Optical position measurer

Abstract

The invention relates to an optical position measurer for determining the relative position of two objects which can be moved relative to each other in at least two measurement directions. To this end, a plurality of scanning units are provided, which are connected to one of the two objects and each comprise at least one light source, one or more gratings and a detector assembly. In addition, a measuring tool is provided, which is connected to a further object. The measuring tool has a two-dimensional measuring scale which is composed of structural elements having different optical properties and which are arranged periodically along two measuring directions. A plurality of reference marks having periodic and non-periodic sub-regions are integrated in the measurement indexing. A corresponding reference signal can be generated at a defined reference position in the measurement direction from the scanning of the reference mark. At least the periodic sub-region of the reference mark has a higher scanning efficiency than the surrounding measurement indexing.

Description

Technical Field

[0001] The invention relates to an optical position measuring device which is suitable for determining the relative position of two objects moving relative to each other with high precision. Background Art

[0002] A position measuring device is known from DE 10 2004 006 067 A1, which is suitable for determining the relative position of two objects, and the objects can move relative to each other along at least two measuring directions. For this purpose, the position measuring device includes a plurality of scanning units, which are connected to one of the two objects and each have at least one light source, one or more gratings and a detector assembly. In addition, the position measuring device has a measuring tool, which is connected to the other object. The measuring tool includes a measuring graduation in the form of a two-dimensional cross grating, which is composed of two superimposed, periodic incremental graduations, and the incremental graduations extend along two measuring directions. Two reference marks are integrated in the cross grating, and corresponding reference signals can be generated from the scanning of the reference marks along each measuring direction at a defined reference position. Here, the use of the reference marks integrated in the cross grating can realize the generation of reference signals along the first measuring direction, regardless of the position of the (one or more) scanning units along the second measuring direction, and vice versa.

[0003] EP 3 527 951 B1 also discloses an optical position measuring device with reference marks integrated in a plurality of measuring graduations. The reference marks provided here include aperiodic and periodic sub-areas. The periodic sub-areas are designed to correspond to the surrounding measuring graduations; the aperiodic sub-areas consist of chirped grating structures, which are each arranged symmetrically with respect to a central axis of symmetry.

[0004] However, the known solutions with reference marks integrated in the measuring graduation have specific problems with regard to the generation of reference signals. As a result, the signal level of the incremental signals generated by the scanning unit drops more or less significantly when each reference mark is passed. In order to avoid this, it is known to increase the optical power of the light source when the reference marks are passed. However, this reduces the so-called control reserve of the light source, that is to say, the light source current is then no longer fully available to compensate for other negative effects, such as aging and / or contamination. Summary of the invention

[0005] The object of the present invention is to provide an optical position measuring device for high-precision position determination in at least two measuring directions, wherein even when passing reference marks integrated in the measuring graduation, the generation of periodic incremental signals with minimal signal interruptions is ensured.

[0006] This object is achieved according to the invention by an optical position measuring device having the features of claim 1 .

[0007] Advantageous embodiments of the optical position measuring device according to the invention result from the measures specified in the dependent claims.

[0008] The optical position measuring device according to the present invention is used to determine the relative position of two objects, and the objects move relative to each other along at least two measuring directions. The position measuring device includes a plurality of scanning units, which are connected to one of the two objects and each have at least one light source, one or more gratings and a detector assembly. In addition, a measuring tool is provided, which is connected to another object. The measuring tool includes a two-dimensional measuring graduation, which is composed of structural elements with different optical properties arranged periodically along two measuring directions. A plurality of reference marks with periodic and non-periodic sub-regions are integrated in the measuring graduation, wherein a reference signal can be generated along the measuring direction at a defined reference position from scanning the reference mark. At least the periodic sub-region of the reference mark has a higher scanning efficiency than the surrounding measuring graduation.

[0009] It is possible to integrate two rectangular reference markings arranged in an L-shape in the measuring graduation, wherein one reference marking is assigned to a first measuring direction and the other reference marking is assigned to a second measuring direction which is oriented orthogonally to the first measuring direction.

[0010] Alternatively, provision can be made for three rectangular reference marks arranged in a U-shape to be integrated in the measuring graduation, two reference marks being assigned to one measuring direction and another reference mark to another measuring direction, which is oriented orthogonally to the first measuring direction.

[0011] It has proven to be advantageous if the reference markings are each arranged in the edge region of the measuring graduation.

