Patent Application
20220244564
The present invention relates to a device, particularly a gimbal, for carrying an optical element.
In optical applications it is often necessary to be able to pivot an optical element in one or two dimensions (i.e. about one axis or two independent axes).
In the state of the art, gimbals are known that comprise one or two static (conventional) bearings per axis. This has the benefit that there is no restitutive force (zero stiffness) in the rotation direction as well as stiffness in all other directions. Furthermore, large angles regarding the pivoting movement/rotation are possible. However, typically, a play is present in such mechanisms that—if not preloaded—will limited precision. Furthermore, static friction, even higher in case of preloading and difficult to control stick slip need to be overcome by the actuator force. Furthermore, many parts are usually involved in such a design and very tight tolerances are mandatory both on parts and assembly. Moreover, conventional bearings are usually not suited for fast (resonant) motions due to missing stiffness.
Furthermore, pivotable joints in bearings based on torsion beams and similar flexures (e.g. one or two torsion beams per rotational axis) undergo elastic deformation in the torsional bars and usually comprise planar structure, defined by the rotational axes. The benefits of such configurations are a simple and cost-effective design needing only a small design space. Furthermore, due to the absence of static friction there is no hysteresis/backlash. Furthermore, there is also no play involved in the motion of the torsion beams and an open loop control is possible by force control. Particularly, a fast operation in resonance is possible. However, the larger stiffness of such a design principle requires a certain force to hold a position of the rotated part and parasitic modes can be encountered especially in a piston mode (out-of-plane mode) which is more critical for large stroke and low resonance frequencies. Furthermore, large displacements/angles are difficult to achieve and large stresses are induced into the elastic elements, especially at large deflections)(>5°. Typically, such a design would also need a larger design space due to longer beams to lower stress.
Based on the above, the problem to be solved by the present invention is to provide a device of the afore-mentioned kind having a simple design that allows to achieve a comparatively large deflection as well as ideally large resonant frequencies at the same time while also reducing play.
This problem is solved by a device having the features of claim 1.
Preferred embodiments of these aspects of the present invention are stated in the corresponding sub claims and are described below.
According to claim 1, a device for carrying an optical element is disclosed, the device comprising:
The pivotable first carrier is arranged to have an optical element, like a mirror, a prism, a lens, a diffusor or a grating attached thereto. Thus, motion of the first carrier is transmitted to the optical element. In particular, the first carrier and the optical element may be formed monolithically.
The first bearing attaches the first carrier to the second carrier or to the mount. The first bearing determines the relative motion of the first carrier with respect to the second carrier or with respect to the mount. In particular the first axis extends a long a main plane of extension of the first carrier. Preferably, the first axis extends along an axis of symmetry of the first carrier and/or the optical element as seen in top view.
The elastic structure is arranged return the first carrier to its non-deflected position, once the first carrier is being pivoted around the first axis. Thus, the resonance frequency of a rotational motion of the first carrier depends on the stiffness of the elastic structure. The first direction extends in a direction perpendicular to main extension direction of the first carrier and/or the optical element. In particular, the first direction extends perpendicular to the first axis.
The elastic structure and the support are both connected to the first carrier respectively. Moreover, either the elastic structure and the support are both connected to the second carrier respectively or the elastic structure and the support are both connected to the mount respectively. Thus, the elastic structure and the support provide a connection between the same elements. In particular, the movement of the first carrier is not driven through the elastic structure or the support. Preferably, the first bearing is arranged to solely guide the motion of the first carrier. In particular, the deflection of the first carrier is directly driven by means of electromagnetic forces acting on the first carrier.
Here and in the following, the first direction extends in a direction obliquely, in particular perpendicular, to the first direction, unless specified differently. Particularly, advantageously, such a design allows tilting about at least one (the first) axis, but also about two axes (2D), with high frequencies in the range from 10 Hz to 1000 Hz, typically 10 Hz to 250 Hz with a high precision, particularly better than 1 mrad accuracy, particularly better than 10 μrad resolution, and large pivoting (rotational) angle (e.g. +/−30°, +/−15°), wherein particularly only small motions are allowed in any other direction than the desirable rotation/pivoting direction which includes undesirable vibration modes in translations or other rotational axes. Preferably, the device can further be operated either resonant (moderate stiffness) or in a static mode (very low stiffness).
