Position measuring device

Abstract

A position measuring system that includes a scale graduation, a scanning unit for scanning the scale graduation. An adjustment device that includes a displacement element for setting a position of the scanning unit with respect to the scale graduation and a gear-down mechanism arranged between the displacement element and the scanning unit, the gear-down mechanism converts a displacement movement of the displacement element into a shorter displacement movement of the scanning unit. The gear-down mechanism includes a lever arrangement with joints, which converts the displacement movement of the displacement element into a linear displacement movement of the scanning unit in relation to the scale graduation.

Description

[0001] The invention relates to a position measuring system in accordance with the preamble of claim 1.

[0002] Such a position measuring system is known from DE 43 17 022 C1. The position of a scanning unit with respect to a graduated disk is adjusted by means of a displacement element of an adjustment device in that the displacement element in the form of a screw acts on a lever of a reduction mechanism and displaces the scanning unit in a geared-down manner. This displacement movement is a pivot movement around a flexible joint of the adjustment device.

[0003] In accordance with DE 28 44 066 A1 and DE 40 01 848 C1, the displacement also takes place by means of a lever which pivots the scanning unit around a flexible joint.

[0004] However, linear displacement movements of the scanning unit with respect to the scale graduation are demanded in actual use, such as has been explained in EP 0 158 066 A1, for example. For adjusting four photoelectric barriers, which are arranged spatially offset with respect to each other, of a scanning unit of an angle measuring system, the scanning unit can be displaced in the radial direction via elongated holes. There, the radial displacement is called parallel displacement and takes place by means of two elongated holes. However, a fine adjustment is not possible with this.

[0005] It is therefore the object of the invention to disclose a position measuring system with an adjustment device, by means of which the scanning device can be linearly displaced with respect to the scale graduation in a highly accurate manner.

[0006] In accordance with the invention, this object is attained by a position measuring system with the characteristics of claim 1.

[0007] The advantage obtained by means of the invention lies in that the scanning unit can be linearly displaced in a highly accurate manner by means of a simple device. The displacement movement of a displacement element is converted in a geared-down manner into a linear displacement movement, by means of which a delicate setting is made possible. Moreover, it is possible to provide a reduced structural size.

[0008] Advantageous embodiments are recited in the dependent claims.

[0009] The invention will be explained in still greater detail in what follows by means of exemplary embodiments. Shown are in:

[0010] FIG. 1, a view from above on an angle measuring system with an adjustment device,

[0011] FIG. 2, the adjustment device in accordance with FIG. 1 in an enlarged representation,

[0012] FIG. 3, the adjustment device in a further adjusting position,

[0013] FIG. 4, a second embodiment of the adjustment device,

[0014] FIG. 5, a third exemplary embodiment of the adjustment device,

[0015] FIG. 6, a fourth exemplary embodiment of the adjustment device,

[0016] FIG. 7, a fifth exemplary embodiment of the adjustment device.

[0017] The angle measuring system in accordance with FIG. 1 consists of a graduated disk 1, which is rotatably seated around the axis of rotation D. The graduated disk has an incremental angle graduation 2 as a scale graduation, whose graduation marks are radially oriented. A scanning unit 4 is adjustably fastened on a stator 3 for measuring the rotated position of the graduated disk 1 with respect to the stator 3. The scanning unit 4 is designed in a known manner, so that only the scanning grating 5 of the scanning unit 4 is represented in FIG. 1.

[0018] The scanning unit 4 is attached to a support 16 of an adjustment device 10. The adjustment device 10 has two levers 11 and 12 with stop faces 11.10 and 12.10. These stop faces 11.10 and 12.10 are used in a known manner (DE 32 28 507 C2) for aligning the scanning unit 4 with respect to the graduated disk 1. For this purpose a centering collar 6, which extends concentrically with respect to the axis of rotation D and on which the adjustment device 10 is brought into contact with the stop faces 11.10 and 12.10, is provided on the stator 3 in which the graduated disk 1 is seated. The diameter of the centering collar 6 is subject to tolerances, so that the radial seating of the scanning unit 4 by means of the centering collar 6 does not always meet the demands. For compensating diameter tolerances of the centering collar 6, the scanning unit 4 must be displaced exclusively radially, without changing the alignment with respect to the axis of rotation D (direction R) linearly. This linear displacement is performed with the adjustment device 10 and will be further explained by means of FIG. 2.

