Position measurement system

Abstract

The present invention relates to a position measurement system for determining spatial position information. It comprises at least one light source and at least one optical receiver unit. This receiver unit has a diffraction grating and an optoelectronic detector whose photosensitive surfaces are oriented towards the grating. The detector has two detector regions arranged in a detection plane symmetrically with respect to a first axis of symmetry passing through the center of the detector in that plane. This first axis of symmetry is orthogonal to the longitudinal direction of the detector regions. Each of the two detector regions is in the shape of an acute isosceles triangle, whose vertices are oriented with the vertex angle towards the center of the detector (Fig. 2a).

Description

AREA OF TECHNOLOGY

[0001] The present invention relates to a position measurement system for determining spatial position information. STATE OF THE ART

[0002] From WO 01 / 38828 A1, an optical position measuring system is known which is designed as a spatial 2D angle measuring system and can be used to determine spatial position information. The position measuring system comprises, on the one hand, a transmitting unit arranged on a measuring object moving in space, whose spatial position and orientation (pose) is to be determined; a suitable light source can, for example, serve as the transmitting unit. On the other hand, one or more optical receiving units are provided, stationary opposite the moving transmitting unit. These receiving units essentially each comprise a scanning grating and an optoelectronic detector arrangement, the light-sensitive surfaces of which are oriented towards the scanning grating. With the aid of such a system, the position of the transmitting unit in space can be determined via a so-called multiangulation.For this purpose, the direction of the line of sight to the transmitting unit is determined from the perspective of the respective receiving unit using two angle measurements. Given a known relative position of two receiving units, the position of the transmitting unit can be determined from the intersection of the determined lines of sight. This measurement principle can be extended by adding further transmitting units, so that the spatial pose of transmitting units can also be determined via corresponding measurements. For further details of such a measurement principle, please refer to the aforementioned publication. SUMMARY OF THE INVENTION

[0003] The present invention is based on the objective of optimizing the generic position measurement system with regard to signal generation and thus increasing the accuracy of the position measurement.

[0004] This problem is solved according to the invention by a position measuring system with the features of claim 1.

[0005] Advantageous embodiments of the position measuring system according to the invention result from the measures listed in the dependent claims.

[0006] The position measuring system according to the invention serves to determine spatial position information. It comprises at least one light source and at least one optical receiving unit, which has a scanning grating and an optoelectronic detector arrangement whose light-sensitive surfaces are oriented in the direction of the scanning grating. The detector arrangement has two detector regions that are arranged in a detection plane in a mirror-symmetrical manner with respect to a first axis of symmetry, which runs through the center of the detector arrangement in the detection plane, wherein the first axis of symmetry is oriented orthogonally to the longitudinal direction of the detector regions. The two detector regions each have the shape of an isosceles, acute-angled triangle, the vertices of which are oriented with the apex angle towards the center of the detector arrangement.

[0007] Preferably, the detector arrangement has two further detector areas that are identical to the two first detector areas and are arranged in a mirror-symmetrical manner with respect to a second axis of symmetry, which runs through the center of the detector arrangement in the detection plane and is oriented orthogonally to the first axis of symmetry.

[0008] It is possible to that each triangle has a tip angle γ for which γ / 2 = 7.125° + / - 5°, and that the triangle tips touch at the tip angle in the center of the detector arrangement.

[0009] In one possible embodiment, a plurality of individual detector elements can be arranged periodically and parallel to each other along an arrangement direction in each detector area, which is oriented perpendicular to the longitudinal extension direction of the detector areas.

[0010] It is advantageous to envisage that that the detector elements are each rectangular in shape and the longitudinal axes of the rectangle are oriented parallel to the longitudinal direction of the detector area, and that every fourth detector element is electrically interconnected along the arrangement direction, so that the scanning of a striped pattern falling on the detector arrangement results in four phase-shifted output signals for further processing.

[0011] Preferably, the ratio of detector element width to detector element periodicity is 1:7.

[0012] It can also be advantageous to provide that the detector element length can be changed along the arrangement direction. dh _ D / dx = + / − 8 applies, with h_D := detector element length, x := arrangement direction.

