Length measuring device

Abstract

To provide a length measuring device which is configured in a simple and compact manner and used to enable accurate position measurement.SOLUTION: A length measuring device has a scale (12), a probe carriage (16) for scanning a graduation (14) on the scale (12), and a connecting body (20) having a connector (22). The connector (22) is attached to an entrained body (26) via a flexure bearing (30). The flexure bearing (30) is formed so as to hold the connector (22) in a freely rotatable state relative to the entrained body (26) about a first rotational axis (R1) extending perpendicularly to a plane (S) of the graduation (14). The connector (22) has at least any one of a lower density than that of steel or a higher Young's modulus than that of steel.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a length measuring device as set forth in claim 1. [Background technology]

[0002] Length measuring devices of this type are used to measure lengths and paths, in particular in machining machines to measure the relative movement of a tool with respect to a workpiece being machined, in coordinate measuring machines and also in the semiconductor industry.

[0003] Patent Document 1 discloses a length measuring device comprising a scale and a probe carriage that scans the scale. The probe carriage is attached to a driver by a connecting body so that it is rigid (sturdy) in the measurement direction but movable in other directions. The connecting body has a coupling member extending in the measurement direction, which is rotatably supported by a first rotary joint on the probe carriage and a second rotary joint on the driver. A first elastic means is provided between the coupling member and the driver, and the elastic means applies a pressing force to the probe carriage, pressing it against the guide surface. A second elastic means is further provided between the connecting member and the probe carriage, and the second elastic means applies a pressing force to the probe carriage, pressing it against the guide surface. The first elastic means is disposed spaced apart from the second elastic means in the measurement direction.

[0004] Further length measuring devices with a connecting body are known from US Pat. No. 5,629,299, US Pat. No. 5,629,299 and US Pat. No. 5,629,299. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] European Patent Application Publication No. 3228993 [Patent Document 2] European Patent No. 2037230 [Patent Document 3] European Patent No. 1180662 [Patent Document 4] DE 3624485 A1 Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present invention is to provide a length measuring device that has a simple and compact configuration and is used to enable accurate position measurement. [Means for solving the problem]

[0007] This problem is solved according to the invention by a length measuring device having the features of claim 1.

[0008] The length measuring device formed according to the present invention comprises a support extending longitudinally in a measurement direction and on which a scale is arranged, a probe carriage for scanning the graduations of the scale, the probe carriage being guided longitudinally in the measurement direction on at least one guide surface, and a coupling body used to rigidly couple the probe carriage to a driver in the measurement direction and passively couple the probe carriage to the driver in a direction transverse to the measurement direction. The coupling body has a connector arranged between a first coupling portion on the probe carriage side and a second coupling portion on the driver side. The connector is attached to the driver at the second coupling portion via a flexure bearing. The flexure bearing is configured to hold the connector in a state where it can freely rotate relative to the driver around a first rotation axis extending perpendicular to the surface of the scale. The connector has at least one of a lower density than steel and a higher Young's modulus than steel.

[0009] For example, the connector has a density in the range of 10 to 80%, 20 to 70%, or 25 to 65% of the density of steel.

[0010] For example, the connector has a Young's modulus in the range of 100 to 500 GPa, in the range of 160 to 440 GPa, or in the range of 250 to 350 GPa.

[0011] It is advantageous if the connecting body has a ball via which the connector is connected to the first connecting part on the probe carriage side, if the connector has a receiving part for receiving the ball, and further if the receiving part is formed without a locking pin and / or a pin for receiving the ball and so that the ball can move in a direction perpendicular to the measuring direction.

[0012] It is also advantageous if the connector has a flat element for connecting the flexure bearing to the connector, and if the connector comprises a plurality of truncated cones that extend at least partially through openings in the corresponding flat elements.

[0013] Preferably, the connector is made largely or entirely of ceramic.

[0014] Alternatively, the connector may be made largely or entirely of carbon fiber reinforced plastic (CFK).

[0015] The flexure bearing is in particular a leaf spring.

[0016] The present invention provides, on the one hand, a relatively high inherent stiffness and, on the other hand, a relatively small mass for the connector. As a result, the position of the frequency band of the system's natural frequency can be significantly shifted toward higher frequencies. This also makes it possible to improve the frequency characteristics of the length measuring device compared to the prior art. Furthermore, it is possible to eliminate the (additional) mass-spring system for materializing the connector, which significantly reduces the measurement accuracy in certain frequency bands due to the natural frequency. Therefore, a simple and compact structure is realized, while, on the other hand, accurate position measurement is possible.

