Position measuring device

Abstract

The present invention provides a position measuring device that enables accurate position measurement regarding the relative positions of two objects that can move relative to each other with multiple degrees of freedom of motion. [Solution] A scale carrier H11, which extends over a long distance in the direction of principal motion, includes a first surface, a second surface, and a third surface, each having at least one measuring scale T11 to T41 on each surface. A scanning assembly H21, movable relative to the scale carrier, comprises a plurality of scanning units A11 to A61, configured to generate displacement-dependent position signals from scanning of the measuring scales, with at least one scanning unit assigned to each surface. A plane defined by the second surface divides the enclosed space into two half-spaces, with the first surface having at least one measuring scale located in the first half-space, and the third surface having at least one measuring scale located in the second half-space.

Description

Technical Field

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[0003]

[0001] The present invention relates to a position measuring device that detects the relative position of two objects that are relatively movable with respect to each other in a plurality of degrees of freedom of movement.

Background Art

[0002] Patent Document 1 (WO2017 / 080612A1) discloses a position measuring device that measures the relative position of two objects that are movable relative to each other in the feed direction and in a further degree of freedom. This position measuring device includes a prismatic carrier body that extends long in the feed direction, and this carrier body has a plurality of surfaces, each of which carries a measurement scale and has a scanning assembly that is movable relative to the measurement scale, and the scanning assembly includes a plurality of scanning units for scanning the measurement scale. Such a position measuring device is applied, for example, to measure the error in a coordinate measuring machine. The measured values detected thereby can be used to correct the error of the coordinate measuring machine and calibrate the coordinate measuring machine.

[0003] In the known position measuring device described in Patent Document 1, on the scanning side, a mechanical holder that surrounds the carrier body for a plurality of scanning units is required. Such an enclosure usually requires a certain installation space, and this installation space cannot be utilized in some applications.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

[0006] According to the present invention, this problem is solved by a position measuring device having the features of claim 1.

[0007] An advantageous embodiment of the position measuring device according to the present invention is characterized by the dependent claims.

[0008] The position measuring device according to the present invention is configured to detect the relative positions of two objects, wherein the objects are movable relative to each other along a translational principal direction of motion and with further degrees of freedom. The device includes a scale carrier that extends along the principal direction of motion, the scale carrier including a first surface, a second surface, and a third surface, each of which defines a plane, with at least one measuring scale located on each surface. Furthermore, a scanning assembly is provided, which is movable relative to the scale carrier and has a plurality of scanning units, the scanning units configured to generate a displacement-dependent position signal from scanning of the measuring scales, with at least one scanning unit assigned to each surface. The plane defined by the second surface divides the surrounding space into two half-spaces, wherein the first surface having at least one measuring scale is located in the first half-space, and the third surface having at least one measuring scale is located in the second half-space.

[0009] Preferably, the angles of intersection between the first plane and the second plane, and the angles of intersection between the second plane and the third plane, are selected within the range of 60° to 179°, where the angle of intersection between the first plane and the second plane is shown in the first half-space, and the angle of intersection between the second plane and the third plane is shown in the second half-space.

[0010] In this case, it is advantageous to choose the two intersection angles such that the first and third planes are oriented parallel to each other.

[0011] Furthermore, the lines of intersection between the first plane and the second plane, and the lines of intersection between the second plane and the third plane, are oriented parallel to the principal direction of motion, and the second surface is provided so as to be located between the two lines of intersection.

[0012] Preferably, the three surfaces of the scale carrier, the measuring scale, and the scanning unit are arranged and configured such that the orientation of the scanning assembly relative to the scale carrier in the six degrees of freedom of motion can be determined.

[0013] In one advantageous embodiment, at least two scanning units are assigned to at least two surfaces.

[0014] Furthermore, at least one surface may be assigned two scanning units having different measurement directions, in which case the measurement direction of one scanning unit indicates the translational displacement direction such that a displacement-dependent position signal can be generated.

[0015] In this case, the scale carrier may have two measuring scales in different orientations on its surface, which are assigned to scanning units having different measuring directions, and the scale lines of the measuring scales are not arranged parallel to each other.

