Optical position-measuring device

Abstract

SOLUTION: The invention relates at least to an optical position-measuring device for determining a relative position of two objects that are movable relatively to one another along two measurement directions. Multiple scanning units are provided therefor which are connected to one of the two objects and each include at least one light source, one or more gratings, and a detector configuration. Further there is provided, a measurement element connected to the other object. The measurement element includes a two-dimensional measuring graduation composed of structure elements which are periodically arranged along the two measurement directions and have different optical properties. Multiple reference marks are integrated into the measuring graduation and have periodic and aperiodic sub-regions. Scanning of each reference mark allows a respective reference signal to be generated at a defined reference position along a measurement direction. At least the periodic sub-regions of the reference marks have higher scanning efficiency than the surrounding measuring graduation.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to an optical position measuring device that is suitable for determining with high precision the relative position of two objects capable of relative motion. [Background technology]

[0002] From DE102004006067A1 a position measuring device is known which is suitable for determining the relative position of two objects which are movable relative to one another along at least two measuring directions. For this purpose, the position measuring device comprises a number 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 arrangement. Furthermore, the position measuring device comprises a measuring element which is connected to the other object. The measuring element comprises a measuring graduation in the form of a two-dimensional cross grating, which consists of two superimposed periodic incremental graduations extending along the two measuring directions. Two reference marks are integrated into the cross grating, from the scanning of which a reference signal can be generated at a defined reference position along each measuring direction, respectively. Here, the use of the reference marks which are integrated into the cross grating allows a reference signal generation along the first measuring direction independently of the position of the scanning unit along the second measuring direction and vice versa.

[0003] Also known from EP 3527951 B1 is an optical position measuring device with a reference mark integrated into a number of measuring graduations. The reference mark provided therein comprises aperiodic and periodic partial areas, where the periodic partial areas are configured identically to the surrounding measuring graduations. The aperiodic partial areas each consist of a chirped grating structure that is arranged symmetrically with respect to a central symmetry axis.

[0004] However, with regard to the generation of the reference signal, known solutions in which reference marks are integrated into the measuring graduation have certain problems: when the scanning unit passes over the respective reference mark, the signal level of the generated incremental signal drops more or less significantly. To avoid this, it is known to increase the light output of the light source when passing over the reference mark. However, this reduces the so-called control reserve of the light source, i.e. the light source current is in this case not sufficiently available to compensate for other negative effects, such as, for example, ageing and / or contamination. Summary of the Invention [Problem to be solved by the invention]

[0005] The object of the present invention is to provide an optical position measuring device for high-precision position determination along at least two measuring directions, in which the generation of periodic incremental signals is guaranteed with as little signal reduction as possible, even when passing over reference marks integrated into the measuring graduation. [Means for solving the problem]

[0006] This problem is solved according to the invention by an optical position measuring device having the features of claim 1. Advantageous embodiments of the optical position measuring device according to the invention result from the measures recited in the dependent claims.

[0007] The optical position measuring device according to the invention is used for determining the relative position of two objects movable relative to each other along at least two measuring directions. The optical position measuring device comprises a number 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 arrangement. Furthermore, a measuring element is provided which is connected to the other object. The measuring element comprises a two-dimensional measuring graduation consisting of structure elements with different optical properties, which are arranged periodically along the two measuring directions. A number of reference marks with periodic and aperiodic partial areas are integrated in the measuring graduation, and a reference signal can be generated from the scanning of the reference marks at each defined reference position along the measuring direction. At least the periodic partial areas of the reference marks have a higher scanning efficiency than the surrounding measuring graduations.

[0008] Two rectangular reference marks can be integrated into the measuring scale in an L-shaped arrangement, the reference marks being assigned to a first measuring direction and a further reference mark being assigned to a second measuring direction oriented perpendicular to the first measuring direction.

[0009] Alternatively, it can be envisaged that three rectangular reference marks are incorporated into the measuring scale in a U-shaped arrangement, with two reference marks being assigned to one measuring direction (x) and a further reference mark being assigned to another measuring direction oriented perpendicular to the first measuring direction (x).

