Device with a spring and an optical element suspended therefrom

Description

[0001] The present invention relates to a device with an optical element which is tiltably mounted on actuators via springs.

[0002] Bimorph actuators typically consist of an active and a passive layer, whereby the actuators use different, for example thermal or piezoelectric, expansion or contraction properties of the layer materials to cause deflections of the actuators.

[0003] Systems with bimorph actuators and an optical element that can be tilted quasi-statically around an axis with large deflections, such as a micromirror, usually require very large component areas of the system, since the deflection of such bimorph actuators and thus the deflection of the optical element depends, among other things, on the length of the actuators. An optical element deflected around two perpendicular torsion axes requires even more space, since additional actuators are arranged. This larger space requirement is a significant disadvantage for MEMS components.

[0004] An embodiment of a micromirror with two perpendicular torsion axes, which is operated quasi-statically in both torsion axes or the resulting rotational movements, is described in the Fig. 2a and 2bfor thermally deflectable actuators and can also be used for piezoelectrically deflectable actuators, for example.

[0005] Fig 2a shows a device with an optical element 12', which is suspended by four multiply bent springs 14'ad on four actuators 16a-d arranged perpendicular to one another, such that they can be tilted about the torsion axes 18a and 18b. Heating elements 52a-d are arranged on the actuators 16a-d and are designed to locally heat the actuators 16a-d. Locally varying thermal expansion coefficients of actuator layers lead to a deflection of the actuators 16a-d and thus to a deflection of the optical element 12' upon heating of the actuators 16a-d.

[0006] The design allows for relatively large tilt angles of the optical element 12', but the actuators 16a-d are long relative to the edge lengths of the optical element 12', which increases the area required by the actuators and thus the device. In addition, the springs 14'ad have a large axial extension. Overall, the area efficiency of the device is low. Since an increase in the effective optical surface of the optical element 12' is accompanied by similarly enlarged actuators 16a-d and springs 14'ad, this design is unsuitable for optical elements with large surfaces.

[0007] Fig. 2b shows the device Fig. 2a in a deflected state. The actuators 16a-d are deflected such that the optical element 12' is tilted about the torsion axis 18a.

[0008] The design of this device is described in [1] for optical coherence tomography.

[0009] US 2008 / 0165402 A1 describes an actuator comprising a movable plate and a support for supporting the movable plate. Connecting devices are configured to connect the movable plate and the support and enable rotation of the movable plate relative to the support.

[0010] It would therefore be desirable to have a device that allows tilting of large optical elements with a high area efficiency and enables a compact design.

[0011] The object of the present invention is therefore to provide a device in which an element is mounted so as to be tiltable in two directions via springs and which allows more efficient operation.

[0012] This problem is solved by the subject matter of the independent patent claims.

[0013] The core idea of ​​the present invention is therefore to have recognized that the above object can be achieved both by an optical element being mounted tiltably about a first and a second axis on exactly two optics-side attachment areas via springs on actuators, and by an optical element being mounted tiltably about two axes via four optics-side attachment areas via springs on actuators, wherein one spring is arranged on each actuator at an angle between 90° and 180°.

[0014] According to one embodiment, an optical element is tiltably suspended via two springs arranged between the optical element and each actuator. The springs are straight and have a short axial extension. This allows the device to exhibit high surface efficiency.

[0015] Further advantageous embodiments are the subject of the dependent patent claims.

