Weight-force compensation device

Abstract

A weight compensating device includes a stator and a translator. The translator is movable relative to the stator along a movement axis. The translator includes a first permanent magnet arrangement with an axial magnetization. The stator includes a second permanent magnet arrangement radially surrounding the first permanent magnet arrangement. The stator includes a third permanent magnet arrangement that is coaxially below the first permanent magnet arrangement and that has an axial magnetization aligned in inverse fashion with respect to the axial magnetization of the first permanent magnet arrangement. The stator includes a magnetic body arrangement that is coaxially above the first permanent magnet arrangement. The first permanent magnet arrangement, the second permanent magnet arrangement, the third permanent magnet arrangement and the magnetic body arrangement form a magnetic unit and, in interaction with one another, form a compensating force that counteracts the weight acting on the translator.

Claims

1. A device, comprising: a stator; and a translator movable relative to the stator along a movement axis, wherein: the translator comprises a first permanent magnet arrangement having an axial magnetization; the first permanent magnet arrangement comprises an axially magnetized ring magnet; the stator comprises a second permanent magnet arrangement radially surrounding the first permanent magnet arrangement; the stator comprises a third permanent magnet arrangement coaxial with the first permanent magnet arrangement; the third permanent magnet arrangement has an axial magnetization inverse to the axial magnetization of the first permanent magnet arrangement; the stator comprises a magnetic body arrangement coaxial to the first permanent magnet arrangement; the third permanent magnet is coxially below the first permanent magnet along a direction of a force due to a weight acting on the translator; the magnetic body arrangement is coaxially above the first permanent magnet arrangement along the direction of the force due to the weight acting on the translator; the first permanent magnet arrangement, the second permanent magnet arrangement, the third permanent magnet arrangement and the magnetic body arrangement define a magnetic unit; in interaction with each other, the first permanent magnet arrangement, the second permanent magnet arrangement, the third permanent magnet arrangement and the magnetic body arrangement define a compensating force that counteracts the weight acting on the translator.

2. The device of claim 1, wherein the magnetic body arrangement comprises a fourth permanent magnet arrangement having an axial magnetization aligned with the axial magnetization of the first permanent magnet arrangement.

3. The device of claim 1, wherein: the first permanent magnet arrangement extends in a first plane; the third permanent magnet arrangement extends in a second plane; the magnetic body arrangement extends in a third plane; each of the first, second and third planes is orthogonal to the movement axis; and each of the first, second and third planes is symmetric with respect to the movement axis.

4. The device of claim 1, wherein at least one member selected from the group consisting of the third permanent magnet arrangement and the magnetic body arrangement comprises an axially magnetized ring magnet.

5. The device of claim 1, wherein at least one member selected from the group consisting of the first permanent magnet arrangement, the third permanent magnet arrangement and the magnetic body arrangement comprises a plurality of nested axially magnetized ring magnets.

6. The device of claim 5, wherein the nested axially magnetized ring magnets are polarized with axially opposite polarity.

7. The device of claim 5, wherein: the nested axially magnetized ring magnets are in a plane; the plane is orthogonal to the movement axis; and the plane is symmetric with respect to the movement axis.

8. The device of claim 1, wherein: at least one member selected from the group consisting of the first permanent magnet arrangement, the third permanent magnet arrangement and the magnetic body arrangement comprises a plurality of ring magnets; and for each of the ring magnets, the ring magnet has a central axis that extends coaxially relative to the movement axis.

9. The device of claim 1, wherein at least one member selected from the group consisting of the first permanent magnet arrangement, the third permanent magnet arrangement and the magnetic body arrangement comprises from two ring magnets to 10 ring magnets.

10. The device of claim 1, wherein the second permanent magnet arrangement has an axial magnetization.

11. The device of claim 1, wherein the second permanent magnet arrangement comprises a plurality of ring magnets axially arranged relative to each other.

