CN101670442A - Method for improving shape accuracy and processing efficiency of off-axis aspheric mirror - Google Patents

Abstract

The invention belongs to the technical field of optical device manufacturing and relates to a method for improving shape accuracy and processing efficiency of an off-axis aspheric mirror, comprising the following steps: (1) designing a rotary aspheric surface as well as a primary and secondary consubstantial structure for the primary body according to the size and the dimension of the off-axis aspheric mirror to be processed, i.e. a secondary body, and determining the amount of the off-axis aspheric secondary bodies to be processed at one time; (2) disposing through holes on a primary body blank piece; (3) placing all secondary body blank pieces into the through holes and fixing on a lathe after integrating into a cylindrical integrated work piece, and processing a spherical surface closest to the rotary aspheric surface on the integrated work piece; (4) generating a processing path of cutting tools based on the shape of the rotary aspheric surface, reprocessing the spherical surface by utilizing an ultra-precision lathe and carrying out form error analysis and compensating processing according to the measured integrated rotary aspheric surface shape. The provided method is simpleand easy to realize, has the advantages of high-efficiency, easy detachability and high shape accuracy and can realize high-efficient processing on an off-axis aspheric surface with high shape accuracy.

Description

A kind of method that improves off-axis aspheric mirror form accuracy and working (machining) efficiency

Technical field

The invention belongs to technical field of optical device manufacturing, relate to a kind of processing method of off-axis aspheric mirror.

Background technology

Utilize the optical system of off-axis aspheric mirror framework have assembly few, do not have block, characteristics such as long-focus, big visual field, broadband, inhibition veiling glare ability are strong, modulation transfer function height, be the indispensable optics of Space Optical System, astronomy and high precision measuring system.Three mirror reflection system are its most typical application, as the core component of space telescope, can avoid central obscuration, can also reduce system bulk and weight, improve the image quality of system simultaneously.Off-axis aspheric mirror can also be used for the lithographic objective of extreme ultraviolet photolithographic (EUVL), cooperate other optical elements to increase collection angle, improve reflection efficiency, realization is that the grenz ray of 11-14nm is the microelectronics photoetching technique of exposure light source with the wavelength, becomes the main flow manufacturing technology of ultra-fine live width integrated circuit.In addition, off-axis aspheric mirror also can be realized high-resolution beam split function, is applied to various interferometers, beam collimator, optical beam expander, spectroscopic detector etc.

Off-axis aspheric mirror is as an aspheric part, and self does not possess axial symmetry, is a kind of typical free form surface optical element, and this shape has been brought difficulty to processing.Simultaneously, the application of off-axis aspheric mirror has determined it need reach the ultraprecise processing request, promptly not only requires to have the surface roughness of nanometer scale, more requires to have the surface figure accuracy (P-V value) of micron even sub-micron.The common process technology is difficult to satisfy its processing request.At present, common aspherical mirror generally adopts technology processing such as diamond cutting, grinding and polishing, can reach the requirement of ultraprecise processing.Single-point diamond cutting can realize single operation processing on optical quality surface, complicated subsequent handling such as does not need to grind.In recent years, along with sharp knife and the slow servo appearance of cutter,, can realize the highly-efficient processing of off-axis aspheric surface for the rotational angle of main shaft has added feedback or control.Yet this Study on Processing Technology also is in the starting stage, is subjected to the restriction of free form surface pattern error analysis evaluation means, the still difficult very high off-axis aspheric mirror of form accuracy that processes.

Summary of the invention

The objective of the invention is to overcome the above-mentioned deficiency of prior art, propose a kind of efficient high form accuracy method for processing of off-axis aspheric surface that is applicable to.