[0016] Preferred embodiments of the present invention are explained below with reference to the accompanying drawings. Fig. 1 is a plan view of a device with an optical element that is tiltably mounted on actuators at two optical-side mounting areas; Fig. 2a is a plan view of a device with a tiltably mounted optical element according to the prior art; Fig. 2b shows the deflected state of the device from Fig. 2a ; Fig. 3 a schematic representation of a device analogous Fig. 1 , in which the optical element comprises a greater distance to a clamping than actuator-side attachment areas; Fig. 4 a schematic side sectional view of a spring; Fig. 5 a schematic plan view of a device comprising actuators, each comprising two actuator elements; Fig. 6 a plan view of a device according to the claimed invention, in which actuators are arranged at an angle to each other; Fig. 7a a schematic side sectional view of an actuator with a functional layer and a measuring element in an undeflected state; Fig. 7b a schematic side sectional view of the actuator from Fig. 7a in a deflected state; Fig. 8 a plan view of a device in which two springs are arranged at an optical-side mounting location; Fig. 9 a plan view of a device with an optical element and four springs arranged at an angle on actuators; Fig. 10 a plan view of a curved spring; Fig. 11 a plan view of a spring with a variable lateral extension; Fig. 12 a plan view of the device from Fig. 1 , which further comprises a control unit which is designed to deflect the actuators; Fig. 13 a plan view of the device from Fig. 9 , which further comprises a control unit configured to deflect the actuators.

[0017] Fig. 1 shows a device 10 with a round optical element 12, the main side of which comprises a center of gravity 13 and is mounted on actuators 16a and 16b via springs 14a and 14b so as to be tiltable about a first torsion axis 18a and a second torsion axis 18b, and the torsion axes 18a and 18b intersect at an angle θ 5 adjacent to the center of gravity 13. The springs 14a and 14b are connected to the optical element 12 or the actuators 16a or 16b at a first end facing the optical element 12 at an optics-side attachment region 22a or 22b, respectively, and at a second end facing the respective actuator 16a or 16b at actuator-side attachment regions 24a or 24b, respectively. The optical-side attachment areas 22a and 22b comprise a lateral extension along a circumference of the main side of the optical element 12, which is each smaller than 10% of the circumference of the main side.

[0018] The actuators 16a and 16b are firmly clamped on one side to a clamping device 26 and are designed to be deflected from a rest position at the end arranged opposite to the fixed clamping device 26 during actuation, wherein an axial extension of the actuators 16a and 16b corresponds to approximately 2.5 times the diameter of the main side of the optical element 12.

[0019] The number of actuators 16a and 16b corresponds to the number of optics-side attachment areas 22a and 22b, so that each optics-side attachment area 22a and 22b can be assigned to an actuator 16a and 16b, to which it is connected via at least one spring 14a or 14b.

[0020] The actuator 16a comprises an actuator profile 28a in an extension direction from the fixed clamping 26 to the actuator-side attachment region 24a. Analogously, the actuator 16b comprises an actuator profile 28b from the fixed clamping 26 to the actuator-side attachment region 24b. A spring profile 32a along an axial extension from the first to the second end of the spring 14a intersects a spring profile 32b along an axial extension from the first to the second end of the spring 14b at an intersection point 34, which is spaced from the center of gravity 13 by an angle θ 6 of approximately 100°. An angle θ 1 describes an alignment of the spring 14a to the actuator 16a and thus the intersection angle of the two courses 28a and 32a, analogously an angle θ 2 describes an alignment of the spring 14b to the actuator 16b and thus the intersection angle of the two courses 28b and 32b.

[0021] The angle θ 5 at which the torsion axes 18a and 18b intersect depends on a spring length along an axial extension from the first end to the second end of the springs 14a and 14b, respectively, as well as the angles θ 1 and θ 2 .

[0022] A distance between the intersection point 34 of the spring curves and the center of gravity 13 results in effectively reflecting edge lengths of the optical element 12, which each describe a greatest distance between two points of the optical element 12 along a straight line perpendicular to any torsion axis, being shorter than geometric edge lengths of the optical element, which describe a greatest distance between any two points within the optical element, whereby this deviation can be stored in a lookup table for an actuator control and thus corrected.

[0023] With a Fig. 1 The geometric adjustment shown is a two-dimensional tilting of the optical element 12 about two torsion axes 18a and 18b using only two actuators 16a and 16b.