Particularly, in an embodiment, the elastic structure is configured to eliminate a play of the support of the first carrier on the second carrier.
Furthermore, according to an embodiment, the elastic structure is configured to provide stiffness for an intended motion direction of the first carrier.
According to a further embodiment, the elastic structure is configured to guide the first carrier in several directions in a play free manner.
Furthermore, the elastic structure is configured to distribute stress.
According to a further preferred embodiment of the present invention, the elastic structure comprises a plurality of spring members, each spring member connecting the first carrier to the second carrier or connecting the first carrier to the mount or connecting the second carrier to the mount.
According to an embodiment, the respective spring member is a flat plate member. particularly cut from a sheet of a suitable material, particularly a metal.
Furthermore, according to a preferred embodiment, the respective spring member comprises a meandering shape.
According to a further preferred embodiment, the spring members extend along a common extension plane, wherein particularly in plane motions of the first carrier along said extension plane are prevented by the spring structure/spring members due to in-plane-stiffness being particularly at least ten times larger than a stiffness of the elastic structure in a torsion mode.
According to yet another embodiment, the spring members are integrally connected to one another and particularly form a single plate member. Preferably, the spring members/said plate member are/is cut (e.g. laser cut or stamped) form a single sheet.
According to a further embodiment of the present invention, the device comprises magnets for pre-loading the elastic structure.
According to a further embodiment, the first carrier comprises a first portion, the first carrier being supported by the support on the second carrier or the mount via the first portion. The first carrier may comprise a second portion, the first carrier being supported by the support on the second carrier or the mount via the second portion. The first and the second portion protruding from opposite sides of the first carrier and the first and the second portion are particularly aligned with one another and with the first axis. Particularly, each of the two portions can be formed as an elongated beam.
According to a preferred embodiment, the spring structure comprises two spring members arranged on either side of the first portion and two spring members arranged on either side of the second portion.
According to a further embodiment, the first portion is supported on the second carrier via a first part of the support. Furthermore, the second portion can be supported on the second carrier via a separate second part of the support.
Preferably, the respective part (i.e. the first part and the second part) of the support can each be one of:
Further, in an embodiment, the respective bearing is pre-loaded, particularly by one of: gravity, the elastic structure (particularly by said spring members), pre-loading springs, by means of magnetic forces provided by magnets.
According to yet another embodiment, the support is formed by the elastic structure. For example, the elastic structure comprises at least one leaf spring, wherein the main extension direction of the leaf spring extends along the first direction. In particular, the elastic structure comprises multiple leaf springs, wherein at least one of the multiple leaf springs provides a support in the first direction.
According to a further embodiment of the device according to the present invention, the first carrier is supported on the second carrier via a damper, particularly comprising no or low static stiffness. In particular, the stiffness is selected depending on the inertia of the first carrier such that the pivotable movement has a maximum resonance frequency of 30 HZ.
The optical device according to one of the preceding claims, wherein the second carrier is pivotably supported on a mount so that the second carrier can be pivoted about a second axis thus allowing the first carrier to be pivoted in two dimensions (i.e. about the first and the second axis independently). In particular, the first bearing connects the first carrier to the second carrier or the first bearing connects the second carrier to the mount. Moreover, the device may comprise a second bearing having a support and elastic structure as described herein, wherein the first carrier and the second carrier are connected by the first bearing and the second carrier and the mount are connected by the second bearing.
Furthermore, according to an embodiment, the first carrier is supported on the second carrier via the elastic structure, wherein the elastic structure comprises a first and a second connecting portion protruding from opposite sides of the first carrier, and wherein the elastic structure comprises two first elastic legs connected to the first connecting portion, wherein the first legs protrude from the first connecting portion and diverge so that the first legs form an angle, particularly an acute angle.
According to one embodiment, the elastic structure comprises two first elastic legs, wherein each elastic leg particularly forms a leaf spring. The first legs diverge so that the first legs form an angle, particularly an acute angle and at least one of the first legs is configured to limit a translation of the first carrier in at least the first direction.