12. The device of claim 11, wherein the second permanent magnet arrangement comprises two axially magnetized ring magnets aligned with each other with opposite polarity.

13. The device of claim 12, wherein the ring magnet of the first permanent magnet arrangement has an axial polarization aligned with the polarization of one of the magnetized ring magnets of the second permanent magnet arrangement.

14. The device of claim 1, wherein an axial extent of the second permanent magnet arrangement is greater than or equal to an axial spacing between the third permanent magnet arrangement and the magnetic body arrangement.

15. The device of claim 1, wherein at least one of the following holds: the second permanent magnet arrangement comprises a plurality of magnets, and an axial spacing between the ring magnets of the second permanent magnet arrangement is adjustable to adjust the compensating force; an axial spacing between the third permanent magnet arrangement and the magnetic body arrangement is adjustable to adjust the compensating force; an axial position along the movement axis of the first permanent magnet arrangement is adjustable to adjust the compensating force; an axial position along the movement axis of the second permanent magnet arrangement is adjustable to adjust the compensating force; and an axial position along the movement axis of the third permanent magnet arrangement is adjustable to adjust the compensating force.

16. The device of claim 1, wherein at least one member selected from the group consisting of the first permanent magnet arrangement, the third permanent magnet arrangement, and the magnetic body arrangement comprises a Halbach arrangement.

17. The device of claim 1, further comprising an actuator coil at the stator, wherein the stator coil and the first permanent magnet arrangement define an actuator configured to deflect the translator.

18. The device of claim 1, further comprising a plurality of magnetic units at the stator and the translator along the movement axis, and the magnetic units define the compensating force.

19. An apparatus, comprising: an illumination system; an optical unit comprising an optical element; and a device according to claim 1, wherein: the device is configured to compensate a weight of the optical element; and the apparatus is a lithography projection exposure apparatus.

20. The apparatus of claim 19, wherein the optical element comprises a mirror.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) In the figures, functionally identical elements are provided with the same reference signs. In the figures, schematically:

(2) FIG. 1 shows an EUV projection exposure apparatus;

(3) FIG. 2 shows a further projection exposure apparatus;

(4) FIG. 3 shows an isometric illustration of an optical element with three weight compensating devices;

(5) FIG. 4 shows an arrangement for holding an optical element with a weight compensating device in a non-deflected position, according to the prior art;

(6) FIG. 5A shows a first embodiment of a weight compensating device according to the disclosure in a deflected position;

(7) FIG. 5B shows a variant of the first embodiment of FIG. 5A with a radially magnetized second permanent magnet arrangement;

(8) FIG. 6 shows a second embodiment of the weight compensating device according to the disclosure in a non-deflected position;

(9) FIG. 7 shows a third embodiment of the weight compensating device according to the disclosure with a Halbach arrangement in a non-deflected position;

(10) FIG. 8 shows a weight compensating device according to the disclosure with three magnetic units arranged with axial offset along the movement axis; and

(11) FIG. 9 shows an exemplary force-distance curve.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

(12) FIG. 1 shows by way of example the basic structure of an EUV projection exposure apparatus 400 for semiconductor lithography in which the disclosure is able to be applied. An illumination system 401 of the projection exposure apparatus 400 includes, besides a radiation source 402, an optical unit 403 for the illumination of an object field 404 in an object plane 405. A reticle 406 arranged in the object field 404 is illuminated, said reticle being held by a reticle holder 407, illustrated schematically. A projection optical unit 408, illustrated merely schematically, serves for imaging the object field 404 into an image field 409 in an image plane 410. A structure on the reticle 406 is imaged on a light-sensitive layer of a wafer 411 arranged in the region of the image field 409 in the image plane 410, said wafer being held by a wafer holder 412 that is likewise illustrated in part. The radiation source 402 can emit EUV radiation 413, in particular in the range of between 5 nanometers and 30 nanometers. Optically differently designed and mechanically adjustable optical elements 415, 416, 418, 419 and 420 are used for controlling the radiation path of the EUV radiation 413. In the case of the EUV projection exposure apparatus 400 illustrated in FIG. 1, the optical elements are designed as adjustable mirrors in suitable embodiments, which are mentioned merely by way of example below.