[0017] Advantageous configurations of the invention are set out in the dependent claims.

[0018] Further details and advantages of the invention will be explained on the basis of the following description of possible embodiments of the invention in conjunction with the drawings. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 2 is a side view of the length measuring device according to the embodiment. [Figure 2] 2 is a cross-sectional view of the length measuring device according to FIG. 1 in the region of the connector; [Figure 3] FIG. 2 is a side view of a connector of the length measuring device shown in FIG. [Figure 4] 1. FIG. 4 is yet another side view of the connector of the length measuring device shown in FIG. 1, for clearly illustrating the connection of the flexure bearing with the connector. [Figure 5] FIG. 2 is a perspective view of a connector of the length measuring device shown in FIG. [Figure 6] FIG. 1 is a side view of a connector of a length measuring device according to the prior art. [Figure 7] FIG. 10 is yet another side view of the connector of the length measuring device according to the prior art, for clearly illustrating the connection of the flexure bearing with the connector. [Figure 8] FIG. 10 is a perspective view of a connector of a length measuring device according to the prior art, which is provided with a locking pin and a pin for receiving a ball. DETAILED DESCRIPTION OF THE INVENTION

[0020] Identical or functionally similar elements are labeled with the same reference numbers in the figures.

[0021] An embodiment will be described below with reference to FIGS. 1 to 5. FIGS. 6 to 8 show components (elements) of a known length measuring device. The length measuring device according to this embodiment is used to measure the relative position of two objects movable relative to each other in a measurement direction X. For the position measurement, a scale 12 of the length measuring device is attached to one of the objects, and a probe carriage 16 of the length measuring device is attached to the other of the objects. The scale 12 is then scanned by the probe carriage 16, which is movable in the measurement direction X relative to the scale 12. The length measuring device has a support 10 extending longitudinally in the measurement direction X. The scale 12 has a scale 14, which is scanned by the probe carriage 16. Furthermore, the probe carriage 16 has an illumination unit that emits a light beam. The light beam is modulated depending on the position of the scale 14 and ultimately enters a light-sensitive scanning sensor of the probe carriage 16. The scanning sensor and illumination unit of the probe carriage 16 are not shown.

[0022] The scale 12 is arranged on a support 10. As shown in FIG. 2, the support 10 is a hollow profile in which the scale 12 and the probe carriage 16 are accommodated in a protected manner. The scale 12 is then joined to the support 10 in a known manner, for example by gluing or fastening. The support 10, which is configured as a hollow profile, has a slit in its longitudinal direction extending in the measuring direction X, which is closed by a roof-shaped, inclined sealing lip 11, through which the follower 26, with its sword-shaped central part 28.1, is inserted. The follower 26 has a mounting part 28.2 by means of which it is attached to one of the objects to be measured, for example to a slider of a machine tool.

[0023] The probe carriage 16 is guided along the scale 12, on the scale itself and / or on the support 10, for precise parallel guidance. To this end, the probe carriage 16 supports itself via guides on a number of guide surfaces 18.1 to 18.3 in the illustrated embodiment. The guide surfaces 18.1 to 18.3 are formed by guide strips attached to the support 10. The guide surfaces 18.2 and 18.3 are oriented parallel to the plane S of the scale 14. The guide surface 18.1 is oriented perpendicular to this plane S. The guides may be sliding elements, but may also be rollers or rollers, in particular supported by ball bearings.

[0024] The probe carriage 16 is rigidly connected to the driver 26 via a connector 20 in the measurement direction X and passively connected to the driver 26 in a direction transverse to the measurement direction. The connector 20 has a connector 22, which is arranged between a first connection point P1 on the probe carriage 16 side and a second connection point P2 on the driver 26 side (see FIG. 3). The connector 22 is attached to the driver 26 at the second connection point P2 via a flexure bearing 30, in particular a leaf spring. The flexure bearing 30 is configured to hold the connector 22 in a state where it can freely rotate relative to the driver 26 around a first rotation axis R1 extending perpendicular to the plane S of the scale 14. The leaf spring is made of, in particular, steel.

[0025] The connector 22 has at least one of a lower density than steel and a higher Young's modulus than steel. For example, the connector 22 has a density in the range of 10 to 80%, 20 to 70%, or 25 to 65% of the density of steel. Furthermore, the connector 22 has a Young's modulus in the range of 100 to 500 GPa, 160 to 440 GPa, or 250 to 350 GPa, for example. In the illustrated embodiment, the connector 22 is mostly or preferably entirely made of ceramic.

