Large-sized optical flat interferometry device and method

Technical Field

This invention belongs to the optical test Technical Field, mainly relates to a to large-scale optical plane interference measuring device and method.

Background Art

As the optical processing and detecting the continuous development, large-aperture optical system in the astronomical, space optical and military fields has become more and more widespread application of the, wherein is used as the plane of the light path is collimated or deflecting the caliber of the reflector is also growing. On the other hand, that the astronomical telescope which is normally used in large-caliber of the paraboloid primary mirror non-like handicapper method also requires high-precision in the large-scale optical plane mirror.

In large-scale optical plane polishing processing stage, mainly utilizes the surface shape error of the laser wavefront interferometer for measurement. However, commonly used laser wavefront interferometer measurable plane effective diameter not larger than the reference lens to-caliber, lead to large-scale optical plane of the traditional measure to become the interference of the difficult problem of the interference measurement. Laser wavefront interferometer products on the market is the 4 [...] (100 mm) or the 6 [...] (150 mm) diameter, large-caliber measuring accuracy of the optical plane must introduce beam expanding lens and other additional device, and does not usually can phase shift measurement, the production of the United States, for example, Zygo Corporation the 32 [...] (800 mm) caliber wavefront interferometer. Another alternative scheme is to adopt the Ritchey-Common measuring method, see Zygo Corporation wavefront interferometer product description, need to attach a large-scale optical spherical reflector, and may introduce off-axis aberration influence the accuracy of the measurement. The above-mentioned two kinds of method is currently widespread use, but will greatly increase the production cost, the production is not easy to use in practice. At the same time, the above-mentioned two kinds of method for measuring the transverse resolution are relatively low, can not meet the requirement of high resolution measurements.

Patent application number in China liu Liren "the 99113590.3 [...] " automatic scan measuring large aperture lens " in, a large aperture lens by automatic scanning measuring instrument, is mainly used for large aperture lens lens or invisible optical center position in the range, the spherical diopter, cylindrical diopter and axial, such as prism and measuring the optical properties of the bottom shaft, and does not involve the measurement of the surface shape error of the lens. Patent application number in China luan Zhu "the 03116349.1 [...] " large caliber wave surface interferometrical instrument " by shearing the interference principle of the invention in a large-caliber, the coherent length of the light source is suitable for the small, wave difference is less than one wavelength of the wave-front measurement, does not involve large-scale method for measuring the surface shape of the optical plane.

The United States Company in QED "An   automated   subaperture   stitching   interferometer workstation   for   aspherical   surfaces   and   spherical", P.E.Murphy, and G.W.Forbes, Proc.SPIE, Vol. 5188,296-307, 2003 and United States Patent " US 6956657B2 the raised in [...] an aspherical mirror surface shape error measurement, the sub-aperture splicing method, aspherical mirror to be measured is divided into a number of smaller-diameter sub-apertures, sub-apertures can be covered with the measuring range of the full-calibre, and a slight overlap between each sub-aperture; through the 6 shaft moving platform is adjusted and tested aspheric surface mirror or interferometer, the sub-aperture of interference measuring, then the algorithm is the testing result of the full caliber, algorithm the imaging distortion error compensation the interferometer, the reference wavefront error and the inclination between the sub-aperture, the out-of-focus error. Algorithm does not need to be iterative, the precision reliability by the hardware. This kind of method is mainly used for 200 mm-calibre the following plane mirror, spherical mirror and appropriate aspherical mirror, for a large-sized optical plane, only needing two axis linear movement adjusting, and increase movement of the stroke of the adjusting platform, and precision requirement is not variable, must adopt new the light path and the structure design.

Evans, Zygo Corporation in the U.S. Patent " US   7221461B2 the raised in [...] suitable for large-sized annular optical plane of the interference measuring method and device, the three displacement sensor measuring the movement of the wave surface interferometer plane relative error, the measured interferometer measuring the wave on the plane of the surface shape of the sub-aperture, and then separated from the kinematic error, splicing be measured the surface shape of the full aperture on the plane. It is not necessary to have aperture of the overlapping region is arranged between the, splicing the algorithm is simple.

