OPTICAL POSITION MEASURING DEVICE

Description

AREA OF TECHNOLOGY

[0001] The present invention relates to an optical position measuring device suitable for determining the relative position of two objects moving relative to each other. STATE OF THE ART

[0002] In known high-precision optical position measuring devices, in addition to intensity-based evaluation methods, polarization-optical methods are also used to generate three or more phase-shifted, displacement-dependent sampling signals for position determination. With regard to the polarization-optical generation of sampling signals, reference is made, for example, to EP 0 481 356 A2 of the applicant.

[0003] The principle underlying signal generation according to EP 0 481 356 A2 is described in Figure 1This is shown in a schematic representation of the unfolded scanning beam path. Here, gratings A and M are arranged relatively freely along the specified measurement direction x relative to the remaining components L1, L2, and AO. The beam incident from the left, polarized by the polarizer P1, is first split into two partial beams by grating A. As shown in the diagram... Figure 1As can be seen, separate polarizing optical components, such as differently oriented lambda / 4 plates PE1 and PE2, are inserted into the beam path of the partial beams to be made to interfere, in which the position information is encoded. The lambda / 4 plates PE1 and PE2 polarize the two passing partial beams orthogonally to each other, i.e., the two partial beams are then, for example, left- and right-circularly polarized. These two partial beams are then superimposed to form a common signal beam (0) and split in a subsequent detection unit or evaluation optics AO into three or more superimposed partial beams I90, I210, I330. After passing through differently oriented polarizers P90, P210, P330, the detector elements D90, D210, D330 ultimately produce sampling signals S90, S210, S330 that are phase-shifted by 120° and can be further processed in a known manner.In addition to the Lambda / 4 plates PE1, PE2, further polarization-optical components in the form of polarizers P2, P3 are often arranged in the beam paths of the split partial beam bundles in order to compensate for incorrect polarizations caused by gratings A, L1, L2 previously passed through by the partial beam bundles.

[0004] A disadvantage of this type of polarization-optical generation of multiple phase-shifted, displacement-dependent scanning signals is the necessity of incorporating separate or additional optical elements, such as lambda / 4 plates and polarizers, into the scanning beam path or the scanning slit between the relative moving components. Such additional components can be problematic if the optical position measuring device has a limited installation volume or a small intended scanning distance. If the position measuring device is to be constructed analogously to the known principles from WO 2008 / 138501 A1, components A, M and L1, L2 are to be made of Figure 1 They are designed as two scales that can be moved relative to each other. In this case, a mechanical mounting of stationary polarizing optical components located between them is often not possible.

[0005] The additional polarization-optical components in the scanning beam path also place increased demands on the flatness, parallelism, and homogeneity of the support structures used; drift-free and stable mounting surfaces are required to accommodate these support structures. Potential material defects can only be compensated for with considerable additional effort using appropriate calibration procedures. This is especially true when long translation-invariant scales are used in corresponding optical position measuring devices.

[0006] Furthermore, additional system properties such as natural frequencies or air currents in the scanning slit can also be negatively affected by the additional polarization-optical components required in the scanning beam paths.

[0007] An optical position measuring device with polarization-optical generation of phase-shifted scanning signals without separate or additional polarization-optical components in the scanning beam paths has already been proposed in DE 10 2010 063 253 A1 by the applicant. According to this solution, the required polarization-optical components are integrated into other components of the scanning beam path, for example, in the form of high-frequency gratings with periodically varying structures. In such a position measuring device, the components used have position-dependent polarization properties in the measuring direction; for example, the scale can be configured to function as a polarization grating. This then consists, for example, of several locally variable layers and includes a high-frequency grating with a division period dR < λ / 2, which only has a zero.The diffraction order is determined by the polarization-optical functionality. The grating orientation of the high-frequency grating changes along the measurement direction with the polarization period dP, which must be significantly larger than the width hwSpot of the illuminated area of ​​the scale, which limits the signal period SP of the generated sampling signals from below; i.e., the relationship dP > hwSpot must be maintained. The partial beams striking different points on the scale thus experience locally different polarization-optical effects, whereby the polarization variation must be precisely adapted to the respective sampling distance. For this purpose, the distance between the points of impact of the partial beams is chosen so that it corresponds to half the grating period of the scale.In the event of a change in the sampling interval, impairments in the modulation level of the sampling signals as well as changes in other signal characteristics result.

