Patent Application
20110109917
The present invention relates to an optical measuring device as generically defined by the preamble to claim 1 and to an optical measuring device as generically defined by the preamble to claim 2.
An optical measuring device of this generic type is known for instance from European Patent Disclosure EP 0 608 209 A2. It includes, besides a measurement graduation, embodied for instance as a linear measurement graduation, a scanning unit that is displaceable in at least one measurement direction relative to the measurement graduation. In the scanning unit, a light source, at least one scanning grating and a detector arrangement, comprising a plurality of photoelements, are provided. In the scanning unit, a so-called optical waveguide or attenuation structure is disposed, which comprises a grating, which is oriented perpendicular to the other gratings in the scanning beam path. With the aid of the additional grating, in this measuring device the light intensity that strikes the detector arrangement can be adjusted in a defined manner. Such adjustment of the light intensity striking the detector arrangement may for instance be necessary if standardized opto-ASICs are supposed to be used in the scanning units of different optical measuring devices. In that case, it can happen that the opto-ASIC, optimized for a first category of optical measuring devices, proves not to be optimal for other categories of optical measuring devices. Thus it is conceivable for instance that the intensity, striking the detector arrangement of opto-ASICs, is variously high in the various measuring devices. By means of the attenuation structure, embodied as an additional grating—as proposed in EP 0 608 209 A2—the overly high signal intensity in the detector arrangement can then be attenuated. Because of the different orientation of this grating, the actual scanning beam path for generating the displacement-dependent scanning signals remains largely unaffected. However, EP 0 608 209 A2 does not teach how and where this kind of attenuation structure is most suitably disposed in the scanning beam path or in the scanning unit and how the attenuation structure is most advantageously embodied.
It is the object of the present invention to create a measuring device of the type mentioned above which makes flexible adjustment of the light intensity striking the detector arrangement possible.
This object is attained according to the invention by a measuring device having the characteristics of claim 1.
This object is furthermore attained according to the invention by a measuring device having the characteristics of claim 2.
Advantageous versions of the measuring devices of the invention will become apparent from the provisions in the various dependent claims.
In a first variant of the measuring device of the invention, it is now provided that the scanning grating and the attenuation structure are disposed on the front and back sides of a transparent carrier element in the scanning beam path.
By way of the provision according to the invention, it is possible in particular to reduce the number of components required in the optical measuring device.
In a second variant of the measuring device, it is provided according to the invention that the attenuation structure has a permeability that varies as a function of location at least along one direction so that a light intensity which is uniform at least in that one direction results on the detector arrangement.
By way of the provisions of the invention, in the second variant of a measuring device of the invention, it can thus be ensured that in the case for instance of a locally varying intensity over the detector arrangement resulting without an attenuation structure, an extensively homogeneous distribution of intensity can be ensured. This kind of varying intensity distribution can result for instance in conjunction with special light sources, which have a defined emission characteristic. In this way, the detection reliability with regard to the image resulting in the detection plane can be markedly increased, since thus beyond the detector arrangement, a homogeneous light distribution, preferably in the measurement direction, is attained. The processing of the resultant light pattern in the detection plane is then not so vulnerable to malfunction.
Manifold embodiment possibilities exist with regard to the two variants of measuring devices of the invention.
Thus the attenuation structure can be embodied as an arrangement of transparent subregions on an opaque layer.
The transparent subregions can be embodied in circular form.
It is furthermore possible that the attenuation structure is embodied as a grating, in which transparent subregions are disposed periodically on the opaque layer.
The transparent subregions of the grating can be embodied in linear form and can be oriented perpendicular to the measurement graduation in the scanning beam path.
The grating of the attenuation structure can have one or more periodicities, which are each markedly less than the extension of the detector arrangement in a direction perpendicular to the measurement direction.
It is furthermore possible that the attenuation structure is embodied as a grating, in which the transparent subregions are disposed radially symmetrically on the opaque carrier element.
It can be provided that the width of the transparent subregions in the radial direction varies.
Alternatively, it is also possible that the attenuation structure comprises concentrically arranged portions, inside which the transparent subregions of the grating are disposed radially symmetrically and periodically, and the periodicities of adjacent portions differ.