[0010] It has proven advantageous if the reference marks are each arranged in the edge region of the measuring graduation. Here, the reference marks assigned to a measuring direction may each have a distance to the edge of the measuring graduation which is smaller than the distance between two adjacent scanning units along this measuring direction.

[0011] In a further embodiment, - a first scanning unit is assigned to a first measuring direction and a second and a third scanning unit are assigned to a second measuring direction; - the second and third scanning units have no offset along the second measurement direction; It can be contemplated that:

[0012] In a further embodiment, - four scanning units are arranged on the other object relative to the measuring scale, - the first and fourth scanning units are assigned to a first measurement direction and the second and third scanning units are assigned to a second measurement direction; - two scanning units assigned to one measuring direction have no offset along the second measuring direction It can be contemplated that:

[0013] It is furthermore possible for a one-dimensional incremental graduation to be arranged in each of the periodic partial regions of the reference mark, in order that the incremental graduations increase the scanning efficiency in the form of a higher diffraction efficiency compared to the surrounding measurement graduations.

[0014] Here, via the one-dimensional incremental graduation in the periodic partial areas of the reference mark, only diffraction of + / -1 diffraction orders along one measuring direction occurs, whereas at the surrounding measuring graduations diffraction of + / -1 diffraction orders along two measuring directions occurs.

[0015] Here, the incremental graduations in the periodic partial areas of the reference mark and the surrounding measuring graduations are preferably each designed as a reflective phase grating. Alternatively, it may be provided that the periodic and non-periodic partial regions of the reference mark have an increased scanning efficiency in the form of a higher reflectivity compared to the surrounding measuring graduations.

[0016] Here, a cross grating is arranged in the periodic partial region of the reference mark, which cross grating, like the surrounding measuring graduation, is configured as a reflective phase grating, and the periodic partial region and the non-periodic partial region of the reference mark are provided with a reflection-enhancing coating.

[0017] Furthermore, it is also possible for the non-periodic partial regions of the reference mark to each have a chirped grating structure, in which the grating period varies locally symmetrically relative to a central axis of symmetry.

[0018] Advantageously, it can furthermore be provided that the periodic partial regions of the reference mark and the non-periodic partial regions of the reference mark are arranged periodically perpendicular to the measuring direction. Furthermore, it is also possible that the periodic and non-periodic partial areas of the reference mark have an area ratio to one another that is not 1:1.

[0019] In one possible embodiment it may further be provided that one- or two-dimensional periodic grating structures are arranged in the periodic partial regions of the reference mark, the periodicity of these periodic grating structures along the one or two measuring directions corresponding to the periodicity of the surrounding measuring graduations along the one or two measuring directions.

[0020] It has been found particularly advantageously that in the optical position measuring device according to the invention, even when passing a reference mark integrated in the measuring graduation, a significant drop in the signal level of the periodic incremental signal no longer occurs, so that an increase in the light source current is no longer necessary and control reserves are sufficiently available to compensate, for example, for the effects of aging or contamination.

[0021] Further details and advantages of the invention will be explained with reference to the following description of an exemplary embodiment of the device according to the invention in conjunction with the drawings. [Brief description of the drawings]

[0022] [Figure 1] FIG. 1 shows a highly schematic plan view of a first exemplary embodiment of an optical position measuring device according to the invention, comprising a measuring graduation configured as a two-dimensional crossed grating in which three reference marks are integrated, and four scanning units; [Diagram 2] FIG. 2 is a plan view showing a partial area of ​​the reference mark of the exemplary embodiment from FIG. [Diagram 3] Figure 3a shows a schematic cross-sectional view including the scanning beam path of a scanning unit of an optical position measuring device according to the invention, and Figure 3b shows a plan view of the scanning unit from Figure 3a. [Figure 4] FIG. 2 shows a highly schematic plan view of a further exemplary embodiment of an optical position measuring device according to the invention, comprising a measuring graduation configured as a two-dimensional crossed grating in which two reference marks are integrated, and three scanning units; [Diagram 5] 4 shows a plan view of a partial area of ​​a reference mark of a further exemplary embodiment of the optical position measuring device according to the invention; [Figure 6] Fig. 6a is a cross-sectional view of the measuring graduation in the region of the reference mark from the exemplary embodiment according to Fig. 5. Fig. 6b is a cross-sectional view of the measuring graduation in the region of the reference mark from the exemplary embodiment according to Fig. 5. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] With reference to figures 1, 2 and 3a and 3b, an exemplary embodiment of an optical position measuring device according to the invention will now be described. The position measuring device shown in Figure 1 is used to determine the relative position of two objects (not shown) movable relative to one another along two measuring directions x, y, which are oriented orthogonal to one another.