[0024] A deflection of an actuator 16a or 16b leads to a tilting of the optical element 12 about the torsion axis 18a or 18b. A tilting of the optical element 12 about the other torsion axis 18a or 18b can be minimized by a geometric adaptation of the device, whereby the angle θ 6 is always less than 180°.

[0025] Although in Fig. 1 the intersection point 34 is arranged within the main side of the optical element 12, embodiments include devices in which the intersection point 34 is arranged outside the optical element 12.

[0026] This embodiment offers high area efficiency for systems with optical elements that require two-dimensional torsional movements and large optical effective surfaces, such as mirror surfaces. The two-dimensional movement is enabled by a customized suspension of the optical element via springs, so that the two-dimensional movement can be achieved with just two actuators.

[0027] Furthermore, the embodiment is also mechanically very efficient. Since the actuator deflection is highly dependent on their length, efficient transmission of the actuator deflection to the optical element is advantageous, and the ratio between the tilt angle of the optical element and the required component area of ​​the system is crucial.

[0028] The connecting springs in a device with four actuators according to the prior art often have to be long and sometimes multiply curved, since the movement of an optical element connected to four reference points is always limited by one or two of these reference points, while the optical element is deflected via the other reference points. Therefore, the springs at the deflecting reference points must be long and thus soft to allow the movement of the optical element. Mutual tilting of the optical element therefore also requires a correspondingly long or soft design of all springs. The disadvantage here is that the deflection of the actuators can only be transmitted to a limited extent by very long or bent springs.

[0029] In the embodiment of the Fig. 1 In contrast, the optical element is connected to actuators via only two optical-side mounting areas, thus not restricting the movement of the optical element. Therefore, the springs between the actuators and the optical element can be short to efficiently transmit the actuator deflection and optimize the dimensions of both the actuators and the springs, thus increasing area efficiency compared to an optical element of the same size.

[0030] Alternative embodiments include actuators having an axial extent that is greater than the diameter of the optical element and less than five times the diameter.

[0031] Fig. 3 shows device 10 analog Fig. 1 , in which the optical element 12 is arranged at a greater distance from the fixed clamping 26 than the actuator-side attachment areas 24a and 24b. The angles θ 1 and θ 2 comprise an angle which is greater than 90°, wherein the angle θ 3 is analogous Fig. 1 is less than 180°.

[0032] Such an arrangement of the optical element 12 can be advantageous if, for example, an optical radiation to be deflected is deflected by an arrangement according to Fig. 1 would be hindered by actuators 16a and 16b blocking optical transmission paths.

[0033] Fig. 4 shows a top view of the spring 14a of the device 10 from Fig. 1 The spring 14a comprises an axial extension x 1 from the first end to the second end of the spring 14a and a lateral extension x 2 arranged perpendicular to the axial extension x 1. The lateral extension x 2 is smaller than the axial extension x 1 multiplied by a factor of 0.3, so that the spring has a large axial length compared to a lateral width. The extension x 1 is smaller than twice the greatest distance between any two points on a main side of the optical element at which the spring 14a is arranged.

[0034] Fig. 5 shows a device 20 in which the actuators 16a and 16b each comprise two spaced-apart actuator elements 54a and 54b or 54c and 54d, wherein the actuator elements 54a and 54b or 54c and 54d are connected to one another at the deflectable end of the actuator 16a or 16b, so that a deflection of one of the actuator elements 54a or 54b or 54c or 54d leads to a deflection of the actuator 16a or 16b, wherein the respective actuator elements 54a and 54b or 54c and 54d of an actuator can be controlled in parallel.

[0035] A combination of several actuator elements 54a-d enables a reduction of transverse contraction effects in piezoelectrically operated actuators, since for each actuator element a ratio of an actuator length to an actuator width is optimized in this way.

[0036] Alternative embodiments show actuator elements that are arranged without a distance from one another and comprise a common substrate, as well as actuator elements that can be controlled separately from one another.

