DE4113046C2 - Optoelectronic position measuring device - Google Patents

Description

The invention relates to an optoelectronic position measuring device according to the preamble of claim 1.

Such a device is known from DE 32 28 064 A1.

DE 39 28 064 A1 describes a photoelectric Position measuring device with a scale grid for generation of at least two diffracted partial beams which pass through Interference can be brought to interference and detected, presented. There is a double grating in a planar waveguide provided that either the ones bent at the scale grid Coupled partial beams in the waveguide, superimposed and Feeds detectors or generates the partial beams that through the Scale grid overlaid and then detectors be fed.

This position measuring device has temperature influences none or only between the coupling elements and the detectors a little influence. Changes in angle or position of the Light source as well as tilting and twisting between Scale grids and planar waveguides cannot be detected, however become and thus lead to measurement errors.

Interferometric measuring devices in which the wavelength of Laser light is used as a reference, are also generally known. When Measuring standards are usually optical diffraction gratings with lattice constants of a few micrometers. To at the incremental path measurement has an accuracy of up to 0.1 µm reach, it is necessary to optically the lattice constants and / or to interpolate electronically. Examples of electronic interpolation z. B. specified in O. Troitscher: On questions of digital path measurement with Photoelectric position measuring devices of high resolution, Optik 28, Issue 3, 1968/69, pp. 210-221.

However, the degree of electronic interpolation is due to the The harmonic content of the signals to be processed is limited. Next electronic interpolation is therefore also optical Interpolation method applied.

By multiple reflection on a grid scale is a Optical interpolation factor of 4 reached (company lettering "Laser linear encoder", Canon Europa N.V., London NW 10 OJF, Brent Trading Center, North Circular Road).

All of these position measuring systems are made of discrete optical and built electronic components. They require a high one Construction and assembly work. In addition, environmental influences affect the adjustment of the components to each other and thus lead to measurement inaccuracies and readjustments make necessary.  

DE 36 25 327 C1 is therefore used to reduce the size and disruptive influences a position measuring device specified at which the ones diffracted at the diffraction grating Partial beams of the same order with different ones Sign coupled into the optical fiber and for Overlay can be fed to a coupler. At the three Outputs of the coupler are out of phase with each other electrical signals detectable, that of an electronic Undergo interpolation. Coupling elements, Optical fibers, couplers and detectors can be used as integrated optical circuit combined on a substrate his. The disadvantage is that tilting and temperature gradients lead to measurement inaccuracies. A further simplification of the Construction and further improvement of interference immunity would be desirable.

Furthermore, a method and an apparatus for measuring the Extent of a movement known (DE 33 16 144 A1), whereby by means of a diffraction grating used as a reference Diffraction light bundles are generated that interact with each other interfere to the extent of the relative movement between Diffraction grating and the rest of the optical system to determine. Such devices are very sensitive to environmental influences sensitive and require a high manufacturing and Assembly effort.

The invention is therefore based on the object of and assembly effort for optoelectronic position measuring devices when realizing small sizes and high resolution to reduce as well as the stability against environmental influences to increase.

This task is accomplished through an optoelectronic Position measuring device with the features of claim 1 solved. A shortening of the optical path and thus miniaturization the size succeeds in an advantageous embodiment of the Invention in that three reflectors (R₁, R₂, R₃) in integrates optical form on the layer waveguide (W) or arranged at the interfaces of the layer waveguide (W) are that by multiple flexion the superimposition of the Partial beams (L₁, L₂) is brought about.  

In another advantageous embodiment of the invention the partial beams (L₁, L₂) by means of a reflector (R) and a divider mirror (T), both integrated in optical Shape formed on the layer waveguide for interference brought. The coupling of the partial beams diffracted at the diffraction grating takes place here through a coupling grid.

The recipient line (E) can be in Hybrid design to the substrate (S), which is more advantageous in this case Way consists of glass, be coupled.

Another advantageous option is to place the recipient line (E) in the integrated optical circuit of layer waveguide (W) and optical elements (R₁, R₂, R₃ or R, T), where silicon is particularly suitable as substrate material in this case is.

In a incident light device using an optical reflection grating (G _R ), both the receiver line (E) and the radiation source (Q), e.g. B. a semiconductor laser diode together with beam shaping elements F, z. B. a lens may be included in the integrated optical circuit. An A III-B V semiconductor is advantageously used as the substrate.

Such an optoelectronic position measuring device can be particularly small and compact due to the high degree of integration manufacture. Since the adjustment of the components to each other in the integrated optical circuit is fixed, interference by Environmental influences largely eliminated.

The evaluation of the entire interference pattern does not only the displacement of the scale embodiment is recorded, but also Drifting such as B. the movement of a laser beam, the change the geometry of a laser beam, temperature drifts, Tilting or twisting accessible.

A highly precise adjustment is not necessary because all necessary calculation parameters by evaluating the pixel image of the interference pattern can be determined. Shifts can be made by comparing images define.

A major advantage of the invention optoelectronic position measuring device is that by arranging the recipient line and selecting the receiver signals to be evaluated an optical interpolation  can be carried out. To increase the resolution of the Position measuring device is also an electronic Interpolation provided in a known manner.

The invention is based on three Embodiments with reference to the drawings are explained in more detail.