[0008] Another optical position measuring device with polarization-optical generation of phase-shifted scanning signals without additional discrete polarization-optical components in the scanning beam paths is also already known from DE 10 2014 211 004 A1 of the applicant. According to this document, under certain conditions, diffraction at gratings on the side of the scale or the scanning plate of an optical position measuring device can be used to set specific polarization states in the diffracted partial beams, e.g., opposite circular polarization states. For this to be possible, however, certain incidence conditions with respect to the beam to be split must be met; furthermore, the corresponding grating must have a very small grating period to set the desired polarization properties in the diffracted partial beams.This possibility of generating polarization-optical effects on the partial beams is therefore subject to certain limitations and cannot be used for every scanning principle. SUMMARY OF THE INVENTION

[0009] The present invention aims to provide an optical position measuring device that does not require additional polarization-optical components in the scanning beam path for the polarization-optical generation of phase-shifted scanning signals and enables the use of different optical scanning principles. The polarization states set in the various partial beams should remain as unchanged as possible even with changing scanning conditions, thus ensuring consistent quality of the generated scanning signals.

[0010] This problem is solved according to the invention by an optical position measuring device with the features of claim 1.

[0011] Advantageous embodiments of the optical position measuring device according to the invention result from the measures listed in the dependent claims.

[0012] The optical position measuring device according to the invention serves to detect the relative position of two objects moving relative to each other along at least one measuring direction, which are connected to a first grating and a second grating. At one grating, an illumination beam emitted by a light source is split into at least two partial beams; the partial beams undergo different polarization-optical effects. After the differently polarized partial beams are recombined at a grating, several phase-shifted, displacement-dependent scanning signals can be generated from the resulting signal beam in a detection unit. No separate polarization-optical components are arranged in the scanning beam paths of the partial beams between splitting and recombination.At least one of the gratings traversed is designed as a polarization grating to generate the different polarization-optical effects on the partial beams. The polarization grating is designed such that, regardless of position, diffraction orders with different polarization states result on the grating. The polarization grating exhibits periodically arranged grating structures both along the measurement direction and orthogonally to the measurement direction, where the orthogonal periodicity (Λ_ortho) is given by... ∧ _ortho < 1.5 ⋅ λ is chosen, with Λ_ortho := orthogonal periodicity of the lattice structures λ := wavelength of the light source used.

[0013] It may be provided that the polarization grating comprises a plurality of arc-shaped curved grating structures in the form of grating bars and grating gaps, the longitudinal direction of which is oriented parallel to the measuring direction.

[0014] It is possible that the polarization grating has strip-shaped grating sections arranged periodically parallel to the measurement direction with a measurement direction periodicity, the longitudinal extension direction of which is oriented perpendicular to the measurement direction, wherein the grating structures in the grating sections are arranged periodically perpendicular to the measurement direction with the orthogonal periodicity.

[0015] Furthermore, it may be provided that between adjacent grating sections of the polarization grating a grid gap is arranged, or a grid bar is arranged, or several grid gaps and grid bars are arranged alternately adjacent to each other.

[0016] Alternatively, it is possible that lattice structures of adjacent lattice sections border each other.

[0017] Furthermore, it may be provided that the area fill ratio FV of the polarization grating is chosen according to the relationship FV < 0.6, where the area fill ratio FV is defined as the ratio of the area of ​​the grating bars in a polarization grating unit cell to the total area of ​​the polarization grating unit cell.

[0018] Furthermore, it is possible that the polarization grating is designed as a reflection phase grating, whose grating webs and grating gaps have different reflection properties.

[0019] In a preferred embodiment, the reflection phase grating can comprise at least the following components: a carrier substrate, a planar reflector layer arranged on the carrier substrate, a grid structure layer arranged above the reflector layer.

[0020] The lattice structure layer can have a layer thickness d, which is chosen according to the relationship d < 0.6 · λ, where λ indicates the wavelength of the light source used.

[0021] Furthermore, it can be provided that a planar phase-shifting layer is arranged between the planar reflector layer and the grid structure layer.

[0022] Furthermore, it is possible to that the reflector layer consists of a metallic reflector layer or a reflective layer stack, and that the lattice structure layer consists of a dielectric material of the group SiO2, TaOx, TiO2, Si, or of a semiconductor material of the group TiN, GaN, or of a layer stack with one or more of the aforementioned dielectric materials and one or more of the aforementioned semiconductor materials.

[0023] Advantageously, the polarization grating is designed such that the resulting + / -1 diffraction orders are polarized orthogonally to each other.

[0024] In a further embodiment of the optical position measuring device according to the invention, it is provided that a first object is connected to a first grating configured as a reflection phase grating or transmission phase grating, a second object is connected to a second grating functioning as a polarization grating configured as a reflection phase grating, wherein a beam of light emitted from the light source is split into two partial beams at the first grating, the partial beams then strike the second grating where each of the two partial beams undergoes diffraction and a change in direction, and wherein the partial beams are orthogonally polarized to each other after striking the second grating, the partial beams strike the first grating again and are recombined there, so that a resulting signal beam is then propagated in the direction of the detection unit.