[0016] Preferably, the measuring scale is configured as an optically scannable incremental scale.

[0017] In one possible embodiment, -Each surface is assigned at least one scanning unit, and the measurement direction of the scanning unit is oriented perpendicular to the principal motion direction. - At least two scanning units are assigned to each of one second surface and one further surface, and the measuring directions of the scanning units are oriented perpendicular to the main movement direction. - At least one scanning unit is assigned to at least one surface, and the measuring direction of the scanning unit is directed parallel to the main movement direction. It is contemplated to be like this.

[0018] Furthermore, in this case - Four scanning units having a measuring direction perpendicular to the main movement direction and arranged along the main movement direction are assigned to two adjacent surfaces, and adjacent scanning units are assigned to different surfaces respectively. - Two further scanning units, to which at least one is assigned to another surface, are arranged along the main movement direction within the space between the four further scanning units. It may be contemplated to be like this.

[0019] Furthermore, it is also possible that the scale lines of the measuring scale and the measuring directions of the scanning units are arranged inclined with respect to the main movement direction or inclined with respect to the perpendicular line to the main movement direction.

[0020] In a further embodiment - Two measuring scales are assigned to each surface, and the scale lines of the measuring scales are arranged mirror-symmetric to each other with respect to the central axis of symmetry and inclined with respect to the main movement direction. - Two measuring scales on each surface are each assigned one scanning unit, and the two scanning units on one surface have measuring directions perpendicular to each other. It may be contemplated to be like this.

[0021] The position measuring device according to the invention enables a compact arrangement of the necessary scanning unit on one side of the scale carrier, thus avoiding the need to surround the scale carrier. Accordingly, the mechanical holder for the scanning unit within the scanning assembly can be made less massive and more rigid than in measuring devices involving surrounding. Furthermore, detection with high sensitivity of degrees of freedom of movement is ensured. Depending on the measurement task, the position measuring device according to the invention can be flexibly designed for specific requirements, for example, for applications requiring a compact overall arrangement or for applications requiring a larger range of movement in a specific direction of movement.

[0022] Further advantages and details of the invention are explained on the basis of the following description of possible embodiments of the invention, together with the drawings.

Brief Description of the Drawings

[0023] [Figure 1a] A cross-sectional view of a first embodiment of the position measuring device of the invention, including a carrier body and a scanning assembly, is shown. [Figure 1b] A top view of the position measuring device of Figure 1a is shown. [Figure 2] A plan view of a second embodiment of the position measuring device of the invention is shown. [Figure 3] A plan view of a third embodiment of the position measuring device of the invention is shown. [Figure 4] A plan view of a fourth embodiment of the position measuring device of the invention is shown.

Modes for Carrying Out the Invention

[0024] Referring to the schematic views of Figures 1a and 1b, a first embodiment of the position measuring device according to the invention is described below. In this case, Figure 1a shows a cross-sectional view of the position measuring device in the xz plane, and Figure 1b shows a top view of the position measuring device from the z direction.

[0025] The position measuring device described is used to detect the relative positions of two objects OBJ1 and OBJ2, shown schematicly only in Figure 1a, in all six degrees of freedom of rigid body motion (hereinafter simply referred to as "degrees of freedom of motion"). The two objects OBJ1 and OBJ2 may be mechanical components that move relative to each other in a defined manner in this application, for example, and whose relative positions must be detected. In the example described, the principal direction of motion of object OBJ1 relative to object OBJ2 extends along the y-axis of the drawn coordinate system M. Thus, in Figure 1a, the principal direction of motion is oriented perpendicular to the plane of the figure. The principal direction of motion is characterized by the fact that along this direction, the position measuring device according to the present invention should be able to enable the largest possible range of motion. In the remaining five degrees of freedom of motion, the motion is considerably smaller. The five additional degrees of freedom for motion are defined as follows with respect to the coordinate system M in Figure 1a. - Translation of object OBJ1 along the x-direction of coordinate system M - Translation of object OBJ1 along the z-direction of coordinate system M - Rotation of object OBJ1 around the x-axis of coordinate system M - Rotation of object OBJ1 around the y-axis of coordinate system M - Rotation of object OBJ1 around the z-axis of coordinate system M

[0026] Object OBJ2 is connected to a scale carrier H11 within the position measuring device according to the present invention. The scale carrier H11 has at least three surfaces on which planes O11, O21, and O31 are defined, and at least one measuring scale T11, T21, T31, and T41 is placed on each surface. For example, the measuring scales T11, T21, T31, and T41 can each be configured as an incremental scale consisting of a periodic arrangement of scale regions.