[0012] In this case, the reference markings assigned to a measuring direction can each be at a distance from an edge of the measuring graduation that is smaller than the distance between two adjacent scanning units along this measuring direction.

[0013] In another embodiment, it can be provided that

[0014] - a first scanning unit is assigned to the first measuring direction and a second scanning unit and a third scanning unit are assigned to the second measuring direction,

[0015] - wherein the second scanning unit and the third scanning unit have no offset along the second measuring direction.

[0016] In another embodiment, it can be provided that

[0017] - four scanning units are arranged on a separate object relative to the measuring scale,

[0018] - wherein a first scanning unit and a fourth scanning unit are assigned to the first measuring direction and a second scanning unit and a third scanning unit are assigned to the second measuring direction, and

[0019] - wherein the two scanning units assigned to the measuring direction have no offset along the second measuring direction.

[0020] Furthermore, it is possible to arrange in each case a one-dimensional incremental graduation in the periodic sub-regions of the reference marking, which incremental graduation has an increased scanning efficiency in the form of a higher diffraction efficiency compared to the surrounding measuring graduation.

[0021] In this case, the one-dimensional incremental graduation in the periodic sub-regions of the reference mark only produces a diffraction of + / -1 diffraction order in one measuring direction, while in the surrounding measuring graduation a diffraction of + / -1 diffraction order in both measuring directions is produced.

[0022] In this case, the incremental graduations in the periodic sub-regions of the reference marking and the surrounding measuring graduations are preferably each designed as reflective phase gratings.

[0023] Alternatively, it can also be provided that the periodic sub-regions and the aperiodic sub-regions of the reference marking have an increased scanning efficiency in the form of a higher reflectivity relative to the surrounding measuring graduations.

[0024] In this case, a cross grating is arranged in the periodic subregions of the reference mark, which cross grating, like the surrounding measuring graduation, is designed as a reflection phase grating, wherein the periodic subregions and the aperiodic subregions of the reference mark are provided with a reflection-increasing coating.

[0025] Furthermore, it is possible for the non-periodic subregions of the reference marking to each have a chirped grating structure, wherein the grating period varies symmetrically in position with respect to the central axis of symmetry.

[0026] Furthermore, it can advantageously be provided that the periodic subregions of the reference marking and the aperiodic subregions of the reference marking are arranged periodically perpendicular to the measuring direction.

[0027] Furthermore, it is possible for the periodic subregion and the aperiodic subregion of the reference marking to have an area ratio different from 1:1 to one another.

[0028] In a possible embodiment, it can also be provided that a one-dimensional or two-dimensional periodic grating structure is arranged in the periodic subregions of the reference marking, the periodicity of the grating structure along one or both measuring directions corresponding to the periodicity of the circumferential measuring graduation along one or both measuring directions.

[0029] It has proven to be particularly advantageous in the optical position measuring device according to the invention that even when passing reference marks integrated in the measuring graduation, no significant disturbances in the signal level of the periodic incremental signal occur. As a result, it is no longer necessary to increase the light source current, and the control reserve is fully available, for example, to compensate for aging effects or contamination effects.

[0030] 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. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The figure shows

[0032] Figure 1 A very schematic top view of a first exemplary embodiment of an optical position measuring device according to the invention having a measuring graduation designed as a two-dimensional crossed grating with three reference marks integrated therein and four scanning units;

[0033] Figure 2 Show Figure 1 A top view of a sub-region of a reference mark of an embodiment of the invention;

[0034] Figure 3a A schematic cross-sectional view showing a scanning beam path of a scanning unit having an optical position measuring device according to the present invention;

[0035] Figure 3b Show Figure 3a A top view of a scanning unit in FIG.

[0036] Figure 4 A very schematic top view of a further exemplary embodiment of an optical position measuring device according to the invention having a measuring graduation designed as a two-dimensional crossed grating with two reference marks integrated therein and three scanning units;

[0037] Figure 5 A plan view showing a sub-region of a reference mark according to a further exemplary embodiment of an optical position measuring device according to the present invention;

[0038] Figure 6a , Figure 6b Shown according to Figure 5 A cross-sectional view of a measuring graduation in the region of a reference mark in an embodiment. DETAILED DESCRIPTION

[0039] In the following text, Figure 1 , Figure 2 as well as Figure 3a and Figure 3b Embodiments of the optical position measuring device according to the present invention are described.

