Optical position measuring device

Abstract

The present invention relates to an optical position measuring device for detecting the relative position of two objects that can be moved relative to each other along at least one measuring direction, wherein the objects are connected to a first grating and to a second grating. Here, a light irradiation beam emitted by a light source is split into at least two sub-beams at a grating; the sub-beams are subjected to different polarization optical effects in the subsequent course of a scanning light path. After the sub-beams polarized in different ways are recombined at a grating, a plurality of phase-shifted, displacement-related scanning signals can be generated from the resulting signal beam in a detection unit. In the scanning light path of the sub-beams, no separate polarization optical device is arranged between the splitting and the recombination, and at least one of the gratings passed through is used as a polarization grating for generating different polarization optical effects on the sub-beams. Here, the polarization grating is designed so that diffraction orders with different polarization states are obtained at each incident location on the grating.

Description

Technical Field

[0001] The invention relates to an optical position measuring device for detecting the relative position of two objects which can be moved relative to each other. Background Art

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

[0003] exist Figure 1 The schematic diagram of the unfolded scanning beam path in FIG. 1 shows the principle on which the signal generation according to EP 0 481 356 A2 is based. Here, the gratings A, M can be arranged together to be movable relative to the remaining components L1, L2, AO along a specified measuring direction x. The beam incident from the left and polarized in a defined manner by the polarizer P1 is first split into two sub-beams by the grating A. Figure 1 It can be seen that separate polarization optical components, for example λ / 4 plates PE1, PE2 with different orientations, are introduced into the optical path of the sub-beams to be interfered, in which the position information is encoded. The λ / 4 plates PE1, PE2 polarize the two sub-beams passing through to be orthogonal to each other, i.e. the two sub-beams are then, for example, left-right circularly polarized. The two sub-beams are then superimposed to form a common signal beam (0) and split into three or more superimposed sub-beams I90, I210, I330 in a subsequent detection unit or evaluation optical device AO. After passing through the differently oriented polarizers P90, P210, P330, scanning signals S90, S210, S330 are finally generated at the detector elements D90, D210, D330, each of which is phase-shifted by 120°, and these scanning signals are further processed in a known manner. Typically, in addition to the λ / 4 plates PE1 , PE2 , further polarization optics in the form of polarizers P2 , P3 are arranged in the beam paths of the split sub-beams in order to compensate for the erroneous polarization caused by the gratings A, L1 , L2 previously passed through by the sub-beams.

[0004] The disadvantage of this polarization-optical generation of multiple phase-shifted, displacement-dependent scanning signals is that separate or additional optical elements, such as a λ / 4 plate and a polarizer, must be introduced into the scanning beam path or into the scanning gap between two components that move relative to each other. Such additional components can cause problems if the structural volume of the corresponding optical position measuring device is limited or the scanning distance is small. If the position measuring device is designed similarly to the principle known from WO 2008 / 138501 A1, then Figure 1The components A, M and L1, L2 in the embodiment are designed as two mutually movable physical measuring tools. In this case, mechanical fixing of the fixed polarization optical device located between them is usually not feasible.

[0005] Furthermore, the additional polarization optics in the scanning beam path also place higher demands on the flatness, parallelism and homogeneity of the carrier structures used; drift-free and stable mounting surfaces are required to accommodate the carrier structures. Possible material defects can only be compensated for with considerable additional effort via corresponding calibration methods. This applies in particular when long, translationally invariant scales are used in corresponding position measuring devices.

[0006] Furthermore, due to the additionally required polarization optics in the scanning beam path, other system properties, such as the natural frequency or the air flow in the scanning gap, also have a wide-ranging influence.

[0007] In the patent DE 10 2010 063 253 A1 of the present applicant, an optical position measuring device has been proposed, which generates a phase-shifted scanning signal in a polarization-optical manner without a separate or additional polarization optical device in the scanning light path. According to this solution, the required polarization optical device is integrally formed in other components of the scanning light path, for example in the form of a high-frequency grating with a periodically varying structure. In such a position measuring device, the components used have position-dependent polarization characteristics in the measuring direction; for example, it can be proposed here that a physical measuring tool is used as a polarization grating. The physical measuring tool is then composed of, for example, a plurality of locally variable layers and includes a high-frequency grating with a graduation period dR<λ / 2, which has only the 0th diffraction order and produces a polarization-optical function. Here, the grating direction of the high-frequency grating is with a polarization period d P The polarization period must be significantly larger than the width hw of the illuminated area of ​​the physical gauge. Spot , which limits the lower limit of the signal period SP of the scan signal that can be generated; that is, the relationship d P >hw Spot The sub-beams incident on different points of the physical measuring tool are therefore subjected to locally different polarization optical effects, wherein the polarization change must be precisely matched to the corresponding scanning distance. For this purpose, the spacing of the incident points of the sub-beams is selected such that the spacing corresponds to half the grating period of the physical measuring tool. In the case of a change in the scanning distance, the degree of modulation of the scanning signal is impaired and other signal characteristics are also changed.