[0027] Alternatively, regarding the examples described, it is certainly possible that the object and scale carrier are configured as a single component. Furthermore, the measurement scale may be configured as an integral component of the scale carrier, rather than being placed as a separate component on the scale carrier.

[0028] The scanning assembly H21 of the position measuring device is connected to the other object OBJ1, and this scanning assembly H21 comprises a plurality of scanning units A11, A21, A31, A41, A51, A61 that are rigidly coupled to one another, each of which is configured to generate a displacement-dependent position signal from scanning of measuring scales T11, T21, T31, T41 on the scale carrier H11. Alternatively, with respect to the example described, it is of course possible for the object and the scanning assembly to be configured as a single component. To detect six degrees of freedom of motion, the scanning module H21 comprises at least six scanning units A11, A21, A31, A41, A51, A61.

[0029] Each individual scanning unit A11 to A61 is configured to detect the displacement of its respective scanning unit A11 to A61 relative to the associated measuring scales T11 to T41 by scanning the corresponding measuring scales T11 to T41. In this invention, scanning units A11 to A61 can utilize optical, magnetic, inductive, or capacitive measurement principles. For example, to measure with high resolution, an optical scanning principle can be used, for example, as known from Patent Document 2 of the present applicant. Furthermore, the associated measuring scales must be configured according to the scanning principle used. For example, in the case of optical scanning, the incremental measuring scale consists of a periodic arrangement of scale regions or scale lines having different optical properties (e.g., scale regions having high reflectivity and low reflectivity).

[0030] The translational displacement direction in which a displacement-dependent position signal can be generated via the scanning unit, or in which the position signal changes most significantly when displaced by a predetermined distance, is also referred to as the measurement direction, and in this case, the measurement direction can be represented by a three-dimensional vector. In the drawings, the measurement directions assigned to scanning units A11 to A61 are indicated by the arrows of scanning units A11 to A61, respectively. In this case, it should be noted that the measurement direction vector is not generally flat within the plane of the drawing, as can be seen, for example, from the drawing in Figure 1a, because the measurement scales T11 to T41 are arranged at an inclination with respect to the plane of the drawing. Typically, the measurement direction of each scanning unit A11 to A61 is determined by the alignment of the corresponding measurement scales T11 to T41, by the alignment of scanning units A11 to A61, and by the specific structure of scanning units A11 to A61. In this invention, for design reasons, only scanning units A11 to A61 that lie in the plane of measurement scales T11 to T41 are used for the measurement direction.

[0031] It should be noted that, for the sake of clarity, the scanning units A11 to A61 used are depicted as separate objects in the drawings. However, in practice, for example, in the case of optical scanning principles, it is also possible to integrate multiple scanning units into a common housing in order to use optical and / or electronic components together using multiple scanning units.

[0032] The following describes various design rules and considerations relating to the geometric configuration of the scale carrier H11, the arrangement of the surfaces including the measurement scales T11, T21, T31, and T41, and the configuration of the scanning assembly H21 in the position measuring device according to the present invention.

[0033] Therefore, the configuration of the scale carrier H11 is intended such that the planes O11, O21, and O31 of the three surfaces intersect at least two lines of intersection S11, S21 that extend along the y-direction and, consequently, parallel to the principal direction of motion.

[0034] The measurement scales T21 and T31 assigned to the second plane O21 or the second surface are located between the two intersection lines S11 and S21 of the second plane O21 with the first plane O11 or the third plane O31.