[0013] Furthermore, it is possible that the scanning grating is arranged in a plane parallel to the detection plane and consists of a periodic arrangement of grating regions along at least one grating direction, wherein the grating direction assumes an angle of 45° to the longitudinal extension direction of the detector regions.

[0014] Advantageously, the scanning grating is designed as a transmittive, combined amplitude-phase grating, wherein In each lattice region, an identically designed, opaque amplitude lattice structure is arranged, and along each lattice direction, a phase-shifting layer is arranged above the amplitude lattice structure in every second lattice region.

[0015] It is possible that the phase-shifting layer is designed with respect to the material and the layer thickness in such a way that it results in a substantial suppression of the 0th diffraction order as well as all even diffraction orders for a certain wavelength range and for a certain angle of incidence range.

[0016] Furthermore, the amplitude grating structure can be designed such that for a certain wavelength range a preferred transmission into the + / - 1st diffraction orders and a largely suppressed odd diffraction orders results.

[0017] In one possible embodiment, the scanning grid may be arranged on the side of a transparent cover plate of the receiving unit that is oriented towards the detector arrangement.

[0018] Preferably, the combined amplitude-phase lattice has a checkerboard structure with a periodic arrangement of square lattice regions along two orthogonal lattice directions.

[0019] It may still be advantageous to plan for, that the amplitude lattice structure consists of opaque lattice bars arranged parallel to each other along the two lattice directions and having at least partially different bar widths, and that the amplitude lattice structures in lattice regions that are adjacent along a lattice direction are each mirror-symmetric to an axis of symmetry that runs along the boundary of the adjacent lattice regions.

[0020] Furthermore, it is possible that the light source is designed as an LED, emitting radiation in the wavelength range λ = 850nm + / - 20nm and possessing a coherence length less than or equal to 7µm.

[0021] The measures according to the invention now ensure that signal-distorting influences, such as unwanted subharmonics, harmonics, and 2D spatial frequencies, are suppressed or filtered out. Furthermore, it is ensured that a sufficient signal strength of the acquired measurement signals results over a large distance range between the light source and the receiving unit for all recorded reception angles. In this way, a significant increase in the accuracy of position measurement in space is possible.

[0022] Further details and advantages of the present invention will be explained with reference to the following description of an embodiment of the device according to the invention in conjunction with the figures. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] It shows Figure 1 is a highly schematic diagram illustrating the measuring principle of the optical position measuring system according to the invention; Figure 2a is a top view of an embodiment of the detector arrangement of the optical position measuring system according to the invention; Figure 2b is an enlarged detail view of a detector area of ​​the detector arrangement made of Figure 2a Figure 3 shows a top view of an embodiment of the scanning grid of the optical position measuring system according to the invention; Figure 4 shows a top view of a part of the scanning grid made of Figure 3 Figure 4: enlarged detail view of the scanning grid. Figure 4a in conjunction with a sectional view of the same; Figure 5, a side-by-side representation of the detector arrangement and the scanning grid from the Figures 2a and 3 . DESCRIPTION OF THE EXECUTION FORMS

[0024] Based on the highly schematic representation in Figure 1The underlying measuring principle of the optical position measuring system according to the invention and its basic structure will be explained below.

[0025] The corresponding optical position measuring system comprises at least one light source LQ and at least one optical receiving unit OE. The light source LQ can, for example, be arranged on a measuring object that moves in space, whose spatial position and orientation (pose) is to be determined with the help of the stationary optical receiving unit OE.

[0026] The light source LQ is preferably designed as an approximate point light source, e.g., as an LED. In an advantageous embodiment, the light source LQ has a very short coherence length, which is selected to be less than or equal to 7 µm; it emits radiation in the wavelength range λ = 850 nm ± 20 nm. The light source LQ emits divergent beams S in the direction of the optical receiving unit OE; that is, no collimation optics are arranged in front of the light source LQ.