Technical scheme of the present invention is as follows:

A kind of method that improves off-axis aspheric mirror form accuracy and working (machining) efficiency is used for a plurality of off-axis aspheric mirrors of time processing, comprises the following steps:

(1) according to off-axis aspheric mirror to be processed be the shape and size amount of daughter, the revolution aspheric surface and the same body structure of primary and secondary of design parent, making all daughters be distributed in the aspheric main rotating shaft of the revolution of parent is the center, with off-axis aspheric surface center offset ρ ₀On the circumference for radius, determine the quantity of time processing off-axis aspheric surface daughter;

(2) through hole is excavated in the daughter position of determining according to step (1) on the parent blank;

(3) each daughter blank is placed through hole, be combined into the column type one-piece machine member after, be fixed on the lathe, on one-piece machine member, process and the aspheric immediate sphere of described revolution;

(4) produce the machining path of cutter according to the aspheric shape of described revolution, utilize super precision lathe that described sphere is reprocessed, obtain needed revolution aspheric surface, realize processing simultaneously to the off-axis aspheric surface of each daughter, in processing, measure whole revolution aspherical shape, carry out shape error analytical and compensation processing, meet the demands until the form accuracy of off-axis aspheric surface according to measurement result.

If continue the processing off-axis aspheric mirror, can prepare other daughter blank again, repeating step (3) and (4); The bore Φ '＞ρ of described aspheric surface parent ₀+ Φ/2, wherein ρ ₀Be the off-axis aspheric surface centre coordinate, Φ is the bore of off-axis aspheric mirror, the quantity of time processing off-axis aspheric surface daughter Wherein Δ d is the distribution interval between the daughter.

Substantive distinguishing features of the present invention is: transfer off-axis aspheric surface processing to axisymmetric aspherical mirror machining by Machine Design, and adopt diamond turning to realize whole high-efficient cutting processing, utilize the ultra precise measurement method to realize integrally-built surface shape measurement, improve the form accuracy of machined surface shape.

The method that the present invention proposes is simple, be easy to realize, and has the characteristics efficient, easily separated, that form accuracy is high, can realize high form accuracy off-axis aspheric surface highly-efficient processing.Particularly, the present invention has following characteristics: (1) daughter separated before ultra-precise cutting with parent, so be easy to separate required off-axis aspheric surface part after processing; (2) a plurality of workpiece of time processing, therefore, the working (machining) efficiency height; (3) the processing roughness and the form accuracy of off-axis aspheric surface are consistent with aspherical mirror machining; (4) parent is reusable, is beneficial to the processing of carrying out off-axis aspheric surface in enormous quantities.

Description of drawings

Fig. 1 primary and secondary consubstantiality processing method schematic diagram.

Fig. 2 off-axis aspheric surface and aspheric surface.

Fig. 3 arc radius compensation model.

Fig. 4 compensates flow process chart.

The specific embodiment

Because of off-axis aspheric mirror is the part of aspheric surface, or off-axis aspheric surface that Sag less less for size can be finished the ultraprecise processing of off-axis aspheric surface by the aspheric processing of integral body, and this method is called as " primary and secondary consubstantiality " processing method.Fig. 1 is the processing schematic diagram, in the method, whole aspheric surface is processing " parent ", n through hole thereon evenly distributes, partly place the off-axis aspheric surface " daughter " of required processing in perforate, form complete aspheric surface with the aspheric surface parent is common, and carry out ultra-precise cutting processing simultaneously, time processing goes out a plurality of off-axis aspheric surfaces.Vacant an amount of zone between the adjacent holes is used for carrying out ultra precise measurement at compensation process, realizes the control of entire compensation allowance.

Aspheric mathematical description is the following formula of unified employing at present:

$z\left(\mathrm{\ρ}\right)=\frac{{\mathrm{c\ρ}}^2}{1+\sqrt{1-(k+1){\mathrm{c\ρ}}^2}}+\underset{i=1}{\overset{n}{\mathrm{\Σ}}}{A}_{2i}{\mathrm{\ρ}}^{2i}---\left(1\right)$

Wherein c is the aspheric surface vertex curvature, and k is the tapering coefficient, A _2iBe asphericity coefficient, ρ is polar utmost point footpath, also is the distance that departs from axis of rotation.The aspheric surface that formula (1) is described is the revolution symmetry.Wherein first a kind of quadratic surface has been described, when the span of K can not described hyperboloid, parabola, ellipsoid, sphere etc. simultaneously.Its remainder is the aspheric surface item, and different asphericity coefficients has determined quadric change amount.Off-axis aspheric surface is the part of aspheric surface disalignment, and as shown in Figure 2, its expression formula off center position on aspheric surface expression formula basis forms,