According to one embodiment, both first legs limit a translation of the first carrier in at least the first direction. Preferably, the elastic structure comprises two second elastic legs (e.g. each forming a leaf spring) connected to the second connecting portion, wherein the second legs protrude from the second connecting portion and diverge so that the second legs form an angle, particularly an acute angle, too. Particularly, each of the four legs comprises an end section forming a fastening region, the respective leg being connected to the second carrier (or a mount) via its fastening region.
Particularly, the first connecting portion and the first elastic legs connected thereto form a first arch-shape member. Likewise, particularly, the second connecting portion and the second elastic legs connected thereto form a second arch-shape member. The arch-shaped members allow pivoting of the first carrier about the first axis being defined by the arch-shaped members by allowing bending of the connecting portions and legs connected thereto.
According to one embodiment the first carrier is pivotably mounted on the second carrier and the second carrier is pivotably supported on a mount so that the second carrier can be pivoted about a second axis, wherein the first bearing connects the first carrier to the second carrier or the first bearing connects the second carrier to the mount.
According to one embodiment, the first carrier is pivotable about the first axis, and the second carrier is pivotable about a second axis.
According to one embodiment the second axis runs orthogonal to the first axis, the first and the second axis intersect in an intersection point, wherein said intersection point is located within the optical element being arranged on the first carrier.
According to a further embodiment, a resonant frequency of a pivoting movement of the respective carrier (and components arranged thereon) about at least one axis of the first and the second axis is above 100 Hz.
Furthermore, according to an embodiment, a resonant frequency of a pivoting movement of the respective carrier (and components arranged thereon) about at least one axis of the first and the second axis is below 30 Hz.
Furthermore, the optical element being arranged on the first carrier (or second part of the first carrier) is preferably one of: a mirror, a transparent window, a prism.
Further features and advantages of the present inventions as well as embodiments of the present invention shall be described in the following with reference to the Figures, wherein
Furthermore, the first bearing 100 comprises an elastic structure 30 being schematically indicated in
Furthermore, the first carrier 10 comprises a first portion 11 and a second portion 12, said portions 11, 12 protruding from opposite sides of the first carrier and being aligned with one another. The two portions 11, 12 define the first axis A and are each supported via a bearing 41, 42 (e.g. a ball bearing or a sliding bearing) on the second carrier 20. I.e. here the support comprises a first part 41 and a second part 42 being formed as bearings 41, 42, respectively, wherein particularly said bearings 41, 42 each limit a translation of the first carrier 10 in a plane perpendicular to the first axis A, i.e. along two linear independent directions D1 and D2 extending orthogonal to the first axis A.
Furthermore, the elastic structure 30 comprises for spring members 31, each spring member 31 comprising a meandering shape and connecting the first carrier 10 to the second carrier 20. The spring members 31 counteracting a movement of the first carrier along the first axis as well as providing a restoring force regarding a pivoting movement/rotation of the first carrier 10 about the first axis A. Preferably, the spring members 31 are integrally connected to one another and form a single flat plate member, as can be seen from
Particularly, the second carrier 20 is supported on the mount 60 via two axis members 51, 52, each axis member being supported in a bearing 53, 54 on the mount 60, wherein the respective bearing 53, 54 can e.g. be a ball bearing or a sliding bearing.
Particularly, the two axis members 51, 52 are aligned with one another and define the second axis B. Preferably, the two axes A, B intersect at an intersection point being located within the optical element 2.
Particularly, in the embodiment shown in
Furthermore,
In the vertical direction, the dampening means can be formed by a fluid FF (e.g. lubricant or ferrofluid). Particularly, each portion 11, 12 of the first carrier 10 can be arranged in an associated opening 41, 42 of the second carrier 20, which forms the respective support 41, 42/bearing surface, wherein the fluid FF is arranged in a gap between an inner side of the opening 41 and the respective portion 11, 12. The respective portion 11, 12 that is arranged in its opening 41 still has some play, otherwise the friction between shafts 11, 12 of the first carrier 10 and the second carrier 20 would be too high. This play, still allows the optical element 2 to catch residual vibrations and move up and down. These vibrations might be small in terms of the allowed error in the position/tilt of the optical element 2 (e.g. mirror) but could be a risk for the long-term integrity of the bearing. This embodiment of the device 1 therefore preferably comprises rather loose bearings for the shafts 11, 12 with a thick layer of viscous lubricant FF that dampens those vibrations. A good solution is to use ferrofluids FF as dampening, as they don't escape from the desired positions if they are maintained in their locations by means of magnets 43. The magnets 43 can form a ring, which distributes the ferrofluid. But the idea is to have a well-defined and stable layer of the liquid such that it dampens a certain level of vibrations.
