Length measuring device

Abstract

A length measuring device comprises a scale (12), a scanning carriage (16) for scanning a measuring scale division (14) of the scale (12) and an adapter (20) comprising a coupling element (22). The coupling element (22) is fixed on a drive element (26) by a solid hinge (30). The solid hinge (30) is configured to carry the coupling element (22) in a manner free to rotate relative to the drive element (26) about a first rotation axis (R1) which extends perpendicular to a plane (S) of the measuring scale division (14). The coupling element (22) has a smaller density and / or a larger modulus of elasticity than steel.

Description

TECHNICAL FIELD

[0001] The invention relates to a length measuring device according to the preamble of claim 1. BACKGROUND

[0002] Such length measuring devices are used for measuring lengths and displacements and, in particular, in machine tools for measuring the relative movement of a tool relative to a workpiece to be machined, in coordinate measuring machines and also increasingly in the semiconductor industry.

[0003] EP 3 228 993 A1 discloses a length measuring device comprising a scale and a scanning carriage which scans the scale. The scanning carriage is rigid along the measurement direction by means of an articulator, otherwise movably fixed on a drive element. The articulator comprises a connecting element which extends along the measurement direction, which is rotatably supported on the scanning carriage at a first articulation and on the drive element at a second articulation. Between the connecting element and the drive element a first spring means is provided which exerts a pressing force onto the scanning carriage and presses against a guide surface. Furthermore, between the connecting element and the scanning carriage a second spring means is provided which exerts a pressing force onto the scanning carriage and likewise presses against the guide surface. The first spring means is arranged spaced apart from the second spring means along the measurement direction.

[0004] Further length measuring devices with an articulator are known from EP 2 037 230 B1, EP 1 180 662 B1 and DE 36 24 485 A1. SUMMARY

[0005] It is the task of the present invention to specify a length measuring device which is easily and compactly constructed and with which precise position measurements are achieved.

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

[0007] The length measuring device according to the invention comprises a support which extends longitudinally along a measuring direction, the support having a scale arranged thereon, a scanning carriage for scanning a measuring division of the scale, wherein the scanning carriage is guided longitudinally along the measuring direction on at least one guide surface, and a coupling device by which the scanning carriage is coupled rigidly along the measuring direction and flexibly transversely to the measuring direction to a drive element. The coupling device comprises a coupling element which is arranged between a first coupling site on the scanning carriage and a second coupling site on the drive element. The coupling element is fixed at the second coupling site to the drive element by means of a solid hinge. The solid hinge is configured to carry the coupling element in such a way that it can rotate freely about a first axis of rotation relative to the drive element, the first axis of rotation extending perpendicular to the plane of the measuring division. The coupling element has a smaller density and / or a greater modulus of elasticity than steel.

[0008] For example, the coupling element has a density in the range of 10 to 80%, in the range of 20 to 70% or in the range of 25 to 65% of the density of steel.

[0009] For example, the coupling element has a modulus of elasticity 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.

[0010] Advantageously, the coupling device comprises a ball, if the coupling element comprises a receiving region for receiving the ball and if the receiving region is free of a stop pin and / or a pin for a ball bearing and is configured in such a way that the ball can move in a direction perpendicular to the measuring direction, the coupling element being coupled to the scanning carriage at the first coupling site by means of the ball.

[0011] Furthermore, advantageously, the coupling device comprises a plate-shaped element for connecting the solid hinge to the coupling element, and the coupling element has a plurality of peg-shaped elements which extend at least partially through respectively assigned openings of the plate-shaped element.

[0012] Preferably, the coupling element is composed predominantly or entirely of ceramic.

[0013] Alternatively, the coupling element can be made predominantly or entirely of carbon fiber-reinforced plastic (CFK).

[0014] The solid hinge is in particular a leaf spring.

[0015] By the present application, on the one hand a relatively large inherent stiffness is achieved, and on the other hand a relatively small mass of the coupling element is achieved. Thereby, the position of the frequency band of the natural frequency of the system can be shifted significantly in the direction of higher frequencies. This in turn can achieve an improved frequency behavior of the length measuring device relative to the prior art. In addition thereto, it is possible to dispense with the (additional) mass spring system for implementing the joint, the natural frequency of which leads to a significant deterioration of the measurement accuracy in a specific frequency band. Thereby, on the one hand a simple and compact construction is achieved, and on the other hand an accurate position measurement.

[0016] Advantageous design solutions of the present application are known from the dependent claims. BRIEF DESCRIPTION OF DRAWINGS

[0017] Further details and advantages of the present application are explained by means of the following description of possible embodiments thereof in conjunction with the drawings.