[0008] Finally, another optical position measuring device has been disclosed from the patent DE 10 2014 211 004 A1 of the present applicant, which generates a phase-shifted scanning signal in a polarization optical manner without an additional discrete polarization optical device in the scanning light path. According to this document, the diffraction of the light at the side of the scanning plate or the physical measuring tool of the optical position measuring device can be used under certain conditions to set a specific polarization state in the diffracted sub-beam. However, for this purpose, on the one hand, it is necessary to comply with the specific incident conditions of the beam to be split; on the other hand, the corresponding grating must have an extremely small grating period in order to set the desired polarization characteristics in the diffracted sub-beam. As a result, this feasibility scheme for generating polarization optical effects on sub-beams is subject to certain restrictions and cannot be used for all scanning principles. Summary of the invention

[0009] The object of the invention is to provide an optical position measuring device which, in order to generate phase-shifted scanning signals in a polarization-optical manner, does not require additional polarization optics in the scanning beam path and can use different optical scanning principles. The polarization states set in the different sub-beams remain largely unchanged even in the case of changes in the scanning characteristics, thus ensuring that the quality of the generated scanning signals remains unchanged.

[0010] According to the invention, this object is achieved by the optical position-measuring device according to the invention.

[0011] Advantageous embodiments of the optical position-measuring device according to the invention result from the measures implemented in the individual exemplary embodiments.

[0012] The optical position measuring device according to the present invention is used to detect the relative position of two objects that can move relative to each other along at least one measuring direction, and the objects are connected to a first grating and a second grating. At a grating, the light irradiation beam emitted by a light source is split into at least two sub-beams; the sub-beams are subjected to different polarization optical effects in the subsequent course of the scanning light path, and after the sub-beams with different polarizations are recombined at a grating, a plurality of phase-shifted, displacement-related scanning signals can be generated from the obtained signal beam in the detection unit. No separate polarization optical device is arranged between the splitting and the recombination in the scanning light path of the sub-beams. At least one of the gratings passed through is designed as a polarization grating for producing different polarization optical effects on the sub-beams. Here, the polarization grating is designed so that diffraction orders with different polarization states are obtained at each incident location on the grating.

[0013] It can be provided that the polarization grating comprises a plurality of arcuately curved grating structures in the form of grating webs and grating slits, the longitudinal extension directions of the grating structures being respectively oriented parallel to the measuring direction, and wherein the grating structures are arranged periodically along the measuring direction and perpendicularly thereto.

[0014] It is possible here that the polarization grating has, parallel to the measuring direction, strip-shaped grating segments which are arranged periodically in the measuring direction and whose longitudinal extension is oriented perpendicular to the measuring direction, wherein in the grating segments the grating patterns are arranged perpendicular to the measuring direction with an orthogonal periodicity.

[0015] Furthermore, it can be provided that between adjacent grating segments of the polarization grating: grating slits; or grating webs; or a plurality of grating slits and grating webs are arranged alternately adjacent to each other.

[0016] As an alternative to this, it is possible for the grating structures of adjacent grating segments to adjoin one another.

[0017] In an advantageous embodiment, the orthogonal periodicity Λ_ortho is selected according to the relation Λ_ortho<1.5·λ, wherein λ specifies the wavelength of the light source used.

[0018] Furthermore, it can be provided that the surface fill factor FV of the polarization grating is selected according to the relationship FV<0.6, wherein the surface fill factor FV is defined as the ratio of the area of ​​the grating webs in a polarization grating cell to the total area of ​​the polarization grating cell.

[0019] It is therefore possible to design the polarization grating as a reflective phase grating, whose grating webs and grating slits have different reflection properties.

[0020] In a preferred embodiment, the reflective phase grating comprises at least the following components: a carrier substrate, a planar reflector layer arranged on the carrier substrate, and a grating structure layer arranged on the reflector layer.

[0021] In this case, the grating structure layer can have a layer thickness d, which is selected in accordance with the relationship d<0.6·λ, wherein λ designates the wavelength of the light source used.

[0022] Furthermore, it can be provided that a planar phase shifting layer is arranged between the planar reflector layer and the grating structure layer.

[0023] It is also possible that the reflector layer consists of a metallic reflector layer or of a reflective layer stack and the grating structure layer consists of a metal from the group consisting of SiO2, TaO x , TiO2, Si or a semiconductor material from the group: TiN, GaN or a layer stack having one or more of the above dielectric materials and one or more of the above semiconductor materials.

[0024] Advantageously, the polarization grating is designed such that the resulting + / -1st diffraction orders are polarized orthogonally to one another.

