CN1529151A - Non-spherical detection method of electronic virtual proof-plate - Google Patents

Abstract

In the invention, three frames of theoretical aspheric interference fringes with equal phasic difference as referenced wave front. CCD pick-up head with high resolution captures one dimension of printing forme of actual fringes of tested aspheric surface measured by digital wave plane interferometer, and captured information through image collection card is input into computer. Three frames of digital electric moire fringe with equal phasic difference are obtained after digital superimposing information of actual fringes. Fringe distribution of continuous face form of the tested surface is obtained after operations of noise removing, phase calculation and wave front reconstruction. Comparing with traditional zero position compensation tests, the invention possesses advantages of simple adjusting, time saving and high accuracy.

Description

Electronic virtual model aspheric surface detection method

Technical field

The invention belongs to the advanced optical length of schooling and make and the detection technique field, relate to a kind of new method of detection optical aspheric surface reflecting element.

Background technology

The most general measuring method of optical aspherical surface element surface face shape is to interfere detection technique, in the middle of this technology, zero compensation interferes detection technique to be widely used in the surface shape measurement in aspheric surface polishing stage, so-called zero compensation method promptly designs a kind of optical system (being referred to as zero compensation machine) that has the certain wave aberration, the design of zero compensation machine wherein is based on desirable aspheric, the check light beam via the digital wavefront interferometer outgoing to compensator, light beam reflects through being verified aspheric surface through compensator again, get back to interferometer through behind the compensator once more, include the check light and the reference light that are verified aspheric surface control information and interfere the formation interference fringe mutually this moment, and interference fringe is analyzed, processing can obtain being verified aspheric face shape error.

In brief, promptly pass through the corrugated compensating action of compensator, plane wave front or spherical wave front are become and be verified the corresponding to wavefront of aspheric desirable face shape, with this wavefront be verified wavefront and compare, and observe difference between the two, thereby determine to be verified the face shape of non-spherical element by the digitalized intervention technology.

But this type of zero compensation interference detection method has certain disadvantages, be in particular in and be directed to the not non-spherical element of coplanar shape, need the different zero compensation machine of design, simultaneously in order to obtain high-precision measurement result, requirement is when the design compensation device, on the one hand enable correction asphere wavefront well, make the residual error minimum, require the tolerances such as thickness, radius-of-curvature, airspace, concentricity of compensating element, to distribute rationally on the other hand.Thus, the error of bucking-out system very easily produces incorrect imaging and causes the appearance of diffraction ring, and because the reflected light of some element and reference light generation interference mutually in the compensator, thereby some pseudo-interference fringes appear on image planes, because a phase shift takes place with check light in these pseudo-stripeds simultaneously, so it is very big to the assay influence.In addition, when considering Effect of Environmental, not only make the collection of measurement data very difficult, will introduce stochastic error simultaneously as air turbulence, vibrations, voltage fluctuation etc.This be since this type of phase measurement in actual applications, the influence of its phase changer self precision is bigger, typical phase changer adopts piezoceramics crystal (PZT), its principle of work is after PZT is pasted on the standard reflection mirror, the DC voltage that utilization is applied thereto produces micro-displacement, thereby mobile standard reflection mirror is realized changing light path and reached the purpose that changes the reference light phase place.The shortcoming of this device is that the angular deviation of 1 ° of light and mirror surface normal angle will produce 1% phase displacement error, simultaneously, owing to need high voltage source with and voltage---non-linear displacement is difficult to obtain high measuring accuracy and is not easy to use.As shown in Figure 1 be exactly a traditional zero compensation interference detection device, include digital wavefront interferometer 1, zero compensation machine 2 and be verified aspheric surface 3.

Summary of the invention

The objective of the invention is to design different zero compensation machines in order to solve in traditional aspheric surface zero compensation interference detection technology to exist at coplanar shape aspheric surface not, simultaneously the manufacturing accuracy of zero compensation machine and assembly precision are difficult to realize, measure deficiencies such as being subjected to all multifactor impacts, and a kind of electronic virtual model detection method that special compensator and phase changer just can detect aspheric surface that do not need to design is provided.