(13) The EUV radiation 413 generated via the radiation source 402 is aligned via a collector integrated in the radiation source 402 in such a way that the EUV radiation 413 passes through an intermediate focus in the region of an intermediate focal plane 414 before the EUV radiation 413 impinges on a field facet mirror 415. Downstream of the field facet mirror 415, the EUV radiation 413 is reflected by a pupil facet mirror 416. With the aid of the pupil facet mirror 416 and an optical assembly 417 having mirrors 418, 419 and 420, field facets of the field facet mirror 415 are imaged into the object field 404.

(14) FIG. 2 illustrates a further projection exposure apparatus 100, for example a DUV (“deep ultraviolet”) projection exposure apparatus. The projection exposure apparatus 100 includes an illumination system 103, a device known as a reticle stage 104 for receiving and exactly positioning a reticle 105, by which the later structures on a wafer 102 are determined, a facility 106 for holding, moving and exactly positioning the wafer 102 and an imaging facility, to be specific a projection lens 107, with multiple optical elements 108, which are held by way of mounts 109 in a lens housing 140 of the projection lens 107.

(15) The optical elements 108 may be designed as individual refractive, diffractive and/or reflective optical elements 108, such as for example lens elements, mirrors, prisms, terminating plates and the like.

(16) The basic functional principle of the projection exposure apparatus 100 makes provision for the structures introduced into the reticle 105 to be imaged onto the wafer 102.

(17) The illumination system 103 provides a projection beam 111 in the form of electromagnetic radiation, which is involved for the imaging of the reticle 105 on the wafer 102. A laser, plasma source or the like may be used as the source of this radiation. Optical elements in the illumination system 103 are used to shape the radiation in such a way that, when it is incident on the reticle 105, the projection beam 111 has the desired properties with regard to diameter, polarization, shape of the wavefront and the like.

(18) An image of the reticle 105 is generated via the projection beam 111 and transferred from the projection lens 107 onto the wafer 102 in an appropriately reduced form. In this case, the reticle 105 and the wafer 102 may be moved synchronously, so that regions of the reticle 105 are imaged onto corresponding regions of the wafer 102 virtually continuously during a so-called scanning operation.

(19) FIG. 2 shows the arrangement of a manipulator 200 in the region between the reticle stage 104 and the first optical element 108 of the projection lens 107. The manipulator 200 serves for correcting image aberrations, wherein an optical element that is contained is mechanically deformed by an actuator system.

(20) The use of actuators of various designs is known for adjusting and/or for manipulating the optical elements 415, 416, 418, 419, 420, 108 of the projection exposure apparatuses 400, 100 illustrated in FIGS. 1 and 2 and the wafers 411, 102.

(21) The apparatus according to the disclosure is particularly suitable for compensating the weight of the individual optical elements 108, 418, 419, 420, parts of these optical elements 108, 418, 419, 420 or any other optical elements of a projection exposure apparatus 400, 100.

(22) The use of the disclosure is not restricted to use in projection exposure apparatuses 100, 400, in particular also not with the described structure.

(23) The disclosure and the following exemplary embodiment should also not be understood as being restricted to a specific design.

(24) FIG. 3 shows a very schematic, isometric view of an optical element, for example a mirror 418, of a projection exposure apparatus 400. However, the arrangement can be used for all optical elements of any projection exposure apparatus. The arrangement includes three weight compensating devices 1 on the back side of the mirror 418. A respective weight compensating device 1 includes a translator 2. The translator 2 is exemplary embodiment embodied as a tubular element that is arranged within a stator 3. The translator 2 transfers the compensating force F.sub.M to the mirror 418. The stator 3 can be secured on a supporting frame (not shown) of the projection exposure apparatus 400.