[0040] exist Figure 1 The position measuring device shown in FIG. 1 is used to determine the relative position of two objects (not shown in the figure) which are movable relative to each other along two measuring directions x, y; the two measuring directions x, y are oriented orthogonally to one another in this case.

[0041] In the following, the measuring direction x is also referred to as the first measuring direction and the measuring direction y as the second measuring direction.The objects can be machine parts that move relative to each other, for example a table and a tool of a semiconductor processing machine.

[0042] Here, a measuring tool 10 of the position measuring device is connected to one of the two objects, and has a two-dimensional reflection measuring graduation 12 on a scale support. The two-dimensional measuring graduation 12 is designed as a so-called cross grating and consists of structural elements 12.1, 12.2 with different optical properties arranged periodically in two measuring directions x, y; in this regard, reference is made in particular to Figure 1 Schematic enlargement of a portion of the measuring graduation 12 in the lower area of ​​. In the reflected light system shown, the measuring graduation 12 is constructed as a reflection phase grating, wherein the structural elements 12.1, 12.2 exert different phase shifting effects on the reflected light beam. In a specific embodiment, a chromium graded grating with a phase swing of 180° and a periodicity of 8μm along the two measuring directions x, y can act as a reflection phase grating. By optically scanning the measuring graduation 12, periodic incremental signals are generated along the two measuring directions x, y, and the incremental signals respectively represent the measure of the relative movement of the two objects along the corresponding measuring directions x, y. A plurality of reference marks 11.x1, 11.x2, 11.y are integrated into the measuring graduation 12, wherein the three rectangular reference marks 11.x1, 11.x2, 11.y are arranged in a U-shaped arrangement, that is, the three reference marks 11.x1, 11.x2, 11.y are arranged in the edge area of ​​the measuring graduation 12 parallel to the three edges. From the optical scanning of the reference marks 11.x1, 11.x2, 11.y, a corresponding reference signal can be generated at a defined reference position in one of the two measuring directions x, y. By calculating the reference signal with the incremental signal, high-resolution absolute position information can be generated in a known manner in both measuring directions x, y. The specific construction of the reference marks 11.x1, 11.x2, 11.y with periodic and aperiodic sub-areas in a specific arrangement is described below with reference to Figure 2 Detailed Explanation The position signals generated by the optical position measuring device according to the invention in the form of periodic incremental signals and reference signals are further processed by a downstream control unit (not shown in the figures), which controls the relative movement of the corresponding machine parts.

[0043] A plurality of scanning units 20.x1, 20.x2, 20.y1, 20.y2 of the optical position measuring device according to the present invention are connected to the other of the two objects, wherein in this example a total of four scanning units 20.x1, 20.x2, 20.y1, 20.y2 are provided. The scanning units 20.x1, 20.x2, 20.y1, 20.y2 each include at least one light source, one or more gratings and a detector assembly. With the aid of the scanning units 20.x1, 20.x2, 20.y1, 20.y2, the measuring graduation 12 is optically scanned and incremental signals and reference signals are generated in two measuring directions x and y. For the specific construction of the scanning units 20.x1, 20.x2, 20.y1, 20.y2, refer to Figure 3a and Figure 3b will be described below.

[0044] The different scanning units 20.x1, 20.x2, 20.y1, 20.y2 are arranged relative to one another in a defined manner in the optical position measuring device according to the invention, which is explained below for the example shown. The four scanning units 20.x1, 20.y1, 20.y2, 20.x2 provided are referred to as the first scanning unit, the second scanning unit, the third scanning unit and the fourth scanning unit 20.x1, 20.y1, 20.y2, 20.x2 from the left.

[0045] In the present case, first scanning unit 20 . x1 and fourth scanning unit 20 . x2 are assigned to first measuring direction x, wherein the two scanning units 20 . x1 , 20 . x2 have a mutual distance Lx1 along the first measuring direction x and have no mutual offset along the second measuring direction y or are arranged at the same height along the second measuring direction y.

[0046] The second scanning unit 20.y1 and the third scanning unit 20.y2 are assigned to the second measuring direction y, the scanning units have a mutual distance Lx2 along the first measuring direction x and have no mutual offset along the second measuring direction y. As can be seen from the figure, the second and third scanning units 20.y1, 20.y2 are arranged between the first and fourth scanning units 20.x1, 20.x2 along the measuring direction x.