$z\left(\mathrm{\ρ}\right)=\frac{{c(\mathrm{\ρ}-{\mathrm{\ρ}}_0)}^2}{1+\sqrt{1-(k+1)c{(\mathrm{\ρ}-{\mathrm{\ρ}}_0)}^2}}+\underset{i=1}{\overset{n}{\mathrm{\Σ}}}{A}_{2i}{(\mathrm{\ρ}-{\mathrm{\ρ}}_0)}^{2i}---\left(2\right)$

ρ wherein ₀Be the off-axis aspheric surface centre coordinate, being described as cartesian coordinate is (x ₀=ρ ₀, y ₀=0), the span of x and y defines the outer contour shape of off-axis aspheric surface.When the workpiece profile is circle, and the workpiece bore is when being Φ, and then the span in utmost point footpath is: | ρ ₀-ρ |≤Ф/2.

In " primary and secondary consubstantiality " processing method, required aspheric bore should be Φ '＞ρ ₀+ Ф/2.Daughter quantity determines to follow the principle of quantity maximum, to guarantee minimum, most effectiveization of cost.It is the center that all daughters are uniformly distributed in the main rotating shaft, with off-axis aspheric surface center offset ρ ₀On the circumference for radius, the distribution between the daughter needs interval delta d, and then daughter quantity is n,

$n\≤\left[\frac{{2\mathrm{\π\ρ}}_0+\mathrm{\Δd}}{\mathrm{\Φ}+\mathrm{\Δd}}\right]---\left(3\right)$

Wherein [] is for rounding symbol.

Adopt above method that off-axis aspheric surface is become axisymmetric aspheric surface, adopt 2 super precision lathes can realize processing.Workpiece is attracted to the rotary main shaft end face by vacuum cup, and main shaft at the uniform velocity rotates, and diamond cutter produces machining path at ρ and z direction according to required aspheric shape motion, realizes the processing of off-axis aspheric surface part simultaneously.When forming machining path, segment the position at each control point as far as possible, and accurately control the coordinate in each motor point.But actual cutter and nonideal cusp will be considered the existence of cutter parameters in the design process of machining path, it is compensated processing, determine correct cutter location, and general processing only need be considered the compensation of arc radius R.For the aspheric surface z (ρ) of given equation, when considering tool radius R compensation, cutting Model can be described as shown in Figure 3.Cutting point p ₀(ρ ₀, z ₀) normal vector of locating model is n, can represent by the equation derivative,

n＝(-z′ _ρ，1) (4)

Z ' wherein _ρBe aspheric derivative

$z_{\mathrm{\ρ}}^{\′}=\frac{{2\mathrm{c\ρ}}^2}{1+\sqrt{1-(k+1){\mathrm{c\ρ}}^2}}+\frac{(k+1)c^2{\mathrm{\ρ}}^3}{{(1+\sqrt{1-(k+1){\mathrm{c\ρ}}^2})}^2\sqrt{1-(k+1){\mathrm{c\ρ}}^2}}+\underset{i=1}{\overset{n}{\mathrm{\Σ}}}{2\mathrm{iA}}_{2i}{\mathrm{\ρ}}^{2i-1}---\left(5\right)$

Cutter location o _t(ρ _t, z _t) should be p ₀Skew on the n direction, side-play amount are R

o _t＝p ₀+n·R (6)

Because machining shape is subjected to the influence of factors such as geometric parameter, spindle rotation accuracy, slide carriage kinematic accuracy, self-vibration and vibration isolation, the stability of a system of cutter, directly designs and obtain form accuracy and still can not satisfy application requirements by path optimization.Generally need to adopt the topography measurement instrument that its machining shape is carried out ultra precise measurement, rely on form variations to compensate the machining path redesign, progressively improve form accuracy.Fig. 4 is the flow chart that compensates processing, employing is carried out shape measure to aspheric surface, the data that obtain are carried out the data necessary processing, as: the Data Matching of measurement data and master pattern, error calculating, form variations data smoothing and compensating for path are adjusted scheduling algorithm.