[0037] Further embodiments show actuators with at least two actuator elements, wherein different actuator elements use different actuation principles, in that one actuator element comprises a piezoelectric functional layer and another actuator element comprises a thermal functional layer.

[0038] Fig. 6 shows a device 30 according to the claimed invention, with an optical element 12 which is arranged tiltably on the actuators 16a and 16b via the springs 14a and 14b, wherein the extension directions of the actuators 16a and 16b are arranged perpendicular to each other.

[0039] The spring 14b comprises two straight sections 55a and 55b, wherein the section 55a is long relative to the section 55b and comprises approximately 97% of the total extension and the section 55b comprises approximately 3% of the total extension along the spring

[0040] A combination of several axial sections of different lengths allows an efficient introduction of torsional moments into the spring,

[0041] Alternative embodiments according to the claimed invention show springs which comprise more than two and a maximum of six straight sections, wherein the sections are formed as an individual section and a section which comprises at least 80% of the total axial extent of the spring course and wherein each of the shorter sections comprises a maximum proportion of 4% of the axial extent of the respective spring.

[0042] Fig. 7a shows a side view of an actuator 16 in an undeflected state. The actuator 16 comprises a substrate 56 and a thermal functional layer 58, which is arranged on the substrate 56 over an axial extent starting from the fixed clamping 26 and extending to a deflectable end of the actuator 16. The functional layer 58 is designed to have an extension different from the substrate 56 when heated, so that an end of the actuator 16 opposite the fixed clamping 26 is deflected. A strain gauge 62 is arranged on a side of the substrate 56 facing away from the functional layer 58, which strain gauge is designed to detect a deflection of the actuator 16 and to provide the detected deflection in the form of a signal.

[0043] Fig. 7b shows the actuator 16 in a deflected state in which an expansion of the functional layer 58 leads to a compression of the strain gauge 62.

[0044] In alternative embodiments, the functional layer comprises piezoelectric materials that are designed to undergo contraction or expansion upon application of an electrical voltage and to deflect the actuator due to the contraction or expansion.

[0045] Depending on the operating state of the actuators and therefore on the expected material load, other measuring methods can also be arranged on the actuators to record the deflection state, for example Bragg gratings, which are incorporated in fiber optic sensors.

[0046] Fig. 8 shows a schematic plan view of a device 40 analogous to device 10 from Fig. 1 , in which an additional spring 14c is arranged between the actuator 16a and the optical element 12 and an additional spring 14d is arranged between the actuator 16b and the optical element 12, wherein the springs 14a and 14c and 14b and 14d are each arranged in pairs on the optics-side attachment areas 22a and 22b, so that the number of support points on the optical element 12 is unchanged, wherein the springs 14a-d each comprise an equal lateral extent.

[0047] An arrangement of several springs allows a more efficient transmission of an actuator deflection to the optical element or an additional stabilization of a position of the optical element, so that weight-related deflections of the optical element are reduced.

[0048] Fig. 9 shows a top view of a device 50 with four actuators 16a-d, on which the optical element 12 is suspended via four springs 14a-d so as to be tiltable about the two torsion axes 18a and 18b. The springs 14a-d are connected to the optical element 12 at four optics-side attachment areas 22a-d. The actuator profile 28a-d of an actuator 16a-d forms an angle θ 1 , θ 2 , θ 3 or θ 4 with the spring profile 32a-d of a spring 14a-d arranged on the respective actuator 16a-d. The actuators 16a-d are arranged such that the curves 28a and 28d as well as the curves 28b and 28c run parallel to each other and the curve 28a is congruent with the curve 28b and the curve 28d is congruent with the curve 28c. The angles θ 1-4 define the position of the torsion axes 18a and 18b, whereby the two torsion axes 18a and 18b intersect at an angle θ 5 and the angle θ 5 is defined by the equation θ 5 = 360 ° − θ 3 + θ 4 is determined so that the directions in which the optical element 12 can be deflected can be defined geometrically by the arrangement of the springs 14a-d with respect to the actuators 16a-d and the optical element 12.

