vertical Feisuo interferometer structure, make effective detection bore reach Φ 245mm, and the new principle of restoring full aperture face shape according to the overlapping interference detection in sub-aperture, adopt the expanding unit of a multifunctional workstation, make the detection aperture of instrument expand to Φ 500mm, realized the high Precision Detection on plane, large aperture by Φ 245mm; 2. interferometer employing liquid level is the reference plane of instrument system error correction, and in liquid level, added the damping sheet of against shock, make that liquid level can be as first benchmark of proofreading and correct the interferometer system error under the general work environment, guaranteed that the apparatus measures aperture is under the situation of Φ 245mm, the optical system quality reaches λ/20, accuracy reaches λ/50, when extending to Φ 500mm, accuracy reaches λ/20, it may be noted that the user can utilize liquid level to carry out self-correcting according to operating position at any time, eliminate systematic error, guarantee the instrument high precision; 3. this instrument adopts the Controlling Source that can produce the nonlinear compensation voltage signal, make the nonlinear displacement error of phase shifter (PZT) obtain proofreading and correct, the correction back is non-linear to reach 0.1%, uses the overlapping method of average again simultaneously, makes that the phase retrieval precision is further guaranteed; 4. the instrument price reduces, and approximately only needs 330,000 Renminbi.

Concrete structure of the present invention is provided by the following drawings and embodiment.

Fig. 1 is the theory diagram of phase-shifting digital planar interferometer of the present invention.

Fig. 2 .1 and 22 is that phase-shifting digital planar interferometer uses the light path synoptic diagram when adjusting.

Light path synoptic diagram when Fig. 3 .1 and 3.2 is the phase-shifting digital planar interferometer measurement.

Fig. 4 is the structural representation of multifunctional workstation in the phase-shifting digital planar interferometer.

Fig. 5 is the structural representation of self-equilibrating brace table in the multifunctional workstation.

Below in conjunction with accompanying drawing the present invention is described in further detail.

Referring to Fig. 1, mainly form by the vertical interferometer 1 of Feisuo type, image capturing system 2, phase shifter 3, drive source 4, Controlling Source 5, AST/386 microcomputer 6 and printer 7 and plotting apparatus 8 according to high-precision large aperture phase-shifting digital planar interferometer of the present invention.It is LASER Light Source that the vertical interferometer 1 of Feisuo adopts He-Ne laser instrument 9, image capturing system 2 is made up of ccd video camera 10, image pick-up card 11 and monitor 12, the target surface of ccd video camera 10 should with the emergent pupil face conjugation of interferometer 1, output terminal and image pick-up card 11 join, image pick-up card 11 is inserted in the microcomputer 6 main frame board slots, be subjected to system controlled by computer, output terminal also joins with monitor 12 simultaneously.Phase shifter 3 is made up of three piezoelectric crystals, and they are evenly distributed on the edge of the bottom of reference planes mirror 13 in the vertical interferometer of Feisuo and hold reference planes mirror 13, see Fig. 2 and Fig. 3.Drive source 4 has three voltage output ends, controls the elongation of three piezoelectric crystals respectively, and three output voltage values can be regulated respectively, reaches consistent with the elongation that guarantees three piezoelectric crystals; Controlling Source 5 is made up of master and slave two 8031 single-chip microcomputers, can produce non-linear voltage signal and sine voltage signal, be used to compensate the nonlinearity erron of phase shifter 3, making phase shifter after the correction non-linear is 0.1%, simultaneously, Controlling Source 5 is joined by RS232 mouth and microcomputer, and is controlled by microcomputer 6, makes the sample-synchronous of phase shifter 3 and image pick-up card 11 carry out.Referring to Fig. 2, Fig. 3, the aperture of reference planes mirror 13 is Φ 250mm, and thickness is 40mm, the flatness of face shape is λ/20, consider the vertical arrow that macropore plane optical element produces,, adopt K9 glass to make so the face shape of reference planes mirror 13 has the low aperture of minute quantity; First reference plane of interferometer 1 is selected liquid level 14, aluminum dish with an aperture Φ 500mm, liquid adopts the whiteruss (reflectivity is 3.56%) with glass-reflected rate basically identical, for the vibrations of damping liquid, also has a damping sheet 16 that is covered with the prismatic convex body in liquid level 14; Below reference planes mirror 13, be provided with a multifunctional workstation 17, referring to Fig. 4, it is by the self-equilibrating brace table, rotating disc 18, lead-screw drive mechanism 19 and level(l)ing mechanism 20 are formed, referring to Fig. 5, the self-equilibrating brace table is made up of platen 21 and three set squares 22, platen 21 and set square 22 are made by aluminium sheet, the platen diameter is 350mm, be drilled with a registration hole 23 along branch radial directions such as 120 degree circumference, a nail 24 all is housed on three angles of set square 22, bottom center also has the pin 25 of a flexible connection, and set square 22 is inserted in the pilot hole 23 of platen 21 by pin 25.See Fig. 4, the self-equilibrating brace table is positioned on the rotating disc 18, rotating disc 18 can 360 ° of rotations, the external belt index dial, precision is that 41 rotating discs 18 are fixed on the supporting seat of lead-screw drive mechanism 19 outsides, the precision of lead-screw drive mechanism 19 is 0.02mm, and stroke is 200mm, and it is fixed on the level(l)ing mechanism 20 of being made up of base plate and microspindle.The present invention is in liquid level adjustment and when test, liquid level 14 and tested sheet glass 15 is placed on respectively on the self-equilibrating brace table get final product, and sees Fig. 2 and Fig. 3.