Patent application number in China li Shengyi "the 200710034359.0 [...] " large caliber and large relative aperture aspherical mirror high-frequency error detection device and method " which provides an aspherical mirror device and method for high-frequency error detection, the five axis motion adjusting platform on measured aspheric mirror interference in the partial area of the measurement, the regional data splicing and algorithm, compensation in the process of measuring six-degree-of-freedom of the position error, the best-fit radius error and the horizontal error in the proportion imaging interferometer.

Content of the invention

The purpose of this invention lies in:to the technical problems of the prior art, provides a low-cost, high-precision, high efficiency of the large-scale optical plane of the interference measuring device and method.

In order to realize the above-mentioned purpose, the invention proposes the large-scale optical plane interference measuring device, comprises an interferometer two axis linear movement adjusting platform, the adjusting platform plane mirror to be measured at the front of the two-dimensional inclination adjusting platform, is arranged on the interferometer two axis linear movement adjusting platform the laser wavefront interferometer, the laser wavefront interferometer and is connected with a built-in measurement data processing algorithm program of the main control computer. The interferometer two axis linear movement adjusting platform is used for adjusting the wavefront interferometer position in the plane of the YZ, measured flat mirror a plurality of measuring interference in the partial area of the zero position, the main control computer according to the measured data obtained by measuring the processing algorithm of the plurality of partial area of the full caliber erroneous surface splicing pattern on the pattern of the high-frequency band erroneous surface , including initial posture determination method, the overlap area data extraction algorithm and splicing algorithm of the area data.

The interferometer two axis linear movement adjusting platform including horizontal direction Y axis motion component and a superimposed Y axis component in the vertical direction of the Z axis motion assembly, Y shaft assembly by the AC servo motor and the encoder thereof, elastic coupling, ball screw and the rolling guide rail pair and Z shaft assembly mounting plate; Z shaft assembly by the AC servo motor and the encoder thereof, elastic coupling, ball screw and the rolling guide rail pair and mounting plate interferometer; Y axis component and Z axis component millimeter level to reach the inferior precision of the movement, they can adopt the prior art.

The tested flat mirror two-dimensional inclination adjusting platform comprises a flat mirror to be measured on the mounting platform and arranged in the plane of the YZ of the two-dimensional inclination adjusting mechanism, the measured plane mirror mounting platform is comprised of a support, and a steel screw is suspended, suspending steel strip through the ring screw fixed on the support; two-dimensional inclination adjusting mechanism comprises a right-angled triangle distribution of the three adjusting screw pair.

The invention the large-scale optical plane interference measuring device, and Patent application number in China li Shengyi" 200710034359.0 the measuring [...] large diameter of the aspheric mirror of the different five-shaft motion platform, which is mainly characterized in that only in the process of measurement of the two axis linear movement adjusting.

The invention the large-scale optical plane interference measuring device, measuring the QED Company 200 mm-calibre the following plane mirror of the six-axis motion platform different, which is mainly characterized in that only in the process of measurement of the two axis linear movement adjusting, it is easy to realize, and movement precision requirement is not high, so the cost is low. In order to ensure the reliability of the measurement results, the measurement data of the processing algorithm must be iterative optimization, to and convergence range.

Using the local device of the invention the large-scale optical plane interference measuring method is as follows:

1st step: two axial straight lines by the interferometer movement adjusting platform adjusting laser wavefront interferometer in position in the plane of the YZ, a test laser beam of the interferometer is irradiated on the mirror to be tested;

2nd step: passing through the measured plane mirror two-dimensional inclination adjusting platform adjustment be measured in the plane of the YZ plane mirror in the two-dimensional inclination, for measuring the laser wavefront interferometer mirror is irradiated surface shape of the partial region, data disk, recording the interferometer two axis linear movement of the displacement of the adjustment platform;

3rd step: in accordance with the measured mirror programme part region, 2nd step is repeated until all the partial region after the measurement is complete, the interferometer two axis linear movement of the displacement of the adjusting platform recording and laser wavefront interferometer measurement data is input to the master control for computer processing algorithms to process the measured data, the measured by the plurality of partial area of the full caliber of the splicing pattern erroneous surface high frequency band of the shape error of the Figure.