Furthermore, the attenuation structure can also comprise a plurality of portions disposed adjacent one another in the measurement direction, which portions each include a grating, disposed periodically in a direction perpendicular to the measurement direction, with linear transparent subregions, which are disposed periodically on the opaque layer on a carrier element, and adjacent portions in the measurement direction have a different periodicity.
In one possible variant of the measuring device of the invention, the elements in the scanning unit are disposed in such a way that
In a further variant of the measuring device of the invention, the elements in the scanning grating are disposed in such a way that
the beams emitted by the light source propagate in the direction of the measurement graduation, thereupon act on the measurement graduation, then travel through the attenuation structure, and because of the interaction with the measurement graduation, a displacement-dependently modulated fringe pattern on the detector arrangement results, and the detector arrangement comprises a periodic arrangement of a plurality of detector elements.
The attenuation structure can be disposed on one side of a transparent carrier element in the scanning beam path.
It is possible that the attenuation structure is embodied as a regular arrangement of transparent subregions on an opaque carrier element.
Furthermore, it can be provided that the attenuation structure, at least in the measurement direction, has a permeability that varies as a function of location.
Further details and advantages of the present invention will be explained in the ensuing description of exemplary embodiments of measuring devices of the invention, in conjunction with the drawings.
These show
a and 2b, the front and back side of the carrier element of the example in
a, the light pattern, resulting in conjunction with a certain light source, in the detection plane of a measuring device of
b, a view of a suitable embodiment of an attenuation structure;
c, the resultant light pattern in the detection plane of a measuring device of
a, the light pattern, resulting in conjunction with a different light source, in the detection plane of a measuring device of
b, a view of a further embodiment of an attenuation structure;
c, the resultant light pattern in the detection plane of a measuring device of
a and 7b, each, one further view of an embodiment of a suitable radially embodied attenuation structure.
In
In the present example, the measuring device of the invention includes a scanning unit 20, which is disposed movably, at least in the measurement direction x, relative to a scale 10 having a measurement graduation 11. The measurement direction x, as indicated in the drawing, is oriented perpendicular to the plane of the drawing. The scale 10 and the scanning unit 20 are connected for instance to two objects, disposed displaceably to one another in the measurement direction x, such as two machine parts movable relative to one another. By way of the displacement-dependent position signals of the measuring device of the invention, a downstream control unit—not shown—can suitably control the motion of these machine parts in a known manner.
In the example shown, the measurement graduation 11 is embodied as a reflection measurement graduation, extending linearly in the measurement direction x, on a carrier body 12, which includes periodically disposed graduation regions with different reflection properties. The line-like graduation regions extend in the indicated y direction, that is, in the measurement graduation plane perpendicular to the measurement direction x. The measurement graduation 11, depending on the scanning principle, can be embodied in a known manner as an amplitude grating or as a phase grating.
In the scanning unit 20, for generating the displacement-dependent position signals, a light source 21, collimator optics 22, a scanning plate 23, and a detector arrangement 26 are disposed in a suitable housing. In this example, an LED is provided as the light source 21. The scanning plate 23, in the example shown, comprises a transparent carrier element 23.1, embodied for instance as a glass plate. A scanning grating 24 is disposed on the front side or underside, facing toward the measurement graduation 11, of the carrier element 23.1. On the back side or top, opposite from it, of the carrier element 23.1, facing toward the detector arrangement 26, an attenuation structure 25 is disposed according to the invention, whose function and specific embodiment will be described in further detail hereinafter.
The scanning grating 24 comprises a periodic arrangement of graduation regions with different optical permeabilities. The graduation regions of the scanning grating 24 are likewise embodied as lines and extend in the indicated y direction, that is, perpendicular to the measurement direction x. Accordingly, the scanning grating 24 is oriented in the scanning beam path in precisely the same way as the measurement graduation 11. Depending on the scanning principle employed for generating the displacement-dependent position signals, the scanning grating 24 can be embodied as an amplitude grating or as a phase grating.
