DE2451333A1 - Photoelectric production of position change signals - is conducted at carrier frequency using double beam system with image formers at different phases - Google Patents

Abstract

The method and arrangement for photoelectric production and evolution of position changing signals at the carrier frequency involves:- a light source, a collimator, mass simulator, object surface, objective, image former objective, grating, component pictures and two receptors. The signals are then processed in elements to be displayed in the position value indicator. With laser beams this results can be achieved without the reproducing optics. A pair of opposite frequency signals are produced which are shifted by the measuring process so that with double sensitivity separate production of reference signals is not required.

Description

Method and arrangement for the photoelectric generation of carrier-frequency, Signals indicating changes in position.

Position determining signals generated by photoelectric scanning are generated by measuring grids are already known as triger-frequency signals. Such signals have the advantage of being generated by AC amplifier techniques can easily be brought to a level that is insensitive to interference. Because the frequency is the essential signal parameter, signal amplitude fluctuations only play one role subordinate role. The arrangements and processes for production that have been used since then Such signals require extensive electromechanical 4 drives and not negligible mass of loaded moving parts, such as rotating mirror polygons or oscillating imaging mirrors. Much must from the movements of the modulating Components additional reference signals are derived, which with the photoelectric Signals are evaluated for phase and beats is the task of the registration Carrier-frequency signals can be generated with simple means, sometimes without moving parts. Preferably, pairs of are opposite in frequency through the measurement process shifted signals generated, so that with doubled sensitivity no additional Reference signal must be generated.

m The symmetrical generation of carrier-frequency signal pairs makes Such measuring systems are particularly insensitive to phase drift errors that cause measuring errors, since these can be made the same in both signal channels.

The methods are suitable for the implementation of two-dimensional movements in measurement signals, since the signal separation according to coordinates can be easily achieved can.

to Understanding of the procedures and arrangements is facilitated by the tracing of the metrologically important processes to the Dopple # -effect of light, the direction and frequency of which is changed on moving structures, the double frequency shift of light that has been deflected into the m th diffraction order at a diffraction grating of the constant g moving at trilt velocity v, the diffraction angle for any light frequency # 0 in the useful spectral range is wavelength-independent despite the wavelength dependency. av r 3rz I / nte that Here, v is the speed component of the division direction, which corresponds to the direction of the diffracted beam projected onto the df'tS grating.

Relatively small frequency shifts in the optical range are only demonstrable by having two coherent groups of different light waves Frequency shifts.

This can be two diffraction orders of different atomic numbers. Will at least one of the diffraction orders in the light frequency by a fixed amount offset, the electrical difference occurs during the backmixing Carrier frequency on the photoreceiver.

The application provides rules for action and has as its object how two or more first coherent bundles (104, 105) are each converted into second bundles (118, 119, 120, 121) by diffraction on at least partially moving structures (6, 26, 27, 107) and both changed in direction and shifted in frequency at least in one of the second sub-bundles in order to then reunite the frequency-shifted bundles in groups to generate carrier-frequency signals and after photoelectric reshaping (14, 113, 113a, 14, 114, 114a) to be processed electrically for carrier demodulation.

The procedure is within the chromatic correction range an optical imaging system (5, 9) can be carried out independently of the wavelength. at Dispensing with beam guidance through imaging systems, there is the possibility of the beam deflections necessary for the local reunification of coherent partial beams to be reached by mirrors (108) or breaking wedges. The lighting rtiuss in this case be monochromatic. (101) In Figs. 1,?, 3, 4 are illustrative Examples of arrangements for carrying out the inventive method are shown.

In Fig. 1) is for the case of measurement in a linear location coordinate the simplified beam path from the light source (1) to the photoelectric Receivers (13, 14) shown.

In Fig. 2) is a block diagram of the processing of the signals from Receiver pair (13, 14) up to the position value transmitter (20) illustrated.

in Fig. 3) is the in Fig. 1) with (21) designated focal surface of Grating imaging optics (5, 9! Shown separately for the case that a two-dimensional Graduation is used at the point of (3) in Fig. 1) and the carrier frequency Light frequency shift made by electro-acoustic-optical converters will.

Fig. 4) shows how with laser lighting the process even without imaging Optics can be realized.