[0025] In another embodiment of the optical position measuring device according to the present invention, it is proposed that: a first object is connected to a first grating, the first grating is designed as a reflection phase grating or a transmission phase grating, and a second object is connected to a second grating acting as a polarization grating, the second grating is designed as a reflection phase grating, wherein the beam emitted by the light source is split into two sub-beams at the first grating, and the sub-beams are subsequently loaded onto the second grating, where each of the two sub-beams is diffracted and changes direction, and wherein the sub-beams are polarized orthogonally to each other after being loaded onto the second grating, and the sub-beams are re-projected onto the first grating and recombined there, so that the resulting signal beam then propagates in the direction of the detection unit.

[0026] Alternatively, it can also be provided that the first object is connected to a first grating acting as a material measure, the first grating being designed as a reflection phase grating or a transmission phase grating, and the second object is connected to a scanning unit, wherein the scanning unit comprises the following components: a light source; a second grating acting as a scanning grating, the second grating also acting as a polarization grating and being designed as a reflection phase grating; a detection unit, wherein the beam emitted by the light source is split into two sub-beams at the first grating, the sub-beams are then impinged upon the second grating, where each of the two sub-beams undergoes a change in direction, and wherein the sub-beams are polarized orthogonally to each other after impinging upon the second grating, the sub-beams are re-impacted on the first grating and recombined there, so that the resulting signal beam then propagates in the direction of the detection unit.

[0027] The measures according to the invention thus provide an optical position measuring device which does not require separate polarization optics in the scanning beam path for polarization-encoded generation of phase-shifted scanning signals. The desired polarization-optical effect on the signal-generating sub-beams can be achieved with the aid of a grating which, in addition to its usual function, also acts as a polarization grating in the scanning beam path. This allows a particularly compact design of the corresponding position measuring device.

[0028] Compared to the previously discussed variant for generating polarization-coded scanning signals without separate polarization optics, the solution according to the invention is not subject to boundary conditions, such as those which exist in the variant, for example, with regard to the angle of incidence of the beam to be split. Furthermore, compared to this solution, impairments to the signal quality are eliminated in the case of changes in the scanning distance. The generation of defined polarization states in the sub-beams for signal gain is, in principle, independent of the corresponding scanning distance in the solution according to the invention.

[0029] The measures according to the invention therefore also make it possible to generate polarization-coded scanning signals in optical position-measuring devices in which the split sub-beams do not extend completely spatially separated. This is not possible in conventional ways, since polarization optics cannot be arranged in the scanning beam path in the superimposed sub-beams.

[0030] Furthermore, the restriction to the extremely small grating period required for beam deflection is also eliminated when so-called high-frequency gratings are used as polarization gratings according to the prior art. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Further details and advantages of the invention are explained with the aid of the following description of exemplary embodiments of the device according to the invention in conjunction with the drawings.

[0032] The accompanying drawings show:

[0033] Figure 1 A schematic diagram showing an optical position measuring device according to the prior art;

[0034] Figure 2 The scanning beam path included in one embodiment of the optical position measuring device according to the present invention, which is designed as a so-called three-grating encoder, is shown;

[0035] Figure 3a , 3b Side views of embodiments of the optical position measuring device according to the present invention, which is designed as a three-grating encoder, are respectively shown;

[0036] Figure 4 Show Figure 3a , 3b A schematic diagram of a detection unit of an embodiment of the present invention;

[0037] Figure 5 Show Figure 3a , 3b A top view of a first grating acting as a physical gauge in the embodiment of FIG.

[0038] Figure 6a Show Figure 3a , 3b A partial top view of a second grating acting as a polarization grating in the embodiment;

[0039] Figure 6b Show Figure 6a Detail of the polarization grating in Figure 1;

[0040] Figure 6c Show Figure 6a Partial cross-section of the polarization grating in ;

[0041] Figure 7a-7eA detailed view of a cell of an alternative embodiment of a polarization grating is shown in each case. DETAILED DESCRIPTION

[0042] Below, according to Figure 2-6c An embodiment of the optical position measuring device according to the present invention is described below. The optical position measuring device is designed as a so-called three-grating encoder. Figure 2 The expanded scanning optical path of the three-grating encoder is shown in FIG. Figure 3a , 3b Different cross-sectional views showing a specific embodiment of such a three-grating encoder, Figure 4 The detection unit is shown. Figure 5 A top view of the solid gauge used is shown and Figure 6a-6c Different views of the polarization grating used in this example are shown.

[0043] A corresponding position measuring device is used to detect the relative position of two objects that can be moved relative to one another along at least one measuring direction x; these objects are not shown in the various figures. The objects that can be moved relative to one another can be, for example, machine parts that can be moved relative to one another along a linear measuring direction x. The scanning signals generated by the position measuring device and relating to the relative position of the machine parts are transmitted to a control unit, which can use the scanning signals to control the movement.