[0027] The optical receiving unit OE essentially comprises an entrance-side scanning grating AG and an optoelectronic detector arrangement D fixed downstream of the scanning grating AG in the beam propagation direction. The scanning grating AG is located on the side of a transparent cover plate DP of the receiving unit OE that is oriented towards the detector arrangement D. All components of the receiving unit OE are arranged in a suitable housing, which is Figure 1 not shown in detail. The light-sensitive surfaces of the detector arrangement D are oriented towards the scanning grating AG and define a detection plane DE in the optical receiver unit OE. The detection plane DE is as shown in Figure 1 The optical sensors are arranged parallel to and at a specific distance d from the scanning grid AG in the receiving unit OE. Regarding a suitable design of the optical receiving unit OE, reference is made here to EP 4 145 083 A1.

[0028] The interaction of the diverging light beams S emitted by the light source LQ with the scanning grating AG results in a spatially structured light field in the form of a fringe pattern SM in the detection plane DE of the detector arrangement D via a grating self-image, which in the lower region of Figure 1This is schematically indicated in a partial top view of the detection plane DE of the detector arrangement D. In the case of a relative movement of the light source LQ with respect to the optical receiving unit OE, the fringe pattern SM moves across the detector arrangement D in the detection plane DE. By detecting the position or change in position of the fringe pattern with the help of the detector arrangement D, the point of intersection DP of the line connecting the light source LQ and the detector arrangement D through the scanning grating AG can then be determined. From the position of the point of intersection DP through the scanning grating AG, in combination with the known distance d between the scanning grating AG and the detector arrangement D, the angle of incidence θ relative to the grating normal GN is obtained.

[0029] In Figure 1Only the relationships with respect to the plane of the drawing are shown; that is, the plane of the drawing represents the measurement plane with respect to the angle of incidence of light θ. In practice, it is advantageous if, in addition to this—as mentioned at the outset—a second angle measurement is performed along a further measurement plane oriented perpendicular to the plane of the drawing. Therefore, in such an embodiment of the device according to the invention, a 2D angle measurement is ultimately performed between the light source LQ and the optical receiving unit OE. Both angle measurements are incremental measurements; that is, when the light source LQ moves from a first position to a second position, the resulting changes in angle in the two measurement planes are recorded using the optical position measuring system according to the invention.In a typical configuration, one signal period of the position-dependent incremental signals generated via the detector arrangement D corresponds to an angle change of a few mrad.

[0030] To ensure the most accurate possible measurement of the fringe pattern position and to avoid potential signal dropouts at varying distances between the light source LQ and the receiver OE, a number of measures prove advantageous in the optical position measuring system according to the invention, particularly on the side of the detector arrangement D and the scanning grating AG in the optical receiver OE. These measures are primarily necessary because the sinusoidal gratings ideally required for measurement by grating self-imaging are not available as scanning gratings due to manufacturing limitations; instead, binary gratings must be used. Ideal sinusoidal gratings are understood to be gratings whose transmission varies spatially in a sin²-like manner. If such sinusoidal gratings are used, only the + / - 1st diffraction orders resulting in transmission would contribute to the grating self-imaging in the detection plane.To ensure sufficiently accurate angle measurements despite the use of binary gratings, the measures described below are advantageous in order to minimize the undesirable effects caused by binary gratings as much as possible. Variants of detector arrangements D and scanning gratings AG, which have been optimized for use in the optical position measuring system according to the invention, are explained in detail below.

[0031] Based on the Figures 2a, 2b First, an embodiment of an advantageous detector arrangement 25 for 2D angle measurement is described.