[0024] In the following, the measurement direction x is also referred to as the first measurement direction and the measurement direction y is also referred to as the second measurement direction.The objects may be machine components capable of relative movement to one another, such as for example a table and a tool of a semiconductor processing machine.

[0025] Here, a measuring element 10 of a position measuring device is connected to one of the two objects, which has a two-dimensional reflective measuring graduation 12 on a scale carrier. The two-dimensional measuring graduation 12 is configured in this case as a so-called cross grating and consists of structural elements 12.1, 12.2 with different optical properties that are arranged periodically along the two measuring directions x, y. See, inter alia, the enlarged schematic view of a part of the measuring graduation 12 depicted in the lower part of FIG. 1. In the illustrated reflected light system, the measuring graduation 12 is configured as a reflective phase grating, in which the structural elements 12.1, 12.2 exert different phase-shift effects on the reflected light beam. In a specific embodiment, a chrome step grating with a phase shift of 180° and a periodicity of 8 μm along the two measuring directions x, y can serve as a reflective phase grating. Via optical scanning of the measuring graduation 12, periodic incremental signals are generated along the two measuring directions x, y, which respectively provide a measure for the relative movement of the two objects along the corresponding measuring directions x, y. A number of reference marks 11.x1, 11.x2, 11.y are integrated into the measuring graduation 12, where three rectangular reference marks 11.x1, 11.x2, 11.y are provided in a U-shaped arrangement, i.e. the three reference marks 11.x1, 11.x2, 11.y are arranged in an edge region of the measuring graduation 12 parallel to the three edges. From the optical scanning of the reference marks 11.x1, 11.x2, 11.y, reference signals are generated at defined reference positions along one of the two measuring directions x, y, respectively. Via calculation of the reference signals and the incremental signals, high-resolution absolute position information can be generated along the two measuring directions x, y in a known manner. The specific configuration of the reference marks 11.x1, 11.x2, 11.y with periodic and non-periodic partial areas in a particular arrangement will be explained in detail below with reference to Fig. 2. The position signal generated by the optical position measuring device according to the invention in the form of a periodic incremental signal and a reference signal is further processed by a downstream control unit (not shown), which thereby controls the relative movement of the corresponding machine parts.

[0026] A number of scanning units 20.x1, 20.x2, 20.y1, 20.y2 of the optical position measuring device according to the invention are connected to the other of the two objects, in this example a total of four scanning units 20.x1, 20.x2, 20.y1, 20.y2 are provided. Each of the scanning units 20.x1, 20.x2, 20.y1, 20.y2 comprises at least one light source, one or more gratings and a detector arrangement. The measuring graduation 12 is optically scanned by the scanning units 20.x1, 20.x2, 20.y1, 20.y2 and incremental and reference signals are generated along the two measuring directions x, y. For the specific configuration of the scanning units 20.x1, 20.x2, 20.y1, 20.y2, please refer to the further following description of Fig. 3a and Fig. 3b.

[0027] In the optical position measuring device according to the invention, the various scanning units 20.x1, 20.x2, 20.y1, 20.y2 are arranged relative to one another in a particular way, which is explained below with reference to an illustrated example, where the four provided scanning units 20.x1, 20.y1, 20.y2, 20.x2 are referred to from the left as the first, second, third and fourth scanning unit 20.x1, 20.y1, 20.y2, 20.x2.

[0028] In this case, a first scanning unit 20.x1 and a fourth scanning unit 20.x2 are assigned to the first measurement direction x, and these two scanning units 20.x1, 20.x2 have a distance Lx1 from each other along the first measurement direction x and have no offset from each other along the second measurement direction y, i.e. are arranged at the same height along the second measurement direction y.