[0035] The second plane O21 divides the space surrounding it into two half-spaces. In this case, one of the half-spaces (hereinafter referred to as the first half-space (lower left in Figure 1a)) contains a first surface O11 including at least one measurement scale T11, and the other half-space (hereinafter referred to as the second half-space (upper right in Figure 1a)) contains a third surface O31 similarly containing at least one measurement scale T41.

[0036] In Figure 1a, the intersection angle between the first plane O11 and the second plane O21 is shown by α, where this intersection angle is located in the first half-space (lower left) where the measurement scale T11 of the first plane O11 is located. In Figure 1a, the intersection angle between the second plane O21 and the third plane O31 is shown by β, where this intersection angle β is located in the other second half-space (upper right) where the measurement scale T41 of the third plane O31 is located. Preferably, the intersection angles α and β are selected within the range of 60° to 179°, respectively. In this case, for practical reasons, the selection α=β may also be preferable. In this case, the two planes O11 and O31 are oriented parallel to each other. Furthermore,

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[0037] As can be seen from Figures 1a and 1b, at least two of the three planes O11, O21, and O31 are each assigned two or more scanning units A11 to A61. In a specific example, two scanning units A11 and A21 are assigned to the first plane O11, and three scanning units A31, A41, and A51 are assigned to the second plane O21.

[0038] Furthermore, at least one of the surfaces or planes O11 to O31 is assigned at least two scanning units A11 to A61 having different measurement directions. In the example in Figures 1a and 1b, on the one hand, scanning unit A51 is assigned to the second surface or second plane O21, with the measurement direction of this scanning unit A51 oriented along the y-direction, and on the other hand, two scanning units A31 and A41 are assigned to this plane O21, with the measurement directions of these two scanning units A31 and A41 oriented perpendicular to the y-direction, respectively. As can be seen from Figure 1b, the two measuring scales T21 and T31 are located on separate tracks on the second surface, and the tick marks on those tracks are not parallel to each other but perpendicular to each other. The measuring scale T21 consists of a periodic arrangement of tick marks along the y-direction, i.e., the measurement direction of the associated scanning unit A51, and the longitudinal direction of the tick marks extends perpendicular to the specified x-direction, i.e., the y-direction. The measuring scale T31 consists of a periodic arrangement of scale lines perpendicular to the y-direction, i.e., the measuring direction of the two associated scanning units A31 and A41. Alternatively, with respect to separate tracks, a measuring scale can be provided that allows the operation of scanning units having different measuring directions on a single track. Specifically, in embodiments of the present invention, a measuring scale of a so-called intersecting grid, scanned by scanning units having mutually orthogonal measuring directions, can also be used.

[0039] In the specific embodiments shown in Figures 1a and 1b, it is further intended that each of the three planes O11, O21, and O31 is assigned at least one scanning unit having a measurement direction perpendicular to the principal direction of motion. According to Figure 1b, these are scanning units A11, A21, A31, A41, and A61. Furthermore, at least two scanning units are assigned to the central plane O2 and at least one further plane O1 or plane O2, and these scanning units include a measurement direction oriented perpendicular to the principal direction of motion. Finally, at least one of the three planes O1, O2, and O3 is assigned a scanning unit, the measurement direction of which is oriented parallel to the principal direction of motion, i.e., the y-direction. In this case, this is scanning unit A51.

[0040] In the example shown in Figures 1a and 1b, the scanning assembly H21 has a flat base surface G21, and the scale carrier H11 has a flat base surface G11. These two base surfaces G21 and G11 are oriented parallel to the principal motion direction, i.e., the y-direction. Furthermore, the two base surfaces G11 and G21 are oriented substantially parallel to each other within the operating tolerance. In this case, as shown in Figure 1a, the inclination angles γ1, γ2, and γ3 between the surfaces O11, O21, O31 of the scale carrier H11 and the base surface G11 can be defined. Then, the intersection angles α and β described above, which characterize the inclination of the various surfaces O11, O21, O32 relative to each other, are defined by the inclination angles γ1, γ2, and γ3 as follows: α = 180° - γ1 - γ2 β=180°-γ2-γ3 It can be decided that way.