[0032] In Figure 2aFigure 1 shows a top view of a corresponding detector arrangement 25 of the optical position measuring system according to the invention. In the present example, the detector arrangement 25 has four detector areas 25.1–25.4, each in the shape of an isosceles acute-angled triangle. The vertices of the triangles, each with the same apex angle γ, are all oriented towards the center Z of the detector arrangement 25. The center Z represents the geometric centroid of the detector arrangement surface. The detector areas 25.1–25.4 are arranged such that two detector areas 25.1, 25.2 and 25.3, 25.4, respectively, are arranged symmetrically with respect to one of the two axes of symmetry S1, S2 of the detector arrangement 25. The axes of symmetry S1, S2 pass through the center Z of the detector arrangement 25 in the detection plane and are orthogonal to each other. Specifically, in the example shown, the two detector areas are 25.1, 25.Detector areas 25.3 and 25.4 are arranged symmetrically about the first axis of symmetry S1, while the two detector areas 25.3 and 25.4 are arranged symmetrically about the second axis of symmetry S2. The detector areas 25.1, 25.2 and 25.3, 25.4, arranged symmetrically about one of the two axes of symmetry S1 and S2 respectively, each have a common longitudinal direction y and x, respectively. Thus, they extend according to... Figure 2a The two detector areas 25.1, 25.2 are oriented along the specified y-direction, and the detector areas 25.3, 25.4 along the x-direction. The longitudinal direction y of the two detector areas 25.1, 25.2 is therefore orthogonal to the first axis of symmetry S1, and the longitudinal direction x of the two detector areas 25.3, 25.4 is orthogonal to the second axis of symmetry S2.

[0033] The two detector areas 25.1, 25.2, whose longitudinal direction is oriented along the specified y-direction, serve to detect a stripe pattern movement along the measurement direction x; via the two other detector areas 25.3, 25.4, whose longitudinal direction is oriented along the x-direction, a stripe pattern movement along the measurement direction y can be detected.

[0034] In the illustrated embodiment of the detector arrangement 25, it is provided that the triangular tips of the detector areas 25.1 - 25.4 touch at the tip angle γ in the center Z of the detector arrangement 25.

[0035] In this example, and for this application with a measuring volume of approximately 1 m³ and an incidence angle range of approximately ±50°, the peak angle γ is selected such that γ / 2 = 7.125° ±5°. In principle, if the measuring range requirements change, a different range for the peak angle γ can be specified, for which γ / 2 = 7.125° ± [-5°, ±20°].

[0036] The length of a detector area 25.1 - 25.4 along its longitudinal extension direction x or y is 5,376 mm in each case; the base length of the triangular envelope is 1,344 mm in each case.

[0037] An enlarged detail view of detector area 25.1 is shown in Figure 2bAs shown in the figure, a plurality of individual, rectangular detector elements 25.1_DE are arranged periodically and parallel to each other in this detector area 25.1. The periodic arrangement in detector area 25.1 is along an arrangement direction x that is oriented perpendicular to the longitudinal extent direction y of the detector area 25.1; the arrangement direction x is therefore oriented parallel to the measurement direction x of this detector area 25.1. As can be seen, the rectangular longitudinal axes of the detector elements 25.1_DE are oriented parallel to the longitudinal extent direction y of the detector area 25.1. Suitable detector elements 25.1_DE include, for example, optoelectronic detector elements in the form of photodiodes.

[0038] Furthermore, how from Figure 2bAs can be seen, in detector area 25.1, every fourth detector element 25.1_DE is electrically interconnected along the arrangement direction x. This is achieved via four busbars 25.1_SL, each of which electrically connects every fourth detector element 25.1_DE. In this way, four periodic output signals A, B, C, D, phase-shifted by 90°, are generated from the scanning of the stripe pattern in the detection plane and made available for further processing. Four contact terminals 25.1_K outside this detector area 25.1 are connected to the four busbars 25.1_SL of detector area 25.1 in the detector arrangement 25, as can be seen from Figure 2a as is evident.

[0039] As part of the signal processing, the 0° output signal A and the 180° output signal C are combined in a known manner via a push-pull circuit to form a first incremental signal S0; the 90° output signal B and the 270° output signal D are also combined via a push-pull circuit to form a second incremental signal S90, which is phase-shifted by 90° relative to the first incremental signal S0.

[0040] In the present embodiment, the width b of a detector element 25.1_DE is selected to be b_D = 12 µm, and the gaps between the detector elements 25.1_DE have a width of 9 µm. The detector element periodicity P with respect to phase-in-phase detector elements P is then P_D = 84 µm, i.e., the ratio of detector element width b_D to detector element periodicity P_D is b_D:P_D = 1:7. A total of 64 detector elements 25.1_DE are provided in the detector area 25.1, resulting in a maximum width of the detector area 25.1 and a base length of the triangular envelope of 1,344 mm.