[0029] The second measuring direction y is assigned to a second scanning unit 20.y1 and a third scanning unit 20.y2, which have a distance Lx2 from each other along the first measuring direction x and have no offset from each other along the second measuring direction y. As can be seen, the second and third scanning units 20.y1, 20.y2 are arranged between the first scanning unit 20.x1 and the fourth scanning unit 20.x2 along the measuring direction x.

[0030] The first scanning unit 20.x1 is disposed at a distance Sx along the first measuring direction x and at a distance Sy along the second measuring direction y relative to the second scanning unit 20.y1.

[0031] As already mentioned above, in the example of Fig. 1 three rectangular reference marks 11.x1, 11.x2, 11.y are integrated into the measuring graduation 12 in a U-shaped arrangement. Similar to the designation of the various scanning units 20.x1, 20.x2, 20.y1, 20.y2, the three provided reference marks 11.x1, 11.y, 11.x2 are also referred to as, from the left, first, second and third reference marks 11.x1, 11.y and 11.x2.

[0032] The first reference mark 11.x1 and the third reference mark 11.x2 are assigned to a first measurement direction x, and the major axes of these two reference marks 11.x1, 11.x2 extend along a second measurement direction y. Thus, via the first reference mark 11.x1 and the third reference mark 11.x2, a reference is possible for a movement along the first measurement direction x. The second reference mark 11.y is assigned to a second measurement direction y, and its major axis extends along the first measurement direction x. Thus, via the second reference mark 11.y, a reference is possible for a movement along the second measurement direction y. From the scanning of the first and third reference marks 11.x1, 11.x2, a reference signal can be generated at a specific reference position along the first measurement direction x, respectively. Through the scanning of the second reference mark 11.y, a reference signal can be generated at a specific reference position along the second measurement direction y.

[0033] 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 illustrated example it is provided that the reference mark 11.x1, 11.x2 or 11.y assigned to the measuring direction x or y has a distance Rx or Ry to 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 this measuring direction x, y, i.e. is selected such that the distance Rx from the reference mark 11.x1, 11.x2 to the respective nearest edge of the measuring graduation 12 is smaller than the distance Sx which indicates the distance of the two adjacent scanning units 20.x1, 20.y1 and the distance of the two adjacent scanning units 20.x2, 20.y2 along the first measuring direction x, respectively. Similarly, the distance Ry from the reference mark 11.y to the adjacent edge of the measuring scale 12 is selected to be smaller than the distance Sy indicating the distance between two adjacent scanning units 20.x1, 20.y1 and the distance between two adjacent scanning units 20.x2, 20.y2 along the second measuring direction y.

[0034] Through the above-mentioned arrangement of the scanning units 20.x1, 20.x2, 20.y1, 20.y2 and the reference marks 11.x1, 11.x2, 11.y, in the illustrated example, localization is possible during sliding of the object along the two measurement directions x, y and during rotation of the object around an axis z oriented perpendicularly to the two measurement directions x, y. Furthermore, such a number and arrangement of the reference marks 11.x1, 11.x2, 11.y and the scanning units 20.x1, 20.x2, 20.y1, 20.y2 also allows possible thermal expansion of the measuring element 10 to be detected.

[0035] Further possibilities regarding the number and arrangement of scanning units and reference marks in the optical position measuring device according to the invention are outlined further below in the present specification. The configuration of the reference marks in an optical position measuring device according to the invention will now be described with reference to Fig. 2. Fig. 2 shows a highly schematic detailed view of the first reference mark 11.x1 from Fig. 1. This view only shows the provided structural details in a small area along the longitudinal extension direction y of the reference mark 11.x1. Fig. 2 is not a to-scale view of the reference mark 11.x1 and serves only to explain the basic configuration of the reference mark 11.x1.