[0025] Alternatively, it may also be provided that a first object is connected to a first grating acting as a measure, which is configured as a reflection phase grating or as a transmission phase grating; a second object is connected to a scanning unit, the scanning unit comprising the following components: a light source; a second grating acting as a scanning grating, which furthermore acts as a polarization grating and is configured as a reflection phase grating; a detection unit, wherein a beam of light emitted by the light source is split into two partial beams at the first grating, the partial beams then strike the second grating, where each of the two partial beams undergoes a change in direction, and wherein the partial beams are orthogonally polarized to each other after striking the second grating, the partial beams strike the first grating again and are recombined there.so that a resulting signal beam is then propagated towards the detection unit.

[0026] The measures according to the invention now make it possible to realize optical position measuring devices that do not require separate polarization-optical components in the scanning beam path for the polarization-coded generation of phase-shifted scanning signals. The desired polarization-optical effects on the signal-generating partial beams can be produced with the aid of a grating that, in addition to its usual function in the scanning beam path, also acts as a polarization grating. This enables a particularly compact design of the corresponding position measuring devices.

[0027] In contrast to the previously discussed variants for generating polarization-coded sampling signals without separate polarization-optical components, the solution according to the invention is not subject to any limiting boundary conditions, such as those relating to the angle of incidence of a beam to be split. Furthermore, unlike these solutions, the impairment of signal quality in the case of a changing sampling distance is eliminated. The generation of defined polarization states in the partial beams used for signal acquisition is fundamentally independent of the respective sampling distance in the solution according to the invention.

[0028] Even in optical position measuring devices where the split partial beams are not completely spatially separated, the measures according to the invention now enable the generation of polarization-coded scanning signals. This would not be possible using conventional methods, since polarization-optical components cannot be arranged in the overlapping partial beams within the scanning beam path. Continued: Original Page 10

[0029] Furthermore, the restriction to the required very small grating periods for beam deflection is also eliminated if, according to the state of the art, so-called high-frequency gratings are used as polarization gratings.

[0030] Further details and advantages of the present invention will be explained with reference to the following description of exemplary embodiments of the device according to the invention in conjunction with the figures. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] It shows Figure 1 shows a schematic representation of an optical position measuring device according to the prior art; Figure 2 shows the unfolded scanning beam path in an embodiment of the optical position measuring device according to the invention, designed as a so-called 3-grid encoder; Figures 3a and 3b each show a side view of an embodiment of an optical position measuring device according to the invention designed as a 3-grid encoder; Figure 4 shows a schematic representation of the detection unit of the embodiment from the Figures 3a, 3b Figure 5 shows a top view of the first grid of the exemplary embodiment, which serves as a dimensional representation. Figures 3a, 3b Figure 6a shows a partial top view of the second grating, which functions as a polarization grating, of the exemplary embodiment from the Figures 3a, 3b Figure 6: Detail view of the polarization grating. Figure 6a Figure 6 shows a partial sectional view of the polarization grating. Figure 6aFigures 7a-7e each show a detailed view of the unit cell of alternative embodiments of polarization gratings. DESCRIPTION OF THE EXECUTION FORMS

[0032] Based on the Figures 2 - 6c An embodiment of an optical position measuring device according to the invention is described below. This device is designed as a so-called 3-grid encoder, whose unfolded scanning beam path is Figure 2 This is illustrated. Figures 3a, 3b show various sectional views of a specific embodiment of such a 3-grid encoder, Figure 4 a detection unit of the same, Figure 5 a top view of the scale used and the Figures 6a - 6c Different representations of the polarization grating used in this example.

[0033] The corresponding position measuring device serves to detect the relative position of two objects moving relative to each other along at least one measuring direction x; these objects are not shown in the various figures. The objects moving relative to each other could, for example, be machine components that can be displaced along a straight measuring direction x. The sampling signals generated by the position measuring device regarding the relative position of the machine components are transmitted to a control unit, which can use them for motion control.

[0034] In general, a first object is connected to a first grating of the position measuring device, and a second object is connected to a second grating. At one of the gratings, an illumination beam emitted by a light source is split into at least two partial beams. As the scanning beams continue their paths, the partial beams undergo different polarization-optical effects and are finally recombined at a grating to form a resulting signal beam. From this signal beam, several phase-shifted, displacement- or position-dependent scanning signals can then be generated in a detection unit.Between the splitting and recombination of the partial beams, no separate polarizing optical components are arranged in the scanning beam paths. Instead, at least one of the gratings traversed acts as a polarizing grating to generate the different polarizing effects on the partial beams. The polarizing grating is designed such that diffraction orders with different polarization states result at each point of incidence on the grating. In principle, by appropriately designing the polarizing grating and selecting the corresponding grating parameters, it is possible to achieve a wide variety of polarization states in the diffracted partial beams. That is, the diffracted partial beams can be linearly, elliptically, or circularly polarized.When splitting an illumination beam into partial beams with different polarization states, it is further advantageous if the split partial beams are each polarized orthogonally to each other in the scanning beam path. In the case of linear polarization, this means that the polarization planes in the split partial beams are oriented perpendicular to each other; in the case of circular or elliptical polarization, orthogonal polarization means that the polarization orientation in the partial beams is opposite to each other.