[0041] Depending on the requirements and boundary conditions of the measurement application, it may be necessary to configure the position measuring device according to the present invention so that it fits between two base surfaces G11 and G21, and the distance between the two base surfaces G11 and G21 is as short as possible. In this case, it may be advantageous to ensure that one of the two intersection lines S11, S21 is located as close as possible to the base surface G11, which in the example shown in Figure 1a is intersection line S21. This moves the scanning units A11 to A61 closer to the scale carrier H11. To achieve this, the widths of the measurement scales T11 to T41, the scale width, and the inclination angles γ1, γ2, γ3 must be selected accordingly. In this case, it is preferable to select smaller inclination angles γ1, γ2, γ3, which, overall, results in a flatter and, consequently, more compact design for the position measuring device.

[0042] If separate scale tracks are required for different measurement directions within a single plane, scanning units with different measurement directions can preferably be located within only one plane O21. In this case, to minimize installation space, it may be further considered to select a tilt angle γ2 of the corresponding plane O21 that is slightly smaller than the other two tilt angles γ1 and γ3. In this way, a greater width is available for the surface allocated to this plane O21 without increasing the overall height of the arrangement above the base surface G11. This makes it easier to arrange two measurement scale tracks on this surface. The other two surfaces or planes O11 and O31 are each allocated only to scanning units A11, A21, and A61, respectively, that have the same measurement direction. Therefore, only space is required for one measurement scale track.

[0043] Furthermore, within certain measurement tasks, it may be necessary for the position measuring device according to the invention to allow for a larger range of motion with respect to the displacement of the scanning assembly H21 in a direction that lies on the base surface G11 and is oriented perpendicular to the main direction of motion. Thus, in the example of FIGS. 1a, 1b, this means that the range of motion in the x-direction becomes larger. In this case, it is found to be advantageous to select the tilt angles γ1, γ2, γ3 to be quite small. This is because when the scanning assembly H21 moves a distance x in the x-direction described above, the distance of the assigned measurement graduations T11 - T41 of the scanning units A11 - A61 to the measurement graduations T11 - T41 up to which the measurement is made changes by an amount of xsinγ1 or xsinγ2 or xsinγ3. For example, if γ1 = γ2 = γ3 = 45° is selected, then for a displacement by the corresponding x, the interval of the measurement graduations T11 - T41 from the measurement graduations T11 - T41 of the scanning units A11 - A61 changes by an amount of xsin(45°) = x / √2. Assuming that the scanning unit fails when the interval to the measurement graduation deviates from the nominal interval by more than h, in the described arrangement, motion along the x-direction is possible within the range of -h√2 < x < h√2 without leading to failure of the scanning unit. This also means that a factor of √2 is obtained as compared to an arrangement where the measurement graduations are arranged perpendicular to the base surface G11.

[0044] However, in certain measurement tasks, the positioning device according to the present invention may require a larger range of motion with respect to the displacement of the scanning assembly H21 in a direction perpendicular to the base surface G11 and oriented perpendicular to the principal direction of motion. Thus, in the example of Figures 1a and 1b, this means a larger range of motion in the z direction. In this case, it is advantageous to select rather large inclination angles γ1, γ2, and γ3. This is because, when the scanning assembly H21 moves a distance z in the z direction as described above, the distance between the measurement scales T11 to T41 assigned to the scanning units A11 to A61 changes by an amount of xcosγ1, xcosγ2, or xcosγ3. For example, if γ1=γ2=γ3=45° is selected, a coefficient of √2 is obtained compared to an arrangement where the measurement scales are positioned parallel to the base surface G11.

[0045] Referring to Figures 1a and 1b, a brief explanation is given below regarding the first embodiment of the position measuring device according to the present invention as described, and how all six degrees of freedom or rigid body degrees of freedom of the motion of the assembly H21 with respect to the scanning scale carrier H11 can be determined.

[0046] For simplicity, it is assumed that all scanning units A11 to A61 have the same sensitivity to translation along their measurement direction. That is, all scanning units A11 to A61 will show the same change in measurement when they are each displaced by the same length along their respective measurement direction.