[0047] The first scanning unit 20 . x1 is arranged at a distance Sx in a first measuring direction x and at a distance Sy in a second measuring direction Sy relative to the second scanning unit 20 . y1 .

[0048] As mentioned above, in Figure 1In the example of FIG. 1 , three rectangular reference marks 11.x1, 11.x2, 11.y arranged in a U-shape are integrated into the measuring graduation 12. Similar to the names of the different scanning units 20.x1, 20.x2, 20.y1, 20.y2, the three reference marks 11.x1, 11.y, 11.x2 provided are referred to as the first reference mark, the second reference mark, the third reference mark 11.x1, 11.y, 11.x2 from the left.

[0049] The first reference mark 11.x1 and the third reference mark 11.x2 are assigned to the first measuring direction x, wherein the longitudinal axes of the two reference marks 11.x1, 11.x2 extend along the second measuring direction y. Thus, the first reference mark 11.x1 and the third reference mark 11.x2 make it possible to make a reference with respect to the movement along the first measuring direction x. The second reference mark 11.y is assigned to the second measuring direction y, wherein the longitudinal axis of the second reference mark extends along the first measuring direction x; with the aid of the second reference mark 11.y, a reference can also be made with respect to the movement along the second measuring direction y. From the scanning of the first and third reference marks 11.x1, 11.x2, a corresponding reference signal can be generated in a specific reference position along the first measuring direction x. By scanning the second reference mark 11.y, a reference signal can be generated in the second measuring direction y at a predetermined reference position.

[0050] With regard to the arrangement of the three reference marks 11.x1, 11.x2, 11.y in the edge region of the measuring graduation 12, in the example shown, it is provided that the reference marks 11.x1, 11.x2, or 11.y, which are assigned to the measuring direction x or y, have a distance Rx or Ry from the adjacent edge of the measuring graduation 12, which is smaller than the distance Sx or Sy of two adjacent scanning units 20.x1, 20.y1 along these measuring directions x, y. That is, the distance Rx of the reference marks 11.x1, 11.x2 from the respectively nearest edge of the measuring graduation 12 is selected to be smaller than the distance Sx, which describes the distance of two adjacent scanning units 20.x1, 20.y1 and two adjacent scanning units 20.x2, 20.y2 along the first measuring direction x. Analogously, distance Ry of reference marking 11 .y from an adjacent edge of measuring graduation 12 is selected to be smaller than distance Sy which represents the distance between two adjacent scanning units 20 .x1 , 20 .y1 and two adjacent scanning units 20 .x2 , 20 .y2 along second measuring direction y.

[0051] By means of the illustrated arrangement of the scanning units 20.x1, 20.x2, 20.y1, 20.y2 and the reference markings 11.x1, 11.x2, 11.y, in the example shown, position determination is possible when the object is moved along the two measuring directions x, y and when the object is rotated about an axis z oriented perpendicularly to the two measuring directions x, y. In addition, any thermal expansion of the measuring tool 10 can be detected using this number and arrangement of the reference markings 11.x1, 11.x2, 11.y and the scanning units 20.x1, 20.x2, 20.y1, 20.y2.

[0052] Further possibilities with regard to the number and arrangement of scanning units and reference markings in the optical position measuring device according to the invention are outlined in the further description of the present specification.

[0053] In the following, with the help of Figure 2 The construction of the reference mark in the optical position measuring device according to the present invention is explained; Figure 2 Show Figure 1 1. Here, only the details of the provided structure in a small region along the longitudinal extension direction y of the reference symbol 11.x1 are shown in the figure. Figure 2 It is not a true-to-scale representation of the reference numeral 11 . x1 , but serves merely to illustrate the basic design of the reference numeral 11 . x1 .