(25) Further, a deflection of the mirror 418 by actuators, more particularly plunger coil actuators, may be provided. The plunger coil actuators (not denoted in any more detail) may be embodied in combination with the weight compensating devices 1 in this case.

(26) FIG. 4 shows a schematic sectional view of a weight compensating device 1 of FIG. 3 according to the prior art. The weight compensating device 1 is constructed rotationally symmetrical with respect to a movement axis A. The translator 2 of the weight compensating device 1 extends along the movement axis A. Here, the translator 2 is connected via connecting elements 4 to the surrounding stator 3 such that the translator 2 is positively guided along the movement axis A. The direction of the movement axis A is likewise the direction in which the weight compensating device 1 exerts the compensating force F.sub.M on the mirror 418 in the movement direction z in order to hold said mirror 418.

(27) The weight compensating device 1 according to the prior art includes a radially magnetized ring magnet 5 and two axially magnetized ring magnets 6. Here, in the figures, the magnetization direction or the polarization or the alignment of the magnetic poles is indicated by arrows in each case, with the arrow, proceeding from one of the first magnetic poles, pointing to a second magnetic pole. According to the usual illustration of field lines, the first magnetic pole can be, in particular a magnetic north pole and the second magnetic pole can be a magnetic south pole. However, the relationships can also be interchanged.

(28) The ring magnet 5 that is fastened to the stator 3 surrounds the ring magnets 6 of the translator 2. In the exemplary embodiment, the translator 2 is embodied as a tube. The two axially magnetized ring magnets 2 are arranged around the translator 2 in a manner spaced apart from one another axially, i.e., along the movement axis A. Here, the ring magnets 5, 6 are arranged and magnetized in such a way that the magnetic interaction ensures that the two axially magnetized ring magnets 6 are pressed out of the radially magnetized ring magnet 5 along the movement axis A (upward in the illustration).

(29) The translator 2 is connected to the mirror 418 in order to exert the compensating force F.sub.M on the mirror 418. The connection is established by way of a coupling device 7 (merely indicated schematically in FIG. 4) assigned to the weight compensating device 1. The coupling device 7 mounts the mirror 418 in a freely movably fashion in a plane perpendicular to the movement axis A. In the direction of the weight F.sub.G, i.e., along the movement axis A, on the other hand, the mirror 418 is held by the weight compensating device 1.

(30) Further, FIG. 4 shows a combination of the weight compensating device 1 with an actuator embodied as a plunger coil actuator.

(31) To this end, two actuator coils 8 (illustrated only schematically and in dashed fashion as blocks) are provided on the stator 3, said actuator coils causing a magnetic interaction with the axially magnetized ring magnets 6 of the translator 2 in the case of an appropriate current feed, as a result of which the translator 2 can be deflected in targeted fashion. As a result of the weight F.sub.G of the mirror 418—as described—already having been compensated, the actuator need not compensate the weight F.sub.G by way of an additional current feed to the actuator coils 8. Therefore, the arrangement has a high efficiency and, in particular, low thermal emissions.

(32) However, the disclosure can also be used for a weight compensating device 1 that includes no additional actuator or no actuator coils 8.

(33) The arrangement of the prior art described above has the disadvantage of a relatively large stray field 9, which may possibly adversely affect adjacent component parts, for example of a projection exposure apparatus 100, 400. By way of example, sensors and actuators and adjoining electronics can be adversely affected by the stray field or fields 9 emanating from the weight compensating device 1. In order to elucidate the issue, FIG. 4 shows a schematic illustration of the distribution of the magnetic field lines of such an arrangement in the image field IV. Here, all that is shown for simplification purposes is the stray field 9 of the right-hand part of the rotationally symmetric arrangement.