[0035] The specific design of suitable polarization gratings and possible embodiments thereof will be explained in detail in the course of the following description.

[0036] In the 3-grid encoder according to the first embodiment, whose unfolded scanning beam path with the beam bundles used for signal generation in Figure 2As shown, the illumination beam B emitted by the light source LQ reaches a first grating G1 and is split by this grating into two partial beams TS1 and TS2, each propagating away from the optical axis OA. The illumination beam B is linearly polarized, as indicated by the double arrow; the two partial beams TS1 and TS2, split by the first grating G1, initially have the same polarization. Further along the scanning beam path, the two partial beams TS1 and TS2 then encounter a second grating G2, which in this example acts as a polarizing grating. The partial beams TS1 and TS2 are diffracted by the second grating G2 and undergo a change in direction, so that they subsequently propagate further as partial beams TS1' and TS2', each in the direction of the optical axis OA.In addition to changing the direction, the second grating G2, which serves as a polarization grating, causes the diffracted partial beams TS1', TS2' to have different polarization states after passing through or striking the grating G2 and to be orthogonally polarized to each other; in principle, as already mentioned above, the partial beams TS1', TS2' can be orthogonally linearly, orthogonally elliptically, or orthogonally circularly polarized to each other. In the example shown, an orthogonal circular polarization of the two partial beams TS1', TS2' is intended. At the third grating G3, the partial beams TS1', TS2' then finally recombine, and a signal beam S with superimposed partial beams TS1', TS2' of different polarizations propagates further towards a detection unit DET, via which the majority of phase-shifted sampling signals S1, S2, S3 are generated from the signal beam S.One possible embodiment of a suitable DET detection unit will be explained in detail in the following description.

[0037] The Figures 3a, 3b Figures 1 and 2 each show a specific embodiment of such a 3-grate encoder, designed as a reflected-light system, in various sectional views. As can be seen from these illustrations, the first grating illuminated by the beam B in the scanning beam path functions as a scale 10. Here, it is designed as a reflection phase grating with division zones 10.1, 10.2 arranged periodically along the measuring direction x, exhibiting different phase-shifting effects; a top view of the scale 10 is shown in Figure 3. Figure 5 shown. The scale body 10 is connected to a first object (not shown). The first grid, or scale body 10, is used as shown in the Figures 3a, 3bThe splitting of the illumination beam B into two partial beams TS1 and TS2 is evident. For the sake of clarity, further diffraction orders resulting from the diffraction and splitting of the illumination beam B at the first grating, which are not used for signal generation, are not shown in the figures.

[0038] In the present embodiment, all other components of the position measuring device according to the invention are arranged in a scanning unit 20, which is connected to the second object (also not shown). Along the specified measuring direction x, the two objects, and thus the measuring element 10 and the scanning unit 20, are arranged to be linearly displaceable relative to each other.

[0039] The scanning unit 20 comprises, in addition to the light source 21 and the detection unit 23, the second grating in the scanning beam path, which in this embodiment is also referred to as the scanning grating 22 and is designed here as a reflection phase grating. In the illustrated optical position measuring device, the scanning grating 22 functions as a polarization grating and, besides diffracting the incident, linearly polarized partial beams TS1, TS2 and causing a change in direction, results in the diffracted partial beams TS1', TS2' being orthogonally polarized to each other after impact on the scanning grating 22. In the illustrated example, this is done in the xz-plane according to the figure shown. Figure 3bDiffraction and back-reflection of the partial beam bundles TS1', TS2' in the direction of incidence are provided. This means that the partial beam bundles TS1, TS2 incident from the scale 10 strike the scanning grating 22 in the xz-plane at the so-called Littrow angle and are thus reflected back to the scale 10 in the xz-plane as partial beam bundles TS1', TS2' at the same angle. In this embodiment, the scale 10, which is struck a second time, serves as the third grating in the scanning beam path. At the scale 10, the partial beam bundles TS1', TS2' incident from the scanning grating 22 are recombined, so that a signal beam bundle S is subsequently propagated towards the detection unit 23. The detection unit 23 converts the signal beam S into three position-dependent sampling signals S1, S2, S3, each phase-shifted by 120° relative to the other, which are then used, for example,The data would be passed to a downstream control unit (not shown in the figures) for further processing. Alternatively, it would of course also be possible to generate four position-dependent sampling signals, each phase-shifted by 90° relative to the others.