Work flow is:

(1) according to off-axis aspheric mirror to be processed be the shape and size amount of daughter, the revolution aspheric surface and the same body structure of primary and secondary of design parent, the main rotating shaft that all daughters are distributed in the aspheric surface parent is the center, with off-axis aspheric surface center offset ρ ₀On the circumference for radius, determine the quantity of time processing off-axis aspheric surface daughter;

(2) through hole is excavated in the daughter position of determining according to step (1) on the parent blank;

(3) each daughter blank is placed through hole, be combined into the column type one-piece machine member after, be fixed on the lathe, on one-piece machine member, process with described aspheric near sphere;

(4) produce the machining path of cutter according to described aspheric shape, utilize super precision lathe that sphere is reprocessed, obtain needed revolution aspheric surface, realize processing simultaneously to the off-axis aspheric surface of each daughter, in processing, measure whole aspherical shape, carry out shape error analytical and compensation processing, meet the demands until the form accuracy of off-axis aspheric surface according to measurement result.

If want to continue the processing off-axis aspheric mirror, prepare other daughter blank again, repeating step (3) and (4).

In an embodiment, the off-axis aspheric surface of being processed is the part of aspheric surface, and aspheric concrete parameter is: c=0.00909mm ^-1, k=-2, A ₄=3.07 * 10 ^-7Mm ^-3, A ₆=-3.53 * 10 ^-11Mm ^-5, A ₈=-2.00 * 10 ^-15Mm ^-7, A ₁₀=-1.25 * 10 ^-19Mm ^-9Off-axis aspheric surface is at distance center 28.0mm place, and bore is 20.0mm.According to designing and calculating, the bore of whole aspheric surface parent is 80.0mm.At first, according to design size parent and daughter are carried out suitable roughing respectively, integrator carries out the whole processing of aspheric surface then, and adopt the probe-type topography measurement instrument of Talyor Hobson to carry out the shape measure of aspheric surface bus, carry out three compensation processing according to the compensation work flow in the patent, the surface figure accuracy (P-V value) after three the compensation processing is respectively: 909.8nm, 457.0nm, 258.5nm.The surface figure accuracy of the off-axis aspheric surface part that finally obtains is in 200nm, and surface roughness Ra is 6.1nm.

Claims (3)

1. a method that improves off-axis aspheric mirror form accuracy and working (machining) efficiency is used for a plurality of off-axis aspheric mirrors of time processing, comprises the following steps:

A) according to off-axis aspheric mirror to be processed be the shape and size amount of daughter, the revolution aspheric surface and the same body structure of primary and secondary of design parent, making all daughters be distributed in the aspheric main rotating shaft of the revolution of parent is the center, with off-axis aspheric surface center offset ρ ₀On the circumference for radius, determine the quantity of time processing off-axis aspheric surface daughter;

B) through hole is excavated in the daughter position of determining according to step (1) on the parent blank;

C) each daughter blank is placed through hole, be combined into the column type one-piece machine member after, be fixed on the lathe, on one-piece machine member, process and the aspheric immediate sphere of described revolution;

D) produce the machining path of cutter according to the aspheric shape of described revolution, utilize super precision lathe that described sphere is reprocessed, obtain needed revolution aspheric surface, realize processing simultaneously to the off-axis aspheric surface of each daughter, in processing, measure whole revolution aspherical shape, carry out shape error analytical and compensation processing, meet the demands until the form accuracy of off-axis aspheric surface according to measurement result.

2. method according to claim 1 is characterized in that, if continue the processing off-axis aspheric mirror, prepares other daughter blank again, repeating step (3) and (4).

3. method according to claim 1 and 2 is characterized in that, the bore Φ '＞ρ of described aspheric surface parent ₀+ Φ/2, wherein ρ ₀Be the off-axis aspheric surface centre coordinate, Φ is the bore of off-axis aspheric mirror, the quantity of time processing off-axis aspheric surface daughter Wherein Δ d is the distribution interval between the daughter.

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