[0054] As described above, the reference mark of the device according to the invention consists of a periodic sub-region 15.1 and an aperiodic sub-region 15.2. The different sub-regions 15.1, 15.2 of the reference mark are designed as a reflective phase grating like the surrounding measuring graduations and are arranged according to Figure 2The top views in the figure each have a rectangular geometry. The rectangular longitudinal axes of the periodic and aperiodic sub-areas 15.1, 15.2 of the reference mark 11.x1 are oriented perpendicularly to the longitudinal axis of the reference mark 11.x1; that is, the rectangular longitudinal axes of the different sub-areas 15.1, 15.2 extend in parallel to the first measuring direction x in the reference mark, and the longitudinal axis of the reference mark 11.x1 extends parallel to the second measuring direction y. The sub-areas 15.1, 15.2 of the reference mark 11.x1 are arranged periodically along the longitudinal axis of the reference mark 11.x1, that is, the periodic sub-areas 15.1 and the aperiodic sub-areas 15.2 are arranged alternately along the direction y. Within the reference mark 11.x1, the periodic sub-region 15.1 and the aperiodic sub-region have an area ratio different from 1:1 to each other, that is, the reference mark 11.x1 consists of different portions consisting of a periodic portion and an aperiodic portion; therefore, the area ratio of the periodic and aperiodic sub-regions 15.1, 15.2 is selected to be different from 0.5. In a possible embodiment, the area ratio of the periodic and aperiodic sub-regions 15.1, 15.2 can be selected within a range greater than or equal to 0.25 and less than 0.5, that is, the periodic portion occupies a smaller area portion than the aperiodic portion. This selection of the area ratio first leads to an increased reference signal. In particular, in conjunction with the amplitude adjustment of the incremental signal, the reference signal is further improved, because the main lobe of the reference signal is amplified compared to the side lobes of the reference signal.

[0055] In a preferred embodiment, for example, it is provided that the width of the periodic sub-region 15.1 along the second measuring direction y is 18 μm and the width of the aperiodic sub-region 15.2 along the second measuring direction y is 22 μm. With such dimensioning, the ratio of the areas of the periodic and aperiodic sub-regions 15.1, 15.2 in the reference marking 11.x1 is 0.45.

[0056] This reference mark periodicity of 40 μm, which is small compared to the signal contribution area of ​​the measuring graduation, has proven to be particularly advantageous when the scanning unit passes over the reference mark at an angle; a reference mark periodicity of less than or equal to 128 μm, in particular less than or equal to 64 μm, is particularly suitable. As a result, the changes in the partial surfaces of the non-periodic and periodic sub-areas participating in the signal formation are very small during the passage. This leads to an improvement in the signal-to-noise ratio of the reference signal and an improvement in the amplitude change of the incremental signal. These advantages also apply even if the scanning unit can enter the reference mark area in different y positions during a straight passage, as is the case in 2D measuring systems.

[0057] Consistent with the first reference mark 11.x1, substantially Figure 1Also formed in FIG. 1 are second and third reference markings 11 . y, 11 . x2 , wherein the second reference marking 11 . y extends in the first measuring direction x after being rotated by 90°.

[0058] The non-periodic sub-regions 15.2 of the reference numerals 11.x1 each have a so-called chirped grating structure. This means that the structural elements 15.2a, 15.2b with different optical properties are not arranged strictly periodically along the corresponding rectangular longitudinal axis, but are arranged with a positionally varying grating period in the corresponding sub-region 15.2. Specifically, in the present embodiment, it is provided that the grating period changes positionally symmetrically with respect to the central symmetry axis of the sub-region 15.2, wherein the increase in the grating period is provided starting from the symmetry axis outwards.

[0059] Decisive for the desired properties of the reference mark 11.1x integrated into the measuring graduation is the periodic sub-areas 15.1 forming the reference mark 11.x1. In this context, it is provided that at least these sub-areas 15.1 have a higher scanning efficiency than the surrounding measuring graduation. This ensures that no significant disturbance of the incremental signal level occurs when the reference mark 11.x1 is passed and therefore no increase in the light source current is required.

[0060] In order to ensure a high scanning efficiency of the periodic sub-regions of the reference marking, there are currently different possibilities; Figure 2 The example in the first variant illustrates that, with the aid of Figure 5 , Figure 6a , Figure 6b Additional feasibility is described in the further description of the process. Figure 2 In the example of , it is provided that a one-dimensional incremental graduation is arranged in the periodic sub-region 15.1 of the reference mark 11.x1, which incremental graduation has a higher diffraction efficiency than the surrounding two-dimensional measuring graduation. Figure 2 As can be seen in FIG. 1 , the incremental graduation consists of a periodic arrangement of structural elements 15.1a, 15.2b with different optical properties along a first measuring direction x; the periodicity of the incremental graduation is selected to coincide with the periodicity of the cross grating along the measuring direction x. Different structural elements 15.1a, 15.1b exert different phase shifting effects on the reflected light beam. In a possible embodiment, the incremental graduation can be implemented, for example, as a chrome graded grating and have a phase swing of 180°.