Explanation of FIG. 1): The light source (1), for example an incandescent lamp or a disc-shaped luminous pn junction of a luminescent diode, is imaged to infinity by a collimator (2). In the illuminated object surface (4), the diffraction grating serving as the measuring scale (3) diffracts with a grating constant g, which is preferably also as a phase grating ; Phase deviation is formed, 40% of the incident intensity in each of the first diffraction orders. The lens (5) generates coherent diffraction images (7 and 8) from the light source (1) in its focal surface. The direct zero order image is suppressed because a movement of (3) with the speed v does not change the frequency of the illuminating light , while in the m th diffraction order the light frequencies of the source be moved. The rays generating these images (7 and 8) are split into mutually coherent partial bundles of rays by diffraction in plane 21 Phase deviation formed. If the radial grating rotates around its center of division with the angular velocity co, the grating constant, which increases linearly with the radius, has no influence on the Doppler frequency shift of the diffracted light, because the ratio remains independent of the pivot point radius. Only the r first orders are taken into account, four sub-bundles symmetrically different in terms of the light frequency.

Through the fixed aperture openings indicated by chalk in the area (21) and the area of (9) the restriction to the four sub-bundles be forced.

In the area conjugated to (3) is the grating (10) with its line direction aligned parallel to the lines of (3).

A pair of bundles in each case hit the same grid surface and represents a moving, sinusoidal grid image there, image scale and lattice constant of (10) are chosen so that rays of the same wavelength, which start from homologous points in the light source images (7 and 8) through which Back flexion at (10) can be directed in the same direction. The inflection at (6) becomes the image of the surface (4) is broken down into two partial images (11, 12) which, if sufficient Line density of (6) and not too high field (4) are separated from each other, thereby a recipient can be assigned to each partial image.

With regard to the two light waves that are on each coherence area If the receivers work together, an intensity-linear receiver has a quadratic one Characteristic. s is the difference in frequency between the two light waves, the amplification and signal processing are removed from the receiver output can. Additional converging lenses can be placed between the grating (10 and the receivers (13, 14) are arranged, the images of the light source images (7 and 8) as superimposed Doppelhilder that can be designed onto the receiving surfaces. Is the local Separation of the partial images (11, 12) inadequate for the geometrically separated forwarding of the light to different receivers, then, if in the plane of the objective 9, the upper and lower to the bent bundle run next to each other, the respective Couple can be identified by a color or polarizing filter, so that after the interaction with the grating (10) the light by physical splitter according to the Identifiers can be separated and fed to the assigned recipients.

In Fig. 1) the respective bundles are assigned to the light source frequency related light frequencies emitted. When the light floats on the receivers, it lifts. the light source frequency. The carrier frequency corresponding to the movement of the modulator grid (6) appears as the signal carrier of the frequency This carrier frequency is lowered by the movement of the grating (3) or the grating (10) in one signal and increased in the other signal, so that a difference frequency of these signals can be removed when moving a grid (3). If the gratings (3 and 10) are connected to one another in more complicated optical structures, for example as diametrical points of a Zrlinder or radial grating or as subfields of a grating surface mapped onto one another, there is a difference frequency of to disposal. To carry out this procedure, for example, the surface (21) can be designed as a mirror with a radial grating, so that the ObåekUv (5) can also take on the role of the objective (9) and the grating (3) the role of the grating (10).

If the grid (10) is not in the area conjugated to grid (3), so the rays are directed in the back diffraction regardless of the focus position, However, homologous beams retain alignment errors proportional to the focus error.

Looking at the through a limb with positive refractive power behind sheared images of the light source, or of the spatial frequency filter aperture in the surface (21), so is the interference modulation inhomogeneous across the image surface, caused by interference of the same inclination, if there are focus differences. If you split this. Light source images geometric in at least two fields with separating edges parallel to the line directions of (10), e.g. by pairs of receivers, focus deviations can be measured. The signals of the two partial areas remain at the same frequency, but the phase difference is related on one of the two signals, this sign is reversed depending on the sign of the focus error around. Either the focus error is derived from the phase differences with the phase angle not linear but coherent, measured, or the phase error is made to zero by a servo circuit via the optimal focus.