[0040] One possible embodiment of a suitable detection unit 23 is shown in Figure 4The diagram is shown schematically. As can be seen, the signal beam S incident from the third grating in the scanning beam path or the measuring instrument, along with the superimposed partial beams TS1', TS2', first reaches a splitting grating 23.1 in the detection unit 23, which splits the signal beam S into three identical partial beams. The split partial beams then pass through three polarizers 23.2a, 23.2b, 23.2c, whose polarization directions are each rotated by 60° relative to each other. With the help of the optoelectronic detectors 23.3a, 23.3b, 23.3c arranged downstream of the polarizers 23.2a, 23.2b, 23.2c, the three partial beam bundles can then be converted into three shift-dependent sampling signals S 1 , S 2 , S 3, each phase-shifted by 120°, and made available for further processing.

[0041] Based on the Figures 6a - 6cAn exemplary embodiment of a polarization grating, such as that used in the optical position measuring device according to the Figures 2 - 5 It can be used as a second applied grating or scanning grating 22 in the scanning beam path. In the following description, the same reference numeral 22 is used for the polarization grating as was used for the scanning grating in the previous description.

[0042] As already explained above, the polarization grating 22 in the optical position measuring device according to the invention serves to exert defined polarization-optical effects on the split partial beams at each point of incidence on the grating, resulting in diffraction orders with different polarization states. This eliminates the need to provide separate polarization-optical components in the scanning beam path. Furthermore, such polarization gratings can also be used with 3-grating encoders according to [reference missing]. Figure 2It is now possible to implement a polarization-optical generation of phase-shifted sampling signals. Due to the typically small distances between the gratings in such systems, there is usually no spatial separation of the split partial beams in the region of the second grating; that is, they overlap in the region of the second grating. Because of this beam overlap, it would therefore not be possible to implement a polarization-optical generation of phase-shifted sampling signals in the conventional way, i.e., using polarization-optical components in the partial beams.

[0043] The corresponding polarization grating 22 in the optical position measuring device according to the invention is designed such that diffraction orders with different polarization states result at each point of incidence on the grating. Preferably, the polarization grating 22 is designed such that the resulting + / - 1st diffraction orders are polarized orthogonally to each other.

[0044] As can be seen from the partial top view of an embodiment of a suitable polarization grating 22 in Figure 6a and in particular from the detailed view of the unit cell of such a polarization grating in Figure 6b As can be seen, the polarization grating 22 comprises a plurality of arc-shaped curved grating structures in the form of grating gaps 22.1 and grating webs 22.2.

[0045] In the present embodiment, the polarization grating 22 is designed as a reflection phase grating. This means that the alternately arranged grating structures or grating gaps 22.1 and grating webs 22.2 have different reflection properties, in particular exert different phase-shifting effects on the incident partial beams.

[0046] The longitudinal direction of the lattice structures, or lattice gaps 22.1 and lattice webs 22.2, is as shown in the Figures 6a, 6bThe grid structures are oriented parallel to the measurement direction x. Both along and perpendicular to the measurement direction x, the grid structures are arranged periodically. Along and parallel to the measurement direction x, a plurality of grid sections 22a, 22b, 22c, 22d are provided, arranged periodically with a measurement direction periodicity Λ; their longitudinal extent is oriented perpendicular to the measurement direction x, i.e., in the specified y-direction. Within the respective grid sections 22a, 22b, 22c, 22d, the arc-shaped grid structures are arranged periodically with an orthogonal periodicity Λ_ortho. It proves particularly advantageous if the orthogonal periodicity Λ_ortho in the polarization grid 22 is selected according to the following relationship 1): ∧ _ortho < 1.5 ⋅ λ with: Λ_ortho := Orthogonal periodicity of the grating structures in the polarization grating λ := Wavelength of the light source used

[0047] By adhering to equation 1), it can be ensured that the corresponding polarization grating 22 exhibits only a weak diffraction effect on the incident partial beams in a direction orthogonal to the principal diffraction direction. The principal diffraction direction lies in the xz-plane, and the diffraction direction orthogonal to it lies in the yz-plane. In this embodiment, diffraction in the xz-plane is crucial for generating the displacement-dependent sampling signals; otherwise, a strong diffraction effect along other planes would result in a reduction of the signal intensity and the polarization effect.