[0061] The one-dimensional incremental graduation in the periodic sub-region 15.1 of the reference mark 11.x1 essentially produces a diffraction of + / -1 diffraction order in the measuring direction x, i.e. the incident intensity is distributed in the reflection mainly to these two diffraction orders. If, by contrast, a two-dimensional measuring graduation is arranged in the periodic sub-region of the reference mark, this results in a diffraction of + / -1 diffraction order in both measuring directions x, y, i.e. a distribution of the incident beam intensity to four reflected diffraction orders. A significant disturbance of the incremental signal when passing the reference mark 11.x1 is an undesirable consequence.

[0062] In the following text, Figure 3a and Figure 3b The scanning beam path in the optical position measuring device according to the present invention is explained. Figure 3a As shown in Figure 1 The cross-sectional view of the scanning beam path of the first scanning unit 20.x1 in the xz plane and the top view of the detection plane of the scanning unit 20.x1 are performed. In principle, Figure 1 The scanning beam path or structure of the fourth scanning unit 20.x2 in the embodiment is consistent with the scanning beam path. The scanning beam paths of the second and third scanning units 20.y1 and 20.y2 are twisted 90° around the z axis, and the movement along the second measuring direction y is detected by the scanning units.

[0063] In the scanning unit 20.x1 of the position measuring device shown, a light source 22 and a detector assembly having an incremental signal detector 25.1 and a reference signal detector 25.2 adjacent thereto are arranged on a carrier element 21. In the light propagation direction, an emission grating assembly is arranged in front of the light source 22 emitting divergent radiation, and the emission grating assembly comprises a periodic transmission emission grating 23.1 and an emission gap 23.2 arranged adjacent thereto.

[0064] The interaction of the light beam emitted from the light source 22 with the grating arranged in the scanning beam path, that is, with the transmission emission grating 23.1, the emission gap 23.2 and the measuring graduation 12, generates a displacement-dependent signal pattern in the detection plane of the detector assembly. By photoelectrically scanning this signal pattern with the aid of the scanning unit 20.x1, a periodic incremental signal and a reference signal are generated along the first measuring direction x.

[0065] In addition, Figure 3a The structure of the measuring tool 10 can be seen in the figure, which has a two-dimensional measuring graduation 12 arranged on a scale support 11.

[0066] Alternative variants of the optical position measuring device according to the invention are explained below with reference to further figures. In this context, only the decisive differences from the above-described exemplary embodiments will be discussed.

[0067] Figure 4 The top view shows a variant in which only two reference markings 111 .x, 111 .y are integrated in the measuring graduation in an L-shaped arrangement; the arrangement of the two reference markings 111 .x, 111 .y is realized in the edge region of the measuring graduation at a distance Rx or Ry from the edge as in the previous exemplary embodiments.

[0068] Here, three scanning units 120.x, 120.y1, 120.y2 are arranged on the scanning side; the first scanning unit 120.x is assigned to the first measuring direction x, and the second scanning unit 120.y1 and the third scanning unit 120.y2 are assigned to the second measuring direction y. As can be seen from the figure, the second and third scanning units 120.y1, 120.y2 have no offset in the second measuring direction y, but are arranged offset by a distance Sy relative to the first scanning unit 120.x in the second measuring direction y. The second scanning unit 120.y1 is arranged offset by a distance Sx in the first measuring direction x; the distance between the second and third scanning units 120.y1, 120.y2 in the first measuring direction x is denoted by Lx in the figure.

[0069] This variant of the optical position measuring device according to the invention can detect relative movements in a first measuring direction x and in a second measuring direction y as well as rotations about a measuring direction z. In accordance with the first exemplary embodiment, both reference markings 111.x, 111.y integrated into a two-dimensional measuring graduation and three scanning units 120.x, 120.y1, 120.y2 are provided.

[0070] according to Figure 5 as well as Figure 6a , Figure 6b As already indicated above, alternative possibilities are explained, such as enabling an increased scanning efficiency to be achieved in sub-regions of the reference markings. Figure 5 and Figure 2 A schematic detail view of the corresponding reference numeral 211.x1 is similarly shown. Figure 6a , Figure 6b A section through the measuring graduation in the region of reference symbol 211 .x1 is shown in each case.