In Fig.2) the signals from the receivers (13, 14) are passed through the amplifier (15, 16) brought to levels that can be passed on and processed. The amplifiers are preferably used as selective amplifiers for a frequency band, symmetrical to Carrier frequency located, formed. Since the measurement information is in the signal frequency the amplifiers can be equipped with automatic gain control or limiting unsuitable characteristics are trained. It is also possible to send the signals only immediately to use by an auxiliary oscillator that is free running on the carrier frequency or a multiple of this frequency is adjusted by the respective measurement signal is synchronized or readjusted in a phase-locked loop. Do the frequency multiplication switchable, so the measuring system can easily be connected to different linear or angular measurement systems can be adapted.

For the inch-a {etrical connection, it is sufficient to use the multiplier factor toggle between 100 and 127. which are preferably square-wave signals in the stationary state of the measuring system by measuring (18) the phase difference evaluated. As a result, changes in position are made up of small fractions of a lattice constant measurable. In the dynamic state of the measuring system, the beats between the Carrier frequency signals are stored integrating with the correct sign. Can do this e.B. an up / down counter (19) is used in which one signal is added and the other signal is stored subtracting. The counting processes can go through : ihlimpulse one of the two signals can be synchronized with simultaneous To ensure the arrival of impulses in the forward and rickety inputs that there are no errors. For measurement and control processes, the up / down counter can be set using set (n) and reset (0) inputs can be programmed in its counter content. An output unit (20), which can be provided with a buffer, establishes the connection to the following Measuring, computing or control systems.

Fig. 3) shows another embodiment for interventions in the Fourier plane of the image of a two-dimensional one used instead of (3) Phase grating (cross line grating). Due to the diffraction in both measurement coordinates In the first instance, coherent partial images of the light source arise in pairs (7x, Sx; 7y, 8y) Diffraction order. The zeroth order of diffraction (1 ') arises with suitable dimensioning of the first two-coordinate measuring grid with low intensity and is faded out.

The radial grating, which is also possible in this application, has been implemented Pairs of diffraction structures (Z6, 26 '; 27, 27') with identical pairs to one another Diffraction angles (lattice constants) replaced. It is shown that it is enough just each time a diffraction structure of a pair of intended for backmixing to be diffracted To move bundles for light modulation.

. is a steady unidirectional movement of the diffraction structure Realizable without constant directed material movement by a running ultrasonic wave by stimulating an electromechanical transducer (24,25) with a generator (22,23) in the optically effective medium (26,27) is generated 0 The running ultrasonic wave is used to avoid a standing wave in an adapted absorber (28,29) reflexionsfret destroyed.

With the transition to a mirror optic, the surface (21) also works be designed as a concave mirror reflecting. (26) and. (27) are then areas into which a running surface acoustic wave is coupled to create a reflective one To generate phase grating through the surface deformation. Of course you can and the diffraction grating pairs (27, 27 '; 26, 26') both as ultrasonic diffraction gratings be designed with the corresponding direction of travel of the sound waves. Even an ultrasound Radial mirror grating can be generated as a surface wave on a mirror ring. Around of sound waves circulating to the right and left in the ring and of temperature dependencies to be free of the speed of sound without frequency readjustment of the generator, the mirror ring can be cut open to couple the sound at one end and destroy at the other end.

In the case of a two-coordinate measuring device, they meet in the area of the backmixing grid eight partial bundles in four union areas. Either all four are union areas Partial areas of a cross line or checkerboard grid also divided into two coordinates, or two union surfaces each belong to a linearly divided grid line system at. In. Both cases can be independent of one another and assigned to the measurement coordinates Pairs of opposing, carrier-frequency signals are generated. By splitting up the sheared superimposed images of the light source or images of the aperture openings the level (21) in fields or even more fields lying next to each other, can convert the two-coordinate measurement into a three-coordinate measurement that determines the focus position be expanded.