(34) FIG. 5A shows a first embodiment of the weight compensating device 1 according to the disclosure and FIG. 5B shows a variant thereof. Here, this is a minimalist embodiment of the disclosure. For reasons of clarity and an improved illustration, all that is shown is a section that represents the arrangement along the stator 3 and the translator 2. The basic structure, i.e., the connection of the translator 2 to the component 418 to be mounted, etc., can correspond as a matter of principle to the known prior art (cf. FIG. 4) and will not be described again in detail.

(35) According to the disclosure, provision is made for the translator 2 to be movable relative to the stator 3 along the movement axis A, as is already known from the prior art. For elucidation purposes, the figures illustrate a clearly visible play between the translator 2 and the surrounding stationary components arranged on the stator 3. The translator 2 includes a first permanent magnet arrangement 10 with an axial magnetization. Further, the stator 3 includes a second permanent magnet arrangement 11, which radially surrounds the first permanent magnet arrangement 10.

(36) According to the disclosure, provision is further made of a third permanent magnet arrangement 12 that is arranged coaxially below the first permanent magnet arrangement 10 and that has an axial magnetization that is aligned in inverse fashion with respect to the axial magnetization of the first permanent magnet arrangement 10. Finally, the stator 3 includes a magnetic body arrangement 13, which is arranged coaxially above the first permanent magnet arrangement 10.

(37) The first permanent magnet arrangement 10, the second permanent magnet arrangement 11, the third permanent magnet arrangement 12 and the magnetic body arrangement 13 form a magnetic unit 14 and, in interaction with one another, generate a compensating force F.sub.M, which counteracts the weight F.sub.G acting on the translator 2.

(38) FIGS. 5 to 7 each indicate a force-free central position z.sub.0 or zero position, in which the first permanent magnet arrangement 10 is aligned in centered fashion between the third permanent magnet arrangement 12 and the magnetic body arrangement 13. In FIGS. 5A, 5B, the translator 2 is deflected from its central position z.sub.0 for clarification purposes (illustrated in exaggerated fashion for elucidation purposes).

(39) The first permanent magnet arrangement 10 and the third permanent magnet arrangement 12 are each formed from an axially magnetized ring magnet 10.1, 12.1 in the exemplary embodiment according to FIGS. 5A-5B. Here, the ring magnets 10.1, 12.1 of the first and third permanent magnet arrangement 10, 12 are magnetized with opposite polarity in relation to one another, i.e., the ring magnets 10.1, 12.1, magnetically repel one another.

(40) In the embodiment of FIG. 5A-5B, the magnetic body arrangement 13 is a soft magnetic annular body 13, in particular made of iron.

(41) As a result of this arrangement, an interaction arises within the magnetic unit 14 such that the first permanent magnet arrangement 10, which is fastened to the translator 2, is magnetically repelled by the third permanent magnet arrangement 12 arranged therebelow and simultaneously magnetically attracted by the magnetic body arrangement 13.

(42) The second permanent magnet arrangement 11 likewise has an axial magnetization in the exemplary embodiment according to FIG. 5A. To this end, the second permanent magnet arrangement 11 includes two axially polarized ring magnets 11.1, 11.2 that are arranged axially above one another. The two ring magnets 11.1, 11.2 of the second permanent magnet arrangement 11 have an alignment with respect to one another with the same polarization in this case, i.e., their magnetic south poles (or, alternatively, their magnetic north poles) are aligned with respect to one another.

(43) Like above, the alignment of the magnetic poles in FIGS. 5A, 5B and in the subsequent figures is also represented by arrows in the respective individual magnetic component parts.

(44) Consequently, the ring magnets 11.1, 11.2 of the second permanent magnet arrangement 11 in the exemplary embodiment of FIG. 5A exert a magnetically repulsive force on one another.

(45) In principle, the axial magnetization (FIG. 5A) of the second permanent magnet arrangement 11 can be as desired; however, the inventors have recognized that an advantageous result, in particular also a stray field-optimized result, is obtained from, in particular, two axially magnetized ring magnets 11.1, 11.2 with a polarization aligned with opposite polarity with respect to one another. In particular, this applies if a radially outermost ring magnet 10.1 of the first permanent magnet arrangement 10 has an axial polarization, the alignment of which corresponds to the polarization of the lowermost ring magnet 11.2 of the second permanent magnet arrangement 11 that is adjacent to the third permanent magnet arrangement 12.