The beams, emitted by the light source 21 and collimated by the collimator optics 22, interact in a known manner with the measurement graduation 11 and the scanning grating 24, so that by way of the detector elements of the detector arrangement 26, position signals can be generated that are modulated as a function of displacement. As a result of the suitable embodiment or arrangement of the scanning grating 24 in the form of scanning grating regions slightly offset from one another, with which regions, toward the detector, specific detector elements of the detector arrangement 26 are associated, it is possible to generate phase-offset position signals; typically, it is provided here that four position signals each offset by 90° be generated, signals that can be further processed in a known manner.
The opto-ASIC used in the detector arrangement 26, which opto-ASIC contains among other things the detector elements as well as further components for signal processing, can be employed in the most various measuring devices that use different optical scanning principles. As a consequence, in some scanning principles the light intensity striking the detector arrangement can be too high. For that reason, in the present exemplary embodiment of a measuring device of the invention, it is provided that the attenuation structure 25, by way of which the light intensity on the detector arrangement 26 can be adjusted in a defined manner, be disposed on the scanning plate 23. Accordingly, the attenuation structure 25 reduces the overly high intensity on the detector arrangement 26 that would otherwise result with the present scanning principle and the light source 21 used here.
According to the invention, in this variant the attenuation structure 25 is disposed on a free surface of an optical component in the scanning beam path, namely on the otherwise unused back side of the carrier element 23.1 of the scanning plate 23, wherein the backside of the carrier element 23.1 is oriented toward the detector arrangement. Accordingly, for the attenuation structure 25, it is unnecessary to provide a further component which might have to be mounted and adjusted in a complicated way in the course of production of the measuring device. In the example shown, the attenuation structure 25 comprises a grating in the form of an amplitude grating, which includes linearly embodied transparent subregions 25.1, which are embodied periodically in an opaque layer; the opaque layer for instance comprises so-called black chrome. Besides the embodiment of the transparent subregions 25.2 in the form of completely absorbent layers, these subregions 25.2 can also be embodied as known stacks of interference layers, in which after multiple reflections, light is no longer let through. In all cases, the result is a grating comprising linear transparent subregions 25.1 and linear opaque subregions 25.2. As can be seen from
If the attenuation structure 25 of the invention is embodied as a grating, as in the present case, and is oriented perpendicular to the other gratings, then both in this example and in the following examples, it furthermore proves advantageous if the periodicity P of the respective grating is selected as markedly less than the extension of the detector arrangement or the length of individual detector elements (if they are present in the form of a substructuring) perpendicular to the measurement direction, or in other words in the y direction. The periodicity P of the grating is selected here, in one possible embodiment, as less by approximately the factor of 10 than the length of a detector element in the y direction. The reason for this is that then the greatest possible homogeneity of the lighting intensity in this direction can be attained. If a grating is arranged with the same orientation as the other gratings in the scanning beam path, which is basically also possible, naturally the length of the detector elements in the measurement direction would have to be taken into account, and so forth.
It is furthermore favorable if the opaque subregions 25.2 of the attenuation structure 25 are optimized with respect to the substrate-air transition, if as provided in
The linear transparent subregions 25.1 of the grating, in this variant of the measuring device of the invention, are disposed perpendicular to the measurement graduation 11 as well as—in the present example—perpendicular to the scanning grating 24 in the scanning beam path, or in other words perpendicular to further graduations or gratings in the scanning beam path. As a consequence of this arrangement of the attenuation structure 25 embodied as a grating, the actual optical scanning beam path for generating displacement-dependent position signals is affected as slightly as possible.
In
In principle, the requisite attenuation action is adjusted by the respective attenuation structure 25 by way of the ratio of the total surface area of the transparent subregions 25.1 to the total surface area of the attenuation structure 25, or in other words, in the final analysis, by way of the suitable choice of the transmission τ of the attenuation structure 25. If reducing the signal intensity on the detector arrangement to 80% is necessary, the corresponding ratio must then be adjusted to 80%, and so forth.
In the first variant described of a measuring device of the invention, the attenuation structure 25, as explained, comprises linear transparent subregions 25.1 on an otherwise opaque layer. However, it is understood that alternatively to this, it is also possible to provide different geometries for the transparent subregions in the opaque layer. For instance, the attenuation structure could also comprise many circular transparent subregions on an opaque layer that are distributed suitably. The distribution of the transparent subregions can be either regular or irregular. Moreover, as an alternative to circular subregions, naturally still other possible geometries for the permeable subregions are feasible within the scope of the present invention.