[0048] The curved grating structures or grating gaps 22.1 and grating webs 22.2 of the polarization grating 22 can be determined in the case of a given coordinate system according to the Figures 6a, 6b for example, analytically described by one of the following relationships 2a), 2b): Y = ∧ / π ⋅ ln 1 / cos x ⋅ π / ∧ with: Λ := Measurement direction periodicity of the grid sections x := Measurement direction Y := Longitudinal direction of the grid sections Y=sqrt∧ / 22−x2 with: Λ := Measurement direction periodicity of the grid sections x := Measurement direction Y := Longitudinal direction of the grid sections

[0049] Here, relationship 2a) characterizes a catenary-shaped lattice structure, and relationship 2b) a circular-shaped lattice structure. As can be seen in particular from... Figure 6a As can be seen in the illustrated embodiment, straight grid bars 22.2a, 22.2b, 22.2c are arranged between adjacent grid sections 22a, 22b, 22c, 22d in the x-direction. The straight grid bars 22.2a, 22.2b, 22.2c have an elongated rectangular shape, with the longitudinal axis of the rectangle extending perpendicular to the measuring direction x, i.e., along the y-direction.

[0050] Alternatively, it is also possible that lattice gaps are arranged between adjacent lattice sections 22a, 22b, 22c, 22d, or that several lattice bars and lattice gaps are arranged alternately adjacent to each other. Furthermore, it is also possible that neither separate lattice gaps nor lattice bars are arranged in these areas, but instead the lattice structures of adjacent lattice sections 22a, 22b, 22c, 22d border each other.

[0051] It is also advantageous if the area fill ratio FV of the polarization grating 22 is chosen according to the following relationship 3): FV < 0.6 where: FV := ratio of the area of ​​the grating bars in a polarization grating unit cell to the total area of ​​the polarization grating unit cell

[0052] Polarization gratings of this size are easier to clean. Furthermore, this ensures that the different grating structures are sufficiently separated from one another; this prevents unwanted coupling effects between adjacent grating structures, which would otherwise lead to a weakening of the intensities in the + / - 1st diffraction orders.

[0053] In connection with the specific grating structure of the polarization grating 22 and suitable materials for such gratings, reference should be made to the presentation of the Figure 6c referenced, which shows a partial sectional view of the polarization grating 22 from the Figures 6a, 6bin the xz-plane. As mentioned above, this embodiment of a polarization grating 22 is designed as a reflection phase grating. It comprises a support substrate 22.10 on which a reflector layer 22.11 is arranged over a planar area. Above the reflector layer 22.11, a planar phase-shifting layer 22.12 is also provided in this example, on which the grating structure layer 22.13 is then arranged, in which the grating structures with the corresponding grating webs 22.2 and grating gaps 22.1 are formed in the geometry or arrangement already described above.

[0054] It proves advantageous in such a construction of the polarization grating 22 if the grating structure layer 22.13 has a layer thickness d which is selected according to the following relationship 4): d < 0.6 ⋅ λ with: d := layer thickness of the lattice structure layer λ := wavelength of the light source used

[0055] In this embodiment, quartz glass or Zerodur is suitable as the support substrate 22.10 for the polarization grating 22.

[0056] The reflector layer 22.11 can be designed as a metallic reflector layer or as a reflective layer stack consisting of several layers with high- and low-refractive-index materials, e.g., TaO₂, TiO₂, Si as high-refractive-index materials and, for example, SiO₂ as a low-refractive-index material. SiO₂ is a suitable material for the phase-shifting layer 22.12.

[0057] With regard to the formation of the lattice structure layer 22.12, it may be provided that a dielectric material from the group SiO₂, TaOₓ, TiO₂, Si is used for this purpose; however, it is also possible to use a semiconductor material such as TiN or GaN or metals with high conductivity such as Al, Ag, Au. Alternatively, the lattice structure layer 22.13 can also consist of a layer stack in which one or more of the aforementioned dielectric materials or semiconductor materials are used.

[0058] In another alternative embodiment, the polarization grating designed as a reflection phase grating can comprise only a support substrate with a reflector layer arranged on it, above which a structured phase-shifting layer is arranged. In this case, the properties described in the example of the Figure 6cThe separate phase-shifting and lattice structure layers provided for are formed together in a single layer, namely in the form of one or more structured layers that are applied directly to the reflector layer without an additional phase-shifting layer.

[0059] To achieve the desired polarization effect of the corresponding polarization grating, in addition to the specific geometry and arrangement of the grating structures, the grating parameters structure width and etching depth, the materials used must of course also be appropriately selected.

[0060] In the Figures 7a - 7e The figures show views of unit cells of alternative embodiments of polarization gratings that can be used in the optical position measuring device according to the invention.

[0061] At the in Figure 7aIn the depicted variant of a polarization grating 122, the grating structures in the form of grating gaps 122.1 and grating bars 122.2 are catenary-shaped and extend in the x-direction to the edge of the unit cell. These grating structures can be characterized analytically by the above relationship 2a).

[0062] In Figure 7b A unit cell of another polarization grating 222 is shown, in which the arc-shaped grating structures or grating gaps 222.1 and grating webs 222.2 are formed in a circular shape and are cut off in the x-direction at the edges of the unit cell.