The measuring data for the existing algorithm processing algorithm, including initial posture determination method, the overlap area data extraction algorithm and splicing algorithm of the area data.

Compared with the prior art, the advantage of this invention lies in:

1, the large-scale optical plane of the present invention apparatus and method for measuring the interference of two axial straight lines by the interferometer realize a plurality of moving adjusting platform interference in the partial area of the zero measurement, by measuring splicing of a data processing algorithm to obtain the surface shape error of the full-calibre on, at the same time improving the lateral resolution, the large-scale optical plane can be obtained high frequency error;

2, the interferometer of the present invention two axis linear movement adjusting platform structure is simple, linear motion accuracy can be on the order of the sub-mm, thereby reducing the cost, and the flat mirror to be measured in addition to the process of measuring the two-dimensional inclination fine, does not need any movement, it is easy to realize large-scale optical plane of the interference measurement;

3, of the measurement of this invention automatically calculating a data processing algorithm of the measured plane mirror interferometer relative to the initial position, automatically determining any two of the measured part of the overlap between the region data, in the process of measurement of the six-degree-of-freedom pose error, thus does not need to pre-processing measurement data, the a priori knowledge of the does not need to be precise, in an efficient manner to obtain the high accuracy of the error detection result of the medium.

The following illustrated in the Figure further detailed description of this invention.

Description of drawings

Figure 1 is a large-scale optical plane interference measuring device schematic diagram;

Figure 2 is the measured mirror and its two-dimensional inclination adjusting platform A to view;

Fig. 3 is an elliptical mirror with the full-calibre on the example of the measured part of the region division schematic;

Figure 4 is located in the central area of the detected flat mirror map measurement result;

Figure 5 the plane mirror to be measured is located on the measurement results of the edge area of the map;

Fig. 6 is flow chart of a data processing algorithm;

Figure 7 is a full-caliber splicing measuring result picture.

Mode of execution

As shown in Figure 1, the large-scale optical of the present invention the plane of the measuring device has an interferometer in two axis linear movement adjusting platform 1, a platform 1 is arranged in front of the plane mirror to be tested two-dimensional inclination adjusting platform 3, adjustment of platform 1 is provided with a laser wavefront interferometer 2, the laser wavefront interferometer 2 is connected with a built-in measurement data processing algorithm program control computer 5, when in measurement, the measured plane mirror 4 is mounted on an adjusting platform 3 on.

Wherein the interferometer two axis linear movement adjusting platform 1 comprises a horizontal direction Y axis motion assembly 11 and superimposed Y axis component in the vertical direction of the Z axis motion assembly 12, Y shaft assembly 11 by the AC servo motor and the encoder thereof, elastic coupling, ball screw and the rolling guide rail pair and Z shaft assembly mounting plate, Z shaft assembly 12 by the AC servo motor and the encoder thereof, elastic coupling, ball screw and the rolling guide rail pair and mounting plate interferometer, Y shaft assembly 11 and Z shaft assembly 12 millimeter level to reach the inferior precision of the movement.