A second variant of a measuring device of the invention is shown in
Once again, the measuring device of the invention includes a scanning unit 120 which is disposed movably at least in the measurement direction x relative to a scale 110 with a measurement graduation 111. The measurement graduation 111 disposed on a carrier body 112, for instance a steel substrate, is embodied as a reflection measurement graduation, as in the above variant.
Once again, of the scanning unit 120, only those elements necessary for explanation of the present invention are shown in the highly schematic view in
A detector arrangement 126 is placed on a carrier circuit board 127 in the scanning unit 120. The detector arrangement 126 serves to scan a fringe pattern in the detection plane and to generate position signals. The fringe pattern in the detection plane results from the optical scanning of the measurement graduation 111 on the scale 110, or in other words from the interaction of the beams, emitted by the light source 121, with the measurement graduation 111. In a distinction from the first variant described above, in the present scanning principle no separate scanning grating is provided in the scanning beam path. Instead, the detector arrangement 126 now comprises a detector array with a periodic arrangement in the measurement direction x of individual detector elements or photodiodes. Thus in this embodiment, the detector arrangement simultaneously takes on the functionality of both the scanning grating and the detector elements.
Above the detector arrangement 126 in the scanning unit 120, a transparent carrier substrate 128, embodied for instance as a platelike glass carrier substrate, is disposed in a central region. The light source 121 is placed on the side of the carrier substrate 128 toward the measurement graduation 111. In the selected scanning principle, a point light source, such as a so-called VCSEL (vertical cavity surface emitting laser) light source preferably functions as the light source 121.
The radiation-emitting surface of the light source 121 is oriented in this variant in the direction of the side of the carrier substrate 128 facing away from the measurement graduation 111. Accordingly, the light source 121 projects away from the measurement graduation 111.
An optical reflector element 122, which is embodied for instance as a grating structure integrated with the carrier substrate 128, or in other words as a diffractive optical element, is disposed on the side of the carrier substrate 128 facing away from the measurement graduation 111. The optical functionality of this reflector element in the scanning beam path will be described in further detail hereinafter.
The beams emitted by the light source 121 are deflected or reflected back—as can be seen from FIG. 3—by the reflector element 122 in the direction of the measurement graduation 111 and then pass through the carrier substrate 128 once again in the opposite direction. Then, the beams reach the measurement graduation 111, where they are in turn reflected back in the direction of the scanning unit 120. In the scanning unit 120, the partial beams arriving from the measurement graduation 111 finally reach the detector arrangement 126, placed in the detection plane, where in the case of the relative motion of the scanning unit 120 and the scale 110 or measurement graduation 111, they generate displacement-dependent position signals. By way of the scanning beam path described and the resultant interactions of the partial beams with the measurement graduation 111, a periodic fringe pattern is generated in the detection plane. In the case of the relative motion of the scanning unit 120 in the scale 110, this fringe pattern is modulated as a function of displacement and converted in a known manner via the detector arrangement 126 into a plurality of phase-displaced incremental signals for further processing.
For the scanning principle used in this variant, it is definitive that the light source 121 employed be disposed as much as possible in the detection plane. Only in that case can the insensitivity of the periodic fringe pattern generated in the detection plane from the applicable scanning spacing be ensured. By skilled design of the scanning beam path and in particular by providing the aforementioned reflector element, an advantageous way of meeting this requirement is provided. Thus by integrating the reflector element 122 with the scanning beam path, it can be attained that the light source 121 is placed virtually in the detection plane, while in fact or in reality it is disposed at some other point of the scanning unit 120, namely, for instance as seen in
The attenuation structure 125 required for adaptation or adjustment of the intensity on the detector arrangement 126 is disposed in this variant in the scanning beam path on the side of the carrier substrate 128 that is oriented away from the measurement graduation and toward the detector arrangement 126. As seen in
In this variant of the measuring device of the invention, a special embodiment of the attenuation structure 125 is now primarily definitive. While in the first variant described above, a uniform reduction of intensity in location-dependent fashion was ensured over the entire surface area of the downstream detector arrangement, it is now provided that an attenuation structure 125 be used which at least in one direction ensures a variation or reduction in intensity varying as a function of location with respect to the radiation intensity let through. For that purpose, the attenuation structure 125 is embodied in such a way that in at least one direction, it has a permeability that varies as a function of location. Preferably, at least in the measurement direction x, a varying permeability of the attenuation structure 125 is provided.