[0026] 3, the connector 22 is bent into a substantially L-shape. Furthermore, the connector 22 is fork-shaped, with upper portions of the connector 22 disposed on both sides of the scale 14 (see FIG. 2). The connector 22 extends between first and second connecting portions P1 and P2. The first connecting portion P1 and the second connecting portion P2 are offset from each other in a direction Z extending perpendicular to the surface S of the scale 14.

[0027] The first connecting sites P1 are preferably arranged, on the one hand, in the plane S of the scale 14 or at least close to this plane S (in the Z direction), and, on the other hand, on either side (in the Y direction) of the scale 14. This is particularly shown in FIG.

[0028] The connector 20 shown in Fig. 3 has a ball 32, via which the connector 22 is connected to the first connection part P1 on the probe carriage 16 side. The connector 22 has a receiving part Q that receives the ball 32. In contrast to the prior art, the receiving part Q does not have a locking pin and / or a pin for receiving the ball, and is formed so that the ball 32 can move in a direction perpendicular to the measurement direction X (i.e., in the YZ plane). For this purpose, at least the receiving part Q must be made of ceramic.

[0029] The connection to the first connection part P1 described with reference to Figure 3 makes it possible to avoid the use of a locking pin or a pin for a ball seat (see elements 2 and 4 in Figure 8), which allows for considerable cost savings in manufacturing the length measuring device compared to the prior art.

[0030] Referring to FIG. 4, the connecting body 20 has a flat element 34, particularly a steel plate, for connecting the flexure bearing 30 to the connecting element 22. The flat element 34 is formed in a substantially rectangular shape when viewed in the Y-axis direction. The connecting element 22 has a plurality of truncated cone-shaped elements 24.1 to 24.3, which extend at least partially through corresponding openings 36.1 to 36.3 in the flat element 34. FIG. 4 shows the connected state of the flexure bearing 30. In the connected state, the flexure bearing 30 is disposed between the flat element 34 and a portion of the connecting element 22 opposite thereto (see part A in FIG. 5). Furthermore, in the connected state, the flat element 34 is attached to the connecting element 22 via a screw 38.

[0031] Referring to FIG. 5, the connector 22 includes first to third truncated cone elements 24.1 to 24.3. The truncated cone elements 24.1 to 24.3 are arranged so as to overlap one another in the Z direction. The first truncated cone element 24.1 is star-shaped to position the flat element 34 through an opening 36.1 (hole) in the flat element 34 provided corresponding to the first truncated cone element 24.1. The second and third truncated cone elements 24.2 and 24.3 abut on both sides against the edges of openings 36.2 and 36.3 (holes) provided corresponding to the second and third truncated cone elements 24.2 and 24.3, respectively, thereby preventing rotation of the flat element 34 about a second rotation axis R2 (see FIG. 3) extending in a direction Y parallel to the surface S of the scale 14 and compensating for distance tolerances (substantially in the Z direction).

[0032] 5, the first truncated cone-shaped element 24.1 is configured so that it can abut the edge of the opening 36.1 over substantially its entire circumference. Furthermore, the second and third truncated cone-shaped elements 24.2 and 24.3 are configured so that they abut the edges of the openings 36.2 and 36.3, respectively, at two points located opposite each other in the X direction. However, the second and third truncated cone-shaped elements 24.2 and 24.3 do not abut the edges of the openings 36.2 and 36.3 in the Z direction.

[0033] Also shown in Figure 5 is an opening 40 located between the first and second frusto-conical elements 24.1, 24.2, which is used to receive the screw 38 (see Figure 4).

[0034] The functionality described in connection with FIG. 5 is also obtained if one of the two truncated cone elements 24.2, 24.3 is omitted.

[0035] Referring to FIG. 5, the second and third frusto-conical elements 24.2, 24.3 are positioned on opposite sides of the opening 40 or on opposite sides of the first frusto-conical element 24.1.

[0036] Advantageously, the truncated cone elements 24.1 to 24.3 are elements produced by molding the part A of the connector 22 facing the flat element 34. This eliminates the need for press-fit pins (see elements 24.1a to 24.3a in FIG. 7) required in the prior art to connect the flexure bearing 30a to the connector 22a. In order to achieve an improved (or more robust) connection of the connector 22 to the second connection part P2, it is furthermore necessary that at least the truncated cone elements 24.1 to 24.3 comprise ceramic.

[0037] In Figures 6 to 8, corresponding or similar elements are given the same reference numerals as in Figures 1 to 5, except for the letter a, or with the letter a omitted.