[0047] The measurement directions of scanning units A11 and A21 are identical. Therefore, the difference in measurements between these two scanning units A11 and A21 represents sensitivity only to rotational degrees of freedom, and not to arbitrary translation (or displacement) of the scanning assembly H21. The maximum sensitivity of the difference in measurements described above is to the rotation of the scanning assembly H21 along a first axis of rotation perpendicular to the plane O11. This first axis of rotation is oriented perpendicular to the principal direction of motion, which extends along a specified y-direction or parallel to the specified y-direction.

[0048] Furthermore, the measurement directions of scanning units A31 and A41 are the same. Therefore, the difference in the measurements of these two scanning units A31 and A41 represents sensitivity only to rotational degrees of freedom, and not sensitivity to arbitrary translation (or displacement) of the scanning assembly H21. The maximum sensitivity of the difference in measurements described above is for the rotation of the scanning assembly H21 along a second rotation axis perpendicular to the plane O21. This second rotation axis is oriented perpendicular to the principal direction of motion. In addition, as described above, the selection of intersection angles α=0 or α=180° is excluded, so the second rotation axis is not oriented parallel to the first rotation axis.

[0049] For the sake of simplicity, the following assumes that α=β holds true, i.e., that planes O11 and O31 are parallel. Furthermore, it is assumed that the center point between scanning positions Q11 and Q21 of scanning units A11 and A21 in coordinate system M has the same y-coordinate, as does scanning position Q61 of scanning unit A61.

[0050] The average of the measurements from scanning units A11 and A21 exhibits the same behavior with respect to sensitivity to the six degrees of freedom of motion as the measurements from a hypothetical scanning unit A71, which has the same measurement direction and a scanning position Q71 that is midway between scanning positions Q11 and Q21 of scanning units A11 and A21.

[0051] The measurement directions of the hypothetical scanning units A71 and A61 described above are the same. Therefore, the difference in measurements between these two scanning units A71 and A61 indicates only the sensitivity to rotational degrees of freedom, and not the sensitivity to arbitrary translation (or displacement) of the scanning assembly H21. The greatest sensitivity is observed to rotation of the scanning assembly H21 along a third rotation axis, i.e., the y-axis, because this axis is perpendicular to the common measurement direction and perpendicular to the spacing vector between scanning positions.

[0052] The first, second, and third rotation axes are vectorially linearly independent of each other. Therefore, in the position measuring device according to the present invention, all three degrees of freedom of rotational motion can be determined independently of each other.

[0053] The measurement directions of scanning units A11 and A31 are perpendicular to the principal motion direction, and since the selection of intersection angles α=0° or α=180° is excluded, they are linearly independent of each other. The measurement direction of scanning unit A51 is parallel to the principal motion direction. As a result, the measurement directions of scanning units A11, A31, and A51 are also linearly independent of each other. Therefore, using the measurements from scanning units A11, A31, and A51, all three translational degrees of freedom of scanning assembly H21 can be determined independently of each other.

[0054] The above description is intended only to schematically illustrate how all six degrees of freedom of motion can be determined using the position measuring device according to the present invention. In practice, the degrees of freedom of motion are usually determined by solving a system of equations. For each scanning unit, an equation can be set up by making the generated measurement equal to the predicted measurement, and this predicted measurement can be expressed as a function of the six degrees of freedom of motion, taking into account the scanning position and measurement direction. When more than six scanning units are used, a preferred method, such as the least squares method, can be used to favorably solve the resulting overdetermined system of equations, taking into account measurement errors.

[0055] Figure 2 shows a plan view of a second embodiment of the position measuring device according to the present invention. Below, only the important differences from the first embodiment will be described.

[0056] This embodiment has the advantage of a particularly compact arrangement of the six scanning units A12 to A62 provided. For this purpose, scanning units having the same measurement direction are arranged to interlock with each other on adjacent measurement scales. On two adjacent surfaces O1 and O2, four scanning units A12, A32, A22, and A42, having the same measurement direction, are arranged separately within the scanning assembly and are alternately aligned according to their position in the main direction of motion, and are assigned to one or the other surface O1, O2 or the associated measurement scales T12, T22. The measurement directions of these four scanning units A12, A32, A22, and A42 are oriented perpendicular to the main direction of motion, i.e., the y-direction, as can be seen in Figure 2. As can be seen, the remaining two scanning units A52 and A62 are advantageously located in the space between the four scanning units A12, A32, A22, and A42 already arranged within the scanning assembly, in relation to their position in the main direction of motion.