[0071] In order to increase the scanning efficiency in the region of the reference mark 211.x1, it is provided that both the periodic subregion 215.1 and the non-periodic subregion 215.2 of the reference mark 211.x1 have a higher reflectivity than the surrounding measuring graduation 212. This is done with the aid of a reflection-enhancing coating 216, which is applied to the grating structure of the reflective phase grating in the entire region of the reference mark 211.x1, that is, both in the periodic subregion 215.1 and in the non-periodic subregion 215.2.

[0072] The grating structure in the non-periodic sub-region 215.2 is as shown in Figure 2 As in the example of FIG. , a grating structure is constructed as a linear frequency modulation. Figure 2 The difference is that a cross grating is arranged in the periodic sub-region 215.1 of the reference mark 211.x1, that is, a grating structure that is consistent with the surrounding measurement graduation 212. Here, the cross grating arranged in the periodic sub-region 215.1 has the same periodicity as the cross grating of the surrounding measurement graduation 212 in both measuring directions x, y.

[0073] In a specific embodiment, the reflective phase grating can be constructed in the region of the reference symbol 211 .x1 as a chromium graded grating with a 180° phase swing; a titanium nitride layer is used as the reflection-enhancing coating 216 .

[0074] If the reference marks are designed in this way, they do not necessarily have to be arranged in the edge region in the two-dimensional measuring graduation. For example, two such reference marks can also be arranged in a crossed 90° arrangement in the measuring graduation, wherein the intersection coincides with the center of the measuring graduation and the reference marks extend parallel to the first measuring direction and the second measuring direction.

[0075] In addition to the exemplary embodiments described above with reference to the figures, further possible embodiments naturally also exist within the scope of the invention.

[0076] It is therefore feasible that, according to Figure 1 In the case of a U-shaped arrangement of three reference marks in a two-dimensional measuring graduation, only three scanning units are provided on the scanning side, i.e., for example, Figure 1 In this case, only translational movements in the x- and y-directions and rotational movements about the z-direction can then be detected.

[0077] Furthermore, it is possible to also design the measuring graduation as a reflection amplitude grating or the like.

Claims

1. An optical position measuring device for determining the relative position of two objects, the objects being movable relative to one another in at least two measuring directions (x, y), the optical position measuring device comprising: a plurality of scanning units (20.x1, 20.x2, 20.y1, 20.y2; 120.x, 120.y1, 120.y2), each of which is connected to one of the two objects and each of which comprises at least one light source (22), one or more gratings (23.1, 23.2) and a detector assembly, and A measuring tool (10; 110) is connected to another object and has A two-dimensional measuring graduation (12; 212) consisting of structural elements (12.1, 12.2) with different optical properties arranged periodically along the two measuring directions (x, y), and A plurality of reference marks (11.x1, 11.x2, 11.y; 111.x, 111.y; 211.x1) integrated into the measuring scale (12; 212), the reference marks having periodic and aperiodic sub-areas (15.1, 15.2; 215.1, 215.2), wherein: A reference signal at a defined reference position along the measuring direction (x, y) can be generated from the scanning of the reference marks (11.x1, 11.x2, 11.y; 111.x, 111.y; 211.x1), It is characterized in that At least a periodic sub-region (15.1; 215.1) of the reference marking (11.x1, 11.x2, 11.y; 111.x, 111.y; 211.x1) has a higher scanning efficiency than the surrounding measuring graduation (12; 212).

2. The optical position measuring device according to claim 1, characterized in that: Two rectangular reference marks (111.x, 111.y) arranged in an L-shape are integrated into the measuring graduation, wherein one reference mark (111.x) is assigned to a first measuring direction (x) and the other reference mark (111.y) is assigned to a second measuring direction (y), which is oriented orthogonally to the first measuring direction (x).

3. The optical position measuring device according to claim 1, characterized in that: Three rectangular reference marks (11.x1, 11.x2, 11.y) arranged in a U-shape are integrated into the measuring graduation (12), wherein two reference marks (11.x1, 11.x2) are assigned to one measuring direction (x) and another reference mark (11.y) is assigned to another measuring direction (y) oriented orthogonally to the first measuring direction (x).

4. The optical position measuring device according to claim 2 or 3, characterized in that: Reference markings (11.x1, 11.x2, 11.y) are each arranged in an edge region of the measuring graduation (12).