[0041] Figure 2bFigure 1 shows in detail the arrangement of the detector elements 25.1_DE in the left base angle region of the detector area 25.1. Accordingly, the detector element that provides the output signal B is located at the left edge of the detector area 25.1, at a distance of 1 / 8 · P_D from the upper left corner of the triangular detector area 25.1. At distances of 1 / 4 · P_D, the detector elements 25.1_DE that provide the output signals C, D, A, etc., follow.

[0042] As further from Figure 2bAs can be seen, due to the triangular shape of the detector area 25.1 described above, the detector elements 25.1_DE have different detector element lengths h_D along the arrangement direction x; in the depicted section, the detector element length h_D increases from left to right until the center of the detector area 25.1; from the center of the detector area 25.1, the length of the detector elements 25.1_DE then decreases again towards the right. Thus, the first detector element 25.1_DE from the left, which provides the output signal B, has a detector element length h_D = 1 · P_D; the second detector element (output signal C) has a detector element length h_D = 3 · P_D; the third detector element (output signal D) has a detector element length h_D = 5 · P_D, etc.

[0043] In an advantageous embodiment, the following applies to the change in the detector element length h_D along the arrangement direction x: dh _ D / dx = + / − 8 , with h_D := detector element length, x := arrangement direction.

[0044] Within detector area 25.1, the detector elements 25.1_DE are arranged symmetrically about a longitudinal axis of symmetry of detector area 25.1, which runs along the y-direction through the apex of the triangle. The two detector elements 25.1_DE that provide the output signals A and B are arranged on either side of this longitudinal axis of symmetry. The detector element providing output signal A is located to the left of the axis of symmetry; the detector element providing output signal B is located to the right of the axis of symmetry. The respective distance to the longitudinal axis of symmetry is ± 1 / 8 · P_D. On the left side, at a distance of 1 / 4 · P_D, is the detector element providing output signal D; on the right side, at a distance of 1 / 4 · P_D, is the detector element providing output signal C, and so on...

[0045] The detector area 25.2 is designed identically with regard to the arrangement of detector elements, wherein detector elements in the two detector areas 25.1, 25.2, which provide phase-coherent output signals A, B, C, D, are arranged symmetrically to the first axis of symmetry S1.

[0046] In contrast, the arrangement of detector elements in the two detector areas 25.3 and 25.4 is rotated by 90°. Within each detector area 25.1–25.4, the design and interconnection of the detector elements are fundamentally identical.

[0047] In addition to the design of the scanning grating, which will be described later, this design of the detector arrangement 25, and in particular the arrangement and interconnection of the detector elements 25.1_DE in the various detector regions 25.1–25.4, contributes to suppressing or filtering out unwanted intensity components of the grating self-image, which would otherwise cause errors in determining the 2D angular positions of the light source. Such unwanted signal components are, for example, harmonics or 2D spatial frequencies, which can be eliminated by the filtering effect of the detector arrangement 25. Furthermore, the corresponding design of the detector regions 25.1–25.4 ensures that reliable 2D angle measurement is possible over a large range of distances between the light source and the receiver; in the present embodiment, distances between the light source and the receiver in the range of 0.2 m to 1.5 m are possible.In this area, the angle of incidence of the beams from the light source can be measured within an angle of incidence range of + / - 50° with respect to a normal to the scanning grating.

[0048] Further measures, which also aim to suppress interference in the device according to the invention, are described with reference to the following explanation of an exemplary embodiment of the scanning grid in the optical receiving unit. Figure 3 This shows a schematic top view of the circular scanning grid 21, which Figures 4a, 4b Detailed representations of parts of the scanning grid 21, including a sectional view of the same. The one in Figure 4b The depicted part of the scanning grid 21 shall in the following also be referred to as the optical unit cell of the scanning grid 21 used.

[0049] The present scanning grating 21, like the detector arrangement 25 described above, is designed for 2D angle measurement. It is configured as a transmittive, combined amplitude-phase grating consisting of a periodic arrangement of square grating regions 21.1, 21.2 along two orthogonal grating directions GR1, GR2. The grating regions 21.1, 21.2 are configured differently and exhibit different optical effects on the incident beams. A combined amplitude-phase grating is defined here as a grating that incorporates both amplitude grating components and phase grating components. For the precise configuration of the scanning grating 21, reference is made to the further description in the following figures.