To achieve these goals, the invention provides a kind of electronic virtual model aspheric surface detection method, this method is at first utilized digital wavefront interferometer directly to detect to be verified aspheric surface and obtained actual striped one dimension printing forme, it is characterized in that this method also comprises following subsequent step: the emission light beam that makes described actual striped one dimension printing forme and a high resolution CCD camera is with optical axis and parallel focusing; The information of the actual striped one dimension printing forme that described high resolution CCD camera is photographed, and stores to computing machine by the image pick-up card real-time Transmission; Utilize the program in the computing machine to carry out following processing successively:

1) utilizes the digital phase-shifting technique technology to fold grid and handle, promptly simulate phasic difference face shape grating such as desirable aspheric three width of cloth, be stored in the computing machine as the reference grating; Be stored in the actual striped one dimension printing forme that obtains by image pick-up card in the computing machine the information grating and described with reference to grating carry out respectively amplifying synchronously in real time, folded grid handle, and produce three width of cloth digital phase-shifting technique electronics Moire fringe;

2) described Moire fringe is carried out medium filtering and handle, promptly with the median of Moire fringe local field gray scale output gray level, the original clear profile of reproduction image as wave filter;

3) Moire fringe after the Filtering Processing is carried out the position and calculate mutually, comprise subtraction and analog to digital conversion, then described Moire fringe is carried out wavefront reconstruction, obtain detected true face shape striped.

Described utilize the digital phase-shifting technique technology fold grid handle be with theoretical striped light distribution as characteristic quantity, extract desirable aspheric surface at three width of cloth gray level images that wait phasic difference place as the reference grating.

When the invention has the advantages that the check aspheric surface, need be at the compensator of different non-spherical element design specialized, thereby avoid the variation of the check Beam Wave-Front that any because compensator manufacturing and rigging error introduce, and then eliminate the appearance that causes having a strong impact on the diffraction ring of measurement result owing to incorrect imaging.When considering Effect of Environmental, as air turbulence, vibrations etc., the method for the invention is subjected to that disturbance is little, analysis result repeatable accuracy height.The resolution of electronic virtual model aspheric surface detection method of the present invention and CCD camera is closely related, because the continuous progress of high resolution CCD camera, so brand-new aspherical detection method provided by the invention in recent years has actual more widely popularizing application prospect.

Description of drawings

Fig. 1 is the zero compensation interference detection device synoptic diagram of prior art.

Fig. 2 obtains to be verified the device synoptic diagram of the actual striped one dimension of aspheric surface printing forme for directly utilizing digital wavefront interferometer.

Fig. 3 is for implementing the schematic representation of apparatus of the method for the invention.

Fig. 4 is the workflow conceptual schema of the method for the invention.

Fig. 5 is a Moire fringe medium filtering processing flow chart of the present invention.

Fig. 6 a, 6b are wavefront reconstruction process synoptic diagram of the present invention.

1 is digital wavefront interferometer, 2 is zero compensation machine, 3 for being verified aspheric surface, and 4 is actual striped one dimension printing forme, and 5 is the high resolution CCD camera, 6 is image pick-up card, 7 is computing machine, and 8 are folded grid handler module, and 9 is the medium filtering handler module, 10 is position phase calculation procedure module, and 11 is the wavefront reconstruction program module.

Embodiment

The invention will be further described below in conjunction with accompanying drawing:

As shown in Figure 2, at first directly utilize digital wavefront interferometer to obtain to be verified the actual striped one dimension of aspheric surface printing forme.Device mainly includes digital wavefront interferometer 1 and is verified aspheric surface 3.