[0044] Here, usually, the first object is connected to the first grating of the position measuring device, and the second object is connected to the second grating. At one of the gratings, the light irradiation beam emitted by the light source is split into at least two sub-beams. In the further course of the scanning light path, the sub-beams are subjected to different polarization optical effects and finally recombined at a grating to form a signal beam. Finally, a plurality of phase-shifted scanning signals related to the displacement or position can be generated from the signal beam in the detection unit. Here, no separate polarization optical device is arranged in the scanning light path between the splitting and recombining of the sub-beams, more precisely, at least one of the gratings passed through acts as a polarization grating to generate different polarization optical effects on the sub-beams. Here, the polarization grating is designed so that diffraction orders with different polarization states are obtained at each incident location on the grating. In principle, here, various polarization states can be set in the diffracted sub-beams by appropriately forming the polarization grating and selecting the corresponding grating parameters. That is to say, the diffracted sub-beams can be linearly polarized, elliptically polarized or circularly polarized. In the case of splitting the illumination beam into sub-beams with different polarization states, it is also advantageous if the split sub-beams are respectively polarized orthogonally to one another in the scanning beam path. In the case of linear polarization, this means that the polarization planes in the split sub-beams are oriented perpendicularly to one another; in the case of circular polarization or elliptical polarization, orthogonal polarization can be understood as: the polarization directions in the sub-beams are oriented oppositely to one another.

[0045] The specific design of a suitable polarization grating and its possible implementation will be explained in detail in the following description.

[0046] In the three-grating encoder according to the first embodiment, Figure 2 , the expanded scanning light path of the three-grating encoder and the beams used to generate signals are shown in FIG. The light beam B emitted by the light source LQ reaches the first grating G1 and is split into two sub-beams TS1 and TS2 via the first grating. The sub-beams propagate away from the optical axis OA. Here, the light beam B is linearly polarized as indicated by the double arrows; the two sub-beams TS1 and TS2 split via the first grating G1 initially have the same polarization. In the further course of the scanning light path, the two sub-beams TS1 and TS2 then impinge on the second grating G2, which acts as a polarization grating in this example. Via the second grating G2, the sub-beams TS1 and TS2 are diffracted and change direction at this point, so that the sub-beams then continue to propagate in the direction of the optical axis OA as sub-beams TS1' and TS2', respectively. In addition to the change in direction, the second grating G2 used as a polarization grating makes the diffracted sub-beams TS1', TS2' have different polarization states and are orthogonally polarized to each other after passing through or loading the grating G2; in principle, as mentioned above, the sub-beams TS1', TS2' can be orthogonally linearly polarized, orthogonally elliptically polarized or orthogonally circularly polarized to each other. In the example shown, two sub-beams TS1', TS2' are provided with orthogonal circular polarization. Then, the sub-beams TS1', TS2' arrive at the third grating G3 and finally recombine, and the signal beam S with the superimposed sub-beams TS1', TS2' of different polarizations continues to propagate in the direction of the detector unit DET, and a plurality of phase-shifted scanning signals S1, S2, S3 are generated from the signal beam S via the detector unit. A feasible embodiment of a suitable detection unit DET will be explained in detail in the following description.

[0047] Figure 3a , 3b Different cross-sectional views of a specific embodiment of such a three-grating transmitter are shown, which is designed as a reflected light system. As can be seen from this view: the first grating loaded by the light beam B acts as a physical measure 10 in the scanning light path. The physical measure is designed as a reflection phase grating, which has graduation areas 10.1 and 10.2 arranged periodically along the measuring direction x, and these graduation areas have different phase offset effects; Figure 5 A top view of the physical measuring tool 10 is shown in FIG. The physical measuring tool 10 is connected to a first object (not shown). Figure 3a , 3bAs can be seen in FIG. 1 , the illumination beam B is split into two sub-beams TS1, TS2 via the first grating or material measure 10. For the sake of clarity, other diffraction orders generated when the illumination beam B is diffracted and split at the first grating are not shown in the figure and are not used to generate signals.

[0048] In the present exemplary embodiment, all other components of the position measurement according to the invention are arranged in the scanning unit 2, which is connected to a second object (also not shown). Two objects and thus the measuring tool 10 and the scanning unit 20 are arranged linearly movable relative to each other along the indicated measuring direction x.

[0049] In addition to the light source 21 and the detection unit 23, the scanning unit 20 also includes a second grating loaded in the scanning light path, which is also referred to as a scanning grating 22 in this embodiment and is designed as a reflection phase grating. The scanning grating 22 acts as a polarization grating in the optical position measuring device shown, and in addition to diffracting the linearly polarized sub-beams TS1 and TS2 incident thereon and causing a change in direction, the scanning grating causes the diffracted sub-beams TS1' and TS2' to be polarized orthogonally to each other after loading the scanning grating 22. In the example shown, here, in the xz plane according to Figure 3b The diffraction and back reflection of the sub-beams TS1' and TS2' in the incident direction are provided. That is to say, starting from the physical measuring tool 10, the incident sub-beams TS1 and TS2 are incident on the scanning grating 22 at the so-called Littrow angle (Littrow-Winkel) in the xz plane and then reflected back to the physical measuring tool 10 at the same angle as the sub-beams TS1' and TS2' in the xz plane. Therefore, in this embodiment, the physical measuring tool 10 loaded for the second time is used as the third grating in the scanning light path. The sub-beams TS1' and TS2' incident from the scanning grating 22 are recombined at the physical measuring tool 10, so that the signal beam S then propagates in the direction of the detection unit 23. Via the detection unit 23, the signal beam S is converted into three position-related scanning signals S1, S2, and S3 that are phase-shifted by 120° from each other, and the scanning signals are then transmitted, for example, to a control unit (not shown in the drawings) arranged downstream for further processing. As an alternative thereto, it is of course also possible to generate four position-dependent scanning signals which are each phase-shifted by 90° with respect to one another.