[0049] Fig. 10 shows a plan view of a spring 66 which comprises a curved profile. The curved profile is designed such that the spring is formed within a spring region 68, wherein the spring region 68 is defined by an overlapping region of two circular arcs. An axis 72 is arranged between the actuator-side attachment region 24 and the optics-side attachment region 22, which axis intersects a connecting line between the attachment regions 24 and 22 at a right angle. The line 72 comprises circular arc centers 74a and 74b, around which circular arcs are arranged with a radius 76a and 76b such that the respective circular arcs intersect the two attachment regions 24 and 22, and wherein the radius 76a or 76b of the respective circular arc is greater than 75% of the distance between the two attachment regions 24 and 22.

[0050] Curved springs allow for a reduction of torsion-induced material stress, thus achieving a longer service life of the device.

[0051] As an alternative to previous embodiments showing springs having a constant lateral extension over the spring path, alternative embodiments show devices with springs having a lateral extension varying over the spring path, as shown below.

[0052] Fig. 11 shows a plan view of a spring 66' with a varying lateral extension over an axial course from the optics-side attachment area 22 to the actuator-side attachment area 24. The spring 66' is formed within the area 68, so that a curved course of a spring 66 from Fig. 10 is encompassed by the spring 66'.

[0053] A varying lateral extension allows a defined absorption of deformation energy over the axial course of the spring.

[0054] Fig. 12 shows device 10 from Fig. 1 , with a control device 78 which is designed to control the actuators 16a and 16b and to cause a deflection of the actuators 16a and 16b, so that the optical element 12 undergoes a tilt.

[0055] Fig. 13 shows device 50 from Fig. 9 , with a control device 78 which is designed to control the actuators 16a-d and to cause a deflection of the actuators 16a-d, so that the optical element 12 undergoes a tilt.

[0056] Although in previous embodiments the optical element is always round, the optical element can comprise any shape, for example elliptical or square.

[0057] The above-described embodiments are merely illustrative of the principles of the present invention. It is understood that modifications and variations of the arrangements and details described herein will be apparent to others skilled in the art. Therefore, it is intended that the invention be limited only by the scope of the following claims and not by the specific details presented in the description and explanation of the embodiments herein. Literatur

[0058] [1] Umer Izhar, Boon S. Ooi, Svetlana Tatic-Lucic, Multi-axis micromirror for optical coherence tomography, Procedia Chemistry, Volume 1, Issue 1, September 2009, pages 1,147-1,150

Claims

1. An apparatus, comprising: a first actuator (16; 16a-d); a second actuator (16; 16a-d); an optical element (12); at least one first spring (14a-d; 66; 66') disposed between the first actuator (16; 16a-d) and the optical element (12); at least one second spring (14a-d; 66; 66') disposed between the second actuator (16; 16a-d) and the optical element (12); wherein the optical element (12) includes exactly two spaced-apart optics-side attachment areas (22; 22a-d); and wherein the at least one first spring (14a-d; 66; 66') is disposed on the first optics-side attachment area (22; 22a-d) and the at least one second spring (14a-d; 66; 66') is disposed on the second optics-side attachment area (22; 22a-d) such that actuation of the first or second actuator (16; 16a-d) causes tilting of the optical element around two axes (18a-b); wherein the first spring (14a-d; 66; 66') is disposed on a first actuator-side attachment area (24; 24a-b) on the first actuator (16; 16a-d) and the second spring (14a-d; 66; 66') is disposed on a second actuator-side attachment area (24; 24a-b) on the second actuator (16; 16a-d); the first spring and the second spring (14a-d; 66; 66') include, between the respective first and respective second end, equal to or less than six portions (55a-b) that are straight in sections; wherein the portions (55a-b) include a different axial expansion along the spring course from the first to the second end of the spring (14a-d; 66; 66') such that the spring (14a-d; 66; 66') includes a long and at least one short portion (55a-b); the long portion (55a-b) includes at least 80% of the overall axial expansion of the course of the spring (14a-d; 66; 66'); and each short portion (55a-b) includes a proportion of the overall axial expansion (x1) of the course of the spring (14a-d; 66; 66') that is less than 4%.