[0057] A particular advantage of this arrangement is its compact design. The interlocking arrangement allows the measurement scales T12-T42 to be configured to be particularly narrow, even when the installation space for scanning units A12-A62 encroaches on the area of ​​another surface. Another advantage is that, despite the compact arrangement, the spacing between scanning units on the same surface and in the same measurement direction—for example, the spacing between scanning units A12 and A22, or between scanning units A32 and A42—is significantly larger than the width of a single scanning unit. As a result, a numerically favorable conditioning of the degrees of freedom of motion is determined. This is because the rotation angle around an axis perpendicular to the plane of the measurement scale must be determined from the difference in measurements between such two scanning units. When the spacing between scanning units is sufficiently large, the difference in measurements resulting from the rotation angle is also sufficiently large, allowing for reliable detection even in the event of potential interference, such as noise.

[0058] Figure 3 shows a plan view of a third embodiment of the position measuring device according to the present invention. Below, only the important differences from the previously described embodiments will be explained.

[0059] As can be seen from Figure 3, in this embodiment, the scale lines of the measuring scale and the measurement direction of the scanning unit are positioned with a slight rotation compared to the two embodiments described above. In other words, the scale lines of the measuring scale and the measurement direction of the scanning unit are positioned at an inclination with respect to the principal direction of motion, or perpendicular to the principal direction of motion. Such a configuration has the advantage that when the scanning assembly moves along the principal direction of motion, all scanning units supply displacement-dependent position signals, and therefore signal compensation or signal correction is always possible.

[0060] A fourth embodiment of the position measuring device according to the present invention is shown in Figure 4, which is a separate plan view. Below, only the important differences from the previously described embodiment will be explained again.

[0061] As can be seen from the figure, each surface O14 to O34 is assigned two measurement scales T14 / T24, T34 / T44, and T54 / T64, respectively. The scale lines of these measurement scales are arranged mirror-symmetrically with respect to the central axis of symmetry R1, R2, and R3, and are similarly inclined with respect to the principal direction of motion which is oriented along the y-direction.

[0062] Each of the three planes O14 to O34 is further assigned a pair of scanning units A14 to A64 whose measurement directions are orthogonal to each other. The measurement directions are also the same as in the previously described embodiment in the planes of the corresponding measurement scales T14 to T64.

[0063] In each scanning unit A14 to A64, a virtual straight line is drawn, starting from scanning positions Q14 to Q64 and continuing in the measurement direction. For each of the aforementioned pairs of scanning units, the lines described intersect at one point. This results in three points in three-dimensional space, which are reference numbered I14, I24, and I34 in Figure 4. These three points must be unfolded on a single plane; that is, they must not lie on a common straight line or coincide at a single point. Otherwise, the correspondingly configured position measuring devices cannot independently determine the six degrees of freedom of motion. For each of the aforementioned pairs of scanning units, one measurement direction must have a component perpendicular to the aforementioned plane.

[0064] Therefore, in this embodiment, with respect to one pair of scanning units, it is advantageous when the offset or arrangement between the scanning units in the principal direction of motion is selected to be significantly different from that of other pairs. For example, according to Figure 4, the spacing between scanning units A34 and A44 on the central surface having two measuring scales T34 and T44 is significantly larger than the spacing between each of the other two pairs of scanning units. As a result, intersection I24 is in a different z-coordinate than the two intersections I14 and I34 of the other pair of scanning units. Thus, it is ensured that intersections I14 to I34 are never located on the same straight line.

[0065] Furthermore, if surfaces O13-O34 have multiple pairs of measuring scales for each of the two measuring directions, one pair of these measuring scales may be configured to have a different scale orientation than the other two pairs of measuring scales. For example, as shown in Figure 4, the linear direction of one pair of measuring scales T34 / T44 is rotated 180 degrees compared to the linear direction of the other pair of measuring scales T14 / T24 or T54 / T64. This method may also be useful for positioning intersections I14-I34 further away from a common straight line.