As shown in Figure 2, the measured plane mirror two-dimensional inclination adjusting platform 3 includes the measured plane mirror mounting platform 31 and in the plane of the YZ two-dimensional inclination adjusting mechanism 32, the measured plane mirror mounting platform 31 by welding making the support of the channel 312 and the suspending steel screw 313 and 311 make up, flag steel band 313 through the ring screw 311 is fixed on the support 312 is, the measured plane mirror 4 by the suspension strip 313 suspension is fixed on the support 312 on; two-dimensional inclination adjusting mechanism 32 comprises a right-angled triangle distribution of the three adjusting screw pair, thread pair of the adjustment nut is fixed on the support (such as welding) 312 is, the adjusting screw and the measured plane mirror 4 slight contact with the back of the, by screwing or unscrewing the screw measured plane mirror 4 of the two-dimensional inclination adjusting, proposed to adopt a fine thread. Flags steel adjusting screw thread pair and the measured mirror according to the layout of the geometric dimensions of the design and material characteristics, such as can be the reference xu Rongwei "large interferometer mirror-supporting design and temperature deformation analysis", optical Journal, 25 (6): 809-815.

Laser wavefront interferometer using FISO (Fizeau) type planar interferometer, the transmitted test beam converted into a plane wave plane of the mirror group. In order to reduce the effects of vibration on the measuring environment, recommendations will be placed in the measuring device on the platform the gas floats the vibration isolation.

Of the measurement of this invention will be obtained by measuring a data processing algorithm of a plurality of splice erroneous surface partial area of the full caliber of the pattern on the pattern of the high-frequency band erroneous surface , including initial posture determination method, the overlap area data extraction algorithm and splicing algorithm of the area data. According to the measuring method for determining the initial pose of two axial straight lines of interferometer in the course of movement of the displacement of the adjusting platform, automatically calculate the measured plane mirror interferometer relative to the initial position; the overlap area data extraction algorithm to an ideal plane according to the data points to the engagement relationship between the projection, any two automatically determining the region of the part to be measured between the overlapping data; splicing region data by iterative optimization algorithm, compensation in the process of measuring six-degree-of-freedom of the position error, so that the all of the overlapping data inconsistency between the minimum, all data points at the same time the best matching with an ideal plane.

Working principle of this invention: in Figure 3, in order to measure a 225 mm × 161 mm oval aperture of the flat mirror, for example, first of all the flat mirror is divided into 11 circular partial region (the upper, the middle and the lower three rows of, the upper, the lower row of the three, the middle five), between adjacent partial region with overlapping each other, can be covered in all regions of the full caliber of the mirror to be measured; the measured plane mirror 4 is mounted in the two-dimensional inclination adjusting platform 3 (see Figure 1) the; interferometer 2 test plane waves emitted by the light beam incident to the partial area of the plane mirror to be measured (for example, located in the centre of the circular part region 0) is, after being reflected test light beam to return to the interferometer, the reference beam of the interferometer form interference is encountered, the measured mirror so as to realize zero interference measurement of the partial region; adjusting the interferometer two axial straight lines of the shaft position in two moving platform, the other mirror to be measured 10 a zero interference measurement of the partial region, for example the measuring area 3 time, the Y-axis translation 40 mm, fine adjustment at the same time a two-dimensional inclined plane mirror to be measured, measuring the partial region 7 time, the Y-axis translation 60 mm, Z shaft to decrease 45 mm, fine adjustment at the same time a two-dimensional inclined plane mirror to be measured; the two shafts will be in the process of measurement and displacement measurement data input into the computer of the interferometer, the measurement data processing algorithm automatically calculating the detection process in the area of the measured plane mirror interferometer relative to the initial position, automatically determining any two of the measured part of the overlap between the region data, finally through the iterative optimization, in the process of compensating the detected six-degree-of-freedom pose error, thereby realizing the pattern erroneous surfacemany partial area of the full caliber of the splice error of the high-frequency band on the surface Figure.