[0038] By using ceramic for the majority (or main) part of the connector, it is possible to achieve the same excellent surface properties and high hardness as ceramic at least in the first and second connecting portions P1 and P2.

[0039] The scale 14 may be an incremental scale, or alternatively, the scale 14 may be an absolute scale and may be formed, for example, as a pseudo-random code.

[0040] The present invention allows for particularly high-resolution position measurements if the scale 14 is made optically scannable, although the scale 14 may alternatively be made magnetically, inductively or capacitively scannable. This application relates to the invention described in the claims, but the disclosure of this application also includes the following: 1. A length measuring device, a support (10) extending longitudinally in a measurement direction (X) and having a scale (12) disposed thereon; a probe carriage (16) for scanning the graduations (14) of the scale (12), the probe carriage (16) being guided lengthwise in a measuring direction (X) on at least one guide surface (18.1-18.3); a coupling body (20) for rigidly coupling the probe carriage (16) to the follower (26) in the measurement direction (X) and passively coupling the probe carriage (16) to the follower (26) in a direction crossing the measurement direction, the coupling body (20) having a connector (22) disposed between a first coupling portion (P1) on the probe carriage (16) side and a second coupling portion (P2) on the follower (26) side; In a length measuring device comprising: The connector (22) is attached to the driver (26) at the second connection portion (P2) via a flexure bearing (30), and the flexure bearing (30) is configured to hold the connector (22) in a state in which it can freely rotate relative to the driver (26) about a first rotation axis (R1) extending perpendicular to the surface (S) of the scale (14); A length measuring device, wherein the connector (22) has at least one of a density lower than that of steel and a Young's modulus higher than that of steel. 2. 2. The length measuring device according to claim 1, wherein the connector (22) has a density in the range of 10 to 80%, 20 to 70%, or 25 to 65% of the density of steel. 3. 3. The length measuring device according to 1 or 2 above, wherein the connector (22) has a Young's modulus in the range of 100 to 500 GPa, 160 to 440 GPa, or 250 to 350 GPa. 4. 4. The length measuring device according to any one of 1 to 3 above, wherein the connector (22) is bent into an L-shape. 5. A length measuring device according to any one of 1 to 4 above, wherein the first connecting portion (P1) and the second connecting portion (P2) are arranged offset from each other in a direction (Z) extending perpendicular to the surface (S) of the scale (14). 6. 6. A length measuring device according to any one of 1 to 5 above, wherein the connecting body (20) has a ball (32), and the connecting element (22) is connected to a first connecting portion (P1) on the probe carriage (16) side via the ball, the connecting element (22) has a receiving portion (Q) that receives the ball (32), and the receiving portion (Q) does not have a locking pin and / or a pin for receiving the ball, and is formed so that the ball (32) can move in a direction perpendicular to the measurement direction (X). 7. 7. The length measuring device according to claim 6, wherein at least the receiving portion (Q) comprises ceramic. 8. 8. The length measuring device according to any one of claims 1 to 7, wherein the connecting body (20) has a flat element (34) for connecting the flexure bearing (30) to the connecting element (22), and the connecting element (22) has a plurality of truncated cone-shaped elements (24.1-24.3), the truncated cone-shaped elements extending at least partially through openings (36.1-36.3) of the flat element (34) provided corresponding to the truncated cone-shaped elements. 9. The connector (22) comprises at least first and second truncated cone-shaped elements (24.1, 24.2), which are arranged so as to overlap in a direction (Z) extending perpendicular to the plane (S) of the scale (14). The first truncated cone-shaped element (24.1) is connected to the flat element (34) through an opening (36.1) in the flat element (34) which is provided corresponding to the first truncated cone-shaped element (24.1). 9. The measuring device according to claim 8, wherein the second truncated cone element (24.2) is formed in a star shape to position the flat element (34), and the second truncated cone element (24.2) abuts on both sides against the edges of an opening (36.2) provided corresponding to the second truncated cone element (24.2) to prevent the flat element (34) from rotating about a second rotation axis (R2) extending in a direction (Y) parallel to the surface (S) of the scale (14) and thereby compensate for distance tolerances. 10. 10. The length measuring device according to claim 8 or 9, wherein the truncated cone-shaped elements (24.1-24.3) are elements formed by molding the portion (A) of the connector (22) facing the flat-plate-shaped element (34). 11. 11. A length measuring device according to any one of claims 8 to 10, wherein at least the truncated cone elements (24.1-24.3) comprise ceramic. 12. 12. The length measuring device according to any one of claims 8 to 11, wherein the flat-plate element (34) is a steel plate. 13. 13. The length measuring device according to any one of 1 to 12 above, wherein the connector (22) is made mostly or entirely of ceramic. 14. 14. The length measuring device according to any one of 1 to 13 above, wherein the flexure bearing (30) is a leaf spring. 15. 15. The length measuring device according to claim 14, wherein the leaf spring is made of steel.