[0036] As already mentioned above, the reference mark of the device according to the invention consists of a periodic partial region 15.1 and an aperiodic partial region 15.2. The various partial regions 15.1, 15.2 of the reference mark, like the surrounding measuring graduations, are configured as reflective phase gratings and each have a rectangular geometry according to the plan view of FIG. 2. The major axes of the rectangles of the periodic and aperiodic partial regions 15.1, 15.2 of the reference mark 11.x1 are oriented perpendicularly to the major axis of the reference mark 11.x1. That is to say, the major axes of the rectangles of the various partial regions 15.1, 15.2 run parallel to the first measuring direction x in this reference mark, and the major axis of the reference mark 11.x1 runs parallel to the second measuring direction y. Along the major axis of the reference mark 11.x1, the partial regions 15.1, 15.2 of the reference mark 11.x1 are arranged periodically, i.e. along the y direction, periodic partial regions 15.1 and aperiodic partial regions 15.2 are arranged alternately. Within the reference mark 11.x1, the periodic partial regions 15.1 and the aperiodic partial regions have an area ratio to each other that is not 1:1, i.e. the reference mark 11.x1 is composed of periodic and aperiodic parts with different proportions. The area ratio of the periodic partial regions 15.1 and the aperiodic partial regions 15.2 is therefore selected such that it is not 0.5. Here, in one possible embodiment, the area ratio of the periodic partial regions 15.1 and the aperiodic partial regions 15.2 can be selected in the range from 0.25 to 0.5, i.e. the periodic parts occupy a smaller area proportion than the aperiodic parts. The selection of such an area proportion leads firstly to an increase in the reference signal. Especially when combined with an amplitude adjustment of the incremental signal, the reference signal is again additionally improved, since the main maxima of the reference signal are amplified compared to the secondary maxima of the reference signal.

[0037] In this regard, in a preferred embodiment, it is envisaged, for example, that the width of the periodic partial areas 15.1 along the second measuring direction y is 18 μm and the width of the non-periodic partial areas 15.2 along the second measuring direction y is 22 μm. With such dimensions, the ratio of the areas of the periodic partial areas 15.1 and the non-periodic partial areas 15.2 in the reference mark 11.x1 is 0.45.

[0038] Such a reference mark periodicity of 40 μm, which is small compared to the signal-contributing area of ​​the measuring graduation, has proven to be particularly advantageous when the reference mark is passed obliquely by the scanning unit. A reference mark periodicity of 128 μm or less, in particular 64 μm or less, is particularly suitable. As a result, the fluctuations in the partial areas of the non-periodic and periodic partial areas involved in signal generation during the pass are small. This improves the signal-to-noise ratio of the reference signal and improves the amplitude fluctuations of the incremental signal. These advantages are also obtained when the scanning unit can enter the reference mark area at different Y positions during a straight pass, as in a 2D measuring system.

[0039] The second and third reference marks 11.y, 11.x2 in FIG. 1 are also configured essentially identically to the first reference mark 11.x1, but the second reference mark 11.y is rotated by 90° and extends along the first measurement direction x.

[0040] Each of the non-periodic partial regions 15.2 of the reference mark 11.x1 is provided with a so-called chirped grating structure, i.e. the structural elements 15.2a, 15.2b with different optical properties are not arranged strictly periodically along the major axis of the respective rectangle, but with a locally varying grating period in the respective partial region 15.2. In particular, in this example it is intended that the grating period varies locally symmetrically with respect to the central symmetry axis of the partial region 15.2, increasing from the symmetry axis outwards.

[0041] The configuration of the periodic partial areas 15.1 of the reference mark 11.x1 is important for the desired properties of the reference mark 11.1x integrated into the measuring graduation. In this regard, it is intended that at least these partial areas 15.1 have a higher scanning efficiency than the surrounding measuring graduation. This makes it possible to ensure that the incremental signal level does not drop significantly when passing the reference mark 11.x1, and therefore no increase in the light source current is required.