[0050] exist Figure 4A possible embodiment of a suitable detection unit 23 is shown in schematic form in FIG. As can be seen therein, the signal beam S with superimposed sub-beams TS1', TS2', which is incident from a third grating through which the scanning beam path or the material measure is passed, first reaches the beam splitting grating 23.1 in the detection unit 23, which splits the signal beam S into three identical sub-beams. The split sub-beams then pass through three polarizers 23.2a, 23.2b, 23.2c, the polarization directions of which are each twisted by 60° relative to one another. With the aid of photoelectron detectors 23.3a, 23.3b, 23.3c arranged downstream of the polarizers 23.2a, 23.2b, 23.2c, the three sub-beams can then be converted into displacement-dependent scanning signals S1, S2, S3, each phase-shifted by 120°, and made available for further processing.

[0051] Below, according to Figure 6a-6c An embodiment of a polarization grating is explained in detail, such as it is for example in accordance with Figure 2-5 In the position measuring device of , it can be used as a second grating or scanning grating 22 impinged 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.

[0052] As already explained above, the polarization grating 22 is used in the optical position measuring device according to the invention to exert a defined polarization optical effect on the split sub-beams at each incident point on the grating, so that diffraction orders with different polarization states are obtained. This makes it possible to avoid the need to additionally arrange separate polarization optical components in the scanning beam path. In addition, it is possible to use such a polarization grating also according to Figure 2 In a three-grating encoder of this type, it is now possible to generate phase-shifted scanning signals in a polarization-optical manner. Since the spacing between the gratings is usually small in such systems, there is usually no spatial separation of the split sub-beams in the area of ​​the loaded second grating, i.e. the sub-beams overlap in the area of ​​the second grating. Therefore, due to this beam superposition, it is not possible in a conventional manner (i.e. by means of polarization optics in the sub-beams) to generate phase-shifted scanning signals in a polarization-optical manner.

[0053] The corresponding polarization grating 22 is designed in the optical position measuring device according to the present invention so that diffraction orders with different polarization states are realized at each incident location on the grating. Preferably, the polarization grating 22 is designed so that the obtained + / -1st order diffraction orders are polarized orthogonally to each other.

[0054] As from Figure 6a Partial details of an embodiment of a suitable polarization grating 22 in FIG. Figure 6bAs can be seen from the detailed view of a cell of such a polarization grating in FIG. 2 , the polarization grating 22 comprises an arc-shaped curved grating structure in the form of a plurality of grating slits 22 . 1 and grating webs 22 . 2 .

[0055] In the present exemplary embodiment, polarization grating 22 is designed as a reflective phase grating, which means that the alternatingly arranged grating structures or grating slits 22.1 and grating webs 22.2 have different reflection properties and in particular exert different phase shifting effects on incident sub-beams.

[0056] The longitudinal extension direction of the grating structure or the grating slits 22.1 and the grating webs 22.2 is as follows: Figure 6a , 6b As can be seen, they are oriented parallel to the measuring direction x. The grating structure is arranged periodically along the measuring direction x and also perpendicular to the measuring direction x. Here, a plurality of grating segments 22a, 22b, 22c, 22d arranged periodically with a measuring periodicity Λ are provided along or parallel to the measuring direction x; the longitudinal extension direction of the grating segments is perpendicular to the measuring direction x, i.e., oriented along the specified y direction. Within the corresponding grating segments 22a, 22b, 22c, 22d, the arcuate grating structure is periodically arranged with an orthogonal periodicity Λ_ortho. It has been proven to be particularly advantageous to select the orthogonal periodicity Λ_ortho in the polarization grating 22 according to the following relationship 1):

[0057] Λ_ortho<1.5·λ (Formula 1)

[0058] Where: Λ_ortho: = the orthogonal periodicity of the grating structure in the polarization grating, λ: = the wavelength of the light source used.

[0059] By complying with relation 1), it can be ensured that the corresponding polarization grating 22 has only a weak diffraction effect on the sub-beams incident thereon in an orthogonal direction relative to the main diffraction direction. Here, the main diffraction direction is located in the xz plane, and the diffraction direction orthogonal thereto is located in the yz plane. In this embodiment, the diffraction in the xz plane is essential for generating the displacement-dependent scanning signal; otherwise, strong diffraction effects along other planes would lead to a reduction in the signal intensity and polarization effect.