With a loss of signal-to-noise ratio and the precision of the Allocation of the phase position of the oscillation signal between the carrier-frequency signals For the measurement paths that are to be regarded as correct, one of the two may even be on top of each other shown, one or two-dimensional grid (3, 10) through a light-scattering Area or even a scene in a landscape. The scattering area and the imaging optics are only to be adapted to one another in such a way that from the scattering surface the spatial frequency range according to magnitude and azimuth with sufficient scattering efficiency with the spatial frequency range that is transmitted by the imaging optics, at least partially coincides. earth scenes recorded by measurement, their cross-sectional areas are large compared to the manageable cross-sectional areas of optical systems, so is the telecentric optics shown in Fig (1) cannot be used. Is the scene distance very large compared to the focal length of the imaging optics, so the Spatial frequency ranges through diaphragms in the pupil plane (21) of a telescope lens be determined. This is where the diffractive structures splitting the bundles are also found (6, 26, 26 ', 27, 27'). With restriction of the transmitted through the lens Spatial frequency range on the spatial frequency band, which by the + first orders of diffraction of the lattice conjugate to the object is given by the corresponding Apertures in the objective aperture regardless of the aperture of the beam cone that the scene is illuminated, ensures that neighboring spatial frequency periods of the object, seen from the aperture pairs of the lens, with each other emit coherently, which is the modulation depth of the signals of a given spatial frequency optimized for a given illumination aperture. In order to use telescope applications, since the The scene involved in the measurement is often not restricted by an illumination field (4) can be, the overlap, multiplied by the diffractive structures To avoid object fields, it is advantageous to initially with the Telescope to frame an image of the scene into a field of view aperture in order to this image section of the intermediate image in a downstream imaging system according to the invention to further process optically.

The optimization of the modulation depth of the signals by pairs of diaphragms results in a limitation of the light flux that can be used for measurement purposes. Is this If the object surface is not, the flow of light is insufficient for the Ausxerting can be enlarged, advantageously several, light from the same object surface using systems that work in parallel, all of which have the optimal aperture configuration have to use. In the tandem arrangement of a telescope with a downstream one For example, it is advantageous to use the intermediate image with an aperture ratio of the telescope to produce a multiple of that required by the optimal aperture Focal ratio is. Each partial opening area available from the intermediate image can with the help of geometric dividers, such as honeycomb lenses, systems of each other inclined mirrors or refracting wedges of different refractive power, one independently effective imaging system can be connected downstream. To simplify the optical This imaging system can have a backmixing grid and one for the respective Radiation groups of common receivers are subordinated. To do this, however, you have to the phase positions of the partial modulations are optically adjusted to the same phase.

In Fig. 4) the process steps are again, without any auxiliary equipment broken down. Because of the path differences of the interfering light, there is one such a high temporal coherence is necessary that only laser illumination (1) is possible, The laser beam (101) is applied to the linear grating signaling position shifts (103) split into orders of diffraction, which only by the f first orders, the are further used, are shown. It also had any combination two other diffraction orders can be used.

The deflecting mirror (108) is designed as a stationary diffraction grating. The electro-acoustic modulator cell (107) with the driver (124) and the generator (122) creates an ultrasonic diffraction grating that acts as a traveling sound wave in the Absorber (128) ends, a partially transparent mirror (110) unites after alignment and direction of the second sub-bundles to the carrier-frequency signals. lBn the alignment and directional conditions must be met, both the lattice constants from (107) and (108), as well as the distances from the beam combiner (110) and the azimuths the "grid lines" will be the same, with the receivers (-113, 114) the counter-rotating converted into carrier-frequency signals, the receivers (113a, 114a) can be out of phase Deliver signals so that differential amplifier inputs are useful for signal processing are, particularly favorable conditions for beam guidance without a projection the separation surface of the first bundle to need the union surface, result with the beam guidance according to Rassudova G. N. Opt.Spectry Vol. 22 73-78, 255-258, 335-340 (1967) or according to Kulinetzki V.V. and Strzhner S.A.

Optical Technology Vol. 38 No. 10 October (1971) pp. 588-590.

If you excite a sound wave in the direction of the latter classification the grating lines of at least one of the two fixed reflection grids, preferably as a traveling surface wave, both diffraction functions of an optically effective surface. The same goes for the transparent one Transmission grid of the grid combinations according to Rassudova. Even with transmitted light systems, those in extension of the arrangements of the above-mentioned authors in the under A 1955; B 2818 dated 3.1.1974 from Ernst Leitz GmbH with the names of the inventors: J. Wilhelm, W, Erbe, F. Hock, Dr. H.D. Yes-.

coby is the carrier frequency generation and beam deflection possible by diffraction on the same surfaces.