(46) However, provision can alternatively also be made for the second permanent magnet arrangement 11 to be radially magnetized, as illustrated in FIG. 5B. In FIG. 5B, the second permanent magnet arrangement 11 is formed from a single, radially magnetized ring magnet 11.1. Here, the dimensions of the ring magnet 11.1 can be determined by simulations and/or calculations and are only illustrated in exemplary fashion in FIG. 5B. Further, the radial magnetization of the ring magnet 11.1 can also be set with opposite polarity to the magnetization illustrated in FIG. 5B. Provision can also be made of a plurality of radially magnetized ring magnets—or of combinations of radially and axially magnetized ring magnets. In the subsequent figures, the second permanent magnet arrangement 11 always has the same embodiment as in the exemplary embodiment of FIG. 5A—however, this should not be construed as a restriction. In principle, the second permanent magnet arrangement 11 of all subsequent exemplary embodiments may also be radially magnetized, for example, as illustrated in FIG. 5B.

(47) Small, closed magnetic circuits are formed by the magnetic unit 14 illustrated in FIGS. 5A, 5B. Only a small stray field 9 is emitted for this reason, wherein a force-distance curve that is suitable for weight compensation can be provided at the same time.

(48) A weight compensating device 1 that is further improved in respect of the magnetic shielding and the force-distance curve is illustrated in FIG. 6.

(49) Here, the magnetic body arrangement 13 is embodied as a fourth permanent magnet arrangement 13, which has an axial magnetization that is formed in accordance with the axial magnetization of the first permanent magnet arrangement 10. Consequently, the magnetization of the first permanent magnet arrangement 10 and the magnetization of the fourth permanent magnet arrangement 13 are chosen in such a way that the first permanent magnet arrangement 10 and the fourth permanent magnet arrangement 13 magnetically attract.

(50) Below, the magnetic body arrangement 13 is always illustrated as a fourth permanent magnet arrangement 13, wherein, within the scope of the disclosure, provision can furthermore also be made for not only permanent magnets to be (exclusively) provided but (also) for magnetic bodies, for example made of a soft iron, to be provided in the fourth permanent magnet arrangement 13.

(51) In this embodiment, the first permanent magnet arrangement 10 is formed from three nested axially magnetized ring magnets 10.1, 10.2, 10.3. In a manner analogous thereto, the third permanent magnet arrangement 12 is formed from three ring magnets 12.1, 12.2, 12.3 and the fourth permanent magnet arrangement 13 is formed from three ring magnets 13.1, 13.2, 13.3.

(52) In principle, provision can be made of any number of ring magnets, more particularly nested ring magnets, for example two to ten ring magnets, preferably three to five ring magnets, and very particularly preferably the respective three ring magnets 10.1, 10.2, 10.3, 12.1, 12.2, 12.3, 13.1, 13.2, 13.3 illustrated in the exemplary embodiment.

(53) The inventors have recognized that an even flatter force-distance curve or even less stiffness can be provided by using a fourth permanent magnet arrangement 13 than if use is made of a soft-magnetic material.

(54) The mutually adjacent ring magnets 10.1 and 10.2, and 10.2 and 10.3, of the first permanent magnet arrangement 10 are each polarized or aligned with axially opposite polarity. Here, the first permanent magnet arrangement 10 has an axial magnetization in which the innermost ring magnet 10.3 is polarized in the direction of the compensating force F.sub.M, the central ring magnet 10.2 is polarized counter to the compensating force F.sub.M and the outer ring magnet 10.3 is, once again, polarized in the direction of the compensating force F.sub.M. The ring magnets 12.1, 12.2, 12.3 of the third permanent magnet arrangement 12, situated therebelow, are magnetized in inverse fashion in relation thereto and the fourth permanent magnet arrangement 13, arranged above the first permanent magnet arrangement 10, is magnetized in corresponding or analogous fashion in relation thereto.