[0019] As shown on a magnified scale in FIG. 2, the adjustment device 10 consists of a symmetrically constructed lever mechanism, having two levers 11, 12, each of which can be pivoted around a flexible joint 14, 15 by means of a common displacement element 13. The flexible joints 14, 15 are arranged between the support 16 of the scanning unit 4 and the levers 11, 12, and are embodied in the form of weakest point joints, so that the adjustment device 10 can be manufactured in one piece.

[0020] Each one of the two levers 11, 12 has a short lever arm 11.1, 12.1 and a longer lever arm 11.2, 12.2, extending from the flexible joint 14, 15. The common displacement element 13, with which the two longer lever arms 11.2, 12.2 are pivoted in opposite directions around the flexible joints 14, 15, acts on the two longer lever arms 11.2, 12.2. The stop faces 11.10, 12.10 are formed on the shorter lever arms 11.1, 12.1. The movement of the displacement element 13 is converted by the two lever arms 11, 12 in a geared-down manner into an oppositely directed movement of the two stop faces 11.10, 12.10. Since the two stop faces 11.10, 12.10 are kept in contact with the centering collar 6, the support 16, and therefore the scanning unit 4, moves linearly in the radial direction R when the displacement element 13 is actuated.

[0021] It is particularly advantageous if the two lever arms 11.2, 12.2 are connected with each other via a common yoke 17, on which the displacement element 13 acts. The yoke 17 connects the two long lever arms 11.2, 12.2 in one piece with each other and is designed as a flexible beam, or deformation member. The displacement element in the form of a screw 13 acts against the center of the yoke 17 and bends the yoke 17 in the radial direction R. In the process the screw 13 is supported on the support 16. The deformation of the yoke 17 causes a shortening of the yoke 17, and thus the pivoting of the two levers 11 and 12 over respectively identical distances in opposite directions. To introduce the pivot movement into the levers 11, 12, it is advantageous if a flexible joint 18, 19 is respectively arranged between the yoke 17 and the longer lever arms 11.2 and 12.2.

[0022] Once the radial position of the scanning unit 4 has been correctly set by the adjustment device 10 with the gear-down mechanism consisting of the levers 11, 12 and the flexible joints 14, 15, it is fixed in place on the stator 3 by fastening means, not represented. The fastening bores 7, 8 provided for this are schematically represented in FIG. 2.

[0023] A displacement of the scanning unit 4 transversely to the radial direction R is also possible by means of the adjustment device 10. A further displacement element 9 is provided for this purpose, which acts on one of the two longer lever arms 11.2, 12.2 and deflects it transversely with respect to the radial direction R. This exemplary embodiment is represented in FIG. 3.

[0024] In FIGS. 2 and 3 the levers 11, 12 are shown by solid lines in the non-deflected position, and by dashed lines in the deflected position, i.e. the adjusted position.

[0025] Alternatively to the yoke 17 in the form of a deformation member, the coupling of the two levers 11, 12 can be performed by means of a displacement element 130 in accordance with FIG. 4. For the pivoting of the two levers 11, 12, they are connected with each other by means of the screw 130. When turning the screw 130, the two levers 11, 12 move in opposite directions over identical distances.

[0026] If only one of the levers 11, 12 is to be pivoted, the screw 130 must be supported on a portion of the stator 3 (stator 3 represented in FIG. 3), or on the support 16, which is indicated by the locking ring 30.

[0027] In a manner not represented, instead of a screw, the displacement element 13 in accordance with FIG. 3 can also be an eccentric, whose eccentric surface is in contact with the yoke 17 for bending the latter or, for deflecting only one lever 11, 12, it can be in contact with the latter. In the exemplary embodiment in accordance with FIG. 4, the oppositely directed displacement of the two levers 11, 12 can also be provied by a wedge which acts simultaneously on the two levers 11, 12.