The invention is not restricted to the arrangements described. More than two coherent bundles of rays in a union field are diverted in the same direction, which contains harmonics Signals caused. Instead of splitting rays associated with changes in angle and union by diffraction (3, 10) can also be birefringent components, such as Wollaston prisms can be used. The interference of beams in the same direction must be forced by analyzers, which are preferably below 450 to the Main directions of vibration are. Combinations of birefringent and diffractive Elements can only be used with monochromatic lighting, since the wavelength dependence the split angle remains uncompensated.

RN is used to obtain signals from high spatial frequencies from remote locations Object surfaces, the aperture distance, or the telescope objective diameter are unwieldy large, the telescope objective can be split into two or four partial objectives whose images are superimposed by a suitable geometrical optical beam guide will. (Basic rangefinder), in addition to the described applications for position measurement there can also be changes in pace differences between coherent partial beams made measurable according to the invention by the various changes in the optical thickness what, in the case of refectometers, is largely independent of absorption the measured substance behind the separation columns of gas or liquid chromatographs can fluctuate very strongly, delivers. Including incident or D-light interference microscopes gain in independence of the measurement results from the light losses at the object when the interference periods are broken down into small fractions.

Claims (9)

Speeches Method for the photoelectric generation of signals indicating carrier frequency changes in position or optical path difference changes by shifting the frequency of light when interacting with moving, diffractive structures, characterized in that a.) The illuminating light in a first flat area of the beam path, preferably on diffracting structures in first partial bundles ( 104, 105), which are at least into a partial bundle not the straight line continuation of the illumination bundle and that b.) The at least in pairs in the further beam path in the direction back mixed (c.) First partial bundles in a second flat area (21) with diffractive Structures (6, 107, leu8, 26, 26 ', 27, 27') interact in at least partially adjacent areas (107, 108, 7, 8, 7x, 8x, 7y, 8y), with unidirectional or oscillating movement of the structure (6, 107, 26, 27) in the second area in at least one of the first cross-section (107) assigned to reil bundles, a frequency difference, independent of the variable to be measured, between second sub-bundles (120, 1; and that c.) in a third planar area (10, 110) sub-bundles, which come from different first sub-bundles, are brought into alignment and direction within the tolerances given by the ability to interfere with the respective bundle cross-section, in that in the third area Preferably diffractive structures deflecting rays on at least two incident partial bundles with a light frequency shifted against each other in the steady state and that d.) each after c.) reunited partial bundles of different optical frequencies are fed to at least one photoelectric converter (13, 14) for generating photoelectric signals and that e,) uie frequency or phase of the signals generated according to d,) are evaluated either with one another by feeding into one or more equalizing stages (17) or that, in addition to at least one photoelectric signal, a comparison signal is fed into a comparing stage (17), which is in close phase correlation to the movement of the structure (6, 26, 27, 107) in the second flat area (21) according to b.). 2. The method according to claim 1, characterized in that according to 1.a) the first flat Area (4) and according to 1, c) third flat area (1-;) are arranged in a surface of a graduation carrier. 3. The method according to claims 1 and 2, characterized that, according to 1.b) in the second flat area (21) a radially divided phase grating (6) is arranged with suppressed zeroth diffraction order, the rotation around the center of division offset, both first bundles with diametrical division fields according to direction and frequency offset, where the ratio of the linear dimension of the illuminated field (4) to the light wavelength is chosen so that the through caused the variation of the grating constant over the diffractive radial grating surface Angular uncertainty still within the coherence ranges two behind the f, beam combiner (10) superimposed images of the radial lattice surfaces (7, 8) sheared on top of each other. 4. The method according to claims 1, 2, 3, characterized that, according to i.b) in the second flat area (21) for measurement in two coordinates two one-dimensionally diffracting, periodic structures are arranged in pairs, whose diffraction angles and directions are the same and whose directions are preferred 90 ° oriented to the coordinate directions are arranged, with at least one the two structures of a pair are moved in such a way that a speed component lies in the direction of division, 5. The method according to claims 1, 2, 3, 4. through this characterized in that, according to 1.b), the diffractive structures in oscillating motion second flat area (21) are inherently rigid and by elastic suspensions, which can be set in torsional or bending vibrations of a degree of freedom, be connected to the beam-guiding components. 