[0063] At the in Figure 7c In the unit cell of a polarization grating 322 shown, the catenary-shaped grating structures or grating gaps 322.1 and grating webs 322.2 are formed from discrete linear sections.

[0064] A slightly modified variant of the unit cell of a polarization grating 422 of the embodiment from Figure 7c is finally in Figure 7d illustrated. In this polarization grating 422, the adjacent linear sections of the grating structures or grating gaps 422.1 and grating webs 422.2 also exhibit an additional offset.

[0065] In Figure 7e Finally, another variant of a unit cell of a polarization grating 522 is shown. In this example, the arc-shaped grating structures in the form of grating gaps 522.1 and grating webs 522 are partially interrupted. For example, the central grating web 522.2 in the unit cell has two interruptions 522.2a, 522.2b.

[0066] The variants in the Figures 7b - 7e These designs prove to be particularly advantageous due to their simpler manufacturability; lattice areas with extremely fine structuring can be avoided in these embodiments.

[0067] In addition to the specific embodiments described, there are of course further embodiment possibilities within the scope of the present invention.

[0068] It is also possible to design the optical position measuring device according to the invention for detecting rotational relative movements of two objects.

[0069] Furthermore, in the case of a 3-grid encoder design, it is by no means mandatory that the first grating (the scale) and the second grating (the scanning or polarizing grating) be reflective. The first grating can, of course, be a transmission phase grating and the second grating can also be a transmission phase grating; likewise, mixed configurations with reflection and transmission phase gratings are possible, such as a transmission scanning or polarizing grating and a reflective scale, or a transmission scanning or polarizing grating and a reflective polarizing grating, etc.

[0070] If the polarization grating is implemented transmittively as a transmission phase grating, it can, for example, comprise a transparent support substrate into which the grating structures are etched. Alternatively, it is also possible to deposit a separate grating structure layer made of dielectric or semiconductor material onto the transparent support substrate, in which the respective grating structures are formed. This grating structure layer can itself be formed from a suitable stack of layers.

[0071] Furthermore, it is of course possible to provide other scanning beam paths in the optical position measuring device according to the invention, in addition to the described scanning according to a 3-grating scanning principle. For example, in so-called strip encoders, such as those known from WO 2008 / 138501 A1 or EP 2450672 A2, one of the gratings can be designed as a polarization grating to enable the polarization-optical generation of phase-shifted scanning signals; an arrangement of additional or separate polarization-optical components is then no longer necessary. In such systems, the first grating can be designed as a reflection phase grating or as a transmission phase grating, and the second grating as a reflection phase grating; the second grating functions as a polarization grating.

[0072] However, with both this scanning principle and other optical scanning principles, any of the applied gratings can alternatively be designed as a polarization grating.

Claims

1. Optical position measuring device for detecting the relative position of two objects which are movable relative to one another along at least one measurement direction (x) and are connected to a first grating and a second grating, wherein an illumination beam emitted by a light source is split into at least two partial beams at a grating, the partial beams experience different polarization-optical effects and after recombination of the differently polarized partial beams at a grating, from the resulting signal beam, a plurality of phase-shifted, shift-dependent scanning signals are generable in a detection unit, wherein in the scanning beam paths of the partial beams between splitting and recombination no separate polarization-optical components are arranged and at least one of the traversed gratings is configured as a polarization grating for generating the different polarization-optical effects on the partial beams, characterized - in that the polarization grating (22; 122; 222; 322; 422; 522) is configured in such a way that orders of diffraction with different polarization states result spatially independently on the polarization grating (22; 122; 222; 322; 422; 522), and - in that the polarization grating (22; 122; 222; 322; 422; 522) has grating structures arranged periodically both along the measurement direction (x) and orthogonally to the measurement direction (x) and wherein the orthogonal periodicity (A_ortho) is selected according to ∧ _ortho < 1.5 ⋅ λ , where Λ_ortho := orthogonal periodicity of the grating structures A := wavelength of the light source used.

2. Optical position measuring device according to Claim 1, characterized in that the polarization grating (22; 122; 222; 322; 422; 522) comprises a plurality of arcuately curved grating structures in the form of grating ridges (22.2; 122.2; 222.2; 322.2; 422.2; 522.2) and grating gaps (22.1; 122.1; 222.1; 322.1; 422.1; 522.1), the longitudinal extension direction of each of which is oriented parallel to the measurement direction (x).

3. Optical position measuring device according to Claim 2, characterized in that the polarization grating (22; 122; 222; 322; 422; 522) has strip-shaped grating sections (22a, 22b, 22c, 22d) arranged parallel to the measurement direction (x) periodically with a measurement direction periodicity (Λ), the longitudinal extension direction of said grating sections being oriented perpendicular to the measurement direction (x), wherein in the grating sections (22a, 22b, 22c, 22d) the grating structures are arranged perpendicular to the measurement direction (x) periodically with the orthogonal periodicity (Λ_ortho).