The measuring step of the present invention are as follows (see Figure 1):

1st step: two axial straight lines by the interferometer movement adjusting platform 1 adjust the laser wavefront interferometer 2 in position in the plane of the YZ, the interferometer 2 a test laser beam is irradiated on the measured plane mirror 4 is;

2nd step: passing through the measured plane mirror two-dimensional inclination adjusting platform 3 adjust the mirror to be measured 4 in the YZ plane of a two-dimensional inclined, laser wavefront interferometer 2 measuring the measured plane mirror 4 is irradiated on the surface shape of the partial area, Figure 4 a central part region is an ellipse plane mirror 0 examples of the measurement results, data disk, recording the interferometer two axis linear movement adjusting platform 1 the displacement;

3rd step: in accordance with the measured mirror programme part region (as shown in Figure 3, the oval flat mirror is divided into 11 a partial region), 2nd step is repeated until all the partial region after the measurement is complete, Figure 5 the edge part area is an ellipse plane mirror 7 embodiment the measurement results; the interferometer two axis linear movement adjusting platform 1 for recording and the displacement of the laser wavefront interferometer 2 the measured data is input to the master control computer 5 for measuring data processing algorithm to carry out the processing.

Of the measurement of this invention as shown in Figure 6 the flow of a data processing algorithm:

1st step: input data, determining an initial position, and other parameters. See fig. 1, the measured plane mirror 4 at the center of the coordinate system of the model building {C_M}, the measured plane mirror 4 is X axis is perpendicular to said plane to be measured; the wavefront interferometer 2 with the optical axis of the mirror to be measured 4 at the intersection of the measuring coordinate system established {C_i}, is fixedly connected with the interferometer. The plane mirror to be measured usually 4 the area of the central part, two coordinate systems are coincident. Assuming that the process of measurement interferometer in two axis linear movement adjusting platform 1 the Y shaft assembly 11 and Z shaft assembly 12 for the displacement of the and y z respectively, the model coordinate system {C_M} relative measurement coordinate system {C_i} to the initial position and posture

gi=1000010-y001-z0001

2nd step: the overlap area data extraction. Assuming that the area of section i part of the interferometer 2 the measured data is {w_j,i = (u_j,i, v_j,i,_j,i)}, j=1, ... , N_i, wherein_j,i into pixel coordinate (u_j,i, v_j,i) the phase difference on, N_i i part to the area of each of the sampling points.

The pose is determined using 1st step {g_i}, the measurement data points into the model coordinate system {C_M} under that can be used for the coordinate of the following formula

In the model coordinate system {C_M} k part of the section under the area and section i part of the measurement data points are all in the area of the projection to an ideal plane on (OYZ coordinate), generating a corresponding set of projection {x_j,k} and {x_j,i}. Use in collecting projection on the plane OYZ projection of the mutual engagement relationship between the, extracting the overlap area data (can be reference li Shengyi and other Chinese Patent application number "200710034359.0 the [...] and Chen," Iterative Algorithm   for   Subaperture   Stitching   Interferometry   for   General   Surfaces " J.OSA.A. 22 (9): 1929-1936,2005).

After extracting the data overlapping region, computing the corresponding measurement data points to an ideal plane of the distance on the root mean square value of the deflections of σ_o, calculations for all at the same time on the plane of measurement data points to the ideal root mean square value of the distance of the σ, wherein σ and σ_o on pose is {g_i} non-linear function.

3rd step: computing the objective function value. The objective function is the linear combination of the dual-purpose

F=μ1σ2+μ2σo2

Wherein μ₁ and μ₂ the weight coefficient is positive, meet μ₁ + μ₂ = 1.

4th step of: judging whether the convergence. Convergence conditions is the objective function value F<ε₁ or two adjacent iterations the difference between the objective function value | F_n-F_n-1 |<ε₂, ε₁ and ε₂ is pre-given constant. If it satisfies the convergence conditions, the end of the algorithm, Figure 7 is the splicing of the elliptical mirror with the embodiment of the top-shaped distribution; otherwise continue on to the next step.

5th step: splicing region data, calculating the new pose parameter. Linearization processing on the target function, the on position and posture parameter expressed as a linear function, thus the objective function minimization problem into linear least squares problem, the solution of a linear system of equations to obtain new pose parameter. Algorithm jump to step 2nd (can be reference Chen, "Iterative   Algorithm   for   Subaperture   Stitching   Interferometry   for General   Surfaces" J.OSA.A. 22 (9): 1929-1936,2005).