Furthermore, due to the fact that the portions 11, 12 are inserted in corresponding openings 41, 42, each opening 41, 42 limits a translation of the first carrier 10 in a plane perpendicular to the first axis A, i.e. along two linear independent directions D1 and D2 extending orthogonal to the first axis A.
These knifes 41, 42 therefore provide two line-contacts between support 41, 42 and first carrier 10. Preferably, the material of the respective knife/edge 41, 42 comprises a higher hardness than the material of the respective portion 11, 12 of the first carrier 10 that rests on the respective edge 41, 42. This results in abrasion on the first and second portion 11, 12 instead of knife 41, 42. Thereby, the knife 41, 42 cuts into the carrier material, which defines the pivot point of the first carrier 10. Furthermore, slipping of the first and second portion 11, 12/first carrier 10 on the respective knife 41, 42 is advantageously prevented. According to an embodiment, the respective edge/blade 41, 42 can be covered with an elastomer in order to prevent slipping of the first carrier 10/portions 11, 12 on the edges 41, 42 to enable a reproducible/repetitive pivoting movement of the first carrier 10 on the support 41, 42 formed by said edges of the second carrier 20. Particularly, the respective edge/knife 41, 42 each limits a translation of the first carrier 10 in a first direction D1 running orthogonal to the first axis A, wherein the limiting particularly corresponds to a hard stop.
Particularly, the two magnets 400, 401 can repel one another. The elastic structure 30 gets pre-loaded due to the magnets 400, 401. This reduces the vertical movement (parallel to the polarization axis of the magnets 400, 401) which one would like to avoid. Instead, the tilting mode that is desire sees only a little effect from the magnets 400, 401.
The respective arch-shaped fixture 33, 35; 34, 36 can be formed out of a single part, e.g. out of a thin sheet material. Preferably, the respective member 33, 35; 33, 36 carries no torsion, but bending forces. The arch-shaped members 33, 35; 33, 36 allow for an improved distribution of stress and further to achieve a large stroke and/or lower stiffness in a desired direction while providing stiffness in other directions at the same time. As indicated in
Preferably, as indicated e.g. in
The elastic structure 30 connects the second carrier 20 to the mount 60, and the support 41, 42 is configured to support the second carrier 20 on the mount 60, wherein the support is configured to limit a translation of the first carrier 10 in at least a first direction D1.
The support is formed by the elastic structure 30. The elastic structure 30 comprises two first elastic legs 35, wherein each elastic leg 35 forms a leaf spring. The first legs 35 diverge so that the first legs 35 form an angle W, particularly an acute angle and at least one of the first legs is configured to limit a translation of the first carrier 10 in at least the first direction D1.
As shown in
The elastic structures 30 provide a force along the first direction, wherein the force acts as a preload on the support 41, 42. The force and the recesses define a position of the spherically shaped support 41, 42 with respect to the link structure, the first carrier 10 and the mount 60.
The device comprises a cage structure 62, 64, 65, which is arranged to maintain the spherically shaped support in a dedicated area. As shown in
The second carrier 20 has essentially the same shape as the link structure 61 in the embodiment shown in
As shown in
| Number | Date | Country | Kind |
|---|---|---|---|
| 102021102166.9 | Jan 2021 | DE | national |
| PCT/IB2021/056871 | Jul 2021 | IB | international |
Benefit is claimed to International Patent Application No. PCT/IB2021/056871, filed Jul. 28, 2021, and to German Patent Application No. 102021102166.9, filed Jan. 29, 2021; the contents of both of which are incorporated by reference herein in their entirety.