[0028] In connection with the exemplary embodiments so far explained, in the course of adjustment it is necessary to advance the entire adjustment device 10 with the scanning unit 4 on the centering collar 6. In the exemplary embodiment explained in what follows, the adjustment device 10 can be rigidly fixed in place on the stator 3 by means of a stationary element 20, and the scanning unit 4 can be set in relation to this stationary fixed element 20 of the adjustment device 10. For this purpose, the adjustment device 10 is aligned on the centering collar 6 by means of the stop faces 11.10, 12.10 and is fixed in place. The fastening bores 27 and 28 are provided for fixing the stator 3 in place.

[0029] The support 16 of the scanning unit 4 can be displaced via a gear-down mechanism in the radial direction R with respect to the stationary element 20, analogous to the already explained exemplary embodiments. Parts with the same function are provided with the same reference numerals in all exemplary embodiments.

[0030] The gear-down mechanism again consists of a laterally-reversed lever arrangement with two levers 11, 12, which can be pivoted in opposite directions by means of a displacement element 13. The levers 11, 12 are hinged on the stationary element 20 via flexible joints 14, 15, and are connected with each other by means of a common yoke 17. The yoke 17 again is a deformation member, on whose center the displacement 13 acts. With a centered bending of the deformation member, the common connection between the two levers 11, 12 is shortened, which results in a deflection of the two levers 11, 12 over identical distances in opposite directions. In this case the displacement element 13 can be supported on the stator 3 or, in accordance with FIG. 6, on the support 16.

[0031] The pivot movement of the two levers 11, 12 is transmitted in a geared-down manner to the support 16 with the scanning unit 4. The pivot movement performed by the long lever arm 11.2, 12.1 is passed on to the shorter lever arm 11.1, 12.1. The further transfer takes place by means of respective guide rods 21, 22 in the form of a pushrod, one end of which is fastened on the short lever arm 11.1, 12.1, and the other end on the support 16. The one end of each guide rod 21, 22 is fastened via a flexible joint 23, 24 on the short lever arm 11.1, 12.1, and the other end via a further flexible joint 25, 26 on the support 16. The guide rods 21, 22 convert the pivot movement of the two levers 11, 12 into a linear displacement movement of the support 16 exclusively in the radial direction R. In this way the scanning unit 4 is coupled via the two fastening points in the form of flexible joints 25, 26 with the lever arrangement 11, 12 and the guide rods 21, 22. By means of the guide rods 21, 22 the pivot movement of the levers 11, 12 is converted into a parallel displacement of the two fastening points.

[0032] The adjustment devices in accordance with FIGS. 5 and 6 additionally permit an adjustment of the scanning unit in a direction transversely to the radial direction R in that—as represented in FIG. 3—a further displacement element 9 only acts on one of the two levers 11, 12.

[0033] After an adjustment has been performed, the scanning unit 4 is fixed in place on the stator 3. Fastening bores 7, 8 are provided for this purpose on the support 16.

[0034] Analogously with the exemplary embodiment of FIG. 4, the two levers 11, 12 can also be connected with each other by means of a common screw 130, as represented in FIG. 7.

[0035] It is particularly advantageous if all levers 11, 12 and flexible joints 14, 15, 18, 23 to 26 of the gear-down mechanism are located on a common plane and are manufactured in one piece. The axes of rotation of the flexible joints 14, 15, 18, 23 to 26 are aligned parallel with each other.

[0036] The device in accordance with the invention can also be employed for adjusting the scanning unit in other straight-line movement directions, for example for setting the scanning distance between the graduation 2 and the scanning grating 5. Moreover, the invention is not limited to the described angle measuring system. In place of a graduated disk 1, the scale graduation can be merely a sector, or a linear scale. The scale graduation can be designed to be scanned photoelectrically, capacitively, magnetically or inductively. The graduation can be an incremental periodic graduation or an absolute single-track or multi-track coding.