As shown in Figure 3, the actual striped one dimension of the aspheric surface printing forme 4 that is verified that utilizes digital wavefront interferometer directly to record is installed on anchor clamps, and by means of an adjustment platform with five dimension degree of freedom with the emission light beam of the high resolution CCD camera 5 that is fixed thereon adjust with actual striped one dimension printing forme 4 with optical axis and parallel focusing; Image pick-up card 6 directly is plugged in PCI slot on the computer motherboard, and is connected in real time with high resolution CCD camera 5 by data line; Starter gear after the program initialization, according to flow processing shown in Figure 4, promptly is stored in the hard disc of computer to image pick-up card 6 with the high resolution CCD camera 5 actual striped one dimension printing formes 4 of shooting and with the information real-time Transmission; Utilize the digital phase-shifting technique technical modelling to go out desirable aspheric shape grating, as the reference grating, particularly be with the striped light distribution as characteristic quantity, extract desirable aspheric surface at three width of cloth gray level images that wait phasic difference (phasic difference is a pi/2) to locate, and be stored in the frame memory of computing machine; At first carry out folded grid handler module 8, be about to be stored in that phasic difference reference light grid such as the information grating of the actual striped one dimension printing forme 4 that is obtained by image pick-up card 6 in the hard disc of computer and three width of cloth amplify respectively in real time synchronously, folded grid are handled, thereby produced three width of cloth digital phase-shifting technique electronics Moire fringe; Because the transmission of image, conversion and stack will cause picture element to descend, and show as high frequency noise composition in the electronics Moire fringe, its characteristics often present isolated discreteness and distribute, and have than notable difference with the field pixel, therefore, in order correctly to carry out interpretation to Moire fringe, need carry out medium filtering handler module 9 to Moire fringe, it handles thought is the output gray level of the median of local field gray scale as wave filter, the signal intermediate value is by the intermediate value after the signal magnitude series arrangement, with a moving window that odd point is arranged, and the value of window center point replaced with the each point Mesophyticum in the window, according to the flow performing filtering shown in Fig. 5, at first select the window of (2n+1) * (2n+1), the span of natural number n is [0,10], here n gets 2, promptly using 5 * 5 window to carry out the displacement of column or row direction along view data slides, after each displacement, resequenced in the window center position, with the original pixels gray-scale value of the resulting Mesophyticum of ordering, carry out and judge and circulation, until the original clear profile of reproduction image for the window center position; Subsequently, execute bit phase calculation procedure module 10, promptly carry out digitizing by subtraction and analog to digital conversion to Moire fringe, after realizing that calculate mutually the position and inquiry obtains in the memory read decode address, just can carry out data processing to the digital phase-shifting technique Moire fringe, but because phasic difference is a light intensity arc tangent form, to cause that the position is mutually discontinuous, and its result of calculation only is confined on third and fourth quadrant, i.e. [pi/2, pi/2], dwindled position phase span, make the optical path difference that obtains be no more than half wavelength.For the problems referred to above, solution of the present invention is to utilize wavefront reconstruction program module 11, at first wavefront position phase mould 2 π shown in the execution graph 6a handle, position phase scope is extended into [0,2 π] interval, particularly be judge the Moire fringe light intensity value positive and negative, whenever actual bit is worth when being the integral multiple of 2 π mutually, calculate income value and return 0, in the wavefront reconstruction process, because detected face is a smooth and continuous, and the result who directly calculates does not convert actual position value mutually to, therefore continue to take the one dimension position phase demodulation shown in Fig. 6 b to handle, the position that is about to mould 2 π changes into the value that can characterize detected face shape mutually, during reconstruct, as long as there is a big uncontinuity to occur, remove with regard to the integral multiple that adds one 2 π or 2 π this discontinuous, thereby obtain detected true face shape striped.

The present invention is applicable to the surface shape of optical aspheric surface of check larger radius of curvature.

Claims (2)

1. electronic virtual model aspheric surface detection method, this method is at first utilized digital wavefront interferometer directly to detect to be verified aspheric surface and obtained actual striped one dimension printing forme, it is characterized in that this method also comprises following subsequent step: the emission light beam that makes described actual striped one dimension printing forme and a high resolution CCD camera is with optical axis and parallel focusing; The information of the actual striped one dimension printing forme that described high resolution CCD camera is photographed, and stores to computing machine by the image pick-up card real-time Transmission; Utilize the program in the computing machine to carry out following processing successively:

1) utilizes the digital phase-shifting technique technology to fold grid and handle, promptly simulate phasic difference face shape grating such as desirable aspheric three width of cloth, be stored in the computing machine as the reference grating; Be stored in the actual striped one dimension printing forme that obtains by image pick-up card in the computing machine the information grating and described with reference to grating carry out respectively amplifying synchronously in real time, folded grid handle, and produce three width of cloth digital phase-shifting technique electronics Moire fringe;

2) described Moire fringe is carried out medium filtering and handle, promptly with the median of Moire fringe local field gray scale output gray level, the original clear profile of reproduction image as wave filter;

3) Moire fringe after the Filtering Processing is carried out the position and calculate mutually, comprise subtraction and analog to digital conversion, then described Moire fringe is carried out wavefront reconstruction, obtain detected true face shape striped.

2. detection method according to claim 1, it is characterized in that: described utilize the digital phase-shifting technique technology fold grid handle be with theoretical striped light distribution as characteristic quantity, extract desirable aspheric surface at three width of cloth gray level images that wait phasic difference place as the reference grating.

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