2. The apparatus according to claim 1, wherein the optical element (12) is disposed between the first and the second actuator (16; 16a-d) and the first spring (14a-d; 66; 66') is disposed on a deflectable end of the first actuator (16; 16a-d) and the second spring (14a-d; 66; 66') is disposed on a deflectable end of the second actuator (16; 16a-d); wherein the first and second actuators (16; 16a-d) extend in a same direction starting from a fixing (26), or wherein each actuator (16) has an actuator course (28) in an expansion direction starting from the fixing (26) to the actuator-side attachment area (24; 24a-b) and the extension directions of the actuators (16; 16a-d) include a right angle.

3. The apparatus according to claim 1 or 2, wherein the optics-side attachment areas (22; 22a-d) include a lateral expansion along a circumference of a main side of the optical element (12) which is less than the circumference of the main side plane multiplied by the factor 0.1.

4. The apparatus according to one of the previous claims, wherein one of the actuators (16; 16a-d) includes a piezo element that is implemented to deflect the actuator (16; 16a-d) from a resting position.

5. The apparatus according to one of the previous claims, wherein one of the actuators (16; 16a-d) includes a thermal controlling element (58) that is implemented to deflect the actuator (16; 16a-d) from a resting position.

6. The apparatus according to one of the previous claims, wherein one of the actuators (16; 16a-d) includes at least a first and a second actuator element (54a-d).

7. The apparatus according to claim 6, wherein the first and the second actuator element (54a-d) can be controlled together.

8. The apparatus according to one of the previous claims, wherein an axial expansion along the extension direction of an actuator (16; 16a-d) is greater than the greatest distance of any two points of the main side of the optical element (12) and equal to or less than five times the greatest distance of any two points of the main side of the optical element (12).

9. The apparatus according to one of the previous claims, wherein a distance between a first end and a second end of the spring (14a-d; 66; 66') is less than the greatest distance of any two points of a main side of the optical element (12) multiplied by the factor 2.

10. The apparatus according to one of the previous claims, wherein one of the springs (14a-d; 66; 66') comprises a lateral expansion that is constant across the axial course (x1).

11. The apparatus according to claim 10, wherein the lateral expansion (x2) is less than the axial expansion (x1) multiplied by the factor 0.3.

12. The apparatus according to one of the previous claims, wherein at least one further spring (14a-d; 66; 66') is disposed on an optics-side attachment point (22; 22a-d), and each of the springs (14a-d; 66; 66') comprises a same lateral expansion (x1).

13. The apparatus to one of claims 1 to 9 or 12, wherein the lateral expansion (x2) of the springs (14a-d; 66; 66') varies across the axial course; wherein the lateral expansion (x2) is implemented within an area (68) defined by circular arcs which intersect the first and the second end of the spring (14a-d; 66; 66'); wherein each circular arc includes a radius (76a-b) that is greater than 0.75 times of a distance between the first end and the second end of the spring (14a-d; 66; 66'); and wherein each circular arc includes a center (74a-b) positioned along a line (72) that is positioned in space to be perpendicular to a straight line connecting the first end and the second end of the spring (14a-d; 66; 66').

14. The apparatus according to one of the previous claims, wherein a measurement element (62) that is implemented to detect the deflection state of the actuators (16; 16a-d) is disposed on an actuator (16; 16a-d).

15. The apparatus according to one of the previous claims, comprising: a control unit (78) implemented to control the actuators (16; 16a-d); wherein the control unit (78) is further implemented to effect tilting of the optical element in a direction differing from the two axes (18a-b).