[0066] In addition to the embodiments described, there are, of course, other possible embodiments of the present invention.

Claims

1. A position measuring device for detecting the relative positions of two objects, The aforementioned objects are capable of moving relative to one another along their principal translational direction of motion, and with further degrees of freedom. The position measuring device comprises a scale carrier that extends elongated in the principal direction of motion, the scale carrier including a first surface, a second surface, and a third surface, each of which defines a plane, and each surface has at least one measuring scale, and The position measuring device comprises a scanning assembly that is movable relative to a scale carrier and has a plurality of scanning units, the scanning units configured to generate displacement-dependent position signals from scanning of a measuring scale, and at least one scanning unit is assigned to each surface. In the position measuring device, A plane defined by a second surface divides the enclosed space into two half-spaces, the first surface having at least one measuring scale is located in the first half-space, and the third surface having at least one measuring scale is located in the second half-space. A position measuring device characterized by the following features.

2. The angles of intersection between the first and second planes, and between the second and third planes, are selected within the range of 60° to 179°, respectively. The intersection angle between the first plane and the second plane is plotted in the first half-space, and the intersection angle between the second plane and the third plane is plotted in the second half-space. The position measuring device according to feature 1.

3. The position measuring device according to claim 2, characterized in that the two intersection angles are selected such that the first plane and the third plane are oriented parallel to each other.

4. The lines of intersection between the first plane and the second plane, and the lines of intersection between the second plane and the third plane, are oriented parallel to the principal direction of motion, and the second surface is located between these two lines of intersection. A position measuring device according to at least one of claims 1 to 3.

5. The position measuring device according to at least one of claims 1 to 4, characterized in that the three surfaces of the scale carrier, the measuring scale, and the scanning unit are arranged and configured such that the orientation of the scanning assembly relative to the scale carrier in six degrees of freedom of motion can be determined.

6. A position measuring device according to at least one of claims 1 to 5, characterized in that at least two scanning units are assigned to at least two surfaces.

7. At least one surface is assigned two scanning units with different measurement directions. The measurement direction of one scanning unit indicates the translational displacement direction so that a displacement-dependent position signal can be generated. A position measuring device according to at least one of claims 1 to 6.

8. The scale carrier has two different orientations of measurement scales on its surface, which are assigned to the scanning unit including different measurement directions, and the scale lines of the measurement scales are not arranged parallel to each other. The position measuring device according to feature 7.

9. The position measuring device according to at least one of claims 1 to 8, characterized in that the measurement scale is configured as an optically scannable incremental scale.

10. - Each surface is assigned at least one scanning unit, and the measurement direction of the scanning unit is oriented perpendicular to the principal motion direction. - Each of the second surface and one further surface is assigned at least two scanning units, the measurement direction of which the scanning units are oriented perpendicular to the principal motion direction. - At least one surface is assigned at least one scanning unit, and the measurement direction of that scanning unit is oriented parallel to the principal motion direction. The position measuring device according to feature 7.

11. - Two adjacent surfaces are assigned four scanning units that are arranged along the principal motion direction and have a measurement direction perpendicular to the principal motion direction, and each adjacent scanning unit is assigned to a different surface. - Two other scanning units, each assigned to at least one of different surfaces, are arranged along the principal motion direction in the space between four other scanning units. The position measuring device according to feature 7.

12. The position measuring device according to claim 7, characterized in that the scale lines of the measurement scale and the measurement direction of the running inspection unit are arranged at an inclination with respect to the main direction of motion, or at an inclination with respect to a line perpendicular to the main direction of motion.

13. - Each surface is assigned two measurement scales, and the scale lines of these scales are arranged mirror-symmetrically with respect to the central axis of symmetry and are inclined with respect to the principal direction of motion. - Each of the two measurement scales on each surface is assigned one scanning unit, and the two scanning units on a single surface have mutually orthogonal measurement directions. The position measuring device according to feature 7.

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