[0018] Figure 1 A side view of a length measuring device according to an embodiment is shown;

[0019] Figure 2 A cross section of a length measuring device according to Figure 1 in the region of the coupling element is shown;

[0020] Figure 3 A side view of a coupling element of a length measuring device according to Figure 1 is shown;

[0021] Figure 4 Another side view of a coupling element of a length measuring device according to Figure 1 is shown for illustrating the connection of the solid hinge to the coupling element;

[0022] Figure 5 A perspective view of a coupling element of a length measuring device according to 1 is shown;

[0023] Figure 6 A side view of a coupling element of a length measuring device according to the prior art is shown;

[0024] Figure 7 Another side view of a coupling element of a length measuring device according to the prior art is shown for illustrating the connection of the solid hinge to the coupling element; and

[0025] Figure 8 A perspective view of a coupling element of a length measuring device according to the prior art is shown, the coupling element having a pin for a stop pin and a ball bearing; DETAILED DESCRIPTION

[0026] Identical or functionally identical elements are provided with the same reference signs in the figures.

[0027] An embodiment will be explained below by means of Figures 1 to 5 an example. Figures 6 to 8 Components (elements) of a known length measuring device are shown. The length measuring device according to the present embodiment serves for measuring the relative position of two objects which can be moved relative to each other along a measurement direction X. For the position measurement, a scale 12 of the length measuring device is fixed on one of the objects and a scanning carriage 16 of the length measuring device is fixed on the other one of the objects. Here, the scale 12 is scanned by the scanning carriage 16 which can be moved relative to the scale 12 along the measurement direction X. The length measuring device has a support 10 which extends longitudinally along the measurement direction X. The scale 12 has a measurement graduation 14 which is scanned by the scanning carriage 16. To this end, the scanning carriage 16 comprises an illumination unit which emits a light beam which is modulated by the measurement graduation 14 depending on the position and finally falls on a light-sensitive scanning sensor of the scanning carriage 16. The illumination unit and the scanning sensor of the scanning carriage 16 are not shown in the figures.

[0028] The scale 12 is arranged on the support 10. As shown in Figure 2 , the support 10 is a hollow profile in which the scale 12 and the scanning carriage 16 are arranged in a protected manner. Here, the scale 12 is connected to the support 10 in a known manner, for example by gluing or clamping. The support 10 which is configured as a hollow profile has a slit which extends along the measurement direction X along its longitudinal direction, which slit is closed by a roof-like inclined sealing lip 11 through which a drive element 26 passes with a sword-shaped intermediate piece 28.1. The drive element 26 has a mounting region 28.2 with which it can be fixed on one of the objects to be measured, for example on a slide of a machine tool.

[0029] The scanning carriage 16 is guided on the scale 12 and / or on the support 10 for precise parallel guidance along the scale 12. The scanning carriage 16 is supported in the shown embodiment for this purpose on a plurality of guide surfaces 18.1 to 18.3. The guide surfaces 18.1 to 18.3 are formed by guide strips which are fixed on the support 10. The guide surfaces 18.2, 18.3 are oriented parallel to a plane S of the measurement graduation 14. The guide surface 18.1 is oriented perpendicular to this plane S. The guide element can be a sliding element, but in particular a ball-bearing roller or a roller.

[0030] The scanning carriage 16 is coupled to the drive element 26 rigidly along the measurement direction X and flexibly transversely to the measurement direction by means of a coupling 20. The coupling 20 comprises a coupling element 22 which is arranged between a first coupling point Pl on the scanning carriage 16 and a second coupling point P2 on the drive element 26 (cf. Figure 3 ). The coupling element 22 is fixed at the second coupling point P2 on the drive element 26 by means of a solid hinge 30, in particular a leaf spring. The solid hinge 30 is configured to carry the coupling element 22 in a manner which is free to rotate about a first rotation axis Rl relative to the drive element 26, the first rotation axis Rl extending perpendicular to the plane S of the measurement scale 14. The leaf spring is in particular made of steel.

[0031] The coupling element 22 has a smaller density and / or a greater modulus of elasticity than steel. For example, the coupling element 22 has a density which lies in the range of 10 to 80%, in the range of 20 to 70% or in the range of 25 to 65% of the density of steel. Furthermore, the coupling element 22 has, for example, a modulus of elasticity which lies 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. In the embodiment shown, the coupling element 22 is made for the most part or preferably entirely of ceramic.