6. The method according to claims 1, 2, 3, 4, 5, characterized that the light-diffractive structures moved according to 1.b) in the second flat area (21) can be generated dynamically by adding a unidirectional to compressible material running sound wave is excited, which either in transmitted light is preferred to the fluctuations in the refractive index or diffracts light waves in incident light at the surface deformations. 7. The method according to claims 1, 2, 3, 4, 5, 6, characterized that the first structures (3) splitting into sub-bundles with preferably chromatic Corrected systems (5, 9) mapped onto the beam-combining structures (10) will. 8. Process according to sen claims 1., 2., 3., 4., 5., 6., 7, thereby characterized in that, images (7, 8, 7y, 8y) of the non-source (1), or one as a light source Acting luminous field diaphragm on the, the first partial bundle in the second partial bundle splitting structures can be designed. 9. The method according to claims 1, 2, 3, 4, 5, 6, 7, 8. characterized in that at least two images (7, 8, 7y, 8y) of the structures splitting the first sub-bundles into second sub-bundles after the remixing (10), sheared over one another capable of interference, to the respective Receiver surfaces (13, 14) are mapped. 10. The method according to claims 1, 2, 3, 4, 5, 6, 7, 8, 9. characterized in that, according to claim 9, on the respective receiver surfaces The images designed over each other are broken down into sub-areas, their dividing lines to the respective beam combiner (10) of the second sub-bundle according to the Direction of the interference fringes oriented with the same inclination with the total difference 0 and that the light fluxes assigned to the partial areas are separate photoreceivers be assigned. 11. Arrangement for carrying out the method according to claims 1 - 10 characterized in that that in the beam path of. the light source (1) to the receivers first in terms of measurement technology essential link is a beam splitter with the property of an incoming beam in at least two outgoing first partial beams of different propagation direction is arranged to be disassembled, and that in each of these first partial beams a further Beam splitter is arranged, which has an input beam and at least two output beams has different directions, and that at least one device for the coupling of movement (22, 24, 23, 25) is present, the at least the structure turns one of the other 3-beam splitters into a light frequency modulator, and that the second partial beams (120, 121, 118, 119) at least one beam combiner (10, 110) is arranged downstream in such a way that at least two from different first partial beams originating rays behind the ray combiner according to alignment and direction at least approximately match, and that at least one photoelectric receiver (113, 114, 13, 14) arranged downstream of at least one recombined second partial beam pair is, of which a signal connection to a carrier frequency signal comparator (17) exists, and that this carrier frequency signal comparator has a second input which is connected to at least one second carrier frequency signal source, that the beat periods of the compared signals in a downstream integrator (19) stored and-sder the beat phase between at least two carrier frequency signals measurement or control tasks are adapted by an evaluation device (18). 12. Arrangement according to claims 1-11, characterized in that, the beam splitter into the first partial beams and / or the beam combiner of the second Partial beams in two, preferably 909 enclosing, periodic structural elements structured with light-diffractive properties is 13. nordm mg according to claims 1 - 11 characterized in that the beam splitter is divided into first partial beams (3, 103) and / or the beam combiner (10, 110) of the second partial beams (118, 119, 120, 121) is an optical polarization component that has two beam directions assigns different beam directions, and that at least one analyzer for the oscillation state of the light is subordinate. 14. Arrangement according to claims 1 - 13, characterized in that, either the beam splitter of the first partial bundle has a light-diffractive-scattering surface that has no special markings. 15. Arrangement according to claims 1 - 14, characterized in that, there are diaphragms that limit the propagation of light in terms of position and direction, that of the angle assignment of the beam directions at the beam combiner (10, 110) of the second partial bundle and the light distribution of the lighting according to location and direction correspond. 16. Arrangement according to responses 1 - 15, characterized in that, a system generating an intermediate image with a large aperture ratio, optical in parallel, at least two arrangements corresponding to the subject of the application are connected downstream of a small opening ratio, which preferably correspond to each other optical outputs have common photoelectric receivers.