[0060] The curved grating structure or grating slits 22.1 and grating webs 22.2 of the polarization grating 22 are arranged according to Figure 6a , 6b In the case of a predetermined coordinate system, it can be described analytically, for example, by one of the following relations 2a), 2b):

[0061] Y=(Λ / π)·ln(|1 / cos(x·π / Λ)|) (Formula 2a)

[0062] Where: Λ: = measurement direction periodicity of the grating segment, x: = measurement direction, Y: = longitudinal extension direction of the grating segment;

[0063] Y = sqrt((Λ / 2) 2 -x 2 ) (Formula 2b)

[0064] Where: Λ: = measurement direction periodicity of the grating segment, x: = measurement direction, Y: = longitudinal extension direction of the grating segment.

[0065] In this case, relation 2a) characterizes a catenary grating structure and relation 2b) characterizes a circular grating structure.

[0066] Especially from Figure 6a It can be seen that in the illustrated embodiment, linear grating webs 22.2a, 22.2b, 22.2c, 22.2d are arranged respectively between adjacent grating segments 22a, 22b, 22c, 22d in the x direction. Here, the linear grating webs 22.2a, 22.2b, 22.2c, 22.2d have an elongated rectangular shape, wherein the longitudinal axis of the rectangle extends perpendicularly to the measuring direction x, i.e., along the measuring direction y.

[0067] Alternatively, it can also be proposed that grating slits are arranged between adjacent grating segments 22a, 22b, 22c, 22d, or that a plurality of grating strips and grating slits are arranged alternately adjacent to each other. In addition, it is also possible that neither individual grating slits nor grating strips are arranged in the region, but instead, the grating structures of adjacent grating segments 22a, 22b, 22c, 22d are adjacent to each other.

[0068] It has also proven to be advantageous to select the surface filling ratio FV of the polarization grating 22 in accordance with the following relationship 3):

[0069] FV<0.6 (Formula 3)

[0070] Where: FV: = the ratio of the area of ​​the grating patch in one polarization grating unit cell to the total area of ​​the polarization grating unit cell.

[0071] Polarization gratings dimensioned in this way can be cleaned more easily. Furthermore, it can be ensured that the grating structures are sufficiently separated from one another, thereby avoiding undesired coupling effects between adjacent grating structures, which would otherwise lead to a reduction in the intensity of the + / -1st diffraction order.

[0072] Referring to the diagram of FIG. 6 in conjunction with the specific grating structure of the polarization grating 22 and the materials suitable for such a grating, it is shown Figure 6a , 6b, a partial cross-sectional view of a polarization grating 22 in the xz plane. As already mentioned above, this embodiment of the polarization grating 22 is designed as a reflection phase grating. The reflection phase grating comprises a carrier substrate 22.10, on which a reflector layer 22.11 is arranged in a planar manner. In this example, a planar phase shift layer 22.12 is also provided on the reflector layer 22.11, on which a grating structure layer 22.13 is arranged, in which a grating structure having corresponding grating webs 22.2 and grating slits 22.1 in the geometric shape or arrangement already explained above is formed.

[0073] In this structure of polarization grating 22, it has proven to be advantageous if grating structure layer 22.13 has a layer thickness d which is selected in accordance with the following relationship 4):

[0074] d<0.6·λ (Formula 4)

[0075] Where: d: = layer thickness of the grating structure layer, λ: = wavelength of the light source used.

[0076] For polarization grating 22 in this exemplary embodiment, suitable carrier substrates 22 . 10 include, for example, quartz glass or glass-ceramic.

[0077] The reflector layer 22.11 can be designed as a metallic reflector layer or as a reflective layer stack consisting of a plurality of layers of a high-refractive index or low-refractive index material, for example TaO. x , TiO2, Si as high refractive index materials and SiO2 as low refractive index materials. For example, SiO2 is considered as a material for the phase shift layer 22.12.

[0078] With regard to the formation of the grating structure layer 22.12, it can be provided that for this purpose a material from the group consisting of SiO2, TaO x , TiO2, Si; however, it is also possible to use semiconductor materials such as TiN, GaN, or metals with high conductivity, such as Al, Ag, Au. Alternatively, the grating structure layer 22.13 can also be composed of a layer stack in which one or more of the above-mentioned dielectric materials or semiconductor materials are used.

[0079] In another optional embodiment, the polarization grating designed as a reflective phase grating can only include a carrier substrate and a reflector layer arranged thereon, wherein a structured phase shifting layer is arranged thereon. Figure 6c The individual phase-shifting and grating structure layers arranged in the example of are formed together in a single layer, ie in the form of one or more structured layers which are applied directly to the reflector layer without an additional phase-shifting layer.

[0080] In order to set the desired polarization effect of a corresponding polarization grating, besides the specific geometry and arrangement of the grating structure, grating parameters structure width and etching depth, the material used can of course also be selected in a suitably adapted manner.

[0081] exist Figure 7a-7e 1 and 2 show a view of a cell of an alternative embodiment of a polarization grating which can be used in the optical position-measuring device according to the invention.