[0032] With reference to Figure 3 , the coupling element 22 is essentially L-shaped in its bending. Furthermore, the coupling element 22 is fork-shaped, wherein an upper section of the coupling element 22 is arranged on both sides of the measurement scale 14 (cf. Figure 2 ). The coupling element 22 extends between the first and second coupling points Pl, P2. The first and second coupling points Pl, P2 are arranged here in a manner which is offset relative to one another in a direction Z which extends perpendicular to the plane S of the measurement scale 14.

[0033] It is preferred that the first coupling point Pl is arranged on the one hand in or at least close to the plane S of the measurement scale 14 (in the Z direction) and on the other hand on both sides of the measurement scale 14 (in the Y direction). This is shown in particular in Figure 2 .

[0034] The coupling 20 shown in Figure 3 comprises a ball 32 by means of which the coupling element 22 is coupled at the first coupling point Pl on the scanning carriage 16. The coupling element 22 comprises a receiving region Q for receiving the ball 32. In contrast to the prior art, the receiving region Q is free of stop pins and / or pins for ball bearings and is configured in such a way that the ball 32 can move in a direction which is perpendicular to the measurement direction X, that is to say in the YZ plane. For this purpose, at least the receiving region Q should have ceramic.

[0035] By referring to Figure 3 the coupling at the first coupling site P1 explained, the use of a stop pin or a pin for a ball bearing (see Figure 8 elements 2 and 4 therein) can be dispensed with. This can save costs significantly compared to the prior art when manufacturing a length measuring device.

[0036] By referring to Figure 4 , the adapter 20 comprises a plate-shaped element 34, in particular a steel plate, for connecting the solid hinge 30 with the coupling element 22. The plate-shaped element 34 is essentially rectangularly configured along the viewing direction towards the Y-axis. The coupling element 22 has a plurality of peg-shaped elements 24.1 to 24.3, which extend at least partially through the respective assigned openings 36.1 to 36.3 of the plate-shaped element 34. In Figure 4 , the connected state of the solid hinge 30 is shown. In the connected state, the solid hinge 30 is arranged between the plate-shaped element 34 and the area of the coupling element 22 opposite the plate-shaped element (see area A in Figure 5 ). Furthermore, in the connected state, the plate-shaped element 34 is fixed on the coupling element 22 by means of screws 38.

[0037] By referring to Figure 5 , the coupling element 22 has first to third peg-shaped elements 24.1 to 24.3. The peg-shaped elements 24.1 to 24.3 are arranged stacked along the Z-direction. The first peg-shaped element 24.1 is configured star-shaped for positioning the plate-shaped element 34 by means of the opening 36.1 (drill hole) of the plate-shaped element 34 assigned to the first peg-shaped element 24.1. The second and third peg-shaped elements 24.2, 24.3 abut on both sides on the edges of the openings 36.2, 36.3 (drill holes) respectively assigned to the second and third peg-shaped elements 24.2, 24.3, in order to prevent a rotation of the plate-shaped element 34 about the second rotation axis R2 and to compensate (essentially along the Z-direction) a spacing tolerance, which second rotation axis extends along the direction Y parallel to the plane S of the measuring scale 14 (see Figure 3 ).

[0038] As shown in Figure 5 , the first peg-shaped element 24.1 is configured here such that it can abut on the edge of the opening 36.1 essentially over its entire circumference. Furthermore, the second and third peg-shaped elements 24.2, 24.3 are configured here such that they abut on the edge of the opening 36.2 or 36.3 at two points opposite along the X-direction, respectively. However, the second and third peg-shaped elements 24.2, 24.3 do not abut on the edges of both openings 36.2, 36.3 along the Z-direction.

[0039] Furthermore, in Figure 5 the opening 40 is shown which is arranged between the first and the second peg element 24.1, 24.2. This opening 40 serves for receiving the screw 38 (see Figure 4 ).

[0040] If one of the two peg elements 24.2, 24.3 is cancelled, the functions described in connection with Figure 5 can also be achieved.

[0041] With reference to Figure 5 , the second and third peg elements 24.2, 24.3 are on opposite sides of the opening 40 or on opposite sides of the first peg element 24.1, respectively.

[0042] The peg elements 24.1 to 24.3 are in an advantageous manner elements which are moulded on the area A of the coupling element 22 which faces the plate element 34. Thereby, the press-in pin procedure (see elements 24.1a to 24.3a in Figure 7 ) which is necessary in the prior art for connecting the solid hinge 30a with the coupling element 22a is cancelled. Furthermore, in order to achieve an improved (or stable) coupling of the coupling element 22 at the second coupling site P2, at least the peg elements 24.1 to 24.3 should have a ceramic.