Claims (1)

1. A kind of high-precision large aperture phase-shifting digital planar interferometer, it mainly comprises Feisuo type interferometer [1], laser instrument [9], image capturing system [2], phase shifter [3] and drive source [4], microcomputer [6] and utility appliance [7], [8], phase shifter [3] is arranged in the bottom of Feisuo type interferometer [1] reference planes mirror [13], and drive by drive source [4] and to hold reference planes mirror [13] displacement together, image capturing system [2] is by ccd video camera [10], image pick-up card [11] and monitor [12] are formed, the emergent pupil face conjugation of the target surface of ccd video camera [10] and interferometer [1] wherein, ccd video camera [10] output terminal and image pick-up card [11] join, image pick-up card [11] is inserted in microcomputer [6] the main frame board slot, be subjected to microcomputer [6] control, image pick-up card [11] also joins with monitor [12]; It is characterized in that phase shifter [3] also controlled by a Controlling Source [5], the input end of Controlling Source [5] and microcomputer [6] join, and by system controlled by computer, output terminal and drive source [4] join, synchronous triggering mouth and image pick-up card [11] join, the Feisuo interferometer is a vertical structure, and the reference plane of the systematic error that rectifies an instrument is liquid level [14], and liquid level is placed with damping sheet in [14]; The below of the reference planes mirror [13] in interferometer [1], a multifunctional workstation [17] is arranged, it is by the self-equilibrating brace table, rotating disc [18], lead screw transmission mechanism [19] and level(l)ing mechanism [20] are formed, the self-equilibrating brace table is made up of platen [21] and three set squares [22], a nail [24] all is housed on three angles of set square [22], there is the pin [25] of a flexible connection in set square [22] bottom center, platen [21] is drilled with a registration hole [23] along three circumference mean lines, set square [22] lays respectively on three circumference mean lines of platen [21], and flexibly connects with platen [21] by pin [25] and pilot hole [23]; Rotating disc [18] is positioned at self-equilibrating brace table below and is attached thereto and connects, and level(l)ing mechanism [20] is made up of base plate and microspindle, and lead-screw drive mechanism [19] is fixed on the base plate of level(l)ing mechanism [20], and be positioned at rotating disc [18] below.

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