[0050] In Figure 3EZ denotes a unit cell of the scanning grating 21 with a total of four grating regions 21.1, 21.2, from which the scanning grating 21 can be constructed by translation along the two grating directions GR1, GR2. In the illustrated embodiment, the periodicities P_GR1, P_GR2 along the two grating directions GR1, GR2 are selected to be identical according to P_GR1 = P_GR2 = 222.85 µm.

[0051] The in Figure 4b The optical unit cell of the scanning grating 21 shown has a periodicity of 157.58µm; this determines the signal period of the position-dependent incremental signals generated via the detector arrangement D with respect to resulting angle changes.

[0052] In each grating region 21.1, 21.2 of the scanning grating 21, an identically designed, opaque amplitude grating structure 21.3 is arranged on a support substrate 21.4, as is shown, for example, in Figure 4bThe amplitude lattice structure consists of opaque lattice bars 21.3_G, which are arranged parallel to each other along the two lattice directions GR1, GR2 and have at least partially different bar widths.

[0053] In each lattice region 21.1, 21.2, the amplitude lattice structure is identical and symmetrical with respect to the center point M of the respective lattice region. Furthermore, in lattice regions 21.1, 21.2 arranged adjacent to each other along a lattice direction GR1, GR2, the amplitude lattice structures are each mirror-symmetrical with respect to an axis of symmetry SG1, SG2, SG3, SG4, which runs along the boundary of the adjacent lattice regions 21.1, 21.2. Thus, from Figure 4bIt is evident, for example, how the widths of the opaque grid bars in the central grid region 21.2 and the adjacent grid region 21.1 at the bottom left exhibit mirror symmetry with respect to the axis of symmetry SG1; analogously, the bar widths in the other three adjacent grid regions 21.1 are formed with respect to the axes of symmetry SG2, SG3, and SG4. This is also clearly visible with respect to the axis of symmetry SG1 in the cross-sectional view of the scanning grid at the bottom right. Figure 4b ; as can be clearly seen from this, the amplitude lattice structure is identical in all lattice regions 21.1, 21.2.

[0054] An amplitude grating structure 21.3 designed in this way ensures that the scanning grating 21 is relatively similar to the ideal sine grating and results in a preferred transmission into the + / - 1st diffraction orders for a certain wavelength range; higher odd-numbered diffraction orders, which may have a negative impact on the quality of the generated signals, are largely suppressed.

[0055] In every second lattice region 21.2 along the two lattice directions GR1, GR2, a phase-shifting layer 21.5 is arranged over the entire surface of the amplitude lattice structure 21.3, as can be seen from the sectional view in Figure 4b This is evident. The periodicity of the phase-shifting layer 21.5 thus corresponds to the periodicities P_GR1 and P_GR2, with which the two lattice regions 21.1, 21.2 are arranged along the two lattice directions GR1, GR2.

[0056] For example, tantalum pentoxide Ta₂O₅ with a refractive index n = 2.122 can be used as a suitable material for the phase-shifting layer 21.5 in the scanning grating 21. With a selected height h = 351 nm, this material ensures that, for incident radiation in the wavelength range of 850 nm ± 20 nm and an angle of incidence between 0° and 50°, both the zeroth diffraction order and all even diffraction orders are suppressed. For a mean angle of incidence of approximately 30°, the phase-shifting layer 21.5 then has a phase shift of 180°. By designing the grating regions 21.2 in this way, further diffraction orders that also negatively affect signal quality can be eliminated; thus, in the device according to the invention, only the ±1st diffraction orders contribute to signal generation.

[0057] From the sectional view in Figure 4bThe structure of the scanning grating 21 is shown in detail. On the upper side of the support substrate 21.4, the amplitude grating structure 21.3 with the opaque grating struts 21.3_G, as described above, is arranged in the two grating regions 21.1 and 21.2, and the phase-shifting layer 21.5 is arranged in grating regions 21.2. On the opposite side of the support substrate 21.4, i.e., on its underside, there is an additional full-surface antireflection layer 21.6.