[0043] In Figures 6 to 8 , the respective or analogous elements are provided with the same reference numerals as in Figures 1 to 5 , but with the addition of the letter a, or with the same reference numerals as in Figures 1 to 5 , but with the deletion of the letter a.

[0044] The use of ceramic for the greater part (or the main part) of the coupling element makes it possible to achieve a high hardness and an outstanding surface quality thereof at least at the first and the second coupling site P1, P2.

[0045] The measurement scale 14 can be an incremental scale. As an alternative, the measurement scale 14 can also be an absolute scale, for example constructed as a pseudo-random code.

[0046] If the measurement scale 14 is constructed in an optically scannable manner, the present application makes it possible to achieve a particularly high-resolution position measurement. As an alternative, the measurement scale 14 can also be constructed in a magnetically, inductively or capacitively scannable manner.

Claims

1. A length measuring device, having A bracket (10) extends longitudinally along the measurement direction (X), the bracket having a scale (12) arranged thereon. A scanning carriage (16) for scanning the measurement graduations (14) of the scale (12), wherein the scanning carriage (16) is longitudinally guided along the measurement direction (X) on at least one guide surface (18.1-18.3); A coupling (20) is provided, through which the scanning carriage (16) is rigidly coupled to the drive member (26) along the measurement direction (X) and flexibly coupled transversely to the measurement direction, wherein the coupling (20) includes a coupling element (22) disposed between a first coupling portion (P1) on the scanning carriage (16) and a second coupling portion (P2) on the drive member (26). Its features are, The coupling element (22) is fixed to the drive member (26) at the second coupling portion (P2) by a solid hinge (30), wherein the solid hinge (30) is configured to carry the coupling element (22) in a manner that allows it to rotate freely relative to the drive member (26) about a first axis of rotation (R1), which extends perpendicular to the plane (S) of the measuring scale (14), and The coupling element (22) has a lower density and / or a higher elastic modulus than steel.

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

3. The length measuring device according to claim 1 or 2, wherein the coupling element (22) has an elastic modulus in the range of 100 to 500 GPa, 160 to 440 GPa, or 250 to 350 GPa.

4. The length measuring device according to any one of the preceding claims, wherein the coupling element (22) is configured in an L-shape.

5. The length measuring device according to any one of the preceding claims, wherein the first coupling portion (P1) and the second coupling portion (P2) are arranged such that they are offset relative to each other in a direction (Z) extending along a plane (S) perpendicular to the measuring graduation (14).

6. The length measuring device according to any one of the preceding claims, wherein the coupling (20) comprises a ball (32), the coupling element (22) being coupled to the scanning carriage (16) at the first coupling portion (P1) via the ball, wherein the coupling element (22) comprises a receiving area (Q) for receiving the ball (32), wherein the receiving area (Q) is without a stop pin and / or a pin for a ball support and is configured such that the ball (32) is movable in a direction perpendicular to the measuring direction (X).

7. The length measuring device according to claim 6, wherein at least the receiving area (Q) is ceramic.

8. The length measuring device according to any one of the preceding claims, wherein the connector (20) includes a plate-shaped element (34) for connecting the solid hinge (30) to the coupling element (22), wherein the coupling element (22) has a plurality of bolt-shaped elements (24.1-24.3) that extend at least partially through the respective assigned openings (36.1-36.3) of the plate-shaped element (34).

9. The length measuring device according to claim 8, wherein the coupling element (22) has at least one first and second pin elements (24.1, 24.2) arranged in a stacked manner along a direction (Z) extending perpendicular to the plane (S) of the measuring scale (14), wherein the first pin element (24.1) is star-shaped to position the plate element (34) on an opening (36.1) of the plate element (34) belonging to the first pin element (24.1), wherein the second pin element (24.2) abuts on both sides against the edges of the opening (36.2) of the second pin element (24.2) to prevent the plate element (34) from rotating about a second axis of rotation (R2) and to compensate for pitch tolerances, the second axis of rotation extending along a direction (Y) parallel to the plane (S) of the measuring scale (14).

10. The length measuring device according to claim 8 or 9, wherein the pin-shaped element (24.1-24.3) is an element formed by molding on the region (A) of the coupling element (22) facing the plate-shaped element (34).

11. The length measuring device according to any one of claims 8 to 10, wherein at least the pin-shaped element (24.1-24.3) is ceramic.

12. The length measuring device according to any one of claims 8 to 11, wherein the plate-shaped element (34) is a steel plate.

13. The length measuring device according to any one of the preceding claims, wherein the coupling element (22) is mostly or entirely made of ceramic.

14. The length measuring device according to any one of the preceding claims, wherein the solid hinge (30) is a leaf spring.

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

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