5. The optical position measuring device according to claim 4, characterized in that Reference marks (11.x1, 11.x2, 11.y; 111.x, 111.y) assigned to a measuring direction (x, y) each have a distance (Rx, Ry) to an edge of the measuring graduation (12) that is smaller than a spacing (Sx, Sy) between two adjacent scanning units (20.x1, 20.x2, 20.y1, 20.y2; 120.x, 120.y1, 120.y2) along the measuring direction (x, y).

6. The optical position measuring device according to claim 2, characterized in that: a first scanning unit (120.x) is assigned to the first measuring direction (x) and a second scanning unit and a third scanning unit (120.y1, 120.y2) are assigned to the second measuring direction (y), The second scanning unit and the third scanning unit (120.y1, 120.y2) have no offset along the second measuring direction (y).

7. The optical position measuring device according to claim 3, characterized in that: Four scanning units (20.x1, 20.x2, 20.y1, 20.y2) are arranged on the other object relative to the measuring scale (12), wherein a first scanning unit and a fourth scanning unit (20.x1, 20.x2) are allocated to the first measuring direction (x), and a second scanning unit and a third scanning unit (20.y1, 20.y2) are allocated to the second measuring direction (y), and In this case, the two scanning units (20.x1, 20.x2; 20.y1, 20.y2) assigned to one measuring direction have no offset along the second measuring direction (y).

8. The optical position measuring device according to claim 1, characterized in that In each of the periodic sub-regions (15.1) of the reference markings (11.x1, 11.x2, 11.y; 111.x, 111.y) there is arranged a one-dimensional incremental graduation which has an increased scanning efficiency in the form of a higher diffraction efficiency compared to the surrounding measuring graduation (12; 112).

9. The optical position measuring device according to claim 8, characterized in that: By means of a one-dimensional incremental graduation in a periodic sub-region (15.1) of the reference mark (11.x1, 11.x2, 11.y; 111.x, 111.y), diffraction in the + / -1 diffraction order is produced only along one measuring direction (x, y), while diffraction in the + / -1 diffraction order is produced along both measuring directions (x, y) in the surrounding measuring graduation (12).

10. The optical position measuring device according to claim 9, characterized in that: The incremental graduations in the periodic sub-regions (15.1) of the reference markings (11.x1, 11.x2, 11.y; 111.x, 111.y) and the surrounding measuring graduations (12; 112) are each designed as reflective phase gratings.

11. The optical position measuring device according to claim 1, characterized in that The periodic sub-region (215.1) and the non-periodic sub-region (215.2) of the reference marking (211.x1) have an increased scanning efficiency in the form of a higher reflectivity relative to the surrounding measuring graduation (212).

12. The optical position measuring device according to claim 11, characterized in that: A cross grating is arranged in the periodic sub-region (215.1) of the reference mark (211.x1), which is constructed as a reflection phase grating like the surrounding measuring graduation (212), wherein the periodic sub-region (215.1) and the non-periodic sub-region (215.2) of the reference mark (211.x1) are provided with a reflection enhancing coating (216).

13. The optical position measuring device according to claim 1, characterized in that The non-periodic subregions (15.2; 115.2; 215.2) of the reference markings (11.x1, 11.x2, 11.y; 111.x, 111.y; 211.x1) each have a chirped grating structure in which the grating period varies symmetrically in position with respect to a central axis of symmetry.

14. The optical position measuring device according to claim 1, characterized in that The periodic sub-regions (15.1; 215.1) of the reference markings (11.x1, 11.x2, 11.y; 111.x, 111.y; 211.x1) and the non-periodic sub-regions (15.2; 215.2) of the reference markings (11.x1, 11.x2, 11.y; 111.x, 111.y; 211.x1) are periodically arranged perpendicular to the measuring direction (x, y).

15. The optical position measuring device according to at least one of the preceding claims, characterized in that The periodic subregion (15.1; 215.1) and the non-periodic subregion (15.2; 215.2) of the reference mark (11.x1, 11.x2, 11.y; 111.x, 111.y; 211.x1) have an area ratio different from 1:1 with respect to each other.

16. The optical position measuring device according to claim 1, characterized in that A one-dimensional or two-dimensional periodic grating structure is arranged in the periodic sub-region (15.1; 215.1) of the reference mark (11.x1, 11.x2, 11.y; 111.x, 111.y; 211.x1), the periodicity of the grating structure along one or two measuring directions (x, y) corresponding to the periodicity of the surrounding measuring graduations (12; 212) along one or two measuring directions (x, y).

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