[0042] Now, there are various possibilities to ensure a higher scanning efficiency of the periodic partial areas of the reference mark. A first variant is described with reference to the example in FIG. 2, and further possibilities are described herein below with the aid of FIGS. 5, 6a, 6b. In the example of FIG. 2, a one-dimensional incremental graduation is arranged in the periodic partial area 15.1 of the reference mark 11.x1, which graduation is intended to have a higher diffraction efficiency than the surrounding two-dimensional measurement graduation. The one-dimensional incremental graduation in the periodic partial area 15.1 consists of a periodic arrangement of structural elements 15.1a, 15.2b with different optical properties along the first measurement direction x, as can be seen from FIG. 2. Here, the periodicity of this incremental graduation is selected to be identical to the periodicity of the cross grating along the measurement direction x. The different structural elements 15.1a, 15.1b exert different phase shift effects on the reflected light beam. In one possible embodiment, the incremental graduation is formed, for example, as a chrome step grating and may have a phase shift of 180°.

[0043] Through the one-dimensional incremental graduation in the periodic partial area 15.1 of the reference mark 11.x1, diffraction into + / -1 diffraction orders along the measuring direction x occurs substantially, i.e. the incident intensity is distributed mainly into these two diffraction orders on reflection. On the other hand, if a two-dimensional measuring graduation is arranged in the periodic partial area of ​​the reference mark, this would result in diffraction into + / -1 diffraction orders along the two measuring directions x, y, i.e. a distribution of the incident beam intensity into four reflected diffraction orders. A significant reduction of the incremental signal when passing through the reference mark 11.x1 would be an undesirable consequence.

[0044] The scanning beam paths in the optical position measuring device according to the invention are described below with reference to Figures 3a and 3b. The description is made with reference to the cross-sectional view of the scanning beam paths for the first scanning unit 20.x1 from Figure 1 in the xz plane and the plan view of the detection plane of this scanning unit 20.x1 shown in Figure 3a. The scanning beam paths or the structure of the fourth scanning unit 20.x2 from Figure 1 are essentially identical to this scanning beam path. The scanning beam paths of the second and third scanning units 20.y1, 20.y2 run rotated by 90° around the z axis, via which movements along the second measuring direction y are detected.

[0045] In the illustrated scanning unit 20.x1 of the position measuring device, a support element 21 is provided with a light source 22 and an adjacent detector arrangement with an incremental signal detector 25.1 and a reference signal detector 25.2. The divergent radiation light source 22 is arranged in the light propagation direction upstream of an emission grating arrangement, which comprises a periodic transmission emission grating 23.1 and an emission slit 23.2 arranged adjacent to it.

[0046] The interaction of the light beam emitted by the light source 22 with the gratings provided in the scanning beam path, i.e. the transmission emission grating 23.1, the emission slit 23.2 and the measuring graduation 12, results in a displacement-dependent signal pattern in the detection plane of the detector arrangement. Via optoelectronic scanning of this signal pattern by means of the scanning unit 20.x1, periodic incremental and reference signals are generated along the first measuring direction x.

[0047] In FIG. 3 a the structure of a measuring element 10 with a two-dimensional measuring graduation 12 arranged on a scale carrier 11 can furthermore be seen. With reference to the further figures, alternative variants of the optical position measuring device according to the invention are described below, substantially only the important differences from the exemplary embodiment described above being mentioned.

[0048] 4 shows a plan view of a variant in which only two reference marks 111.x, 111.y are incorporated into the measuring graduation in an L-shaped arrangement, which are arranged in the edge region of the measuring graduation at a distance Rx or Ry to the edge, as in the previous exemplary embodiment.

[0049] Here, three scanning units 120.x, 120.y1, 120.y2 are provided on the scanning side. Here, the first scanning unit 120.x is assigned to the first measurement direction x, and the second scanning unit 120.y1 and the third scanning unit 120.y2 are assigned to the second measurement direction y. As can be seen from the figure, the second scanning unit 120.y1 and the third scanning unit 120.y2 have no offset along the second measurement direction y, but are each offset by a distance Sy along the second measurement direction y relative to the first scanning unit 120.x. Along the first measurement direction x, the second scanning unit 120.y1 is offset by a distance Sx. In the figure, the distance between the second scanning unit 120.y1 and the third scanning unit 120.y2 along the first measurement direction x is indicated with Lx.

[0050] Via this variant of the optical position measuring device according to the invention it is possible to detect relative movements along the first measuring direction x and along the second measuring direction y as well as a rotation around the measuring direction z. The reference marks 111.x, 111.y integrated in the two-dimensional measuring graduation and the three scanning units 120.x, 120.y1, 120.y2 are configured identically to the first exemplary embodiment.