[0058] Based on the representation in Figure 5 Finally, it will be explained how the detector arrangement 25 and the scanning grid 21 described above are preferably arranged relative to each other in the optical receiving unit of the position measuring system according to the invention; the corresponding relative arrangement represents a further measure for filtering undesirable influences on the generated signals, particularly in the case of 2D angle measurement. For this purpose, Figure 1 shows Figure 5Side-by-side top views of the detector arrangement 25 and the scanning grid 21. As shown by Figure 1 As explained, in the real system the scanning grid 21 with the periodic arrangement of grid areas 21.1, 21.2 along the two grid directions GR1, GR2 in a plane parallel to the detection plane and spaced apart at a distance d is arranged in the housing of the receiving unit.

[0059] According to the representation in Figure 5The scanning grating is arranged such that, in this case, the two grating directions GR1 and GR2 each form an angle of 45° with respect to the longitudinal directions x and y of the detector areas 21.1–21.4. This relative arrangement of the scanning grating 21 and the detector arrangement 25 prevents a complete signal loss that could occur at certain angles of incidence of the light source beams onto the scanning grating. In other words, this measure ensures reliable 2D angle measurement across the entire measurement range.

[0060] In addition to the described embodiment of the device according to the invention, there are of course further possibilities for its design within the scope of the present invention.

[0061] While the example described above enables 2D angle measurement in space, it is also possible to implement the optical position measuring system according to the invention in which only a 1D angle measurement is performed between the light source and the optical receiving unit in a measuring plane.

[0062] In this case, only two of the four detector areas 25.1 - 25.4 would be used in the detector arrangement. Figure 2a to use, namely two opposing detector areas such as the detector areas 25.1, 25.2 extending along the y-direction.

[0063] In such a variant, the scanning grating would consist of a periodic arrangement of grating regions along only one grating direction, with the grating regions themselves being configured as a combined amplitude-phase grating. Each grating region also exhibits an amplitude grating structure, and in every second grating region, a phase-shifting layer is arranged above the amplitude grating structure. In this case, the amplitude grating structure would not be a two-dimensional structure as described above, but rather a one-dimensional arrangement of opaque grating bars with partially differing bar widths, arranged along the grating direction. In this case, the grating direction corresponds to the arrangement direction of the detector elements in the two detector regions 25.1 and 25.2, i.e., the x-direction. Figure 2aThis ensures that the grating struts are aligned parallel to the detector elements. The arrangement of the grating struts is again such that, as in the example above, undesired odd-numbered diffraction orders are suppressed. For this purpose, a mirror-symmetric arrangement of the grating struts with respect to an axis of symmetry is provided, which runs through the boundary of adjacent grating regions.

Claims

1. Position measuring system for determining spatial position information comprising at least one light source and at least one optical receiving unit comprising a scanning grating and an optoelectronic detector arrangement, the light-sensitive surfaces of which are oriented in the direction of the scanning grating, characterized - in that the detector arrangement (D; 25) has two detector regions (25.1, 25.2) arranged in a detection plane (DE) mirror-symmetrically with respect to a first axis of symmetry (S1) running in the detection plane (DE) through the centre (Z) of the detector arrangement (D; 25), the first axis of symmetry (S1) being oriented orthogonally with respect to the longitudinal extension direction (y) of the detector regions (25.1, 25.2), and - in that the two detector regions (25.1, 25.2) each have the shape of an isosceles acute triangle whose triangular vertices with the vertex angle (γ) situated between the sides of equal length are oriented in the direction of the centre (Z) of the detector arrangement (D; 25).

2. Position measuring system according to Claim 1, characterized in that the detector arrangement (D; 25) has two further detector regions (25.3, 25.4), which are embodied identically to the first two detector regions (25.1, 25.2) and are arranged mirror-symmetrically with respect to a second axis of symmetry (S2), which runs in the detection plane (DE) through the centre (Z) of the detector arrangement (D; 25) and is oriented orthogonally with respect to the first axis of symmetry (S1).