[0082] In the polarization grating 22 Figure 7a In the variant shown in , the grating structure in the form of grating slits 122.1 and grating webs 122.2 is designed in a catenary-shaped manner and extends in the x direction to the edge of the cell. This grating structure can be characterized analytically, for example, by the above-mentioned relation 2a).

[0083] exist Figure 7b 2 shows a cell of another polarization grating 222 , wherein the arcuate grating structure or grating slits 222 . 1 and grating webs 222 . 2 are designed to be circular and are respectively trimmed at the edge of the cell in the x direction.

[0084] In the polarization grating 322 Figure 7c In the cell shown in FIG. 3 , the catenary-shaped grating structure or the grating slits 322 . 1 and the grating webs 322 . 2 are formed by combining separate linear segments.

[0085] Finally, in Figure 7d Description Figure 7c 4. A slightly modified variant of the cell of the polarization grating 422 of the exemplary embodiment in FIG. In this polarization grating 422, adjacent linear sections of the grating structure or grating slits 422.1 and grating webs 422.2 additionally have an offset.

[0086] Finally, in Figure 7e 5 shows another variant of a cell of a polarization grating 522. In this example, the arcuate grating structure in the form of grating slits 522.1 and grating webs 522.2 is partially interrupted. Thus, the central grating web 522.2 in the cell has, for example, two interruptions 522.2a, 522.2b.

[0087] Figure 7b-7e The variant in has proven to be particularly advantageous due to its simpler producibility; grating regions with extremely fine structuring can be avoided in this embodiment.

[0088] Besides the specifically described embodiments, further possible configurations are obviously also possible within the scope of the invention.

[0089] It is therefore also possible for the optical position-measuring device according to the invention to be designed for detecting a rotational relative movement of two objects.

[0090] Furthermore, in the case of a three-grating encoder, it is not mandatory to design the first grating in the form of a physical gauge and the second grating in the form of a scanning grating or a polarization grating to be reflective. Therefore, the first grating can naturally also be designed as a transmission phase grating and the second grating can also be designed as a transmission phase grating; similarly, structural variants with a mixture of reflection and transmission phase gratings are feasible, i.e., for example, a transmission scanning or polarization grating and a reflection physical gauge or a transmission physical gauge and a reflection polarization grating, etc.

[0091] If the polarization grating is transmissively formed as a transmission phase grating, the deflection grating can, for example, comprise a transparent carrier substrate etched with a grating structure. Alternatively, it is also possible to apply a separate grating structure layer made of a dielectric material or semiconductor material to a transparent carrier substrate, in which the corresponding grating structure is formed. Here, the grating structure layer can also be formed from a suitable layer stack.

[0092] Furthermore, it is naturally possible to provide other scanning beam paths in addition to the described scanning according to the three-grating principle in the optical position measuring device according to the invention. For example, in so-called strip encoders, as are known, for example, from WO 2008 / 138501 A1 or EP 2450672 A2, one of the gratings can be designed as a polarization grating in order to thereby achieve the generation of a phase-shifted scanning signal in a polarization-optical manner; the arrangement of an additional or separate polarization optical device is then no longer necessary. In such a system, the first grating can be designed as a reflection phase grating or a transmission phase grating and the second grating as a reflection phase grating; the second grating acts as a polarization grating.

[0093] As an alternative to this, however, in scanning principles and in other optical scanning principles, it is in principle possible to design each impinged grating as a polarization grating.

Claims

1. An optical position measuring device for detecting the relative position of two objects that can be moved relative to each other in at least one measuring direction, the objects being connected to a first grating and a second grating, wherein: At a grating, a light illumination beam emitted by a light source is split into at least two sub-beams; the sub-beams are subjected to different polarization optical effects, and after the sub-beams of different polarizations are recombined at a grating, a plurality of phase-shifted, displacement-related scanning signals can be generated in a detection unit from the resulting signal beam, wherein no separate polarization optical device is arranged between the splitting and the recombining in the scanning optical path of the sub-beams, and at least one of the gratings passed through is designed as a polarization grating for generating different polarization optical effects on the sub-beams, It is characterized in that The polarization grating (22; 122; 222; 322; 422; 522) is designed so that a diffraction order with a different polarization state is obtained at each incident point on the polarization grating (22; 122; 222; 322; 422; 522), and The polarization grating (22; 122; 222; 322; 422; 522) has a grating structure that is periodically arranged along the measuring direction and perpendicular to the measuring direction and wherein the orthogonal periodicity Λ_ortho is based on Λ_ortho < 1.5 • λ Select, where Λ_ortho:= orthogonal periodicity of the grating structure λ:= wavelength of the light source used.

2. The optical position measuring device according to claim 1, characterized in that The polarization grating (22; 122; 222; 322; 422; 522) comprises a plurality of arc-shaped curved grating structures in the form of grating webs (22.2; 122.2; 222.2; 322.2; 422.2; 522.2) and grating slits (22.1; 122.1; 222.1; 322.1; 422.1; 522.1), wherein the longitudinal extension direction of the grating structures is respectively oriented parallel to the measuring direction.