[0051] With reference to Figure 5 and Figures 6a, 6b, an alternative possibility is explained, by which an increase in the scanning efficiency can be realised in partial areas of the reference mark, as already alluded to above: Figure 5 shows, like Figure 2, a schematic detail of the corresponding reference mark 211.x1, while Figures 6a, 6b respectively show cross-sections of the measuring graduation in the area of ​​the reference mark 211.x1.

[0052] In order to increase the scanning efficiency in the region of the reference mark 211.x1, it is provided here that both the periodic partial regions 215.1 and the aperiodic partial regions 215.2 of the reference mark 211.x1 have a higher reflectivity than the surrounding measuring graduation 212. This is achieved by 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, i.e. both in the periodic partial regions 215.1 and in the aperiodic partial regions 215.2.

[0053] The grating structure in the non-periodic partial region 215.2 is configured as a chirped grating structure, as in the example of Fig. 2. In contrast to Fig. 2, a cross grating, i.e. the same grating structure as the surrounding measuring graduation 212, is arranged in the periodic partial region 215.1 of the reference mark 211.x1. Here, the cross grating arranged in the periodic partial region 215.1 has the same periodicity along the two measuring directions x, y as the cross grating of the surrounding measuring graduation 212.

[0054] In one specific exemplary embodiment, the reflective phase grating in the area of ​​the reference mark 211.x1 may be configured as a chrome step grating with a phase shift of 180°. A titanium nitride layer serves as the reflection enhancing coating 216.

[0055] When the reference marks are configured in this way, they do not necessarily have to be arranged in edge regions within the two-dimensional measuring graduation: for example, it is also possible to provide the measuring graduation with two such reference marks in a 90° crossed arrangement, with the crossing point overlapping the centre of the measuring graduation and the reference marks extending parallel to the first and second measuring directions.

[0056] In addition to the exemplary embodiments described above with reference to the figures, there are, of course, still further possible embodiments within the scope of the present invention. In the case of a U-shaped arrangement of three reference marks on a two-dimensional measuring graduation according to Fig. 1, it is also possible to provide only three scanning units on the scanning side, i.e. for example to omit the fourth scanning unit 20.x2 in Fig. 1. In that case it would be possible to detect only translational movements along the x and y directions as well as rotational movements around the z direction.

[0057] Furthermore, it would also be possible for the measuring graduation to be configured as a reflection amplitude grating, for example. [Explanation of symbols]

[0058] 10 Measurement elements 11.x1 fiducial mark 11.x2 Fiducial Mark 11.y Reference mark 12 Measuring scale 12.1 Structural elements 12.2 Structural elements 15.1 Periodic subregions 15.2 Aperiodic subregions 20.x1 Scanning unit 20.x2 Scanning Unit 20.y1 Scanning unit 20.y2 Scanning unit 21 Supporting elements 22 Light source 23.1 Periodic transmission and emission gratings 23.2 Exit Slit 25.1 Incremental Signal Detector 25.2 Reference Signal Detector

Claims

1. 1. An optical position measuring device for determining the relative position of two objects movable relative to one another along at least two measuring directions (x, y), comprising: a number of scanning units (20.x1, 20.x2, 20.y1, 20.y2; 120.x, 120.y1, 120.y2) connected to one of said two objects and each including at least one light source (22), one or more gratings (23.1, 23.2) and a detector arrangement; a measuring element (10; 110) connected to the other object, said measuring element (10; 110) - a two-dimensional measuring graduation (12; 212) consisting of structure elements (12.1, 12.2) with different optical properties, which are arranged periodically along the two measuring directions (x, y), a plurality of reference marks (11.x1, 11.x2, 11.y; 111.x, 111.y; 211.x1) with periodic and aperiodic partial areas (15.1, 15.2; 215.1, 215.2) integrated into said measuring graduation (12; 212), wherein a reference signal can be generated at defined reference positions along the measuring direction (x, y) from a scanning of the reference marks (11.x1, 11.x2, 11.y; 111.x, 111.y; 211.x1), In an optical position measuring device, At least the periodic partial areas (15.1; 215.1) of the reference mark (11.x1, 11.x2, 11.y; 111.x, 111.y; 211.x1) have a higher scanning efficiency than the surrounding measuring graduations (12; 212).