Claims

1. A length measuring device, a support (10) extending longitudinally in a measurement direction (X) and on which a scale (12) is arranged; a probe carriage (16) for scanning a graduation (14) of the scale (12), the probe carriage (16) being guided longitudinally in the measurement direction (X) on at least one guide surface (18.1-18.3); a coupling body (20) for rigidly coupling a probe carriage (16) to a follower (26) in a measurement direction (X) and passively coupling the probe carriage (16) to the follower (26) in a direction crossing the measurement direction, the coupling body (20) having a connector (22) arranged between a first coupling portion (P1) on the probe carriage (16) side and a second coupling portion (P2) on the follower (26) side; In a length measuring device comprising: The connector (22) is attached to the driver (26) at the second connection portion (P2) via a flexure bearing (30), the flexure bearing (30) being a leaf spring and configured to hold the connector (22) in a state in which it can freely rotate relative to the driver (26) about a first rotation axis (R1) extending perpendicular to the surface (S) of the scale (14); A length measuring device, wherein the connector (22) has at least one of a density lower than that of steel and a Young's modulus higher than that of steel.

2. 2. The length measuring device according to claim 1, wherein the connector (22) has a density in the range of 10 to 80%, 20 to 70%, or 25 to 65% of the density of steel.

3. 3. The length measuring device according to claim 1, wherein the connector (22) has a Young's modulus in the range of 100 to 500 GPa, in the range of 160 to 440 GPa, or in the range of 250 to 350 GPa.

4. 4. The length measuring device according to claim 1, wherein the connector (22) is bent into an L-shape.

5. 5. A length measuring device according to claim 1, wherein the first connecting portion (P1) and the second connecting portion (P2) are arranged offset from each other in a direction (Z) extending perpendicular to the surface (S) of the scale (14).

6. 6. A length measuring device according to claim 1, wherein the connecting body (20) has a ball (32) via which the connector (22) is connected to a first connecting portion (P1) on the probe carriage (16) side, the connector (22) has a receiving portion (Q) that receives the ball (32), the receiving portion (Q) does not have a locking pin and / or a pin for receiving the ball, and is formed so that the ball (32) can move in a direction perpendicular to the measurement direction (X).

7. 7. A length measuring device according to claim 6, wherein at least the receiving part (Q) comprises ceramic.

8. 8. The length measuring device according to claim 1, wherein the connecting body (20) has a flat element (34) for connecting the flexure bearing (30) to the connecting element (22), and the connecting element (22) has a plurality of truncated cone-shaped elements (24.1-24.3), the truncated cone-shaped elements extending at least partially through openings (36.1-36.3) of the flat element (34) provided corresponding to the truncated cone-shaped elements.

9. The connector (22) comprises at least first and second truncated cone-shaped elements (24.1, 24.2), which are arranged to overlap each other in a direction (Z) extending perpendicular to the plane (S) of the scale (14). The first truncated cone-shaped element (24.1) is connected to the flat element (34) through an opening (36.1) in the flat element (34) which is provided corresponding to the first truncated cone-shaped element (24.1).

9. The length measuring device according to claim 8, wherein the second truncated cone element (24.2) is formed in a star shape to position the flat element (34), and the second truncated cone element (24.2) abuts on both sides against the edges of an opening (36.2) provided corresponding to the second truncated cone element (24.2) to prevent the flat element (34) from rotating about a second rotation axis (R2) extending in a direction (Y) parallel to the surface (S) of the scale (14) and thereby compensate for distance tolerances.

10. 10. A length measuring device according to claim 8 or 9, wherein the truncated cone-shaped elements (24.1-24.3) are elements produced by molding the part (A) of the connector (22) facing the flat-plate-shaped element (34).

11. 11. A length measuring device according to any one of claims 8 to 10, wherein at least the truncated cone elements (24.1-24.3) comprise ceramic.

12. 12. A length measuring device according to claim 8, wherein the flat-plate element (34) is a steel plate.

13. 13. The length measuring device according to claim 1, wherein the connector (22) is made mostly or entirely of ceramic.

14. 14. The length measuring device according to claim 1, wherein the leaf spring is made of steel.

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