(55) The first permanent magnet arrangement 10, the third permanent magnet arrangement 12 and the fourth permanent magnet arrangement 13 extend in a radial plane, in each case orthogonal and symmetric with respect to the movement axis A, and accordingly extend in plane parallel fashion with respect to one another. Further, the nested ring magnets of the corresponding permanent magnet arrangements 10, 12, 13 are each arranged at the same axial position along the movement axis A. Finally, the number, dimensions (apart from the radial dimensions), i.e., more particularly the cross-sectional area, and structure of the ring magnets 10.1, 10.2, 10.3, 12.1, 12.2, 12.3, 13.1, 13.2, 13.3 of the first, third and fourth permanent magnet arrangement 10, 12, 13 are identical. This can be advantageous from a manufacturing point of view since a modular kit of ring magnets can be provided as a result thereof.

(56) Further, FIG. 6 illustrates a few geometric specifications, which preferably can be used to tune the magnetic unit 14. Here, it is possible to identify that the axial extent d.sub.2b of the second permanent magnet arrangement 11, i.e., of the two ring magnets 11.1, 11.2 arranged axially with respect to one another, is slightly larger than the axial spacing d.sub.34 between the third permanent magnet arrangement 12 and the fourth permanent magnet arrangement 13. However, a structure in which the axial extent d.sub.2b of the second permanent magnet arrangement 11 is equal to or smaller than the axial spacing d.sub.34 between the third permanent magnet arrangement 12 and the fourth permanent magnet arrangement 13 is also possible.

(57) For the purposes of facilitating an adjustment of the weight compensating device 1, provision can be made for the axial spacing d.sub.2a between the ring magnets 11.1, 11.2 of the second permanent magnet arrangement 11, the spacing d.sub.34 between the third permanent magnet arrangement 12 and the permanent magnet arrangement 13 and/or the axial position along the movement axis A of the first, second, third and/or fourth permanent magnet arrangement 10, 11, 12, 13 to be adjustable, as a result of which the compensating force F.sub.M can be adapted.

(58) In order to elucidate the improved properties in respect of a reduced stray field 9, FIG. 6 illustrates a further schematic illustration of a characteristic profile in the image field VI. Here, in a manner analogous to the illustration in FIG. 4, only the right-hand part of the rotationally symmetric arrangement has been imaged. It is possible to identify that the magnetic unit 14 forms smaller, closed magnetic circuits than the magnetic arrangement of the prior art. As a result of this, the magnetic field lines or the stray field 9 are/is (at least substantially) restricted to the magnetic unit 14 itself.

(59) Optionally, the magnetic field of the magnetic unit 14 or the magnetic circuit can be further improved or focused by virtue of using a Halbach arrangement 15. This is depicted in an exemplary manner in FIG. 7. Here, in principle, FIG. 7 shows a weight compensating device 1 which, in respect of the axially magnetized ring magnets 10.1, 10.2, 10.3, 11.1, 11.2, 12.1, 12.2, 12.3, 13.1, 13.2, 13.3, is constructed like the embodiment illustrated in FIG. 6. However, for the purposes of focusing the magnetic field, respectively two radially magnetized ring magnets 15.1, 15.2 for embodying a Halbach arrangement, known in principle, are provided between the respective three axially magnetized ring magnets 10.1, 10.2, 10.3, 12.1, 12.2, 12.3 of the first and third permanent magnet arrangements 10, 12.

(60) Alternatively (not illustrated), provision can also be made for respectively one Halbach arrangement between the ring magnets 10.1, 10.2, 10.3 of the first permanent magnet arrangement 10 and the ring magnets 13.1, 13.2, 13.3 of the fourth permanent magnet arrangement 13.