This kind of embodiment of the attenuation structure 125 is advantageous in this variant of a measuring device of the invention, especially because of the light source 121 used. As mentioned above, it is embodied as a VCSEL light source, and because of its emission characteristics, it does not provide sufficiently homogeneous lighting intensity over the radiation-sensitive surface of the detector arrangement 126. Instead, without the provisions of the invention, the result is an intensity, increasing outward, of the light pattern on the detector arrangement 126. A plan view on the resultant light pattern or its intensity distribution in the detection plane of the detector arrangement 126 of
b, in a plan view on the scanning unit 120, shows an exemplary embodiment of an attenuation structure 125 embodied according to the invention, which as a function of location affects or attenuates this kind of varying intensity distribution in the measurement direction x. In the final analysis, the result in the detection plane is a light pattern with a uniformly reduced intensity distribution, at least in the measurement direction x. It is understood that it is naturally also possible to provide the attenuation structure in a plurality of directions with permeabilities that vary as a function of location.
Fundamentally, as already in the first variant, an attenuation structure 125 of this kind comprises a defined geometric arrangement of transparent subregions 125.1, on an otherwise opaque layer in which the opaque subregions 125.2 are then embodied. The corresponding subregions 125.1, 125.2 can in turn be embodied in linear form, that is, as gratings, or have other geometries.
In the exemplary embodiment shown in
The again linear transparent subregions 125.1 of the various portions A1-A8 of the attenuation structure 125, as in the first variant, are disposed perpendicular to the measurement graduation in this exemplary embodiment. The corresponding subregions 125.1, like the opaque subregions 125.2, accordingly extend in the x direction, that is, perpendicular to the y direction in which the graduation regions of the measurement graduation extend. In this way, once again, the least possible optical influence on the scanning beam path is ensured.
For designing the transmission τ(k), which varies as a function of location in this variant, of the attenuation structure 125, the least intensity i0 of the light pattern, measured on the detector arrangement 126, is determined. If i(k) represents the intensity of the light pattern measured at the location k, the requisite location-dependent transmission τ(k) of the attenuation structure 125 then becomes τ(k)=i0/i(k). This is fundamentally true whenever larger regions are viewed and discretization of the location-dependent transmission τ(k) is done.
Finally, in
The case of a different resultant intensity distribution on the detector arrangement of a measuring device of
a, analogously to
In order in turn to ensure the sought homogeneous intensity distribution on the detector arrangement 126, at least in the measurement direction x, an attenuation structure 125′ is used according to the invention, of the kind shown in
The transparent subregions 125.1′, which again are linear, of the various portions A1′-A7′ of the attenuation structure 125′ are each disposed perpendicular to the measurement graduation, as in the foregoing exemplary embodiments. The corresponding subregions 125.1′, like the opaque subregions 125.2′, accordingly extend in the x direction, that is, perpendicular to the y direction in which the graduation regions of the measurement graduation extend.
The light pattern on the detector arrangement 126 that results with the aid of an attenuation structure 125′ embodied in this way is shown in
A further alternative embodiment of an attenuation structure of the invention is shown in
The attenuation structure 225 in the example of
In closing, further embodiments of attenuation structures, which each have a permeability that varies as a function of location, will be described in conjunction with
The attenuation structures 325, 425 with radial symmetry, shown in
The exemplary embodiment of an attenuation structure 325 shown in
In the exemplary embodiment of an attenuation structure 425 with radial symmetry shown in
As in the examples described above, in the radially symmetrical variants of an attenuation structure, the various transparent subregions are embodied in an otherwise opaque layer.
Within the scope of the present invention, manifold possibilities thus exist for embodying suitable attenuation structures in the scanning beam path of optical measuring devices. It is understood that the possibilities described in conjunction with the description can be combined suitably as needed and adapted to the particular situation accordingly.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2008 025 870.9 | May 2008 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2009/053797 | 3/31/2009 | WO | 00 | 11/29/2010 |