4. Optical position measuring device according to Claim 2 or 3, characterized in that between adjacent grating sections (22a, 22b, 22c, 22d) of the polarization grating (22; 122; 222; 322; 422; 522) - a grating gap is arranged, or - a grating ridge is arranged, or - a plurality of grating gaps and grating ridges are arranged alternately adjacently.

5. Optical position measuring device according to Claim 2 or 3, characterized in that grating structures of adjacent grating sections adjoin one another.

6. Optical position measuring device according to at least one of the preceding claims, characterized in that the area filling ratio FV of the polarization grating (22; 122; 222; 322; 422; 522) is selected according to the relation FV < 0.6, wherein the area filling ratio FV is defined as the ratio of the area of the grating ridges (22.2; 122.2; 222.2; 322.2; 422.2; 522.2) in a polarization grating unit cell to the total area of the polarization grating unit cell.

7. Optical position measuring device according to at least one of the preceding claims, characterized in that the polarization grating (22; 122; 222; 322; 422; 522) is configured as a reflection phase grating, the grating ridges (22.2; 122.2; 222.2; 322.2; 422.2; 522.2) and grating gaps (22.1; 122.1; 222.1; 322.1; 422.1; 522.1) of which have different reflection properties.

8. Optical position measuring device according to Claim 7, characterized in that the reflection phase grating comprises at least the following components: - a carrier substrate (22.10), - a planar reflector layer (22.11) arranged on the carrier substrate (22.10), - a grating structure layer (22.13) arranged above the reflector layer (22.11).

9. Optical position measuring device according to Claim 8, characterized in that the grating structure layer (22.13) has a layer thickness d selected according to the relation d < 0.6 - λ, where λ indicates the wavelength of the light source (LQ; 21) used.

10. Optical position measuring device according to Claim 8, characterized in that a planar phase shifting layer (22.12) is arranged between the planar reflector layer (22.11) and the grating structure layer (22.12).

11. Optical position measuring device according to Claim 8, characterized - in that the reflector layer (22.11) consists of a metallic reflector layer or of a reflective layer stack, and - in that the grating structure layer (22.13) consists of a dielectric material from the group SiO2, TaOx, TiO2, Si, or of a semiconductor material from the group TiN, GaN, or of a layer stack comprising one or more of the aforementioned dielectric materials and one or more of the aforementioned semiconductor materials.

12. Optical position measuring device according to at least one of the preceding claims, characterized in that the polarization grating (22; 122; 222; 322; 422; 522.1) is configured in such a way that resulting + / -1st orders of diffraction are polarized orthogonally to one another.

13. Optical position measuring device according to at least one of the preceding claims, characterized in that - a first object is connected to a first grating configured as a reflection phase grating or a transmission phase grating, - a second object is connected to a second grating, which functions as a polarization grating (22; 122; 222; 322; 422; 522) and is configured as a reflection phase grating, - wherein a beam (B) emitted by the light source (21) is split into two partial beams (TS1, TS2) at the first grating, - the partial beams (TS1, TS2) subsequently impinge on the second grating, where each of the two partial beams (TS1, TS2) experiences diffraction and a change in direction, and wherein the partial beams (TS1', TS2') are polarized orthogonally to one another after impinging on the second grating, - the partial beams (TS1', TS2') are incident on the first grating (10) again and are recombined there, so that a resulting signal beam (S) subsequently propagates in the direction of the detection unit (23).

14. Optical position measuring device according to at least one of Claims 1 - 12, characterized in that - a first object is connected to a first grating (G1), which functions as a material measure (10) and is configured as a reflection phase grating or as a transmission phase grating, - a second object is connected to a scanning unit (20), wherein the scanning unit (20) comprises the following components: - a light source (LQ; 21), - a second grating (G2), which functions as a scanning grating, furthermore acts as a polarization grating (22; 122; 222; 322; 422; 522) and is configured as a reflection phase grating, - a detection unit (DET; 23), - wherein a beam (B) emitted by the light source (LQ; 21) is split into two partial beams (TS1, TS2) at the first grating (G1), - the partial beams (TS1, TS2) subsequently impinge on the second grating (G2), where each of the two partial beams (TS1, TS2) experiences a change in direction, and wherein the partial beams (TS1', TS2') are polarized orthogonally to one another after impinging on the second grating (G2), - the partial beams (TS1', TS2') are incident on the first grating (G1) again and are recombined there, so that a resulting signal beam (S) subsequently propagates in the direction of the detection unit (DET; 23).