Claims

1. A position measuring system, comprising a scale graduation (2), a scanning unit (4) for scanning the scale graduation (2), an adjustment device (10) with a displacement element (13, 130) for setting the position of the scanning unit (4) with respect to the scale graduation (2), wherein a gear-down mechanism is arranged between the displacement element (13, 130) and the scanning unit (4), which converts a displacement movement of the displacement element (13, 130) into a shorter displacement movement of the scanning unit (4), characterized in that the gear-down mechanism has a lever arrangement (11, 12) with joints (14, 15, 18, 19, 21, 22, 23, 24), which converts the displacement movement of the displacement element (13, 130) into a linear displacement movement of the scanning unit (4) in relation to the scale graduation (2).

2. The position measuring system in accordance with claim 1, characterized in that the displacement element (13, 130) acts simultaneously on two levers (11, 12), and each of the two levers (11, 12) is seated so that it is pivotable around a flexible joint (14, 15).

3. The position measuring system in accordance with claim 2, characterized in that the two levers (11, 12) are coupled together by means of a yoke (17), on which the common displacement element (13) acts, wherein the two levers (11, 12) can be pivoted in opposite directions when the displacement element (13, 130) is actuated.

4. The position measuring system in accordance with claim 3, characterized in that the yoke (17) is a deformation member, which is formed in one piece on the two levers (11, 12).

5. The position measuring system in accordance with one of the preceding claims, characterized in that the adjustment device (10) has stop faces (11.10, 12.10) spaced apart from each other, by means of which the scanning unit (4) can be oriented with respect to the scale graduation (2), and that these stop faces (11.10, 12.10) can be displaced over the lever arrangement (11, 12) by means of a common displacement element (13, 130).

6. The position measuring system in accordance with claim 5, characterized in that the scale graduation (2) is an angle graduation (2), which is seated in a stator (3) and can be rotated around an axis of rotation (D), and a centering collar (6), which extends concentrically with respect to the axis of rotation (D), is arranged on the stator (3), against which the adjustment device (10) rests by means of two stop faces (11.10, 12.10), and the lever arrangement (11, 12) for displacing the stop faces (11.10, 12.10) is arranged between the displacement element (13, 130) and the stop faces (11.10, 12.10).

7. The position measuring system in accordance with claim 6, characterized in that the lever arrangement comprises two levers (11, 12), each of which can be pivoted in opposite directions around a respective flexible joint (14, 15), wherein one of the flexible joints (14, 15) is respectively arranged between the scanning unit (4) and one of the levers (11, 12).

8. The position measuring system in accordance with claim 7, characterized in that each one of the two levers (11, 12) has a short lever arm (11.1, 12.1) extending from the flexible joint (14, 15), and a longer lever arm (11.2, 12.2) extending from the flexible joint (14, 15), wherein the displacement element (13, 130) acts on the longer lever arm (11.2, 12.2), and one of the stop faces (11.10, 12.10) is arranged on the shorter lever arm (11.1, 12.1).

9. The position measuring system in accordance with one of claims 1 to 4, characterized in that the adjustment device (10) has a stationary element (10), to which the scanning device (4) is coupled by means of flexible joints (25, 26), and the flexible joints (25, 26) can be displaced parallel to each other on the scanning unit (4) by means of the lever arrangement (11, 12).

10. The position measuring system in accordance with claim 9, characterized in that the lever arrangement consists of two levers (11, 12), wherewith respectively one lever (11, 12) acts on one of the flexible joints (25, 26) of the scanning unit (4), and the two levers (11, 12) can be pivoted together via the displacement element (13, 130).

11. The position measuring system in accordance with claim 10, characterized in that the two levers (11, 12) are coupled to a guide rod (21, 22), which converts the pivot movement of the levers (11, 12) into a parallel movement of the flexible joints (25, 26) of the scanning unit (4).

12. The position measuring system in accordance with claim 11, characterized in that each of the guide rods (21, 22) is coupled to the scanning unit (4) by means of the respective flexible joint (25, 26), and they are coupled to the lever (11, 12) by means of a further flexible joint (23, 24).