3. The optical position measuring device according to claim 2, characterized in that The polarization grating (22; 122; 222; 322; 422; 522) has strip-shaped grating segments (22a, 22b, 22c, 22d), which are periodically arranged in parallel with the measuring direction and in a periodic manner in the measuring direction, and the longitudinal extension direction of the grating segments is oriented perpendicular to the measuring direction, wherein, in the grating segments (22a, 22b, 22c, 22d), the grating structure is periodically arranged perpendicular to the measuring direction and in the orthogonal periodicity Λ_ortho.

4. The optical position measuring device according to claim 2 or 3, characterized in that Between adjacent grating segments (22a, 22b, 22c, 22d) of the polarization grating (22; 122; 222; 322; 422; 522) Arranged with grating slits, or Arranged with grating tabs, or A plurality of grating slits and grating webs are arranged alternately adjacent to each other.

5. The optical position measuring device according to claim 2 or 3, characterized in that: The grating structures of adjacent grating segments adjoin one another.

6. The optical position measuring device according to claim 2, characterized in that The surface filling ratio FV of the polarization grating (22; 122; 222; 322; 422; 522) is selected according to the relationship FV < 0.6, wherein the surface filling ratio FV is defined as the ratio of the area of ​​the grating patch (22.2; 122.2; 222.2; 322.2; 422.2; 522.2) in one polarization grating unit cell to the total area of ​​the polarization grating unit cell.

7. The optical position measuring device according to claim 1, characterized in that: The polarization grating (22; 122; 222; 322; 422; 522) is designed as a reflection phase grating, and the grating webs (22.2; 122.2; 222.2; 322.2; 422.2; 522.2) and grating slits (22.1; 122.1; 222.1; 322.1; 422.1; 522.1) of the polarization grating have different reflection characteristics.

8. The optical position measuring device according to claim 7, characterized in that The reflective phase grating comprises at least the following components: Carrier substrate (22.10), a planar reflector layer (22.11) arranged on the carrier substrate (22.10), A grating structure layer (22.13) is arranged above the reflector layer (22.11).

9. The optical position measuring device according to claim 8, characterized in that The grating structure layer (22.13) has a layer thickness d, which is selected according to the relationship d < 0.6 • λ, wherein λ specifies the wavelength of the light source (LQ; 21) used.

10. The optical position measuring device according to claim 8, characterized in that A planar phase shift layer (22.12) is arranged between the planar reflector layer (22.11) and the grating structure layer (22.13).

11. The 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 The grating structure layer (22.13) is made of the group consisting of SiO2, TaO x , TiO2, Si or consists of a semiconductor material from the group: TiN, GaN, or consists of a layer stack having one or more of the dielectric materials and one or more of the semiconductor materials.

12. The optical position measuring device according to claim 1, characterized in that The polarization grating (22; 122; 222; 322; 422; 522) is designed so that the obtained + / -1st diffraction orders are polarized orthogonally to each other.

13. The optical position measuring device according to claim 1, characterized in that The first object is connected to a first grating, wherein the first grating is designed as a reflection phase grating or a transmission phase grating, The second object is connected to a second grating acting as a polarization grating (22; 122; 222; 322; 422; 522), the second grating being designed as a reflective phase grating, The beam (B) emitted by the light source (21) is split into two sub-beams (TS1, TS2) at the first grating. The sub-beams (TS1, TS2) are then loaded onto the second grating, where each of the two sub-beams (TS1, TS2) is diffracted and changed in direction, and wherein the sub-beams (TS1', TS2') are polarized orthogonally to each other after loading onto the second grating, The sub-beams (TS1', TS2') strike the first grating (10) again and recombine there, so that the resulting signal beam (S) then propagates in the direction of the detection unit (23).

14. The optical position measuring device according to claim 1, characterized in that The first object is connected to a first grating (G1) serving as a physical measuring tool (10), wherein the first grating is designed as a reflection phase grating or a transmission phase grating. The second object is connected to a scanning unit (20), wherein the scanning unit (20) comprises the following components: Light source (LQ; 21), a second grating (G2) acting as a scanning grating, the second grating also acting as a polarization grating (22; 122; 222; 322; 422; 522) and being designed as a reflective phase grating, Detection unit (DET; 23), The beam (B) emitted by the light source (LQ; 21) is split into two sub-beams (TS1, TS2) at the first grating (G1). The sub-beams (TS1, TS2) are then loaded onto the second grating (G2), where each of the two sub-beams (TS1, TS2) undergoes a change of direction, and wherein the sub-beams (TS1', TS2') are polarized orthogonally to each other after loading the second grating (G2), The sub-beams (TS1', TS2') strike the first grating (G1) again and recombine there, so that the resulting signal beam (S) then propagates in the direction of the detection unit (DET; 23).

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