(61) Since Halbach arrangements are preferably not provided simultaneously in all inner permanent magnet arrangements 10, 12, 13, but always only in two adjacent permanent magnet arrangements or in a pair of permanent magnet arrangements, the position or alignment and/or dimensions of the ring magnets of the permanent magnet arrangement not equipped with a Halbach arrangement can be adapted accordingly. To this end, the ring magnets 13.1, 13.2, 13.3 of the fourth permanent magnet arrangement 13 are enlarged in the exemplary embodiment of FIG. 7, wherein gaps have been avoided between the ring magnets 13.1, 13.2, 13.3. As an alternative and/or in addition to an enlargement, provision can be made of dummy elements between the ring magnets 13.1, 13.2, 13.3, wherein the dummy elements can preferably includes a non-magnetic substance, e.g., a plastic. However, the dummy elements can also include a magnetic substance, e.g., iron. By way of example, the dummy elements can be embodied and/or positioned in such a way that the ring magnets of the inner permanent magnet arrangements 10, 12, 13 may remain unchanged in terms of their dimensions. Simulations and calculations may serve to optimize the magnetic circuit and to select the dummy elements or determine position and/or dimensions of the ring magnets of the permanent magnet arrangement not equipped with a Halbach arrangement. Optionally, the dummy elements can also be dispensed with, i.e., air or a gas, a liquid or a vacuum may also be situated between possible gaps in the ring magnets.

(62) A further improvement in the stray field 9 can also be achieved by virtue of the weight compensating device 1 providing a plurality of magnetic units 14. This is depicted in an exemplary manner in FIG. 8. Here, FIG. 8 illustrates a weight compensating device 1 including three magnetic units 14 which substantially correspond to the embodiment in FIG. 5A in terms of their structure, wherein, however, the magnetic body arrangement 13 of FIG. 5A is embodied as a fourth permanent magnet arrangement 13 with a ring magnet 13.1.

(63) The individual, smaller magnetic units 14 overall form the compensating force F.sub.M, which counteracts the weight F.sub.G acting on the translator 2. Since each of the individual component parts of the magnetic units 14 can have a smaller embodiment as the compensating force F.sub.M is now distributed among a plurality of magnetic units 14, it is possible to obtain a further improved stray field characteristic as the magnetic field lines can short one another more directly or scatter less intensively. In principle, any number of magnetic units 14 can be provided in the weight compensating device 1.

(64) Provision can also be made for a magnetic unit according to the prior art (cf., for example, FIG. 4) to be provided multiple times in a weight compensating device 1 according to the prior art in order to improve the stray field characteristic.

(65) In principle, as already described in relation to the prior art, at least one actuator coil 8 can be arranged at the stator 3 in the weight compensating device 1 according to the disclosure, said actuator coil, in conjunction with the first permanent magnet arrangement 10, forming an actuator for deflecting the translator 2.

(66) Finally, FIG. 9 illustrates an exemplary force-distance curve. In principle, the magnetically generated compensating force F.sub.M is dependent on the deflection z of the translator 2 from the zero position z.sub.0. In order to be able to compensate the weight F.sub.G relatively ideally over a large range or within an expected deflection range □z.sub.max, the force-distance curve should extend relatively flat and linear within this range of maximum deflection □z.sub.max. It should be possible to neglect, to the greatest reasonable extent, a change in the force □F.sub.M over the maximum deflection range □z.sub.max. In FIG. 9 the relationships are illustrated in greatly exaggerated fashion (and hence actually in disadvantageous fashion) for elucidation purposes.

(67) The inventors have recognized that a particularly flat or linear force-distance curve is achievable by a magnetic unit 14 according to the disclosure, particularly when using a fourth permanent magnet arrangement 13. The stiffness of such a weight compensating device 1 can be significantly improved in comparison with the known prior art. At the same time, a weight compensating device 1 according to the disclosure has a small stray field 9 and a simple structure.