The basic view shows schematically:

Fig. 1 shows a simple position measuring system;

Fig. 2 is a position measuring system, in addition, the receiver array is optically integrated;

Fig. 3 shows a position measuring system in which the radiation source and receiver line are optically integrated.

In Fig. 1 a Auflichtmeßeinrichtung is shown in which a light emitted from a not shown source of radiation parallel beam L incident on an optical reflection diffraction grating _GR with a grating constant g (z. B. 8 microns) and reflective diverging into two at a diffraction angle R sub-beams L₁, L₂ of the same order are bent with different signs. The reflection diffraction grating G _R is on a movable machine part transversely to the radiation direction of the radiation source, for. B. the support of an NC machine tool attached. Between the reflection grating G _R and the radiation source is, together with this attached to a fixed part of the machine tool, a substrate S, for. Example, made of glass, which is formed on its surface as a layer waveguide W, for example by doping, and its interfaces are provided with reflectors R₁, R₂ and R₃ in such a way that the partial beam L₁ (+ n order) at all three Reflectors is reflected, the partial beam L₂ (-n order), however, only on reflectors R₂ and R₃. The interfaces can advantageously be coated with metal vapor deposition layers to increase the reflectance. In an analog embodiment, however, they can also be formed directly in the layer waveguide as trenches.

After reflection on the reflector R₃, both partial beams interfere with each other. A recipient line E, e.g. B. a line of discrete receiver components (photodiodes or transistors) or a CCD line is coupled in hybrid construction to the substrate in such a way that the interference fringe pattern arises as an image of the optical diffraction grating G _R serving as the measuring standard. The intensity distribution registered by the receiver line E at the individual measuring points is converted into corresponding electrical signals and fed to an electronic evaluation unit (not shown in more detail), where they are evaluated in a manner known from incremental position measuring devices. Thus, displacements of the optical diffraction grating are transformed into generally digitally displayed machine movements.

Fig. 2 shows an embodiment according to the transmitted light principle. The measuring device has a laser, not shown, as the radiation source. The optical diffraction grating is designed as a transmission grating G _T.

The layer waveguide W formed on the surface of the substrate S, which is preferably made of silicon, contains, in an integrated optical form, a reflector R and a splitter mirror T, each tilted relative to one another, and additionally the receiver line E, e.g. B. from discrete photodiodes. Of the partial beams L 1, L 2 generated by diffraction at the transmission grating G _T , the partial beam L 1 reaches the + n. Order via the reflector R on the divider mirror T, where a part L _1.1 is reflected again and another part L _1.2 passes unhindered in the direction of the receiver line. The partial beam L₂ of the -n order occurring on the divider mirror T passes this unhindered to part L _2.1 and is reflected to another part L _2.2 in the direction of the receiver line E. By superimposing the partial beams L _1.2 and L _2.2 in the receiver line E, an interference image is created there, which is evaluated analogously to Example 1. The partial beams L _1.1 and L _{2.1 also} interfere with each other and can also be evaluated. The coupling in of the transmission grating T _T diffracted partial beams L 1 and L 2 takes place via the line surface or with a coupling grating (not shown).

In a reflected light arrangement according to FIG. 3, the radiation source S, a laser diode with a lens as a beam-shaping element F, in the film waveguide W with the reflector R and the splitter mirror T is optically integrated in addition to the receiver E-line. An A III-B V semiconductor serves as substrate material.

Claims (6)

1.Optoelectronic position measuring device for measuring the relative position of two objects according to the transmitted light or reflected light principle, with an optical diffraction grating arranged movably transversely to the radiation direction of a radiation source, by means of which at least two partial beams of the same order are generated with different signs, and with one arranged on a substrate Layer waveguide, in which the partial beams are coupled, brought to interference by means of integrated optical elements and converted into electrical signals by the receivers, characterized in that the receivers form at least one receiver line (E), the integrated optical elements (R1, R₂, R₃ or R, T) bring the partial beams (L₁, L₂) to interference so that on the at least one receiver line (E) an interference fringe pattern is created as a modified image of the diffraction grating (G _R or G _T ) and the electrical signals at least one receiver line (E) depends on the position of the interference fringe pattern on the receiver line (E). 2. Optoelectronic position measuring device according to claim 1, characterized in that the integrated optical elements from three reflectors (R₁, R₂, R₃) exist on the Layer waveguide (W) or at its interfaces like this are arranged to each other that the bent Partial beams (L₁, L₂) by multiple reflection for Interference.   3. Optoelectronic position measuring device according to claim 1, characterized in that the integrated optical elements from a reflector (R) and a divider mirror (T), which are arranged so that the interference the partial beam (L₁, L₂) in the layer waveguide (W) is produced. 4. Optoelectronic position measuring device according to one of claims 1 to 3, characterized in that the integrated optical elements (R₁, R₂, R₃ or R, T) and the layer waveguide (W) on one Glass substrate (S) are arranged and the radiation source (Q) and the at least one receiver line (E) in hybrid construction to the Substrate (S) are coupled. 5. Optoelectronic position measuring device according to one of claims 1 to 3, characterized in that the at least one recipient line (E) in the integrated optical circuit is included and the substrate (S) consists of silicon. 6. Optoelectronic position measuring device according to one of claims 1 to 3, characterized in that the radiation source (Q) with jet form elements (F) and the at least one receiver line (E) in the integrated optical circuit are included and the substrate (S) from an A III-B V Semiconductor exists.