3. Position measuring system according to Claim 1 or 2, characterized - in that the triangles each have a vertex angle γ for which γ / 2 = 7.125° + / - 5° holds true, and - in that the triangular vertices with the vertex angle (γ) touch one another in the centre (Z) of the detector arrangement (D; 25).

4. Position measuring system according to at least one of the preceding claims, characterized in that in each detector region (25.1 - 25.4) a plurality of individual detector elements (25.1_DE) are arranged periodically and parallel to one another along an arrangement direction (x, y) oriented perpendicularly to the longitudinal extension direction (y, x) of the detector regions (25.1 - 25.4).

5. Position measuring system according to Claim 4, characterized - in that the detector elements (25.1_DE) are each rectangular in shape and the rectangular longitudinal axes are oriented parallel to the longitudinal extension direction (y, x) of the detector region (25.1 - 25.4), and - in that every fourth detector element (25.1_DE) is electrically interconnected along the arrangement direction (x, y), so that four phase-shifted output signals (A, B, C, D) for further processing result from the scanning of a stripe pattern (SM) incident on the detector arrangement (D; 25).

6. Position measuring system according to Claim 5, characterized in that the ratio of detector element width (b_D) and detector element periodicity (P_D) is 1:7.

7. Position measuring system according to Claim 5, characterized in that for the change in the detector element length (h_D) along the arrangement direction (x) it holds true that dh_D / dx = + / - 8, where h_D := detector element length, x := arrangement direction.

8. Position measuring system according to at least one of the preceding claims, characterized in that the scanning grating (AG; 21) is arranged in a plane parallel to the detection plane (DE) and consists of a periodic arrangement of grating regions (21.1, 21.2) along at least one grating direction (GR1, GR2), wherein the grating direction (GR1, GR2) forms an angle of 45° relative to the longitudinal extension direction (y, x) of the detector regions (25.1 - 25.4).

9. Position measuring system according to at least one of the preceding claims, characterized in that the scanning grating (AG; 21) is embodied as a transmissive, combined amplitude-phase grating, wherein - an identically formed, opaque amplitude grating structure (21.3) is arranged in each grating region (21.1, 21.2), and - a phase shift layer (21.5) is arranged along each grating direction (GR1, GR2) in every second grating region above the amplitude grating structure (21.3).

10. Position measuring system according to Claim 9, characterized in that the phase shift layer (21.5) is embodied with respect to the material and the layer thickness (h) in such a way as to result in extensive suppression of the 0th order of diffraction and of all even orders of diffraction for a specific wavelength range and for a specific angle of incidence range.

11. Position measuring system according to Claim 9 or 10, characterized in that the amplitude grating structure (21.3) is embodied in such a way that, for a specific wavelength range, this results in a preferred transmission into the + / - 1st orders of diffraction and extensive suppression of odd orders of diffraction.

12. Position measuring system according to at least one of the preceding claims, characterized in that the scanning grating (AG; 21) is arranged on that side of a transparent cover plate (DP) of the receiving unit (OE) which is oriented in the direction of the detector arrangement (D; 25).

13. Position measuring system according to at least one of Claims 9 - 11, characterized in that the combined amplitude-phase grating has a chequerboard structure with a periodic arrangement of square grating regions (GR1, GR2) along two orthogonal grating directions (GR1, GR2).

14. Position measuring system according to Claim 13, characterized - in that the amplitude grating structure (21.3) consists of opaque grating ridges (21.3_G) which are arranged parallel to one another along the two grating directions (GR1, GR2) and have at least partially different ridge widths, and - in that the amplitude grating structures (21.3) in grating regions (21.1, 21.2) arranged adjacent along a grating direction (GR1, GR2) are each embodied mirror-symmetrically with respect to an axis of symmetry (SG1, SG2, SG3, SG4) running along the boundary of the adjacent grating regions (21.1, 21.2).

15. Position measuring system according to at least one of the preceding claims, characterized in that the light source (LQ) is embodied as an LED which emits radiation in the wavelength range λ = 850 nm + / - 20 nm and has a coherence length of less than or equal to 7 µm.

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