1. An optical position measuring device comprising:

2. 2. The optical position measuring device according to claim 1, characterized in that two rectangular reference marks (111.x, 111.y) are integrated into the measuring graduation in an L-shaped arrangement, the reference mark (111.x) being assigned to a first measuring direction (x) and the further reference mark (111.y) being assigned to a second measuring direction (y) oriented perpendicular to the first measuring direction (x).

3. 2. The optical position measuring device according to claim 1, characterized in that three rectangular reference marks (11.x1, 11.x2, 11.y) are integrated into the measuring graduation (12) in a U-shaped arrangement, two reference marks (11.x1, 11.x2) being assigned to one measuring direction (x) and a further reference mark (11.y) being assigned to another measuring direction (y) oriented perpendicular to the first measuring direction (x).

4. 4. The optical position measuring device according to claim 2, wherein the reference marks (11.x1, 11.x2, 11.y) are each arranged in the edge region of the measuring graduation (12).

5. 5. The optical position measuring device according to claim 4, characterized in that the 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 the distance (Sx, Sy) of 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. a first scanning unit (120.x) is assigned to said first measuring direction (x) and a second and a third scanning unit (120.y1, 120.y2) are assigned to said second measuring direction (y), the second and third scanning units (120.y1, 120.y2) have no offset along the second measuring direction (y); 3. An optical position measuring device according to claim 2 .

7. - four scanning units (20.x1, 20.x2, 20.y1, 20.y2) are arranged on the other object relative to the measuring graduation (12), a first and a fourth scanning unit (20.x1, 20.x2) are assigned to said first measuring direction (x) and a second and a third scanning unit (20.y1, 20.y2) are assigned to said second measuring direction (y), 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); 4. An optical position measuring device according to claim 3, characterized in that

8. 8. The optical position measuring device according to claim 1 , wherein a one-dimensional incremental graduation is arranged in each of the periodic partial areas (15.1) of the reference mark (11.x1, 11.x2, 11.y; 111.x, 111.y), and the incremental graduation has an increased scanning efficiency in the form of a higher diffraction efficiency compared to the surrounding measuring graduations (12; 112).

9. 9. The optical position measuring device according to claim 8, characterized in that via the one-dimensional incremental graduation in the periodic partial areas (15.1) of the reference mark (11.x1, 11.x2, 11.y; 111.x, 111.y) only diffraction of + / - 1 diffraction order occurs along one measuring direction (x, y), whereas at the surrounding measuring graduations (12) diffraction of + / - 1 diffraction order occurs along two measuring directions (x, y).

10. 10. The optical position measuring device according to claim 9, characterized in that the incremental graduations in the periodic partial areas (15.1) of the reference mark (11.x1, 11.x2, 11.y; 111.x, 111.y) and the surrounding measurement graduations (12; 112) are each constructed as a reflective phase grating.

11. 8. The optical position measuring device according to claim 1 , wherein the periodic partial areas (215.1) and the non-periodic partial areas (215.2) of the reference mark (211.x1) are provided with an improved scanning efficiency in the form of a higher reflectivity compared to the surrounding measuring graduations (212).

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

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

14. 14. An optical position measuring device as claimed in claim 1, characterized in that the periodic partial areas (15.1; 215.1) of the reference mark (11.x1, 11.x2, 11.y; 111.x, 111.y; 211.x1) and the non-periodic partial areas (15.2; 215.2) of the reference mark (11.x1, 11.x2, 11.y; 111.x, 111.y; 211.x1) are arranged periodically perpendicular to the measuring direction (x, y).

15. 15. An optical position measuring device according to claim 1, characterized in that the periodic partial areas (15.1; 215.1) and the non-periodic partial areas (15.2; 215.2) of the reference mark (11.x1, 11.x2, 11.y; 111.x, 111.y; 211.x1) have an area ratio to one another that is not 1:

1.

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

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